Variable Resonant Transducer

Abstract

The application of lateral forces by a relatively stiff structure such as a small iron vise to one end of a longitudinally vibrating crystal or composite bar, e.g., a crystal and backing plate, has been used to control and vary the resonant frequency of the system. A change in resonant frequency of over an octave for a composite system has been measured. It is believed that the phenomenon depends upon the (dynamic) elastic range of friction as first noted for the static case by J. S. Stevens in 1899, in addition to the elastic parameters. It is noted that for a given crystal (material and dimensions) and backing plate (material) there are optimum backing plate lengths to obtain both maximum and minimum changes in resonant frequency. For example a one inch 45° Y-cut Rochelle salt crystal with a one-half inch steel backing plate can undergo a continuous change in resonant frequency from 26.5 to 66.7 kc. The same crystal with a three inch backing plate will only change from 22.2 to 24.4 kc. It was found that the type of clamping herein described results in an additional mode of vibration which may be very low in frequency depending on the lateral force.