| 摘要 |
<P>PROBLEM TO BE SOLVED: To effectively prevent radio wave interference occurring in a RF (Radio Frequency) tag system. <P>SOLUTION: A radio wave limiting device 5 is arranged at a side facing a reader/writer 1 by placing an RF tag 4 therebetween. If a frequency measuring portion and an electric field strength measuring portion measure a frequency f and a field strength E of a carrier transmitted from the reader/writer 1, a control signal formation portion and a transmitter oscillate and output a signal having the same frequency as that of the received signal and adjust the amplitude of the signal to be equal to the strength E of the received signal. Then, if the control signal formation portion changes the phase of a signal generated by an oscillator to the opposite phase and appends a phase differential θ to the signal according to a distance between a receiving antenna and a transmitting antenna, a disturbance wave is transmitted to a direction opposite to an incoming direction of the received radio wave signal by the transmitting antenna. <P>COPYRIGHT: (C)2009,JPO&INPIT |
