Enhanced magnetic permeability and electromagnetic noise suppression by sieved and oriented large flaky sendust particles

In order to obtain enhanced permeability and electromagnetic noise suppression at low frequency, microwave absorbing composites with oriented large flaky sendust particles are proposed. Large sendust particles with an averaged aspect ratio of more than 100 that is twice the existing value are obtained by a simple sieving method, which are found to have almost equivalent saturation magnetization (Ms) but lower coercivity (Hc) with respect to other small-size particles because of increased shape anisotropy. The improvement in magnetic permeability by large particles at low frequencies is slight but can be greatly promoted by orientation of the particles using a blade coating method due to the maximum shape anisotropy effect. Consequently, the bandwidth that has power loss ratio of electromagnetic noise suppression more than 90% extends its lower boundary from 2.2 GHz to 1.3 GHz. This work not only provides a simple solution to low frequency noise suppression, but also reveals the effectiveness of further increasing particle size of flaky absorbents on improving magnetic permeability in the assistance of particle orientation.