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We theoretically investigate multifrequency cloak based on multishell by using transformation medium. As for each shell, we use the Maxwell–Garnett theory and the spectral representation theory to design the permittivity profile for the transverse magnetic wave. The plasma frequencies of the metals used in the inner (B) and outer (C) shells must satisfy ω1<ωpC<ω2<ωpB. In such case, incident electromagnetic wave of lower frequency ω1 will be distorted only by the outer shell C without entering the inner shell B to achieve invisibility. However, at the higher operating frequency ω2, the outer shell C is transparent by choosing the materials appropriately, and the incident electromagnetic wave will be distorted only by the inner shell B to achieve invisibility. So, the multishell cloak can work simultaneously on two different optical frequencies. Furthermore, we use the anisotropic differential effective dipole theory to evaluate the efficiency of the cylindrical cloak. [ABSTRACT FROM AUTHOR]

We apply a Langevin model to investigate the nonlinear ac responses of electro-magnetorheological (ERMR) fluids under the application of two crossed dc magnetic (z axis) and electric (x axis) fields and a probing ac sinusoidal magnetic field. We focus on the influence of the magnetic fields which can yield nonlinear behaviors inside the system due to the particles with a permanent magnetic dipole moment. Based on a perturbation approach, we extract the harmonics of the magnetic field and orientational magnetization analytically. To this end, we find that the harmonics are sensitive to the degree of anisotropy of the structure as well as the field frequency. Thus, it is possible to real-time-monitor the structure transformation of ERMR fluids by detecting the nonlinear ac responses. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A theoretical study of the dielectrophoretic (DEP) spectrum of a pair of touching colloidal particles or biological cells in a host fluid under the application of a nonuniform alternating current (ac) electric field is presented. The main objective of this work is to investigate the correlation effects due to the presence of mutual polarization on the DEP spectrum. In particular, we employ the multiple image method to account for the effect of multiple images, and obtain an analytic expression for the DEP force. It is found that, at low frequencies, the DEP force can be enhanced (reduced) significantly for the longitudinal (transverse) field case due to the presence of multiple images. The numerical results can be well understood in the spectral representation theory. To first order in the dipole interaction, our results reduce to the established formula derived by an alternative method. Our approach demonstrates the importance of the correlation effects in ac electrokinetic phenomena of colloidal suspensions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]