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Peierls transition that modifies electronic band structure has attracted intensive attention in solid state physics. In the present work, a photonic analog of Peierls transition has been observed in a 1-D triangular metal diaphragm array, where the photonic bandgap structures have been designed at will by adjusting periodically the metal diaphragm positions. It is shown by the numerical analysis that the transmission and radiation effect of the present periodic metal structure designed through the Peierls transition rule exhibits the behavior significantly different from the original periodic structure with each unit cell containing a metal diaphragm. The near- and far-field measurement results are in good agreement with our theoretical simulation. The present effect of photonic Peierls transition can serve as a working mechanism for designing new types of guided wave devices. It can be seen that the photonic Peierls transition would be one of the simplest ways for modifying the transport characteristics of periodic structures.

The traditional use of cement for soil stabilisation is challenged by peat due to the high organic content in peat and the associated unfavourable environmental and economic impacts. This study explores the potential and benefits of using manufactured sand, an economical, easily accessible and environmentally friendly construction material, with cement for peat stabilisation. Experiments were conducted with a view to investigating the optimal dosage of manufactured sand and cement, as evidenced by the improvement in the physico-chemical and mechanical qualities of stabilised peat. Based on the required strength of 1.00 MPa in engineering practice, an optimal configuration was determined with the ratio of manufactured sand to peat being 5:5, and the cement content 36.15%. At the optimal configuration, the unconfined compressive strength of stabilised peat was 2.33 times greater than the specimens without sand, and the void ratio was reduced from 1.72 of natural peat to less than 0.58. Optimal configuration can reduce cement dosage by 36.36%, hence carbon emissions by 36.36%, and costs by 38.28%. This study established that using manufactured sand with cement offered an economical, efficient and environmentally friendly engineering solution to peat stabilisation.

A viable wide-band circuit model of parallel corrugated differential transmission line is established. By solving for the even- and odd-modes in this structured differential transmission line, the equivalent capacitance, inductance, resistance, and conductance per unit length are calculated, then the characteristic impedances of differential and common signals are obtained. The ${S}$ -parameters obtained from the equivalent circuit model agree well with the full-wave simulation results with a deviation of only about 0.036 dB in the frequency range of 10 GHz. Experimentally, the characteristic impedances are measured for the differential and common signals using a time domain reflectometer (TDR). The deviation between the experimental and theoretical results was less than 1.05%. Based on the equivalent circuit model, it is feasible to implement this type of structured differential line directly into real circuits.

We have theoretically investigated surface magnetoplasmons (SMPs) in a waveguide consisting of a uniaxial μ -near-zero (UMNZ) material slab sandwiched between two ferrite materials with opposite remanences. It is shown that this waveguide can support robust unidirectional SMP (USMP), whose electric field extends almost uniformly in the UMNZ layer, hence USMP can acquire modal sizes far larger than the wavelength. We have demonstrated that such large-area USMP (LUSMP) provides many degrees of freedom to manipulate waves. Using LUSMP, waves can be completely trapped with hot spots of wavelength size.

We propose a uniform backfire-to-endfire leaky-wave antenna (LWA) based on a topological one-way waveguide under external bias magnetic field. We systematically analyze the dispersion, showing that the proposed structure supports leaky mode arisen from total internal reflection. By means of tuning frequency or magnetic field, we obtain fixed-bias frequency and fixed-frequency bias LWA with continuous beam scanning from backward, broadside to forward direction. More importantly, we, for the first time, demonstrate that this proposed LWA shows mechanical tunability, allowing us to manipulate the radiation direction from backward, broadside to forward direction by mechanically tuning the air layer thickness. The simulated results show that our system exhibits super low 3dB beam width, high radiation efficiency as well as high antenna gain. Being provided such multiple controlled (especially mechanically) beam scanning manners, the present LWA paves an advanced approach for continuous beam scanning, holding a great potential for applications in modern communication and radar system.

In this paper, the characteristics of a class of transmission lines which support spoof surface plasmon polaritons are investigated both numerically and experimentally. In order to provide the characteristic impedance of spoof surface plasmon polaritons for PCB designers, the equivalent circuit parameters of the microstrip line periodically structured on subwavelength scale are extracted with the numerical method. It is found that the equivalent circuit parameters significantly vary with frequency when the subwavelength periodic structure is introduced into the edge of the conventional microstrip line. The results of time-domain measurements show that spoof surface plasmon polaritons have remarkable advantage over conventional microstrip lines and can be directly used in actual high-speed circuits, which is helpful for eliminating the doubts whether the metamaterials can be directly used in actual circuits.

Nowadays, the terahertz (THz) communication is believed to be a potential solution to the communication blackout for reentry vehicles. In this paper, a numerical hypersonic fluid model was introduced to obtain the realistic plasma sheaths. The onboard antenna which is installed on the wall was assumed to be conformal. The transmission of obliquely incident THz waves in the plasma sheaths was analyzed. According to this paper, the power transmission coefficient decreases with the increase of reentry speed since both the electron density and the electron collision frequency near the onboard antenna increase with the reentry speed. In addition, the relation between the wave transmission and the reentry speed is revealed. The power transmission coefficient decreases with the increase of incident angle, because the conformal antenna cannot receive the field component which is perpendicular to the wall. Two supplemental schemes to enhance the transmission rate for THz signals were discussed based on this paper.

One-way electromagnetic mode that is guided by the mechanism of total internal reflection (TIR) can be realized in terahertz regime. In the optical system consisting of a dielectric layer sandwiched between magnetized semiconductor and metal, the one-way TIR mode can be immune to backscattering at imperfections. This mode possesses a broad band when high-order TIR modes are suppressed in the relevant semiconductor bandgap. Furthermore, it is shown that compared with one-way surface magnetoplasmons, the one-way TIR mode can more effectively match with the fundamental mode of conventional optical waveguide.

A lattice Boltzmann model is presented for simulating heat transfer with phase change in saturated soil. The model includes a quartet structure generation set for creating soil structure, double di...

Photonic crystal (PhC) consisting of a square lattice of ferrite rods with remanence in the air is theoretically investigated. It is shown that such a PhC can possess a large band gap with a nontrivial topological property. By interfacing the PhC with different cladding materials, which have (bulk-mode) band gaps with different topological properties, different types of one-way modes that are immune to backscattering are achieved in the absence of an external magnetic field. It is numerically demonstrated that by using such one-way modes, waves can be flexibly and effectively manipulated in PhC systems without almost any power loss.

Ultrawideband unidirectional surface magnetoplasmons (USMPs) are theoretically achieved in both planar and coaxial configurations without an external magnetic field. It is shown that the two proposed structures, which are formed by ferrite layers with opposite remanences, can support USMP without low-frequency cutoff, thus the USMP bandwidth is increased at least twice compared to (microwave) USMPs previously reported. For the coaxial structure, the dispersion of USMP is closely dependent on the thickness of the ferrite layers, and based on this, USMP can be slowed down significantly by reducing the ferrite-layer thickness. Moreover, by using a tapered coaxial structure, subwavelength focusing can be realized with a giant enhancement of the magnetic field.

We propose a Leaky-Wave Antenna (LWA) based on one-way yttrium-iron-garnet (YIG)-air-metal waveguide. We first analyze the dispersion of the LWA, showing the one-way feature and the radiation loss. Owing to the unique one-way dispersive property, the beam radiated from the LWA can have very narrow beam width, at the same time having large scanning angle. The main beam angle obtained by full-wave simulation is consistent with our theoretical prediction with the aid of the dispersion. For a given frequency, we can realize continuous beam scanning by varying the magnetic field, where the 3 dB beam width is much narrower than previously demonstrated. Our results pave a new way to realize continuous angle scanning at a fix frequency for modern communications.

Two-dimensional materials supporting deep-subwavelength plasmonic modes can also exhibit strong magneto-optical responses. Here, we theoretically investigate magnetoplasmons (MPs) in monolayer black phosphorus (BP) structures under moderate static magnetic fields. We consider three different structures, namely, a continuous BP monolayer, an edge formed by a semi-infinite sheet, and finally, a triangular wedge configuration. Each of these structures shows strongly anisotropic magneto-optical responses induced both by the external magnetic field and by the intrinsic anisotropy of the BP lattice. Starting from the magneto-optical conductivity of a single-layer of BP, we derive the dispersion relation of the MPs in the considered geometries, using a combination of analytical, semi-analytical, and numerical methods. We fully characterize the MP dispersions and the properties of the corresponding field distributions, and we show that these structures sustain strongly anisotropic subwavelength modes that are highly tunable. Our results demonstrate that MPs in monolayer BP, with its inherent lattice anisotropy as well as magnetically induced anisotropy, hold potential for tunable anisotropic materials operating below the diffraction limit, thereby paving the way for tailored nanophotonic devices at the nanoscale., Comment: 5 pages, 3 figures

Trapped rainbow effects have been realized in many systems while they are all characterized by electric-field enhancement. The trapped rainbow with strong magnetic-field enhancement has yet to be studied. Here, we achieve the trapped magnetic rainbow effect in a novel metal-air-YIG (yttrium-iron-garnet)-metal (MAYM) waveguide applied with a continuously decreasing magnetic field. The proposed system supports a one-way propagation feature, leading to the suppressed reflection. We systemically analyze the dispersion and the modal properties, showing the transition from the SMP (surface magnetoplasmon)-like mode to magnetostatic-like mode and the change of the group velocity when decreasing the external magnetic field along thepropagation direction of the wave. We obtain the trapped magnetic rainbow effects as well as magnetic hotspots both in frequency- and time-domain simulations. The trapped rainbow effect with strong magnetic field enhancement paves a promising way for many applications including magnetic sensing to magnetic non-linearity.

Ferrimagnetic material with remanence holds the potential to realize unidirectional propagation of the electromagnetic field by taking advantage of magnetoplasmon in the subwavelength regime. Here, we theoretically investigate magnetoplasmons in a layered structure consisting of a dielectric sandwiched by two magnetic materials with anti-parallel remanent magnetization directions, which shows a complete unidirectional propagating region for both even and odd symmetry modes when the thickness of the dielectric is smaller than a certain value. Additionally, the even symmetry mode supported by such a one-way waveguide can be effectively, with low insertion loss, excited by the fundamental transverse-electric mode of a traditional metal slab waveguide. Relying on low insertion loss and a one-way propagation feature, we propose a broadband and subwavelength isolator working at the microwave region. Our results demonstrate that remanence based magnetoplasmons provide a promising way to realize devices below the diffraction limit with new functionalities.

Surface magnetoplasmon (SMP) supported at an interface between magnetized plasmonic and dielectric materials has been widely explored; however, it suffers with narrow bandwidth for one-way propagation. Here we propose a novel metal-semiconductor-dielectricmetal (MSDM) structure showing the large bandwidth for the complete one-way propagation (COWP). Because of the compression of the zone for two-way propagating modes in the semiconductor layer by reducing semiconductor thickness, the bandwidth is significantly increased by several times. More importantly, in such MSDM structure, the SMP dispersion can be engineered by controlling the semiconductor thickness, and based on this, slowing wave and trapping rainbow can be realized in a tapered system at terahertz frequencies.

The subwavelength focusing based on surface plasmon polaritons (SPP) has been widely explored in tappered metallic structures. However, the efficiency of energy localization is relatively weak, largely due to high propagation loss and strong back reflection. Here, we propose a straight-tapered 3-dimensional (3D) one-way surface magnetoplasmon (SMP) waveguide with the ending surface of $\sim 10^{-4}\lambda_0 \times 10^{-4}\lambda_0$ to achieve the energy focusing in the microwave regime. Due to low propagation loss of SMP, we achieve huge magnetic field enhancement in such an ultra-subwavelength area, by five orders of magnitude. Instead of using an external static magnetic field, our proposed SMP waveguide replies on remanence, which is very convenient for operating practical 3D applications. These results show promising applications in magnetic-field enhancing or quenching fluorescence, luminescence or nonlinearity of 2D materials, novel scanning near-field microwave microscopy and energy storage.

A lattice Boltzmann model is proposed to simulate the forming process of artificial frozen soil wall. The enthalpy method is applied to deal with the latent-heat source term, and the adjustable thermal diffusivity is utilized to handle the change of thermophysical parameters. The model is tested by the heat conduction with solid&ndash, liquid phase change in semi-infinite space, which shows a good consistence between the numerical and analytical solutions, and the mesh resolution has little effect on the numerical results. Lastly, the development of frozen soil wall is discussed when the freezing pipes are arranged in a square. The results show that the evolution of temperature field with time is closely related to the distance from the freezing pipe. For the soil near freezing pipe, the temperature gradient is larger, the soil temperature drops rapidly and freezes in a short time. The time history curve of temperature is relatively smooth. For the soil far away from freezing pipe, the temperature evolution curve has obvious multistage, which can be divided into four stages: cooling, phase change, partly frozen and completely frozen. The spacing of freezing pipes has a significant influence on the overlapping time of artificial frozen soil wall, and there is a power function relationship between them.

A platy isolator for plane waves at microwave frequencies is proposed and investigated theoretically. The isolator is a layered structure which consists of a dielectric layer sandwiched by two yttrium-iron-garnet (YIG) layers with opposite remanences. In this isolator structure, there exists a nonreciprocal transverse resonance within the band gap of the YIG materials. The guiding mode related to the transverse resonance exhibits one-way propagation and simultaneously possesses a dispersion band within the light cone in air. Therefore, this nonreciprocal transverse resonance can be excited in the isolator by plane waves incident from air. By using the transfer matrix method, it is shown that high isolation and efficient transmission can be achieved for the proposed isolator without external magnetic field.

Surface magnetoplasmons (SMPs) in the three-layer structure of semiconductor, dielectric, and photonic crystal (PhC) are theoretically investigated. The PhC portion in the structure is designed properly so that its band gap covers the one-way propagation range of SMPs. In such an all-dielectric system, robust one-way propagation is available for SMPs at terahertz frequencies, and SMP band gap also occurs due to the PhC effect. With the use of a heterostructure of dielectric layer in the all-dielectric system, two different approaches for trapping terahertz radiation are proposed and verified by numerical simulations.

Rainbow trapping arisen from slow light effect has been attracted lots of attention for the past two decades. However, until now only unidirectional rainbow trapping has been proposed, which relies on a complicated configuration or technique. Here we propose and investigate a metal–dielectric-semiconductor-dielectric-metal structure, where the semiconductor layer is applied with an external DC magnetic field. We show that in such a waveguide configuration there exist branches of dispersion curves showing slow-light bands at finite propagation constants. The positions of the slow-light bands can be tuned by varying the thickness of the semiconductor or the dielectric layers in the waveguide. By tapering the waveguide, we first demonstrate bidirectional rainbow trapping in such a simple waveguide configuration, and more importantly the trapped rainbow can be easily released by changing the external magnetic field.

In their paper in Optica 6, 104 (2019)OPTIC82334-253610.1364/OPTICA.6.000104, Mann et al. claim that linear, time-invariant nonreciprocal structures cannot overcome the time-bandwidth limit and do not exhibit an advantage over their reciprocal counterparts, specifically with regard to their time-bandwidth performance. In this Comment, we argue that these conclusions are unfounded. On the basis of both rigorous full-wave simulations and insightful physical justifications, we explain that the temporal coupled-mode theory, on which Mann et al. base their main conclusions, is not suited for the study of nonreciprocal trapped states, and instead direct numerical solutions of Maxwell’s equations are required. Based on such an analysis, we show that a nonreciprocal terminated waveguide, resulting in a trapped state, clearly outperforms its reciprocal counterpart; i.e., both the extraordinary time-bandwidth performance and the large field enhancements observed in such modes are a direct consequence of nonreciprocity.

Magnetoplasmon and guided modes of a coaxial waveguide constituted by a hollow cylinder made of a magnetized magneto-optical material and a metal wire at the axis are investigated, showing their dispersion relation and electromagnetic field distribution are highly influenced by the operating frequency and the physical dimensions of the structure. It is demonstrated that there exist three different types of modes, that is bulk-mode, surface mode and regular mode. By adjusting the operating frequency and reducing the inner diameter of the hollow cylinder, regular mode is suppressed and only the surface mode remains, which shows one-way propagating property. Moreover, one-way surface mode is robust against backscattering at defect and surface roughness, which has a good potential in practice. The unique properties of this waveguide are demonstrated through mode analysis as well as numerical simulations.

A microwave one-way waveguide of three-dimensional configuration is proposed and investigated theoretically. In this waveguide there exists a complete one-way propagation band, where the mode propagates only in one direction and can be immune to backscattering. By terminating the one-way waveguide with metal slab, one-way propagating waves in this waveguide system can be stopped at the terminal end without any backscattering. Meanwhile, a hotspot with extremely enhanced magnetic-field amplitude is generated in this 3D waveguide system. For an incident microwave pulse, the trapped wave packet can be compressed to deep subwavelength scale besides the magnetic field enhancement. Moreover, the magnetic field enhancement of trapped waves can be further largely increased by tapering laterally the waveguide system. The approach for trapping microwaves has promising applications in magnetic sensing and magnetic non-linearity.

Electromagnetic edge mode in a photonic crystal (PhC), which is a square array of semiconductor rods in air, is theoretically investigated for terahertz frequencies. In the PhC, gyroelectric anisotropy is introduced in the semiconductor rods by applying an external magnetic field and consequently, a degeneracy point, at which two dispersion surfaces intersect, is lifted and a new band gap is created. The edge mode sustained by the PhC possesses the character of one-way propagation, and it even can be immune to backscattering at large defect on the wavelength scale and 90° sharp bend. The properties of the one-way mode are closely dependent on the cladding layer structure of the PhC.

A plasmonic nanostructure (PNS) which integrates metallic and dielectric media within a single structure has been shown to exhibit specific plasmonic properties which are considered useful in refractive index (RI) sensor applications. In this paper, the simultaneous realization of sensitivity and tunability of the optical properties of PNSs consisting of alternative Ag and dielectric of nanosphere/nanorod array have been proposed and compared by using three-dimensional finite element method. The proposed system can support plasmonic hybrid modes and the localized surface plasmonic resonances and cavity plasmonic resonances within the individual PNS can be excited by the incident light. The proposed PNSs can be operated as RI sensor with a sensitivity of 500 nm/RIU (RIU = refractive index unit) ranging from UV to the near-infrared. In addition, a narrow bandwidth and nearly zero transmittance along with a high absorptance can be achieved by a denser PNSs configuration in the unit cell of PNS arrays. We have demonstrated the number of modes sustained in the PNS system, as well as, the near-field distribution can be tailored by the dielectric media in PNSs.

One of the aims for modern hypersonic cruise flight is hypersonic global reach. The length of route for such flights could be up to thousands of kilometers. The atmospheric conditions on the route are complicated. On the other hand, hypersonic flights used to suffer from communication blackout. The sub-THz communication is considered as a potential solution to the `blackout'. In the present study the propagation for sub-THz signals in hypersonic plasma sheaths was modeled under different atmospheric conditions. According to the study, the electron density and the electron collision frequency near the onboard antenna linearly increase with the atmospheric mass density around the vehicle, hence the attenuation of sub-THz signals in hypersonic plasma sheaths increases with the atmospheric mass density. The impact led by the atmospheric temperature is ignorable. Based on the study a new sub-THz signals' propagation model was developed, which could be utilized for quick estimation for signal propagation under different atmospheric conditions. The geographical difference of signal propagation over the whole globe was obtained with the new model. The results showed that the signal attenuation in plasma sheaths varies with latitude and longitude. The maximum signal attenuation occurs in Alaska, Canada and Russia.

K.L.T. gratefully acknowledges the support of the Eugen Lommel fellowship of the Max Planck Institute for the Science of Light (Erlangen) and R.W.B. the Canada Excellence Research Chairs Program. H.A. and K.L.T. supported by European Commission Horizon 2020 (grant no. FETOPEN-737071), ULTRA-CHIRAL Project. L.S. supported by National Natural Science Foundation of China grant no. 61372005 and key project grant no. 41331070 A century-old tenet in physics and engineering asserts that any type of system, having bandwidth Δω, can interact with a wave over only a constrained time period Δt inversely proportional to the bandwidth (Δt·Δω ~ 2π). This law severely limits the generic capabilities of all types of resonant and wave-guiding systems in photonics, cavity quantum electrodynamics and optomechanics, acoustics, continuum mechanics, and atomic and optical physics but is thought to be completely fundamental, arising from basic Fourier reciprocity. We propose that this “fundamental” limit can be overcome in systems where Lorentz reciprocity is broken. As a system becomes more asymmetric in its transport properties, the degree to which the limit can be surpassed becomes greater. By way of example, we theoretically demonstrate how, in an astutely designed magnetized semiconductor heterostructure, the above limit can be exceeded by orders of magnitude by using realistic material parameters. Our findings revise prevailing paradigms for linear, time-invariant resonant systems, challenging the doctrine that high-quality resonances must invariably be narrowband and providing the possibility of developing devices with unprecedentedly high time-bandwidth performance. Postprint

The guiding properties of spoof surface plasmon polaritons (SPPs) in an array of hollowed-out metallic blocks standing on a metallic surface are theoretically investigated in this study. For such spoof SPPs, there exists an additional guiding mode except for the fundamental mode and the former is closely related to hollowing out metal blocks. The dispersion band of this additional mode has a negative slope (corresponding to a group velocity) and it intersects the light line and then enters the radiation region as the frequency grows, which leads to a frequency steering pencil-like radiation. The transmission and radiation properties of the additional mode of spoof SPPs are finally verified experimentally.