Multi-Stage MEMS Accelerometer with Mechanical Stops
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Solution Overview
Problem
Capacitive based MEMS accelerometers face challenges in achieving higher full-scale ranges without degrading sensitivity or worsening strain immunity, as existing design changes to accommodate high dynamics are often unnecessary and result in signal-to-noise ratio degradation.
Innovation Solution
A multi-stage MEMS accelerometer design featuring suspended structures with varying stiffness and mechanical stops, allowing one structure to contact stops at high accelerations while the other continues to move with increased stiffness, counteracting nonlinear capacitive effects and enabling higher full-scale range operation without sensitivity loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If MEMS sensor design changes are made to accommodate higher dynamics (making the sensor stiffer or increasing capacitive gap), then full-scale range is improved, but sensitivity is degraded resulting in higher signal-to-noise ratio or worse strain immunity
Solution Approach 1:
The accelerometer is divided into two separate sensing structures: a first suspended structure for measuring low g-level accelerations with high sensitivity, and a second suspended structure for measuring high g-level accelerations. Each structure is optimized independently for its specific measurement range, allowing the system to achieve both high sensitivity for low accelerations and high full-scale range for high accelerations without compromise
Solution Approach 2:
The system dynamically switches between different sensing structures based on the acceleration level being measured. The switch is triggered when the second structure contacts mechanical stops at high g-levels. This dynamic operation allows the system to adapt its measurement characteristics to match the input signal magnitude, maintaining optimal sensitivity across the full measurement range
2Adaptability or versatility
If the MEMS sensor is designed for rare high dynamics occasions, then the sensor can handle peak accelerations, but sensitivity is degraded during normal operation when high dynamics do not occur
Solution Approach 1:
The accelerometer employs separate sensing structures optimized for different operating conditions: the first structure maintains high sensitivity for normal low-g operations, while the second structure handles rare high-g events. This segmentation allows the system to be highly sensitive during normal operation while still possessing the adaptability to measure high dynamics when they occur
Solution Approach 2:
The patent uses two suspended structures that both measure acceleration but are designed with different stiffness characteristics. The second structure acts as a copy with modified properties (higher stiffness) specifically for high-g measurement, allowing the system to maintain optimal sensitivity for normal operations while copying the measurement capability for extreme conditions
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 multi-stage design allows for higher full-scale range operation without degrading sensitivity or strain immunity, effectively counteracting nonlinear capacitive effects and maintaining sensitivity and strain immunity, enabling accurate acceleration measurement across varying dynamics.
Implementation Method 1
a first suspended structure attached to, or formed in, the substrate by a first suspension member having a first stiffness and configured to move in response to input acceleration
Implementation Method 2
capacitive based micro-electromechanical systems (MEMS) accelerometers
Data Source
AI summary
A multi-stage MEMS accelerometer is disclosed that includes a MEMS sensor that has two suspended structures (proof masses) suspended by suspension members. The suspended structures move together in response to input acceleration when less the acceleration is less than a threshold value. When the input acceleration is greater than the threshold value, one of the suspended structures makes contact with a mechanical stop while the other suspended structure continues to move with increased stiffness due to the combined stiffness of the suspension members. The contact with the mechanical stop contributes a nonlinear mechanical stiffening effect that counteracts the nonlinear capacitive effect inherent in capacitive based MEMS accelerometers. In some embodiments, more than two suspended structures can be used to allow for optimization of sensitivity for multiple full-scale ranges, and for higher fidelity tuning of mechanical sensitivity with nonlinear capacitance. In some embodiments, compliant mechanical stops are used.