Abstract A high-Q sapphire dielectric motion sensing transducer that operates at microwave frequencies has been developed. The device uses cylindrical whispering gallery modes of quality factor greater than 105 at room temperature and greater than 108 at 4 K. The tuning coefficient of the transducer resonance frequency with respect to displacement was measured to be of the order of a few MHz/micro m. An electromagnetic model that predicts the resonant frequency and tuning coefficient has been developed and was verified by experiment. We implemented the model to determine what aspect ratio and what dielectric mode is necessary to maximize the sensitivity. We found that the optimum mode type was a TM whispering gallery mode with azimuthal mode number of about 7 for a resonator of 3 cm in diameter. Also, we determined that the tuning coefficients were maximized by choosing an aspect ratio that has a large diameter with respect to the height. By implementing a microwave pump oscillator of SSB phase noise -125 dBc/Hz at 1 kHz offset, we have measured a sensitivity of order 10-16 m/square root(Hz). We show that this can be improved with existing technology to 10-18 m/square root(Hz), and that in the near future this may be further improved to 10-19 m/square root(Hz).
1998 IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 45:1303-1313
© 1998, by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.