Ultrasonic Absorption Microscope

This paper constitutes a progress rersort on the develol•ment of an ultrasonic instrument for detecting microstructure. The principle of operation of the device (designated by the term "ultrasonic microscope") is as follows: The specimen is imbedded in a liquid, which closely matches it in acoustic impedance, and is irradiated with sho•t pulses of highdreqnency hound. Some of the ultrasonic energy ia absorbed in the sl-Jecimen and the remainder leaves it and excites a small thermoelectric probe placed immediately adjacent to the region being investigated. As the specimen, which is between the sound source and the 0robe, is moved in a direction normal to the direction of sound propagation, a vaxying acoustic signal will be detected by the probe. This is a consequence of the fact that the amonnt of acoustic energy absorbed by the specimen in the portion immediately adjacent to the probe is determined by the structure of that part of the specimen. Preliminary experimental results obtained with such a "microscope" operating at a frequency of 1• mc/sec are presented.