MEMS Accelerometer Cantilever Design for Multi-Directional Vibration Detection
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Solution Overview
Problem
MEMS accelerometers face challenges in achieving a balance between cost and performance due to residual mechanical stresses in membrane structures and reduced sensitivity in cantilever elements, which are primarily uniaxial and sensitive only to out-of-plane accelerations, and have differing resonance frequencies when multiple cantilever elements are present.
Innovation Solution
A MEMS accelerometer design featuring a supporting structure with multiple cantilever elements and suspended groups, where each cantilever element is connected by spring structures to form a cross-shaped piece, allowing for sensitivity to accelerations in multiple directions while minimizing the impact of residual stresses and resonance frequency differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If membrane structures are used in MEMS accelerometers, then manufacturing cost is reduced, but residual mechanical stresses degrade performance
Solution Approach 1:
The patent extracts the problematic distributed constraints from the membrane structure by transitioning to a cantilever-based design where masses are suspended by single-point constraints. This removes the source of residual mechanical stresses while maintaining the MEMS manufacturing process benefits.
Solution Approach 2:
The patent changes the constraint configuration parameter from distributed constraints (membrane) to single-point constraints (cantilever). This parameter change eliminates residual stresses while preserving the low-cost MEMS fabrication approach.
2Reliability
If cantilever elements are used in MEMS accelerometers, then residual mechanical stresses are reduced, but sensitivity is limited to out-of-plane accelerations only
Solution Approach 1:
The patent adds a second dimension of sensitivity by arranging cantilever elements in orthogonal orientations (e.g., X and Y directions). This allows the accelerometer to detect accelerations in multiple directions while each individual cantilever maintains its single-point constraint advantage.
Solution Approach 2:
The patent segments the sensing function across multiple cantilever elements oriented in different directions. Each cantilever handles a specific directional component, and the combined output provides multi-directional sensitivity while maintaining low residual stress in each element.
3Adaptability or versatility
If multiple cantilever elements are used to achieve multi-directional sensitivity, then acceleration detection capability is improved, but resonance frequencies differ reducing sensitivity
Solution Approach 1:
The patent applies local quality by making each cantilever element identical in geometry and material properties, ensuring they all share the same resonance frequency. This local uniformity compensates for the multi-directional configuration, maintaining high sensitivity across all sensing axes.
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 enables high sensitivity to vibrations in orthogonal directions with high frequencies (up to 10-20 kHz) while maintaining resilience to undesired mechanical stresses, improving detection accuracy and reliability.
Implementation Method 1
The deformable portion (21*, 22*, 23* and 24*) of the first, second, third and fourth cantilever elements (21, 22, 23 and 24) is overlaid by a piezoelectric detection structure (51, 52, 53 and 54).
Data Source
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Figure 3~4
AI summary
A MEMS accelerometer including a supporting structure (2; 102) and at least one deformable group (21*, 51; 121*, 151) and one second deformable group (22*, 52; 122*, 152), which include, respectively, a first deformable cantilever element (21*; 121*) and a second deformable cantilever element (22*; 122*), which each have a respective first end, which is fixed to the supporting structure (2; 102), and a respective second end. The first and second deformable groups (21*, 51; 121*, 151) further include, respectively, a first piezoelectric detection structure (51; 151) and a second piezoelectric detection structure (52; 152). The MEMS accelerometer (1; 101) further includes: a first mobile mass (31, 131) and a second mobile mass (32, 132), which are fixed, respectively, to the second ends of the first and second deformable cantilever elements (21*, 22*; 121*, 122*) and are vertically staggered with respect to the first and second deformable cantilever elements (21*, 121*; 22*, 122*), respectively; and a first elastic structure (M1, M1'), which elastically couples the first and second mobile masses (31; 131; 32, 132).