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Next Generation of Smart Sensors
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Michael E. Stanley, Stéphane Gervais-Ducouret
Stand-alone consumer accelerometers do not usually have their chambers evacuated. Gas molecules within the MEMS chamber provide a damping effect that is advantageous in shaping the transfer function of the accelerometer. Conversely gyroscopes work better when motion damping is not present. The Coriolis effect leveraged by gyroscopes requires a proof mass that oscillates at high speeds. The same effect that is helpful for accelerometers increases power required for the gyro drive circuitry. To support higher levels of integration, MEMS structures will most likely be designed to operate at the same pressure. The accelerometer circuitry will need to be designed for force feedback (to ensure the accelerometer proof mass stays centered) if vacuum is used for both gyro- and accelerometer. Conversely, additional drive capabilities may be required if the gyroscope pressure is raised. Finding the right “sweet spot” will be even more complicated when we consider inclusion of a pressure sensor on the same die.
Optical MEMS: An introduction
Published in Guangya Zhou, Chengkuo Lee, Optical MEMS, Nanophotonics, and Their Applications, 2017
A majority of the sensors based on Fabry–Pérot interferometers are constructed in an out-of-plane configuration due to the high-quality mirror surfaces. A large number of sensors are demonstrated including pressure [127], acoustic and ultrasound [128–130], temperature [131], and chemical detectors [126]. Some are the stand-alone types with integrated photodetectors [126], and some are integrated with optical fibers for light input and output as shown in Figure 1.26c. For the fiber-based type, the movable reflector can be micromachined membranes coated with high-reflective coatings, high contrast gratings [132], or photonic crystal mirrors [133]. The stationary mirror can be fabricated on the substrate or directly coated on the fiber end face. The fiber and machined chip are usually aligned and fixed with epoxy. The measurand to be detected changes the gap between two mirrors thereby affecting the sensor output. There are also optical MEMS sensors reported based on Fabry–Pérot interferometers in an in-plane configuration including chemical sensors [134] and accelerometers [135]. The latter is illustrated schematically in Figure 1.26d. It is fabricated in a thick device layer on an SOI wafer. As shown, the two distributed Bragg reflectors (DBR) are formed by etching air slots in silicon structures. The accelerometer is constructed by fixing one DBR and attaching the other to a suspended proof mass. Transmission of the Fabry–Pérot interferometer is monitored by guiding the light in and out using a silicon waveguide.
Positioning and Tracking Approaches and Technologies
Published in Hassan A. Karimi, Advanced Location-Based Technologies and Services, 2016
Dorota Grejner-Brzezinska, Allison Kealy
Accelerometers use a known mass (proof-mass) attached to one end of a damped spring, which is attached to the accelerometer housing. Under no external acceleration condition, the spring is at rest and exhibits zero displacement. An external force applied to the housing will cause its acceleration; however, due to inertia, the proof-mass will lag behind, resulting in a displacement. The displacement of the mass and extension/compression of the spring is proportional to the acceleration of the housing (Allen et al., 2001; Jekeli, 2001). Since, according to Einstein’s principle of equivalence, accelerometers do not sense the presence of gravitational field (but can sense the reaction due to the gravitational forces), external gravity information must be provided to obtain navigation information. In inertial navigation, the velocity and position are obtained through real-time integration of the governing differential equations (equations of motion), with accelerometer-measured specific force as an input. More details on inertial navigation can be found in Allen et al. (2001), Grejner-Brzezinska (1999), Grejner-Brzezinska (2001a, 2001b), and Jekeli (2001).
Fractional Order Fuzzy Dynamic Backstepping Sliding Mode Controller Design for Triaxial MEMS Gyroscope Based on High-gain and Disturbance Observers
Published in IETE Journal of Research, 2021
Sayed Bagher Fazeli Asl, Seyyed Sajjad Moosapour
Assume that the gyroscope is moving with a constant linear speed while rotating at a constant angular velocity. Due to small displacements, the centrifugal forces,, and , are considered negligible. The dynamic equations of a MEMS triaxial gyroscope that rotates on the x, y and z axis can be written as [49]: where is the mass of proof mass; are the proof mass coordinates relative to the frame. , , and denote connection errors, coupled damping and spring terms, respectively. The spring coefficients are while represent the damping coefficients. are the angular velocities along each axis of the gyroscope frame; and are the control inputs.
A Robust Two-axis Tilt Angle Sensor Based on Air/Liquid Two-phase Dielectric Capacitive Sensing Structure
Published in IETE Journal of Research, 2020
Ha Tran Thi Thuy, Tiep Dang Dinh, Tuan Vu Quoc, Thinh Pham Quoc, Masahiro Aoyagi, My Bui Ngoc, Van Thanh Dau, Tung Thanh Bui
There are several kinds of commercial sensor for tilt angle measurement, which can be divided into two main kinds: solid-based and fluid-based mechanisms, depending on their working principles. The research on sensors of solid-based tilt angle has matured over the course of many applications. This kind of sensor consists of a proof mass suspended by a cantilever, spring, hinged bar or roller ball [5–9]. When the sensor body rotates around vertical or horizontal reference orientation, under the influence of the gravity, the suspended solid structure is deformed; this deformation is measured in terms of tilt angle. Recent technological advancements in the manufacturing of tilt sensors have improved the sensing accuracy, reduced the fabrication cost, increased the working lifetime, and enhanced their performances [10–13]. The main issue for these sensors is that it is easy for them to get damaged by the external forces, such as vibration or mechanical shock.
A new control method for global stabilisation of translational oscillator with rotational actuator
Published in International Journal of Systems Science, 2019
Ancai Zhang, Jinhua She, Jianlong Qiu, Chengdong Yang, Fawaz Alsaadi
In Figure 1, M and are the mass and the translational position of the cart, respectively; m, r, J, and are the mass, the rotary radius, the moment of inertia and the rotational angle of the proof mass, respectively; k is the stiffness factor of the spring; is the input torque applied to the proof mass. Since the motion of the TORA occurs in a horizontal plane, the gravitational forces does not affect the motion of the system. Moreover, the external disturbances and friction do not be considered in this study for simplicity. By using the Euler-Lagrange modelling method (Zhang et al., 2010), it is not difficult to get the dynamic equations of the TORA system as where , , and . The commonly discussed control objective for (1) is to design a controller F that makes x, θ, and converge to zero. The physical meaning of this objective is to stop the cart at the position while the spring is rest and to de-spin the proof mass at the spinning-down position.