Infrared extinction of the powder of brass 70Cu/30Zn modeled through a random process

One of the military applications of electromagnetic absorption and scattering of a powder of brass 70Cu/30Zn (70% of Cu and 30% of Zn) is the tank detection avoidance technique. Tanks must be protected to avoid any detection, and be provided with the best means of protection. The finite-difference time-domain (FDTD) method was used to calculate the specific extinction cross section of the powder of brass 70Cu/30Zn with 10/sup 3/ to 2.16/spl times/10/sup 5/ cubical particles for cell sizes in the range of 0.025 to 0.5 /spl mu/m at infrared frequency. The digitized models with a random process using the turning bands method were simulated for the powder of brass 70Cu/30Zn. From theoretical calculations, the value of the specific extinction cross section of the powder of brass 70Cu/30Zn is between 0.1 to 4.6 m/sup 2//g. While from the experimental measurement, the value of the specific extinction cross section is between 0.58 to 3.78 m/sup 2//g. Most of the theoretical results were in good agreement with those obtained from the experimental measurements for the cell sizes of particles in the range of 0.025 to 0.5 /spl mu/m. From the numerical calculations, it was also found that there was a resonant extinction value at the resonant particle size d/sub 0/ which may be approximately described by 2.54/spl times/n/sub p//sup -0.293/ /spl mu/m determined by a least square curve fitting method, where n/sub p/ is the number of particles. The resonant value calculated by the numerical solution is larger than the maximum value obtained from the experimental measurement.