Abstract

We demonstrate composite media with ferromagnetic wires that exhibit a frequency region at the microwave regime with scattering spectra strongly dependent on an external magnetic field or stress. These tunable composite materials have recently been proposed theoretically; however, no direct experimental verification has been reported. We used composite materials with predominantly oriented CoFeCrSiB glass-coated amorphous wires having large magnetoimpedance at GHz frequencies. The free-space measurements of reflection and transmission coefficients were conducted in the frequency range 1-8 GHz in the presence of an external static magnetic field or stress applied to the whole sample. In general, the transmission spectra show greater changes in the range of 15 dB for a relatively small magnetic field of 5-10 Oe or stress of 0.1 MPa. The obtained results are quantitatively consistent with the theoretical spectra predicted by the effective medium arguments for permittivity in conjunction with the wire electric polarization dependent on the ac surface impedance. A number of applications of proposed materials are discussed, including the field tunable microwave surfaces and the self-sensing media for the remote nondestructive evaluation of structural materials.