Force Sensitive Capacitive Sensor with Segmented Ground Shielding
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Solution Overview
Problem
Conventional capacitive touch sensors often register accidental touches and are complicated by gloved fingers, particularly in automotive applications, due to the insulating air gap between the touch-sensitive button and the grounded frame, leading to unintended registration of inputs.
Innovation Solution
A capacitive sensor design featuring a first and second flexible capacitive plate with a spacer and a flexible touch plate, where the plates are laminated together to allow for a change in air gap thickness detection upon touch, with a continuous ground plane on the second plate to shield from external electric fields and prevent accidental actuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional capacitive touch sensor uses an insulating air gap between the touch button and grounded frame, then the sensor structure is simple, but the sensor registers accidental touches and is sensitive to external electric fields
Solution Approach 1:
The sensor is divided into multiple functional layers: a first capacitive plate with touch-sensitive buttons, a dielectric layer, a second capacitive plate with ground segments, and a conductive frame. This segmentation allows the internal ground segments to shield the air gap from external electric fields while maintaining the simple air gap structure for accidental touch rejection.
Solution Approach 2:
Internal ground segments are introduced as intermediary elements positioned between the external environment and the capacitive sensing elements. These segments act as shields that block external electric fields from interfering with the capacitive measurement, thereby improving reliability without requiring the entire sensor structure to be complex.
2Measurement precision
If the air gap between capacitive plates is made thinner to improve sensitivity, then touch detection sensitivity increases, but the sensor becomes more prone to accidental activation and environmental interference
Solution Approach 1:
The internal ground segments are positioned in advance to preemptively block external electric fields and accidental touches from reaching the capacitive plates. This preliminary shielding action prevents harmful factors from affecting the thin air gap, allowing the sensor to maintain high sensitivity without increased susceptibility to false activations.
3Ease of manufacture
If conventional capacitive sensors use a simple air gap design, then manufacturing is easy, but the sensors cannot reliably distinguish between deliberate and accidental touches
Solution Approach 1:
The ground system is segmented into internal ground segments integrated within the sensor structure and an external conductive frame surrounding the sensor. This segmentation enables the internal segments to provide shielding for accurate touch detection while the external frame provides additional environmental protection, all while maintaining a manufacturing process that builds upon the simple air gap design.
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 enhances the accuracy of touch registrations by requiring deliberate actuation and minimizing accidental inputs, allowing for reliable operation even with gloved fingers, and provides improved haptic feedback through flexible components.
Implementation Method 1
The insulating gap between the button and the frame creates a capacitor. When a human finger contacts the button or comes within close proximity of the button, the finger displaces air and acts as a parallel capacitor
Implementation Method 2
a second flexible capacitive plate spaced from the first capacitive plate... a flexible touch plate overlying the second capacitive plate
Data Source
AI summary
A capacitive sensor that responds by measuring a change in capacitance induced by application of force includes a first capacitive plate having an electrically conductive touch cell, a second capacitive plate spaced from the first capacitive plate and having an electrically conductive area generally parallel with and overlapped with the touch cell, an incompressible spacer between the capacitive plates and having an aperture defining an air gap adjacent the touch cell, and a flexible dielectric touch plate overlying a flexible one of the first and second capacitive plates. The flexibility of the touch plate and adjacent capacitive plate allows finger pressure on the touch plate at the touch cell to change the dimension of the air gap and capacitance between the touch cell and a conductive region of the second capacitive plate.