Multi-frequency interrogation technique applied to conducting polymer gas and odour sensors

Certain electrically conducting polymers, such as polypyrrole, exhibit reversible changes in their direct cut-rent (DC) resistance on exposure to a variety of odours and gases. This phenomenon has immense practical use in a variety of industrial and research environments. Commercially available instruments exploiting this effect employ arrays of conducting polymer sensors, each element of which has broad, but overlapping specificity to a range of volatiles. The authors show that similar descriptors can be generated by using alternating current (AC) measurements over a wide range of frequencies to follow the changes in electrical characteristics of a single sensor. This approach is shown to give rise to impressive improvements in sensor sensitivity and discrimination.