Capacitive micromachined ultrasonic transducers for robotic sensing applications

Ultrasonic ranging is the most common method used in robotic systems for distance or proximity sensing. The heart of the method is an ultrasonic transducer that emits and detects ultrasound. There are mainly two types of transducers existing in the market today; piezoelectric and electrostatic. In this paper, we propose the use of a new type of transducer, which is capacitive micromachined ultrasonic transducer (CMUT). CMUTs were introduced about a decade ago, and were shown to be a good alternative for conventional transducers in various aspects, such as sensitivity, efficiency and bandwidth. CMUTs are basically the micromachined versions of the electrostatic transducers. Many enhanced features of the transducer are enabled with the micromachining technology. Micromachining allows miniaturization of the device dimensions and produces capacitive transducers that outperform their piezoelectric and electrostatic counterparts. This paper describes the fabrication process briefly, and the performance of the CMUT transducers is evaluated by demonstrating characterization results. It is also shown that CMUTs can be used for pulse-echo measurements in air up to MHz frequencies.