Resonant Force Sensor With Electrostatic Stress Compensation
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Solution Overview
Problem
MEMS&NEMS accelerometers have a limited operating range due to buckling and tensile failure of nanometric resonators, constrained by internal compressive stress during manufacturing, which reduces their measurement range and sensitivity.
Innovation Solution
A resonant force sensor with a micrometric-sized test body and strain gauge mechanically separated, using electrostatic coupling to apply stretching stress and cancel internal stresses, allowing for mechanical decoupling and extended operating range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If nanometric resonators are used to increase sensitivity, then measurement precision is improved, but the operating range is limited by buckling and tensile failure
Solution Approach 1:
The invention separates the test body from the strain gauge mechanically, using electrostatic coupling instead of direct mechanical connection. This segmentation allows the nanometric resonator to function solely as a sensitive strain gauge while the test body handles the mechanical loading, thus preserving both high sensitivity and extended operating range.
Solution Approach 2:
Electrostatic coupling acts as an intermediary between the test body and the nanometric strain gauge. This intermediary transmits force information without requiring direct mechanical contact, enabling the fragile nanoresonator to measure forces beyond its own mechanical limits while maintaining high sensitivity.
2Ease of manufacture
If internal compressive stress is present in the nanometric layer, then manufacturing is simplified, but the operating range is reduced due to buckling risk
Solution Approach 1:
The invention applies preliminary electrostatic stretching stress to the nanometric strain gauge before actual measurement begins. This pre-applied counter-stress compensates for the internal compressive stress from manufacturing, preventing buckling during operation and enabling the sensor to handle larger forces while maintaining manufacturing simplicity.
3Force
If the test body is mechanically coupled to the strain gauge, then force transmission is direct, but stress concentration limits the measurement range
Solution Approach 1:
Electrostatic coupling serves as a non-contact intermediary that transmits force information from the test body to the strain gauge without mechanical contact. This eliminates stress concentration at connection points while maintaining accurate force transmission, thereby extending the measurable force range.
Solution Approach 2:
The invention replaces the traditional mechanical coupling system with an electrostatic coupling system. This substitution eliminates the stress concentration inherent in mechanical connections while preserving the force transmission function, allowing for extended measurement range.
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
The solution extends the operating range and increases sensitivity by releasing internal stresses and applying tensile forces, enhancing the dynamic range beyond traditional limits.
Implementation Method 1
electrostatic coupling means between the mass and the strain gauge which, on the one hand, apply in the rest state a stretching stress induced by an initial electrostatic force
Implementation Method 2
at least one resonator suspended between the support and the mass. The resonator is for example formed by a vibrating beam, i.e. a beam vibrated at its resonant frequency by electrodes
Implementation Method 3
When the mass moves under the effect of an acceleration, the beam which is mechanically integral with the mass is compressed or stretched, which modifies its resonant frequency
Data Source
Figure 1A~2
Figure 3A~3B
Figure 4A~4B
AI summary
Micro-electromechanical accelerometer comprising a support (2), at least one mass (4) suspended by suspension means with respect to the support and able to move in the plane of the accelerometer, measurement means (8) for measuring the movement of the seismic mass, having at least one first vibrating beam (10) of nanometric section and first means of electrostatic coupling (C1) between the seismic mass (4) and the at least one first vibrating beam (10), which are configured to ensure a mechanical decoupling between the first vibrating beam (10) and the seismic mass (4) so that, at rest, the first means of electrostatic coupling (C1) generate a traction on the first vibrating beam (10), and so that, under the effect of an acceleration, they modify the state of stress of the first vibrating beam (10).