Capacitive Sensor Stepped Electrode Linearity
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Solution Overview
Problem
Capacitive sensors face linearity errors due to non-planar displacement of the moving electrode, especially in small capacitive pressure, acceleration, and angular velocity sensors, where existing solutions either require complex electronics, calibration, or suffer from hysteretic behavior and poor pressure tolerance.
Innovation Solution
A capacitive sensor design featuring a stationary electrode with a stepped, concave, or convex shape, optimized to touch the movable electrode at multiple points, reducing linearity errors and manufactured using thin-film technology with unequal metal layer thicknesses and different metals, supported by torsion or bending springs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the movable electrode is made thin to enable small sensor size, then sensitivity is improved, but linearity deteriorates due to non-planar displacement
Solution Approach 1:
The stationary electrode is designed with a curved surface (concave or convex) instead of a flat surface. This curvature is specifically optimized to match the non-planar displacement pattern of the thin movable electrode, ensuring that the gap between electrodes remains uniform during bending, thereby maintaining linearity while preserving the thin-film sensitivity
Solution Approach 2:
The invention changes the geometric parameter of the stationary electrode from flat to curved, with specific radius of curvature optimized based on the movable electrode's bending characteristics. This parameter modification transforms the capacitor geometry to accommodate non-planar displacement while maintaining linear capacitance-output relationship
2Manufacturing precision
If stiffeners are added to the movable electrode to improve linearity, then linearity is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
Instead of modifying the movable electrode with stiffeners to achieve planar displacement, the invention inverts the approach by modifying the stationary electrode's surface geometry. The stationary electrode is made curved to match the natural non-planar bending of the thin movable electrode, achieving linearity without adding structural complexity to the movable side
Solution Approach 2:
The curved surface of the stationary electrode is optimized locally to match the specific displacement pattern of the movable electrode. The radius of curvature and surface profile are tailored to the local bending characteristics, ensuring uniform gap maintenance across the electrode area without requiring global structural modifications
3Manufacturing precision
If touch-mode operation is used to achieve linear pressure response, then linearity and sensitivity are improved, but pressure tolerance deteriorates due to hysteretic behavior
Solution Approach 1:
The curved stationary electrode surface enables the sensor to operate in a regime where the capacitor gap remains uniform during pressure-induced bending, achieving linear response without requiring touch-mode operation. This allows the movable electrode to maintain larger clearance, improving pressure tolerance and eliminating hysteretic behavior while preserving linearity through geometric optimization
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 significantly improves linearity and pressure handling capabilities, making the sensor appear as a planar capacitor, reducing non-linearity and enhancing sensitivity while maintaining cost-effectiveness.
Implementation Method 1
The capacitive measuring is based on a change in the gap between two surfaces of a pair of electrodes of the sensor. The capacitance between the surfaces, i.e. the capacity for storing electric charge, depends on the area of the surfaces and on the distance between the surfaces.
Data Source
AI summary
The present invention relates to measuring devices for use in physical measuring, and in particular to capacitive sensors. In the sensor according to the invention, the shape of the stationary electrode (3), (4), (12), (17-20), (27-28) is stepped. Through the invention, a method for manufacturing a capacitive sensor with improved linearity is achieved, as well as a capacitive sensor suitable for use particularly in small capacitive sensor solutions.