Capacitive micromachined ultrasonic transducer as a resonant temperature sensor

The capacitive ultrasonic transducer (CMUT) was initially proposed for temperature measurement. A simple CMUT structure and the corresponding matching circuits were designed. Then the effects of vibration modes and bias voltage on sensitivity were analyzed by the finite element method. The results showed that the resonant frequency varied almost linearly with the temperature over the range of 45 °C to 120 °C, and the sensitivity and the nonlinear error were about -1931.6ppm/°C (or -21.2 kHz /°C) and 1.33% respectively when the CMUT working at the first order vibration mode with a bias voltage of 22.05V. It was demonstrated that the first order vibration mode had a higher sensitivity than the other three higher modes and the sensitivity could be adjusted by the bias voltage.