Effect of Acoustic Field in Lens on Ultrasonic Microscopy

Ultrasonic microscopy is highly regarded as a method for measuring the properties of materials by detecting the velocity of leaky surface acoustic waves. This velocity can be detected by measuring the output voltage of the transducer of an ultrasonic microscope as a function of the defocus of the acoustic lens [ V(z) curve]. The V(z) curve is obtained by the interference of ultrasonic waves generated by several reflections or refractions in the material. The complicated interference modes cause the misunderstanding of the results measured using an ultrasonic microscope. Therefore, well-analyzed characteristics of the acoustic lens are expected to avoid the misunderstanding. In this report, an optimum lens design method is proposed. Good acoustic characteristics of the lens are obtained by setting the aperture angle to the first zero point of the potential at the back focal plane of the lens.