| Popis: |
The growth of langasite (LGS) and certain of its isomorphs has recently been undertaken in the U.S. In parallel with this effort, PTI and the University of Central Florida are conducting a study of the material and bull-wave resonator properties of these materials. In this paper, we report our initial results for the design and fabrication of contoured thickness-mode resonators using langasite (LGS) and langatate (LGT). Since these materials and their isomorphs are in the same crystal class as quartz, well-known methods of trapped-energy resonator design, which are quite accurate for quartz, can be formally applied. Because these materials are somewhat softer than quartz, polishing techniques must be modified. Since their chemical composition is much more complex than that of quartz, cleaning and etching processes are less straightforward. Y-cut piano-convex resonators of both LGS and LGT have been designed and fabricated. Comparison of measured and calculated frequencies and equivalent circuit parameters for overtones 1-9 of LGS shows excellent agreement. For the 11/sup th/ and 13/sup th/ overtones, no significant response is observed, and these modes are therefore believed to be untrapped. For LGT, the agreement between measured and calculated parameters is poor to fair; the 11/sup th/ and 13/sup th/ overtones also appear to be untrapped for this material. The measured frequency temperature characteristic of the LGT resonators is parabolic, and is closely similar for all odd overtones through the 9/sup th/. Of particular interest is the resonator quality factor frequency product, Q/spl middot/f; the best value we have measured to date is 13.4 million for LGS and 16.0 million for LGT. Interestingly enough, this latter value is equal to the asymptotic value for natural quartz AT quartz resonators measured by Warner (19960). |
