Characterisation and comparison of a cMUT versus a piezoelectric transducer for air applications

The main objectives with this investigation are firstly to compare important parameters of a capacitive micromachined ultrasonic transducer (cMUT) for air applications with a corresponding piezoelectric ultrasonic transducer. Secondly, to characterise the cMUT´s radiation field using light diffraction tomography. The cMUTs consist of a silicon backplate with small pyramid-shaped cavities and a metallised polymeric membrane. The piezoelectric transducers are nonfocused with a resonance frequency of 450 kHz. Time waveforms, FFT-spectra, S/N-ratio, linearity plots and distance working range are presented for different kinds of combinations of cavity size, membrane thickness and bias voltage. Pressure maps from light diffraction tomography measurements are also presented. The principal conclusions are that the cMUTs have comparable linearity and sensitivity but exhibit superior bandwidth to the compared piezoelectric transducers.