Two-Mass MEMS Accelerometer for Vibration-Rejected 3-Axis Sensing
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Solution Overview
Problem
Existing MEMS accelerometers that measure acceleration in three orthogonal directions face challenges with sensitivity to external vibrations when using a single proof mass suspended for all directions, and systems with multiple proof masses are costly and inefficient in terms of surface area.
Innovation Solution
A two-mass, three-axis accelerometer design where the first and second proof masses are suspended and coupled to synchronize their movements in opposite directions in response to accelerations along the x, y, and z axes, using suspension and coupling structures to minimize the effect of external vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single proof mass is suspended to allow movement in all three directions, then the device complexity and surface area are reduced, but the measurement precision deteriorates due to sensitivity to external vibrations
Solution Approach 1:
The single proof mass is divided into two separate proof masses (first proof mass and second proof mass). Each mass is suspended by its own suspension structure, allowing independent movement control. This segmentation enables differential measurement where the two masses move in opposite directions in response to acceleration, while external vibrations affect both masses similarly and can be cancelled out through differential processing.
2Measurement precision
If multiple proof masses with separate suspensions are used for three-axis measurement, then the measurement precision is improved, but the device complexity and surface area increase
Solution Approach 1:
The two proof masses are coupled together through a coupling structure that allows them to move in a coordinated manner. The coupling structure synchronizes the movement of the two masses so that they move in opposite directions in response to acceleration along any axis. This merging approach maintains the vibration-rejection benefits of multiple masses while reducing the overall structural complexity compared to three completely independent mass systems.
3Measurement precision
If two proof masses are used with synchronized opposite movement, then the measurement precision is improved by canceling vibration effects, but the device complexity increases compared to a single mass system
Solution Approach 1:
The two proof masses are positioned asymmetrically with respect to the suspension and coupling structures. The first proof mass is suspended from first anchor points by a first suspension structure, while the second proof mass is suspended from second anchor points by a second suspension structure. This asymmetric arrangement allows the masses to move in opposite directions in response to acceleration while maintaining a relatively simple overall structure that can be implemented in a planar MEMS fabrication process.
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 design effectively cancels the impact of external rotational vibrations on acceleration measurements by differential measurement, providing accurate acceleration readings while optimizing surface area usage and reducing costs.
Implementation Method 1
When the accelerometer undergoes acceleration, the proof mass moves in relation to the fixed structure
Implementation Method 2
The coupling structure synchronizes movement of the first and second proof masses so that the first and second proof masses are linearly displaced from the respective rest positions in a same direction parallel to the x-axis when the accelerometer undergoes acceleration in the direction of the x-axis
Data Source
AI summary
An accelerometer comprising a first proof mass and a second proof mass which are coupled to each other with a coupling structure which extends from the first proof mass to the second proof mass. The coupling structure synchronizes the movement of the first and second proof masses so that the first and second proof masses may be linearly displaced from their rest position in the x-direction, rotationally displaced in opposite in-plane directions and rotationally displaced in opposite out-of-plane directions.