Capacitive Switch Circuit With Grounded Shield for Pressure Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive sensing technologies face challenges with robustness against RF noise and accidental activation, particularly in the presence of water or objects, lacking the immunity provided by inductive sensing technologies.
Innovation Solution
A capacitive sensing implementation where a capacitive sense plate is closely covered by a grounded metal or electrically conductive surface, shielding it from noise and external influences, and varying the distance between the sense plate and the grounded surface to enhance sensitivity and detect mechanical pressure effectively, similar to inductive sensing technologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a grounded conductive surface extensively covers the sense plate, then shielding against noise and external influences is improved, but capacitive sensing sensitivity deteriorates due to very high capacitance to ground
Solution Approach 1:
The invention divides the conductive surface into two distinct layers: a first conductive layer that is grounded to provide shielding, and a second conductive layer that is not grounded and serves as the sensing element. This segmentation allows each layer to perform its specific function without interfering with the other, resolving the contradiction between shielding effectiveness and sensing sensitivity.
Solution Approach 2:
The first grounded conductive layer acts as an intermediary between the external environment and the second sensing conductive layer. It provides electromagnetic shielding and blocks external capacitive influences while allowing the second layer to maintain its sensitivity to genuine touch inputs through the measurement circuit.
2Object-affected harmful factors
If a grounded conductive surface is placed close to the sense plate, then noise shielding is improved, but the capacitive value between sense plate and ground becomes very high reducing sensitivity
Solution Approach 1:
The invention segments the conductive surface into a grounded first layer for shielding and a non-grounded second layer for sensing. This allows the first layer to be positioned close to the sense plate for effective noise shielding without creating high capacitance that would reduce sensitivity, as the second layer remains electrically isolated for accurate measurement.
3Measurement precision
If capacitive sensing is used without a grounded shield, then sensitivity is maintained, but robustness against RF noise and accidental activation deteriorates
Solution Approach 1:
The invention divides the conductive surface into a grounded first layer for shielding and a non-grounded second layer for sensing, allowing both sensitivity and robustness to coexist.
Solution Approach 2:
The grounded first conductive layer serves as an intermediary shield that blocks RF noise and prevents accidental activation from objects near the device, while the second conductive layer remains sensitive to intentional touch inputs through capacitive coupling.
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 approach provides robustness against noise and accidental activation, maintains low power consumption, and offers reliable operation while allowing for the detection of proximity, touch, and pressure, enhancing the sensitivity and reliability of capacitive sensors.
Implementation Method 1
When contact measurements are made this electrically conductive surface is connected to the system ground. This is directly against the normal practice of designing with capacitive sensing technology, as almost all of the capacitive flood lines will flow to the grounded surface. If the grounded conductive surface is big enough to substantially or extensively cover the sense plate, no capacitive sensing is possible from the sense plate beyond the grounded surface. However, this is an advantage in terms of shielding the capacitive sensor from noise (RF or other), water and other fluids, moisture or any capacitive objects in touch or in close proximity with the grounded surface covering the sense plate.
Implementation Method 2
an electronic measurement circuit attached to at least one sense plate wherein the sense plate is substantially covered by an electrically conductive layer that is connected to ground during specific measurements
Implementation Method 3
A different type of such switch sensor is shown in Figure 2. A space 14 between the sense pad and the conductive layer forms a dielectric 14A and creates a structure similar to that of a parallel plate capacitor.
Data Source
Figure 1~2(a)
Figure 3~5
Figure 6
AI summary
A user interface which includes a capacitive measurement circuit with a sense plate covered by an electrically conductive cover which is movable relative to the sense plate,wherein the circuit distinguishes between the following situations: an object in proximity to the cover, an object in contact with the cover, and the cover in contact with the sense plate.