Extinction of carbon-fiber powder calculated by the FDTD and turning bands methods at 35 GHz

The finite-difference time-domain (FDTD) method is used to calculate the specific extinction cross-section (SECS) of the carbon-fiber powder at 35 GHz. The digitized models with a random process using the turning bands method are simulated for the carbon-fiber powder. The digitized models of the carbon-fiber power having 12500 to 5832000 cubical particles with sell sizes in the range of 7 to 100 μm. It is found that the numerical result of SECS obtained by using the diameter of a cylindrical carbon-fiber particle as the cubical cell size for simulations makes good agreement with the measurement data. It is also found that the SECS is directly proportional to the particle number at 35 GHz. It is also found that the maximum extinction occurs at a resonant particle size. Using curve fitting technique together with Newton´s Iteration method, the resonant particle size may be expressed by δ₀=3408×n_p^-0.344 μm, where n_p is the number of particles.