Conducting polymer composite materials for smart microwave windows

Samples of poly(aniline)-silver-polymer electrolyte particulate composites have been characterised at microwave frequencies when small d.c. electric fields (similar to 10V cm(-1)) are applied across them in both coaxial line and waveguide measurement test sets. The experimental data shows that the initial conductivity of the materials is dependent on the concentration of silver metal and suggests that changes in resistance due to chemical switching take place, at least in part, in the manufacture of the composites. When silver is used as the electrodes, the experimental data show that changes in the slope of the cyclic voltammograms coincide with large changes in microwave reflectivity or transmission consistent with increasing conductivity of the composites when fields are applied. The reverse change occurs when the fields are removed. Measurements have shown that the composites are able to switch between the two impedance states in times of less than one second for well over a million cycles with no apparent depreciation in material properties. Large area (29x21cm) films have also been prepared and studied using the 'free space' technique.