Taiwei Yue

Compact, Wideband Antennas Enabled by Interdigitated Capacitor-Loaded Metasurfaces

In this paper, a class of integrated metasurface (MS)-based planar antennas are proposed, which are fed by monopoles operating below their fundamental modes. Various interdigitated capacitor (IC) loading schemes for a metallic sheet backed MS are investigated, which provide footprint miniaturization and bandwidth enhancement. A linearly polarized (LP) MS-based antenna, loaded by ICs, provides a 15% impedance bandwidth and a gain higher than 6.67 dBi. The radiation mechanism and resonant frequency dependence were revealed via a dispersion analysis, which serves to explain the working principle of the proposed antenna. Next, a miniaturized antenna with doubly loaded ICs was introduced, achieving an impedance bandwidth of 10%, a gain above 6 dBi, and a more than 30% footprint reduction. A more advanced compact, circularly polarized (CP) MS-based antenna with a compact footprint, and improved 3-dB axial ratio (AR) bandwidth were also presented, by introducing triangular IC and diagonal slot loadings to the MS. It is demonstrated that this antenna achieves an impedance bandwidth of 16%, a gain above 5.5 dBi, and an AR <;3 dB bandwidth of 10%. Three antenna prototypes were fabricated and measured, with good correspondence between the experimental results and simulation predictions, confirming the proposed design methodologies. These compact and well-performing MS-based antennas have promising potential for applications in modern wideband wireless systems.

Handedness Dependent Electromagnetically Induced Transparency in Hybrid Chiral Metamaterials

We provide the first experimental demonstration of the handedness dependent electromagnetically induced transparency (EIT) in chiral metamaterials during the interaction with circularly polarized waves. The observed chiral-sensitive EIT phenomena arise from the coherent excitation of a non-radiative mode in the component split ring resonators (SRRs) produced by the corresponding Born−Kuhn type (radiative) resonators that are responsible for the pronounced chirality. The coherent coupling, which is dominated by the bonding and antibonding resonances of the Born−Kuhn type resonators, leads to an extremely steep dispersion for a circularly polarized wave of predefined handedness. Accordingly, retrieved effective medium parameters from simulated results further reveal a difference of 80 in the group indices for left- and right-handed circularly polarized waves at frequencies within the EIT window, which can potentially result in handedness-sensitive pulse delays. These chiral metamaterials which enable a handedness dependent EIT effect may provide more degrees of freedom for designing circular polarization based communication devices.

Closed-Form Expressions for the Radiation Properties of Nanoloops in the Terahertz, Infrared and Optical Regimes

Since the pioneering work of Heinrich Hertz, perfect-electric conductor (PEC) loop antennas for RF applications have been studied extensively. Meanwhile, nanoloops are promising in the optical regime for their applications in a wide range of emerging technologies. Unfortunately, analytical expressions for the radiation properties of conducting loops have not been extended to the optical regime. This paper presents closed-form expressions for the electric fields, total radiated power, directivity, and gain for thin-wire nanoloops operating in the terahertz, infrared and optical regimes. This is accomplished by extending the formulation for PEC loops to include the effects of dispersion and loss. The expressions derived for a gold nanoloop are implemented and the results agree well with full-wave computational simulations, but with a speed increase of more than 300×. This allows the scientist or engineer to quickly prototype designs and gain a deeper understanding of the underlying physics. Moreover, through rapid numerical experimentation, these closed-form expressions made possible the discovery that broadband super-directivity occurs naturally for nanoloops of a specific size and material composition. This is an unexpected and potentially transformative result that does not occur for PEC loops. Additionally, the Appendices give useful guidelines on how to efficiently compute the required integrals.

A low-profile unidirectional antenna enabled by interdigital capacitor loaded metasurface

In this paper, a compact footprint and low-profile metasurface-enabled unidirectional antenna that operates from 4.11GHz to 4.26GHz with a center frequency at 4.2GHz is presented. The miniaturized metasurface, which has a reflection phase of -150 degree at 4.2GHz, was made possible by interdigital capacitor loading, resulting in a unit cell with an electrical dimension of only 0.02λ02. A finite-sized metasurface with two by three elements was integrated with a planar microstrip fed monopole antenna, enabling a total antenna footprint of around 0.13λ02 and a thickness of 0.05λ0. Full-wave simulations show that, even with such a small footprint, the antenna achieves a large front-to-back ratio and a high gain within the targeted operational frequency band.

A compact dual-band patch antenna enabled by complementary split ring resonator loaded metasurfaces

Metasurfaces, also known as metafilms, have recently been developed by researchers for various applications that exploit their exotic electromagnetic characteristics which cannot be found in nature. These applications include compact filter designs, electromagnetic cloaking and illusion coatings, miniaturized waveguides, and many new types of antennas with enhanced functionalities. Specifically, metasurfaces have been proven to be particularly beneficial in patch antenna designs. Among these designs, metasurfaces have been introduced as artificial ground planes and/or radiating components, which are comprised by unit cells arranged in a one-dimensional or two-dimensional periodic array configuration. By virtue of these metasurfaces, highly-directive radiating beam(s), compact antenna form factors, high radiation efficiency, and multiple frequency-bands/operational-modes along with other desired features of patch antennas can be realized. In this contribution, we demonstrate that a complementary split ring resonator loaded metasurface can be employed to design a compact dual-band antenna. The compact size of our proposed dual-band antenna is attributed to the well-known capability of complementary split ring resonators for miniaturizing numerous microwave devices, including patch antennas. Moreover, due to the self-resonance of the complementary split ring resonators, the resonant frequency associated with the dominant mode of the original patch antenna is split into two modes, thereby giving rise to a dual-band functionality. The novel metasurface-enabled patch antenna proposed here not only possesses compact size, but also realizes multiple operational bands, making it a promising candidate for todays highly-integrated communication systems.

Theoretical derivation of the radiation parameters for thin-wire nanoloop antennas

Conducting loops have been rigorously analyzed in the microwave/RF regime due to their simplicity and versatility. In the terahertz, infrared and optical regimes nanoloops are extremely promising for a variety of applications, including as solar cells or optical sensors. However, due to the complex behavior of metals, a complete theoretical derivation of the radiation parameters of a nanoloop at these frequencies has not yet been performed. This paper will extend the formulation of thin-wire Perfect-Electric Conductor (PEC) loops to include the effects of loss and dispersion. Closed form expressions for the radiated fields, directivity and gain will be presented. The expressions involve integrals of Bessel and Lommel-Weber functions as well as Q-type integrals. Various series representations for these integrals will be presented along with guidelines on which are the most efficient. Validation of the equations will be provided through a comparison with full-wave solvers. While these simulations take on the order of hours, the analytical expressions can be evaluated on the order of seconds.

A highly-confined dielectric waveguide enabled by conformal anisotropic impedance surfaces

In this paper, we report the analysis, design, and experimental validation of a conformal coating approach for achieving a highly-confined mode in a dielectric waveguide with a low dielectric constant. By controlling the surface electromagnetic response of the anisotropic impedance surface, it is shown that the original loose confinement of the guided mode of the dielectric waveguide can be dramatically improved over a broad bandwidth. The tensor impedance surface was further realized by an array of short dipole elements and characterized. The good agreement between simulated and measured results confirms the proposed concept and associated design methodology.

Compact dual-band dual-polarized antenna enabled by a CSRR loaded metasurface

In this paper, the design of a compact dual-band dual-polarized antenna with unidirectional radiation patterns is introduced. The metasurface, loaded with complementary split ring resonators (CSRRs) not only converts the linearly polarized (LP) signal radiated by the monopole antenna to a circularly polarized (CP) signal in the broadside direction, but also provides dual-band dual-polarized functionality. Based on full-wave simulations, it is found that the proposed antenna can achieve RHCP and LHCP within the first and the second operational band respectively with moderate gain performance around 6 dBi and high front-to-back ratio (FBR).

Reconfigurable nanowire assembly enabled field-switchable broadband polarizers

In this paper, a switchable broadband polarizer based on the electric field directed reconfigurable assembly of gold nanowires (NWs) is presented. Taking advantage of the collective optical properties of the two-dimensional gold NW lattices, we have experimentally demonstrated that transmission of linear polarized light can be purposely controlled using a dual electrode design to reversibly rotate the lattice by 90° on-demand. In addition, our experiments reveal that the transmission control is closely related to the geometrical dimensions of the NWs as well as the applied electric field conditions.

A compact dual-band dual-mode metasurface-enabled antenna

In this paper, a compact dual-band dual-mode antenna based on metasurface technology is proposed. Through full-wave simulations, it is found that the proposed antenna can achieve broadside and end-fire radiation at two distinct operational frequency bands centered at 1.94 GHz and 2.50 GHz, respectively. The proposed antenna is a promising candidate for many emerging applications including on/off-body communication systems.