Microdefocusing method for measuring acoustic properties using acoustic microscope

Many papers have been reporting on measuring acoustic properties of materials by acoustic microscopy. In a conventional method of V(z) curve analysis, the phase velocity and the propagation attenuation of a leaky surface acoustic wave (LSAW) are determined from the interference period Delta z and the slope of the V(z) curve, respectively. For this method it is necessary to measure the V(z) curve for a period several times as long as the interference period Delta z. Therefore, it is difficult to measure the acoustic properties of a sample with high resolution by the method. In order to overcome these problems, a method called the microdefocusing method is proposed. The method determines the acoustic properties of a sample by analyzing V(z) values measured in the microdefocusing region within an interference period Delta z near a focal plane. An ultrasonic transducer called the butterfly transducer is proposed to be applied to this microdefocusing method and a digital signal processing procedure is developed to analyze the output of the ultrasonic transducer. Basic experiments are performed to confirm the principles of the new method.<>