Effective negative refractive index of graded granular composites with metallic magnetic particles

The effective refractive index of a granular composite with graded metallic magnetic particles randomly embedded in a host matrix is investigated. Based on differential effective dipole approximation (DEDA) and Clausius-Mossotti relation, we calculated the effective refractive index of the graded granular composite. It is found that there exists a frequency region, where the effective refractive index is negative. And the gradient profiles of permittivity and magnetic permeability inside particles can affect the effective negative refractive index significantly. The gradient profile of permittivity plays more important role in an enhancement of effective negative refractive index than that of magnetic permeability, whereas it is on the contrary in the adjustment of characteristic frequency, at which the effective negative refractive index reaches to a maximum. Therefore, in theoretical, it is possible to gain an enhancement of the effective negative refractive index and appropriate characteristic frequency by adjusting the gradient profiles of permittivity and magnetic permeability inside particles.