Capacitive Perspiration Sensor with Absorbent Dielectric
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Solution Overview
Problem
Existing perspiration sensors fail to provide a quantitative measurement of perspiration levels over time, relying on electrical resistance measurements that do not accurately indicate volume or level of moisture.
Innovation Solution
A capacitive sensor with ground-shielded parallel electrodes and a moisture-absorbent dielectric material, such as tufted microfiber cloth, is coupled to the skin to measure changes in capacitance as perspiration is absorbed, stabilizing the signal and minimizing noise through capacitive coupling to earth ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If galvanic skin response devices are used to measure electrical resistance of the skin, then the measurement process is simple, but the quantitative indication of perspiration volume or level over time is not provided
Solution Approach 1:
The patent replaces the electrical resistance measurement system with a capacitive sensing system. The capacitive sensor measures changes in capacitance caused by perspiration absorption in the dielectric material, providing quantitative perspiration volume measurement without the limitations of galvanic skin response devices.
Solution Approach 2:
The patent uses a composite structure combining a capacitive sensor with a moisture-absorbent dielectric material (such as microfiber cloth). This composite system allows the sensor to absorb perspiration and translate it into measurable capacitance changes, enabling quantitative measurement while maintaining practical device complexity.
2Reliability
If the capacitive sensor is shielded and stabilized to reduce noise by electrically coupling the capacitor dielectric material to the skin, then the signal stability is improved, but the device complexity increases
Solution Approach 1:
The patent introduces an intermediary grounding system where the dielectric material is electrically coupled to the skin, which serves as a reference potential. This intermediary coupling stabilizes the capacitive signal by providing a consistent reference, reducing noise while avoiding the need for complex active shielding circuits.
Solution Approach 2:
The patent establishes equipotential conditions by electrically coupling the dielectric material to the skin and providing a ground reference. This creates a stable potential reference that minimizes noise and signal drift, improving measurement reliability without requiring complex active stabilization circuits.
3Measurement precision
If a moisture absorbent dielectric material is used in the capacitive sensor, then the sensitivity to perspiration is improved, but the response time may be affected by absorption rate
Solution Approach 1:
The patent employs a porous moisture-absorbent dielectric material (such as microfiber cloth) that rapidly absorbs perspiration through capillary action. The porous structure provides high surface area for quick moisture uptake, achieving both high sensitivity to perspiration and fast response time simultaneously.
Solution Approach 2:
The patent optimizes the local properties of the dielectric material by selecting a moisture-absorbent material with specific capillary characteristics. The material's local structure is tailored to rapidly wick and absorb perspiration at the skin interface, ensuring fast response while maintaining high sensitivity throughout the sensing area.
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 a stable and quantitative measurement of perspiration levels by accurately tracking changes in capacitance due to moisture absorption, offering improved sensitivity and reduced noise interference.
Implementation Method 1
a moisture absorbent dielectric material (e.g., a microfiber cloth)
Implementation Method 2
the dielectric material can be electrically coupled (e.g., capacitively coupled) to the skin of the user
Implementation Method 3
a capacitive sensor that can be coupled to the skin and utilize capacitance to measure perspiration
Implementation Method 4
the skin is capacitively coupled to earth ground which is weakly capacitively coupled to the ground of signal measurement circuit
Data Source
AI summary
A moisture sensor includes a pair of electrode plates separated by a moisture absorbent material that forms the dielectric of a capacitive sensor. As the absorbent dielectric material absorbs moisture, such as perspiration, the capacitance of the sensor changes reflecting a quantitative measure of perspiration absorbed. The sensor can be stabilized by capacitively coupling the dielectric material to the skin of the user to improve sensor stability and noise rejection. The sensor can include a capacitive sensing integrated circuit that measures the capacitance of the sensor in close proximity to the electrodes to limit the introduction of noise.