| 摘要 |
PCT No. PCT/JP96/01678 Sec. 371 Date Mar. 25, 1998 Sec. 102(e) Date Mar. 25, 1998 PCT Filed Jun. 19, 1996 PCT Pub. No. WO97/01223 PCT Pub. Date Jan. 9, 1997An antenna coil (21) for generating a magnetic field (25) to supply power to a transponder (26) is energized through switching devices (23 and 24) connected between Vcc and GND of a D.C. power supply (20) and having contacts S1 and S2 that are actuated in opposite phases in accordance with a carrier signal. Both of the switching devices (23 and 24) are turned OFF while the carrier signal is absent. Accordingly, the oscillating current flowing through a series resonance circuit of the antenna coil (21) and a capacitor (22) quickly attenuates, thereby dropping the intensity of the magnetic field (25).
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