Measuring and testing – Vibration – By mechanical waves
Patent
1986-03-04
1987-04-07
Birmiel, Howard A.
Measuring and testing
Vibration
By mechanical waves
73627, 73633, G01N 2900
Patent
active
046550836
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a surface ultrasonic wave interference microscope which excites leaky elastic surface waves on the surface of a sample and detects their reradiated waves, thereby measuring elastic properties of the sample qualitatively and quantitatively.
BACKGROUND ART
In recent years, there has been developed a mechanically scanning ultrasonic microscope for observing and measuring microscopic structural and acoustic characteristics of a material through use of a focused ultrasonic beam. This ultrasonic microscope, in principle, applies a conically focused ultrasonic beam to a sample, shifts the focal point of the ultrasonic beam in the plane of the sample, or in a direction perpendicular thereto, detects, by means of an ultrasonic transducer, reflected or transmitted ultrasonic waves resulting from different elastic properties of the sample at different points therein and converts them into electric signals for a two-dimensional display on a CRT screen to obtain an ultrasonic microscopic image, or for recording into an X-Y recorder or the like. Typical transducers for producing the focused ultrasonic beam are of the lens system and of the type in which an ultrasonic transducer is disposed on a concave or convex spherical surface. Furthermore, ultrasonic microscopes are divided into the transmission type and the reflection type according to the location of the ultrasonic transducer (for example, "Acoustic Microscopy with Mechanical Scanning--A Review", Proceeding of the IEEE, Vol. 67, No. 8, August 1979, pp. 1092-1113).
FIG. 1 is a block diagram illustrating the conventional reflection type ultrasonic microscope, which employs an acoustic lens for creating a focused ultrasonic beam and in which high-frequency pulses (a so-called burstlike signal) from a high-frequency pulse generator 1, which are obtained through ON-OFF modulation of a carrier with pulses, are applied via a directional coupler 2 to a focusing ultrasonic transducer 3, wherein they are converted into a conically focused ultrasonic beam 17, which is directed via a liquid acoustic field medium 4 to a sample 6 fixed to a holder 5. The sample 6 is disposed in the vicinity of the focal point of the ultrasonic beam. The holder 5 is moved by an XY-direction driver 7 in two perpendicularly intersecting X- and Y-directions which are perpendicular to the center axis of the ultrasonic beam 17. It is also possible, of course, to move the focusing ultrasonic transducer 3 in the X- and Y-directions instead of moving the holder 5. The XY-direction driver 7 is controlled by a scanning control signal from a scanning control circuit 8. Reflected waves from the sample 6 are collected or received by the focusing ultrasonic transducer 3, wherein they are converted into electric signals, and the received signals are provided via the directional coupler 2 to a display 9, the display screen of which is scanned two-dimensionally by the scanning control signal from the scanning control circuit 8, providing an ultrasonic microscopic image on the screen.
For the mechanism that produces contrast in the microscopic image obtainable with the conventional reflection type ultrasonic microscope, the relation between the focal point of the acoustic lens and the position of the sample is of importance, and this is explained as follows: FIG. 2 is a diagram for explaining it. In FIG. 2, the surface 6a of the sample 6 which is to be observed is slightly deviated from the position of the focal point F.sub.p of the ultrasonic beam toward an acoustic lens 11. Among incident waves of the ultrasonic beam 17 which are radiated from the acoustic lens 11 of a wide angular aperture, those incident waves which lie within a critical angle .theta.c, which is dependent upon the sound velocity ratio between the liquid sound field medium 4 and the sample 6, are reflected in the same phase. Among such incident waves, a vertical incident wave which is incident to the sample surface 6a vertically thereto is reflected back to a transducer element 16, such as a
REFERENCES:
patent: 4459852 (1984-07-01), Chubachi et al.
patent: 4503708 (1985-03-01), Kino et al.
patent: 4541281 (1985-09-01), Chubachi
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