Proximity Sensor Using a Single Piezoceramic Ultrasonic Transducer
Original Publication Date: 1986-Jul-01
Included in the Prior Art Database: 2005-Mar-09
For the detection of an object, certain products employ a matched pair of piezoceramic ultrasonic transducers with the ceramic crystal and the mechanical housing resonance frequency being set to the oscillating frequency. One disadvantage of such an arrangement is that as a result of aging or temperature changes, the crystal's resonance frequency drifts out of the allowed bandwidth. This article discloses the use of a single piezoceramic ultrasonic transducer for the detection of an object along with a circuit to automatically compensate for any change in the crystal's resonance frequency as a result of age or temperature change. In the figure there is shown a piezoceramic device 1, operating at or near its natural resonance frequency, which is driven by the voltage-controlled oscillator 2.