P2 - New Method for Determination of Surface Distribution of Elastic Properties by Surface Acoustic Waves

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings OPTO 2011
OP - Poster Session
O. Mokryy, V. Koshovyy - Lviv Polytechnic National University (Ukraine)
111 - 116


Surface acoustic waves (SAW) are used for determination of the space distribution of the elastic properties of a solid state. The elastic properties depend on temperature, mechanical stress, structural change of the sample and other characteristics. Therefore to determine space distribution of the elastic properties is actual problem of a nondestructive test. The tomography methods are used for finding the space distribution of the elastic properties. We propose another way of looking at this problem by new method of measurement velocity of SAW. The velocity of SAW on a small area of the sample may be measured by this method. Optical detection SAW by the Michelson interferometer is used to measure the SAW velocity.

In this scheme is a certain angle between interfering beams. This angle appears as a result of the inclination of interferometer mirror. The presence of angle between interfering beams results in appearance of the spatial periodically modulated interference pattern.

The Michelson interferometer detects SAW and is stabilized against the change of length path difference when there is a certain angle between interfering beams as well as certain width of optical beam. The width of optical beam, when interferometer is stabilized is determined by the SAW wavelength. This fact is the basis of the method which is proposed for the measurement of the SAW velocity.

The process of measurement involves modulation of the length path difference by vibration of the interference mirror and change of the width of optical beam by the diaphragm. The photocurrent is modulated by the vibration of the interference mirror. The width of optical beam is selected with on the condition that the depth modulation of photocurrent is minimal.

The proposed method was analyzed by the numerical simulation and confirmed by the experimental research. Experimental measurement of the SAW velocity was also carried out. The magnitude of SAW velocity was determined for glass sample by proposed method and it determined by the pulse method too. On the surface of the sample the SAW with frequency of 2.5 MHz generated by prismatic piezoelectric transducer was propagated. The magnitude of SAW velocity measured by the pulse method and the velocity measured by proposed method differ by a few percent.