ANTENNA DEVICE AND COMMUNICATION DEVICE

• US 20130169398A1
• Filed: 11/16/2011
• Published: 07/04/2013
• Est. Priority Date: 12/01/2010
• Status: Active Grant

• Current Assignee: Dexerials Corporation
• Original Assignee: Dexerials Corporation
• Inventors: Sugita, Satoru, Yokota, Toshiaki, Takahashi, Yoshimi, Orihara, Katsuhisa
• Granted Patent: US 9,082,545 B2
• Time in Patent Office: Days
• US Class Current: 336/179
• CPC Class Codes: H01F 38/14 Inductive couplings for wireless supply or distribution of electric power using inductive coupling H02J50/10
• CPC Class Codes: H01Q 1/002 Protection against seismic waves, thermal radiation or other disturbances, e.g. nuclear explosion; Arrangements for improving the power handling capability of an antenna
• CPC Class Codes: H01Q 1/2225 used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
• CPC Class Codes: H01Q 1/243 with built-in antennas
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop

Abstract

An antenna device, capable of stable communications without increasing a space of the entire device by keeping a resonance frequency substantially constant even if the temperature changes, includes: an antenna circuit having an antenna coil with an electrically connected capacitor; the coil receiving a magnetic field transmitted from a reader/writer at a predetermined oscillation frequency; the circuit becoming communicable when inductively coupled to the reader/writer; and a magnetic sheet formed at a position superposed on the coil to change its inductance, wherein the coil has a temperature characteristic in which the inductance is changed with a temperature change, and the sheet has a temperature characteristic of changing the inductance to achieve a characteristic inverse to the inductance change with the temperature change in a predetermined use temperature range, and substantially matching a resonance frequency of the circuit with the oscillation frequency in the use temperature region.

Claims

1. An antenna device comprising:

a resonant circuit having an antenna coil and a capacitor electrically connected to the antenna coil, the antenna coil receiving a magnetic field transmitted from a transmitter at a predetermined oscillation frequency, the resonant circuit becoming communicable when inductively coupled to the transmitter; and

a magnetic sheet to be formed at a position superposed on the antenna coil to change an inductance of the antenna coil, wherein

the antenna coil has a temperature characteristic in which the inductance is changed with a temperature change, and

the magnetic sheet is made of a magnetic material having a temperature characteristic of changing the inductance of the antenna coil so as to achieve a characteristic inverse to the change of the inductance of the antenna coil with the temperature change in a predetermined use temperature range and substantially matching a resonance frequency of the resonant circuit with the oscillation frequency in the use temperature region.

2. The antenna device according to claim 1, wherein

the antenna coil has a temperature characteristic in which the inductance is monotonously changed with the temperature change in the use temperature range, and

the magnetic sheet has a temperature characteristic of monotonously decreasing the inductance of the antenna coil with the temperature change in the use temperature range.

3. The antenna device according to claim 2, wherein

the magnetic sheet is a ferrite with a Sb oxide and a Co oxide contained in a Ni—

Zn—

Cu-based magnetic material.

4. The antenna device according to claim 3, wherein

the magnetic sheet is made of the ferrite containing 0.7 weight % to 1.25 weight % of the Sb oxide in Sb₂O₃ terms and 0 to 0.2 weight % of the Co oxide in CoO terms.

5. A communication device comprising:

a resonant circuit having an antenna coil and a capacitor electrically connected to the antenna coil, the antenna coil receiving a magnetic field transmitted from a transmitter at a predetermined oscillation frequency, the resonant circuit becoming communicable when inductively coupled to the transmitter;

a magnetic sheet to be formed at a position superposed on the antenna coil to change an inductance of the antenna coil; and

a communication processing unit to be driven by a current flowing through the resonant circuit to perform communications, wherein

the antenna coil has a temperature characteristic in which the inductance is changed with a temperature change, and

the magnetic sheet is made of a magnetic material having a temperature characteristic of changing the inductance of the antenna coil so as to achieve a characteristic inverse to the change of the inductance of the antenna coil with the temperature change in a predetermined use temperature range and substantially matching a resonance frequency of the resonant circuit with the oscillation frequency in the use temperature region.