The potential of stop band material in multi-frequency ultrasonic transducers

Ultrasonic transducers play a major role in surround sensing for automotive and industrial applications. The development of autonomous driving functions is one of the top challenges for mobility solutions of the 21st century. In this context, surround sensing systems with high performance serve as a key enabler. This leads to an increasing number of sensors which are desired to operate in parallel or in shorter intervals. Hence, measurements should be conducted with two different frequencies to discriminate the sensor signals. Known multi-frequency ultrasonic transducers mostly employ multiple electro-mechanical coupling elements which require more complex sensor electronics. To overcome this issue, the authors present a study on multi-frequency ultrasonic transducers using only one electro-mechanical coupling element. In order to achieve suitable sound radiation properties at two well separated operating frequencies, spatially distributed stop band material is employed. As a result, the operational deflection shape can be controlled at a certain frequency. In finite element simulation, the relation between spatially distributed stop band material and the resulting operational deflection shapes is investigated. The sound radiation behavior is estimated using the numerical results from a harmonic analysis as input for the Rayleigh integral. In experimental investigations, the presented approach is validated. Finite element simulation and experimental testing show good accordance. Based on the results of the presented study, it is possible to realize a multi-frequency ultrasonic sensor with one electro-mechanical transducer element only and suitable sound radiation behavior at multiple operating frequencies.