The aim of this project is to carry out detailed theoretical and experimental investigation of acoustic waves propagating in thin piezoelectric plates. By thin we mean plates whose thickness h is much less than the acoustic wavelength . The main tasks that will be undertaken during the course of this project include: (1) Theoretical analysis of plate wave propagation in a number of useful materials such as quartz, lithium niobate, lithium tantalate, potassium niobate, langasite, langatate, etc. The aim of this analysis is to identify materials and crystal cut/propagation directions that can provide large values of electromechanical coupling coefficient K 2 together with zero or low values of TCD (temperature coefficient of time delay) and PFA (power flow angle). Results obtained from theoretical calculations will be experimentally verified. (2) Theoretical and experimental investigation of the influence of a thin film of arbitrary conductivity deposited on the surface of a plate wave device. (3) Measurement of mechanical and electrical properties of liquids using plate waves and development of a system for identifying liquids based on their electrical properties. (4) Development of techniques to fabricate devices on plates as thin as a few micrometers (um) and integration of the resulting acoustic device with silicon substrate, and (5) Investigation of plate wave propagation in the presence of a biasing electric field and use of this work to realize devices with electronically tunable characteristics. Intellectual Merit: The research proposed in this project will produce major advances in the field of acoustic wave sensors. Devices based on acoustic waves in piezoelectric solids are currently receiving much attention for use as chemical and biological sensors. A number of different types of acoustic waves have been investigated for sensor applications. At present, best performance is obtained by using surface acoustic waves (SAWs) for sensing in the gas or vapor phase, and shear horizontal surface acoustic waves (SH-SAW) for sensing in the liquid phase. Sensors based on thin plate waves can provide following important advantages over SAW and SH-SAW sensors. (i) A number of chemical and biological sensors are based on detecting the change in mass on the sensor surface. For the same operating wavelength, the mass loading sensitivity of a thin plate device can be greater than that of a SAW or SH-SAW device by more than a factor of 10. (ii) Acoustic waves in thin plates can provide values of coupling coefficient K 2 that are 5 to 10 times greater than K 2 of SAWs and SH-SAWs. This will produce corresponding increase in the sensitivity of chemical and biological sensors which operate by detecting changes in electrical properties of the bio(chemical) coating. (iii) The energy of a plate wave is present on both surfaces of the plate. Thus one can enclose one side of the senor to protect it from environmental attack while allowing wave interaction at the other surface. (iv) The thin plate device can be integrated with silicon substrate which can contain the electronic circuitry associated with the sensor. This will greatly reduce size and cost of the overall sensor package while simultaneously improving its reliability. Broader Impacts: Various educational activities will form an important and integral part of this project. These include: (1) Hands-on-mini course for junior and senior year high school students, (2) Seminar and laboratory course for freshman students in our engineering college, (3) Opportunity for undergraduate students to participate in research through the REU program, (4) Establishing partnerships with high school teachers through the RET program, and (5) Graduate student mentoring. In selecting student and teacher participants, special efforts will be made to seek qualified candidates from groups underrepresented in science and engineering. As a result of previous NSF grants, the PI has mentored eight REU students, out of which two were female students and two were male students belonging to groups currently underrepresented in science and engineering. Successful completion of the work proposed in this project will lead to the development of fully integrated, low cost, high performance sensors. Sensors play an important role in all facets of our lives such as environmental monitoring, pollution control, counter terrorism measures, biomedical devices, etc. The research proposed in this project has many beneficial effects for society and will contribute towards improving the quality of our lives, health, and environment.
