Yoichi Wada

Composite electromagnetic wave absorber made of permalloy or sendust and effect of sendust particle size on absorption characteristics

The effects of the size and shape of sendust particles on the absorption characteristics of composite electromagnetic wave absorbers made of polystyrene resin and sendust were investigated. We also investigated the difference in the absorption characteristics between permalloy and sendust. The sendust particles were granular or flakes and those of permalloy were granular. The size of sendust particles was varied in the range from approximately 5 to 20μm. A metal-backed single layer absorber made of a composite containing small sendust particles absorbed more than 99% of electromagnetic wave power in the frequency range from 1 to 3GHz. The values of the real part μr of the relative complex permeability μ ∗ r for both magnetic materials became less than unity and had a minimum value at frequencies above 10 GHz. The composite made of small sendust particles exhibited a return loss of less than −20 dB at frequencies near 35GHz for a suitable sample thickness.

Effect of sendust particle size on absorption characteristics of composite electromagnetic wave absorber

The effects of the particle size of sendust, which is an alloy of Al 5%, Si 10%, and Fe 85%, on the absorption characteristics of composite electromagnetic wave absorbers made of polystyrene resin and sendust were investigated in the frequency range from 1 to 40 GHz. The size of sendust particles was varied between approximately 5 and 20 m. A metal-backed single-layer absorber made of 20 m sendust particles absorbed more than 99% of electromagnetic wave power at frequencies above 20 GHz. Meanwhile, a composite made of 5 m particles exhibited a return loss of less than −20 dB in the frequency range of not only several GHz but also above 30 GHz. In addition, the relative complex permeability r* was shown to be controlled by adjusting the particle size of sendust, and an electromagnetic wave absorber with a flexible design was proposed.

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

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

Design of Composite Electromagnetic Wave Absorber Made of Soft Magnetic Materials Dispersed and Isolated in Polystyrene Resin

Composite electromagnetic wave absorbers made of a soft magnetic material (permalloy or sendust) and polystyrene resin were investigated. The volume mixture ratio of magnetic material was varied in the range from 18 vol% to 75 vol%. The composites with the low volume mixture ratio of soft magnetic material absorbed more than 99% of electromagnetic wave power in the frequency rage from 1 GHz to 12 GHz. The values of the real part μr of the relative complex permeability μr for both magnetic materials were less than unity at frequencies above approximately 6 GHz as the volume mixture ratio of magnetic material increased. This result suggests the possible realization of an electromagnetic wave absorber that can operate above 10GHz.