Tunable Microwave Composites Containing Ferromagnetic Microwires
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1223-EE03-04
Tunable Microwave Composites Containing Ferromagnetic Microwires Mihail Ipatov 1, Larissa Panina 2, Gloria R. Aranda 1, Valentina Zhukova 1, Arcady Zhukov 1 and Julian Gonzalez 1 1
Dpto. Física de Materiales, Facultad de Química, Paseo Manuel de Lardizabal3, Universidad del País Vasco, 20018 San Sebastián, Spain. 2
School of Computing, Communications and Electronics, University of Plymouth, Drake Circus, Plymouth, Devon PL4 8AA, UK.
ABSTRACT The effect of the external magnetic field on the dispersion of the effective permittivity in arrays of parallel CoFe-based amorphous wires is demonstrated by measuring S-parameters in free space in the frequency band of 0.9-17 GHz. The magnetic field is applied along the wires sensitively changing their magnetization and high frequency impedance. Based on the measurements of magneto-impedance in a single wire and transmission/reflection spectra of composites in free space, we show the correlation between magneto-impedance and the field dependence of the effective permittivity.
INTRODUCTION The response of a homogeneous material to electromagnetic radiation is described by two macroscopic parameters: dielectric permittivity ε and magnetic permeability µ. Artificially structured materials often referred to as metamaterials can be also assigned certain averaged εef and µef with values not readily found in natural materials. In particular, utilising conducting fibres in composites makes it possible to engineer diluted dielectrics with unusual frequency dispersion of εef in the GHz frequency band [1-4]. In composites containing periodically arranged arrays of continuous parallel metallic wires, the effective permittivity is of a plasmonic type having a negative real part below the plasma frequency. These composites have attracted much interest as a constitute part of a metamaterial with simultaneously negative εef and µef [5,6]. Whilst the practical realisation of fascinating properties of such materials (superimaging, invisibility) is still doubtful, they can be useful to realize tunable and self-sensing materials with electromagnetic properties dependent on external stimuli or an internal state of the material. For example, a material with self-monitoring properties could be able to visualize structural damages, defects, excessive loadings, local stress and temperature distribution, thus be suitable for in-situ health monitoring of large scale objects such as infrastructure (bridges, buildings, etc.). Previously, similar effects have been investigated in short-cut magnetic wire composites having damped resonance dispersion of the effective permittivity [7-11]. It was demonstrated that underlying physical mechanism involves the dependence of the system damping on the surface impedance of the wire and magnetoimpedance effect (MI) at GHz frequencies. In the case of periodic lattices of continuous wires, the dispersion of the effective permittivity is demonstrated to also depend on the surface impedance of wires. Therefore, for MI-wire grids ,
the microwave response
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