Liwei Lin (Advisor)

Gas sensors can provide information about the presence of dangerous gases in industrial and residential sites, allowing for improved environmental protection and human health and safety. In order to enable ubiquitous wireless monitoring of combustible and toxic gases, sensor elements with low power consumption are required. Two common types of gas sensors, namely calorimetric and conductometric sensors, rely on heated sensor elements to activate the appropriate reactions with the gas of interest, resulting in high power requirements to maintain the necessary operating temperatures....

In the modern age of gas sensing technologies for broad applications such as internet of things, the capability to make selective, small form factor, and highly responsive sensors for applications such as wearable devices and cell phones could revolutionize the fields of gas sensing systems and fabrications. This thesis aims at developing a millimeter-sized and microwatt-powered sensor prototype using graphene field effect transistors (FETs) by exploring various DC and AC modulation techniques to realize the critical gas sensing features of selectivity and fast recovery speed at room...

The potential widespread usages of ultrasonic transducer technology have inspired the development of microelectromechanical systems (MEMS)-based devices. The research presented in this dissertation focuses on enhancing the performance of piezoelectric micromachined ultrasonic transducers (PMUTs) by devising innovative design structures, analytically deriving models to understand and optimize performance, and using these findings to demonstrate PMUT-based systems with increased capabilities. The ring-shaped PMUT is firstly introduced as a high-performance PMUT architecture, which is...

This letter describes a blood flowmeter by the pulsed wave Doppler (PWD) ultrasound detection procedure utilizing piezoelectric micromachined ultrasonic transducers (pMUTs) with the aluminum nitride (AlN) film as the piezoelectric material. The transceiver electronics for the PWD scheme is constructed for system control and signal processing, and a blood-mimicking fluid (BMF) is synthesized for flow velocity tests. Both the average Doppler frequency and Doppler power spectrum density (PSD) shift with respect to the flow velocity have been characterized and validated and the flow...