Optimum design of wave absorbers using foamed polyimide containing carbon black based on genetic algorithm

In this paper, a foamed polyimide which has a feature of light-weight and heat-resistance have been focused attention on using in the way of a lossy dielectric material. As an expression of heat-resistance, relative permittivity of respective heating temperature was measured. As the results, both real and imaginary part of relative permittivity decreased by 5.0 and 6.4% compared to non-heating at 300°C, but each of them decreased by 22.1 and 45.3% at 400°C. An empirical formula was calculated using the measured results when the content rate of carbon black changed. Then a two-layered type wave absorber was designed based on genetic algorithm. Its characteristics indicated the center frequency of 38 GHz, 20 dB fractional bandwidth of 51.3%, and measurements of absorption characteristics gave close agreement with designed ones.