Multi-plate underwater transducers and arrays

Abstract

The present invention relates to multi-plate underwater transducers and arrays for generating and receiving acoustic waves underwater. The present invention provides for the design and manufacture of a compact piston-type underwater transducer with low to medium operating center frequency made from piezoelectric single crystals that does not require a preload mechanism. The present invention uses a multi-plate pipe-shaped single crystal motor section made of piezoelectric single crystals with high transverse mode piezoelectric coefficient and low acoustic impedance, and a small diameter and light weight head mass.The present invention also discloses various means of increasing the bandwidth of multi-plate underwater transducers, including miniature 2D and 3D omnidirectional transducers, various designs of planar, conformal and shaped arrays, high density arrays, and single or dual frequency band low drop down ratio parametric arrays, as well as derivative underwater transducers and arrays made from these underwater transducers.

Description

[Technical field]

[0001] The present invention relates to transducers, and more particularly to underwater transducers and arrays for generating and receiving sound waves underwater. [Background technology]

[0002] An underwater transducer is a device that converts energy from one form to another. This underwater transducer can then be used as both a transmitter and a receiver of acoustic waves underwater. These underwater transducers are generally called SONAR (Sound Navigation and Ranging). SONAR can also be used for maritime surveillance, underwater object detection and identification, depth finding, bathymetry imaging and underwater communications. Conventional underwater transducers generate and transmit signals in the form of pulses of sound. An "echo" of the signal is then received and detected. The time between transmission and reception of the pulse can be used to measure the distance traveled by the sound wave.

[0003] Conventional underwater transducers utilize piezoelectricity. Piezoelectric transducers convert applied electrical signals into vibrational mechanical energy and vice versa. A common piezoelectric material is lead zirconate titanate (Pb[Zr 1-x Ti x ]O3 or PZT), which have been used in this technology for decades.

[0004] Most underwater transducers use PZT rings or stacked plates driven in the longitudinal (33) mode. The 33-mode piezoelectric active element not only has a high piezoelectric strain coefficient, but also a high acoustic impedance compared to water. This causes a significant portion of the sound waves to reflect at the water-ceramic interface, reducing the power efficiency of the device. To improve both transmit and receive power efficiency, various acoustic matching techniques have been developed and utilized.

[0005] Underwater transducers for generating sound, operating in the frequency range from a few kHz to a few hundred kHz, are of the common design tonpilz ("tonpilz" is German for "singing mushroom") or piston type. In this design, a piston with a radiating surface area larger than the load-bearing area of ​​the active material is used to reduce the acoustic impedance mismatch between the piezoelectric ceramic and the water. FIG. 1 shows the general structure of a Tonpilz underwater transducer and its main components, such as the piston (head mass) 12 , electrode 14 , tail mass 16 , stress rod 18 , disc spring 20 , insulator 22 and PZT ring 24 .

[0006] There is a large mismatch in acoustic impedance between PZT piezoelectric ceramics and water, typically 15 to 25 times. For this reason, the Tonpilz design requires a large piston area that is 15 to 25 times larger than the load-bearing area of ​​the piezoelectric ceramic. Nevertheless, for reasons explained below, the piston area of ​​conventional Tonpilz transducers is significantly smaller, typically with a diameter of about λ w It remains at / 2. Here, λ w is the operating center frequency of the transducer's operating frequency band (f c ) is the wavelength in water. Therefore, the typical diameter of the piston in a conventional Tonpilz transducer is f c λ for =7.5kHz w / 2=100mm, f c λ for =75kHz w / 2=Varies up to 10mm.

[0007] An inverted mushroom-shaped piston head with ample thickness is used to prevent piston flex which may adversely affect acoustic performance. As a result, the piston of the Tonpilz projector is bulky and heavy. This part is generally called the head mass.

[0008] Due to inertial effects, during operation of the transducer, the head mass and the top portion of the piezoelectric active material exert dynamic stresses on the underlying piezoelectric active material and the various adhesive joints contained therein. Thus, in conventional Tonpilz underwater transducers, the heavier the head mass, the higher the induced dynamic stresses.

[0009] Conventional underwater transducer materials also pose problems. Piezoelectric ceramics are brittle and adhesive bonds can weaken when subjected to tensile forces. A preload mechanism consisting of a stress rod, a resilient member such as a coil or disc spring, and a locking nut can be incorporated to apply the appropriate compressive force to the piezoelectric ceramic active material and the various adhesive joints. This can prevent or limit tensile loads during operation. These preload mechanisms are now a standard design feature of Tonpilz transducers (see Figure 1 for an example). These components add complexity to the design. It also adds weight and reduces bandwidth.

[0010] The piston size of the Tonpilz transducer is approximately λ in diameter. w / 2 (λ w One reason for this is that in array formation, the spacing between multiple transducer elements is typically about λ to avoid significant side lobes during beamforming. w This is because they are arranged so that the number of bits is equal to or less than / 2. As a result, the transducer density in a conventional array is typically w / 2×λw There is approximately one transducer per half-inch. Furthermore, because the piston diameter and height of the Tonpilz transducer increases with decreasing center frequency, the low to mid-frequency operating frequencies driven by the PZT ceramics of the Tonpilz transducer make it less suitable for creating small, conformal arrays, let alone high density geometry arrays for certain desired acoustic performance characteristics.

[0011] In recent years, there has been a great deal of effort focused on improving the materials used in underwater transducers. Lead zinc niobate-lead titanate (Pb[Zn 1 / 3 Nb 2 / 3 ]O3-PbTiO3 or PZN-PT), lead magnesium niobate-lead titanate (Pb[Mg 1 / 3 Nb 2 / 3 ]O3-PbTiO3 or PMN-PT), lead magnesium niobate-lead zirconate titanate (Pb[Mg 1 / 3 Nb 2 / 3 ]O3-Pb[Zr 1-x Ti x ]O3 or PMN-PZT) solid solution piezoelectric single crystals, as well as their doped and / or modified ternary and quaternary derivatives, have been extensively studied. These new piezoelectric materials exhibit superior piezoelectric and electromechanical properties compared to PZT piezoelectric ceramics.

[0012] Piezoelectric single crystals are anisotropic materials and exhibit different properties when poled and / or activated in different crystallographic directions. For example, a

[0011] poled single crystal bar exhibits very large transverse strain when the induced strain is measured along the

[0100] crystallographic direction. The transverse piezoelectric strain coefficients (d in the literature) of the various lead-based relaxor-PT solid solution single crystals mentioned above 32 The CdTe-CdTe (denoted as CdTe-CdTe) has been reported to be in the range of 1200 to 3000 pC / N. In contrast, commercially available PZT piezoelectric ceramics have a d 33 is 200 to 600 pC / N, d 31is 150 to 280 pC / N.

[0013] US Pat. No. 5,399,433 describes a new type of high linear axial displacement actuator. This design is shown in FIG. In this multi-plate actuator design, the plates are identical piezoelectric single crystal active elements having the appropriate composition and cuts 31 . The single crystal elements are bonded in the desired configuration with epoxy using shaped edge stiffeners 32 and shaped end cap and / or washer stiffeners 34 on both ends. Lead wires are attached to the electrode surfaces of the crystal to complete the device (not shown). The thick lines indicate the epoxy joints 33 . In this design, the same rectangular d 32 The extremely high lateral (d 32 ) Utilizing the piezoelectric strain coefficient. The resulting "multi-plate" actuator exhibits large, yet linear, nearly history-free axial displacement, in contrast to the nonlinear, history-effect strain behavior of conventional stack actuators made from 33-mode PZT piezoelectric ceramics.

[0014] The multi-plate actuator's hollow pipe-like structure provides increased bending and torsional stiffness and strength despite the small load-bearing crystal area and volume. This is d 32 The relatively high elastic compliance of transverse mode lead-based relaxor-lead titanate solid solution single crystals, combined with the fact that they have low acoustic impedance in the active

[0100] crystal direction, means that when single crystal multi-plate actuators are used as the single crystal motor portion of underwater transducers, acoustic matching to water can be achieved with much smaller diameters and lighter head masses.

[0015] While piezoelectric actuator technology is advancing, improvements in underwater transducers are needed. The present invention includes an underwater transducer that is driven by a transverse mode single crystal actuator composed of multiple plates having a small and extremely lightweight head mass and does not require a preload mechanism. Also disclosed are various means for improving the bandwidth of underwater transducers of this design, and the various types of arrays which may be formed thereby.

[0016] The objective of the present invention is to provide a small, lightweight underwater transducer made of piezoelectric single crystals and its basic design considerations, in particular, an operating center frequency in the range of a few kHz (e.g., 3 kHz) to several hundred kHz (e.g., 300 kHz). SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide various means for designing and fabricating broadband single crystal underwater transducers, particularly single crystal underwater transducers with operating center frequencies ranging from a few kHz to a few hundred kHz.

[0017] It is also an object of the present invention to provide various means for designing and fabricating miniature 2D and 3D omnidirectional underwater transducers made of piezoelectric single crystals with low to moderate operating center frequencies and wide bandwidths.

[0018] A further object of the present invention is to provide an acoustically tunable λ tunable device made of a piezoelectric single crystal. w and providing a method for designing and fabricating λ / 2 size transducer elements, particularly transducer elements having low to medium operating center frequencies and wide bandwidths, w is the wavelength in water at the operating center frequency of the operating frequency band of the underwater transducer.

[0019] It is a further object of the present invention to provide methods for designing and manufacturing planar, conformal and shaped arrays of underwater transducers made from piezoelectric single crystals, particularly those having low to moderate operating center frequencies and wide bandwidths.

[0020] It is a further object of the present invention to provide a method for designing and manufacturing high density transducer arrays that overcome the limitations of conventional tonpilz or piston type transducers, including planar, conformal and shaped arrays with a variety of engineered acoustic beam patterns and performance characteristics.

[0021] It is a further object of the present invention to provide a method for designing and manufacturing dual operating frequency band transducer arrays, including planar, conformal and shaped arrays, with a variety of engineered acoustic beam patterns and performance characteristics.

[0022] It is a further object of the present invention to provide a method for designing and manufacturing single or dual frequency band low drop down ratio parametric arrays, not possible with conventional tonpilz or piston type transducers.

[0023] The above and other objects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings. In the accompanying drawings, there is disclosed by way of illustration and example at least one embodiment of the present invention. [Prior art documents] [Patent documents]

[0024] [Patent Document 1] U.S. Patent No. 9,673,374(B2) Summary of the Invention [Means for solving the problem]

[0025] In a first aspect, the present invention is a multi-plate gyroscope, which is composed of a plurality of spaced plates or a plurality of joined plates in the shape of hollow polygonal pipes or oriented in parallel, d 32 or d 31A piston-type underwater transducer is provided that includes a single crystal motor section composed of multiple units of transverse mode piezoelectric single crystals and at least one head mass, and the head mass does not require a preload mechanism because of its small size and light weight.

[0026] In one embodiment, a piston-type underwater transducer is described that operates in the center frequency range of 3 kHz to 300 kHz without a preload mechanism. The underwater transducer may include a single crystal motor portion, a first head mass, a second head mass, a housing, and a sound-transmissive window material. The single crystal motor part is composed of a hollow polygonal pipe shape or a plurality of spaced plates or a plurality of coupled plates oriented in parallel, and has a rectangular

[0011] polarization d 32 or d 31 It can be composed of multiple units of transverse mode piezoelectric single crystals, and the total load-bearing area of ​​the single crystal motor is 40mm 2 is less than. The first head mass and the second head mass may each have a diameter less than 0.4 times the wavelength of an acoustic wave at the operating centre frequency in a surrounding medium. The first head mass and the second head mass may each weigh less than 4 grams. The housing and the sound-transmissive window material can protect the single crystal motor portion, the first head mass, and the second head mass from an ambient medium. The first head mass and the second head mass are capable of radiating sound waves through the sound-transmissive window material to the surrounding medium.

[0027] According to an embodiment related to the first aspect of the present invention, the piezoelectric single crystal is lead zinc niobate-lead titanate (Pb[Zn 1 / 3 Nb 2 / 3 ]O3-PbTiO3 or PZN-PT), lead magnesium niobate-lead titanate (Pb[Mg 1 / 3 Nb 2 / 3]O3-PbTiO3 or PMN-PT), lead magnesium niobate-lead zirconate titanate (Pb[Mg 1 / 3 Nb 2 / 3 ]O3-Pb[Zr 1-x Ti x ]O3 or PMN-PZT), lead indium niobate-lead magnesium niobate-lead titanate (Pb[In 1 / 2 Nb 1 / 2 ]O3-Pb[Mg 1 / 3 Nb 2 / 3 ]O3-PbTiO3 or PIN-PMN-PT) and lead indium niobate-lead zinc niobate-lead titanate (Pb[In 1 / 2 Nb 1 / 2 ]O3-Pb[Zn 1 / 3 Nb 2 / 3 ]O3-PbTiO3 or PIN-PZN-PT), as well as their attached and / or compositionally modified derivatives, are lead-based relaxor-PT solid solution single crystals of the following composition:

[0028] According to an embodiment related to the first aspect of the invention, the head mass is composed of one or more of aluminium and aluminium alloys, aluminium beryllium alloys, aluminium lithium alloys, magnesium and magnesium alloys, titanium and titanium alloys, metal matrix composites thereof and / or monolithic alloys with various types of micro hollow spheres, high specific modulus engineering ceramics including machinable glass ceramics, or fibre reinforced polymer matrix composites.

[0029] In one embodiment, the underwater transducer operates in a center frequency range of 3 kHz to 300 kHz.

[0030] According to an embodiment relating to the first aspect of the invention, the diameter or radiating surface area of ​​the head mass provides an optimum acoustic match with the surrounding medium.

[0031] In one embodiment, the area ratio of the head mass to the load bearing area of ​​the piezoelectric single crystal is between 3 and 10.

[0032] According to an embodiment related to the first aspect of the invention, the head mass weighs less than 0.5 grams (g).

[0033] In one embodiment, the first head mass and the second head mass are equal or substantially equal in size and weight, and the first head mass and the second head mass radiate acoustic waves into a surrounding medium in a λ / 2 mode.

[0034] According to an embodiment related to the first aspect of the invention, the two head masses have unequal weights. The heavy head mass acts as a tail mass and only the light head mass radiates sound waves into the surrounding medium in a λ / 4 mode or a mode close to it.

[0035] According to an embodiment related to the first aspect of the invention, the single crystal motor portion includes a vibrating crystal having an active length of less than 9 mm to promote an end constraint effect for improved bandwidth.

[0036] According to an embodiment related to the first aspect of the present invention, the single crystal motor part is of a two-layer or multi-layer multiple plate configuration.

[0037] According to an embodiment related to the first aspect of the invention, the device further comprises two head masses, the two head masses having different masses, one or both head masses radiating sound waves simultaneously into the surrounding medium.

[0038] According to an embodiment relating to the first aspect of the invention, the transducer includes means for applying a downward or compressive force through the sound-transmissive window material onto the head mass and underlying crystal.

[0039] In a second aspect, the present invention provides a two-dimensional omnidirectional underwater transducer including a plurality of underwater transducer units constructed of piston-type multiple plates providing a derivative underwater transducer two-dimensional omnidirectionality.

[0040] In a third aspect, the present invention provides a three-dimensional omnidirectional underwater transducer including a plurality of underwater transducer units constructed of piston-type multiple plates providing three-dimensional omnidirectionality of a derivative underwater transducer.

[0041] In a fourth aspect, the present invention provides a λ transducer including multiple units of a piston-type multiple-plate underwater transducer. w / 2 size underwater transducer, λ w The / 2 size transducer elements are acoustically tunable using appropriate associated electronics.

[0042] In a fifth aspect, the present invention provides a λ / 2 mode piston-type multi-plate underwater transducer, with both head masses radiating sound waves using either a simple baffle or a cavity baffle to increase the sound pressure level.

[0043] In a sixth aspect, the present invention provides a planar, conformal or shaped array of piston-type multi-plate underwater transducers comprising multiple units of piston-type underwater transducers at a higher array density than is possible with conventional underwater transducer arrays.

[0044] In a seventh aspect, the present invention provides a dual frequency underwater transducer array including a plurality of units of a piston-type multi-plate underwater transducer.

[0045] In an eighth aspect, the present invention provides a parametric array including a plurality of units of a piston-type multi-plate underwater transducer, the parametric array having a low drop-down ratio and either a single frequency band or a dual frequency band.

[0046] In a ninth aspect, the present invention provides a dual mode underwater transducer including a piston-type multi-plate underwater transducer, the dual mode underwater transducer generating and receiving underwater acoustic waves.

[0047] In a tenth aspect, the present invention provides a dual mode underwater transducer array, including a planar array, a conformal or shaped array, a dual frequency underwater transducer array, or a parametric array.

[0048] In an eleventh aspect, the present invention provides an underwater transducer comprising a plurality of plates including a single crystal motor part, a first head mass, and a second head mass, the single crystal motor part being configured in a hollow polygonal or pipe shape. 32 or d 31 The underwater transducer is composed of a transverse mode piezoelectric single crystal coupled to a small diameter, lightweight piston, the underwater transducer has a piston to crystal area ratio of between 4 and 10, and has no preload mechanism. [Brief description of the drawings]

[0049] [Figure 1] A typical prior art Tonpilz underwater transducer with a piston (head mass) and a heavy tail mass is shown, along with a preload mechanism for applying the appropriate compressive force to the piezoelectric ceramic active element and the various adhesive joints involved.

[0050] [Diagram 2] 1 shows a prior art multi-plate single crystal actuator design.

[0051] [Diagram 3] 1 illustrates one embodiment of a λ / 2 mode underwater transducer of the present invention.

[0052] [Figure 4]Figure 3 is a graph of the transmit voltage response (TVR) of the underwater transducer, in which the multi-plate square pipe motor section is made of four identical rectangular 0011 polarized d32 mode PZN-5.5%PT single crystals with dimensions of 25mm (L) x 4.2mm (W) x 0.4mm (T) and a total weight of about 1.4g. Each of both head masses is made of aluminum, has a diameter of about 7mm, a thickness of 2.0mm, and weighs about 0.2g. Acoustic results were obtained with the acoustic axis perpendicular to the axis of the underwater transducer and both head masses radiating sound waves simultaneously.

[0053] [Diagram 5] This is a plot of the TVR for the same underwater transducer shown in Figure 4, but with the acoustic axis parallel to the axis of the transducer, and with the acoustic window of one head mass covered with a metal end cap to isolate it from the water medium, so that only the facing head mass radiates sound waves.

[0054] [Figure 6] 1 shows another embodiment of a multi-plate underwater transducer of the present invention, in which one of the head masses is much heavier than the other head masses and acts as a substantially non-vibrating tail mass, forming a λ / 4 mode underwater transducer.

[0055] [Figure 7] This is a graph of the TVR of the underwater transducer shown in Figure 6, which is composed of multiple plates and has the same square pipe cross section as Figure 5, but the motor part is composed of multiple plates in λ / 4 mode with a crystal length of 9 mm.

[0056] [Figure 8] 8A, 8B, 8C and 8D show a multi-plate transducer design of the present invention having a simple single crystal motor section structure.

[0057] [Figure 9]This is a graph of the TVR of another λ / 4 mode underwater transducer having a single crystal motor part with the same square pipe cross section as in Figure 7, but with a shorter crystal length of 5 mm.

[0058] [Figure 10] This shows a λ / 4 mode underwater transducer with a single crystal motor section made of two layers of multiple plates.

[0059] [Figure 11] 8 is a plot of the TVR of a λ / 4 mode, two-layer, multi-plate underwater transducer having the same crystal length and equivalent total crystal cross-sectional area as shown in FIG. 7.

[0060] [Figure 12] A multi-plate underwater transducer with λ / 2 mode and non-uniform mass design is shown.

[0061] [Figure 13] Graphs of TVR for underwater transducers with multiple plates of unequal mass design. In Fig. 13A, only the light head mass is used as the sound radiating surface (the heavy head mass side is covered with a metal end cap), and the acoustic axis is aligned with the axis of the underwater transducer. In Fig. 13B, both head masses radiate simultaneously, and the acoustic axis is perpendicular to the axis of the underwater transducer. In both cases, no baffles are used.

[0062] [Figure 14] 14A, 14B and 14C show a transducer design in which a pull-down force (and therefore a compressive stress) is generated through a sound-transmissive window material onto the head mass and underlying crystal.

[0063] [Figure 15]Figures 15A and 15B are perspective views of a compact 2D omnidirectional radiating device made by cross-arranging two units of the λ / 2 mode multi-plate underwater transducer shown in Figure 4. The diameter and height of this derivative underwater transducer are both less than 40 mm.

[0064] [Figure 16A] 16 is a graph of the TVR of the underwater transducer shown in FIG. 15.

[0065] [Figure 16B] 16 is a graph of the beam pattern of the underwater transducer shown in FIG. 15.

[0066] [Figure 17] Figures 17A and 17B show a miniature three-layer 2D omnidirectional radiating device made by placing three units of the λ / 2 mode multi-plate underwater transducer shown in Figure 3 at 60° from each other. The diameter of this derived underwater transducer is less than 40 mm and the height is less than 60 mm.

[0067] [Figure 18] 18A and 18B show 2D omnidirectional transducers made of multiple units of the inventive multi-plate underwater transducer in (a) λ / 4 mode and (b) λ / 2 mode, respectively. The dashed lines indicate the areas that can be filled with sound-transmitting material to make the whole underwater transducer cylindrical for flow smoothing purposes.

[0068] [Figure 19] 1 shows another example of a 2D omnidirectional transducer made up of multiple units of a multi-plate underwater transducer.

[0069] [Figure 20]Figures 20A and 20B show another example of a 2D omnidirectional transducer made up of multiple units of a multi-plate underwater transducer, with Figure 20B showing the device encapsulated in a sound-transmitting material 408 such as polyurethane (PU).

[0070] [Figure 21] To increase the sound pressure level, an omnidirectional underwater transducer is shown formed by stacking two units of the 2D omnidirectional underwater transducer shown in Figure 17.

[0071] [Figure 22] 22A and 22B show another design of a stacked omnidirectional underwater transducer.

[0072] [Diagram 23] 1 shows another design of a stacked omnidirectional underwater transducer.

[0073] [Figure 24] It shows a λw / 2 size transducer element made of seven units of an underwater transducer composed of multiple plates of λ / 4 mode to improve acoustic characteristics, where λw is the wavelength in water at the operating center frequency of the operating frequency band of the λw / 2 size underwater transducer.

[0074] [Diagram 25] A high-density planar array made of multiple units of a single-head mass λ / 4 mode multi-plate underwater transducer is shown.

[0075] [Figure 26] 1 is a graph of the TVR of an underwater transducer measured over a wider frequency range, showing the dimensions of λw / 2 in water at various frequencies and typical head mass diameters for a multi-plate underwater transducer of the present invention;

[0076] [Figure 27]TVR plot of another λ / 2 mode multi-plate underwater transducer with its acoustic axis perpendicular to the underwater transducer axis and both head masses radiating simultaneously under three different baffle conditions: (a) no baffle, (b) with a rigid simple baffle, and (c) with a semicircular hollow rigid baffle of R=12mm that helps to deflect the acoustic energy along the acoustic axis.

[0077] [Figure 28] 1 shows a slim planar array made of underwater transducers constructed from multiple plates with hollow baffles.

[0078] [Figure 29] 29A and 29B show a conformal array made of underwater transducers constructed from multiple plates with hollow baffles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0079] Reference herein to "one embodiment / aspect" or "an embodiment / aspect" means that a particular feature, structure, or characteristic described in connection with that embodiment / aspect is included in at least one of the disclosed embodiments / aspects. The phrases "one embodiment / aspect" or "another embodiment / aspect" used in various places in this specification are not necessarily all referring to the same embodiment / aspect or to different or alternative embodiments / aspects mutually exclusive of other embodiments / aspects. Moreover, various features are described that are exhibited in some embodiments / aspects and not in others. Similarly, various requirements are described that are requirements of some embodiments / aspects but not others. The embodiments and aspects may be used interchangeably in certain cases. The terms used in this specification generally have their ordinary meanings in the art, the context of the disclosure, and the specific context where each term is used. Certain terms used in describing the disclosure are explained below, or elsewhere in the specification, to provide additional guidance to practitioners regarding the description of the disclosure.

[0080] Without intending to further limit the scope of the disclosure, examples of devices, apparatus, methods and their related results according to embodiments of the present invention are set forth below. Please note that titles or subtitles may be used as examples for the convenience of the reader, but do not limit the scope of the disclosure. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, the present document, including definitions, will take precedence. [Multiple-plate underwater transducer]

[0081] Embodiments include underwater transducers, methods of making and using same. Specific embodiments include the design and manufacture of small, lightweight piston-type underwater transducers made from piezoelectric single crystals, with low to medium center frequencies of operation. This underwater transducer can use a multi-plate pipe-shaped motor section made of a piezoelectric single crystal with a high transverse mode piezoelectric coefficient and low acoustic impedance, and a small-diameter, very light head mass, and does not require a preload mechanism. Embodiments also include various methods for increasing the bandwidth of multi-plate underwater transducers. Also disclosed are derivative transducers and arrays made with transducer elements of multi-plate design, including acoustically tunable λ wThese include 1 / 2 size transducer elements, miniature two-dimensional (2D) and three-dimensional (3D) omnidirectional transducers of various designs, high density planar arrays with single or dual operating frequency bands, conformal and shaped arrays, and miniature parametric arrays with low drop down ratios in single or dual frequency bands.

[0082] FIG. 3 shows the design of a λ / 2 mode multi-plate underwater transducer 100. The single crystal motor section contains four identical rectangular piezoelectric single crystals 101 that are joined to a square pipe structure using edge guides 102. Each end of the single crystal motor section, which is made up of multiple plates, is joined to a head mass. In this embodiment, the two head masses 103, 104 are approximately the same in design and weight, except that one of them includes wiring grooves for the internal electrode wiring (neither the grooves nor the wiring are shown in the figures for clarity). This assembly is inserted into a cylindrical cavity of a metal housing 105 using a centering and cushioning O-ring 106, and both open ends of the housing cavity are further sealed with a sound-transmitting material 107 for waterproof purposes. When actuated with an alternating voltage signal, the crystal vibrates resonantly in the λ / 2 mode, causing both head masses to vibrate in response and radiate acoustic waves through the acoustic window into the adjacent water medium. Conventional underwater transducers of the Tonpilz design require a preload mechanism. For reasons explained below, the underwater transducer of the present invention does not require a preload mechanism.

[0083] As mentioned above, the single crystal motor section contains four piezoelectric single crystals arranged in multiple plates in a square pipe. Both head masses have a shorter diameter and thickness, making them lighter.

[0084] In an embodiment, a rectangular piezoelectric single crystal is poled in the

[0011] crystal thickness direction, with its active direction along the orthogonal

[0100] crystal direction. The above crystal fragments have been reported in the literature by scientists and researchers as 32 (or d 32 ) mode crystal, where "d" is the symbol for the piezoelectric strain coefficient, the first digit "3" is conventionally used to indicate the polarization direction, which here is the <0011> crystal direction but may be any crystal direction, and the second digit "2" defines that the active direction of the crystal is the <0100> crystal direction which is different from and perpendicular to the polarization (3) direction. If the active direction is another orthogonal [0-11] crystal direction, the second subscript is changed to "1" and the crystal cut is 31 (or d 31 ) mode crystal.

[0011] Polarization d 32 Mode crystal and d 31 Both mode crystals are transverse mode crystals since the crystallographic direction and the active direction are perpendicular to each other. On the other hand, the vertical (33 or d 33 In a ) mode crystal, the polarization direction and the activation direction are in the same direction.

[0085] In an embodiment, the rectangular piezoelectric single crystal is a lead-based relaxor-PT solid solution single crystal in the following material system: lead zinc niobate-lead titanate (Pb[Zn 1 / 3 Nb 2 / 3 ]O3-PbTiO3 or PZN-PT), lead magnesium niobate-lead titanate (Pb[Mg 1 / 3 Nb 2 / 3 ]O3-PbTiO3 or PMN-PT), lead magnesium niobate-lead zirconate titanate (Pb[Mg 1 / 3 Nb 2 / 3 ]O3-Pb[Zr 1-x Ti x ]O3 or PMN-PZT), lead indium niobate-lead magnesium niobate-lead titanate (Pb[In 1 / 2 Nb 1 / 2 ]O3-Pb[Mg 1 / 3 Nb 2 / 3 ]O3-PbTiO3 or PIN-PMN-PT), and lead indium niobate-lead zinc niobate-lead titanate (Pb[In1 / 2 Nb 1 / 2 ]O3-Pb[Zn 1 / 3 Nb 2 / 3 ]O3-PbTiO3 or PIN-PZN-PT) solid solution crystals, or derivatives with additives and / or modified compositions.

[0086] The

[0011] -poled single crystal of the above composition has extremely high d 32 The transverse mode piezoelectric strain coefficients are shown. For example, the poled PZN-5.5%PT single crystal is a PZT piezoelectric ceramic. 31 values ​​of less than 300 pC / N, as opposed to d values ​​of approximately 2200 pC / N. 32 Indicates the value. The

[0011] -poled single crystals of the above compositions also exhibit high d 32 Indicates the value.

[0087] Furthermore, the

[0011] polarization d 32 Modal single crystals have sufficient strength and suitable transformation properties, such as transformation temperature, electric field, and axial stress, making them candidate active materials for underwater transducers.

[0088] The

[0011] thickness polarization d of the above-mentioned lead-based relaxor-PT solid solution 32 For a modal single crystal, the elastic compliance, and hence the sound velocity along the active

[0100] crystallographic direction, is much lower than that of PZT piezoelectric ceramics. This results in

[0011] polarization d 32 Underwater transducers made using modal crystals have a low acoustic impedance.

[0089] For example,

[0011] polarization d 32 For the modal PZN-5.5%PT single crystals, the acoustic impedance along the active <0100> crystal direction ranges from 7 MRayls to 8.5 MRayls, as opposed to 22 MRayls to 38 MRayls for conventional PZT piezoelectric ceramics. As a result, an optimal acoustic match with water, which has an acoustic impedance of 1.5 MRayls, is readily achievable with a piston to crystal area ratio of about 4 to 8. The other lead-based relaxor-PT single crystals mentioned above have higher acoustic impedances, but they are still much lower than the acoustic impedance of PZT-based piezoelectric ceramics. As a result,

[0011] polarization d 32 When the mode crystal is used as the motor portion of an underwater transducer, a piston to crystal area ratio of 10 or less is sufficient for optimal acoustic impedance matching with water.

[0090] The actuator, which is made up of multiple plates, has a hollow pipe-like structure, so the load-bearing area of ​​the entire crystal is d 33 The overall load-bearing area of ​​a conventional Tonpilz transducer driven by a modal PZT ring stack is many times smaller. This, combined with the low piston to crystal area ratio required for good acoustic impedance matching as discussed above, means that the multi-plate underwater transducer of the present invention can have a smaller piston or head mass diameter and therefore area.

[0091] Since the bending modulus of a head mass is inversely proportional to the square of its diameter, for the same head mass stiffness, i.e. the same fundamental dome mode frequency, a much thinner head mass is sufficient in the present invention. As a result, a much lighter head mass can be used with the underwater transducer of the present invention.

[0092] In an embodiment, the individual head masses are made of high modulus lightweight materials, including, but not limited to, light metals and alloys such as aluminum and aluminum alloys, aluminum-beryllium alloys, aluminum-lithium alloys, magnesium and magnesium alloys, titanium and titanium alloys, metal matrix composites of these alloys including composites of these and / or monolithic alloys of these with various types of micro hollow spheres, machinable glass ceramics, high specific modulus engineering ceramics such as alumina, aluminum nitride, boron carbide, silicon nitride, silicon carbide, and fiber reinforced polymer matrix composites.

[0093] For example, four identical

[0011] polarizations d 32 When the mode is composed of multiple plates of square pipes made of PZN-5.5%PT single crystals (each with a cross-sectional area of ​​approximately 4 mm (W) x 0.42 mm (T)), the diameter (d in Figure 3) p ) A head mass of approximately 7mm provides near optimum acoustic matching with the surrounding medium (such as water). If the head mass is made of aluminum and has a thickness of 1.0 mm to 1.5 mm, the weight is less than 0.2 g and the fundamental resonant frequency of the dome mode is greater than 100 kHz.

[0094] Diameter (d p A unique feature of the present invention is the extremely small and lightweight head mass, typically less than 10 mm in diameter and weighing less than 0.5 g. With only two lateral adhesive joints (below each head mass), the dynamic tensile stresses induced by the vibrating head masses in the piezoelectric crystals and adhesive joints are significantly reduced. Therefore, the underwater transducer of the present invention, which is constructed from multiple plates, does not require a preload mechanism. This reduces the structural complexity of the device, resulting in a smaller, lighter device. In contrast, the preload mechanism is essential to ensure safe operation of conventional Tonpilz transducers. As a result, conventional Tonpilz transducers are more complex, bulkier and much heavier.

[0095] The effective head mass of the multi-plate underwater transducer of the present invention, consisting of the head mass and a portion of the vibrating crystal, is typically less than 5 g, making it much smaller than the effective head mass of conventional Tonpilz transducers. Due to the excellent acoustic matching and very light head mass, the underwater transducer of the present invention is able to offer a wider bandwidth than conventional Tonpilz transducers. If the crystal is long enough and allowed to vibrate relatively freely with minimal end constraint effects, the expected bandwidth is typically between 25% and 40% of the transducer's central operating frequency.

[0096] The transmit voltage response (TVR) of the underwater transducer is 1V for the single crystal motor. rms This indicates the sound pressure level generated at a distance of 1 meter when an alternating current (AC) voltage of Four

[0011] polarized d 32 The TVR of the underwater transducer composed of multiple plates of λ / 2 mode shown in Figure 3 with a square pipe motor section made of a mode PZN-5.5%PT single crystal and two identical aluminum head masses of about 0.2 g each is shown in Figure 4. In this view, the acoustic axis is perpendicular to the axis of the multi-plate underwater transducer. In the absence of a baffle, both head masses would radiate sound waves into the water simultaneously. Despite its small size, the operating center frequency is relatively low at around 12kHz to 13kHz, the relative bandwidth is 40%, and the TVR is quite high at 144.5dB (re 1μPa / V at 1m).

[0097] With a thickness of 0.4mm to 0.5mm, the underwater transducer crystal can withstand 35V before the crystal begins to depolarize. rmsto 45V rms It can be driven up to This results in sound pressure levels in the range of 175dB to 178dB (re 1μPa / V at 1m) despite the compact size.

[0098] Figure 5 shows the TVR for the same multi-plate underwater transducer, but with the acoustic axis aligned with the axis of the underwater transducer. Here, only one of the opposing head masses emits sound waves into the water. The head mass on the opposite side is protected by cushioning material and further covered with a metal end cap to isolate it from the water medium. The frequency response is similar to that of Figure 4, but in this case the TVR level is reduced because only one of the two head masses is used to generate the underwater sound.

[0099] Another embodiment of a multi-plate underwater transducer 200 of the present invention is shown in FIG. In this embodiment, the single crystal motor part is a structure made up of multiple similar square pipe plates having four piezoelectric single crystals 201 thereon. One of the head masses 202 acts as a much heavier, substantially non-vibrating tail mass, converting the device into a λ / 4 mode sound radiator. The sound radiating head mass 203 is lightweight, typically less than 0.5g, and no preload mechanism is used. Here, there is only one opening in the housing 204 . The underwater transducer is disposed in the center of the housing via a high-damping cushion material 205 and an O-ring 206 on the tail mass side, and another O-ring 207 on the head mass side. The head mass is further waterproofed with a sound-transmitting material 208 to allow the transmission of sound waves to the adjacent water medium.

[0100] FIG. 7 is a graph of the TVR of a λ / 4 mode multi-plate underwater transducer fabricated as shown in FIG. The single crystal motor part has the same square pipe cross section as that described in Figure 4, but the crystal length is shorter at 9 mm. Again, despite the small size, the operating center frequency is relatively low at about 30 kHz, the relative bandwidth is 35% and the TVR is fairly high at about 145 dB (re 1 μPa / V at 1 m).

[0101] For the same crystal thickness, square or polygonal tubular structures of single crystal plates firmly bonded with edge guides and stiffeners provide the highest bending and torsional strength for long crystals. Nevertheless, underwater transducers made with unedge-guided crystals in a similar arrangement have also been shown to work well. However, bending and torsional strength may decrease, especially in longer crystals. Care must be taken when handling during manufacture and use.

[0102] Other designs of single crystal motor parts are possible and will function similarly, provided they have sufficient bending and torsional strength for handling during manufacture and / or use. 8A to 8D show a single crystal motor part design with a relatively simple structure. Each may contain multiple well-spaced or evenly spaced parallel oriented crystals or bonded crystal assemblies, or circumferentially arranged single crystals in any polygonal shape, such as triangles, squares, hexagons, etc., with or without edge guides.

[0103] Depending on the actual design operating center frequency, TVR and sound pressure level, the single crystal motor part is

[0011] polarization d 32 When made of a single mode piezoelectric crystal, the total load-bearing area of ​​the crystal is typically several square millimeters (mm 2 ) to 30mm 2 The range is as follows: The corresponding head mass typically ranges from a few millimeters (mm) to 12 mm in diameter and weighs from less than 0.2 grams (g) to 1 g. For underwater transducers with low operating center frequencies (eg, a few kHz) and / or high TVR and sound pressure levels, it may be possible to have a larger crystal load-bearing area and piston diameter. [Broadband multi-plate underwater transducer]

[0104] The head mass of the underwater transducer of the present invention is thin and light, yet has a small diameter, resulting in a high resonant frequency in bending mode. Thus, during operation, it behaves like a rigid head mass. As mentioned above, when using a sufficiently long single crystal with an optimum crystal to piston area ratio for acoustic impedance matching with water, the bandwidth achievable with the multi-plate underwater transducer of the present invention is typically 25% to 40%.

[0105] The present invention also includes various methods by which the bandwidth of a multi-plate underwater transducer can be further increased.

[0106] One way to increase the bandwidth of the multi-plate underwater transducer of the present invention is to further reduce the thickness, and therefore the weight, of the head mass in the absence of the flapping effect of the head mass. Magnesium-based head masses, aluminum-beryllium and aluminum-lithium head masses, light metal and / or polymer matrix composite head masses, and high specific modulus ceramic head masses are suitable for such applications.

[0107] Another method is to introduce an appropriate mechanical constraint effect into the free vibration of the crystal. One such constraint is that imposed by head mass and / or tail mass. This end constraint effect is also present in the TVR transducer embodiments shown in FIGS. However, the crystals used in these examples are long, so the affected length represents a small percentage of the total crystal length.

[0108] FIG. 9 is a graph of the TVR of another fabricated λ / 4 mode multi-plate underwater transducer having a single crystal motor section with the same cross section as that described in FIG. 7, but with a crystal length of 5 mm. With proper design, this underwater transducer exhibits a significantly wider bandwidth of over 60%. This result may be due to the effect of the end constraints imposed by both the head and tail masses on the short oscillating crystal, and is valid for short oscillating crystals. This is especially true for multi-plate underwater transducers with higher operating frequency bands, for example those with central operating frequencies of 30 kHz or greater.

[0109] Yet another effective method for improving the bandwidth of underwater multi-plate transducers is to introduce lateral mechanical constraints to the vibrating crystal via a multi-layer multi-plate structure. FIG. 10 shows an example where the single crystal motor section includes eight piezoelectric single crystals 301 and 302 coupled to a two-layer multi-plate square pipe structure using edge guides 303.

[0110] FIG. 11 is a plot of the TVR of a λ / 4 mode, two-layer, multi-plate underwater transducer having the same crystal length and equivalent total crystal cross-sectional area as that described in FIG. Note that in this case the bandwidth is improved despite the small difference of 0.5 mm between the widths of the inner and outer layers of the crystal (4.2 mm and 4.7 mm, respectively).

[0111] FIG. 12 illustrates another embodiment of a multi-plate underwater throw device of the present invention. In this embodiment, the weights of the two head masses are different. More specifically, one of the head masses, head mass 401, is kept light (eg, less than 0.3 g) as previously described, while the opposing head mass 402 is slightly heavier (eg, less than 1 g). No preload mechanism is required. In such a design, one or both of the head masses can be used to transmit sound into the water. When properly designed, this non-uniform mass multi-plate underwater transducer can improve the TVR bandwidth.

[0112] 13A and 13B show the TVR of the inventive multi-plate underwater transducer of unequal mass design described in FIG. In FIG. 13A, only the light head mass is used as the radiating surface (the heavy head mass side is covered with a metal end cap), and the acoustic axis is aligned with the axis of the underwater transducer. FIG. 13B shows the case where both head masses radiate sound simultaneously, with the acoustic axis perpendicular to the axis of the underwater transducer. In both cases, no baffles are used.

[0113] The laterally constrained and non-uniform mass designs for improved bandwidth are suitable for multi-plate underwater transducers requiring long crystal active lengths, such as those with low operating center frequencies. However, it is also an effective means of improving bandwidth for underwater transducers with short crystal active lengths and high operating center frequencies.

[0114] The various broadband designs of multi-plate underwater transducers described above, i.e., very light head mass, end constrained effects (short active material), lateral constrained effects (multi-layer multi-plate designs), and non-uniform mass designs, and combinations thereof, are collectively referred to hereinafter as "broadband multi-plate designs." Also, the resulting transducer will be referred to below as a "single head mass" or "lambda / 4 mode multiple plate configuration" underwater transducer if it uses only one head mass to radiate sound into the underwater medium.

[0115] When used underwater, a compressive force is applied to the head mass by water pressure, and a compressive force is also applied to the crystal of the single crystal motor portion of the underwater transducer of the present invention. The compressive stress, amplified by the area ratio of the piston to the crystal, compresses the adhesive joint between the head mass and the crystal and the single crystal, which is beneficial to the operation of the underwater transducer of the present invention.

[0116] If the head mass and the head mass end of the crystal move in perfect synchronism, the dynamic stresses that the head mass exerts on the crystal are minimized. Therefore, the dynamic stresses actually produced are those resulting from the relative displacement between the head mass and the top face of the crystal during operation of the underwater transducer.

[0117] The above-mentioned relative displacement during operation of the underwater transducer is usually a fraction of the relative displacement when only the crystal is vibrating and the head mass is stationary. Taking this percentage to be 20% and taking into account the loading effect of the area ratio between the head mass and the crystal, calculations show that for a very light head mass (e.g., about 0.2 g), the dynamic stresses generated by the head mass are very small and a water depth of 5 meters is sufficient to generate adequate compressive stresses to ensure the safe operation of the underwater transducer.

[0118] For example, a λ / 4 mode underwater transducer made according to the present invention, consisting of multiple plates, was driven for 1 hour at a depth of 0.9 meters with a design sound pressure level of 176 dB (re 1 μPa / V at 1 m) and a duty cycle of 10%. Immediately after this endurance test, the TVR of the underwater transducer was measured at a low alternating current (AC) voltage. The results revealed that no degradation was observed in the TVR. This indicates that the multi-plate underwater transducer works well even at very shallow depths.

[0119] If desired, but not required, suitable mechanical means may be used to apply a light but beneficial compressive force through the sound-transmissive window material to the head mass and underlying crystals. An example is shown in Figures 14A to 14C.

[0120] FIG. 14A shows a design with a polyurethane (PU) window material that is molded to shrink when installed, exerting a downward force on the head mass and the crystals below it. FIG. 14B shows a design in which the housing has a base that can be adjusted upwards to push the transducer up against a shaped PU window, allowing the PU window to exert a downward force on the head mass and crystal below it. In FIG. 14C, a removable window end cap having a downward projection is used to apply a downward force to the perimeter area of ​​the PU window material and head mass during assembly. The dashed lines in these figures show the profile of the PU window material in an unstressed state (Figure 14A), before the housing base is inserted (Figure 14B), and before the top window end cap is applied (Figure 14C). [Compact, omnidirectional underwater transducer]

[0121] FIG. 15A illustrates another embodiment of the present invention. In this embodiment, as shown in the longitudinal section of Figure 15B, a small two-dimensional (2D) omnidirectional underwater transducer is realized by cross-arranging two units of an underwater transducer composed of multiple λ / 2 mode plates. This derivative 2D omnidirectional underwater transducer remains compact in size, less than 40 mm in diameter and height.

[0122] FIG. 16A shows the TVR of the underwater transducer of FIG. FIG. 16B shows the horizontal beam pattern in the azimuth plane of the underwater transducer.

[0123] FIG. 17 shows another embodiment of a three-layer miniature 2D omnidirectional underwater transducer with the same design as FIG. 15 but including three units of underwater transducers composed of λ / 2 mode multi-plates arranged at 60° intervals. In this embodiment, the derivative underwater transducer has a diameter of less than 40mm and a height of less than 60mm.

[0124] The three-layer omnidirectional transducer shown in Figures 17A and 17B can be fitted with a λ / 2 mode multi-plate underwater transducer with non-uniform head mass as shown in Figure 12 to improve bandwidth.

[0125] 18A, 18B, 19, 20A and 20B show another configuration of a miniature 2D omnidirectional underwater transducer made from multiple units of a multi-plate underwater transducer of the present invention. The dashed lines indicate areas that can be filled with sound-transmitting material to make the entire underwater transducer cylindrical for flow smoothing purposes. FIG. 20B shows the device encapsulated in a sound-transmitting material 408 such as polyurethane (PU).

[0126] Figures 21, 22A, 22B and 23 show that by stacking multiple omnidirectional underwater transducer units (shown in Figures 15, 17, 18, 19 and 20) along an axis, it is possible to create an omnidirectional underwater transducer with increased sound pressure levels. The dashed lines in Figures 22A, 22B and 23 indicate areas that can be filled with sound-transmitting material to make the entire underwater transducer cylindrical for flow smoothing purposes. Stacked underwater transducers have a donut-shaped beam pattern in the vertical plane, the beam width of which decreases with the number of stacks in the device.

[0127] By designing the pitch center diameter to height ratio (e.g., D / H ratio in Figures 19 and 20A), the number of transducer elements composed of multiple plates, and the relative head mass position in each layer (e.g., h value in Figure 20A) of the underwater transducer, and utilizing the baffle effect provided by the housing frame structure, different designs of 3D omnidirectional underwater transducers can also be realized using the housing designs shown in Figures 19 and 20A, as well as other suitable housing designs. [Acoustic adjustable λ w / 2 size transducer elements]

[0128] As mentioned before, to improve acoustic impedance matching, conventional Tonpilz-type underwater transducers made of PZT piezoelectric ceramics have a much larger head mass diameter and are located approximately λ away from the operating center frequency in water. w It is equal to or slightly less than / 2. In other words, each piezoelectric ceramic transducer in the Tonpilz design is itself a "lambda w / 2 size element". (To further improve the acoustic impedance matching) the piston diameter is increased to approximately λ w One reason for keeping the size at 1 / 2 and no larger is to facilitate fabricating a transducer array of desired acoustic performance with controlled sidelobe strength.

[0129] The diameter of the head mass of the underwater transducer made of multiple plates of the present invention is λ w / 2, multiple units of the underwater transducer made of multiple plates can be placed at λ w / 2×λ w By packing the individual λ w It is possible to create elements of size / 2. FIG. 24 shows an example of such a design. Here, λ wThe / 2 size element contains seven units of a single head mass λ / 4 mode multi-plate underwater transducer, effectively achieving a sound pressure level seven times or 19 dB higher than that of individual multi-plate underwater transducers.

[0130] What is even more interesting is that the conventional λ w Unlike 1 / 2 size elements, the above-mentioned λ w The / 2 size factor is acoustically tunable with respect to TVR response, beam pattern and beam steerability. If desired, a similar approach can be used to change the lateral dimension of w It is possible to manufacture underwater transducer elements smaller than 1 / 2. [High-density underwater transducer array]

[0131] Underwater transducers of the Tonpilz design are often used in the form of regularly spaced arrays. In this way, not only does the overall sound pressure level of the resulting device increase, but the attachment of auxiliary electronics allows the beam pattern to be altered to steer the acoustic beam. Furthermore, if the size of the array is large enough, a multi-beam scanning device is feasible.

[0132] When forming an array, the spacing between the transducer elements is typically λ w / 2 or less. Here, λ w is the wavelength in water at the operating center frequency of the array. This is because the spacing between transducer elements is λ w / 2, the side lobe intensity can become very high. High side lobe strengths are highly undesirable since they produce strong, but unwanted, echo signals. The piston diameter of a conventional Tonpilz element is typically about λ w / 2, so the density of the conventional array is λ w / 2×λ w This results in a relatively low density of one transducer per half the array projected area.

[0133] In contrast, the head mass of the multi-plate underwater transducer of the present invention is so small in size that it allows arrays with much higher array densities than are possible with conventional Tonpilz elements.

[0134] FIG. 25 shows an example of a high density planar array formed in this manner. Such high density transducer arrays can be planar, conformal, or shaped for various desired acoustic beam patterns and performance characteristics, such as designing half-cone angle beams, focused beams, etc.

[0135] The acoustic characteristics of the high density transducer arrays described above can be altered or tuned for each multi-plate transducer or group of underwater transducers using appropriate electronics and drive signals. Such a high density array is also very suitable as a multi-scan beam generator. [Dual-frequency underwater transducers and arrays]

[0136] FIG. 26 shows the TVR of the underwater transducer of the present invention measured over a wider operating frequency range. In addition to the fundamental TVR peak mentioned above, it is then clear that there is a comparable TVR peak and bandwidth for the higher resonant modes. In other words, the individual multi-plate underwater transducers of the present invention are also suitable for use as wide bandwidth dual or multi-frequency generators.

[0137] Figure 26 shows the λ spectrum in water for various frequencies. w Dimensions of the 1 / 2 transducer and typical head mass dimensions of the multi-plate underwater transducer of the present invention are shown. The head mass dimension is set to λ of the operating center frequency of the high resonance mode.w It is interesting to note that the dimensions are equal to or smaller than 1 / 2. In other words, the underwater transducer of the present invention is suitable for producing a dual frequency array with controlled side lobe strength in both the fundamental and the next higher operating frequency bands.

[0138] The dual frequency transducer arrays described above may be planar, conformal or shaped to suit desired acoustic beam patterns and performance characteristics. [Low drop-down ratio parametric array for improved energy conversion efficiency]

[0139] In a parametric array, two high-pressure primary sources radiate sound waves at slightly different frequencies. These sources interact violently, generating two secondary waves. One of the secondary waves has the sum frequency of the two primary sources, and the other secondary wave has the difference frequency. The higher frequency secondary waves are quickly absorbed by the medium, while the lower frequency secondary waves continue to propagate deeper into the medium. In this case, the low difference frequency beam has a narrow beamwidth of a few degrees and acts like a collimated, non-diverging sound source.

[0140] The aforementioned parametric arrays typically have low energy conversion efficiency, i.e. the sound pressure level of the resulting difference frequency secondary beam is only a few percent of the sound pressure level of the individual primary sources. In general, the higher the drop down ratio (DDR), i.e., the ratio of the primary source frequency to the desired secondary beam frequency, the lower the energy conversion efficiency. In conventional parametric arrays, DDRs of 10 to 20 are common, and energy conversion efficiencies are typically 2% to 4%.

[0141] The compact nature of the multi-plate underwater transducer of the present invention allows it to be used as the primary source of a parametric array. Due to the low to medium operating center frequency, parametric arrays with low drop down ratios (less than 10) are feasible, which can improve the energy conversion efficiency. In such applications, higher source level elements may be substituted for the broadband multi-plate underwater transducers of the present invention in order to reduce array size.

[0142] More interestingly, due to the small head mass of the multi-plate underwater transducer of the present invention, it can also be used to create compact dual frequency band parametric arrays. Such a compact dual frequency band parametric array with improved energy conversion efficiency has not been realized to date.

[0143] The acoustic characteristics of the parametric arrays described above can be further modified, tuned and shaped using appropriate drive electronics to obtain desired acoustic performance as well as to form parametric sound sources that emit multi-scan beams. [High-density array of underwater transducers composed of λ / 2 mode multiple plates]

[0144] It would be interesting to see whether a slim transducer array could be formed using the horizontally oriented λ / 2 mode multi-plate underwater transducer of the present invention (whose typical TVR response is shown in Figures 4 and 13B) and whether the acoustic performance of such an array could be improved using various baffles.

[0145] Figure 27 shows the TVR of a λ / 2 mode multi-plate underwater transducer with the same structure and test arrangement as described in Figure 4 but with three different baffle conditions: (a) no baffle, (b) with a rigid simple baffle, and (c) with a semicircular rigid cavity baffle. As previously mentioned, baffles can be used to enhance acoustic energy in the acoustic axis of an underwater transducer. In the case of a cavity baffle, the cavity has a radius of 12 mm and may be filled with a sound-transmitting material. This figure shows that both the simple baffle and the cavity baffle are effective in improving the TVR, especially the cavity baffle.

[0146] FIG. 28 shows another embodiment of the present invention, showing an example of a slim planar array less than 30 mm thick made of multiple units of underwater transducers constructed from λ / 2 mode multiple plates with cavity baffles. In this embodiment, each transducer element is a λ / 2 mode multi-plate underwater transducer 414 with dimensions of approximately 30(L)×30(W)×24(H) mm 3 and a housing 412 containing two semicircular cavities 410. This example shows that by incorporating cavity baffles into the housing design, a higher density array can be achieved, resulting in improved array performance. The cavity in FIG. 28 can be filled with PU if desired.

[0147] 29A and 29B show yet another embodiment of the present invention. These figures show an example of a matched arrangement of λ / 2 mode multi-plate transducers with cavity baffles as described in FIG. FIG. 29B shows the arrangement encapsulated in a sound-transmitting material such as PU. [d 31 Underwater transducers and arrays constructed with modal multi-plates

[0148] The above explanation and the acoustic measurement results show that the polarization of the active crystal in the

[0011] direction is 32 This paper deals with an underwater transducer consisting of multiple plates made of piezoelectric single crystals.

[0149]

[0011] Polarization d of the composition described above (e.g., paragraphs

[0082] to

[0085] ) 32For the mode single crystal, its axial transformation compressive stress is in the range of 10 MPa to 40 MPa. Thus, under optimal acoustic matching conditions (i.e., near-optimal piston to crystal area ratios of 4 to 10, depending on the actual single crystal composition), multi-plate underwater transducers of the present invention made therefrom have a maximum operating depth of several hundred meters. Beyond this depth, the crystals undergo a phase transformation which, although not damaging the crystals (and therefore the transducer), adversely affects the performance of the transducer.

[0150] In order to improve the maximum operating depth, the [0-11] active crystal direction is perpendicular to the

[0011] polarization. 31 Mode lead-based relaxor-PT solid solution single crystals can be used. This d 31 Mode single crystal is d 32 They have much higher transformation stresses in the axial direction, 8 to 15 times higher than mode single crystals.

[0151] The above description is based on the polarization d of the above-mentioned composition (e.g., paragraph

[0085] ). 31 This also applies to underwater transducers consisting of multiple plates made of mode single crystals, but d 31 The elastic stiffness and acoustic impedance of the mode single crystal are d 32 are approximately four and two times the mode crystals, so appropriate design modifications are required.

[0152] As mentioned above, d 31 Mode lead-based relaxor-PT solid solution single crystals have very high axial transformation stresses, so that properly designed multi-plate underwater transducers and arrays made from them are expected to have maximum operating depths of hundreds to thousands of meters. [Transmit and receive dual mode transducers and arrays]

[0153] The primary objective of this invention is to demonstrate the construction and performance of underwater transducers and arrays composed of multiple plates made of transverse mode piezoelectric single crystals for generating underwater acoustic waves at low to moderate operating center frequencies, but which also function as highly sensitive underwater acoustic receivers over the design frequency range. In other words, it can be used as a transmit and receive dual mode underwater transducer and array if desired.

[0154] As the various embodiments described above demonstrate, the small size and light weight of the individual multi-plate underwater transducers of the present invention allows for design flexibility, enabling the development of miniature omnidirectional underwater transducers and slim planar, conformal and / or shaped arrays with a variety of configurations and acoustic characteristics to suit a variety of applications.

[0155] It will be apparent to those skilled in the art that the configuration, dimensions, and material selection of the individual multi-plate underwater transducers, their derivative transducers, and underwater transducer arrays of the present invention may be adapted, modified, improved, or substituted with slightly different equivalent methods or designs without departing from the essential features of the operating principles of the present invention, and additional features may be added to enhance the performance and / or reliability of the underwater transducers and arrays. These alternatives, modifications, or improvements are deemed to fall within the scope and language of the following claims.

Claims

1. A piston-type underwater transducer without a preload mechanism, operating in a central frequency range of 3 kHz to 300 kHz, The device includes a single crystal motor portion, a first head mass, a second head mass, a housing, and a sound-transmitting window material; The single crystal motor part is composed of a hollow polygonal pipe shape or a plurality of spaced plates or a plurality of coupled plates oriented in parallel, and has a rectangular [011] polarization d ３２ Or d ３１ It is composed of multiple units of transverse mode piezoelectric single crystals, and the overall load-bearing area of ​​the single crystal motor part is 40 mm ２ is less than a diameter of each of the first head mass and the second head mass is less than 0.4 times the wavelength of an acoustic wave at the operating center frequency in a surrounding medium; the first head mass and the second head mass each have a weight of less than 4 grams; the housing and the sound-transmitting window material protect the single crystal motor portion, the first head mass, and the second head mass from an ambient medium; A piston-type underwater transducer, wherein at least one of the first head mass and the second head mass radiates sound waves through the sound-transmissive window material into the surrounding medium.

2. The piezoelectric single crystal is made of lead zinc niobate-lead titanate (Pb[Zn １／３ Nb ２／３ ]O ３ -PbTiO ３ or PZN-PT), lead magnesium niobate-lead titanate (Pb[Mg １／３ Nb ２／３ ]O ３ -PbTiO ３ or PMN-PT), lead magnesium niobate-lead zirconate titanate (Pb[Mg １／３ Nb ２／３ ]O ３ -Pb[Zr １－ｘ Ti ｘ ]O ３ or PMN-PZT), lead indium niobate-lead magnesium niobate-lead titanate (Pb[In １／２ Nb １／２ ]O ３ -Pb[Mg １／３ Nb ２／３ ]O ３ -PbTiO ３ or PIN-PMN-PT), or lead indium niobate-lead zinc niobate-lead titanate (Pb[In １／２ Nb １／２ ]O ３ -Pb[Zn １／３ Nb ２／３ ]O ３ -PbTiO ３ 2. The piston-type underwater transducer according to claim 1, which is a lead-based relaxor-PT solid solution single crystal composed of a lead-based relaxor-PT (or PIN-PZN-PT) or a derivative having an additive and / or a composition changed thereto.

3. 2. The piston-type underwater transducer of claim 1, wherein the area ratio of head mass to the total load-bearing area of ​​the piezoelectric single crystal is between 3 and 10.

4. The load-bearing area of ​​the entire crystal is 25 mm ２ is less than 2. The piston-type underwater transducer of claim 1, wherein the radiation area of ​​the first head mass and the second head mass is four to eight times the load-bearing area of ​​the entire crystal of the piezoelectric single crystal.

5. the first head mass and the second head mass are equal or substantially equal in size and weight, or are different in size and weight; 2. The piston-type underwater transducer of claim 1, wherein the first head mass and the second head mass radiate acoustic waves into a surrounding medium in a λ / 2 mode.

6. The second head mass is heavier than the first head mass, 2. The piston-type underwater transducer of claim 1, wherein the first head mass radiates acoustic waves into a surrounding medium in a λ / 4 mode.

7. 7. The piston-type underwater transducer of claim 1, wherein the first head mass and the second head mass are made of one or more of aluminum and aluminum alloys, aluminum beryllium alloys, aluminum lithium alloys, magnesium and magnesium alloys, titanium and titanium alloys, or monolithic alloys thereof with micro hollow spheres.

8. 7. The piston-type underwater transducer of claim 1, wherein the first head mass and the second head mass are constructed from one or more of a high specific modulus metal matrix composite, a ceramic, or a fiber-reinforced polymer matrix composite.

9. 7. A piston-type underwater transducer as claimed in claim 1, wherein the single crystal motor section is constructed with an active crystal length of less than 9 millimeters.

10. 7. A piston-type underwater transducer according to claim 1, wherein the single crystal motor portion has a structure composed of two or more layers of plates.

11. the first head mass and the second head mass have different weights; 7. The piston-type underwater transducer of claim 1, wherein at least one of the first head mass and the second head mass radiates acoustic waves into a surrounding medium.

12. 7. The piston-type underwater transducer of claim 1, wherein the sound-transmissive window material exerts a downward force on at least one of the first head mass and the second head mass.

13. 7. The piston-type underwater transducer of claim 1, wherein the housing applies a downward force to at least one of the first head mass and the second head mass through the sound-transmitting window material during assembly.

14. A two-dimensional omnidirectional underwater transducer having a plurality of units of the piston-type underwater transducer according to any one of claims 1 to 6, A two-dimensional omnidirectional underwater transducer configured to provide two-dimensional omnidirectionality.

15. A three-dimensional omnidirectional underwater transducer having a plurality of units of the piston-type underwater transducer according to any one of claims 1 to 6, A three-dimensional omnidirectional underwater transducer configured to provide three-dimensional omnidirectionality.

16. An acoustically tunable λ / 4 transducer having a plurality of units of the piston-type λ / 4 mode underwater transducer according to any one of claims 1 to 6. ｗ / Two sizes of piston-type underwater transducers.

17. 6. The piston-type .lambda. / 2 mode underwater transducer of claim 5, further comprising a rigid simple baffle or a rigid cavity baffle.

18. 18. A planar, conformal or shaped array comprising a plurality of units of a piston-type underwater transducer according to any one of claims 1 to 6 and 17.

19. λ ｗ / 2xλ ｗ A planar array, a conformal array or a shaped array including at least two units of a piston-type underwater transducer according to any one of claims 1 to 6 and claim 17 per 2 array projected area, λ ｗ is the wavelength of sound in water at the operating center frequency of the operating frequency range of the planar, conformal or shaped array.

20. A dual frequency underwater transducer array comprising a plurality of units of the piston-type underwater transducer according to any one of claims 1 to 6 and 17.

21. A parametric array including a plurality of units of a piston-type underwater transducer according to any one of claims 1 to 6 and 17, A parametric array having a drop down ratio of less than 10 and having a single frequency band or dual frequency bands.

22. 18. A dual mode underwater transducer of the piston type underwater transducer of any one of claims 1 to 6 and claim 17 for generating and receiving sound waves underwater.

23. 18. A dual mode underwater transducer array comprising a plurality of units of a piston type underwater transducer according to any one of claims 1 to 6 and claim 17 for generating and receiving acoustic waves underwater.

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