A new signal detection method for capacitive micromachined ultrasonic transducers

Abstract

Capacitive micromachined ultrasonic transducers (cMUT) have become an alternative to piezoelectric transducers in the past few years. They are constructed by integrating many small circular membranes in parallel. In this thesis, we demonstrate a new signal detection method for cMUT’s. We model the membranes as capacitors, and the interconnection lines between the membranes as inductors. The resulting circuit is an artificial transmission line with a certain electrical length. The vibrations of the membranes modulate the electrical length of the transmission line, which is proportional to the frequency of the signal through it. By measuring the electrical length of the artificial transmission line using a high RF frequency (in the GHz range), the vibrations of the membranes can be detected in a very sensitive manner. Typically, the improvement over the conventional method is two orders of magnitude. For the devices we measured we observed a minimum detectable displacement in the order of 10"^ A/V^.