Abstract: An ultrasonic transducer includes a wear plate (2), a piezoelectric element (8) arranged rearwards of the wear plate and a rigid block (16) arranged rearwards of the piezoelectric element and configured to provide a backing mass for the piezoelectric element. The wear plate extends across the piezoelectric element and rearwards so as to provide a cap over the piezoelectric element and sides of at least a forward portion of the rigid block.

Abstract: Apparatus and methods of connecting mechanical resonating structures to a body are described. Multi-element anchors may include a flexible portion that flexes when the mechanical resonating structure vibrates. The flexible portion may have a length related to the resonance frequency of the mechanical resonating structures. Some of the multi-element anchors include elements that are oriented perpendicularly to each other. MEMS incorporating such structures are also described.

Abstract: A system and method for removing unwanted heat generated by a piezoelectric element of an ultrasound transducer. Some implementations have high thermal conductivity (HTC) material placed adjacent to the piezoelectric element. The HTC material can be thermally coupled to one or more heat sinks. Use of HTC material in conjunction with these piezoelectric element surfaces is managed to avoid degradation of propagating acoustic energy. Use of the HTC material in conjunction with heat sinks allows for creation of thermal paths away from the piezoelectric element. Active cooling of the heat sinks with water or air can further draw heat from the piezoelectric element. Further implementations form a composite matrix of thermally conductive material or interleave thermally conductive layers with piezoelectric material.

Abstract: The invention relates to an ultrasonic generator (1) with a resonator (3) for transmitting ultrasonic sound to a medium (6) arranged in a receptacle (5). In order to efficiently transmit the ultrasonic sound from the resonator (3) to the medium (6) via the receptacle (5) the resonator (3) comprises a clamping opening (4) for clampingly receiving the receptacle (5).

Abstract: A system and method for an ultrasonic array transducer is provided. The system includes a plurality of transducer elements, each including a positive electrode and a ground electrode. The system includes a plurality of twisted pair cables. Each twisted pair cable is operatively connected to a respective transducer element by way of a circuit connected therebetween. The circuit includes a plurality of first circuit conductors and a plurality of second circuit conductors. Each first circuit conductor is operatively connected to a respective ground electrode and to a respective twisted pair cable. Each second circuit conductor is operatively connected to a respective positive electrode and to a respective twisted pair cable. The system allows for discrete connections to be made at individual ground electrodes in the transducer array. As a result, appreciable time and labor savings in the process of forming the transducer system can be realized.

Abstract: Embodiments of thermal-acoustic sections for an aircraft for reducing noise along an acoustic path produced from an acoustic source are provided herein. The thermal-acoustic section comprises a first porous layer having a first characteristic acoustic impedance. A second porous layer is disposed adjacent to the first porous layer and has a second characteristic acoustic impedance that is greater than the first characteristic acoustic impedance. The thermal-acoustic section is configured to be positioned along the acoustic path such that at least a portion of the noise from the acoustic source is directed through the first porous layer to the second porous layer to promote absorption of the noise.

Abstract: An energy harvesting apparatus and method that is especially well suited for harvesting low frequency broadband vibration energy from a vibrating structure is presented. The apparatus includes a pair of disc springs that are arranged in an opposing relationship. A threaded fastening member and a threaded nut extend through apertures in each of the disc springs and enable a predetermined preload force to be applied to the disc springs. The preload effectively “softens” the disc springs, thus heightening the sensitivity of the disc springs to low frequency, low amplitude vibration energy. A piezoelectric material ring is secured to each of the disc springs. Each piezoelectric material ring experiences changes in strain as its associated disc spring deflects in response to vibration energy experienced from a vibrating structure.

Abstract: The present disclosure provides a micro device. The device has a micro-electro-mechanical systems (MEMS) movable structure, a plurality of metal loops over the MEMS movable structure, and a piezoelectric element over the MEMS movable structure. Frontside and backside capping wafers are bonded to the MEMS structure, with the frontside and backside capping wafers encapsulating the MEMS movable structure, the plurality of metal loops, and the piezoelectric element. The device further includes a magnet disposed on the frontside capping wafer over the plurality of metal loops.

Abstract: According to one embodiment, an ultrasonic probe includes a plurality of piezoelectric elements, a first electrode, a plurality of second electrodes, a plurality of stacked flexible printed circuit boards, and a plurality of connection portions. The plurality of piezoelectric elements are arrayed. The first electrode is provided on the emitting surface side of the plurality of piezoelectric elements. The plurality of second electrodes are respectively provided on the rear surface sides of the plurality of piezoelectric elements. The plurality of stacked flexible printed circuit boards respectively include a plurality of terminals. The plurality of connection portions electrically connect the second electrodes to the terminals. At least one of the flexible printed circuit boards extends longer than the flexible printed circuit board serving as an upper layer.

Abstract: The method of changing ultrasound wave frequency by using the acoustic matching layer presents a replaceable acoustic matching layer to offer an effective means of filtering the original broadband frequency of an ultrasonic transducer into certain composite discontinuous frequencies. The filtering effect could be improved by connecting the electrodes of the acoustic matching layer when it is made of a poled piezoelectric material. This method may provide novel applications for commercial ultrasonic transducers.

Abstract: An ultrasound probe includes a backing member, inorganic piezoelectric elements arranged on a top surface of the backing member, an acoustic matching layer disposed on and extending over the inorganic piezoelectric elements, and organic piezoelectric elements arranged on the acoustic matching layer.

Abstract: Disclosed is a transducer of an ultrasonic diagnosis device. Electrode patterns are formed inside a backing block, as one body, and thus, a prior art FPCB may be omitted.

Abstract: A transducer device includes a coupling cavity, a first resonant element and a second resonant element. The first resonant element is coupled to the coupling cavity and configured to send or receive acoustic signals. The second resonant element is coupled to the coupling cavity and configured to modify a frequency response of the first resonant element via the coupling cavity.

Abstract: An ultrasonic motor, comprising: a member to be driven including a contact surface; a vibrator including at least one contact part, and a piezoelectric element, the vibrator driving the member to be driven by an ultrasonic vibration excited by the piezoelectric element; a retention part for retaining the vibrator; and a pressurization unit including an elastic member so as to apply an impressing force on the at least one contact part against the member to be driven, wherein: the retention part includes an abutting part including a line contact part that receives the impressing force from the elastic member and comes into line contact with the pressurization unit; the abutting part has a shape formed of a part of a cylinder; and a center axis of the cylinder is parallel to the at least one contact part and perpendicular to a driving direction of the member to be driven.

Abstract: The present application provides a multilayer lateral mode coupling method for phased array construction and transducer devices built accordingly. This disclosure describes and demonstrates that the electrical impedance of a phased array can be substantially reduced and readily controlled to be close to the source impedance. The fabrication process is relatively simple and inexpensive. In addition, the elements are robust for use in 1.5, 2, 3 or other dimensional configurations, over an extended period of operation, without structural failure, and providing a high power output required for imaging and/or medical therapy applications.

Abstract: Matching layers improve the performance of ultrasonic transducers. Such layers have traditionally required significant effort and expense to be added to ultrasonic transducers. The present invention discloses a method of producing ultrasonic transducers with a matching layer, specifically for ultrasonic transducers utilizing piezopolymer transducer materials. Rather than the conventional method of forming the piezopolymer on a substrate and then attaching a matching layer through which the transducer emits its ultrasound energy, we teach depositing the piezopolymer on a substrate that also serves as a matching layer through which the ultrasound is emitted. Methods of how to select materials and modify their ultrasonic characteristics are also discussed.

Abstract: In an oscillator (100), a plurality of piezoelectric vibrators (111 to 113) supported by vibrator support mechanisms (120) individually output highly directional sound waves. The plurality of piezoelectric vibrators (111 to 113) is formed by dividing a laminated body of an elastic member and a piezoelectric substance by the vibrator support mechanisms (120). Since it is not necessary to arrange the plurality of piezoelectric vibrators in a matrix, the entirety of a device can be small-sized. A sound deflection unit that deflects a sound wave which is output by at least one of the piezoelectric vibrators may be further included.

Abstract: An ultrasonic probe includes a piezoelectric element including a support body, a lower electrode layer, first and second piezoelectric layers, and an upper electrode layer. The support body has an opening section and a displacement section covering the opening section on one side of the support body. The lower electrode layer is disposed on the one side of the support body and continuously extending from an inside to an outside of the opening section when viewed in a plan view along a thickness direction of the support body. The first piezoelectric layer is disposed on the lower electrode layer and positioned inside of the opening section when viewed in the plan view. The upper electrode layer is disposed on the first piezoelectric layer. The second piezoelectric layer is disposed on the lower electrode layer and positioned outside of the opening section when viewed in the plan view.

Abstract: Provided is a piezoelectric ceramics that can achieve both high piezoelectric performance and a high Curie temperature. Also provided are a piezoelectric element, a liquid discharge head, an ultrasonic motor, and a dust removing device, which use the piezoelectric ceramics. The piezoelectric ceramics include a perovskite-type metal oxide expressed by a general formula (1): xBaTiO3-yBiFeO3-zBi(M0.5Ti0.5)O3, where M represents at least one type of element selected from the group consisting of Mg and Ni, x satisfies 0.40?x?0.80, y satisfies O?y?0.30, z satisfies 0.05?z?0.60, and x+y+z=1 is satisfied, and are oriented in a (111) plane in a pseudocubic expression.

Abstract: Described herein are electrical connections to acoustic elements, e.g., piezoelectric elements. In an exemplary embodiment, a transducer comprises an acoustic element, a passive layer attached to the acoustic element, and a conductive post embedded in the passive layer to provide a direct low resistance electrical connection to the acoustic element. In one embodiment, the conductive post has an exposed side surface allowing electrical connections to be made from the side of the transducer. In another embodiment, the conductive post has an exposed bottom surface allowing electrical connections to be made from the bottom of the transducer. In another embodiment, the transducer comprises an extension substrate adjacent to the acoustic element for protecting the acoustic element from thermal stress when a connection is made to the transducer at high temperatures. In one embodiment, a circuit is integrated on the extension substrate to process signals to or from the acoustic element.

Abstract: An ultrasonic transducer array and method of making an ultrasonic transducer array. The array comprising a plurality of individual array elements made from a piezoelectric composite which is made from a plurality of individual piezoelectric segments; a passive filler between the piezoelectric segments; and, one or more electrodes for driving the array elements formed from the piezoelectric segments; wherein the spatial pattern of the piezoelectric segments of the piezoelectric composite defines one or more non-linear, irregular channels which separate the piezoelectric segments thereby minimising interaction between the individual array elements and minimising spurious modes in the ultrasound transducer array.

Abstract: An oscillator includes a piezoelectric vibrator (10), a vibrating member (20) which is larger than the piezoelectric vibrator (10) when seen in a plan view and restrains one surface of the piezoelectric vibrator (10), a vibrating member (25) which is larger than the piezoelectric vibrator (10) when seen in a plan view and restrains the other surface of the piezoelectric vibrator (10), an elastic member (30) which supports an edge of the surface of the vibrating member (20), which restrains the piezoelectric vibrator (10), and supports an edge of the surface of the vibrating member (25), which restrains the piezoelectric vibrator (10), and a supporting member (35) which is located around the elastic member (30) and supports the elastic member (30).

Abstract: Ultrasound transducers and methods of making ultrasound transducers with improved thermal characteristics are provided. An ultrasound transducer includes a piezoelectric element defining a front side and a back side. The ultrasound transducer includes a lens connected to the front side of the piezoelectric element, a heat sink connected to the back side of the piezoelectric element, and a backside matching layer disposed between the piezoelectric element and the heat sink. The backside matching layer is thermally connected to the piezoelectric element and the heat sink, and the backside matching layer is configured to conduct heat from the piezoelectric element to the heat sink.

Abstract: The present invention provides a method of packaging surface microfabricated transducers such that electrical connections, protection, and relevant environmental exposure are realized prior to their separation into discrete components. The packaging method also isolates elements of array transducers. Post processing of wafers consisting of transducers only on the top few microns of the wafer surface can be used to create a wafer scale packaging solution. By spinning or otherwise depositing polymeric and metallic thin and thick films, and by lithographically defining apertures and patterns on such films, transducers can be fully packaged prior to the final dicing steps that would separate the packaged transducers from each other. In the case of microfabricated ultrasonic transducers, such packaging layers can also enable flexible transducers and eliminate or curtail the acoustic cross-coupling that can occur between array elements.

Abstract: An ultrasonic transducer includes a case, a reflective portion, and a piezoelectric body. The case has a substantially cylindrical shape including one closed end in the center axis direction that defines a top. The piezoelectric body is disposed on the inner surface of the top of the case. The reflective portion is arranged to oppose and be spaced apart from the piezoelectric body. The distance between the piezoelectric body and the reflective portion is greater than the maximum displacement of the piezoelectric body and is substantially an odd number multiple of a ¼ wavelength of sound waves or less than or equal to the ¼ wavelength.

Abstract: A sonotrode comprising: a head defining a sealing surface elongated along a first direction; and a first and a second drive unit distinct from one another, each comprising at least one piezo-electric element; wherein first and second drive unit may be electrically fed by an unique generator to cause oscillation of head; the height of head measured along a second direction transversal to sealing surface being substantially equal to half the wavelength of wave oscillating in second direction; at least one slot extending through head transversally to first and second direction; a finite number of nodal points at which amplitude of oscillation of head is substantially equal to zero; and a plane on which at least some nodal points lie and which divides head in a first portion and second portion; the slot extends completely within one only between first and second portion and at a certain distance by plane.

Abstract: In one general aspect, various embodiments are directed to an ultrasonic surgical instrument that comprises a transducer configured to produce vibrations along a longitudinal axis at a predetermined frequency. In various embodiments, an ultrasonic blade extends along the longitudinal axis and is coupled to the transducer. In various embodiments, the ultrasonic blade includes a body having a proximal end and a distal end, wherein the distal end is movable relative to the longitudinal axis by the vibrations produced by the transducer.

Abstract: An ultrasonic transducer is configured to transmit and receive ultrasonic waves. The ultrasonic transducer includes a vibrating member and a piezoelectric member coupled to the vibrating member. The piezoelectric member includes a first piezoelectric part configured and arranged to be deformed by applied voltage to vibrate the vibrating member or configured and arranged to be deformed by vibration of the vibrating member to produce a potential difference, and a second piezoelectric part configured and arranged to be deformed by applied voltage to statically deflect the vibrating member.

Abstract: An illustrative embodiment of a temperature-activated voltage generator includes a generator housing having a housing interior; a flexible, temperature-sensitive bimetallic element disposed in the housing interior; and a piezoelectric element carried by the generator housing. The bimetallic element is positional between a first position wherein the bimetallic element disengages the piezoelectric element and a second position wherein the bimetallic element engages the piezoelectric element. Electrical voltage output leads are electrically connected to the piezoelectric element. A voltage-generating method is also disclosed.

Abstract: In one aspect, matching layers for an ultrasonic transducer stack having a matching layer comprising a matrix material loaded with a plurality of micron-sized and nano-sized particles. In another aspect, the matrix material is loaded with a plurality of heavy and light particles. In another aspect, an ultrasound transducer stack comprises a piezoelectric layer and at least one matching layer. In one aspect, the matching layer comprises a composite material comprising a matrix material loaded with a plurality of micron-sized and nano-sized particles. In a further aspect, the composite material can also comprise a matrix material loaded with a plurality of heavy and light particles. In a further aspect, a matching layer can also comprise cyanoacrylate.

Abstract: A physical shield placed on the face of a high intensity focused ultrasound transducer for medical applications is described. The shield may be shaped or angled to match a particular pattern of mechanical or acoustic energy that may damage the transducer during operation. The shield may be ablative, replaceable or modified as needed. Methods of manufacturing a transducer with a shield are also disclosed.

Abstract: An ultrasound transducer that includes a backing layer, an insulating layer disposed on top of the backing layer, and a plurality of conductive traces disposed on top of the insulating layer are disclosed. Each of the conductive traces has an upper face. A plurality of transducer elements, each having (a) a core of piezoelectric material and (b) a conductive coating disposed beneath the core, are bonded directly to the upper face of a respective one of the plurality of conductive traces. Methods for fabricating ultrasound transducers are also disclosed.

Abstract: An ultrasound transducer (10) comprises an application specific integrated circuit (ASIC) (14), an array of acoustic elements (20), and a pitch independent interposer (12). The ASIC (14) includes a plurality of contact pads (16) on a surface of the ASIC that are separated from adjacent ones thereof by a first pitch. The acoustic elements (22) of the array (20) are separated from adjacent ones thereof by a second pitch. In addition, the pitch independent interposer (12) features a plurality of conductive elements (26) separated from adjacent ones thereof by a third pitch different from both the first pitch and the second pitch.

Abstract: An electroacoustic transducer assembly and probe for emitting and receiving acoustic radiation beams. The transducer assembly comprising a plurality of transducer elements, each one composed of an electroacoustic element, arranged side by side and spaced apart along a row having a first end. Starting from transducer element proximate to the first end, adjacent transducer elements are constructed and arranged create an electroacoustic pair. A first element of the electroacoustic pair is constructed and arranged to only transmit acoustic pulses and a second element of the electroacoustic pair is constructed and arranged to only receive acoustic pulses. Each electroacoustic pair share a common connection line which branches off into a transmit branch connected to the first element and a receive branch connected to the second element.

Abstract: A technology is disclosed for actualizing an ultrasound probe that can obtain a high-resolution diagnostic image and is highly reliable. In the technology, a piezoelectric element has a predetermined thickness, a ground electrode is formed on one surface in a thickness direction, and a signal electrode is formed on the other surface. When an acoustic matching layer is laminated on a ground electrode formation surface of the piezoelectric element, the acoustic matching layer is configured by a composite material made of a plurality of materials including at least a conductive member. The conductive member has portions penetrating in a layer thickness direction at a plurality of sections on the one electrode formation surface of the piezoelectric element.

Abstract: Piezo-electric actuator 50 of the present invention comprises piezo-electric element 10 for performing expansion/contraction motions in accordance with an electric field condition, seat 20 to which piezo-electric element 10 is adhered on at least one surface thereof, and supporting member 45 for supporting piezo-electric element 10 and seat 20, wherein piezo-electric element 10 and seat 20 vibrate up and down in accordance with the expansion/contraction motions of piezo-electric element 10. Seat 20 is connected to supporting member 45 through vibration 30 film which is less rigid than this seat 20.

Abstract: Apparatus and methods to form high efficiency and uniform Fresnel lens arrays for ultrasonic liquid manipulation are provided. An ultrasonic transducer array may be fabricated by forming top and bottom electrodes on top and bottom surfaces of a sensor plate. The ultrasonic transducer array may generate ultrasonic energy to manipulate one or more samples. Each of the top and bottom electrodes may be coupled to a radio frequency source and arranged to form one of a solid shape or a pattern. Additional apparatus and methods are disclosed.

Abstract: In one general aspect, various embodiments are directed to an ultrasonic surgical instrument that comprises a transducer configured to produce vibrations along a longitudinal axis at a predetermined frequency. In various embodiments, an ultrasonic blade extends along the longitudinal axis and is coupled to the transducer. In various embodiments, the ultrasonic blade includes a body having a proximal end and a distal end, wherein the distal end is movable relative to the longitudinal axis by the vibrations produced by the transducer.

Abstract: Provided is an ultrasonic probe, which uses a composite piezo-electric element, which includes a piezo-electric wafer made of piezo-electric material and having a lattice shape, and a polymer filled between the lattices of the piezo-electric wafer. The ultrasonic probe has a high power and a wide band width simultaneously. In addition, since the ultrasonic probe further includes a heat exhaust unit for exhausting the heat generated at the ultrasonic probe to the outside, the temperature of an acoustic lens which contacts patients may be lowered.

Abstract: The invention relates to an insonification device (100) comprising a plurality of elementary ultrasonic transducers (110) each comprising at least one electro-acoustic element (111) and distributed on a chassis (120, 140) so that the electro-acoustic elements (111) are distributed on a so-called front surface (120?) of the device (100) intended to be placed facing the medium to be insonified. According to the invention, as each transducer (110) comprises a longitudinal body (113) made in a heat conducting material at the so-called front end of which the electro-acoustic element (111) is placed, the chassis (120, 140) comprises a sealed cooling chamber (130) placed behind the front surface (120?), crossed by the bodies of the transducers (113) and intended to be gone through by a coolant fluid flow.

Abstract: A megasonic processing apparatus and method has one or more piezoelectric transducers operating in thickness mode at fundamental resonant frequencies of at least 300 KHz. A generator powers the transducers with a variable-frequency driving signal that varies or sweeps throughout a predetermined sweep frequency range. The generator repeatedly vanes or sweeps the frequency of the driving signal through a sweep frequency range that includes the resonant frequencies of all the transducers.

Abstract: A transducer with triangular cross-sectional shaped pillars is described for suppressing lateral modes within a composite, and a method for producing the same. According to one aspect of the present application, a plurality of triangular cross-sectional shaped pillars extends outwardly from a substrate and form an array of pillars. The resulting array of pillars is configured to suppress the lateral modes of the transducer at higher operating frequencies, such as, at or above 15 MHz, at or above 20 MHz, or at or above 30 MHz.

Abstract: An ultrasonic sensor includes a casing body and a piezoelectric element. The casing body has a base wall and a surrounding wall that cooperates with the base wall to define an interior space. The base wall has a top surface and a bottom surface. The top surface has a first section, a second section that extends between the first section and the surrounding wall, and a connecting section interconnecting the first and second sections. A distance between the second section and the bottom surface is larger than that between the first section and the bottom surface such that the connecting section and the first section cooperate to define a recess. The piezoelectric element is confined in the recess.

Abstract: A high power ultrasonic transducer includes a first ultrasonic transducer cell and at least one second ultrasonic transducer cell disposed on the first ultrasonic transducer cell. The at least one second ultrasonic transducer cell oscillates together with the first ultrasonic transducer cell.

Abstract: In accordance with a representative embodiment, a BAW resonator structure comprises: a first BAW resonator comprising a first lower electrode, a first upper electrode and a first piezoelectric layer disposed between the first lower electrode and the first upper electrode; and a second BAW resonator comprising a second lower electrode, a second upper electrode and a second piezoelectric layer disposed between the second lower electrode and the second upper electrode. The BAW resonator structure also comprises a single-material acoustic coupling layer disposed between the first and second BAW resonators. The single-material acoustic coupling layer comprises an inhomogeneous acoustic property across a thickness of the single-material acoustic coupling layer.

Abstract: A system and method for determining optimal values for the geometrical features of an ultrasonic transducer having one or more elements, the method including backprojection ray-tracing to determine the parameters required for apertures located on an ultrasonic probe surface. The ultrasonic probe design system includes an interface for inputting statement parameters, insonification requirements, and geometric constraints, with an engine responsive to the interface and configured to determine and provide an optimized transducer geometric design output.

Abstract: An ultrasonic piezoelectric transducer device includes a transducer array consisting of an array of vibrating elements, and a base to which the array of vibrating elements in the transducer array are attached. The base include integrated electrical interconnects for carrying driving signals and sensed signals between the vibrating elements and an external control circuit. The base can be an ASIC wafer that includes integrated circuitry for controlling the driving and processing the sensed signals. The interconnects and control circuits in the base fit substantially within an area below the array of multiple vibrating elements.

Abstract: A technique that provides: an ultrasonic transducer in which the accurate arrangement of piezoelectric elements and the electric conductive state between electrode layers are reserved; and an ultrasonic diagnosis apparatus and an ultrasonic flaw inspection apparatus which use the ultrasonic transducer is provided. According to the technique, a plurality of piezoelectric elements 1, each being a stacked body in which predetermined numbers of piezoelectric layers 2 and electrode layers 3 are alternately stacked and although this has both sides that are substantially flat along a stacking direction, side electrodes 6 to connect the predetermined electrode layers 3 are placed outside both of the sides, are arranged in a direction orthogonal to the stacking direction, wherein an interval holding member 10 having a predetermined thickness is put between the sides on which the side electrodes 6 of the piezoelectric elements 1 adjacent to each other are formed.

Abstract: An impedance conversion layer useful for medical imaging ultrasonic transducers comprises a low impedance polymer layer and a high impedance metal layer. These layers are combined with corresponding thicknesses adapted to provide a function of converting from a specific high impedance to specific low impedance, wherein the polymer layer is at the high impedance side and the metal layer is at the low impedance side. The effective acoustic impedance of the polymer and metal layer combination may be adapted to configure an impedance converter in the same way as a quarter wavelength impedance converter, converting from low impedance to high impedance (metal to polymer) or from a high impedance to low impedance (polymer to metal). This structure may be used for front matching with the propagation medium and back matching with an absorber for ultrasonic transducers.

Abstract: An apparatus comprises a first transducer support configured to receive a first transducer in a first opening. A face of the first face of the transducer is located in a first plane. The apparatus also comprises a second transducer support configured to receive a second transducer in a second opening. A face of the second transducer is located in a second plane substantially parallel to the first plane.