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 proces s monitoring and control, automotive techniques and chemical analysis. These applications have enjoyed a rapid increase of interest in recen t years. The development of new ultrasonic sensors or systems was and is essentially accelerated by the progress in electronics, by new piez oelectric materials, by exploitation of new technologies and by the ne ed for new or more accurate analysis methods in many industrial branch es. A review of ultrasonic sensors based on piezoelectric materials an d resonators is presented, First, the physical background for ultrason ic wave propagation and corresponding technical applications is given. A definition of the ultrasonic sensor system is introduced later beca use an ultrasonic sensor alone makes no sense. For an efficient use of this sensor principle, a well-developed transmitter and receiver elec tronics and intelligent data-acquisition electronics are necessary. Se condly, it is shown that ultrasonic sensors can be divided into four g roups depending on how the ultrasonic signal has been changed on its p ath during propagation or the transducer properties are changed by int eraction with the surroundings. The present state of established senso rs for how, distance and level is discussed, Ultrasonic sensors for pr ocess monitoring are described. New application fields for these senso rs can be predicted. Finally, ultrasonic microsensors are introduced. A description of their state-of-the-art and application examples are g iven. 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.