Design, Simulation, and Characterization of a Novel Optical-Piezoelectric Micromechanical Ultrasonic Transducer (OpMUT)

In this study, we use piezoelectric materials to overcome the high impedance and electromagnetic interference susceptibility of piezoelectric micromachined ultrasonic transducers (pMUTs). We demonstrate the design and simulation of a novel optical-pMUT (OpMUT) that integrates a photonic ring resonator into the traditional pMUT. When the OpMUT receives ultrasound waves, its diaphragm vibrates, and the length of the ring waveguide changes. Consequently, the ring waveguide’s coupling wavelength will shift, and the variation of the bus waveguide’s output light intensity can represent the acoustic signals. This study uses the finite element method (FEM) and numerical analysis to optimize the optical ring resonator’s width, radius, and placement. We compare the signal-to-noise ratio (SNR) and noise-equivalent pressure (NEP) of the proposed OpMUT with those of the state-of-the-art pMUT, which has an SNR of 37.3 dB at 1 Pa and an NEP of 0.0014 Pa. When the radii of the ring waveguides are 10.63, 21.27, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$35.45~\mu $ </tex-math></inline-formula>m, the SNR values of the 150-kHz OpMUTs are 50.8, 67.2, and 72.6 dB at 1 Pa, whereas the NEPs are 0.00174, 0.00067, and 0.00029 Pa. Hence, the proposed OpMUT is considerably better than its competitor. Future improvements in the sensing capability of the micromachined ultrasonic transducers are expected.