Inductive Rotary Interface Through Thick Conductive Overlays
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Solution Overview
Problem
Inductive sensing-based user interface devices face limitations in sensing through conductive barriers due to eddy current losses, particularly when the barrier thickness exceeds the skin depth of the material at the operating frequency, which restricts the thickness of conductive overlays and requires lower excitation frequencies, limiting their application in UI devices with static, non-deflecting conductive overlays.
Innovation Solution
The use of apertures or holes in conductive overlays in conjunction with magnetic members to focus and direct magnetic flux through these apertures, allowing inductive sensing across conductive barriers of substantial thickness without the need for frequency reduction, thereby enabling sensing through thicker conductive materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conductive overlay is used for inductive sensing, then sensing capability is provided, but the thickness is limited by skin depth which causes eddy current losses
Solution Approach 1:
The conductive overlay is segmented by introducing apertures or slots that divide the continuous conductive layer into separate regions. This segmentation interrupts eddy current paths, reducing eddy current losses and allowing thicker overlays to be used without compromising sensing capability through the barrier.
Solution Approach 2:
portions of the conductive overlay are removed to create apertures or holes at specific locations. These extracted regions allow magnetic flux to penetrate through the conductive barrier more effectively, enabling inductive sensing through thicker overlays by eliminating the eddy current blocking effect in those specific areas.
2Length of stationary object
If excitation frequency is reduced to sense through thicker conductive barriers, then sensing through thicker barriers becomes possible, but UI device performance is limited
Solution Approach 1:
Instead of uniformly reducing excitation frequency across the entire sensing system, the patent applies local modifications to the conductive overlay by creating apertures or slots at specific locations. This allows the excitation frequency to be maintained at optimal levels for UI performance while still enabling sensing through thicker barriers at the aperture locations where eddy current losses are reduced.
3Length of stationary object
If magnetic flux is focused through apertures in conductive overlay, then sensing through thicker barriers is enabled, but device complexity increases
Solution Approach 1:
The conductive overlay is designed with a porous-like structure containing apertures or slots distributed throughout. This porous configuration allows magnetic flux to pass through the conductive barrier at multiple locations, enabling sensing through thicker overlays while maintaining a relatively simple overall structure that can be manufactured using standard techniques.
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 enables inductive sensing across conductive barriers of greater thickness than previously possible, enhancing the functionality of user interface devices by allowing for linear, rotational, or translational movements to be detected without the need for deflection of the conductive overlay, while minimizing eddy current losses and maintaining practical coil sizes for small UI devices.
Implementation Method 1
magnetic members to focus and direct magnetic flux through these apertures
Implementation Method 2
Inductive sensing based user interface (UI) devices
Implementation Method 3
eddy current losses
Data Source
AI summary
An inductive sensing-based user interface device which includes a conductive barrier with at least one aperture, a magnetic flux modifier attached to a rotary member on one side of the barrier and an inductive structure on an opposed side of the barrier aligned with the aperture, magnetically coupled to the flux modifier, wherein a change in sensed inductance is used to determine rotational input.