In this paper, three different types of graphene based tapered slot antennas are designed for ultrawideband (UWB) applications. The taper profiles for three antenna types are linear, exponential, and constant width. A single layer graphene sheet of 35 μm thickness is used to model the radiating element and feeding structure of the designed antennas. To feed the antennas, microstrip to slotline transition technique is adopted. An approximate analytical theory based on conical transmission line model is considered to authenticate the design of graphene based tapered slot antennas. Better impedance matching over 2-20 GHz is obtained by designing a balun in the form of a radial stub. Return loss, bandwidth, radiation pattern, and directive gain are the considered antenna performance parameters. Time domain solver of CST MWS software is used to evaluate the performances of linearly tapered slot antenna (LTSA), exponentially tapered slot antenna (Vivaldi), and constant width slot antenna (CWSA). The results obtained from CST are compared with that from HFSS to further validate the design. Simulation results with extensive parametric study confirm that the novel 2-D material graphene can be considered as a promising one to model UWB tapered slot antennas. Furthermore, the effectiveness of designed graphene based tapered slot antennas is revealed by comparing their performances with other existing UWB antennas. Moreover, as a UWB application, Vivaldi antenna shows promising results in microwave brain tumor detection.
The article presents a new topology of the high-speed synchronous electrical machines with permanent magnets with the tooth-coil windings with a stator magnetic core made of amorphous alloys for prospective unmanned aerial vehicles. This is a multidisciplinary design algorithm with optimization elements, which are proposed to design such machines. Based on the proposed algorithm, calculations of several topologies were performed by using computer simulation methods. In addition, the analysis of the rotor dynamics as part of the turbojet engine of the unmanned aerial vehicle and the calculations of the mechanical rotor strength were performed. To minimize the eddy-current losses in permanent magnets, the multicriteria optimization of the slotted zone was carried out by using genetic algorithms. A cooling system was proposed, and thermal calculations were performed. To verify the proposed design algorithm and to evaluate the efficiency of the amorphous alloy, a full-sized 5 kW experimental sample with a rotational speed of 60,000 rpm was created. Results can be used to create new promising UAVs and to design electrical machines for other industrial applications.
Understanding wireless channels in complex mining environments is critical for designing optimized wireless systems operated in these environments. In this paper, we propose two physics-based, deterministic ultra-wideband (UWB) channel models for characterizing wireless channels in mining/tunnel environments --- one in the time domain and the other in the frequency domain. For the time domain model, a general Channel Impulse Response (CIR) is derived and the result is expressed in the classic UWB tapped delay line model. The derived time domain channel model takes into account major propagation controlling factors including tunnel or entry dimensions, frequency, polarization, electrical properties of the four tunnel walls, and transmitter and receiver locations. For the frequency domain model, a complex channel transfer function is derived analytically. Based on the proposed physics-based deterministic channel models, channel parameters such as delay spread, multipath component number, and angular spread are analyzed. It is found that, despite the presence of heavy multipath, both channel delay spread and angular spread for tunnel environments are relatively smaller compared to that of typical indoor environments. The results and findings in this paper have application in the design and deployment of wireless systems in underground mining environments.
Ultra-wideband (UWB) antennas have advantages such as high data rates, improved multipath resistance and lower power consumption. In this work, UWB patch antennas based on electrically conductive adhesive were manufactured with a simple technique and evaluated in the laboratory. Results showed that the thickness of the samples ranged from 207 to 261 μm. The bandwidth optimization obtained was 200% compared to a traditional copper-layer antenna. UWB antennas showed an average bandwidth of 8.558 GHz in the region 609 MHz to 9.105 GHz. The antennas covered the whole of UHF band, L band, S band, C band and part of X band. Finally, the proposed technique allows reducing the size of patch by 70% for low frequencies of operation, while achieving a similar performance.
This study presents a novel technique for designing an ultra-wideband (UWB) filtering-antenna with dual sharp band notches. This design composed of a modified monopole antenna integrated with resonant structures. The monopole antenna is modified using microstrip transition between the feedline and the patch. In addition, block with a triangle-shaped slot is loaded on both sides of the ordinary circular patch to produce wide bandwidth with better return loss and higher frequency skirt selectivity. The resonant structures based on two double split ring resonators (DSRR) loaded above the ground plane of the antenna design to produce dual notched bands, and filter out WiMAX (3.3-3.7 GHz) and HiperLAN2 (5.4-5.7 GHz) frequencies. The band notch position is controlled by varying the length of the DSRR. The reconfigurability feature is achieved by using two PIN diode switches employed in the two DSRR. The measured results show that the proposed filtering-antenna provides wide impedance bandwidth from 2.58 to 15.5 GHz with controllable dual sharp band notches for WiMAX and HiperLAN, peak realized gain of 4.96 dB and omnidirectional radiation pattern.
A decoupling network for a pair of strongly coupled MIMO antennas is presented. The decoupling network is composed of two inverters and two split ring resonators (SRRs) that are also coupled. By properly transforming the mutual admittance of the original coupled antennas and properly designing the coupling between the two SRRs, more than 20dB isolation between the two antennas can be achieved while their respective matching performances remain good. To validate the concept, a microstrip decoupling network is designed and implemented for a pair of wideband printed monopole antenna elements. Measurement results have demonstrated that nearly 10% bandwidth for 20 dB isolation can be achieved. Measured radiation patterns have demonstrated a significant reduction of the correlation coefficient, which makes the proposed technique a promising candidate for both current and future generations of MIMO-enabled mobile terminals.
In this paper, a novel microwave planar resonant sensor is designed and developed for simultaneous detection of permittivity and permeability of an unknown sample using a nondestructive technique. It takes advantage of two-pole filter topology where the interdigitated capacitor (IDC) and spiral inductor are used for placement of a sample with significant relative permittivity and permeability values. The developed sensor model has the potential for differentiating permittivity and permeability based on the odd mode and even mode resonant frequencies. It operates in the ISM (industrial, scientific and medical) frequency band of 2.2-2.8 GHz. The sensor is designed using the full wave electromagnetic solver, HFSS 13.0, and an empirical model is developed for the accurate calculation of complex permittivity and permeability of an unknown sample in terms of shifts in the resonant frequencies and transmission coefficients (S21) under loaded condition. The designed resonant sensor of size 44x24 mm2 is fabricated on a 1.6 mm FR4 substrate and tested, and corresponding numerical model is experimentally verified for various samples (e.g., magnetite, soft cobalt steel (SAE 1018), ferrite core, rubber, plastic and wood). Experimentally, it is found that complex permeability and permittivity measurement is possible with an average error of 2%.
A miniaturized self-matched negative group delay (NGD) microwave circuit without the need for external matching networks is proposed. The NGD circuit is based on a modified parallel-type RLC resonator, in which lumped elements (capacitors and inductors) are implemented by microstrip gaps and high-impedance and short-circuited microstrip lines. To verify the design concept, an NGD circuit with the size of 0.21λg×0.29λg is designed and fabricated. From the measurement results, the NGD time of -5.9 ns at the center frequency of 1.532 GHz is obtained with insertion loss of less than 12.5 dB, return losses of more than 25 dB and the NGD bandwidth of 45 MHz.
A new design of wideband directional couplers using a semi-elliptical edge-coupled structure is presented. This structure consists of two semi-elliptical patches on the top layer and an elliptical defected ground plane on the bottom layer to increase the coupling coefficient and operating bandwidth. Even and odd mode analysis is performed, and sets of design graphs are formulated to facilitate the design of the coupler on substrate with dielectric constants of 2.2 and 3.38. The operating frequency and coupling are controlled by the dimensions of the elliptical patch and the size of the air gap. Compared to the conventional parallel-microstrip coupler which requires extremely narrow air gap to achieve tighter coupling factor, the semi-elliptical coupler allows for wider air gap to be used, and it reduces fabrication difficulty. Both simulation and measurement results show that the proposed design exhibits wideband characteristic with a bandwidth ratio of more than 2.4 with acoupling deviation of ±1 dB.
When deriving a range-Doppler image or a time-frequency image of a fast-maneuvering target at long range, existing range alignment methods yield poor results due to the large numbers of range profiles (RPs) and range bins that are required for this task. This paper proposes a three-step range alignment method to overcome the problems of these existing methods and to yield focused images: (1) coarse alignment using the interpolated center of mass of each RP, (2) fine alignment with an integer step using an entropy cost function, and (3) fine-tuning using particle swarm optimization. Compared to existing methods, the proposed method is computationally more efficient and provides better image focus.
In this paper, a new high performance slotted waveguide antenna incorporated with negative refractive index metamaterial structure is proposed, designed and experimentally demonstrated. The metamaterial structure is constructed from a multilayer two-directional structure of electrically split ring resonator which exhibits negative refractive index in direction of the radiated wave propagation when it is placed in front of the slotted waveguide antenna. As a result, the radiation beams of the slotted waveguide antenna are focused in both E and H planes, and hence the directivity and the gain are improved, while the beam area is reduced. The proposed antenna and the metamaterial structure operating at 10 GHz are designed, optimized and numerically simulated by using CST software. The effective parameters of the eSRR structure are extracted by Nicolson Ross Weir (NRW) algorithm from the s-parameters. For experimental verification, a proposed antenna operating at 10 GHz is fabricated using both wet etching microwave integrated circuit technique (for the metamaterial structure) and milling technique (for the slotted waveguide antenna). The measurements are carried out in an anechoic chamber. The measured results show that the E plane gain of the proposed slotted waveguide antenna is improved from 6.5 dB to 11 dB as compared to a conventional slotted waveguide antenna. Also, the E plane beamwidth is reduced from 94.1 degrees to about 50 degrees. The antenna return loss and bandwidth are slightly changed. Furthermore, the proposed antenna offers easier fabrication processes with a high gain than the horn antenna, particularly if the proposed antenna is scaled down in dimensionality to work in the THz regime.
In scattering experiments, incident fields are usually produced by aperture antennas or lasers. Nevertheless, incident plane waves are usually preferred to simplify theoretical analysis. The aim of this paper is the analysis of the electromagnetic scattering from a perfectly electrically conducting polygonal cross-section cylinder when a Gaussian beam impinges upon it. Assuming TM/TE incidence with respect to the cylinder axis, the problem is formulated as electric/magnetic field integral equation in the spectral domain, respectively. The Method of analytical preconditioning is applied in order to guarantee the convergence of the discretization scheme. Moreover, fast convergence is achieved in terms of both computation time and storage requirements by choosing expansion functions reconstructing the behaviour of the fields on the wedges with a closed-form spectral domain counterpart and by means of an analytical asymptotic acceleration technique.
This paper deals with the design and experiments of a dual-band circularly polarized rectenna at 1.85 and 2.45 GHz. It uses a single antenna and a single RF-to-dc rectifier. The circuit contains a dual-band circularly polarized antenna and a dual-band RF-to-dc rectifier based on a miniaturized 180° hybrid ring junction. The ring junction is used to independently match the sub-rectifiers at each frequency. The proposed rectenna was experimented with single-tone and multi-tone incident waves. It achieves more than 300 mV and 40 % efficiency, across a 4-kΩ resistive load, at very low power density of 1.13 µW/cm² at 1.85 GHz and 1.87 µW/cm² at 2.45 GHz. It also achieves more than 150 mV under the same load condition and in the critical case when receiving only one of the two frequency bands. It is dedicated to harvest RF energy in the GSM 1800 and the 2.45-GHz ISM bands, regardless the polarization angle of the incident waves.
This paper talks about a simple printed reconfigurable antenna for cognitive radio. This antenna can be switched between ultra-wideband (UWB) and two other narrow bands. To achieve frequency reconfigurability, horizontal slots are inserted in the partial ground plane, and their lengths are varied by using ideal switches. These switches are incorporated so that they can be turned ON/OFF independently. The proposed antenna is suitable for cognitive radio as it is capable of sensing whole UWB from 3.1 GHz to 10.6 GHz (7.5 GHz bandwidth) and switching between two different narrow bands viz. 3.1 GHz and 8.23 GHz, and the corresponding observed gain and radiation pattern are also as per the requirement.
The paper presents a study of dynamic thermal processes in ultra-high-speed microgenerators power of 55 W with the rotational speed of 800,000 rpm for UAV. A large-scale study of current works devoted to this topic were done where the main shortcomings were identified. A mathematical description of heat exchange processes in microelectromechanical energy converters with a flight time of no more than 10 minutes was developed in a non-stationary formulation. A study of the thermal state of the microgenerator operating in a short-term mode without a special cooling system is conducted. An experimental study of the heating dynamics of its active parts is carried out using the method of physical analogies. On the basis of experimental studies, the FEMM model is verified. Afterwards, combined electromagnetic and thermal calculations of microgenerator are conducted.
Linear-to-circular polarizers operating from roughly 17 to 65 GHz, and angles of incidence up to 60° are reported. These polarizers convert incident, linearly polarized radiation into circular polarization upon transmission. First, previous designs inspired by the optics community using cascaded waveplates are scaled down to mm-wave frequencies. The naturally occurring anisotropic crystals that the optics community employed are replaced here with metamaterials. The range of incidence angles is improved by utilizing biaxial, artificial dielectrics whose permittivity in the $x$, $y$ and $z$ directions are all engineered. Next, an ultra-wideband linear-to-circular polarizer consisting of cascaded sheet impedances is reported. The cascaded sheet impedance polarizer utilizes a combination of meanderline and metallic patch geometries. The principal axes of each patterned metallic sheet are oriented at an optimized angle, which increases the design degrees of freedom and performance. This polarizer has the advantages of being thinner and easier to fabricate than the polarizer utilizing cascaded waveplates, but is more difficult to design. Both polarizers rely heavily on genetic algorithm optimization in the design process to realize multiple octaves of bandwidths and robust performance at wide angles of incidence. The polarizers are fabricated with commercial printed-circuit-boards, and then experimentally characterized.
In this paper, the AC interference produced by an overhead power transmission line on a buried metallic pipeline is estimated using a circuital method based on the well-known Carson's formulae and a two-dimensional finite element numerical code. The finite element formulation used in this paper implicitly takes into account the mutual inductive coupling between all the considered conductors, and it allows a more detailed analysis in cases where a nonhomogeneous soil is present. The FEM approach includes a procedure which has been developed to enforce that the sum of the currents flowing through the soil, pipeline and eventual overhead ground wire is equal to zero. A case study has been identified, and the results obtained by the two approaches have been compared and discussed
In South East Asian countries, particularly in a developed Asian city, open-trench drains systems are prominent due to climatic differences. Open-trench drain structures occupy a great part of the terrain topography in Malaysia, and therefore this project aims to further investigate the impacts that open-trench drain systems have on radio propagation prediction in a low density urban environment. Towards that end, we have engaged an interactive 3D ray-tracing tool to build the environment depicting a low density setting with clusters of low rise building structures oriented far apart from each other. The existence of open-trench drains is incorporated into a mock city model to obtain propagation prediction results for different operating frequencies. One of the primary differences this study in comparison to the existing studies on ray-tracing modeling of an urban city with open-trench drains is that the quantity of building models and open-trench drain structures are generated over a wider area to mimic actual low dense city settings. When such scenarios are considered, the impacts of open-trench drain structures fade away.
This paper presents a study of planar silicon lens antennas with up to three steppedimpedance matching regions. The eective permittivity of the matching regions is tailor-made by etching periodic holes in the silicon substrate. The optimal thickness and permittivity of the matching regions were determined by numerical optimization to obtain the maximum wide-band aperture eciency and smallest side-lobes. We introduce a new geometry for the matching regions, referred to as shifted matching regions. The simulation results indicate that using three shifted matching regions results in twice as large aperture eciency as compared to using three conventional concentric matching regions. By increasing the number of matching regions from one to three, the band-averaged gain is increased by 0.3 dB when using concentric matching regions, and by 3.7 dB when using shifted matching regions, which illustrates the advantage of the proposed shifted matching region design.
A distortion-less ultra-wideband tapered slot antenna is designed to achieve wide band impedance matching and high gain without requiring coupling liquids. The antenna is embedded in a suitable dielectric material for compact size and performance improvement. The near-field test is simulated by placing several field probes near the antenna to plot the radiation pattern and polarization isolation. The antenna exhibits a highly directive pattern and polarization isolation in near field. The time domain antenna distortion is tested by calculating the fidelity and group delay. The results show low distortion and also show the importance of covering the antenna by dielectric layers for bandwidth increment and distortion reduction. To evaluate the antenna performance in breast cancer detection, three breast phantoms are imaged by using the raster scan imaging method. Two approaches are proposed to detect tumors without the need of breast background data. The approaches based on the effect of the tumor on transmission and reflection parameters on the frequency band allowed for medical applications. The obtained images show the antenna to be a strong candidate for breast imaging as well as in tumor detection for different scenarios that include complex multi-layer phantom and small tumor.