Ultrasonic transducer

Abstract

An ultrasonic transducer and methods of designing and manufacturing the same are provided. The ultrasonic transducer includes a piezoelectric composite layer for acoustic communication with a sample and having at least partially decoupled acoustic and electrical impedance characteristics. The piezoelectric composite material layer comprises an array of spaced piezoelectric areas made of free piezoelectric materials, a filling material which is located between the adjacent spaced piezoelectric areas and comprises a polymer matrix, and a non-piezoelectric material in contact with the polymer matrix. In some embodiments, an ultrasonic transducer includes an electrically insulating non-piezoelectric composite layer extending over a piezoelectric composite layer for electrically insulating the piezoelectric composite layer from a sample, the electrically insulating non-piezoelectric composite layer acoustically matching the piezoelectric composite layer and the sample.

Description

[0001] This application is a divisional application of the patent application with application number 201980049864.3 filed on July 31, 2019 and invention name “Ultrasonic Transducer”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to patent application US 62 / 712,595 filed on July 31, 2018, the specification of which is incorporated herein by reference.

[0004] The technical field generally relates to the field of acoustic energy, and more particularly to an ultrasonic transducer, related equipment, devices methods and techniques. Background Art

[0005] The transmission of acoustic energy toward and from an ultrasonic transducer is at least partially affected by an acoustic impedance mismatch, e.g., a difference in acoustic impedance between a material contained in the ultrasonic transducer (e.g., a piezoelectric ceramic) and a material to which the ultrasonic transducer is acoustically coupled. Generally, when the acoustic impedances of an ultrasonic transducer and a material are matched, energy transfer between them is improved.

[0006] It is generally known to those skilled in the art that there are impedance matching techniques for improving the transmission efficiency of sound waves across different materials. Such impedance matching techniques generally involve a trade-off between bandwidth and efficiency and have a certain degree of complexity. When a large bandwidth is required, the design of the ultrasonic transducer, including the matching system, becomes more complex. Such complexity significantly increases the cost of the ultrasonic transducer. Designing and implementing an ultrasonic transducer with a large bandwidth remains a challenge, so the solutions known in the art are still fundamentally limited bandwidth.

[0007] A variety of materials sometimes need to be acoustically coupled to an ultrasonic transducer. Such materials can be used in many industrial and medical applications. Common examples include, but are not limited to, biological tissues (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 acoustic impedance of the above materials ranges from about 1 MegaRayle (MR) to over 60 MR.

[0008] Materials that acoustically couple to an ultrasonic transducer can be divided into four categories: materials with higher acoustic impedance than piezoelectric materials (referred to herein as the "first category"), materials with acoustic impedance close to that of piezoelectric materials (referred to herein as the "second category"), materials with lower acoustic impedance than piezoelectric materials (referred to herein as the "third category"), and biomaterials with much lower acoustic impedance than most piezoelectric materials (referred to herein as the "fourth category").

[0009] Examples of the first category of materials are, for example, but not limited to, tungsten, molybdenum, nickel, and gold. The acoustic impedance of these materials exceeds about 45 MR. Examples of the second category of materials are, for example, but not limited to, brass, silver, zirconium, and cast iron. The acoustic impedance of these materials is between about 30 MR and about 40 MR. Examples of the third category of materials are, for example, but not limited to, magnesium, aluminum, indium, titanium, and tin. The acoustic impedance of these materials ranges from about 10 MR to about 30 MR. Examples of the fourth category of materials are, for example, but not limited to, fat, muscle, or organs. The acoustic impedance of these materials is typically between about 1.2 MR and about 1.8 MR. Bone is another example of the fourth category of materials and can have an acoustic impedance between about 5 MR and about 8 MR. However, it should be noted that this value can vary greatly.

[0010] There remains a need for techniques, devices, apparatus and methods that can alleviate or mitigate the problems in the prior art. Summary of the invention

[0011] According to one aspect, an ultrasonic transducer is provided, comprising a piezoelectric composite material layer, the piezoelectric composite material layer being used to acoustically communicate with a sample and having acoustic impedance and electrical impedance characteristics that are at least partially decoupled; and one or more electrodes in electrical communication with the piezoelectric composite material layer, the piezoelectric composite material layer comprising an array of spaced piezoelectric regions, each spaced piezoelectric region being made of a piezoelectric material having a first acoustic impedance and a first relative dielectric constant; a filling material, which is located between adjacent spaced piezoelectric regions, the filling 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 relative dielectric constant being less than the first relative dielectric constant; and a non-piezoelectric material, which is in contact with the polymer matrix, the non-piezoelectric material having a third acoustic impedance and a third relative dielectric constant, the third acoustic impedance being greater than the second acoustic impedance, and the third relative dielectric constant being less than the first relative dielectric constant.

[0012] In some embodiments, the piezoelectric composite layer is used to generate a probing acoustic signal toward the sample; and the one or more electrodes are operable to send the probing electrical signal to the piezoelectric composite layer, thereby generating the probing acoustic signal.

[0013] In some embodiments, the piezoelectric composite layer is used to receive a sample acoustic signal emitted from the sample, thereby generating a sample electrical signal toward one or more electrodes, the sample electrical signal representing the sample acoustic signal.

[0014] In some embodiments, the polymer matrix is ​​made of epoxy resin.

[0015] In some embodiments, the non-piezoelectric material is hafnium oxide powder.

[0016] In some embodiments, the ultrasound transducer further includes one or more electrically insulating regions located between adjacent spaced piezoelectric regions, the one or more electrically insulating regions being in contact with the filler material.

[0017] In some embodiments, the one or more electrically insulating regions have a fourth acoustic impedance and a fourth relative permittivity, the fourth acoustic impedance being close to the first acoustic impedance, and the fourth relative permittivity being less than the first relative permittivity.

[0018] In some embodiments, one or more electrically insulating regions are made of ceramic.

[0019] In some embodiments, one or more electrically insulating regions are made of glass.

[0020] In some embodiments, one or more electrically insulating regions have an elongated shape.

[0021] In some embodiments, the one or more electrically insulating regions define a rod-shaped electrically insulating region.

[0022] In some embodiments, one or more electrically insulating regions define a columnar electrically insulating region.

[0023] In some embodiments, the ultrasound transducer further comprises one or more electrically insulating regions that are spherical.

[0024] In some embodiments, the non-piezoelectric material is embedded in a polymer matrix.

[0025] In some embodiments, the piezoelectric material is continuous in one direction; and the filler material is continuous in three directions.

[0026] In some embodiments, the piezoelectric material is continuous in two directions; and the filler material is continuous in two directions.

[0027] In some embodiments, 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.

[0028] In some embodiments, the piezoelectric material is lead zirconate titanate (PZT).

[0029] In some embodiments, the acoustic impedance characteristics are in a range of about 15 MR to about 30 MR.

[0030] In some embodiments, the first acoustic impedance is in a range from about 30 MR to about 40 MR.

[0031] In some embodiments, the third acoustic impedance is in a range from about 7 MR to about 8 MR.

[0032] In some embodiments, the piezoelectric composite layer is acoustically matched to the sample and electrically insulated from the sample.

[0033] In some embodiments, the ultrasound transducer further includes a backing layer in electrical communication with the one or more electrodes.

[0034] In some embodiments, the backing layer is a dematching layer.

[0035] In some embodiments, the ultrasound transducer further includes a ground electrode.

[0036] In some embodiments, the ground electrode is configured as a heat sink.

[0037] In some embodiments, an acoustic path is defined between the piezoelectric composite material layer and the sample, and the ultrasonic transducer further includes a nearly lossless acoustic matching layer located between the piezoelectric composite material layer and the sample along the acoustic path.

[0038] In some embodiments, the ultrasonic transducer further comprises a wear-resistant layer, the wear-resistant layer being acoustically matched to the piezoelectric composite layer.

[0039] In some embodiments, the piezoelectric composite layer has a thickness of approximately 2400 microns.

[0040] In some embodiments, each spaced piezoelectric region is spaced 200 microns apart from one another and has a square cross-section that is 1000 microns by 1000 microns.

[0041] In some embodiments, the piezoelectric composite layer has a piezoelectric volume fraction of about 70% to about 80%.

[0042] In some embodiments, the ultrasound transducer further includes an electrically insulating housing for housing the piezoelectric composite material layer therein.

[0043] According to another aspect, an ultrasonic transducer for emitting an acoustic signal toward a target is provided, the ultrasonic transducer comprising a piezoelectric composite material layer having acoustic impedance and electrical impedance characteristics that are at least partially decoupled; and one or more electrodes in electrical communication with the piezoelectric composite material layer, the one or more electrodes being operable to send an electrical signal to the piezoelectric composite material layer, thereby generating an acoustic signal toward the target, the piezoelectric composite material layer comprising: an array of spaced piezoelectric regions, each spaced piezoelectric region being made of a piezoelectric material having a first acoustic impedance and a first relative dielectric constant; a filling material located between adjacent spaced piezoelectric regions, the filling 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 relative dielectric constant being less than the first relative 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 relative dielectric constant, the third acoustic impedance being greater than the second acoustic impedance, and the third relative dielectric constant being less than the first relative dielectric constant.

[0044] In some embodiments, the polymer matrix is ​​made of epoxy resin.

[0045] In some embodiments, the non-piezoelectric material is hafnium oxide powder.

[0046] In some embodiments, the ultrasound transducer further includes one or more electrically insulating regions located between adjacent spaced piezoelectric regions, the one or more electrically insulating regions being in contact with the filler material.

[0047] In some embodiments, the one or more electrically insulating regions have a fourth acoustic impedance and a fourth relative permittivity, the fourth acoustic impedance being close to the first acoustic impedance, and the fourth relative permittivity being less than the first relative permittivity.

[0048] In some embodiments, one or more electrically insulating regions are made of ceramic.

[0049] In some embodiments, one or more electrically insulating regions are made of glass.

[0050] In some embodiments, one or more electrically insulating regions have an elongated shape.

[0051] In some embodiments, the one or more electrically insulating regions define a rod-shaped electrically insulating region.

[0052] In some embodiments, one or more electrically insulating regions define a columnar electrically insulating region.

[0053] In some embodiments, one or more electrically insulating regions are spherical.

[0054] In some embodiments, the non-piezoelectric material is embedded in a polymer matrix.

[0055] In some embodiments, the piezoelectric material is continuous in one direction; and the filler material is continuous in three directions.

[0056] In some embodiments, the piezoelectric material is continuous in two directions; and the filler material is continuous in two directions.

[0057] In some embodiments, 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.

[0058] In some embodiments, the piezoelectric material is lead zirconate titanate (PZT).

[0059] In some embodiments, the acoustic impedance characteristics are in a range of about 15 MR to about 30 MR.

[0060] In some embodiments, the first acoustic impedance is in a range from about 30 MR to about 40 MR.

[0061] In some embodiments, the third acoustic impedance is in a range from about 7 MR to about 8 MR.

[0062] In some embodiments, the piezoelectric composite layer is acoustically matched to the sample and electrically insulated from the sample.

[0063] In some embodiments, the ultrasound transducer further includes a backing layer in electrical communication with the one or more electrodes.

[0064] In some embodiments, the backing layer is a dematching layer.

[0065] In some embodiments, the ultrasound transducer further includes a ground electrode.

[0066] In some embodiments, the ground electrode is configured as a heat sink.

[0067] In some embodiments, an acoustic path is defined between the piezoelectric composite material layer and the sample, and the ultrasonic transducer further includes a nearly lossless acoustic matching layer located between the piezoelectric composite material layer and the sample along the acoustic path.

[0068] In some embodiments, the ultrasonic transducer further comprises a wear-resistant layer, the wear-resistant layer being acoustically matched to the piezoelectric composite layer.

[0069] In some embodiments, the piezoelectric composite layer has a thickness of approximately 2400 microns.

[0070] In some embodiments, each spaced piezoelectric region is spaced 200 microns apart from one another and has a square cross-section that is 1000 microns by 1000 microns.

[0071] In some embodiments, the piezoelectric composite layer has a piezoelectric volume fraction of about 70% to about 80%.

[0072] In some embodiments, the ultrasound transducer further includes an electrically insulating housing for housing the piezoelectric composite material layer therein.

[0073] According to another aspect, an ultrasonic transducer is provided, comprising a piezoelectric composite layer, the piezoelectric composite layer being used for acoustically communicating with a sample and having acoustic impedance and electrical impedance characteristics that are at least partially decoupled; an electrically insulating non-piezoelectric composite layer extending over the piezoelectric composite layer, being used 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, the piezoelectric composite layer comprising: an array of spaced piezoelectric regions, each spaced piezoelectric region being made of a piezoelectric material; a filling material, which is located between adjacent spaced piezoelectric regions, the filling material comprising a polymer matrix; and a non-piezoelectric material, which is in contact with the polymer matrix.

[0074] In some embodiments, the electrically insulating non-piezoelectric composite material layer includes a region of high acoustic impedance electrically insulating material in contact with a second polymer matrix filled with a high density electrically insulating powder.

[0075] In some embodiments, the electrically insulating non-piezoelectric composite material layer includes an electrically insulating ceramic region in contact with a second polymer matrix filled with a high density electrically insulating ceramic powder.

[0076] In some embodiments, the electrically insulating non-piezoelectric composite material layer includes an electrically insulating glass region in contact with a second polymer matrix filled with a high density electrically insulating ceramic powder.

[0077] In some embodiments, the electrically insulating non-piezoelectric composite material layers are in a 1:3 configuration.

[0078] In some embodiments, the electrically insulating non-piezoelectric composite material layers are in a 2:2 configuration.

[0079] In some embodiments, the piezoelectric composite layer is used to generate a probing acoustic signal toward the sample; and the one or more electrodes are operable to send the probing electrical signal to the piezoelectric composite layer, thereby generating the probing acoustic signal.

[0080] In some embodiments, the piezoelectric composite layer is used to receive a sample acoustic signal emitted from the sample, thereby generating a sample electrical signal toward one or more electrodes, the sample electrical signal representing the sample acoustic signal.

[0081] In some embodiments, the polymer matrix is ​​made of epoxy resin.

[0082] In some embodiments, the non-piezoelectric material is hafnium oxide powder.

[0083] In some embodiments, the ultrasound transducer further includes one or more electrically insulating regions located between adjacent spaced piezoelectric regions, the one or more electrically insulating regions being in contact with the filler material.

[0084] In some embodiments, the one or more electrically insulating regions have a fourth acoustic impedance and a fourth relative permittivity, the fourth acoustic impedance being close to the first acoustic impedance, and the fourth relative permittivity being less than the first relative permittivity.

[0085] In some embodiments, one or more electrically insulating regions are made of ceramic.

[0086] In some embodiments, one or more electrically insulating regions are made of glass.

[0087] In some embodiments, one or more electrically insulating regions have an elongated shape.

[0088] In some embodiments, the one or more electrically insulating regions define a rod-shaped electrically insulating region.

[0089] In some embodiments, one or more electrically insulating regions define a columnar electrically insulating region.

[0090] In some embodiments, one or more electrically insulating regions are spherical.

[0091] In some embodiments, the non-piezoelectric material is embedded in a polymer matrix.

[0092] In some embodiments, the piezoelectric material is continuous in one direction; and the filler material is continuous in three directions.

[0093] In some embodiments, the piezoelectric material is continuous in two directions; and the filler material is continuous in two directions.

[0094] In some embodiments, 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.

[0095] In some embodiments, the piezoelectric material is lead zirconate titanate (PZT).

[0096] In some embodiments, the acoustic impedance characteristics are in a range of about 15 MR to about 30 MR.

[0097] In some embodiments, the first acoustic impedance is in a range from about 30 MR to about 40 MR.

[0098] In some embodiments, the third acoustic impedance is in a range from about 7 MR to about 8 MR.

[0099] In some embodiments, the piezoelectric composite layer is acoustically matched to the sample and electrically insulated from the sample.

[0100] In some embodiments, the ultrasound transducer further includes a backing layer in electrical communication with the one or more electrodes.

[0101] In some embodiments, the backing layer is a dematching layer.

[0102] In some embodiments, the ultrasound transducer further includes a ground electrode.

[0103] In some embodiments, the ground electrode is configured as a heat sink.

[0104] In some embodiments, an acoustic path is defined between the piezoelectric composite material layer and the sample, and the ultrasonic transducer further includes a nearly lossless acoustic matching layer located between the piezoelectric composite material layer and the sample along the acoustic path.

[0105] In some embodiments, the ultrasonic transducer further comprises a wear-resistant layer, the wear-resistant layer being acoustically matched to the piezoelectric composite layer.

[0106] In some embodiments, the piezoelectric composite layer has a thickness of approximately 2400 microns.

[0107] In some embodiments, each spaced piezoelectric region is spaced 200 microns apart from one another and has a square cross-section that is 1000 microns by 1000 microns.

[0108] In some embodiments, the piezoelectric composite layer has a piezoelectric volume fraction of about 70% to about 80%.

[0109] In some embodiments, the ultrasound transducer further includes an electrically insulating housing for housing the piezoelectric composite material layer therein.

[0110] Other embodiments are provided below.

[0111] According to another aspect, techniques, devices, apparatus, and methods are provided for independently adjusting the electrical impedance and acoustic impedance of a piezoelectric composite. Apparatus and methods that allow for decoupling of the electrical and acoustic impedance of a piezoelectric composite device can be implemented by combining a piezoelectric composite with three (3) materials, rather than the conventional two (2) materials. Decoupling of the acoustic impedance of the composite from the electrical impedance manipulation is provided by using a high acoustic impedance material, such as a non-piezoelectric ceramic, in addition to using a typically relatively low acoustic impedance kerf filler and piezoelectric material. In some embodiments, the non-piezoelectric ceramic is alumina.

[0112] According to another aspect, an ultrasonic transducer is provided for use with a target material having an acoustic impedance in the range of about 15 MR to about 30 MR. The ultrasonic transducer includes a complete acoustic path extending from a piezoelectric element to a target material or a device under test (DUT). The ultrasonic transducer includes a piezoelectric layer incorporating a piezoelectric element, a ground electrode, a thermal management layer, an electrical insulation layer, and an external wear-resistant surface that can adapt to the acoustic impedance of the target material to be insonated. The provided ultrasonic transducer does not require the use of an acoustic impedance matching layer, so that the solution has the same efficiency at all frequencies below an upper cutoff frequency. The upper cutoff frequency is limited only by the composite design parameters required to achieve effective performance of the composite element, resulting in a practical bandwidth from near DC to the upper cutoff frequency, and the upper cutoff frequency is at least several times the design center frequency of the device.

[0113] According to another aspect, an ultrasonic transducer is provided for use with materials having an acoustic impedance in the range of about 15 MR to about 30 MR. The ultrasonic transducer includes an acoustically matched composite material. Because the ultrasonic transducer does not use a matching layer, the bandwidth of the ultrasonic transducer is limited only by the inherent bandwidth imposed by the design and selection of materials including the piezoelectric element.

[0114] In some embodiments, the ultrasound transducer includes a heat resistant backing layer, which can also be configured as a heat sink proximal to the piezoelectric layer. In some embodiments, the backing layer can also serve as a dematching layer.

[0115] In some embodiments, the ultrasonic transducer includes a high acoustic impedance cut-out filling design. The high acoustic impedance cut-out filling design allows the piezoelectric element to be adapted to various materials with an acoustic impedance in the range of 15 to 30 MR. Materials with 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 a group of materials with an acoustic impedance of about 15 MR to 30 MR, the ultrasonic transducer provides a method for effectively coupling ultra-wideband ultrasound into these materials.

[0116] In some embodiments, the ultrasonic transducer includes a piezoelectric composite material layer designed to match the acoustic impedance of the DUT, and a non-piezoelectric electrically insulating composite material layer designed to match the acoustic impedance of the DUT. The non-piezoelectric layer is inserted between the piezoelectric composite material layer and the DUT. The non-piezoelectric composite material layer provides an effective wide bandwidth acoustic path from the piezoelectric composite material transducer element of the DUT while providing electrical insulation between the transducer and the DUT.

[0117] In some embodiments, the electrical impedance and acoustic impedance of the ultrasound transducer can be independently configured, or at least partially decoupled. The electrical impedance, acoustic impedance, or both can be configured by using a hybrid non-piezoelectric / piezoelectric composite material configuration.

[0118] In some embodiments, the ultrasound transducer can be configured as a single element, a notchless annular array, a notched annular array, a notched linear array, a notchless linear array, a notchless 2D matrix array, or a notched 2D matrix array.

[0119] According to another aspect, a method of manufacturing a piezoelectric layer having an adapted acoustic impedance is provided.

[0120] Other features and advantages of the present description will become more apparent on reading the following non-limiting description of specific embodiments, which are given by way of example only with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0121] Figure 1 A cross-sectional view of an ultrasound transducer according to one embodiment is illustrated.

[0122] Figure 2 A cross-sectional view of an ultrasound transducer according to another embodiment is illustrated.

[0123] Figure 3 A top view of a piezoelectric composite layer for an ultrasound transducer is shown according to one embodiment.

[0124] Figure 4 A top view of a piezoelectric composite layer for an ultrasound transducer according to another embodiment is shown.

[0125] Figure 5A Depicted is a perspective view of an ultrasound transducer according to one embodiment.

[0126] Figure 5B Depicted Figure 5A An exploded cross-sectional view of an ultrasonic transducer in FIG. DETAILED DESCRIPTION

[0127] In the following description, similar features in the accompanying drawings have been given similar reference numerals, and in order not to make the accompanying drawings unduly limited, if some elements have been identified in one or more previous drawings, these elements may not be indicated in some drawings. It should also be understood in this article that since the emphasis is placed on clearly illustrating the elements and structures of the present embodiment, the elements of the accompanying drawings do not have to be drawn to scale. The terms "a", "an" and "one" are defined herein as meaning "at least one", that is, unless otherwise specified, these terms do not exclude multiple elements. It should also be noted that the values, conditions or features of the features of the exemplary embodiments, such as "substantially", "usually" and "approximately", should be understood to mean that the value, condition or feature is limited to the acceptable tolerance of the appropriate operation of the exemplary embodiment for its intended application.

[0128] In this specification, the terms "connected", "coupled" and their variations and derivatives refer to any connection or coupling between two or more elements, whether direct or indirect. The connection or coupling between the elements can be acoustic, mechanical, physical, optical, operational, electrical, wireless or a combination thereof.

[0129] It should be understood that for ease of description and clarity, positional descriptors indicating the position or orientation of one element relative to another element are used herein, and unless otherwise specified, these descriptors should be adopted in the context of the drawings and should not be considered limiting. It should be understood that in addition to the positions and orientations illustrated in the drawings, spatial relative terms (e.g., "external" and "inner", "outer side" and "inner side", "peripheral" and "central", and "top" and "bottom") are also intended to cover different positions and orientations used or operated in the present embodiment.

[0130] General Theory Overview

[0131] There are many methods and materials that can be used to produce 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.

[0132] One large class of relatively high performance piezoelectric materials is known as ferroelectric materials. Ferroelectric materials are the most commonly used piezoelectric materials in acoustic transducers (such as ultrasonic transducers). Ferroelectric materials typically have acoustic impedance characteristics in the range of about 30MR to about 40MR. For example, one of the most common ferroelectric ceramics, a series of preparations commonly referred to as lead zirconate titanate (PZT) typically have an acoustic impedance in the range of about 33MR to about 35MR. Another class of relatively high performance piezoelectric materials is single crystal ferroelectric materials, which include but are not limited to lithium niobate (PMN-PT or PIN-PMN-PT). The acoustic impedance of these single crystal ferroelectric materials is in the range of about 30MR to about 35MR. Yet another class includes emerging lead-free ferroelectric materials, such as, for example but not limited to (K 0.5 Na 0.5 )NbO3(KNN) and (K 0.48 Na 0.52 ) 0.96 Li 0.04 Nb 0.85 Ta 0.15O3(KNLNT). The acoustic impedance of these materials is about 31MR, slightly lower than most variants of PZT. Yet another example class of piezoelectric materials includes piezoelectric polymers such as PVDF and copolymers such as P(VDF-TrFE). These polymer-based ferroelectric materials have much lower electromechanical efficiency than relaxor-based single crystals and ceramics, however, they have very low acoustic impedance and unique properties that are generally well suited to perform as receivers in immersion-based systems.

[0133] Although there are many potential piezoelectric materials, PZT and related relaxor-based ferroelectric materials remain the dominant class due to their performance being sufficient to outperform most other materials, leaving other piezoelectric materials in small application areas. Therefore, most transducers rely on piezoelectric materials with very similar acoustic impedances falling within a small range of about 33MR to about 38MR. Ultrasonic transducers based on piezoelectric materials with acoustic impedances that are closely matched to the material being ultrasonically processed can improve the efficiency of the system, whether by reducing matching requirements or increasing overall transmission efficiency and bandwidth. Some piezoelectric materials are acoustically well matched to some materials. However, many materials that do not have suitable acoustically matched transducer materials need to be ultrasonically processed, ultrasonically inspected and / or tested.

[0134] The acoustic impedance of a piezoelectric material can be reduced, while potentially increasing the electromechanical efficiency of the piezoelectric material, by creating a composite material of the piezoelectric material and another, typically lower acoustic impedance material that acts as a filler and forms a support matrix surrounding the piezoelectric material in one of a variety of ways. However, it should be understood that there is a trade-off between acoustic efficiency, electrical impedance, and acoustic impedance when making piezoelectric composites.

[0135] Composite materials commonly used in ultrasonic transducers are usually 1 3 or 2 2 configurations, 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 examples of methods for creating composite piezoelectric materials include cutting, etching, molding, or random stacking of piezoelectric materials, and filling or bonding other materials such as elastomers, epoxies, polymers, or gases interspersed between piezoelectric posts or beams to form a composite material.

[0136] Examples of composites in a 1 3 configuration include cut and filled composites with square cross-section pillars, and cutouts filled with a material having a lower acoustic impedance. Such composites can exploit rod mode resonances in piezoelectric pillars, making it possible to obtain a more efficient electromechanical coupling coefficient, which is governed by the k of the piezoelectric material. 33 The lower k efficiency limits the performance of the plate mode vibration (typically 0.7 for PZTs) rather than limiting the performance of the plate mode vibration (more typical in simple longitudinal disk or plate-based transducers). t(Typically 0.5 for PZT). Note that based on many design parameters of the composite geometry and the material properties of the piezoelectric and filler materials, the acoustic impedance of the composite can be lower than that of the pure piezoelectric material at some point between the piezoelectric material and the matrix filler. Thus, the difficulty of matching lower acoustic impedance materials is reduced and a higher signal-to-noise ratio is achieved.

[0137] In the biomedical field, much work has been done on the development of composite transducers, and has focused on developing efficient composite materials designed to be compatible with biological tissues. Therefore, many commercially available composite materials and transducers are optimized to have a combination of the lowest possible acoustic impedance while achieving the highest possible electromechanical efficiency for biological tissue and / or water immersion applications. The acoustic impedance of such composite materials is typically in the range of 8MR to 16MR. However, many practical applications require that acoustic energy be effectively transmitted from and toward an ultrasonic transducer coupled to a material whose acoustic impedance is not adequately matched to these piezoelectric materials. That is, the piezoelectric materials described above may not be suitable for other types of materials being ultrasonically processed. For example, due to the lack of ideal materials for traditional acoustic stack designs, materials with acoustic impedances between about 15MR and 30MR are particularly difficult to match with piezoelectric composites.

[0138] In these cases, various techniques are known to overcome the inherent acoustic discontinuity between the piezoelectric material and the medium. For example, a common method to match the acoustic impedance of a piezoelectric material to the desired medium is to use a 1 / 4 wave matching layer. Another example is the use of a spring mass matching layer system applied at high frequencies. Yet another example is the design of a horn structure. Such acoustic impedance matching techniques can be applied to piezoelectric transducer designs to facilitate the efficient transmission of acoustic radiation from the transducer to the medium being ultrasonically treated, and are typically operated in a reciprocating manner. However, one thing remains common to all acoustic impedance matching methods, and that is that they have a limited effective bandwidth. Outside of this bandwidth, their effectiveness drops rapidly, and when operated far enough away from the expected center frequency, unwanted artifacts may be generated.

[0139] While acoustic impedance matching is important in transducer design, in many practical applications, it is also necessary to electrically insulate the piezoelectric transducer assembly from the material being sonicated. In these cases, an electrically insulating layer must also be included in the transducer stack. For example, in fields such as non-destructive testing (NDT), it is sometimes necessary to electrically insulate the ultrasonic transducer from electrically sensitive components, devices, or structures while also matching the acoustic impedance of the transducer to the material or object being scanned. This is particularly important in medical applications. In fact, electrically insulating the transducer assembly from the human body (the medium being sonicated) is important to help prevent harm to the patient. For example, in medical diagnostic ultrasound (and other medical ultrasound applications including but not limited to therapeutic applications such as HIFU), for efficiency reasons, the acoustic impedance of the transducer should be matched to living tissue while also being electrically isolated from the patient. In other medical devices that use acoustic energy for acoustic ablation or mechanical enhancement of surgical tools, for example, for efficiency reasons, it is also necessary to match the acoustic impedance of the transducer to the medium (biological tissue or in some cases, components of an acoustic medical device) while electrically isolating the transducer from the patient.

[0140] In many cases, when the acoustic impedance of the target material is below about 10 MR, mature techniques are readily available to designers to address the need to acoustically match the transducer to the target and simultaneously electrically isolate it.

[0141] In medical diagnostic ultrasound, a typical solution for ultrasound transducers that come into contact with the patient is to select a lens or cover material that is well matched to living tissue, such as silicone or polyurethane, for example, which can be designed to have an acoustic impedance that closely matches the acoustic impedance of the tissue (about 1.5 MR) while still acting as an effective lens and electrical insulation material. Another common practice is to use an acoustically matched, electrically insulating matching layer. These matching materials include various glasses, polymers, elastomers, powder-loaded polymers, and epoxies. For example, ceramic powder-loaded epoxies, such as, for example, epoxy filled with alumina powder, can form various matching layers while maintaining the excellent resistivity required for electrical isolation. However, powder-loaded composite materials (such as powder-loaded epoxies, silicones, and polymers) typically show higher attenuation than homogeneous materials, and may not be able to make an appropriate compromise between the design parameters of the matching layer (such as thickness) and the acceptable loss of the device acoustic path and the required electrical isolation.

[0142] Additionally, the fabrication of powder-loaded composites is limited when high powder-to-polymer volume fractions are reached. For example, above about 12 MR, the common practice of loading powders with epoxy to improve acoustic impedance is not practical. Additionally, epoxy-filled porous sintered materials are expensive to design and difficult to precisely control. They can also be lossy if not fully filled. This is especially true for electrically insulating matching layers above 15 MR and below 30 MR.

[0143] It is important to note that the use of matching layers in ultrasonic transducer design is problematic when a broadband transducer is required, as broadband performance requires multiple matching layer solutions. Designing broadband ultrasonic transducers for coupling into 10MR to 30MR targets is difficult. These challenges are compounded when the transducer needs to be electrically isolated from the target material.

[0144] When the target material has an acoustic impedance in the range of about 15 MR to about 30 MR, it is increasingly difficult to apply existing solutions with a high degree of effectiveness. This is because there are relatively few electrically insulating materials that can serve as conventional matching layers that can satisfy the acoustic, thermal, and electrical properties of the target material having an acoustic impedance in the range of about 15 MR to about 30 MR.

[0145] There is a need in fields such as, for example but not limited to, NDT and medical device development for an ultrasonic transducer capable of transmitting high power, broadband acoustic pulses to materials having an acoustic impedance in the range of about 15 MR to about 30 MR. There is also a need for an electrical insulating layer having an acoustic impedance substantially similar (or nearly identical) to the target material and the piezoelectric layer. Currently, piezoelectric composite designs and existing solutions do not allow for changing the acoustic impedance of the piezoelectric composite without affecting its electrical impedance (or vice versa).

[0146] It has been discovered that electrical impedance and acoustic impedance can be independently manipulated (i.e., at least partially decoupled) by introducing high acoustic impedance non-piezoelectric materials into piezoelectric composite designs in addition to conventional materials used to make piezoelectric composites, as opposed to the typical approach of incorporating low acoustic impedance cut-fill materials used in conventional piezoelectric composite designs.

[0147] Ultrasonic transducer

[0148] Turning now to the drawings, various embodiments of ultrasound transducers will now be described. Figure 1 and Figure 2 Two embodiments of an ultrasound transducer 100 including a piezoelectric composite layer 102 are shown.

[0149] The piezoelectric composite material layer 102 is used for acoustic communication with a sample or target material. The piezoelectric composite material layer 102 has acoustic impedance and electrical impedance characteristics that are at least partially decoupled, that is, the combination of materials included in the piezoelectric layer 102 allows for partial decoupling of electrical impedance from acoustic impedance. The piezoelectric composite material layer 102 is generally made of at least three materials. Figure 3 and Figure 4 As shown, the piezoelectric layer 102 includes an array of spaced piezoelectric regions 10, a filling material 12, and a non-piezoelectric material 15. Each spaced piezoelectric region 10 is made of a piezoelectric material having a first acoustic impedance and a first relative dielectric constant. The filling material 12 is located between adjacent spaced 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 relative dielectric constant is less than the first relative dielectric constant. The non-piezoelectric material 15 is in contact with the polymer matrix and has a third acoustic impedance and a third relative dielectric constant. The third acoustic impedance is greater than the second acoustic impedance, and the third relative dielectric constant is less than the first relative dielectric constant. In some embodiments, the non-piezoelectric material 15 is embedded in the polymer matrix. Return to reference Figure 1 and Figure 2 , the ultrasound transducer 100 includes one or more electrodes 112 in electrical communication with the piezoelectric composite layer 102 .

[0150] Now refer to Figure 1 and Figure 2 , a cross-sectional view of one embodiment of an ultrasonic transducer 100 is provided. As shown, the ultrasonic transducer 100 has an acoustic stack design (i.e., multiple layers) that includes a cut and filled piezoelectric composite element / layer 102 that is acoustically matched to a target material 104. In some embodiments, which will be described in more detail below, the ultrasonic transducer 100 can be electrically insulated from the target material 104. The piezoelectric composite element 102 has a proximal surface 106 and a distal surface 108 relative to an ultrasonic signal source 110. An acoustic path extends between the piezoelectric composite layers 102 through the target material 104.

[0151] In some embodiments, such as Figure 3 and Figure 4 As shown, the piezoelectric composite layer 102 can be made of a ferroelectric piezoelectric material such as, for example but not limited to, PZT. In the variant shown, the piezoelectric regions 10 form pillars or beams 130 and are spaced apart from each other in a typical manner of a 1:3 or 2:2 composite material, meaning that the piezoelectric material 10 is continuous in one direction and the filling material 12 is continuous in three directions, or the piezoelectric material 10 is continuous in two directions and the filling material 12 is continuous in two directions.

[0152] This embodiment enables the electrical impedance of the piezoelectric composite to be significantly increased while maintaining the desired acoustic impedance. Figure 4 In the embodiment of the present invention, the space provided between adjacent piezoelectric regions 10 is a cutout 128. The cutout 128 is filled with epoxy resin 12. In some embodiments, the epoxy resin 12 includes a matrix material filled with HFO powder.

[0153] It is noted that although the piezoelectric regions 10 are shown as squares, they may have any shape, such as, for example but not limited to, triangles, cylinders, or hexagons.

[0154] In some embodiments, it is desirable to reduce the volume fraction of the piezoelectric material (e.g., the PZT fraction) in the piezoelectric composite layer 102 to achieve a better, improved, or more ideal electrical impedance requirement for the transducer. However, the higher the acoustic impedance requirement for the ultrasonic transducer 10, the higher the volume fraction of PZT is desired. In such embodiments, the matrix material filled with HFO powder is insufficient to achieve the desired properties. In these cases, as in Figure 4 As shown in , the matrix material of the HFO powder filling can be replaced or partially replaced with a non-piezoelectric material, such as, for example but not limited to, alumina rods. Such materials allow for higher acoustic impedance in the piezoelectric composite layer 102 while reducing the effective relative dielectric constant. In another embodiment, other relatively high acoustic impedance materials can be used.

[0155] In some embodiments, the cutout 128 is filled with alumina rods 14. Alumina generally has an acoustic impedance of about 35 MR and a dielectric constant of about 10. Figure 4 In the embodiment shown, the rod is sized to fill approximately 70% of the width of the cutout 128, leaving the remaining 30% of the cutout to be filled with epoxy 12. It should be appreciated that different filler materials and different epoxy materials and other ratios may be used to achieve the desired acoustic impedance and / or electrical impedance characteristics, depending, inter alia, on the target material being sonicated.

[0156] It should be noted that the non-piezoelectric material 15 need not be limited to alumina rods. For example, but not limited to, the alumina rods can be replaced by alumina balls mixed into HFO epoxy resin, or by cuts of a composite material made of HFO epoxy resin containing alumina balls. It should also be noted that similar results can be obtained by adjusting the ratio (i.e., volume fraction) of the cut, filler, and epoxy resin, so that the electrical impedance and acoustic impedance of the piezoelectric composite material layer 102 can be independently adjusted to match the desired (e.g., target material) acoustic and / or electrical properties. It should be understood that the proportions of materials forming the piezoelectric composite material layer 102 can vary greatly depending on the desired results. As a result of this design, the composite piezoelectric material can be designed, adjusted, and adapted to have a wider range of electrical impedance for a given size while maintaining the desired acoustic impedance. The added third material, i.e., the non-piezoelectric material 15, preferably has a high acoustic impedance, i.e., an acoustic impedance similar to or comparable (if possible) to the piezoelectric material, and the relative dielectric constant of the third material is much lower than that of the piezoelectric material. In this way, the piezoelectric composite layer 102 can be designed or adjusted to have a desired acoustic impedance and a desired dielectric constant, so that neither acoustic impedance matching technology nor electrical impedance matching circuits are required.

[0157] As previously mentioned, the ultrasonic transducer 100 includes one or more electrodes, such as a signal electrode 112. Figure 1 and Figure 2 As shown. In some embodiments, the piezoelectric composite material layer 102 is used to generate a detection acoustic signal toward the sample 104, and the electrode (e.g., the signal electrode 112) is operable to send the detection electrical signal to the piezoelectric composite material layer 102, thereby generating a detection acoustic signal. In some embodiments, the piezoelectric composite material layer 102 is also used to receive a sample acoustic signal emitted from the sample 104, thereby generating a sample electrical signal toward one or more electrodes (e.g., the signal electrode 112), and the sample electrical signal represents the sample acoustic signal. In this way, the ultrasonic transducer 100 can be used to send and / or receive ultrasound.

[0158] In some embodiments, such as Figure 1 and Figure 2As shown in , the electrode 112 is located on the proximal surface 106 of the piezoelectric composite material layer 102. The electrode 112 can have a conductive backing layer 114 located on the proximal surface 116 of the signal electrode 112. In other embodiments, the backing layer can be electrically insulating. The backing layer 114 can be operably or electrically connected to the signal electrode 112. In one embodiment, the backing layer 114 is made of titanium and can have a thickness of about 200 microns. The backing layer 114 can be made of a sufficiently high acoustic impedance material to also serve as a dematching layer. Typically, such a dematching function requires that the acoustic impedance of the backing layer is at least twice the acoustic impedance of the piezoelectric material, thereby providing higher bandwidth and sensitivity. For example, the dematching layer 114 can be made of, for example, but not limited to, molybdenum, tungsten, or tungsten carbide.

[0159] 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 described, the piezoelectric material may be lead zirconate titanate (PZT).

[0160] In some embodiments, the polymer matrix is ​​made of epoxy and the non-piezoelectric material is hafnium oxide powder.

[0161] The ultrasonic transducer 100 may also be provided with one or more electrically insulating regions, which are located between adjacent spaced piezoelectric regions 10, and the one or more electrically insulating regions are in contact with the filling material 12. The electrically insulating region has a fourth acoustic impedance and a fourth relative dielectric constant. In some embodiments, the fourth acoustic impedance is close to the first acoustic impedance, and the fourth relative dielectric constant is less than the first relative dielectric constant. For example, but not limited to, the electrically insulating region can be made of ceramic or glass. The shape of the electrically insulating region can vary. They can have, for example, but not limited to, an elongated shape, a rod-shaped electrically insulating region, a defined or spherical shape.

[0162] Turning now to the materials used in the ultrasonic transducer, it should be understood that the use of different volume fractions of filler powders and / or different filler powders in the matrix material will allow the filler to have different acoustic impedances. For example, it will be understood by those skilled in the art that by mixing epotek 301 epoxy and HFO powder in varying volume fractions, a powder-loaded epoxy material having an acoustic impedance of about 3MR to about 10MR can actually be obtained. In one embodiment, the filler material 12 is designed to have an acoustic impedance of about 7MR to about 8MR. It should also be understood that the piezoelectric composite layer 102 will exhibit different properties from non-composite piezoelectric materials. For example, non-composite piezoelectric materials can have relatively high Q factors, making them inherently relatively low-bandwidth materials. However, in this embodiment, the use of a lower impedance matrix material to form a 1 3PZT piezoelectric composite can provide higher bandwidth and efficiency compared to a simple PZT plate-based element. In addition, compared to pure PZT, the 13 composite PZT also exhibits a lower dielectric constant, thereby enabling a more practical electrical impedance to be obtained through a large unit element design. It should be understood that other piezoelectric materials may be used in other embodiments without departing from the scope of the present specification. 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 having suitable properties (such as higher bandwidth, higher sensitivity, or lower cost) for the desired application. Therefore, when compared to existing piezoelectric composites that are typically constructed using fillers in the range of 1MR to 3MR, for example but not limited to when one wishes to match a piezoelectric composite transducer with a material having a relatively high acoustic impedance (such as, for example, titanium or zirconium), the use of relatively high acoustic impedance powder-loaded cut fillers between piezoelectric columns allows for a more adequate trade-off between acoustic impedance, electrical impedance, and column aspect ratio at an increased degree of freedom. In some cases, the higher acoustic impedance cut filler may result in reduced acoustic isolation between the columns, thereby reducing the electromechanical coupling coefficient of the composite. However, the proposed trade-off may be considered acceptable given the improved acoustic match and the bandwidth of the resulting acoustic path from the composite to the target material or DUT. Using a matrix material filled with HFO powder, a relatively low volume fraction of piezoelectric material (e.g., 73% PZT volume / volume) can be used to achieve an average acoustic impedance of 27.4MR. In comparison, for a typical 3MR unfilled epoxy, existing piezoelectric composites require approximately 78%. The lower volume fraction of piezoelectric material in the piezoelectric composite layer 102 allows for higher electrical impedance without sacrificing acoustic match. In addition, the 73% volume fraction enables more efficient cutting, allows the use of larger blades, simplifies the manufacturing process, and enhances the designer's freedom to optimize the aspect ratio of the column to achieve optimal rod mode resonance.Another benefit of using a powder-loaded matrix in the composite is the ability to change the powder-loaded epoxy matrix to fine tune the acoustic impedance of the piezoelectric composite without having to change the size and cut of the posts. Such changes in post design and post size and associated cuts are known to be costly.

[0163] Turning now to the acoustic impedance of the ultrasonic transducer 100, in some embodiments, the acoustic impedance characteristic of the piezoelectric composite material layer 102 is in the range of about 15MR to about 30MR. As previously determined, this impedance characteristic is a combination of the impedances of each material forming the piezoelectric composite material layer 102. In this regard, in some embodiments, the first acoustic impedance is in the range of about 30MR to about 40MR, and the third acoustic impedance is in the range of about 7MR to about 8MR. It should be noted that the piezoelectric composite material 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 material layer 122.

[0164] 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 cases, the backing layer can function as a dematching layer.

[0165] The ultrasonic transducer may include a ground electrode 118, such as Figure 1 and Figure 2 The ground electrode 118 is located on the distal surface 108 of the piezoelectric composite element 102. In some embodiments, the ground electrode 118 can also be used as a heat sink to diffuse the heat generated by the ultrasonic transducer 100. It should be noted that the ground electrode 118 does not necessarily need to be used as a heat sink.

[0166] An acoustic path is defined between the piezoelectric composite material layer 102 and the sample or target material 104. In some embodiments, the ultrasonic transducer 100 further includes a nearly lossless acoustic matching layer 120 located between the piezoelectric composite material layer 102 and the sample 104 along the acoustic path. The nearly lossless acoustic matching layer 120 is positioned adjacent to and in contact with the distal surface of the ground electrode 118. The nearly lossless acoustic matching layer 120 is conductive and has a substantially low thermal impedance. When the ultrasonic transducer is used to ultrasonically process titanium, the acoustic matching layer 120 can be made of titanium. It should be noted that the acoustic matching layer 120 is optional and, in some embodiments, can be used as a heat sink as well as a mechanical support layer. Mechanical support enhances the ground layer and is also beneficial in the process of manufacturing the ultrasonic transducer 100. Usually, there may be no acoustic matching layer 120, but in fact, all layers in the ultrasonic transducer 100 are acoustically matched. The acoustic matching layer 120 is an effective heat sink and may not be included in the acoustic design just next to the piezoelectric element 102. Generally, it is desirable that the material of the acoustic matching layer is the same as the material of the DUT. That is, the transducer 100 is designed to be the same material to which it is matched. However, when the DUT is titanium, another sufficiently matched material with the desired properties may be selected, such as, but not limited to, selecting the material of the acoustic matching layer 120 to be zinc, which has relatively better thermal conductivity than titanium, but has an acoustic impedance that is almost equivalent to titanium. In an acoustically matched stack, this may be less challenging to design because the thickness of the layer and the properties other than the acoustic impedance can be easily accommodated in the design.

[0167] In some embodiments, the ultrasonic transducer 100 further includes a wear layer 124. The wear layer 124 is acoustically matched to the piezoelectric composite material layer 102. The wear layer 124 can 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 material layer 122. The wear layer 124 can be the same material as the DUT, especially if the material is almost as lossless as many metals. For example, in one embodiment designed to allow titanium to be ultrasonically processed, the wear layer 124 is made of 3 mm thick titanium. In this embodiment, the wear layer 124 is used to electrically insulate the transducer signal and the ground, thereby allowing the transducer assembly to be electrically isolated from the DUT.

[0168] In some embodiments, a heat-resistant and mechanical grounding structure is provided to support and help cool the piezoelectric composite layer 102. In a non-limiting embodiment, the piezoelectric composite layer 102 is adhered to a 3 mm thick titanium disk, thereby establishing a thermal cooling path to the electrical ground conductor and establishing a ground electrode. The substrate can also be used as a mechanical support to help manufacture piezoelectric composites and stacks. In some embodiments, the conductive disk can be selected to match the acoustic impedance or target material of the target material and / or for a wide range of applications of the ultrasonic transducer 100 (covering an acoustic impedance ranging from about 10 MR to more than 30 MR). In some cases, when the target material 104 is conductive, for example, when the target material is a metal, 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 electrical insulating layer to provide additional mechanical support for the insulating layer, as well as excellent moisture resistance. Typically, the wear plate can be made of the target material itself, and in the case of the exemplary embodiment, a 3 mm thick titanium is selected.

[0169] In some embodiments, the piezoelectric composite material layer 102 has a thickness of about 2400 microns. It should be noted that the ultrasonic transducers of the prior art generally have restrictions on the thickness of each layer provided. Because all layers of the ultrasonic transducer 100 have the same acoustic impedance, there is no limit or a reduced limit on the thickness of the layer. These layers can be thicker or thinner depending on the application requirements. In one embodiment, the acoustic matching layer 120 is thicker to provide sufficient mass to serve as a heat sink. Therefore, as long as the acoustic impedance of the layers at the far end of the piezoelectric layer is matched or nearly matched, the transducer layer at the far end of the piezoelectric layer 102 can have any thickness. Such a configuration makes it possible to optimize other characteristics of the distal layer without relying on the thickness of the layer. In one embodiment, the matching layer 120 can be thickened to obtain mechanical robustness with less impact on acoustic performance, or can be thinned to reduce costs without affecting acoustic performance. Similarly, the layers of the ultrasonic transducer 100 adjacent to and proximal to the piezoelectric layer 102 should have appropriate thickness and material to enhance the output efficiency of the transducer 100.

[0170] In some embodiments, each spaced piezoelectric region 10 is spaced 200 microns apart from one another and has a square cross-section that is 1000 microns by 1000 microns. The piezoelectric composite material layer 102 can have different piezoelectric volume fractions depending on the target material 104. In some embodiments, the piezoelectric composite material layer 102 has a piezoelectric volume fraction of about 70% to about 80%.

[0171] The ultrasonic transducer 100 or components thereof may be housed in an electrically insulating housing.

[0172] 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 (eg, a wire). This provides an electrical connection to the ultrasound signal source 110.

[0173] In some embodiments, a copper (Cu) ground and thermal loop 132 is also provided. The Cu ground and thermal loop 132 provides a housing that at least partially houses the Cu cap 132, the backing layer and / or the dematching layer 114, the electrode 112, the piezoelectric composite material layer 102, and the ground 118. It should be understood that the Cu ground and thermal loop 132 can have any suitable shape for housing the above items. In the embodiment shown in the drawings, the shape of the Cu ground and thermal loop 132 is annular. The copper of the copper cap 134 can be used to conduct heat and / or electricity. In some embodiments, the Cu cap 134, the Cu ground and thermal loop 132, the dematching / backing layer 114, the electrode 112, the PZT composite material 102, and the ground 118 can be pressed together to form a single unit. The ground 118 can optionally include a knurled edge to ensure good thermal and electrical contact with the Cu ground and thermal loop 132.

[0174] As previously mentioned, the techniques, devices, apparatuses, and methods described in this specification can be implemented to generate and transmit ultrasound ("transmission mode"), detect and receive ultrasound ("detection mode"), or both. In some embodiments, the ultrasonic transducer according to the present disclosure can also be used to deliver acoustic energy for other purposes, such as, for example, but not limited to, a transducer designed to drive a medical shock wave therapy system. In some embodiments, the ultrasonic transducer 100 is used to transmit an acoustic signal toward a target. In these embodiments, the ultrasonic transducer also includes a piezoelectric composite material layer 102 having at least partially decoupled acoustic impedance and electrical impedance characteristics. The piezoelectric composite material layer 102 includes an array of spaced piezoelectric regions 10, a filling material, and a non-piezoelectric material 15. Each spaced piezoelectric region 10 is made of a piezoelectric material having a first acoustic impedance and a first relative dielectric constant. The filling material 12 is located between adjacent spaced 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 relative dielectric constant. The second acoustic impedance is less than the first acoustic impedance (of the piezoelectric material), and the second relative dielectric constant is less than the first relative dielectric constant, and the third acoustic impedance is greater than the second acoustic impedance, and the third relative dielectric constant is less than the first relative dielectric constant. The ultrasonic transducer according to this embodiment further includes one or more electrodes 112 in electrical communication with the piezoelectric composite material layer 102. The electrodes 112 are operable to send electrical signals to the piezoelectric composite material layer 102, thereby generating an acoustic signal toward a target.

[0175] As previously mentioned, it is sometimes useful to electrically insulate the ultrasonic transducer 100 from the material being sonicated, for example, but not limited to, in the case of medical applications or when the material being sonicated is susceptible to electrical damage. This embodiment of the ultrasonic transducer 100 can be similar to the embodiments previously described and includes a piezoelectric composite material layer 102 for acoustic communication with a sample 104 and having at least partially decoupled acoustic impedance and electrical impedance characteristics. The piezoelectric composite material layer 102 according to this embodiment includes an array of spaced piezoelectric regions 10 (wherein each spaced piezoelectric region 10 is made of a piezoelectric material), a filling material 12 located between adjacent spaced piezoelectric regions 10 (wherein the filling material 12 includes a polymer matrix 13), and a non-piezoelectric material 15 in contact with the polymer matrix 13. As Figure 1 and Figure 2 As shown, the ultrasonic transducer 100 according to this embodiment further includes an electrically insulating ceramic composite layer 122 extending on or in contact with the piezoelectric composite layer 102, for electrically insulating 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 some embodiments, the electrode 112 is in electrical communication with the piezoelectric composite layer 102.

[0176] In some embodiments, the electrically insulating ceramic composite layer 122 is acoustically matched and is a cut and filled electrically insulating ceramic composite layer 122. The ceramic composite layer 122 may be located on the distal surface of the lossless acoustic layer 120 as described above and / or in mechanical contact therewith. It should be noted that the insulating layer 122 is generally not lossless, and the thickness is a compromise between electrical insulation and acceptable acoustic loss. In a non-limiting embodiment, the thickness of the electrically insulating layer 122 is 1.4 mm, the spacing is 950 μm, with a 750 μm column and a 200 μm cut. The cut filling material for the electrically insulating layer 122 may be HFO epoxy. In another non-limiting embodiment, the electrically insulating layer 122 includes a base ceramic made of alumina. In yet another non-limiting embodiment, the base ceramic may be any other ceramic having an acoustic impedance exceeding about 30 MR. It should be understood that in the context of this embodiment, the general problem to be solved is the lack of electrically insulating materials having an acoustic impedance of about 15 MR to 30 MR. The use of the electrically insulating layer 122 solves this general problem because only the degree of isolation and acceptable acoustic loss are considered with respect to the thickness of the layer. It is important to note that there is no significant effect on the bandwidth or frequency response of the device as the thickness of the electrically insulating layer 122 varies. In some embodiments, the ultrasonic transducer 100 includes an electrically insulating housing 136 for housing the ultrasonic transducer.

[0177] In some embodiments, the ultrasonic transducer 100 further includes an acoustically matched insulating layer 122 positioned adjacent to and in contact with the distal end of the ground electrode layer 118. The layer 122 can be made of a solid insulating material or a composite material and should exhibit the desired acoustic impedance and acceptable acoustic loss, as well as having sufficient dielectric strength and dielectric constant to achieve the electrical isolation required for the device. In one embodiment, the insulating layer includes a 1:3 composite layer of alumina and HFO-filled epoxy to achieve an acoustic impedance of about 27 MR, making it acoustically matched to titanium. It should be understood that the matching insulating layer 122 is not a matching layer, but rather it is itself adapted in a manner similar to the piezoelectric composite layer, so that it actually has the same acoustic impedance as the target material. The matching insulating layer 122 is inherently broadband and has a flat frequency transmission coefficient that is below the upper cutoff frequency determined by the size and spacing of the pillars, which is the usual case for acoustic composites. The thickness of the electrical insulating layer is independent of frequency and is only a design factor because it involves managing acceptable attenuation and acceptable leakage current.

[0178] Implementation Example

[0179] Different possible implementations of the ultrasound transducer will now be described.

[0180] In one embodiment, the ultrasonic transducer 100 is a single-element transducer. The single-element transducer may have the following characteristics: a single-element acoustic hole of 50 mm, an electrical impedance of 50 Ohm at the center frequency, a broadband frequency response (a 6 dB fractional bandwidth of about 100% in one direction), a center frequency of about 0.6 MHz, and an acoustic resistance matched to titanium (about 27.4 MR + / - about 0.5 MR). In addition to these characteristics, due to the inclusion of a relatively thick thermally conductive layer, the embodiment also exhibits high power handling capabilities and heat dissipation characteristics, thereby enhancing the electrical effectiveness of the ground electrode, but mainly enhancing the thermal effectiveness of the ground electrode. For example, if the DUT is metal, such as titanium, the layer can be made of the same material as the DUT material. This inclusion is possible because the entire portion of the acoustic stack is adjacent to the far side of the piezoelectric element and includes a piezoelectric composite element having the same acoustic impedance as the DUT material. In this embodiment, the piezoelectric composite layer 102 can be a 1:3 composite material of PZT, and the filling material 12 can be made of an epoxy resin loaded with HFO powder, and the epoxy resin is designed to have an acoustic impedance very close to about 27.4MR, resulting in acoustic matching with titanium. It should be understood that this is relatively low in acoustic impedance of non-composite PZT (about 34.5MR) and much higher than typical polymer-filled PZT piezoelectric composite materials (typically between 8MR and 16MR). In this embodiment, PZT is selected because it takes into account both efficiency and heat resistance. HFO powder-loaded epoxy resin is selected as the matrix material for filling the cutouts in the PZT plate to create a composite material. The HFO powder-loaded epoxy resin has a relatively high acoustic impedance of about 7MR to about 8MR, so that the acoustic impedance of the resulting 1:3 composite material is closely matched to the acoustic impedance of titanium. In this embodiment, the piezoelectric composite layer 102 has 1000 μm by 1000 μm PZT pillars (with a square cross section) occurring at 1200 micron intervals and regularly separated by 200 micron cuts. The thickness of the composite piezoelectric element / layer 102 is 2400 μm.

[0181] In another embodiment, an electrically isolated transducer is provided, which has a broadband and low-loss coupling mechanism to the intended acoustic load medium, and the center frequency and frequency response can be optimized almost entirely by optimizing the piezoelectric composite layer and designing the backing and / or dematching layer. No matching is required on the far side of the piezoelectric composite, and an almost completely flat frequency response of the acoustic stack can be achieved at all frequencies below the effective cutoff frequency, which is determined by the column size and spacing selected for the piezoelectric composite and ceramic composite elements. This embodiment allows the design of ultrasonic transducers with a unidirectional fractional bandwidth of more than 140%, as long as they are used with the specified target medium without any distal end matching layer. There are many different metals and other conductive loads that can benefit from ultrasonic transducers that can adapt their corresponding acoustic impedances, such as, for example, but not limited to, titanium and its alloys, tin, aluminum and many aluminum alloys, zinc, zirconium, lead and other alloys with acoustic impedances of about 15MR to about 30MR. In addition, non-metallic materials with acoustic impedances in the above range can also benefit from this embodiment to closely match their respective acoustic impedances.

[0182] method

[0183] A method for manufacturing an embodiment of the ultrasonic transducer 100 previously described is also provided. In one embodiment, the ultrasonic transducer 100 manufactured is designed to operate at a center frequency of about 600kHz. The method includes the step of cutting a PZT plate having a thickness of about 2600μm. The cuts are made by parallel slits. In one embodiment, this step results in a 700μm cut from the center to the center of about 1.7mm, leaving about 1mm of uncut material between the cuts. The method also includes the steps of providing an alumina rod (e.g., having a width of about 400μm) to be embedded in the cut, and filling the cuts on both sides of the alumina with 150μm of epoxy resin (e.g., powder-loaded epoxy resin and allowing it to cure) strips and gluing them in place. The method also includes the step of cutting the plate at 90 degrees relative to the first set of cuts, thereby defining similar cuts (center-to-center spacing of about 1.7mm, cuts of about 700μm). The cut slits can then be filled with similar 400 μm wide alumina rods and the slits filled with powder loaded epoxy. The resulting piezoelectric composite layer has an acoustic impedance equivalent to that of an 82% PZT composite and can be acoustically matched to titanium, for example but not limited to. However, the electrical impedance of this composite is close to that found in a 59% PZT composite.

[0184] Several alternative embodiments and examples have been described and illustrated herein. The above-described embodiments are intended to be exemplary only. Those skilled in the art will appreciate the features of the various embodiments and the possible combinations and variations of the components. Those skilled in the art will further appreciate that any embodiment may be provided in any combination with other embodiments disclosed herein. Therefore, the present embodiments and embodiments should be considered illustrative and not restrictive in all respects. Therefore, although specific embodiments have been shown and described, more modifications are conceivable without significantly departing from the scope defined in the current specification.

Claims

1. An ultrasonic transducer, comprising: A piezoelectric composite material layer having at least partially decoupled acoustic and electrical impedance characteristics, the piezoelectric composite material layer comprising: at least two piezoelectric regions separated by a gap, each piezoelectric region being made of a piezoelectric material having a first acoustic impedance and a first relative dielectric constant; A filling material, located in the gap and contacting the at least two piezoelectric regions, the filling material comprising: a substrate having a second acoustic impedance and a second relative dielectric constant, the second acoustic impedance being less than the first acoustic impedance and the second relative dielectric constant being less than the first relative dielectric constant; and a non-piezoelectric material embedded in the matrix, the non-piezoelectric material having a third acoustic impedance and a third relative dielectric constant, the third acoustic impedance being greater than the second acoustic impedance, and the third relative dielectric constant being less than the first relative dielectric constant; and One or more electrodes are in electrical communication with the piezoelectric composite layer.

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

3. The ultrasonic transducer of claim 1, wherein the non-piezoelectric material is hafnium oxide powder. 4 . The ultrasonic transducer according to claim 1 , further comprising one or more electrically insulating regions located between the at least two piezoelectric regions, the one or more electrically insulating regions being in contact with the filling material.

5. The ultrasonic transducer according to claim 4, wherein the one or more electrically insulating regions have a fourth acoustic impedance and a fourth relative permittivity, the fourth acoustic impedance is close to the first acoustic impedance, and the fourth relative permittivity is smaller than the first relative permittivity.

6. The ultrasonic transducer of claim 4, wherein the one or more electrically insulating regions are made of ceramic.

7. The ultrasound transducer of claim 4, wherein the one or more electrically insulating regions are made of glass.

8. The ultrasonic transducer of claim 4, wherein the one or more electrically insulating regions have an elongated shape.

9. The ultrasound transducer of claim 4, wherein the one or more electrically insulating regions define a rod-shaped electrically insulating region.

10. The ultrasound transducer of claim 4, wherein the one or more electrically insulating regions define a cylindrical electrically insulating region.

11. The ultrasound transducer of claim 4, wherein the one or more electrically insulating regions are spherical.

12. The ultrasonic transducer of claim 1, wherein the non-piezoelectric material is embedded in the polymer matrix.

13. The ultrasonic transducer according to claim 1, wherein: The piezoelectric material is continuous in one direction; and The filling material is continuous in three directions.

14. The ultrasonic transducer according to claim 1, wherein: The piezoelectric material is continuous in two directions; and The filling material is continuous in two directions.

15. 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.

16. The ultrasonic transducer of claim 15, wherein the piezoelectric material is lead zirconate titanate (PZT).

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

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

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

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

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