Antenna device, card-type communication device, and communication terminal apparatus
An antenna device includes an antenna resonance circuit connected to a power supply circuit and a variable-frequency resonance element including a resonance circuit which is coupled with the antenna resonance circuit via an electromagnetic field. The resonant frequency of the resonance circuit is variable within a predetermined frequency band.
1. An antenna device comprising:
a wireless communication tag including an antenna resonance circuit connected to an RFID IC chip and having a fixed resonant frequency, the antenna resonance circuit including a first coil defining a radiation element capable of sending and receiving a high-frequency signal with a reader/writer; and
a variable-frequency resonance element, which is an additional device to the wireless communication tag, including a variable-frequency resonance circuit including a second coil being coupled with the first coil via an electromagnetic field and also including a control circuit configured to sweep a resonant frequency of the variable-frequency resonance circuit within a predetermined frequency band so as to sweep a resonant frequency of the antenna resonance circuit.
2. The antenna device according to claim 1 , wherein:
the variable-frequency resonance element further includes a variable capacitor.
3. The antenna device according to claim 2 , wherein the variable-frequency resonance element further includes a battery and a control circuit, the control circuit being connected to the variable-frequency resonance element.
4. The antenna device according to claim 3 , wherein the control circuit is configured utilize as power, a current rectified from a high frequency signal radiated from an antenna of the reader/writer.
5. The antenna device according to claim 1 , wherein a variable frequency band of the variable-frequency resonance element covers the resonant frequency of the antenna resonance circuit.
6. A card communication device for use with an IC card including a wireless communication tag including an antenna resonance circuit connected to an RFID chip and having a fixed resonant frequency, the antenna resonance circuit including a first coil defining a radiation element capable of sending and receiving a high-frequency signal with a reader/writer, the card communication device comprising:
a variable-frequency resonance element, which is an additional device to the wireless communication tag, including a variable-frequency resonance circuit including a second coil being coupled with the first coil via an electromagnetic field and also including a control circuit configured to sweep a resonant frequency of the variable frequency resonance circuit within a predetermined frequency band so as to sweep the resonant frequency of the antenna resonance circuit.
7. The card communication device according to claim 6 , wherein:
the variable-frequency resonance element further includes a variable capacitor.
8. The card communication device according to claim 7 , wherein the variable-frequency resonance element further includes a battery and a control circuit, the control circuit being connected to the variable-frequency resonance element.
9. The card communication device according to claim 8 , wherein the control circuit is configured utilize as power, a current rectified from a high frequency signal radiated from an antenna of the reader/writer.
10. The card communication device according to claim 6 , wherein a variable frequency band of the variable-frequency resonance element covers the resonant frequency of the antenna resonance circuit.
11. A communication terminal apparatus including a wireless communication tag including an antenna resonance circuit connected to an RFID chip and having a fixed resonant frequency, the antenna resonance circuit including a first coil defining a radiation element capable of sending and receiving a high-frequency signal with a reader/writer, the communication terminal apparatus comprising:
a variable-frequency resonance element, which is an additional device to the wireless communication tag, including a variable-frequency resonance circuit including a second coil being coupled with first coil via an electromagnetic field and also including a control circuit configured to sweep a resonant frequency of the variable-frequency resonance circuit within a predetermined frequency band so as to sweep the resonant frequency of the antenna resonance circuit.
12. The communication terminal apparatus according to claim 11 , wherein:
the variable-frequency resonance element further includes a variable capacitor.
13. The communication terminal apparatus according to claim 12 , wherein the variable-frequency resonance element further includes a battery and a control circuit, the control circuit being connected to the variable-frequency resonance element.
14. The communication terminal apparatus according to claim 13 , wherein the control circuit is configured utilize as power, a current rectified from a high frequency signal radiated from an antenna of the reader/writer.
15. The communication terminal apparatus according to claim 11 , wherein a variable frequency band of the variable-frequency resonance element covers the resonant frequency of the antenna resonance circuit.