CMUT with mechanically coupled plate actuators for low frequencies

In this paper we present a structural analytical model for a capacitive micromachined ultrasonic transducer (CMUT), based on a sacrificial release fabrication process and comprised of electro-mechanical plate actuators transferring their motion to a coupling roof structure on top. The structure features a larger average displacement compared to conventional designs at lower operational frequencies. Low operational frequencies in the range of 40 kHz-1 MHz are beneficial for airborne applications due to their frequency-dependent strong wave attenuation in air, limiting the signal-to-noise ratio. The eigenfrequency dependence on the roof mass is calculated analytically and lumped elements, which can be used in equivalent circuits, are extracted. In addition, finite element analyses utilizing a shell-beam model are conducted. Experimental results, based on digital holographic microscopy, reveal the usability of the deduced model within an uncertainty of 8%. The developed dimensionless form of the analytical model can be used for future design purposes.