NDT techniques. Acoustic microscopy and holography

Acoustic waves can penetrate into materials, and thus it is possible to study the microstructure of materials, detect small defects, study adhesive interfaces, and also gain information about elasticity and absoprtion. Ultrasonic waves of frequencies from about 10MHz to 2GHz are used for acoustic microscopy. Imaging techniques for these applications are scanning acoustic microsopy, high-frequency acoustic imaging, and scanning laser acoustic microscopy.