Composite Electromagnetic Wave Absorber Made of Soft Magnetic Material Particle and Metal Particle Dispersed in Polystyrene Resin

Abstract

The development of an electromagnetic wave absorber suitable for frequencies higher than 1 GHz is required with the increasing use of wireless telecommunication systems. Moreover, new wireless telecommunication devices will be developed owing to the advances in the information and telecommunication field in the future. For this reason, electromagnetic wave absorber suitable for these new devices is required, especially at frequencies above 10 GHz. In this chapter, we deal with a metal-backed single-layer absorber that has a low cost and is easy to fabricate. To design a metal-backed single-layer absorber, the control of the frequency dependences of the relative complex permeability μr* and the relative complex permittivity ┝r* is important because the absorption of an electromagnetic wave is determined by both μr* and ┝r*. In particular, μr’, the real part of μr*, must be less than unity to satisfy the non-reflective condition of electromagnetic wave for a metal-backed singlelayer absorber at frequencies above 10 GHz. Therefore, the frequency dependences of μr*, ┝r*, and the absorption characteristics of a composite made of a soft magnetic material dispersed in an insulating matrix have been investigated (aKasagi et.al., 1999; Lim et. al., 2005; Song et. al., 2005). However, the frequency dependences of μr’ and μr”, the imaginary part of μr*, has not been investigated at frequencies above 10 GHz. Thus, for the purpose of designing electromagnetic wave absorbers with good absorption properties at frequencies above 10 GHz, the frequency dependences of μr*, ┝r*, and the return loss were investigated for the composite made of particles of soft magnetic material dispersed in polystyrene resin in the frequency range from 100 MHz to 40 GHz. Soft magnetic material used in this study is sendust (an alloy of Al 5%, Si 10%, and Fe 85%), because sendust is a low-cost material and does not contain any rare metals and sendust is suitable for use in a practical absorber. In addition, the frequency dependences of μr*, ┝r*, and the return loss of the composite made of permalloy (an alloy of Ni 45%, Fe 55%) were also investigated for the comparison. Both sendust and permalloy have high permeability values in the frequency range above 1 GHz. This characteristic makes it possible to fabricate an electromagnetic wave absorber suitable for this frequency band. Moreover, the values of μr’ for the composite made of sendust or permalloy dispersed in polystyrene resin are expected to be less than unity because of the natural magnetic resonance and magnetic moment