Novel High-Resolution Lateral Dual-Axis Quad-Beam Optical MEMS Accelerometer Using Waveguide Bragg Gratings

Abstract

A novel lateral dual-axis a-Si/SiO2 waveguide Bragg grating based quad-beam accelerometer with high-resolution and large linear range has been presented in this paper. The sensor consists of silicon bulk micromachined proof mass suspended by silica beams. Three ridge gratings are positioned on the suspending beam and proof mass to maximize sensitivity and reduce noise. Impact of external acceleration in the sensing direction on the Bragg wavelength of gratings and MEMS structure has been modelled including the effects of strain, stress and temperature variation. Acceleration induces stress in the beam thus modifying the grating period and introducing chirp. The differential wavelength shift with respect to reference grating on the proof mass is the measure of acceleration. To compensate for the effect of the weight of the proof mass and increase the sensitivity of the sensor, electrostatic force of repulsion is applied to the proof mass. For the chosen parameters, the designed sensor has a linear response over a large range and a sensitivity of 30 pm/g. The temperature of surroundings, which acts as noise in sensor performance is compensated by taking differential wavelength shift with respect to reference grating. By design and choice of material, low cross-axis sensitivity is achieved. The proposed design enables a high-resolution well below 1 μ g/ Hz and is suitable for inertial navigation and seismometry applications.

Optical Interferometric MEMS Accelerometers

“…Sun et al designed a monolithic integrated MEMS accelerometer based on the Michelson interferometer, which integrated a mode point converter, sensing optical path, phase modulator, [54] Copyright 2020, MDPI. (b) Reproduced with permission.…”

“…The Waveguide Bragg gratings accelerometers based on a) Quad-Beam and b) Crab-Leg beam. (a) Reproduced with permission [54]. Copyright 2020, MDPI.…”

Adaptive opto-electromechanical silicon-on-insulator increased bandwidth accelerometer

“…The optical readout sensing methods continued dominating the attention in recent years for various applications, e.g. [13][14][15][16], for their high performance and immunity against electromagnetic interference (EMI). The noise cancelation circuit needs to be placed close to the capacitive or piezoelectric sensor itself to reduce the EMI effect resulting in increasing the bulk size of the sensor probe.…”

“…Malayappan et al [14] presented a waveguide Bragg grating-based quad-beam accelerometer that could achieve a high figure of sensitivity of 30 pm/g. The proposed sensor consists of Si bulk micromachined proof mass suspended by four silica beams.…”

An efficient design of dual-axis MEMS accelerometer considering microfabrication process limitations and operating environment variations

“…This method also minimizes the packaging cost, but the problems of large device size and high noise floor still remain. To minimize the device size and fabrication cost and to achieve better performance, two or three axes MEMS accelerometer, which consists of only a single proof mass, have been reported in the literature (Aydemir et al, 2016;Malayappan et al, 2020;Mohammed et al, 2018;Hemmati and Ganji, 2020). As a single proof mass is used in such designs, the mechanical design thus requires critical considerations to achieve both high thermal stability and minimum cross-axis sensitivity.…”