RF Transparent Capacitive Touch Pad with Segmented Shielding
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Solution Overview
Problem
Capacitive touch pads on processor-based devices often interfere with radio frequency transmissions due to the need for electrical shielding, which can prevent the transmission and reception of radio frequencies and is difficult to tune, leading to inefficiencies and manufacturing challenges.
Innovation Solution
A radio frequency transparent capacitive touch system with patterned shielding that allows radio frequencies to pass through by creating openings in the shielding layer, minimizing induced current from NFC antennas and reducing power consumption, while maintaining effective shielding of mutual capacitance junctions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solid ground plane shielding is used to protect the touch pad from electrical noise, then the shielding effectiveness is improved, but the radio frequency transmission capability deteriorates
Solution Approach 1:
The ground plane shielding is segmented into multiple isolated ground regions rather than a continuous solid plane. Each ground region is electrically isolated from others, creating gaps that allow radio frequencies to pass through while still providing local shielding protection for the touch pad sensor elements.
Solution Approach 2:
The shielding structure transitions from uniform solid coverage to non-uniform distributed coverage. Ground regions are strategically placed only where needed for noise protection (near sensor elements) while leaving other areas open for radio frequency transmission, optimizing both shielding and RF performance locally.
2Use of energy by moving object
If the ground plane shielding is hatched to allow some radio frequencies through, then the radio frequency transmission is improved, but the shielding effectiveness deteriorates
Solution Approach 1:
Instead of hatching (creating a grid pattern), the shielding is segmented into discrete isolated ground regions. This segmentation provides equivalent RF transparency while maintaining better shielding effectiveness because the isolated regions create more significant gaps for RF signals compared to hatched patterns.
3Adaptability or versatility
If the antenna is placed near the touch pad to enable radio frequency communication, then the communication capability is improved, but the interference with touch pad function increases
Solution Approach 1:
The harmful electromagnetic interference from the antenna is extracted and directed away from the touch pad sensor elements. The segmented ground structure serves as an electromagnetic shield that blocks interference paths while maintaining RF signal transmission paths, effectively separating the harmful effects from the useful functions.
Solution Approach 2:
Electromagnetic shielding is applied locally only where needed (near sensor elements) rather than uniformly across the entire touch pad area. This localized shielding approach protects sensitive areas from antenna interference while allowing RF signals to pass through uncovered areas.
4Use of energy by moving object
If the antenna is tuned to transmit through the shielding, then the radio frequency transmission is improved, but the manufacturing complexity increases
Solution Approach 1:
The segmented ground structure is designed with regular, repeating patterns that are inherently easier to manufacture than complex tuned antenna-shielding combinations. The segmentation creates natural RF transmission paths without requiring precise tuning, simplifying both design and manufacturing processes.
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
Enables efficient transmission and reception of radio frequencies through capacitive touch pads without compromising touch pad performance, reducing manufacturing complexity and power consumption, and improving the overall functionality of devices with integrated radio frequency and touch input capabilities.
Implementation Method 1
capacitive touch pads often require electrical shielding to prevent noise from the processor-based device from interfering with normal touch pad functions
Implementation Method 2
The patterned shielding replaces the typical ground plane with a layer that is designed to shield the mutual capacitance junctions but leave the center of each touch pad sensor cell open (to allow radio frequency to pass through)
Data Source
AI summary
Touch sensor systems and methods are disclosed including a radio frequency antenna that can be placed on or very near the touch pad. The touch pad sensor includes a patterned shielding that shields the touch pad sensor from back-side signals and has opening that are large enough to allow radio frequencies to pass through the touch pad sensor.