MEMS Accelerometer with Surface Electrostatic Coupling
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Solution Overview
Problem
Existing acceleration sensors, particularly MEMS-type sensors, face significant measurement bias due to low deformation of resonance frequency under acceleration, which is similar to parasitic deformations caused by temperature variations or stress relaxation, leading to inaccurate readings.
Innovation Solution
The sensor design incorporates two resonators with symmetrically arranged second bodies connected to a frame via suspension means, featuring surface electrostatic coupling that adjusts electrostatic stiffness in response to displacement, allowing for increased modal mass and reduced temperature sensitivity, while utilizing both pendular and vibrating modes for improved performance and redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single beam resonator is used to detect acceleration through frequency variation, then the sensor structure is simple, but the measurement bias is high due to low deformation and similarity with parasitic deformations
Solution Approach 1:
The single beam resonator is segmented into a tuning fork structure with two beams that undergo stresses of opposite signs. This segmentation allows differential measurement where the acceleration effect adds while parasitic effects cancel out, significantly improving measurement precision while maintaining relatively simple structure
Solution Approach 2:
The patent applies asymmetric stress distribution to the two beams of the tuning fork - one beam experiences compressive stress while the other experiences tensile stress under acceleration. This asymmetric configuration ensures that acceleration-induced frequency shifts are additive while thermal and stress relaxation effects are differential, resolving the measurement bias problem
2Measurement precision
If electrostatic stiffness is added in parallel with mechanical beam stiffness to reduce measurement bias, then the amplitude of frequency variation increases, but the device complexity increases with additional electrodes
Solution Approach 1:
The patent merges the mechanical beam structure with electrostatic coupling elements into an integrated resonator design. The electrostatic stiffness is combined in parallel with the mechanical beam stiffness, creating a unified structure that amplifies frequency variation amplitude without requiring separate independent electrode assemblies, thus improving measurement precision while controlling device complexity
3Measurement precision
If comb electrodes are used to generate electrostatic stiffness variation through air gap modification, then the frequency variation amplitude increases, but the linearity and sensitivity to parasitic effects worsen
Solution Approach 1:
Instead of using air gap modification between comb electrodes which creates non-linear effects and temperature sensitivity, the patent inverts the approach by using surface electrostatic coupling where the electrostatic stiffness is generated through surface interaction. This inversion eliminates the air gap non-linearity and reduces sensitivity to temperature and stress relaxation, while still achieving large frequency variation amplitudes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design significantly reduces measurement bias and enhances sensor performance by linearly varying electrostatic coupling, providing more accurate and robust acceleration measurements with reduced sensitivity to temperature and assembly stress.
Implementation Method 1
surface electrostatic coupling means connecting each second body to the first body in such a way that a displacement of the first body relative to the frame along the sensitive axis causes an increase in the electrostatic coupling for one of the pairs of second bodies and a decrease in electrostatic coupling for the other of the pairs of second bodies
Implementation Method 2
transducer members connected to a control unit for detecting a position of the first body relative to the frame, vibrating the second bodies along the axis of vibration and detecting a frequency of vibration of the second bodies
Data Source
Figure 1~2
AI summary
The invention relates to a sensor comprising: a frame; a first body moving along a sensitive axis; two pairs of second bodies positioned symmetrically relative to the first body along the sensitive axis; transducers for detecting a position of the first body relative to the frame, vibrating the second bodies along a vibration axis, and detecting a vibration frequency of the second bodies; and means for surface electrostatic coupling connecting each second body to the first body such that a movement of the first body relative to the frame along the sensitive axis respectively causes an increase and a decrease in the electrostatic torque for one and the other of the pairs of second bodies. The invention also relates to methods for controlling such a sensor.