Zener Effect in Metal Bars in Transverse Vibration

When a metal is stressed, the temperature in the compressed parts rises, and in the stretched parts it falls. This gives rise to thermal conduction currents which, Zener showed, lead to losses of a relaxation type which are especially important in transversally vibrating bars. An apparatus is described in which nodally supported bars are excited electrostatically and their amplitude detected electrostatically. The driving prove and the vibrating metal bar are used as the plates of tank circuit of an FM oscillator which is in turn coupled to an amplifier and ratio detector. This permits simultaneous electrostatic drive and independent detection, which greatly facilitates precise tuning of the driving generator to the resonant frequencies of the bar. Decay measurements are taken with a level recorder to determine the “Q” of the bars at the several frequencies. Measurements on several different metals show substantial agreement with the Zener theory especially as regards the relaxation frequency and the shap...