Variable-Area Comb Capacitor MEMS Gravimeter
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Solution Overview
Problem
Existing MEMS gravimeters face challenges with low displacement sensing accuracy, slow response speed, and high thermal noise due to thin device layers and small mass, limiting their precision and reliability in measuring gravity fields.
Innovation Solution
A variable-area comb capacitor-based MEMS relative gravimeter probe with a special-shaped comb finger structure and electrostatic feedback control, utilizing a spring structure to convert gravitational acceleration into displacement and a differential capacitance signal, enhancing sensitivity and reducing noise through thick silicon layer integration and closed-loop feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If thin device layers and small mass are used in comb accelerometers, then device size and power consumption are reduced, but thermal noise increases and accuracy deteriorates
Solution Approach 1:
The patent changes the geometric parameters of the comb fingers by making the bottom portion narrower than the top portion, creating a variable-area structure. This parameter change allows the same physical structure to provide both compact size and reduced thermal noise through optimized mass distribution and surface area characteristics
Solution Approach 2:
The patent employs composite material structures in the proof mass and comb fingers, combining different materials with complementary properties to achieve both low thermal noise and compact dimensions. The composite construction allows optimization of mechanical properties while maintaining small size
2Volume of moving object
If thin device layers are used in comb accelerometers, then device size is reduced, but mechanical thermal noise increases
Solution Approach 1:
The patent modifies the comb finger geometry with a variable area profile (narrower bottom, wider top) to change the moment of inertia and mass distribution. This parameter change reduces mechanical thermal noise while maintaining compact device dimensions through optimized structural parameters
3Device complexity
If optical shadow displacement transducer is used in open-loop MEMS gravimeter, then device structure is simple, but displacement sensing accuracy is low and response speed is slow
Solution Approach 1:
The patent implements a closed-loop feedback control system using comb capacitors to sense displacement and generate feedback force. This feedback mechanism significantly improves displacement sensing accuracy and response speed while maintaining relatively simple device structure through the self-balancing characteristic of the comb capacitor system
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 solution improves displacement sensing sensitivity, reduces mechanical and thermal noise, and enhances response speed and stability, enabling high-precision gravity measurements while simplifying processing and reducing device volume compared to magnetic feedback systems.
Implementation Method 1
the spring structure is used to convert a gravitational acceleration change to be measured into a displacement change of the proof mass
Implementation Method 2
the comb finger top portions of the movable comb fingers and the comb finger top portions of the fixed comb fingers form a variable-area differential comb capacitor structure, configured to convert the displacement change into a differential capacitance signal
Implementation Method 3
the electrostatic feedback actuator is used to receive the feedback voltage, and to generate, according to a satisfied relationship between the feedback voltage and an electrostatic feedback force, an electrostatic feedback force for controlling the proof mass to remain at the balanced position
Data Source
AI summary
A gravimeter probe includes a spring structure, a proof mass, movable comb fingers, fixed comb fingers, and an outer frame. A fixed end of the spring structure is arranged on the outer frame and a free end thereof is connected to the proof mass. The movable comb fingers are arranged on upper and lower surfaces of the proof mass, and the fixed comb fingers are correspondingly arranged on the outer frame. Each of the movable comb fingers and the fixed comb fingers has a special-shaped comb finger structure. The special-shaped comb finger structure includes a comb finger bottom portion and a comb finger top portion, and the width of the comb finger bottom portion is smaller than the width of the comb finger top portion.