Three Dimensional Ultrasonic Ranging Using a Split Diaphragm Capacitive Sensor

The development of a novel capacitive sensor for three dimensional airborne ultrasonic ranging is described. In addition to the conventional range measurement obtained by ultrasonic sensors, our sensor provides angular information about echo signal bearing. The metallized coating of the transducer has been split in half by chemical etching in order to obtain a two element array for measuring the bearing angles associated with the range finders. A cross correlation technique has been applied to process the raw signal data in order to obtain the desired echo-signal phase delays. As a result, a low dispersion and linear relationship between the phase delays and bearing has been obtained within a 20deg cone. Unlike the other methods for bearing measurement, the described method uses the steady-state component in the transducer response to recognize the echoes in the noisy signal. This gives the method high robustness along with good accuracy characteristics, both of which are needed in practical applications