Effective Epsilon-near-zero Research Articles

5 GHz high gain slotted SIW epsilon near zero antenna array for wireless communications

New types of antennas such as Substrate Integrated Waveguide (SIW) antennas are being used for high frequency applications. In this paper, the development of an array of novel slotted SIW epsilon near zero (ENZ) antenna is presented. Due to the limited fabrication facilities, the study is conducted in the 5 GHz band. The effective permittivity falls to zero at the cut off frequency of the waveguide. This impact is utilized to make an effective ENZ material in an ENZ super tunnelling waveguide. The design of 1 × 2, 1 × 4 antenna array is presented. The design of microstrip power dividers for feeding the array element is discussed. The presented antenna array achieve higher gain than the previously designed antennas. The prototype of the 1 × 4 SIW ENZ antenna array is fabricated and the measurement results are compared with the simulated studies. This work pertains to investigation on the array of SIW antennas for millimetre wave applications.

Effective Epsilon-Near-Zero (ENZ) Antenna Based on Transverse Cutoff Mode

In this paper, inspired by the homogeneous field configuration and the exotic flexibility of the epsilon-near-zero (ENZ) metamaterial, an effective ENZ antenna is proposed with length-irrelevant operating frequency and controllable radiation pattern. In our approach, the ENZ response is achieved by using the substrate-integrated waveguide at its cutoff frequency, with two open ends for radiation. Interestingly, this transverse cutoff mode decouples the operating frequency and the spacing distance between the radiating apertures, such that the radiation pattern can readily be adjusted by stretching or even bending the structure without changing the operating frequency. The prototypes with straight and planar-curved styles are designed and experimentally tested, both working on transverse cutoff mode at 3.5 GHz while offering the difference pattern and the broadside fan-shape pattern, respectively. The measured radiation patterns are in a good agreement with the simulation, with the peak total efficiencies higher than 63%. In addition, the high quality factor with narrow bandwidth (~0.5%) is observed and discussed. With devisable radiation pattern and extremely low profile ( $\sim 0.02\lambda _{0}$ ), the proposed ENZ antenna exhibits promising potentials for sensing, conformal, and reconfigurable applications.

Exceptional points and spectral singularities in active epsilon-near-zero plasmonic waveguides

We present a nanoscale active plasmonic waveguide system consisting of an array of periodic slits that can exhibit exceptional points and spectral singularities leading to several novel functionalities. The proposed symmetric active system operates near its cut-off wavelength and behaves as an effective epsilon-near-zero (ENZ) medium. We demonstrate the formation of an exceptional point (EP) that is accessed with very low gain coefficient values, a unique feature of the proposed nanoscale symmetric plasmonic configuration. Reflectionless ENZ transmission and perfect loss-compensation are realized at the EP which coincides with the effective ENZ resonance wavelength of the proposed array of active plasmonic waveguides. When we further increase the gain coefficient of the dielectric material loaded in the slits, a spectral singularity occurs at the ENZ resonance leading to super scattering (lasing) response at both forward and backward directions. These interesting effects are achieved by materials characterized by very small gain coefficients with practical values and at subwavelength scales due to the strong and homogeneous field enhancement inside the active slits at the ENZ resonance leading to enhanced light-matter interaction. We theoretically analyze the obtained EP, as well as the divergent spectral singularity, using a transmission-line model and investigate the addition of a second incident wave and nonlinearities in the response of the proposed active ENZ plasmonic system. Our findings provide a novel route towards interesting nanophotonic applications, such as reflectionless active ENZ media, unidirectional coherent perfect absorbers, nanolasers, and strong optical bistability and all-optical switching nanodevices.

Tunable nonlinear coherent perfect absorption with epsilon-near-zero plasmonic waveguides.

We propose a scheme to realize nonlinear coherent perfect absorption (CPA) at the nanoscale using epsilon-near-zero (ENZ) plasmonic waveguides. The general conditions to achieve CPA in a linear ENZ plasmonic waveguide are analyzed and presented. The proposed ENZ waveguides support an effective ENZ response at their cutoff frequency, where the CPA effect occurs under the illumination of two counterpropagating plane waves with equal amplitudes and appropriate phase distributions. In addition, the strong and uniform field enhancement inside the nanochannels of the waveguides at the ENZ resonance can efficiently boost Kerr nonlinearities, resulting in a new all-optical switching intensity-dependent CPA phenomenon that can be tunable with ultrafast speed. The proposed free-standing ENZ structures combine third-order nonlinear functionality with standing wave CPA interference effects in a nanoscale plasmonic configuration, thus leading to a novel degree of tunable light-matter interactions achieved in subwavelength regions. Our findings provide a new platform to efficiently excite nonlinear phenomena at the nanoscale and design tunable coherent perfect absorbers.

Spoof surface plasmons tunneling through an epsilon-near-zero material channel

In this paper, squeezing and tunneling of spoof surface plasmon polaritons (SSPPs) are realized by introducing an effective epsilon-near-zero (ENZ) material channel between two plasmonic waveguides constructed from dielectric filled rectangular waveguide etched with deep sub-wavelength periodical transverse slots on the upper wall. The tunneling frequency can be flexibly tuned by changing the relative permittivity of the effective ENZ material and the SSPPs can tunnel efficiently through a straight or an arbitrarily bent effective ENZ channel with ultra-low loss. This simple design holds great promise in significantly increasing the propagation length or arbitrarily tuning the propagation direction of the SSPPs in the microwave and terahertz frequencies.

Supercoupling of surface waves withε-near-zero metastructures

It is known that $\ensuremath{\epsilon}$-near-zero (ENZ) structures may provide exciting possibilities for light-matter interaction, including the phenomenon of supercoupling, i.e., channeling of wave energy through ultranarrow conduits connecting two waveguides. Here, we extend this concept to the surface waves using structures with effective ENZ properties, exploring how surface waves can tunnel through such structures with essentially no reflection, even in the presence of sharp bends. Such ENZ metastructures support tunneling of waves with longitudinal wave numbers near zero. The surface waves may include examples of transverse electric (TE) surface waves along the grounded dielectric slabs (e.g., in the microwave regime) and TE surface-plasmon polariton waves along the negative-permeability interfaces. The ENZ metastructures can transfer the surface wave energy from one side to another by an anomalous squeezing effect, which is effectively independent of the length and the shape of the ENZ metastructures. The interaction of electromagnetic waves with such systems offers exciting possibilities for the design of flat photonic devices and components.

Multi-passband tunneling effect in multilayered Epsilon-Near-Zero Metamaterials

Recently, several experimental results verified the tunneling effect theory of that the electromagnetic energy can be squeezed through an ultra-narrow channel filled with epsilon-near-zero (ENZ) medium. However, the energy squeezing can be only achieved in a narrow region. Here, we present a full-wave simulation of the tunneling effect in multilayered channels full of thin ENZ metamaterials with different plasma frequencies. Thin metallic wires arrays with different radiuses are employed to form these effective ENZ media, whose plasma frequencies are different. The appearance of several passbands in the transmission curve verifies that multi-passband energy tunneling effect can be implemented by multilayer ENZ channels. There are two possible reasons for these peaks, one is the ENZ tunneling effect, and the other is the Fabry-Pérot resonance. For each transmission peak corresponding two-spatial maps of electric field are given, in order to distinguish the causes.