Tag responsive to high-frequecy for varying capacitance of tuning capacitor

DETAILED DESCRIPTION This invention aims to provide a RF-TAG capable of obtaining an optimum supply voltage and an information exchange system using it.
The RF-TAG according to this invention is provided with a tuning circuit which has a tuning coil and a tuning capacitor and receives a high frequency wave having a tuning frequency, a power source which rectifies the output of the tuning circuit to obtain an operating power, a receiver which receives electrical power from the power source to receive a signal from the tuning circuit, and a transmitter which receives electrical power from the power source to supply a transmission signal to the tuning circuit.
Also, the tuning capacitor is characterized by that its capacitance is variable.
Thus, this invention can vary a capacitance of the tuning capacitor.
A change in capacitance of the tuning capacitor can adjust the tuning frequency to suit a radio wave transmitted.
Consequently, the variations occurring in the production process can be compensated to suitably receive the radio wave.
Sufficient electrical power can be derived from the radio wave transmitted and a range of the transmitted radio wave can be increased.
In addition, the tag of this invention is provided with a temperature sensor which detects a temperature, a memory which stores capacitance values of the tuning capacitor optimum for temperatures, and a capacitance value adjusting means which adjusts the capacitance values of the tuning capacitor; and is characterized by that an optimum capacitance value of the tuning capacitor at a detected temperature is read from the memory and a capacitance value of the tuning capacitor is set to an optimum capacitance value.
Thus, optimum capacitance values corresponding to temperatures are stored in the memory to control the capacitance of the tuning capacitor according to temperatures, constantly enabling satisfactory receipt of a radio wave regardless of a change in temperature.
The information exchange system according to this invention is a system for exchanging prescribed information using a plurality of RF-TAGs which derive electrical power from a high-frequency wave transmitted from an antenna installed at a prescribed position, and effect communications with the antenna