Infrared extinction of the powder of brass 70Cu/30Zn calculated by the FDTD and turning bands methods [military smoke screening applications]

The finite-difference time-domain (FDTD) method is used to calculate the specific extinction cross section of the powder of brass 70Cu/30Zn with 10³ to 2.16-10⁵ cubical particles for cell sizes in the range of 0.025 to 0.5 μm at infrared frequency. The digitized models with a random process using the turning bands method are 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 m²/g. While from the experimental measurement, the value of the specific extinction cross section is between 0.58 to 3.78 m²/g. Most of the theoretical results make a good agreement with those obtained from the experimental measurements for the cell sizes of particles in the range of 0.925 to 0.5 μm. From the numerical calculations, it is also found that there is a resonant extinction value occuring at the resonant particle size d₀ which is approximately 2.54-n_p ^-0.293 μm determined by a least square curve fitting method, where n_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. The work has applications to military smoke screening