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Amplitude-phase control for circular polarized (CP) waves is experiencing a research upsurge in electromagnetics owing to the kaleidoscopic electromagnetic responses and promising application prospects of circular polarizations, and chiral metasurfaces are more facile to achieve a series of intriguing chiral phenomena than natural materials. However, it is difficult for most existing chiral metasurfaces to independently tailor the amplitude and phase of left-handed circular polarized and right-handed circular polarized waves at the same frequency as they suffer the drawbacks of large thickness, multiple layers, and complex structure. Herein, an innovative strategy of single-layer achiral metasurfaces of thickness 0.13λ

We propose a method to construct the broadband 90° balun with low-phase-imbalance performance based on a U-shaped periodic slow wave structure (PSWS) transmission line (TL), whose dispersion curve has a linear region in a wide frequency band. By introducing meander lines and U-shaped TLs, the linearity, cutoff frequencies and slope of dispersion curves of PSWS can be controlled flexibly. Simulated and measured results show good agreements. Both reflection coefficient and isolation of the proposed balun are below −15 dB from 1.5 to 2.0 GHz. The phase deviation is within ±3°, covering a fractional bandwidth of 28.6%. Compared with that based on the traditional corrugated periodic slow wave TL unit, the operating bandwidth of the proposed balun is increased by more than six times. Moreover, the proposed PSWS keeps excellent ability of field confinement and therefore improves the isolation between the output ports. In a word, based on the proposed method, the microwave devices and circuits which realize the function of phase shifting can be designed.

The fifth-generation (5G) wireless communication has an urgent need for target tracking. Digital programmable metasurface (DPM) may offer an intelligent and efficient solution owing to its powerful and flexible controls of electromagnetic waves and advantages of lower cost, less complexity and smaller size than the traditional antenna array. Here, we report an intelligent metasurface system to perform target tracking and wireless communications, in which computer vision integrated with a convolutional neural network (CNN) is used to automatically detect the locations of moving targets, and the dual-polarized DPM integrated with a pre-trained artificial neural network (ANN) serves to realize smart beam tracking and wireless communications. Three groups of experiments are conducted for demonstrating the intelligent system: detection of moving targets, detection of radio-frequency signals, and real-time wireless communications. The proposed method sets the stage for an integrated implementation of target identification, radio environment tracking, and wireless communications. This strategy opens up a new avenue for intelligent wireless networks and self-adaptive systems.

Metasurfaces have intrigued long-standing research interests and developed multitudinous compelling applications owing to their unprecedented capability for manipulating electromagnetic waves, and the emerging programmable coding metasurfaces (PCMs) provide a real-time reconfigurable platform to dynamically implement customized functions. Nevertheless, most existing PCMs can only act on the single polarization state or perform in the limited polarization channel, which immensely restricts their practical application in multitask intelligent metadevices. Herein, an appealing strategy of the PCM is proposed to realize tunable functions in co-polarized reflection channels of orthogonal circularly polarized waves and in co-polarized and cross-polarized reflection channels of orthogonal linearly polarized waves from 9.0 to 10.5 GHz. In the above six channels, the spin-decoupled programmable meta-atom can achieve high-efficiency reflection and 1-bit digital phase modulation by selecting the specific ON/OFF states of two diodes, and the phase coding sequence of the PCM is dynamically regulated by the field-programmable gate array to generate the desired function. A proof-of-concept prototype is constructed to verify the feasibility of our methodology, and numerous simulation and experimental results are in excellent agreement with the theoretical predictions. This inspiring design opens a new avenue for constructing intelligent metasurfaces with higher serviceability and flexibility, and has tremendous application potential in communication, sensing, and other multifunctional smart metadevices.

A dual-mode ultrawideband (UWB) antenna is proposed in this communication. The proposed antenna is composed of a monopole and a dipole sharing the same structure, which is excited by a coplanar waveguide (CPW) in even mode and odd mode, respectively. To achieve this kind of excitation, we present a dual-mode feeding structure with high isolation. Because the field distributions for the odd and even modes in CPW are opposite, and far-field patterns radiated by the two modes are orthogonal, this antenna has high isolation between two feeding ports. Fabricated antennas are measured, and good agreement with the simulation results is observed. The achieved impedance bandwidths of 10 dB return loss are 2.8–20 GHz and 4.4–17.6 GHz, with the isolation of 15 dB over the entire operating bandwidth, making it a good candidate for UWB multiple-input-multiple-output applications.

With the large swings in factor performance since the Global Financial Crisis, factor research and factor timing have garnered a lot of attention. Investors looking to add value on top of meager asset returns are expanding their toolkit to include factor timing. Within fixed income strategies, active managers have explored regime models, economic cycle indicators, and factor research to manage portfolio-level exposures to beta, regions, industries, duration, and credit. In light of these developments, we analyze historical manager returns to assess the impact of static factor exposures, factor tilts, and security selection. We find that most managers overweighted credit consistently and this largely explained the patterns of active returns over time. We also find that although factor timing has not added value for all the funds in aggregate, there are funds with persistent positive and negative contributions from factor tilts. Finally, across all funds, factor exposures, both strategic and tactical, are significant predictors of future active returns, thus emphasizing the importance of factors in fixed income strategies. TOPICS:Factor-based models, style investing, fixed-income portfolio management Key Findings • We decompose historical manager returns into contributions from static factor exposures, factor tilts, and security selection for US fixed income strategies. • The active returns of most funds have been driven by their overweights to credit-related instruments. • Although factor timing has generally detracted from returns, there is persistence in this component, implying that both skilled and unskilled factor timers can be identified. • Factor exposures, both strategic and tactical, drive future active returns.

In undergraduate courses on classical electromagnetism, it is taught that a perfect conductor expels the electromagnetic (EM) field, and hence its surface is not able to support the propagation of bound EM waves. However, when the surface of a perfect conductor is structured at a length scale much smaller than the operating wavelength, geometrically induced surface EM modes can be supported. Owing to their similarities with the surface plasmon polaritons (SPPs) in the optical regime, these surface EM modes were named spoof surface plasmons. The concept of spoof surface plasmons has opened up a new line of research within plasmonics with the aim of transferring all the potentialities of SPPs in the optical regime to lower frequencies (microwave, terahertz, and midinfrared regimes) in which a metal behaves as a quasiperfect conductor. In recent years, several research groups have extended this concept from planar surfaces to waveguides, and eventually to resonators, covering the entire range of structures studied in standard plasmonics. This review provides a detailed perspective on the recent developments in spoof surface plasmon photonics from both the fundamental and applied sides., F.J. G.-V and A.I.F.-D. acknowledge funding from the Ministry of Science and Innovation and “ERDF: A Way of Making Europe” through Grants No. RTI2018-099737-B-I00 and No. CEX2018-000805-M (through the María de Maeztu Program for Units of Excellence in R&D), as well as 2020 CAM Synergy Project No. Y2020/TCS-6545 (NanoQuCo-CM). L.M.-M acknowledges Project No. PID2020-115221GB-C41, which was financed by the Spanish State Research Agency and the Aragon Government through Project No. Q-503 MAD. T.J. C. acknowledges the support of the National Key Research and Development Program of China (Grants No. 2017YFA0700201, No. 2017YFA0700202, and No. 2017YFA0700203), the National Natural Science Foundation of China (Grants No. 61631007 and No. 61571117), and the 111 Project (Grant No. 111-2-05).

As-cast, as-extruded and T6 heat-treated Mg-2Zn-0.3Mn-[x] wt.% Y (x = 0, 0.4, 0.8) alloys were formed via a melting process, an extrusion process and T6 aging treatment, respectively. Microstructural analysis showed that the addition of yttrium (Y) resulted in grain refinement in the samples. The hot extrusion process and T6 heat treatment contributed to the precipitation of second phases and a reduction of the dislocation density as well as to a reduction of the lattice distortion. The thermal conductivity of the T6 heat-treated samples was the highest because it had the lowest lattice distortion. A higher Y content did not result in increased thermal conductivity. However, the yield strength and tensile strength of the alloys increased with increasing Y content. Fine-grain strengthening and dispersion strengthening were responsible for the higher yield strength and ultimate tensile strength of the as-extruded and T6 heat-treated samples.

Programming electromagnetic spectra have become key technology affecting the development of the information industry, arousing widespread interest of researchers. Here, we propose a route to realize a programmable spectrum based on time-coding spoof surface plasmon polaritons (SSPPs) to implement the customized harmonic generations and amplitude manipulations. The proposed time-coding SSPPs are experimentally demonstrated to flexibly control both frequencies and amplitudes of the harmonics, providing the possibility of reprogrammable outputs of different spectra. In addition, two kinds of improved time-coding SSPP structures are presented, which can be applied to realize reprogrammable spectra without the fundamental component and with customized asymmetric spectra.

The electromagnetic (EM) behavior of a microwave sensor has specific relationship with the physical properties of the materials to be detected, e.g. the concentration of solution and the permittivity of gas. The microwave sensor can detect changes of EM response in real time, and obtain the material properties with low sample consumption, high efficiency and dispersion characteristics. This work presents a microfluidic sensor using spiral resonators and plasmonic metamaterials with confined EM fields for intensive resonance. Two microfluidic chips with spiral channels engraved in polydimethylsiloxane are also adopted to enhance the interaction between the EM fields and the carried liquids at resonance frequencies. The permittivity of liquid samples can be detected through the shift of resonance frequency. A prototype of the sensor is fabricated and tested with several regular solutions and organic solvents, showing a good performance in terms of low liquid consumption (8 μl), good sensitivity (410 MHz frequency offset when ϵr changes from 1 to 36.7) and low cost.

Reflection- and transmission-type metasurfaces have great potentials in wireless communications. In this letter, we propose an absorption-transmission-type multifunctional coding metasurface composed of an absorptive layer and a transmissive layer. For incident waves at different frequencies with different polarizations, the proposed coding metasurface can perform three different functions independently: wave absorption at low frequencies, vortex-wave generation for the x-polarized wave and beam deflection for the y-polarized wave at high frequencies. Both numerical and experimental results verify the excellent performance of low-frequency absorptions and high-frequency dual-polarization transmissions. This work provides a method for developing multifunctional and reconfigurable components for the wireless communications in the future.

Glide symmetry, which is one kind of higher symmetry, is introduced in a special type of plasmonic metamaterial, the transmission lines (TLs) of spoof surface plasmon polaritons (SSPPs), in order to control the dispersion characteristics and modal fields of the SSPPs. We show that the glide-symmetric TL presents merged pass bands and mode degeneracy, which lead to broad working bandwidth and extremely low coupling between neighboring TLs. Dual-conductor SSPP TLs with and without glide symmetry are arranged in parallel as two channels with very deep subwavelength separation (e.g., λ0 / 100 at 5 GHz) for the application of integrated circuits and systems. Mutual coupling between the hybrid channels is analyzed using coupled mode theory and characterized in terms of scattering parameters and near-field distributions. We demonstrate theoretically and experimentally that the hybrid TL array obtains significantly more suppressed crosstalk than the uniform array of two nonglide symmetric TLs. Hence, it is concluded that the glide symmetry can be adopted to flexibly design the propagation of SSPPs and benefit the development of highly compact plasmonic circuits.

A metamaterial sensor is proposed to detect the random location of a sub-wavelength metallic object. The sensor is composed of a transmission line (TL), which supports the propagation of spoof surface plasmon polaritons (SSPPs) with localized electromagnetic (EM) field, and a complementary spiral resonator (CSR) that resonates strongly at designed frequencies around 0.9 and 2.7 GHz. Based on the shift of the resonance frequencies, this sensor is able to detect the location of a sub-wavelength metallic object (whose diameter is smaller than 0.6 mm) randomly attached to the CSR. A prototype of the sensor is fabricated and tested. In practice, the CSR is excited through the EM coupling of the SSPP TL, and the location of the metallic object is obtained through the transmission coefficient (S21). To improve the accuracy, a retrieval curve for locating is generated and calibrated. It is proved that the random location of the sub-wavelength object can be accurately detected inside an area of 9π mm2 with a low error of 2‰.

In modern microwave technology, multi-layer structure is widely adopted in compact circuit design. In a multi-layer microwave system, the transmission line (TL) plays an important role. The multi-layer TLs need to have high cross-layer transmission efficiency, which is a big challenge in highly integrated circuits. Spoof surface plasmon polaritons (SSPP) possess good performance on field confinement and low transmission loss at microwave and terahertz frequencies, and can achieve the compact design in planar microwave circuits. In this article, a new type of multi-layer SSPP TL is proposed and tested. Taking advantage of the properties of SSPPs, the proposed TLs achieve high transmission efficiency for both in-layer and cross-layer situations. The proposed SSPP TLs have great prospect in the future multi-layer circuit design.

In the 1990s, it was recognized that light beams carrying orbital angular momentum (OAM) have benefited applications ranging from optical manipulation to quantum information processing. In recent years, attention has been directed towards the opportunities for communication systems due to the inspiring application potential in both the optical and microwave fields. In this paper, a polarization-independent quadri-channel vortex beam generator based on transmissive metasurface is proposed that can achieve selectivity of polarization, 2-bit OAM modes and spatial distribution in the quadri-channel simultaneously. The transmissive metasurface consists of four metallic layers and three dielectric layers and is designed, fabricated, and experimentally demonstrated to generate multi-mode and dual-polarization OAM vortex beams at 10.0 GHz. Orthogonal polarization and 2-bit information are carried by OAM modes +1, −1 + 2 and −2 and a different phase gradient is superimposed at each channel to realize beam steering, ensuring the accuracy and integrity of the information. The simulation and experimental results verify that the vortex beams with different OAM modes in dual polarizations can be flexibly generated by using transmissive metasurfaces. The proposed method and metasurface pave a way to add extra channels to create an additional set of data carriers for space-division multiplexing (SDM).

Metamaterials (MTMs) are artificial structures characterized by flexible and designable electromagnetic (EM) properties, including permittivity, permeability, and refractive index. Because of their subwavelength‐scale composing units, MTMs are able to manipulate the propagation of EM waves at extremely fine resolutions and offer solutions for new‐concept devices and components with novel functionalities and challenge‐breaking properties. From among the attractive applications of MTMs, this review article focuses on MTM lenses (also termed metalenses) developed in recent years for the purpose of microwave engineering, including beam forming, beam steering, and imaging. Bulk lenses made of 3D MTMs and planar lenses made of 2D transmission‐type metasurfaces are both involved and investigated. Different categories of metalenses, together with the theory, principles, methods, and advantages of their designs, are introduced and discussed. Potential and future applications of metalenses at microwave frequencies are also presented.

With the demand of Internet video multicast service and the advantages of SDN (soft defined network), a multi-factor adaptive SDN video multicast routing algorithm is proposed. The algorithm combines hop count, bandwidth and load balancing, and realizes the multicast system simulation based on this routing algorithm. The simulation results show that with the increase of the number of members in multicast group, the packet loss rate and RTT and packet-in of the controller of the whole system do not change much, and the network performance of the whole system is stable. It is suitable for solving the problem of unstable video communication effect caused by network congestion and packet loss.

Terahertz (THz) technology has great potential in applications of material, chemical, communication and life sciences. The development of low loss THz devices has been promoted in recent years to boost the technologies. Here, the 0.95MgTiO 3 –0.05CaTiO 3 and TiO 2 ceramic systems have been investigated. The influence of sintering process, microstructure has been discussed to optimize the THz performance. The 0.95MgTiO 3 –0.05CaTiO 3 ceramics can possess permittivity of 18 and ultra-low loss of 1.9 × 10−3 the TiO 2 ceramics show high permittivity of 102 and ultra-low loss of 4.2 × 10−3.

As-cast and as-extruded Mg-[x]Zn-0.3Mn (x=1.5, 2.0 wt.%) alloys were prepared by means of medium-frequency induction-heating technique and extrusion process, respectively. The microstructural characteristics, thermal conductivity and mechanical properties of the samples were characterized. The research results show that the samples are composed of major α-Mg and minor second phases MgZn2. For the as-extruded samples, the grain size is refined. After extrusion, much more second phases were precipitated from α-Mg matrix and the dislocations were reduced. The degree of lattice distortion was decreased for as-extruded samples. Because of the decline of lattice distortion degree, the as-extruded samples display much higher thermal conductivity than the as-cast samples. Additionally, on account of lower lattice distortion, Mg-1.5Zn-0.3Mn alloy has a bit larger thermal conductivity than Mg-2Zn-0.3Mn alloy. Finally, the as-extruded alloys present good mechanical properties based on the fine-grained strengthening and second-phase strengthening mechanism.

Plasmonic circuits, which support the propagation of spoof surface plasmon polaritons (SSPPs) at microwave frequencies, have been developed in recent years as an expected candidate for future highly integrated systems, mainly because of their extraordinary field confinements and sub-wavelength resolution. On the other hand, artificial electromagnetic (EM) resonators are widely adopted in metamaterial design for flexible resonance and band gaps. In this work, an electrically small complementary spiral, which is made up of six helix branches sculptured in the ground, is proposed to achieve independent resonances at six different frequency bands. Combined with the grounded corrugated transmission line (TL), the proposed component can provide designable multi-band rejection, and compose frequency coding circuits with a compact size (less than &lambda, 0/4). The complementary spirals excited with the bending TL and the straight one are both investigated, and independence band rejections and designed 6-bit coding sequences in the frequency spectrum are demonstrated numerically and experimentally. Hence, it is concluded that such compact components can be adopted to flexibly control the rejection of waves in multi-frequency bands, and benefits the development of frequency-identification circuits and systems.

In recent years, spoof surface plasmon polaritons (SPPs) have been investigated at microwave and THz frequencies for engineering purpose. Due to momentum mismatch, the SPP mode cannot be directly converted from the spatial mode, and vice versa. Stimulating schemes have been developed to transform spatial waveguide modes to SPP modes with high efficiency. On the other hand, the question may arise that, is it possible to transform the propagating SPP waves to directive radiating waves for wireless communication? In view of this, this paper introduces the new-concept antennas based on spoof SPPs at microwave frequencies. Methods of transforming SPP modes to radiating modes are studied, whilst a series of antenna designs are presented and discussed. Feeding networks for antenna arrays using SSPP TLs are also investigated. Most works reviewed in this paper are fulfilled at Southeast University in China.