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

Abstract 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 ( μ ″; 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 ( λ s ), and their frequency ( f r(DIII) ) and magnitude ( μ ″ (DIII) ) of Dispersion DIII were investigated. It was found that the NSS containing flakes with higher λ s exhibited higher f r(DIII) and higher μ ″ (DIII) / μ ″ (DII) , which was ratio of μ ″ (DIII) to the magnitude of Dispersion DII ( μ ″ (DII) ). The f r(DIII) for the NSS having the highest λ s containing Fe-Co alloy flake reached 7.45 GHz and μ ″ 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 Ω, NSS with larger f r(DIII) 2  ·  μ ″ (DIII)  ∝  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 λ s and M s was suitable for suppressing low SHF band noises.