Ultrasonic transducer

Abstract

To provide an impedance-matched ultrasonic transducer.SOLUTION: The ultrasonic transducer acoustically communicates with a sample or target material and includes a piezoelectric composite layer 102 having at least partially separated acoustic impedance and electrical impedance characteristics. The piezoelectric composite layer 102 includes an array of spaced-apart piezoelectric regions 10, each made from a piezoelectric material, a filler material 12 including a polymer matrix 13 positioned between adjacent spaced-apart piezoelectric regions, and a non-piezoelectric material 15 in contact with the polymer matrix 13.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] Related patent applications This application claims priority to U.S. Patent Application No. 62 / 712,595, filed July 31, 2018, the specification of which is incorporated herein by reference.

[0002] The technical field relates generally to the field of acoustic energy, and more particularly to ultrasound transducers and related devices, apparatus methods, and techniques. [Background technology]

[0003] The transmission of acoustic energy to and from an ultrasonic transducer is affected, at least in part, by an acoustic impedance mismatch, e.g., the difference in acoustic impedance between the material contained in the ultrasonic transducer (e.g., a piezoelectric ceramic) and the material acoustically coupled to the ultrasonic transducer. In general, matching the acoustic impedance between the ultrasonic transducer and the material improves the energy transmission between them.

[0004] It is generally known by those skilled in the art that there are impedance matching techniques to improve the transmission efficiency of acoustic waves across different materials. Such impedance matching techniques generally involve a trade-off between bandwidth and efficiency, resulting in a certain degree of complexity. When a wide bandwidth is required, the design of an ultrasonic transducer, including a matching system, becomes more complex. Such complexity particularly adds cost to the ultrasonic transducer. Designing and implementing an ultrasonic transducer with a wide bandwidth remains a challenge, and therefore, solutions known in the art are still fundamentally bandwidth-limited.

[0005] A wide variety of materials may be required to be acoustically coupled with an ultrasound transducer. Such materials can be used in many industrial and medical applications. Common examples include, but are not limited to, biological tissue (e.g., human and animal bodies), organic materials (e.g., wood and polymers), inorganic materials (e.g., metals), composite materials (e.g., carbon composites), and ceramics. The above materials have acoustic impedances ranging from approximately 1 Megaray (MR) to over 60 MR.

[0006] Materials that are acoustically coupled to ultrasound transducers are classified into four categories: materials with a higher acoustic impedance than piezoelectric materials (referred to herein as the "first category"), materials with an acoustic impedance close to that of piezoelectric materials (referred to herein as the "second category"), materials with a lower acoustic impedance than piezoelectric materials (referred to herein as the "third category"), and biological materials with an acoustic impedance much lower than that of most piezoelectric materials (referred to herein as the "fourth category").

[0007] Examples of materials in the first category include, but are not limited to, tungsten, molybdenum, nickel, and gold. These materials have an acoustic impedance of greater than about 45 MR. Examples of materials in the second category include, but are not limited to, brass, silver, zirconium, and cast iron. These materials have an acoustic impedance of about 30 MR to about 40 MR. Examples of materials in the third category include, but are not limited to, magnesium, aluminum, indium, titanium, and tin. These materials have an acoustic impedance in the range of about 10 MR to about 30 MR. Examples of materials in the fourth category include, but are not limited to, fat, muscle, or organs. These materials typically have an acoustic impedance of about 30 MR to about 40 MR. It has an acoustic impedance of about 1.2 MR to about 1.8 MR. Bone is another example of a material in the fourth category, and can have an acoustic impedance of about 5 MR to about 8 MR. However, it should be noted that this value can vary greatly.

[0008] There remains a need for techniques, apparatus, devices and methods that alleviate or mitigate the problems of the prior art. Summary of the Invention [Problem to be solved by the invention]

[0009] According to one aspect, a piezoelectric composite layer configured to be in acoustic communication with a sample and having at least partially decoupled acoustic impedance and electrical impedance characteristics includes an array of spaced apart piezoelectric regions, each spaced apart piezoelectric region made from a piezoelectric material having a first acoustic impedance and a first electrical relative permittivity, and a filler material disposed between adjacent spaced apart piezoelectric regions, the filler material being a polymer matrix having a second acoustic impedance and a second electrical relative permittivity. and one or more electrodes in electrical communication with the piezoelectric composite layer.

[0010] In some embodiments, the piezoelectric composite layer is configured to generate a probing acoustic signal directed toward the sample, and the one or more electrodes The piezoelectric composite layer is operable to transmit a probing electrical signal to the piezoelectric composite layer, thereby generating a probing acoustic signal.

[0011] In some embodiments, the piezoelectric composite layer is configured to receive a sample acoustic signal emanating from the sample and thereby generate a sample electrical signal directed to one or more electrodes, the sample electrical signal being representative of the sample acoustic signal.

[0012] In some embodiments, the polymer matrix is ​​made from an epoxy.

[0013] In some embodiments, the non-piezoelectric material is hafnium oxide powder.

[0014] In some embodiments, the ultrasonic transducer further includes one or more electrically insulating regions disposed between adjacent spaced apart piezoelectric regions, the one or more electrically insulating regions in contact with the filler material.

[0015] In some embodiments, the one or more electrically insulating regions have a fourth acoustic impedance and a fourth dielectric constant, where the fourth acoustic impedance is close to the first acoustic impedance and the fourth dielectric constant is less than the first dielectric constant.

[0016] In some embodiments, one or more electrically insulating regions are made from ceramic.

[0017] In some embodiments, one or more electrically insulating regions are made from glass.

[0018] In some embodiments, one or more electrically insulating regions have an elongated shape.

[0019] In some embodiments, the one or more electrically insulating regions define a bar-shaped electrically insulating region.

[0020] In some embodiments, the one or more electrically insulating regions define pillar-shaped electrically insulating regions.

[0021] In some embodiments, the ultrasound transducer further includes one or more electrically insulating regions being spherical in shape.

[0022] In some embodiments, the non-piezoelectric material is embedded within a polymer matrix.

[0023] In some embodiments, the piezoelectric material is continuous along one direction and the filler material is continuous along three directions.

[0024] In some embodiments, the piezoelectric material is continuous along two directions and the filler material is continuous along two directions.

[0025] In some embodiments, the piezoelectric material is selected from the group consisting of ferroelectric materials, single crystal ferroelectric materials, lead-free ferroelectric materials, and piezoelectric polymeric materials.

[0026] In some embodiments, the piezoelectric material is lead zirconate titanate (PZT).

[0027] In some embodiments, the acoustic impedance characteristic ranges from about 15 MR to about 30 MR.

[0028] In some embodiments, the first acoustic impedance ranges from about 30 MR to about 40 MR.

[0029] In some embodiments, the third acoustic impedance ranges from about 7 MR to about 8 MR.

[0030] In some embodiments, the piezoelectric composite layer is acoustically matched to and electrically isolated from the sample.

[0031] In some embodiments, the ultrasound transducer further includes a backing layer in electrical communication with the one or more electrodes.

[0032] In some embodiments, the backing layer is a de-matching layer.

[0033] In some embodiments, the ultrasonic transducer further includes a ground electrode.

[0034] In some embodiments, the ground electrode is configured as a heat spreader.

[0035] In some embodiments, the piezoelectric composite layer and the sample define an acoustic path therebetween, and the ultrasonic transducer further includes a substantially lossless acoustic matching layer disposed along the acoustic path between the piezoelectric composite layer and the sample.

[0036] In some embodiments, the ultrasonic transducer further includes a wear layer, the wear layer being acoustically matched to the piezoelectric composite layer.

[0037] In some embodiments, the piezoelectric composite layer has a thickness of approximately 2400 microns.

[0038] In some embodiments, the spaced apart piezoelectric regions are spaced 200 microns apart from one another and have a square cross section, the square cross section being 1000 microns by 1000 microns.

[0039] In some embodiments, the piezoelectric composite layer has a piezoelectric volume fraction in the range of about 70% to about 80%.

[0040] In some embodiments, the ultrasonic transducer further comprises an electrically insulating housing for containing the piezoelectric composite layer therein.

[0041] According to another aspect, an ultrasonic transducer for emitting an acoustic signal toward a target is provided, the ultrasonic transducer comprising: a piezoelectric composite layer having at least partially decoupled acoustic impedance and electrical impedance characteristics, the piezoelectric composite layer comprising an array of spaced apart piezoelectric regions, each piezoelectric region made from a piezoelectric material having a first acoustic impedance and a first dielectric constant; and a filler material disposed between adjacent spaced apart piezoelectric regions, the filler material including a polymer matrix having a second acoustic impedance and a second dielectric constant, the second acoustic impedance being and the second dielectric constant is less than the first dielectric constant; and a non-piezoelectric material in contact with the polymer matrix, the non-piezoelectric material having a third acoustic impedance and a third dielectric constant, the third acoustic impedance being greater than the second acoustic impedance and the third dielectric constant being less than the first dielectric constant; and one or more electrodes in electrical communication with the piezoelectric composite layer, the one or more electrodes operable to transmit an electrical signal to the piezoelectric composite layer, thereby generating an acoustic signal toward the target.

[0042] In some embodiments, the polymer matrix is ​​made from an epoxy.

[0043] In some embodiments, the non-piezoelectric material is hafnium oxide powder.

[0044] In some embodiments, the ultrasonic transducer further includes one or more electrically insulating regions disposed between adjacent spaced apart piezoelectric regions, the one or more electrically insulating regions in contact with the filler material.

[0045] In some embodiments, the one or more electrically insulating regions have a fourth acoustic impedance and a fourth dielectric constant, where the fourth acoustic impedance is close to the first acoustic impedance and the fourth dielectric constant is less than the first dielectric constant.

[0046] In some embodiments, one or more electrically insulating regions are made from ceramic.

[0047] In some embodiments, one or more electrically insulating regions are made from glass.

[0048] In some embodiments, one or more electrically insulating regions have an elongated shape.

[0049] In some embodiments, the one or more electrically insulating regions define a bar-shaped electrically insulating region.

[0050] In some embodiments, the one or more electrically insulating regions define pillar-shaped electrically insulating regions.

[0051] In some embodiments, one or more electrically insulating regions are spherical in shape.

[0052] In some embodiments, the non-piezoelectric material is embedded within a polymer matrix.

[0053] In some embodiments, the piezoelectric material is continuous along one direction and the filler material is continuous along three directions.

[0054] In some embodiments, the piezoelectric material is continuous along two directions and the filler material is continuous along two directions.

[0055] In some embodiments, the piezoelectric material is selected from the group consisting of ferroelectric materials, single crystal ferroelectric materials, lead-free ferroelectric materials, and piezoelectric polymeric materials.

[0056] In some embodiments, the piezoelectric material is lead zirconate titanate (PZT).

[0057] In some embodiments, the acoustic impedance characteristic ranges from about 15 MR to about 30 MR.

[0058] In some embodiments, the first acoustic impedance ranges from about 30 MR to about 40 MR.

[0059] In some embodiments, the third acoustic impedance ranges from about 7 MR to about 8 MR.

[0060] In some embodiments, the piezoelectric composite layer is acoustically matched to and electrically isolated from the sample.

[0061] In some embodiments, the ultrasound transducer further includes a backing layer in electrical communication with the one or more electrodes.

[0062] In some embodiments, the backing layer is a mismatched layer.

[0063] In some embodiments, the ultrasonic transducer further includes a ground electrode.

[0064] In some embodiments, the ground electrode is configured as a heat spreader.

[0065] In some embodiments, the piezoelectric composite layer and the sample define an acoustic path therebetween, and the ultrasonic transducer further includes a substantially lossless acoustic matching layer disposed along the acoustic path between the piezoelectric composite layer and the sample.

[0066] In some embodiments, the ultrasonic transducer further includes a wear layer, the wear layer being acoustically matched to the piezoelectric composite layer.

[0067] In some embodiments, the piezoelectric composite layer has a thickness of approximately 2400 microns.

[0068] In some embodiments, the spaced apart piezoelectric regions are spaced 200 microns apart from one another and have a square cross section, the square cross section being 1000 microns by 1000 microns. do.

[0069] In some embodiments, the piezoelectric composite layer has a piezoelectric volume fraction in the range of about 70% to about 80%.

[0070] In some embodiments, the ultrasonic transducer further comprises an electrically insulating housing for containing the piezoelectric composite layer therein.

[0071] According to another aspect, an ultrasonic transducer is provided, the ultrasonic transducer including: a piezoelectric composite layer configured to acoustically communicate with a sample and having at least partially decoupled acoustic impedance and electrical impedance characteristics, the piezoelectric composite layer including an array of spaced apart piezoelectric regions, each spaced apart piezoelectric region being made from a piezoelectric material, a filler material disposed between adjacent spaced apart piezoelectric regions and including a polymer matrix, and a non-piezoelectric material in contact with the polymer matrix; an electrically insulating non-piezoelectric composite layer extending above the piezoelectric composite layer to electrically insulate the piezoelectric composite layer from the sample, the electrically insulating non-piezoelectric composite layer being acoustically matched to the piezoelectric composite layer and the sample; and one or more electrodes in electrical communication with the piezoelectric composite layer.

[0072] In some embodiments, the electrically insulating non-piezoelectric composite layer includes a region of high acoustic impedance electrically insulating material in contact with a second polymer matrix, the second polymer matrix being filled with a high density electrically insulating powder.

[0073] In some embodiments, the electrically insulating non-piezoelectric composite layer includes an electrically insulating ceramic region in contact with a second polymer matrix, the second polymer matrix being filled with a high density electrically insulating ceramic powder.

[0074] In some embodiments, the electrically insulating non-piezoelectric composite layer includes an electrically insulating glass region in contact with a second polymer matrix, the second polymer matrix being filled with a high density electrically insulating ceramic powder.

[0075] In some embodiments, the electrically insulating non-piezoelectric composite layer is of a 1 / 3 configuration.

[0076] In some embodiments, the electrically insulating non-piezoelectric composite layer is of a 2x2 construction.

[0077] In some embodiments, the piezoelectric composite layer is configured to generate a probing acoustic signal directed toward the sample, and the one or more electrodes are operable to transmit a probing electrical signal to the piezoelectric composite layer, thereby generating the probing acoustic signal.

[0078] In some embodiments, the piezoelectric composite layer is configured to receive a sample acoustic signal emanating from the sample and thereby generate a sample electrical signal directed to one or more electrodes, the sample electrical signal being representative of the sample acoustic signal.

[0079] In some embodiments, the polymer matrix is ​​made from an epoxy.

[0080] In some embodiments, the non-piezoelectric material is hafnium oxide powder.

[0081] In some embodiments, the ultrasonic transducer further includes one or more electrically insulating regions disposed between adjacent spaced apart piezoelectric regions, the one or more electrically insulating regions in contact with the filler material.

[0082] In some embodiments, the one or more electrically insulating regions have a fourth acoustic impedance and a fourth dielectric constant, where the fourth acoustic impedance is close to the first acoustic impedance and the fourth dielectric constant is less than the first dielectric constant.

[0083] In some embodiments, one or more electrically insulating regions are made from ceramic.

[0084] In some embodiments, one or more electrically insulating regions are made from glass.

[0085] In some embodiments, one or more electrically insulating regions have an elongated shape.

[0086] In some embodiments, the one or more electrically insulating regions define a bar-shaped electrically insulating region.

[0087] In some embodiments, the one or more electrically insulating regions define pillar-shaped electrically insulating regions.

[0088] In some embodiments, one or more electrically insulating regions are spherical in shape.

[0089] In some embodiments, the non-piezoelectric material is embedded within a polymer matrix.

[0090] In some embodiments, the piezoelectric material is continuous along one direction and the filler material is continuous along three directions.

[0091] In some embodiments, the piezoelectric material is continuous along two directions and the filler material is continuous along two directions.

[0092] In some embodiments, the piezoelectric material is selected from the group consisting of ferroelectric materials, single crystal ferroelectric materials, lead-free ferroelectric materials, and piezoelectric polymeric materials.

[0093] In some embodiments, the piezoelectric material is lead zirconate titanate (PZT).

[0094] In some embodiments, the acoustic impedance characteristic ranges from about 15 MR to about 30 MR.

[0095] In some embodiments, the first acoustic impedance ranges from about 30 MR to about 40 MR.

[0096] In some embodiments, the third acoustic impedance ranges from about 7 MR to about 8 MR.

[0097] In some embodiments, the piezoelectric composite layer is acoustically matched to and electrically isolated from the sample.

[0098] In some embodiments, the ultrasound transducer further includes a backing layer in electrical communication with the one or more electrodes.

[0099] In some embodiments, the backing layer is a mismatched layer.

[0100] In some embodiments, the ultrasonic transducer further includes a ground electrode.

[0101] In some embodiments, the ground electrode is configured as a heat spreader.

[0102] In some embodiments, the piezoelectric composite layer and the sample define an acoustic path therebetween, and the ultrasonic transducer further includes a substantially lossless acoustic matching layer disposed along the acoustic path between the piezoelectric composite layer and the sample.

[0103] In some embodiments, the ultrasonic transducer further includes a wear layer, the wear layer being acoustically matched to the piezoelectric composite layer.

[0104] In some embodiments, the piezoelectric composite layer has a thickness of approximately 2400 microns.

[0105] In some embodiments, the spaced apart piezoelectric regions are spaced 200 microns apart from one another and have a square cross section, the square cross section being 1000 microns by 1000 microns.

[0106] In some embodiments, the piezoelectric composite layer has a piezoelectric volume fraction in the range of about 70% to about 80%.

[0107] In some embodiments, the ultrasonic transducer further comprises an electrically insulating housing for containing the piezoelectric composite layer therein.

[0108] Other embodiments are provided below.

[0109] According to another aspect, techniques, devices, apparatus, and methods are provided for independently tuning the electrical and acoustic impedances of piezoelectric composite materials. Devices and methods capable of decoupling the electrical and acoustic impedances of piezoelectric composite devices may be embodied by piezoelectric composites incorporating three materials, rather than the traditional two. Decoupling the manipulation of the acoustic impedance of a composite separately from its electrical impedance typically requires the use of a non-metallic material, in addition to a kerf filler and piezoelectric material with a relatively low acoustic impedance. This is provided by the use of a high acoustic impedance material such as a piezoelectric ceramic, hi some embodiments, the non-piezoelectric ceramic is alumina.

[0110] According to another aspect, an ultrasonic transducer is provided for use with a target material having an acoustic impedance in the range of approximately 15 MR to approximately 30 MR. The ultrasonic transducer includes a complete acoustic path extending from a piezoelectric element to the target material or device under test (DUT). The ultrasonic transducer includes a piezoelectric layer incorporating the piezoelectric element, a ground electrode, a thermal management layer, an electrically insulating layer, and an outer wear surface capable of matching the acoustic impedance of the target material being sonicated. The provided ultrasonic transducer does not require the use of an acoustic impedance matching layer, making the solution equally efficient at all frequencies below an upper cutoff frequency. The upper cutoff frequency is limited only by the composite design parameters necessary to achieve effective behavior of the composite material elements, resulting in a practical bandwidth near DC up to an upper cutoff frequency at least several times the designed center frequency of the device.

[0111] According to another aspect, an ultrasonic transducer for use with a material having an acoustic impedance in the range of about 15 MR to about 30 MR is provided. The ultrasonic transducer includes an acoustically matched composite. Because the ultrasonic transducer does not use a matching layer, the ultrasonic transducer bandwidth is limited only by the inherent bandwidth imposed by the design and selection of the material comprising the piezoelectric element.

[0112] In some embodiments, the ultrasonic transducer includes a thermally robust backing layer that can also be configured as a heat spreader proximal to the piezoelectric layer. In some embodiments, the backing layer can also function as a mismatch layer.

[0113] In some embodiments, the ultrasonic transducer includes a high acoustic impedance kerf fill design. The high acoustic impedance kerf fill design allows the piezoelectric element to be compatible with a variety of materials having an acoustic impedance in the range of 15 to 30 MR. Materials having an acoustic impedance range of about 15 MR to about 30 MR include, but are not limited to, titanium, aluminum, tin, lead, zirconium, some ceramics, and composite materials. For the group of materials having an acoustic impedance of about 15 MR to about 30 MR, the ultrasonic transducer provides a means to efficiently couple very broadband ultrasonic waves into these materials.

[0114] In some embodiments, an ultrasonic transducer includes a piezoelectric composite layer designed to match the acoustic impedance of a DUT, and a non-piezoelectric, electrically insulating composite layer designed to match the acoustic impedance of the DUT. The non-piezoelectric composite layer is inserted between the piezoelectric composite layer and the DUT. The non-piezoelectric composite layer provides an efficient, wide-bandwidth acoustic path from the piezoelectric composite transducer element of the DUT while also providing electrical isolation between the transducer and the DUT.

[0115] In some embodiments, the electrical impedance and acoustic impedance of the ultrasonic transducer are independently configurable or at least partially decoupled. The electrical impedance, the acoustic impedance, or both may be configured using a hybrid non-piezoelectric / piezoelectric composite structure.

[0116] In some embodiments, the ultrasound transducer may be configured as a single element, a kerfless annular array, a kerfed annular array, a kerfed linear array, a kerfless linear array, a kerfless 2D matrix array, or a kerfed 2D matrix array.

[0117] According to another aspect, a method for fabricating a piezoelectric layer having a tailored acoustic impedance is provided.

[0118] Other features and advantages of the present description will become more apparent on reading the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0119] [Figure 1] 1 is a cross-sectional view of an ultrasound transducer according to one embodiment. [Figure 2] FIG. 10 is a cross-sectional view of an ultrasound transducer according to another embodiment. [Figure 3] FIG. 1 is a top view of a piezoelectric composite layer for an ultrasound transducer, according to one embodiment. [Figure 4] FIG. 10 is a top view of a piezoelectric composite layer for an ultrasound transducer according to another embodiment. [Figure 5A] FIG. 1 is a perspective view of an ultrasound transducer, according to one embodiment. [Figure 5B] FIG. 5B is an exploded cross-sectional view of the ultrasonic transducer of FIG. 5A. DETAILED DESCRIPTION OF THE INVENTION

[0120] In the following description, like features in the drawings will be given like reference numerals, and some elements may not be shown in a drawing if they have already been identified in a previous drawing, so as not to unduly clutter the figures. It should also be understood that elements in the figures are not necessarily drawn to scale, with emphasis placed on clearly illustrating the elements and structure of the present embodiments. The terms "a," "an," and "one" are defined herein to mean "at least one." That is, these terms do not exclude a plurality of elements, unless expressly stated otherwise. It should also be noted that terms such as "substantially," "generally," and "about," which modify a value, condition, or characteristic of an exemplary embodiment, should be understood to mean that the value, condition, or characteristic is defined within a tolerance range allowed for proper operation of this exemplary embodiment for its intended use.

[0121] In this description, the terms "connected," "coupled," and variations and derivatives thereof refer to any direct or indirect connection or coupling between two or more elements. The connection or coupling between the elements may be acoustic, mechanical, physical, optical, operational, electrical, wireless, or a combination thereof.

[0122] It will be understood that position descriptors indicating the location or orientation of one element relative to another are used herein for ease and clarity of description and, unless otherwise specified, should be interpreted in the context of the figures and should not be considered limiting. It will be understood that spatially relative terms (e.g., "outside" and "inside," "external" and "internal," "periphery" and "center," and "above" and "below") are intended to encompass different positions and orientations in use or operation of the present embodiments in addition to the positions and orientations illustrated in the figures.

[0123] General theoretical overview There are many methods and materials that can be used to fabricate electromechanical acoustic transducers. Some examples include piezoelectric crystals, ferroelectric ceramics, ferroelectric single crystals, ferroelectric polymers, capacitive micromachined ultrasonic transducers (CMUTs), piezoelectric micromachined ultrasonic transducers (PMUTs), and dynamic coil-based systems.

[0124] A broad category of relatively high performance piezoelectric materials is referred to as ferroelectric materials. Ferroelectric materials are some of the most commonly used piezoelectric materials in acoustic transducers, such as ultrasound transducers. Ferroelectric materials typically have acoustic impedance characteristics in the range of about 30 MR to about 40 MR. For example, one of the most common ferroelectric ceramics, the family of compounds commonly known as lead zirconate titanate (PZT), typically has an acoustic impedance in the range of about 33 MR to about 35 MR. Another category of relatively high performance piezoelectric materials is single crystal ferroelectric materials, which include, for example, without limitation, lithium niobate (PMN-PT or PIN-PMN-PT). These single crystal ferroelectric materials have an acoustic impedance in the range of about 30 MR to about 35 MR. Yet another category is single crystal ferroelectric materials, which include, for example, without limitation, lithium niobate (PMN-PT or PIN-PMN-PT). 0.5 Na 0.5 )NbO3(KNN) and (K 0.48 Na 0.52 ) 0.96 Li 0.04 Nb 0.85 Ta 0.15 These include new lead-free ferroelectric materials such as O3(KNLNT). These materials have an acoustic impedance of approximately 31 MR, slightly lower than most variations of PZT. Yet another exemplary category of piezoelectric materials includes piezoelectric polymers such as PVDF and copolymers such as P(VDF-TrFE). These polymer-based ferroelectric materials have much higher electromechanical efficiency than relaxor-based single crystals and ceramics. Although the acoustic impedance is very low, it is suitable for immersion-based systems. They have unique properties that make them suitable to function as receptors in the system.

[0125] Despite the wide variety of potential piezoelectric materials, the dominant category remains PZT and related relaxor-based ferroelectric materials, which outperform most other materials by a sufficient margin to relegate other piezoelectric materials to niche applications. As a result, most transducers have very similar acoustic impedances that fall within a small range, from about 33 MR to about 38 MR. Ultrasonic transducers based on piezoelectric materials with acoustic impedances that closely match the material being sonicated improve the efficiency of the system by reducing the matching requirements or increasing the overall transmission efficiency and bandwidth. Some piezoelectric materials are well acoustically matched to some materials. However, many materials need to be sonicated, ultrasonically inspected, and / or tested for which there is no suitable acoustically matched transducer material.

[0126] The acoustic impedance of a piezoelectric material can be reduced in conjunction with potentially increasing the electromechanical efficiency of the piezoelectric material by creating a composite of the piezoelectric material with another, generally lower acoustic impedance material that acts as a filler and forms a support matrix surrounding the piezoelectric material by one of many means. However, it is understood that when creating a piezoelectric composite, there is a trade-off between acoustic efficiency, electrical impedance, and acoustic impedance.

[0127] Composites commonly used in ultrasound transducers are generally in a 1 / 3 or 2 / 2 configuration, where the first number indicates the number of directions in which the piezoelectric material is continuous throughout the structure and the second number indicates the number of directions in which the filler material is continuous throughout the structure. Some example methods for creating composite piezoelectric materials include dicing, etching, molding, or random packing of piezoelectric material and filling or bonding other materials such as elastomers, epoxies, polymers, or gases interspersed between the piezoelectric pillars or beams to form the composite.

[0128] Examples of 3-configuration composites include die-and-fill composites, which have square cross-section pillars and kerfs filled with a material with a lower acoustic impedance. Such composites exploit the bar mode resonance of the piezoelectric pillars to overcome the inefficient k-mode that limits the performance of plate mode vibrations more typical of simple longitudinal disk or plate-based transducers. t (typically 0.5 for PZT) 33 This allows for a more effective electromechanical coupling factor (typically 0.7 for PZT), limited by the properties. Note that the acoustic impedance of the composite can be reduced compared to the pure piezoelectric material, somewhere between the piezoelectric material and the matrix filler, based on several design parameters of the composite geometry and the material properties of both the piezoelectric and filler materials. Thus, matching materials with lower acoustic impedance becomes less challenging, resulting in a higher signal-to-noise ratio.

[0129] Much research in the field of composite transducer development has focused on the development of efficient composites designed for compatibility with biological tissue in the biomedical field. Consequently, many commercially available composite materials and transducers have been optimized to combine the lowest possible acoustic impedance with the highest possible electromechanical efficiency for biological tissue applications and / or water immersion applications. Such composite materials typically have acoustic impedances ranging from 8 MR to 16 MR. However, many practical applications require efficient transfer of acoustic energy between these piezoelectric materials and ultrasound transducers coupled to materials with acoustic impedances that do not adequately match these materials. This means that the above piezoelectric materials may not be suitable for other classes of materials being sonicated. For example, materials with acoustic impedances of approximately 15 MR to 30 MR are particularly difficult to match with piezoelectric composites due to the lack of ideal materials for conventional acoustic stack designs.

[0130] In these cases, various techniques are known to overcome the inherent acoustic discontinuity between the piezoelectric material and the medium. For example, a common way to match the acoustic impedance of a piezoelectric material to the desired medium is to use a quarter-wave matching layer. Another example is to use a spring-mass matching layer system applied at high frequencies. Yet another example is a horn structure. Such acoustic impedance matching techniques are applied to the design of piezoelectric transducers to facilitate the efficient transfer of acoustic radiation from the transducer to the medium being sonicated, and are usually reciprocal. However, all acoustic impedance matching approaches have one thing in common: they have a finite bandwidth over which they are effective. Outside this bandwidth, their effectiveness quickly decreases, and if operated far enough away from the intended center frequency, unwanted artifacts may occur.

[0131] While acoustic impedance matching in transducer design is important, many practical applications also require the piezoelectric transducer assembly to be electrically isolated from the material being sonicated. In these scenarios, an electrical insulating layer must also be included in the transducer stack. For example, in fields such as non-destructive testing (NDT), it may be necessary to electrically isolate the ultrasound transducer from electrically sensitive assemblies, devices, or structures while simultaneously matching the transducer's acoustic impedance to the material or object being scanned. This is particularly important in medical applications. Indeed, electrically isolating the transducer assembly from the human body (the medium being sonicated) is crucial to prevent patient injury. For example, for efficiency reasons, in medical diagnostic ultrasound (and other medical ultrasound applications, including but not limited to therapeutic applications such as HIFU), the transducer's acoustic impedance must be matched to biological tissue while simultaneously being electrically isolated from the patient. For example, in other medical devices that use acoustic energy for acoustic ablation or mechanical reinforcement of surgical instruments, it is also desirable for efficiency reasons to match the acoustic impedance of the transducer to the medium (biological tissue, or possibly components of the acoustic medical device) while electrically isolating the transducer from the patient.

[0132] In many cases, when the target material has an acoustic impedance of less than about 10 MR, there are well-developed techniques readily available to the designer to address the need to acoustically match and simultaneously electrically isolate the transducer from the target.

[0133] A typical solution applied to medical diagnostic ultrasound of patients in contact with an ultrasound transducer is to select a lens or cover material that closely matches biological tissue, such as silicone or polyurethane, both of which are designed to have an acoustic impedance that closely matches the acoustic impedance of tissue (approximately 1.5 MR) while functioning as an effective lens and electrical insulator. Another common practice is to use an acoustically matched, electrically insulating matching layer. These matching materials include various glasses, polymers, elastomers, power-loaded polymers, and epoxies. For example, ceramic powder-loaded epoxies, such as alumina powder-loaded epoxies, can form various matching layers while maintaining the excellent resistance required for electrical insulation. However, powder-loaded composites such as power-loaded epoxies, silicones, and polymers typically exhibit higher attenuation than homogeneous materials and may not provide the necessary electrical insulation and a good compromise between the design parameters (e.g., thickness) of the matching layer and the acceptable loss in the device's acoustic path.

[0134] Furthermore, high powder-to-polymer volume fractions limit the fabrication of powder-loaded composites. For example, the common use of powder-loaded epoxy to increase acoustic impedance becomes impractical above approximately 12 MR. Furthermore, epoxy-loaded porous sintered materials are costly to design and difficult to precisely control. They can also be lossy if not completely filled. This is especially true for electrically insulating matching layers above 15 MR and below 30 MR.

[0135] The use of matching layers in ultrasonic transducer design is beneficial for broadband performance. Note that problems arise when broadband transducers are required, as multiple matching layer solutions are required. Designing a broadband ultrasonic transducer to couple to a 10 MR to 30 MR target is difficult. These challenges are further complicated when the transducer must be electrically isolated from the target material.

[0136] When the target material has an acoustic impedance in the range of about 15 MR to about 30 MR, it becomes increasingly difficult to apply existing solutions effectively because there are relatively few electrically insulating materials available for use as conventional matching layers that meet the acoustic, thermal, and electrical properties of target materials having an acoustic impedance in the range of about 15 MR to about 30 MR.

[0137] For example, but not by way of limitation, fields such as NDT and medical device development require ultrasonic transducers capable of transmitting high-power, broadband acoustic pulses into materials with acoustic impedances ranging from about 15 MR to about 30 MR. Electrically insulating layers with acoustic impedances substantially similar (or nearly identical) to the target material and piezoelectric layer are also required. Currently, piezoelectric composite designs and existing solutions are unable to change the acoustic impedance of a piezoelectric composite without affecting its electrical impedance (and vice versa).

[0138] It has been found that the electrical and acoustic impedances can be independently engineered (i.e., at least partially decoupled) by incorporating high acoustic impedance non-piezoelectric materials into the design of piezoelectric composites in addition to the conventional materials used in the fabrication of piezoelectric composites, as opposed to the common approach of typically incorporating low acoustic impedance kerf filler materials used in conventional piezoelectric composite designs.

[0139] Ultrasonic Transducer Turning now to the drawings, different embodiments of ultrasound transducers will now be described. Figures 1 and 2 show two embodiments of an ultrasound transducer 100 including a piezoelectric composite layer 102.

[0140] The piezoelectric composite layer 102 is configured to acoustically communicate with a sample or target material. The piezoelectric composite layer 102 has at least partially decoupled acoustic and electrical impedance characteristics. That is, the combination of materials included in the piezoelectric layer 102 allows the electrical impedance to be partially decoupled from the acoustic impedance. The piezoelectric composite layer 102 is typically made of at least three materials. As shown in FIGS. 3 and 4 , the piezoelectric layer 102 includes an array of spaced apart piezoelectric regions 10, a filler material 12, and a non-piezoelectric material 15. Each spaced apart piezoelectric region 10 is made of a piezoelectric material having a first acoustic impedance and a first dielectric constant. The filler material 12 is disposed between adjacent spaced apart piezoelectric regions 10 and includes a polymer matrix 13 having a second acoustic impedance and a second dielectric constant. The second acoustic impedance is less than the first acoustic impedance, and the second dielectric constant is less than the first dielectric constant. The non-piezoelectric material 15 is in contact with the polymer matrix and has a third acoustic impedance and a third dielectric constant. The third acoustic impedance is greater than the second acoustic impedance, and the third dielectric constant is less than the first dielectric constant. In some embodiments, the non-piezoelectric material 15 is embedded within the polymer matrix. Referring back to Figures 1 and 2, the ultrasound transducer 100 includes one or more electrodes 112 in electrical communication with the piezoelectric composite layer 102.

[0141] 1 and 2, a cross-sectional view of an embodiment of an ultrasonic transducer 100 is provided. As illustrated, the ultrasonic transducer 100 is an acoustic transducer including a die and filled piezoelectric composite element / layer 102 that acoustically matches a target material 104. The ultrasonic transducer 100 has a stack design (i.e., multiple layers). In some embodiments, described in more detail below, the ultrasonic transducer 100 may be electrically isolated from the target material 104. The piezoelectric composite element 102 has a proximal face 106 and a distal face 108 relative to an ultrasonic signal source 110. An acoustic path extends between the piezoelectric composite layer 102 and the target material 104.

[0142] 3 and 4, the piezoelectric composite layer 102 may be made from a ferroelectric piezoelectric material such as, for example, without limitation, PZT. In the illustrated variation, the piezoelectric regions 10 form pillars or beams 130 and are spaced apart from one another in a manner typical of 1 / 3 or 2 / 2 composites, meaning that the piezoelectric material 10 is continuous along one direction and the filler material 12 is continuous along three directions, or that the piezoelectric material 10 is continuous along two directions and the filler material 12 is continuous along two directions.

[0143] This embodiment, in particular, allows for increasing the electrical impedance of the piezoelectric composite while maintaining a desired acoustic impedance. In Figure 4, the space provided between adjacent piezoelectric regions 10 is a kerf 128. Kerf 128 is filled with epoxy 12. In some embodiments, epoxy 12 comprises an HFO powder-filled matrix material.

[0144] It should be noted that although the piezoelectric regions 10 are illustrated as square, they may be any shape, such as, for example, without limitation, triangular, cylindrical, or hexagonal.

[0145] In some embodiments, it may be desirable to reduce the volume fraction of piezoelectric material (e.g., the percentage of PZT) in the piezoelectric composite layer 102 to achieve better, improved, or more ideal electrical impedance requirements for the transducer. However, the acoustic impedance requirements of the ultrasound transducer 10 may need to be higher, suggesting that a higher volume fraction of PZT is desirable. In such embodiments, using an HFO powder-filled matrix material is not sufficient to achieve the required properties. In these scenarios, such as those shown in FIG. 4, the HFO powder-filled matrix material may be replaced or partially replaced with a non-piezoelectric material, such as, for example, without limitation, an alumina bar. Such a material would enable a higher acoustic impedance in the piezoelectric composite layer 102 while reducing the effective dielectric constant. In other embodiments, other relatively high acoustic impedance materials may be used.

[0146] In some embodiments, the kerf 128 is filled with a bar of alumina 14. Alumina typically has an acoustic impedance of about 35 MR and a dielectric constant of about 10. In the embodiment illustrated in Figure 4, the bar is sized to fill approximately 70% of the width of the kerf 128, with the remaining 30% being filled with kerf-filling epoxy 12. It will be appreciated that different filler materials and different epoxy materials, as well as other ratios, can be used to achieve desired acoustic and / or electrical impedance characteristics, depending in particular on the target material being sonicated.

[0147] It should be noted that the non-piezoelectric material 15 is not necessarily limited to alumina bars. For example, and without limitation, the alumina bars could be replaced by alumina spheres mixed in HFO epoxy, or cut from a composite made from HFO epoxy containing alumina spheres. It should also be noted that similar results can be achieved by adjusting the ratios (i.e., volume fractions) of the kerf, filler, and epoxy, thereby independently adjusting the electrical and acoustic impedance of the piezoelectric composite layer 102 to match desired acoustic and / or electrical properties (e.g., of a target material). It will be appreciated that the ratios of materials forming the piezoelectric composite layer 102 can vary widely depending on the desired results. As a result of this design, is a composite piezoelectric that can be designed, tuned, and tailored to have a wider range of electrical impedance for a given size while maintaining a desired acoustic impedance. The added third material, i.e., non-piezoelectric material 15, preferably has a high acoustic impedance, i.e., an acoustic impedance similar or equivalent to that of the piezoelectric material (if possible), and a much lower dielectric constant than that of the piezoelectric material. Thus, the piezoelectric composite layer 102 can be designed or tailored to have a desired acoustic impedance and a desired dielectric constant, eliminating the need for both acoustic impedance matching techniques and electrical impedance matching circuits.

[0148] 1 and 2, the ultrasonic transducer 100 includes one or more electrodes, e.g., the signal electrode 112. In some embodiments, the piezoelectric composite layer 102 is configured to generate a probing acoustic signal directed toward the sample 104, and the electrode (e.g., the signal electrode 112) is operable to transmit a probing electrical signal to the piezoelectric composite layer 102, thereby generating the probing acoustic signal. In some embodiments, the piezoelectric composite layer 102 is configured to receive a sample acoustic signal emanating from the sample 104, and thereby generate a sample electrical signal directed toward one or more electrodes (e.g., the signal electrode 112), the sample electrical signal representing the sample acoustic signal. Thus, the ultrasonic transducer 100 can be used to transmit and / or receive ultrasonic waves.

[0149] In some embodiments, as shown in FIGS. 1 and 2 , the electrode 112 is disposed on the proximal surface 106 of the piezoelectric composite layer 102. The electrode 112 can have a conductive backing layer 114 disposed on the proximal surface 116 of the signal electrode 112. In yet other embodiments, the backing layer can be electrically insulating. The backing layer 114 can be operatively or electrically connected to the signal electrode 112. In one embodiment, the backing layer 114 can be made of titanium and have a thickness of approximately 200 microns. The backing layer 114 can be made of a material with a sufficiently high acoustic impedance to also function as a mismatching layer. Such a mismatching function generally requires that the backing layer have an acoustic impedance at least twice that of the piezoelectric material, thereby providing improved bandwidth and sensitivity. For example, the mismatching layer 114 can be made of, for example, without limitation, molybdenum, tungsten, or tungsten carbide.

[0150] In some embodiments, the piezoelectric material is selected from the group consisting of ferroelectric materials, single crystal ferroelectric materials, lead-free ferroelectric materials, and piezoelectric polymer materials. For example, as previously mentioned, the piezoelectric material can be lead zirconate titanate (PZT).

[0151] In some embodiments, the polymer matrix is ​​made from epoxy and the non-piezoelectric material is hafnium oxide powder.

[0152] The ultrasonic transducer 100 may also be provided with one or more electrically insulating regions disposed between adjacent spaced apart piezoelectric regions 10 and in contact with the filler material 12. The electrically insulating regions have a fourth acoustic impedance and a fourth dielectric constant. In some embodiments, the fourth acoustic impedance is close to the first acoustic impedance and the fourth dielectric constant is less than the first dielectric constant. For example, without limitation, the electrically insulating regions may be made from ceramic or glass. The shape of the electrically insulating regions may vary. For example, without limitation, the electrically insulating regions may have an elongated shape, define a bar-shaped electrically insulating region, define a spherical shape, or be spherical.

[0153] Turning now to the materials used in ultrasound transducers, it will be appreciated that using different volume fractions of filler powder and / or different filler powders in the matrix material allows for fillers with different acoustic impedances. For example, one skilled in the art will appreciate that: It will be appreciated that by mixing Epotec 301 epoxy and HFO powder at various volume fractions, powder-loaded epoxy materials with acoustic impedances ranging from approximately 3 to approximately 10 MR can be practically realized. In one embodiment, the filler material 12 is designed to have an acoustic impedance of approximately 7 to approximately 8 MR. It will also be appreciated that the piezoelectric composite layer 102 exhibits properties different from non-composite piezoelectrics. For example, non-composite piezoelectric elements can have relatively high Q factors, which inherently result in materials with relatively low bandwidth. However, in this embodiment, using a low-impedance matrix material to form a 1 / 3 PZT piezoelectric composite provides improved bandwidth and efficiency when compared to simple PZT plate-based elements. Furthermore, 1 / 3 composite PZT also exhibits a lower dielectric constant compared to pure PZT, allowing for more practical electrical impedances from large single-element designs. It will be appreciated that other piezoelectric materials may be used in other embodiments without departing from the scope of the current description. Such piezoelectric materials include, but are not limited to, lithium niobate, various PZT-based materials (e.g., PZT 8 or PZT 5H), ferroelectric relaxor-based ceramics and relaxor-based single crystals (e.g., PMN-PT), quartz, and other piezoelectric materials with properties suitable for the desired application, such as higher bandwidth, higher sensitivity, or lower cost. Therefore, using a relatively high acoustic impedance powder-loaded kerf filler between piezoelectric pillars allows for a better tradeoff between high degrees of acoustic impedance, electrical impedance, and pillar aspect ratio compared to existing piezoelectric composites, which are typically constructed using fillers in the 1 MR to 3 MR range, for example, when adapting piezoelectric composite transducers to materials with relatively high acoustic impedances, such as, but not limited to, titanium or zirconium. In some scenarios, a high acoustic impedance kerf filler may reduce the acoustic isolation between the pillars and reduce the electromechanical coupling coefficient of the composite. However, the proposed trade-off may be considered acceptable in light of the improved acoustic match and bandwidth of the resulting acoustic path from the composite to the target material or DUT.Using an HFO powder-loaded matrix material, an average acoustic impedance of 27.4 MR can be achieved using a relatively low volume fraction of piezoelectric material (e.g., 73% PZT vol / vol). By comparison, existing piezoelectric composites require approximately 78% for a typical 3 MR unfilled epoxy. The lower volume fraction of piezoelectric material in the piezoelectric composite layer 102 allows for higher electrical impedance to be achieved without sacrificing acoustic matching. Furthermore, a 73% volume fraction makes dicing more efficient, allowing for the use of larger blades, which not only eases the manufacturing process but also gives designers more freedom to optimize the pillar aspect ratio to achieve optimal bar mode resonance. Another advantage of using a powder-loaded matrix in a composite is that the powder-loaded epoxy matrix can be modified to fine-tune the acoustic impedance of the piezoelectric composite without having to change the pillar dimensions and dicing. Such changes in pillar design and pillar dimensions and associated dicing are known to be costly.

[0154] Turning now to the acoustic impedance of the ultrasound transducer 100, in some embodiments, the acoustic impedance characteristic of the piezoelectric composite layer 102 ranges from about 15 MR to about 30 MR. As previously established, this impedance characteristic is a combination of the impedances of the materials forming the piezoelectric composite layer 102. In this regard, in some embodiments, the first acoustic impedance ranges from about 30 MR to about 40 MR, and the third acoustic impedance ranges from about 7 MR to about 8 MR. It should be noted that the piezoelectric composite layer is acoustically matched to the sample and, in some embodiments, can be electrically isolated from the sample by including an electrically insulating non-piezoelectric composite layer 122.

[0155] In some embodiments, the ultrasound transducer 100 further includes a backing layer 114 in electrical communication with the one or more electrodes 112. In some scenarios, the backing layer may function as a mismatching layer.

[0156] 1 and 2, the ultrasonic transducer may include a ground electrode 118. The ground electrode 118 is disposed on the distal surface 108 of the piezoelectric composite element 102. In some embodiments, the ground electrode 118 may also function as a heat spreader to spread heat generated by the ultrasonic transducer 100. It should be noted that the ground electrode 118 does not necessarily function as a heat spreader.

[0157] The piezoelectric composite layer 102 and the sample or target material 104 define an acoustic path therebetween. In some embodiments, the ultrasonic transducer 100 further includes a substantially lossless acoustic matching layer 120 disposed along the acoustic path between the piezoelectric composite layer 102 and the sample 104. The substantially lossless acoustic matching layer 120 is disposed adjacent to and in contact with the distal surface of the ground electrode 118. The substantially lossless acoustic matching layer 120 is electrically conductive and has a substantially low thermal impedance. When the ultrasonic transducer is used to sonicate titanium, the acoustic matching layer 120 may be made of titanium. Note that the acoustic matching layer 120 is optional and, in some embodiments, can function as a thermal heat spreader as well as a mechanical support layer. The mechanical support reinforces the ground layer and may also be beneficial during fabrication of the ultrasonic transducer 100. Generally, it is not possible to have the acoustic matching layer 120 due to the fact that all layers in the ultrasonic transducer 100 are acoustically matched. The acoustic matching layer 120 is an effective heat spreader that would not normally be included in the acoustic design immediately adjacent to the piezoelectric element 102. Typically, the acoustic matching layer material is expected to be the same as the material of the DUT, i.e., the same material that the transducer 100 is designed to match. For example, and without limitation, if the DUT is titanium, it is possible to select the acoustic matching layer 120 material as another well-matched material with desirable properties, such as zinc, which has a relatively better thermal conductivity than titanium but an acoustic impedance similar to titanium. This is possible with an acoustically matched stack, which minimizes design challenges, since properties other than layer thickness and acoustic impedance can be easily accommodated in the design.

[0158] In some embodiments, the ultrasonic transducer 100 further includes a wear layer 124. The wear layer 124 is acoustically matched to the piezoelectric composite layer 102. The wear layer 124 may be acoustically matched to other layers of the ultrasonic transducer 100. In some embodiments, the wear layer 124 is in acoustic contact with the distal surface of the electrically insulating ceramic composite layer 122. The wear layer 124 may be the same material as the DUT, especially if that material is nearly lossless, like many metals. For example, in one embodiment designed to sonicate titanium, the wear layer 124 is made from a 3 mm thick layer of titanium. In this embodiment, the wear layer 124 is configured to be electrically isolated from the transducer signal and ground, allowing the transducer assembly to be electrically isolated from the DUT.

[0159] In some embodiments, a robust thermal and mechanical grounding structure is provided to aid and facilitate cooling of the piezoelectric composite layer 102. In one non-limiting embodiment, the piezoelectric composite layer 102 is bonded to a 3 mm thick titanium disk, thus establishing a thermal cooling path to an electrical ground conductor and establishing a ground electrode. The base also serves as mechanical support to aid in the fabrication of the piezoelectric composite and stack. In some embodiments, the conductive disk can be selected to match the target material and / or acoustic impedance for a wide range of applications of the ultrasonic transducer 100, covering an acoustic impedance range of approximately 10 MR to over 30 MR. In some scenarios, if the target material 104 is conductive, for example, if the target material is metallic, the disk can actually be the same material as the target material. A low-loss wear plate can then be bonded to the distal surface of the electrically insulating layer to provide additional mechanical support for the insulating layer and provide excellent moisture resistance. Generally, the wear plate is made of a material that is not electrically conductive, such as the target material itself. The thickness of the titanium plate is selected to be 3 mm in the exemplary embodiment.

[0160] In some embodiments, the piezoelectric composite layer 102 has a thickness of approximately 2400 microns. It should be noted that prior art ultrasonic transducers typically have constraints on the thickness of all layers provided. Because the ultrasonic transducer 100 has all layers with the same acoustic impedance, there is no limit or reduction in layer thickness. Layers can be thicker or thinner as needed by the application. In one embodiment, the acoustic matching layer 120 is thicker to provide sufficient mass to act as a heat sink. Therefore, the layers of the transducer distal to the piezoelectric layer 102 can be any thickness, provided that the acoustic impedance of the layers distal to the piezoelectric layer is matched or nearly matched. Such a configuration enables the possibility of optimizing other properties of the distal layers, regardless of layer thickness. In one example, the matching layer 120 can be thickened to achieve mechanical robustness with less concern for acoustic performance, or thinned to reduce cost without affecting acoustic performance. Additionally, the layers of the ultrasound transducer 100 adjacent and proximal to the piezoelectric layer 102 should be of an appropriate thickness and material to enhance the output efficiency of the transducer 100 .

[0161] In some embodiments, the spaced apart piezoelectric regions 10 are spaced 200 microns apart and have a square cross-section, where the square cross-section is 1000 microns by 1000 microns. The piezoelectric composite layer 102 can have different piezoelectric volume fractions depending on the target material 104. In some embodiments, the piezoelectric composite layer 102 has a piezoelectric volume fraction ranging from about 70% to about 80%.

[0162] The ultrasonic transducer 100 or its components may be housed in an electrically insulating housing.

[0163] An RF electrical connector 138 may also be provided. The RF electrical connector 138 is operably connected to the electrode 112 via an electrical connection (e.g., a wire), which provides an electrical connection to the ultrasound signal source 110.

[0164] In some embodiments, a copper (Cu) ground and heat return 132 is also provided. The Cu ground and heat return 132 at least partially provides a housing for containing the Cu lead 132, backing and / or mismatch layer 114, electrode 112, piezoelectric composite layer 102, and ground 118. It will be understood that the Cu ground and heat return 132 may be of any suitable shape for containing the aforementioned items. In the illustrated embodiment shown in the figures, the Cu ground and heat return 132 is annular in shape. The Cu lead 134 copper serves to conduct heat and / or electricity. In some embodiments, the Cu lead 134, Cu ground and heat return 132, mismatch / backing layer 114, electrode 112, PZT composite 102, and ground 118 are pressed together to form a single unit. The ground 118 may optionally include a knurled edge to ensure good thermal and electrical contact to the Cu ground return and heat return 132 .

[0165] As previously mentioned, the techniques, devices, apparatus, and methods described in the present description can be implemented to generate and transmit ultrasound waves ("transmission mode"), to detect and receive ultrasound waves ("detection mode"), or both. In some implementations, ultrasound transducers according to the present disclosure may be used to deliver acoustic energy for other purposes, such as, for example, without limitation, transducers designed to drive medical shock wave therapy systems. In these implementations, the ultrasound transducer 100 is configured to emit an acoustic signal toward a target. In these embodiments, the ultrasound transducer The sensor also includes a piezoelectric composite layer 102 having at least partially decoupled acoustic impedance and electrical impedance characteristics. The piezoelectric composite layer 102 includes an array of spaced apart piezoelectric regions 10, a filler material, and a non-piezoelectric material 15. Each spaced apart piezoelectric region 10 is made from a piezoelectric material having a first acoustic impedance and a first dielectric constant. The filler material 12 is disposed between adjacent spaced apart piezoelectric regions 10 and includes a polymer matrix 13 having a second acoustic impedance and a second dielectric constant. The non-piezoelectric material 15 is in contact with the polymer matrix 13 and has a third acoustic impedance and a third dielectric constant. The second acoustic impedance is less than the first acoustic impedance (of the piezoelectric material), the second dielectric constant is less than the first dielectric constant, and the third dielectric constant is greater than the second acoustic impedance and less than the first dielectric constant. The ultrasonic transducer according to this implementation further includes one or more electrodes 112 in electrical communication with the piezoelectric composite layer 102. The electrodes 112 are operable to transmit an electrical signal to the piezoelectric composite layer 102, thereby generating an acoustic signal directed toward a target.

[0166] As previously mentioned, it may be useful for the ultrasound transducer 100 to be electrically isolated from the material being sonicated, for example, without limitation, in medical application situations or when the sonicated material can be easily damaged by electricity. Such an implementation of the ultrasound transducer 100 may be similar to the previously described embodiments and includes a piezoelectric composite layer 102 configured to be in acoustic communication with a sample 104 and having at least partially decoupled acoustic and electrical impedance characteristics. The piezoelectric composite layer 102 according to this implementation includes an array of spaced apart piezoelectric regions 10, each spaced apart piezoelectric region 10 made from a piezoelectric material and a filler material 12 disposed between adjacent spaced apart piezoelectric regions 10, the filler material 12 including a polymer matrix 13 and a non-piezoelectric material 15 in contact with the polymer matrix 13. 1 and 2, the ultrasound transducer 100 according to this implementation further includes an electrically insulating ceramic composite layer 122 extending over or in contact with the piezoelectric composite layer 102 to electrically isolate the piezoelectric composite layer 102 from the sample 104. The electrically insulating ceramic composite layer 122 is acoustically matched to the piezoelectric composite layer 102 and the sample 104. In these implementations, the electrode 112 is in electrical communication with the piezoelectric composite layer 102.

[0167] In some embodiments, the electrically insulating ceramic composite layer 122 is acoustically matched and is a die-and-filled electrically insulating ceramic composite layer 122. The ceramic composite layer 122 may be disposed on and / or mechanically contacted to the distal surface of the lossless acoustic layer 120 described above. Note that the insulating layer 122 is generally not lossless; its thickness is a compromise between electrical insulation and acceptable acoustic loss. In one non-limiting embodiment, the electrically insulating layer 122 is 1.4 mm thick and has a 950 μm pitch with 750 μm pillars and a 200 μm kerf. The kerf filler material of the electrically insulating layer 122 may be HFO epoxy. In another non-limiting embodiment, the electrically insulating layer 122 includes a base ceramic made from alumina. In yet another non-limiting embodiment, the base ceramic may be any other ceramic with an acoustic impedance greater than about 30 MR. In the context of this embodiment, it will be appreciated that the general problem to be solved is the lack of electrically insulating material having an acoustic impedance of about 15 MR to 30 MR. The use of electrically insulating layer 122 has addressed this general problem, since the degree of isolation and acceptable acoustic loss are the only considerations regarding the thickness of the layer.

[0168] It should be noted that thickness variations to the electrically insulating layer 122 do not significantly affect the bandwidth or frequency response of the device. In some embodiments, the ultrasonic transducer 100 includes an electrically insulating housing 136 for containing the ultrasonic transducer.

[0169] In some embodiments, the ultrasonic transducer 100 further includes an acoustic matching insulation layer 122 positioned adjacent to and in contact with the distal surface of the ground electrode layer 118. The layer 122 can be made of a solid insulating material or composite and should exhibit both the desired acoustic impedance and acceptable acoustic loss, as well as have sufficient dielectric strength and permittivity to achieve the electrical isolation required for the device. In one embodiment, the insulation layer is constructed of a 1 / 3 composite layer of alumina and HFO-filled epoxy to achieve an acoustic impedance of approximately 27 MR and provide an acoustic match to titanium. It should be understood that this matching insulation layer 122 is not a matching layer, but is itself matched in a manner similar to a piezoelectric composite layer, so that it has substantially the same acoustic impedance as the target material. The matching insulation layer 122 is inherently broadband, with a flat frequency transmission coefficient below an upper cutoff frequency determined by the pillar size and pitch, as is typically the case for acoustic composites. The thickness of the electrical insulation layer is frequency-independent and is merely a design factor as it relates to acceptable attenuation and management of acceptable leakage currents.

[0170] Implementation example Various possible implementations of the ultrasound transducer are described.

[0171] In one implementation, the ultrasonic transducer 100 is a single-element transducer. The single-element transducer has the following characteristics: a 50 mm single-element acoustic aperture, an electrical impedance of 50 ohms at the center frequency, a broadband frequency response (one-way, approximately 100% -6 dB fractional bandwidth), a center frequency of approximately 0.6 MHz, and an acoustic impedance matched to titanium (approximately 27.4 MR + / - approximately 0.5 MR). In addition to these characteristics, this implementation exhibits high power handling capabilities and heat dissipation characteristics due to the inclusion of a relatively thick thermally conductive layer that enhances the effectiveness of the ground electrode both electrically but primarily thermally. For example, if the DUT is a metal, such as titanium, this layer can be made of the same material as the DUT material. This inclusion is possible for the entire portion of the acoustic stack, including the piezoelectric composite element adjacent to the distal side of the piezoelectric element and having the same acoustic impedance as the DUT material. In this implementation, the piezoelectric composite layer 102 may be a PZT 1 / 3 composite, and the filler material 12 may be an HFO powder-loaded epoxy designed to have an acoustic impedance very close to approximately 27.4 MR, resulting in an acoustic match to titanium. It should be appreciated that this is relatively lower than the acoustic impedance of uncomposite PZT, which is approximately 34.5 MR, and much higher than typical polymer-filled piezoelectric composites of PZT, which typically range from 8 MR to 16 MR. In this implementation, PZT is selected for its blend of efficiency and thermal robustness. The HFO powder-loaded epoxy is selected as the matrix material used to fill the kerfs in the PZT plate to create the composite. The HFO powder-loaded epoxy has a relatively high acoustic impedance, approximately 7 MR to approximately 8 MR, allowing the resulting 1 / 3 composite to have an acoustic impedance closely matched to that of titanium. In this implementation, the piezoelectric composite layer 102 has 1000 μm×1000 μm pillars of PZT (with square cross section) occurring at a pitch of 1200 μm and regularly separated by 200 μm kerfs. The thickness of the composite piezoelectric element / layer 102 is 2400 μm.

[0172] In another implementation, an electrically isolated transducer is provided with a broadband and low-loss coupling mechanism to the intended acoustic loading medium, which can be optimized for center frequency and frequency response almost exclusively through optimization of the piezoelectric composite layers and design of the backing and / or mismatching layers. No matching is required on the distal side of the piezoelectric composite, and a nearly perfectly flat frequency response of the acoustic stack is achieved at all frequencies below the effective cutoff frequency, determined by the pillar size and spacing selected for both the piezoelectric composite and the ceramic composite element. This implementation allows an ultrasonic transducer with a unidirectional fractional bandwidth of greater than 140% to be used in conjunction with a designated target medium, providing excellent performance at the distal end. The design can be implemented without the need for a matching layer at the interface. For example, there are many different metals and other conductive loads that can benefit from an ultrasonic transducer that can be matched to their respective acoustic impedance, such as, but not limited to, titanium and its alloys, tin, aluminum and many aluminum alloys, zinc, zirconium, lead, and other alloys with acoustic impedances ranging from about 15 MR to about 30 MR. Additionally, non-metallic materials with acoustic impedances in the above ranges can also benefit from this implementation to closely match their respective acoustic impedances.

[0173] method A method for fabricating an embodiment of the previously described ultrasound transducer 100 is also provided. In one embodiment, the fabricated ultrasound transducer 100 is designed to operate at a frequency centered around approximately 600 kHz. The method includes kerf-cutting a plate of PZT having a thickness of approximately 2600 μm. The kerfs are made from parallel cuts. In one embodiment, this step results in 700 μm kerfs spaced approximately 1.7 mm apart, leaving approximately 1 mm of uncut material between the kerfs. The method also includes providing a bar of alumina (e.g., having a width of approximately 400 μm) that fits into the kerfs and is glued in place with 150 μm strips of kerf-filled epoxy (e.g., powder-loaded epoxy, which is allowed to harden) on either side of the alumina. The method also includes cutting the plate at 90 degrees to the first set of cuts, thereby defining similar kerfs (with approximately 700 μm kerfs spaced approximately 1.7 mm apart). The cut kerf can then be filled with a similar 400 μm wide alumina bar and kerf-filling powder-loaded epoxy. The resulting piezoelectric composite layer has an acoustic impedance comparable to that of an 82% PZT composite and can be acoustically matched to, for example, without limitation, titanium. However, the electrical impedance of such a composite is closer to that found in a 59% PZT composite.

[0174] Several alternative embodiments and examples are described and illustrated herein. The above-described embodiments are for illustrative purposes only. Those skilled in the art will appreciate the features of the individual embodiments and the possible combinations and variations of the components. Those skilled in the art will further appreciate that any of the embodiments may be provided in any combination with the other embodiments disclosed herein. The present examples and embodiments should therefore be considered in all respects as illustrative and not restrictive. Thus, while specific embodiments have been illustrated and described, numerous modifications are contemplated without significantly departing from the scope defined in the present description.

Claims

1. a piezoelectric composite layer configured to be in acoustic communication with a sample and having at least partially decoupled acoustic impedance and electrical impedance characteristics, the piezoelectric composite layer comprising: an array of spaced apart piezoelectric regions, each spaced apart piezoelectric region made from a piezoelectric material having a first acoustic impedance and a first dielectric constant; a filler material disposed between adjacent spaced apart piezoelectric regions, the filler material comprising a polymer matrix having a second acoustic impedance and a second dielectric constant, the second acoustic impedance being less than the first acoustic impedance and the second dielectric constant being less than the first dielectric constant; a non-piezoelectric material in contact with the polymer matrix, the non-piezoelectric material having a third acoustic impedance and a third dielectric constant, the third acoustic impedance being greater than the second acoustic impedance and the third dielectric constant being less than the first dielectric constant; a piezoelectric composite layer comprising: one or more electrodes in electrical communication with the piezoelectric composite layer; An ultrasonic transducer comprising:

2. the piezoelectric composite layer is configured to generate a probing acoustic signal directed toward the sample; The ultrasonic transducer of claim 1 , wherein the one or more electrodes are operable to transmit a probing electrical signal to the piezoelectric composite layer, thereby generating the probing acoustic signal.

3. 3. The ultrasonic transducer of claim 1, wherein the piezoelectric composite layer is configured to receive a sample acoustic signal emanating from the sample and thereby generate a sample electrical signal directed to the one or more electrodes, the sample electrical signal representing the sample acoustic signal.

4. 4. The ultrasonic transducer of claim 1, wherein the polymer matrix is ​​made from epoxy.

5. 5. The ultrasonic transducer of claim 1, wherein the non-piezoelectric material is hafnium oxide powder.

6. 6. An ultrasonic transducer as described in any one of claims 1 to 5, further comprising one or more electrically insulating regions disposed between adjacent spaced apart piezoelectric regions, the one or more electrically insulating regions being in contact with the filler material.

7. 7. The ultrasonic transducer of claim 6, wherein the one or more electrically insulating regions have a fourth acoustic impedance and a fourth dielectric constant, the fourth acoustic impedance being close to the first acoustic impedance and the fourth dielectric constant being less than the first dielectric constant.

8. 8. The ultrasonic transducer of claim 6, wherein the one or more electrically insulating regions are made from ceramic.

9. 8. The method according to claim 6, wherein the one or more electrically insulating regions are made of glass. Ultrasonic transducer.

10. 10. The ultrasonic transducer of claim 6, wherein the one or more electrically insulating regions have an elongated shape.

11. 10. An ultrasonic transducer according to claim 6, wherein the one or more electrically insulating regions define a bar-shaped electrically insulating region.

12. 10. An ultrasonic transducer according to claim 6, wherein the one or more electrically insulating regions define pillar-shaped electrically insulating regions.

13. 10. An ultrasonic transducer according to claim 6, wherein the one or more electrically insulating regions are spherical in shape.

14. 14. The ultrasound transducer of claim 1, wherein the non-piezoelectric material is embedded within the polymer matrix.

15. The piezoelectric material is continuous along one direction, 15. The ultrasonic transducer of claim 1, wherein the filler material is continuous along three directions.

16. the piezoelectric material is continuous along two directions; 15. The ultrasonic transducer of claim 1, wherein the filler material is continuous along two directions.

17. 17. The ultrasonic transducer of claim 1, wherein the piezoelectric material is selected from the group consisting of a ferroelectric material, a single crystal ferroelectric material, a lead-free ferroelectric material, and a piezoelectric polymer material.

18. 18. The ultrasonic transducer of claim 17, wherein the piezoelectric material is lead zirconate titanate (PZT).

19. 19. The ultrasonic transducer of claim 1, wherein the acoustic impedance characteristic is in the range of about 15 MR to about 30 MR.

20. 20. The ultrasonic transducer of claim 1, wherein the first acoustic impedance is in the range of about 30 MR to about 40 MR.

21. 21. The ultrasonic transducer of claim 1, wherein the third acoustic impedance is in the range of about 7 MR to about 8 MR.

22. 22. An ultrasound transducer according to any one of claims 1 to 21, wherein the piezoelectric composite layer is acoustically matched to and electrically isolated from the sample.

23. 23. The ultrasound transducer of claim 1, further comprising a backing layer in electrical communication with the one or more electrodes.

24. 24. The ultrasonic transducer of claim 23, wherein the backing layer is a mismatched layer.

25. 25. The ultrasonic transducer of claim 1, further comprising a ground electrode. Consumer.

26. 26. The ultrasonic transducer of claim 25, wherein the ground electrode is configured as a heat spreader.

27. 27. An ultrasonic transducer as described in any one of claims 1 to 26, wherein the piezoelectric composite layer and the sample define an acoustic path therebetween, and the ultrasonic transducer further comprises a substantially lossless acoustic matching layer disposed along the acoustic path between the piezoelectric composite layer and the sample.

28. 28. The ultrasonic transducer of claim 1, further comprising a wear layer, the wear layer being acoustically matched to the piezoelectric composite layer.

29. 29. An ultrasonic transducer according to any one of claims 1 to 28, wherein the piezoelectric composite layer has a thickness of approximately 2400 microns.

30. 30. An ultrasonic transducer as described in any one of claims 1 to 29, wherein each spaced apart piezoelectric region is spaced 200 microns from each other and has a square cross section, the square cross section being 1000 microns by 1000 microns.

31. 31. The ultrasonic transducer of claim 1, wherein the piezoelectric composite layer has a piezoelectric volume fraction in the range of about 70% to about 80%.

32. 32. An ultrasonic transducer according to any one of claims 1 to 31, further comprising an electrically insulating housing for containing the piezoelectric composite layer therein.

33. an ultrasonic transducer for emitting an acoustic signal toward a target, 1. A piezoelectric composite layer having at least partially decoupled acoustic impedance and electrical impedance characteristics, the piezoelectric composite layer comprising: an array of spaced apart piezoelectric regions, each spaced apart piezoelectric region made from a piezoelectric material having a first acoustic impedance and a first dielectric constant; a filler material disposed between adjacent spaced apart piezoelectric regions, the filler material comprising a polymer matrix having a second acoustic impedance and a second dielectric constant, the second acoustic impedance being less than the first acoustic impedance and the second dielectric constant being less than the first dielectric constant; a non-piezoelectric material in contact with the polymer matrix, the non-piezoelectric material having a third acoustic impedance and a third dielectric constant, the third acoustic impedance being greater than the second acoustic impedance and the third dielectric constant being less than the first dielectric constant; a piezoelectric composite layer comprising: one or more electrodes in electrical communication with the piezoelectric composite layer, the one or more electrodes operable to transmit an electrical signal to the piezoelectric composite layer, thereby generating the acoustic signal directed toward the target; An ultrasonic transducer comprising:

34. 34. The ultrasound transducer of claim 33, wherein the polymer matrix is ​​made from epoxy.

35. 35. The ultrasonic transducer of claim 33 or 34, wherein the non-piezoelectric material is hafnium oxide powder.

36. 36. An ultrasonic transducer as described in any one of claims 33 to 35, further comprising one or more electrically insulating regions disposed between adjacent spaced apart piezoelectric regions, the one or more electrically insulating regions in contact with the filler material.

37. 37. The ultrasonic transducer of claim 36, wherein the one or more electrically insulating regions have a fourth acoustic impedance and a fourth dielectric constant, the fourth acoustic impedance being close to the first acoustic impedance and the fourth dielectric constant being less than the first dielectric constant.

38. 38. An ultrasonic transducer according to claim 36 or 37, wherein the one or more electrically insulating regions are made from ceramic.

39. 38. An ultrasonic transducer as described in claim 36 or 37, wherein the one or more electrically insulating regions are made from glass.

40. 40. An ultrasonic transducer as described in any one of claims 36 to 39, wherein the one or more electrically insulating regions have an elongated shape.

41. 40. An ultrasonic transducer according to any one of claims 36 to 39, wherein the one or more electrically insulating regions define a bar-shaped electrically insulating region.

42. 40. An ultrasonic transducer according to any one of claims 36 to 39, wherein the one or more electrically insulating regions define pillar-shaped electrically insulating regions.

43. 40. An ultrasonic transducer according to any one of claims 36 to 39, wherein the one or more electrically insulating regions are spherical in shape.

44. 44. An ultrasound transducer according to any one of claims 33 to 43, wherein the non-piezoelectric material is embedded within the polymer matrix.

45. The piezoelectric material is continuous along one direction, 45. An ultrasonic transducer as claimed in any one of claims 33 to 44, wherein the filler material is continuous along three directions.

46. the piezoelectric material is continuous along two directions; 45. An ultrasonic transducer as claimed in any one of claims 33 to 44, wherein the filler material is continuous along two directions.

47. 47. An ultrasonic transducer as described in any one of claims 33 to 46, wherein the piezoelectric material is selected from the group consisting of ferroelectric materials, single crystal ferroelectric materials, lead-free ferroelectric materials, and piezoelectric polymer materials.

48. 48. The ultrasonic transducer of claim 47, wherein the piezoelectric material is lead zirconate titanate (PZT).

49. 49. An ultrasonic transducer according to any one of claims 33 to 48, wherein the acoustic impedance characteristic is in the range of about 15 MR to about 30 MR.

50. 3. The method of claim 2, wherein the first acoustic impedance is in the range of about 30 MR to about 40 MR.

50. An ultrasonic transducer according to any one of claims 3 to 49.

51. 51. The ultrasonic transducer of any one of claims 33 to 50, wherein the third acoustic impedance is in the range of about 7 MR to about 8 MR.

52. 52. An ultrasonic transducer according to any one of claims 33 to 51, wherein the piezoelectric composite layer is acoustically matched to and electrically isolated from the sample.

53. 53. An ultrasound transducer as described in any one of claims 33 to 52, further comprising a backing layer in electrical communication with the one or more electrodes.

54. 54. The ultrasonic transducer of claim 53, wherein the backing layer is a mismatched layer.

55. 55. An ultrasonic transducer as described in any one of claims 33 to 54, further comprising a ground electrode.

56. 56. The ultrasonic transducer of claim 55, wherein the ground electrode is configured as a heat spreader.

57. 57. An ultrasonic transducer as described in any one of claims 33 to 56, wherein the piezoelectric composite layer and the sample define an acoustic path therebetween, and the ultrasonic transducer further comprises a substantially lossless acoustic matching layer disposed along the acoustic path between the piezoelectric composite layer and the sample.

58. 58. The ultrasonic transducer of any one of claims 33 to 57, further comprising a wear layer, the wear layer acoustically matched to the piezoelectric composite layer.

59. 59. An ultrasonic transducer as described in any one of claims 33 to 58, wherein the piezoelectric composite layer has a thickness of approximately 2400 microns.

60. 60. An ultrasonic transducer as described in any one of claims 33 to 59, wherein each spaced apart piezoelectric region is spaced 200 microns apart from each other and has a square cross section, the square cross section being 1000 microns by 1000 microns.

61. 61. The ultrasonic transducer of any one of claims 33 to 60, wherein the piezoelectric composite layer has a piezoelectric volume fraction in the range of about 70% to about 80%.

62. 62. An ultrasonic transducer as described in any one of claims 33 to 61, further comprising an electrically insulating housing for containing the piezoelectric composite layer therein.

63. a piezoelectric composite layer configured to be in acoustic communication with a sample and having at least partially decoupled acoustic impedance and electrical impedance characteristics, the piezoelectric composite layer comprising: an array of spaced apart piezoelectric regions, each spaced apart piezoelectric region made from a piezoelectric material; a filler material disposed between adjacent spaced apart piezoelectric regions, the filler material comprising a polymer matrix; a non-piezoelectric material in contact with the polymer matrix; a piezoelectric composite layer; an electrically insulating non-piezoelectric composite layer extending above the piezoelectric composite layer to electrically insulate the piezoelectric composite layer from the sample, the non-piezoelectric composite layer being acoustically matched to the piezoelectric composite layer and the sample; an electrically insulating non-piezoelectric composite layer bonded to the piezoelectric substrate; one or more electrodes in electrical communication with the piezoelectric composite layer; An ultrasonic transducer comprising:

64. 64. The ultrasonic transducer of claim 63, wherein the electrically insulating non-piezoelectric composite layer comprises a region of high acoustic impedance electrically insulating material in contact with a second polymer matrix, the second polymer matrix being filled with a high density electrically insulating powder.

65. 64. The ultrasonic transducer of claim 63, wherein the electrically insulating non-piezoelectric composite layer comprises an electrically insulating ceramic region in contact with a second polymer matrix, the second polymer matrix being filled with a high density electrically insulating ceramic powder.

66. 64. The ultrasonic transducer of claim 63, wherein the electrically insulating non-piezoelectric composite layer comprises an electrically insulating glass region in contact with a second polymer matrix, the second polymer matrix being filled with a high density electrically insulating ceramic powder.

67. 67. An ultrasonic transducer as described in any one of claims 63 to 66, wherein the electrically insulating non-piezoelectric composite layer is of a 1 / 3 construction.

68. 67. An ultrasonic transducer as claimed in any one of claims 63 to 66, wherein the electrically insulating non-piezoelectric composite layer is of 2:2 construction.

69. the piezoelectric composite layer is configured to generate a probing acoustic signal directed toward the sample; 69. An ultrasonic transducer as described in any one of claims 63 to 68, wherein the one or more electrodes are operable to transmit a probing electrical signal to the piezoelectric composite layer, thereby generating the probing acoustic signal.

70. 70. An ultrasonic transducer as described in any one of claims 63 to 69, wherein the piezoelectric composite layer is configured to receive a sample acoustic signal emanating from the sample and thereby generate a sample electrical signal directed to the one or more electrodes, the sample electrical signal representing the sample acoustic signal.

71. 71. An ultrasonic transducer as described in any one of claims 63 to 70, wherein the polymer matrix is ​​made from epoxy.

72. 72. An ultrasonic transducer as claimed in any one of claims 63 to 71, wherein the non-piezoelectric material is hafnium oxide powder.

73. 73. An ultrasonic transducer as described in any one of claims 63 to 72, further comprising one or more electrically insulating regions disposed between adjacent spaced apart piezoelectric regions, the one or more electrically insulating regions being in contact with the filler material.

74. 74. The ultrasonic transducer of claim 73, wherein the one or more electrically insulating regions have a fourth acoustic impedance and a fourth dielectric constant, the fourth acoustic impedance being close to the first acoustic impedance and the fourth dielectric constant being less than the first dielectric constant.

75. 75. An ultrasonic transducer as described in claim 73 or 74, wherein the one or more electrically insulating regions are made from ceramic.

76. 75. An ultrasonic transducer as described in claim 73 or 74, wherein the one or more electrically insulating regions are made from glass.

77. 77. An ultrasonic transducer as described in any one of claims 73 to 76, wherein the one or more electrically insulating regions have an elongated shape.

78. 77. An ultrasonic transducer as described in any one of claims 73 to 76, wherein the one or more electrically insulating regions define a bar-shaped electrically insulating region.

79. 77. An ultrasonic transducer as described in any one of claims 73 to 76, wherein the one or more electrically insulating regions define pillar-shaped electrically insulating regions.

80. 77. An ultrasonic transducer as described in any one of claims 73 to 76, wherein the one or more electrically insulating regions are spherical in shape.

81. 81. An ultrasound transducer as described in any one of claims 63 to 80, wherein the non-piezoelectric material is embedded within the polymer matrix.

82. The piezoelectric material is continuous along one direction, 82. An ultrasonic transducer as described in any one of claims 63 to 81, wherein the filler material is continuous along three directions.

83. the piezoelectric material is continuous along two directions; 82. An ultrasonic transducer as described in any one of claims 63 to 81, wherein the filler material is continuous along two directions.

84. 84. An ultrasonic transducer as described in any one of claims 63 to 83, wherein the piezoelectric material is selected from the group consisting of ferroelectric materials, single crystal ferroelectric materials, lead-free ferroelectric materials, and piezoelectric polymer materials.

85. 85. The ultrasonic transducer of claim 84, wherein the piezoelectric material is lead zirconate titanate (PZT).

86. 86. An ultrasonic transducer as described in any one of claims 63 to 85, wherein the acoustic impedance characteristic is in the range of about 15 MR to about 30 MR.

87. 87. An ultrasonic transducer as described in any one of claims 63 to 86, wherein the first acoustic impedance is in the range of about 30 MR to about 40 MR.

88. 88. An ultrasonic transducer as described in any one of claims 63 to 87, wherein the third acoustic impedance is in the range of about 7 MR to about 8 MR.

89. 89. An ultrasonic transducer as described in any one of claims 63 to 88, wherein the piezoelectric composite layer is acoustically matched to and electrically isolated from the sample.

90. 90. An ultrasonic transducer as described in any one of claims 63 to 89, further comprising a backing layer in electrical communication with the one or more electrodes.

91. 91. The ultrasonic transducer of claim 90, wherein the backing layer is a mismatched layer.

92. 92. An ultrasonic transducer as described in any one of claims 63 to 91, further comprising a ground electrode.

93. 93. The ultrasonic transducer of claim 92, wherein the ground electrode is configured as a heat spreader.

94. An ultrasonic transducer as described in any one of claims 63 to 93, wherein the piezoelectric composite layer and the sample define an acoustic path therebetween, and the ultrasonic transducer further comprises a substantially lossless acoustic matching layer positioned along the acoustic path between the piezoelectric composite layer and the sample.

95. 95. An ultrasonic transducer as described in any one of claims 63 to 94, further comprising a wear layer, the wear layer being acoustically matched to the piezoelectric composite layer.

96. 96. An ultrasonic transducer as described in any one of claims 63 to 95, wherein the piezoelectric composite layer has a thickness of approximately 2400 microns.

97. 97. An ultrasonic transducer as described in any one of claims 63 to 96, wherein each spaced apart piezoelectric region is spaced 200 microns apart from each other and has a square cross section, the square cross section being 1000 microns by 1000 microns.

98. 98. An ultrasonic transducer as described in any one of claims 63 to 97, wherein the piezoelectric composite layer has a piezoelectric volume fraction in the range of about 70% to about 80%.

99. 99. An ultrasonic transducer as described in any one of claims 63 to 98, further comprising an electrically insulating housing for containing the piezoelectric composite layer therein.

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