Piezoelectric Stabilization of High Frequencies

It is shown that moderately thick plates of both quartz and tourmaline may be successfully employed for crystal stabilization in the frequency range from 5 to 65 megacycles/sec. Specimens which were tested by a beat method exhibited a degree of stability far within that required of commercial broadcast stations. A higher degree of stability was obtained from this thicker type of plate than was obtained from a thin plate which had been ground elsewhere. The applicability of thicker plates was foreseen from the observations that at higher frequency the modes of vibrations of plates of either quartz or tourmaline are not the longitudinal or shear thickness modes, but are rather those in which the longitudinal, flexural, or torsional wave trains are propagated in a more complicated manner throughout the body of the plate. Several of these modes are briefly described. Contrary to the conclusions drawn by Straubel, these experiments indicate that tourmaline does not possess any important advantages over quartz in the stabilization of high frequencies. Most of the plates could be caused to stabilize at several widely separated frequencies. It is shown that the resonance frequencies of quartz plates are mechanically reproducible even at 60 megacycles/sec.