| 摘要 |
PURPOSE:To exactly measure a general characteristic of a sheet-like object by allowing a laser light to be made incident on one point B of the surface of the sheet-like object at an arbitrary angle from the X - Z directions, and giving vibration to the point B through the sheet-like object. CONSTITUTION:A pulse signal is outputted to a vibrator 19 from a power source 17, and time t1 of that time is inputted to a time measuring device 20. An ultra sonic wave from the vibrator 19 is propagated through a sheet 16 and reaches a point B, and by this vibration, a laser light 5 receives a Doppler shift. The Doppler shift is converted 3 to an electric signal, and time T2 of that time is inputted. t2 - t1 is regarded as a propagation speed of an ultrasonic signal propagated in the sheet 16. The Doppler shift occurs only in beams 8 (7) which are made incident from the Y (X) directions against the sheet 16 through mirrors 13 (12) in the longitudinal (transverse) waves, and in the wave vertical to the sheet surface, the Doppler shift is large by a beam 9 which is made incident from the Z direction through a mirror 11. Accordingly, by checking which direc tion Doppler shift is large, the vibration direction of the ultrasonic wave is known. |
