Passive Temperature Sensing Tag for Sensor Networks

A novel passive temperature sensing tag for a long reading range composed of a divided microstrip antenna and a rectifying circuit boosting the DC voltage is proposed. Experimental study of fabricated passive tag using varactor diodes, in which 30 m range response can be achieved in the 4 W EIRP reader at 860-960 MHz band, is described. Passive tags for temperature-monitoring system in the 4 W EIRP reader at 2.45 GHz band are also fabricated to demonstrate validity of proposed tags for a range longer than 9 m. The tags have sizes of 90 times 60 times 4 mm and 60 times 25 times 4 mm for 900 MHz and 2.45 GHz bands, respectively.