Computerized Acoustic Spectrometer for Polymeric Solids at Low Temperatures

A force, flexural resonance spectrometer at acoustic frequencies with an automatic data acquisition system is designed to measure the dynamic mechanical properties of polymeric solids from 10 to 500 K. The sample is clamped at its nodal points and driven by a voltage-controlled oscillator through an electromagnetic transducer. Two small iron tabs are glued to either ends of the sample to provide magnetic coupling. A similar transducer is used to receive the response of the sample. The bandwidth method is employed to determine the internal friction. An electronic circuit is devised to measure the frequency at the maximum amplitude and those at the half-power points of the amplitude-frequency curve. These readings, as well as the voltage output from the thermocouple, are digitally recorded on a paper-tape punch. Data are then transferred onto cards and processed on a computer. Results are displayed in analog form via a CalComp plotter. Measurements for polyethyl methacrylate, polyethylene, and paraffin wax are reported.