Article
Tuning Squeeze-film Damping in an Air-coupled Electrostatic Ultrasonic Transducer by a Structured Cavity (en)
* Presenting author
Abstract:
Lateral electrostatically driven actuators enable air-coupled ultrasound transducers (L-cMUTs) with resonance frequencies in the kHz range, targeting low absorption losses in free-field. The CMOS-compatible device, driven with low voltages, allows a broadband response. Potential applications are gesture recognition, ultrasound imaging, distance as well as flow measurements. In contrast to piezoelectric (pMUTs) and membrane-based, capacitive transducers (cMUTs), they utilize the chip volume pointing towards higher sound pressure levels per area. A periodic volume change caused by the actuator movement in an acoustic cavity generates the sound signal. The smaller the distance between the actuator and the stator electrode, the stronger the driving force. Contrary, the squeeze-film damping increases with smaller distances. High damping restricts the frequency range, while low damping can lead to resonances and instabilities. By structuring the stator not only the driving force but also the damping can be tuned. Recently, a one-degree-of-freedom model was presented for a stator whose geometric shape corresponds to the bending mode of the actuator. Here, this approach is numerically extended to other stator geometries and compared with modal FEM-simulations. Not only the cavity’s volume but also its geometric shape plays a decisive role for the damping. This approach is exemplified for ultrasound-relevant applications.