Effects of wire properties on the field-tunable behaviour of continuous-microwire composites

The microwire composites consisting of continuous Co-rich amorphous glass-coated ferromagnetic microwires embedded in a E-glass prepreg matrix were fabricated, and the influences of wire periodicity (b), composition and radius on the field-tunable properties have been systematically investigated in a broad microwave frequency range of 0.9-18 GHz. It has been found that the field tunability, effective operational frequency and field of the composites are strongly dependent on these factors. With decreasing b from 15 to 7 mm, the field tunability of effective permittivity (nɛ) increases from 0.77% to 16% m/A by more than 20 times. The detected cups and resonances of the transmission and reflection spectra are identified. Their changes with wire periodicity have been shown to be due to a combination of the dielectric and magnetic response arising from the interactions between microwave and microwires and microwires by themselves. The best possible field tunability occurs below the plasma frequency. The effective magnetic field for realisation of the field-tunable properties has been found to be about 500 A/m, which is associated with the anisotropy field. In addition, field tunability is found to be positively correlated with the magnetic softness and GMI properties of the wire fillers, which are determined by the wire composition and geometry. These findings are of practical importance in developing multifunctional microwire composites for a broad range of engineering applications, such as structural health monitoring, NDT and microwave tunable devices.