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Foreign object detector, power transmitting device and power receiving device for wireless power transmission, and wireless power transmission system

  • US 10,170,939 B2
  • Filed: 02/28/2014
  • Issued: 01/01/2019
  • Est. Priority Date: 02/28/2014
  • Status: Active Grant
First Claim
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1. A foreign object detector comprising:

  • a first resonator;

    an oscillator circuit that is connected to the first resonator and oscillates at a first frequency (f1) which is lower than a resonant frequency (fr) of a second resonator and at a second frequency (f2) which is higher than the resonant frequency (fr), the second resonator being electromagnetically coupled to the first resonator and being a parallel resonant circuit including a coil and a capacitor; and

    a measurement circuit that measures an inductance value of the first resonator while the first and second resonators are electromagnetically coupled to each other, wherein;

    the measurement circuit measures an input inductance value Lin(f1) of the first resonator while the oscillator circuit is oscillating at the first frequency f1 and an input inductance value Lin(f2) of the first resonator while the oscillator circuit is oscillating at the second frequency f2, calculates a coupling coefficient k which is calculated by the equation k2=1−

    Lin(f2)/Lin(f1), and detects a metallic foreign object between the first resonator and the second resonator based on the coupling coefficient k;

    while the coil is short-circuited, the input inductance value Lin(f1) of the first resonator and the input inductance value Lin(f2) of the first resonator are identical; and

    while the coil is open, the input inductance value Lin(f1) of the first resonator and the input inductance value Lin(f2) of the first resonator are identical.

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