Dispersion of dielectric composites : quasi-dynamic characterizations and applications

Characterization of the dispersion of macroscopic electromagnetic properties of composite materials is a challenging task, but it offers an efficient and effective path to interpret features or phenomena, and to design artificial structures with desired properties. In this thesis, the quasi-dynamic homogenization is performed to characterize the dispersive electric properties of a class of dielectric composites. Although their geometry configurations are very simple, many fundamental yet significant features as well as problems appear during the quasi-dynamic homogenization process, and are thus studied in detail. The quasi-dynamic region is defined to include the quasi-static one and the frequency range close to the quasi-static limit. This thesis focuses on various homogenization models and techniques. In addition, the homogenization results by the proposed techniques are applied to explore several significant homogenization-related problems, such as quantification of the quasi-static limit, evaluation of a homogenization model, as well as the temporal pulse dynamics in dielectric (composite) materials

Different homogenization methods based on scattering parameters of dielectric-composite slabs

The dispersion of the effective permittivity of a dielectric-composite slab is analyzed in a quasi-dynamic range using the simulated transmission and reflection data from the slab illuminated by an obliquely incident plane wave. Based on the retrieval results, the procedure for finding the dynamic trust region of the quasi-static Lord Rayleigh estimate for the effective permittivities of such composites is then developed. According to this process, the upper frequency limit of this trust region is numerically determined by an interpolation function. The proposed function of the inclusion area fraction p and relative permittivity ɛi is demonstrated as a good predictor within the ranges 0.1 ≤ p ≤ 0.5 and 10 ≤ ɛi ≤ 60. It is further shown that within the above ranges the effective wavelength inside the material should be at least 33 times the edge length of the unit cell, in order to ensure that the defined relative difference between the retrieved effective permittivity and the quasi-static estimate is not larger than 1%.Peer reviewe

Analytical characterization of antennas loaded with finite-grounded complementary split ring resonator

The Complimentary Split Ring Resonator (CSRR) is now popular in microwave devices. However, the analytical interpretations of its resonance frequencies, especially that with finite grounds, remains elusive. We demonstrate in this letter a novel method of unveiling the resonance mechanisms of antennas loaded with a finite-grounded CSRR (FG-CSRR) based on the equivalent circuit models. As a proof-of-concept, a triple-band antenna with FG-CSRR structure is explored, whose inner patch is loaded with additional elements with negligible impact on the inherent resonances of FG-CSRR. Various FG-CSRR-loaded antennas with different parameters are furthermore applied to validate our method. The proposed analytical model would facilitate the design of the operating mechanism of these antennas. Moreover, less metallic coating and the independent resonances of FG-CSRR promise its suitability for miniaturized microwave systems

Meta-Imaging

AAM 12 kk embargo / mmImaging equipment is one of the most powerful tools for the human to explore the world. Devices utilizing various portions of the electromagnetic spectrum are developed to reveal the fine details of objects and extend the sensing range. Recently, the advent of metamaterials/metasurfaces has significantly advanced the evolution of both imaging components and techniques. Many promising imaging methods based on metamaterials/metasurfaces arise owing to their superior spatial modulation capabilities over the electromagnetic waves. This review focuses on applications of metamaterials/metasurfaces in the electromagnetic/optical imaging, and summarizes the recent developments of metamaterial/metasurface imaging in a new perspective, which can be categorized into the non-computational and the computational ones. First, the purposes, principles, methodology of non-computational meta-imaging are presented, which covers the evanescent-wave-collecting lens with sub-diffraction-limited imaging potentials and the focal metalens with Fourier transformation functionalities. Second, the principles of various computational meta-imaging methodologies are elucidated, including mainly the Born approximation, the synthetic aperture radar, and the ghost imaging. Finally, a brief conclusion and prospects to meta-imaging will be provided.Peer reviewe

Ultrathin Multi-mode Fabry-Perot-Cavity With Wide Phase Resonance Bandwidth Enabled By Janus Partially Reflective Surface

Publisher Copyright: IEEEFabry-Perot-Cavity (FPC) of a less than λ/2 height often suffers from a narrow phase resonance bandwidth. This is mainly due to the violated cavity phase condition originating from the single intracavity resonance mode. By enriching the mode, the phase resonance relationship can be expanded and made easier to meet within a broader band. The enriched intracavity resonance mode is accomplished by an anisotropic Janus partially reflective surface which offers three types of reflection phase. By combining the resonance bandwidth of each mode, an FPC with a wide phase bandwidth is obtained. The ultrathin cavity is implemented by an isotropic artificial magnetic conductor. Finally, based on this FPC, a reflection-type FPC antenna adopting an external feed antenna is designed. The FPC antenna achieves a 3-dB gain bandwidth of 20.8% (5.47−6.74 GHz) with a peak gain of 14.0 dBi under a 0.3 mm (λ/180) cavity which reduces the profile of the reflection-type FPC antenna. The S11 performance of the antenna keeps less than−10 dB within 5.50−6.67 GHz.Peer reviewe

A large field-of-view metasurface for complex-amplitude hologram breaking numerical aperture limitation

Owing to the potential to manipulate simultaneously amplitude and phase of electromagnetic wave, complex-amplitude holographic metasurfaces (CAHMs) can achieve improved image-reconstruction quality compared with amplitude-only and phase-only ones. However, prevailing design methods based on Huygens–Fresnel theory for CAHMs, e.g., Rayleigh–Sommerfeld diffraction theory (RSDT), restrict acquisition of high-precision reconstruction in a large field of view (FOV), especially in the small numerical aperture (NA) scenario. To this end, a CAHM consisting of Sine-shaped meta-atoms is proposed in a microwave region, enabled by a novel complex amplitude retrieval method, to realize large FOV holograms while breaking the large NA limitation. Calculations and full-wave simulations demonstrate that the proposed method can achieve superior-quality holograms, even for nonparaxial holograms in a relatively small NA scenario, thus improving FOV and aperture utilization efficiency of CAHMs. The reconstruction comparison of a complex multi-intensity field distribution between CAHM prototypes designed by our method and by RSDT further confirms this point. We also compare both theoretically and experimentally the CAHM by our method with the phase-only metasurface by weighted Gerchberg–Saxton algorithm. Superior-quality holograms with suppressed background noise and relieved deformation, promised by the extra amplitude manipulation freedom, is witnessed. Finally, due to its wavelength irrelevance, the proposed method is applicable to the entire spectrum, spanning from microwave to optics