Transparent ultrasonic transducer using beam shaping and assembly method thereof

Abstract

A transparent ultrasonic transducer device for performing multi-mode optical imaging on a target object is provided. The device includes a transparent piezoelectric transducer, one or more conductive wires, and an optical lens. The transparent piezoelectric transducer having a first acoustic impedance is configured to receive acoustic waves from the target object. The transparent piezoelectric transducer has a first surface and a second surface. The first surface and the second surface are coated with a transparent conductive coating. The optical lens contacts the first surface of the transparent piezoelectric transducer and is optically coupled to the first surface. The optical lens is made of a material having a second acoustic impedance, and the first acoustic impedance and the second acoustic impedance are substantially similar to minimize acoustic impedance mismatch, thereby improving the sensitivity of the device.

Description

Technical Field

[0001] The present disclosure relates generally to the technical field of imaging and biomedical imaging, and in particular to a TUST device capable of shaping a light beam of a multi-mode imaging system for multi-mode optical imaging. Background Art

[0002] In the field of biomedical imaging, photoacoustic ultrasound (PAM) is an imaging method based on the photoacoustic effect, which combines optical illumination and acoustic detection to achieve high-resolution images at great depths. To perform PAM, an excitation beam is generated and focused onto body tissue. Due to the transient thermoelastic expansion of light-absorbing molecules, the absorbed light energy is converted into acoustic waves. The acoustic waves are then transmitted and detected by a piezoelectric transducer. Since the light source and ultrasound receiver must be located on the same side of the body tissue, integrating the light beam and acoustic waves into the same imaging system can be challenging and requires both optical and acoustic components. However, commonly used ultrasound transducers are made of opaque materials and may completely block light transmission. Optical components, on the other hand, have a higher acoustic impedance than air, which may reflect or scatter the acoustic signal and reduce its amplitude.

[0003] To address this issue, it has been proposed to bend the beam around the ultrasound transducer using prisms or mirrors [6] or to deliver the light to the body tissue through the opening of a hollow or annular transducer [5]. However, the complexity of the structure and beam geometry can be challenging, making the design less feasible and detrimental to the overall performance.

[0004] Several TUST devices have also been proposed. The first TUST device was introduced by Brodie et al. in 2014 [1], which is shown in Figure 1A. The optically transparent TUST device was coated with ITO on a wafer of LNO single crystal for ultrasonic particle manipulation. Despite early efforts to use optically transparent LNO for PAM purposes, the proposal was not supported by a well-defined acoustic focus, and the TUST device could not provide optimal detection conditions for PA signals.

[0005] Dangi et al. introduced another TUST device for low-frequency (14.5 MHz) applications in 2019 [2] and applied for international patent WO 2020167870 A1. A 2.5 mm × 2.5 mm transparent photoacoustic transducer 30 having a copper housing 20 and integrated with an optical fiber 10 is shown in FIG1B. The TUST device is fabricated by coating the top and bottom surfaces of LNO with transparent ITO electrodes. The resulting TUST device shows an optical transparency of >80% in the selected wavelength range, and the reflected photoacoustic image is formed by raster scanning. The TUST device is not focused, so the unfocused beam results in low imaging resolution.

[0006] Ruimin et al. developed another TUST device for high-frequency (36.9 MHz) applications [3], as shown in Figure 1C. This TUST device uses LNO single crystals and ITO electrodes and achieves an optical transmittance of up to 90% in the visible to near-infrared spectrum. Specifically, the TUST device includes a parylene film, an insulating and optically transparent epoxy resin for support, and a transparent LNO with ITO electrodes, which are mounted on a brass housing.

[0007] Another example of a TUST device was proposed by Fang et al. [4] and is shown in FIG1D . In this paper, a focusing TUST device is described that uses a PVDF film coated with ITO and a metal electrode. The optical transmittance of this TUST device is 60% (532 nm), which has the advantages of easier alignment of optical excitation and acoustic focus and compact configuration. However, due to its very low dielectric constant, it is difficult to manufacture a TUST device with a small aperture (e.g., <2 mm).

[0008] With the aforementioned development of photoacoustic effect-based TUST devices for PAM, all proposed TUST structures are not inherently compatible with any optical components. Therefore, the TUST device must be integrated with an optical imaging system, which requires additional space to secure the optical imaging system. Furthermore, the use of a light-tight metal housing on the TUST device limits certain applications, particularly those performing multimodal imaging.

[0009] Ultrasound imaging has become widely used, particularly in clinical diagnosis. It can be used to detect breast cancer, intravascular atherosclerotic plaques, gastrointestinal tumors, and vaginal diseases, among other applications. However, the diagnostic information obtained using a single imaging modality is limited. In recent years, an increasing number of multimodal imaging systems have been developed in the hope of providing more comprehensive information for clinical diagnosis. Conventional devices are often complex due to the opaque nature of the ultrasound transducer.

[0010] Therefore, there is a need in the art for a TUST device that attempts to address at least some of the above-mentioned problems and limitations encountered in PAM.Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and background of the disclosure. Summary of the Invention

[0011] A TUST device for performing biomedical imaging is provided herein. An object of the present disclosure is to provide a fully transparent TUST device capable of shaping a beam for a multi-modality imaging system.

[0012] The TUST device includes a transparent piezoelectric transducer having a first acoustic impedance, one or more wires, and an optical lens. The transparent piezoelectric transducer is configured to receive acoustic waves from a target object, wherein the transparent piezoelectric transducer includes a first surface and a second surface. The first surface and the second surface are coated with a transparent conductive coating. One or more wires connect the first surface and the second surface to an external connector. The optical lens contacts the first surface of the transparent piezoelectric transducer as a backing material and is optically coupled to the first surface of the transparent piezoelectric transducer for transmitting a light beam to the target object. The optical lens is made of a material having a second acoustic impedance. The first acoustic impedance and the second acoustic impedance are substantially similar to minimize acoustic impedance mismatch, thereby improving the sensitivity of the device.

[0013] In some embodiments, the optical lens is a GRIN lens. A GRIN lens is designed to shape a light beam into a focused beam, a collimated beam, or a diverging beam by changing the refractive index and the pitch length.

[0014] In some embodiments, the second surface is a concave surface having a radius of curvature determined based on the focal length, the concave surface being used to focus the acoustic waves from the target object and emit the focused acoustic waves from the TUST device.

[0015] In certain embodiments, the TUST device further comprises a transparent housing arranged to house a transducer unit formed by contacting an optical lens with a first surface of the transparent piezoelectric transducer, wherein the transparent housing is made of a transparent material such as glass or acrylic.

[0016] In yet another embodiment, a method for assembling a TUST device for multi-mode optical imaging on an object is disclosed. The TUST device includes a transparent piezoelectric transducer having a first surface and a second surface, and an optical lens. The method includes the following steps: (1) processing a piezoelectric substrate to form the second surface having a concave surface; (2) coating the first surface and the second surface with a transparent conductive coating; (3) contacting the optical lens with the transparent piezoelectric transducer to obtain a transducer unit; and (4) connecting one or more wires from the first surface and the second surface to an external connector.

[0017] In some embodiments, the method further includes (5) assembling the transducer unit into the transparent housing; and (6) filling a gap between the transparent housing and the transducer unit with a transparent epoxy resin.

[0018] In some embodiments, the step of processing the piezoelectric substrate to form a second surface having a concave surface further includes polishing the piezoelectric substrate to obtain a concave surface having a radius of curvature determined based on the focal length, the concave surface being used to focus acoustic waves from the target object and emit focused acoustic waves from the TUST device.

[0019] This summary is provided to introduce some concepts in a simplified form, which will be further described in the detailed description below. This summary is neither intended to identify key features or essential features of the claimed subject matter nor to help determine the scope of the claimed subject matter. As shown in the following examples, other aspects and advantages of the present invention are disclosed. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings contain figures that serve to further illustrate and elaborate the above and other aspects, advantages, and features of the present disclosure. It will be understood that these drawings depict only certain embodiments of the present disclosure and are not intended to limit its scope. It will also be understood that these drawings are shown for simplicity and clarity and are not necessarily drawn to scale. The present disclosure will now be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:

[0021] FIG1A is a photograph of a TUST device according to the disclosure of Brodie et al. [1];

[0022] FIG1B is a photograph of a LNO-based TUST device according to the disclosure of Dangi et al. [2];

[0023] FIG1C is a photograph of a high-frequency TUST device according to the disclosure of Chen et al. [3];

[0024] FIG1D is a photograph of a focused TUST device using a PVDF membrane according to the disclosure of Fang et al. [4];

[0025] Figure 2 depicts a perspective view of a TUST device according to an embodiment of the present disclosure;

[0026] Figure 3A Depicts a first step for preparing a transparent piezoelectric transducer according to an embodiment of the present disclosure;

[0027] Figure 3B depicts a second step for preparing a transparent piezoelectric transducer according to an embodiment of the present disclosure;

[0028] Figure 3C depicts a third step for preparing a transparent piezoelectric transducer according to an embodiment of the present disclosure;

[0029] Figure 4A Described is a method for manufacturing a Figure 2 The first step of the TUST device;

[0030] Figure 4B Described is a method for manufacturing a Figure 2 The second step of the TUST device;

[0031] Figure 4C Described is a method for manufacturing a Figure 2 The third step of the TUST device;

[0032] Figure 4D Described is a method for manufacturing a Figure 2 The fourth step of the TUST device;

[0033] Figure 5A Depicts a method for focusing a light beam according to an embodiment of the present disclosure. Figure 2 Operation of the TUST device;

[0034] Figure 5B Depicts a method for collimating a light beam according to an embodiment of the present disclosure. Figure 2 The operation of the TUST device; and

[0035] Figure 5C Depicts a method for diverging a light beam according to an embodiment of the present disclosure. Figure 2 Operation of the TUST device. DETAILED DESCRIPTION

[0036] The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or its application and / or use. It should be understood that a large number of variations exist. The detailed description will enable those skilled in the art to implement the exemplary embodiments of the present disclosure without undue experimentation, and it should be understood that various changes or modifications may be made to the functions and structures described in the exemplary embodiments without departing from the scope of the present disclosure as set forth in the appended claims.

[0037] Benefits, advantages, solutions to problems, and any element that may cause any benefit, advantage, or solution to occur or become apparent should not be construed as a critical, required, or essential feature or element of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.

[0038] As used herein, the term "light beam" refers to any beam of electromagnetic radiation, including but not limited to visible light, ultraviolet light, infrared light, and microwaves. The light beam can be generated by a light source such as a laser (single wavelength laser or multi-wavelength laser), a laser diode, an LED, or a microwave generator. In certain embodiments, the light source can be provided by an optical fiber. A combination of two or more types of light sources can be used. The light source can emit a light beam having a predetermined wavelength range. For example, the wavelength of the light beam can vary between 400 nm and 2000 nm. In another example, the wavelength of the light beam can vary between 400 nm and 700 nm.

[0039] For ease of description, terms such as "inner", "outer", "outermost", "top", "bottom" and variations thereof are used herein to facilitate explanation of the positioning of an element or the positioning of one element relative to another element and are not intended to be limited to a particular orientation or position. The vertical axis V is defined by gravity, as Figure 2 As shown, it extends from the bottom of the TUST device 100 to the top of the TUST device 100. Terms such as "first," "second," and variations thereof are used herein to describe various elements, regions, sections, etc., and are not intended to be limiting.

[0040] Terms such as "connect," "attach," "couple" and variations thereof are used broadly and encompass direct and indirect connections, attachments, and mountings; and are not limited to electrical, physical, optical, or mechanical connections, attachments, or mountings.

[0041] The present disclosure generally relates to the technical field of imaging and biomedical imaging. More specifically, but not by way of limitation, the present disclosure relates to a TUST device 100 capable of shaping a beam for a multi-mode imaging system to provide multi-mode optical imaging. In certain embodiments, the multi-mode optical imaging includes photoacoustic imaging and OCT imaging. Obviously, the present disclosure can be applied to other combinations of photoacoustic imaging without departing from the scope and spirit of the present disclosure. Figure 2 The TUST device 100 may be implemented as an optically transparent and compact device including a transparent piezoelectric transducer 110 , an optical lens 120 , a transparent epoxy resin 130 , a transparent housing 140 , and a wire 150 .

[0042] The TUST device 100 is configured to perform multi-mode optical imaging, in particular photoacoustic imaging, on a target object and receive acoustic waves therefrom. Figures 5A to 5C In the present invention, the target object and the acoustic wave are represented as 300 and 230, respectively. The target object 300 can be a human body, a human organ, a fetus, a non-organic object inside a human body, an animal, an animal organ, a non-organic object inside an animal, or any object (living or non-living) that can absorb light energy and convert it into acoustic wave 230 through transient thermoelastic expansion. The TUST device 100 is used to perform PAM, which essentially provides optical illumination of an excitation signal in the form of a light beam and focuses the light beam onto the target object. The excitation signal is absorbed by the target object 300 and converted into acoustic wave 230 through transient thermoelastic expansion of light-absorbing molecules in the target object 300. The acoustic wave 230 is then transmitted back to the TUST device 100 for detection by the transparent piezoelectric transducer 110.

[0043] The transparent piezoelectric transducer 110 is arranged to receive a photoacoustic response from the target 300 in the form of an acoustic wave 230 generated by the transient thermoelastic expansion. The transparent piezoelectric transducer 110 is preferably made of LNO and, in certain embodiments, may be made of other transparent materials such as PVDF, PMN-PT, a transparent polymer, a transparent ceramic, or single-crystal LNO. For single-crystal LNO, the transparent piezoelectric transducer 110 typically has a first acoustic impedance of approximately 34.1 MRayls. For PMN-PT, the first acoustic impedance is typically approximately 30.85 MRayls. For PVDF, the first acoustic impedance is approximately 3.8 MRayls. Figures 3A to 3C The steps for preparing the transparent piezoelectric transducer 110 are shown.

[0044] To prepare the transparent piezoelectric transducer 110, a piezoelectric substrate 111 may be used. The piezoelectric substrate 111 is also referred to as a transparent piezoelectric wafer. The transparent piezoelectric transducer 110 or the piezoelectric substrate 111 includes a first surface 112 and a second surface 113. Figure 3B. The first surface is a flat surface and is generally referred to as the back side of the transparent piezoelectric transducer 110. The second surface 113 has a concave surface 113B and is generally referred to as the front side of the transparent piezoelectric transducer 110. It should be apparent that, as used herein, the terms "front" and "back" refer only to respective proximity to a target object and are not intended to be limited to a particular orientation or position.

[0045] The concave surface 113B of the second surface 113 is typically smooth and continuous, with a radius of curvature determined based on the focal length. This concave surface is used to focus acoustic waves from the target 300 and transmit focused acoustic waves from the TUST device 100. In certain embodiments, the periphery 113A of the concave surface 113B is smooth and flat. The piezoelectric substrate 111 is processed on the front side to form the second surface 113 having the concave surface 113B and the periphery 113A. In contrast, the first surface 112 is generally substantially smooth. The term "smooth" refers to a surface that is substantially free of protrusions, depressions, etc. In practice, due to the fragile nature of the piezoelectric substrate 111, it is difficult to manufacture the concave surface of the second surface 113. The present disclosure provides a method for obtaining the concave surface 113B by polishing the piezoelectric substrate 111. The polishing step can also be achieved by various means and methods without departing from the scope and spirit of the present disclosure. The resulting concave surface can be focused at a position defined by the radius of curvature to receive the acoustic wave 230.

[0046] The first surface 112 and the second surface 113 may be coated with a transparent conductive coating 114 to obtain a transparent piezoelectric transducer 110, such as Figure 3C . Preferably, the transparent conductive coating 114 is made of ITO. In some other cases, tin oxide, indium oxide, zinc oxide, or any combination thereof may also be used. After coating, the first surface 112 can be considered as the first transducer electrode, and the second surface 113 can be considered as the second transducer electrode. Other materials can also constitute other transparent electrodes. The two transducer electrodes are physically and electrically separated. Optionally, a shielding wire can be added between the two transducer electrodes to prevent any short circuit path from forming.

[0047] Reference Figures 4A to 4D, according to the present disclosure, steps for manufacturing a TUST device 100 are shown. An optical lens 120 is arranged to contact a transparent piezoelectric transducer 110 as a backing material along a vertical axis V and optically coupled to the transparent piezoelectric transducer 110 to obtain a transducer unit 105. In one embodiment, the contact is firmly fixed by adhesively attaching the optical lens 120 to the first surface 112 of the transparent piezoelectric transducer 110. The optical lens 120 serves as a backing layer for the transducer unit 105. In some embodiments, the optical lens 120 is a GRIN lens made of a material having a second acoustic impedance. Since the material can be quartz, silicon dioxide, or glass, the second acoustic impedance is typically approximately 11 to 16 MRayls. The material can also be a suitable transparent optical material. Advantageously, the first acoustic impedance and the second acoustic impedance of the two materials are substantially similar to minimize the acoustic impedance mismatch, so that light passing through the optical lens 112 to the transparent piezoelectric transducer 110 has less reflection. Therefore, by using the optical lens 120 as the backing material, the sensitivity of the device 100 is improved, and the signal-to-noise ratio of the transparent piezoelectric transducer 110 is very high. In contrast, conventionally, optically transparent epoxy resins are used as backing materials, which have an acoustic impedance of approximately 1 to 3 MRayls. Therefore, transparent epoxy resins have a high acoustic impedance mismatch, which affects detection sensitivity.

[0048] Next, the transducer unit 105 is connected to enable measurement of the acoustic waves 230 reflected from the target 300. In one embodiment, the transparent piezoelectric transducer 110 captures the photoacoustic response. Figure 4B As shown in , one or more wires 150 are connected to the first surface 112 and the second surface 113 using conductive glue. The amount of conductive glue should be appropriately controlled to avoid a short circuit between the first surface 112 and the second surface 113. The first surface 112 and the second surface 113 are connected to an external connector (not shown) at the distal end 151 via a first terminal 152 and a second terminal 153, respectively. In one embodiment, the first terminal 152 is a positive terminal electrically connected to the first surface 112, and the second terminal 153 is a negative terminal electrically connected to the second surface 113. The one or more wires 150 can be, for example, nanosilver wires, coaxial wires, insulated wires, twisted pair wires, etc. The external connector allows electrical connection to a multi-mode optical imaging system to analyze the acoustic response.

[0049] Reference Figure 4C and Figure 4D, the transducer unit 105 is assembled in a transparent housing 140. The transparent housing 140 is made of glass, acrylic, or other transparent materials. The transparent housing 140 has a larger diameter than the transducer unit 105, and the transducer unit 105 is arranged to serve as an outer protective layer for the transducer unit 105. Preferably, the TUST device 100 further includes a parylene film 141, which is applied as the outermost layer covering the transparent housing 140. The parylene film 141 is a matching layer and a waterproof layer of the TUST device 100. In one embodiment, the TUST device 100 further includes a transparent epoxy resin 130, which fills the gap between the transparent housing 140 and the internal structure of the transducer unit 105. The transparent epoxy resin 130 is also transparent and provides additional support and protection for the transducer unit 105. During application of the transparent epoxy 130 on the transducer unit 105 , gas should be evacuated from the transparent epoxy 130 to ensure vacuum in the gap for promoting uniform curing of the transparent epoxy 130 .

[0050] Another aspect of the present disclosure provides for the use of an optical lens 120 for modifying the pattern of a light beam 220 emitted from a TUST device 100. Figures 5A to 5C . The light source 210 is configured to generate a light beam 220 to provide light illumination and excitation to the target 300. In some embodiments, the light source 210 may include an optical fiber that receives light from an input end and emits light from an output end. In some other embodiments, the light source 210 may include one or more LEDs or other light sources known in the art. The TUST device 100 of the present disclosure is substantially transparent (except for one or more wires 150), which allows at least 90% or approximately 100% of light within a defined wavelength range to pass through. This enables the TUST device 100 to be used in various optical imaging applications.

[0051] The optical lens 120 is configured to shape the light beam 220 by focusing, collimating, or diverging the light beam 220, which enables multi-mode imaging. In one embodiment, the optical lens 120 may include one or more optical elements selected from the group consisting of one or more mirrors, lenses, collimators, prisms, diverging elements, and diffraction elements. Therefore, by appropriately arranging the optical elements, the optical lens 120 can be customized as a focusing lens 120A, a collimating lens 120B, or a diverging lens 120C. In another embodiment, the optical lens 120 can be a GRIN lens. Since the GRIN lens affects the light path by changing the refractive index within the lens body 121 and the length of the lens body 121, the GRIN lens can be designed to shape the light beam into a focused beam, a collimated beam, or a diverging beam.

[0052] In some embodiments, the optical lens 120 is customized as a focusing lens 120A, such as Figure 5A The incident light beam 220 is refracted into a focused light beam inside the lens body 121 by one or more optical elements to thereby focus the light beam 220 onto a predetermined focal point.

[0053] In another embodiment, the optical lens 120 is customized as a collimating lens 120B, such as Figure 5B The incident light beam 220 is refracted by one or more optical elements into a collimated light beam inside the lens body 121 , and the collimated light beam 220 is emitted toward the target 300 .

[0054] In yet another embodiment, Figure 5C As shown in FIG, the optical lens 120 is customized as a diverging lens 120C. The incident light beam 220 is refracted into a diverging light beam inside the lens body 121 by one or more optical elements, so that the light beam 220 diverges and is emitted toward the target 300.

[0055] As shown, the TUST device 100 uses an optical lens 120 as a backing layer, which provides a higher acoustic impedance than the transparent epoxy resin conventionally used in the prior art. This design is simple, without the need for a complex and cumbersome configuration to combine light and acoustic signals. The entire device (except for one or more wires 150) is almost transparent, which allows the light beam 220 to pass through in different ways, thereby enabling multi-modal imaging. The transparent nature also enables the TUST device 100 to be combined with a variety of different optical imaging modes, including white light imaging, photoacoustic imaging, optical coherence tomography, fluorescence imaging, and other imaging modes.

[0056] The TUST device 100 described above is easy to manufacture and is compatible with most commonly used ultrasound devices and lighting devices to achieve high-sensitivity multi-mode optical imaging. The TUST device 100 can be scalable to suit various applications and can have different sizes and dimensions. In certain embodiments, the TUST device 100 can be mounted on different test equipment, portable devices, tablets, or other measurement systems.

[0057] This shows a TUST device 100 according to the present disclosure, which is capable of shaping a beam 220 for a multi-mode imaging system to provide multi-mode optical imaging. It is obvious that variations or alternatives to the other features and functions disclosed above can be combined into many other devices. Therefore, the present embodiment should be considered in all respects as illustrative and not restrictive. The scope of the present disclosure is indicated by the appended claims rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be included therein.

[0058] References

[0059] The following is a list of references occasionally cited in the specification. The disclosures of each of these references are incorporated herein by reference in their entirety.

[0060] [1] Graham WJ Brodie et al., “Optically transparent piezoelectric transducers for ultrasonic particle manipulation,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 61, No. 3, March 2014.

[0061] [2] Ajay Dangi et al., “Lithium niobate-based transparent ultrasound transducers for photoacoustic imaging,” Optical Society of America, Optics Express, vol. 44, no. 21, November 1, 2019.

[0062] [3] Ruimin Chen et al., “Transparent high-frequency ultrasonic transducers for photoacoustic microscopy applications,” IEEE Transactions on Ultrasound, Ferroelectrics, and Frequency Control, Vol. 67, No. 9, September 2020.

[0063] [4] Cheng Fang et al., “Focusing optically transparent PVDF transducer for photoacoustic microscopy,” IEEE Sensors Magazine, Vol. 20, No. 5, March 1, 2020.

[0064] [5] T. Wang et al., “Multiparameter photoacoustic microscopy of the mouse brain with 300kHz A-line rate,” Neurophotonics, Vol. 3, No. 4, 2016, Article No. 045006.

[0065] [6] Hu, S. et al., “Second-generation optical-resolution photoacoustic microscopy with improved sensitivity and speed,” Optics Express, vol. 36, no. 7, April 1, 2011, pp. 1134–1136.

[0066] List of abbreviations

[0067] GRIN Gradient Index

[0068] ITO Indium Tin Oxide

[0069] LED light-emitting diode

[0070] LNO Lithium Niobate (LiNbO3)

[0071] OCT Optical Coherence Tomography

[0072] PA signal Photoacoustic signal

[0073] PAM photoacoustic microscopy

[0074] PMN-PT Lead Magnesium Niobate / Lead Titanate

[0075] PVDF polyvinylidene fluoride

[0076] TUST transparent ultrasound transducer.

Claims

1. A transparent ultrasonic transducer device for performing multi-mode optical imaging on a target object, the device comprising: a transparent piezoelectric transducer having a first acoustic impedance, the transparent piezoelectric transducer being configured to receive an acoustic wave from the target object, wherein the transparent piezoelectric transducer comprises a first surface and a second surface, and wherein the first surface and the second surface are coated with a transparent conductive coating; connecting the first surface and the second surface to one or more wires of an external connector, wherein the first surface is a flat surface and the second surface is a concave surface having a radius of curvature determined based on the focal length; and an optical lens in direct contact with the first surface of the transparent piezoelectric transducer and optically coupled to the first surface of the transparent piezoelectric transducer, the optical lens serving as a backing layer for improving the signal-to-noise ratio of the transparent piezoelectric transducer and configured to transmit a light beam to the target object, in: The optical lens is made of a material having a second acoustic impedance; and The first acoustic impedance and the second acoustic impedance are substantially similar to minimize acoustic impedance mismatch, thereby increasing sensitivity of the device.

2. The device according to claim 1, wherein The optical lens is a gradient-index GRIN lens.

3. The device according to claim 2, wherein The GRIN lens is designed to shape the light beam into a focused beam, a collimated beam, or a diverging beam by changing the refractive index.

4. The device according to claim 1, wherein The material is a transparent optical material.

5. The device according to claim 1, wherein The material is quartz, silicon dioxide or glass.

6. The device according to claim 1, wherein The optical lens is adhesively attached to the first surface of the transparent piezoelectric transducer.

7. The device according to claim 1, wherein The transparent conductive coating is made of indium tin oxide (ITO), tin oxide, indium oxide, zinc oxide, or any combination thereof.

8. The device according to claim 1, wherein The transparent piezoelectric transducer is made of one of lithium niobate (LNO), polyvinylidene fluoride (PVDF), lead magnesium niobate-lead titanate (PMN-PT), a transparent polymer, and a transparent ceramic.

9. The device according to claim 1, wherein The concave surface is used to focus sound waves from the target object and transmit the sound waves from the transparent ultrasound transducer device.

10. The device according to claim 1, further comprising a transparent housing arranged to accommodate a transducer unit formed by bringing the optical lens into contact with the first surface of the transparent piezoelectric transducer, wherein The transparent shell is made of glass or acrylic. 11 . The device according to claim 10 , further comprising a parylene film coated as an outermost layer covering the transparent casing. 12 . The device according to claim 10 , further comprising a transparent epoxy resin filling a gap between the transparent housing and the transducer unit.

13. The device according to claim 1, wherein The optical lens is a focusing lens, a collimating lens or a diverging lens.

14. A method for assembling a transparent ultrasonic transducer device for performing multi-mode optical imaging on a target object, the transparent ultrasonic transducer device comprising a transparent piezoelectric transducer having a first surface and a second surface and an optical lens, wherein: The first surface is a flat surface, and the method comprises the following steps: processing the piezoelectric substrate to form a second surface having a concave surface, wherein the piezoelectric substrate is polished to obtain the concave surface having a radius of curvature determined based on a focal length; coating the first surface and the second surface with a transparent conductive coating; bringing the optical lens into direct contact with the first surface of the transparent piezoelectric transducer and optically coupled to the first surface of the transparent piezoelectric transducer to obtain a transducer unit, the optical lens serving as a backing layer for improving a signal-to-noise ratio of the transparent piezoelectric transducer; and One or more wires are connected from the first surface and the second surface to an external connector.

15. The method according to claim 14, further comprising the steps of: Assembling the transducer unit into a transparent housing; and A gap between the transparent housing and the transducer unit is filled with transparent epoxy resin. 16 . The method according to claim 15 , further comprising the step of coating the transparent casing with a parylene film as an outermost layer.

17. The method according to claim 15, wherein: The step of filling the gap with the transparent epoxy resin includes the step of extracting gas from the transparent epoxy resin.

18. The method according to claim 14, wherein The step of bringing the optical lens into direct contact with the first surface of the transparent piezoelectric transducer includes the step of adhesively attaching the optical lens to the first surface of the transparent piezoelectric transducer.

19. The method according to claim 14, wherein The concave surface is used to focus sound waves from the target object and transmit the sound waves from the transparent ultrasound transducer device.

20. The method according to claim 14, wherein The one or more conductive wires are connected to the first surface and the second surface using conductive glue.

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