Measuring Properties of Composite Magnetic Materials

The availability of novel materials is one of the bases of the development of science and technology. During the last decades, the research on artificial materials exhibiting novel electrical and magnetic properties received significant attention from the scientific and industrial communities. In particular, the so-called metamaterials represent an interdisciplinary field of investigation nowadays and offer promising applications in many fields, such as electromagnetism, optics, thermal, and acoustics. Metamaterials are engineered composite structures which can exhibit physical properties not readily observed in common materials available in nature. Their crucial aspect is to reproduce structured materials, whose repeated elementary cell represents the 'metamolecule.' The linear dimensions of the cells are sub-wavelength. As a consequence, the material behaves uniformly. Special attention was received by metamaterials showing negative values of the effective permittivity and permeability in a given frequency range. In this paper, we revisit the concept of such macroscopic parameters, in particular, from the measurement point of view on a macroscopic scale. Indeed, an accurate characterization of such material properties is a key issue for paving new technological applications. Thus, we start from the very definition of the quantities of interest at a macroscopic level. We focus on the meaning of measurement of magnetism in composite magnetic materials, deriving the relevant measurement models.