Full-circular surface acoustic wave excitation for high resolutionacoustic microscopy using spherical lens and time gate technology

摘要

With a fixed gate width under the condition where the focus of annacoustic lens was set inside the sample, we varied signal taking-inntime. Discrimination was made between differences in time required fornan ultrasonic signal reflected from the sample to reach the acousticnlens. This process also enabled three types of images to be obtainednseparately: the surface reflection wave image, a combination of imagesnbased on the interference of the surface reflection wave with surfacenacoustic waves, and the surface acoustic wave image. Thus it wasnpresumed that this process also would reveal the causes of imagencontrast and allow an easy interpretation of images. Furthermore, thenimage resolution was improved, because the surface acoustic wave imagenwas drawn by an ultrasonic beam produced by full-circular surfacenacoustic wave excitation propagating toward the center convergingnconcentrically; the theoretical resolution was 0.4 times the value ofnthe surface acoustic wave wavelength ΛR andnindependent of the defocus value of the acoustic lens. Several kinds ofnsamples were observed with this method. The results showed that the newnmethod permitted observation of the internal structures of samples whilenoffering new knowledge through the data reflecting the ultrasonic wavendamping and scatter drawn on the display