Search Results (4)

This treatise studies the thermal sensitivity of the mechanical and optical transmission coefficients of a microoptoelectromechanical (MOEM) accelerometer based on evanescent coupling in a temperature range from minus 40 to plus 125 °C. Two types of optical measuring transducers are considered: based on a directional coupler and a resonator. This analysis covers the optical and mechanical components of the thermal sensitivity of the transmission coefficient. In terms of the mechanical part, the temperature effect induces changes to the linear dimensions of the structure and material characteristics and causes internal mechanical stresses as well. The temperature effect on the optical system of the accelerometer is conditioned by the thermo-optic effect of the materials the optical waveguides are made of. This study includes experiments on the refraction index dependence on the temperature of the optical films that compose the optical system of the MOEM accelerometer. The experiment shows that the refraction index of the films grows with temperature and amounts to 0.12642 ppm/°C for silicon nitride on the SiO₂/Si substrate. For the optical measuring transducer based on a directional coupler, the thermal sensitivity of the accelerometer’s optical transmission coefficient is 580 ppm/°C. For the resonator-based transducer, the thermal sensitivity is 0.33 °C⁻¹. The thermal sensitivity of the normalized mechanical transmission coefficient of the accelerometer is 120 ppm/°C. For optical measuring transducers based on a directional coupler, the contribution of the temperature dependent refraction index alteration to the overall error is 5 times larger than that of the MOEM accelerometer’s mechanical parameters, while for the resonator-based transducer the difference reaches 3000 times. This means its operability is only possible in a thermostatic environment. Full article

This treatise studies a microoptoelectromechanical accelerometer (MOEMA) with an optical measuring transducer built according to the optical tunneling principle (evanescent coupling). The work discusses the design of the accelerometer’s microelectromechanical sensing element (MSE) and states the requirements for the design to achieve a sensitivity threshold of 1 µg m/s² at a calculated eigenvalue of the MSE. The studies cover the selection of the dimensions, mass, eigenfrequency and corresponding stiffness of the spring suspension, gravity-induced cross-displacements. The authors propose and experimentally test an optical transducer positioning system represented by a capacitive actuator. This approach allows avoiding the restrictions in the fabrication of the transducer conditioned by the extremely high aspect ratio of deep silicon etching (more than 100). The designed MOEMA is tested on three manufactured prototypes. The experiments show that the sensitivity threshold of the accelerometers is 2 µg. For the dynamic range from minus 0.01 g to plus 0.01 g, the average nonlinearity of the accelerometers’ characteristics ranges from 0.7% to 1.62%. For the maximum dynamic range from minus 0.015 g to plus 0.05 g, the nonlinearity ranges from 2.34% to 2.9%, having the maximum deviation at the edges of the regions. The power gain of the three prototypes of accelerometers varies from 12.321 mW/g to 26.472 mW/g. The results provide broad prospects for the application of the proposed solutions in integrated inertial devices. Full article

Micro-opto-electro-mechanical (MOEM) accelerometers that can measure small accelerations are attracting growing attention thanks to their considerable advantages—such as high sensitivity and immunity to electromagnetic noise—over their rivals. In this treatise, we analyze 12 schemes of MOEM-accelerometers, which include a spring mass and a tunneling-effect-based optical sensing system containing an optical directional coupler consisting of a fixed and a movable waveguide separated by an air gap. The movable waveguide can perform linear and angular movement. In addition, the waveguides can lie in single or different planes. Under acceleration, the schemes feature the following changes to the optical system: gap, coupling length, overlapping area between the movable and fixed waveguides. The schemes with altering coupling lengths feature the lowest sensitivity, yet possess a virtually unlimited dynamic range, which makes them comparable to capacitive transducers. The sensitivity of the scheme depends on the coupling length and amounts to 11.25 × 10³ m⁻¹ for a coupling length of 44 μm and 30 × 10³ m⁻¹ for a coupling length of 15 μm. The schemes with changing overlapping areas possess moderate sensitivity (1.25 × 10⁶ m⁻¹). The highest sensitivity (above 6.25 × 10⁶ m⁻¹) belongs to the schemes with an altering gap between the waveguides. Full article

The Micro-Opto-Electro-Mechanical Systems (MOEMS) accelerometer is a new type of accelerometer that combines the merits of optical measurement and Micro-Electro-Mechanical Systems (MEMS) to enable high precision, small volume, and anti-electromagnetism disturbance measurement of acceleration, which makes it a promising candidate for inertial navigation and seismic monitoring. This paper proposes a modified micro-grating-based accelerometer and introduces a new design method to characterize the grating interferometer. A MEMS sensor chip with high sensitivity was designed and fabricated, and the processing circuit was modified. The micro-grating interference measurement system was modeled, and the response sensitivity was analyzed. The accelerometer was then built and benchmarked with a commercial seismometer in detail. Compared to the previous prototype in the experiment, the results indicate that the noise floor has an ultra-low self-noise of 15 ng/Hz^1/2. Full article