Smart Composites With Short Ferromagnetic Microwires for Microwave Applications

Smart composites with short-cut Co_68.7Fe₄Ni₁B₁₃Si₁₁Mo_2.3 microwires were prepared and studied in terms of their microwave tunable properties. It is shown that the frequency dependence of effective permittivity relaxes with the application of magnetic field till around the anisotropy field of the microwire due to the increase of internal losses. There exists a significant field tunable effect in the transmission and reflection spectra, featured as a resonance-relaxation transformation; a step-like shift of reflection phase was also observed with increasing applied magnetic field, which can be exploited especially for the sensing applications such as field/stress monitoring. Notably, with increasing microwire concentration from 0.06 cm^-2 to 0.24 cm^-2 , the microwave absorption is more than doubled; the reflection phase shift corresponding to the magnetic field change from 500 to 1000 A/m is also increased from 1.2 to 1.3. These results indicate that the developed short-wire composites have the potential for microwave absorption and remote sensing applications.