Antenna device and communication device

摘要

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.

主权项

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, the antenna coil having a temperature characteristic in which the inductance is monotonously changed with a temperature change in a use temperature range, and the magnetic sheet being made of a magnetic material having a temperature characteristic of monotonously decreasing 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 the use temperature range and substantially matching a resonance frequency of the resonant circuit with the oscillation frequency in the use temperature range.