Design and evaluation of noise suppression sheet for GHz band utilizing magneto-elastic effect

Feasibility of realizing a noise suppression sheet (NSS) coping with the low SHF band such as the 5 GHz band was investigated, which was composed of soft magnetic metal flakes dispersed in a polymer. For suppressing noises, the higher frequency one of the bimodal frequency dispersion (lower frequency one: Dispersion DII, higher frequency one: Dispersion DIII) seen in the imaginary permeability (mu ''; magnetic loss component) spectrum of the NSS was aimed to utilize. Referring to the previous finding that Dispersion DIII is originated from a magneto-elastic effect, several magnetic composite sheets were prepared using various alloy flakes with different saturation magnetostriction (lambda(s)), and their frequency (f(r(DIII))) and magnitude (mu ''((DIII))) of Dispersion DIII were investigated. It was found that the NSS containing flakes with higher lambda(s) exhibited higher f(r(DIII)) and higher mu ''((DIII))/mu ''((DII)), which was ratio of mu ''((DIII)) to the magnitude of Dispersion DII (mu ''((DII))). The f(r(DIII)) for the NSS having the highest lambda(s) containing Fe-Co alloy flake reached 7.45 GHz and mu '' in the 5 GHz band was approximately twice as high as the conventional NSS containing Fe-Si-Al alloy flake. For transmission attenuation power ratio (R-tp) when an NSS was placed on a microstrip line with characteristic impedance of 50 Omega, NSS with larger f(r(DIII))(2) . mu ''((DIII)) (sic) M-s(2) (M-s: saturation magnetization), which theoretically gave the frequency limit of imaginary permeability for a thin film, exhibited larger R-tp in the low SHF band. These results suggested that an NSS containing a magnetic flake material with both large lambda(s) and M-s was suitable for suppressing low SHF band noises. (C) 2017 Elsevier B.V. All rights reserved.