Capacitive Proximity Switch Layout Using a Faraday Cage Cavity
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Solution Overview
Problem
Capacitive proximity switches are susceptible to electromagnetic and capacitive interference, leading to malfunctions, especially from adjacent lines and drive circuits of displays, which disrupt the evaluation of the sensor surface.
Innovation Solution
The capacitive proximity switch design includes an electrically conductive body that acts as a Faraday cage, shielding electronic components of the evaluation circuit from interference by arranging them within a cavity surrounded by the conductive body, and using active shielding to minimize parasitic capacitances, allowing reliable operation near metallic parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the evaluation circuit is arranged close to the sensor surface for compact design, then device complexity is reduced, but electromagnetic and capacitive interference from adjacent lines and drive circuits disrupts the evaluation
Solution Approach 1:
The evaluation circuit is segmented into two parts: the active component (e.g., operational amplifier) is placed inside the Faraday cage formed by the electrically conductive body, while other components remain outside. This segmentation allows the critical sensitive components to be shielded from electromagnetic and capacitive interference while maintaining a compact overall structure.
Solution Approach 2:
The electrically conductive body acts as an intermediary Faraday cage between the sensor surface and the evaluation circuit. This intermediary structure provides electromagnetic shielding and capacitive isolation, protecting the evaluation circuit from interference signals generated by adjacent lines and drive circuits while allowing electrical connection between the sensor surface and the evaluation circuit.
2Reliability
If shielding structures are added to protect electronic components from interference, then reliability is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The electrically conductive body serves multiple functions simultaneously: it acts as a Faraday cage for electromagnetic shielding, provides mechanical support for the evaluation circuit, and serves as an electrical connection element between the sensor surface and the evaluation circuit. This multi-functionality reduces the need for additional separate shielding structures, thereby limiting the increase in device complexity while achieving reliable interference protection.
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
This design significantly reduces interference-related malfunctions, ensuring accurate evaluation of capacitance changes and improving the reliability of the proximity switch by shielding both the evaluation circuit and sensor surface from environmental interference.
Implementation Method 1
The electrically conductive body forms a kind of Faraday cage for the electronic component of the evaluation circuit, as a result of which it is shielded from electromagnetic or capacitive interference signals from the environment.
Implementation Method 2
The sensor surface forms one plate of an open capacitor, the capacitance of which depends on the distance to a second plate (e.g. earth), which is changed, for example, by the proximity of a user's finger.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
The invention relates to a capacitive proximity switch comprising an electrically conductive sensor area, which is covered by an electrically-insulating cover plate (2), as part of a capacitor having a capacitance which varies as a result of proximity, comprising an associated evaluation circuit, and comprising an electrically-conducting body (8), via which the sensor area is connected to the evaluation circuit and which is arranged between the electrically-insulating cover plate (2) and a mount (5) arranged at a distance therefrom, and relates to a domestic appliance comprising such a proximity switch (4). At least one electronic component (18, 23) of the evaluation circuit is arranged on the mount (5) such that it protrudes into a cavity (34), which is surrounded by the electrically conductive body (8).