Precision ultrasonic range sensor using one piezoelectric transducer with impedance matching and digital signal processing

The simplicity of the fundamental principle of ultrasonic range sensors allows their wide use in many technical branches, such as mobile robotics, automotive or industrial automation. However, in most cases these sensors are able to provide only information about the distance to the nearest detectable object. This may limit their use in applications where other obstacles can be found in the vicinity of measured object. This paper presents one way of measuring distances to multiple objects with high precision by one piezoelectric ultrasonic sensor. Method, which is described in this paper, is based on digital signal processing, mainly on digital filtering and combination of cross-correlation and phase shifting methods. Only one piezoelectric transducer was used for transmitting and receiving ultrasonic waves to reduce the number of needed elements. The impedance matching circuit to the piezoelectric transducer was designed to increase signal to noise ratio and to improve measurement accuracy. These methods of acquired signal processing allowed measuring of multiple object distances with 1 mm resolution for more than 3 m by using low cost piezoelectric transducers with resonant frequency of 40 kHz.