Ultrasonic sensors for process monitoring and chemical analysis: state-of-the-art and trends

Ultrasonic sensors are used in a large variety of ways. New fields of ultrasonic sensor and ultrasonic sensor system applications are process monitoring and control, automotive techniques and chemical analysis. These applications have enjoyed a rapid increase of interest in recent years. The development of new ultrasonic sensors or systems was and is essentially accelerated by the progress in electronics, by new piezoelectric materials, by exploitation of new technologies and by the need for new or more accurate analysis methods in many industrial branches. A review of ultrasonic sensors based on piezoelectric materials and resonators is presented, First, the physical background for ultrasonic wave propagation and corresponding technical applications is given. A definition of the ultrasonic sensor system is introduced later because an ultrasonic sensor alone makes no sense. For an efficient use of this sensor principle, a well-developed transmitter and receiver electronics and intelligent data-acquisition electronics are necessary. Secondly, it is shown that ultrasonic sensors can be divided into four groups depending on how the ultrasonic signal has been changed on its path during propagation or the transducer properties are changed by interaction with the surroundings. The present state of established sensors for how, distance and level is discussed, Ultrasonic sensors for process monitoring are described. New application fields for these sensors can be predicted. Finally, ultrasonic microsensors are introduced. A description of their state-of-the-art and application examples are given. To conclude, the use of new technologies for the manufacture of miniaturized ultrasonic sensors and future developments are discussed. (C) 1998 Published by Elsevier Science S.A. All rights reserved.