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In this article, a classified system with a relay is investigated in wireless body area networks (WBANs), where some on-body sensors are divided into several sensor groups on the basis of different body parts. Not only can the network detect basic vital signs but also the physiological signals of special diseases. All groups of sensors and the relay harvest energy by the radio-frequency (RF) source broadcasting, then the same group of sensors simultaneously sends common information through cooperation to the source. Since the classified system is a confined system, we maximize the system throughput with a joint power allocation on maximum ratio combining (JPA-MRC) protocol, where the transmission power allocation at the relay is unequal for each relaying subslot. The optimal problem is solved by the Lagrange multiplier method and the Karush–Kuhn–Tucker (KKT) optimal conditions. To further the obtain optimal solution, we simplify co-optimization of relay power and sensor power to the optimization of single power by the equivalent channel gains. Analytical and simulation results show that our proposed optimal method can greatly improve the information throughput compared to the conventional mean power allocation method. In addition, the protocol based on the classified scheme outperforms than that of the conventional unclassified scheme. The impacts of various important system parameters are analyzed, which provide useful design insights under different cases.

Online health consultation (OHC) provides an alternative mechanism of healthcare delivery, which could enhance healthcare efficiency, reduce cost, and solve healthcare inequalities. Understanding w...

Metasurfaces have been extensively investigated to achieve radar cross section (RCS) reduction over a wide frequency band. In this article, we propose the design of a novel metasurface with a transmission window within the wide RCS reduction band. The function of this metasurface is similar to rasorbers, whereas the mechanism behind the wideband RCS reduction is scattering cancellation rather than absorption. To this end, the ideal reflection and transmission properties of the metasurface unit cell are firstly revealed. And then an anisotropic unit cell composed of multilayered metallic patterns is designed to obtain the desired reflection and transmission properties. The bottom layer is composed of the typical patch-grid-patch bandpass frequency selective surface, which allows for high transmission in the transparent window and also behaves as a metallic-like reflection sheet in the RCS reduction band. Two metasurfaces, with checkerboard and aperiodic configurations, respectively, were designed, fabricated, and measured, as a proof-of-concept demonstration. A good agreement between the simulations and measured results provides a solid verification for our design. The results here provide an alternative method to open a transparent window within the RCS reduction band and may find potential applications in stealth radomes.

The combination of two frontier technologies, health informatics and cloud computing, is known as Health Informatics as a Service (HIaaS). Considering the importance of privacy issues in HIaaS context, we empirically investigated the antecedents and consequences of patients' information privacy concerns for HIaaS in this paper. An integrated framework that consists of multiple dimensions of privacy concern antecedents and consequences is proposed and validated. Structural equation modeling method was employed to estimate the significance of the path coefficients. Five antecedent factors at different levels influence patients' privacy concern for HIaaS, including privacy awareness (patient level), perceived informativeness (service level), information sensitivity (information contingency), regulatory expectations (macro-environmental level), and importance of information transparency (organizational level). Privacy concern for HIaaS significantly affects patients' trust belief, perceived privacy risk, and adoption intention. This study is among the first to investigate privacy issues in an understudied context – HIaaS, which is different from extant HIaaS literature from conceptual and technological perspectives. In addition, this research provides a more holistic picture about the formation and consequence of patients' information privacy concerns.

In this letter, an active metasurface for vortex beam generation is proposed. This metasurface can transform the incident plane wave into beams carrying orbital angular momentum of three different orders. This active metasurface is composed of an array of varactor diodes loaded unit cells. The transmission phase of each metasurface unit cell can be fully controlled by the capacitance of the varactor diodes. Different modes of vortex beams can be separately generated by simply changing the transmission phase distribution on the metasurface aperture. The properties of the proposed active metasurface are demonstrated by simulation and measurement results, which have a good agreement with each other.

This paper proposed a cross-polarization converter, which can fully control the transmission phase and then manipulate the direction of refracted wave. A multi layered unit cell was designed and the transmission phase is continuously controlled by a single geometric parameter, which brings great convenient for simultaneously manipulating the polarization and propagation direction of the transmitted wave. The cross-polarized transmittance of the proposed polarization converter is higher than 0.9. In addition, the transmitted wave has an extremely low co-polarized component. Thus, the polarization conversion ratio is nearly 100%. Anomalous refraction was also realized by configuring a designed transmission phase distribution on the aperture of the cross-polarization converter. The proposed device was demonstrated by both simulation and measurement.

The amount of waste generation has been increasing with a significant amount being landfilled. These non-recyclable wastes contain large number of fiber and plastic wastes which can be treated with thermal processes to turn them into energy sources since they have high calorific values, are abundant and usually tipping fees are paid to handle them. This paper studied the torrefaction of non-recyclable paper (fiber) wastes, mixed plastic wastes (MPW) and their blends at different ratios in the temperature range of 250–400°C through thermogravimetric analysis (TGA). The solid residues after the experiments were analyzed by nuclear magnetic resonance (NMR) spectroscopy. Significant synergy between fiber and MPW were observed at the range 250–300°C, showing both increase in the reaction rate as well as the overall mass loss. At 250°C, the maximum mass loss rate was more than two times higher and the mass loss at the end of the experiments were also much higher compared to the expected results. In addition, synergy was weakened with an increase of temperature, disappearing at 400°C. The existence of such interactions between fiber and plastic wastes indicates that the natural energy barriers during the individual torrefaction in paper waste or plastic waste could be bypassed, and the torrefaction of fiber and plastic blend can be achieved at lower temperatures and/or shorter residence times. The MPW and fiber wastes were also compounded by extrusion (to produce pellets) at 220°C with different blend ratios. The fiber-MPW pellets from extrusion were characterized by IR spectroscopy, rheology, thermal analysis and flexural properties and showed significant chemical changes from the non-extruded blends at the same ratios. From IR characterization, it was found that there was significant increase in hydroxyl (OH) group on account of the carbonyl (C = O) and etheric (C-O-C) groups. The interaction between paper and MPW can be attributed to the plastic polymers acting as a hydrogen donor during the reactive extrusion process. Synergistic effects were also found from mechanical and rheological properties.

This paper considers the distributed “nonsmooth+nonsmooth” composite optimization problems for which n agents collaboratively minimize the sum of their local objective functions over the directed networks. In particular, we focus on the scenarios where the sought solutions are desired to possess some structural properties, e.g., sparsity. However, to ensure the convergence, most existing methods produce an ergodic solution via the averaging schemes as the output, which causes the desired structural properties of the output to be destroyed. To address this issue, we develop a new decentralized stochastic proximal gradient method, termed DSPG, in which the nonergodic (last) iteration acts as the output. We also show that the DSPG method achieves the nonergodic convergence rate \(O(\log (T)/\sqrt{T})\) for generally convex objective functions and \(O(\log (T)/T)\) for strongly convex objective functions. When the structure-enhancing regularization is absent and the simple and suffix averaging schemes are used, the convergence rates of DSPG reach \(O(1/\sqrt{T})\) for generally convex objective functions and O(1/T) for strongly convex objective functions, showing improvement relative to the rates \(O(\log (T)/\sqrt{T})\) and \(O(\log (T)/T)\) provided by the existing methods. Simulation examples further illustrate the effectiveness of the proposed method.

In this paper, the magnetic squeezing effect in metamaterials is explored and applied to achieve wideband absorption in low-frequency microwave bands. To this end, a metamaterial absorber (MA) is proposed, which consists of a square lattice of a split ring resonator (SRR) placed on top of a magnetic absorbing material (MAM) layer backed by a conducting ground. In the positive resonance region of SRRs, a strong magnetic squeezing effect occurs and more concentrated magnetic field lines are confined within SRRs. This results in significant magnetic field enhancement within the MAM layer, which provides a prerequisite for high-efficiency absorption enhancement at low frequencies. To verify this method, we fabricated a prototype using a 3.0 mm thick silicone MAM sheet. Both the simulation and experiment results show that with the assistance of magnetic squeezing in the SRR array, the absorption at lower frequencies is significantly enhanced and is above 90% in 1.25–2.31 GHz under normal incidence. Furthermore, the MA exhibits satisfactory stability for different polarization states and incident angles due to the square lattice of the SRR array. This design method may find potential applications in fields such as electromagnetic compatibility, wireless communication, and others.

With the rapid development of communication industry, the miniaturization technology of antennas is increasingly required. In this paper, a printed PCB antenna with a low profile of 0.116λ 0 based on spoof surface plasmon polaritons (SSPP) theory is presented. The SSPP antenna can launch vertical polarized waves in omnidirection with a low profile. The proposed antenna is composed of two parts, a feeding part of a coplanar waveguide and a radiating part of a SSPP structure. The profile of the antenna can be reduced using the deep-subwavelength property of the SSPP. Simulation results show that the proposed antenna has good omnidirectional vertically polarized radiation with low crossover-polarized radiation. The peak gain at 2.4GHz is 0.89dBi. The pattern roundness in H plane is from 0.0313dB to 0.0319dB. It is believed that the proposed SSPP antenna is a potential candidate for short-range wireless transmission in ISM frequency band.

The amount of solid waste generated annually is increasing around the world. Although the waste has a high calorific value, one major obstacle that may prevent it from becoming a feedstock for power applications is the existence of polyvinyl chloride (PVC), which causes corrosion and emission issues after combustion due to its high chlorine content. Torrefaction is known to release hydrochloric acid, thus, it has been applied in this study for the reduction of chlorine from potential waste feedstocks. Fiber-plastic (60&ndash, 40%) waste blends, with different chlorine content levels, as well as PVC were used in the current study. Torrefaction was conducted at 400 &deg, C. Chlorine and heat content were measured. Experimental results showed that organically bonded chlorine was reduced during torrefaction as a function of mass loss. The chlorine removal efficiency was only dependent on temperature and residence time, not chlorine level. The heat content of the sample increased with mass loss up to a maximum of ~34 MJ/kg at ~45% mass loss. It was also observed that at ~30% mass loss, the organic chlorine content per unit heat content reduced by ~90%, while the heat content was ~32 MJ/kg, and ~90% energy was retained.

Current autonomous driving systems are composed of a perception system and a decision system. Both of them are divided into multiple subsystems built up with lots of human heuristics. An end-to-end approach might clean up the system and avoid huge efforts of human engineering, as well as obtain better performance with increasing data and computation resources. Compared to the decision system, the perception system is more suitable to be designed in an end-to-end framework, since it does not require online driving exploration. In this paper, we propose a novel end-to-end approach for autonomous driving perception. A latent space is introduced to capture all relevant features useful for perception, which is learned through sequential latent representation learning. The learned end-to-end perception model is able to solve the detection, tracking, localization and mapping problems altogether with only minimum human engineering efforts and without storing any maps online. The proposed method is evaluated in a realistic urban driving simulator, with both camera image and lidar point cloud as sensor inputs. The codes and videos of this work are available at our github repo and project website., Comment: 8 pages, 10 figures, 2 tables

Reinforcement learning methods have been developed to achieve great success in training control policies in various automation tasks. However, a main challenge of the wider application of reinforcement learning in practical automation is that the training process is hard and the pretrained policy networks are hardly reusable in other similar cases. To address this problem, we propose the cascade attribute network (CAN), which utilizes its hierarchical structure to decompose a complicated control policy in terms of the requirement constraints, which we call attributes, encoded in the control tasks. We validated the effectiveness of our proposed method on two robot control scenarios with various add-on attributes. For some control tasks with more than one add-on attribute attribute, by directly assembling the attribute modules in cascade, the CAN can provide ideal control policies in a zero-shot manner., Comment: arXiv admin note: text overlap with arXiv:1711.09142

In this paper, we propose a new method for image restoration problems, which are degraded by impulsive noise, with nonconvex data fitting term and nonconvex regularizer.The proposed method possesses the advantages of nonconvex data fitting and nonconvex regularizer simultaneously, namely, robustness for impulsive noise and efficiency for restoring neat edge images.Further, we propose an efficient algorithm to solve the “Nonconvex+Nonconvex” structure problem via using the alternating direction minimization, and prove that the algorithm is globally convergent when the regularization parameter is known. However, the regularization parameter is unavailable in general. Thereby, we combine the algorithm with the continuation technique and modified Morozov’s discrepancy principle to get an improved algorithm in which a suitable regularization parameter can be chosen automatically. The experiments reveal the superior performances of the proposed algorithm in comparison with some existing methods.

In this paper, we proposed a radiation pattern reconfigurable waveguide slot array antenna using liquid crystal (LC). Together with the waveguide slot, the designed complementary electric-field-coupled resonator functions like a switch controlled by the dielectric constant of the LC, which can control the antenna element to radiate or not. Thus, the array factor and radiation pattern can be manipulated. The proposed antenna was simulated, fabricated, and measured. Its radiation direction can be reconfigured to 46° or 0° at about 15 GHz.

A novel mixed mode radar coincidence imaging (MMRCI) system, which combines the coherent radar detection and incoherent radar coincidence imaging function during the radar coincidence imaging (RCI) process, is presented in this paper. The target location function of the MMRCI system gives the target position information synchronously with imaging tests, and this makes the MMRCI work independently with low target position estimation error. In the MMRCI system, the resolution of target distance estimation is proportional to the whole bandwidth assisted by the double-frequency linear frequency modulation (DFLFM) signal when the occupied bandwidth of the DFLFM signal is less than one-tenth of the whole bandwidth. The target position estimation error caused by the target motion can be reduced effectively so that the image quality of the moving target can be guaranteed in a longer detection time. The RCI is reconstructed using the incoherent part of the transmitting signal. A general relationship between the spatial correlation of the random radiation field in the imaging plane and the deployments of linear random source is analyzed in the paper. The imaging efficiency is ensured through the grading imaging method based on the imaging requirement. The effectiveness of the MMRCI method is validated via a set of simulations and experiments, including superresolution RCI of both stationary and moving targets in various scenes using the convex optimization algorithms.

The spatial modulation coincidence imaging (SMCI), as a novel kind of microwave coincidence imaging method, is proposed in this paper. The SMCI system provides a new way to produce the time-space independent signal instead of multitransmitter architecture with wideband randomly modulated signal in radar coincidence imaging. Due to some special features, metamaterial plate is utilized as the reflective surface to modulate the incident signal to construct random radiation field. The resolution of SMCI system is analyzed under large viewing angle with two different transmitting signals. Reflective surface is nonuniformly divided to derive the expression of resolution. The analysis results show that the resolution of SMCI system is mainly determined by the size of reflective surface and center frequency, which is similar to the traditional aperture. The SMCI system is low cost and flexible in design. Simultaneously, it can avoid the synchronization problem between subsources. Moreover, the SMCI system can achieve the resolution of space target through single transmitter–single receiver radar system. High-resolution image can be reconstructed since the tests are nonlinear. Finally, a series of simulation experiments is presented based on the nondirect-viewing scene we proposed. Using the algorithm based on a compressed sensing theory, we reconstructed the target image with high resolution.

In this paper, we propose a theory by extending the Babinet principle to periodic subwavelength anisotropic metallic crevice elements $A^{e}$ in the interface of different substrates. The significance of the proposed theory is that it can readily be used to transfer the solution of $A^{e}$ to that of its complementary metallic elements $A^{c}$ . First, the Babinet principle is established for $A^{e}$ and its complementary magnetic elements $A^{m}$ according to the uniqueness theorem of boundary conditions, and $A^{m}$ is replaced with the corresponding metallic elements $A^{c}$ based on the dual principle. Then, the waves associated with $A^{e}$ and $A^{c}$ are considered as plane waves since their period is smaller than the operation wavelength. Thereby, the Babinet principle is reexpressed as mathematical relations between tangential transmission matrices of $A^{e}$ and $A^{c}$ . Next, the tangential transmission matrices of $A^{c}$ are solved using the corresponding circuit model, where the effective relative permeability is introduced to describe the inductive influence of the dual substrate. Finally, the tangential transmission matrices of $A^{e}$ are derived, and the proposed theory is verified by two examples. The theoretical results agree well with the simulated ones at normal incidence (for various substrates) and over a large range of incidence angles (up to 75° and 60° for the two examples, respectively). The measured results support the simulation and the proposed theory.

A novel method of designing the frequency selective surface (FSS) based on spoof surface plasmon polariton (SSPP) modes is proposed and demonstrated. The high-efficiency transmission and a stopband with a steep falling edge can be mediated by the SSPP modes below and above the cutoff frequency, respectively. So the prolific filtering performances can be customized by integrating with the traditional FSSs. As examples, the two kinds of FSSs were designed and demonstrated by simulations and experiments. A bandstop FSS with the suppression level more than 28 dB is first realized in the frequency region of 9.0–14.7 GHz with the steep rising and falling edges. Then, a dual bandpass FSS is designed by sandwiching the SSPP structure array between the two layers of traditional FSSs. It is indicated that the designed FSS shows two passbands in the frequency ranges of 4.2–4.3 GHz and 8.7–10.3 GHz, and the insert loss is less than 0.5 dB.

We proposed a simple method to realize a bidirectional endfire antenna based on spoof surface plasmon polaritons (SPPs). The bidirectional “8”-shaped radiation characteristic is achieved by the backfeeding method and the spoof SPPs structure, and the endfire radiation is obtained by loading parasitic strips at the ends of two dipoles. The overall dimension is ${\text{3.33}}\lambda \, \times \, {\text{0.74}}\lambda \, \times \, {\text{0.015}}\lambda $ , showing low-profile characteristic. The proposed antenna is optimized to operate in the 5G WiFi frequency range. The realized gain is over 7 dBi, and the total radiation efficiency is over 85% from 5.3 to 5.7 GHz. The experimental results of S 11, normalized radiation pattern at different frequencies, the realized gain, and the radiation efficiency curves all agree well with the simulated ones. The proposed bidirectional endfire antenna will have potential applications in the spoof-SPPs-based communication system.

Carbon fibers (CFs) have been widely used as absorbing materials for radar cross section (RCS) reduction. Here, an alternative approach for CFs is proposed to achieve the same goal and has been performed by the glass fabric composites loaded with a small number of CFs. The reduction mechanism of our proposal is phase cancellation instead of absorption. Two prototypes in chessboard and random patterns are analyzed numerically and measured experimentally. The short CF yarns are designed as the patterned configurations and embedded into the composite surface layers. It is demonstrated that the proposed composites allow for remarkable suppressing of the specular scattering over a broad frequency band. The designed RCS reduction level more than 10 dB covers the frequency range from 8.7 to 19.2 GHz, while the overall thickness is 2.7 mm. The proposed composites are of a simple configuration and robust for the defects. It is also believed that the study of this work can be easily extended to the curved surfaces.

Paper waste generation has been rising in the past decades, with a large amount being landfilled. These paper wastes can be great energy sources after thermal treatment since they are considered carbon neutral. These wastes contain mainly cellulose, hemicellulose, lignin, and some minerals. The thermal decomposition of cellulose, hemicellulose, and lignin have been extensively studied, however, the knowledge of thermal degradation of paper wastes at lower temperatures, which are more practical for industrial applications are still lacking. In this study, paper wastes have been characterized and thermogravimetric analyses were performed from 200°C to 400°C and the char produced were analyzed by nuclear magnetic resonance (NMR) spectroscopy and Fourier-transform infrared (FTIR) spectroscopy. Two kinetic approaches were taken while developing the kinetic model of paper waste thermal degradation: (i) reconstructing the TGA results of paper waste thermal degradation by an additive law of the degradation of cellulose, hemicellulose and lignin; (ii) considering paper waste as one material and develop a multi-step consecutive reaction mechanism that focuses on solid products at different temperatures. It was observed that there are potential interactions between cellulose, hemicellulose and lignin during paper waste degradation. Therefore, the second approach was concluded to be more plausible, and one set of kinetic parameters were determined according to the experimental results at different temperatures. These results provided insights into the degradation kinetic mechanism and solid product distribution of the paper waste. It was found that the first reaction was due to dehydration of cellulose and the 6th and 7th reaction can be attributed to the thermal degradation of lignin. The NMR and FTIR results also validated that the cellulose started degrading at lower temperatures, and lignin degradation became more pronounced at higher temperatures.

There has been a growing concern over recent years regarding the phenomenon of local heating of composite insulators. In this paper, the influences of humidity, contamination and local electric field on the temperature and dielectric properties of field-aged insulators were studied experimentally. Aging of the silicone rubber (SIR) material on the weathershed surface, rather than resistive current flow from contamination, was found to be the major cause of local heating observed by thermography. The aged SIR material exhibited strong dielectric loss under high localized AC electric field and high relative humidity. A hypothesis was developed to mitigate the moisture induced local heating on composite insulators.

In this paper, a novel regularization method for image restoration and reconstruction is introduced which is accomplished by adopting a nonconvex nonsmooth penalty that depends on the eigenvalues of structure tensor of the underlying image. At first, an alternating minimization scheme is developed in which the problem can be decomposed into three subproblems, two of them are convex and the remaining one is smooth. Then, the convergence of the sequence which generate by the alternating minimization algorithm is proved. Finally, the efficient performance of the proposed method is demonstrated through experimental results for both grayscale and vector-value images.

The traditional time delay methods cannot obtain the time delay efficiently in the digital predistortion subsystem (DPDS) when the wide bandwidth, multi-carrier signals with large frequency space is used in the communication system. A time delay estimation method, which can estimate the loop delay between the time delayed feedback signal and the input signal in DPDS with high accuracy and high efficiency, is proposed in this paper. The piecewise-parabolic filter and the bisection method are used to change the sampling start of the feedback signal and to choose the loop delay adjustment range, respectively. Compared with the conventional, the proposed loop delay estimation method can obtain the accurate loop delay using various configuration communication signals in DPDS. Results from experiments validate the proposed method.

In this letter, an analytical design of the cross polarization converter is proposed in microwave regime. The gangbuster metasurface is constructed by the periodic metallic cutlines placed on the substrate layer with back metallic sheet. Based on the circuit model and network transmission theory, the reflection coefficients of the metasurface can be calculated even though the substrate layer or metallic elements change. Conversely, when the resonant frequencies and substrate layer are previously given according to the actual situation, the geometric parameters of the metasurface can be analytically solved. Theoretical and simulated results are highly consistent for three different designed cross polarization converters, and one polarization converter is verified to work with the minimal conversion efficiency of 99.36% from 18 to 22 GHz.

A dual-band frequency selective surface (FSS) with different polarizations is proposed in this letter. The unit cell of the FSS is composed of three metallic layers and two intermediate dielectric layers. Each metallic layer has a square loop and a circular patch with a twisted slot. When the incident wave illuminates the surface, the polarizations of the transmission waves in the two bands are different, i.e., one is copolarization and the other is cross polarization. The performance of the surface has been validated by both the simulated and measured results that are in good agreement.

In this letter, we present a theoretical study on a cross-polarized converter based on the reflective metasurface that is composed of slanted metallic cut-lines on a perfect electrical conductor backed substrate. According to the model, although reflection and refraction laws are still applicable in the interface between the air and the substrate, the metallic cut-lines break the original boundary condition. In order to describe the broken boundary condition, the generalized Fresnel's formulas are established based on the traditional Fresnel's formulas and the induced radiation of the metallic cut-lines. Finally, multiple reflections and refractions are resulted from the back metallic sheet in the interface of metallic cut-lines, and the total reflected wave is obtained by summing all waves except the incident wave in air. The theoretical results agree well with the simulated and measured results at the oblique incidence. When incidence angle varies from 0° to 25°, the metasurface can convert more than 99% incident wave into its cross-polarized reflected wave within a relative bandwidth of 22%.

In this letter, a reflective metasurface composed of double-layer metallic L-patterns is designed. Both the simulated and measured results demonstrate that when the incident angle ranges from 0° to 30°, the metasurface can be regarded as a three-band polarization converter. On the one hand, the metasurface can convert TM (TE) polarized incident wave into right (left)-handed circularly polarized wave from 9.1 to 16.5 GHz as well as left (right)-handed circularly polarized wave from 20.0 to 25.4 GHz. On the other hand, the metasurface can realize cross-polarization conversion between TM and TE polarized waves from 17.4 to 18.9 GHz. In addition, the transmission model is expanded from monolayer reflective metasurface to multilayer reflective metasurface to explain the conversion mechanism whose theoretical results are highly consistent with the simulated and measured results.

A novel hybrid system radar coincidence imaging (HSRCI) is proposed in this paper. Radar coincidence imaging (RCI), as a novel kind of radar imaging system, has attracted widespread attention. RCI has the characteristics of high resolution and anti-interference. In addition, the RCI system can image not depend on the range-Doppler (RD) principle and simplify the receiver complexity. So it is considered as a good complement to synthetic aperture radar (SAR). However, the RCI system also has a lot of problems. Since RCI requires the transmit signal has the characteristics of time-space independence. Its pattern has anisotropy, so that the energy can not be gathered in the main lobe direction. This phenomenon will greatly affect the detection range. We propose a HSRCI system, its transmit signal consists of time-space independent signal and a fixed power signal together. HSRCI not only has the characteristics of RCI system. Simultaneously, it can also solve the problem of detection range. Simulation results demonstrate the effect of the HSRCI system. The HSRCI system has a positive effect on solving the problems of RCI.

This paper proposes a reconfigurable polarization converter based on a p-i-n diode controlled active metasurface (AMS). The AMS consists of a thin dielectric substrate and is tuned by two identical layers of elliptic split rings loaded with p-i-n diodes. The p-i-n diodes are positioned between the split gaps and biased through the interconnected elliptic split rings without extra bias network. The active design achieves conversion from linear to circular polarization when the p-i-n diodes are OFF, whereas no conversion takes place when the diodes are ON. A prototype of the proposed design is fabricated, and the operational characteristics are measured. Both the simulated and the experimental results verify the viability of the design. Subsequently, the converter is applied to a linearly polarized horn antenna as a superstrate, making the polarization of the antenna reconfigurable.

With the continued growing U.S. population, solid waste generation will increase, which will lead to undesired and significant growth in landfilling. Thermal treatment can turn these high calorific value wastes into fuels that can be used in small-to-large power plants. This article focuses on using blends with 40% plastic and 60% fiber wastes and converting them into densified solid fuel by torrefaction and extrusion. The material was torrefied at 300 °C to obtain torrefied samples with different mass losses, ranging from 0% to a maximum of 51%. The torrefaction results showed a clear synergy between plastics and fibers. The torrefied material was then extruded into 9 mm diameter rods and the products were characterized by molecular functional group analysis, thermomechanical analysis, dynamic mechanical analysis, dynamic rheological measurement, density measurement, flexural testing, water absorption test, size distribution measurement, heat content test, and combustion test. The fiber content in the material decreased as mass loss increased, and the process reduced significantly the variability of the material. The heat content increased as the mass loss increased. The plastic in the feedstock acted as a process enabler as it imparted properties like bindability, water resistance, high heat content, and increased degradation reaction rate.

In this paper, metasurfaces with both cross-polarization conversion and vortex beam-generating are proposed. The proposed finite metasurface designs are able to change the polarization of incident electromagnetic (EM) waves to its cross-polarization. In addition, they also can modulate the incidences into beams carrying orbital angular momentum (OAM) with different orders ( l = + 1 , l = + 2 , l = &minus, 1 and l = &minus, 2 ) by applying corresponding transmission phase distribution schemes on the metasurface aperture. The generated vortex beams are at 5.14 GHz. The transmission loss is lower than 0.5 dB while the co-polarization level is &minus, 10 dB compared to the cross-polarization level. The measurement results confirmed the simulation results and verified the properties of the proposed designs.

In this paper, we design a novelty metasurface for achieving radar cross section (RCS) reduction. The proposed metasurface can achieve phase difference by rotating its unit cells to different rotating angles as traditional Pancharatnam–Berry (P–B) phase. However, compared with traditional P–B phase metasurface, the unit cells of this proposed metasurface do not possess certain period, it indicates that random phase gradients can easily produce on this proposed metasurface. The direction and the scalar of these produced random phase gradients are all random, and the incident waves can be diffused by these random phase gradients, realizing wideband, wide angle, polarization-independent RCS reduction. The design of units without fixed period increases the freedom of controlling electromagnetic wave. Both the simulation and experiment show that the proposed metasurface is valuable for stealth technology.

Microwave devices with polarization conversion and band-pass filtering response have great application prospects on radomes. Here, the concepts of band-pass filters and cross-polarization converters are combined to realize a band-pass filtering cross-polarization converter with an extremely high polarization-conversion ratio. Most importantly, the device has an excellent out-of-band rejection level, above 30 and 40 dB for the lower and upper edges, respectively. In addition, the transmission zeros of the passband can be flexibly tuned independently. The band-pass filtering polarization converter was simulated, fabricated, and measured, and the measured results were found to be in good agreement with the simulation results.

A high-isolation coaxial-fed antenna array is proposed through the integration of metamaterial. To this end, a magnetic metamaterial, the substrate-integrated split-ring resonator (SI-SRR), is designed and integrated in the shared substrate between two closely spaced antennas. Due to negative permeability of SI-SRR, magnetic fields are blocked in the shared substrate. By suppressing the near-field magnetic coupling, enhanced isolation between the two antennas is obtained. The antenna array was fabricated and measured. Both the simulated and measured results show that the proposed antennas can provide an isolation of 34.5 dB in the operation band, even when the gap between the two antennas is only nearly about 0.033λ. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2321–2325, 2016

In this article, a wide impedance bandwidth and gain bandwidth Fabry–Perot resonator microstrip patch antenna based on metamaterials was presented. The metamaterial superstrate, which is constructed by a doubly periodic array of complementary cross elements, achieved stable reflection phase response within the wide desired operation frequency range to broaden the bandwidth. This antenna worked at 13 GHz, and the simulated and measured impedance bandwidth (S11

Recently, decentralized optimization (DO) has received widespread attentions. Since the scale of DO is usually very large, research on acceleration has become a hotspot. However, the error caused by the global information deficiency for each agent becomes the key problem cumbering the existing elaborately designed accelerated methods from being applied to DO, directly. On the other hand, recent studies illustrate that a group of accelerated methods can be covered from a viewpoint of momentum. In this paper, we propose to follow this methodology to design accelerated algorithms and adapt them to DO over time-varying directed networks, of which the main benefit is that, because the proposed algorithms are derived from momentum, they not only avoid the design of elaborate iterative structures but also inherit the physical interpretability of momentum. Furthermore, we show that our proposed algorithms can achieve sharper convergence rates than their competitors under the same condition. In the end, experiments on a number of benchmark datasets validate well the competitiveness of our algorithms.

Wireless sensing is widely adopted in internet of things (IoT) systems, but battery replacement is a critical issue for these devices. Triboelectricity, solar, heat, and vibration can be potential energy sources. Piezoelectric energy harvesters that can obtain energy from ambient vibrations are thought to be a promising approach to this problem. However, state-of-the-art energy harvesters made from cantilever-structured piezoelectric ceramics exhibit low output power densities. In this paper, we propose a bridge-type shear-mode piezoelectric energy harvester based on Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals. Owing to the large figure-of-merit d15 × g15 (1.296 × 10 −10C V m N−2) of the crystal and the higher electromechanical transfer efficiency of the flex-tensional structure when compared to a ceramic cantilever structure, the newly designed shear-mode energy harvester exhibits a power density of up to 1.378 × 10 4 W m−3. This is much higher than the power densities provided by conventional cantilever energy harvesters based on piezoelectric ceramics (~ 10 2 W m−3). The output voltage and maximum output current are 21.6 Vpp and 6 × 10 −4 App, respectively under an inertial force of 0.25 N. This output current and power density are 5.5 times and 3.0 times, respectively, higher than those of the same structured energy harvester made from soft piezoelectric ceramics. A sample wireless sensing and data transmission system is successfully powered by the newly designed energy harvester. This work may help to address the issue of sustainable energy supplies for IoT systems.

Power generation facilities in the U.S. are looking for a potential renewable fuel that is sustainable, low-cost, complies with environmental regulation standards and is a drop-in fuel in the existing infrastructure. Although torrefied woody biomass, meets most of these requirements, its high cost, due to the use of woody biomass, prevented its commercialization. Industrial waste blends, which are also mostly renewable, are suitable feedstock for torrefaction, and can be an economically viable solution, thus may prolong the life of some of the existing coal power plants in the U.S. This paper focuses on the torrefaction dynamics of paper fiber-plastic waste blend of 60% fiber and 40% plastic and the characterization of its torrefied product as a function of extent of reaction (denoted by mass loss). Two forms of the blend are used, one is un-densified and the other is in the form of pellets with three times the density of the un-densified material. Torrefaction of these blends was conducted at 300°C in the mass loss range of 0-51%. The torrefied product was characterized by moisture content, grindability, particle size distribution, energy content, molecular functional structure, and chlorine content. It was shown that although torrefaction dynamics is of the two forms differs significantly from each other, their properties and composition depend on the mass loss. Fiber content was shown to decrease relative to plastic upon the extent of torrefaction. Further, the torrefied product demonstrates a similar grinding behavior to Powder River Basin (PRB) coal. Upon grinding the fiber was concentrated in the smaller size fractions, while the plastic was concentrated in the larger size fractions.

The metasurfaces have recently been demonstrated to provide full control of the phase responses of electromagnetic (EM) wave scattering over subwavelength scales, enabling a wide range of practical applications. Here, a method for fast design of polarization-independent metasurfaces is proposed. A nonlinear fitting scenarios is employed to precisely predict reflective phase response of the metasurface. To obtain the optimal performance, nonlinear fitting scheme and genetic algorithm are combined. Since low-Q-factor resonant able to introduce wideband and smooth phase response, combining with lossless substrate, the metasurface with high reflective amplitude and wideband corresponding phase response can be obtained. As verify, two types metasurface examples characterized of coding metasurface on RCS reduction and reflective focusing lens are demonstrated.

A reconfigurable polarization converter that enables transparent polarization tunable is presented. The converter has simple metal structure and the transmitted wave can be tuned between linear polarization (LP) and circular polarization (CP) by adjusting the state of the switches inserted into the structure. The simulated and experimental transmission parameters were obtained to verify the polarization tunability for LP incident waves at two ideal states of the switches.

This work proposes a synthetic design for a microwave absorber and antireflection to achieve reduction of wideband scattering. Simultaneous control of the absorption and scattering pattern of metasurfaces can be achieved by theoretical analysis and calculation aimed at improving the reduction of backward reflection. With a topologically optimized design and antenna array synthesis, customized absorption and an optimal arrangement can be achieved over a broad spectrum within an integrative optimization procedure. To validate the design method, a wideband low radar cross-section metasurface is proposed, for which good agreement is observed between simulations and experiment with pronounced reflection suppression from 9 to 23.9 GHz. This work reveals the opportunity for use of a metasurface in effective manipulation of microwaves and a synthesis optimization method for designing a high-performance flexible low-scattering platform.

This work presents a study of a PIN tuned active phase gradient metasurface to be used for beam-steering application. The unit cell of the active metasurface consists of square-loop slot loaded with PIN diodes. The phase difference between the unit cells of the metasurface is generated by different position of the PIN diodes welded in the unit cell. And the refractive beam angle of the metasurface can be tuned by changing the state of the PIN diodes. The active metasurface is designed at S band and the effectiveness of the design is validated by numerical simulation.

In this paper, nonconvex and nonsmooth models for compressed sensing (CS) and low rank matrix completion (MC) is studied. The problem is formulated as a nonconvex regularized leat square optimization problems, in which the l0-norm and the rank function are replaced by l1-norm and nuclear norm, and adding a nonconvex penalty function respectively. An alternating minimization scheme is developed, and the existence of a subsequence, which generate by the alternating algorithm that converges to a critical point, is proved. The NSP, RIP, and RIP condition for stable recovery guarantees also be analysed for the nonconvex regularized CS and MC problems respectively. Finally, the performance of the proposed method is demonstrated through experimental results., 19 pages,4 figures

Based on effective medium theory and dielectric resonator theory, we propose the design of reconfigurable all-dielectric metamaterial frequency selective surfaces (FSSs) using high-permittivity ceramics. The FSS is composed of ceramic resonators with different band stop responses under front and side incidences. By mechanically tuning the orientation of the ceramic resonators, reconfigurable electromagnetic (EM) responses between two adjacent stopbands can be achieved. The two broad stopbands originate from the first two resonant modes of the ceramic resonators. As an example, a reconfigurable FSS composed of cross-shaped ceramic resonators is demonstrated. Both numerical and experimental results show that the FSS can switch between two consecutive stopbands in 3.55–4.60 GHz and 4.54–4.94 GHz. The design method can be readily extended to the design of FSSs in other frequencies for high-power applications.

In this paper, a self-adaption matched filter (SMF) and bi-directional difference techniques are proposed to detect a small moving target in urban environments. Firstly, the SMF technique is proposed to improve the signal-to-interference-noise ratio (SINR) by using the power factor. The properties of the transmitting signal, the target echoes and the interference and noise are considered during the power factor generation. The amplitude coherent accumulation technique that extracts the coherent amplitude information of echoes after being processed by the SMF, is used to improve the SINR based on multiple measurements. Finally, the bi-directional difference technique is proposed to distinguish the target echoes and the interference/noise. Simulations and experiments are conducted to validate and demonstrate that small moving targets can be detected with high probability using the proposed method in urban environments, even with just one measurement.

A hybrid frequency selective surface (FSS) with low-frequency absorption and high-frequency transmission is designed and demonstrated experimentally. The waveguide array with the spatial filtering characteristics of low-frequency reflection and high-frequency transmission is firstly proposed and the resistor-loaded loop array is then introduced on the top layer. Since the metal-like behavior of the waveguide array at low frequencies, the hybrid FSS can achieve strong absorption, while the transmission at high frequencies can be kept all the same. Simulated results show that the proposed hybrid structure can achieve broadband absorption with the efficiency more than 90% in the frequency range of 7.7-12.4 GHz and effective transmittance more than 80% from 16.5 to 18.0 GHz. The maximum transmittance of 89% can be gained at 17.4 GHz. Finally, the experimental measurement has also been performed to provide a good demonstration.

In this paper, we propose the design of a hybrid surface with a low radar cross section (RCS) at lower frequencies and a transmission window at higher frequencies. The hybrid surface comprises two parts: a frequency selective surface (FSS) on the bottom and a checkerboard metasurface on the top. The FSS exhibits low-stop and high-pass properties, which reflects waves at lower frequencies and allows transmission of waves at higher frequencies. The checkerboard metasurface, with a reflective substrate, can reduce RCS at lower frequencies by means of scattering cancellation. Due to the low-stop property of the FSS, the hybrid surface can achieve broadband RCS reduction at low frequencies since the FSS acts as the reflective substrate. Simultaneously, the transmission window at higher frequencies of the FSS can be kept. Simulation results show that the RCS can be reduced by more than 10 dB in 4.1–7.7 GHz and the insertion loss in the transmission window is lower than 1.0 dB in 11.3–13.3 GHz. A prototype was fabricated and measured. The experimental results agree well with the simulation results. This work provides an effective alternative to the design of functional devices such as stealthy radomes, etc.