Design and application of a wireless, passive, resonant-circuit environmental monitoring sensor

A wireless, passive, remote query sensor platform is presented capable of m onitoring the complex permittivity of a surrounding medium, temperature, hu midity, and pressure. The sensor is a planar two-dimensional inductor-capac itor circuit, of scaleable-size, that resonates at a characteristic frequen cy the value of which is dependent upon the parameters of interest. The res onant frequency of the sensor is detected remotely with one or a pair of lo op antennas by measuring the impedance or voltage spectrum of the antenna(s ), with the environmental parameters of interest then calculated from the m easured resonant frequency. The wireless, remote query nature of the platfo rm enables the LC sensor to monitor the environmental conditions from withi n sealed opaque containers. The paper describes the operational principles, design criteria, illustrative applications, and performance limitations of the sensor platform. (C) 2001 Elsevier Science B.V. All rights reserved.