Composite structural adhesive compositions and related methods

Abstract

Various embodiments described herein include adhesive compositions for high pressure focused ultrasound applications. In one aspect, an ultrasound transducer includes a plurality of patches. Each patch includes a first conductive layer, a second conductive layer, a plurality of transducer elements disposed between the first conductive layer and the second conductive layer, and a composite structural adhesive, the composite structural adhesive (a) is disposed between the first conductive layer and the second conductive layer and (b) is disposed between respective adjacent transducer elements of the plurality of transducer elements. The composite structural adhesive includes an epoxy resin, fumed silica, and a powder selected from the group consisting of (i) micronized mica, (ii) a bioactive glass powder, and (iii) micronized mica and bioactive glass powder.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 341,556, filed on May 13, 2022, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates generally to adhesive compositions and, more particularly, to composite structural adhesives for use in high pressure focused ultrasound applications. Background Art

[0004] Focused ultrasound (i.e., sound waves having a frequency greater than about 20 kilohertz) can be used to image or treat tissue in the body of a patient. For example, ultrasound can be used for applications involving ablation of tumors, thereby eliminating the need for invasive surgery, targeted drug delivery, control of the blood-brain barrier, lysis of blood clots, and other surgical procedures. During tumor ablation, an ultrasound transducer is placed outside the patient, but very close to the tissue to be ablated (i.e., the target). The ultrasound transducer converts an electronic drive signal into mechanical vibrations, resulting in the emission of sound waves. The transducer can be geometrically shaped and positioned together with other such transducers so that the ultrasound energy they emit collectively forms a focused beam in a "focal area" corresponding to (or within) the target tissue area. Alternatively or in addition, a single transducer can be formed of multiple individually driven transducer elements, the phases of which can be independently controlled. This "phased array" transducer facilitates manipulating the focal area to different positions by adjusting the relative phase between the transducers. As used herein, the term "element" means an individual transducer in an array or an independently drivable portion of a single transducer. In some cases, magnetic resonance imaging (MRI) may be used to visualize the patient and target, and thereby guide the ultrasound beam.

[0005] Conventional ultrasonic transducers are multilayer structures laminated between two electrode layers in a stacked configuration to provide high power delivery efficiency. The number and order of layers and their thicknesses can be selected based on the desired frequency response curve. Typically, at least one of the layers is formed of a piezoelectric (e.g., piezoelectric ceramic) material that can be driven by an electrical signal to generate ultrasonic energy. Other intervening layers contribute to mechanical stability and efficient delivery of energy. Because each layer can have different acoustic parameters, the combination of layers can generate a desired operating frequency response with a suitable bandwidth. But maintaining the overall mechanical integrity of the transducer structure, especially preventing the layers from delaminating over time, can be challenging.

[0006] An exemplary transducer structure includes three intervening layers: resin-impregnated graphite, piezoelectric lead zirconate titanate (PZT), and copper-impregnated graphite. The operating voltage depends on the necessary acoustic power delivery. For imaging applications, ultrasound transducers can be driven at tens of volts; for therapeutic applications that require delivery of high acoustic power levels to damage or ablate tissue, the transducer can be driven at hundreds of volts. Some therapeutic applications (such as histotripsy) can drive the transducer at thousands of volts in order to achieve very high instantaneous power levels and induce cavitation at internal anatomical targets.

[0007] Typically, adhesives used to bond transducer elements should exhibit good mechanical properties, a high glass transition temperature (Tg), and adaptability to coating using, for example, electroless copper plating processes. However, for high-voltage focused ultrasound applications, the adhesive must also be able to tolerate the stresses generated, while at the same time providing sufficient electrical isolation to prevent arcing across the bonded elements. Many adhesives that meet the basic performance criteria do not meet the latter requirement. Therefore, there is a need for an adhesive composition that can be applied using conventional techniques but still provides high strength, durability, and strong electrical isolation. Summary of the invention

[0008] The present disclosure relates to composite structural adhesives for high pressure focused ultrasound applications. The composite structural adhesives contain epoxy resins and fillers, including amorphous powders and fumed silica. After curing, they exhibit good mechanical properties, high glass transition temperatures, and adaptability to coating using common techniques.

[0009] In various embodiments of the present disclosure, the composite structural adhesives described herein (i) have a sufficient heat deformation temperature (HDT) of at least 120°C; (ii) have structural stability during fabrication and operation of the transducer (e.g., at >3000V); (iii) have adhesion to copper (e.g., by an electroplating process, such as an electroless plating process or an electroplating process); (iv) have high electrical resistance; and / or (v) have zero or minimal interference with the electrical impedance and acoustic impedance of the piezoelectric material.

[0010] In some embodiments, the ultrasonic transducer comprises a plurality of pieces, each piece comprising a first conductive layer, a second conductive layer, a plurality of transducer elements disposed (e.g., sandwiched) between the first conductive layer and the second conductive layer, and a composite structural adhesive. In some embodiments, the composite structural adhesive (a) is disposed (e.g., sandwiched) between the first conductive layer and the second conductive layer, and (b) is disposed between corresponding adjacent transducer elements in the plurality of transducer elements. In some embodiments, the composite structural adhesive comprises an epoxy resin, fumed silica, and a powder selected from the group consisting of: (i) micronized mica, (ii) bioactive glass powder, and (iii) micronized mica and bioactive glass powder.

[0011] In some embodiments, the composite structural adhesive is in direct contact with the first conductive layer and the second conductive layer. In some embodiments, a plurality of transducer elements form a curved array of transducer elements. In some embodiments, corresponding transducer elements in a plurality of transducer elements are separated by a first spacing. In some embodiments, the first spacing is no more than 1 mm. In some embodiments, the first spacing is no more than 500 μm. In some embodiments, the first spacing is no more than 300 μm. In some embodiments, the powder comprises particles having a maximum diameter no more than the first spacing. In some embodiments, the powder comprises particles having an average diameter no more than 300 μm. In some embodiments, each of the first conductive layer and the second conductive layer is formed by electroplating. In some embodiments, each of the first conductive layer and the second conductive layer is formed by electroless plating. In some embodiments, each of the first conductive layer and the second conductive layer comprises a copper layer.

[0012] In various embodiments of the present disclosure, the composite structural adhesive comprises an epoxy resin, fumed silica, and a powder selected from the group consisting of: (i) micronized mica, (ii) bioactive glass powder, and (iii) micronized mica and bioactive glass powder. In some embodiments, the composite structural adhesive is used for focused ultrasound applications.

[0013] In some embodiments, the powder is composed of micronized mica. In some embodiments, the powder is composed of bioactive glass powder. In some embodiments, the powder is composed of micronized mica and bioactive glass powder. In some embodiments, the powder comprises particles having an average diameter of no more than 300 μm. In some embodiments, the epoxy resin is bisphenol A diglycidyl ether epoxy resin. In some embodiments, the glass transition temperature (Tg) of the epoxy resin after thermal curing is 90°C. In some embodiments, the epoxy resin is a combination of a hardener and a resin that produces a threshold Tg of 90°C. In some embodiments, after curing, the adhesive exhibits a thermal deformation (e.g., heat distortion temperature) of at least 120°C.

[0014] In various embodiments of the present disclosure, a method for manufacturing an ultrasonic transducer segment comprises casting an epoxy resin mixture on a piezoelectric ceramic segment to form a cast assembly. The epoxy mixture comprises epoxy resin, fumed silica, and powder. The powder consists essentially of: (i) micronized mica, (ii) bioactive glass powder, or (iii) micronized mica and bioactive glass powder. The method comprises curing the cast assembly to form a cured assembly. The method comprises electroplating a copper layer over the cured assembly.

[0015] In some embodiments, the method further comprises pressing the cast assembly into a curved shape while curing the cast assembly. In some embodiments, the method further comprises operating the ultrasonic transducer tiles at an operating voltage of 3000 V after electroplating a copper layer over the curing assembly. In some embodiments, the method further comprises assembling the ultrasonic transducer tiles into a single multi-tile transducer array comprising a plurality of ultrasonic transducer tiles after electroplating a copper layer over the curing assembly.

[0016] Thus, composite structural adhesives for high pressure focused ultrasound applications are provided.

[0017] Note that the various embodiments described above may be combined with any other embodiments described herein. The features and advantages described in this specification are not all inclusive, and in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Furthermore, it should be noted that the language used in this specification is primarily selected for readability and instructional purposes, and may not be selected to delineate or limit the subject matter of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In the accompanying drawings, the same reference numerals generally refer to the same parts in different views. In addition, the drawings are not necessarily drawn to scale, but the emphasis is generally placed on illustrating the principles of the present disclosure. In the following description, various embodiments of the present disclosure are described with reference to the following drawings, in which:

[0019] Figure 1A An exemplary ultrasound system according to various embodiments of the present disclosure is schematically depicted.

[0020] Figure 1B An exemplary MRI system according to various embodiments of the present disclosure is schematically depicted.

[0021] Figure 2 Embodiments of acoustic reflectors are depicted that are generally proximate to a target area, according to some embodiments.

[0022] Figure 3A and 3B A transducer tile is depicted according to some embodiments.

[0023] Figure 3C Depicted is an exemplary process for fabricating a curved array of transducer elements according to some embodiments.

[0024] Figure 4 The results of various formulation experiments according to some embodiments of the present disclosure are detailed.

[0025] Figure 5 As shown in the reference Figure 4 Chemical and physical properties of micronized mica used in the described experiments.

[0026] Figure 6 Experimental details for optimizing mica and CABOSIL filler formulations to achieve satisfactory copper adhesion according to some embodiments of the present disclosure are presented.

[0027] Figure 7 Shown are averages based on four individual measurements, converted to weight (w / w) percentages in the total epoxy formulation.

[0028] Figure 8 A flow chart of a method of manufacturing an ultrasound transducer tile is shown according to some embodiments. DETAILED DESCRIPTION

[0029] Figure 1A An exemplary ultrasound system 100 is shown for generating and delivering a focused acoustic energy beam to a target area 101 within a patient. The illustrated system 100 includes a phased array 102 of transducer elements 104, a beamformer 106 that drives the phased array 102, a controller 108 that communicates with the beamformer 106, and a frequency generator 110 that provides an input electronic signal to the beamformer 106.

[0030] The array 102 may have a curved (e.g., spherical or parabolic) or other wavy shape suitable for placement on the surface of the patient's body, or may include one or more flat or otherwise shaped sections. Its size may vary between millimeters and tens of centimeters. The transducer elements 104 of the array 102 may be piezoelectric ceramic elements and may be mounted in silicone rubber or any other material suitable for attenuating the mechanical coupling between the elements 104. Piezoelectric composites may also be used, or substantially any material capable of converting electrical energy into acoustic energy. To ensure maximum power delivery to the transducer elements 104, the elements 104 may be configured for electrical resonance at 50Ω, thereby matching the input connector impedance.

[0031] The transducer array 102 is coupled to a beamformer 106, which drives the individual transducer elements 104 so that they collectively produce a focused ultrasound beam or field. For n transducer elements, the beamformer 106 may contain n driver circuits, each circuit including or consisting of an amplifier 118 and a phase delay circuit 120; each driver circuit drives one of the transducer elements 104. The beamformer 106 receives a radio frequency (RF) input signal, typically in the range of 0.1 MHz to 10 MHz, from a frequency generator 110, which may be, for example, a model DS345 generator available from Stanford Research Systems. The input signal may be split into n channels for the n amplifiers 118 and delay circuits 120 of the beamformer 106. In some embodiments, the frequency generator 110 is integrated with the beamformer 106. The RF generator 110 and the beamformer 106 are configured to drive the individual transducer elements 104 of the transducer array 102 at the same frequency but at different phases and / or different amplitudes.

[0032] The amplification or attenuation factors α1-αn and phase shifts a1-an applied by the beamformer 106 are used to transmit and focus the ultrasonic energy through the intervening tissue between the transducer element 104 and the target area onto the target area 101, and take into account the wave distortion caused in the intervening tissue. The amplification factor and phase shift are calculated using a controller 108, which can provide calculation functions through software, hardware, firmware, hard wiring or any combination thereof. In various embodiments, the controller 108 uses a general or dedicated digital data processor programmed with software in a conventional manner and without excessive experimentation to determine the frequency, phase shift and / or amplification factor required to obtain the desired focus or any other desired spatial field pattern at the target area 101. In some embodiments, the calculation is based on detailed information about the characteristics of the intervening tissue (e.g., type, size, location, characteristics, structure, thickness, density, structure, etc.) between the transducer element 104 and the target and its effect on the propagation of acoustic energy. Such information can be obtained from the imager 112. The imager 112 may be, for example, a magnetic resonance imaging (MRI) device, a computed tomography (CT) device, a positron emission tomography (PET) device, a single photon emission computed tomography (SPECT) device, or an ultrasound examination device. Image acquisition may be three-dimensional (3D), or alternatively, the imager 112 may provide a set of two-dimensional (2D) images suitable for reconstructing a three-dimensional image of the target area 101 and / or other areas (e.g., the area around the target 101 or another target area). Image manipulation functionality may be implemented in the imager 112, in the controller 108, or in a separate device. In some embodiments, the ultrasound system 100 and / or the imager 112 may be used to detect signals from acoustic reflectors (e.g., microbubbles) substantially near the target area 101. Additionally or alternatively, the system 100 may include an acoustic signal detection device (e.g., a hydrophone or a suitable alternative) 124 that detects ultrasound waves transmitted or reflected from the acoustic reflectors and may provide its received signals to the controller 108 for further processing. In addition, the ultrasound system 100 may include an administration system 126 for parenterally introducing the acoustic reflector into the patient. The imager 112, the acoustic signal detection device 124, and / or the administration system 126 may be operated using the same controller 108 that facilitates the operation of the transducer; alternatively, they may be individually controlled by one or more separate controllers that communicate with each other.

[0033] Figure 1BAn exemplary imager, namely an MRI device 112, is shown. The device 112 may include a cylindrical electromagnet 134 that generates a necessary static magnetic field within a bore 136 of the electromagnet 134. During a medical procedure, a patient is placed within the bore 136 on a movable support table 138. An area of ​​interest 140 (e.g., the patient's head) within the patient's body may be positioned within an imaging region 142, wherein the electromagnet 134 generates a substantially uniform field. A set of cylindrical magnetic field gradient coils 144 may also be provided within the bore 136 and around the patient. The gradient coils 144 generate magnetic field gradients of predetermined amplitudes at predetermined times and in three mutually orthogonal directions. Using the field gradients, different spatial locations may be associated with different precession frequencies, thereby providing a magnetic resonance (MR) image with its spatial resolution. An RF transmitter coil 146 surrounding the imaging region 142 transmits RF pulses into the imaging region 142 to cause the patient's tissue to emit MR response signals. The raw MR response signals are sensed by the RF coil 146 and passed to the MR controller 148, which then calculates an MR image that can be displayed to a user. Alternatively, separate MR transmitter and receiver coils may be used. Images acquired using the MRI device 112 can provide radiologists and physicians with visual contrast between different tissues and detailed internal views of patient anatomy that cannot be visualized using conventional x-ray techniques.

[0034] The MRI controller 148 can control the pulse sequence, i.e., the relative timing and intensity of the magnetic field gradients and RF excitation pulses and the response detection period. The MR response signals are amplified, conditioned and digitized into raw data using a conventional image processing system, and further converted into an image data array by methods known to those of ordinary skill in the art. Based on the image data, the target area (e.g., tumor, blood clot, specific brain tissue or target BBB) can be identified.

[0035] In order to perform targeted drug delivery or tissue or tumor ablation, it is necessary to determine the location of the target area 101 with high accuracy. Therefore, in various embodiments, the imager 112 is first activated to acquire images of the target area 101 and / or non-target areas (e.g., healthy tissue surrounding the target area, intervening tissue between the transducer array 102 and the target area 101, and / or any area near the target), and based on this, determine the anatomical characteristics associated therewith (e.g., tissue type, location, size, thickness, density, structure, shape, vascularization). For example, a tissue volume can be represented as a 3D voxel set based on a 3D image or a series of 2D image slices, and can include the target area 101 and / or non-target areas.

[0036] In order to produce high quality focus at the target area 101, it may be necessary to calibrate the transducer elements 104 and account for transducer geometry imperfections caused by, for example, movement, displacement, and / or deformation of the transducer elements 104 from their intended positions. Additionally, because ultrasound waves may be scattered, absorbed, reflected, and / or refracted when traveling through inhomogeneous intervening tissue positioned between the transducer elements 104 and the target area 101, it may also be necessary to account for these wave distortions to improve the focusing characteristics at the target area 101.

[0037] refer to Figure 2 In various embodiments, calibration of the transducer geometry and correction of beam distortion caused by inhomogeneous tissue are facilitated by employing an acoustic reflector 202 substantially proximal to the target area 101. Ultrasound waves propagated from all (or at least some) transducer elements 104 are reflected by the reflector 202. The acoustic reflector 202 may consist essentially of microbubbles generated by ultrasound and / or introduced parenterally via an administration system. In some embodiments, the administration device 126 introduces seed microbubbles into the target area 101; the transducer 102 is then activated to transmit ultrasound waves to the seed microbubbles to generate a cloud of microbubbles. For example, PCT Publication No. WO No. 2018 / 020315, PCT Application No. PCT / US2018 / 064058 (filed on December 5, 2018), No. PCT / IB2018 / 001103 (filed on August 14, 2018), No. PCT / US2018 / 064892 (filed on December 11, 2018), No. PCT / IB2018 / 000841 (filed on Methods for generating microbubbles and / or introducing microbubbles into the target area 101 are provided in U.S. Patent Application No. 15 / 837,392 (filed on December 11, 2017), the contents of which are incorporated herein by reference.

[0038] Figure 3AAn exemplary transducer tile 300 according to some embodiments is shown. In some embodiments, the ultrasound transducer includes one or more transducer tiles 300, each tile including a corresponding number of transducer elements 304 (e.g., transducer element 304-1 and transducer element 304-2). In some embodiments, each transducer element 304 in the tile is independently controllable. In some embodiments, not every transducer element 304 is independently controllable; instead, the transducer elements 304 in a given group 302 are wired and controlled at the group level (e.g., group 302-1 and group 302-1), and each group in the group 302 is independently wired. In some embodiments, the group 302 includes any between 2 and 10, 2 and 15, 2 and 20, 2 and 25, 2 and 30, or 2 and 50 transducer elements. The corresponding group 302 includes a circle, an ellipse, or an N-shaped closed shape, where N is a value between 1 and 20.

[0039] Figure 3B 300 or a portion thereof, according to some embodiments. Transducer elements 304 (e.g., transducer elements 304-3, 304-4, 304-5, 304-6, 304-7, and 304-8) are disposed (e.g., sandwiched) between a first layer 306 and a second layer 310. Respective (e.g., adjacent) transducer elements are separated by a spacing 317, as shown in FIG. Figure 3B As shown in the inset 301 of FIG. According to an embodiment, the spacing 317 does not exceed 2 mm, 1 mm, 500 μm, 300 μm or 250 μm.

[0040] In some embodiments, each of the transducer elements 304 is in direct contact with the first layer 306. In some embodiments, each of the transducer elements 304 is in direct contact with the second layer 310.

[0041] Figure 3B Also shown is a composite structural adhesive 308 disposed (e.g., sandwiched) between adjacent transducer elements 304. In some embodiments, the composite structural adhesive 308 is in direct contact with the first layer 306. In some embodiments, the composite structural adhesive 308 is in direct contact with the second layer 310. In some embodiments, the composite structural adhesive 308 is electrically insulating.

[0042] In some embodiments, the first layer 306 is a conductive layer. In some embodiments, the first layer 306 comprises copper. In some embodiments, the first layer 306 is formed by electroplating. In some embodiments, the first layer 306 is formed by electroless plating.

[0043] In some embodiments, the second layer 310 is a conductive layer. In some embodiments, the second layer 310 comprises copper. In some embodiments, the second layer 310 is formed by electroplating. In some embodiments, the second layer 310 is formed by electroless plating.

[0044] Figure 3B Also shown, in some embodiments, the transducer tile 300 includes a matching layer 314 located below the second layer 310. In some embodiments, the matching layer 314 includes graphite and is glued to the second layer 310 using a conductive glue 312, which in some embodiments includes graphite. In some embodiments, the other side (surface 316) of the matching layer is connected to a ground plane with a conductive adhesive.

[0045] Figure 3C An exemplary process 320 for fabricating a curved array of transducer elements 304 is depicted in accordance with some embodiments.

[0046] In some embodiments, the process begins with step (i) and continues to steps (ii) and (iv). The process begins by arranging a plurality of transducer elements 304 on a planar surface, as shown in step (i). As shown in step (ii), a composite structural adhesive 308 is cast on the transducer elements 304 to form a cast transducer element array. The method includes forming the cast array into a curved array (e.g., by pressing the cast array into a curved shape) as shown in step (iv), while curing the cast array.

[0047] In some embodiments, the process begins at step (iii) and continues to step (iv). In these embodiments, the process begins by arranging a plurality of transducer elements 304 on a curved surface, as depicted in step (iii). When the transducer elements 304 are located on the curved surface, the composite structural adhesive 208 is cast on the transducer elements to form a cast curved array, as depicted in step (iv), and the curved array continues to cure.

[0048] In some embodiments, composite structural adhesive 308 comprises an electrically insulating adhesive. In some embodiments, composite structural adhesive 308 comprises an epoxy resin and a filler. In some embodiments, the filler comprises or consists essentially of an amorphous powder and fumed silica.

[0049] In some embodiments, the amorphous powder can be bioactive glass or micronized mica. The term "micronized mica" herein generally refers to mica (phyllosilicate mineral) in powder form. According to embodiments, the amorphous powder can be one or more of: (i) mica (e.g., 325 mesh mica) (e.g., particle size of about 44 μm); (ii) bioactive glass (e.g., VITRYXX bioactive glass product MD01); or (iii) a combination of mica and bioactive glass (e.g., VITRYXX product G018-270).

[0050] In some embodiments, the fumed silica is hydrophilic (e.g., CABOSIL hydrophilic fumed silica). The fumed silica increases the surface 319 ( Figure 3B Inset 301 ) has wettability (e.g., the ability of a liquid to spread on a surface), which facilitates coating the first layer 306 and / or the second layer 310 over the surface of the composite structural adhesive 308.

[0051] In some embodiments, while there may be no fixed lower limit to the acceptable powder size, a practical upper limit may be determined by the spacing 317 (e.g., gap) between adjacent transducer elements 304 filled by the composite structural adhesive 308. For example, according to an embodiment, the powder may include particles having a maximum diameter not exceeding 2 mm, 1 mm, 500 μm, 300 μm, or 250 μm. Further, according to an embodiment, the powder may include particles having an average diameter not exceeding 2 mm, 1 mm, 500 μm, 300 μm, or 250 μm.

[0052] The choice of epoxy resin for the composite structural adhesive 308 can be determined for a particular application based on a threshold glass transition temperature Tg (optionally, a safety margin can be applied by slightly increasing Tg). For example, for an ultrasound treatment procedure that thermally ablates a target tissue (e.g., brain tissue or uterine fibroids) by subjecting it to continuous ultrasonic energy, the focused ultrasonic transducer can reach 90-110°C when a voltage is applied. For such embodiments, the epoxy resin can be a combination of a hardener and a resin that produces a threshold Tg of at least 90°C, 95°C, 100°C, or 105°C. In principle, any combination of a hardener and a resin that produces a threshold Tg (e.g., at least 90°C, 95°C, 100°C, or 105°C) can potentially be used. Bisphenol A diglycidyl ether epoxy resin (also known as diglycidyl ether of bisphenol A (DGEBA)) resin used with different hardeners during development may be sufficient for applications that require thermal deformation to approximately 120°C. A hardener containing a small amount of epoxy resin (e.g., an adduct hardener or other type of hardener) can be used. The adduct hardener may be any suitable amine hardener, i.e., a monoamine, diamine, triamine, or polyamine, etc. Suitable amine hardeners include ethyleneamines (e.g., diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and N-aminoethylpiperazine), alicyclic compounds (e.g., bis-(p-aminocyclohexyl)methane, diaminocyclohexane, and bis-(dimethyldiaminocyclohexyl)methane), and aromatic compounds (e.g., methylenedianiline, m-phenylenediamine, and diaminophenylsulfone).

[0053] In practice, mica and fumed silica can be mixed with the resin, degassed and then mixed with the hardener. When casting the epoxy resin, additional degassing can be performed. The epoxy resin combined with the mica and fumed silica filler can be stored for long periods of time and can be mixed before use to produce a homogenous fluid for casting.

[0054] Figure 4 The results of various formulation experiments according to some embodiments of the present disclosure are described in detail. Figure 4 As shown, the "unfilled formulation" (i.e., epoxy resin only) and the inclusion of micronized mica ( Figure 4 "Mica" in the Figure 4 Experiments were conducted with either "active glass" in ) or "filler formulations" of both mica and active glass. Control experiments were conducted with insulating glass and adducts (see Figure 4 The adduct hardener is isophoronediamine (IPDA) or "Part C", which refers to diethylenetriamine (DETA). "Active Glass" refers to VITRYXX bioactive glass.

[0055] For the formulation experiments, each formulation was tested for heat distortion temperature (HDT) and copper plating adhesion. The copper plating adhesion test was performed by adhering Kapton tape to the first layer 306 and the second layer 310 (e.g., copper coating), then removing the Kapton tape from the first and second layers and inspecting the tape for signs of copper removal. Figure 4 The last column in the table shows the results of the copper plating adhesion test. The number following the "Pass" entry indicates the relative quality of the copper coating, where higher values ​​correspond to better quality.

[0056] like Figure 4 As shown in the last data row in , insulating glass (whose chemical formula is the same as active glass) did not produce formulations with satisfactory results. The possible reason is that insulating glass is composed of spherical particles (e.g., H20 hollow glass microsphere products supplied by Sinosteel Maanshan New Material Technology, Maanshan, China) and does not present sufficient surface roughness to provide sufficient copper adhesion for epoxy resin. In contrast, bioactive glass (such as mica) may have a significantly higher degree of surface roughness, which promotes good copper adhesion through staggered bonding.

[0057] Figure 5 As shown in the reference Figure 4 Chemical and physical properties of the micronized mica used in the described experiments. Figure 5 As shown, the average specifications of the micronized mica correspond to physical properties such as specific gravity of 2.85%, refractive index of 1.5-1.6, pH of 9-9.5, and fineness of 325 mesh.

[0058] Figure 6 Experimental details for optimizing mica and CABOSIL (eg, fumed silica) filler formulations to achieve satisfactory copper adhesion according to some embodiments of the present disclosure are presented.

[0059] from Figure 4 It can be seen that various formulations including micronized mica, bioactive glass, or both types of powders exhibited high HDT and satisfactory copper adhesion. Figure 6 As shown, the filler composition comprising 3 mL of mica and 1 ml of CABOSIL produced the best results. Figure 7 Shown are averages based on four individual measurements, converted to weight (w / w) percentages in the total epoxy formulation.

[0060] More generally, 10.55-28% w / w of micronized mica in epoxy formulations was found to be able to adhere adequately to electroplated copper. CABOSIL helps control the viscosity of the epoxy, thereby preventing the powder from settling during curing. It has minimal impact on copper plating, and can therefore be added in large quantities (up to 12% w / w in epoxy formulations). However, if the viscosity is too high, it may interfere with the production process. For example, CABOSIL levels above 0.6% w / w in uncured epoxy may produce viscosities that are too high for common production sequences.

[0061] Figure 8 A flow chart of a method 800 of manufacturing an ultrasound transducer tile according to some embodiments is shown. The ultrasound transducer tile may be manufactured by machining.

[0062] The method includes casting (802) an epoxy resin mixture on a piezoelectric ceramic piece to form a cast assembly. The epoxy mixture comprises epoxy resin, fumed silica and powder. The powder is essentially composed of: (i) micronized mica, (ii) bioactive glass powder, or (iii) micronized mica and bioactive glass powder. In some embodiments, a mixture of epoxy resin and filler (fumed silica and powder) is combined with a hardener and cast on a machined piece in a vacuum chamber (dryer). After degassing in the chamber for 15 minutes, the piece is removed from the dryer and pressed to form the desired curvature. During pressing, the piece and epoxy resin are subjected to thermal curing (after 6 hours at 75°C, 4 hours at room temperature).

[0063] The method 800 includes curing ( 804 ) the cast assembly to form a cured assembly.

[0064] In some embodiments, the method includes pressing (806) the cast component into a curved shape while curing the cast component.

[0065] In some embodiments, the method includes electroplating (808) a copper layer over the cured assembly. In some embodiments, the cured surface of the piezoelectric ceramic tile (cured assembly) is then prepared for electroplating by stone polishing after sandblasting and acid etching. One or more layers of copper are applied by electroless plating, with a typical thickness of 3 μm. The electroplated tile can then be post-cured at 120° C. for 40 minutes after being glued to a graphite matching layer (e.g., matching layer 314). Multiple tiles prepared according to this sequence can then be assembled into a single multi-tile transducer array and wired.

[0066] In some embodiments, the method includes operating (810) the ultrasonic transducer tile at 3000 V after electroplating the copper layer over the cured assembly. In some embodiments, the ultrasonic tile is configured to operate at voltages up to 3000 V or higher.

[0067] In some embodiments, the method includes assembling (812) the ultrasound transducer tiles into a single multi-tile transducer array comprising a plurality of ultrasound transducer tiles after electroplating a copper layer over the cured assembly.

[0068] The terms and expressions used herein are used as terms and expressions of description rather than limitation, and in the use of such terms and expressions, it is not intended to exclude any equivalents of the features shown and described or portions thereof. In addition, having described certain embodiments of the present disclosure, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the present disclosure. Therefore, the described embodiments should be considered in all respects as illustrative only and not restrictive.

[0069] As used herein, the term "substantially" means ±10%, and in some embodiments, means ±5%. References throughout this specification to "an example," "an example," "an embodiment," "an embodiment" mean that a particular feature, structure, or characteristic described in conjunction with the example is included in at least one example of the technology of the present invention. Therefore, the phrases "in an example," "in an example," "an embodiment," or "an embodiment" that appear in various places throughout this specification do not necessarily all refer to the same example. In addition, particular features, structures, routines, steps, or characteristics may be combined in any suitable manner in one or more examples of the technology. The titles provided herein are for convenience only and are not intended to limit or interpret the scope or meaning of the claimed technology.

[0070] In addition, the term "controller" used herein broadly includes all necessary hardware components and / or software modules to perform any functionality described above; a controller may include multiple hardware components and / or software modules, and the functionality may be distributed among different components and / or modules.

[0071] Certain embodiments of the present disclosure are described above. However, it should be expressly noted that the present disclosure is not limited to those embodiments; rather, additions and modifications to what is expressly described herein are also included within the scope of the present disclosure.

Claims

1. An ultrasonic transducer comprising a plurality of pieces, each piece include: a first conductive layer; a second conductive layer; a plurality of transducer elements disposed between the first conductive layer and the second conductive layer; and A composite structural adhesive (a) disposed between the first conductive layer and the second conductive layer and (b) disposed between respective adjacent transducer elements of the plurality of transducer elements, the composite structural adhesive comprising: Epoxy resin; Fumed silica; and A powder selected from the group consisting of: (i) micronized mica, (ii) bioactive glass powder, and (iii) micronized mica and bioactive glass powder.

2. The ultrasonic transducer of claim 1, wherein the composite structural adhesive is in direct contact with the first conductive layer and the second conductive layer.

3. An ultrasound transducer according to claim 1 or claim 2, wherein the plurality of transducer elements forms a curved array of transducer elements.

4. The ultrasonic transducer of claim 1, wherein the corresponding ones of the plurality of transducer elements are separated by a first pitch. The ultrasonic transducer according to claim 4 , wherein the first spacing is no more than 1 mm. The ultrasonic transducer according to claim 4 , wherein the first pitch is no greater than 500 μm.

7. The ultrasonic transducer according to claim 4, wherein the first pitch is no greater than 300 μm.

8. The ultrasonic transducer according to any one of claims 4 to 7, wherein the powder comprises particles having a maximum diameter not exceeding the first spacing.

9. The ultrasonic transducer according to any one of claims 1 to 8, wherein the powder comprises particles having an average diameter of not more than 300 μm. 10 . The ultrasonic transducer according to claim 1 , wherein each of the first conductive layer and the second conductive layer is formed by electroplating. 11 . The ultrasonic transducer according to claim 1 , wherein each of the first conductive layer and the second conductive layer is formed by electroless plating. 12 . The ultrasonic transducer according to claim 1 , wherein each of the first conductive layer and the second conductive layer comprises a copper layer.

13. A composite structural adhesive comprising: Epoxy resin; Fumed silica; and A powder selected from the group consisting of: (i) micronized mica, (ii) bioactive glass powder, and (iii) micronized mica and bioactive glass powder.

14. The adhesive of claim 13, wherein the powder consists of micronized mica.

15. The adhesive of claim 13, wherein the powder consists of bioactive glass powder.

16. The adhesive of claim 13, wherein the powder consists of micronized mica and bioactive glass powder.

17. The adhesive according to any one of claims 13 to 16, wherein the powder comprises particles having an average diameter of not more than 300 μm.

18. The adhesive according to any one of claims 13 to 17, wherein the epoxy resin is bisphenol A diglycidyl ether epoxy resin.

19. The adhesive according to any one of claims 13 to 18, wherein the epoxy resin has a glass transition temperature (Tg) of 90°C after thermal curing.

20. An adhesive according to any one of claims 13 to 19, wherein the epoxy resin is a combination of a hardener and resin that produces a threshold Tg of 90°C.

21. The adhesive of any one of claims 13 to 20, wherein after curing, the adhesive exhibits a heat distortion temperature of at least 120°C.

22. A method for manufacturing an ultrasonic transducer tile, the method comprising: Casting an epoxy mixture on the piezoelectric ceramic block to form a cast assembly, the epoxy mixture comprising epoxy resin, fumed silica, and powder consisting essentially of (i) micronized mica, (ii) bioactive glass powder, or (iii) micronized mica and bioactive glass powder; curing the cast assembly to form a cured assembly; and A copper layer is electroplated over the cured assembly.

23. The method of claim 1, further comprising pressing the cast component into a curved shape while curing the cast component.

24. The method of claim 22 or claim 23, further comprising: After electroplating the copper layer over the cured assembly, the ultrasonic transducer chip was operated at an operating voltage of 3000V.

25. The method according to any one of claims 22 to 24, further comprising: After electroplating the copper layer over the cured assembly, the ultrasonic transducer tiles are assembled into a single multi-tile transducer array comprising a plurality of ultrasonic transducer tiles.

26. A method according to any one of claims 22 to 25, wherein the powder consists of micronized mica.

27. The method according to any one of claims 22 to 26, wherein the powder consists of bioactive glass powder.

28. The method according to any one of claims 22 to 27, wherein the powder consists of micronized mica and bioactive glass powder.

29. A method according to any one of claims 22 to 28, wherein the powder comprises particles having an average diameter of no more than 300 μm.

30. The method of any one of claims 22 to 29, wherein the epoxy resin is bisphenol A diglycidyl ether epoxy resin.

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