Backlit Inductive Touch Buttons Using Segmented Metal Targets
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Solution Overview
Problem
Inductive touch sensor keys and buttons are unable to be backlit due to their light opaque deformable metal target layers, which restricts visual feedback and visibility under poor lighting conditions.
Innovation Solution
The use of a molded spacer layer and a discrete metal disk with side-illuminating LEDs or a suspended metal target allows for backlighting, enabling the placement of light emitting diodes on the circuit board and using a translucent material as a light pipe to illuminate the buttons while maintaining impedance detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous conductive metal sheet is used for the target layer, then inductive sensor detection is achieved, but light cannot pass through the button
Solution Approach 1:
The continuous metal sheet is segmented into discrete metal disks or traces that are patterned on the circuit board. This segmentation allows light to pass through the gaps between the metal elements while maintaining the inductive coupling necessary for sensor detection. The metal is divided into functional segments that preserve electrical properties while enabling optical transparency.
Solution Approach 2:
The metal target layer is designed with a porous or discontinuous structure rather than a solid continuous sheet. This porous configuration allows light transmission through the button while the distributed metal elements maintain the inductive sensing function. The effective permeability of the metal structure enables both optical and electromagnetic functionality.
2Measurement precision
If the metal target layer is placed close to the inductive coil for optimal sensing, then detection precision is improved, but backlighting is blocked
Solution Approach 1:
The metal target is segmented into discrete elements that can be strategically positioned near the inductive coil for optimal sensing while allowing light to pass through the spaces between segments. The segmented structure enables proximity to the coil without forming a continuous light-blocking layer.
Solution Approach 2:
Different regions of the button structure have different properties: the metal target elements near the coil provide sensing functionality, while the spaces between them and other structural regions allow light transmission. The local quality varies across the button to satisfy both sensing and illumination requirements.
3Illumination intensity
If a thick spacer layer is used to enable backlighting, then light can pass through, but the inductive sensor performance may be affected
Solution Approach 1:
The spacer structure is segmented or configured to provide light pathways while maintaining the mechanical coupling necessary for inductive sensing. The segmented spacer allows light transmission without compromising the proximity relationship between the metal target and the inductive coil.
Solution Approach 2:
Thin film or flexible spacer structures are used that are sufficiently transparent to light while maintaining the mechanical connection and proximity required for inductive sensing. The thin film properties enable both optical transmission and functional 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 solution provides visual feedback and improved visibility under poor lighting conditions by allowing backlighting of inductive touch sensor keys and buttons, enhancing their functionality in various applications.
Implementation Method 1
When the deformable metal target layer is depressed, the inductive sensor detects a change in its impedance
Implementation Method 2
a translucent material as a light pipe to illuminate the buttons
Data Source
Figure 1
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Figure 4
AI summary
Backing lighting of induction touch keys is accomplished with a spacer layer surrounding an inductive touch sensor coil and a light source on a substrate, and light transmissive layer having a suspended metal disk proximate to the inductive touch sensor coil. A protective fascia may be placed over the light transmissive layer and spacer layer. When the light transmissive layer is displaced toward the inductive touch sensor coil the impedance value of the inductive touch sensor coil changes and the change is detected. Materials used that are translucent (light transmissive) may be continuous and solid, and opaque materials may have openings therein for transmission of light therethrough.