Tokyo Keiki, Inc.

This paper reports an electrostatically levitated inertia measurement system which is based on the principle of a rotational gyro.The device has several advantages: the levitation of the rotor in a vacuum eliminates mech. friction resulting in high sensitivity; the position control for the levitation allows accelerations to be sensed in the tri-axis; and the fabrication of the device by a micromachining technique has the cost advantages afforded by miniaturization.Latest measurements yield a noise floor of the gyro and that of the accelerometer as low as 0.15 deg/h^1/2 and 30 μG/Hz^1/2, resp.This performance is achieved by a new sensor design.To further improve of the previous device, a ring-shaped structure is designed and fabricated by deep reactive ion etching using inductively coupled plasma.The rotor levitation is performed with capacitive detection and electrostatic actuation.Multiaxis closed-loop control is realized by differential capacitance sensing and frequency multiplying.The rotation of the micro gyro is based on the principle of a planar variable capacitance motor.

Mode analysis of a LiTaO3 (LTO) plate has been carried out numerically, and an interference-free shear horizontal acoustic plate mode (SH-APM) suitable for measuring the liquid viscosity was found. A viscosity sensor having a liquid container on the side opposite to interdigital transducers (IDTs) was fabricated on X-cut 148° Y-prop LTO. Satisfactory agreement was obtained between the calculated frequency spectrum and the experimental one. A loading test was carried out for a series of Newtonian liquids, which showed good agreement with the perturbation theory.