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Methods and systems for detecting foreign objects in a wireless charging system

  • US 9,825,486 B2
  • Filed: 09/29/2015
  • Issued: 11/21/2017
  • Est. Priority Date: 09/27/2012
  • Status: Active Grant
First Claim
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1. A wireless power charging system for charging a separate device having a power receiver coil, the wireless power charging system comprising:

  • at least one power transmitter coil configured to;

    transmit, during a first time period, electromagnetic energy to pre-charge the power charging system through the power receiver coil in the separate device,transmit, based on an indication of an absence of a foreign object disposed between the power transmitter coil and the power receiver coil, power by inductive coupling to the power receiver coil in the separate device, the power transmitter coil characterized by a transmitter coil dimension that is a lateral dimension of the power transmitter coil; and

    a foreign object sensor including at least one foreign object detection (FOD) coil positioned at the center of the power transmitter coil, the FOD coil characterized by a FOD coil dimension that is the lateral dimension of the FOD coil and that is smaller than the transmitter coil dimension, the foreign object sensor configured to;

    determine an initial amplitude level of an electromagnetic foreign object detection signal during a calibration operation when the foreign object is not disposed between the power transmitter coil and the power receiver coil,generate, during a second time period subsequent to the first time period, the electromagnetic foreign object detection signal having a current amplitude level,determine whether the current amplitude level of the electromagnetic foreign object detection signal is lower than the initial amplitude level, andgenerate an indication of the presence of the foreign object disposed between the power transmitter coil and the power receiver coil responsive to a determination that current amplitude level is lower than the initial amplitude level, and otherwise generate the indication of the absence of the foreign object disposed between the power transmitter coil and the power receiver coil.

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