Improvement in resolution with imaging method using leaky surface acoustic wave by scanning acoustic microscope and applications to materials evaluation

摘要

With a fixed gate width under the condition where the focus of an acoustic lens was set inside the sample, we varied signal taking-in time. Discrimination was made between differences in time required for an ultrasonic signal reflected from thesample to reach the acoustic lens. This process also enabled three types of images to be obtained separately the surface reflection wave image, a combination of the surface reflection wave image and the interference image of surface acoustic waves, andthe surface acoustic wave image. Thus it was presumed that this process would also reveal the causes of image contrast and allow an easy interpretation of images. Furthermore, the image resolution was improved, since the surface acoustic wave image wasdrawn by an ultrasonic beam produced by a wave propagating toward the center converging concentrically the theoretical resolution was 0.4 times the value of the surface acoustic wave wavelengthλ{sub}R and independent of the defocus value of the acousticlens. Several kinds of samples were observed with this method. The results showed that the new method permitted observation of the internal structures of samples, while offering new knowledge through the data reflecting the ultrasonic wave damping andscatter drawn on the display.