Ultrasonic sensors are well known for various applications such as NDT, ultrasound imaging, and proximity sensing. Conventional ultrasound transducers are bulky, work at notoriously high voltages, and consume significant power. Microfabrication techniques are leading to a paradigm shift in the field of ultrasonics by enabling development of low power - small footprint ultrasound transducers. This work focuses on the development of piezoelectric type flexural mode micromachined ultrasound transducer also known as PMUTs. We start by establishing a system level analytical model of a PMUT and use it to offer insights into scaling of the performance of the transducer with respect to various design parameters. In this analysis we give special attention to residual stresses thus establishing a contrast between membrane type and plate type PMUTs. After going through various steps of material development and microfabrication, we obtain arrays of PMUTs with different designs. PZT thin films deposited by sol-gel method are used as the piezoelectric layer in the multilayer stack. Further, we present a thorough characterization of fabricated PMUTs which includes measurement of the piezoelectric properties of the embedded PZT thin film, electrical impedance of the electromechanical transducer, its vibrational charac-teristics and acoustic radiation from a single PMUT cell. We also develop a pre-amplifier circuit for a PMUT receiver and present its working as a simple proximity sensor. After establishing the repeatability and predictability of our PMUT sensors we delve into application development beyond ultrasound imaging. Experiments and analysis of PMUTs submerged in water show strong structural-acoustic coupling between the PMUT membrane and the surrounding fluid. We hypothesize the applicability of this feature to sense changes in the acoustic environment of a PMUT. To this end, we integrate an array of PMUTs with a micro-fluidic chip and study the changes in the vibrational behaviour of the PMUT in response to change in the air-water ratio in a closed cell around a PMUT membrane. We also present our preliminary results on presence of micro-bubbles in the closed cell around the PMUT.

<p>Piezoelectric micromachined ultrasound transducer (pMUT) two-dimensional (2D) arrays have been proposed as an alternative to conventional bulk-PZT thickness-mode transducers for high frequency, forward-looking, catheter-based ultrasound imaging of the cardiovascular system. The appeal of pMUTs is based on several key advantages over conventional transducer technologies, including high operational frequencies, small element size, and low cost due to their microelectromechanical system (MEMS) silicon-based fabrication. While previous studies have demonstrated acoustic performance characteristics suitable for ultrasound image formation, pulse-echo B-mode imaging of tissue and tissue-like phantoms using 2D pMUT arrays small enough for forward-looking catheter-based applications have been demonstrated only at Duke University by Dausch et al.</p><p>Having demonstrated the suitability of 2D pMUT arrays for tissue imaging, an important step is to demonstrate effective design control. The frequency of operation is a fundamental component of transducer design. Previous modeling efforts for pMUT vibration have used classical/Kirchoff thin plate theory (CPT) or Mindlin thick plate theory, however pMUTs with geometric dimensions similar to those explored here, have not been modeled with experimental comparison to physical devices.</p><p>It is hypothesized that the frequency of vibration of pMUTs can be predictively modeled based on experimental data from various pMUT configurations. Experimental frequency results were acquired and used to develop an empirical model based on a modified Mindlin thick plate theory. This dissertation presents the development of the frequency design theory culminating in a set of predictive design equations for the frequency of vibration of 2D pMUT arrays aimed at improving their use in high-frequency, forward-looking, catheter-based ultrasound imaging applications.</p> / Dissertation

3D display technology is limited by the user's ability to interact with displays without being connected to external equipment. In order to feel tactile feedback in conjunction with displays, ultrasonic sound pressure fields have been created; however, ceramic transducers interfere with the user's immersive experience. We have created transparent ultrasonic transducers using capacitive micromachined ultrasonic transducer (CMUT) and piezoelectric micromachined ultrasonic transducer (PMUT) technology that allow the user to remain immersed in the experience while interacting with the display. Individual transparent piezoelectric transducers made with indium tin oxide (ITO) and polyvinylidene fluoride (PVDF) generate 66.9dB with 91.6% transparency. Samples were phased and modulated using a field programmable gate array (FPGA) in a 36-element array.