Ultrasonic Absorption Microscope

TLDR

The amount of acoustic energy absorbed adjacent to the probe reflects the specimen’s microstructure. This progress report describes the development of an ultrasonic microscope for microstructure detection. The device immerses the specimen in an impedance‑matched liquid, emits high‑frequency pulses, and uses a thermoelectric probe to detect transmitted energy while scanning normal to the beam, producing a signal that varies with microstructure. Preliminary experiments with the microscope at 12 MHz show measurable absorption signals.

Abstract

This paper constitutes a progress report on the development 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 short pulses of high-frequency sound. Some of the ultrasonic energy is absorbed in the specimen 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 probe, is moved in a direction normal to the direction of sound propagation, a varying acoustic signal will be detected by the probe. This is a consequence of the fact that the amount 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 12 mc/sec are presented.