Unitary MEMS Accelerometer Proof Mass with Shared Capacitor Connections
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Solution Overview
Problem
MEMS accelerometers require multiple electrical connections for capacitor fingers, leading to increased size, cost, and manufacturing complexity, and lack sensitivity to accelerations in multiple perpendicular directions.
Innovation Solution
A compact accelerometer design with a unitary movable proof mass and support, using shared electrical connections for capacitor fingers and stop formations to limit movement and prevent finger contact, allowing for sensitivity in two perpendicular directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple electrical connections are provided for capacitor fingers, then the accelerometer can function properly, but the device size increases and manufacturing complexity increases
Solution Approach 1:
The patent combines multiple capacitor finger groups into a single movable proof mass structure, where all capacitor fingers are attached to the same movable mass. This allows multiple capacitance measurements to be taken from a single moving component, reducing the number of separate electrical connections needed while maintaining full functional operation of the accelerometer
2Reliability
If multiple electrical connections are provided for capacitor fingers, then the accelerometer can function properly, but the device size increases
Solution Approach 1:
The patent merges multiple capacitor finger groups onto a single movable proof mass, allowing all capacitance sensing elements to be integrated within a compact area. This consolidation reduces the overall device footprint while ensuring proper functional operation through unified movement of all capacitor fingers
3Strength
If the proof mass is made larger to withstand large accelerations, then the device can handle high g-forces, but the device size increases
Solution Approach 1:
The patent employs composite material structures for the proof mass, combining materials with different mechanical properties to achieve high strength and acceleration withstand capability in a compact form. The composite construction allows the proof mass to resist large accelerations without requiring increased overall device size
4Strength
If stop formations are added to limit movement, then the device can withstand large accelerations without damage, but the device complexity increases
Solution Approach 1:
The patent incorporates stop formations that engage beforehand to limit the travel distance of the proof mass during extreme acceleration events. These stops prevent damage by restricting movement to safe limits, while being integrated into the existing structure to minimize additional complexity
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 results in a compact, cost-effective accelerometer with reduced connections, capable of withstanding large accelerations without damage and maintaining operational integrity, while enabling two-axis monitoring with minimal disruption.
Implementation Method 1
If the object is accelerated in the sensing direction, it will be appreciated that the inertia of the proof mass will result in the proof mass moving relative to the support member, the mounting legs flexing and applying a restoring force urging the proof mass back towards its rest position.
Implementation Method 2
the mounting legs flexing and applying a restoring force urging the proof mass back towards its rest position
Implementation Method 3
Movement of the proof mass relative to the support member results in relative movement of adjacent ones of the interdigitated fingers. By taking appropriate capacitance measurements, the position or movement of the proof mass relative to the support member can be determined.
Data Source
AI summary
An accelerometer comprises a support, a first mass element and a second mass element, the mass elements being rigidly interconnected to form a unitary movable proof mass, the support being located at least in part between the first and second mass elements, a plurality of mounting legs securing the mass elements to the support member, at least two groups of movable capacitor fingers provided on the first mass element and interdigitated with corresponding groups of fixed capacitor fingers associated with the support, and at least two groups of movable capacitor fingers provided on the second mass element and interdigitated with corresponding groups of fixed capacitor fingers associated with the support.