Fully Flexible PMUT Based on Polymer Materials and Stress Compensation by Adaptive Frequency Driving

A flexible PMUT device which can be applied on curved surfaces is presented. The oscillation behavior of the device under different curvatures (from κ = 0 to κ = 20 m^-1), shows both modal frequency and vibration velocity shifts. The impact of bending of the device is discussed, in terms of stress given to the diaphragm. When the device is curved, additional stress is added to the diaphragm, opposite to the process-originated stress already presents on the device. An analytical model is introduced that explains the mechanical boundary condition of the diaphragm, which is altered when the device is laminated on a curved surface. The model can predict driving frequency and optimum design of the device according to the bending curvature. When the device is bent with a curvature of κ = 20 m^-1, a driving frequency shift of around 10 kHz, which is 2% of the center frequency (503kHz) is predicted as well as measured, compared to device on the flat surface. The oscillation performance of the device increases by 37%, following the prediction of the model.