Modelling infrared extinction of high aspect ratio, highly conducting small particles

Infrared extinction cross sections and volume extinction coefficients have been calculated for high aspect ratio cylindrical fibres and thin disc flakes with microscale and nanoscale minor dimensions. The extinction dependence on conductivity and particle dimension has been predicted. A range of scattering models have been employed and include the method of moments, the finite difference time domain method and the exact analytical solutions for an equivalent surface area sphere (Mie theory) and an infinite cylinder. Choice of model depended upon particle size, geometry and conductivity. Experimental measurements of extinction for metal flake samples were also performed and compared to the theoretical predictions. Extremely large volume extinction coefficients (> 1000 m(2) cm(-3)) are predicted for selected major dimension and sufficiently large aspect ratios and conductivity. Corrections to the bulk conductivity have been made due to the particle minor dimension being of the order of the mean free electron path length. Optimum particle minor dimensions resulting in maximum volume extinction have been identified for a given conductivity.