MEMS Capacitive Strain Sensor with Independent Comb Structures
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Solution Overview
Problem
Current strain sensors are unable to effectively measure bending and axial strain in a capacitive manner, as existing designs either fail to actuate properly under bending conditions or lack sufficient vertical dimension to determine deformation accurately.
Innovation Solution
A three-dimensional micro-electro-mechanical-systems (MEMS) capacitive sensor featuring two independent comb structures with suspended crystalline interdigitated fingers that can displace independently, allowing for a change in spacing and capacitance output, is fabricated without the need for expensive silicon-on-insulator wafers, enabling mechanical actuation and battery-less operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If existing strain sensor designs are used, then they can measure axial strain, but they fail to actuate properly under bending conditions or lack sufficient vertical dimension to determine deformation accurately
Solution Approach 1:
The sensor is divided into two independent comb structures that can displace independently relative to each other. This segmentation allows each comb structure to respond to different types of strain (bending and axial), enabling the sensor to measure both deformation modes simultaneously with high precision
Solution Approach 2:
The patent introduces a vertical dimension by elevating the comb structures above the substrate plane. This vertical displacement capability allows the combs to move in response to bending strain, creating the necessary vertical dimension to accurately determine deformation that planar sensors cannot detect
2Measurement precision
If complex array of elevated comb structures with vertical sidewalls is used, then axial strain measurement is improved, but the sensor cannot actuate while undergoing bending strain due to attachment method
Solution Approach 1:
The comb structures are designed with dynamic attachment methods that allow movement rather than rigid fixation. The combs can dynamically adjust their position and orientation in response to both axial and bending strain, transforming a static structure into a dynamic sensing system that adapts to different deformation modes
3Ease of manufacture
If standard capacitive sensor design is used, then manufacturing is simplified, but high voltage inputs are required which increases power consumption
Solution Approach 1:
The patent changes the electrical parameters of the capacitive structure by using interdigitated comb fingers with optimized geometry and spacing. This parameter optimization allows the sensor to achieve sufficient capacitance change with low voltage inputs, reducing power consumption while maintaining ease of manufacture through standard MEMS fabrication processes
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 sensor achieves low power consumption and can be used in implantable medical devices, providing objective data on fusion progression without the need for costly surgeries, by accurately measuring strain changes through capacitive changes without requiring high voltage inputs.
Implementation Method 1
A change in spacing between the interdigitated fingers outputs a change in capacitance of the sensor and is the primary mode of operation of the device
Data Source
AI summary
A three-dimensional micro-electro-mechanical-systems (MEMS) capacitive bending and axial strain sensor capacitor is described. Two independent comb structures, incorporating suspended polysilicon interdigitated fingers, are fabricated simultaneously on a substrate that can displace independently of each other while attached to a substrate undergoing bending or axial deformation. A change in spacing between the interdigitated fingers will output a change in capacitance of the sensor and is the primary mode of operation of the device. On the bottom and to the end of each comb structure, a glass pad is attached to the comb structure to allow for ample surface area for affixing the sensor to a substrate. During fabrication, tethers are used to connect each comb structure to maintain equal spacing between the fingers before attachment to the substrate. After attachment, the tethers are broken to allow independent movement of each comb structure.