| Piezoelectric sensors are widely applied in automotive, aerospace, energy, chemical, biomedical and electronic industries due to their high sensitivity, simple reading circuitry, low power consumption, and cost-effectiveness. Particularly, accelerometers for ultra-high temperature applications (> 1000 °C) are of great interest for monitoring of turbine engine and power plant. However, there are no accelerometers which can operate properly at such a high temperature. As another example, tactile sensors are in great demand for various biomedical applications, such as surgical tools and service robotics. However, it has been a challenge for both elasticity and force measurement using existing tactile sensing techniques. Inspired by the sensing technique needs for these applications, my dissertation research focuses on two main innovations: (1) a piezoelectric accelerometer for ultra-high temperature applications (> 1000 °C); and (2) a piezoelectric tactile sensor utilizing the acoustic wave sensing technique for elasticity and force sensing applications.;For high temperature accelerometers, YCa4O(BO3) 3 (YCOB) single crystal was identified as a sensing material due to its high temperature stability up to 1500 °C. The accelerometer was designed to operate in shear-mode which can offer the best overall sensor performance at high temperatures, minimizing the thermal transient and base bending effects. A clamping assembly was chosen, rather than an adhesive assembly, to prevent mechanical failures at high temperatures. In addition, the accelerometer was designed to operate without thin film electrodes, which can offer more stable sensing performance than the thin film electroded sensors, because that thin metal films tend to fail at elevated temperatures. The prototyped accelerometer was tested at temperatures ranging from room temperature to 1000 °C. The sensitivity of the prototype was measured to be 5.9 +/- 0.06 pC/g throughout the tested frequency, temperature and acceleration ranges. The accelerometer retained the same sensitivity at 1000 °C for a dwell time of 9 hours, exhibiting high stability and reliability.;Acoustic wave sensing technique was deployed in the tactile sensor design, where the acoustic load impedance can be sensed by measuring the electrical impedance of the tactile sensor. Firstly, the effect of surface loads on Pb(Mg 1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystal resonators in different vibration modes including thickness mode, thickness-shear mode, and face-shear mode was investigated. It was observed that the face-shear mode resonator possessed more than one order of magnitude higher sensitivity (ratio of electrical impedance change to acoustic impedance load change) than the other existing resonators. Secondly, using face-shear mode PMN-PT single crystal, a 6 x 6 piezoelectric tactile sensor array was designed, fabricated, and characterized for tissue elasticity and force measurements. Tissue mimicking phantoms with different elastic moduli and acoustic impedances were prepared for the elasticity sensing experiment. For the force measurement test, external forces were applied to the array's sensing layer whose acoustic impedance varied with applied force. The prototyped sensor array exhibited an elasticity sensitivity of 23.52 Ohm/MPa with a resolution of 4.25 kPa and a force sensitivity of 19.27 Ohm/N with a resolution of 5.19 mN. Finally, the mapping of the phantom's elastic modulus and applied force using the 6 x 6 tactile sensor array was successfully demonstrated. |
