The progressions in the field of wireless technology can be highly attributed to the development of antennas, which can access high data rates, provide significant gain and uniform radiation characteristics. One such antenna called the Vivaldi antenna has attracted the utmost attention of the researchers owing to its high gain, wide bandwidth, low cross-polarization, and stable radiation characteristics. Over the years, different procedures have been proposed by several researchers to improve the performance of the Vivaldi antennas. Some of these different approaches are feeding mechanisms, integration of slots, dielectric substrate selection, and radiator shape. Correspondingly, the performance of a Vivaldi antenna can be increased by including dielectric lens, parasitic patch in between two radiators, corrugations, as well as metamaterials. This paper gives a systematic identification, location, and analysis of a large number of performance enhancement methods of Vivaldi antenna design depicting their concepts, advantages, drawbacks, and applications. The principal emphasis of this article is to offer an outline of the developments in the design of Vivaldi antennas over the last few years, where the most important offerings, mostly from IEEE publications, have been emphasized. This review work aims to reveal a promising path to antenna researchers for its advancement using Vivaldi antennas.

In mathematical definition, a fractal is a self-similar subset of Euclidean space whose fractal dimension strictly exceeds its topological dimension which in turn involves a recursive generating methodology that results in contours with infinitely intricate fine structures. Fractal geometry has been used to model complex natural objects such as clouds coastlines, etc., that has space-filling properties. In the past years, several groups of scientists around the globe tried to implement the structure of fractal geometry for applications in the field of electromagnetism, which led to the development of new innovative antenna configurations called “fractal antennas” which is primarily focused in fractal antenna elements, and fractal antenna arrays. It has been demonstrated that by exploiting the recursive nature of fractals, several marvellous kinds of properties can be observed in antennas and arrays. The primary focus of this article is to provide a compressed overview of the developments in fractal-shaped antennas as well as arrays over the last few decades where the most prominent contributions mostly from IEEE journals have been highlighted. The open intention of this review work is to show an encouraging path to antenna researchers for its advancement using fractal geometries.

This literature presents a comprehensive, technical review of circularly polarized (CP) antennas for different applications in wireless communication, emphasizing on the recent developments in the concerned research. The article also presents a comparative study of various works reported in the open literature, with an aim to highlight the contribution of CP antenna systems in the chronological development of the wireless communication technology. The primary motive of this review is to (a) highlight the methodologies used by different researchers to portray and analyze the different aspects in which CP antennas find their applications in modern-day wireless communication, (b) provide a practical viewpoint of the future scope of the study, based upon the past and present state-of-art research trends and (c) provide a conceptual and technical support to present-day antenna designers to help the process of furtherance of innovation and multiple system integration. In conclusion, the article also throws some light upon the future scope of research in the vast domain of CP antenna applications.

This paper presents Parallel World Framework as a solution for simulations of complex systems within a time-varying knowledge graph and its application to the electric grid of Jurong Island in Singapore. The underlying modeling system is based on the Semantic Web Stack. Its linked data layer is described by means of ontologies, which span multiple domains. The framework is designed to allow what-if scenarios to be simulated generically, even for complex, inter-linked, cross-domain applications, as well as conducting multi-scale optimizations of complex superstructures within the system. Parallel world containers, introduced by the framework, ensure data separation and versioning of structures crossing various domain boundaries. Separation of operations, belonging to a particular version of the world, is taken care of by a scenario agent. It encapsulates functionality of operations on data and acts as a parallel world proxy to all of the other agents operating on the knowledge graph. Electric network optimization for carbon tax is demonstrated as a use case. The framework allows to model and evaluate electrical networks corresponding to set carbon tax values by retrofitting different types of power generators and optimizing the grid accordingly. The use case shows the possibility of using this solution as a tool for CO2 reduction modeling and planning at scale due to its distributed architecture.

This paper presents the design and analysis of a miniaturized, coplanar waveguide-fed ultra-wideband monopole on-chip antenna with band-notch characteristics. By incorporating a “U”-shaped slot in the feedline, a band-notch is realized in the frequency range of 7.9–8.4 GHz to avoid interference from the X-band uplink satellite communication system. The proposed antenna achieved good voltage standing wave ratio (VSWR) characteristics with VSWR value <2 for the frequency range of 2.5–20.1 GHz excluding the band-notched frequencies. The fractional bandwidth and bandwidth ratio are obtained as 156% and 8.04:1, respectively. Dominant factors that affect the center frequency and bandwidth of the notched band are thoroughly investigated. This paper addresses both frequency as well as time domain behavior of the proposed structure. Standard 675 µm thick, high resistive silicon substrate (ρ≥8 kΩ-cm, εr = 11.8, and tan δ = 0.01) is used to design the proposed compact antenna structure with a layout area of 8.5 × 11.5 mm2. Fabrication process steps along with simulated and measured data are presented here. A close analogy between simulated and measured data is observed.

The changes in physical environmental parameters have severe impacts on food safety and security. Therefore, it is important to understand micro-level physical parameter changes occurring inside food packages to ensure food safety and security. The emergence of smart packaging has helped to track and inform the specific changes such as a change in humidity, temperature, and pH taken place in the microenvironment in the food package. Moreover, these key physical parameters help determine the freshness of the food as well. Radio-frequency identification (RFID)-based sensors are an emerging technology that has been used in smart packaging to detect changes in the physical stimuli in order to determine food freshness. This review looks at the key environmental factors that are responsible for food safety and food freshness, the role of smart packaging with sensors that can measure changes in physical stimuli in the microclimate and the detailed review of RFID-based sensors used in smart packaging for food-freshness applications and their existing limitations.

Using the data obtained from Kepler satellite, we have analyzed an F-type ultra-fast rotator KIC 6791060. We derive a rotational period of 0.34365±0.00004 d. Multiple periodicity with a period separation of ~0.00016 d was detected, which appears to be a result of the relative velocity between the multiple spot-groups in different stellar latitudes due to the surface differential rotation. Modeling of the surface inhomogeneities using the light curve of 3899 epochs shows the evidence of single active longitude region. The active longitude is found to drift along the longitude at a rate similar to the detected period separation of the F-type star. The surface coverage of cool spots is found to be in the range of ~0.07–0.44%. The low value of the spottedness can be interpreted probably due to the thinner convection zone on the F-type star.

We consider semilinear elliptic problems on two-dimensional hyperbolic space. A model problem of our study is

where H 1(𝔹2) denotes the Sobolev space on the disc model of the hyperbolic space and f(x, t) denotes the function of critical growth in dimension 2. We first establish the Palais–Smale (PS) condition for the functional corresponding to the above equation, and using the PS condition we obtain existence of solutions. In addition, using a concentration argument, we also explore existence of infinitely many sign-changing solutions.

The plasmas in space, cosmic and astrophysical environments are long known to consist of numerous massive ionic components contributing to various wave instability fluctuation phenomena. Indeed, the ion-inertial effects need to be incorporated into realistic analyses, rather than treating the gravitating ionic species traditionally as a Boltzmann distributed fluid. Herein, we present an atypical theoretical model setup to study gravito-electrostatic mode-fluctuations in self-gravitating inhomogeneous interstellar dust molecular clouds (DMCs) on the astrophysical fluid scales of space and time. The main goal is focused on investigating the influence of self-consistent dynamic ion-inertial effects on the stability. Methodological application of standard multiple scaling techniques reduces the basic plasma structure equations into a unique pair of decoupled Korteweg–de Vries (KdV) equations for the weak fluctuations. In contrast, the fully nonlinear counterparts are shown to evolve as a new gravito-electrostatically coupled pair of the Sagdeev energy-integral equations. In both the perturbation regimes, excitation of two distinct eigenmode classes – electrostatic compressive solitons and self-gravitational rarefactive solitons with unusual and unique parametric features – is demonstrated and portrayed. The graphical shape analysis reflects new plasma conditions for such eigenspectral patterns to coevolve in realistic interstellar parameter windows hitherto remaining unexplored. It is seen that the inertial ions play a destabilizing influential role leading to enhanced fluctuations toward establishing a reorganized gravito-electrostatic equilibrium structure. Finally, we discuss the consistency of our results in the framework of existing inertialess ion theories, experimental findings and multiple space satellite-based observations, together with new implications.

Aulacophora foveicollis Lucas causes economic losses to creeping cucumber [Solena amplexicaulis (Lam.) Gandhi] growers in India and Bangladesh because adults feed on the leaves and flowers causing death of the plant. The insect is a generalist herbivore as it also causes damage to pumpkin, bottle gourd, sponge-gourd and gac fruit production by feeding on leaves and flowers of these plants. At present, insects are controlled with insecticides, which are harmful to human health and the environment. We studied the behavioural responses of adult A. foveicollis to flower surface waxes and synthetic compounds mimicking flower surface waxes to determine their potential for monitoring this pest. The gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detector (GC-FID) analyses of S. amplexicaulis flower (50 g) surface waxes indicated presence of 17.9 and 3.1 mg alkanes and free fatty acids, respectively. Seventeen n-alkanes from n-C15 to n-C34 and 16 free fatty acids from C10:0 to C22:0 were detected in the flower surface waxes. Heptacosane was predominant among n-alkanes representing 2748.1 µg; whereas, pentadecanoic acid was the major fatty acid accounting for 466.6 µg. Aulacophora foveicollis were attracted to the flower surface waxes at concentrations of 4 to 8 μg/ml, as demonstrated by a Y-tube olfactometer bioassay. Using a dose response bioassay, the insect was shown to be attracted to individual synthetic pentadecane, heptacosane, nonacosane, undecanoic acid and nonadecanoic acid at 0.70, 0.70, 1.20, 1.60 and 1.40 µg/ml, respectively. The insect displayed highest attraction to a synthetic mixture of 0.70, 1.23, 0.77, 0.84, 0.94 and 0.74 µg/ml of pentadecane, heptacosane, nonacosane, undecanoic acid, lauric acid and nonadecanoic acid, respectively, and hence, this combination might be used for insect pest management such as in baited traps.

This article presents a modeling and parametric investigation of printed circuit board (PCB) coils used in inductive power charging systems by using intensive full-wave electromagnetic simulations. Low frequencies applications (below 1 MHz) are targeted. The proposed modeling approach and design methodology are validated for wireless power transfer systems including transmitting (Tx) and receiving (Rx) coils. The impact of ferrite materials used for shielding and efficiency improvement is also analyzed. Optimized PCB coils allowing a theoretical efficiency of 88.7% at 100 kHz and 98.5% at 1 MHz confirms that PCB coils are appropriate for wireless power transfer at such frequencies.

This paper presents a study of Schottky diode rectenna (rectifying antenna) for radiofrequency (RF) energy-harvesting systems. These rectennas are suitable for wireless sensors with the rechargeable battery technology especially at low-power densities. A rectifying circuit is proposed with single high responsivity Schottky diode for RF–DC conversion. A matching circuit is optimized to improve not only the power transfer between the antenna and the diode, but also to reject harmonic signals. The radiating part is a monopole antenna, with a large bandwidth in the frequency domain and an omni-directional radiation pattern in the azimuthal plane. We show that antenna frequency response takes part in the improvement of the efficiency. The rectifier is integrated with the antenna on a printed circuit board, leading to 30% of size reduction with the same performance. The aim is to reach the highest efficiency with a single tone signal and a compact rectenna. This rectenna was simulated using both Agilent ADS and Ansoft HFSS software. An output DC voltage of 210 mV was measured inside an anechoic chamber which received a single tone signal of 2 µW/cm2 power density. The highest efficiency of 34% was obtained at a power density of 1.3 µW/cm2.

The electromagnetic (EM) imaging technique at mm-band 60 GHz is proposed for data encoding purpose in the chipless Radio Frequency Identification (RFID) systems. The fully printable chipless RFID tag comprises tiny conductive EM polarizers to create high cross-polar radar cross-section. Synthetic aperture radar approach is applied for formation of the tag's EM-image and revealing the tag's content. The achieved high data encoding capacity of 2 bits/cm2 in this technique based on a fully printable tag is very convincing for many applications. The system immunity to multipath interference, bending effect, and printing inaccuracy suggests huge potentials for low-cost item tagging. Tags are also readable through a tick paper envelop; hence secure identification is provided by the proposed technique.

In the past few years Radio Frequency Identification (RFID) has grown to be one of the most popular technologies in the area of identification systems. Following a brief survey of RFID systems, this paper provides a technical review of work undertaken in the field of time-domain chipless RFID tags and sensors. This paper aims not only to address the chipless tags which use Time Domain Reflectometry (TDR) concept for data encoding but also for the use of Ultra-Wideband Impulse-Radar (UWB-IR) as a time-domain measurement technique. The penultimate section intends to focus on time-domain reading setups and finally, a brief comparison between this method and other chipless techniques is provided.

This work proposes a chipless radio frequency identification approach based on the working principle of the harmonic radar. A frequency multiplication stage is performed by a non-linearity (i.e. a Shottky diode) on the tag in order for the tag answer to be insulated from the interrogation signal, thus avoiding the need for clutter cancellation techniques. Firstly, the performance of a simple one-bit harmonic tag relying on a low-power frequency doubler is analyzed and then a novel crack sensor, implemented by adding a disposable band-stop filter, is presented. Both solutions demonstrate tag-to-reader operational distances beyond 1 m. The characterizing blocks (namely the frequency doubler and the filter) are fabricated on cellulose substrates (i.e. regular photographic paper), thus being conformal to their implementation for applications in the new paradigm of Internet of Things.

Current robotic systems have achieved great sophistication in kinematic motion, control, and neural processing. One of the most challenging limitations imposed on modern robotics is the portable power source needed to sustain tether-free operation. Energy storage devices such as batteries and combustion engines may be heavy, require a great deal of space, and invariably have a finite energy capacity. Methods to control such devices may also impose limitations as most robotic systems rely on either tethered or radiative communication. The unavoidable repercussion of these limitations is the ultimate reduction of mobility and operation time to achieve specific tasks. To address these challenges, we apply our quasi-wireless powering methodology to show the operation of two robotic devices over a 1×1 m2 surface. Both power and control signals are transmitted simultaneously, producing seamless storage-free functionality over the entire area with a communication technique that is not line-of-sight or radiation dependent. We demonstrate an average power transfer efficiency of 93% using commercially available toy robots and discuss parameters relating to the power and communication performance.

This paper discusses the electromagnetic (EM) signature of Arabic alphabets that can be considered as standards particles to form chipless tags. Normalized Arial font is suited as example but the method can be applied for any other font. The letters are realized by metallic strips or better, by conductive ink. All the 28 letters have been simulated and their EM signatures for both field polarizations are extracted. It is demonstrated that combining vertical and horizontal responses allow the identification of letters without ambiguity. Moreover, the case of letter with punctuation (one to three points) is considered in more details. Indeed, we propose to modify very slightly these letters by connecting the points to the body of the letters. This connection is made by a unique straight and very thin strip. Under this modification these letters exhibit more exploitable signatures. Finally, a lookup table for identification of the 28 letters is carried out.

Wireless charging is emerging as a viable technology in many industries, including consumer, medical, and sensor electronics. An investigation of design principles is conducted for a wireless charging platform that is designed to charge devices of different sizes and technologies, using only through vias. It is shown that at a 5 mm separation distance, a coupling coefficient can be achieved which varies from 0.12 to 0.37 when staggered hexagonal transmitter coils (approximately 5 cm across) are used with an unstaggered square receiver coil, which declines to 0.06–0.11 at 2 cm separation. Without design measures, the coupling coefficient will approach zero at certain positions. The quality factors of the coils can be improved by stacking the coils in parallel, enabling the use of only through-vias, while the inductance can be controlled horizontally by increasing the number of turns in the inductor.

The design of magnetic couplers for inductive power transfer has probably become the major challenge for those who wish to enter this promising research field. The number of variables that determine physical dimensions of a coupler is typically too high to allow analytical (exact) solutions in practical time when realistic magnetic materials are to be included. Thus, this paper suggests and describes a series of algorithms based on the finite element method (FEM) able to convert basic inputs (target inductances, primary current, frequency, and mechanical restrictions) into a geometric solution that satisfies user-defined targets for uncompensated power, open-circuit voltage, and short-circuit current. Advantages of these algorithms when compared with other existing design methods are: simplicity in terms of structure at the same time that require minimum user intervention to complete a full design; do not rely in expensive finite element solvers; user does not require previous background in FEM formulation. Experimental results show that the proposed design method based on two-dimensional FEM has errors of <8% when compared with three-dimensional FEM and can perform iterations in seconds. It is expected that the proposed routines encourage and provide design insights for practitioners, enthusiasts, and non-specialized engineers.