Foreign object detection device, foreign object detection method, and non-contact charging system

1. A foreign object detector comprising:

a detection coil;

a transmitting circuit generating RF power of a predetermined frequency;

a directional coupler outputting the RF power supplied from the transmitting circuit to the detection coil, and extracting reflected power that is a power component reflected by the detection coil; and

a detection circuit receiving the reflected power extracted by the directional coupler, and detecting a foreign object by sensing a change in frequency characteristic of the reflected power.

2. The foreign object detector of claim 1 , wherein the detection circuit detects the foreign object based on the amount of change in the matching frequency of the reflected power.

3. The foreign object detector of claim 1 , wherein

the detection circuit recognizes the foreign object as metal if a matching frequency of the reflected power is higher than a reference matching frequency, and

recognizes the foreign object as water if the matching frequency of the reflected power is lower than the reference matching frequency.

4. The foreign object detector of claim 1 , wherein

the detection coil includes a plurality of coils, and

the foreign object detector further comprises a short circuit in which both terminals of a non-selected one of the plurality of coils in the detection coil are short-circuited together.

5. The foreign object detector of claim 1 , further comprising:

a transmitting coil case housing a transmitting coil, wherein

the detection coil is arranged above the transmitting coil, and housed in the transmitting coil case, and

the detection coil is arranged such that a distance between a surface of the transmitting coil case and the detection coil is shorter than a distance between the transmitting coil and the detection coil.

6. A non-contact charging system comprising:

the foreign object detector of claim 1 ;

a transmitting coil; and

an RF oscillation source supplying RF power of a predetermined frequency to the transmitting coil.

7. A method of detecting a foreign object, the method comprising:

outputting RF power generated at a predetermined frequency to a detection coil;

extracting, using a directional coupler, a power component reflected by the detection coil; and

detecting the foreign object by sensing a change in frequency characteristic of the reflected power that is the power component reflected by the detection coil and extracted by the directional coupler.