Fluid impermeable ultrasonic transducer and method of forming the same

Abstract

This invention provides a fluid-impermeable transducer and a method for forming a liquid-impermeable ultrasonic transducer. The transducer includes: a liquid-impermeable metal housing; a liquid-impermeable transducer head including a metal focusing lens, the transducer head having a rear surface and a front surface, the metal focusing lens being formed on the front surface and configured to focus ultrasound toward a focal point; an actuator coupled to the rear surface of the transducer head and operable to generate oscillating mechanical vibrations of the metal focusing lens, such that ultrasound is emitted from the metal focusing lens toward the focal point; and a backing material configured to attenuate the acoustic energy transmitted by the actuator, the actuator being located between the backing material and the metal focusing lens. The metal housing and the transducer head are integrally formed as a single part and permanently connected in a liquid-impermeable manner to prevent liquid from entering the metal housing.

Description

[0001] This application is a divisional application of the application filed on March 29, 2019, with Chinese national application number 201980035708.1 (international application number PCT / US2019 / 024837) and entitled "fluid impermeable ultrasonic transducer". Technical Field

[0002] This invention relates to a fluid-impermeable ultrasonic transducer and a method for forming the same. Background Technology

[0003] Ultrasonic transducers are used in a wide variety of applications, such as in medical imaging, procedures for applying ultrasonic energy to heat or destroy tissues within a living organism, and processes for ejecting fluid droplets. Any or all of these applications may require an ultrasonic transducer capable of focusing acoustic energy to a small focal point. For example, some methods for generating fluid droplets using acoustic methods include those described in U.S. Patent No. 8,544,976 to Ellson and U.S. Patent No. 6,416,164 to Stearns et al., both of which are incorporated herein by reference for all purposes.

[0004] Ultrasonic radiation can be focused in a variety of ways. For example, curved surfaces can be used to direct or redirect acoustic radiation toward a focal point. For processes that generate fluid droplets, the focal point can be positioned near the fluid surface. One such technique is described in U.S. Patent No. 4,308,547 to Lovelady et al. Some commercially available acoustic transducers focus acoustic energy through curved surfaces, including some focusing immersion transducers manufactured by Camasonics (Wiltshire, UK), GE / Krautkramer, Sonic Concepts, Inc. (Bassau, Washington, USA), Sonotec (Halle, Germany), and Ultran Group (Pennsylvania State University, USA). Other methods of focusing acoustic energy include the use of Fresnel lenses, as described, for example, in U.S. Patent No. 5,041,849 to Quate et al. Various general-purpose curved and spherical surface transducers are used in the nondestructive testing (NDT) industry, the medical industry, and others. As used herein, “Immersion” refers not only to the conventional definition of immersion for NDT (where the transducer is partially or completely immersed in the fluid coupling), but also in a more general sense to applications that include any part of the transducer being exposed to the fluid, i.e., a portion of the transducer being in fluid coupling contact.

[0005] Ultrasonic transducers typically include an actuator and a focusing element that concentrates the acoustic energy generated by the actuator. Some examples of actuators include piezoelectric elements and magnetostrictive elements. In operation, the actuator is driven by a signal at an ultrasonic drive frequency, generating ultrasonic vibrations in an active physical element. These vibrations are emitted into the surrounding medium, such as a liquid or gel (e.g., water), and from there to the structure or medium of interest. For example, in applications involving droplet ejection, acoustic energy can be transmitted from the transducer in the form of ultrasonic vibrations through an acoustically conductive fluid or coupling fluid, such as water, and from there to a reservoir from which droplets are ejected. Transducers designed to focus acoustic energy primarily or significantly when immersed in a liquid medium are generally called immersion transducers.

[0006] Focused immersion transducers employ shaped active physical elements, which may include, for example, curved surfaces, or Fresnel lenses or similar structures. In such cases, this surface must be made of a material that can be precisely shaped into a focusing form and can easily transmit acoustic energy into the liquid medium. For this purpose, conventional focused immersion ultrasonic transducers use hard-cured epoxy resin, ceramics, composite materials, or similar materials to form the focusing lens shape. While such focusing lens materials can be formed by molding or another net-forming manufacturing method, and while generally waterproof for a limited duration, these materials have been found to be prone to degradation and may tend to gradually absorb water when exposed to water for extended periods, leading to deformation, altered acoustic properties, and ultimately transducer failure. While such transducers are suitable for short-term immersion applications, applications requiring long-term immersion demand higher precision and durability. Typical immersion transducers, such as those used in conventional NDT procedures, have a relatively low duty cycle in liquids compared to droplet jet transducers and do not require a constant focal length over time. However, for acoustic droplet jetting applications, device performance depends more on the consistency of focusing, especially over long immersion periods. Therefore, it is desirable to have a series of transducers that operate within a narrow range of focusing behavior and remain within that narrow range even when the transducers are immersed for extended periods. Summary of the Invention

[0007] The embodiments described herein include a transducer comprising an assembly of a housing and a transducer head having a focusing lens facing forward and a rear portion facing backward. The housing is connected to the transducer head and extends in the backward direction, wherein an actuator is disposed behind the rear portion of the transducer head within the housing and operable to transmit acoustic energy through the transducer head in the forward direction. As described herein, fluid impermeability may be applied at least to the portion of the transducer that is inevitably immersed in the working fluid during use. For example, according to various embodiments, the transducer head and housing may define a fluid-impermeable working portion of the transducer. Fluid impermeability may also include, for example, impermeability to water or similarly viscous reactive and non-reactive solvents, or impermeability to penetration of common liquid and / or solvent systems, including nonpolar, polar proton, and polar aprotic solvents, and particularly water / aqueous solutions (including brine), DMSO, ethanol, alkanes, oils, surfactants, etc. In some embodiments, fluid impermeability also includes impermeable vapors, such as solvent vapors, water vapors, air, or other similar gases, under normal operating conditions and under elevated temperatures / pressures (such as those used during sterilization procedures). According to some other embodiments, not only the working portion of the transducer may be fluid impermeable; for example, in some embodiments, the housing may be completely sealed to prevent liquid ingress.

[0008] According to various embodiments, the housing and transducer head are formed of one or more fluid-impermeable, non-absorbent solid materials, such as metallic elements, metal alloys, ceramics, or similar materials. Either or both of the transducer head and housing may be formed of any suitable impermeable material with appropriate acoustic properties. The material (if a single component) or assembly (if multiple components) preferably provides Hermiticity and fluid (including but not limited to water) impermeability, and the transducer head preferably has an acoustic impedance that does not result in high acoustic loss and / or increased "ringing," as discussed below. Suitable materials may include, for example, aluminum, beryllium, cadmium, germanium, lead, silver, tin, titanium, zinc, zirconium, alloys of any of the above, or compositions containing any of the above materials, with or without sealants, dopants, or similar substances for mitigating corrosion, toxicity, or structural weaknesses. The material selection for the transducer head (or lens) contrasts with conventional epoxy lenses not only in terms of fluid impermeability but also in terms of relatively uniform mechanical properties. The transducer head (or lens) thus maintains mechanical uniformity during immersion, resulting in good beam symmetry that persists throughout the transducer's service life.

[0009] The housing and transducer head are preferably joined in a manner that creates an impermeable and non-absorbent joint formed by common parts, such as by welding or brazing, or otherwise permanently and impermeably joined. The transducer head is preferably formed of a material capable of transmitting reproducible sound velocities for high-precision applications, thus materials with high sound velocities are preferred. Alternatively, some portions of the housing and transducer head may be made of various materials, such as ceramics or combinations of plastics and metals, provided that the assembly does not compromise long-term Hermitian properties. For example, a plastic or ceramic sleeve may be disposed around a metal housing, or may be plated with metal inside or outside the assembly containing the transducer head and / or transducer head components, or both inside and outside.

[0010] According to various embodiments, the housing and transducer head may be formed from continuous elements defining a working portion, wherein a focusing lens is formed directly on the transducer head portion of the continuous elements, and an actuator is positioned behind the focusing lens in the housing.

[0011] According to some embodiments, a focusing lens is formed by a recessed portion of a transducer head configured to focus acoustic energy. This recessed portion may be formed by a spherical acoustic lens, a cylindrical acoustic lens, or other suitable acoustic focusing shape. In some embodiments, the focusing lens may include a diffractive acoustic lens configured to focus acoustic energy. A peripheral portion defining the focusing lens may define an edge of the transducer head, and in some embodiments, an attenuation layer is positioned on the edge of the transducer head, wherein the attenuation layer is operable to absorb acoustic energy. In some embodiments, an auxiliary transducer may be positioned on the attenuation layer and separated from the transducer by the attenuation layer.

[0012] The transducer head may also include a matching layer disposed on the focusing lens to reduce the loss of acoustic signals transmitted from the focusing lens through the matching layer into the medium. Therefore, the matching layer may be selected in part based on the acoustic properties of the medium with which the transducer is intended to work. Typical acoustic media include water, aqueous solutions, or other fluids with a viscosity similar to water, and various low-loss gels, such as, but not limited to, water / propylene glycol-based gel coupling agents like SONOGLIDE (Sonotech, Bellingham, Washington) or SONOGEL (Sonogel Vertriebs GmbH, Bad Campbell, Germany), or solid dry coupling agents like AQUALENE (Canadian patent application CA2127039 A1). The matching layer has an acoustic impedance between the acoustic impedance of the transducer head and the acoustic impedance of the medium, typically close to the matching value defined below with reference to Equation 1. The matching layer has a thickness corresponding to an odd multiple of the quarter wavelength of the acoustic signal passing through the matching layer at the nominal frequency.

[0013] The embodiments described herein also include methods for forming fluid-impermeable transducers. For example, according to various embodiments, a fluid-impermeable transducer can be manufactured by the following steps: forming a substantially hollow housing having an internal cavity and an open first end from a fluid-impermeable material; removing material from a head element formed of the fluid-impermeable material to form a focusing lens on the head element; and connecting the head element to the first end of the housing to form a fluid-impermeable connector. The head element is positioned such that the focusing lens is directed away from the housing, and an actuator can be inserted into the housing adjacent to the transducer head. An attenuation layer can be applied to the periphery of the head element adjacent to the focusing lens.

[0014] A method for forming a fluid-impermeable transducer may further include: forming a substantially hollow housing having an internal cavity and a closed first end defining a transducer head from a fluid-impermeable material; removing material from the outer surface of the closed first end to form a focusing lens on the closed first end; and inserting an actuator adjacent to the transducer head into the housing. The head element may include a concave acoustic lens formed in the head element through a precision machining process, and a matching layer may be applied to the focusing lens, the matching layer having a matching acoustic impedance less than a first acoustic impedance of the transducer head.

[0015] The embodiments described herein also include a method of ejecting droplets from a fluid reservoir using a fluid-impermeable transducer according to any embodiment of the fluid-impermeable transducer described herein. Specifically, such embodiments include immersing a focusing lens of the fluid-impermeable transducer in an acoustic medium or coupling medium positioned to couple acoustic energy from the transducer to a reservoir continuously supplied with fluid for droplet ejection. In some embodiments, the fluid reservoir and the acoustic medium may be the same fluid or may be a continuous reservoir. However, generally, the acoustic medium will be a fluid or gel medium located between the transducer and the reservoir, and the reservoir will contain a different fluid separate from the coupling medium. The transducer generates acoustic pulses via an actuator at a frequency configured to eject droplets from the fluid surface of the reservoir, and the acoustic pulses are transmitted from the actuator via the focusing lens and through the acoustic medium to the fluid reservoir.

[0016] The embodiments described herein also include methods for performing non-destructive acoustic testing (NDT) on a structure using a fluid-impermeable transducer according to any embodiment of the fluid-impermeable transducer described herein. Specifically, such embodiments include immersing a focusing lens of the fluid-impermeable transducer in an acoustic medium in fluid contact with the structure, and generating acoustic pulses directed at a scanned area of ​​the structure by an actuator. The echoes of the acoustic pulses corresponding to the scanned area are received by the same transducer in "listening" mode or by a second transducer, and the physical parameters of the scanned area of ​​the structure are determined based on the characteristics of the echoes. Attached Figure Description

[0017] Various embodiments according to this disclosure will be described with reference to the accompanying drawings, in which:

[0018] Figure 1 A simplified side cross-sectional schematic diagram of a conventional prior art ultrasonic transducer is shown;

[0019] Figure 2 A side view of a first fluid-impermeable ultrasonic transducer according to some embodiments of the present disclosure is shown;

[0020] Figure 3 It shows Figure 2 A schematic diagram of the side cross-section of an impermeable ultrasonic transducer;

[0021] Figure 4 It shows Figures 2-3 A schematic diagram of the end section of an ultrasonic transducer that is impermeable to fluids;

[0022] Figure 5 It shows Figures 2-4 A perspective view of the other side cross-section of a fluid-impermeable ultrasonic transducer, focusing on the actuator and focusing lens;

[0023] Figure 6 Showing more details Figure 5 A portion of the perspective view, focusing on the actuator;

[0024] Figure 7 A side view of a second fluid-impermeable ultrasonic transducer according to some embodiments of the present disclosure is shown;

[0025] Figure 8 It shows Figure 7 A schematic diagram of the side cross-section of an impermeable ultrasonic transducer;

[0026] Figure 9 It shows Figures 7-8 A schematic diagram of the side cross-section of a fluid-impermeable ultrasonic transducer, focusing on the actuator and focusing lens;

[0027] Figure 10 A side view of a third fluid-impermeable ultrasonic transducer according to some embodiments of the present disclosure is shown;

[0028] Figure 11 It shows Figure 10 A schematic diagram of the side cross-section of an impermeable ultrasonic transducer;

[0029] Figure 12 A simplified schematic diagram of the working components of an immersion transducer employing a matching layer according to some embodiments of the present disclosure is shown;

[0030] Figure 13A simplified schematic diagram of the working components of an immersion transducer employing multiple matching layers according to some embodiments of the present disclosure is shown;

[0031] Figure 14 A simplified schematic diagram of the working components of an immersion transducer employing a diffractive focusing lens according to some embodiments of the present disclosure is shown.

[0032] Figure 15 A simplified side view schematic diagram of a curved focusing lens having a relatively large focusing area according to some embodiments is shown;

[0033] Figure 16 It shows a curved focusing lens (similar to) Figure 15 A graphical illustration of the echo signal caused by the curved focusing lens shown in the figure;

[0034] Figure 17 A simplified side view schematic diagram of a curved focusing lens having a relatively small focusing area and an external absorption layer and a focusing lens according to some embodiments is shown;

[0035] Figure 18 It shows a curved focusing lens (similar to) Figure 17 A graphical illustration of the echo signal caused by the curved focusing lens shown in the figure;

[0036] Figure 19 A graphical illustration of echo signals for transducers with different aperture sizes according to various embodiments is shown;

[0037] Figure 20 A graphical illustration of the beam size associated with transducers having different aperture sizes according to various embodiments is shown;

[0038] Figure 21 An exemplary system for generating a focusing lens for use in a fluid-impermeable ultrasonic transducer, according to an embodiment, is shown;

[0039] Figure 22 A first exemplary process for producing a fluid-impermeable ultrasonic transducer according to an embodiment is shown;

[0040] Figure 23 A second exemplary process for producing a fluid-impermeable ultrasonic transducer according to an embodiment is shown;

[0041] Figure 24 A third exemplary process for producing a fluid-impermeable ultrasonic transducer according to an embodiment is shown;

[0042] Figure 25This is a graph showing the echo amplitude based on the echo delay of a fluid-impermeable transducer, which is used to estimate the characteristic time of flight (ToF) corresponding to the focal length of the transducer; and

[0043] Figure 26 It is a contour plot showing the echo amplitude across the focal plane of a fluid-impermeable transducer, which is used to estimate the beam shape and symmetry at the focal plane. Detailed Implementation

[0044] In the following description, various embodiments will be described. Specific configurations and details are set forth for illustrative purposes in order to provide a thorough understanding of the embodiments. However, it will also be apparent to those skilled in the art that other configurations or no specific details may be practiced. Furthermore, well-known features may be omitted or simplified so as not to obscure the described embodiments.

[0045] The embodiments of ultrasonic transducers described herein include immersion ultrasonic transducers employing fluid-impermeable transducer heads. Fluid-impermeable ultrasonic transducers may also include a fluid-impermeable housing, which may be an integral part forming the housing and focusing lens, and the actuator and associated electrical components are also contained therein. In such cases, the fluid-impermeable housing and focusing lens may be formed from the same fluid-impermeable portion. A matching layer may also be included on the focusing lens, which improves the transmission of acoustic energy from the focusing lens to the liquid medium.

[0046] According to some embodiments, the ultrasonic transducer housing may include a fluid-impermeable transducer head including a focusing lens with focusing devices, the transducer head being permanently attached to the fluid-impermeable housing, for example by welding, sintering, or similar waterproof attachment methods. An actuator is disposed inside the housing and adjacent to the rear of the transducer head, opposite the focusing lens, such that the actuator can drive vibrations into and through the transducer head when activated by a drive signal. The actuator may include, for example, any suitable electromechanical actuator, such as, but not limited to, a piezoelectric actuator.

[0047] Fluid impermeability as described herein may include, for example, impermeability to water or similar viscous reactive and non-reactive solvents, or impermeability to penetration of common liquid and / or solvent systems, including nonpolar, polar protic, and polar aprotic solvents, and particularly water / aqueous solutions (including brine), DMSO, ethanol, alkanes, oils, surfactants, etc. In some embodiments, fluid impermeability also includes impermeability to vapors, such as solvent vapors, water vapor, air, or other similar gases, under normal operating conditions and under elevated temperatures / pressures (such as those used during sterilization procedures).

[0048] In some embodiments, fluid-impermeable transducers as described herein remain fluid-impermeable under a wide range of conditions, potentially beyond normal atmospheric conditions, as envisioned in this disclosure. Fluid (including vapor) impermeability is desirable under normal laboratory pressures and temperatures, as well as at elevated pressures and temperatures, because these are factors that can propel a permeant into the transducer. For example, there is considerable practicality in facilitating the sterilization of the transducer, and thus at least some embodiments are impermeable to liquids and / or vapors under at least autoclaving conditions (e.g., at more than two, preferably more than three atmospheres, at approximately 130°C) without any detectable change in performance. Transducer performance criteria may include, but are not limited to, focal length, efficiency, beam shape or eccentricity, adaptability to intrusion or other environmental factors, consistency of operation over time, and / or signal-to-noise requirements. According to some embodiments, any connectors associated with the transducer (e.g., RF connectors, etc.) can be sealed during exposure to extreme conditions within the cover; or can be designed to be immersed in fluids under extreme pressure and temperature by using standard high-pressure / high-temperature hermetically sealed RF connector designs and laser welding techniques to attach the connector to the transducer housing.

[0049] The focusing lens of an ultrasonic transducer can be shaped to focus acoustic energy. In some specific embodiments, the focusing lens may have a concave spherical, parabolic, cylindrical, or other focusing shape. The focusing lens can be shaped by molding, casting, precision machining, 3D printing, flow spinning, coating, etching, or other suitable forming or shaping methods or combinations thereof. According to some embodiments, a matching layer is also included on the focusing lens. The matching layer is formed of a thin layer of material having acoustic impedance between the acoustic impedance of the focusing lens and the acoustic impedance of the liquid medium, and is configured to transmit acoustic energy according to a step transition between the materials of the focusing lens, the matching layer, and the liquid medium in order to reduce total transition loss.

[0050] The rear of the transducer head can be attached to the actuator by epoxy resin or alkoxysilane or other suitable, stable, permanent adhesive, so that vibrations caused by the actuator are reliably transmitted to the transducer head and away from the focusing lens to the adjacent material, which is usually a coupling agent, thereby transmitting acoustic energy toward its focal point.

[0051] According to some embodiments, the actuator may be sandwiched between the rear portion of the transducer head and the backing material. This facilitates the forward guidance of acoustic energy from the actuator through the transducer head and into the liquid medium, and helps absorb acoustic energy traveling toward the rear of the actuator layer, thereby suppressing reverberation in the actuator, reducing echoes, and producing a clearer signal. For example, in some embodiments, the backing material may include an acoustic scattering material such as copper, lead indium, titanium dioxide, tungsten, or a combination of these or similar materials. Furthermore, in some embodiments, the acoustic absorbing material in the backing material may be a combination of epoxy resin, polyurethane, silicone, or similar materials. Both the scattering and absorbing materials may exist as particles and dispersed within the matrix of the acoustic absorbing material. The actuator may be bonded to one or both of the transducer head and the backing material by a thin layer of permanent adhesive (e.g., thermosetting epoxy resin, etc.).

[0052] The backing layer, and especially its homogeneity, can affect the overall performance of the transducer. Specifically, for backing layer compositions comprising more than one component, the spatial distribution of the components can be an important consideration. For example, for a backing layer comprising sound-scattering material suspended within an acoustically absorbing material, where there is a significant density difference between the two, care must be taken during manufacturing to maintain homogeneity to avoid settling due to one component becoming more resistant to the movement of the other, for example, due to crosslinking, cooling, gelation, polymerization, or other processes that may occur during formation. Homogeneity of the backing layer material can be achieved through various manufacturing methods. For example, methods such as flipping during manufacturing can be used to ensure that the density difference within the backing layer material is large enough to mitigate buoyancy that could lead to uneven distribution when relative movement occurs between the components.

[0053] The actuator can be any suitable electromechanical actuator, such as a piezoelectric actuator. In a specific embodiment, the actuator is a piezoelectric disk, such as, but not limited to, a thin ceramic piezoelectric element. Such an element comprises a thin piezoelectric ceramic element having an anode and a cathode coupled thereto, wherein one of the anode and cathode is formed by a thin conductive disk covering the center, and some or most of the disk surface is on one side of the ceramic element, while the other of the anode and cathode is formed by another thin conductive disk wound around one side of the actuator disk to the back side of the actuator disk. Electrical connection to the anode and cathode is provided by a conductor ring made of insulating material in the shape of a cylindrical ring, located on the back side of the actuator. The conductor ring has electronically conductive traces, such as copper, which are coated on the inner and outer surfaces. The conductor ring is located on or around the edge of the ceramic element and is electrically connected to the anode and cathode conductive disks by any suitable method (e.g., conductive epoxy, welding, or similar methods). Therefore, when an electrical drive signal, such as a short pulse or short tone-burst waveform, is supplied to the anode and cathode via a conductor loop, the ceramic element acts as a separator and vibrates according to the drive signal. Suitable piezoelectric ceramic elements include, but are not limited to, barium titanate, polyvinylidene fluoride, lead zirconate titanate fractions, lithium titanate, zinc oxide, aluminum nitride, and similar materials.

[0054] The specific embodiments are described in detail below with reference to the accompanying drawings.

[0055] Figure 1 A simplified side-section schematic diagram of a conventional ultrasonic transducer 100 is shown, which includes a housing 102 and a transducer head 104 inserted into the housing adjacent to an actuator 116. The transducer head 104 may be formed of, for example, molded epoxy resin, silicone, or other similar materials. The transducer head 104 has an interface 108 between the transducer head and the housing 102, wherein the transducer head is theoretically sized to prevent liquid intrusion between the transducer head and the housing; however, over time, the transducer head 104 may absorb liquid and degrade, or deform to allow liquid to pass through the interface. This absorption or degradation may ultimately allow liquid to intrude into the actuator 116, or may cause the transducer head 104 to detach from the actuator. The deformation of the transducer head 104 manifests as a shift in focal length over time, or a shift in the beam pattern generated by the transducer head. Similarly, stripping can lead to a significant loss of power efficiency and / or uniformity of acoustic transmission from actuator 116 to transducer head 104 over time.

[0056] and Figure 1 Compared to the traditional ultrasonic transducer 100, Figure 2An example of a liquid-impermeable ultrasonic transducer 200 is shown, which is not easily degraded over time due to liquid absorption. The liquid-impermeable ultrasonic transducer 200 includes a housing 202 and a transducer head 204. The housing 202 includes a permanently connected transducer head section 202a and a body section 202b. Suitable connection techniques for sealing the housing 202 may include, for example, welding (laser welding, friction welding, etc.) or similar methods, thereby creating a fluid-impermeable joint 242. Figure 3 In some cases, the housing 202 may be a single integral part, as will be discussed below with reference to other embodiments. The housing 202 and the transducer head 204 form the working part of the transducer, which is completely impermeable to fluids and protects the contents of the housing from water intrusion.

[0057] The transducer head 204 is formed by the forward-facing portion of the housing 202 (forward-facing meaning in the direction of expected acoustic energy transmission). Other externally visible components of the transducer 200 include a connector 208 for electrically connecting the transducer to a signal source (not shown), which is attached to the housing 202, for example, at a nut 210, which is permanently attached around the housing 202 and the connector 208 to provide the user with a means of adjusting the position of the transducer. The housing 202, which contains the electronic components, may also be backfilled with a sealing material (e.g., epoxy resin), which can be inserted through a gap 206 in the housing. Reference planes (3) and (4) refer to... Figure 3 and Figure 4 The cross-sectional view shown.

[0058] Figure 3 It shows Figure 2 A side cross-sectional schematic diagram of a fluid-impermeable ultrasonic transducer 200, focusing on its internal details. The housing 202 includes a transducer head 204 comprising a concave focusing lens 212 defined by a narrow transducer head edge 214. The focusing lens 212 includes a thin acoustic matching layer disposed across all or most of the lens surface. See below for reference. Figure 9 and Figures 12-13 To discuss matching layers in more detail, for example, matching layer 370 ( Figure 9 ).

[0059] Opposite to the concave focusing lens 212, the rear portion 216 of the transducer head is connected to the actuator 222, which is a piezoelectric disk. The actuator 222 includes a positive electrode 226 and a negative electrode 228. The positive electrode is arranged across the center of the actuator towards the inner cavity 218, and the negative electrode is arranged in a ring around the periphery of the actuator and across the actuator towards the transducer head 204, as shown in the following reference. Figure 6Further discussion follows. It will be understood that this electrode arrangement is particular for a particular type of actuator, and this disclosure covers electromechanical actuators that may have electrodes with different arrangements. Furthermore, in alternative embodiments, actuator 222 may be an actuator of a different type from a piezoelectric actuator, such as a magnetostrictive actuator, a voice coil actuator, or other similar electromechanical actuator.

[0060] Actuator 222 is coupled or bonded to the rear portion 216 of the transducer head, allowing the actuator to apply vibrations through the transducer head 204. According to some embodiments, actuator 222 is bonded to the rear portion 216 of the transducer head by an adhesive, such as a layer of high-strength epoxy resin or a similar material. The bonding is preferably achieved through a thin and substantially uniform adhesive layer to maximize the coupling of acoustic energy from the actuator to the transducer head while minimizing the possibility of peeling. Actuator 222 is also connected to a backing material 224 comprising a loaded matrix. Backing material 224 is composed of one or more materials having a suitable mass to firmly hold actuator 222 in place against the rear portion 216 of the transducer head during operation, and having a suitable acoustic impedance to effectively block reverberation returning through the housing 202, thereby minimizing or preventing echo effects from interfering with the acoustic signal generated at the actuator. According to some embodiments, the acoustic impedance of backing material 224 is approximately 15 megayl (Mirailli). In various embodiments, the acoustic impedance of the backing material 224 may vary, for example, from about 13.5 Mrayl to about 16.5 Mrayl, or from about 8 Mrayl to about 28 Mrayl. The backing material 224 may be composed of any suitable sound-absorbing material, such as an epoxy resin. In a specific embodiment, the backing material 224 is a composite material formed from a damping polymer matrix impregnated with one or more ceramic and / or metallic materials or particles, such as an epoxy resin impregnated with copper, silicon carbide, titanium dioxide, tungsten, etc.

[0061] The specific concentration and composition of particles in the backing material can be varied to tune the acoustic impedance. The ideal acoustic impedance of the backing material is typically between the maximum value of the acoustic impedance for piezoelectric materials and a minimum value approximately one-third of that maximum. A tighter match in acoustic impedance results in higher efficiency, although with more pronounced reverberation; however, increasing the impedance gap reduces reverberation at the cost of efficiency. Therefore, the specific acoustic impedance of the backing material can be selected in part based on the specific application the transducer is intended for, ranging from high-power applications where reverberation is acceptable to high-precision applications where reverberation response is minimized. According to some embodiments, the backing layer can be formed of more than one material and can include particles of acoustic scattering material suspended within the acoustically absorbing material. Such a backing layer is preferably acoustically homogeneous. This homogeneity can be achieved by manufacturing the backing layer such that the particle distribution is also uniform throughout the backing layer.

[0062] The backing material 224 substantially fills the space directly behind the actuator 222, with channels and gaps therein for accommodating electrical connections to the actuator 222. According to some embodiments, a conductive ring 220 is positioned around the backing material 224 for contacting external portions of the actuator 222. Positive circuit 226 and negative circuit 228 are connected therein to transmit electrical signals to the positive electrode 230 portion and the negative electrode 232 portion of the actuator 222, as will be referred to below. Figures 4-6 This is shown in more detail. According to some embodiments, the outer portion 220b of the conductive ring 220 can be used as a contact element for the negative electrode 232, and the inner portion 220a of the conductive ring can be used as a contact element for the positive electrode 230, wherein the remaining portion of the conductive ring insulates the inner portion from the outer portion. However, it should be understood that this arrangement can be reversed. The electrical signals carried by the positive circuit 226 and the negative circuit 228 can be controlled, regulated, and guided to the circuit via electronics within the signal board 236. The signal board 236 is operatively connected to the connector 208 via electrical pins 238 and sockets 240. Reference is made below. Figure 4 Describe the specific details of the operation of signal board 236.

[0063] The remaining space in cavity 218 inside housing 202 can be filled with an inert sealant material (e.g., epoxy resin) operable to secure internal components within housing 202. This sealant also prevents water ingress into cavity 218 when the connector end of transducer 200 is exposed to liquid or submerged. Cavity 218 can be accessed via gap 206 ( Figure 2 The gap is filled away from the positioning of the focusing lens 212, and therefore away from the positioning of the working fluid into which the transducer is immersed during use.

[0064] Figure 4 It shows Figures 2-3 A schematic cross-sectional view of a fluid-impermeable ultrasonic transducer 200 is shown, specifically a cross-section of a signal plate 236. As shown, the signal plate 236 includes an electrical matching network 246, which may include inductors (not shown) and connects an array of positive circuits 226 together. The positive circuits 226 are arranged together in such a way as to provide reliable signal transmission across the entire positive electrode 230 of the actuator 222 during operation of the transducer 200. The signal plate 236 also includes a gap 252 for passage through a negative (or ground) circuit 228. Figure 2 An array of positive circuits 226. Similarly, negative (or ground) circuits 228 are arranged to contact the negative electrode 232 of actuator 222 in a uniform manner. Network 246 is operatively connected to the array of positive circuits 226 to more effectively couple incoming electrical signals to the transducer. Network 246 is preferably a passive circuit. According to some embodiments, network 246 may be an inductive passive circuit.

[0065] Figure 5 Illustrations are shown according to some embodiments Figures 2-4 A perspective view of another cross-section of the fluid-impermeable ultrasonic transducer 200, focusing on the actuator 222 and the focusing lens 212. The actuator 222, sandwiched between the transducer head 204 and the backing material 224, makes array electrical contact with the positive circuit 226 and, via a conductive outer ring 220, also within the housing 202, with the array electrical contact with the negative (or ground) circuit 228. The actuator 222 is coaxially aligned with the focusing lens 212 and within the area defined by the transducer head edge 214. The negative electrode 232 is wound around the actuator 222 near the outer edge, while the positive electrode 230 is connected to the internal portion of the actuator 222, as per the description of the internal portion. Figure 6 More detailed illustrations are provided.

[0066] Figure 6 Some embodiments are shown in more detail. Figure 5 A portion of the perspective view focuses on actuator 222, positive electrode 230, and negative electrode 232. The thickness of positive electrode 230 and negative electrode 232 can be very small, on the order of micrometers or nanometers; therefore, Figure 6 Features are not shown to scale; the thickness of the electrodes is only visible for illustrative purposes. Electrodes 230 and 232 may be formed of a conductive material (e.g., gold, silver, copper, aluminum, or similar materials) approximately 300 nanometers thick. Actuator 222 may consist of a thin piezoelectric disk formed of a piezoelectric material (e.g., lithium niobate, barium titanate, polyvinylidene fluoride, lead zirconate titanate fraction, zinc oxide, aluminum nitride, or similar). To maximize efficiency, the thickness of actuator 222 is chosen to be close to half the wavelength of the sound wave determined by the desired vibration center frequency and sound velocity in the piezoelectric disk, but in various embodiments, the thickness may be close to any suitable odd multiple of half the wavelength. For desired frequencies above 100 MHz, the optimal thickness may be less than 10 micrometers. For desired frequencies below 1 MHz, the thickness may exceed 1 millimeter. At approximately 10 MHz, the optimal thickness is in the range of several hundred micrometers for typical piezoelectric disk materials. In some specific embodiments, for example, for a design center frequency of approximately 12 MHz, the optimal thickness is preferably approximately 275 micrometers (or an odd multiple of 275 micrometers). The positive electrode 230 and the negative electrode 232 are electrically isolated from each other, with the negative electrode 232 wound around the circumference of the actuator 222 and the positive electrode 230 occupying the space within that circumference. A gap or void 250 may exist between the actuator and the housing 202, positioned around the periphery of the actuator 222; and the conductive outer ring 220 and the backing material 224 may also be electrically isolated from each other by the conductive ring gap 248. The two gaps 250 and 248 may be filled with an electrically insulating material (e.g., epoxy resin).

[0067] Various other embodiments of the transducer may include those referenced above. Figures 1-6 The features of the described transducer 200 are similar to those of alternative components having a housing and transducer head-face parts. Where possible, similar designations are used throughout to describe components of various transducers having similar functions. It should be understood that, unless specifically prohibited, components of one transducer assembly may be combined with components of another transducer assembly disclosed herein without departing from the spirit of this disclosure.

[0068] Figure 7 A side view of a second fluid-impermeable ultrasonic transducer 300 according to some embodiments of the present disclosure is shown. The transducer 300 includes a housing 302 having the same characteristics as described above. Figures 2-6 The transducer 200 has similar external features to those described above; and an interface 308 for operatively connecting the transducer to a signal source. The transducer 300 also includes an attenuation layer 350 located around the periphery of the transducer head 304 on the housing 302 and defining an aperture lens 312. Figure 8 Note that in various embodiments, the attenuation layer 350 may be omitted. Figures 2-6 Compared to the transducer 200 (in which the housing 202 and the transducer head 204 are connected), the transducer 300 is waterproof because the transducer head 304 is an integral part of the housing 300.

[0069] Figure 8 An example is shown. Figure 7 A schematic diagram of the side cross-section of a fluid-impermeable ultrasonic transducer 300. Similar to... Figures 2-6 The transducer 200 and transducer 300 include an actuator 322 located between a transducer head 304 and a backing material 324, the actuator head and backing material having a similar composition and construction as described above for the transducer head 204 and backing material 224. The internal cavity 318 of the housing 302 may also be filled with an insulating and waterproof filling material, such as epoxy resin. The actuator 322 may be operatively connected to the signal board 336 in a manner similar to that described above for the actuator 222 and signal board 236. The actuator 322 is sandwiched between the transducer head 304 and the backing layer 324 and is surrounded by a conductive ring 320 providing an electrical connection to the actuator 322. For the lens shape shown in transducers 200 and 300 (i.e., Figure 3 The aperture lens 212 shown is relatively large. Figure 7 The aperture lens 312 shown is smaller) is not limited to these corresponding housing types ( Figure 3 The transducer head / housing shown is connected. Figure 7It is used on the integrated transducer head / housing shown. Unless otherwise explicitly stated, the structural features of each transducer described are interchangeable. If desired, the shape of the lens and the size of the transducer electrodes coupled to the lens can be adjusted to control the beam size of the transducer.

[0070] Transducer 300 provides transducer head 304 as mentioned above. Figures 2-6 The transducer head 204 described has a different configuration. The transducer head 304 includes a focusing lens 312 defining a focusing shape having a smaller diameter than the actuator 322. This configuration differs from the transducer head 204 in which the diameter of the focusing lens 212 is larger than that of the actuator 222. Figures 2-6 This creates a contrast. The smaller geometry of the focusing lens 312 is used to reduce the effects of internal acoustic reflections in the material of the transducer head 304, as shown in the reference. Figures 15-18 As shown and discussed below, the focusing lens 312 is coated with a coating similar to... Figures 2-6 The matching layer on lens surface 212. See below for reference. Figure 9 and Figures 12-13 Details regarding the matching layer are discussed. The attenuation layer 350 or the external absorption layer defines the focusing lens 312 to reduce or eliminate unfocused vibrations that may originally originate from the larger transducer head edge 314.

[0071] An attenuation layer 350 is located on the transducer head 304, specifically on the transducer head edge 314, adjacent to and surrounding the periphery of the transducer end face 312. The attenuation layer 350 is configured to prevent unintentional transmission of unfocused or reflected vibrations from the transducer head edge 314. A central gap 352 in the attenuation layer 350 allows vibrations to pass unimpeded from the focusing lens 312 in a focused manner. The diameter 354 of the central gap is preferably the same as the size of the transducer end face 312. The width 358 of the attenuation layer 350 is preferably wider than the actuator 222, such that little or no unfocused or reflected vibrations are transmitted by the actuator from the transducer head edge 314. In some embodiments, the attenuation layer 350 may extend far beyond the edge of the housing 302. The depth 356 of the attenuation layer 350 is sufficient to provide adequate attenuation to absorb substantially all transmittable vibrations from the transducer head edge 314. In some embodiments, the attenuation layer 350 is thick enough (i.e., has a minimum thickness) to absorb at least 90% of the acoustic energy each time it passes through the attenuation layer (i.e., reduces acoustic energy by 10 dB). In a specific embodiment, the depth 356 of the attenuation layer 350 can range from about 0.5 mm to 5 mm. The total depth 360 from the actuator 322 to the end of the attenuation layer 350 can range from about 0.6 mm to about 10 mm. However, the thickness of the absorption layer is preferably selected as the minimum thickness that attenuates at least 10 dB.

[0072] Figure 9 It shows Figures 7-8 A side cross-sectional schematic diagram of a fluid-impermeable ultrasonic transducer 300, focusing on the actuator and focusing lens. As shown, a housing 302 terminates at a transducer head 304, which includes a peripheral portion defining a transducer edge 314 and a central portion defining a focusing lens 312. An attenuation layer 350 is positioned adjacent to the head face 312 on the transducer head edge 314. The width 358 of the attenuation layer 350 occupies a large portion of the width 360 of the transducer head edge 314. Within the transducer housing 302, a cavity 318 includes an actuator 322 pressed against the transducer head 304 and clamped between the transducer head and the backing layer 324. A negative electrode or ground electrode 332 is located on the actuator 322, adjacent to the transducer head 304, and connected around the edge of the actuator 322 together with a conductive ring 320. A positive lead is routed adjacent to the conductive ring 320 to contact the positive electrode 330 located between the actuator 322 and the backing layer 324. A matching layer 370 is positioned on the headpiece 312 to improve acoustic transmission from the headpiece. (Reference) Figures 12-13 Let's discuss the matching layer 370 in more detail.

[0073] According to some alternative embodiments, additional transducer elements may be referenced above. Figures 2-9 One or more combined configurations of the described transducers. For example, Figure 10 A side view of a third fluid-impermeable ultrasonic transducer 400 having a second transducer element 462 according to some embodiments of the present disclosure is shown. The transducer 400 includes a housing 402 having features similar to the housings 202, 302 of the transducers 200, 300 described above, wherein an interface 408 is used for operatively connecting the transducer to a signal source. The transducer 400 also includes a dual-purpose backing and attenuation layer 450 located on the housing 402, and a second transducer element 462 located on the backing / attenuation layer.

[0074] Figure 11 It shows Figure 10 A schematic side cross-section of a fluid-impermeable ultrasonic transducer 400, showing its relationship with... Figures 7-9The transducer 300 shown has features and components similar to those shown, and similar parts have similar numbering. Notably, the second transducer element 462 (which may include its own actuation and focusing mechanism (not shown)) is connected to a backing / attenuation layer 450, which is connected to the transducer head 404, such that the backing / attenuation layer acts both as a backing layer for the second transducer element and as an attenuation layer for the acoustic energy emitted by the main actuator 422. The second transducer element 462 may be arranged in a ring around the main focusing lens 412 of the transducer 400, may operate in conjunction with or independently of the main actuator 422, and may operate within the same or preferably different acoustic frequency ranges. The main actuator 422 and head 412 as shown herein are similar to... Figures 7-9 The actuator 322 and head face 312 of the transducer 300 are shown. According to some embodiments, the second transducer element 462 has an open inner diameter 464 that substantially matches the inner diameter 452 of the attenuation layer 450. The thickness 456 of the backing / attenuation layer 450 is here sufficient not only to attenuate vibrations caused by the main actuator 422 through the edge 414 of the main transducer head, but also to block echoes transmitted from the second transducer element 462.

[0075] The transducer embodiments discussed above are suitable for propagating acoustic waves into a medium based on an electrical signal provided therein to the actuator. However, embodiments may include additional features for enhancing the transfer of acoustic energy from the actuator to the medium. Primarily, one or more matching layers may be used on the focusing lenses (e.g., headfaces 212, 312, 412) to improve energy transfer.

[0076] Figure 12 A simplified schematic diagram of the operating components of an immersion transducer 500 employing a matching layer or matching layer 514 according to some embodiments of the present disclosure is shown. See above reference. Figures 2-11 The characteristics of each of the transducers 200, 300, and 400 discussed are used in various aspects of transducer 500.

[0077] Transducer 500 includes a transducer head element 510, an actuation element 530, a backing element 540, a backing cavity 544, and an electrical matching network or control element 550. In operation, an electrical signal that defines the desired acoustic output is passed through input circuitry 554 to the electrical matching network element 550. This electrical matching network element 550 may include suitable electronics to filter, attenuate, amplify, or otherwise correct the electrical signal to effectively connect the input signal (e.g., a drive signal) to an electrical load such as the transducer actuation element 530. According to some embodiments, the matching network element 550 may include a sensing high-pass circuit 552, or other suitable filtering circuitry for conditioning the input signal. In operation, the matching network element 550 may include a simple high-pass filter that allows high-frequency electrical signals to pass through without significant attenuation (e.g., the high-frequency drive signal corresponding to the acoustic signal) while filtering low-frequency signals to block low-frequency phenomena. According to various other embodiments, the control element 550 may include any suitable filter or combination of filters for attenuating the signal from input circuitry 554.

[0078] The control element 550 is operatively connected to the actuation element 530 via an interconnect 538. The actuation element 530 includes an actuator 536, which may be a piezoelectric disc or a similar actuator. The actuator 536 is connected on opposite sides to a positive electrode 534 (shown here connected to the interconnect 538) and a negative or ground electrode 532 (connected to ground or a negative circuit, not shown). The actuator 536 responds to a drive signal by generating physical vibrations according to the frequency of the drive signal. The actuation element 530 is defined on one side by a transducer head element 510 and on the opposite side by a backing element 540 in a backing cavity 544. The backing element 540 is composed of a backing material 542 having a composition and / or microstructure adapted to absorb vibrations when in contact with the actuation element 530 and simultaneously bias the actuation element 530 toward the transducer head element 510. The backing cavity 544 may be open or filled with insulating and / or waterproof material to isolate the actuator element 530 from moisture or other external contaminants.

[0079] Transducer head element 510 faces medium 502, and transducer 500 is configured to direct acoustic energy into this medium. Transducer head element 510 includes a body of transducer head 512, a focusing lens 518, and a rear portion 520 of the transducer head positioned adjacent to actuator element 530. The focusing lens 518 consists of a matching layer 514 positioned on a surface 516 of the transducer head body 512. The transducer head body 512 is preferably made of a non-absorbent, rigid, lightweight, and non-porous material. For example, according to some embodiments, the transducer head body 512 may be a preferably corrosion-resistant metal or metal alloy. In various embodiments, the transducer head material may include, but is not limited to: aluminum (Al), beryllium (Be), cadmium (Cd), carbon (C), chromium (Cr), copper (Cu), germanium (Ge), gold (Au), iron (Fe), lead (Pb), manganese (Mn), molybdenum (Mo), nickel (Ni), niobium (Nb), phosphorus (P), platinum (Pt), selenium (Se), silicon (Si), silver (Ag), tin (Sn), titanium (Ti), tungsten (W), vanadium (V), zinc (Zn), or zirconium (Zr), and alloys or composites of any two or more of the foregoing, including composite alloys (such as stainless steel) that may also contain some non-metallic or non-semi-metallic components. Suitable non-metallic or non-semi-metallic components may include, for example, silicon, glass, quartz, or various ceramics. The transducer head is preferably corrosion-resistant and liquid-impermeable, particularly fluid-impermeable, so that the transducer head surface and shell not only repel liquids but also resist degradation or shape change when exposed to liquids for extended periods. In some embodiments, the transducer head material may be completely inert to the fluid coupling agent (e.g., water), with zero long-term penetration depth and zero weight loss due to corrosion. The transducer head body 512 may be integrally connected to, or may include, a housing surrounding the internal components of the transducer 500. For completely inert materials, zero penetration depth and weight loss may be assumed (or penetration / loss may be immeasurable). For minimally reactive materials, permissible penetration depth and weight loss depend on the target lifespan of the transducer and acceptable variations in lens focusing characteristics over that lifespan. In some embodiments, the maximum permissible weight loss of the material is approximately 0.1% per year or less.

[0080] Matching layer 514 is made of a material having an acoustic (i.e., mechanical) impedance between the impedance of the transducer head body 512 and the impedance of the medium 502. This matching layer 514 can significantly improve the transmission of acoustic energy into the medium 502, especially when the transducer head body 512 is made of a material with high impedance. Fluid-impermeable metals and metal alloys with favorable corrosion properties cover a wide range of acoustic impedances and typically have values ​​from 10 to 100 MRayl. Preferably, the transducer head and housing materials should be selected to match the acoustic impedance of the selected piezoelectric material of the actuator 536 as closely as possible. For typical piezoelectric materials that are ceramic and have an acoustic impedance in the range of approximately 15 to 43 MRayl, fluid-impermeable metals and metal alloys with an acoustic impedance in the lower range of 10-100 MRayl are preferred to promote acoustic energy transfer efficiency. For example, in a specific embodiment where the transducer head body 512 is composed of vanadium, the expected acoustic impedance of the transducer head body is approximately 36.2 MRayl.

[0081] Acoustic matching layer 514 is selected to facilitate acoustic energy transfer from transducer head body 512 to medium 502, which is typically a coupling agent such as water, gel, or another aqueous solution. For example, water has an acoustic impedance of approximately 1.5 MRayl. Acoustic energy transfer loss occurs when sound waves propagate directly from one medium across a step acoustic impedance to another, where optimal coupling is achieved by a single intermediate layer according to Equation 1 below, where Z m It is the interlayer impedance, Z l and Z c These are the impedances of the transducer head body 512 and the dielectric 502, respectively.

[0082]

[0083] Equation 1

[0084] According to embodiments, the matching layer 514 is made of a material selected to maximize acoustic energy transfer between the transducer head body 512 and the medium 502. This material is also adapted to permanently bond with the surface 516 of the transducer head body and simultaneously possess elasticity to resist intrusion or degradation by the medium. In a particular embodiment where the transducer head body 512 is vanadium with an acoustic impedance of approximately 36.2 Mrayl and the medium is water or a similar aqueous solution with an acoustic impedance of approximately 1.5 Mrayl, the optimal acoustic impedance of a single intermediate layer is approximately 7.3 Mrayl. According to various embodiments, the matching layer 514 is made of a material with an acoustic impedance of approximately 7.3 Mrayl. According to some specific embodiments, the matching layer 514 is composed of a fluoropolymer (such as polyvinylidene fluoride (PVDF)) or a similar polymer coating with an acoustic impedance between approximately 4-10 Mrayl, or in some cases, approximately 4-5 Mrayl. According to some other embodiments, the matching layer 514 may be composed of a graphite coating with an acoustic impedance between approximately 6-8 Mrayl. According to various embodiments, the matching layer 514 has an acoustic impedance in the range of about 5-10 Mrayl, about 4-10 Mrayl, or about 6-8 Mrayl. In some specific embodiments, the matching layer 514 has an impedance of about 4 Mrayl. According to various embodiments, the matching layer may consist of any of the following: PVDF, graphite, amorphous carbon, or polymer / particulate composites, including but not limited to polymer matrices (e.g., epoxy resins or the like) and alumina, tungsten, glass, or other similar particulate materials.

[0085] In some embodiments, the efficiency of acoustic energy transfer between the focusing lens body 512 and the medium 502 is improved by tuning the thickness of the matching layer 514. The matching layer 514 is preferably applied using a coating technique, such as spraying, spin coating, sputtering, diffusion bonding, etc., and subsequently made to have a uniform thickness. The thickness of the matching layer 514 can be adjusted by, for example, machining, pressing, spinning, or any suitable combination of the above or similar processes. Preferably, the thickness of the matching layer 514 is adjusted to match a quarter wavelength corresponding to a target frequency at which the transducer 500 is expected to pass through the selected material of the intermediate layer at the speed of sound. Alternatively, the matching layer 514 may have a thickness of approximately 3 / 4 wavelength or any other odd multiple of a quarter wavelength, such that reflections or destructive interference are minimized. For example, for an ultrasonic transducer with a target frequency (or nominal frequency) of approximately 12 MHz, a suitable matching layer 514 may have a thickness of approximately 60 μm (e.g., for graphite). For a given intermediate layer, the transducer can generate focused acoustic energy at wavelengths varying from approximately -25% to approximately +25% of the nominal wavelength corresponding to the target frequency. Therefore, according to some embodiments, a transducer with a single intermediate layer of thickness tuned for 12 MHz can accommodate signals in the range of approximately 9 MHz to approximately 15 MHz at high frequencies (typically about 10% to 20%), and can be used with lower efficiency outside this range. For example, a fluid-impermeable transducer can also have a nominal frequency in the range of 2 to 15 MHz. According to various embodiments, the thickness of the matching layer 514 can vary between approximately 30 and 80 μm. In some embodiments, the thickness of the matching layer 514 can vary from approximately 14% or less from the nominal thickness. However, using more than one intermediate layer can provide further flexibility in material selection, efficiency, and target frequency. In various alternative embodiments, the matching layer thickness can be approximately an odd multiple of the nominal value corresponding to a quarter wavelength of the target frequency.

[0086] Figure 13 A simplified schematic diagram of the operating components of an immersion transducer 600 employing multiple matching layers 614, 620 according to some embodiments of the present disclosure is shown. The transducer 600, as shown, has the same characteristics as described above. Figure 12The transducer 500 has similar features, with similar parts being given similar designations. For a transducer head body 612 formed of a fluid-impermeable metal or metal alloy having an acoustic impedance of 17 to 42 Mrayl, and a medium 602 of water or any similar aqueous substance having an acoustic impedance of about 1.5 Mrayl, the optimal acoustic impedance of a single intermediate layer will be approximately 5 to 8 Mrayl. However, acoustic energy can be transferred from the transducer head body 612 to the medium 602 through a first intermediate layer 614 having a first acoustic impedance, and subsequently through a second intermediate layer 620 having a second acoustic impedance, wherein the first intermediate layer has a higher acoustic impedance than the second intermediate layer, and wherein the first and second intermediate layers satisfy Equation 1 above to optimize acoustic energy transfer relative to each other. For example, the acoustic impedance of the first intermediate layer 614 (i.e., Z) m1 ) in Z l Acoustic impedance of the second intermediate layer 620 (i.e., Z) m2 Between these layers, the equations in Equation 2 below are satisfied. During assembly, acoustic energy is transferred from the transducer head body 612 through the first intermediate layer 614 and from the first intermediate layer interface 618 to the second intermediate layer 620. The acoustic energy is then transferred through the second intermediate layer 620 and exits the focusing lens 622 into the medium 602. Each respective intermediate layer 614, 620 is formed with a corresponding thickness by the selected material of each respective intermediate layer, the corresponding thickness corresponding to a quarter wavelength of the nominal frequency of the transducer 600, as described above with reference to a single intermediate layer 514 (…). Figure 5 (This is a discussion of the topic.)

[0087]

[0088]

[0089] Equation 2

[0090] Figure 14 A simplified schematic diagram of the working components of an immersion transducer 700 employing a diffraction focusing lens 714, according to some embodiments of the present disclosure, is shown. The transducer 700, as shown, has the same features as described above... Figures 12-13 The transducers 500 and 600 have similar features, and similar parts are given similar designations. The transducer head element 710 differs from the transducer head elements 510 and 610 described above in that it includes a transducer head body 712 defining a diffraction head surface 714 opposite to the rear portion 716 of the transducer head. The diffraction head surface 714 includes a set of diffractive infrared gratings operable, according to an embodiment, to direct acoustic energy to a predetermined focal length.

[0091] As discussed above, focusing lenses (e.g., head and face 212, 312, 412, ...) Figure 3 , Figure 8 and Figure 11 The transducer is sized to receive acoustic energy from the actuator (e.g., actuators 222, 322, 422) and redirect the acoustic energy from the transducer toward the focal point distal to the focusing lens. However, the focusing lens can be larger than, smaller than, or approximately the same size (diameter) as the actuator. Slightly different structures are suitable depending on whether the acoustic head surface is smaller or larger than the actuator. Such structures are more readily observed when the transducer is used as both a transmitter and a receiver. The transducer's actuator can be used to sense the emitted acoustic energy reflected back to the transducer as an echo, as well as to sense the acoustic energy reflected within the transducer's components. See below for reference. Figures 15-20 This paper discusses the impact of transducer head geometry on this type of sensing application.

[0092] Figure 15 A simplified side view schematic diagram of an assembly 800 having a transducer head 802 with a curved focusing lens 806 and an actuator 804 according to some embodiments is shown. According to some embodiments, the transducer head 802 defines a relatively large focusing region 816 of the focusing lens 806, which is larger than the diameter 814 of the associated actuator 804. Figure 15 The arrangement is similar to that described above regarding focusing lens 212 ( Figure 3 The arrangement is shown in the diagram. The focusing lens 806 shown herein is a concave curved surface of the transducer head 802 defining a focusing region 816. An actuator 814 is positioned behind the transducer head 802 and propels sound waves forward into the transducer head. A first subset 808 of the acoustic energy is transmitted directly through the transducer head 802 and emitted from the focusing lens 806 at a low angle, causing the acoustic energy to converge. However, before being emitted from the focusing lens 806, a second subset 810 of the acoustic energy encounters a steeper angle than the first subset and can be reflected 812 in the material of the transducer head 802. Reflection 812 can result in a degree of noise reflected back to the actuator, which in some cases may affect the transducer's use as both a transmitter and sensor in the same application, as this noise can be sufficiently delayed in time to affect the transducer during the period when it is used as a sensor. For reference, the location of a sample microporous plate 820 is shown, which includes a top surface 822 of the aperture and a bottom surface 824 of the plate. The exact location can vary depending on the height of the fluid in the orifice and the size of the orifice, and assembly 800 can accommodate sample microplates of many types and sizes. Acoustic reflection can occur at material boundaries, such as either the top surface 822 or the bottom surface 824 of the microplate 820, and at the fluid / air boundary 826. For sensing applications, such as detecting the height of the fluid in the orifice, the fluid / air boundary 826 does not need to be close to the focal plane of the transducer head 802. For droplet jetting applications, the transducer head 802 or the microplate 820 will be moved to position the focal plane near the fluid / air boundary 826.

[0093] Figure 16 It shows a curved focusing lens (similar to) Figure 15 The diagram illustrates a graphical representation of echo signal data 900 generated by a curved focusing lens 806. Echo signal data 900 includes: a first signal 902 corresponding to two echoes caused by acoustic reflections from different parts of the plate (e.g., top surface 822 and bottom surface 824), and may include tailing or ringing caused by acoustic energy reflections and / or redirection within the transducer head; and a second signal 904 corresponding to the transducer acoustically probing the medium and receiving the echoes (i.e., receiving the echoes from the fluid / air boundary 826). The two echoes occurring in the first signal 902 are visible at approximately 20-30 μs and 30.5 to 32 μs, respectively. Both the first signal 902 and the second signal 904 are distinct from the background, and therefore noise can be easily identified and ignored. However, if the transducer receives multiple acoustic signals in a short sequence, distinguishing the multiple echo signals from each other or from the background noise can be challenging. The ringing effect and "double echo" effect caused by reflections within the transducer head 802 are exacerbated by the use of rigid, non-porous materials (such as impermeable metals or metal alloys).

[0094] As discussed above, suitable acoustic / mechanical properties of lens materials include: acoustic impedance typically in the range of 10–30 MRayl, relatively high and consistent sound velocity (e.g., 4 km / s or higher), and resistance to corrosion, water absorption, bending, and acoustic absorption. The acoustic effects induced in such materials are generally reproducible and can be corrected in software. For example, means of mitigating or correcting acoustic effects may include echo cancellation software, as used in conventional audio applications, and applied to reduce secondary reflections after the initial peak of the signal. Furthermore, such materials generally transmit acoustic energy more efficiently than the more malleable and formable materials used in conventional transducers for NDT applications, resulting in significantly less energy required to generate an acoustic signal compared to systems using conventional materials. It has been found that reducing the size of the focusing lens relative to the actuator can shorten and reduce the noise distribution relative to the signal, and further reducing the noise distribution can be achieved by adding acoustic damping material to the periphery of the transducer head.

[0095] Figure 17 A simplified side view of an assembly 1000 with a transducer head 1002 having a curved focusing lens 1006 and an actuator 1004 according to some embodiments is shown. The assembly 1000 includes an outer absorption layer 1014 that defines a focusing region 1012 of the focusing lens. As shown, the focusing region 1012 is slightly larger than the diameter 1010 of the actuator, but the extent of the focusing lens 1006 is similar to... Figure 15The reduced range of the focusing lens 806 makes its concavity less pronounced, thereby reducing the angle at which the acoustic energy 1008 encounters the boundary of the head and face. This reduced angle results in significantly less acoustic energy being reflected inside the transducer head 1002, thus reducing overall noise when the transducer emits acoustic energy. In some embodiments, an external absorption layer 1014 may be added to the transducer head 1002 outside the focusing lens 1006, which absorbs stray acoustic energy reflected inside the transducer head without leaving the focusing lens. Figure 15 Compared to component 800, the arrangement of the illustrated component 1000 can significantly reduce noise and signal, thereby increasing signal resolution relative to noise. In some embodiments, actuator 1004 may have the same size as the focusing region 1012 of focusing lens 1006, or in some cases, slightly larger than the diameter 1010 of the focusing region. For reference, the position of the sample microporous plate 820 is reproduced, including the top surface 822 of the orifice and the bottom surface 824 of the plate. The exact position may vary depending on the height of the fluid in the orifice and the size of the orifice, and component 1000 can be adapted to many types and sizes of sample microporous plates. Acoustic reflection may occur at material boundaries, such as at either the top surface 822 or the bottom surface 824, or from the fluid / air boundary 826, which typically corresponds to the height of the fluid in the orifice of the microporous plate 820.

[0096] Figure 18 It shows the combination of and Figure 17 A graphical illustration of the echo signal data 1100 caused by a component similar to component 1000, to be compared with... Figure 16 The echo signal data 900 shown is compared. Signal 1102 consists of two pulses reflected from the bottom and top of the orifice plate, and signal 1104 is caused by reflection from the surface of the fluid in the orifice (i.e., the fluid / air interface 826). This signal can be compared with... Figure 16 The signal 902 is compared. Specifically, compared to Figure 16 The corresponding first signal 902 shown is as follows: Figure 18 The first signal 1102 shown is narrower and more clearly separated from each other. Additionally, the echo signal data 1100 has less background noise than the echo data signal 900, especially after each of the initial echo signals (1102, 902). This increased clarity and reduced background noise are evident in the transducer head assembly 1000 ( Figure 17 How the characteristics of a focus area reduce echo and improve resolution. Generally, reducing the focus area (e.g., Figure 15 and 17The size of the focused regions (816, 1012) shown reduces the signal, and also reduces noise or ringing associated with the signal, but not at the same rate. Therefore, the size of the focused region of the tunable transducer to optimize the resolution of the echo signal and reduce the likelihood that noise events will be misclassified as surface reflections.

[0097] Figure 19 A graphical illustration of echo signal data 1200 for transducers with different aperture sizes according to various embodiments is shown. Transducer echo signal data 1202, 1204, 1206, 1208, and 1210 are reproduced together on the same graph to illustrate the variation of echo signal data associated with the corresponding size of the signal generation area or aperture for each transducer. For each transducer, a first signal 1220 corresponds to acoustic energy reflection within the transducer, shown here as the echo from the bottom of the orifice plate, and a second signal 1222 corresponds to the signal caused by the reflection of acoustic energy from a target (in this case, the free surface of the fluid in the aperture). As the aperture size decreases (e.g., from a diameter of 17.5 mm for transducer data 1202 to a diameter of 10 mm for transducer data 2110), a decrease in the amplitude of both signals and a decrease in the ringing associated with the first signal 1220 are observed. Therefore, depending on the transducer's intended application (i.e., from simply generating a high-power signal to signal detection), an aperture size can be selected that provides sufficient power while mitigating noise and / or ringing. Similarly, the aperture size affects the beam size of the acoustic signal at the focal point, as shown in the reference... Figure 20 shown.

[0098] Figure 20 Transducers 1202, 1204, 1206, 1208, and 1210 with different aperture sizes are shown according to various embodiments. Figure 19 A graphical illustration of the associated beam size data 1300. The Y-axis shows the amplitude of the acoustic signal at a certain distance from the central axis of the beam path, acquired at the transducer's focal length and normalized for the amplitude of the acoustic signal at the focal point. Wider curves indicate more defocused beams, and narrower curves indicate more focused beams. As shown in the figure, when the aperture size is 1202-1210 ( Figure 19 As the size of the focusing aperture decreases, the width of the defocusing curves 1302-1310 increases. Therefore, the increased aperture size produces improved focusing, while being inversely correlated with signal sharpness. However, the increased focusing aperture size exhibits a diminishing return in improving beam focusing, as shown by the relatively small difference between defocusing curves 1302-1306 compared to the difference between defocusing curves 1306-1310.

[0099] For applications requiring high power handling capability, a large aperture area is generally desirable because power is roughly proportional to the aperture area. Therefore, for a given target F-number or target beam angle, the focal length and aperture size can be increased to accommodate the increased power handling desired. However, the larger focal length resulting from this increase in size will increase the length of the beam path in the medium, thus increasing attenuation. Therefore, depending on the intended application, the aperture size is selected to balance the need for focusing with the need to mitigate noise or ringing. According to some embodiments, the aperture size can range from about 10 mm to about 17.5 mm. In some specific embodiments, the aperture size can range from about 10 mm to about 13 mm, or it can be about 11.5 mm. A suitable F-number for high-power applications can vary, but in specific embodiments, it can range from about 0.8 to 4, or preferably from about 1.5 to 3, or about 2 to 2.5.

[0100] As described above, adjusting the lens aperture diameter affects the beam size and ringing level during focusing. However, these parameters can, or preferably can, be tuned by adjusting the size or diameter of the electrodes connected to the actuator. Return to Reference Figure 3 For example, actuator 222 is a piezoelectric disk, wherein a positive electrode 226 is disposed across the center of the disk toward the inner cavity 218, and a negative electrode 228 is disposed in a circular pattern around the periphery of the actuator. In such embodiments, adjusting the size of the positive electrode 226 can particularly control the area of ​​the acoustic power generation region of the actuator, where a larger area is associated with a higher amplitude and a wider beam area. Adjusting the electrode diameter can help suppress the beam size in order to reduce reverberation and ringing, as referenced above. Figures 17-20 shown.

[0101] In various other embodiments, the lens thickness can be adjusted to alter the time delay of reverberation within the lens material. For example, in at least one specific embodiment, the thickness at the center of the lens is matched to a quarter-wavelength based on the transducer's nominal frequency. Setting the center lens thickness to this quarter-wavelength value improves acoustic coupling from the actuator to the medium. In one embodiment, the nominal lens thickness is 0.15 mm (for a transducer designed to operate in the 10-12 MHz range), but can vary within a range of approximately 0.1 to 0.2 mm.

[0102] According to various embodiments, the focusing lens (e.g., Figure 4 , Figure 8 , Figure 11 The focusing lenses 212, 312, 312 can be connected to the main body of the transducer housing (202, 302, 402), or can be integrally connected to the housing. The focusing lenses are formed from the housing through a precision forming process. Figure 21This is a simplified block diagram illustrating a system 2100 for generating a focusing lens according to an embodiment. System 2100 may include a user input module 2102 for receiving user input, which includes specific dimensions and / or performance criteria (e.g., desired focal length, efficiency, and / or signal-to-noise requirements) of the transducer's aperture, depth, and shape. This may or may not depend on the desired target medium, nominal focal length, and / or material selection. A modeling module 2104 may determine the desired focusing lens shape based on the user input. In some cases, the modeling module 2104 may determine the characteristics of a matching layer added to the focusing lens based on the selected material and target medium of the focusing lens. The modeling module 2104 may also be used to generate performance criteria 2110 for testing and / or verifying the transducer's performance.

[0103] The focusing lens can be manufactured using a manufacturing module 2106 that may include one or more automated or semi-automated manufacturing mechanisms, such as laser ablation or precision CAD processing equipment for selectively removing material, or material manufacturing mechanisms such as 3D printing methods or vapor deposition equipment. This may include: applying or adjusting the thickness of the matching layer; and assisting assembly tasks, including assembling the internal components of the transducer to the rear of the focusing lens, and optionally (e.g., by welding) assembling the focusing lens to the transducer housing. The assembled transducer can be inserted into a test module 2108, which can iteratively generate and / or receive acoustic signals via the transducer to measure the focusing performance or efficiency of the transducer as a transmitter, or to determine the signal-to-noise ratio, noise attenuation, and / or sensitivity of the transducer when operating as a sensor. In some embodiments, the test module 2108 can operate over long timescales to provide performance metrics under prolonged immersion. Performance criteria can be evaluated 2110 and used iteratively to adjust the parameters defining the focusing lens at the modeling module 2104 by adding or removing lens or matching layer material.

[0104] Figure 22 An exemplary process 2200 for manufacturing a watertight ultrasonic transducer according to an embodiment is shown. Process 2200 can be combined with, for example... Figure 21 The system 2100 shown is used for implementation. Some or all of process 2100 (or any other process described herein, or variations and / or combinations thereof) can be executed under the control of one or more computer systems configured with executable instructions, and can be implemented as code (e.g., executable instructions, one or more computer programs, or one or more application programs) executed jointly by hardware or a combination thereof on one or more processors. The code can be stored on a computer-readable storage medium, for example, in the form of a computer program comprising multiple instructions executable by one or more processors. The computer-readable storage medium can be non-transitory.

[0105] Process 2200 includes receiving input indicating one or more transducer performance criteria (Action 2202). The input may include the transducer's expected nominal operating frequency, material selection, preferred focal length when focused, or desired beam profile or other characteristics. Next, the focusing lens geometry can be defined based on the input (Action 2204), including aperture size (i.e., the diameter of the recessed portion of the focusing lens) and the shape or depth of the focusing lens. A waterproof transducer head may be formed, for example, by precision machining or similar methods to conform to the defined focusing lens geometry (Action 2206), and the transducer head may subsequently be connected to a waterproof housing by waterproof means (e.g., permanent bonding, contact, and / or laser welding, or other similar methods) (Action 2208). Transducer electronics may be assembled with the transducer head and housing (Action 2210), the transducer electronics including, for example, an actuator coupled to the rear of the transducer head, as well as a backing and electronic components, as described above regarding transducers 200-700 (…). Figures 2-14 As discussed in [the original text], it should be understood that the step of connecting the transducer head and housing can be omitted by forming the transducer head and housing from a single part, allowing the components to be integrally connected, such as [the original text]. Figure 23 As shown in the image.

[0106] Figure 23 An exemplary process 2300 for forming a transducer head and housing from a single integral part is shown. Process 2300 includes receiving input (action 2302) defining a focusing lens geometry, which can be defined according to any suitable performance criteria for the ultrasonic transducer, as referenced above. Figure 22 As discussed above, an impermeable housing closed at one end can be formed from an impermeable material (e.g., a non-corrosive metal or alloy housing) by a combination of casting, machining, or similar methods (Action 2304), wherein the closed end is sized and has sufficient thickness to accommodate a focusing lens therein. The focusing lens can then be formed by removing material from the closed end of the housing, for example, by precision machining or similar methods (Action 2306). The housing and transducer head formed in this way can then be assembled with the various transducer electronics described above.

[0107] Any transducer head material with an acoustic impedance significantly different from that of the target medium (e.g., a ratio exceeding 5 between a typical metal with an acoustic impedance Z > 10 MRayl and an aqueous solution with an acoustic impedance Z < 2 MRayl) will tend to dissipate acoustic energy at the boundary between the focusing lens and the medium, where the greater the impedance difference, the greater the resulting loss. In conventional immersion transducers, the transducer head is typically constructed of a material with low acoustic impedance to minimize transmission losses; and absorbs or attenuates some of the acoustic energy passing through it, thus attenuating noise. However, in the embodiments described herein, the focusing lens is a completely impermeable material, such as a metallic (e.g., stainless steel or platinum) housing. Such materials can be more efficient emitters, absorbing less energy passing through them. However, if such transducers emit directly into a low-impedance medium, they may lose a significant amount of acoustic energy at the medium boundary (transition loss) and may be prone to high noise and internal reflections. These disadvantages are described below. Figure 24 The methods discussed can alleviate this.

[0108] Figure 24 An exemplary process 2400 according to an embodiment is illustrated for modifying a transducer head and / or housing to mitigate transition losses and / or noise. Process 2400 includes receiving inputs including information about the acoustic impedance of the transducer head material and the target medium in which the transducer is intended to operate (Action 2404). One (or more) matching materials are selected based on the acoustic impedance of each material to facilitate acoustic energy transfer between the focusing lens and the target medium (Action 2406). A single matching material may be selected according to the reference above. Figure 12 The matching layers can be selected from any suitable combination of the parameters discussed in Equation 1. In some cases, multiple matching layers can be selected, in which case they can be chosen based on the parameters discussed above. Figure 13 Any suitable combination of the parameters discussed and the system of equations in Equation 2 can be used to select the appropriate material.

[0109] Next, the nominal thickness of the matching layer material can be determined based on the acoustic impedance of the selected material and the transducer's expected operating frequency (Action 2308). See reference... Figure 12 The nominal thickness discussed here is preferably a quarter wavelength associated with the nominal frequency of the sound wave passing through the matching layer material, or alternatively, any odd multiple of a quarter wavelength (e.g., three-quarters of the wavelength). The matching layer is applied to the focusing lens with a thickness equal to or greater than the nominal thickness (Action 2410). In some cases, when the matching layer is deposited in a manner that distributes the material uniformly and precisely, the matching layer can be applied directly to the preferred thickness. However, in some cases, the matching layer can be partially removed (e.g., by precision machining) so that the entire matching layer conforms to the preferred nominal thickness (Action 2412).

[0110] Other materials may be applied to the transducer head and adjacent to the focusing lens to reduce noise or ringing. For example, an attenuation layer formed of sound-absorbing material may be applied around the periphery of the focusing lens (Action 2414). In some cases, the attenuation layer may be used as a backing material for other components (e.g., one or more small additional transducers), which may then be stacked on the attenuation layer and operated using the attenuation layer as a backing material (Action 2416), as in reference transducer 400 above. Figures 10-11 As described in ( ).

[0111] Compared to conventional transducer designs, the impermeable transducers described above offer exceptionally uniform performance over time and do not degrade in response to fluid exposure. Despite immersion, these transducers can be expected to maintain consistent performance from manufacturing time to long-term use. For example, two identical transducers with the same acoustic focusing should be interchangeable and produce droplets of the same size when used in droplet delivery applications, even if one is used for 5 years (with the instrument exterior kept dry) while the other is submerged for 5 years. Similar consistency can be expected over long-term use in other immersion applications such as NDT.

[0112] The performance consistency of fluid-impermeable transducers can be characterized in several ways, including but not limited to consistent focal length, eccentricity, and symmetry. The focal length can be empirically determined by measuring the amplitude of the sound beam along the axis passing through the apex of the lens. Figure 25 This is a graph showing an exemplary focusing sweep along this axis, illustrating the echo amplitude based on the echo delay or time-of-flight (ToF) corresponding to the distance from the lens. Similarly, the shape of the focus (e.g., eccentricity, symmetry) can be empirically determined by measuring the amplitude of the sound beam across a two-dimensional plane corresponding to the focal length (i.e., the focal plane). Figure 26 This is a contour plot showing the echo amplitude measured across an exemplary focal plane of a sound beam generated by a fluid-impermeable transducer.

[0113] The procedure for measuring the focal length of a transducer is as follows. A flat, solid plate is mounted on a mechanical translation platform in front of the transducer, such that the plate is perpendicular to the sound beam radiated from the transducer. The translation platform should be configured to move the plate such that the distance between the apex of the lens and the plate can vary around the desired focal plane of the lens. The space between the transducer and the plate is filled with a suitable coupling fluid, such as, but not limited to, distilled water, in a temperature-controlled environment. A flat, smooth stainless steel plate can be used as the solid part. The transducer is positioned at discrete intervals from the plate, and at each interval is excited with a short "ping" waveform. Each ping excites a short acoustic pulse traveling from the transducer to the plate, which is reflected back to the lens and converted back into an electrical signal at the transducer. For each ping, the peak amplitude of the echo and the delay between the reflected echo and the applied ping signal are measured, and this process is repeated at each consecutive transducer-plate interval. The corresponding echo peak amplitude and delay can be plotted, such as... Figure 25 As shown in the diagram. The delay for obtaining the highest echo return is the characteristic time of flight (ToF) corresponding to the focal length of the transducer. If desired, curve fitting can be used to smooth out unavoidable noise in the received echo to obtain a consistent estimate of the focusing ToF. The fluid-impermeable transducer disclosed herein can maintain its lens shape during prolonged immersion, thereby maintaining a consistent focal length even after prolonged immersion. According to some embodiments, the fluid-impermeable transducer disclosed herein can generate a sound beam with a focal length within 0.1% of the initial focal length of the initial sound beam generated immediately after the initial immersion, even after one year of immersion. This consistency can also extend to beam eccentricity and symmetry after prolonged immersion.

[0114] The procedure for measuring the spatial characteristics of the sound beam generated by the transducer, and thereby measuring its eccentricity and symmetry, is as follows. First, a needle reflector is mounted on a set of xy-double mechanical translation platforms in front of the transducer, such that the needle is aligned with the sound beam radiated from the transducer and the tip is at the focal plane of the lens. The translation platforms should be configured to move the needle in the lateral direction around the desired focal point of the lens. The space between the transducer and the needle is filled with a suitable coupling fluid, typically distilled water, in a temperature-controlled environment. Once assembled, the needle is moved in small xy-step increments using the translation platforms with a grating pattern, while the transducer emits and records the acoustic signal. At each xy position, the following steps are performed: (a) the transducer is excited with a short “ping” waveform, (b) the ping excites a short acoustic pulse traveling from the transducer to the needle, (c) the needle reflects the sound beam back to the lens of the transducer, (d) the transducer signal converts the echo back into an electrical signal, and (e) the peak amplitude of the reflected echo is recorded and correlated with the corresponding xy position. You can compare it as follows Figure 26The peak echo signal records are plotted at the xy positions shown in the contour plot. Surface fitting can be used to estimate the eccentricity or concentricity of the sound beam emitted from the transducer.

[0115] Compared to transducers using materials that gradually absorb, degrade, or deform in liquids, the spatial characteristics of the sound beam generated by the fluid-impermeable transducers disclosed herein are remarkably consistent over time and after immersion. This consistency can be described by symmetry, eccentricity, concentricity, or other properties. According to some embodiments, after one year of immersion in a liquid, the eccentricity of the sound beam generated by the fluid-impermeable transducer is consistent within 0.1% of the initial eccentricity of the initial sound beam generated immediately after the initial immersion. The fluid-impermeable material for the transducer lens, as well as the backing layer and actuator disclosed herein, can also provide a lens shape with improved accuracy and produce a sound beam shape superior to that of previously available transducers. Therefore, a precise sound beam shape with an eccentricity of less than 0.1% (i.e., perfectly concentric or nearly concentric) is achievable and can be maintained during prolonged immersion.

[0116] In some alternative embodiments, impermeable transducers as described herein may be used in transducer arrays for specific applications (e.g., NDT and analytical applications, high-power applications, etc.). Conversely, impermeable transducers as described herein may also be used to replace transducer arrays in applications traditionally reserved for transducer arrays. Such transducer arrays are described in detail, for example, U.S. Patent No. 8,544,976. Methods known in the art can be used to determine the physical parameters of these structures based on the characteristics of the echoes returned from the scanned structure through a scanning operation. Various physical parameters and echo characteristics used for NDT, as well as scanning parameters, are known in the art and are disclosed in the following references, which are incorporated herein by reference for all purposes: VM Ristic, “Principles of Acoustic Devices”, John Wiley and Sons (1983); G. Crowe, “An Introduction to Nondestructive Testing”, (2009). https: / / www.ndt.org / ;and https: / / asnt.org / Home .

[0117] The various computational methods discussed above can be executed in conjunction with or using a computer or other processor having hardware, software, and / or firmware. The various method steps can be executed by modules, and modules can include any of a variety of digital and / or analog data processing hardware and / or software arranged to perform the method steps described herein. The module may optionally include data processing hardware adapted to perform one or more of these steps by means of appropriate machine-programmed code associated therewith. In any of a wide range of integrated and / or distributed processing architectures, modules for two or more steps (or portions of two or more steps) are integrated into a single processor board or partitioned across different processor boards. These methods and systems will typically employ tangible media containing machine-readable code with instructions for performing the method steps described above. Suitable tangible media may include memory (including volatile and / or non-volatile memory), storage media (such as magnetic recording on floppy disks, hard disks, magnetic tapes, etc.; optical storage, such as CDs, CD-R / Ws, CD-ROMs, DVDs, etc.; or any other digital or analog storage media), and so on.

[0118] The specific details shown herein are merely examples and for the purpose of illustrative discussion of preferred embodiments of the invention only, and are presented to provide a description of the principles and concepts of the various embodiments of the invention that are considered most useful and readily understood. In this regard, no attempt is made to show the structural details of the invention in more detail than is necessary for a basic understanding of the invention, and the description, accompanied by drawings and / or examples, will make it apparent to those skilled in the art how the invention can be embodied in practice in several forms.

[0119] Unless explicitly and unambiguously modified in the following instances, or where the application of the meaning renders any construct meaningless or substantially meaningless, the following definitions and interpretations are intended to control any future constructs. Where the construct of a term would render it meaningless or substantially meaningless, the definition should be obtained from Webster's Dictionary, its third edition, or a dictionary known to those skilled in the art, such as the Oxford Dictionary of Biochemistry and Molecular Biology (Ed. Anthony Smith, Oxford University Press, Oxford, 2004).

[0120] Unless the context explicitly requires otherwise, throughout the description and claims, the terms "comprise / comprising," etc., shall be understood to have an inclusive meaning, the opposite of an exclusive or exhaustive meaning; that is, meaning "including but not limited to." Terms using singular or plural numerals also include plural and singular numerals, respectively. Furthermore, when used in this application, the terms "in this document," "above," and "below," and similarly introduced terms, shall refer to the application as a whole and not to any particular part thereof.

[0121] The description of embodiments of this disclosure is not intended to be exhaustive or to limit this disclosure to the precise forms disclosed. While specific embodiments and examples of this disclosure have been described herein for illustrative purposes, various equivalent modifications are possible within the scope of this disclosure, as will be recognized by those skilled in the art.

[0122] All references, including patent applications (including patents, patent applications and patent publications), scientific journals, books, papers, technical references and other publications and materials discussed in this application, are incorporated herein by reference in their entirety for all purposes.

[0123] If necessary, aspects of this disclosure may be modified to incorporate the systems, functions, and concepts of the foregoing documents and applications to provide further embodiments of this disclosure. These and other changes may be made to this disclosure based on the detailed description.

[0124] Specific elements of any of the foregoing embodiments may be combined or substituted for elements in other embodiments. Furthermore, while advantages associated with certain embodiments of this disclosure have been described in the context of these embodiments, other embodiments may also exhibit such advantages, and not all embodiments are required to demonstrate such advantages to fall within the scope of this disclosure.

[0125] While a full and complete disclosure of exemplary embodiments of the invention has been provided above, various modifications, alternative constructions, and equivalents may be made as needed. Therefore, although embodiments have been described by way of example and in some detail for clarity of understanding, various modifications, alterations, and adaptations will be apparent to those skilled in the art. Consequently, the foregoing description and illustrations should not be construed as limiting the invention, which is defined by the appended claims.

[0126] Other variations are within the spirit of this disclosure. Therefore, while the disclosed technology is susceptible to various modifications and alternative constructions, certain illustrated embodiments are shown in the drawings and have been described in detail above. However, it should be understood that this disclosure is not intended to be limited to any particular form or certain forms disclosed, but rather, it is intended to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of this disclosure as defined in the appended claims.

[0127] In the context of describing the disclosed embodiments (particularly in the context of the following claims), the terms “a / an” and “the,” and similar references, should be interpreted to cover both singular and plural forms, unless otherwise specified herein or clearly conflict with the context. Unless otherwise indicated, the terms “comprising,” “having,” “including,” and “containing” should be interpreted as open-ended terms (i.e., meaning “including, but not limited to”). The term “connected” should be interpreted as partially or completely contained, attached to, or linked together, even in the presence of intermediates. Unless otherwise indicated herein, references to ranges of values ​​herein are intended only as a shorthand method for individually referring to each individual value falling within that range, and each individual value is incorporated into this specification as if individually stated herein. Unless otherwise specified herein or otherwise clearly conflict with the context, all methods described herein can be performed in any suitable order. The use of any and all instances or exemplary language (e.g., “such as”) provided herein is intended only to better illustrate embodiments of this disclosure and does not limit the scope of this disclosure unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element necessary for the practice of this disclosure.

[0128] Unless otherwise explicitly stated, disjunctive language such as the phrase “at least one of X, Y, or Z” is intended to be understood in the context of common use to indicate that an item, term, etc., may be X, Y, or Z, or any combination thereof (e.g., X, Y, and / or Z). Therefore, such disjunctive language is generally not intended and should not imply that some embodiments require the presence of at least one X, at least one Y, or at least one Z.

[0129] Preferred embodiments of this disclosure are described herein, including the best modes known to the inventors for carrying out this disclosure. Variations of these preferred embodiments will become apparent to those skilled in the art upon reading the foregoing description. The inventors intend that those skilled in the art will adopt these variations as appropriate, and that this disclosure will be practiced in ways other than those specifically described herein. Therefore, this disclosure includes all modifications and equivalents of the subject matter set forth in the appended claims as permitted by applicable law. Furthermore, unless otherwise indicated herein or otherwise clearly contradicted by the context, any combination of the foregoing elements in all possible variations is covered by this disclosure.

[0130] All references cited in this document, including publications, patent applications and patents, are incorporated herein by reference to the same extent that each reference is individually and specifically indicated as incorporated herein by reference and set forth in its entirety.

[0131] Further examples are described below to facilitate understanding of the invention:

[0132] Example A. A transducer comprising: a housing; a fluid-impermeable transducer head including a metal focusing lens having a rear surface and a front surface, the metal focusing lens being disposed on the front surface and configured to focus ultrasound toward a focal point; and an actuator coupled to the rear surface of the transducer head and operable to generate oscillating mechanical vibrations of the metal focusing lens, such that ultrasound is emitted from the metal focusing lens toward the focal point, wherein the housing and the transducer head are connected in a fluid-impermeable manner to prevent liquid from entering the housing.

[0133] Example B. The transducer according to any one of the preceding examples, wherein the housing comprises a metal housing connected to the metal focusing lens via a fluid-impermeable connector.

[0134] Example C. The transducer according to Example B, wherein the fluid-impermeable joint includes a welded joint.

[0135] Example D. The transducer according to any one of the preceding examples, wherein the housing and the transducer head are connected in a fluid-impermeable manner to prevent gas from entering the housing.

[0136] Example E. The transducer according to any one of the preceding examples, wherein the housing and the metal focusing lens are integrally formed.

[0137] Example F. The transducer according to any one of the preceding examples, wherein the focusing lens comprises a spherical concave surface.

[0138] Example G. The transducer according to any one of the preceding examples, wherein the focusing lens includes a cylindrical concave surface.

[0139] Example H. The transducer according to any one of the preceding examples, wherein the actuator is a piezoelectric transducer.

[0140] Example I. A transducer according to any one of the preceding examples, wherein the front surface of the transducer head includes a peripheral portion surrounding the focusing lens, and further includes an attenuation layer in contact with the peripheral portion and configured to absorb ultrasonic energy emitted from the actuator through the peripheral portion.

[0141] Example J. The transducer according to any one of the foregoing examples further includes a matching layer coupled to the focusing lens to transmit ultrasound from the focusing lens to the medium, the matching layer being configured to enhance ultrasound transmission from the focusing lens to the medium compared to direct ultrasound transmission from the focusing lens to the medium.

[0142] Example K. The transducer according to Example J, wherein the focusing lens has a first acoustic impedance, the medium has a second acoustic impedance different from the first acoustic impedance, and the matching layer has a matching acoustic impedance between the first acoustic impedance and the second acoustic impedance.

[0143] Example L. The transducer according to Example K, wherein the matched acoustic impedance is according to equation Z. m =√(Z l Z c (Approximately equal to Z) m Z l It is the first acoustic impedance, Z c It is the second acoustic impedance.

[0144] Example M. The transducer according to Example L, wherein the matched acoustic impedance is in Z m Within 10%.

[0145] Example N. The transducer according to Example L, wherein the matched acoustic impedance is in Z m Within 5%.

[0146] Example O. The transducer according to Example K, wherein the matched acoustic impedance is in the range of about 4-10 Mrayl.

[0147] Example P. The transducer according to Example K, wherein the matched acoustic impedance is in the range of about 6-8 Mrayl.

[0148] Example Q. The transducer according to any one of Examples JP, wherein the matching layer comprises graphite.

[0149] Example R. The transducer according to any one of Examples JP, wherein the matching layer comprises a fluoropolymer layer.

[0150] Example S. The transducer according to any one of Examples JP, wherein the matching layer comprises polyvinylidene fluoride.

[0151] Example T. A transducer according to any one of Examples JS, wherein the thickness of the matching layer corresponds to an odd multiple of a quarter wavelength of the acoustic signal passing through the matching layer at the nominal frequency.

[0152] Example U. The transducer according to Example T, wherein the thickness of the matching layer is within 20% of the nominal thickness defined by an odd multiple of the quarter wavelength.

[0153] Example V. The transducer according to Example T, wherein the thickness of the matching layer is within 10% of the nominal thickness defined by an odd multiple of the quarter wavelength.

[0154] Example W. The transducer according to any one of Examples TV, wherein the nominal frequency is in the range of 2 to 15 MHz.

[0155] Example X. The transducer according to any one of Examples TW, wherein the matching layer has a thickness ranging from 30 to 80 μm.

[0156] Example Y. The transducer according to any one of the foregoing examples further includes a first matching layer disposed on the front surface and a second matching layer disposed on the first matching layer, the first matching layer and the second matching layer being configured to enhance the transmission of ultrasound from the focusing lens to the medium compared to direct transmission of ultrasound from the focusing lens to the medium.

[0157] Example Z. The transducer according to Example Y, wherein: the focusing lens has a first acoustic impedance; the medium has a second acoustic impedance different from the first acoustic impedance; the first matching layer has a first matching acoustic impedance between the first acoustic impedance and the second acoustic impedance; and the second matching layer has a second matching acoustic impedance between the first matching acoustic impedance and the second acoustic impedance.

[0158] Example AA. According to the transducer described in Example Z, wherein the first matched acoustic impedance and the second matched acoustic impedance are approximately equal to Z. m1 and Z m2 Z m1 =√(Z l Z m2 ) and Z m2 =√(Z m1 Z c), and Z l Corresponding to the acoustic impedance of the metal focusing lens, Z c The acoustic impedance corresponding to the medium.

[0159] Example AB. The transducer according to any one of the foregoing examples, wherein the diameter of the focusing lens is larger than that of the actuator.

[0160] Example AC. A transducer according to any one of the foregoing examples, wherein the transducer head is formed of metal or metal alloy.

[0161] Example AD. The transducer according to any one of the foregoing examples, wherein the transducer head comprises one or more of aluminum (Al), beryllium (Be), cadmium (Cd), carbon (C), chromium (Cr), copper (Cu), germanium (Ge), gold (Au), iron (Fe), lead (Pb), manganese (Mn), molybdenum (Mo), nickel (Ni), niobium (Nb), phosphorus (P), platinum (Pt), selenium (Se), silicon (Si), silver (Ag), tin (Sn), titanium (Ti), tungsten (W), vanadium (V), zinc (Zn), or zirconium (Zr).

[0162] Example AE. A transducer according to any one of the foregoing examples, wherein the transducer head and housing are characterized in that the liquid penetration depth and the resulting material loss are zero when immersed in a liquid.

[0163] Example AF. The transducer according to any one of the foregoing examples, wherein the transducer head and housing are characterized in that the annual material weight loss in contact with the liquid is less than 0.1%.

[0164] Example AG. A transducer according to any one of the foregoing examples, wherein the thickness of the actuator is approximately half the nominal acoustic wavelength of the acoustic signal at the nominal frequency generated by the transducer.

[0165] Example AH. A transducer according to any one of the foregoing examples, wherein the thickness of the actuator is approximately 275 μm.

[0166] Example AI. The transducer according to any one of the foregoing examples further includes a backing material configured to attenuate the acoustic energy transmitted by the actuator, the actuator being located between the backing material and the metal focusing lens.

[0167] Example AJ. The transducer according to Example AI, wherein the backing material comprises particles of acoustic scattering material uniformly suspended in an acoustic damping material.

[0168] Example AK. The transducer according to Example AI, wherein the backing material comprises a damping polymer matrix.

[0169] Example AL. The transducer according to Example AI, wherein the backing material comprises a damping polymer matrix impregnated with silicon carbide particles.

[0170] Example AM. According to the transducer described in Example AI, the backing material comprises a damping polymer matrix impregnated with tungsten particles.

[0171] Example AN. A transducer according to any one of Examples AI-AM, wherein the backing material has an acoustic impedance ranging from 13.5 to 16.5 Mrayl.

[0172] Example AO. The transducer according to any one of Examples AI-AN further includes a sealant that substantially fills the interior space of the housing, and the backing material is disposed between the actuator and the sealant.

[0173] Example AP. A transducer according to any one of the foregoing examples, wherein the focal length of the sound beam generated by the transducer is sufficiently stable such that the focal length changes at a rate of less than 0.1% per year in contact with the liquid.

[0174] Example AQ. A transducer according to any one of the preceding examples, wherein the eccentricity of the sound beam generated by the transducer is sufficiently stable such that the eccentricity changes at a rate of less than 0.1% per year in contact with the liquid.

[0175] Example AR. A transducer according to any one of the foregoing examples, wherein the transducer is fluid impermeable when exposed to temperatures exceeding 130°C at pressures exceeding 2 atmospheres and is resilient to performance changes.

[0176] Example AS. A method of forming a fluid-impermeable ultrasonic transducer, the method comprising: forming a substantially hollow housing from a fluid-impermeable material, the housing having an internal cavity and an open first end; forming a transducer head element from the fluid-impermeable material, the transducer head element being sized to connect to the open first end of the housing; forming a focusing lens on a front surface of the head element, the focusing lens being configured to focus ultrasound toward a focal point; connecting the head element to the first end of the housing to form a fluid-impermeable connector, the head element being positioned such that the focusing lens is directed away from the housing; and attaching an actuator to a rear surface of the transducer head opposite the front surface, the actuator being operable to generate oscillating mechanical vibrations of the focusing lens, such that ultrasound is emitted from the focusing lens toward the focal point.

[0177] Example AT. The method according to Example AS, wherein connecting the head element to a first end of the housing includes welding the head element to the housing.

[0178] Example AU. The method according to any one of the foregoing examples, wherein forming the focusing lens includes removing material from the front surface of the head element through a precision machining process.

[0179] Example AV. The method according to any one of the foregoing examples further includes: inserting a backing material into the housing near and behind the actuator; and substantially filling the remaining portion of the internal cavity of the housing with a sealant.

[0180] Example AW. The method according to any of the foregoing examples further includes: applying a matching layer to the focusing lens, the matching layer comprising having a corresponding to the equation Z. m =√(Z l Z c Z m Materials for matching acoustic impedance, where Z l Z corresponds to the first acoustic impedance of the head element. c This corresponds to the second acoustic impedance of the medium.

[0181] Example AX. The method according to Example AW further includes: reducing the thickness of the matching layer such that the thickness is an odd multiple of a quarter wavelength of the acoustic signal passing through the matching layer at the nominal frequency.

[0182] Example AY. The method according to Example AW further includes: applying the matching layer with a thickness corresponding to an odd multiple of a quarter wavelength of the acoustic signal passing through the matching layer at the nominal frequency.

[0183] Example AZ. The method according to any one of the foregoing examples further includes: inserting a backing material into the housing near and behind the actuator; inserting a conductive ring element adjacent to the actuator and around the periphery of the backing material into the housing, the conductive ring having an inner conductive portion and an outer conductive portion; contacting a first electrode of the actuator with the inner conductive portion of the conductive ring element; and contacting a second electrode of the actuator with the outer conductive portion of the conductive ring element.

[0184] Example BA. The method according to any one of the foregoing examples further includes: applying an attenuation layer adjacent to the focusing lens to the periphery of the head element.

[0185] Example BB. The method according to any one of the foregoing examples further includes: applying a matching layer to the focusing lens, the matching layer having a matching acoustic impedance smaller than the first acoustic impedance of the transducer head.

[0186] Example BC. A method of forming a fluid-impermeable ultrasonic transducer, the method comprising: forming a substantially hollow housing having an internal cavity and a closed first end defining a transducer head element from a fluid-impermeable material; forming a focusing lens on a front surface of the head element, the focusing lens being configured to focus ultrasound toward a focal point; and attaching an actuator to a rear surface of the transducer head opposite the front surface, the actuator being operable to generate oscillating mechanical vibrations of the focusing lens such that ultrasound is emitted from the focusing lens toward the focal point.

[0187] Example BD. According to the method described in Example BC, forming the focusing lens includes removing material from the front surface of the head element.

[0188] Example BE. The method according to any one of the foregoing examples further includes: inserting a backing material into the housing near and behind the actuator; and substantially filling the remaining portion of the internal cavity of the housing with a sealant.

[0189] Example BF. The method according to Example BE further includes: inserting a conductive ring element adjacent to the actuator and around the periphery of the backing material into the housing, the conductive ring having an inner conductive portion and an outer conductive portion; contacting a first electrode of the actuator with the inner conductive portion of the conductive ring element; and contacting a second electrode of the actuator with the outer conductive portion of the conductive ring element.

[0190] Example BG. The method according to any of the foregoing examples further includes: applying a matching layer to the focusing lens, the matching layer comprising having a corresponding to the equation Z. m =√(Z l Z c Z m Materials for matching acoustic impedance, where Z l Z corresponds to the first acoustic impedance of the head element. c This corresponds to the second acoustic impedance of the medium.

[0191] Example BH. The method according to Example BG further includes: reducing the thickness of the matching layer such that the thickness is an odd multiple of a quarter wavelength of the acoustic signal passing through the matching layer at the nominal frequency.

[0192] Example BI. The method according to Example BG further includes: applying the matching layer with a thickness corresponding to an odd multiple of a quarter wavelength of the acoustic signal passing through the matching layer at the nominal frequency.

[0193] Example BJ. The method according to any one of the foregoing examples further includes: applying an attenuation layer adjacent to the focusing lens to the periphery of the head element.

[0194] Example BK. The method according to any one of the foregoing examples further includes: applying a matching layer to the focusing lens, the matching layer having a matching acoustic impedance smaller than the first acoustic impedance of the transducer head.

[0195] Example BL. A method for ejecting droplets from a fluid reservoir, the method comprising: using a fluid-impermeable transducer including a transducer according to any one of Examples A-AR; immersing a focusing lens in an acoustic medium positioned to couple acoustic energy from the transducer to the reservoir; generating an acoustic pulse by an actuator at a frequency configured to eject droplets from a fluid surface of the reservoir; and transmitting the acoustic pulse from the actuator to the fluid reservoir through the focusing lens.

[0196] Example BM. A method for performing ultrasonic testing on a structure, the method comprising: using a fluid-impermeable transducer comprising a transducer according to any one of Examples A-AR; immersing the focusing lens in an acoustic medium in fluid contact with the structure; generating an acoustic pulse by the actuator and directing it toward a scanned area of ​​the structure; receiving an echo of the acoustic pulse corresponding to the scanned area; and determining physical parameters of the scanned area of ​​the structure based on the characteristics of the echo.

[0197] Different arrangements of the components depicted in the drawings or described above, as well as components and steps not shown or described, are possible. Similarly, some features and sub-combinations are useful and can be used without reference to other features and sub-combinations. Embodiments of the invention have been described for illustrative and non-limiting purposes, and alternative embodiments will become apparent to the reader of this patent. Therefore, the invention is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications can be made without departing from the scope of the appended claims.

Claims

1. A fluid-impermeable transducer, comprising: Liquid-impermeable metal casing (302); A liquid-impermeable transducer head (304) includes a metal focusing lens (312), the transducer head (304) having a rear surface (216) and a front surface, the metal focusing lens (312) being formed on the front surface and configured to focus ultrasound toward a focal point; An actuator (322) is attached to the rear surface (216) of the transducer head (304) and is operable to generate an oscillating mechanical vibration of the metal focusing lens (312) such that ultrasound is emitted from the metal focusing lens (312) toward the focal point. as well as A backing material (542) is configured to attenuate the acoustic energy transmitted by the actuator (322), which is located between the backing material (542) and the metal focusing lens (312). Its features are, The metal housing (302) and the transducer head (304) are integrally formed as a single part and permanently connected in a liquid-impermeable manner to prevent liquid from entering the metal housing (302).

2. The transducer of claim 1, wherein the front surface of the transducer head includes a peripheral portion (314) surrounding the focusing lens, and further includes: An attenuation layer (350) is attached to the peripheral portion and is configured to absorb ultrasonic energy emitted from the actuator (322) through the peripheral portion (314).

3. The transducer according to any one of the preceding claims further includes a matching layer (514) coupled to the focusing lens (312) to transmit ultrasound from the focusing lens (312) to the medium (502), the matching layer (514) being configured to enhance the transmission of ultrasound from the focusing lens (312) to the medium (502) compared to direct transmission of ultrasound from the focusing lens (312) to the medium (502).

4. The transducer according to claim 3, wherein the focusing lens (312) has a first acoustic impedance, the medium (502) has a second acoustic impedance different from the first acoustic impedance, and the matching layer (514) has a matching acoustic impedance between the first acoustic impedance and the second acoustic impedance.

5. The transducer of claim 4, wherein the matched acoustic impedance is in the range of about 4-10 Mrayl.

6. The transducer according to any one of claims 4 to 5, wherein the thickness of the matching layer (514) corresponds to an odd multiple of a quarter wavelength of the acoustic signal passing through the matching layer at the nominal frequency.

7. The transducer of claim 6, wherein the nominal frequency is in the range of 2 to 15 MHz.

8. The transducer according to any one of the preceding claims further comprises a first matching layer (614) disposed on the front surface and a second matching layer (620) disposed on the first matching layer (614), the first matching layer (614) and the second matching layer (620) being configured to enhance the transmission of ultrasound from the focusing lens to the medium (502) compared to direct transmission of ultrasound from the focusing lens to the medium (502); wherein: The focusing lens has a first acoustic impedance; The medium (502) has a second acoustic impedance that is different from the first acoustic impedance; The first matching layer (614) has a first matching acoustic impedance between the first acoustic impedance and the second acoustic impedance; and The second matching layer (620) has a second matching acoustic impedance between the first matching acoustic impedance and the second acoustic impedance.

9. The transducer according to any one of the preceding claims, wherein the transducer head (304) and the metal housing (302) are characterized in that the liquid penetration depth and the resulting material loss are zero when immersed in a liquid.

10. The transducer according to any one of the preceding claims, wherein the transducer head (304) and the metal housing (302) are characterized in that the annual material weight loss upon contact with the liquid is less than 0.1%.

11. The transducer of claim 10, wherein the backing material (542) has an acoustic impedance ranging from 13.5 to 16.5 Mrayl.

12. The transducer according to any one of the preceding claims, wherein the focal length of the sound beam generated by the transducer (304) is sufficiently stable such that the focal length changes at a rate of less than 0.1% per year in contact with the liquid.

13. The transducer according to any one of the preceding claims, wherein the eccentricity of the sound beam generated by the transducer (304) is sufficiently stable such that the eccentricity changes at a rate of less than 0.1% per year in contact with the liquid.

14. The transducer according to any one of the preceding claims, wherein the transducer (304) is liquid impermeable when exposed to temperatures exceeding 130°C at pressures exceeding 2 atmospheres and has elasticity to resist changes in performance.

15. A method for forming a liquid-impermeable ultrasonic transducer (300), the method comprising: A substantially hollow metal shell is formed from a fluid-impermeable metal, the metal shell having an internal cavity and an integrally formed closed first end defining a transducer head element (304). A focusing lens (312) is formed on the front surface of the transducer head element (304), and the focusing lens (312) is configured to focus ultrasound toward a focal point away from the metal housing (304); An actuator (322) is attached to the rear surface of the transducer head element (304) opposite the front surface. The actuator (322) is operable to generate an oscillating mechanical vibration of the focusing lens (312) such that ultrasound is emitted from the focusing lens toward the focal point. as well as The backing material (542) is inserted into the housing near and behind the actuator (322), which is located between the backing material (542) and the focusing lens (312).

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