title: Nonlinear alternating current responses of graded materials.
abstract: When a composite of nonlinear particles suspended in a host medium is subjected to a sinusoidal electric field, the electrical response in the composite will generally consist of alternating current (ac) fields at frequencies of higher-order harmonics. The situation becomes more interesting when the suspended particles are graded, with a spatial variation in the dielectric properties. The local electric field inside the graded particles can be calculated by the differential effective dipole approximation, which agrees very well with a first-principles approach. In this work, a nonlinear differential effective dipole approximation and a perturbation expansion method have been employed to investigate the effect of gradation on the nonlinear ac responses of these composites. The results showed that the fundamental and third-harmonic ac responses are sensitive to the dielectric-constant and/or nonlinear-susceptibility gradation profiles within the particles. Thus, by measuring the ac responses of the graded composites, it is possible to perform a real-time monitoring of the fabrication process of the gradation profiles within the graded particles.
authors.affiliation: Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
authors.forename: J P
authors.initials: JP
authors.lastname: Huang
authors.forename: L
authors.initials: L
authors.lastname: Gao
authors.forename: K W
authors.initials: KW
authors.lastname: Yu
authors.forename: G Q
authors.initials: GQ
authors.lastname: Gu