MEMS Sensor Suspension Beam Stress Distribution
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Solution Overview
Problem
Existing physical quantity sensors using silicon MEMS technology face a risk of breakage due to stress concentration at the connecting interface between the fixing anchor and the suspension beam, particularly under impact conditions.
Innovation Solution
The design incorporates a suspension beam with a narrower width on the side opposite to the fixing anchor, and optionally includes recesses or through-holes to reduce mass and stress concentration, while maintaining the strength of the connecting interface, and may feature a connecting portion or overlapping anchor configuration to alleviate impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the suspension beam is made with uniform width from the fixing anchor, then the structural simplicity is maintained, but stress concentration occurs at the connecting interface leading to breakage risk under impact
Solution Approach 1:
The suspension beam is designed with non-uniform width where the width varies along its length. Specifically, the width at the connecting interface with the fixing anchor is greater than the width at other portions, creating local reinforcement at the stress concentration point while maintaining lighter mass elsewhere. This local quality change resolves the contradiction by strengthening the vulnerable interface without requiring the entire beam to be thick.
2Strength
If the suspension beam width is increased to strengthen the connecting interface, then the strength is improved, but the mass of the suspension beam increases
Solution Approach 1:
The suspension beam features localized width variation where only the connecting interface portion has increased width while the rest of the beam maintains a narrower profile. This local reinforcement approach provides the necessary strength at the critical interface without proportionally increasing the overall mass of the suspension beam, thus resolving the contradiction between strength and weight.
Solution Approach 2:
The suspension beam is effectively segmented into different width zones: a wider connecting interface zone and a narrower spanning zone. This segmentation allows each portion to be optimized for its specific function - the wider zone for strength at the interface and the narrower zone for reduced mass - thereby resolving the strength-weight contradiction.
3Weight of moving object
If recesses or through-holes are added to the suspension beam to reduce mass, then the weight is reduced, but the structural integrity may be compromised
Solution Approach 1:
The suspension beam incorporates recesses or through-holes only in specific portions away from the critical connecting interface, while maintaining full width and structural integrity at the interface region. This localized material removal allows mass reduction without compromising the strength where it is most needed, resolving the contradiction between weight reduction and structural integrity.
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 design reduces the risk of breakage and enhances the robustness and sensitivity of the physical quantity sensor by distributing stress and reducing mass without compromising the strength of the connecting interface.
Implementation Method 1
a capacitance-type physical quantity sensor including a fixed electrode fixedly disposed by one anchor, and a movable electrode provided so as to face the fixed electrode at an interval and to be displaceable, and measuring physical quantities such as an acceleration and an angular velocity based on the capacitance between these two electrodes
Implementation Method 2
a movable electrode provided so as to face the fixed electrode at an interval and to be displaceable
Data Source
AI summary
A physical quantity sensor includes a base, a suspension beam facing the base, a fixing anchor fixing the suspension beam to the base, a fixed electrode extending orthogonally from the suspension beam, and a movable electrode facing the fixed electrode at an interval. The width of a distal end of the suspension beam distant from the fixing anchor is narrower than the width of a proximal end adjacent to the fixing anchor.