Theoretical research on ultrasonic sensors based on high-order Lamb waves

In an ultrasonic sensor, the electromechanical coupling coefficient, sensitivities related to the mass load and conductivity variation, insert loss and minimum detectable mass are important parameters determining the performance of the sensor, while it is challenging to optimize the abovementioned five parameters simultaneously. In this paper, we show that the multi-mode characteristic of Lamb wave provides possibilities to improve the performance of ultrasonic sensors by simultaneously considering the five parameters. According to the simulated results, piezoelectric films, relative thicknesses of films and substrates, structures of interdigital transducers, operating wavelengths and frequencies are optimized based on properly selected operating modes of Lamb wave. Then, high performance of Lamb wave sensors can be realized, in which high electromechanical coupling coefficients, mass sensitivities and conductivity sensitivities in addition to low insert losses and minimum detectable masses are simultaneously achieved. (C) 2014 AIP Publishing LLC.