Membrane hydrophone for high-frequency ultrasound and method for manufacturing hydrophone

Abstract

To provide a method for manufacturing a hydrophone or membrane hydrophone used to measure acoustic energy from a high frequency ultrasonic transducer.SOLUTION: In a hydrophone with a waterproof casing, a membrane assembly 1200 is supported by a frame 1210 and includes a piezoelectric body attached or disposed on a member 1230. The hydrophone also includes an electrode pattern (signal trace) formed on the piezoelectric body to define an active area. In addition, the hydrophone includes an integrated coaxial trace 1240 connected to the active area.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] This application claims the benefit of U.S. Provisional Application No. 62 / 206,808, filed Aug. 18, 2015; U.S. Provisional Application No. 62 / 297,763, filed Feb. 19, 2016; U.S. Application No. 15 / 241,021, filed Aug. 18, 2016; and U.S. Application No. 16 / 579,348, filed Sep. 23, 2019, the entire disclosures of which are incorporated herein by reference.

[0002] The disclosed technology relates to a hydrophone for testing ultrasonic transducers, and more particularly, to a hydrophone used for testing high-frequency ultrasonic transducers.

Background Art

[0003] Ultrasonic imaging operates by sending a number of short pulses of acoustic energy from a transducer into a region of interest and collecting the information contained in the corresponding echo signals. FIG. 1A shows a simplified ultrasonic transducer having a number of individual transducer elements 12 (not drawn to scale) that vibrate and generate ultrasonic acoustic signals when a varying voltage is applied across the elements. Also, the elements generate an electrical signal when the element receives acoustic energy. The elements 12 are typically arranged in a one- or two-dimensional array that includes one or more matching layers 14 and a fixed lens 16. By carefully selecting the time at which the amplitude and drive signal are applied to each of the transducer elements, the acoustic signals constructively combine to form a beam having a focal zone at a desired location. As the operating frequency of the transducer increases, the size of the focal zone (often the shape of a rice grain) decreases. For example, at a center frequency of 15 MHz, the size of the focal zone is about 500×300 pm. At 30 MHz, the size of the focal zone drops to about 280×150 pm, and at 50 MHz, the size of the focal zone is less than 200×100 pm. In addition to ultrasonic arrays, ultrasonic signals can also be generated by a single-element transducer 17, as shown in FIG. 1B.

[0004] Ultra-high frequency (UHF) diagnostic ultrasound has advanced substantially in the past decade in both preclinical and clinical industries with the introduction of systems having 50 MHz center frequency arrays with upper corner frequencies of 70 MHz and above. There are many new scientific and medical possibilities that can be explored due to the higher resolution and bandwidth of UHF ultrasound, but with the new applications and capabilities come new challenges for testing and characterization. As will be understood by those skilled in the art, as the transducer pushes the frequency even higher, the wavelength decreases accordingly and various other mechanisms such as the non-linear propagation of sound waves in water become more prevalent. Currently, it is necessary to scientifically understand the nature of UHF ultrasound in water for both scientific and regulatory purposes of medical and preclinical devices. In addition, in order to utilize modern sophisticated FEA modeling, it is necessary to accurately measure the acoustic field at or even below the pitch of the array. Clearly, smaller-aperture hydrophones with higher frequency calibration are needed to ensure accurate measurement of harmonics and reduce the spatial uncertainty resulting from short-wavelength sound waves measured with relatively large-aperture hydrophones.

[0005] Before an ultrasonic transducer can be approved by the US Food and Drug Administration (FDA) for clinical use in the United States or obtain a CE mark for clinical use in Europe, the acoustic energy generated by the transducer must be characterized. The characterization involves ensuring that the focal zone is well-defined and that the transducer is To ensure that no energy hotspots are generated at the intended location, a map of pressure intensity is generated. Similarly, the characterization confirms that the generated energy is not so large as to cause cavitation within the tissue being examined and that the power output is within the tolerance limits imposed by various tissues. There are well-established criteria for defining the test procedures and results required for regulatory approval. However, UHF ultrasound has been increasingly pushing these tests to and beyond their limits due to the lack of appropriately small hydrophone aperture sizes and sufficiently high frequency calibration data.

[0006] As shown in FIG. 2, most transducer tests are performed by operating the transducer 20 within a liquid bath 40 (typically degassed water, although another liquid may be used). The hydrophone 50 is placed on a computer-controlled stage (not shown) within the path of the ultrasonic beam. When the transducer is operated, the stage is moved to cause the hydrophone to measure the position of the focal zone and the intensity of the beam at a number of positions. The signal from the hydrophone is stored by a computer system to confirm that the transducer is operating as intended. A plot of the intensity measurements in space defines the characteristics of the ultrasonic transducer beam.

[0007] Most desirably used when sampling an ultrasonic beam is a membrane type hydrophone. This is because of its flat frequency response and the simple interaction with the radiation pattern created by the device under test (DUT). To enable effective sampling of the beam, the active area of the hydrophone must be substantially smaller than the focal zone of the transducer being inspected. In the past, it has been difficult to reliably manufacture a membrane type hydrophone with a sufficiently small active area that can be used for testing high frequency ultrasonic transducers. Therefore, users have been forced to use needle type hydrophones that exhibit unwanted resonances and interactions with the measured radiation pattern. Additionally, specially shaped needle hydrophones designed to minimize unwanted resonances, such as so-called "lipstick style" hydrophones, are used. However, in practice, it is difficult to accurately manufacture such shapes on a scale small enough for very high frequency ultrasonic characterization. As a result, it has been found that needle type hydrophones are not as accurate as membrane type hydrophones in characterizing high frequency beam patterns.

Summary of the Invention

Problems to be Solved by the Invention

[0008] Considering these problems, there is a need for an improved membrane type hydrophone for high frequency ultrasound, similar to the method of manufacturing such a hydrophone.

Means for Solving the Problems

[0009] To address these and other problems, the techniques disclosed herein relate to a novel membrane-type hydrophone design and a method of manufacturing a membrane-type hydrophone for use in characterizing the properties of high-frequency ultrasonic transducers. Such characterization can be used to prove transducers for clinical use, but can also be used in the development and testing of ultrasonic transducer designs. In one embodiment, the hydrophone includes a piezoelectric membrane that extends across a support structure and is covered on both sides with a conductive material such as a thin layer of gold or gold + chromium. A portion of the conductive material is then removed from each side of the piezoelectric membrane to create a positive electrode on one side of the membrane and a negative electrode on the other side. The positive and negative electrodes overlap in a small region that defines the active area of the hydrophone. In one embodiment, the active area has dimensions between 10 and 30 microns in diameter.

[0010] In some embodiments, a patterning tool such as an excimer laser is used to selectively remove a portion of the conductive material from the piezoelectric membrane to create electrodes on the thin film. In one embodiment, the conductive material on both sides of the membrane is removed by exposing the membrane to laser energy from the same side of the membrane, for example, without the need to flip the piezoelectric membrane. In some embodiments, one or more alignment features or fiducial points are created within the membrane to enable the piezoelectric membrane to be accurately positioned relative to the coordinate system of the patterning tool. Once aligned, the conductive material can be accurately removed from the membrane.

[0011] In some embodiments, the hydrophone includes positive and negative electrodes that overlap on both sides of the piezoelectric membrane, and the positive electrode on one side of the membrane is electrically connected to the corresponding positive electrode on the other side of the membrane. Similarly, the negative electrode on one side of the membrane is electrically connected to the corresponding negative electrode on the other side of the membrane. In some embodiments, the overlapping electrodes are electrically connected to one or more conductive vias that are generated within the piezoelectric membrane using a laser and filled with a conductive material.

[0012] The active region of the hydrophone is formed where a part of the positive electrode on one side of the membrane overlaps with the negative electrode on the other side of the membrane.

[0013] In some embodiments of the disclosed invention, the element is fabricated from a fully polarized piezoelectric polymer or copolymer film, enabling the maximum sensitivity achieved by the active poling of the raw film. This can lead to issues related to spurious signals detected at locations away from the intended active aperture. In some embodiments of the disclosed technology, the piezoelectric film is processed into the device in an unpolarized state, and as a result, the electrodes may be used to spot-polarize the active region. This approach can reduce or eliminate many spurious signals but may result in a decrease in sensitivity and variations in spot size. In some embodiments, overlapping polar electrodes are used to clamp the electric field within the film to achieve greater spatial specificity in spot poling, and thus a more accurate and predictable active spot size is obtained.

[0014] In some other embodiments, in order to reduce the electrical response of the membrane to acoustic energy received in undesirable locations, which allows for more aggressive polling of the entire membrane (as compared to spot polling), a portion of the piezoelectric membrane is selectively depolarized before coating the portion with a conductive material. In one embodiment, the piezoelectric membrane is selectively depolarized in regions away from the active region of the hydrophone. In one embodiment, a laser patterning tool is used to depolarize the piezoelectric membrane in all regions except the active region of the hydrophone by modifying the polymer with UV laser energy such that the membrane remains mechanically intact but has low piezoelectric efficiency. In yet another embodiment, an unpolarized piezoelectric copolymer membrane is processed within the device, and a laser patterning tool is used to modify the membrane to reduce the piezoelectric potential of the membrane in all regions except the active region, ensuring that spot polling can occur effectively only in the unmodified active region, and electrodes are deposited such that they are aligned with the active region and the membrane is spot polled. In yet another embodiment, the previous approach is combined with a build-up-like polar electrode design to achieve an extremely well-defined active aperture after spot polling.

[0015] Certain non-limiting embodiments include a hydrophone for measuring acoustic energy from a high-frequency ultrasonic transducer. The hydrophone can include a frame and a membrane assembly supported by the frame and comprising a piezoelectric body. The hydrophone can also include an electrode pattern formed on the piezoelectric body to define an active region. Further, the hydrophone can include a built-in coaxial layer connected to the active region.

[0016] Certain non-limiting embodiments include a method for manufacturing a hydrophone for measuring acoustic energy from a high-frequency ultrasonic transducer. For example, the method can include a membrane fi It can include stretching the lumen across the frame and disposing a piezoelectric body on the membrane film. This method can also include selectively removing a portion of the piezoelectric body to create an active region and connecting a coaxial layer to the active region.

Brief Description of the Drawings

[0017]

FIG. 1A

FIG. 1B

FIG. 2

FIG. 3A

FIG. 3B

FIG. 4

FIG. 5A

FIG. 5B

FIG. 6

FIG. 7

FIG. 8

FIG. 9

FIG. 10

FIG. 11

FIG. 12

FIG. 13

FIG. 14

FIG. 15

FIG. 16

FIG. 17

[0018] As will be described in further detail below, the disclosed technology is a membrane type hydrophone having one or more small active regions that can be used to characterize a high frequency ultrasonic transducer. In one embodiment, the membrane is, for example, 3 to 12 microns thick It is made of a thin-film piezoelectric copolymer such as P(VDF-TrFE) having a thickness between... However, other thicknesses or other piezoelectric materials (such as PVDF) can be used. The film is preferably stretched across the frame in a way that removes any wrinkles from the film. In one embodiment, the film is held on an outer hoop and then, like a drum head, is stretched around its perimeter simultaneously by an inner hoop that presses a portion of the film circumferentially into a groove to stretch it wrinkle-free. When the film is stretched, the film is adhered to a circular frame that fits within the inner hoop, and the excess film outside the frame is cut off. The frame is then used to form part of a hydrophone. In one embodiment, the frame has a diameter of about 2 cm, but larger or smaller frames can be used.

[0019] The frame is attached to a metal support and then coated with a metal conductor such as gold or gold + chromium (or other metal conductor) by sputtering or another process. In one embodiment, the thickness of the conductor disposed on the thin film is in the range of 1500 - 2500 angstroms. However, much thinner or thicker conductor coatings such as 300 angstroms to 5000 angstroms can be used, but are not limited thereto.

[0020] Next, the conductive coatings on both sides of the film are patterned to form overlapping portions of the conductor on the upper and lower surfaces of the film that form the active regions of the hydrophone. The overlapping conductive regions must be precisely aligned. In some embodiments, the ends of which are on the order of 10 - 30 microns, and the technology described in US Provisional Application No. 62 / 206,808 heretofore could not reliably manufacture.

[0021] Figures 3A and 3B show an embodiment of a hydrophone 100 constructed in accordance with one embodiment of the disclosed technology. The hydrophone 100 includes a generally circular disk of piezoelectric film 102 adhered to a circular frame 104, which is then secured to a support 105. In one embodiment, the support 105 is made of a conductive metal such as titanium. A first electrode 106 is patterned on one side of the piezoelectric film, and a second electrode (not shown) is patterned on the other side of the piezoelectric film. In some embodiments, the piezoelectric film may include a pair of registration features or fiducial points 108, 110 (not drawn to scale), which are cut through the piezoelectric film to align the film with a laser patterning system. The registration features can be created with a laser and can have substantially any shape (square, rectangle, cross, etc.). In one embodiment, the registration features are squares approximately 10 microns per side. The corners of the registration features enable the piezoelectric film to be aligned with sub-micron level accuracy.

[0022] When both sides of the film are covered with a metal conductor, a portion of the conductive coating is removed from the surface of the piezoelectric film using an excimer laser or other patterning tool so that the film is relatively unaffected.

[0023] In one embodiment, once the electrode pattern is created on the first side of the film, the film is flipped over and aligned with the patterning tool using one or more registration features 108, 110. Once aligned, the patterning tool forms an electrode on the second side of the film. In one embodiment of the disclosed technology, the electrode on the first side of the film forms the positive electrode of the hydrophone, while the second, larger electrode on the other surface of the piezoelectric film is grounded.

[0024] In another embodiment described in detail below, substantially most of the electrodes on both sides of the film can be generated by exposing a single side of the film to laser energy. In this embodiment, registration features or fiducial points may not be required.

[0025] A thin wire 120 (e.g., a gold bonding wire or a silver-plated copper bus wire) can be connected to the first electrode on the thin film. In addition, the bonding wire can similarly be connected to the second electrode, or if the frame 104 and / or the support 105 is conductive, the frame can be used to connect to the second electrode. In one embodiment, an acoustically matching elastomer 126 is poured on the back side of the hydrophone. In another embodiment, for maximum sensitivity, the matching elastomer can be omitted, leaving both sides of the membrane uncovered with each electrode. In one embodiment, the elastomer 126 is made of a silicone rubber having an acoustic impedance that closely matches the impedance of water.

[0026] In some embodiments, it may be advantageous to attach a buffer amplifier to a printed circuit board disposed on the support 105 or directly on the membrane of the hydrophone. The buffer amplifier can increase the gain of the generated signal and / or buffer the signal so that it can be carried by a signal cable (not shown). In one embodiment, an SMA or other style connector 128 is attached to the support 105 of the hydrophone. The SMA connector 128 is a coaxial connector in which the outer shield is connected to the conductive support 105 or the negative electrode and the center conductor is connected to the positive electrode (or the output of the buffer amplifier if used). Optionally, the connection to the SMA connector can be reversed.

[0027] Another embodiment of the membrane-type hydrophone is shown in FIG. 4. In this embodiment, the conductors on the membrane are patterned to create electrodes that substantially align with the top and bottom surfaces of the membrane. In this embodiment, the two positive electrodes on the top and bottom surfaces of the piezoelectric membrane overlap each other, and the two negative electrodes on the top and bottom surfaces of the piezoelectric membrane overlap each other. The positive electrode on the top surface does not overlap with the negative electrode on the bottom surface (or vice versa) except in the active region of the hydrophone. FIG. 4 is a partial, three-dimensional cross-sectional view of a hydrophone 200 in which the electrode pattern shown by the solid line is on the top surface of the membrane and the electrode pattern shown by the dashed line is on the bottom surface of the membrane. The top surface of the membrane includes a T-shaped electrode 210 (not drawn to scale) surrounded by a ground plane or ground electrode 214. A substantially identical T-shaped electrode 212 is formed on the bottom surface of the membrane and is located directly below the electrode 210 on the top surface of the membrane. A corresponding ground plane or ground electrode 216 having substantially the same shape as the ground plane electrode 214 is located on the bottom surface of the membrane directly below the ground plane 214 on the top surface of the membrane. In some embodiments, the ground plane electrodes 214, 216 are separated from the positive electrodes 210, 212 by a gap that surrounds the perimeter of the positive electrodes on all sides.

[0028] In some embodiments, the positive electrodes on the top and bottom surfaces of the piezoelectric film, and the negative or ground electrodes on the top and bottom surfaces of the piezoelectric film are electrically connected. In some embodiments, to electrically connect the upper positive electrode 210 to the lower positive electrode 212, one or more vias 220 are filled with conductive epoxy or other conductive material. Similarly, one or more filled vias electrically connect the upper ground electrode 214 to the lower ground electrode 216. The vias can be formed by a laser to burn holes through the piezoelectric film, and then filled with a conductive material such as conductive epoxy. The vias 220 may also remain unfilled if the film is cut into the film before the film is sputtered and may be sputtered. If the frame supporting the stretched piezoelectric film or a part thereof is conductive, the electrodes 214, 216 are electrically connected through the frame, and the vias for the larger negative electrodes 214, 216 can be removed. In the illustrated embodiment, the overlapping T-shaped electrodes 210, 212 are the positive electrodes for the hydrophone, while the overlapping ground planes 214, 216 are electrically grounded. However, the polarities can be reversed.

[0029] In a membrane-type hydrophone, there is a tab portion 212a of the bottom positive electrode 212 under the corresponding-shaped tab portion 214a of the top ground plane electrode 214. The overlap between the two tab portions 212a, 214a forms the active region of the hydrophone, which generates a signal when exposed to acoustic energy. In some embodiments, the overlapping positive and ground electrodes The area is approximately 900 square microns. However, the overlapping region (or active region) of other embodiments of the hydrophone disclosed herein can be between approximately 100 square microns and approximately 10,000 square microns. However, larger or smaller overlapping regions can also be used. The optimal size of the active region depends on the operating frequency of the ultrasonic transducer being analyzed. If the active region is too small, the sensitivity may be too low, resulting in an unacceptable SNR, increased uncertainty, and increased test time. On the other hand, if the active region is too large, spatial averaging can cause inaccuracies that result in unacceptable spatial and spectral uncertainties.

[0030] In the illustrated embodiment, there is a gap 211 between the tab portion 214a of the ground plane 214 and the positive electrode 210 on the upper surface of the membrane. Similarly, there is a gap 213 between the tab portion 212a of the positive electrode 12 and the ground plane 216 around the bottom surface of the membrane. In one embodiment, the gaps 211, 213 are linear such that the overlapping portion (e.g., the active region) of the electrodes is approximately square. In another embodiment, the gaps can be curved such that the active region is approximately circular. Other shapes (e.g., elliptical, star-shaped, etc.) of the active region can also be created with patterning tools.

[0031] In one embodiment, the gaps 211 and 213 have a similar width of approximately 5 um. However, they could be made as small as approximately 1.5 pm up to a length of 100 microns. The gap 211 may have the same width as the gap 213 or a different width. The width of the gap in combination with the length of the active region defined by the regions in the tabs 212a and 214a is adjusted in relation to the gaps 211 and 213, and the effective spot size of the active region can be controlled by considering the abnormal electric field components within the membrane. For example, if a square effective active region is desired, a smaller overlapping length can be employed by decreasing the distance between the proximal edges of the gaps 211 and 213 with respect to the width of the tabs 212a and 214a.

[0032] The conductor 224 connects the signal electrodes 210, 212 to a broadband buffer amplifier (not shown), which amplifies the signal generated by the overlapping regions of the electrodes when exposed to high-frequency ultrasonic signals. In the illustrated embodiment, the conductor 224 is connected to the positive electrode 212 on the lower side of the hydrophone. However, the conductor could be connected to the positive electrode on the upper surface of the hydrophone. In one embodiment, the signal electrodes are capacitively coupled to the broadband buffer amplifier to ensure that there is no DC offset between the signal electrode and the ground electrode. In one embodiment, the signal electrodes may be connected to the input of the broadband amplifier by a series-connected capacitor 226 having a value of about 10 nF. Those skilled in the art will understand that other values can be used depending on the desired frequency and impedance characteristics. In one embodiment, the ground planes 214, 216 are shorted to the frame that supports the film with solder. The signal from the amplifier can be carried by a coaxial cable, or other electrical conductor, to receiving electronics (not shown) that stores and analyzes the signal to characterize the beam pattern generated by the ultrasonic transducer. As shown in FIG. 5A, the completed membrane-type hydrophone is fixed to the post 228, and this post can be attached to a movable stage arranged at various positions with respect to the transducer to which the hydrophone is to be tested. FIG. 5A is drawn more enlarged and reduced, and in the illustrated embodiment, the length of the T-shaped electrode is approximately 7.5 mm, while the length of the overlapping electrode portion is approximately 30 pm. For comparison, the grains of sand on the beach are 100 pm or more. Therefore, a precise patterning tool is required to accurately form the overlapping regions on the film.

[0033] To create the electrode pattern, the conductive coating on the film is patterned with a laser that removes the conductor without damaging the film itself. In one embodiment, the first laser pulse removes the conductor on the upper surface of the film, and the second pulse at the same position (and on the same side of the film) removes the conductor on the bottom surface of the film. Thus, to fabricate the T-shaped electrode, a double pulse is used for the T-shaped electrode It is used to draw the contours of the shapes of 210 and 212. To form a gap 211 between the end of the T-shaped electrode 210 and the tab portion 214a of the ground plane 214, the size of the laser pulse is set to the desired size of the gap, and a single pulse is used to remove only the conductor on the upper surface of the film when the laser is moved. By accurately controlling the laser pulse, it is guaranteed that the electrode material is removed only on one side of the film, and the electrode on the other side remains without damage.

[0034] To form a gap 213 between the tab portion 212a of the bottom T-shaped electrode 212 and the surrounding ground plane 216, the film is inverted and a single pulse is used to remove the conductor on the bottom surface of the film. Since the film is substantially transparent to both visible and UV light when the conductor is removed, the registration of the film to the laser alignment system is simplified. Furthermore, since the upper and lower electrodes can be patterned from the same side of the film using a laser, the alignment of the upper and lower electrodes is highly accurate. The precise definition of the electrodes and the small and precise gaps 211 and 213 enable a highly accurate and predictable active region, which becomes important as the dimensions of the active region get closer to the thickness of the film, and enables precise control and minimization of the abnormal electric field components.

[0035] It will be understood that the disclosed embodiments use T-shaped electrodes, but other shapes such as "I-shaped" or "L-shaped" electrodes or other shapes can also be used.

[0036] Using double electrodes on both sides of the piezoelectric film has proven to be advantageous, particularly when using a polarization film in the structure of a hydrophone. In the illustrated embodiment, the overlapping electrodes enforce zero (or near zero) electric field conditions in all regions of the film including the signal electrode traces and all regions including the ground electrodes. In some previous embodiments, due to the slight conductivity of water and the sensitive electronics in the buffer circuit connected to the electrodes and the thin piezoelectric film, a hydrophone without double electrodes does not require a ground electrode to generate a signal, and an unramped signal trace can generate spurious signals. This situation is particularly exacerbated by the use of a thin piezoelectric film described as being desirable in hydrophones for high frequency ultrasonic waves where very small amounts of charge are detected in the sensitive electronics required to measure the signal from the active region.

[0037] In another embodiment, it is possible to start with an unpolarized film. Electrodes are created and the active region is spot poled using an appropriate combination of voltage and temperature applied to the active region. Using a non-poling film with a double electrode design and then performing spot poling effectively removes signals outside the very precisely defined active overlap region defined by tabs 214a and 212a, and gaps 211 and 213.

[0038] In the illustrated embodiment, a rectangular or square active region in the electrode design was employed to simplify the laser manufacturing of the hydrophone for development. The disclosed technique can be adapted to manufacture round electrodes as described above. Any electrode shape that can be made through a photoablation laser mask (e.g., even round, square, elliptical, or star-shaped) can be made by removing the metal conductor through the piezoelectric film (registration through the film without cutting the film).

[0039] In some embodiments, to ensure that no conductive metal remains in the area photoablated by the laser, conductor removal is further enhanced by a weak metal etching (e.g., 5% acetic acid) applied to the finished electrode pattern. While it may be possible to remove 100% of the metal electrodes with a laser, it is difficult to fully tune the laser to achieve 100% electrode removal. Thus, in one embodiment, the hydrophone membrane is immersed in a weak chemical etch designed to remove 100 - 200 angstroms of metal, ensuring that any remnants of the electrodes that may have remained after photoablation are removed from the surface of the membrane. As will be understood by those skilled in the art, this chemical etching process can be finely tuned in many ways to optimize material removal as needed. The process ensures that any remaining material from the electrodes that may have been left after photoablation is removed from the surface of the membrane. As will be understood by those skilled in the art, this chemical etching process can be finely tuned in many ways to optimize material removal as needed.

[0040] In addition, in one embodiment, the electrodes on both sides of the membrane may be covered with a thin photoresist or other material resistant to wet etching materials, and the laser may be used to remove both the resist and the conductor material to create the necessary electrode pattern. As will be understood by those skilled in the art, when such a resist layer is used, the wet etching used can be much more aggressive without causing degradation of the desired remaining electrodes. Care must be taken to understand the laser interaction with the photoresist to properly account for the absorption of laser energy by the resist in this method employed in the special gap regions used to create the overlapping electrode regions 212a and 214a. However, the resist can be easily employed in any area where both the top and bottom electrodes are to be removed with multiple laser pulses. However, the wet etch must be carefully selected to ensure chemical and thermal compatibility with the thin polymer membranes used in the configuration of the micro - aperture hydrophones described herein.

[0041] The technology disclosed herein enables the removal of a substantially completely registered area of electrode material from both the front and back sides of a hydrophone by controlling the characteristics of a laser used to remove the electrode material such that the conductors on the front and back sides of the membrane can be removed from the same side of the membrane. This allows for the creation of a substantially entire electrode pattern from one side of the membrane in order to ensure sub-micron accuracy on the front side of the hydrophone relative to the back side of the hydrophone.

[0042] In some embodiments, the disclosed technology also includes vias for electrically connecting overlapping electrodes from the front side to the back side. The vias can be created with a laser or other means, and a conductive epoxy or other conductive means (sputtering, wire, etc.) used to conductively connect the front electrode and the back electrode. Means other than vias (e.g., wire) can be used to electrically connect the electrodes on one side to the corresponding electrodes on the other side, but the vias enable the creation of a connection with very low impedance and low inductance by simply cutting using a laser in a membrane that has little or no mechanical stress. Such low inductance and low impedance connections ensure that the membrane can be clamped to a nearly zero electric field between the electrodes, even under high dynamic RF conditions.

[0043] After the electrode pattern and vias are completed, one embodiment covers the rear electrodes with a polymer elastomer 126 such as silicone as shown in FIGS. 5B and 6, covering the rear or bottom electrodes. As those skilled in the art will understand, some silicones have very good acoustic matching to water and very high electrical insulation properties that prevent the signal electrodes from generating any spurious acoustic signals within the region of a single electrode separation band, but have relatively high acoustic losses at high frequencies. Also, silicone serves to protect the electrodes and the membrane from wear and damage, significantly increasing the rigidity of the membrane and enabling faster scanning and less stringent vibration reduction specifications for the scanning system. Epoxies or engineering plastics that match well with water such as TPX or LDPE, or elastomers such as polyurethane or latex materials, or other polymers such as specially developed acoustic polymer materials can be used as acoustic backing or coating as long as they match well with water and can be applied to the thin hydrophone membrane with low stress (e.g., poured in liquid form and cured in place).

[0044] As shown in FIG. 5B, in some embodiments, a portion of the positive electrode on the top surface of the membrane is also covered by the acoustic matching elastomer 126. In one embodiment, the elastomer is applied to the top electrode using a toothpick or other small applicator under a microscope. However, it will be understood that other precision material deposition tools can be used. In the illustrated embodiment, there is no acoustic matching elastomer across the active region of the hydrophone. In one embodiment, the electrodes are patterned on the coated P(VDF TrFE) membrane using a UV laser adjusted to remove electrode material in a first pulse from the front of the membrane and in a second pulse from the back of the membrane, with the membrane itself remaining undamaged. The single front electrode from the membrane

[0045] ​Remove an area and insulate the signal electrode from the ground plane / electrode on the front side of the membrane. Then, turn the membrane over and align it visually with the pattern on the rear of the membrane (produced by laser ablation through the transparent membrane). Once aligned, a single area of the rear electrode is removed and the signal electrode is insulated from the ground plane / electrode on the rear side of the thin film. A part of the ground electrode pattern on the front side of the membrane overlaps a part of the signal electrode pattern on the back side of the membrane (or vice versa). This is the only place on the membrane where the signal electrode and the ground electrode overlap. There are only two places on the membrane where electrodes exist and do not overlap (e.g., small isolation regions or gaps 211 and 213 that define the overlapping electrodes).

[0046] In one embodiment, the conductive material is Cr / Au applied with a thickness of 1900 angstroms (other conductive materials and thicknesses can be used). The conductive material is removed from both the front and rear sides of the membrane by ablation with an excimer laser acting through a mask and a 10x reduction optical system from one side of the membrane. The laser wavelength is set to 248 nm and the fluence is selected to be below the ablation threshold of the membrane. In one embodiment, the fluence is selected to be 0.25 J / cm2. This pulse characteristic allows the electrode material to be removed from the front side of the membrane in a single pulse without affecting the electrode on the rear side. Then, a second identical pulse is used to remove the conductive material from the rear side of the membrane. This is done without adversely affecting the membrane itself. This approach removes the problem of aligning the edges of the overlapping electrodes on opposite sides of the membrane.

[0047] Other combinations of laser power, wavelength, and fluence can be used to remove the top electrode without affecting the bottom electrode, or to remove both the top and bottom electrodes. The goal is to use laser pulses that are not strongly absorbed by the polymer film used in the piezoelectric element, but are strongly absorbed by the electrode material. In one embodiment, a 248 nm excimer laser with a pulse duration of -15 ns was used. Additionally, by using photoablation, complex patterns can be focused onto the film, thereby creating gaps in a single pulse.

[0048] According to one embodiment of the disclosed technology, a membrane-type hydrophone for high-frequency ultrasonic waves includes a piezoelectric film having a conductive material on its opposite side. If it is desirable to fabricate electrodes by removing the conductor from each side of the film, it is advantageous to form one or more registration features in the front and back electrode materials by front resection and back membrane-penetrating resection, ensuring excellent registration of the reference points on the front and back sides. The first side of the piezoelectric film includes a first electrode pattern formed by removing a portion of the conductive material. The second side of the piezoelectric film includes a second electrode pattern formed by removing a portion of the conductive material. The first and second electrode patterns overlap in the active region of the hydrophone.

[0049] In some embodiments, it is advantageous to "depolarize" the piezoelectric film in regions excluding the active region of the hydrophone. FIG. 7 shows a portion of a piezoelectric film 300 that is treated by a laser over region 302 in a manner that reduces the piezoelectric response of the film. In one embodiment, the treatment is performed in all regions excluding the active region of the hydrophone. The treatment is performed before applying a conductive coating onto the film. In one embodiment, once the electrode pattern is formed, one or more reference points 310, 312 are created within the film so that the active region of the hydrophone can be formed in the region that was left untreated.

[0050] The treatment performed by the laser modifies the piezoelectric film so that the film is less responsive to the acoustic energy it receives. This reduces artifacts created by regions of the electrodes other than those created by the active region. In one embodiment, the treatment within region 302 is performed by patterning the piezoelectric film with a series of pulses at a laser fluence of 0.5 - 1 J / cm2 and a pulse repetition frequency of about 20 Hz for about 15 ns. is done.

[0051] Figure 8 shows a circuit for receiving and buffering a signal generated by a hydrophone before being transmitted to processing electronics within a remote computer system (not shown). The circuit includes a buffer amplifier 400 which, in one embodiment, is an integrated circuit (model number AD8045 from Analog Devices) connected in unity gain configuration with a positive input connected to the positive electrode of the hydrophone via capacitor 226. The negative electrode of the hydrophone is connected to the ground connection of the printed circuit board. Coaxial cable 406 is used to carry the signal amplified by buffer amplifier 400 to further signal processing circuitry (preamplifier, A / D converter, DSP, etc.), and the positive and negative voltage supplies for the buffer amplifier, as well as the ground connection for the printed circuit board on which the buffer amplifier is mounted, are supplied via separate wires. In a particular embodiment, a differential amplifier configuration can be incorporated into the circuit configuration shown in Figure 8. In one embodiment, a printed circuit board carried by the support 126 of the hydrophone. The entire circuit board is potted in a waterproof sealant so that the circuit operates underwater.

[0052] Figure 9 is a diagram showing an alternative embodiment of a hydrophone configured according to an embodiment of the disclosed technology. In this embodiment, the grid hydrophone includes a number of thin electrodes on each surface of the membrane. The individual electrodes overlap each other at a number of positions that form a number of active regions of the hydrophone. In the illustrated embodiment, a number of positive electrodes 500a, 500b, ··· 500f are patterned on one side of the membrane, and a number of negative electrodes are formed on the other side of the membrane. The active regions of the hydrophone are formed at each position where the positive electrode overlaps the negative electrode. As will be appreciated, each of the electrodes must be individually connected to either a separate buffer amplifier or a common buffer amplifier using a multiplexer or the like.

[0053] The array-type hydrophone shown in FIG. 9 allows multiple locations to be sampled by selecting which positive and negative electrodes to connect to the receiving electronic device and whether it is necessary to move the hydrophone itself. In one embodiment, the overlapping electrodes can be fabricated by patterning each side of the membrane or by patterning regions that require removal from both sides of the material from a single side of the membrane as described above.

[0054] Since higher frequency ultrasonic waves are finding additional clinical uses, it will be necessary to test high frequency ultrasonic transducers to confirm that they are safe for use on patients. The disclosed technology enables the membrane-type hydrophone to be manufactured with sufficiently small active regions so that it can be used to analyze the beam patterns from these high frequency ultrasonic transducers having center frequencies of 20 - 50 MHz or higher. In other embodiments, the high frequency can be 15 MHz or higher.

[0055] Figure 10 is a diagram showing a hydrophone assembly according to a particular non-limiting embodiment of the disclosed subject matter. As described above, the hydrophone can be constructed by suspending a piezoelectric diaphragm over a dielectric membrane that can vibrate across a desired bandwidth. The piezoelectric body can be plated with a conductive material, thereby generating electrodes on each surface of the piezoelectric body. Next, the active region can be cut into the plating on both sides of the piezoelectric material to form a separation between the region capable of generating signals and the remaining region. The remainder can become part of the electrical reference or ground of the device. The active region can be electrically connected to the hydrophone electronics by a coaxial connection, and the coaxial connection is built into a membrane or film. In certain non-limiting embodiments, the shield can provide the hydrophone electronics amplifier from electrical noise along the signal path. The coaxial connection can be referred to as a connection trace or coaxial connection, and can also be referred to as coaxial or coaxial.

[0056] Figure 10 shows a hydrophone 1000 with a waterproof casing. The casing can be made of, for example, a dielectric, insulating, non-corrosive material. In certain non-limiting embodiments, the hydrophone can be housed within a plastic housing that can prevent water from contacting the electrical components disposed within the hydrophone. Using a non-corrosive material can prevent ions from being released from the casing during submersion. Such ion release can create an undesirable charge in the water, which can thereby affect the hydrophone measurements. The casing can be composed of any available plastic or thermoplastic, such as carbon fiber or elastomer that can include polyurethane. In one example, the casing can be composed, in part or in whole, of VeroWhitePlus, which can provide a watertight casing. For example, VeroWhitePlus can have a tensile strength between 7,250 and 9,450 pounds-force per square inch (psi), shore hardness (D) of 83 to 86, and / or a polymerization density of 1.17 to 1.18 grams per centimeter cube (g / cm3) and can have.

[0057] The casing 1020 shown in FIG. 10 can be formed into a clam shell formation including a lower shell 1021 and an upper shell 1022. In other embodiments, the casing 1020 can be any other shape that encloses the electronic components of the hydrophone. The lower shell 1021 and the upper shell 1022 can be connected using one or more screws 1050. The connection can create a seal between the lower and upper shells 1021, 1022 that can prevent water, in which the hydrophone is submerged, from reaching any of the electrical components or parts contained within the casing 1200. As can be seen from FIG. 11, the lower shell 1021 can include a protrusion 1023 that helps to further waterproof or seal the components of the hydrophone. The protrusion 1023 can be composed of any non-metallic, non-corrosive material, such as room temperature vulcanizing (RTV) silicone.

[0058] The membrane and / or diaphragm assembly 1010 can be attached to any part of or inside the casing 1020, depending on different bandwidths and / or spot sizes. In certain embodiments, the membrane and / or diaphragm assembly 1010 can be included within a separate front-end component 1040 of the casing 1020. In some examples, the membrane and / or diaphragm assembly 1010 can be attached to the front-end component 1040, and the membrane and / or diaphragm assembly 1010 and the front-end component 1040 are modular with respect to the rest of the housing. As shown in FIG. 10, the front-end component 1040 can be attached to the upper shell 1022 of the casing 1020 via one or more screws 1050. The screws can be made of any non-corrosive material. For example, the screws can be made of nylon, a material the same as or similar to the casing 1020, or any other non-corrosive material. In certain non-limiting embodiments, the hydrophone 1000 can be fixed to a post 1060 that can place the hydrophone at various positions with respect to the transducer being tested on a movable stage. The post 1060 serves to attach or connect the hydrophone 1000 to the movable stage and can include one or more vertical threads. Also, the threads can be horizontal, helical, or of any other shape or orientation. In some non-limiting embodiments, the post 1060 can be part of the hydrophone 1000.

[0059] In certain embodiments, the hydrophone 1000 can be manufactured using a 3D printer. For example, the 3D printer can be performed using selective laser sintering, stereolithography, binder jetting, or polyjet. In other embodiments, the hydrophone 1000 can be manufactured using injection molding, machining, such as CNC machining, forming, or joining.

[0060] FIG. 11 is a diagram showing an exploded view of a hydrophone assembly according to a particular non-limiting embodiment of the disclosed subject matter. In particular, FIG. 11 illustrates a lower shell 1021 including a protrusion 1023 that connects to an upper shell 1022. The protrusion 1023 can serve as a joining ridge between the lower shell 1021 and the upper shell 1022. The lower and upper shells 1021, 1022 can be connected using one or more screws 1050. For example, as shown in FIG. 11, eight screws 1050 are used. In the embodiment shown in FIG. 11, four screws 1050 can be attached to connect the lower shell 1021 to the upper shell 1022, while four screws can be used to attach the front end component 1040 to the upper shell 1022. In other embodiments, any number of screws or other attachment members can be used to attach the bottom and upper shells 1021, 1022. In some embodiments, screws cannot be used, and the casing can alternatively include a press-fit mechanism and / or a snap-lock mechanism. In other non-limiting embodiments, the front end component 1040 can be molded up to the upper shell 1022. The lower shell 1021 may include one or more protrusions 1024 that can be inserted into cavities within the upper shell 1022. For example, one or more protrusions 1024 can help align the lower shell 1021 with the upper shell 1022 and / or the printed circuit board 1070.

[0061] The electrical components of the hydrophone 1000 can be housed between the lower shell 1021 and the upper shell 1022. In certain non-limiting embodiments, the lower shell 1021 can include a cavity in which at least a portion of the electrical components are housed. The electrical components can include, for example, a buffer circuit 1070, one or more signal coaxial cables and / or shielded power cables 1030 connected to the buffer circuit 1070, and one or more coaxial vertical spring pins 1080 used to connect the buffer circuit 1070 to the membrane and / or diaphragm assembly 1010 through two holes in the upper shell 1022. FIG. 11 shows the use of two spring pins, but in certain embodiments, only a single spring pin is used. The membrane and / or diaphragm assembly 1010 can be disposed between the front-end component 1040 and the upper shell 1022. As shown in the embodiment of FIG. 11, the membrane and / or diaphragm assembly 1010 can be disposed within a cavity provided within the upper shell 1022. In some examples, the shape and / or design of the hydrophone 1000 can help reduce the area between the active region, such as the buffer circuit board 1070, and the electronics of the hydrophone. In some non-limiting embodiments, the interior of the housing can be electrically shielded around the circuit board 1070. For example, a metallization layer can be provided on the inner surface of the housing cavity. The metallization layer can be connected to electrical ground in one example, and in other examples, the metallization layer is not connected to electrical ground.

[0062] In certain non-limiting embodiments, the membrane and / or diaphragm assembly 1010 and / or the front-end component 1040 can be removed and replaced by removing the screws 1050. The membrane and / or diaphragm assembly 1010 , can be replaced with different membranes that can have different amplification or impedance characteristics. In other words, the hydrophone 1000 can allow for the selective removal and replacement of the membrane and / or diaphragm assembly 1010 based on one or more electrical characteristics of the membrane or diaphragm assembly 1010 and / or the piezoelectric diaphragm suspended therein.

[0063] The materials of the hydrophone casing 1020, the protrusion 1023, and / or the screw 1050 are selected so that no water enters any of the electrical components of the hydrophone 1000. The materials can also be selected to limit or prevent any acoustic impedance caused by the materials. In other words, the materials can help limit or prevent any distortion or reflection of the transducer signal detected by the hydrophone 1000. For example, the acoustic impedance of the materials can match or closely match the impedance of the water in which the hydrophone is submerged. For example, closely matching can mean that the impedance can be 4 megarayls or less, or any other value.

[0064] FIG. 12 is a diagram showing an example of a hydrophone membrane and diaphragm assembly according to a particular non-limiting embodiment of the disclosed subject matter. In particular, the hydrophone membrane and / or diaphragm assembly 1200, which may be referred to as a membrane assembly, may be similar to the membrane and / or diaphragm assembly 1010 shown in FIGS. 10 and 11. As described above, the membrane assembly 1200 can be used to convert the detected acoustic signal into an electrical signal that can be processed by a remote computer system. For example, as shown in FIG. 12, the membrane assembly 1200 may include a frame 1210 having a membrane film 1220 located therein. The membrane film 1220 can be an insulating member. The membrane assembly 1200 may include a member 1230 attached to a conductive layer and / or a piezoelectric body. The active region can be located within the outer diameter of the member 1230.

[0065] In addition, the membrane assembly 1200 may include a coaxial trace 1240 for connecting an active region located within the member 1230 to the back of the frame 1250. The back of the frame 1250 can provide an electrical connection between the active region and the hydrophone electronics, as shown in FIG. 11. The back of the frame 1250 can be electrically connected to the buffer circuit 1070 using one or more coaxial vertical spring pins 1080. The member 1230 and / or the coaxial trace 1240 can be sputtered one or more times with a conductive trace such as gold. The membrane assembly 1200 may include one or more layers sputtered with gold, gold and chromium, and / or any other conductive material.

[0066] In certain embodiments, the coaxial trace 1240 shown in FIG. 12 may be a built-in coaxial layer, also referred to as a coaxial layer or intermediate layer, which helps transmit electrical signals from the active region. In some embodiments, the hydrophone membrane and diaphragm assembly 1200 can include one or more additional layers such as a dielectric, insulating layer, and / or other coaxial layers that help shield the built-in coaxial layer. One or more dielectric layers and / or insulating layers can be composed of, for example, an adhesive.

[0067] As shown in FIG. 12, the member 1230 can be attached or disposed on top of the piezoelectric body. The member 1230 can be, for example, a semi-annular body, also referred to as a semi-ring or semi-donut, spherical, or any other spherical or non-spherical shape. The member can have, for example, an inner diameter of 150 micrometers (μm), or can have an inner diameter of 200 - 300 μm.

[0068] FIG. 13 is a diagram showing an example of a hydrophone membrane according to a particular non-limiting embodiment of the disclosed subject matter. In particular, FIG. 13 illustrates a membrane film 1310 similar to the membrane film 1220 shown in FIG. 12. The membrane film 1310 is, for example, a polyimide such as Kapton It can be composed of a film. In certain embodiments, the membrane film 1310 can be stretched across and adhered to the membrane frame. The membrane frame can be attached to the rest of the hydrophone housing. One or more holes 1320 for electrical connection can be cut in the membrane film 1310. The vias can be disposed within one or more of the holes 1320. The vias can be sputtered, for example, with a conductive material to enable connection at a certain interval between conductors on either side of the membrane. The vias 1320 can be used to electrically connect one or more layers or parts of the membrane assembly to the built-in coaxial layers. The membrane film 1310 can be an insulating layer including a central opening 1330 called an acoustic aperture that can pass sound waves. The active region of the piezoelectric body can be located within the central opening or hole 1330.

[0069] FIG. 14 is a diagram showing an example of a hydrophone membrane according to a particular non - limiting embodiment of the disclosed subject matter. The active region of the hydrophone membrane can be located within the hole of the member 1430. In some other embodiments, the holes included within the member 1430 can be filled. In the exemplary embodiment shown in FIG. 15, the diaphragm or membrane film located under the hole of the member 1430 can be metallized or made conductive so as to act as a ground or shield. As shown in FIG. 12, the member 1430 is attached, connected, or disposed to the conductive layer or piezoelectric body. In a particular non - limiting example, the member 1430 may include an adhesive or any other non - conductive material. Then, in certain embodiments, the member 1430 can be plated with a conductive trace such as gold. In other words, the member 1430 can be sputtered with gold. The member 1430 has a donut shape, but in certain other embodiments, the member can assume any other shape, whether spherical or non - spherical.

[0070] The central coaxial layer 1440 can be disposed between the member 1430 and the back of the frame 1450 and can be used to connect the active area to other electrical components of the hydrophone. In particular, the signal trace 1420 can span from the active area over the top surface of the member 1430, along the central coaxial layer 1440, across the vertical plane of the frame, and directly across a portion of the back of the frame 1450. The signal trace can be composed of, for example, a conductive material and can be referred to as an electrode pattern. Thus, a portion of the frame can be plated to create a trace that can be connected to the electronics of the hydrophone.

[0071] In the embodiment shown in FIG. 14, the signal trace 1420 can be V-shaped and the width of the signal trace can become narrower as it approaches the active area. However, in other embodiments, the signal trace 1420 can take any other shape. The rear portion of the frame 1450 can include a cutout that contours around the signal trace 1420. The outline can be cut, for example, using a laser. The signal trace 1420 can be located within the outline, while the ground trace 1410 can be located outside the outline. The ground trace 1410 can also be referred to as a shield or zero-volt trace. In certain non-limiting embodiments, the dielectric insulator and / or the upper coaxial layer can cover at least a portion or all of the signal trace or the ground trace.

[0072] FIG. 15 is a diagram showing an example of a diaphragm according to a particular non-limiting embodiment of the disclosed subject matter. In particular, FIG. 15 illustrates a close-up of a cross-section of the member 1430 outlined by the rectangular dashed line shown in FIG. 14. As shown in FIG. 15, the active area 1460 can be substantially square or rectangular in shape. In one non-limiting example, the length of the active area can be 20 μm, while the width of the active area can be 20 μm. In other words, the active area can be 400 square micrometers. Also, the active area can be of any other size or shape, such as circular or any type of polygon This is also possible. In some non-limiting embodiments, the shape of the active region may depend on the tool used to cut the active region during the manufacturing process. In other examples, the active region can be cut by plating on both sides of the piezoelectric material to create a separation between the region that generates the signal and the remaining region. The square active region 1460 shown in FIG. 15 can be a region of the piezoelectric body that generates a signal.

[0073] In certain non-limiting embodiments, the active region 1460 can be located inside a hole or opening in the member 1430. The opening in the member 1430 can expose a diaphragm or membrane film. The hole can be an acoustic aperture and can allow pressure waves to pass through. The signal trace can connect the active region 1460 within the hole to the remaining electronics of the hydrophone. For example, the signal trace can start at the active region 1460, extend beyond the outer boundary of the member 1430, and continue along the coaxial layer 1440 to the rear of the frame 1450. In some non-limiting embodiments, one or more coaxial vertical spring pins 1080 used to connect the buffer circuit 1070 to the signal trace 1420 can be used to connect the rear portion of the frame 1450 to the buffer circuit board. The spring pins can electrically connect the buffer circuit to the coaxial layer.

[0074] After the membrane assembly is completed or assembled, it can be attached to the housing of the hydrophone to which the electronics are attached. For example, as shown in FIGS. 10 and 11, the membrane assembly can be attached to the front-end component 1040 of the casing 1020. The membrane assembly can then be electrically connected to the remaining hydrophone components, for example, using one or more coaxial vertical spring pins 1080 that protrude through the housing and are directed and connected to the board 1070. In other embodiments, any other pins, plugs, vias, conductive materials, or wires can be used to connect the substrate 1070 to the membrane assembly.

[0075] FIG. 16 is a diagram showing an example of a circuit board according to a particular non-limiting embodiment of the disclosed subject matter. In particular, buffer circuit board 1600 shown in FIG. 16 may be similar to buffer circuit board 1070 shown in FIG. 11. For example, buffer circuit board 1600 can be a printed circuit board used to connect a membrane assembly to the remaining electronic components of the hydrophone. In a particular non-limiting embodiment, buffer circuit board 1600 can include one or more mounting holes 1610 for holding a pair of spring pins 1180, as shown in FIG. 11. In other words, the mounting holes can be provided for electrical connection to signals and / or ground traces coming from the diagraph assembly. The ground plane 1620 included on buffer circuit board 1600 can be smaller than the entire surface of the printed circuit board, as shown in FIG. 16. In other words, the ground plane 1620 of buffer circuit board 1600 can be reduced or minimized.

[0076] FIG. 17 is a diagram showing an example of a circuit according to a particular non-limiting embodiment of the disclosed subject matter. In particular, circuit 1700 can be a buffer circuit incorporated in the hydrophone shown in FIGS. 10 and 11. For example, circuit 1700 can receive and / or buffer one or more signals generated by the hydrophone. As shown in FIG. 17, circuit 1700 includes a reference voltage, also referred to as zero volts (V), ground (GND), or coaxial shield, and a signal voltage from the piezoelectric active region of the hydrophone. Circuit 1700 can also include four resistors shown as R1, R2, Rf, and Rg in FIG. 17. In other embodiments, circuit 1700 can include any number of resistors and capacitors. In a particular non-limiting embodiment, circuit 1700 may include a differential amplifier.

[0077] Particular embodiments disclose one or more methods of manufacturing a hydrophone. For example, the manufacturing The manufacturing method can include stretching a thin film across a frame. The method can also include disposing a piezoelectric body on the film and selectively removing a portion of the piezoelectric body to create an active region. The member can, in some examples, be disposed on the piezoelectric body, and the member includes an opening that exposes the piezoelectric body. Further, the method can include connecting a coaxial layer to the active region. In some non-limiting embodiments, the film can be attached to the frame and / or the built-in coaxial layer can be disposed on the film frame. A plurality of vias can be disposed to electrically connect the film and the coaxial layer. The method can also include connecting an insulating layer to the coaxial layer.

[0078] In addition to the specific embodiments claimed below, the disclosed subject matter is also directed to other embodiments having the dependent features claimed below and any other possible combinations of the features disclosed above. As such, the specific features presented in the dependent claims and disclosed above can be combined in possible combinations with each other. Accordingly, the foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be limiting or exhaustive of the disclosed subject matter to the embodiments disclosed.

[0079] In the detailed description herein, references to "embodiment", "embodiments", "one embodiment", "various embodiments", "specific embodiments", "some embodiments", "other embodiments", "specific other embodiments", etc. indicate that the described embodiments (the "plurality") can include certain features, structures, or characteristics, but not all embodiments necessarily include the certain features, structures, or characteristics. Further, such phrases do not necessarily refer to the same embodiment. Further, when a certain feature, structure, or characteristic is described in relation to an embodiment, it is submitted that it is within the knowledge of those skilled in the art to effect such feature, structure, or characteristic in relation to other embodiments, whether or not such feature, structure, or characteristic is explicitly described. After reading the description, the manner of implementing the disclosure in alternative embodiments will be apparent to those skilled in the relevant art (the "s").

[0080] From the above, it will be understood that the specific embodiments of the present invention have been described herein for purposes of illustration, but various modifications may be made without departing from the scope of the present invention. Accordingly, the present invention is not limited except as by the appended claims.

Claims

1. A hydrophone for measuring acoustic energy from a high-frequency ultrasonic transducer, comprising: a frame; a membrane assembly supported by the frame and comprising a piezoelectric body; an electrode pattern formed on the piezoelectric body to define an active region; a membrane film made of an insulating member and attached to the frame, the membrane film exposing the active region; a built-in coaxial layer disposed in the central portion of the membrane film as viewed in the plane of the membrane film, connecting the active region to the frame and disposed in the membrane film; a hydrophone.

2. The hydrophone according to claim 1, further comprising an insulating layer connected to the coaxial layer.

3. The hydrophone according to claim 1, further comprising a plurality of vias for electrically connecting the membrane film and the built-in coaxial layer.

4. The hydrophone according to claim 1, wherein the membrane film includes an acoustic aperture.

5. The hydrophone according to claim 2, wherein the insulating layer covers at least a part of a ground trace of the built-in coaxial layer.

6. The hydrophone according to claim 1, further comprising a member disposed on the piezoelectric body, the member including an aperture for exposing the piezoelectric body.

7. The hydrophone according to claim 6, wherein the active region is located inside the aperture of the member.

8. The hydrophone according to claim 6, wherein at least one of the member or the built-in coaxial layer is sputtered.

9. The hydrophone according to claim 1, wherein the hydrophone comprises a waterproof casing.

10. A method of manufacturing a hydrophone for measuring acoustic energy from a high-frequency ultrasonic transducer, the method comprising: stretching a membrane film across the frame; disposing a piezoelectric body on the membrane film; attaching a membrane film made of an insulating member to the frame; selectively removing a part of the piezoelectric body to generate an active region disposed in the central portion of the membrane film as viewed in the plane of the membrane film, and connecting the active region to the frame by a coaxial layer; disposing the coaxial layer in the membrane film; a method including.

11. The method according to claim 10, further comprising connecting an insulating layer to the coaxial layer.

12. The method according to claim 10, further comprising disposing a plurality of vias for electrically connecting the membrane film and the coaxial layer.

13. The method according to claim 10, wherein the membrane film includes an acoustic aperture.

14. The method according to claim 11, further comprising covering at least a part of the ground trace of the coaxial layer with an insulating layer.

15. The method according to claim 10, further comprising disposing a member on the piezoelectric body, the member including an aperture exposing the piezoelectric body.

16. The method according to claim 15, wherein the active region is located inside the aperture of the member.

17. The method according to claim 15, wherein at least one of the member or the coaxial layer is sputtered.

18. The method according to claim 10, wherein the hydrophone comprises a waterproof casing.

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