Influence of magnetic and dielectric loss of polymer composites containing magnetic flake particles (Sendust,Permalloy) on noise absorption in microstrip lines

Magnetic and dielectric loss have been systematically controlled by using two kinds of high-permeability particles with different electrical conductivity (Sendust, Permalloy), and the effect of the magnetic and dielectric loss on the noise-absorbing properties has been investigated. Noise-absorbing sheets are composite materials of magnetic flake particles of high aspect ratio dispersed in a polymer matrix. The frequency dispersion of the complex permeability was almost the same for the Sendust and Permalloy composite specimens. However, the complex permittivity of the Permalloy composite (ε _r′ ≈ 250, ε _r″ ≈ 50) was much greater than that of the Sendust composite (ε _r′ ≈ 70, ε _r″ ≈ 0). Enhancement of the space-charge polarization between the highly conductive Permalloy particles results in the high values of ε _r′ and ε _r″. Due to the large dielectric loss of the Permalloy composite (in addition to its inherent magnetic loss), the bandwidth of noise absorption is increased, especially in the lower frequency region. Dielectric loss should be considered in the design of broad-bandwidth noise-absorbing composites.