JPH04315923A - Elastic wave transmitting speed measuring method for crystal surface - Google Patents

Abstract

PURPOSE:To make the constitution of a measuring device unnecessary to change even though the sort of the elastic body crystal is changed, and to carry out the measurement of the elastic wave transmitting speed in a desired area of a crystal surface. CONSTITUTION:While elastic waves are generated by driving an elastic body crystal 1 by a transducer 2, a speckle pattern on a crystal surface at a standard time which is generated by radiating laser beams and a speckle pattern after a specific time passes are compared in an image processing device 7. And depending on the resultant speckle movement amount and the specific time, the elastic wave transmitting speed on the surface of the crystal 1 is calculated.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method for measuring the propagation velocity of an elastic wave propagating on the surface of an elastic crystal, and in particular,
This invention relates to a measurement method for non-contact and non-destructive measurement of the propagation velocity of elastic waves at any location or region on a crystal surface.

0002

2. Description of the Related Art When measuring the propagation velocity of an elastic wave on a crystal surface, conventionally, as shown in FIG. A power source 12 is supplied to generate an elastic wave, and a similar receiving interdigital electrode (not shown) is provided near the electrode 11, and the frequency characteristics of the received elastic wave are detected with a spectrum analyzer or the like. The speed is calculated accordingly. To explain specifically, in FIG.
The width of 1 is h, the gap is a, and the distance between their centers is d (=a+h
), the propagation speed of the elastic wave is v, and the wavelength is λ0, then the center frequency f0 (= v / λ0 = v
/2(a+h)) wave. Distance between electrode centers d (=
a+h) is clear at the design stage, and the center frequency is f
Since the zero wave is obtained by the spectrum analyzer 3 or the like, the propagation velocity v can be calculated from this.

[0003] Furthermore, recently, a technique has been proposed for easily measuring the propagation velocity of an elastic wave without forming an interdigital electrode on the surface of a crystal to be measured (Japanese Patent Laid-Open No. 60-91224). In short, this technique involves providing an elastic wave generation/transmission means on the surface of an elastic crystal substrate, and arranging a crystal to be measured of the same type as the elastic crystal substrate in parallel to and close to the elastic wave generation/transmission means. The idea is to allow an elastic wave to propagate, detect frequency difference data and phase difference data before and after the propagation using a counter, etc., and calculate the propagation speed of the elastic wave based on these detected data.

0004

[Problems to be Solved by the Invention] However, in the conventional method shown in FIG. 2, each time the propagation velocity v is measured, it is necessary to form an interdigital electrode by making full use of microfabrication, photolithography, etc. The disadvantage is that measurement takes a lot of time and cost.

[0005] The technique disclosed in JP-A-60-91224 has the advantage of directly measuring the propagation velocity with a simple means, but on the other hand, as a pre-measurement step, it is necessary to measure the elasticity of the same material as the crystal to be measured. There is a problem in that a body crystal substrate must be prepared and an elastic wave generation and transmission means must be constructed on the substrate. In other words, if the material of the crystal to be measured changes, the measuring device must be reconfigured accordingly, making it unsuitable for measuring the propagation speed of elastic waves on the surfaces of multiple types of crystals.

Furthermore, since the above methods all measure using the entire crystal surface, the calculated propagation velocity is the average velocity on the crystal surface. Therefore, if the crystal is partially non-uniform, measurement errors occur. Also,
There are cases where it is desired to measure the propagation velocity in only one pattern in the electrode mask to know the state of that pattern, but partial measurement is not possible with the above methods.

The present invention was devised in view of the above problems, and its purpose is to eliminate the need to change the device configuration even if the type of crystal to be measured changes, and to eliminate the need for arbitrary changes on the surface of the crystal. An object of the present invention is to provide a method for measuring the propagation velocity of an elastic wave on a crystal surface, which enables the measurement of the propagation velocity in a location and region.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention excites an elastic crystal to generate an elastic wave, and irradiates the elastic crystal with a laser beam to generate a reference point in time. The speckle pattern on the crystal surface is compared with the speckle pattern after a predetermined time, and the elastic wave propagation speed on the surface of the crystal is calculated based on the amount of speckle movement obtained as a result of the comparison and the predetermined time. It is something.

[0009]

[Operation] By excitation of the elastic crystal, the strain on the crystal surface moves and an elastic wave propagates. Here, when the surface of the elastic crystal is irradiated with laser light, an irregularly shaped speckle pattern is generated in the diffusely reflected light from the crystal surface due to the coherence of the laser light. This speckle pattern moves as the strain moves, so by comparing the one at the reference time and the one after a predetermined time, the amount of strain movement at that time can be determined, and based on this, the propagation speed of the elastic wave can be determined. can be calculated.

This method uses the speckle method to measure the amount of strain movement on the crystal surface in a non-contact manner, so there is no particular restriction on the material of the crystal to be measured, and the hologram can be adjusted by adjusting the optical system. Since the imaging area can be arbitrarily set, it is also possible to measure the propagation velocity in a part of the crystal surface.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram of the configuration of an elastic wave propagation velocity measuring device according to an embodiment of the present invention. In the figure, 1 is the crystal to be measured, 2 is the transducer, 3 is the laser, 4 is the beam expansion lens for diffusing the laser beam, 5 is the half mirror (beam splitter), and 6 is the reference diffuser whose surface is smooth. 7 is an image processing device.

The transducer 2 is a crystal to be measured 1
This method generates elastic waves by applying strain to the crystal surface, for example, by applying an electric field of a predetermined frequency to an electrode formed by mask vapor deposition on the crystal surface. It is also possible to locally irradiate a high-power laser to any location on the crystal surface to cause thermal distortion, thereby generating elastic waves in a non-contact manner. In addition, the reference diffusion surface is placed on the half mirror 5 at a position where the distance from the half mirror 5 is almost the same as the distance to the crystal 1 to be measured.
The image processing device 7 is arranged perpendicularly to the optical axis of the laser beam that passes through the reference diffusing surface 6, and is arranged at a position where it can simultaneously receive the reflected light from the reference diffusing surface 6 and the diffusely reflected light from the crystal 1 to be measured. The image processing device 7 uses, for example, a microcomputer device that operates according to a predetermined image processing program.

Note that the laser 3 may be combined with an amplifier to increase its output (light amount), if necessary.

Next, a method of measuring the propagation velocity of an elastic wave by speckle interferometry using the elastic wave propagation velocity measuring apparatus having the above configuration will be explained.

The laser beam output from the laser 3 and expanded by the beam expansion lens 4 is reflected by the half mirror 5 and then irradiated onto the surface of the crystal 1 to be measured. At this time, if the crystal 1 to be measured is excited by the transducer 2, its surface is distorted, so the laser light is scattered at various parts and interferes with each other in an irregular phase relationship, resulting in diffuse reflection. The light becomes light, passes through the half mirror 5, and is guided to the image processing device 7. On the other hand, half mirror 5
The laser beam that has passed through is reflected by the reference diffusing surface 6, then reflected again by the half mirror 5, and guided to the image processing device 7. This light becomes a reference light whose phase does not change irregularly like diffusely reflected light. These two lights guided to the image processing device 7 interfere with each other and convert phase changes into a high contrast speckle pattern. This pattern is recorded in the image processing device 7.

Next, the surface of the crystal to be measured 1 is irradiated with laser light again at a predetermined time difference, and a speckle pattern representing the distortion state of the crystal surface at this time is recorded in the image recording device 7, and the previously recorded speckle is Electrically superimpose the pattern. This causes moiré fringes due to interference between the two patterns. These fringes correspond to contour lines that represent the movement of speckles, that is, the displacement of strain on the crystal surface in a certain direction, and the interval between the fringes is 1/1 of the elastic wave.
There are 2 wavelengths.

Therefore, the propagation velocity of the elastic wave can be determined with high precision by analyzing the moiré fringes with the image processing device 7 to detect the amount of distortion displacement, and by calculating with time as a parameter using a calculation device (not shown). Can be done.

In this way, in this example, the amount of strain displacement of the crystal to be measured is detected in a non-contact manner using speckle interferometry, so there is no particular restriction on the material of the crystal to be measured. Moreover, it does not matter whether the propagation direction of the elastic waves is unidirectional or omnidirectional. Therefore, unlike conventional methods, there is no need to provide two sets of interdigital electrodes for transmission and reception, or to reconfigure the measurement device each time the crystal material changes. It becomes possible to measure speed with high precision.

Furthermore, since the irradiation area of the laser beam can be arbitrarily set by adjusting the irradiation amount of the laser beam, the reflection angle on the half mirror 5, etc., it is also possible to measure the propagation velocity in a part of the crystal surface. . Therefore, it is also possible to measure the propagation velocity of elastic waves propagating only through a specific pattern of the electrode mask.

[0021] Although the method for measuring the elastic wave propagation velocity using speckle interferometry has been explained above, the same method can be used to determine speckle movement using speckle photography or speckle correlation method. It has the effect of

In the speckle photography method, the surface of the crystal to be measured is irradiated with a single laser beam, and the speckle pattern before and after distortion due to excitation is double exposed on a film. The obtained negative is called a specklegram, and when its entire surface is irradiated with monochromatic light such as a laser beam or a mercury lamp and observed from an oblique direction, the diffracted light from two speckle patterns that are shifted from each other interferes. The contour lines of the speckle movement component that occur due to the interaction can be seen on the specklegram. This is recorded on the camera to determine speckle movement. Unlike speckle interferometry, this method does not require a reference beam, so the optical system is compact, and the fringe sensitivity can be adjusted freely.

In the speckle correlation method, the surface of the crystal to be measured is irradiated with a narrow laser beam, and a one-dimensional image sensor is placed in the diffusely reflected light. The orientation of the sensor is adjusted to match the direction of speckle movement, and the beam diameter of the laser beam and the sensor distance from the reflection point are adjusted so that the resolving power of the sensor is smaller than the average diameter of the speckles. In this state, the sensor outputs before and after the strain on the surface of the crystal to be measured are stored in the memory of the microcomputer, the polarity cross-correlation between them is calculated, and the speckle movement is directly determined from the correlation peak position. This method has the advantage of being able to obtain a movement smaller than the speckle diameter.

[0024]

[Effects of the Invention] As explained above, according to the present invention,
Elastic wave propagation velocity on the crystal surface that does not require changing the equipment configuration even if the type of elastic crystal to be measured changes, and enables highly accurate propagation velocity measurement at any location or region on the crystal surface. A measurement method can be provided.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the configuration of an elastic wave propagation velocity measuring device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of elastic wave generating means in a conventional elastic wave propagation velocity measuring device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Crystal to be measured, 2... Transducer, 3... Laser, 4... Beam expansion lens, 5... Half mirror, 6... Reference diffusing surface, 7... Image processing device.

Claims (1)

[Claims] Claim 1: Exciting an elastic crystal to generate an elastic wave, and irradiating the elastic crystal with a laser beam to produce a speckle pattern on the surface of the crystal at a reference time and a speckle pattern after a predetermined time. A method for measuring an elastic wave propagation speed on a crystal surface, characterized in that the elastic wave propagation speed on the surface of the crystal is calculated based on the amount of speckle movement obtained as a result of the comparison and a predetermined time.