Single Proof Mass MEMS Accelerometer with Asymmetric Springs
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Solution Overview
Problem
MEMS accelerometers face challenges in reducing size while maintaining sensitivity and reliability, especially when sensing motion along multiple axes, as smaller sizes make them vulnerable to high impact loads and difficult to meet sensitivity and reliability requirements.
Innovation Solution
The implementation of a three-axis MEMS accelerometer with a single proof mass that decouples sense motions in two directions (X and Y) using translatory spring elements with asymmetric stiffness to compensate for asymmetric mass, allowing accurate detection of acceleration in three orthogonal directions (X, Y, and Z) without cross-axis distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple movable structures are used to sense motion along multiple axes, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple movable structures into a single integrated proof mass that can sense acceleration along multiple axes simultaneously. This single proof mass includes first and second movable structures that are mechanically coupled, allowing the device to measure acceleration in X, Y, and Z directions while reducing the total number of independent movable components and simplifying the overall device structure.
Solution Approach 2:
The single proof mass is designed to perform multiple sensing functions simultaneously. It can detect acceleration forces along three orthogonal axes (X, Y, and Z directions) using the same movable structure, eliminating the need for separate movable structures for each axis and achieving multi-axis sensing capability with a unified component.
2Volume of moving object
If the size of movable structures is reduced, then device size is decreased, but reliability deteriorates
Solution Approach 1:
By merging multiple movable structures into one larger single proof mass, the patent increases the size and mass of the movable element. This larger proof mass has greater mechanical strength and resistance to high impact loads compared to smaller individual movable structures, thereby improving reliability while maintaining a compact overall device footprint through efficient space utilization.
3Volume of moving object
If the size of movable structures is reduced, then device size is decreased, but sensitivity deteriorates
Solution Approach 1:
The patent combines multiple movable structures into a single proof mass with increased total mass compared to individual small movable structures. The larger mass provides greater sensitivity to acceleration forces while the integrated design maintains a compact device footprint, achieving both small device size and high sensitivity simultaneously.
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 approach enables a small form factor MEMS device with enhanced sensitivity and reliability by isolating sense motions, effectively measuring acceleration in all three directions with minimal cross-axis interference, thus improving sensitivity and mechanical robustness.
Implementation Method 1
translatory spring elements with asymmetric stiffness configured to compensate for asymmetric mass
Implementation Method 2
asymmetric mass used to sense in the third direction (e.g., the Z-direction)
Implementation Method 3
The movement of the movable structure changes capacitance, and an electrical circuit connected to the MEMS accelerometer structure measures the change in capacitance to determine the acceleration forces
Data Source
AI summary
A microelectromechanical systems (MEMS) device, such as a three-axis MEMS device can sense acceleration in three orthogonal axes. The MEMS device includes a single proof mass and suspension spring systems that movably couple the proof mass to a substrate. The suspension spring systems include translatory spring elements and torsion spring elements. The translatory spring elements enable translatory motion of the proof mass relative to the substrate in two orthogonal directions that are parallel to the plane of the MEMS device in order to sense forces in the two orthogonal directions. The torsion spring elements enable rotation of the proof mass about a rotational axis in order to sense force in a third direction that is orthogonal to the other two directions. The translatory spring elements have asymmetric stiffness configured to compensate for an asymmetric mass of the movable element used to sense in the third direction.