EQUALIZATION FOR MATRIX BASED LINE IMAGERS FOR ULTRASOUND IMAGING SYSTEMS
Disclosed herein are ultrasonic transducer systems comprising: an ultrasonic imager comprising a plurality of pMUT transducer elements; and one or more circuitries connected electronically to the plurality of transducer element, the one or more circuitries configured to enable: pulse transmission and reception of reflected signal for the ultrasonic transducer, where inductors are used to equalize impedance to obtain greater pressure output. Also disclosed are methods of altering a pressure of an ultrasonic wave emitted by an ultrasonic transducer.
This application is a continuation application of Ser. No. 17/156,058, filed Jan. 22, 2021, which is incorporated herein by reference in its entirety and to which application we claim priority under 35 USC § 120.
For ultrasound imaging, transducers are used to transmit an ultrasonic beam towards the target to be imaged and a reflected waveform is received by the transducer. The received waveform is converted to an electrical signal and with further signal processing an ultrasound image is created. Conventionally, for two-dimensional (2D) imaging, the ultrasonic transducer includes a one-dimensional (1D) transceiver array for emitting an ultrasonic beam. It is desirable to generate high pressure levels in the ultrasonic beam transmitted.
SUMMARYPiezoelectric sensors have been used for medical imaging for more than two decades. These are typically built using bulk piezoelectric films. These films form piezoelectric elements which are arranged along columns in the azimuth direction. Each column can be driven by transmit drivers. By using different time delays on successive columns, it may be possible to focus transmitted beams in the azimuth direction.
The elevation disposition of the array of piezoelectric elements can permit the beam of the array to be electronically focused into a narrow beam in the elevation plane. The single row of piezoelectric elements of the transceiver array does not enable electronic focusing in the elevation or thickness dimension of the 2D ultrasound image. A traditional 2D ultrasound image is in the azimuth plane with some thickness in the elevation direction (i.e., the conventional technique for restricting the beam to a thin image slice is to mechanically focus the beam in this transverse or elevational dimension, either by contouring the piezoelectric elements in this dimension or lensing each element.). A 2D array of transducers can be arranged such that elements in the elevation direction allow electronic focusing in the elevation direction while also allowing azimuth electronic focusing that is traditionally done in legacy systems.
For optimal transfer of power from an input source to another circuit, the output impedance of the source should be a complex conjugate of the input impedance of the circuit it is driving. In particular optimally, the real parts of both impedances should be equal and the complex parts should be complex conjugates of one another. Transducers using piezoelectric micromachined ultrasound transducer (pMUT) implementations are highly capacitive in nature. For a transmit driver trying to transmit ultrasonic signals into tissue, the driver's impedance needs to match the transducer's input impedance as described above. However, pMUT based transducers are highly capacitive and this requires inductors to be used in series with source drivers to maximize power transferred to the transducer.
In an aspect, an ultrasonic imaging system comprising a transducer is disclosed. The transducer comprises at least one transducer element. Each transducer element has two terminals. The at least one transducer element is in a transmit mode. The transducer also comprises at least one transmit driver. The each transmit driver is connected to each first terminal of the at least one transducer element. The transducer also comprises at least one inductor comprising two terminals. Each first terminal of each inductor is connected to each second terminal of each transducer element. Each second terminal of each inductor is connected to a bias voltage.
In some embodiments, the transducer is a piezoelectric micro machined transducer (pMUT) device.
In some embodiments, the transducer is a capacitive micromachined ultrasonic transducer (cMUT) device or a bulk piezo transducer.
In some embodiments, the at least one transducer element is a plurality of transducer elements organized in an array.
In some embodiments, the array is organized in rows and columns. A plurality of transducer elements in a column is electronically selected to define a column of transducer elements.
In some embodiments, a plurality of transducer elements in a row is selected electronically to define a row of transducer elements.
In some embodiments, delays of transducer elements in a first column are independent from delays of transducer elements in a second column and delays of transducer elements in a first row are independent from delays of transducer elements in a second row.
In some embodiments, transducer elements on a column have different delays.
In some embodiments, the bias voltage is selected from a group consisting of ground, negative, and positive voltages.
In some embodiments, a bandwidth of the transducer is increased in a region of interest.
In some embodiments, at least one value of the at least one inductor is selected to provide a pressure output increase in a frequency range of interest.
In some embodiments, at least one value of the at least one inductor is chosen to be large enough to offset changes in phase introduced by at least one capacitance of the at least one transducer element.
In some embodiments, a bandwidth of the transducer is controlled by selecting a number of transducer elements on a column.
In some embodiments, a pressure output for the selected transducer elements is adjusted by changing a plurality of voltage drive levels of a plurality of transmit drivers of the selected transducer elements.
In some embodiments, the voltage drive levels are changed using a multilevel transmit drive pulse and selecting a desired digital drive level.
In some embodiments, the voltage drive levels are further controlled using pulse width modulation on a transmit pulsar waveform.
In some embodiments, the transducer is configured to provide electronic control of elevation focus in an elevation direction along the column.
In some embodiments, a transducer element along the column is driven by a multilevel pulse.
In some embodiments, a transducer element on a column is driven by a sequence of multilevel pulses.
In some embodiments, pulse magnitude, width, shape, pulse frequency, and combinations thereof of a multilevel pulse of the sequence of multilevel pulses are electrically programmable.
In some embodiments, a delay of an onset of the multilevel pulse is electrically programmable.
In some embodiments, the delay for an element indexed by a row and a column is calculated by summing a delay for the column with a delay for the row.
In some embodiments, a delay may be a summation of a coarse delay and a fine delay.
In some embodiments, the delay of pulse onset is programmable in an X direction.
In some embodiments, the delay of pulse onset is programmable in a Y direction.
In some embodiments, a shape of the multilevel pulse is selected from a group consisting of sinusoidal and digital square.
In some embodiments, the transmit driver is configured to drive the one or more transducer elements along a column. The transmit driver is driven by signals from a transmit channel. The signals of the transmit channel are delayed electronically relative to delay applied to other transmit channels driving other transducer elements on different columns.
In some embodiments, the one or more transducer elements along the column operate with substantially identical delays.
In some embodiments, the transmit channel and additional transmit channels are configured to electrically control relative delays between adjacent columns. The control circuit is configured to set relative delays for a first number of transducer elements on the columns such that the first number of transducer elements in a same row share substantially identical relative delays with a second number of transducer elements of a starting row.
In some embodiments, a transducer element of the plurality of transducer elements comprises a top section, a central section, and a bottom section, each of which comprise a number of rows and a number of columns for pulse transmission and reception of the reflected ultrasonic signal. The pulse transmission and reception of the reflected ultrasonic signal from the top section, central section, and bottom section is used for focusing the reflected ultrasonic signal in an azimuth direction using a first beamformer. An elevation focus is achieved using a second beamformer.
In some embodiments, a focal distance in an elevation direction is electronically programmed.
In some embodiments, the pulse transmission and reception of the reflected signal of the top section and the bottom section are performed simultaneously.
In some embodiments, the transducer elements perform parallel beamforming to develop a plurality of scan lines.
In some embodiments, two adjacent transducer elements on a row of the one or more rows are addressed together and wherein a transducer of the plurality of transducer elements comprises a top section, a central section, and a bottom section, each of which comprise a first number of rows and a second number of columns for the ultrasonic pulse transmission and reception of the reflected ultrasonic signal. The ultrasonic pulse transmission and reception of the reflected ultrasonic signal from the sections are used for focusing the reflected ultrasonic signal in an azimuth direction using a first beamformer. The elevation focus is achieved using a second beamformer. For imaging using a B mode, a receive channel is assigned to two transducer elements on a same row, one of the two transducer elements from the top section and the other of the two elements from the bottom section, and another channel is assigned to two transducer elements of the central section.
In some embodiments, 2N receive channels are used to address N columns.
In some embodiments, all of the plurality of transducer elements selected electronically are operated on to generate pressure with elevation focus in a transmit operation. In a receive operation, all of the plurality of transducer elements separately electronically selected are used to reconstruct an image with focusing in the azimuth direction and an elevation plane.
In some embodiments, the ultrasonic imaging system further comprises a control circuit configured to electrically control relative delays along a column to be a summation of a linear delay and an arbitrary fine delay.
In some embodiments, the linear delay and arbitrary fine delays of the column are independent from other linear delay and arbitrary fine delays of other columns of the transducer, thereby allowing for arbitrary steering and focusing in three dimensions.
In some embodiments, each transducer element exhibits multiple modes of vibration, where only one mode of vibration is triggered when input stimulus is bandlimited to be less than frequencies of adjacent modes.
In some embodiments, each transducer element exhibits multiple modes of vibration, where frequencies generated from a first mode of vibration overlaps those from a second mode of vibration.
In some embodiments, each transducer element exhibits multiple modes of vibration simultaneously when driven by a wide band frequency input that includes center frequencies.
In an aspect, an ultrasonic imaging system comprising an ultrasonic transducer is disclosed. The transducer comprises a bias voltage. The transducer also comprises a column of transducer circuits. The transducer circuit comprises a transducer element, comprising a transducer for converting an electrical signal into an ultrasonic wave. The transducer element has a first terminal and a second terminal. The transducer also comprises a circuitry comprising an input drive device for supplying a potential to the transducer element, connected to the first terminal of the transducer element. The transducer also comprises an inductor connected to the second terminal of the transducer element. The transducer also comprises and a switch for connecting the transducer circuit to the bias voltage.
In some embodiments, the ultrasonic transducer is a pMUT device.
In some embodiments, the ultrasonic transducer is a cMUT device or a bulk piezo transducer.
In some embodiments, the ultrasonic imaging system further comprises a switch connected in parallel with the inductor, for the purpose of shorting the inductor.
In some embodiments, the ultrasonic imaging system comprises a plurality of columns.
In some embodiments, a column of the plurality of columns contains an inductor connected in series with the transducer element.
In some embodiments, the ultrasonic imaging system further comprises a switch connected in parallel with the inductor, for the purpose of shorting the inductor.
In some embodiments, the ultrasonic imaging system further comprises an inductor connected in series between the plurality of columns of transducer circuits and the bias voltage.
In some embodiments, the transducer element is configured to transmit a signal including a delay.
In some embodiments, the one or more transducer elements on the column operate with different delays.
In some embodiments, the delay for an element indexed by a row and a column is calculated by summing a delay for the column with a delay for the row.
In some embodiments, a delay profile comprising delays from one or more transducer elements with a common column index is symmetrical.
In some embodiments, the delay is a summation of a coarse delay and a fine delay.
In some embodiments, the coarse delay is linear between one or more adjacent transducer elements.
In some embodiments, the delay for a transducer element with a column index and a row index is a summation of a column delay, a linear coarse row delay, and a fine row delay.
In an aspect, a method for increasing a pressure of an ultrasonic wave emitted by a transducer comprising at least one transducer element. The method comprises using at least one transmit driver connected to the at least one transducer element, placing the at least one transducer element in a transmit mode. Each transducer element has a first terminal and a second terminal. The method also comprises for at least one inductor, connecting a first terminal of each of the at least one inductor to the second terminal of each transducer element. The second terminal of the at least one inductor is connected to a bias voltage. The at least one inductor is not integrated with the transducer element. The transducer also comprises connecting each of at least one transmit driver to each first terminal of each of the at least one transducer element.
In some embodiments, the at least one transducer element is a plurality of transducer elements organized in an array.
In some embodiments, the array is organized in rows and columns. The method further comprises electronically selecting a multiplicity of transducer elements in a column to define a column of transducer elements.
In some embodiments, a plurality of transducer elements in a row is selected electronically to define a row of transducer elements.
In some embodiments, a plurality of delays of transducer elements in a first column are independent from a plurality of delays of transducer elements in a second column and a plurality of delays of transducer elements in a first row are independent from a plurality of delays of pMUT transducer elements in a second row.
In some embodiments, transducer elements on a column have different delays.
In some embodiments, the method further comprises performing 3D imaging by applying a plurality of delays in an azimuth direction for a set to transmissions with a fixed steering angle in an elevation direction controlled by a plurality of delays applied to transducer elements on a column and repeating the sequence with different steering angles in an elevation plane and reconstructing an image using received echo from the transducer.
In some embodiments, the method further comprises performing volume imaging by focusing on an azimuth plane by varying a plurality of delays along an azimuth and also focusing or steering a beam in an elevation plane by varying a plurality of delays for a transducer on a column.
In some embodiments, the method further comprises selecting the bias voltage from a group consisting of ground, negative, and positive voltages.
INCORPORATION BY REFERENCEAll publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. Rathod, Vivek T. 2019. A Review of Electric Impedance Matching Techniques for Piezoelectric Sensors, Actuators, and Transducers. Lingvall, F., 2004. Time-domain Reconstruction Methods for Ultrasonic Array Imaging: A Statistical Approach.
A better understanding of the features and advantages of the present subject matter will be obtained by reference to the following detailed description that sets forth illustrative embodiments and the accompanying drawings.
Ultrasonic imaging traditionally has used bulk piezo electric films as a transducer. However, these tend to be expensive to use and also require high voltages to operate, typically in the 100 to 200V range. Recently, transducers capable of being mass produced on a silicon wafer using piezo films dispensed or sputtered on a silicon wafer substrate have become available. These have significant advantages with respect to their ability to integrate systems in a more compact or smaller form factor, with operating lower power requirements and cost compared to legacy systems. Additionally, other transducer technologies (such as cMUT) have emerged that may be manufactured on silicon wafers, to a significant manufacturing cost advantage. However, these transducers (as well as legacy transducers) may exhibit significant capacitive load to a transmit driver. For applications requiring significant pressure output, tuning the impedance of the circuit for maximum power transfer is employed. It is well known that power transfer is maximized when the impedance of the driver is a complex conjugate of the load. Legacy techniques have shown that use of an inductor between the driver and load has helped improve pressure outputs. However, this technique is not implementable for an integrated portable application or use case, due to size and parasitic impedance issues. A novel technique will be shown to achieve the integration needed at low cost and also to achieve pressure outputs desired. This technique is applicable to pMUTs and also other transducers with a significant capacitive load such as legacy bulk piezo and cMUTs (capacitive micromachined ultrasonic transducer). Further, a goal would be to implement this in a manner that enables the exceptional capabilities that are possible with use of 2D arrays of transducers and associated circuitry housed in or with ASICs. This enables both the generation of 3D images and electronic focusing in azimuth and elevation directions. Such capabilities have previously not been implemented successfully in handheld ultrasound imaging devices due to the cost, power and size constraints in legacy systems.
Traditionally, a 2D ultrasound image can be created by employing a variety of algorithms. One example of this is using relative delay for driving signals along the columns of piezoelectric elements in the azimuth direction. Beams can be focused in the azimuth direction electronically by altering electronically programmable delay applied to signal for different columns in the azimuth direction. However, focus in a direction orthogonal to the azimuth direction (e.g., the elevation direction) typically is achieved by using a mechanical lens. A mechanical lens may allow only one focus at a time, thus different elevation focus may require different design of the lens. Further, a fixed mechanical lens does not provide the focus required for 3D ultrasound imaging.
Disclosed herein in some embodiments are systems and methods configured for enabling low cost, low power, portable high resolution ultrasonic transducers and ultrasound imaging systems configured for ultrasonic imaging. Enabling these low cost, high performance systems can be dependent on using pMUTs that can be manufactured on a semiconductor wafer in high volume and low cost similar to high volume semiconductor processes. In exemplary embodiments, such pMUTs are arranged in a 2D array where each element in the array is connected to an electronic circuit, where the pMUT array and the circuit array are aligned together on different wafers and integrated together to form a tile, where each piezo element is connected to a controlling circuit element, where each piezo element may have 2 terminals as shown in
The disclosed ultrasonic transducer may be a capacitive micromachined ultrasonic transducers (cMUT) device. Such a transducer may include a large array of cMUT elements. A cMUT array may provide larger bandwidth compared to other transducer technologies and may easily achieve high frequency operation.
Use of inductors is disclosed using fixed mechanical lenses. Additionally, imaging systems disclosed herein also use electronic lenses that advantageously eliminate the need to build a mechanical lens with a fixed focal length. Further, the electronic lenses disclosed herein allow great flexibility of being able to alter the focal length in the elevation plane and allow dynamic focus as a function of depth.
In an aspect, an ultrasonic imaging system comprising a transducer is disclosed. The transducer comprises at least one transducer element. Each transducer element has two terminals. The at least one transducer element is in a transmit mode. The transducer also comprises at least one transmit driver. The each transmit driver is connected to each first terminal of the at least one transducer element. The transducer also comprises at least one inductor comprising two terminals. Each first terminal of each inductor is connected to each second terminal of each transducer element. Each second terminal of each inductor is connected to a bias voltage.
In some embodiments, the transducer is a piezoelectric micro machined transducer (pMUT) device.
In some embodiments, the transducer is a capacitive micromachined ultrasonic transducer (cMUT) device or a bulk piezo transducer.
In some embodiments, the at least one transducer element is a plurality of transducer elements organized in an array.
In some embodiments, the array is organized in rows and columns. A plurality of transducer elements in a column is electronically selected to define a column of transducer elements.
In some embodiments, a plurality of transducer elements in a row is selected electronically to define a row of transducer elements.
In some embodiments, delays of transducer elements in a first column are independent from delays of transducer elements in a second column and delays of transducer elements in a first row are independent from delays of transducer elements in a second row.
In some embodiments, transducer elements on a column have different delays.
In some embodiments, the bias voltage is selected from a group consisting of ground, negative, and positive voltages.
In some embodiments, a bandwidth of the transducer is increased in a region of interest.
In some embodiments, at least one value of the at least one inductor is selected to provide a pressure output increase in a frequency range of interest.
In some embodiments, at least one value of the at least one inductor is chosen to be large enough to offset changes in phase introduced by at least one capacitance of the at least one transducer element.
In some embodiments, a bandwidth of the transducer is controlled by selecting a number of transducer elements on a column.
In some embodiments, a pressure output for the selected transducer elements is adjusted by changing a plurality of voltage drive levels of a plurality of transmit drivers of the selected transducer elements.
In some embodiments, the voltage drive levels are changed using a multilevel transmit drive pulse and selecting a desired digital drive level.
In some embodiments, the voltage drive levels are further controlled using pulse width modulation on a transmit pulsar waveform.
In some embodiments, the transducer is configured to provide electronic control of elevation focus in an elevation direction along the column.
In some embodiments, a transducer element along the column is driven by a multilevel pulse.
In some embodiments, a transducer element on a column is driven by a sequence of multilevel pulses.
In some embodiments, pulse magnitude, width, shape, pulse frequency, and combinations thereof of a multilevel pulse of the sequence of multilevel pulses are electrically programmable.
In some embodiments, a delay of an onset of the multilevel pulse is electrically programmable.
In some embodiments, the delay for an element indexed by a row and a column is calculated by summing a delay for the column with a delay for the row.
In some embodiments, a delay may be a summation of a coarse delay and a fine delay.
In some embodiments, the delay of pulse onset is programmable in an X direction.
In some embodiments, the delay of pulse onset is programmable in a Y direction.
In some embodiments, a shape of the multilevel pulse is selected from a group consisting of sinusoidal and digital square.
In some embodiments, the transmit driver is configured to drive the one or more transducer elements along a column. The transmit driver is driven by signals from a transmit channel. The signals of the transmit channel are delayed electronically relative to delay applied to other transmit channels driving other transducer elements on different columns.
In some embodiments, the one or more transducer elements along the column operate with substantially identical delays.
In some embodiments, the transmit channel and additional transmit channels are configured to electrically control relative delays between adjacent columns. The control circuit is configured to set relative delays for a first number of transducer elements on the columns such that the first number of transducer elements in a same row share substantially identical relative delays with a second number of transducer elements of a starting row.
In some embodiments, a transducer element of the plurality of transducer elements comprises a top section, a central section, and a bottom section, each of which comprise a number of rows and a number of columns for pulse transmission and reception of the reflected ultrasonic signal. The pulse transmission and reception of the reflected ultrasonic signal from the top section, central section, and bottom section is used for focusing the reflected ultrasonic signal in an azimuth direction using a first beamformer. An elevation focus is achieved using a second beamformer.
In some embodiments, a focal distance in an elevation direction is electronically programmed.
In some embodiments, the pulse transmission and reception of the reflected signal of the top section and the bottom section are performed simultaneously.
In some embodiments, the transducer elements perform parallel beamforming to develop a plurality of scan lines.
In some embodiments, two adjacent transducer elements on a row of the one or more rows are addressed together and wherein a transducer of the plurality of transducer elements comprises a top section, a central section, and a bottom section, each of which comprise a first number of rows and a second number of columns for the ultrasonic pulse transmission and reception of the reflected ultrasonic signal. The ultrasonic pulse transmission and reception of the reflected ultrasonic signal from the sections are used for focusing the reflected ultrasonic signal in an azimuth direction using a first beamformer. The elevation focus is achieved using a second beamformer. For imaging using a B mode, a receive channel is assigned to two transducer elements on a same row, one of the two transducer elements from the top section and the other of the two elements from the bottom section, and another channel is assigned to two transducer elements of the central section.
In some embodiments, 2N receive channels are used to address N columns.
In some embodiments, all of the plurality of transducer elements selected electronically are operated on to generate pressure with elevation focus in a transmit operation. In a receive operation, all of the plurality of transducer elements separately electronically selected are used to reconstruct an image with focusing in the azimuth direction and an elevation plane.
In some embodiments, the ultrasonic imaging system further comprises a control circuit configured to electrically control relative delays along a column to be a summation of a linear delay and an arbitrary fine delay.
In some embodiments, the linear delay and arbitrary fine delays of the column are independent from other linear delay and arbitrary fine delays of other columns of the transducer, thereby allowing for arbitrary steering and focusing in three dimensions.
In some embodiments, each transducer element exhibits multiple modes of vibration, where only one mode of vibration is triggered when input stimulus is bandlimited to be less than frequencies of adjacent modes.
In some embodiments, each transducer element exhibits multiple modes of vibration, where frequencies generated from a first mode of vibration overlaps those from a second mode of vibration.
In some embodiments, each transducer element exhibits multiple modes of vibration simultaneously when driven by a wide band frequency input that includes center frequencies.
In an aspect, an ultrasonic imaging system comprising an ultrasonic transducer is disclosed. The transducer comprises a bias voltage. The transducer also comprises a column of transducer circuits. The transducer circuit comprises a transducer element, comprising a transducer for converting an electrical signal into an ultrasonic wave. The transducer element has a first terminal and a second terminal. The transducer also comprises a circuitry comprising an input drive device for supplying a potential to the transducer element, connected to the first terminal of the transducer element. The transducer also comprises an inductor connected to the second terminal of the transducer element. The transducer also comprises and a switch for connecting the transducer circuit to the bias voltage.
In some embodiments, the ultrasonic transducer is a pMUT device.
In some embodiments, the ultrasonic transducer is a cMUT device or a bulk piezo transducer.
In some embodiments, the ultrasonic imaging system further comprises a switch connected in parallel with the inductor, for the purpose of shorting the inductor.
In some embodiments, the ultrasonic imaging system comprises a plurality of columns.
In some embodiments, a column of the plurality of columns contains an inductor connected in series with the transducer element.
In some embodiments, the ultrasonic imaging system further comprises a switch connected in parallel with the inductor, for the purpose of shorting the inductor.
In some embodiments, the ultrasonic imaging system further comprises an inductor connected in series between the plurality of columns of transducer circuits and the bias voltage.
In some embodiments, the transducer element is configured to transmit a signal including a delay.
In some embodiments, the one or more transducer elements on the column operate with different delays.
In some embodiments, the delay for an element indexed by a row and a column is calculated by summing a delay for the column with a delay for the row.
In some embodiments, a delay profile comprising delays from one or more transducer elements with a common column index is symmetrical.
In some embodiments, the delay is a summation of a coarse delay and a fine delay.
In some embodiments, the coarse delay is linear between one or more adjacent transducer elements.
In some embodiments, the delay for a transducer element with a column index and a row index is a summation of a column delay, a linear coarse row delay, and a fine row delay.
In an aspect, a method for increasing a pressure of an ultrasonic wave emitted by a transducer comprising at least one transducer element is disclosed. The method comprises using at least one transmit driver connected to the at least one transducer element, placing the at least one transducer element in a transmit mode. Each transducer element has a first terminal and a second terminal. The method also comprises for at least one inductor, connecting a first terminal of each of the at least one inductor to the second terminal of each transducer element. The second terminal of the at least one inductor is connected to a bias voltage. The at least one inductor is not integrated with the transducer element. The transducer also comprises connecting each of at least one transmit driver to each first terminal of each of the at least one transducer element.
In some embodiments, the at least one transducer element is a plurality of transducer elements organized in an array.
In some embodiments, the array is organized in rows and columns. The method further comprises electronically selecting a multiplicity of transducer elements in a column to define a column of transducer elements.
In some embodiments, a plurality of transducer elements in a row is selected electronically to define a row of transducer elements.
In some embodiments, a plurality of delays of transducer elements in a first column are independent from a plurality of delays of transducer elements in a second column and a plurality of delays of transducer elements in a first row are independent from a plurality of delays of pMUT transducer elements in a second row.
In some embodiments, transducer elements on a column have different delays.
In some embodiments, the method further comprises performing 3D imaging by applying a plurality of delays in an azimuth direction for a set to transmissions with a fixed steering angle in an elevation direction controlled by a plurality of delays applied to transducer elements on a column and repeating the sequence with different steering angles in an elevation plane and reconstructing an image using received echo from the transducer.
In some embodiments, the method further comprises performing volume imaging by focusing on an azimuth plane by varying a plurality of delays along an azimuth and also focusing or steering a beam in an elevation plane by varying a plurality of delays for a transducer on a column.
In some embodiments, the method further comprises selecting the bias voltage from a group consisting of ground, negative, and positive voltages.
Certain DefinitionsUnless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present subject matter belongs.
As used herein, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Any reference to “or” herein is intended to encompass “and/or” unless otherwise stated.
As used herein, the term “about” refers to an amount that is near the stated amount by about 10%, 5%, or 1%, including increments therein.
In some embodiments, the imagers (interchangeably here as “transducers”) herein can be used to perform but is not limited to perform: 1D imaging, also known as A-Scan, 2D imaging, also known as B scan, 1.5D imaging, 1.75D imaging, 3D and Doppler imaging. Also, the imager herein can be switched to various imaging modes which are pre-programmed. Also, biplane imaging mode may be implemented using transducers herein.
In some embodiments, transducer elements herein (e.g., pMUT elements, cMUT elements) are interchangeable with transceiver elements. Specifically, pMUT elements herein are interchangeable with piezoelectric elements and piezo elements. In some embodiments, the transducer element herein may include one or more of: a substrate, a membrane suspending from the substrate; a bottom electrode disposed on the membrane; a piezoelectric layer disposed on the bottom electrode; and one or more top electrodes disposed on the piezoelectric layer.
In this particular embodiment, the display unit 112 and/or at least part of the electronic communication control unit in 110 may be located on the assembly 108. In some embodiments, the display unit 112 or part of the control unit 110 could be external to the imager but connected to the ultrasonic imager assembly 108 and its elements therewithin with a communication interface 124, which can be a wired communication interface and/or a wireless communication interface. For wired connections, many protocols for data interchange such as USB2, Lightning and others can be used. Similarly, for wireless communications, a commonly used protocol such IEEE 802.11 (Wi-Fi) or other wireless communication protocols can be used. Similarly, the data recording unit 114 can also be external to the probe and can also communicate with probe 126 using wireless communication interface or wired communication interface. In some embodiments, the display 112 may have an input device, e.g., touch screen, a user-friendly interface, e.g., graphical user interface (GUI), to simplify user interaction.
In the same embodiment, the pMUT array 102 is coupled to an application specific integrated circuit (ASIC) 106 located on another substrate and in close proximity to the pMUT array 102. The array may also be coupled to impedance lowering and/or impedance matching material 104 which can be placed on top of the pMUT array. In some embodiments, the imager 126 includes a rechargeable power source 127 and/or a connection interface 128 to an external power source, e.g., a USB interface. In some embodiments, the imager 126 includes an input interface 129 for an ECG signal for synchronizing scans to ECG pulses. In some embodiments, the imager 126 has an inertial sensor 130 to assist with user guidance.
Conventional transducer arrays use piezoelectric material, e.g., lead zirconate titanate (PZT) formed by dicing a block of bulk PZT to form individual piezo elements. These tend to be expensive. In contrast, pMUT arrays disclosed herein are disposed on a substrate (e.g., wafer). The wafer can be in various shapes and/or sizes. As an example, the wafer herein can be of sizes and shapes of wafers in semiconductors processes used for building integrated circuits. Such wafers can be produced in high volume and with low cost. Exemplary wafer sizes are: 6, 8 and 12 inches in diameter.
In some embodiments, many pMUT arrays can be batch manufactured at low cost. Further, integrated circuits can also be designed to have dimensions such that connections needed to communicate with pMUTs are aligned with each other and pMUT array (102 of
The arrow 114 shows ultrasonic transmit beams from the imager assembly 108 targeting a body part 116 and imaging a target 118. The transmit beams are reflected by the target being imaged and enters the imager assembly 108 as indicated by arrow 114. In addition to ASIC 106, the imaging system 100 may include other electronic control, communication and computational circuitry 110. It is understood that the ultrasonic imager 108 can be one self-contained unit as shown in
During operation, the user may cause the pMUTs 102 surface, covered by interface material 104 to make contact with a body part area upon which ultrasonic waves are transmitted towards the target 118 being imaged. The imager receives reflected ultrasonic beams from the imaging target and processes it or transmit it to an external processor for image processing and/or reconstruction, and then to a portable device 101 for displaying an image. Other data may also be collected, calculated, derived, and displayed on the display to a user.
When using the imager, for example to image human or animal body part the transmitted ultrasonic waveform is directed towards the target. Contact with the body is achieved by holding the imager in close proximity of the body, usually after a gel is applied on the body and the imager placed on the gel, to allow superior interface of ultrasonic waves being emitted to enter the body and also for ultrasonic waveforms reflected from the target to reenter the imager, where the reflected signal is used to create an image of the body part and results displayed on a screen, including graphs, plots, statistics shown with or without the images of the body part in a variety of formats.
It should be noted that the probe 126 may be configured with certain parts being physically separate, yet connected through a cable or wireless communications connection. As an example, in this particular embodiment, the pMUT assembly and the ASIC and some control and communications related electronics could reside in a unit often called a probe. The part of the device or probe that contacts the body part contains the pMUT assembly.
Piezoelectric elements have been used for decades for ultrasonic medical imaging. However, the piezoelectric element can be thick, for example, approaching around 100 μm and typically may require+100V to −100V alternating current (AC) drive across it to create an ultrasonic pressure wave of sufficient strength to enable medical imaging. The frequency of this AC drive signal may be around the resonating frequency of the piezoelectric structures and can be above 1 MHz for medical imaging applications.
In some embodiments, the power dissipated in driving the piezoelectric element is proportional to C*V2, where C is capacitance of the piezo element and V is the maximum voltage across the piezoelectric layer. When transmitting, a multiplicity of piezoelectric elements can be driven together with somewhat different delay to focus a beam or to steer a beam. The simultaneous drive of many elements can cause temperature to rise on the surface of the elements. It is highly desirable or required not to exceed a threshold temperature so as not to injure the subject being imaged. Thus, this threshold temperature limits the number of elements that can be driven and the time period for which they can be driven.
Disclosed herein, in some embodiments, the piezoelectric elements are much thinner, approximately 1 to 5 μm thick, compared to around 100 μm thickness of conventional bulk piezo elements. Such large decrease in thickness may enable use of lower voltage drive signals for the piezoelectric elements to maintain electric field strength similar to conventional elements. For example, the piezoelectric elements disclosed herein may require drive voltages ranging from around 5V to 20V peak to peak.
The capacitance of the piezo element may also be increased by the reduction in thickness for certain piezoelectric materials. Thus, as an example, when drive voltage decreases from 100 V to 10 V when driving 10× times thinner film, capacitance may increase by a factor of 10 for the thinner piezoelectric materials, and power dissipation may be reduced by a factor of 10. This reduction in power dissipation also can reduce heat generation and temperature rise in the imaging probe. Thus, using lower drive voltages, the temperature of the pMUT surface can be lowered.
In some embodiments, for a given temperature, when using low voltage pMUTs, more pMUT elements can be driven to illuminate a larger area. This may allow faster scanning of the target, especially if multiple emissions are needed to scan an entire target to form an image. Often, a target area may be scanned with multiple emissions using different steering angles and image data combined to obtain a higher quality image.
It may also be desirable to image at a high frame rate. A frame rate measures how many times a target is imaged per minute. It is desirable to image at a high frame rate, when tissue motion is involved to observe targets moving without image blurring. In some embodiments, the ability to drive more piezoelectric elements enables more coverage of the transducer aperture per emission, minimizing the number of emissions needed to cover entire aperture, thus increasing frame rates.
In some embodiments, image quality can be improved by combining several frames of images into one resultant lower noise frame. However, this can reduce frame rate. When using low power pMUT with higher frame rate compared with that of the conventional piezo films, for a given rise in pMUT temperature, this averaging technique can be used due to low voltage pMUTs having lower power thus enabling inherently higher starting frame rates. In some embodiments, a synthetic aperture method of ultrasound imaging can be used to allow compounding of images.
In some embodiments, the ability of drive more piezoelectric elements at a time improves signal to noise ratio (SNR) and enables better quality of the reconstructed image.
Further, as noted in
In some embodiments, an element may consist of more than 2 subelements, where the first electrode of all subelements are connected together, typically to a drive signal and the second electrode of all subelements are also connected together, typically to a bias voltage.
Due to non-symmetry in the crystalline structure of PZT, an electrical polarity develops, creating electric dipoles. In a macroscopic crystalline structure, the dipoles by default can be found to be randomly oriented, for example as shown in
Piezoelectric thin films therefore may need to be poled initially before being used. This can be accomplished when the film is sputtered under a field. This can also be done post fabrication by applying a high voltage across the film, typically at high temperature (e.g., 175° C.) for some time (e.g., 1-2 minutes or more). In the piezo element of
Prior art pMUTs or other piezo elements from bulk PZT typically have two electrodes. As disclosed herein, the piezoelectric element may have 2 (in
The piezoelectric element in an exemplary embodiment utilizes transverse strain, leveraging PZT transverse strain constant d31, the piezoelectric coefficient, to create movement of a membrane or convert movement of a membrane into charge. The PZT element of
In receive mode, the orthogonal poling direction may create more charge to be sensed by a LNA. The LNA connections are shown symbolically in
Traditional 2D imaging is done using columns of elements that are arranged in a rectangular shape. Alternately, 2D imaging may be achieved by taking many smaller elements arranged in a column. Individual array elements may be combined to act as a single larger 1D array element to make up a column. This is achieved by hardwiring these individual elements, to create a larger element which has one signal conductor and a common ground conductor. Transmit drive, receive sense and control are implemented for this one combined and larger two-lead pMUT.
The conductor of each piezoelectric element is connected to the electrode and is named Oxy, where x ranges from 1 to 3 and y ranges from 1 to 3, in
For simplicity,
In some embodiments, conductor 612 in
A line imager herein may include a multiplicity of piezo element columns, each column is connected by at least a signal and bias leads to a controller. Pulses of an appropriate frequency drive a line. The other lines are driven with delayed versions of this pulse. The amount of delay for a certain line is such that it allows the resultant beam transmitted to be steered at an angle or be focused at a certain depth, with operations known as beamforming.
The line imagers of
It is desirable in a 2D or 3D imager to image a thin slice of the elevation plane as shown in
If the beam spreads well beyond the intended slice thickness, it could potentially hit targets outside the desired range and reflections from those will create clutter in the reconstructed image. A mechanical lens formed on the transducer surface can focus beams in the elevation plane to a fixed elevation slice thickness as seen in
In some embodiments, this is achieved by dividing the transducer into a number of different strips. Referring to
In some embodiments, the top section A is organized such that all elements in that section are driven by transmit driver(s) intended for the column that the element(s) are in. In this embodiment, in a transmit operation, N transmit driver with unique delays driving N composite columns (each composite column may include elements from rows from strip(s) A or B or C) are used to focus an ultrasound beam in the azimuth plane 1202. During receive operation, reflected signal that impinges in section A is beamformed to create scan line A1, A2, A3, etc. as shown in
Although the process described in
In some embodiments, the top section, the central section, and/or the bottom section can be divided into one or more subsections, each of which include a number of rows for pulse transmission and signal receiving. In some embodiments, each subsection can be used to form multiple scan lines in a manner similar to what has been disclosed herein.
In some embodiments, the transducer element array can be divided into more than 3 strips, for example, 4, 5, 6, 7, etc. In some embodiments, scan line in each strip can be performed either sequentially or simultaneously. In some embodiments, in simultaneous transmission, scan line from strips symmetrical to the center strip are obtained. In some embodiments, the delays for elements in same column are identical for sections operated on simultaneously.
The focus can also be assisted by further employing a lower amplitude of voltage for a part of the two outer sections of the transducer with respect to remaining parts of the transducer.
In some embodiments, a unique programmable delay along the elevation direction is implemented for each element of all columns. All N columns may receive drive signals that are delayed relative to each other. Additional delays can be generated to add further delay along the column elements, where each element along the column can be delayed differently relative to its adjacent neighbor(s) on the same column. A delay profile example is shown in
In some embodiments, the delay profile is shown in
The procedure to obtain a scan line using the systems and methods herein, in some embodiments, is shown in
In some embodiments, focusing a beam in the receive direction utilizes more than one RF signals, e.g., S1, S2, etc. along the azimuth direction (Y), which are digitized output samples known as RF signals. In some embodiments, the RF samples are delayed, for example, with a delay profile along the Y direction and the resulting signal, can be weighted and summed to form a scan line.
As illustrated in
Referring to
Unlike mechanical lenses, as disclosed herein with synthetic lenses, the focal distance can be electronically programmed into the beamformer. In some embodiments, the process may require a number of transmissions and receptions (e.g., 1 transmission and reception from N lines to form scan line A1) to form a scan line from any sections of the transducer, e.g., (sections A, B, and C). To form a frame, R scan lines are required to scan full area to be imaged. Further in this case, 3 separate frames A, B, C are needed. In some embodiments, it is desirable to have a high frame rate in an image. A frame may include many scan lines. However, if the number of transmissions and receptions can be reduced while the same number of scan lines can be developed, then the frame rate will be increased. In some embodiments, increased frame rate can be achieved by combining the transmission and reception from two sections (e.g., A and C). Since these regions are symmetrical with respect to a central region, the delays needed for example as shown in
In some embodiments, the number of rows used to form A, B, C is programmable. The number of rows can be adjusted depending on what anatomies are being imaged and can be set using presets, for example, based on anatomies or patient information, in the user interface.
In some embodiments, an electronic synthetic lens offers dynamic focusing and dynamic aperture. For example, in near field, the weights for A and C can be minimal and gradually increase with depth, thus resulting in change in aperture.
In some embodiments, sections (e.g., A and C) are apodized during transmission and reception. Apodization can be achieved by pulse width modulation (PWM) of the Transmit (Tx) drive waveform. A unapodized pulse drive has a nominal pulse width. When pulse width is changed, e.g., reduced, the pressure output from the pMUT can reduced. In some embodiments, apodization is a tapering of weights for elements as they go from the center of the transducer to the edges. This can reduce side lobes and create higher quality images. By applying apodization to the procedure described, signals leaking outside of the elevation plane can be reduced.
In some embodiments, the apodization can be achieved by using a multi-level transmit drive, for example, 3 or 5 or 7 levels. By choosing different levels of this drive signal, apodization can be created by applying amplitude varying transmit drive signals that are lower in amplitude for element closer to the edge than the center of the transducer. In this example, all elements on outer rows compared to central rows can have lower drive voltages, by digital decoding and selecting, certain drive levels may be available to form the multi-level outputs. A three level decoding example is shown in
In some embodiments, apodization is implemented by employing piezoelectric elements of smaller size at edges compared to those at the center of the transducer aperture.
In an embodiment, the circuit employs programmable delays along the elevation direction for all columns. All N columns may receive drive signals that are delayed with respect to each other. Additional delays are generated to add further delays along the column elements, where each element along a column can be delayed differently with respect to its adjacent neighbor on the same column. A delay profile example is shown in
τi,j=τj+τi (1)
Where in one embodiment:
τj=√{square root over ((x−xj)2+z2)}/c (2)
τi=√{square root over ((y−yi)2+z2)}/c (3)
In the above equations, the focal point on transmit is at position (x,y,z) and the delays are calculated independently for the element at position xj,yi. The variable c is the assumed speed of sound in the propagating medium. Note that in the case of perfect, non-separable focusing, the delay for transducer element, elei,j, is computed as:
τi,j=√{square root over ((x−xj)2+(y−yi)2+z2)}/c (4)
The separability assumption of the delays in azimuth and elevation is not perfect and the largest errors in the delay profile will occur on the outer elements of the focusing aperture. However, for small steering angles, and large f/#'s this separability assumption provides satisfactory results and ease of electronic implementation.
The delays for all column elements along the elevation are similar. The delay profile can be symmetrical, with a maximum delay at the center for a focus in the elevation plane. The amount of delay determines the focal length. Shallow focus depth requires a relatively longer delay, for example on the order of hundreds of nanoseconds, while deeper focus depth requires shorter delays, for example on the order of a few nanoseconds. Another technique employs a programmable delay along the elevation direction for all columns. All N columns may receive drive signals that are delayed with respect to each other. Additional delays are generated to add further delay along the column elements, where an element along the column can be delayed differently with respect to its adjacent neighbor on the same column. Asymmetrical delays with respect to the center element on a column thus can also be achieved.
In another embodiment, programmable delays are employed along the elevation direction, where the elevation delays are a summation of a coarse, linear delay and a fine, arbitrary delay. Again, all N columns receive drive signals that are delayed with respect to each other. Elevation delays are generated to add further delay along the column elements, where each element along the column is delayed by a coarse and fine delay, where the coarse delay may be linear between adjacent elements and the fine delay may be linear or non-linear between adjacent elements. The linear delay and fine delay along the column elements can be different from column to column. Therefore, the effective delay for an array element elei,j will be the summation of the group column delay, τj, the linear coarse row delay, τi,coarse, and the fine row delay, τi,fine.
τi,j=τj+τi,coarse+τi,fine (5)
Where in one preferred embodiment:
τj=(√{square root over ((x−xj)2+(y−ymin)2+z2)}−√{square root over (x2+y2+z2)})/c (6)
τi,j,fine=(√{square root over ((x−xj)2+(y−ymin)2+z2)}/c−τj−τi,j,coarse (7)
In the above equations, the focal point on transmit is at position (x,y,z) and the delays are calculated independently for the element at position xj,yi. The variable c is the assumed speed of sound in the propagating medium. In equation (6) the ymin parameter is calculated by projecting the focal point, (x,y,z) onto the 2D transducer plane and calculating the transducer row position with minimum distance to the projected focal point. The slope of the coarse delay, Δτ, can be calculated such that the fine delay can be used to give a good approximation of the perfect 2D delays.
It should be clear to one skilled in the art that the above methodology for calculating delays gives a much better approximation to the 2D focal delays of equation (4) compared to the X-Y separable delays previously mentioned. The improved delay calculation comes at the expense of requiring a coarse delay clock, fine delay clock, and some more register bits for implementing the different delays on a column by column basis. However, this method is easier to implement in an integrated circuit than a fully arbitrary delay in two dimensions with fine clock delays and individual element routing. In another embodiment, a cascaded series of flip flops gate a clock arriving at the column from the Tx beamformer with appropriate delay. This delay is then propagated in the column by a different clock whose frequency is programmable, but synchronized to Tx clock that generated the delay for drivers for the various column drivers. For symmetrical delay around a central element on the column, the flip flop chain generating the delays stop at the central element of the column, where the delay profile is symmetrical around the center as noted in
In some embodiments, each element on a column has a dedicated transmit driver. In some embodiments, each element driver includes a digital delay circuit driven by a clock, e.g., TxB Clk. The delay circuit in one embodiment comprises multiple flip flops as shown in
Referring to
In some embodiments, a cascaded series/chain of flip-flops gate the transmit clock arriving at one or more column from the transmit driver for that column with a pre-determined or pre-programmed delay that is appropriate. In some embodiments, this delay is then propagated in the column by a different clock whose frequency is programmable, but synchronized to the transmit clock that generating the delay for drivers for the various column drivers. In some embodiments, the flip-flop chain generating the delay(s) stop at the central element of the column, where the delay profile is symmetrical around the center as in
In embodiments, elevation focus is achieved using various delay profile. Using a linear delay profile in the elevation direction such that delay monotonically increases or decrease from bottom to top of column may steer the beam in the elevation direction. On top of that, some additional curvature to the beam, where curvature is zero at ends of columns, may allow focus in addition to beam steering. Linear approximations of theoretical delays needed can be sufficiently accurate to provide steering and focus and allow economic implementations described in embodiments herein.
In embodiments, the O electrodes in each column (e.g., 2003-11-2003-m1) may be electrically coupled to a common conductor. For instance, the circuit elements in the ASIC chip may be electronically controlled so that the O electrodes in each column may be electrically coupled to each other. In such a configuration, the O electrodes in each column may receive the same electrical pulse through a common transmit driver or per a multiplicity of drivers with identical electrical drive signals during the transmit mode. Similarly, the O electrodes in each column may simultaneously transmit the electrical charge to a common amplifier during the receive mode. Stated differently, the piezoelectric element in each column may be operated as a line unit (or equivalently line element).
In embodiments, during the transmit mode, a signal may be transmitted from a transmit driver (e.g., 2916-1) to a column of second O electrodes via a conductor (e.g., O12) so that the column of piezoelectric elements may generate pressure waves as a line unit. During the transmit mode, each switch (e.g., 2912-1) may be toggled to a corresponding transmit driver (e.g., 2916-1).
In embodiments, the imaging system 2900 may process the reflected pressure waves in two different methods. In the first method, the amplifiers 2910-1-2910-n may receive electric charge signals from the first O electrodes, i.e., each amplifier may receive signals from a row of the first O electrodes. This method allows biplane imaging/mode, where for a two dimensional image, the biplane image may provide orthogonal perspectives. Also, this method may provide more than two dimensional imaging capability. The biplane imaging may be helpful for many applications, such as biopsy. It is noted that, in this method, the transmitting and receiving modes may be performed simultaneously. In the second method, the switches 2912 may be toggled to the amplifiers 2914 so that each amplifier may receive and process the electrical charge signals from a corresponding column of the second O electrodes.
In embodiments, a line unit, which refers to a column (or row) of O electrode electrically coupled to an O conductor, may operate as a transmit unit or a receive unit or both. In embodiments, even though the conductors O1-Om are arranged in orthogonal directions to the conductors O12-On2, the directions may be electronically programmed and electronically adjustable. For instance, the gain of the amplifiers 2910 and 2914 may be adjustable electronically, where gain control leads are implemented in the amplifiers. In embodiments, the length of each line elements (i.e., the number of piezoelectric elements in each line element) may also be electronically adjusted. In embodiments, this may be achieved by connecting all signal electrodes of every piezoelectric element to corresponding nodes in the ASIC chip and, where the ASIC programs the connection between the signal electrodes of the elements to be connected to each other, transmit drivers or amplifiers as appropriate.
In embodiments, a circuit element 3001 may be electrically coupled to the piezoelectric element 3000 and include two amplifiers 3010 and 3016, such as low noise amplifiers, and a transmit driver 3018. In embodiments, the switch 3014 may have one end connected to the O electrode 3004 through the conductor 3012 and the other end that may toggle between the amplifier 3016 for the receive mode and a transmit driver 3018 for the transmit mode. In embodiments, the amplifier 3016 may be connected to other electronics to further amplify, filter and digitize a receive signal, even though an amplifier is used to symbolically represent the electronics. The transmit driver 3018 may be a multistage drive and may generate an output with two or more levels of a signaling. The signaling can be unipolar or bipolar. In embodiments, the transmit driver 3018 may include a switch interconnecting an input to an output of a driver under electronic control of the driver, which is not explicitly shown in
In embodiments, the signal of the transmit driver 3018 may be pulse width modulated (PWM), where, by controlling the pulse widths on a per element basis, a weighting function may be created on a transmitted ultrasound signal. This may for example perform a windowing function, where the transmit signal is weighted by a window function. In embodiments, the weighting coefficients may be achieved by varying the duty cycle of the transmit signal as is done during PWM signaling. This kind of operations may allow for transmit apodization, where the side lobes of a radiated signal are greatly attenuated, allowing for a higher quality image.
In embodiments, a transceiver array may be disposed in a transceiver substrate and include an n×n array of the piezoelectric element 3000 and an n×n array of the circuit elements 3001 may be disposed in an ASIC chip, where each piezoelectric element 3000 may be electrically coupled to a corresponding one of the n×n array of the circuit elements 3001. In such a case, the transceiver substrate may be interconnected to the ASIC chip by 3n2 bumps. In embodiments, each column (or row) of piezoelectric element array may be operated a line unit, as discussed in conjunction with
In embodiments, the sub-piezoelectric element 3021-1 may be in the receive mode during the entire operational period while the sub-piezoelectric element 3021-2 may be in either transmit or receive mode. In embodiments, the simultaneous operation of transmit and receive modes may allow the continuous mode Doppler imaging.
In embodiments, when the transmit driver 3018 transmits a signal to the electrode 3004, the power levels of the pressure wave generated by the sub-piezoelectric element 3021-2 may be changed by using pulse width modulation (PWM) signaling. This is important, for example, when switching from B mode to Doppler Mode imaging, signal power transmitted into the human body may be long and if power levels are not reduced, tissue damage may occur. Typically, in the conventional systems, different fast settling power supplies are used for B Mode and various Doppler Mode imaging to allow transmit drive voltages to differ in the 2 cases to for example not create excessive power in Doppler mode. Unlike the conventional systems, in embodiments, the power level may be changed by using the PWM signals on the transmit without using the conventional fast settling power supplies. In embodiments, rapid switching between Doppler and B mode imaging is desired to co-image these modes together. In embodiments, the ground electrodes of the piezoelectric element may also be separated from each other and connected to the ground separately. In embodiments, this independent grounding may reduce the noise and result in faster settling times. In embodiments, power transmitted may also be reduced by reducing the height of the transmit columns under electronic control. This again facilitates use of same power supply for both Doppler and B mode and meet power transmission requirements in each mode. This also allows co imaging.
As depicted in
In embodiments, the control unit 3150 may decide which piezoelectric elements need to be turned on during the transmit mode. If the control unit 3150 decides not to turn on a second piezoelectric element, the first switch (e.g., 3102-2) and the second switch (e.g., 3104-2) may be turned off, while the third switch (e.g., 3106-2) may be turned on so that the O and X electrodes have the same electrical potential (i.e., there is a net zero volt drive across the piezoelectric layer). In in embodiments, the third switches 3106 may be optional.
In embodiments, during the receive mode, the first switch (e.g., 3102-1) may be turned on so that the electrical charge developed in the O electrode may be transmitted through the conductors 3110-1 and 3120 to the amplifier 3128. Then, the amplifier 3128 may receive electrical charge signal (or, equivalently, sensor signal) 3126 and amplify the sensor signal, where the amplified signal may be further processed to generate an image. During the receive mode, the second switch (e.g., 3104-1) and the third switch (e.g., 3106-1) may be turned off so that the received signal may not be interfered. It is noted that the entire array of the circuit element 3140-1-3140-n may share a common amplifier 3128, simplifying the design of the circuit 3100. In embodiments, the X electrodes of the piezoelectric elements may be electrically coupled to the ground or a DC bias voltage via the conductors 3112-1-3112-n, where the conductors 3112-1-3112-n may be electrically coupled to a common conductor 3152.
In embodiments, the circuit 3100 may be coupled to a column of piezoelectric elements (e.g., 2002-11-2002-n1) in
In embodiments, the frequency of the pulses in the waveforms 3300 and 3400 may vary depending on the nature of the signal needed and need to contain the frequency at which membrane underlying the pMUT is responsive to. In embodiments, the waveforms may also be complex signals, such as linear or non-linear frequency modulated chirp signals, or other coded signals using the Golay codes.
In embodiments, the circuits for driving the piezoelectric elements may further be designed such that the transmit output from the underlying membrane may be symmetrical in shape. In embodiments, for each signal pulse in the waveform 3300 (or 3400), the rising edge of the pulse may be substantially symmetrical to the falling edge of the pulse with respect to the center of the pulse. This symmetry lowers the harmonic content of the transmit signal, especially the second harmonic and other even order harmonics signal. In embodiments, the signal pulse in the waveform 3300 (or 3400) may be a pulse width modulated (PWM) signal.
During the transmit operation, the transmit drive, e.g., 3018 in
In embodiments, the imager 126 may use a harmonic imaging technique, where the harmonic imaging refers to transmitting pressure waves on the fundamental frequency of the membrane and receiving reflected pressure waves at second or higher harmonic frequencies of the membrane. In general, the images based on the reflected waves at the second or higher harmonic frequencies have higher quality than the images based on the reflected waves at the fundamental frequency. The symmetry in the transmit waveform may suppress the second or higher harmonic components of the transmit waves, and as such, the interference of these components with the second or higher harmonic waves in the reflected waves may be reduced, enhancing the image quality of the harmonic imaging technique. In embodiments, to reduce the second or higher harmonic waves in the transmit waves, the waveform 3300 may have 50% duty cycle.
In
In some embodiments, apodization herein includes using variable voltage drive, for example, with lower weights near edges and fuller weights near the central parts of ultrasonic pulses. Apodization may also be implemented by changing the number of elements along each column or rows, either alone or in combination with other methods disclosed herein.
In embodiments, the reduction in the voltage of the pulses or waveforms may lower the temperature at the transducer surface. Alternately, for a given maximum acceptable transducer surface temperature, transducers operating at lower voltages may deliver better probe performance, resulting in better quality images. For example, for a probe with 192 piezoelectric elements to reduce power consumption, transmit pressure waves may be generated by using only a portion of probe (i.e., a subset of the piezoelectric elements) and scanning the remaining elements sequentially in time using a multiplexer. Therefore, at any point of time, in the conventional systems, only a portion of the transducer elements may be used to limit the temperature rise. In contrast, in embodiments, the lower voltage probe may allow more piezoelectric elements to be addressed simultaneously, which may enable increased frame rates of the images and enhanced image quality. Significant power is also consumed in the receive path where the received signal is amplified using LNAs. An imaging system typically uses a number of receive channels, with an amplifier per receiver channel. In embodiments, using temperature data, a number of receiver channels can be turned off to save power and reduce temperature.
In embodiments, the apodization may be achieved by varying the number of piezoelectric elements in each line unit according to a window function. In embodiments, such a window approximation may be achieved by electronically controlling the number of piezoelectric elements on a line or by hardwiring the transducer array with the required number of elements. Apodization can also be created by using a fixed number of elements, but driving these elements with varying transmit drive voltage. For example, for apodization in the elevation direction, maximum drive is applied to central elements on the column and lower driver level are applied to outer elements on both side of the column around the central element on the column. Apodization can also be achieved by varying the poling strength of elements based on location on a column.
In general, the heat developed by a probe may be a function of the pulse duration in the transmit pulse/waveform. In general, to make the pressure waves penetrate deep in the target with better signal to noise ratio (SNR), a piezoelectric element may require long pulse trains. However, this also degrades axial resolution and also generates more heat in the piezoelectric elements. So, in the conventional systems, the number of pulses emitted is small, sometimes one or two. Since longer pulses may create more heat energy, making it impractical for their use in the conventional systems. In contrast, in embodiments, the pulses and waveforms 3300 and 3400 may have significantly lower peak values, which may enable the use of long pulse trains, chirps or other coded signaling. In embodiments, the longer pulse trains do not degrade axial resolution since in the receiver matched filtering is performed to compress the waveform to restore resolution. This technique allows a better signal to noise ratio and allows signal to penetrate deeper into the body and allows for high quality imaging of targets deeper in the body.
In embodiments, a layer of Polydimethylsiloxane (PDMS) or other impedance matching material may be spun over the transducer elements. This layer may improve the impedance matching between the transducer elements and the human body so that the reflection or loss of pressure waves at the interface between the transducer elements and the human body may be reduced.
In
As shown in
In embodiments, smaller capacitance of each pixel may be driven efficiently by the distributed drive circuitry without other equalizing elements in between driver and pixel, eliminating the difficulty of driving a very large line capacitance. In embodiments, driver optimization may allow symmetry in rising edge and falling edges, allowing better linearity in transmit output, enabling harmonic imaging. (The symmetry is described in conjunction with
In embodiments, each line unit may be designed to consist of several sub units with separate control for each sub unit. The advantage of these sub units is that it may alleviate the difficulty of driving a large capacitive load for a line unit using one singe external transmit driver. For example, if two line units are created in the place of one line unit that includes the entire piezoelectric elements in a column, two different transmit drivers may be employed and each transmit driver may control half of the load of the full line unit. Also, even if one driver is used, driving the first half of the line unit and the second half of the line unit separately may improve the drive situation due to lower resistance connection to both ends of the line unit.
In embodiments, both the length and orientation of the line units may be controlled. For instanceE the line units may be arranged in both x and y directions. By way of example, in
Arrays of transducers may be made of elements such as shown in
In some embodiments, the X (or T) electrodes in a column may be electrically coupled to a conductor. In embodiments, these conductors may be electrically coupled to one common conductor. For instance, the conductors may be electrically coupled to one common conductor line so that all of the T electrodes in the array may be connected to the ground or a common DC bias voltage.
In some embodiments, each array may include piezoelectric elements that are arranged in a two dimensional array (e.g.,
In embodiments, the ASIC chip coupled to the transducer substrate may contain temperature sensors that measure the surface temperatures of the imaging device 120 facing the human body during operation. In embodiments, the maximum allowable temperature may be regulated, and this regulation may limit the functionality of the imaging device since the temperatures should not rise beyond the allowable upper limit. In embodiments, this temperature information may be used to improve image quality. For example, if temperature is below the maximum allowed limit, additional power may be consumed in the amplifiers to lower its noise and improve system signal-to-noise ratio (SNR) for improved quality images.
In embodiments, the power consumed by the imaging device 126 increases as the number of line units that are driven simultaneously increases. All line units in the imaging device 126 may need to be driven to complete transmitting pressure waves from the whole aperture. If only a few line units are driven to transmit pressure waves, wait and receive the reflected echo at a time, it will take more time to complete one cycle of driving the entire line units for the whole aperture, reducing the rate at which images can be taken per second (frame rate). In order to improve this rate, more line units need to be driven at a time. In embodiments, the information of the temperature may allow the imaging device 120 to drive more lines to improve the frame rate.
In some embodiments, each piezoelectric element may have one bottom electrode (O) and one or more top electrodes (X and T) and have more than one resonance frequency.
In embodiments, the electrical charge developed during the receive mode is transferred to an amplifier, such as 2910, 2914, 3010, 3016, 3128, and 3806. Then, the amplified signal may be further processed by various electrical components. As such, it should be apparent to those of ordinary skill in the art that the each of the amplifiers 2910, 2914, 3010, 3016, 3128, and 3806 collectively refers to one or more electrical components/circuits that process the electrical charge signal, i.e., each amplifier symbolically represents one or more electrical components/circuits for processing the electrical charge signal.
In embodiments, the receiver multiplexer 3820 may include multiple switches 3822 and the receiver AFE 3830 may include multiple amplifiers 3832. In embodiments, each of the switches 3822 may electrically connect/disconnect a circuit 3804 to/from an amplifier 3832. In embodiments, the transmitter multiplexer 3824 may include multiple switches 3826 and the transmit beamformer 3834 may include multiple transmit driver 3836 and other circuitry not shown to control the relative delay between transmit driver waveform of the various drivers, and other circuitry not shown to control the frequency and the number of pulses for each of the transmit drivers. In embodiments, each of the switches 3826 turn on during a transmit operation and connect to circuit 3804, while switches 3822 turn off, while switch 3810 connects to transmit driver 3808. Similarly, during a receive operation, switches 3826 turn off while switches 3822 turn on, while switch 3810 is connected to amplifier 3806.
In embodiments, the switches 3810 may be toggled to the transmit drivers 3808 during the transmit mode and toggle to the amplifiers 3806 during the receive mode. In embodiments, a portion of the switches 3822 may be closed so that the corresponding circuits 3804 may be set to the receive mode. Similarly, a portion of the switches 3826 may be closed so that the corresponding circuits 3804 may be set to the transmit mode. Since a portion of the switches 3822 and a portion of the switches 3826 may be closed simultaneously, the imager assembly may be operated in both transmit and receive modes simultaneously. Also, the receiver multiplexer 3820 and the transmitter multiplexer 3824 reduce the number of ASIC pins. In embodiments, the receiver multiplexer 3820, receiver AFE 3830, transmitter multiplexer 3824, and transmitter beamformer 3834 may be included in the circuits 202a or portions may also reside in 215a in
In embodiments, each piezoelectric may have more than two electrodes, where one electrode may be in the transmit mode to generate pressure waves while the other electrode may be simultaneously in the receive mode to develop electrical charge. This simultaneous operation of transmit and receive modes allow for better Doppler imaging
Movement in target being imaged may cause errors in the resulting image and it may be desirable to reduce these errors. An example of movement is when performing cardiac imaging where the heart tissue is moving. High frame rates can be desirable to reduce impact of movements. Therefore, improving frame rates while maintaining electronic azimuth and elevation focus and apodization can be important. This may not only reduce burring in images but also allow for better images using dynamic focus in the receiver by electronically altering azimuth and electronic focus as a function of depth. Frame rate improvement can be achieved in a dual stage beamformer illustrated in
It may be desirable to output a larger pressure level (without exceeding regulatory limits) to improve image quality. The value of equalization is the increase in pressure output in the frequency region of interest. This increase in pressure output results in a larger signal output that results in an improved signal to noise ratio and improved signal penetration into the tissue, improving imaging depth. PMUTs are highly capacitive and adding inductances in series with them can help reduce reactance and better match driver impedance to assist with increased power transfer.
The circuit of
In the embodiment of
In some embodiments, although electronic or electrical connections between individual elements shown in figures herein are hardwired or physical connections, different digital connections may be used to thus enable programmable and more flexible digital communications. In some embodiments, such digital connections may include but not limited to switches, plugs, gates, connectors, etc.
Although certain embodiments and examples are provided in the foregoing description, the instant subject matter extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses, and to modifications and equivalents thereof. Thus, the scope of the claims appended hereto is not limited by any of the particular embodiments described. For example, in any method or process disclosed herein, the acts or operations of the method or process may be performed in any suitable sequence and are not necessarily limited to any particular disclosed sequence. Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding certain embodiments; however, the order of description should not be construed to imply that these operations are order dependent. Additionally, the structures, systems, and/or devices described herein may be embodied as integrated components or as separate components.
For purposes of comparing various embodiments, certain aspects and advantages of these embodiments are described. Not necessarily all such aspects or advantages are achieved by any particular embodiment. Thus, for example, various embodiments may be carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may also be taught or suggested herein.
As used herein A and/or B encompasses one or more of A or B, and combinations thereof such as A and B. It will be understood that although the terms “first,” “second,” “third,” etc. may be used herein to describe various elements, components, regions and/or sections, these elements, components, regions and/or sections should not be limited by these terms. These terms are merely used to distinguish one element, component, region or section from another element, component, region or section. Thus, a first element, component, region or section discussed below could be termed a second element, component, region or section without departing from the teachings of the present disclosure.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including,” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components and/or groups thereof.
As used in this specification and the claims, unless otherwise stated, the term “about,” and “approximately,” or “substantially” refers to variations of less than or equal to +/−0.1%, +/−1%, +/−2%, +/−3%, +/−4%, +/−5%, +/−6%, +/−7%, +/−8%, +/−9%, +/−10%, +/−11%, +/−12%, +/−14%, +/−15%, or +/−20% of the numerical value depending on the embodiment. As a non-limiting example, about 100 meters represents a range of 95 meters to 105 meters (which is +/−5% of 100 meters), 90 meters to 110 meters (which is +/−10% of 100 meters), or 85 meters to 115 meters (which is +/−15% of 100 meters) depending on the embodiments.
While preferred embodiments have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the scope of the disclosure. It should be understood that various alternatives to the embodiments described herein may be employed in practice. Numerous different combinations of embodiments described herein are possible, and such combinations are considered part of the present disclosure. In addition, all features discussed in connection with any one embodiment herein can be readily adapted for use in other embodiments herein. It is intended that the following claims define the scope of the disclosure and that methods and structures within the scope of these claims and their equivalents be covered thereby.
Claims
1. An ultrasonic imaging system comprising a transducer comprising:
- a) at least one transducer element, wherein each transducer element has two terminals, wherein the at least one transducer element is in a transmit mode;
- b) at least one transmit driver, wherein each transmit driver is connected to each first terminal of the at least one transducer element; and
- c) at least one inductor comprising two terminals, wherein each first terminal of each inductor is connected to each second terminal of each transducer element, wherein each second terminal of each inductor is connected to a bias voltage.
Type: Application
Filed: Oct 5, 2022
Publication Date: Jun 29, 2023
Inventors: Yusuf HAQUE (Woodside, CA), Sandeep AKKARAJU (Wellesley, MA), Janusz BRYZEK (Oakland, CA), Andalib CHOWDHURY (San Jose, CA)
Application Number: 17/938,075
