Abstract: A method and system for compensating for steering anomalies by adjusting aperture in steered phased array transducer systems adjusts the aperture of a transducer array to effectively compensate for the steering anomalies. The aperture of the transducer array can be varied depending upon the steering angle of the beam and the resultant steering angle anomalies.

Abstract: The invention pertains a bathymetric sonar system involving a single swept transmit beam projector system which compensates for ship attitude and positioning changes. A sonar transducer array has a matrix of acoustic projector elements arranged in a plurality of substantially parallel rows and a plurality of substantially parallel columns; and means for causing each of the projector elements to generate an acoustic signal at a frequency and phase independently from each other projector element. Preferably the transducer array is operated by causing the projector elements to generate an acoustic signal at a frequency and phase independently from each other projector element, at a frequency and phase which is initially the same as the frequency and phase of each other element in its column and such that the frequency and phase of the projector elements in each column is different from each other column. Thus a single swept beam is projected toward the ocean floor.

Abstract: The interferometer, which is preferably in the form of a sonar, can have a single projector array and a single receiver array. The projector array comprises a first subset of projector elements that function as a first pseudo projector and a second subset of projector elements that function as a second pseudo projector. One or more of the projector elements belong in both the first and the second subsets, such that one or more of the projector elements function as part of both the first and the second pseudo projectors. A receiver is operative for receiving reflected portions of the signals emitted by the pseudo projectors. A processing system analyzes the signals received by the receiver to at least partially determine the position of an object.

Abstract: For improving 3D focussing and side lobe suppression in a direction finding system identical groups of transducers are provided at each side of a first and a second axis, which are inclined by an angle 0°≠&psgr;<180°, preferable &psgr;=90°. A first magnitude summation signal is derived from the first pair of transducer groups associated with the first axis and a second magnitude summation signal is derived from the second pair of transducer groups associated with the second axis. Furthermore, a differential signal is derived between the complex output signal of each pair of transducers. For each axis the absolute value of said differential signal is subtracted from the associated magnitude summation signal. The resulting two output signals, associated with said two axis, are then combined to finally obtain a three-dimensionally focussed beam pattern.

Abstract: The device comprises a transmitter (7) transmitting ultrasound into a predetermined space (5), a sensor (8) which senses the echoes from the transmission by the transmitter into the space in order to deliver a signal representative of the echoes, and electronic device for processing the signal in order to diagnose the possible presence of a moving body in the space (5). It further comprises a) device (10) for scanning the space (5) with the ultrasound beam output by the transmitter (7) and (b) device (11) for simultaneously moving the echo sensor (8) so as to optimize the signal/noise ratio of the output of the sensor (8).

Abstract: A phased-beam transducer is disclosed for transmitting and receiving steered acoustic beam signals that includes a sheet of piezoelectric material such as Polyvinylidene Fluoride (PVDF), a copolymer, piezo-rubber, quartz, 1-3 PZT composite, or similar transducer material. The transducer includes specially designed electrode on each side of the piezoelectric sheet. The transducer is a two channel device with a sine channel, cosine channel and a ground lead. A summing circuit is used to sum the sine and cosine channels with a 90 .degree. phase shift applied by a phase shift circuit to one of the two channels, for example, the sine channel. The transducer is designed to form a predetermined steered beam at a particular frequency. If a different sound wave frequencies are used, the transducer will form useful directional beams with different steer angles and beamwidths. Variable sector coverage is achieved by forming beams at different frequencies.

Abstract: An apparatus and method for filtering the effects of large amplitude signal fluctuations from elements of the cross-spectral density matrix of a detor array. The outputs of the array are sampled T times, and the values of each element of the matrix formed by using: ##EQU1## where Z.sub.li is the complex output of an sensor of the array at time i; Z*.sub.mi is the complex conjugate of the output of an array sensor at said time i; and k is an integer greater than 1. Because of the exponent k, small, relatively constant, terms will dominate, reducing the effect of large amplitude fluctuations. Preferably, the above value will be scaled according to: ##EQU2## which, besides being similarly filtered by the exponential terms, the resultant matrix element will have a magnitude corresponding to the actual power of the detected signal, after filtering.

Abstract: A feature imaging and adaptive focusing synthetic aperture processing met provides improved sharpness and easier classification of images derived from radar and sonar echo data by applying adaptive focusing and feature imaging to a sequence of echo data.

Abstract: An apparatus and method are provided for tracking the position in three dimensions of one or more objects underwater. Two multibeam sonar heads are positioned to operate in intersecting planes. The two multibeam sonar heads are synchronized to the time signals are emitted from a transmitter. The echoes of the emitted signals are detected by both heads and the data from the two sonar heads is transmitted to a computer that processes the data and can display the position of the one or more objects.

Abstract: An adaptive beamforming system for broadband sonar with a convergence time on the order of the pulse duration and effective interference nulling capabilities which enhance desirable echoes. The method uses an element based time implementation algorithm in which beam data that is formed in the direction of each interferer is successively subtracted from the element data using an adaptive FIR filter. The system can be applied to impulsive source sonar data and passive sonar data.

Abstract: A sonar sensor array having a multi-layer tiling arrangement for the indiual elements that increases surface area available for each element while maintaining the inter-element spacing required to avoid spatial aliasing when the received signals are combined to form a sonar beam. The array comprises outer and inner arrays of transducer elements for converting an acoustic signal to an electrical response. The transducer elements of the outer array are positioned such than a grid of isolation spaces separates each of the transducer elements. The transducer elements of the inner array are also positioned such that a grid of isolation spaces separates each one of the transducer elements. The electrical response generated by the transducer elements of the inner and outer arrays are coupled to a beamformer which processes the responses to produce an output signal.

Abstract: For improving the focussing of a direction finding system comprising at least two identical transducers or groups of transducers (W.sub.L, W.sub.R), on the one hand a magnitude summation signal (.vertline..vertline.+.vertline..vertline.) and on the other hand a differential signal (.vertline.-.vertline.) are derived from the transducer output signals (,). Thereafter the magnitude of the differential signal is subtracted from the magnitude summation signal.

Abstract: The advanced vertical array beamformer signal processor accomplishes acoustic beamforming of an underwater vertical array used in shallow water utilizing matched beam processing to suppress generated noise and/or ship radiated noise thereby increasing the detectability of a submerged source emitting only a low noise signal. The processor exploits the difference of the signal arrival angle of both active and passive signals with that of the wind generated noise and ship radiated noise which is prominent in downward refractive sound speed profiles. After filtering the undesired noise, the processor uses the depth of the source as a clue for detection; the processor is an energy detector focused on the returns of a deep source.

Abstract: This disclosure relates to a system for automatically measuring and compensating for any angle of misalignment of a forward-looking sensor of a vehicle. The sensor provides data representing the azimuth angle and the range of a target such as another vehicle. For each angle and range reading of the sensor, the location point of the target is estimated; after a series of such readings, the trajectory line of the target is estimated. The angle of misalignment is estimated from the angle between the trajectory line and the path of travel of the host vehicle. In subsequent readings of the sensor, the estimated angle of misalignment is subtracted from the measured azimuth angle to produce an accurate azimuth angle of the target. The accurate azimuth angle is provided for use by another unit such as a collision warning system and/or an intelligent cruise control.

Abstract: The system provides three-dimensional real time imaging, with features that serve to control acoustic effects that cause interference. Systems are disclosed for medical imaging and other applications in fields that utilize radiated wave signals. The system includes visualization methods to enable guidance of surgical instruments as well as general medical diagnostic usage. The present invention uses a beamformed television method which achieves visual format imaging. Beamformed television includes orthogonal arrays to efficiently resolve two dimensions of a scene with measures to control grating lobes. Beamformed television also includes a method that reduces the time to transmit and receive signals by use of a single burst transmission of multiple frequency codes from each transducer which causes multiple, coded transmit beams that are radiated simultaneously. The addition of step chirp operations achieves highly precise range resolution which makes visual format imaging possible at selected ranges.

Abstract: A microelectromechanical sensor for detecting acoustic signals propagating through the ground, including reflected signals, has a cantilever provided with capacitance measurement to detect deflection or twisting of the cantilever due to the presence of acoustic signals. The cantilever size and shape may be changed to increase sensitivity to a particular frequency. An array of sensors may be used to detect buried objects, such as land mines.

Abstract: A sonar system includes a pulse generator that produces an electrical signal having a plurality of frequencies. An acoustic radiator formed as a first blazed acoustic array is arranged to be driven by the electrical signal from the pulse generator. The blazed acoustic array includes a plurality of acoustic elements rotated away from the general plane of the array. The acoustic elements are arranged to be driven by the electrical signal from the pulse generator so that they radiate a sonic field that includes a plurality of sonic frequencies with each frequency being radiated at a characteristic angle. An acoustic receiver formed as a second blazed acoustic array is arranged such that components of the acoustic field reflected from the target toward the acoustic receiver produce acoustic waves having frequencies that correspond to the angles of incidence of the reflected acoustic field components. The signals indicative of the reflected frequencies are processed to form an image of the target.

Abstract: The sonar array post processor employs an adaptive processing, known as matched beam processing, in the beam domain which takes analog or digital conventional beamforming outputs from a sonar array, multiplies them by a set of adaptive weighting coefficients and produces a new set of beams. The new output beam of highest intensity yields the ideal maximum signal gain and correct target bearing. Continuous target tracking provided by the sonar array post processor in the endfire direction of a horizontal line array minimizes the towing ships maneuvers and for, a bottom mounted surveillance system, a smaller number of arrays are required.

Abstract: An array transducer ultrasound beamformer includes a plurality of processing channels, one for each active element of the transducer array. Each channel includes a digitizing unit for converting the received signal to digital samples and a time multiplexed delay unit for producing a primary stream of delayed TDM samples corresponding to one or more beams. Within each channel, the primary stream of delayed TDM samples is demultiplexed in order to separate the stream in a plurality of secondary streams of delayed TDM samples, wherein each of the secondary streams corresponds to a portion of a beam or a single beam.

Abstract: Sonar signal processing apparatus for use with an array of transducers, comprising means for reconstructing delayed time series data from an original sampled data stream.

Abstract: A method of measuring an angle in three dimensions relative to a reference direction. In the method:a transducer array emitter is placed in a known position relative to the reference direction;the transducers of the array are excited so as to emit ultrasound waves in air mainly in a firing direction;by applying phase offsets between the excitation signals for the transducers of the array, the firing direction is varied, thereby causing it to scan a given observation zone, while simultaneously the echo received in the vicinity of the emitter is measured; andthe looked-for angle is determined from the known position of the emitter relative to the reference position, and from the firing direction at the moment when the echo amplitude is at a maximum.

Abstract: A broadband sonar system is configured to be coupled to a narrow band sonar sensor array having a plurality of sensor groups configured in subarrays. Each of the sensor groups within a subarray is spaced equidistantly from adjacent sensor groups within the same subarray. The sonar system includes a plurality of signal compensation filters, each being coupled to a respective one of the sensor groups for receiving signals from the respective sensor group and weighting the signals to generate respective output signals. The weighting of the signal from a first sensor group having a first SNR is greater than the weighting for the signal from a second sensor group that has a second SNR when the first SNR is greater than the second SNR, so as to maximize the SNR of the array. At least one broadband beamformer is coupled to the signal compensation filters for combining the output signals for determining ranges to targets.

Abstract: A system for generating a wide-angle, forward-looking bathymetric map of an region ensonified by single ping. A transmitter generates a large angle transmit pulse. An array of acoustic transducer elements operates to transmit the pulse, receive acoustic return signals and convert the returns into digital acoustic data. A receiver matched filters, shades and steers the data through a series of horizontal angles. For each horizontal angle steered to, the receiver generates vertical beams and identifies detections as those vertical beams having magnitudes greater than a detection threshold. Vertical beam forming and detection identification is repeated for each time slice in a series of time slices over the ping cycle. The identified detections are refined using a curve fitting analysis and stored in equal angular vertical bins. A bottom profile is generated from the refined angles and magnitudes.

Abstract: A method and apparatus for preventing the occurrence of range ambiguities and Doppler ambiguities in both a radar and sonar environment. A series of N pulses are produced, each of which contains a number of contagious subpulses. Each of the subpulses exhibit a different frequency than the remaining subpulses in that particular pulse. Furthermore, the order of appearance of the subpulses in each of the pulses is unique with respect to the remaining pulses in the series. A matched filter receiver and Doppler processor are used to provide auto correlations and cross correlations to prevent the range ambiguities and Doppler ambiguities.

Abstract: A process and device for detecting objects, in particular mines, dispersed in an area of land. The process implements a plurality of acoustic transducers. After determination of an optimal operational frequency, a brief acoustic pulse is emitted into the ground and then successive temporal reversals of signals received by the transducers focus detection on a first object. At least two transducers for which the propagation times are roughly equal are located and at least one location direction, defined as the mean perpendicular of the segment joining the at least two transducers, is determined.

Abstract: An acoustic imaging apparatus and method that achieves desired delays with coded signals. Linear, curved linear and sector scanning is provided in 1-D arrays and planar, curved planar and sector scanning is provided in 2-D arrays. Composite and non-linear implementations are presented. Dynamic and discrete dynamic focusing is disclosed for the relevant arrays. The 2-D array makes possible 3-D imaging.

Abstract: A beamformer includes an array having a plurality of channels of delay elements which are constructed of charge coupled devices (CCDs). Each channel has a first plurality of delay elements cells which perform beam focussing and a second plurality of delay elements which perform beam steering. In this manner beam steering delays and beam focussing delays may be calculated independently. Typically, the second plurality of delay elements have a resolution which is typically coarser than the resolution of the first plurality of delay element cells which function to focus the beam. A signal may be inserted into any one of the delay elements of the first plurality to provide an appropriate delay. The signal is then output from the last delay element of the first plurality to the second plurality. The signal is delivered from a selected delay element of the second plurality to a charge sum data bus, which combines the signals output from each of the channels.

Abstract: An apparatus and method for beamforming for a toroidal volume search sonar. onar array vehicle motion is used to reduce reverberation by fixing beams geometrically in space to prevent beam contact, prior to a specified range, with the sea surface or sea bottom interfaces. Reverberation is further reduced by creating a composite beam from one scanned beam containing the target dominated by surface reverberation and another dominated by bottom reverberation. A correlation and averaging procedure is applied to the two scanned beams to further reduce the reverberation in the composite beam. To further reduce reverberation, the two beams selected for correlation and averaging processing are chosen such that the number of common elements associated with the two beams is a minimum within a given angular separation.

Abstract: Many transducers suffer from the problem that the way they behave in response to actuating signals of different frequencies, and particularly their directional properties, or beamwidth, depends on their physical size and shape. What is required is a transducer which changes its effective size as a function of frequency, and the present invention proposes such a transducer in which the transducer element (11, 12, 13)--the active part of the transducer, such as the diaphragm in a loudspeaker--permits automatic frequency-sensitive control of the beamwidth by providing frequency-dependent "shading" of the local response to the signal across the face of the element, using a resistive coating (11) in association with a capacitive layer (12, through which the currents representing that signal travel) such that the CR value of the combination varies over the surface of the element.

Abstract: Method and means for preventing trespassing and/or unauthorized staying in an area outdoors or indoors, e.g. in a building, part of a building, in vehicles, vessels, etc., sound signals with periodically varying frequencies with the variation of the frequencies out of phase are transmitted from several sound generators in such directions that the sound waves from the sound generator meet within the area to be protected.

Abstract: A broadband sonar system in which a broadband output from a conventional narrowband sonar sensor array is used to capture broadband acoustical input signals. A single broadband beamformer receives the input from each of the sensors (such as hydrophones) of the array. The broadband output signal from each sensor of a particular subarray is coupled to a corresponding one of a plurality of first filters. Each first filter emphasizes those frequencies of each subarray which have the least noise. In addition, the output is attenuated for frequencies below the design frequency, with lower frequencies being attenuated to a greater degree than higher frequencies. A plurality of second and third filters, each corresponding to a subarray, are provided to compensate for the effects of the frequency and sensor spacing on the signal as the beam rotates.

Abstract: A sonar apparatus using a phased array technique for steering an acoustical beam for scanning an underwater area. The sonar apparatus includes a scanning transducer having multiple elements for transmitting and steering the acoustical beam and receiving its reflection from an object, an electronic control circuit for generating steering information and computing a relative location of the object, and an input/output section for displaying the relative location to a user. The control circuit includes a software level/align control for compensating for mis-leveling or mis-alignment during installation, a scan control capable of selecting a scan center direction and a scan width in one degree increments, a forward gain control for optimizing the sensitivity of the sonar apparatus in a forward looking scan, and a combination of a time variable gain control and an autorange control for minimizing the reflection of sidelobes of the acoustical beam.

Abstract: An integrated torpedo sonar signal processor having an integrated analog-digital conversion component is provided. The torpedo sonar signal processor has four groups of low-pass filtered analog-to-digital converters, each group containing thirteen converters. The output of a group (thirteen converters) is a serial data signal which is outputted to a field programmable gate array which, in turn, converts the combined signal to parallel data word. The parallel data word is outputted to a first digital signal processor which in turn outputs to a second dual-port digital signal processor, the processor providing prefiltering and space-time processing. The output signal is then sent to a beamformer dual-port digital signal processor which has an attached external memory. The beamformer signal is then outputted to a signal processor component containing four dual-port digital signal processors and a common external memory.

Abstract: A method and apparatus for determining the depth of a marine target relat to the surface of the water which encompasses an analog processing circuit for detecting and analyzing signals reflected respectively from a target and the water surface, a timing and gating circuit respectively responsive to a target echo signal for initiating a timing sequence and to a surface echo signal for terminating the timing sequence, and a depth readout circuit for indicating the depth of the target below the surface at the instant the surface echo signal terminates the timing sequence.

Abstract: A shallow water sonar apparatus and a method of processing outputs from a shallow water sonar array, where the array consists of at most two elements for receiving the acoustic energy from a plurality of directions. The apparatus also includes a beamformer for processing the acoustic energy received by the two elements to produce a tapered beam pattern which approximates a beamformer output from an array including substantially more than two elements. The tapered beam pattern is produced by asymmetrically amplitude shading outputs of the two elements, such that the output of one of the two elements is summed, without shading, with an output of the second element, shaded by a coefficient factor of 0.23.

Abstract: An acoustic ranging and detection system comprises an acoustic transmitter for producing an acoustic ranging signal and first and second acoustic receivers positioned on either side of the acoustic transmitter. A support mounts the acoustic transmitter and both acoustic receivers for concurrent rotation about a central axis passing through the acoustic transmitter. A first motor is connected to the first acoustic receiver and is adapted to impart independent rotative movement thereto. A second motor is connected to the second acoustic receiver and is adapted to impart independent rotative movement thereto. A control system is responsive to echo signals from a target that are received by the first and second acoustic receivers to rotate the support to point the transmitter at the target and further operates the first and second motors to cause the respective acoustic receivers to be repositioned so as to manifest receiving beam patterns which exhibit central axes that intersect in the region of the target.

Abstract: A transducer capable of generating a phase-encoded wavefield is described. The encoded phase is related to the angular co-ordinates of direction of transmission. By decoding the phase values of the received wavefield, a direction can be obtained. Therefore, in navigation applications this transmitter gives additional location information not available from a single received signal using traditional methods such as "range-range" and "hyperbolic" systems. In its simplest configuration, the new transducer comprises two transducers which can be individually controlled. In more complex constructions use of more than two transducers increases the controllability of the desired phase characteristics of the resulting wavefield.

Abstract: In a digital ultrasound imaging system, artifacts due to spurious ultrasound reflections from a highly reflective object outside the region of interest are reduced in magnitude by apparatus included in the beamforming system of the digital imaging system. A null is formed in a specified direction in the ultrasound beam patterns by perturbing the time delay on each receive channel. After estimating the direction of the highly reflective, interfering object and computing a time delay perturbation using a very fast algorithm, a null approximately 10 dB deep is introduced into each beam in the direction of the interfering object. This null reduces the magnitude of artifacts in the image, thereby providing image enhancement.

Abstract: A pulsed-transmission, single frequency echo-ranging sonar system has a w-beam acoustic projector with sharp cutoff of energy radiated in directions other than the desired field of view and a nearly constant amount of acoustic energy throughout the desired vertical field.

Abstract: In accordance with the principles of the present invention, advantage is taken by the inventors of the fact that the speed of operation of the digital hardware in a digital beamformer can be reduced by providing, for example, multiple phases of the data signals and then processing the multi-phase data in N parallel summing paths. An interpolation-decimation filter receives the multi-phase data from the N parallel summing paths and provides at its output a signal having a reduced data rate (1/N). In accordance with this technique, the speed of operation of the individual digital circuits for forming the required beamforming delays is not increased as compared to conventional post-beamforming interpolation schemes, so that hereby the effective data rate is increased by a factor N and results in a decrease of the delay quantization error by a factor N. In accordance with the principles of the invention, the interpolation-decimation filter is incorporated into the beamformer at a most advantageous place.

Abstract: A pre-processor and adaptive beamformer processes an echo received by an array of receiving elements from a distant target from a transmitted signal having an arbitrary waveform capable of being represented as a complex modulation of a carrier frequency. Time blocks are formed from each element output represented by a series of time windows extending from an initial time appropriate to the arrival time of the echo to a final time appropriate to the time block. A correlation is performed of each time block with a replica of the transmitted signal. The correlation products are aligned with respect to time difference to within one sample period. The beamformer further aligns the correlation products with respect to time difference to substantially the same phase for each steering direction. Covariance estimates are formed using techniques of spatial averaging to generate adaptive weights optimized to suppress interfering signals without requiring the use of time averaging.

Abstract: An acoustic transducer is constructed as a stacked configuration of multiyer transducer elements separated from one another by an electrical insulating material. Each multi-layer transducer element has a layer of acoustically transparent electro-acoustic transducer material having opposing planar surfaces with electrically conductive material deposited thereon. For each multi-layer transducer element, the electrically conductive material is formed into parallel strips electrically isolated from one another on at least one of each element's opposing planar surfaces. The parallel strips associated with each multi-layer transducer element have a unique angular orientation.

Abstract: A transmitter for generating a steerable, variable frequency signal from an rray of projectors. An analog signal to be transmitted is sampled, digitized and stored in a circulating memory. A delay storage circuit includes time delays for each projector for each of predetermined beam directions. The successive locations in the recirculating memory correspond to signals having a time correspondence at predetermined unit delays from the signal then at the input terminal. The delay storage unit then produces a reading address for recovering, for each of the projector drivers, a signal value corresponding to an appropriate delay for obtaining the desired steering angle with a constant beamwidth signal. Frequency sensing circuitry can further compensate the signals by assigning each to a frequency bin and utilizing that bin to further define the delay for each projector and control the amplitude of the signal being sent to each projector.

Abstract: A multiple frequency acoustic transducer is constructed as a stacked confration of N groups of multi-layer transducer elements separated from one another by an electrical insulating material. Each multi-layer transducer element in an n-th one of the N groups has a layer of acoustically transparent electroacoustic transducer material whose thickness is determined by the n-th frequency of operation. Each multi-layer transducer element has opposing planar surfaces with electrically conductive material deposited thereon. For each multi-layer transducer element, the electrically conductive material is formed into parallel strips electrically isolated from one another on at least one of each element's opposing planar surfaces. The parallel strips associated with each multi-layer transducer element in any one of the n-th groups have a unique angular orientation in the n-th group.

Abstract: An acoustic transducer produces a limited diffraction beam during the transmit portion of a pulse-echo sequence that has sidelobes extending away from the beam axis in defined sectors. During the receive portion of the pulse-echo sequence a receive aperture for a limited diffraction beam is employed having sidelobes extending away from the beam axis in defined sectors that do not overlap the transmit sidelobes. Both limited diffraction Bessel beams and limited diffraction X waves are employed, and an acoustic transducer producing tenth derivative X waves is described.

Abstract: An ultrasonic imaging system provides dynamic focusing by using dynamic group delay in addition to dynamic phase focus. FIFO memory storage capacity in the beamforming circuit is increased to provide improved resolution of the data samples stored therein. These samples are selected by an address counter in response to both the advance of time and the accumulation of a phase advance clock count. After a Read Start signal, indicating the start of a beam, is supplied to the FIFO memory, the FIFO memory address is advanced, on each read instruction, by the number of address locations corresponding to the period of a pipeline channel. In addition, the address is incremented whenever the accumulated count of a phase advance clock exceeds an amount corresponding to the smallest increment of the data stored in the FIFO memory.

Abstract: A time delay-phase shift combination beamformer for applications where the required time delays for time delaying the received signal to achieve coherency exceed the reciprocal of the incoming signal's bandwidth, and having a time delay stage for coarse beamforming at a particular range and first beam direction and a phase shift stage for fine beam steering in a second direction at the particular range.

Abstract: A pulsed transmission, single frequency, high resolution sonar system has duced grating (side) lobes achieved by employing mechanically fixed antenna array stave tilt angles together with electronic focussing in which phase shifts are substituted for time delays.

Abstract: In accordance with the principles of the present invention, advantage is taken by the inventors of the fact that the speed of operation of the digital hardware in a digital beamformer can be reduced by providing, for example, multiple phases of the data signals and then processing the multi-phase data in N parallel summing paths. An interpolation-decimation filter receives the multi-phase data from the N parallel summing paths and provides at its output a signal having a reduced data rate (1/N). In accordance with this technique, the speed of operation of the individual digital circuits for forming the required beamforming delays is not increased as compared to conventional post-beamforming interpolation schemes, so that hereby the effective data rate is increased by a factor N and results in a decrease of the delay quantization error by a factor N. In accordance with the principles of the invention, the interpolation-decimation filter is incorporated into the beamformer at a most advantageous place.

Abstract: A curvilinear wideband, projected derivative-matched continuous aperture acoustic transducer includes a first curvilinear sensor having a predetermined spatial shading which is constrained to zero at its ends and has amplitude continuity between its ends; and a second curvilinear sensor area having a spatial shading which is the projected spatial derivative of the spatial shading of said first area and which has a discontinuous amplitude at its ends; the first and second spatially shaded areas being superimposed and coextensive along the sensing axis.