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Electromagnetic(EM)waves in the gigahertz(GHz)range are widely applied in wireless communication,networks,high frequency circuit devices,and radar detection producing serious problem like EM interference and information leakage.EM wave absorbing materials with strong microwave absorption ability have been proposed as an effective way to lessen EM pollution and to minimize the detecting probability by radar surveillance in military stealth.An excellent microwave absorption material is required to cover a wide frequency range,have low density and be thin.Traditional EM wave absorbents include carbon materials,rubber,ceramic dielectrics,ferromagnetic alloys and ferrites,etc.Novel nanostructured materials have been investigated as promising microwave absorbing materials.It is acceptable that in order to become an excellent EM wave absorbent,the material needs to possess good impedance matching to allow the incidence of the EM wave and strong absorption performance to attenuate the EM wave.Both the EM parameters characterized by the complex permeability(εr =ε-iε")and the complex permittivity(μr =μ-iμ")and microstructure are important for designing microwave materials with excellent performance.On the basis of our recent studies in the magnetic/dielectric heterogeneous composites,it becomes increasingly attractive to take advantage of their interface polarization and/or point discharge effect to improve EM impedance matching and gain excellent synergistic effect of the dielecticand the magnetic-losses.Magnetic nanocapsules with carbon shells serving as dielectric component were fabricated by arc discharge method.The relative complex permittivity can be adjusted through the dielectric modulation and the mechanism was investigated.Dielectric modulation was carried out by the following ways: introducing silicides into the carbon shells,changing the disorder levels of carbon shells,designing core/double shells nanocapsules and mixing magnetic nanocapsules with conductive materials.