Experimental demonstration of tunable scattering spectra at microwave frequencies in composite media containing CoFeCrSiB glass-coated amorphous ferromagnetic wires and comparison with theory

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 10dB for a relatively small magnetic field of few Oe or stress of 0.1 MPa. The obtained results are quantitatively consistent with the analytical expressions predicted by the effective medium arguments. The incident electromagnetic wave induces an electrical dipole moment in each wire, the aggregate of which forms the effective dipole response of the whole composite structure in the radiative near or far field region. The field and stress dependences of the effective response arise from a field or tensile stress sensitivity of the ac surface impedance of a ferromagnetic wire. In the vicinity of the antenna resonance the variations in the magnetoimpedance of the wire inclusions result in large changes of the total effective response. A number of applications of proposed materials is discussed including the field tunable microwave surfaces and the self-sensing media for the remote non-destructive evaluation of structural materials.

Engineering of giant magnetoimpedance effect of amorphous and nanocrystalline microwires

“…In the case of plasmonic wire arrays, this will result in considerable decrease in the absolute value of the permittivity and will enhance the wave propagation. Similarly, in cut-wire composites, the increase in relaxation broadens the permittivity dispersion which may even show transformation from resonance to relaxation behaviour [1][2][3]. Therefore, in composites containing ferromagnetic wires exhibiting GMI effect at GHz frequencies the effective permittivity will depend on the wire magnetic properties via the corresponding dependence of its impedance.…”

“…Composite structural materials containing periodic or random arrays of metallic wires often referred to as wire metamaterials have a strong dispersion of the dielectric function in the GHz frequency band. This behaviour could be of plasmonic or resonance type for long or short-cut wires, respectively [1,2]. In both cases, the real part of the permittivity can be negative in the dispersion region resulting in many fascinating effects including negative refraction and frequency selective band-gap or band-pass regimes [1][2][3].…”

“…One of the perspective materials is the tuneable metamaterial utilising thin ferromagnetic wires exhibiting magnetoimpedance effect (MI) [1,2]. Our and some other groups work demonstrates that this leads to powerful adjustment of their electromagnetic properties, in particular, effective permittivity, by a weak magnetic field or a mechanical stress [1][2][3]. Composite structural materials containing periodic or random arrays of metallic wires often referred to as wire metamaterials have a strong dispersion of the dielectric function in the GHz frequency band.…”

“…This behaviour could be of plasmonic or resonance type for long or short-cut wires, respectively [1,2]. In both cases, the real part of the permittivity can be negative in the dispersion region resulting in many fascinating effects including negative refraction and frequency selective band-gap or band-pass regimes [1][2][3]. In thin conducting wires the currents that are responsible for effective permittivity are constrained with the associated resonances determined by the geometrical parameters.…”

Stress and field contactless sensor based on the scattering of electromagnetic waves by a single ferromagnetic microwire

“…9 There is much literature regarding microwave related applications of microwires or microwire-based materials. [20][21][22][23][24] Some of these articles have nicely shown how different arrangements of microwires forming arrays or embedded in different types of matrixes may be used for enhancing their sensitivity as GMI elements. In particular, the use of specific frequency dispersion of the wire arrays leads to outstanding GMI response.…”