This dissertation presents a new micro rate sensor (MRS) based on the SAW gyroscopic effect intended for extremely high-shock military applications.
The SAW gyroscopic effect, which is defined that a rotation vector perpendicular to a propagating axis causes a change of wave velocity proportional to the input rotation by the Coriolis force, is described through the theoretical analysis as well as the pictorial representation. The SAW gyroscopic gain factor in ST-cut quartz is not only mathematically derived by introducing a wave-velocity ratio and the perturbation method, but also compared with experimental results. The particle displacement on isotropic media and the charge distribution on arbitrary IDT structure are simulated as a function of normalized depth and as a method of moments, respectively.
The proposed SAWMRS, which consists of a pair of delay-line oscillators with opposite directions, especially operates as a differential scheme for the purpose of improving the sensitivity and removing common error sources. To estimate an inherent insertion loss of a delay line structure, we apply the equivalent circuit model to a design process. Different variants of SAWMRS, which operate around 80 MHz and 100 MHz respectively, are designed in order to figure out the effect depending on the operating frequency.
The 9℃×9㎟ delay-line structure was fabricated on different substrates including a normal ST-cut quartz and a quartz with 33.3˚a cut angle to study the gyroscopic gain factor according to a substrate cut angle. The fabricated SAWMRS was respectively mounted on a low temperature co-fired ceramic (LTCC) package as well as a PCB package with the object of comparing the RF characteristics. Two types driving electronics for self-oscillating loop were fabricated using different frequency-band amplifiers in order to figure out the harmonic properties of split-finger IDT.
The center frequency and the insertion loss of the delay line on the SAWMRS100 are measured at 98.6 MHz and 15.2 dB, respectively. The SAWMRS is not only automatically excited with a rise time of 15 ？？s but also is able to operate at third harmonic frequency regardless of another fabrication. We evaluated the performance of the delay-line oscillator and the SAWMRS, using a rate table and a stochastic noise analysis (PSD, Allan variance), revealing a sensitivity of 0.431 Hz/deg/s in the angular rates up to 2,000 deg/s and a white noise of 0.55 deg/s/∇Hz, respectively. Experimental results indicate that the effect according to a substrate cut angle is negligible in the sensitivity of the SAWMRS.
Consequently, the feasibility of the proposed SAWMRS was verified, through a set of performance evaluations, confirming the theoretical predictions.