Application of Fe-based Alloy Powder to Noise Suppression Sheet for GHz-band

The communication frequency band for small communication terminals are shifting to the Super High Frequency (SHF) band (3 GHz – 30 GHz) by the 5th generation mobile communication system (5G). Accordingly, a Noise Suppression Sheet (NSS), which have been used to solve electromagnetic interference problems inside small communication terminals, are required to have effective noise attenuation characteristics in the SHF band. The NSS is a composite sheet of flat magnetic powder and polymer. Noise attenuation characteristics of the NSS is mainly determined by the imaginary part (μ
r
´´) of the complex specific permeability. In this study, the design guideline of the NSS for SHF band was verified by measuring μ
r
´´ spectra of NSS to which flat powders obtained from Fe-based alloy powders with different phases were applied. Fe-based alloy powders with multiple crystalline phases tend to become flat powders with low aspect ratio by micro-forging. It is shown that powder design with high saturation magnetization and low aspect ratio is important to realize effective NSS in the SHF band.