HIGH-FREQUENCY AC INVESTIGATION OF CONDUCTING POLYMER GAS SENSORS

Conducting organic polymers may be used for the detection of vapours a nd gases. A new development is the interrogation of conducting polymer sensors using high-frequency a.c. measurements. This new gas-sensing technique needs investigation of the electrical behaviour at high freq uency (1 MHz-1 GHz) of a number of organic conducting polymers. A sens or prototype consisting of two straight parallel copper strips on a fi breglass substrate and a polypyrrole (PPY) layer deposited between the m is used for this purpose. A mathematical model of this prototype has been developed using transmission-line theory for modelling its respo nse over the frequency range 1 MHz-1 GHz. The model permits one to obt ain the input sensor impedance versus frequency when the PPY complex p ermittivity (versus frequency, temperature, humidity, gas concentratio n, etc.) is known, and vice versa.