Abstract
Radar absorbing materials (RAMs) also known as microwave absorbers, which can absorb and dissipate incident electromagnetic wave, are widely used in the fields of radar-cross section reduction, electromagnetic interference (EMI) reduction and human health protection. In this study, the synthesis of functionally graded material (FGM) (CI/Polyurethane composites), which is fabricated with semi-sequentially varied composition along the thickness, is implemented with a genetic algorithm (GA) to optimize the microwave absorption efficiency and bandwidth of FGM. For impedance matching and broad-band design, the original 8-layered FGM was obtained by the GA method to calculate the thickness of each layer for a sequential stacking of FGM from 20, 30, 40, 50, 60, 65, 70 and 75 wt% of CI fillers. The reflection loss of the original 8-layered FGM below –10 dB can be obtained in the frequency range of 5.12∼18 GHz with a total thickness of 9.66 mm. Further optimization reduces the number of the layers and the stacking sequence of the optimized 4-layered FGM is 20, 30, 65, 75 wt% with thickness of 0.8, 1.6, 0.6 and 1.0 mm, respectively. The synthesis and measurement of the optimized 4-layered FGM with a thickness of 4 mm reveal a minimum reflection loss of –25.2 dB at 6.64 GHz and its bandwidth below – 10 dB is larger than 12.8 GHz.
Highlights
The elimination of unwanted electromagnetic radiation with the use of radar absorbing materials (RAM) or microwave absorbers has important implications in the fields of stealth technology for aircrafts and warships, electromagnetic interference (EMI) shielding of electronic devices for high-speed wireless communication, and protection of human health from overexposure of electromagnetic emissions in the gigahertz (GHz) range
The reflection loss of the original 8-layered functionally graded material (FGM) below –10 dB can be obtained in the frequency range of 5.12∼18 GHz with a total thickness of 9.66 mm
Further optimization reduces the number of the layers and the stacking sequence of the optimized 4-layered FGM is [20, 30, 65, 75] wt% with thickness of 0.8, 1.6, 0.6 and 1.0 mm, respectively
Summary
The elimination of unwanted electromagnetic radiation with the use of radar absorbing materials (RAM) or microwave absorbers has important implications in the fields of stealth technology for aircrafts and warships, electromagnetic interference (EMI) shielding of electronic devices for high-speed wireless communication, and protection of human health from overexposure of electromagnetic emissions in the gigahertz (GHz) range. Carbonyl iron (CI) particles possessing relatively low permittivity, high Curie temperature, and high specific saturation magnetization intensity, 4πMS and high resistivity can be embedded in an insulating polymer matrix to become an effective magnetic absorber for the higher frequency ranging from 2 to 18 GHz.[1,2,3,4,5] a single layer of magnetic absorber possesses narrow bandwidth and the bandwidth cannot be widened through the increase of thickness nor the weight percentage of the magnetic fillers. Graded materials (FGMs) are a new class of two-component composite materials in which the composition or the microstructure is varied in one specific direction. Compared with a single-layered absorber, the FGM-typed absorber can increase the microwave absorbing efficiency and widen
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