Transparent ultrasonic transducer and manufacturing method thereof
The ultra-small, thin-film transparent ultrasonic transducer addresses the challenge of integrating ultrasound and optical coherence imaging in intravascular catheters by providing a non-perforated optical path, ensuring high-quality imaging within a 1 mm probe diameter.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- POSTECH ACADEMY INDUSTRY FOUNDATION
- Filing Date
- 2025-12-09
- Publication Date
- 2026-06-18
AI Technical Summary
Conventional intravascular imaging catheters face challenges in simultaneously integrating ultrasound and optical coherence imaging due to the difficulty in placing both transceivers within a limited probe diameter and length, leading to degraded image quality and signal issues.
Development of an ultra-small, thin-film transparent ultrasonic transducer with a piezoelectric unit, transparent electrodes, and conductive members that allow for an optical path without perforation, enabling coaxial arrangement with an optical sensor and maintaining ultrasonic performance.
The solution ensures high-quality ultrasonic imaging by preserving ultrasonic performance and achieving a probe diameter of 1 mm or less, while supporting simultaneous ultrasound and optical coherence imaging.
Smart Images
Figure KR2025021152_18062026_PF_FP_ABST
Abstract
Description
Transparent ultrasonic transducer and method of manufacturing the same
[0001] The present invention relates to a transparent ultrasonic transducer and a method for manufacturing the same, and more specifically, to an ultra-small, thin-film transparent ultrasonic transducer of a size suitable for insertion into a blood vessel and a method for manufacturing the same.
[0002] Intravascular imaging catheters are implantable medical imaging devices used to acquire high-quality images of lesions in cardiovascular and cerebrovascular diseases. By enhancing diagnostic accuracy and facilitating the establishment of precise treatment protocols, they significantly contribute to improving clinical prognosis.
[0003] Intravascular imaging catheters primarily acquire cross-sectional images of blood vessels using ultrasound or optical coherence. Ultrasound is used to measure indicators such as plaque burden and external elastic membrane diameter, while optical coherence is used for stent malocclusion and measuring the thickness of thin-cap fibroatheromas. Analyzing both images together offers the advantage of more accurate analysis of lipid and calcium tissues. Accordingly, catheter products supporting simultaneous ultrasound and optical coherence imaging are being released.
[0004] However, for simultaneous imaging support, there is a difficulty in placing both the ultrasound transceiver and the optical signal transceiver within a limited probe diameter and length. To access vascular occlusive lesions, imaging catheters typically have a diameter of less than 1 mm, including the outer tube. In order to simultaneously image the same point with an optically opaque ultrasound transducer and an optical sensor while also considering the diameter and length issues, the opaque ultrasound transducer inevitably has to be damaged.
[0005] In fact, conventional technology involves perforating opaque ultrasonic transducers to secure an optical path, and closely overlapping the acoustic and optical transceivers. The area loss caused by this transducer perforation is detrimental to the formation of ultrasonic wavefronts, reducing the main lobe and increasing the side lobes. This leads to negative consequences, such as degradation of ultrasonic image quality, a decrease in the signal-to-noise ratio, and an increase in false signals.
[0006] Therefore, although there is a demand for ultrasound / optical coherence fusion catheters in the current clinical setting, there is no way to fully maintain the performance of both imaging devices, achieve coaxial placement, and limit the probe diameter to 1 mm.
[0007] The problem that the present disclosure aims to solve is to provide an ultra-small, thin-film transparent ultrasonic transducer that can be applied as a component in an ultrasonic / optical fusion catheter, etc.
[0008] In addition, the problem that the present disclosure aims to solve is to provide a transparent ultrasonic transducer and a method for manufacturing the same, which can secure an optical path without perforation to preserve ultrasonic performance and achieve coaxial arrangement with an optical sensor, and at the same time achieve a thickness of about 0.5 mm or less so that the probe diameter can be limited to about 1 mm or less even after assembly of optical components.
[0009] A transparent ultrasonic transducer according to one aspect of the present invention for solving the above technical problem may include: a thin-film transparent piezoelectric unit that generates vibration by an electrical signal or generates an electrical signal by vibration; first and second plate-shaped transparent electrodes respectively disposed on both sides of the transparent piezoelectric unit; an insulating support layer disposed on the side of the transparent piezoelectric unit; first and second wires respectively connected to the first and second plate-shaped transparent electrodes; and first and second conductive members respectively connecting the first and second plate-shaped transparent electrodes and the first and second wires. The first and second wires are aligned in one direction, and the sum of the thicknesses of the first and second wires may be smaller than the length of the longest part of the transparent piezoelectric unit. The insulating support layer may connect and support two or more of the transparent piezoelectric unit, the first wire, and the first conductive member, and may connect and support two or more of the transparent piezoelectric unit, the second wire, and the second conductive member. The first and second conductive members and the first and second wires may be positioned along an insulating support layer located at the edge of the piezoelectric unit.
[0010] The sum of the thicknesses of the transparent piezoelectric unit and the first and second plate-shaped transparent electrodes in the sound wave transmission direction may be within 0.4 mm and greater than 0.03 mm.
[0011] Such a transparent ultrasonic transducer may further include one or more non-conductive matching layers formed on the first plate-shaped transparent electrode or the second plate-shaped transparent electrode. The non-conductive matching layers may be partially removed to expose the first plate-shaped transparent electrode or the second plate-shaped transparent electrode, or may include a heterogeneous structure.
[0012] At this time, the above heterogeneous structure may be a photoresist or a material with mechanical properties different from the above non-conductive matching layer.
[0013] Alternatively, the above heterogeneous structure may be a metal and a conductive epoxy.
[0014] Such a transparent ultrasonic transducer may further include a non-conductive front matching layer on the front surface of the transparent piezoelectric unit, having an acoustic impedance of 5 MRayl or more and 9 MRayl or less and a light transmittance of 70% or more.
[0015] Such a transparent ultrasonic transducer may further include a transparent polymer layer having an acoustic impedance of 1 MRayl or more and 4 MRayl or less on the front surface of the front matching layer.
[0016] Such a transparent ultrasonic transducer may further include a non-conductive back-matching layer on the back of the transparent piezoelectric unit having an acoustic impedance of 3.5 MRayl or more and 7 MRayl or less and a light transmittance of 70% or more.
[0017] Such a transparent ultrasonic transducer may further include a transparent polymer layer having an acoustic impedance of 1 MRayl or more and 3.5 MRayl or less on the back surface of the back surface matching layer.
[0018] The above insulating support layer may have a structure that is insulated from the first and second plate-shaped electrodes by forming a step difference by being thinner or thicker than the sum of the thicknesses of the transparent piezoelectric unit and the first and second plate-shaped transparent electrodes.
[0019] Such a transparent ultrasonic transducer may further include a metal thin film disposed at the edges of the first and second plate-shaped transparent electrodes, respectively.
[0020] A method for manufacturing a transparent ultrasonic transducer according to one aspect of the present invention may include the steps of preparing a piezo substrate, forming a grid-shaped kerf on the piezo substrate, injecting an insulator into the kerf and curing the insulator, and cutting along the kerf so that the insulator remains on the cut surface.
[0021] The method for manufacturing such a transparent ultrasonic transducer may further include the step of forming a transparent conductive layer on the upper and lower surfaces of the piezo substrate after the step of curing the insulating material.
[0022] The method for manufacturing such a transparent ultrasonic transducer may further include the step of forming a thin film metal layer on top of the transparent conductor layer.
[0023] The method for manufacturing such a transparent ultrasonic transducer may further include the step of forming a front matching layer on the transparent conductive layer formed on the upper surface of the piezo substrate.
[0024] The method for manufacturing such a transparent ultrasonic transducer may further include the step of forming an sound-absorbing layer below the transparent conductive layer formed on the lower surface of the piezo substrate.
[0025] According to the present invention described above, a practical ultrasound / optical fusion catheter can be developed by closely assembling an optical component to the rear surface of a micro-thin transparent ultrasound transducer.
[0026] FIGS. 1 to 14 are drawings illustrating a process for determining the allowable thickness of a micro-thin transparent ultrasonic transducer and improving bandwidth and sensitivity in an embodiment of the present invention.
[0027] FIGS. 15 to 29 are drawings for explaining a wiring process that can be employed in a method for manufacturing a micro-thin film transparent ultrasonic transducer in another embodiment of the present invention.
[0028] FIG. 30 is a diagram illustrating a wiring process that can be employed in a method for manufacturing a micro-thin film transparent ultrasonic transducer according to another embodiment of the present invention.
[0029] FIG. 31 is a diagram illustrating the performance of ultra-small thin-film transparent ultrasonic transducers that can be employed in the manufacturing method of the ultra-small thin-film transparent ultrasonic transducers of the embodiments.
[0030] FIGS. 32 and FIGS. 33 are graphs showing the frequency response characteristics between low-conductivity ITO and high-conductivity ITO that can be employed in the method for manufacturing a micro-thin transparent ultrasonic transducer of the present embodiment.
[0031] FIGS. 34 to 36 are drawings for explaining the performance according to whether a gold border is provided on the high-conductivity ITO that can be employed in the manufacturing method of the ultra-small thin-film transparent ultrasonic transducer of the present embodiment.
[0032] FIGS. 37 to 40 are drawings showing a transducer manufactured by the method of manufacturing a micro-thin film transparent ultrasonic transducer of the present embodiment and its performance.
[0033] FIG. 41 is a schematic exploded perspective view illustrating a micro-thin film transparent ultrasonic transducer according to another embodiment of the present invention.
[0034] To manufacture a transparent matching layer having acoustic impedance between MRayl, a method of mixing ceramic particles and a transparent polymer material was used in the prior invention. When using the matching layer, it is applied and cured without gaps on the electrode layer above the piezoelectric unit, and then cut to control the thickness and flatness.
[0035] Therefore, for wiring, a portion of the edge of the non-conductive matching layer covering the electrode layer must be removed; however, in microtransducers, it is difficult to precisely peel off only the edge corners.
[0036] To solve this problem, conductive members are laminated at each corner of the piezoelectric unit before the application of the matching layer, and then the thickness and flatness are controlled after the matching layer is applied. At this time, the thickness of the laminated conductive members is made thicker than the target thickness of the matching layer so that the conductive members are exposed to the outside at the final thickness. In the same way, conductive members are laminated not only in the front matching layer but also in the rear matching layer and the sound-absorbing layer, thereby enabling electrode connections without an edge corner peeling process.
[0037] The third embodiment is a metallic auxiliary electrode formed along the edge of the electrode layer. Transparent electrodes have a higher sheet resistance compared to metallic opaque electrodes. Typically, ITO (indium tin oxide) is commonly used as a transparent electrode due to its high durability, transparency, and high conductivity. The sheet resistance of ITO can be reduced to 10 ohm / sq when subjected to a high-temperature annealing process of 200 degrees or higher, but piezoelectric elements such as PMN-PT used in ultra-small transparent ultrasonic transducers lose their piezoelectric performance at temperatures above approximately 150 degrees. The sheet resistance of ITO deposited at temperatures below 150 degrees is generally reported to be 100 ohm / sq, and has been reported to be as low as 30 ohm / sq when improved using special conditions.
[0038] In particular, FIG. 25 illustrates a design structure for minimizing the thickness of a transparent ultrasonic transducer by including a prism in the sound-absorbing layer. Since the sound-absorbing layer is thick, it may not be easy to remove during the wiring process. According to the present embodiment, a wiring structure can be provided that allows the use of a conductive or non-conductive transparent sound-absorbing layer by embedding a prism in a structure in which a conductive block that does not obstruct the optical path is pre-formed next to the prism on the rear side, just as a conductive block is pre-formed in the front matching layer.
[0039] FIG. 31 is a diagram illustrating the performance between ultra-small thin-film transparent ultrasonic transducers that can be employed in the manufacturing method of the ultra-small thin-film transparent ultrasonic transducers of the embodiments. FIG. 32 and FIG. 33 are graphs showing the frequency response characteristics between low-conductivity ITO and high-conductivity ITO that can be employed in the manufacturing method of the ultra-small thin-film transparent ultrasonic transducer of the embodiments. FIG. 34 to 36 are diagrams illustrating the performance according to whether the high-conductivity ITO has a gold border that can be employed in the manufacturing method of the ultra-small thin-film transparent ultrasonic transducer of the embodiments. FIG. 37 to 40 are diagrams showing the transducer manufactured by the manufacturing method of the ultra-small thin-film transparent ultrasonic transducer of the embodiments and its performance. FIG. 41 is a schematic exploded perspective view illustrating an ultra-small thin-film transparent ultrasonic transducer according to another embodiment of the present invention.
[0040] Simulations and experiments were conducted based on a 30 MHz, 1 mm × 1 mm size transducer.
[0041] On the other hand, when using a sheet resistance of approximately 30 ohm / sq in high-dielectric constant piezoelectric elements such as PMN-PTs, two problems arise. Based on a 30 MHz PMN-PT-based transducer, due to the reduction in phase velocity, voltage is not applied to the entire transducer for a quasi-zero time corresponding to 1 / 20 of the period, so about half of the transducer is not activated within this quasi-zero time. 2) Due to the high sheet resistance and high dielectric constant conditions, the damping constant increases, and the transparent electrode located far from the wire connection is subjected to a voltage of less than 50% of the initial applied voltage. In particular, the above problems become more severe as the frequency increases.
[0042] Accordingly, during the pulse-echo test of the ultrasonic transducer, it can be observed that the peak-to-peak voltage decreases and the high-frequency band is lost. Gold and silver electrodes, which can be used in opaque transducers, do not exhibit this phenomenon; because they have low sheet resistance, the entire transducer is activated within a near-zero time despite the high dielectric constant, and the voltage drop at a distance from the connection point is approximately 10%. In other words, problems such as signal magnitude reduction and signal loss in the high-frequency range caused by sheet resistance are limited to ultra-small transparent ultrasonic transducers.
[0043] A common solution is to use high-conductivity transparent electrodes, but increasing the conductivity of transparent electrodes is not easy because there are process limitations such as temperature, and increasing the thickness to achieve high conductivity severely degrades transparency.
[0044] A simpler way to address this is to deposit a metallic auxiliary electrode on the edges of the transparent ultrasonic transducer, specifically in the areas where light does not pass. This improves sheet resistance, thereby enhancing peak-to-peak voltage and bandwidth. In particular, it prevents high-frequency signal loss, allowing for the maintenance of high resolution. Furthermore, since the thickness of the transparent electrode can be slightly reduced when using an auxiliary electrode, it effectively improves transparency.
[0045] A method for forming a metallic edge auxiliary electrode is formed by shielding the central part for light transmission using techniques such as masking using an exposure process, shadow mask, or silk screen, cleaning edge contaminants, and depositing a metal layer only on the edges through a deposition method such as sputtering.
[0046] Meanwhile, in the above-described embodiment, the transparency of the TUT is not only a concept that includes the transparency of the piezoelectric unit and the first transparency of the first composite material forming the front matching layer, but may also include at least one of the second transparency of the second composite material forming the rear matching layer and the third transparency of the sound-absorbing layer.
[0047] In this embodiment, the first composite material can be obtained by optimizing the refractive index and particle size between the ceramic and the polymer. In particular, the transparency of the first composite material can be determined by the average size of the ceramic particles, the volume ratio of the ceramic particles, the shape of the ceramic particles, the refractive index of the ceramic particles, and the refractive index of the polymer in the ceramic-polymer double bond structure.
[0048] In addition, the material of the front matching layer can be obtained by measuring the scattering coefficient of each material according to light scattering theory, calculating transparency, and selecting a group of candidates with low scattering. This front matching layer may contain silicon dioxide (SiO2), and the silicon dioxide grains may have a particle size of approximately 3 μm in diameter.
[0049] Transparency may mean that when the front matching layer has an acoustic impedance of 7 to 9 MRayl and at a thickness of 1 / 4 wavelength to 1 / 2 wavelength, it transmits 80% or more of light, preferably 95% or more (has a transmittance). This may mean that, in particular, by maintaining the optical image of light passing through the front matching layer, the context of the rear side from the front of the front matching layer can be substantially and clearly seen.
[0050] Additionally, the acoustic impedance of the front matching layer can be determined by the bulk and shear modulus and density of the first composite material. The bulk and shear modulus and density of the composite material can be determined by the bulk and shear modulus and density of the polymer and ceramic particles, and the volume ratio of the ceramic particles in the composite material. The average size of the ceramic particles, determined by the bulk and shear modulus and density of the composite material, can be controlled to less than 1 / 4 wavelength.
[0051] The viscosity of the mixture of the first composite material before curing can be determined according to the average size of the ceramic particles, the volume ratio of the ceramic particles, and the shape of the ceramic particles. The viscosity of the mixture of the first composite material before curing can be 108 cPs or less. Viscosity may refer to dynamic viscosity (η) or absolute viscosity, which represents the degree of stickiness that resists the direction of fluid flow, i.e., the direction of motion, in an absolute magnitude in a fluid flow state, and may be expressed in centipoise (cP or cPs) units corresponding to 0.01 times the equilibrium (poise) state in the CGS unit system.
[0052] The scattering of light passing through the front matching layer formed by the first composite material can be determined by the volume ratio of the ceramic particles, the size and shape of the ceramic particles, and the difference in refractive index between the ceramic and the polymer. The first composite material that meets these conditions can maintain the optical image of the transmitted light. The transparency of the first composite material after curing can be 80% or more, more specifically 95% or more.
[0053] The shape of the ceramic particles may include spherical, porous spherical, elliptical, plate-like, cylindrical, conical, or a combination thereof. It is preferable that the shape of the ceramic particles be one that can optimize the viscosity and transparency of the composite material.
[0054] A method for manufacturing a transparent ultrasonic transducer comprises a series of processes including applying a mixture (first composite material) in which first particles are dispersed in a polymer material to one surface of a piezoelectric unit, degassing and curing the paste applied to one surface of the piezoelectric unit in a predetermined atmosphere, and lapping and polishing the cured first composite material to a design thickness to form a full-surface matching layer on one surface of the piezoelectric unit.
[0055] Here, the first particle comprises a glass or ceramic material, and the glass or ceramic material may contain one or more materials selected from the silicate series, aluminum salt series, zirconium chloride series, and magnesium fluoride series. The glass or ceramic material may include one or more materials selected from ytterbium salt, yttrium salt, and samarium salt. In addition, the polymer material may include one or more materials selected from silicone, epoxy, urethane, polyethylene, polystyrene, acrylic-based, and sulfate-based polymer resins.
[0056] In addition, the method for manufacturing a transparent ultrasonic transducer may further include the process of forming a front secondary matching layer on a front matching layer, forming a rear matching layer by applying a liquid or clay-textured material to another surface of a piezoelectric unit, or forming a rear secondary matching layer or a rear polymer layer on the rear surface of the piezoelectric unit or on the rear matching layer.
[0057] The thickness of the piezoelectric unit may be half the transmission wavelength (λ), and the thickness of each of the front matching layer and the front secondary matching layer may be one-fourth the transmission wavelength (λ). In another embodiment, the thickness of each of the piezoelectric unit, the front matching layer, and the front secondary matching layer may be approximately half the transmission wavelength (λ).
[0058] In addition, the method for manufacturing a transparent ultrasonic transducer may further include the process of forming plate-shaped transparent electrodes on the front and rear surfaces of a piezoelectric unit.
[0059] In addition, the method for manufacturing a transparent ultrasonic transducer may further include the process of placing a conductive ring member connected to transparent electrodes and the process of placing a case member that accommodates a piezoelectric unit, a front matching layer, and a laminated structure of the conductive ring member.
[0060] The methods according to the present invention described above may be implemented in the form of program instructions that can be executed through various computer means and recorded on a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, etc., either alone or in combination. The program instructions recorded on the computer-readable medium may be those specifically designed and configured for the present invention, or they may be those known and available to those skilled in the art of computer software.
[0061] Examples of computer-readable media include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, and flash memory. Examples of program instructions include machine code, such as that produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter, etc. The aforementioned hardware devices may be configured to operate as at least one software module to perform the operation of the present invention, and vice versa.
[0062] Some aspects of the invention have been described in the context of a device, but may also be described according to a corresponding method, wherein a block or device corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of a method may also be described according to a corresponding block or item or a feature of a corresponding device. Some or all of the method steps may be performed by (or using) a hardware device, such as, for example, a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, at least one of the most important method steps may be performed by such a device.
[0063] In the embodiments, a programmable logic device, for example, a field-programmable gate array, may be used to perform some or all of the functions of the methods described herein. In the embodiments, the field-programmable gate array may operate with a microprocessor to perform one of the methods described herein. Generally, it is preferable that the methods be performed by some hardware device.
[0064] Although the invention has been described with reference to the above embodiments, those skilled in the art will understand that various modifications and changes can be made to the invention without departing from the spirit and scope of the invention as described in the following claims.
Claims
1. A thin-film transparent piezoelectric unit that generates vibrations by an electric signal or generates electric signals by vibrations; First and second plate-shaped transparent electrodes respectively disposed on both sides of the above transparent piezoelectric unit; An insulating support layer disposed on the side of the above-mentioned transparent piezoelectric unit; First and second wires respectively connected to the first and second plate-shaped transparent electrodes; and First and second conductive members connecting the first and second plate-shaped transparent electrodes and the first and second wires, respectively; Includes, The first and second wires are aligned in one direction, and the sum of the thicknesses of the first and second wires is smaller than the length of the longest part of the transparent piezoelectric unit. The insulating support layer connects and supports two or more of the transparent piezoelectric unit, the first wire, and the first conductive member, and connects and supports two or more of the transparent piezoelectric unit, the second wire, and the second conductive member. The first and second conductive members and the first and second wires are located along an insulating support layer located at the edge of the piezoelectric unit. Transparent ultrasonic transducer.
2. In Claim 1, The sum of the thicknesses of the transparent piezoelectric unit and the first and second plate-shaped transparent electrodes in the sound wave transmission direction is within 0.4 mm and 0.03 mm or more, 3. In Claim 1, One or more non-conductive matching layers formed on the first plate-shaped transparent electrode or the second plate-shaped transparent electrode; Includes more, The above non-conductive matching layer is partially removed to expose the first plate-shaped transparent electrode or the second plate-shaped transparent electrode, or comprises a heterogeneous structure. Transparent ultrasonic transducer.
4. In Claim 3, The above heterogeneous structure is a photoresist or a material having mechanical properties different from the above non-conductive matching layer, Transparent ultrasonic transducer.
5. In Claim 3, The above heterogeneous structure is a metal and a conductive epoxy, Transparent ultrasonic transducer.
6. In Claim 1, A non-conductive front matching layer further comprising, on the front surface of the above transparent piezoelectric unit, an acoustic impedance of 5 MRayl or more and 9 MRayl or less and a light transmittance of 70% or more, Transparent ultrasonic transducer.
7. In Claim 6, A transparent polymer layer having an acoustic impedance of 1 MRayl or more and 4 MRayl or less, further comprising on the front surface of the above-mentioned front matching layer. Transparent ultrasonic transducer.
8. In Claim 1, A non-conductive rear matching layer further comprising, on the rear surface of the above transparent piezoelectric unit, an acoustic impedance of 3.5 MRayl or more and 7 MRayl or less and a light transmittance of 70% or more, Transparent ultrasonic transducer.
9. In Claim 8, A transparent polymer layer having an acoustic impedance of 1 MRayl or more and 3.5 MRayl or less, further comprising on the rear surface of the above rear surface matching layer. Transparent ultrasonic transducer.
10. In Claim 1, The above insulating support layer is thinner or thicker than the sum of the thicknesses of the transparent piezoelectric unit and the first and second plate-shaped transparent electrodes, thereby forming a step and having a structure that is insulated from the first and second plate-shaped electrodes. Transparent ultrasonic transducer.
11. A metal thin film disposed at the edges of the first and second plate-shaped transparent electrodes, respectively; further comprising Transparent ultrasonic transducer.
12. Step of preparing the piezo substrate; A step of forming a grid-shaped kerf on the piezo substrate; Steps for injecting an insulator into the above cuff and curing the insulator; and A step of cutting along the cuff so that the non-conductive material remains on the cut surface; Method for manufacturing a transparent ultrasonic transducer.
13. In Claim 12, After the step of curing the above-mentioned insulator, the method further comprises the step of forming a transparent conductive layer on the upper and lower surfaces of the above-mentioned piezo substrate. Method for manufacturing a transparent ultrasonic transducer.
14. In Claim 13, A method further comprising the step of forming a thin film metal layer on top of the above transparent conductive layer. Method for manufacturing a transparent ultrasonic transducer.
15. In Claim 13, The method further comprises the step of forming a front matching layer on the upper surface of the transparent conductive layer formed on the upper surface of the piezo substrate. Method for manufacturing a transparent ultrasonic transducer.
16. In Claim 13, The method further comprises the step of forming a sound-absorbing layer below the transparent conductive layer formed on the lower surface of the piezo substrate. Method for manufacturing a transparent ultrasonic transducer.