Microwave absorption of lambda/4 wave absorbers using high permeability magnetic composites in quasimicrowave frequency band

Abstract

For the aim of thin electromagnetic wave absorbers used in quasimicrowave frequency band, this study proposes the high-permeability magnetic composite sheets of quarter wavelength thickness (lambda/4 spacer) coated with resistive film of 377 Omega/sq (impedance transformer). For the lambda/4 spacer, flexible magnetic composite sheets containing Fe(85)Si(9.5)Al(5.5) flake particles are used. Due to high permeability and high permittivity of the composite sheets, lambda/4 thickness can be reduced as low as 0.5 mm in 2 GHz. By coating the conductive paste with surface resistance close to 377 Omega/sq on the lambda/4 spacer, the reflection loss can be reduced to as low as -11 dB (90% power absorption). This is attributed to the wave impedance matching led by the resistive film of free-space impedance combined with a lambda/4 thickness of high-permeability magnetic spacer. (C) 2008 American Institute of Physics.