EP0033751B1 - Transducteur ultrasonore utilisant une très haute fréquence - Google Patents

Transducteur ultrasonore utilisant une très haute fréquence Download PDF

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Publication number
EP0033751B1
EP0033751B1 EP19800100662 EP80100662A EP0033751B1 EP 0033751 B1 EP0033751 B1 EP 0033751B1 EP 19800100662 EP19800100662 EP 19800100662 EP 80100662 A EP80100662 A EP 80100662A EP 0033751 B1 EP0033751 B1 EP 0033751B1
Authority
EP
European Patent Office
Prior art keywords
lens
ultrasonic transducer
aperture
ultrasonic
sound pressure
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP19800100662
Other languages
German (de)
English (en)
Other versions
EP0033751A1 (fr
Inventor
Hiroshi Kanda
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hitachi Ltd
Original Assignee
Hitachi Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hitachi Ltd filed Critical Hitachi Ltd
Priority to DE8080100662T priority Critical patent/DE3063803D1/de
Priority to EP19800100662 priority patent/EP0033751B1/fr
Publication of EP0033751A1 publication Critical patent/EP0033751A1/fr
Application granted granted Critical
Publication of EP0033751B1 publication Critical patent/EP0033751B1/fr
Expired legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/18—Methods or devices for transmitting, conducting or directing sound
    • G10K11/26—Sound-focusing or directing, e.g. scanning
    • G10K11/30—Sound-focusing or directing, e.g. scanning using refraction, e.g. acoustic lenses

Definitions

  • the present invention relates to ultrasonic transducers for use with devices using high frequency acoustic radiation and more particularly to such transducers which are suitable for use in acoustic microscopes.
  • Recent evolution of generation and detection of high frequency acoustic waves extending up to 1 GHz can provide an acoustic wave length of about 1 micron under water, giving rise to availability of an acoustic microscope.
  • an acoustic wave beam of an extremely small size is produced which is projected on a target specimen and propagation loss of acoustic radiation due to reflection, scattering and penetrant attenuation at the target is detected to obtain information representative of elastic properties of the target.
  • propagation loss of acoustic radiation due to reflection, scattering and penetrant attenuation at the target is detected to obtain information representative of elastic properties of the target.
  • a surface of the specimen is scanned two-dimensionally with the focused acoustic wave beam and the perturbed energy is displayed on a cathode-ray tube in synchronism with the scanning.
  • a prior art ultrasonic transducer as shown in Fig. 1, directed to such a reduction has a cylindrical crystalline lens body 20 as an ultrasonic wave propagation medium of sapphire, for example, with one flat surface optically polished and opposite surface formed with a concaved recess 25.
  • An RF electric signal produced from an electric signal source 10 is applied to a piezoelectric film 15 which in turn transmits an RF acoustic wave in the form of a plane wave into the crystalline lens body 20.
  • the acoustic plane wave is focused at a given focal point F by means of a positive acoustical lens 40 formed at an interface between the arcuate recess 25 and an ultrasonic wave focusing medium 30, typically water.
  • a sufficiently small ratio between focal length and aperture size that is, a sufficiently small F-number of the lens can contribute to generation of the ultrasonic wave beam of a small size which approximates its wave length.
  • perturbed ultrasonic energy is produced from the target.
  • R, C 1 and C 2 denote the radius of curvature of the concaved ultrasonic lens 4 ⁇ , the speed of sound in the lens body material and the speed of sound in the focusing medium, respectively.
  • the front-face focal length F is, and the back-face focal length F' is,
  • the lens effect can be determined by multiplying a sound pressure distribution on the back-face focal plane by a pupil function of the lens and subjecting the product to a two-dimensional Hankel transformation.
  • the sound pressure distribution lie on the back-face focal plane and that the sound pressure distribution on the back-face focal plane be of a uniform amplitude and phase of a plane wave or subject to a Gaussian distribution in respect of amplitude and phase of a plane wave.
  • Another amplitude distribution may also attain the focussing effect but it requires a great number of multi-lens systems for elimination of the lens aberration and is unpractical for industrial purposes.
  • a curve above the horizontal axis represents a sound pressure distribution along the lens axis and curves below it represent orientational distributions at distances in terms of normalized I by p o 2 l ⁇ , ⁇ being the wavelength of acoustic wave used.
  • the acoustic wave obviously assumes the Gaussian-like sound pressure distribution on the back-face focal plane.
  • the distance between the back-face focal plane of the lens and the piezoelectric film is reduced to an extent that no interference of ultrasonic wave occurs. While this second design has many applications in the range of MHz frequencies, it is almost unpractical in the range of GHz frequencies. Because with sapphire as a lens material, the ultrasonic wave at 1 GHz has a wavelength of about 11 1 ⁇ m and this needs preparation of an extremely thin lens. Therefore, the first design alone is practical.
  • the desirable lens aperture is 100 pm but a piezoelectric film of the corresponding 100 pm aperture is difficult to prepare and to handle and in addition, has a high impedance level for which the impedance matching is difficult at RF electric signal supplied.
  • the prior art measure has many difficulties for production of an ultrasonic transducer since it requires an extensively elongated crystalline lens body and a piezoelectric film of a reduced aperture of the same size as a reduced lens aperture.
  • An object of the present invention is to provide an ultrasonic transducer using ultra high frequency wherein attenuation of the acoustic wave can be minimized.
  • Another object of the invention is to provide an ultrasonic transducer which can yield a high resolution with a piezoelectric element of a larger aperture than that of a lens.
  • the present inventor analyzed the sound pressure distribution to find, within the Fresnel focal point, axial points at which Gaussian-like distributions of sound pressure occur and which correspond to 1/N (N:any odd number greater than one) of the Fresnel focal distance, and the present invention is based on this analytical result.
  • the present inventor has made a mathematical approach to sound pressure distributions in the near field which are normally difficult to analyze to find that Gaussian-like sound pressure distributions pursuant to an optical lens theory occur within the Fresnel focal distance. It was then proven that a lens subject to such a sound pressure distribution which occurs at a back-face focal plane of the lens can yield a good focusing characteristic.
  • a Gaussian-like sound pressure distribution occurs at an axial point other than the ⁇ o 2 / ⁇ point, for example, at point A 3'
  • the present invention is based on the aforementioned analytical result and grounded on the fact that there are axial points within the Fresnel focal distance at which the Gaussian-like distribution occurs, that these points correspond to 1/N (N: any odd number greater than one) of the Fresnel focal distance, and that the width of the Gaussian-like distribution to meet the present invention is 1/N of the aperture size of the piezoelectric element.
  • Fig. 5 schematically shows one embodiment of an ultrasonic transducer in accordance with the teachings of the present invention.
  • a cylindrical crystalline body 150 serving as an acoustic wave propagation medium and made of such a material as sapphire or fused silica has one surface on which a piezoelectric element 145 is mounted and the opposite surface in which a concaved lens 155 is formed.
  • the portion of the crystal-water interface 200 other than the lens aperture 2a o is applied with an absorbant 160 such as a plastic material of epoxy resin or a vinyl tape, thereby preventing the sidelobe being transmitted into the medium 170.
  • the portion other than the lens aperture is also tapered to prevent the transmission of the sidelobe into the medium 170 and to mitigate the multiple echo within the lens.
  • a piezoelectric film with an aperture diameter 2a of 286 ⁇ m would be required which is very difficult to handle practically, and this film would have an impedance level of 1 ⁇ .
  • the piezoelectric film of this embodiment is easy to match with a 50 ⁇ coaxial cable.
  • the present invention can offer the piezoelectric film of the aperture size which is easy to impedance-match with the electrical system and easy to handle, and the lens aperture size which is 1/N (N:any odd number greater than one) of the piezoelectric film aperture, thereby highly mitigating difficulties in lens design of the acoustic microscope.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

Claims (3)

1. Transducteur à ultrasons utilisant des hyperfréquences, du type comportant un milieu (150) de propagation des ondes acoustiques, un élément piézo-électrique (145) monté sur une surface du milieu de propagation (150) et une lentille ultrasonique (155) formée sur la surface opposée du milieu de propagation (150), et possédant une distance focale prédéterminée, caractérisée en ce que la distance entre l'élément piézo-électrique (145) et le plan focal image de la lentille (155) est égal à 1/N (N étant tout nombre entier impair supérieur à 1) fois une distance qui est définie par le quotient ρo 2/λ du carré du rayon Po de l'élément piézo-électrique (145) par la longueur d'onde de l'onde acoustique produite par l'élément piézo-électrique, et que le diamètre de l'ouverture de la lentille est égal à 2 ρo/N.
2. Transducteur à ultrasons selon la revendication 1, caractérisé en ce la partie (200) de ladite surface opposée du milieu de propagation entourant ladite lentille (155) possède une forme rétrécie conique.
3. Transducteur à ultrasons selon la revendication 1, caractérisé en ce qu'un milieu (160) absorbant 1 énergie ultrasonique est appliqué contre ladite partie de la surface opposée du milieu de propagation entourant ladite lentille (155).
EP19800100662 1980-02-08 1980-02-08 Transducteur ultrasonore utilisant une très haute fréquence Expired EP0033751B1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
DE8080100662T DE3063803D1 (en) 1980-02-08 1980-02-08 Ultrasonic transducer using ultra high frequency
EP19800100662 EP0033751B1 (fr) 1980-02-08 1980-02-08 Transducteur ultrasonore utilisant une très haute fréquence

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP19800100662 EP0033751B1 (fr) 1980-02-08 1980-02-08 Transducteur ultrasonore utilisant une très haute fréquence

Publications (2)

Publication Number Publication Date
EP0033751A1 EP0033751A1 (fr) 1981-08-19
EP0033751B1 true EP0033751B1 (fr) 1983-06-22

Family

ID=8186593

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19800100662 Expired EP0033751B1 (fr) 1980-02-08 1980-02-08 Transducteur ultrasonore utilisant une très haute fréquence

Country Status (2)

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EP (1) EP0033751B1 (fr)
DE (1) DE3063803D1 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4881618A (en) * 1986-06-06 1989-11-21 Olympus Optical Co., Ltd. Acoustic lens for use in acoustic microscope
US4751529A (en) * 1986-12-19 1988-06-14 Xerox Corporation Microlenses for acoustic printing
CN111112037A (zh) * 2020-01-20 2020-05-08 重庆医科大学 透镜式多频聚焦超声换能器、换能系统及其声焦域轴向长度的确定方法

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2504988C2 (de) * 1974-02-15 1984-08-23 The Board Of Trustees Of The Leland Stanford Junior University, Stanford, Calif. Akustisches Mikroskop
US3958559A (en) * 1974-10-16 1976-05-25 New York Institute Of Technology Ultrasonic transducer

Also Published As

Publication number Publication date
EP0033751A1 (fr) 1981-08-19
DE3063803D1 (en) 1983-07-28

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