A highly directional ultrasonic sensor

This paper is concerned with the design and performance of an ultrasonic sensor for detection purposes. The device consists of a thin metal blade which is carried into flexural vibration when hit by acoustic waves. Two small bars of piezoelectric material are fixed at the best position near one end of the blade. This end is clipped tightly to form a cantilever system. The frequency of the incidence acoustic wave is the dominant parameter to be used to calculate the thickness of the blade. The important feature of the sensor is the impedance mismatch between the material of the blade and the medium to which it is coupled. The paper considers some specific designs and discusses the similarities between this device and the piston type structures. Sensing of ultrasonic waves is governed by what is known as `wavelength coincidence condition´. The performance of the system for a double-blade configuration is also presented. The behaviour of the sensor might be affected by variations in the frequency of the receiving wave. It is less susceptible to interference than broad-side sensors. Thus it is a reliable and inexpensive system for use in nondestructive ultrasonic sensing