High-Accuracy Ultrasonic Rangefinders via pMUTs Arrays Using Multi-Frequency Continuous Waves

This paper presents a high accuracy air-coupled reflective ultrasonic rangefinder based on piezoelectric micromachined ultrasonic transducers (pMUTs) using multi-frequency continuous waves (MFCWs). Two pieces of 5 times 5 AlN pMUTs arrays at the resonant frequency of 492 kHz are employed to transmit and receive ultrasonic signals, respectively. The MFCW method, where the distance information is calculated from the phase difference, can cancel out the random noise in numerous repeating periods. Therefore, high-accuracy range measurement is achieved. The 3σ accuracy of the short distance measurement (<; 100 mm) is 0.0711 mm with 0.096 mm/° first-order resolution and 1.934 μm/° second-order resolution. For long distance measurement (100-300 mm), the 3σ accuracy is 1.8208 mm with 0.481 mm/° first-order resolution and 1.954 μm/° second-order resolution. The MFCW-based rangefinder using pMUTs is a good candidate for short distance measurement with high accuracy. [2018-0267].