@article{cao_yuan_li_2014, title={A super-compact metamaterial absorber cell in L-band}, volume={115}, ISSN={["1089-7550"]}, DOI={10.1063/1.4875835}, abstractNote={A super-compact metamaterial absorber (SMA) unit cell in L band (1–2 GHz) is proposed, which is composed of a pair of electric ring resonator (ERR) and its complementary ERR (CERR) with a high dielectric substrate sandwiched in between. The CERR has a cross sectional area where approximately the etched copper foil in ERR is now retained, and the remaining region is now etched. In contract with quarter-wavelength (λ/4) thickness which is required for conventional absorbers, the largest in-plane dimension and thickness of the SMA cell are only λ/33 and λ/250, respectively, leading to a super compact cell volume. While traditionally the long straight wire is introduced in electric-LC resonators for increasing inductance, the CERR achieves similar inductance with much shorter lengths. Thus, its cell dimensions can be drastically reduced without compromising its performance. In addition, simulations together with an automated phase correction algorithm show that the SMA is a type of metamaterial possessing simultaneous negative electric permittivity (NEP) and negative magnetic permeability (NMP). Further the SMA has a very large imaginary part of the NEP and NMP, resulting in significantly large imaginary part of the refractive index at resonant frequency. These properties are well suited to design excellent absorbers. In addition, numerical results demonstrate that the maximum absorption coefficient of the SMA can reach greater than 99% at resonant frequency, and the full-width half-maximum is roughly 1% of the operating frequency, and a wide incident angle of ±49° over 90% absorption. Meanwhile, it is pointed out that this type of absorber is rather sensitive to polarization characteristic of the incident electromagnetic wave.}, number={18}, journal={JOURNAL OF APPLIED PHYSICS}, author={Cao, Z. X. and Yuan, F. G. and Li, L. H.}, year={2014}, month={May} }
 @article{cao_yuan_li_2014, title={An automated phase correction algorithm for retrieving permittivity and permeability of electromagnetic metamaterials}, volume={4}, ISSN={["2158-3226"]}, DOI={10.1063/1.4882155}, abstractNote={To retrieve complex-valued effective permittivity and permeability of electromagnetic metamaterials (EMMs) based on resonant effect from scattering parameters using a complex logarithmic function is not inevitable. When complex values are expressed in terms of magnitude and phase, an infinite number of permissible phase angles is permissible due to the multi-valued property of complex logarithmic functions. Special attention needs to be paid to ensure continuity of the effective permittivity and permeability of lossy metamaterials as frequency sweeps. In this paper, an automated phase correction (APC) algorithm is proposed to properly trace and compensate phase angles of the complex logarithmic function which may experience abrupt phase jumps near the resonant frequency region of the concerned EMMs, and hence the continuity of the effective optical properties of lossy metamaterials is ensured. The algorithm is then verified to extract effective optical properties from the simulated scattering parameters of the four different types of metamaterial media: a cut-wire cell array, a split ring resonator (SRR) cell array, an electric-LC (E-LC) resonator cell array, and a combined SRR and wire cell array respectively. The results demonstrate that the proposed algorithm is highly accurate and effective.}, number={6}, journal={AIP ADVANCES}, author={Cao, Z. X. and Yuan, F. G. and Li, L. H.}, year={2014}, month={Jun} }