Capacitive Pressure Sensor With Interlocking Projections
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Solution Overview
Problem
Existing sensors for monitoring respiration and body movements via pressure are not sensitive enough, generate noise, and are not comfortable for users, especially when used on deformable surfaces like mattresses and chairs, as they require AC signals and interlocking projections which limit sensitivity and comfort.
Innovation Solution
A capacitive pressure sensor with interlocking projections on two elastic members separated by a thin dielectric, where the projections engage and increase contact area with pressure, enhancing sensitivity and allowing for differential pressure measurement without user restraint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If piezo-based sensors are used for respiration monitoring, then AC signals can be obtained, but the sensor causes user discomfort and is not suitable for deformable surfaces
Solution Approach 1:
The patent replaces piezoelectric mechanical sensing with a capacitive sensing mechanism. Instead of using piezoelectric materials that generate AC signals through mechanical stress, the invention uses two conductive surfaces separated by a dielectric layer where capacitance changes directly reflect pressure variations. This substitution eliminates the need for rigid piezoelectric elements while maintaining signal quality for detecting respiration-induced pressure changes.
Solution Approach 2:
The patent employs flexible conductive surfaces and thin dielectric layers that can conform to deformable surfaces like mattresses and pillows. The conductive surfaces are made from flexible materials such as conductive fabric or elastomer, and the dielectric layer is a thin flexible insulator, allowing the sensor to adapt to body contours and surface deformations without causing discomfort while still detecting pressure changes accurately.
2Ease of operation
If conventional capacitance-based sensors are used, then flexibility is achieved, but sensitivity is insufficient for detecting small pressure modulations
Solution Approach 1:
The patent enhances sensitivity by utilizing the third dimension - the distance between conductive surfaces. By making the dielectric layer extremely thin and allowing it to compress under pressure, the capacitance change becomes significantly more pronounced. The capacitance C is proportional to the area A and inversely proportional to the distance d between surfaces, so reducing d through thin dielectric layers amplifies the capacitance signal for small pressure changes, thereby improving measurement precision while maintaining flexibility.
3Measurement precision
If projections are added to increase contact area, then sensitivity improves, but the projections cannot interlock effectively
Solution Approach 1:
The patent extracts the projection structure from one surface only, placing deformable projections solely on the upper conductive surface while keeping the lower surface flat. This eliminates the problem of mutual offset between opposing projections that prevents effective interlocking. The single-sided projections can deform and contact the flat lower surface effectively, maximizing contact area and sensitivity without the engagement issues that arise when both surfaces have offset projections.
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 provides high sensitivity and low signal-to-noise ratio for monitoring respiration and body movements, ensuring comfort and effective detection of breathing phases without discomfort, even on deformable surfaces.
Implementation Method 1
two conductive surfaces of area A separated by a dielectric of thickness d generate capacitance C that is proportional to A/d
Implementation Method 2
Flexible sensors that convert pressure into capacitance
Implementation Method 3
separated by a thin elastic dielectric
Implementation Method 4
first and second mutually displaceable elastic members
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3(a)~3(c)
AI summary
A capacitive pressure sensor includes first and second of mutually displaceable elastic members (100, 150) each having a respective electrically conductive surface separated by a thin elastic dielectric. Variations in area of pressure-induced contact between the first and second members are used to vary capacitance of the sensor that allows determination of differential pressure between the two elastic members. Both of the elastic members have respective projections, the projections of the first elastic member being disposed in interlocking relationship with the projections of the second elastic member and configured so that as the elastic members are pressed toward each other their respective projections progressively engage and create increasing areas of contact.