Overtone-Drive in Marx's Composite Oscillator Method

We developed Marx's composite oscillator method to an automatic control system to keep the strain amplitude constant at fundamental and third overtone frequency. Stability of this control system is analyzed by an automatic control theory in the measurement of internal friction with varying strain amplitude, temperature, and external field. It is applied to measurement of a relaxation peak at a fundamental frequency of 50 kHz and overtone 150 kHz of the same specimen to study the relaxation process of AgCl.