Model-based Diagnosis for Sandwiched Ultrasonic Transducers

The overall performance of sandwiched ultrasonic transducers can be substantially degraded due to defects. Model-based diagnosis can be an attractive technique for monitoring the performance of sandwiched ultrasonic transducers. Using electromechanical models of the transducer, most parameters of the system can be determined based on measurements of electrical input quantities only. This contribution concentrates on the investigation of the effects of some typical defects, like loss of pre-stress. Measured input admittances of a custom-made transducer for various levels of pre-stress are used to identify the parameters of the electromechanical model with nonlinear least-square estimation techniques. By monitoring resonance frequency and admittance maxima during operation of the transducer the resulting model can be used to detect loss of pre-stress and thus possible failure. Operating parameters like driving frequency or voltage can be adopted to achieve optimum characteristics.