Capacitive Proximity Sensor Layout for Water Rejection
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Solution Overview
Problem
Conventional capacitive proximity sensors in portable devices struggle to reliably distinguish between a user's body proximity and water contamination, leading to false detection signals due to water's high dielectric constant and conductivity, which can mimic body presence.
Innovation Solution
A capacitive proximity sensor system with multiple input channels and a shield electrode, utilizing offset subtraction and differential capacity measurements between a main and reference electrode to differentiate between body proximity and water-induced signals, effectively rejecting false water detection by analyzing the ratio of capacity changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional capacitive proximity sensor is used, then the device can detect body proximity with simple structure and low cost, but water contamination causes false detection signals due to water's high dielectric constant
Solution Approach 1:
The sensor is divided into multiple independent capacitive electrodes (first electrode, second electrode, third electrode) that can be read separately. This segmentation allows the system to analyze capacity changes from different spatial positions, enabling discrimination between water contamination and actual body proximity through comparative analysis of multiple measurement channels.
Solution Approach 2:
A shield electrode is introduced as an intermediary element between the sensing electrodes and the external environment. This shield electrode helps to stabilize the electric field distribution and reduces the direct influence of water contamination on the measurement, allowing more accurate detection of body proximity while filtering out false signals.
2Measurement precision
If optical detection techniques are used to discriminate water, then water detection accuracy improves, but power consumption and component cost increase
Solution Approach 1:
The patent replaces optical detection mechanisms with an improved capacitive sensing system that uses electrical field measurements instead of light. By utilizing multiple capacitive electrodes and analyzing capacity ratios, the system achieves water discrimination capability without requiring optical components, thereby reducing power consumption and component costs while maintaining measurement precision.
Solution Approach 2:
The system changes the measurement parameter from direct capacity values to capacity ratios between different electrodes. By calculating the ratio of capacity changes between the first and second electrodes relative to the third electrode, the system creates a new parameter that is insensitive to water contamination but sensitive to body proximity, achieving accurate water discrimination through parameter transformation rather than requiring additional optical sensors.
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 enhances the reliability of proximity detection by reducing false positives from water, allowing for accurate determination of user proximity while minimizing power consumption and component costs.
Implementation Method 1
the sensor is a simple conductive electrode, easy to integrate on a printed circuit board. However it can give rise to false detection because conventional capacitive systems are incapable of discriminating between a large object at a certain distance, and a small one at closer distance.
Implementation Method 2
Water, due to its large dielectric constant and conductivity is a source of special concern. A thin film or some drops of water on the detector can change the capacity perceived by the electrode enough to generate a false proximity signal.
Data Source
AI summary
A proximity sensor, and a portable device equipped therewith, with at least two superposed sense electrodes, one partially screening the other. By reading the capacity first of one electrode, then of the other, while setting the potential of the counter-electrode either to ground or to guard, the sensor of the invention discriminates between a body part, or another electrically equivalent object, and water drops at closer distance.