Abstract

Several sensors are provided for determining one of a number of physical properties including pressure, temperature, and other physical conditions. In general, the sensors feature a resonant circuit with an inductor coil which is electromagnetically coupled to a transmitting antenna. When an excitation signal is applied to the antenna, a current is induced in the sensor circuit. This current oscillates at the resonant frequency of the sensor circuit. The resonant frequency and bandwidth of the sensor circuit is determined using an impedance analyzer, a transmitting and receiving antenna system, or a chirp interrogation system. The resonant frequency may further be determined using a simple analog circuit with a transmitter. The sensors are constructed so that either the resonant frequency or bandwidth of the sensor circuit, or both, are made to depend upon the physical properties such as pressure, temperature, presence of a chemical species, or other condition of a specific environment. The physical properties are calculated from the resonant frequency and bandwidth determined.