Transparent Capacitive Interface With Equipotential Guarding
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Solution Overview
Problem
Existing capacitive gesture interfaces struggle with sensitivity issues due to parasitic capacitances and electromagnetic interference, limiting their ability to detect and locate objects at distances beyond a few millimeters, and are not well-suited for non-planar surfaces.
Innovation Solution
A capacitive sensor system with independent measuring electrodes and a guard made of transparent conductive material, excited at an identical potential, allows for precise detection of objects up to several centimeters away, using floating-bridge electronics to eliminate parasitic capacitances and improve sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive sensors with pseudo-guard are used to reduce parasitic capacitance, then sensitivity improves slightly, but detection range remains limited to a few millimeters
Solution Approach 1:
The guard electrode is excited at an identical alternating electrical potential to the measuring electrode, creating an equipotential surface that eliminates voltage differences and prevents parasitic capacitance formation. This allows the sensor to detect objects at distances of several centimeters without the sensitivity limitations imposed by parasitic capacitances.
2Ease of manufacture
If capacitive technologies are used for contactless proximity detection, then integration into screens is improved, but sensitivity is insufficient to detect finger approach
Solution Approach 1:
The harmful parasitic capacitances are extracted and eliminated by using a guard electrode excited at identical potential, which isolates the measuring electrode from parasitic effects. This allows the capacitive sensor to achieve the necessary sensitivity for contactless finger detection while maintaining integration advantages.
Solution Approach 2:
The electrical potential parameter of the guard electrode is changed to match the measuring electrode's potential exactly, transforming the sensor's electrical characteristics to eliminate parasitic capacitance and enable long-range contactless detection.
3Ease of operation
If active guarding with unity-gain amplifier is used, then guard voltage is generated, but parasitic capacitances from electronics add to measurement error
Solution Approach 1:
Instead of using an amplifier to generate guard voltage, the system directly excites the guard electrode at identical potential to the measuring electrode. This eliminates the amplifier and its associated input capacitance, removing the source of measurement error while maintaining effective guard functionality.
4Adaptability or versatility
If capacitive sensors are used for gesture interface, then virtual control is enabled, but detection precision degrades beyond 40 centimeters
Solution Approach 1:
The system replaces optical detection mechanisms with an improved capacitive sensing approach using equipotential guarding. This substitution enables gesture control with enhanced detection precision that maintains accuracy at distances beyond 40 centimeters, overcoming the limitations of conventional capacitive 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 system achieves high-resolution, long-range detection of objects and contact with surfaces, enabling reliable command validation and integration into various geometries without interference, suitable for diverse applications including medical and automotive interfaces.
Implementation Method 1
electronic excitation and processing means for exciting the measuring electrodes to an alternating electrical potential and processing the signals from said measuring electrodes, so as to measure the capacitance between said measuring electrodes and an object
Implementation Method 2
a guard made of electrically conductive material disposed near the measuring electrodes at least on their face substantially opposite to the active surface, which guard being excited at an alternating electrical potential substantially identical to that of the measuring electrodes
Data Source
Figure 1~2(c)
Figure 3~4
Figure 5~6(c)
AI summary
The present invention relates to a control interface device sensitive to the movement of a body or object, comprising (i) a sensing surface (4), (ii) at least one capacitive sensor, each sensor(s) comprising a measuring electrode (2) having an active surface oriented towards the sensing surface (4), or substantially coinciding with said sensing surface, (iii) electronic excitation and processing means (7, 9, 12) for exciting the measuring electrodes (2) at an alternating electrical potential and processing the signals from said capacitive sensors, so as to provide distance information (13) between the active surface of the electrodes (2) and one or more objects (11), (iv) a guard made of electrically conductive material (3) disposed near the measuring electrodes (2) at least along their face substantially opposite the active surface,which guard (3) is excited at an alternating electrical potential substantially identical to that of the measuring electrodes (2), wherein the measuring electrodes (2) and the guard (3) are made of substantially transparent conductive materials, and the control interface device is substantially transparent. The invention also relates to a method implemented in this device and to control equipment.