Multiple-frequency continuous wave ultrasonic system for accurate distance measurement

Abstract

A highly accurate multiple-frequency continuous wave ultrasonic range-measuring system for use in air is described. The proposed system uses a method heretofore applied to radio frequency distance measurement but not to air-based ultrasonic systems. The method presented here is based upon the comparative phase shifts generated by three continuous ultrasonic waves of different but closely spaced frequencies. In the test embodiment to confirm concept feasibility, two low cost 40 kHz ultrasonic transducers are set face to face and used to transmit and receive ultrasound. Individual frequencies are transmitted serially, each generating its own phase shift. For any given frequency, the transmitter/receiver distance modulates the phase shift between the transmitted and received signals. Comparison of the phase shifts allows a highly accurate evaluation of target distance. A single-chip microcomputer-based multiple-frequency continuous wave generator and phase detector was designed to record and compute the phase shift information and the resulting distance, which is then sent to either a LCD or a PC. The PC is necessary only for calibration of the system, which can be run independently after calibration. Experiments were conducted to test the performance of the whole system. Experimentally, ranging accuracy was found to be within ±0.05 mm, with a range of over 1.5 m. The main advantages of this ultrasonic range measurement system are high resolution, low cost, narrow bandwidth requirements, and ease of implementation.

Robust High-Accuracy Ultrasonic Range Measurement System

“…However the maximum range that can be estimated using this technique alone is limited to one wavelength of the carrier frequency which means that at 40 KHz the maximum range is limited to 8.575 mm assuming a sound velocity of 343 m/s. Multi-frequency continuous wave phase shifts [13], [14] was used to increase range by using the difference in phase between frequencies (∆θ) and the difference in frequencies (∆F) . However the maximum range is still limited to (C/∆F) where C is the sound velocity.…”

“…Many ultrasonic range measurement methods have been proposed in the literature [12][13][14][15][16][17][18][19]. Time of Flight (TOF) and phase shift methods are used in most ultrasonic range measurement systems.…”

New implementation of high-precision and instant-response air thermometer by ultrasonic sensors

“…The detection of the phase shift is based on TFCW [12,13]. The method underlying TFCW is as follows.…”

Distance and Speed Measurements using FPGA and ASIC on a high data rate system

“…Distance and speed measurement systems are widely used in many areas including automobiles, defense etc [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The system can measure the time interval between two laser pulses, one reference pulse which is sent out by the system and one echo pulse which is reflected back to the system.…”