A high resolution ultrasonic range measurement method using double frequencies and phase detection

An ultrasonic range measurement method is presented which uses a pair of transmit signals with different frequencies from each other and phase detection of a pair of received signals corresponding to the pair of transmit signals, respectively. Uncertainty of detected phases in relation to integral multiples of 2 /spl pi/ is eliminated using the pair of phases and one of the envelopes of the received signals. High resolution can be obtained since the range is detected based on the information of the phases of the received signals. Experiments were done in air using the frequencies of 180 kHz and 210 kHz, and resolution of 1% of the wavelength corresponding to the frequency of 210 kHz was obtained.