WO2005017965A2 - Reseaux de transducteurs a air ultrasonores utilisant des films piezoelectriques polymeres et structures d'adaptation d'impedance pour reseaux de transducteurs polymeres ultrasonores - Google Patents

Reseaux de transducteurs a air ultrasonores utilisant des films piezoelectriques polymeres et structures d'adaptation d'impedance pour reseaux de transducteurs polymeres ultrasonores Download PDF

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Publication number
WO2005017965A2
WO2005017965A2 PCT/US2004/025189 US2004025189W WO2005017965A2 WO 2005017965 A2 WO2005017965 A2 WO 2005017965A2 US 2004025189 W US2004025189 W US 2004025189W WO 2005017965 A2 WO2005017965 A2 WO 2005017965A2
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Prior art keywords
film
transducer
ultrasonic
thin walls
arcuated
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PCT/US2004/025189
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English (en)
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WO2005017965A3 (fr
Inventor
Minoru Toda
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Measurement Specialities, Inc.
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Application filed by Measurement Specialities, Inc. filed Critical Measurement Specialities, Inc.
Publication of WO2005017965A2 publication Critical patent/WO2005017965A2/fr
Publication of WO2005017965A3 publication Critical patent/WO2005017965A3/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
    • B06B1/0688—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction with foil-type piezoelectric elements, e.g. PVDF

Definitions

  • the present invention relates to ultrasonic transducers. More particularly, the present invention relates to ultrasonic air transducer arrays utilizing polymer piezoelectric films and impedance matching structures for ultrasonic polymer transducer arrays.
  • PNDF polyvinylidene fluoride
  • a PNDF film-based ultrasonic transducer for high directional speaker applications (ultrasonic wave is modulated by audio signal and audible sound is heard by ear via demodulation due to non-linearity in propagation), requires a large transducer area to obtain sufficient acoustic pressure and broadband resonance performance. Because of material costs, only PVDF film-based transducers serve this purpose. More specifically, ceramic-based transducers have too narrow a bandwidth because of sharp resonance. Moreover, ceramic-based transducers have cost problems and the audio reproduction quality of ceramic-based transducers is poor.
  • PVDF-film-based transducers can be formed by multiple sections of curved PVDF film.
  • the most important requirements for curved and clamped PVDF film transducer structures are forming an accurate curvature and forming a good, uniform clamp.
  • Another important requirement is matching the thermal expansion between PVDF film and the holder material.
  • the curvature of the film 10 has to be formed by supporting the film 10 with cylindrical surfaces 12a, 12b located at two regions on an axis A-A' along a cylindrical surface 12 as shown in FIGS. lA-lC.
  • the film curvature is formed by two supporting surfaces with the correct curvature and clamps.
  • the clamp regions each have a certain area for holding the film 10.
  • the clamp regions should each form a cylindrical surface 14a, 14b consistent with film curvature as shown in FIG. IB, or each form a flat surface 14a', 14b'that is tangential to the cylindrical surface 12 at the boundary line L between free film and clamp as shown in FIG. lC.
  • the film surface should be cylindrical as close as possible to an ideal one, or smoothly curved. Any deformation, such as a dent, a pleat or a wrinkle, will cause a reduction of acoustic output.
  • PVDF has thermal expansion coefficient of 119 ppm/ °C in the direction perpendicular to the stretched (machined) direction, and 25 ppm/ °C in the stretched direction.
  • the clamp is applied along a line perpendicular to the stretched direction of the curved film, to which direction, the PVDF film has high thermal expansion coefficient.
  • thermal expansion of the clamp material is much lower than that of the film (119 ppm/ °C)
  • a high temperature causes greater expansion of the film than the clamp material, therefore, causing the film to become pleated or wrinkled.
  • the film buckles and permanent deformation is formed along the clamp.
  • the temperature returns to room temperature this deformation is visible and looks very ugly.
  • the performance of the transducer is degraded.
  • ultrasonic transducers have a higher mechanical impedance (i.e., a stiff, heavy, and large force has to be applied to obtain a vibration motion) than that of the propagation medium, which is typically air or some other gas. Accordingly, ultrasonic transducers have a large vibrational force, however, this force is not used and its displacement is small and not enough to create strong acoustic waves. In other words, acoustic wave excitation in air or gas requires a large displacement but, does not require a large force.
  • a very well known impedance matching concept involves inserting a material having an impedance of a geometrical mean value of the transducer and air, with the thickness of the inserted layer being set a quarter of its wavelength.
  • a well known impedance matching structure is a horn.
  • a horn was used for musical instruments or loudspeakers.
  • a horn is basically a hole of a small size communicating with an aperture of a large size from which acoustic radiation takes place.
  • High acoustic pressure existing at the source region (high impedance) is gradually converted to low acoustic pressure towards the exit area (low impedance) and the impedance of the vibration source matches to that of free air.
  • N.H. Fletcher and S. Thwaites Ultrasonics, vol. 30, no. 2, pp.
  • the size of the obstructing structure is smaller than the wavelength, the transmission reduction does not necessarily take place, because the waves can go around the small obstructing structure. This is the concept of diffraction, which is well known in optics.
  • the size of the impedance matching structure discussed in the present invention is comparable or smaller than the wavelength and it does not simply shade, but reflection from the obstructing structure plays an important role.
  • the radiation source When the radiation source is in a propagation medium, the radiation source sees a certain impedance of the propagation medium.
  • the distance and size of the obstructing structure When the distance and size of the obstructing structure is appropriately adjusted, the reflection from the obstruction influences the impedance of the propagation medium so that it is possible to match the source impedance to the propagation medium.
  • microwave waveguide components where impedance matching component is composed of metallic structures. The microwave or electromagnetic wave does not propagate into metal, but the size of the metallic structure is smaller than or comparable to the wavelength.
  • An example is a stub tuner.
  • a metallic post is inserted into waveguide from the wall (normal to the wall surface), and by adjusting the depth of the insertion and the position of location of the stub, impedance matching is performed and the output from source increases, or receiving signal from a detector increases for an appropriate design.
  • the optimum condition involving the position of *be plate from transducer surface, the size and the density of the holes (passage rate) and the thickness of plate are described in Toda, but these are different for different frequencies, and also, the best condition is different for different transducers with different impedances. Therefore, the best condition can be found only by calculations or experimental testing and there are no easy methods for finding the best condition.
  • the thickness of plate may be in a range of about 0.1 mm to a few mm
  • the passage rate may be 10% to 50%
  • the position of plate may be 0 mm to 0.5 mm from the surface of the transducer. The optimum values become smaller for higher frequencies.
  • An ultrasonic transducer array structure including: a first lattice structure including a first plurality of arcuated and clamping thin walls; a second lattice structure including a second plurality of arcuated and clamping thin walls; and a polymer piezoelectric film held between the first and second lattice structures, the arcuated and clamping thin walls of the first and second lattice structures forming the film into an array of curved transducers elements.
  • FIGS. 1 A - 1C illustrate a film with cylindrical surfaces
  • FIGS. 2, 2A and 2B illustrate an exemplary embodiment of a CCUTA structure according to an aspect of the present invention
  • FIG. 2C illustrates an exemplary embodiment of a CCUTA structure according to an aspect of the present invention
  • FIGS. 3 and 3 A illustrates an exemplary embodiment of a CPFUTA structure according to an aspect of the present invention
  • FIGS. 4, 5, and 5A collectively an exemplary embodiment of a CPFUTA structure according to an aspect of the present invention
  • FIG. 6 illustrates a view of a corrugated device according to an aspect of the present invention
  • FIGS. 7 and 7 A illustrate an embodiment of an impedance matching structure according to an aspect of the present invention
  • FIG. 7B illustrates an ultrasonic polymer transducer array according to an aspect of the present invention
  • FIGS. 7C and 7D collectively illustrate an ultrasonic polymer corrugated transducer array according to an aspect of the present invention
  • FIGS. 8 and 8 A illustrate an embodiment of an impedance matching structure according to an aspect of the present invention
  • FIG. 8B illustrates an ultrasonic polymer transducer array according to an aspect of the present invention
  • FIGS. 9 and 10 illustrate a film and backing according to aspects of the present invention
  • FIGS. 11 and 12 illustrate systems according to aspects of the present invention
  • An aspect of the present invention is a large area, curved, clamped ultrasonic air transducer array (CCUTA) structure.
  • CCUTA structure of the present invention denoted generally by reference numeral 100, includes a polyvinylidene fluoride (PVDF) piezoelectric film held 110 or sandwiched between first and second lattice structures, 120, 130.
  • First lattice structure 120 includes a first peripheral holding frame 121 with arcuated side walls 122 (only one is shown) and non-arcuated end walls 123 (only one shown).
  • the arcuated side walls 122 have periodically arcuated inner surfaces 122a formed by a plurality of curved surfaces 122b, which each curve in a first direction (concave).
  • the non-arcuated end walls 123 have flat, end wall inner surfaces 123 a.
  • a plurality of laterally-spaced, arcuated thin walls 124 extend parallel to one another between the non-arcuated end walls 123 of the first peripheral holding frame 121, and a plurality of laterally-spaced, clamping thin walls 126, which are perpendicular to arcuated thin walls 124, extend parallel to one another between the arcuated side walls 122 of the first peripheral holding frame 121.
  • the arcuated thin walls 124 have periodically arcuated inner surfaces 124a formed by a plurality of curved surfaces 124b, which each curve in the first direction.
  • the clamping thin walls 126 have flat inner (clamp) surfaces 126a, which extend between the curved surfaces 124b of the arcuated thin wall inner surfaces 124a at junctures 127, thereby forming a plurality of rectangular units 128. It may be noted that the position of the rubber may be at a convex position where the film is clamped. During the assembly process, while the first and second lattices are positioned closer and closer, the film may slipped and be clamped only at the final stage.
  • the second lattice structure 130 includes a second peripheral holding frame 131 with arcuated side walls 132 (only one is shown) and non-arcuated end walls 133 (only one shown).
  • the arcuated side walls 132 have periodically arcuated inner surfaces 132a formed by a plurality of curved surfaces 132b, which each curve in a second direction (convex) complementary to the first direction (concave).
  • the non-arcuated end walls 133 have flat, end wall inner surfaces 133a.
  • a plurality of laterally-spaced, arcuated thin walls 134 extend parallel to one another between the non-arcuated end walls 133 of the second peripheral holding frame 131, and a plurality of laterally-spaced, clamping thin walls 136, which are perpendicular to arcuated thin walls 134, extend parallel to one another between the arcuated side walls 132 of the second peripheral holding frame 131.
  • the arcuated thin walls 134 have periodically arcuated inner surfaces 134a formed by a plurality of curved surfaces 134b, which each curve in the second direction.
  • the clamping thin walls 136 have flat inner surfaces 136a, which extend between the curved surfaces 134b of the arcuated thin wall inner surfaces 134a at junctures 137, thereby forming a plurality of rectangular units 138.
  • the bottoms of the rectangular units 138 are closed by backwall 139.
  • the PVDF film 110 is clamped between rubber strips 140 running along the flat inner surfaces 136a of the clamping thin walls 136 of the second lattice structure 130 and the flat inner surfaces 126a of the clamping thin walls 126 of the first lattice structure 120. This forms the PVDF film 110 into an array of upwardly curved transducer elements.
  • the rubber strips 140 run along the flat inner surfaces 126a of the clamping thin walls 126 of the first lattice structure 120, and the PVDF film 110 is formed into an array of downwardly curved transducer elements. Electrodes (not shown) are attached in known manner onto the surfaces of the PVDF film 110.
  • the stretched direction of PVDF is parallel to the arcuated walls 122, 124, 132, 134, of the first and second lattice structures 120, 130 and perpendicular to the non-arcuated walls 123, 126, 133, 136 of the first and second lattice structures 120, 130.
  • the thickness of the thin walls 124, 126, 134, 136 has to be as thin as possible but not too thin to be fragile, typically, 1-2 millimeters (mm). If the wall thickness is too great, the thin walls 124, 126, 134, 136 occupy too much space and the total device becomes excessively heavy and large, and a greater area of PVDF film is necessary. [00043]
  • the side and end walls 122, 123, 132, 133 of the first and second peripheral frames 121, 131 are heavier and thicker.
  • thermal expansion matched material for the peripheral frames 121, 131 and thin walls 124, 126, 134, 136, including, without limitation, cellulose acetate, vinylidene chloride, polybutylene, acrylic, polypropylene, epoxy nylon, silicone plastic, etc.
  • the backwall 139 of the second lattice structure 130 suppresses the back wave so that it does not propagates to the front side and interfere with the main front wave.
  • the material for the backwall 139 may be a stiff, heavy, or absorptive material such as metal, plastic, wood, or wrinkled tissue paper, when the frequency is high (i.e. greater than 20 KHz).
  • CPFUTA corrugated PVDF film ultrasonic transducer array structure
  • the purpose of CPFUTA structure is to provide a transducer that can be easily mass-produced with high accuracy and high reproducibility of film curvature.
  • an exemplary embodiment of the CPFUTA structure of the present invention denoted generally by reference numeral 200, includes a PVDF film held 210 or sandwiched between first and second lattice structures, 220, 230, such that the film 210 is accurately maintained in a corrugated shape.
  • First lattice structure 220 includes a first peripheral holding frame 221 with side walls 222 (only one is shown) and end walls 223 (only one shown).
  • a plurality of laterally-spaced, thin walls 224 extend parallel to one another between the end walls 223 of the first peripheral holding frame 221.
  • the thin walls 224 define wavy inner surfaces 225 formed by alternating concave wave surfaces 226 and convex wave surfaces 227.
  • the second lattice structure 230 includes a second peripheral holding frame 231 with side walls 232 (only one is shown) and end walls 233 (only one shown).
  • a plurality of laterally- spaced, thin walls 234 extend between the end walls 233 of the second peripheral holding frame 231.
  • the thin walls 234 define wavy inner surfaces 235 formed by alternating convex wave surfaces 236 and concave wave surfaces 237 which are respectively complementary to the alternating concave wave surfaces 226 and convex wave surfaces 227 of the wavy inner surfaces 225 of the thin walls 224 of the first lattice structure 220.
  • the bottom of the second lattice structure 230 may be closed by a backwall 239.
  • the thin walls 224, 234 of the CPFUTA structure 200 extend parallel to the stretched direction of PNDF film 210. Electrodes (not shown) are attached in known manner onto the surfaces of the PVDF film 210.
  • the resistivity of the metallic surface electrode is generally high, and the electrical connection is through at least one of the thin walls 224.
  • a narrow strip region of silver ink (very low resistivity) is deposited on the metallized surface of the PVDF film 210, and the thin wall 224 utilized for electrical connection, contacts the silver ink region.
  • the silver ink region is underneath the connecting thin wall 224. Since silver ink absorbs vibration, the majority of the surface of the PVDF film 210 should be coated by the thin metallic layer.
  • the backwall 239 of the second lattice structure 230 suppresses the back wave so that it does not propagates to the front side and interfere with the main front wave.
  • the material for the backwall 239 may be a stiff, heavy, or absorptive material such as metal, plastic, wood, or wrinkled tissue paper, when the frequency is high (i.e. greater than 20 KHz).
  • the CPFUTA structure 200 does not utilize clamping thin walls extending perpendicular to the thin walls 224, 234 with the wavy inner surfaces 225, 235.
  • the CPFUTA structure 200 is different from the CCUTA structure 100.
  • the first half cycle and next half cycle are smoothly connected (continuous delivative) and form one cycle.
  • the next cycle repeats exactly the same shape and so on, therefore, forming a shape substantially identical to a wave.
  • each opposing pair of complementary wavy surfaces 225 and 235 it is not necessary for each opposing pair of complementary wavy surfaces 225 and 235 to clamp the film 210 with a strong force. More preferably, it is desirable to hold apart each opposing pair of complementary wavy surfaces 225 and 235 by a small gap G, as shown in FIG. 3A, which, for example, can be about lOOum.
  • the purpose of the gap G is to form an accurate film shape, but not to clamp it.
  • Gap G may be a little larger than the film thickness, for example.
  • a 30um thick PVDF film expands in the gap G and the thermal expansion of peripheral holding frames 221, 231 and movement of the thin walls 224, 234 (by thermal expansion but with a different value) do not stress the film. Therefore, any material can be used for holder frames 221, 231 and the thin walls 224, 234 of the first and second lattice structures 220 and 230.
  • the CPFUTA structure of FIGS. 3 and 3 A preferably includes a small gap G between each opposing pair of complementary wavy surfaces 225 and 235 to maintain an accurate film shape.
  • film vibration e.g. at 40 KHz
  • This sound is generated by soft touching of the film 210 to some portion of the wavy surfaces 225, 235 because the film 210 is vibrating and the touching receives a repulsion force from the touched solid, which causes a slight deformation of the film.
  • the deformation of the film recovers with a much longer period of vibration and then the film 210 touches some portion of the wavy surfaces 225, 235 again.
  • FIGS. 4, 5, and 5A collectively show an alternative embodiment of the CPFUTA structure of the present invention, denoted generally by reference numeral 200', which solves the film touching problem described immediately above.
  • the CPFUTA structure 200' is substantially identical to the previous CPFUTA structure 200 except, the CPFUTA structure 200' includes a PVDF film 210' having laterally spaced, thin, narrow strips of metal material 215, such as aluminum, bonded to opposing sides of the film 210' as shown in FIG. 4.
  • metal material 215 such as aluminum
  • the height and period of the corrugated aluminum strip pairs 215 are made to exactly match the height and period of the wavy surfaces 225', 235' of the thin walls 224', 234', and the aluminum strip enforced corrugated PVDF film 210' is held between the wavy surfaces 225', 235 'as shown in FIG. 5A.
  • the vibration of the aluminum strips 215 is much less than that of the film 210' such that the CPFUTA structure 200' does not make the earlier described touching noise.
  • the corrugation shape of the PVDF film 210' can be formed by first annealing the aluminum strips 215 at a temperature of about 600 °C, which is below the aluminum strips melting temperature of about 660 °C. After, annealing, the yield point for elasticity becomes very low and the elastic property of the strips 215 is lost such that the strips 215 act non- elastically, as if they were made from lead.
  • the strips 215 are each made flat by pressing them between two flat plates.
  • the strips 215 are then bonded to the PVDF film 210' as shown in FIG. 4.
  • the bonding material may be for example, epoxy or cyano-acrylic.
  • the aluminum strip enforced PVDF film 210' is placed between the wavy surfaces 225', 235' of the first and second lattice structures 220' and 230', which are used as shape formers.
  • the corrugation shape is sequentially formed from one side of the PVDF film 210' to the other so that the shape of the corrugation exactly matches with the shapes of the wavy surfaces 225', 235'.
  • a corrugated device with a large surface area cannot be ideally flat, i.e., where flat is defined as planes PI and P2 defined by the top and bottom surfaces of the corrugated surface S. Since the wavelength is 8 mm at 40 KHz, if the flatness deviates by 4 mm, the acoustic wave coming out from the deviated region does not effectively add to the acoustic total power, and instead, cancels the power because 4 mm is half of the wavelength. Therefore, the corrugated surface S has to be flat within an error of 1-2 mm (for a 40 kHz device for example), which is a very difficult requirement to achieve.
  • FIGS. 7 and 7 A an embodiment of the impedance matching structure of the present invention is shown, denoted by reference numeral 300.
  • the impedance matching structure 300 is shown at the front of a curved film transducer 330 having a dimension H (height) extending in the axial direction AD- AD' of a cylindrical curvature forming member 332.
  • the transducer further includes a PVDF film 334 clamped to the cylindrical curvature forming member 332.
  • the impedance matching structure (IMS) 300 is somewhat similar to an acoustic horn, without actually being a horn.
  • the IMS 300 comprises two block-like members 302 made from a solid plastic or metal material, and may be unitarily formed with the curvature forming member 332 of the transducer 330.
  • the bottom surface 303 of each block member 302 defines a recess 304, such that a narrow space S is formed between the top surface 334a of the curved film 334 and the recess 304 of the block members 302.
  • the two block members 302 define opposing inclined surfaces 305, which together define a V-shaped, elongated slit 306 running parallel to the axial direction AD-AD' of the curvature forming member 332.
  • the slit 306 becomes larger in the acoustic wave propagation direction.
  • the curved plane may be substantially straight, as shown by dotted line 350.
  • This IMS 300 is different from conventional multi-horn designs, which have a small inlet with a circular cross-sectional shape and a cross sectional area that becomes gradually larger in the propagation direction while maintaining the generally circular cross-sectional shape.
  • the inlet area 306a of the elongated slit 306 has a ratio of length to separation of at least 5 to 1 and typically 20 to 1 or more, and the exiting area 306b has much smaller ratio of length to separation because of the wider separation s.
  • the acoustic pressure output for a 40 KHz transducer 330 measured at a certain distance, improved by 50-100%.
  • the inlet area 306a had a 1-2 mm slit and the space S between the bottom surfaces 303 of the block members 302 and the surface 334a of the curved film 334 was about 0.02 mm to about 0.5 mm.
  • FIG. 7B shows an ultrasonic polymer transducer array 330' that utilizes a plurality of IMSs, denoted by reference numeral 300'.
  • Each IMS 300' is basically identical to the IMS 300 of FIGS. 7 and 7A, including two block members 302' with opposing inclined surfaces 305' defining a V-shaped, elongated slit 306' that becomes larger in the acoustic wave propagation direction.
  • the transducer array 330' includes multiple curved PVDF film transducer elements 331'. Such a transducer array would typically be used to produce high acoustic pressures.
  • the multiple curved film transducer elements 331' are connected in parallel and aligned on a flat plane.
  • the plurality of IMSs 300' may be unitarily formed with the film curvature former members 332'.
  • Each IMS 300' provides impedance matching for two or more, curved film transducer elements 331'.
  • FIGS. 7C and 7D collectively show an ultrasonic polymer corrugated transducer array 330' ' which utilizes a plurality of EVISs, denoted by reference numeral 300' ' , to increase the acoustic output for certain applications.
  • the transducer array 330' ' includes a backplate 332' ' with corrugation forming members 332a" and a corrugated PVDF film 334" with alternating convex and concave curve portions as described in U.S. Patent 6,411, 015 issued to Minoru Toda and assigned to Measurement Specialties, Inc., the assignee herein.
  • Each IMS 300" is basically identical to the IMS 300 of FIGS.
  • the EVISs 300" are combined as a single unitary impedance matching member 333" and include corrugation forming members 332b".
  • the top surface 333a" of the impedance matching member 333" may be wavy as shown in FIG. 7C or flat as shown in FIG. 7D. Again, the plane may be wavier or flat, as is generally designated by reference numeral 350.
  • FIGS. 8 and 8 A show another embodiment of the IMS of the present invention, denoted by reference numeral 400, as utilized with a curved film transducer 430 formed by a curved PVDF film 434 clamped to a cylindrical curvature forming member 432.
  • the IMS 400 includes a curved plate 402 having a constant thickness T.
  • the bottom surface 403 of the curved plate 402 defines a recess 404, such that a narrow space S is formed between the top surface 434a of the curved film 434 and the bottom surface 403 of the plate 402.
  • the plate 402 is curved to complement the curved PVDF film 434 of the transducer 430, so that the space S between the surface of the film 434a and surface 404a of the recess 404 of the curved plate 402 is kept constant.
  • the curved plate 402 is provided with a plurality of small openings or slits 406.
  • the openings 406 may be formed in any desired shape.
  • the area of each opening 406 occupies a small percentage of total surface area of plate 402 and should be specified such that the passage rate is through the plate 402 is about 10% to about 50%.
  • the thickness T of plate is typically about 1 mm to about 4 mm and the space S is typically about 0.03 mm to about 0.5 mm for a 40 KHz transducer 430. For other frequency transducers, the values and combinations are different, but generally the thickness T and the space S become smaller with higher frequency transducers.
  • FIG. 8B shows an ultrasonic polymer transducer array 430' that utilizes a plurality of EVISs, denoted by reference numeral 400'.
  • Each S 400' is basically identical to the IMS 400 of FIGS. 8 and 8 A, including a curved plate 402' having a bottom surface recess 404' forming a narrow space S.
  • the transducer array 430' includes multiple curved PVDF film transducer elements 431'.
  • the multiple curved film transducer elements 431' are connected in parallel and aligned on a flat plane.
  • the plurality of EVISs 400' may be unitarily formed with the film curvature former members 432'.
  • Each IMS 400' provides impedance matching for two or more curved film transducer elements 431'.
  • condition a peak may be formed.
  • the reflecting surface 930 of plate 910 non-flat so that reflection has different phase depending on the position.
  • the difference of the height may be ⁇ quarter of the wavelength (i.e., 2mm for 40KHz).
  • the shape may take the form of a randomly coarse plane such as a wrinkle of paper or cloth.
  • Another way is to remove back plate so back waves are not reflected.
  • the thickness of PVD has to be thick, for example 110 ⁇ m may be used, while, in certain circumstances 28 or 52 ⁇ m may not be sufficient.
  • vibration amplitude is deformed from a sinusoidal wave, and the deformed wave has spectrum at a frequency other than main resonance which excites spurious resonance, and output at main resonance is decreased.
  • electrode material may influence vibration amplitude.
  • the electrode 1000 is a thin metal 1100 (500-2000 Angstrom - deposited by sputtering)
  • vibration is higher, and so is acoustic output, as compared to a silver ink electrode (-10 ⁇ m).
  • thin metal has a high resistivity, such that there may be a problem of too high current density near the lead connection area, where electrode sublimate and thin electrode metal disappears.
  • a narrow strip region of silver ink 1010 may be deposited, on one or both sides, so that current flows parallel on the surface 1020, and lead wires are connected narrow strips of silver ink electrode.
  • the location of the silver ink 1010 may be chosen to be underneath of wavier plates 1030 forming the film into a wave shape, and thus be less visible.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Transducers For Ultrasonic Waves (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

Abstract

L'invention concerne une structure de réseau de transducteur ultrasonore comprenant : une première structure de réseau comprenant une première pluralité de parois minces de serrage et de parois minces arquées ; une seconde structure de réseau comprenant une seconde pluralité de parois minces de serrage et de parois minces arquées ; ainsi qu'un film piézoélectrique polymère retenu entre les première et seconde structures de réseau, les parois minces de serrage et les parois minces arquées des première et seconde structures de réseau formant le film en un réseau d'éléments de transducteurs incurvés.
PCT/US2004/025189 2003-08-06 2004-08-05 Reseaux de transducteurs a air ultrasonores utilisant des films piezoelectriques polymeres et structures d'adaptation d'impedance pour reseaux de transducteurs polymeres ultrasonores WO2005017965A2 (fr)

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