| 摘要 |
PURPOSE: To enable using of surfaces of a material layer even when one of the surfaces is hard to approach by a method wherein an admitted ultrasonic wave is reflected on a surface opposite to a layer of material after passing through the material in one direction and passes through the layer again in the opposite direction to reach an electroacoustic receiving converter. CONSTITUTION: A sine electrical signal P with a cycle generated 4 is applied to a convertor 5 by a connection 11. In response to the application of the signal, the converter 5 generates a sine ultrasonic wave with a frequency I/λat the same phase as that of the signal P, the ultrasonic wave passes through a layer of material 1 on a surface 3 through a waveguide tube 9 to be reflected on a surface 2 and is passed through the material 1 again toward a waveguide tube 10 in the reverse direction. During the double passage through the layer of the material 1, the ultrasonic wave undergoes a phase shift proportional to the thickness (e) thereof at which the ultrasonic wave passes twice through the material. Therefore, the ultrasonic wave transmitted to a receiving converter 6 by the waveguide tube 10 is shifted in phase with respect to the ultrasonic wave generated by the converter 5. The converter 6 receiving the ultrasonic wave passing through the layer 1 generates a sine wave electrical signal S with the cycleλand the signal is shifted in phase with respect to the signal P. Then, the signals P and S are applied to a phase meter 7 to calculate a changeΔe in thickness by a calculation means 8.
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