Non-destructive means for determining mode shape in thickness-shear resonators

A review of different methods of plotting the vibrational distribution of resonators is given. This includes a method that is applicable to thickness-shear modes at high frequencies. The method uses light as a probe in a similar way as a toothpick is commonly used in the quartz industry. There the toothpick is gently tracked across the surface of the resonator while the electrical response of the crystal is monitored. A mixture of damping and loading by the toothpick alters the crystal in both the frequency and amplitude domains. Using light, however, the effect is to locally perturb the standing wave of the resonating area. This perturbation manifests itself as a transitory change in the frequency of the resonance. This change is proportional to the magnitude of the standing wave. Thus by rastering the pulsed light beam across the area of the resonator and monitoring the change in its resonant frequency, the vibrational distribution can be mapped. The basic principle of the method is applicable to any device whose operating parameter has a temperature coefficient