MEMS Accelerometer Off-Axis Shock Protection
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Solution Overview
Problem
Microelectromechanical Systems (MEMS) sensors, particularly accelerometers, are vulnerable to device failure due to insufficient robustness against off-axis shock events, as their spring suspension designs are not resistant to high acceleration forces.
Innovation Solution
The design incorporates a movable mass configuration with a first portion limited to single-axis motion and a second portion provided with additional flexibility via a spring system, allowing it to move into motion limiting structures during off-axis shock events, thereby enhancing suspension robustness without disrupting the sensor's performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spring suspension design is used to suspend the movable mass, then the sensor can detect acceleration forces, but the suspension is not robust against off-axis shock events leading to device failure
Solution Approach 1:
The movable mass is divided into a first portion and a second portion. The first portion is suspended by springs that are constrained to move only in the sensing direction, while the second portion is provided with motion limiting structures. This segmentation allows different parts of the movable mass to have different mechanical properties, with the first portion maintaining suspension flexibility and the second portion providing shock protection.
Solution Approach 2:
Motion limiting structures are pre-positioned to prevent the second portion of the movable mass from moving beyond a predetermined distance in off-axis directions. These structures are positioned in advance to counteract the harmful effects of high acceleration shocks before they can damage the suspension system.
2Measurement precision
If the movable mass is constrained to single-axis motion, then sensing precision is maintained, but robustness to off-axis shock events deteriorates
Solution Approach 1:
Different portions of the movable mass are given different mechanical characteristics. The first portion is designed with spring suspension that allows motion only in the sensing direction to maintain measurement precision, while the second portion is designed with motion limiting structures to provide local robustness against off-axis shocks. This local differentiation of mechanical properties resolves the contradiction between precision and reliability.
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 configuration increases the robustness of single-axis MEMS sensors to off-axis high acceleration forces, protecting the transducer suspension and anchoring system from damage while maintaining the device's desired performance.
Implementation Method 1
a spring system interconnecting the first portion of the movable mass with the second portion of the movable mass, the spring system enabling movement of the second portion of the movable mass in response to a first force imposed upon the movable mass in a first direction that is orthogonal to a sense direction, wherein the spring system inhibits movement of the first portion of the movable mass in the first direction
Data Source
Figure 1~2
Figure 3
AI summary
A microelectromechanical systems (MEMS) device, such as a single axis accelerometer, includes a movable mass suspended from a substrate. The movable mass has a first portion and a second portion. A first spring system interconnects the first portion of the movable mass with the second portion of the movable mass. A second spring system interconnects the first portion with an anchor system. The first spring system enables movement of the second portion of the movable mass in response to a shock event force imposed on the movable mass in a first direction that is orthogonal to a sense direction, wherein the first spring system inhibits movement of the first portion of the movable mass in the first direction in response to the shock event force. However, the first and second movable masses move together in response to an acceleration force in the sense direction.