CN114423530A

CN114423530A - Membrane hydrophone for high-frequency ultrasonic waves and manufacturing method thereof

Info

Publication number: CN114423530A
Application number: CN202080066543.7A
Authority: CN
Inventors: 奥列格·伊凡尼斯基; 庞国锋; 亚历山大·布尔霍; 马吕斯·摩斯基金斯基; 尼古拉斯·克里斯托弗·沙格尔
Original assignee: Fujifilm Sonosite Inc
Current assignee: Fujifilm Sonosite Inc
Priority date: 2019-09-23
Filing date: 2020-09-23
Publication date: 2022-04-29
Anticipated expiration: 2040-09-23
Also published as: JP2022551418A; CN114423530B; WO2021061779A1; EP4034307A4; EP4034307A1

Abstract

A hydrophone for measuring acoustic energy from a high frequency ultrasonic transducer, or a method of making a membrane hydrophone. The membrane assembly is supported by the frame and includes a piezoelectric body. The hydrophone also includes an electrode pattern formed in the piezoelectric body to define an active region. In addition, the hydrophone includes a built-in-situ coaxial layer connected to the active region.

Description

Membrane hydrophone for high-frequency ultrasonic waves and manufacturing method thereof

Cross Reference to Related Applications

The present application claims united states provisional application No. 62/206,808 filed on 8/18/2015, united states provisional application No. 62/297,763 filed on 2/19/2016, united states non-provisional application No. 15/241,021 filed on 8/18/2016, and united states non-provisional application No. 16/579,348 filed on 9/23/2019, which are incorporated herein by reference in their entirety.

Technical Field

The disclosed technology relates to hydrophones for testing ultrasonic transducers, and more particularly to hydrophones for testing high frequency ultrasonic transducers.

Background

Ultrasound imaging operates by transmitting a plurality of short pulses of acoustic energy from a transducer to a region of interest and collecting the information contained in the corresponding echo signals. Fig. 1A shows a simplified ultrasound transducer having a plurality of individual transducer elements 12 (not drawn to scale). When a varying voltage is provided across the elements, the transducer elements vibrate and generate an ultrasonic acoustic signal. When the element receives acoustic energy, the element also generates an electrical signal. The elements 12 are typically arranged in a one-or two-dimensional array, including one or more matching layers 14 and a fixed lens 16. By carefully selecting the amplitude and time at which the drive signals are applied to each transducer element, the acoustic signals combine constructively to form a beam with a focal zone at the desired location. As the transducer operating frequency increases, the size of the focal zone (typically the shape of a rice grain) decreases. For example, at a 15MHz center frequency, the size of the focal zone is about 500x 300 pm. At 30MHz, the size of the focal region drops to approximately 280x150 pm. At 50MHz, the size of the focal region is less than 200x100 pm. In addition to an ultrasound array, the ultrasound signals may also be generated by a single element transducer 17 as shown in FIG. 1B.

Ultra High Frequency (UHF) diagnostic ultrasound has made significant advances in the preclinical and clinical industries over the last 10 years, introducing systems with a 50MHz center frequency array, whose upper angular frequency exceeds 70 MHz. Many new scientific and medical possibilities can be explored due to the higher resolution and bandwidth of UHF ultrasound, but new testing and characterization challenges come with new applications and capabilities. As those skilled in the art will appreciate, as transducer frequencies become higher, the wavelengths decrease accordingly, and various other mechanisms, such as nonlinear propagation of sound waves in water, become more prevalent. Currently, there is a need to understand the characteristics of UHF ultrasound in water for scientific and medical and preclinical device surveillance purposes. Furthermore, in order to take advantage of modern complex FEA modeling, it is necessary to accurately measure the sound field at or even below the array pitch. There is clearly a need for smaller aperture hydrophones with higher frequency calibration to ensure accurate measurement of harmonics and to reduce spatial uncertainty caused by short wavelength acoustic waves measured by relatively large aperture hydrophones.

Acoustic energy generated by an ultrasound transducer must be characterized before the transducer is approved for clinical use by the Food and Drug Administration (FDA) in the united states or a CE marker for clinical use in europe. This characterization generates a pressure intensity map to ensure that the focal region is well defined and that the transducer does not create energy hot spots at undesired locations. Similarly, the characterization confirms that the energy generated is not so great as to cause cavitation in the tissue being examined, and that the power output is within acceptable ranges specified for various tissues. There are well established standards that specify the test protocols and results required for regulatory approval. However, UHF ultrasound is increasingly pushing these tests to and even beyond limits due to the lack of suitable small hydrophone aperture sizes and sufficiently high frequency calibration data.

As shown in FIG. 2, most transducer tests are performed by operating the transducer 20 in a liquid bath 40 (typically degassed water, but could be another liquid). The hydrophone 50 is placed on a computer console (not shown) in the path of the ultrasound beam. As the transducer is operated, the stage is moved to cause the hydrophones to measure the beam intensity at the location of the focal zone and at a plurality of locations. The signals from the hydrophones are stored by the computer system to confirm that the transducer is operating as intended. The intensity measurement map in space defines the characteristics of the ultrasound transducer beam.

Membrane hydrophones are best suited for sampling ultrasound beams because of their flat frequency response and simple interaction with the radiation pattern produced by the Device Under Test (DUT). To be able to effectively sample the beam, the active region of the hydrophone must be substantially smaller than the focal area of the transducer being examined. In the past, it has been difficult to reliably manufacture a membrane hydrophone with a sufficiently small active area that can be used for testing high frequency ultrasonic transducers. Therefore, the user has to use a needle-type hydrophone. Such hydrophones exhibit undesirable resonances and interactions with the radiation pattern being measured. In addition, specially shaped needle hydrophones are used. Such needle-type hydrophones are designed to minimize unwanted resonances, such as the so-called "lipstick style" hydrophones. However, in practice, it is difficult to accurately manufacture such shapes to a scale small enough for very high frequency ultrasound characterization. The result is that needle hydrophones are less accurate than membrane hydrophones in characterizing high frequency beam patterns.

In view of these problems, there is a need for improved high frequency membrane hydrophones and methods of making such hydrophones.

Disclosure of Invention

To address these and other problems, the technology disclosed herein relates to a novel membrane hydrophone design and method of manufacturing a membrane hydrophone for characterizing high frequency ultrasound transducers. Such characteristics may be used to demonstrate clinical use of the transducer, but may also be used in the development and testing of ultrasound transducer designs. In one embodiment, the hydrophone includes a piezoelectric membrane. The piezoelectric film is stretched over a support structure and coated on both sides with a thin layer of a conductive material, such as gold or gold + chromium. A portion of the conductive material is then removed from each side of the piezoelectric film to create a positive electrode on one side of the film and a negative electrode on the other side of the film. The positive and negative electrodes overlap in a small area defining the active region of the hydrophone. In one embodiment, the active region has a dimension between 10-30 microns in diameter.

In some embodiments, a patterning tool, such as an excimer laser, is used to selectively remove portions of the conductive material from the piezoelectric film to form electrodes on the 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, e.g., without flipping the piezoelectric membrane. In some embodiments, one or more alignment features or fiducials are created in the film to allow accurate placement of the piezoelectric film relative to the coordinate system of the patterning tool. Once aligned, the conductive material can be accurately removed from the film.

In some embodiments, the hydrophone includes positive and negative electrodes that overlap on either side of the piezoelectric membrane, with the positive electrode on one side of the membrane being electrically connected to a corresponding positive electrode on the other side of the membrane. Similarly, the negative electrode on one side of the membrane is electrically connected to a corresponding negative electrode on the other side of the membrane. In some embodiments, the overlapping electrodes are electrically connected with one or more conductive vias. The one or more conductive vias are created in the piezoelectric film with a laser and filled with a conductive material.

The active region of the hydrophone is formed where a portion of the positive electrode on one side of the membrane overlaps the negative electrode on the other side of the membrane.

In some embodiments of the disclosed invention, the device is made of a fully polarized piezoelectric polymer or copolymer film to allow maximum sensitivity by positive polling (poling) of the original patch. This may lead to challenges associated with stray signals detected at locations far from the intended active aperture. In some embodiments of the disclosed technology, the piezoelectric film is fabricated into the device in a non-polarized state, such that the electrodes can be used to spot-polarize the active region. This approach may reduce or eliminate many spurious signals, but may result in reduced sensitivity and spot size variations. In some embodiments, overlapping homopolar electrodes are used to clamp the electric field in the membrane, thereby achieving greater spatial specificity in spot polling (spot poling), resulting in more accurate and predictable active spot sizes.

In some other embodiments, portions of the piezoelectric membrane are selectively depolarized prior to coating with the conductive material to reduce the membrane's electrical response to acoustic energy received at an undesired location, thereby allowing more aggressive polling of the entire piezoelectric membrane (as compared to spot polarization). In one embodiment, the piezoelectric membrane is selectively depolarized in a region away from the active region of the hydrophone. In one embodiment, a laser patterning tool is used to depolarize the piezoelectric membrane, such that the membrane remains mechanically intact but less piezoelectrically efficient in all areas of the hydrophone except the active region, by modifying the polymer with ultraviolet laser energy. In yet another embodiment, unpolarized piezoelectric copolymer films are fabricated into the device, a laser patterning tool is used to modify the film, lower the piezoelectric potential of the film in all areas except the active area, ensure that spot-polling can only effectively occur in the unmodified active area, electrodes are deposited such that they are aligned with the active area and the film is spot-polled. In yet another embodiment, the previous approach is combined with an overlapping homopolar electrode design to achieve a very well-defined active aperture after point polling.

Certain non-limiting embodiments include a hydrophone for measuring acoustic energy from a high frequency ultrasound transducer. The hydrophone may include a frame and a membrane assembly supported by the frame and including a piezoelectric body. The hydrophone may also include an electrode pattern formed in the piezoelectric body to define an active region. Furthermore, the hydrophone may comprise a built-in-situ coaxial layer connected to the active region.

Certain non-limiting embodiments include methods of making hydrophones for measuring acoustic energy from high frequency ultrasound transducers. For example, the method may include stretching a membrane over a frame and placing a piezoelectric body over the membrane. The method may also include selectively removing a portion of the piezoelectric body to create an active region, and connecting an in-situ coaxial cable layer to the active region.

Drawings

FIG. 1A schematically illustrates a beam pattern formed by a conventional ultrasound transducer array;

FIG. 1B illustrates a beam pattern formed by a conventional single element ultrasound transducer;

FIG. 2 illustrates a conventional system for testing an ultrasonic transducer having hydrophones;

FIGS. 3A and 3B illustrate an exemplary high frequency membrane hydrophone, in accordance with embodiments of the disclosed technology;

FIG. 4 illustrates a partial 3D cross-sectional view of a membrane hydrophone constructed in accordance with one embodiment of the disclosed technology;

FIG. 5A shows a completed hydrophone mounted on a support column, in accordance with one embodiment of the disclosed technology;

FIG. 5B shows a portion of an electrode on the top surface of a hydrophone coated with an elastomeric material that is well acoustically matched to water in accordance with embodiments of the disclosed technology;

FIG. 6 illustrates a bottom surface of a hydrophone coated with an elastomer that is well acoustically matched to water in accordance with embodiments of the disclosed technology;

FIG. 7 illustrates how a piezoelectric film may be treated prior to application of a conductor in accordance with another embodiment of the disclosed technology;

FIG. 8 illustrates one embodiment of a buffer circuit for conditioning signals from a membrane hydrophone in accordance with another aspect of the disclosed technology;

FIG. 9 illustrates an arrayed membrane hydrophone with multiple active regions constructed in accordance with another embodiment of the disclosed technology;

FIG. 10 illustrates a hydrophone assembly, in accordance with certain non-limiting embodiments of the disclosed subject matter;

FIG. 11 illustrates an exploded view of a hydrophone assembly, in accordance with certain non-limiting embodiments of the disclosed subject matter;

FIG. 12 illustrates an example of a hydrophone membrane and diaphragm assembly, in accordance with certain non-limiting embodiments of the disclosed subject matter;

FIG. 13 illustrates an example of a hydrophone membrane in accordance with certain non-limiting embodiments of the disclosed subject matter;

FIG. 14 illustrates an example of a hydrophone membrane and diaphragm assembly, in accordance with certain non-limiting embodiments of the disclosed subject matter;

FIG. 15 illustrates an example of a septum in accordance with certain non-limiting embodiments of the disclosed subject matter;

FIG. 16 illustrates an example of a circuit board in accordance with certain non-limiting embodiments of the disclosed subject matter; and

fig. 17 illustrates an example of a circuit in accordance with certain non-limiting embodiments of the disclosed subject matter.

Detailed Description

As will be described in further detail below, the disclosed technology is a membrane hydrophone having one or more small active regions that can be used to characterize high frequency ultrasound transducers. In one embodiment, the membrane is made of a thin film piezoelectric copolymer such as P (VDF-TrFE), for example, having a thickness of between 3 and 12 microns. However, other thicknesses or other piezoelectric materials (e.g., PVDF) may be used. The membrane is preferably stretched across the frame in such a way as to remove any wrinkles from the membrane. In one embodiment, the membrane is held on the outer cuff and then simultaneously stretched around its periphery by the inner cuff. The inner cuff presses a portion of the membrane circumferentially into the groove to stretch it without wrinkling as with a drum head. Once the membrane is stretched, the membrane is adhered to a circular frame mounted within the inner cuff, and the excess membrane outside the frame is cut. The frame is then used to form a portion of the hydrophone. In one embodiment, the frame has a diameter of about 2 cm. But larger or smaller frames may be used.

The frame is mounted to a metal bracket and then a metal conductor, such as gold or gold + chromium (or other metal conductor), is applied by sputtering or other process. In one embodiment, the conductor disposed on the film has a thickness of 1500-. However, thinner or thicker conductor coatings may be used, such as, but not limited to, 300 angstroms to 5000 angstroms.

The conductive coatings on both sides of the membrane are then patterned to form overlapping portions of the conductors on the top and bottom surfaces of the membrane to form the active region of the hydrophone. The overlapping conductive areas must be precisely aligned and in some embodiments on the order of 10-30 microns, which was not possible to reliably manufacture prior to the technique described in U.S. provisional application No. 62/206,808.

Fig. 3A and 3B illustrate one embodiment of a hydrophone 100 constructed in accordance with embodiments of the disclosed technology. The hydrophone 100 comprises a generally circular disc of piezoelectric membrane 102 glued to a circular frame 104, which circular frame 104 is in turn fixed to a support 105. In one embodiment, the support 105 is made of a conductive metal such as titanium. The first electrode 106 is patterned on one side of the piezoelectric film, while the 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 fiducials 108, 110 (not drawn to scale) cut through the piezoelectric film to allow the film to be aligned with a laser patterning system. The registration features may be created with a laser and may have virtually any shape (square, rectangular, cross-shaped, etc.). In one embodiment, the registration features are squares of about 10 microns on each side. The corners of the registration features allow the piezoelectric film to be aligned with sub-micron accuracy.

In the case where both sides of the film are coated with a metallic conductor, an excimer laser or other patterning tool is used to remove portions of the conductive coating from the surface of the piezoelectric film so that the film is relatively unaffected.

In one embodiment, once the electrode pattern is formed on the first side of the film, the film is flipped over and aligned with the patterning tool using the 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 technique, the electrode on a first side of the membrane forms the anode of the hydrophone, while the larger second electrode on the other surface of the piezoelectric membrane is grounded.

In another embodiment, described in detail below, a majority of the electrodes on both sides of the film may be created by exposing a single side of the film to laser energy. In this embodiment, no registration features or fiducials may be required.

A thin wire 120 (e.g., a gold bond wire or silver-plated copper bus wire) may be connected to the first electrode on the film. Furthermore, the bond wire may also be connected to the second electrode, or the frame may be used to connect to the second electrode if the frame 104 and/or the mount 105 are electrically conductive. In one embodiment, the acoustically matched elastomer 126 is cast on the back of the hydrophone. In another embodiment, the matching elastomer may be omitted, leaving both sides of the membrane with the respective electrodes uncovered for maximum sensitivity. In one embodiment, the elastomer 126 is made of silicone rubber with an acoustic impedance closely matching that of water.

In some embodiments, it may be advantageous to mount the buffer amplifier to a printed circuit board placed on the support 105 or to mount the buffer amplifier directly to the membrane of the hydrophone. The buffer amplifier may increase the gain of the generated signal and/or buffer the signal so that it may be carried by a signal cable (not shown). In one embodiment, the hydrophone frame 105 is mated with an SMA or other type of connector 128. The SMA connector 128 is a coaxial connector in which the outer shield is connected to the conductive support 105 or to the negative pole and the centre conductor is connected to the positive pole (or output of the buffer amplifier if used). The connection to the SMA connector may also be reversed if desired.

Another embodiment of a membrane hydrophone is shown in fig. 4. In this embodiment, the conductors on the film are patterned to produce substantially matching electrodes on the top and bottom surfaces of the film. In this embodiment, the two positive electrodes of the top surface and the bottom surface of the piezoelectric film overlap each other, and the two negative electrodes of the top surface and the bottom surface of the piezoelectric film overlap each other. Except for the active region of the hydrophone, the positive electrodes on the top surface do not overlap the negative electrodes on the bottom surface (or vice versa). FIG. 4 is a partial perspective cross-sectional view of a hydrophone 200 with the electrode pattern shown in solid lines on the top surface of the membrane and the electrode pattern shown in dashed lines 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. Substantially identical T-shaped electrodes 212 are formed on the bottom surface of the film and directly below the electrodes 210 on the top surface of the film. 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 located on the top surface of the membrane. In some embodiments, the

ground plane electrodes

214, 216 are separated from the

anodes

210, 212 by a gap on all sides around the perimeter of the anodes.

In some embodiments, the positive electrodes on the top and bottom surfaces of the piezoelectric film are electrically connected to the negative or ground plane electrodes on the top and bottom surfaces of the piezoelectric film. In some embodiments, one or more vias 220 are filled with a conductive epoxy or other conductive material to electrically connect the top positive electrode 210 to the bottom positive electrode 212. A similar one or more filled vias electrically connect the top ground plane electrode 214 with the bottom ground plane electrode 216. The vias may be formed with a laser to burn holes in the piezoelectric film, which are then filled with a conductive material such as a conductive epoxy. Vias 220 may also remain unfilled and sputtered through if they are cut into the film before it is sputtered. If the frame or a portion thereof supporting the stretched piezoelectric film is conductive, the

electrodes

214, 216 may be electrically connected through the frame and vias for the larger

negative electrodes

214, 216 may be eliminated. In the illustrated embodiment, the overlapping T-

electrodes

210, 212 are the anodes of the hydrophones, while the overlapping ground planes 214, 216 are electrically grounded. However, the polarity may be reversed.

In a membrane hydrophone, the tab portion (tab portion)212a of the bottom anode electrode 212 is located below the correspondingly 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. The active region generates a signal when exposed to acoustic energy. In some embodiments, the area of the overlapping positive and ground electrodes is about 900 square microns. However, the overlap region (or active region) of other embodiments of the hydrophones disclosed herein may be between about 100 square microns and about 10,000 square microns. However, larger or smaller overlap regions may also be used. The optimal size of the active region depends on the operating frequency of the ultrasound transducer to be analyzed. If the active area is too small, the sensitivity may be too low, resulting in unacceptable SNR, increased uncertainty, and increased test time. On the other hand, if the active area is too large, spatial averaging may lead to inaccuracies, resulting in unacceptable spatial and spectral uncertainties.

In the embodiment shown, there is a gap 211 between the tab portion 214a of the ground plane 214 and the anode 210 on the top surface of the film. Similarly, there is a gap 213 between the tab portion 212a of the positive electrode 12 and the surrounding ground plane 216 on the bottom surface of the membrane. In one embodiment, the

gaps

211, 213 are straight such that the overlapping portions of the electrodes (e.g., the active regions) are generally square. In another embodiment, the gap may be curved such that the active region is generally circular. Other shapes of active regions (oval, star, etc.) may also be created using the patterning tool.

In one embodiment,

gaps

211 and 213 have a similar width of about 5 μm. However, they may be as small as about 1.5pm, up to 100 microns. Gap 211 may have the same width as gap 213 or they may be different widths. The width of the gap, in combination with the length of the active region defined by the footprint of tabs 212a and 214a, can be adjusted in conjunction with

gaps

211 and 213 to control the effective spot size of the active region by taking into account non-normal field components within the film. For example, if a square effective active area is desired, a smaller overlap length may be employed by reducing the distance between the proximal edges of

gaps

211 and 213 relative to the width of tabs 212a and 214 a.

Electrical conductors 224 connect the

signal electrodes

210, 212 to a broadband buffer amplifier (not shown). The broadband buffer amplifier amplifies a signal generated by the overlapping region of the electrodes when exposed to a high frequency ultrasound signal. In the illustrated embodiment, the conductor 224 is connected to the anode 212 on the underside of the hydrophone. However, the conductor may be connected to the positive pole on the top surface of the hydrophone. In one embodiment, the signal electrode is capacitively coupled to a broadband buffer amplifier to ensure that there is no DC offset between the signal electrode and the ground electrode. In one embodiment, the signal electrode may be connected to the input of the broadband amplifier by a series capacitor 226 having a value of about 10 nF. Those skilled in the art will appreciate that other values may be used depending on the desired frequency and impedance characteristics. In one embodiment, the ground planes 214, 216 are shorted to a frame that supports the membrane with solder. The signal from the amplifier may be transmitted to receiving electronics (not shown) via a coaxial cable or other electrical conductor. The receiving electronics store and analyze the signals to characterize the beam pattern produced by the ultrasound transducer. The completed membrane hydrophone is mounted on a column 228, as shown in FIG. 5A. The posts 228 allow the hydrophones to be mounted in a movable stage that is positioned at different locations relative to the transducer being measured. Fig. 5A is drawn to scale and in the embodiment shown, the length of the T-shaped electrode is about 7.5mm and the length of the overlapping electrode portion is about 30 μm. In contrast, one beach sand is 100pm or greater. Therefore, a precise patterning tool is required to accurately form the overlapping region on the film.

To create the electrode pattern, the conductive coating on the film is patterned with a laser. The laser removes the conductor without damaging the film itself. In one embodiment, a first laser pulse removes the conductor on the top surface of the film and a second pulse at the same location (and on the same side of the film) removes the conductor on the bottom surface of the film. To create the T-shaped electrodes, double pulses are therefore used to outline the shape of the T-shaped

electrodes

210, 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 top surface of the film as the laser is moved. Precise control of the laser pulses ensures that only the electrode material on one side of the film is removed leaving the electrode on the other side intact.

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. Registration of the film with the laser alignment system is simplified because the film is substantially transparent to both visible and ultraviolet light when the conductor is removed. Furthermore, since most of the top and bottom electrodes can be patterned from the same side of the film using a laser, the alignment of the top and bottom electrodes is very accurate. Accurate electrode definition and

small precision gaps

211 and 213 allow for highly accurate and predictable active regions, which is critical as the active region dimensions become closer to the thickness of the film, allowing for precise control and minimization of non-normal electric field components.

Although the disclosed embodiment uses T-shaped electrodes, it should be understood that other shapes, such as "I-shaped" or "L-shaped" electrodes, or other shapes may be used.

The use of dual electrodes on both sides of the piezoelectric film has proven advantageous, particularly when using pre-polarized films in the construction of hydrophones. In the illustrated embodiment, the overlapping electrodes force a zero (or near zero) electric field condition in all areas of the film containing the signal electrode traces and all areas containing the ground electrode. In some of the previous embodiments, it was found that hydrophones without dual electrodes did not require a ground electrode to generate the signal and any undamped signal traces could generate spurious signals due to the slight conductivity of the water and sensitive electronics in the buffer circuit connected to the electrodes and the thin piezoelectric film. This situation is particularly exacerbated when using the thin piezoelectric film required in high frequency hydrophones because of the very small amount of charge detected in the sensitive electronics required to measure the signal from the active region.

In another embodiment, one may start with a non-polarizing film. An appropriate combination of voltage and temperature applied to the active region is used to create the electrodes and spot polarize the active region. The use of a non-polarized sheet in conjunction with a two-electrode design followed by spot polling virtually eliminates signals outside the very precisely defined active overlap region defined by tabs 214a and 212a and

gaps

211 and 213.

In the illustrated embodiment, rectangular or square active regions are employed in the electrode design to simplify laser fabrication of hydrophones for development. The disclosed technique may be adapted to produce circular electrodes as described above. Any electrode shape (e.g., circular, square, oval, or even star) that can be made by photoablation laser masking can be made by removing the metal conductor through the piezoelectric film (by film registration without cutting the film).

In some embodiments, conductor removal is further enhanced by a weak metal etch (e.g., 5% acetic acid) applied to the finished electrode pattern to ensure that no conductive metal remains in the areas that have been photoablated by the laser. While 100% of metal electrodes can be removed with a laser, it is challenging to perfectly tune the laser to achieve 100% electrode removal. Thus, in one embodiment, the hydrophone membrane is immersed in a weak chemical etchant. The weak chemical etchant is designed to remove 100-200 angstroms of metal, ensuring that any electrode residue that may remain after photoablation is removed from the film surface. As will be appreciated by those skilled in the art, the chemical etching process can be fine tuned in a number of ways to optimize material removal as desired.

Further, in one embodiment, the electrodes on both sides of the membrane may be coated with a thin photoresist or other material that is resistant to wet etch materials, and a laser may be used to remove both the photoresist and the conductor material to produce the desired electrode pattern. As will be appreciated by those skilled in the art, when such a resist layer is used, the wet etchant employed may be more aggressive without risking damage to the remaining electrodes required. Care must be taken to understand the interaction of the laser with the photoresist to properly account for the absorption of the laser energy by the photoresist to employ this method in the particular gap regions used to create the overlapping electrode regions 212a and 214 a. However, the resist can be readily applied to any area where multiple laser pulses are required to remove the top and bottom electrodes. However, the wet etchant must be carefully selected to ensure chemical and thermal compatibility with the thin polymer films used to construct the small-bore hydrophones described herein.

The techniques disclosed herein allow for the removal of nearly perfectly registered regions of electrode material from the front and back faces of the hydrophone by controlling the characteristics of the laser used to remove the electrode material, so that the conductors on the front and back faces of the film can be removed from the same side of the film. This allows the creation of almost the entire electrode pattern from one side of the membrane, ensuring sub-micron accuracy of the hydrophone front face relative to the hydrophone back face.

In some embodiments, the disclosed technology further includes vias that electrically connect the overlapping electrodes from front to back. The vias may be created with a laser or other means and conductive epoxy or other conductive means (sputtering, wire, etc.) for conductively connecting the front and back electrodes. Although means other than vias (e.g., wires) may be used to electrically connect the electrodes on one side to the corresponding electrodes on the other side, vias allow very low impedance and low inductance connections to be made simply using laser cut films with little or no mechanical stress. This low inductance and low impedance connection ensures that the membrane can be clamped between the electrodes with a near zero electric field even under high dynamic radio frequency conditions.

After the electrode pattern and vias are completed, one embodiment covers the back or bottom electrode with a polymeric elastomer 126 (e.g., silicone) covering the back signal and ground electrodes, as shown in fig. 5B and 6. As will be appreciated by those skilled in the art, some silicones have a very good acoustic match with water, and have relatively high acoustic losses at high frequencies, with very high electrical insulation properties, thereby preventing the signal electrodes from generating any stray acoustic signals in the region of the single electrode isolation strip. The silicone may also protect the electrodes and membrane from wear and greatly increase the stiffness of the membrane, thereby enabling faster scanning and less stringent damping specifications for the scanning system. Other polymers (such as epoxy) or engineering plastics that match well with water (such as TPX or LDPE) or elastomers (such as polyurethane) or latex materials or specially developed acoustic polymer materials can be used as acoustic liners or overlays as long as they match well with water and can be applied to thin hydrophone membranes with low stress (e.g., cast in liquid form and cured in place).

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 an acoustically matched elastomer 126. In one embodiment, the elastomer is applied to the top electrode under a microscope using a toothpick or other small applicator. However, it should be understood that other precision material deposition tools may be used. In the illustrated embodiment, there is no acoustically matched elastomer over the active region of the hydrophone.

In one embodiment, the electrodes are patterned on the coated p (vdf trfe) film using a UV laser. The UV laser was tuned to remove electrode material from the front of the film in 1 pulse and from the back of the film in the second pulse leaving the film itself intact. A single area of the front electrode is removed from the membrane to isolate the signal electrode from the ground plane/ground electrode on the front side of the membrane. The film was then flipped over and visually aligned with the pattern on the back of the film (which was created by laser ablation through the transparent film). Once aligned, a single area of the back electrode is removed to isolate the signal electrode from the ground plane/ground electrode on the back side of the film. A portion of the ground electrode pattern on the front side of the membrane overlaps a portion of the signal electrode pattern on the back side of the membrane (or vice versa). This is the only location on the membrane where the signal and ground electrodes overlap. There are only two locations on the membrane where the electrodes are present and do not overlap (e.g., defining small isolated areas or

gaps

211 and 213 that overlap the electrodes).

In one embodiment, the conductive material is Cr/Au applied at a thickness of 1900 angstroms (other conductive materials and thicknesses may be used). Ablation was performed from one side of the film through a mask and 10x reduction optics using an excimer laser to remove the conductive material from the front and back of the film. The laser wavelength is set at 248nm and the energy density (fluence) is chosen to be below the ablation threshold of the membrane. In one embodiment, the energy density is selected to be 0.25J/cm². This pulsed nature allows electrode material to be removed from the front surface of the membrane in a single pulse without affecting the electrode on the back surface. A second identical pulse is then used to remove the conductive material from the back surface of the film. This does not adversely affect the membrane itself. This approach eliminates the challenge of aligning the edges of the overlapping electrodes on opposite sides of the membrane.

Other combinations of laser power/wavelength/energy density may 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 significantly absorbed by the polymer film used for the piezoelectric element, but strongly absorbed by the electrode material. In one embodiment, a 248nm excimer laser with pulses of-15 ns duration is used. Furthermore, the use of optical ablation allows complex patterns to be focused on the membrane, allowing gaps to be formed in a single pulse.

In accordance with one embodiment of the disclosed technique, a high frequency membrane hydrophone includes a piezoelectric membrane. The piezoelectric film has a conductive material on opposite sides thereof. If it is desired to form the electrodes by ablating conductors from each side of the film, it is advantageous to form one or more registration features on the front and back electrode materials by ablation on the front surface and through-film ablation of the back surface, ensuring good registration of the front and back side reference points. The first side of the piezoelectric film includes a first electrode pattern formed by removing some of the conductive material. The second side of the piezoelectric film includes a second electrode pattern formed by removing some of the conductive material. The first and second electrode patterns overlap in the active region of the hydrophone.

In some embodiments, it may be advantageous to "depolarize" the piezoelectric membrane in areas other than the active region of the hydrophone. Fig. 7 shows a portion of a piezoelectric film 300 that is processed by a laser over an area 302 in a manner that reduces the piezoelectric response of the film. In one embodiment, the processing occurs in all but the active region of the hydrophone. The above treatment is performed before the conductive coating is applied to the film. In one embodiment, one or

more reference points

310, 312 are formed in the membrane so that the active regions of the hydrophones can be formed on the untreated areas once the electrode pattern is formed.

The treatment by the laser alters the piezoelectric film so that the film is less responsive to the received acoustic energy. This reduces artifacts created by the electrode area rather than by the active region. In one embodiment, the treatment in region 302 is by using a series of pulses at about 15ns, at 0.5 and 1J/cm²Laser fluence of between and about 20Hz and a pulse repetition frequency of about 20 Hz.

Fig. 8 illustrates circuitry for receiving and buffering the signals generated by the hydrophones before transmission to processing electronics in a remote computer system (not shown). The circuit includes a buffer amplifier 400. In one embodiment, the circuit is an integrated circuit (model AD8045 from Analog Devices) connected in a unity gain configuration with a positive input. The positive input is connected to the positive pole of the hydrophone via a capacitor 226. The negative pole on the hydrophone is connected with the grounding connector on the printed circuit board. Coaxial cable 406 is used to convey the signals amplified by buffer amplifier 400 to further signal processing circuitry (preamplifiers, a/D converters, DSPs, etc.). The positive and negative voltage supplies for the buffer amplifier and the ground connection of the printed circuit board on which the buffer amplifier is mounted are provided via separate wires. In some embodiments, a differential amplifier configuration may be incorporated into the circuit configuration shown in fig. 8. In one embodiment, the printed circuit board is carried on the hydrophone frame 126. The entire circuit board is encapsulated in a waterproof sealant so that the circuit can operate underwater.

FIG. 9 illustrates an alternative embodiment of a hydrophone constructed in accordance with embodiments of the disclosed technology. In this embodiment, the lattice hydrophone includes a plurality of thin electrodes on each surface of the membrane. The individual electrodes overlap one another at a plurality of locations that form a plurality of active regions of the hydrophone. In the illustrated embodiment, a plurality of positive electrodes 500a, 500b.. 500f are patterned on one side of the membrane and a plurality of negative electrodes are formed on the other side of the membrane. The active region of the hydrophone is formed at each location where the anode and cathode overlap. As will be appreciated, each electrode must be connected to a separate buffer amplifier separately or to a common buffer amplifier using a multiplexer or the like.

The array-type hydrophone shown in FIG. 9 allows sampling of multiple locations by selecting which anodes and cathodes are connected to the receiving electronics, and without having to move the hydrophone itself. In one embodiment, the overlapping electrodes may be fabricated by patterning each side of the film, or the regions where material needs to be removed from both sides may be patterned from a single side of the film as described above.

As high frequency ultrasound finds more clinical use, high frequency ultrasound transducers need to be tested to ensure that they can be safely used on patients. The disclosed technique allows membrane hydrophones to be fabricated with active areas that are small enough so that they can be used to analyze beam patterns from these high frequency ultrasound transducers having center frequencies of 20-50MHz and higher. In other embodiments, the high frequency may be 15MHz or higher.

FIG. 10 illustrates a hydrophone assembly, in accordance with certain non-limiting embodiments of the disclosed subject matter. As described above, a hydrophone can be constructed by suspending a piezoelectric diaphragm on a dielectric film that can vibrate over a desired bandwidth. The piezoelectric body may be plated with a conductive material to form an electrode on each face of the piezoelectric body. Active areas can then be cut in the plating on both sides of the piezoelectric material, thereby creating a separation between the areas where signals can be generated and the remaining areas. The remaining area may become part of the electrical reference or ground of the device. The active region may be electrically connected to the hydrophone electronics by a coaxial connection. The coaxial connection is built in situ on the membrane or diaphragm. In certain non-limiting embodiments, shielding from electrical noise along the signal path to the hydrophone electronics amplifier may be provided. The coaxial connectors may be referred to as connection traces or coaxial connectors, which may also be referred to as coaxial connections (coax) or coaxial cables (coax).

Fig. 10 illustrates a hydrophone 1000 having a water-tight housing. For example, the housing may be made of a dielectric, insulating, non-corrosive material. In certain non-limiting embodiments, the hydrophone may be included within a plastic housing, wherein the plastic housing may prevent water from contacting electronic components located within the hydrophone. The use of non-corrosive materials helps prevent the housing from releasing ions during immersion. This release of ions can create unwanted charges in the water, thereby affecting the hydrophone measurements. The housing may be composed of any useful plastic or thermoplastic, such as carbon fiber or an elastomer, which may include polyurethane. In one example, the housing may be partially or completely comprised of vero whiiteplus, which may provide a watertight housing. For example, VeroWhitePlus has a tensile strength of between 7,250 and 9,450 pounds force per square inch (psi), a Shore hardness (D) of between 83 and 86, and/or a polymerization density of between 1.17 and 1.18 grams per cubic centimeter (g/cm)³)。

The enclosure 1020 shown in fig. 10 may be in the form of a clam shell comprising a bottom shell 1021 and a top shell 1022. In other embodiments, the housing 1020 can be any other shape that surrounds the electronic components of the hydrophone. The bottom shell 1021 and the top shell 1022 may be connected using one or more screws 1050. This connection may form a seal between the bottom shell 1021 and the top shell 1022, which may prevent water in which the hydrophone is submerged from flowing out of any electronic components or parts within the housing 1200. As shown in fig. 11, the bottom shell 1021 may include protrusions 1023 to help further waterproof or seal the hydrophone components. The protrusion 1023 may be constructed of any non-metallic, non-corrosive material, such as Room Temperature Vulcanizing (RTV) silicone.

Depending on the different bandwidths and/or dot sizes, the membrane and/or diaphragm assembly 1010 may be attached to or within any portion of the housing 1020. In certain embodiments, the membrane and/or septum assembly 1010 may be included within a separate front portion 1040 of the housing 1020. In some examples, the membrane and/or septum assembly 1010 may be mounted to the front portion 1040, with the membrane and/or septum assembly 1010 and the front portion 1040 being modular to the remainder of the housing. As shown in fig. 10, the front end section 1040 may be attached to the top shell 1022 of the outer shell 1020 by one or more screws 1050. The screws may be made of any non-corrosive material. For example, the screws may be made of nylon, the same or similar material as the housing 1020, or any other non-corrosive material. In certain non-limiting embodiments, the hydrophone 1000 may be affixed to the column 1060. The column 1060 may allow the hydrophones to be placed in a movable stage that is positioned at different locations relative to the transducer being measured. The column 1060 may include one or more vertical threads that may help mount or connect the hydrophone 1000 to a movable stage. The threads may also be horizontal, helical, or any other shape or orientation. In some non-limiting embodiments, the column 1060 may be part of the hydrophone 1000.

In certain embodiments, the hydrophone 1000 can be manufactured using 3D printing. For example, 3D printing may be performed using selective laser sintering, stereolithography, adhesive jetting, or polyjet. In other embodiments, the hydrophone 1000 can be manufactured using injection molding, machining, such as CNC machining, molding, or bonding.

FIG. 11 illustrates an exploded view of a hydrophone assembly, in accordance with certain non-limiting embodiments of the disclosed subject matter. In particular, fig. 11 shows a bottom case 1021 including a protrusion 1023 connected to a top case 1022. The protrusion 1023 may be an engagement ridge between the bottom case 1021 and the upper case 1022. The bottom shell 1021 and the top shell 1022 may be connected using one or more screws 1050. For example, as shown in fig. 11, eight screws 1050 are used. In the example embodiment shown in fig. 11, four screws 1050 may be attached to connect the bottom shell 1021 to the top shell 1022, while four screws may be used to attach the front piece 1040 to the top shell 1022. In other embodiments, any number of screws or other attachment members may be used to attach the bottom shell 1021 and the top shell 1022. In some embodiments, screws may not be used, and the housing may optionally include a press-fit and/or snap-lock mechanism. In other non-limiting embodiments, front end component 1040 can be molded to top shell 1022. The bottom shell 1021 may include one or more tabs 1024 that may be inserted into cavities of the top shell 1022. For example, the one or more protrusions 1024 may help align the bottom shell 1021 with the top shell 1022 and/or align the bottom shell 1021 with the printed circuit board 1070.

The electrical components of the hydrophone 1000 can be housed between a bottom shell 1021 and a top shell 1022. In certain non-limiting embodiments, the bottom case 1021 may include a cavity in which at least a portion of the electrical components are housed. The electrical components may include, for example, a buffer circuit board 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-loaded pins 1080 connecting the buffer circuit 1070 to the membrane and/or diaphragm assembly 1010 through two holes in the upper shell 1022. Although fig. 11 illustrates the use of two spring-loaded pins, in some embodiments only a single spring-loaded pin is used. The membrane and/or septum assembly 1010 may be placed between the front portion 1040 and the upper shell 1022. As shown in the embodiment of fig. 11, the membrane and/or diaphragm assembly 1010 may be placed in a cavity disposed 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 of the hydrophone and the electronics (e.g., the buffer circuit board 1070). In some non-limiting embodiments, the interior of the housing may be electrically shielded around the circuit board 1070. For example, the metallization layer may be disposed on an inner surface of the housing cavity. In some examples, the metallization layer may be connected to an electrical ground, while in other examples, the metallization layer is not connected to an electrical ground.

In certain non-limiting embodiments, the membrane and/or septum assembly 1010 and/or the front portion 1040 can be removed and replaced by back-out screws 1050. The membrane and/or diaphragm assembly 1010 may be replaced with a different membrane, which may have different amplification or impedance characteristics. In other words, the hydrophone 1000 may allow for selective removal and replacement of the membrane and/or diaphragm assembly 1010 based on one or more electrical properties of the membrane or diaphragm assembly 1010 and/or the piezoelectric membrane suspended therein.

The materials of the hydrophone housing 1020, the projections 1023 and/or the screws 1050 are selected to prevent any water from seeping into the electrical components of the hydrophone 1000. The material may also be selected to limit or prevent any acoustic impedance caused by the material. In other words, the material may help limit or prevent any distortion or reflection of the transducer signal detected by the hydrophone 1000. For example, the acoustic impedance of the material may match or closely match the impedance of the water in which the hydrophone is immersed. For example, close matching may mean that the impedance may be less than or equal to 4 mrayl, or any other value.

FIG. 12 illustrates an example of a hydrophone membrane and diaphragm assembly, in accordance with certain non-limiting embodiments 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 may be used to convert detected acoustic signals into electrical signals that may be processed by a remote computer system. For example, as shown in fig. 12, membrane assembly 1200 may include a frame 1210. The membrane 1220 is located in the frame 1210. The diaphragm 1220 may be an insulating member. The membrane assembly 1200 may include a member 1230 attached to the conductive layer and/or the piezoelectric. The active region may be located within the outer diameter of the member 1230.

Membrane assembly 1200 may also include coaxial traces 1240 for connecting active areas located within member 1230 with the rear of frame 1250. The back of the frame 1250 can provide electrical connections between the active area and the hydrophone electronics, as shown in FIG. 11. The rear of frame 1250 may be electrically connected to buffer circuit 1070 using one or more vertical spring-loaded pins 1080. Member 1230 and/or coaxial trace 1240 may be sputtered one or more times with a conductive trace such as gold. The membrane assembly 1200 may include one or more layers that have been sputtered with gold, and chromium and/or any other conductive material.

In some embodiments, coaxial trace 1240, shown in fig. 12, may be a built-in-situ coaxial layer, also referred to as a coaxial (coax) layer or an intermediate layer, which may help transmit electrical signals from the active region. In some embodiments, the hydrophone and membrane modules 1200 may include one or more additional layers, such as dielectric layers, insulating layers, and/or other coaxial layers, which may help shield the built-in-situ coaxial layers. For example, the one or more dielectric layers and/or insulating layers may be comprised of glue.

As shown in fig. 12, the member 1230 may be attached or placed on top of the piezoelectric. For example, member 1230 may be annular, also referred to as semi-annular or semi-annular, spherical, or any other spherical or non-spherical shape. For example, the member may have an inner diameter of between 150 micrometers (μm) or 200 and 300 μm.

FIG. 13 illustrates an example of a hydrophone membrane in accordance with certain non-limiting embodiments of the disclosed subject matter. In particular, fig. 13 shows a diaphragm 1310 similar to diaphragm 1220 shown in fig. 12. For example, the film 1310 may be composed of a polyimide film (e.g., Kapton). In some embodiments, the film sheet 1310 may be stretched and adhered to a film frame. The membrane frame may be attached to the rest of the hydrophone housing. One or more holes 1320 for electrical connections may be cut into the diaphragm 1310. Vias may be placed within one or more holes 1320. The vias may be sputtered with a conductive material, for example, to allow connections at regular intervals between conductors on both sides of the film. Vias 1320 may be used to electrically connect one or more layers or portions of the membrane assembly to the built-in-situ coaxial layer. The membrane 1310 may be an insulating layer that includes a central aperture 1330 (referred to as an acoustic aperture) that may allow sound waves to pass through. The active region of the piezoelectric may be located within a central hole or bore 1330.

FIG. 14 illustrates an example of a hydrophone membrane in accordance with certain non-limiting embodiments of the disclosed subject matter. The active regions of the hydrophone membranes may be located in the pores of the member 1430. In some other embodiments, the holes included in the member 1430 may be filled. In the example embodiment shown in FIG. 15, the film or diaphragm located below the aperture of member 1430 may be metallized or made conductive to act as a ground or shield. As shown in fig. 12, a member 1430 is attached, connected, or placed over the conductive layer or piezoelectric. In certain non-limiting examples, member 1430 may include glue or any other non-conductive material. In some embodiments, the member 1430 may then be plated with conductive traces, such as gold. In other words, member 1430 may be sputtered with gold. Although member 1430 has a circular ring shape, in certain other embodiments, the member can take on any other shape, whether spherical or non-spherical.

A middle coaxial layer 1440 may be placed between the member 1430 and the rear of the frame 1450, which may be used to connect the active region to other electrical components of the hydrophone. In particular, the signal traces 1420 may span from the active region, over the top surface of the member 1430, along the intermediate coaxial layer 1440, over the vertical surface of the frame, and directly to the rear of the frame 1450. For example, the signal traces may be composed of a conductive material and may be referred to as an electrode pattern. A portion of the frame can be plated to create traces that can be connected to the hydrophone electronics.

In the embodiment shown in fig. 14, the signal trace 1420 may be V-shaped, with the width of the signal trace narrowing as it approaches the active region. However, in other embodiments, the signal trace 1420 may take any other shape. The rear of the frame 1450 may include a sculpted portion that creates a contour around the signal traces 1420. For example, a laser may be used to cut the profile. The signal traces 1420 may be located within the outline and the ground traces 1410 may be located outside the outline. The ground trace 1410 may also be referred to as a shield or zero voltage trace. In some non-limiting embodiments, the dielectric insulator and/or the top coaxial layer may cover at least a portion or all of the signal or ground trace.

Fig. 15 illustrates an example of a septum in accordance with certain non-limiting embodiments of the disclosed subject matter. In particular, FIG. 15 shows a close-up of a portion of the member 1430 outlined by the rectangular dashed line shown in FIG. 14. As shown in fig. 15, the active region 1460 may be generally square or rectangular. In one non-limiting example, the length of the active region may be 20 μm, while the width of the active region may be 20 μm. In other words, the active area may be 400 square microns. The active area may also be of any other size or shape, such as circular or any type of polygon. In some non-limiting examples, the shape of the active region may depend on the tool used to cut the active region during the fabrication process. In other examples, active regions may be cut into the plating on both sides of the piezoelectric material, thereby creating a separation between the area where the signal is generated and the remaining area. The square active region 1460 shown in fig. 15 may be a piezoelectric region that generates a signal.

In certain non-limiting embodiments, the active region 1460 can be located in an opening or hole in the member 1430. The holes in the member 1430 may expose the diaphragm or membrane. The aperture may be an acoustic aperture that allows the passage of pressure waves. Signal traces may connect the active region 1460 in the hole to the remaining electronics of the hydrophone. For example, signal traces may begin in active region 1460, extend over the outer boundary of member 1430, and continue along coaxial layer 1440 to the rear of frame 1450. In some non-limiting embodiments, the rear of frame 1450 may be connected to a buffer circuit board using one or more vertical spring-loaded pins 1080 for connecting buffer circuit 1070 to signal traces 1420. The spring-loaded pins may electrically connect the buffer circuit to the coaxial layer.

After the membrane module is completed or assembled, it can be installed into a hydrophone housing in which the electronics are mounted. For example, as shown in fig. 10 and 11, the membrane assembly may be attached to the front-end component 1040 of the housing 1020. The membrane assembly can then be electrically connected to the remaining hydrophone components using, for example, one or more coaxial spring-loaded pins 1080. The one or more coaxial spring-loaded pins 1080 protrude through the housing and are directly connected to plate 1070. In other embodiments, any other pin, plug, via, conductive material, or wire may be used to connect plate 1070 to the diaphragm assembly.

Fig. 16 illustrates an example of a circuit board in accordance with certain non-limiting embodiments of the disclosed subject matter. In particular, buffer circuit board 1600 shown in fig. 16 may be similar to buffer circuit 1070 shown in fig. 11. For example, the buffer circuit board 1600 may be a printed circuit board used to connect the membrane module to the remaining electronic components of the hydrophone. In certain non-limiting embodiments, the buffer circuit board 1600 may include one or more mounting holes 1610 for holding a pair of spring-loaded pins 1180, as shown in fig. 11. In other words, the mounting holes may provide for electrical connection to signal and/or ground traces from the diaphragm assembly. As shown in fig. 16, the ground plane 1620 included on the buffer circuit board 1600 may be smaller than the entire surface of the printed circuit board. In other words, the ground plane 1620 of the buffer circuit board 1600 may be reduced or minimized.

Fig. 17 illustrates an example of a circuit in accordance with certain non-limiting embodiments of the disclosed subject matter. In particular, the circuit 1700 may be a buffer circuit incorporated into the hydrophone shown in FIGS. 10 and 11. For example, the circuitry 1700 may receive and/or buffer one or more signals generated by the hydrophones. As shown in fig. 17, the circuit 1700 includes a reference voltage (also referred to as zero volts (V), Ground (GND), or coaxial shield) and a signal voltage from the active region of the piezoelectric of the hydrophone. The circuit 1700 may also include four resistors, denoted as R in FIG. 17₁、R₂、R_fAnd R_g. In other embodiments, circuit 1700 may include any number of resistors and capacitors. In some non-limiting embodiments, the circuit 1700 may include a differential amplifier.

Certain embodiments disclose one or more methods of making a hydrophone. For example, the method of manufacture may include stretching the film across a frame. The method may also include placing a piezoelectric on the membrane and selectively removing a portion of the piezoelectric to create an active region. In some examples, a member may be placed on the piezoelectric body, the member including an aperture exposing the piezoelectric body. Further, the method may include connecting the in-situ coaxial layer to the active region. In some non-limiting embodiments, the membrane may be attached to a frame, and/or a built-in-situ co-axial layer may be placed on the membrane frame. A plurality of vias may be placed to electrically connect the diaphragm and the in-situ coaxial layer. The method may further include coupling the insulating layer to the in-situ coaxial layer.

In addition to the specific embodiments claimed below, the disclosed subject matter also relates to other embodiments having any other possible combination of the dependent features claimed below and those disclosed above. The particular features set out in the dependent claims and disclosed above may thus be combined with each other in other possible combinations. Thus, the foregoing descriptions of specific embodiments of the disclosed subject matter have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.

In the detailed description herein, references to "an embodiment", "one embodiment", "in various embodiments", "certain embodiments", "some embodiments", "other embodiments", "certain other embodiments", etc., indicate that the embodiment(s) being described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading this description, it will become apparent to a person skilled in the relevant art how to implement the disclosure in alternative embodiments.

From the foregoing it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

Claims

1. A hydrophone for measuring acoustic energy from a high frequency ultrasound transducer, comprising:

a frame;

a membrane assembly supported by the frame and including a piezoelectric body;

an electrode pattern formed within the piezoelectric body to define an active region; and

a built-in-situ coaxial layer connected to the active region.

2. The hydrophone of claim 1, further comprising:

an insulating layer coupled to the in-situ coaxial layer.

3. The hydrophone of claim 1, further comprising:

a membrane sheet attached to the frame, wherein the built-in-situ co-axial layer is placed on the membrane frame.

4. The hydrophone of claim 3, further comprising:

a plurality of vias electrically connecting the diaphragm and the built-in-situ coaxial layer.

5. The hydrophone of claim 3, wherein the diaphragm comprises an acoustic aperture.

6. The hydrophone of claim 2, wherein the insulating layer covers at least a portion of a ground trace on the in-situ coaxial layer.

7. The hydrophone of claim 1, further comprising:

a member placed on the piezoelectric body, wherein the member includes a hole exposing the piezoelectric body.

8. The hydrophone of claim 7, wherein the active region is located within the aperture of the member.

9. The hydrophone of claim 7, wherein at least one of the members or the built-in-situ co-axial layers is sputtered.

10. A membrane hydrophone as claimed in claim 1 in which the hydrophone includes a water-proof shell.

11. A method of manufacturing a hydrophone for measuring acoustic energy from a high frequency ultrasound transducer, comprising:

stretching the membrane over the frame;

placing a piezoelectric body on the diaphragm;

selectively removing a portion of the piezoelectric body to create an active region; and

an in-situ coaxial layer is connected to the active region.

12. The method of claim 11, further comprising:

an insulating layer is connected to the in-situ coaxial layer.

13. The method of claim 11, further comprising:

attaching a membrane to the frame; and

placing the in-situ co-axial layer on the membrane frame.

14. The method of claim 13, further comprising:

placing a plurality of vias electrically connecting the diaphragm with the in-situ coaxial layer.

15. The method of claim 13, wherein the diaphragm comprises an acoustic aperture.

16. The method of claim 12, further comprising:

covering at least a portion of a ground trace on the in-situ coaxial layer with the insulating layer.

17. The method of claim 11, further comprising:

placing a member on the piezoelectric body, wherein the member includes a hole exposing the piezoelectric body.

18. The method of claim 16, wherein the active region is located within the aperture of the component.

19. The method of claim 16, wherein at least one of the member or the in-situ co-axial layer is sputtered.

20. The method of claim 11, wherein the hydrophone comprises a water-resistant housing.