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A broadband dual circularly polarized (dual-CP) reflectarray based on 3-D printed dielectric materials is proposed in this article. A novel 3-D dielectric array element that enables the broadband linearly polarization (LP) to CP transformation is proposed. The unit cell consists of two orthogonal dielectric cuboids that adjust the phases of the two orthogonal LP waves independently and then combine them into a CP wave. The innovative unit cell design provides an extra degree of freedom in varying the geometries of the array elements in all three dimensions, which enables us to independently control the phases of the two LP waves. This maintains an equal amplitude and 90° phase difference condition across the entire reflectarray surface, realizing a broadband and high gain LP–CP reflectarray. The placement of the feed is also optimized to achieve the highest aperture efficiency. Finally, an off-set reflectarray was designed and fabricated using lost-cost 3-D printing. The reflectarray is able to provide both left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP), with just an LP feed. The measurements agree well with simulated results where the maximum realized gain and directivity at 34 GHz are measured as 27.9 and 28.1 dBi, respectively. The measured 3 dB gain bandwidth and aperture efficiency are 30% and up to 38%, respectively. More importantly, a broad 3 dB axial ratio (AR) bandwidth greater than 40% has been achieved for both LHCP and RHCP, covering almost the entire frequency band of interest, ranging from 26 to 40 GHz. [ABSTRACT FROM AUTHOR]

Based on the static capacitance-voltage (${C}-{V}$) model, a new analytical frequency-dependent ${C}-{V}$ model of thin-film transistors (TFTs) is derived from a modified transmission line method (TLM), which is built by embedding an equivalent circuit corresponding to the trapped electrons effect into the traditional TLM. The proposed model is well verified by the measured ${C}-{V}$ characteristics of bottom-gated indium-zinc–oxide (IZO) TFTs with ${W} / {L} =100 \boldsymbol {\mu }{\text {m}} /10 \boldsymbol {\mu }\text {m}$ and ${W} / {L} =100 \boldsymbol {\mu }\text {m} /40 \boldsymbol {\mu }\text {m}$ , where frequencies vary from 1 kHz to 1 MHz. The cutoff frequency of metal oxide TFTs is furthermore analyzed based on the proposed model compared with the traditional TLM. [ABSTRACT FROM AUTHOR]

This paper describes the design and testing of a multiple-in multiple-out (MIMO) antenna for metal-frame smartwatch applications. The antenna operates from 2.4 to 2.49 GHz, which can cover Bluetooth/WiFi band. The design procedure is based on the theory of characteristic modes and it is discussed thoroughly. By employing a pair of degenerated modes to design the MIMO antenna, a high port-to-port isolation can be achieved over the operating frequency band. Simulated and measured results are presented to verify the antenna design. Furthermore, the antenna has a low envelope correlation coefficient and a high effective diversity gain even when it is mounted on the human phantom. Hence, the proposed antenna proves to be a good candidate for smartwatch applications. [ABSTRACT FROM AUTHOR]

A new miniature circular high-impedance surface (HIS) is used to design a compact and low-profile multi-in multi-out (MIMO) antenna for wearable applications. The antenna is designed to operate from 2.4 to 2.49 GHz for wireless local area network application. By employing a pair of degenerated characteristic modes of a circular loop antenna, the MIMO antenna can achieve a good port-to-port isolation (>15 dB) without increasing its geometric size. A four-element HIS is chosen to match the antenna profile, and a 2 dBi antenna gain improvement is observed. The design was optimized considering the effect of packaging and then a prototype with the optimal parameters was fabricated and tested. Measurement results are in good agreement with simulation results. Furthermore, the loading effect due to lossy human tissue is also considered and the results show that the antenna has a robust performance against the human phantom and a low specific absorption rate can also be obtained. [ABSTRACT FROM AUTHOR]

Local optimization is a routine approach for fullwave optimization of microwave filters. For filter optimization problems with numerous local optima or where the initial design is not near to the optimal region, the success rate of the routine method may not be high. Traditional global optimization techniques have a high success rate for such problems, but are often prohibitively computationally expensive considering the cost of full-wave electromagnetic simulations. To address the above challenge, a new method, called surrogate model-assisted evolutionary algorithm for filter optimization (SMEAFO), is proposed. In SMEAFO, considering the characteristics of filter design landscapes, Gaussian process surrogate modeling, differential evolution operators, and Gaussian local search are organized in a particular way to balance the exploration ability and the surrogate model quality, so as to obtain high-quality results in an efficient manner. The performance of SMEAFO is demonstrated by two real-world design cases (a waveguide filter and a microstrip filter), which do not appear to be solvable by popular local optimization techniques. Experiments show that SMEAFO obtains high-quality designs comparable with global optimization techniques but within a reasonable amount of time. Moreover, SMEAFO is not restricted by certain types of filters or responses. The SMEAFO-based filter design optimization tool can be downloaded from http://fde.cadescenter.com. [ABSTRACT FROM AUTHOR]

In this communication, the design procedure of a wideband antenna with omnidirectional radiation pattern is demonstrated based on the theory of characteristic modes. Consisting of a dipole and a loop antenna, the antenna has a very simple structure. A wide impedance bandwidth is obtained because of the simultaneous excitation of the antenna’s first two modes. Meanwhile, due to the fact that these two modes share a similar omnidirectional radiation pattern, a stable radiation pattern is also achieved across the operating frequency band. In order to identify the antenna’s different modes, a characteristic mode analysis of the antenna is carried out first. Then, a feed configuration is specifically designed to excite the desired modes. To validate the antenna design, a prototype was fabricated and tested. Measured results agree well with the simulated ones. Measurement shows that a wide impedance bandwidth of 44.2% with \vert \textS11\vert < -10 dB (1.85–2.9 GHz) and stable radiation patterns at both E-plane and H-plane were achieved over the operating frequency band. [ABSTRACT FROM PUBLISHER]

The “invisible carpet cloak” has recently been created and demonstrated as a novel device that serves to conceal conducting objects from external detections (J. Li and J. B. Pendry, “Hiding under the carpet: A new strategy for cloaking,” Phys. Rev. Lett., vol. 101, no. 20, p. 203901, 2008). In this work, we have explored its new function as a new type of stealth radome to protect antennas. A technique called “virtual boundary” is implemented to the carpet cloak to ensure that a conducting antenna element located beneath the carpet can transmit and receive signals, while being undetectable to the external incidences. Meanwhile, the carpet cloak functions as a novel lens to create highly directive beams. Numerical simulations based on finite-difference time-domain (FDTD) method have demonstrated the expected performances over the frequency range from 8 GHz to 12 GHz (the X-band). [ABSTRACT FROM PUBLISHER]

Drived by a µs pulse high-voltage power supply, a homogeneous DBD in atmospheric air is generated between two plane-parallel electrodes, with PTFE plates as dielectric barriers. The discharge generated shows homogeneous discharge characteristics. The light emission is radially homogeneous and covers the entire surface of the electrodes, and a single current pulse with duration of about 1 µs and amplitude of less than 1 A appears in each voltage pulse. The homogeneous DBD is used to treat the polyethylene terephthalate (PET) films to improve their surface hydrophilicity, and as the main operating parameters, the effects of discharge power density of the homogeneous DBD on the surface treatment are also studied. The surface properties of PET films before and after treatments are studied using the following: 1) contact angle and surface energy measurement; 2) attenuated total reflection fourier transform infrared spectroscopy (ATR-FTIR); 3) x-ray photoelectron spectroscopy (XPS); and 4) scanning electron microscopy (SEM). The results of contact angle and surface energy measurements reveal that the homogeneous DBD treatment can improve the surface hydrophilicity of PET films, as it can induce a remarkable decrease in water contact and a remarkable increase in surface energy. The results of SEM, XPS, and FTIR shows that improvement of the hydrophilicity due to both the introduction of oxygen-containing polar groups onto the surface and the etching of the surface. It is found that increasing discharge power density of homogeneous DBD can induce more effective treatment of PET films, and less treatment time is needed to achieve the same level of surface treatment by increasing the discharge power density. [ABSTRACT FROM AUTHOR]

A conformal dispersive finite-difference time-domain (FDTD) method is developed for the study of one-dimensional (1-D) plasmonic waveguides formed by an array of periodic infinite-long silver cylinders at optical frequencies. The curved surfaces of circular and elliptical inclusions are modelled in orthogonal FDTD grid using effective permittivities (EPs) and the material frequency dispersion is taken into account using an auxiliary differential equation (ADE) method. The proposed FDTD method does not introduce numerical instability but it requires a fourth-order discretisation procedure. To the authors' knowledge, it is the first time that the modelling of curved structures using a conformal scheme is combined with the dispersive FDTD method. The dispersion diagrams obtained using EPs and staircase approximations are compared with those from the frequency domain embedding method. It is shown that the dispersion diagram can be modified by adding additional elements or changing geometry of inclusions. Numerical simulations of plasmonic waveguides formed by seven elements show that row(s) of silver nanoscale cylinders can guide the propagation of light due to the coupling of surface plasmons. [ABSTRACT FROM AUTHOR]

Presents information pertaining to the electromechanical structures of finite-difference time-domain (FDTD) algorithm. Basis of the algorithm; Calculations of the curved boundaries; Description of the algorithm.

State estimation is one of the main challenges in the microgrids, due to the complexity of the system dynamics and the limitations of the communication network. In this regard, a novel real-time event-based optimal state estimator is introduced in this article, which uses the proposed adaptive send-on-delta (SoD) nonuniform sampling method over wireless sensors networks. The proposed estimator requires low communication bandwidth and incurs lower computational resource cost. The threshold for the SoD sampler is made adaptive based on the average communication link delay, which is computed in a distributed form using the event-based average consensus protocol. The SoD nonuniform signal sampling approach reduces the traffic over the wireless communication network due to the events transmitted only when there is a level crossing in the measurements. The state estimator structure is extended on top of the traditional Kalman filter with the additional stages for the fusion of the received events. The error correction stage is further improved by optimal reconstruction of the signals using projection onto convex sets algorithm. Finally, an Internet of things (IoT) experimental platform based on LoRaWAN and IEEE 802.11 (WiFi) protocols are developed to analyze the performance of the state estimator for the IEEE 5 Bus case study microgrid. [ABSTRACT FROM AUTHOR]

In , there are some mistakes in the antenna dimensions in on page 2672 and on page 2674. These two figures should be corrected as follows: [ABSTRACT FROM AUTHOR]

Surface electromagnetics (SEM), as a sub-discipline of electromagnetic (EM) science, is strongly linked with the ability to manipulate an arbitrary EM wavefront. This exceptional capability of manipulating the surface-bound and free-space EM waves for the guidance and control of anomalous reflection, refraction and transmission has catapulted an abundance of new research frontiers. This has resulted in the realization of many novel applications for modern real-life platforms and the introduction of several new modelling techniques and engineering approaches to give rise to some unconventional devices. Consequently, EM engineered metasurfaces, due to numerous emerging applications, are beginning to revolutionize the EM industry. Recently, the practical usage of metasurfaces has gained a substantial amount of interest and traction for a wide range of applications in microwave, millimetre-wave (mmWave), Terahertz (THz) and even optical wavelengths. This tutorial is aimed at presenting a plethora of EM metasurface applications and research frontiers to illustrate a broader impact of SEM in real-world platforms, advanced communication systems and new devices. [ABSTRACT FROM AUTHOR]

In this paper, a pervasive wireless channel modeling theory is first proposed, which uses a unified channel modeling method and a unified equation of channel impulse response (CIR), and can integrate important channel characteristics at different frequency bands and scenarios. Then, we apply the proposed theory to a three dimensional (3D) space-time-frequency (STF) non-stationary geometry-based stochastic model (GBSM) for the sixth generation (6G) wireless communication systems. The proposed 6G pervasive channel model (6GPCM) can characterize statistical properties of channels at all frequency bands from sub-6 GHz to visible light communication (VLC) bands and all scenarios such as unmanned aerial vehicle (UAV), maritime, (ultra-)massive multiple-input multiple-output (MIMO), reconfigurable intelligent surface (RIS), and industry Internet of things (IIoT) scenarios. By adjusting channel model parameters, the 6GPCM can be reduced to various simplified channel models for specific frequency bands and scenarios. Also, it includes standard fifth generation (5G) channel models as special cases. In addition, key statistical properties of the proposed 6GPCM are derived, simulated, and verified by various channel measurement results, which clearly demonstrates its accuracy, pervasiveness, and applicability. [ABSTRACT FROM AUTHOR]

A correction to the article "Design of a Carpet Cloak to Conceal an Antenna Located Underneath," that was published in the vol. 61, no.5, May 2013 issue, is presented.

On-body radio propagation in the 2.45-GHz industrial-scientific-medical frequency band (2.40–2.48 GHz) was investigated during three different activities: jogging, rowing and cycling. Four different links were examined, from the waist to the wrist, ankle, chest and back; it was observed that the channel behavior could be related to the repetitive nature of the activities. Furthermore, combinations of the wrist, ankle, and chest channels could potentially be used to identify the activity, while the waist-back channel shows little variation between activities (roughly 2 dB, compared to 6–15 dB for the other links). The results also show that dynamic on-body radio channels contain rich biomechanical information, such as motion pattern, heartbeat, and breathing process. It is demonstrated that physiological and kinetic features can, therefore, be extracted through some known signal-processing techniques. For example, the repetitive nature of the activities introduces harmonics into the signal via fading, which correspond to the speed of motion. In addition, the mechanical motion of the torso during respiration and cardiac activity also introduce harmonics due to changes in the path loss, albeit with low magnitudes. The detection of such signals is discussed. [ABSTRACT FROM PUBLISHER]

We demonstrate a broadband near-100%-efficiency ultrathin metasurface operating at microwave and millimeter-wave frequencies. We develop and employ two orthogonally polarized metallic gratings to form a Fabry–Perot cavity and incorporate a subwavelength metallic double-split-ring resonator at the center of each unit cell. It allows arbitrary amplitude-phase combinations with no coupling between amplitude and phase or between transmitted and reflected waves, leading to the design of an ultrathin but highly efficient broadband metasurface with multiple functionalities. Furthermore, the proposed metasurface can generate diffractive beams with different orders and vortex beams with different orbital angular momentum (OAM) modes in reflection and transmission spaces simultaneously. Both numerical and experimental results verify that the proposed metasurface has superior performance to its counterparts that are based solely on phase control. The proposed metasurface presents a lightweight, low-cost, and easily deployable flat device for microwave and millimeter-wave applications. [ABSTRACT FROM AUTHOR]

Tissue mimicking phantoms (TMPs) replicating the dielectric properties of wet skin, fat, blood, and muscle tissues for the 0.3 to 20 GHz frequency range are presented in this paper. The TMPs reflect the dielectric properties with maximum deviations of 7.7 units and 3.9 S/m for relative dielectric constant and conductivity, respectively, for the whole band. The dielectric properties of the blood mimicking material are further investigated by adding realistic glucose amounts and a Cole–Cole model used to compare the behavior with respect to changing glucose levels. In addition, a patch resonator was fabricated and tested with the four-layered physical phantom developed in house. It was observed that the input impedance of the resonator is sensitive to the changes in the dielectric properties and, hence, to the realistic glucose level changes in the blood layer. [ABSTRACT FROM PUBLISHER]

Terahertz (THz) communication is now being considered as one of possible technologies for the sixth generation (6G) wireless communication systems. In this paper, a novel three-dimensional (3D) space-time-frequency non-stationary theoretical channel model is first proposed for 6G THz wireless communication systems employing ultra-massive multiple-input multiple-output (MIMO) technologies with long traveling paths. Considering frequency-dependent diffuse scattering, which is a special property of THz channels different from millimeter wave (mmWave) channels, the relative angles and delays of rays within one cluster will evolve in the frequency domain. Then, a corresponding simulation model is proposed with discrete angles calculated using the method of equal area (MEA). The statistical properties of the proposed theoretical and simulation models are derived and compared, showing good agreements. The accuracy and flexibility of the proposed simulation model are demonstrated by comparing the simulation results of the relative angle spread and root mean square (RMS) delay spread with corresponding measurements. [ABSTRACT FROM AUTHOR]

The on-body channel was characterised at various points on the human torso in an anechoic chamber using a pair of wireless sensor modules. The performance of wireless IEEE 802.15.4 sensor nodes operating in the 2.45 GHz ISM frequency band (2.40–2.4835 GHz) is presented over each of the 16 different channels. It is shown that the response at individual carrier frequencies is dependent not only on the initial antenna response, as determined by the on-body measurement in isolation, but also on the overall system performance. Measurement results are also compared with those from the conventional technique using a Vector Network Analyzer. [ABSTRACT FROM PUBLISHER]

A fold monopole/dipole/loop antenna offers unique advantages over a conventional Planar Inverted-F Antenna (PIFA) and monopole antenna for a mobile cellular device. Perhaps the most significant benefit is the fact that up to three resonant modes could be generated in a single continuous loop structure. In this paper, a novel hexa-band internal folded monopole/dipole/loop antenna has been proposed. The proposed antenna has four resonances in which three of them are 0.5\lambda, 1\lambda and 1.5\lambda modes. The distinctive feature of the antenna is an extra 2\lambda folded dipole mode, which has not been reported so far, is excited and utilized. All these four modes can be employed to cover the Low LTE700/GSM850/900 Band (LB: 698–960 MHz) and the High GSM1850/1900/UMTS2100 Band (HB: 1710–2170 MHz). The proposed loop antenna has been simulated, prototyped and tested. It is shown that the numerically simulated results are in close agreement with the experimental prototype results and proved that the antenna operates as proposed. [ABSTRACT FROM PUBLISHER]

Two-phase nanocomposite heteroepitaxial films with vertical microstructures hold great promise for various (multi)functional (e.g., multiferroic) electronic device applications. With the aim of creating addressable arrays, it is necessary to form spontaneously ordered structures over large areas. However, such structures have not, so far, been demonstrated. We have recently produced remarkable spontaneously ordered phase assemblies and find that these structures form concomitantly with 2-D vertical strain control, i.e., strain in the 2 phases is controlled along the vertical interface between them rather than being influenced by the substrate. In this paper, we report on our findings in the BiFeO3 and BaTiO3 ferroelectric systems. [ABSTRACT FROM AUTHOR]

In this paper, polyethylene terephthalate (PET) films are modified using nonequilibrium plasma generated by homogeneous dielectric barrier discharges (DBDs) in air at medium pressure, and the results are compared to those treated by using filamentary DBDs in air at atmospheric pressure. The characteristics of homogeneous DBDs are studied and compared with those of filamentary DBDs by measuring their electrical discharge parameters and observing their light-emission phenomena, and the surface properties of PET films before and after the treatments are studied using contact-angle and surface-energy measurements, X-ray photoelectron spectroscopy, and scanning electron microscopy. It is found that the homogeneous DBD is quite homogeneous and stable in the whole gas gap, which differs from the filamentary DBD, and the plasma treatments modify the PET surface in both morphology and composition. The PET films modified in both treatments show a remarkable decrease in water contact and a remarkable increase in surface energy due to both the introduction of oxygen-containing polar groups onto the surface and the improvement in surface roughness. It is found that the homogeneous DBD is more effective in PET surface modification than the filamentary DED as it can make the contact angle decline to a lower level by introducing more oxygen-containing groups, and the possible reason for this effect is discussed. [ABSTRACT FROM AUTHOR]

A radially-dependent dispersive finite-difference time-domain (FDTD) method is proposed to simulate electromagnetic cloaking devices. The Drude dispersion model is applied to model the electromagnetic characteristics of the cloaking medium. Both lossless and lossy cloaking materials are examined and their operating bandwidth investigated. It is demonstrated that the perfect "invisibility" of electromagnetic cloaks is only available for lossless metamaterials and within an extremely narrow frequency band. [ABSTRACT FROM AUTHOR]

This article proposes a method of using a highly efficient spoof surface plasmon polariton (SSPP) endfire sensor for monitoring of aqueous glucose solutions and on-body glucose measurements. Occupying an area of around (52 mm $\times24$ mm), the proposed sensor radiates an endfire beam into a glucose water solution with a substantially reduced effective aperture. At the coplanar waveguide (CPW) port of the sensor, a pair of triangular ground planes was added to suppress the sidelobes, which have been proven to be counter-productive in glucose sensing. The slow-wave nature of the proposed SSPP endfire sensor has further advantageously enabled the glucose concentrations to be measured with an increased sensitivity. The guiding body of the sensor was designed to simulate an electromagnetic beam propagating in a dense dielectric medium with a group velocity comparable to the phase velocity of light propagating in a glucose solution. Consistent with the results of our analysis, the experimental results of this work revealed that the gradual transition of slow electromagnetic wave from the SSPP endfire sensor to the glucose water solution has successfully enabled the glucose concentrations of a solution to be measured and displayed in the form of highly observable resonant frequency shifts in S 11 parameters. The proposed design has achieved a high sensitivity of 150 MHz/mgmL−1 during on-body measurements. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surfaces (RISs) or intelligent reflecting surfaces (IRSs) are regarded as one of the most promising and revolutionizing techniques for enhancing the spectrum and/ or energy efficiency of wireless systems. These devices are capable of reconfiguring the wireless propagation environment by carefully tuning the phase shifts of a large number of low-cost passive reflecting elements. In this article, we aim to answer four fundmental questions: 1) Why do we need RISs? 2) What is an RIS? 3) What are RIS's applications? 4) What are the relevant challenges and future research directions? In response, eight promising research directions are pointed out. [ABSTRACT FROM AUTHOR]

An improved zero-current-switching pulsewidth-modulated (ZCS-PWM) commutation cell is presented, which is suitable for high-power applications using insulated gate bipolar transistors (IGBTs) as the power swithches. It provides ZCS operation for active switches and zero-voltage-switching (ZVS) operation for passive swithches. Besides operating operating at constant frequency and reducing commutation losses, the proposed ZCS-PWM switch cell has no additional current stress and conduction loss in the main switch. To demonstrate the feasibility of the proposed ZCS-PWM commutation cell, it was applied to a boost converter. Operating principle, theoretical analysis, design guidelines, and a design example are described and verified by expriment results obtained from a prototype rated 1 kW and operating at 40 kHz. The PWM switch model and state-space averaging approach is also used to estimate and examine the steady-state and dynamic character of ZCS-PWM boost converter system. Finally, the application of the proposed soft-switching technique in the dc-dc nonisolated converters is presented. [ABSTRACT FROM AUTHOR]

Connected vehicles are highly expected to be proactive, cooperative, well-informed, and coordinated. Therefore, high-reliable connected vehicle channels are required. It is widely accepted that the local scatterers appreciably affect wireless propagation channels and connected vehicle channels have no exception. This paper presents a general and highly efficient channel modeling method where electromagnetic (EM) scattering from local scatterers is calculated separately and then combined with ray tracing (RT) results; the method is named as layered-broadband channel model (LBCM) in this study and it is of great value as it could accurately simulate scatterer-included connected vehicle channels. The idea of the LBCM was arisen by the fact that EM scattering from scatterers displays point-scattering-like behaviors. Therefore, the scattering can be parameterized with a sparse point set and then the set could be efficiently implemented in broadband RT channel simulations. In order to validate the capability of proposed LBCM, a traffic sign was first taken as a typical example of local scatterers and its EM scattering was closely studied; then an urban intersection of typical vehicle-to-vehicle scenario was selected, where detailed comparisons were carried out between an LBCM-simulated channel and measured one. The validation processes present an integration of the full-wave simulation, analytical models, and measurement; and their results strongly confirm the feasibility and reliability of the LBCM. [ABSTRACT FROM AUTHOR]

This paper presents a SPICE-like graphene field-effect transistor (GFET) model with an improved carrier mobility analysis. The model considers the mobility difference between the electrons and the holes in graphene, as well as the mobility variation against the carrier density. Closed-form analytical solutions have been derived, and the model has been implemented in Verilog-A language. This was compiled into an advanced design system. The proposed model gives excellent agreement between the simulation results and the measurement data for both the hole and electron conduction simultaneously. The model is suitable for the exploration of GFET-based applications, especially for those using the ambipolar transfer property of GFET. [ABSTRACT FROM PUBLISHER]

The great flexibility offered by transformation optics for controlling electromagnetic radiation by virtually re-shaping the electromagnetic space has inspired a myriad of dream-tailored electromagnetic devices. Here we show a 3D-transformed microwave Luneburg lens antenna which demonstrates high directivity, low side-lobe level, broadband response and steerable capabilities. A conventional Luneburg lens is redesigned accounting for dielectric materials that implement a coordinate transformation, modifying the lens geometry to accommodate its size and shape for easy integration with planar microwave antenna applications. An all dielectric lens is manufactured following a thorough holistic analysis of ceramic materials with different volume fractions of bi-modal distributed titanate fillers. Fabrication and measurements of a 3-D flat Luneburg lens antenna validate the design and confirm a high-directivity performance. A directivity of 17.96 dBi, low side-lobe levels for both main planes \sim -26~dB, excellent directivity performance within the X-band and beam-steering up to 34^\circ were achieved. [ABSTRACT FROM PUBLISHER]

A new class of dielectric sheet antennas is presented based on transformation optics. Specifically, we successfully implement the transformation with a consideration of surface wave eigenmode properties, and carry out a practical perforated design by drilling holes to synthesize the required dielectric constants for their potential realization. The full wave simulation shows that our surface wave transformation lens antenna is capable of obtaining a greatly improved directivity, while maintaining the original low profile. [ABSTRACT FROM PUBLISHER]

Recent advancements in transformation optics (TO) and metamaterials have inspired tremendous interest in the electromagnetic community, creating a variety of novel antennas with enhanced performance, such as broad bandwidth, large gain, and high polarization efficiency. Although there could be infinitely many transformations for designing a given device, most of them result in rather complicated material compositions. This paper compares two recently introduced TO techniques, both of which lead to much simpler material requirements. In particular, a linear geometrical transformation or a quasi-conformal mapping was employed to design multi-beam collimating lenses, which possess either homogeneous or isotropic constituent materials. A systematic comparison is made for the first time between these two TO design approaches for a specific example of a quad-beam focusing lens, where the advantages and disadvantages of each method are clearly identified. Full-wave numerical simulations were performed to demonstrate the well-collimated beams produced by the TO lenses designed by either transformation. The characteristics of the two lens antennas, such as radiation pattern and bandwidth, were contrasted, providing valuable guidance on design tradeoffs for a specific application. [ABSTRACT FROM PUBLISHER]

A great amount of work on antennas and propagation for body-centric wireless communication has been studied at frequencies up to X band; however, on-body radio propagation at millimeter/sub-millimeter wave frequencies still remains largely unexplored. This paper presents a study of on-body radio propagation at 94 GHz, particularly focusing on the analysis of specific channels such as waist-to-torso and head-to-shoulder links. Measured data are compared with results obtained with numerical simulations emphasizing the sensitivity of the simulated path loss to the positioning of the receivers with respect to the human body. [ABSTRACT FROM PUBLISHER]

Transformation electromagnetics provides a practical approach to control electromagnetic fields at will. Based on this principle, novel devices such as the invisible cloak have been proposed. Here we examine the extension of this technique as applied to the design of flat devices in antenna systems. A method using discrete coordinate transformation is proposed, which allows the conversion of conventional devices with curved shapes into flat systems, while preserving their non-dispersive, isotropic, broadband, and lossless properties. Two specific design examples, a flat reflector and a flat lens embedded in free space, are presented. To avoid the loss and narrow bandwidth issues typically present in metamaterials, appropriate approximations and simplifications are introduced to make the all-dielectric devices, which are more practical to build. It is also shown that the discrete coordinate transformation is valid for both the E and H polarizations, as long as the local coordinates of the system remain near-orthogonal. Finite-Difference Time-Domain simulations are used to verify the performances of these designs, and show that the all-dielectric devices have similar broadband performances compared to the conventional ones, while possessing the advantages of flat profiles and small volumes. [ABSTRACT FROM AUTHOR]

Given the trend towards a user-centric concept in mobile communications, body area networks have received increasing attention within the wireless personal and body area networks community. In this paper, an experimental investigation is presented to derive suitable radio propagation models for ultra wideband (UWB) body-centric wireless communications. The performance of the body-centric UWB radio channel is investigated by considering several on-body links, including different body postures. System-level modeling of potential multiband orthogonal frequency-division multiplexed UWB system has been conducted and system performance is measured using bit error rate (BER) and signal-to-noise ratio. The conducted system analysis demonstrated that for 78% in the static case and 75% and 61% for stable and unstable transmitter locations in the pseudodynamic in-motion scenarios (respectively) of the specified on-body radio links, the BER is equal to or less than 0.1%. This demonstrates promising applications of the proposed UWB body-centric radio system. Based on these results, clear recommendations are given for best on-body locations leading to optimal system performance. [ABSTRACT FROM AUTHOR]

An experimental investigation to characterize the transient and spectral behavior of the ultrawideband (UWB) on-body radio propagation channel for body-centric wireless communications is presented. The measurements were performed considering over thirty on-body links in the front of human body in the anechoic chamber, and in indoor environment. Two different pairs of planar antennas have been used, namely, CPW-fed planar inverted cone antennas (PICA), and miniaturized CPW-fed tapered slot antennas (TSA). A path loss model is extracted from measured data, and a statistical study is performed on the time delay parameters. The goodness of different statistical models in fitting the root mean square (RMS) delay has been evaluated. Results demonstrate that the TSA, due to its more directive radiation behavior is less affected from the reflections from body parts and surrounding environment. The antenna shows significant size reduction and improved time delay behavior, and hence is an ideal candidate for UWB body area networks (BAN). [ABSTRACT FROM AUTHOR]

This paper aims at tracking vehicles from monocular intensity image sequences and presents an efficient and robust approach to three-dimensional (3-D) model-based vehicle tracking. Under the weak perspective assumption and the ground-plane constraint, the movements of model projection in the two-dimensional image plane can be decomposed into two motions: translation and rotation. They are the results of the corresponding movements of 3-D translation on the ground plane (GP) and rotation around the normal of the GP, which can be determined separately. A new metric based on point-to-line segment distance is proposed to evaluate the similarity between an image region and an instantiation of a 3-D vehicle model under a given pose. Based on this, we provide an efficient pose refinement method to refine the vehicle's pose parameters. An improved EKF is also proposed to track and to predict vehicle motion with a precise kinematics model. Experimental results with both indoor and outdoor data show that the algorithm obtains desirable performance even under severe occlusion and clutter. [ABSTRACT FROM AUTHOR]