EP0210358A2 - Dispositif de focalisation acoustique - Google Patents
Dispositif de focalisation acoustique Download PDFInfo
- Publication number
- EP0210358A2 EP0210358A2 EP86106659A EP86106659A EP0210358A2 EP 0210358 A2 EP0210358 A2 EP 0210358A2 EP 86106659 A EP86106659 A EP 86106659A EP 86106659 A EP86106659 A EP 86106659A EP 0210358 A2 EP0210358 A2 EP 0210358A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- lens arrangement
- acoustic lens
- arrangement according
- transducer
- sound
- 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.)
- Granted
Links
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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
- G10K11/28—Sound-focusing or directing, e.g. scanning using reflection, e.g. parabolic reflectors
-
- 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
- G10K11/36—Devices for manipulating acoustic surface waves
-
- 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
- G10K15/00—Acoustics not otherwise provided for
Definitions
- the invention relates to an acoustic lens arrangement according to the preamble of claim 1.
- a lens assembly of this type is known, for example, from U.S. Patent No. 4,028,933.
- a piezoelectric transducer is arranged on one side of a cylindrical sapphire rod and a spherical hollow surface is incorporated on the opposite side.
- An electrical high-frequency field applied to the transducer creates a flat acoustic wave field in the sapphire rod, which is focused by the spherical hollow surface in an adjacent immersion liquid.
- the lens arrangement is part of an acoustic microscope.
- An object to be examined is brought into the acoustic focus.
- acoustic waves emanate from it, which are captured by the same or another acoustic lens and im piezoelectric transducers can be converted into electrical signals.
- the acoustic waves that are regularly reflected or transmitted on the object are used for acoustic microscopy.
- acoustic waves that hit a surface of the object at a certain material-dependent angle (Rayleigh angle ⁇ R ) excite surface waves in this surface (surface acoustic waves, SAW).
- SAW surface acoustic waves
- the SAW scatter acoustic waves out of the object (leaky waves, leak waves).
- These waves can also be detected and converted into electrical signals.
- they are superimposed on the regular signal, especially when focusing on an object area lying below the object surface. They can also be evaluated separately using special circuit measures (cf. DE Pat. Application P 34 09 929.8).
- the SAW When the SAW encounters inhomogeneities in the object surface, the SAW are reflected on it, so that they change their direction of propagation. The result of this is that leakage waves also occur increasingly in this direction. Since the SAW penetrate relatively deeply into the object surface, they are now increasingly becoming one used to determine material properties of different objects.
- the particular advantage is that it is a non-destructive measurement method that also allows quantitative measurements. For this purpose, it is necessary that local Auf engineerssvermö - to increase gen and improve the signal yield.
- the first problem is to generate the SAW as efficiently as possible in the surface of the material to be examined, which is usually not piezoelectric.
- the second problem is to focus the generated SAW on the smallest possible spot size.
- Narrow ring area of the radiation surface of the acoustic lens originates, for which the already mentioned Rayleigh angle is observed with regard to the beam inclination.
- the remaining energy of the emitted sound wave field is reflected on the object surface or converted into longitudinal waves (bulk waves).
- the invention was therefore based on the object of specifying an acoustic lens arrangement which, with the highest possible conversion rate of the radiated sound wave field into SAW, enables point-by-point focusing of the SAW, which is simple to manufacture and ensures a high signal yield.
- V 1 is the rate of propagation in this medium. If it is a solid transmission medium, V 1 can be the propagation speed of the longitudinal waves or the shear waves in the solid, but it can also be the propagation speed in a gaseous medium.
- the speed of sound propagation in the object area depends on different material properties, such as the structure, density, elasticity or a layer structure. A distinction is made between different propagation speeds V R for
- the incident acoustic beam should be represented by a plane wave of the form exp [fj (k ⁇ y + k z ⁇ z)].
- exp [fj (k ⁇ y + k z ⁇ z)].
- a parabolic cylindrical mirror focuses a vertically striking plane wave in a line
- an obliquely striking plane wave is focused in a line with a linearly variable phase.
- the wave fronts are conical and in the present case the axis of the cone coincides with the focal line of the parabolic cylinder.
- an ultrasound beam excites the more intensely the angle of incidence coincides with the Rayleigh angle as it passes through a liquid / solid interface in the surface of the solid SAW.
- this fact is combined with the special properties of the reflector described, in that the angle of incidence of the beam generated by the acoustic transducer on the reflector is selected to be equal to the Rayleigh angle.
- the wavefront running towards the interface with the object then cuts the object surface in an arc with a decreasing radius.
- Each surface wave generated will amplify the surface wave generated in front of it with a larger radius, since the selected special angle of incidence of the acoustic wavefront matches the k-vector component of the surface wave along the transition interface.
- the generated SAW have a limited lifespan and are ultimately scattered back into the liquid layer as longitudinal waves. These waves, also known as leakage waves, can already arise at the moment when the surface waves are generated. If the surface of the object is perfectly flat and has no imperfections, ie there are no surface reflectors, almost no leakage waves will return to the transducer. Since the incident beam is limited in diameter and plane waves are also contained in its angular spectrum, SAW can also be excited towards the reflector, ie it runs backwards. The leakage waves resulting from these SAWs will then generate an output signal at the acoustic transducer, even if there are no defects in the surface. However, this effect is very low and can be further suppressed by appropriate beam expansion and suitable shaping of the reflector.
- the acoustic transducer only receives a sufficiently strong signal when the propagation direction direction of the forward running SAW is changed at any fault point.
- the SAW is reflected on it and runs back as a circularly divergent wave.
- the waves scattered back into the liquid reassemble in the original conical wavefront and are returned to the acoustic transducer by the reflector as a collimated beam. If the point of impurity is not exactly in the focus point, the wavefront reflected on it will not be able to exactly restore the originally radiated beam, so that the output signal of the converter is smaller than in the in-focus position.
- the acoustic lens arrangement consists of an acoustic transducer 1, a cylindrical mirror 2 and a mechanical connection 3, with which the angle of inclination and the position of the transducer 1 can be adjusted relative to the mirror 2 so that the transducer sonicates the entire mirror surface regardless of the angle of inclination.
- the arrangement is immersed in a water bath 4 serving as immersion during operation.
- the mirror 2 is arranged on the object 5 to be examined so that the longitudinal axis 6 of its cylindrical hollow surface 7 is perpendicular to the object surface.
- the pulsed sound wave field 8 generated by the transducer 1 falls on the mirror 2 at the Rayleigh angle ⁇ R.
- the plane phase front produces a conically shaped phase shape 9, which also strikes the object surface at the Rayleigh angle eR and excites SAW 10 in it.
- the rays reflected from the object surface are picked up by the transducer 1 and converted into corresponding electrical signals which are displayed on an oscilloscope (not shown).
- a micropositioning system also not shown, permits a raster-shaped relative displacement between acoustic lens arrangement 1, 2, 3 and object 5 to be examined.
- the converter 1 consists of a flat ceramic disk, the thickness of which is designed for a resonance frequency of 1 MHz.
- the transition surface to the immersion liquid 4 is provided with an X / 4 adaptation layer, not shown.
- the transducer is driven by a voltage pulse lasting approximately 0.2 microseconds, which generates a sinusoidally falling pressure pulse.
- the emitted ultrasound pulse is about 5 microseconds long and has a center frequency of 1 MHz.
- the cylindrical hollow surface 7 should have a parabolic shape. Since this is difficult to manufacture, experiments with a circular cylindrical mirror surface have been successfully carried out as an approximation to this shape.
- the geometric limitation of this simplified hollow surface was chosen so that when the reflector is sonicated with a flat wavefront, the marginal rays form the central ray a. Have a path difference of not more than ⁇ / 4, where X is the wavelength of the ultrasound beam in the immersion liquid 4.
- a certain focal length must be selected, which depends on the frequency of the ultrasonic wave field used and the material to be examined.
- the optimal focal length f opt can be read from FIG. 2.
- f opt is normalized with respect to the Schoch shift ⁇ s and plotted as a function of ⁇ s / ⁇ , where X is the sound wavelength in the immersion liquid.
- X is the sound wavelength in the immersion liquid.
- the ratio ⁇ s / ⁇ is given by With where V is the speed of sound in the immersion liquid and V s , V I and V R denote the Sche-r, the longitudinal and the Rayleigh sound speeds in the solid to be examined.
- f opt is equal to half the radius.
- An f opt of 12.5 mm can be realized with a cylinder of 50 mm diameter and an f opt of 1.05 mm with a cylinder of 4.2 mm diameter.
- the maximum width 2x of the reflector with no significant cylindrical aberrations can be calculated using the following formula: With this value, the lens arrangement achieves a maximum resolution. It is 22.4 mm for aluminum at 1.5 MHz ultrasound frequency and 1.22 mm for Al 2 0 3 at 100 MHz.
- the aperture (f number) of the lens arrangement can be as follows using the values already determined be true: and gives 0.56 for aluminum and 0.86 for Al 2 O 3 .
- the height H of the reflector should be equal to f opt cot ⁇ R when the base of the reflector almost touches the object surface to be examined.
- the optimal height is 21.7 for aluminum at 1.5 MHz and 4 mm for Al 2 0 3 at 100 MHz.
- Suitable as mirror material e.g. Brass, which has a high acoustic impedance compared to the immersion liquid water.
- the mirror had a height of 38 mm, a width of 37 mm and a cylinder radius of 50 mm. These dimensions deviate slightly from the theoretical limits for the investigation of aluminum. However, it has been shown that the losses in signal power due to this are negligible.
- an ultrasonic frequency of 1 MHz results in a wavelength of the SAW of 2.85 mm, which also means the diameter diffraction-limited focus and the layer thickness of the object surface in which the SAW run. Inhomogeneities lying within this layer thickness can be recognized on the basis of the sound waves reflected back at them.
- a 10 mm thick test plate therefore looks like an almost infinitely thick object for the SAW.
- the acoustic lens arrangement should initially be arranged in the middle of a sufficiently large test area. This case is shown schematically in FIG. 3.
- the oscilloscope image of the measurement signal shown in FIG. 3a shows only one echo pulse 20.
- This signal is due to the fact already described that the acoustic wave front generated by the acoustic transducer is not exactly flat and that beam components also hit the reflector 2 whose angles of incidence deviate more or less from the Rayleigh angle ⁇ R. These are reflected at the edge between the object surface and the cylindrical hollow surface and generate the echo signal.
- This signal can be minimized by optimizing the transducer and reflector geometry and setting a suitable detection sensitivity. If the acoustic lens arrangement, as shown in FIG. 4, is shifted to the edge of the test surface such that the focus of the SAW lies exactly on the edge, then a second significantly larger echo pulse 21 is observed in the oscillogram. This is shown in FIG. 4a and enlarged again in FIG. 4b.
- the distance between the two echo pulses 20, 21 is 17 microseconds. This corresponds to the running time of the SAW for a distance of 50 mm, ie twice the focal length. From this, a very simple method for the exact setting of the Rayleigh angle ⁇ R between the beam direction of the plane sound wave field emanating from the transducer and the longitudinal axis of the reflector can be derived.
- the reflector is to be arranged at a distance of its focal length from an edge of the object to be examined and the angle of inclination of the transducer is to be changed until the amplitude of the echo pulse 21 has a maximum.
- the device for adjusting the angle of inclination between the transducer and reflector is used primarily to optimize the object-dependent Raylelgh angle ⁇ R for the almost lossless conversion of the radiated sound wave field into SAW.
- other waves in the object can also be excited, which also depend on the angle of incidence of the ultrasound beams depend on the liquid / object interface.
- Such waves are known for example under the designation love waves, Stonely waves and Sezewa waves. If, for example, the object to be examined has several layers of different materials lying one above the other, these waves can be selectively excited if the angle of incidence in the liquid is set appropriately.
- the waves entering the object are focused in a similar way to the SAW. This makes it possible to achieve a greater depth of penetration for the acoustic focus than with the SAW.
- the device according to the invention has been described above for applications with relatively low ultrasound frequencies. However, it can also be used in acoustic microscopes that use ultrasound frequencies up to the GHz range.
- a suitable lens arrangement is shown in FIG. 5.
- a rod 40 made of a material with low acoustic losses, such as sapphire, is provided with parallel, flat polished end faces.
- An acoustic transducer 41 (ZnO) is located on one side and lies between two gold electrodes 42, 43. The other side is provided with an X / 4 antireflection coating made of glass or carbon with suitable acoustic impedance in order to achieve a good adaptation for the transition of the ultrasound rays into the immersion liquid, not shown.
- the cylindrical, preferably parabolically shaped reflector 44 is glued to this side of the rod 40 so that a be right Rayleigh angle ⁇ R to its longitudinal axis. It consists, for example, of aluminum or another solid material with high acoustic impedance.
- the geometric dimensions (height and width) and the focal length must be adapted to the intended ultrasound frequency. They decrease almost linearly in proportion to the quantities mentioned for 1 MHz with the increase in the ultrasound frequency. For this reason, it will be expedient to provide different fixed lens arrangements with a reflector inclined according to the required Rayleigh angle ER for the examination of different materials. In principle, however, the angle of inclination can also be made adjustable here, which allows an individual adaptation to the examination object.
- the transducer 1 and the cylindrical surface 7 that is hollow relative to the transducer are formed on the outer surfaces of a solid body 60 suitable for sound transmission.
- a metal layer is evaporated onto the cylinder surface 7.
- An immersion liquid can also be inserted between the exit surface of the lens arrangement and the object surface for better coupling of the focused sound beam to the object surface.
- FIG. 7 Another embodiment is shown in FIG. 7. With this arrangement, the sound focusing is now generated by refraction on such a surface instead of a reflection on the cylinder surface perpendicular to the object surface.
- the sound transmission from the transducer 1 takes place through a solid body 70 to the cylindrical hollow surface 7, which in this case is curved towards the transducer and the longitudinal axis 6 of which is perpendicular to the object surface 5.
- the normal direction on the flat sound wave field emanating from the transducer is inclined at an angle ⁇ i with respect to the object surface.
- the space between the hollow surface 7 and the object surface 5 is filled by an immersion liquid, not shown.
- the hollow surface 7 acts in the horizontal direction like a cylindrical lens.
- Snell's law of refraction must be observed in the vertical direction: V solid state and V immersion denote the phase velocities of the sound waves in the two transmission media. After the refraction, a conical wavefront is created again as in the case of the before described reflection lens assemblies.
- the inclination of the transducer level is to be selected so that the sound waves hit the object surface at the critical angle%, taking into account the refraction at the hollow surface 7. Then SAW are generated in the object surface, which are focused at one point. It should also be mentioned that both longitudinal waves and shear waves can be excited in the sound propagation in the solid body 70. V solid then means the phase velocity for the wave type used in each case. To avoid transmission losses, the hollow surface 7 must be provided with a suitable anti-reflective coating.
- the maximum size of the angle (90-ers R ) is determined by the choice of the solid 70 and the immersion liquid. Due to this fact, the selection of the solid transmission medium is restricted depending on the material properties of the object to be examined. The basic principle is that the sound propagation speed in the solid body 70 must be lower than in the object surface 5.
- the acoustic transducer is usually used alternately as a transmitter and a receiver in the pulse-echo method.
- the sound waves returning from the object are also radiated in Interfer ten so that a phase-modulated signal is generated at the converter.
- FIG. 8 shows an embodiment with two confocal lens arrangements, one of which serves as a transmitter and the other as a receiver for the sound waves, as indicated by the arrow directions. Both arrangements are on the same axis of SAW propagation. Such a structure can of course work with both continuous and pulsed sound wave generation. In pulse-echo mode, two signals can be obtained which are assigned to the sound wave components scattered backwards in the direction of the transmitter and to the sound wave components scattered forward in the direction of the receiver.
- the arrangement of two confocal lens arrangements shown in FIG. 9 is selected such that the directions of the SAW propagation form an angle ⁇ with one another. This angle can be made adjustable. This arrangement is also suitable for continuous and pulsed sound generation. It can be used in particular to determine anisotropies in the SAW reflection.
- FIG. 10 works with only one reflector and a two-part converter, one of which can be used as a transmitter and the other as a receiver in both continuous and pulsed operation.
- the picture proper shafts of the reflector ensure sufficient directional selection between the transmitted and the received sound beam, so that the two beams do not interfere with each other or only to a very small extent, regardless of the orientation of the dividing line between the transducers.
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Multimedia (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
- Surgical Instruments (AREA)
- Diaphragms For Electromechanical Transducers (AREA)
- Analysing Materials By The Use Of Radiation (AREA)
- Transducers For Ultrasonic Waves (AREA)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT86106659T ATE77708T1 (de) | 1985-06-24 | 1986-05-14 | Akustische fokussierungsanordnung. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE19853522491 DE3522491A1 (de) | 1985-06-24 | 1985-06-24 | Akustische linsenanordnung |
DE3522491 | 1985-06-24 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0210358A2 true EP0210358A2 (fr) | 1987-02-04 |
EP0210358A3 EP0210358A3 (en) | 1989-03-29 |
EP0210358B1 EP0210358B1 (fr) | 1992-06-24 |
Family
ID=6273994
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP86106659A Expired - Lifetime EP0210358B1 (fr) | 1985-06-24 | 1986-05-14 | Dispositif de focalisation acoustique |
Country Status (5)
Country | Link |
---|---|
US (1) | US4779241A (fr) |
EP (1) | EP0210358B1 (fr) |
JP (1) | JPS6255556A (fr) |
AT (1) | ATE77708T1 (fr) |
DE (2) | DE3522491A1 (fr) |
Families Citing this family (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE3931048A1 (de) * | 1989-09-16 | 1991-04-11 | Leica Industrieverwaltung | Konisches ultraschallwellen-ablenkelement |
JP2551639Y2 (ja) * | 1992-01-14 | 1997-10-27 | ダイキン工業株式会社 | 空気調和装置 |
US6327538B1 (en) * | 1998-02-17 | 2001-12-04 | Halliburton Energy Services, Inc | Method and apparatus for evaluating stoneley waves, and for determining formation parameters in response thereto |
WO1999044757A1 (fr) * | 1998-03-03 | 1999-09-10 | Sensotech Ltd. | transducteur ultrasonore |
TW490559B (en) * | 1999-07-30 | 2002-06-11 | Hitachi Construction Machinery | Ultrasonic inspection apparatus and ultrasonic detector |
KR100548076B1 (ko) * | 2002-04-25 | 2006-02-02 | 학교법인 포항공과대학교 | 기체 음향렌즈 부착형 음향집중 스피커 |
DE102006003649B4 (de) * | 2006-01-26 | 2009-03-19 | Gitis, Mihail, Prof. Dr.Dr. | Verfahren und Einrichtung zur Qualitätsüberwachung von technischen Einkomponenten und Mehrkomponentenflüssigkeiten mittels Ultraschall On-Line Messungen ihrer Viskosität, Dichte, Kompressibilität und Volumenviskosität |
JP4902508B2 (ja) * | 2007-12-03 | 2012-03-21 | 日本電信電話株式会社 | 成分濃度測定装置及び成分濃度測定装置制御方法 |
US8616329B1 (en) | 2012-10-30 | 2013-12-31 | The United States Of America As Represented By The Secretary Of The Air Force | Air coupled acoustic aperiodic flat lens |
RU2618600C1 (ru) * | 2016-02-09 | 2017-05-04 | Федеральное государственное бюджетное образовательное учреждение высшего образования "Сибирский государственный университет геосистем и технологий" (СГУГиТ) | Акустическая линза |
JP7173931B2 (ja) * | 2019-06-07 | 2022-11-16 | 日立Geニュークリア・エナジー株式会社 | 超音波検査装置 |
US20240111037A1 (en) * | 2022-09-29 | 2024-04-04 | Navico, Inc. | Reflective surface beamforming |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4028933A (en) * | 1974-02-15 | 1977-06-14 | The Board Of Trustees Of Leland Stanford Junior University | Acoustic microscope |
EP0155504A2 (fr) * | 1984-03-17 | 1985-09-25 | Leica Industrieverwaltung GmbH | Procédé pour la représentation de paramètres élastiques de surfaces d'objets |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2611445A (en) * | 1948-01-29 | 1952-09-23 | Stromberg Carlson Co | Echo ranging system |
US3159023A (en) * | 1957-10-28 | 1964-12-01 | Budd Co | Ultrasonic testing apparatus |
US3028752A (en) * | 1959-06-02 | 1962-04-10 | Curtiss Wright Corp | Ultrasonic testing apparatus |
US3389372A (en) * | 1965-06-23 | 1968-06-18 | Smiths Industries Ltd | Echo-ranging apparatus |
US4332016A (en) * | 1979-01-26 | 1982-05-25 | A/S Tomra Systems | Method, apparatus and transducer for measurement of dimensions |
-
1985
- 1985-06-24 DE DE19853522491 patent/DE3522491A1/de not_active Withdrawn
-
1986
- 1986-05-14 AT AT86106659T patent/ATE77708T1/de not_active IP Right Cessation
- 1986-05-14 DE DE8686106659T patent/DE3685779D1/de not_active Expired - Fee Related
- 1986-05-14 EP EP86106659A patent/EP0210358B1/fr not_active Expired - Lifetime
- 1986-06-23 JP JP61145016A patent/JPS6255556A/ja active Granted
- 1986-06-24 US US06/877,752 patent/US4779241A/en not_active Expired - Fee Related
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4028933A (en) * | 1974-02-15 | 1977-06-14 | The Board Of Trustees Of Leland Stanford Junior University | Acoustic microscope |
EP0155504A2 (fr) * | 1984-03-17 | 1985-09-25 | Leica Industrieverwaltung GmbH | Procédé pour la représentation de paramètres élastiques de surfaces d'objets |
Non-Patent Citations (2)
Title |
---|
APPLIED PHYSICS LETTERS, Band 42, Nr. 5, 1. M{rz 1983, Seiten 412-413, American Institute of Physics, New York, US; I.R. SMITH et al.: "Confocal surface acoustic wave microscopy" * |
JOURNAL OF APPLIED PHYSICS, Band 55, Nr. 1, 1. Januar 1984, Seiten 75-79, American Institute of Physics, New York, US; B. NONGAILLARD et al.: "A new focusing method for nondestructive evaluation by surface acoustic wave" * |
Also Published As
Publication number | Publication date |
---|---|
ATE77708T1 (de) | 1992-07-15 |
EP0210358A3 (en) | 1989-03-29 |
EP0210358B1 (fr) | 1992-06-24 |
JPH0529064B2 (fr) | 1993-04-28 |
DE3522491A1 (de) | 1987-01-02 |
JPS6255556A (ja) | 1987-03-11 |
DE3685779D1 (de) | 1992-07-30 |
US4779241A (en) | 1988-10-18 |
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