Sense Coil Geometries for Metallic Object Detection
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Solution Overview
Problem
Conventional sense coils in wireless power transfer systems suffer from reduced sensitivity when detecting metallic objects, especially when they are centered or of smaller size, leading to potential heating issues and interference with the magnetic field.
Innovation Solution
The use of non-conventional sense coil geometries such as clover leaf, double-D, quadruple-D, and hexagonal shapes, where the conductor bows toward the center, enhancing sensitivity by varying electrical characteristics in the presence of metallic objects, and coupled with detection circuits to differentiate measured values from reference values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional square or rectangular shaped sense coils are used, then the structure is simple and easy to manufacture, but the detection sensitivity is reduced when metallic objects are located at the center of the coil
Solution Approach 1:
The patent applies asymmetry by transitioning from conventional symmetric square or rectangular sense coils to asymmetric geometries such as clover leaf, double-D, quadruple-D, and hexagonal shapes. These asymmetric configurations create non-uniform magnetic field distributions that enhance the interaction with metallic objects positioned at the coil center, thereby improving detection sensitivity without significantly complicating the manufacturing process
Solution Approach 2:
The patent employs curvature by introducing bowed conductors that bow toward the center of the coil, replacing straight linear segments with curved paths. This curvature modifies the magnetic field distribution to concentrate flux lines in the central region, enhancing the coupling with metallic objects and improving detection sensitivity while maintaining manufacturing feasibility
2Measurement precision
If the sense coil dimensions are considerably larger than the metallic objects, then the coverage area is increased, but the sensitivity to detect the objects is reduced
Solution Approach 1:
The patent applies local quality by designing sense coil geometries that concentrate magnetic flux density in specific local regions, particularly at the center area where metallic objects are most likely to be positioned. The bowed conductor configuration and multi-loop structures create localized high-field zones within the larger coil area, maintaining both extensive coverage and high detection sensitivity for small objects
3Reliability
If sense coils are located over the magnetics of a transmitter, then the wireless power transfer function is enabled, but the magnetic field causes undesirable interference with the sense coils
Solution Approach 1:
The patent employs the intermediary principle by using geometric configuration and conductor arrangement as mediating elements between the transmitter magnetic field and the sense coil detection function. The specific bowed and multi-loop geometries act as intermediaries that differentiate between the power transfer magnetic field and the perturbation signals caused by metallic objects, enabling discrimination through electrical characteristic variations
Solution Approach 2:
The patent applies parameter changes by utilizing the variation of electrical characteristics (such as impedance, resonant frequency, or inductance) of the sense coil in response to metallic object presence. The unique geometry causes these electrical parameters to change differently compared to conventional coils, allowing detection algorithms to distinguish object-induced changes from background magnetic field interference
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
These geometries improve the detection sensitivity and accuracy of metallic objects, reducing false alarms and heating risks, while maintaining or increasing the sensitivity across the coil's cross-section, allowing for more efficient and safer operation of wireless power transfer systems.
Implementation Method 1
the wireless magnetic field may induce eddy currents in any metallic object located within a predetermined space near the wireless charging system
Implementation Method 2
wireless charging systems are capable of transferring power in free space, e.g., via a wireless magnetic field
Data Source
AI summary
This disclosure provides systems, methods and apparatus for detecting a presence of an object. In one aspect an apparatus for detecting a presence of an object is provided. The apparatus includes a sense coil formed from a conductor having a predetermined shape configured to attenuate currents induced in the conductor by an external time-varying magnetic field. The sense coil has an electrical characteristic that varies as a function of the presence of the object. The apparatus comprises a detection circuit coupled to the sense coil and configured to detect the presence of the object in response to detecting a difference between a measured value of the electrical characteristic and a reference value for the electrical characteristic. The reference value for the electrical characteristic is substantially the same as the measured value of the electrical characteristic in the absence of the object over at least a portion of the sense coil.