Experimental measurement of the frequency shifts of degenerate thickness-shear modes in a rotated Y-cut quartz resonator subject to diametrical forces

We report the first experimental measurement of the stress-induced frequency shifts of degenerate thickness-shear modes in a rotated Y-cut quartz resonator. Two distinct but nominally degenerate modes shifted toward higher frequencies at different rates and merged into a single mode as diametrical forces were applied gradually. The single mode split into the two distinctive modes progressively as the diametrical forces were released. The experimental results are in excellent agreement with previous theoretical results and may provide an insight into mode-coupling phenomena as a possible cause of frequency jumps in quartz resonators.