Capacitive Foreign Object Detection in Wireless Power Transmitters
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Solution Overview
Problem
Wireless charging systems face challenges in detecting foreign objects, such as coins and paper clips, which can cause eddy currents and elevate temperatures, leading to inefficient power transfer and potential damage.
Innovation Solution
The implementation of capacitive sensing using an array of capacitive sensor electrodes to detect foreign objects by analyzing capacitance measurements, coupled with control circuitry that halts wireless power transmission if a foreign object is present, ensuring safe and efficient charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If wireless power transmission is performed using a transmitting coil, then power transfer efficiency is improved, but foreign objects may cause eddy currents and temperature elevation leading to safety issues
Solution Approach 1:
The system performs foreign object detection before initiating wireless power transmission by measuring capacitance values of sensor electrodes. This preliminary detection identifies foreign objects that could cause eddy currents and temperature elevation, allowing the system to prevent power transmission to areas with foreign objects present
Solution Approach 2:
The system continuously monitors capacitance values during wireless power transmission and compares them against reference values. When capacitance changes indicate the presence of a foreign object, the system provides feedback to halt or adjust power transmission, preventing harmful temperature elevation while maintaining efficient power transfer when safe
2Reliability
If foreign object detection is implemented using capacitive sensing, then safety is improved, but device complexity increases due to additional sensor array and control circuitry
Solution Approach 1:
The housing structure serves multiple functions: it provides mechanical support, acts as a mounting surface for capacitive sensor electrodes, and forms part of the charging surface. This multi-functionality reduces the need for separate structural components, thereby limiting the increase in device complexity while enabling foreign object detection capability
Solution Approach 2:
The capacitive sensor electrodes utilize the housing itself as part of the sensing structure, and the control circuitry integrates foreign object detection functionality into the existing wireless power control system. This self-service approach allows the system to perform both wireless power transmission and foreign object detection using shared components, minimizing additional complexity
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
Effectively prevents damage by detecting foreign objects and halting power transmission, maintaining efficient and safe wireless charging operations.
Implementation Method 1
Capacitive sensing is used to detect foreign objects. An array of capacitive sensor electrodes is supported by the housing at a location that overlaps the wireless power transmitting coil. Capacitive sensor measurements from the capacitive sensor array are analyzed to determine whether a foreign object such as a coin or paperclip is present
Implementation Method 2
The wireless power transmitting device uses a wireless power transmitting coil to transmit wireless power signals to the wireless power receiving device
Implementation Method 3
The wireless power receiving device has a coil and rectifier circuitry. The coil receives alternating-current wireless power signals from the wireless charging mat. The rectifier circuitry converts the received signals into direct-current power
Implementation Method 4
foreign objects such as coins and paper clips are detected. The wireless power system has a wireless power transmitting device and a wireless power receiving device... If a foreign object is detected, wireless power transmission with the wireless power transmitting coil is halted... foreign objects such as coins and paper clips, which can cause eddy currents and elevate temperatures
Data Source
AI summary
A wireless power transmitting device uses a wireless power transmitting coil to transmit wireless power signals to a wireless power receiving device. The wireless power transmitting coil is located in a housing. The housing has a circular outline and contains one or more magnets that couple to corresponding magnets in the wireless power receiving device to help align a wireless power receiving coil in the wireless power receiving device to the wireless power transmitting coil in the wireless power transmitting device. A circular array of capacitive sensor electrodes is supported by the housing at a location that overlaps the wireless power transmitting coil. Capacitive sensor measurements from the capacitive sensor array are analyzed to determine whether a foreign object such as a coin or paperclip is present between the housing and the wireless power receiving device.