Physics, Instrumentation and Sensing

Miniature Vibrating Inertial Sensors

Vibrating inertial sensors, which are vibrating beam accelerometers and rate gyros with Coriolis effect, are a breakthrough technology over conventional inertial sensors (pendular type accelerometers, optical gyro with Sagnac effect, or mechanical gyro based on the conservation of the kinetic moment). The physical principles involved in vibrating sensors make it possible to design monolithic sensitive elements that can be made by collective machining processes, which makes them relatively easy to produce and miniaturize. In the medium term, vibrating inertial sensors should find applications both in the field of vehicle stabilization and dynamic control and in hybrid inertial navigation systems with other localization systems such as radio navigation.

Physical principles of vibrating inertial sensors

- Vibrating beam accelerometer

The accelerometer's sensitive element is a bending vibrating beam that is continuously excited at its resonance frequency by an electronic oscillator circuit. The acceleration applied to a proof mass generates axial stresses in the vibrating beam, thereby modifying its resonance frequency (somewhat like a guitar string whose frequency varies when its tension is changed). The output signal from the vibrating beam accelerometers is thus a frequency whose variations are representative of the acceleration applied.

- Vibrating rate gyro with Coriolis effect

These gyros measure the Coriolis accelerations generated in a resonator that is continuously excited at its resonance frequency (pulse pilot mode) by an oscillator circuit. These Coriolis accelerations are alternative to the pulsation and excite in forced vibration a transverse mode whose amplitude is proportional to the applied speed of rotation and inversely proportional to the difference of the specific pilot and transverse mode pulsations. For gyros operating in an open loop, the amplitude of the transverse motion is measured to determine the applied speed of rotation. In closed loop operation, this transverse motion is slaved to zero and the measured slaving force is representative of the applied speed of rotation.

Onera has been developing two vibrating inertial sensors over the past few years: the VIA accelerometer and the VIG rate gyro. The concepts retained, in monolithic and planar sensor configurations, are of the Mems type and the sensors are made today in quartz, a piezoelectric crystal with excellent mechanical properties and whose piezoelectric character makes it possible to create very easily the excitations and useful vibration detections involved in this type of sensor (the gold-plated zones on the crystal correspond to the excitation and vibration detection electrodes).

Quartz vibrating inertial sensors developed at Onera.
Two monolithic inertial sensors with flat structure have been developed: the VIA accelerometer and the VIG gyro. A collective technology has been optimized for manufacturing each of the sensors, by chemical engraving of quartz wafers.

Last Update: 6 December 2006 - © ONERA 2009 - Terms of use