BOOK_CONTENT
From Global Positioning Systems, Inertial Navigation, and Integration

9.1.7 MEMS Technology

Microelectromechanical systems (MEMS) evolved from silicon semiconductor manufacturing in the late 1970s as an inexpensive mass manufacturing technology for sensors at sub-millimeter scales. At these scales, the ratio of surface area to volume becomes enormous, and electrostatic forces are significant. Vibration frequencies also scale up as size shrinks, and this makes vibratory coriolis gyroscopes very effective at MEMS scales. Electrostatic or piezoelectric forcing is used in most MEMS vibratory coriolis gyroscopes.

9.1.7.1 Open-Loop MEMS Accelerometers Many MEMS accelerometers are "open loop," in the sense that no force-feedback control loop is used on the proof mass. The cantilever beam accelerometer design illustrated in Fig. 9.7b senses the strain at the root of the beam resulting from support of the proof mass under acceleration load. The surface strain near the root of the beam will be proportional to the applied acceleration. This type of accelerometer can be manufactured relatively inexpensively using MEMS technologies, with a surface strain sensor (e.g., piezoelectric capacitor or ion implanted piezoresistor) to measure surface strain.

9.1.7.2 Rotational Vibratory Coriolis Gyroscope (RVCG) Many vibratory coriolis gyroscopes are MEMS devices. The rotational vibratory coriolis gyroscope is a MEMS device first developed at C. S. Draper Laboratory in the 1980s, then jointly with industry. It uses a momentum wheel coupled to a torsion spring and driven by a rotational electrostatic "comb drive" at resonance to create sinusoidal angular momentum in the wheel. If the device is turned about any axis in the plane of the wheel, the coriolis effect will introduce sinusoidal tilting about the orthogonal axis in the plane of the wheel, as illustrated in Fig. 9.12a. This sinusoidal tilting is sensed by four capacitor sensors in close proximity to the wheel underside, as illustrated in Fig. 9.12b. All the supporting electronics for controlling the momentum wheel and extracting the angular rate measurements fits on an application-specific integrate circuit (ASIC) that is only slightly bigger than the active device.

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Topics of Interest

9.2 INERTIAL SYSTEMS TECHNOLOGIES 9.2.1 Early Requirements The development of inertial navigation in the United States started around 1950, during the Cold War with the Soviet Union. Cold War weapons...

9.1.4 Rotating Coriolis Multisensors 9.1.4.1 Coriolis Effect Gustav Gaspard de Coriolis (1792-1843) published a report in 1835 [39] describing the effects of coordinate rotation on Newton s laws of...

9.1.3 Feedback Control Technology 9.1.3.1 Feedback Control Practical inertial navigation began to evolve in the 1950s, using technologies that had evolved in the early twentieth century, or were...

Two types of motion sensors, accelerometers and gyroscopes, are needed for detecting the complete motion of a moving object. Accelerometers sense linear motions, and gyroscopes sense angular motions.

A/D Analog-to-digital (conversion) ADC Analog-to-digital converter ADR Accumulated delta range ADS Automatic dependent surveillance AGC Automatic gain control AHRS Attitude and heading reference...