The Acoustic Thruster And Detector Based On MEMS

Micro-Electrical-Mechanical Systems (MEMS) are the integration of mechanical elements, such as sensors and actuators, and electronics on a wafer, which are relied on micro-fabrications. People use well-established IC fabrication techniques with chemical and mechanical processes to construct micro structures and devices. At the microscopic level, MEMS bridge the gap between the "electrical/computer world" and the real physical world, which is a great-leap-forward development. Since the first electrostatic micro-motor demonstrated in 1988, MEMS have been increasingly developed in the worldwide.The study on MEMS is divided into two parts:micro-structures and micro-transducers. Micro-structures include micro-lens, micro-nozzles, micro-probes and micro-fluidic systems, while micro-transducers always refer to mirco-sensors and micro-actuators. As an important MEMS transducer, piezoelectrical acoustic transducers lens have been developed by Dr. Kim’s group at the University of Southern Califonia, USA. Following their research, in this thesis, we focus on the acoustic MEMS devices include underwater thruster and FBAR based sensors.1. The paper describes a tested prototype for a controllable directional underwater thruster with no moving parts. During operation, high intensity acoustic wave creates directional water jets and the device moves itself in the opposite direction. When the underwater thruster moves along a non-vertical angle, it can produce straight backward thrust of 2.3mN and lateral thrust of 0.4mN in parallel with the device surface, with total thrust/weight ration of 2:1. To enhance the acoustic streaming effect, the self-focusing acoustic transducer (SFAT) with air reflectors is used to focus the acoustic wave.2. The paper investigated an infrared (IR) sensitive Film Bulk Acoustic Resonator (FBAR). The resonant frequency of the FBAR decreased when there was IR (peak wavelength at 750nm) illumination on the device. A linear relationship between the resonant frequency and the IR intensity was obtained. The sensing mechanism is attributed to the fact that the Young’s modulus of the resonator material (ZnO) depends on temperature. In general, for a resonator operating in a bulk mode, a change in the Young’s modulus translates into a shift of the resonant frequency. Thus, the sensitivity of the FBAR relies on its temperature coefficient of resonant frequency (TCF).3. This paper describes room temperature ozone sensing with a ZnO based film bulk acoustic resonator (FBAR). The resonant frequency of FBAR decreased upon ozone exposure. For 1400 ppb ozone, the frequency downshift was 131 kHz with a response time of 12 s. The frequency decrease of the FBAR sensor was proposed to be due to the density increase of the ZnO film. Ozone can be adsorbed on the ZnO surface by capturing free electrons from the film, which increases the film density. An analytical model was developed to predict the relationship between resonant frequency and ozone concentration. In agreement with the experiment, a linear function was obtained...