A non-contact method for measuring surface acoustic impedance

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A new method to investigate the conditions of concrete structure and to search land mines using sound property has been proposed in this study. The surface conditions of the specimen is measured in term of the surface acoustic impedance without contact. The following three subjects were mainly investigated:(1) The relationships between the surface condition and the acoustic impedance(2) The formulation of the acoustic impedance and the surface condition with the sound pressure at two points(3) A novel method to measure the sound field distribution without disturbing the field to be measured.We demonstrated the experiments of the surface acoustic impedance measurements for a bottle embedded in a shallow land. The possibility of finding the embedded object through the sound impedance measurements was confirmed as the result of the experiment. The equations denoting the relationship between the surface condition and the acoustic impedance were deduced. An optical method to measure the sound field distribution in a pipe is newly invented in this study. A combination of a low-coherent light source and an adjustable optical path length enabled us the measurements of sound field with spatial resolution in the longitudinal direction. In conclusion, the basic theory and the instrumentation have been founded for the purpose in this study.