This work provides an in-depth study on a linear antenna array that consists of 32 elements of CRLH unit cells, and the main radiating beam can be controlled by changing the capacitance of the varicap diode that was designed and simulated with Advanced Design System (ADS 2014) software. ADS software was selected because of its flexibility in accommodating complex design equations. Results show that the main beam can be steered up to 50 degrees from the direction of maximum radiation by changing the capacitances. The main beam gain of the antenna array at boresight of 12 dB has been achieved with an impedance bandwidth of 3 GHz at 10 dB gain threshold. The antenna array performance was analysed in the mmWave frequency range at centre frequency of 28 GHz making it suitable for the upcoming 5G applications. The mmWave path losses were handled by increasing the gain of the antenna array and steering the main lobe over 50 degrees to balance the gain coverage trade-off. The direction of the main beam is controlled by changing the varicap capacitance accordingly.
Magnetic field intensity is modeled using Laplacian equations to study the spatial distribution of magnetic field under spherical shell plasma. The influences of different internal and external radii are also considered. In addition, the magnetic field calculation of plasma space is analyzed. The main conclusions are as follows. The external uniform magnetic field H0 is the scalar magnetic bit, and the magnetic charge of the shell of the plasma is equivalent to that of a magnetic dipole. The magnetic field in the spherical shell is a super position of a uniform field and a magnetic dipole field. The uniform field is composed of an externally applied uniform field H0 and a uniform field generated by the magnetic charge on the outer surface of the ball. The magnetic dipole field is generated by the magnetic charge on the inner surface of the shell, and the inside of the shell is a uniform magnetic field. When μ2/μ1 is high and a/b is low, the ratio of the magnetic field strength H3 (the regionis r<a) to the magnetic field strength H0 (the region is r>b) is low. By contrast, when μ2/μ1 and a/b are high, the ratio of the magnetic field strength H3 to the magnetic field strength H0 is high. When the magnetic permeability of the inner object is small and the spherical shell is thick, the produced plasma sheath is thick, and the external magnetic field in the spherical shell is weak. Therefore, when the shielding effect is good, the possibility that the ``black barrier'' phenomenon will occur is high, and ground radar detection will be difficult.
A one-shot rescaling process, namely Automated Scaling Region of Interest (AS-ROI), is combined with an inversion technique of Forward-Backward Time-Stepping (FBTS). The purpose is to alleviate the ill-posedness and nonlinearity of inverse problem by reducing the size of the unknown problem. The inversion solution is carried out to reconstruct tumour as an unknown object in coarse investigation domain of lung area which is then rescaled down corresponding to object location and size. In this paper, edge preserving methods consisting of edge preserving regularization and anisotropic diffusion are imposed alternately on the solution and reconstructed profiles to improve the current method of AS-ROI. Results on the reconstructed lungs and tumours give significant insight of the proposed work. Accuracy level for the reconstructed profiles are significantly improved in spite that spatial resolution is retained as the original setting of FBTS.
Research on RCS evaluation for electrically large objects has been a hot topic for decades. Although multilevel fast multipole algorithm (MLFMA) has been the most popular method in scattering computation, due to the limitation of both CPU speed and memory size in a single computer, realistic large targets require discretization with millions of unknowns still cannot be solved by sequential implementations of MLFMA. In this paper, we introduce a Docker-enabled parallel MLFMA computing system based on MPI, which is proved to be friendly for deployment and economical for scalability, to solve electrically large scattering problems. In addition, the capability of the proposed system has been demonstrated by several canonical examples.
An omnidirectional compact antenna based on dual-band Split Ring Resonators (SRRs) for 2.45 GHz wireless local area network (WLAN) and 3.5 GHz worldwide interoperability for microwave access (WiMAX) applications is presented. Dierent and new properties of SRRs, such as dual-band or multi-band performance in the design of compact antennas, can be obtained by making the rings unequal and asymmetric. The dual-band SRR antenna is designed with a bandwidth control technique based on stored electromagnetic energy on the resonator rings. The obtained results show that the SRR antenna has good omnidirectional radiation pattern for both bands and good impedance bandwidth. In addition, compactness and flexibility are obtained with a simple structure of the SRRs.
Generally, the null steering is performed by controlling the amplitude and/or phase weightings of all element excitations or only a small number of them. In such cases, a need for extra RF components such as variable attenuators and variable phase shifters with each element in the array is inevitable. In this paper, an alternative method is introduced where the null steering is performed by thinning (or turning off) only a small subset of the elements in the uniform linear arrays. To find an optimum combination of active (on) and inactive (off) elements, a binary genetic algorithm is used. In large arrays, the number of required nulls is much smaller than the total number of array elements, thus only a small subset of the array elements could be sufficient for producing the required nulls rather than optimizing all the array elements. By this way, a faster convergence speed of the optimizer and lowest peak sidelobe level can be obtained. The effectiveness of the proposed method with various subset configurations will be demonstrated and compared with some standard null steering methods.
In-Service Inspection (ISI) plays a critical role in ensuring the safety and security of nuclear power plant and personnel. The limited access and high ambient temperature conditions impel the need for remote inspection techniques using semi automated vehicle. The electrical actuators driving the ISI robotic vehicle must satisfy the requirements of high operating temperature, high torque density,compact size and low weight.Currently, permanent magnet brushless motors are used due to its compact size and high eciency. However, due to risk of demagnetization at high temperature as well as due to depleting resources of rare earth material alternate topologies without using permanent magnets shall be considered. This paper investigates the performance of Permanent Magnet (PM) brushless motor and Switched Reluctance (SR) motors for high temperature applications. SR motor is designed as per fundamental design equations satisfying the application requirements. Electromagnetic performance isveried by Finite Element Analysis (FEA) and thermal performance is veried by lumped parameter thermal analysis. Finally the performance of SR motor is compared with PM motor in terms of torque, eciency, weight,cost and temperature rise.
In order to energize the biomedical implantable electronic devices wirelessly for in vivo health monitoring of patients in remote and inaccessible areas, an alternate driving energy source is highly desirable and increasingly important. In pertinent to this, a thermal energy driven resonant inductively coupled wireless energizing scheme has been developed for powering biomedical implantable devices. The system is designed to convert the generated heat energy to a high frequency energy source so as to facilitate energy transfer through resonant inductive link to the automated biomedical sensing system allied with the receiver unit. The automated biomedical smart sensor is competent to acquire the body parameter and transmit the consequent telemetry data from the body to the data recording segment. The real-time body temperature parameter in different conditions has been experimented. To ensure its accuracy, the sensed data have been matched with the observations carried out by a calibrated device. The intended scheme can be utilized for wireless monitoring of other health parameters like physiological signals and bladder as well as blood pressure of the patients.
This paper deals with the calculation of electric field in a copper piece of cubic shape which is submitted to a sinusoidal magnetic field. This 3D problem is set into equation and solved by means of two different approaches. A stochastic method for 3-D electric field computations is presented and compared to a finite element method. The main goal of this paper is to compare these two methods on a classical problem putting forward the advantages of the chosen method. First of all, we present the problem modelling. Then, the Monte-Carlo method used to solve 3D time dependent problem is described and is compared to the finite element method, in the last part.
The location and topology of grounding grid conductors are necessary to corrosion diagnosis and digging in most cases. In this paper, an integrated detecting device for grounding conductor buried position is designed. Based on the principle of magnetic field method, a multi-layer cascade PCB hollow coil sensor is designed. AC excitation current source, 16-channel control circuit, lock-in amplifier (LIA) circuit and 4-channel synchronous acquisition circuit are realized. The experimental test is completed for the integrated detection device, and results verify the feasibility of the system.
A superconducting synchronous generator (SSG) is proposed for wind power, in which magnesium diboride (MgB2) superconducting coils are employed as field windings. The stator is composed of conventional copper coils and iron core, while the rotor has no iron core. The whole refrigeration method is adopted in this paper. The thermal barrier is not placed in between the stator and the rotor as compared with the prior HTS generators, so a small air gap width would be possible. In order to study the electromagnetic characteristics of the SSG, finite element method (FEM) is implemented to optimize the SSG and obtain the no-load and load performance of the initial and optimized SSG. Finally, the optimized SSG is compared with a traditional synchronous generator (TSG) of the same power. The results indicate that the optimized SSG has many merits such as small size, light weight, high efficiency and high power factor.
Processing over-the-horizon radar (OTHR) signals is challenging due to appearance of several very close components in the time-frequency plane, strong noise and clutter, multipath propagation, and aliasing. We propose a two-stage procedure for estimating multipath signal components from the received mixture. In the first stage, the instantaneous frequency is estimated from the time-frequency representation of the received signal. The random samples consensus algorithm is applied to the instantaneous frequency estimate to improve the robustness of the procedure against various effects in the underlying signals. In the second stage, the MUSIC algorithm is applied to the dechirped and downsampled signal. The effectiveness of the proposed approach is verified using real-life signals.
A microwave diplexer implemented by using the twenty-first century substrate integrated waveguide (SIW) transmission line technology is presented. No separate junction (be it resonant or non-resonant) was used in achieving the diplexer, as the use of an external junction for energy distribution in a diplexer normally increases design complexity and leads to a bulky device. The design also featured a novel input/output coupling technique at the transmit and receive sides of the diplexer. The proposed SIW diplexer has been simulated using the full-wave finite element method (FEM), Keysight electromagnetic professional (EMPro) 3D simulator. The design has also been validated experimentally and results presented. Simulated and measured results show good agreement. The measured minimum insertion losses achieved on transmit and receive channels of the diplexer are 2.86 dB and 2.91 dB, respectively. The measured band isolation between the two channels is better than 50 dB.
A novel compact CPW (coplanar waveguide-fed) CPSS (Circularly polarized square slot) antenna is presented. The proposed single-layer antenna is composed of a rectangular ground plane embedded with two equal-size patches along two orthogonal directions. Equal amplitudes with 90˚ phase difference values of two patches is capable are generating a resonant mode for exciting two orthogonal E vectors. Axial ratio (AR) bandwidth is significantly enhanced due to slot corner modification. The designed CPSS antenna is compact in nature with volume of 0.37λ0× 0.34λ0 × 0.012λ0 mm3 (λ0= free space wavelength at centre frequency of the CP bandwidth). It has impedance bandwidth between 4.65-6.72 GHz (36.41%) and 3-dB axial-ratio bandwidth of 520 MHz (4.85-5.37 GHz), which covers 4.9 GHz (802.11j) WLAN for public safety ranging from 4.94 GHz to 4.99 GHz and WLAN (U-NII-1 and U-NII-2A) ranging from 5.150-5.350 GHz for indoor use. The gain variation for the frequencies within the CP bandwidth is also observed to be less than 0.6 dBic. The design is successfully implemented, and measured results are compared with the simulated ones, which are found in good agreement.
A triply primed array (TPA) is configured on three mutually primed integers (N1, N2 and N3), which operates with O(N1N2N3) degree-of-freedoms to estimate the direction-of-arrivals (DOAs) of multiple incident quasi-stationary signals. The set of unique and contiguous lags of the proposed TPA is searched and verified. Simulation results verify that the proposed TPA can detect more incident signals with higher accuracy than its compatible counterparts.
This paper presents an efficient hybrid method consisting of finite-difference time-domain (FDTD) method, transmission line (TL) equations, and a fast calculation method for excitation fields, which can be applied to the coupling analysis of the shielded cable on the ground excited by plane wave rapidly. It can avoid modeling the infinite ground and the structure of the shielded cable directly. In this hybrid method, the shielded cable is decomposed into external and internal transmission line models, and the corresponding TL equations for the external and internal TL models are established necessarily. Then the FDTD method is utilized to solve the TL equations to obtain the transient responses on the shielding layer and core wires of the cable. A numerous examination of the coupling of coaxial cable exhibits that this hybrid method has very high accuracy and efficiency compared with the SPICE method. Finally, the methods of effective shielding protection of the cable have been proposed by analyzing the influences of the grounding states of the shielding layer, the electromagnetic parameters of the ground and the heights of the cable on the transient responses of the cable.
Non-Foster matching circuits are those that can function as negative capacitors or inductors, and can thus overcome the gain bandwidth limitation of passive matching circuits for antennas. This paper presents a non-Foster matching circuit (NFC) for a very low frequency (VLF) receiver loop antenna. The bandwidth of the antenna was improved by 383%, and the average gain was improved in most bands compared to a passive matching circuit (over 15-30 kHz). In contrast to circuits reported in other publications, the signal to noise ratio (SNR) of the passive matching network performed better than the non-Foster matching network. To analyze this phenomenon, a noise model was developed for the simplified balanced NFC, and noise analysis was conducted between the non-Foster and passive matching networks, which indicates that the non-Foster matching circuits cannot provide a better SNR performance than the passive matching circuits under low noise figure level receiver conditions.
This paper reviews the motion of a charged particle in the electrostatic field of two coaxial likely charged rings located at some distance from one another. The charges of rings and that of the particle are of the same sign. Initial conditions of motion of the particle relatively to the rings under which the particle overcomes the electrostatic repulsion of rings and localises along a particular circular trajectory laying in the internal space between the rings were determined.
In this paper, a channel characterization of an RF link using circularly polarized antennas inside a mine is performed. The association of circular polarization with multiple-input-multiple-output (MIMO) radio technologies represents a powerful tool to improve the performance of an underground RF channel. The statistical parameters of the channel are derived from in-mine measurements at the 2.4 GHz band for both co-polarization (CP) and cross-polarization (XP) scenarios. Results show a remarkable improvement through the use of MIMO combined with circular polarization compared to the regular patch MIMO antenna system, in terms of channel capacity and path loss. This improvement increases significantly at the XP scenarios, reaching up to 18 bps/Hz for channel capacity and up to 21 dB for path loss. The RMS delay spread for a circularly polarized setup is generally higher than the linearly polarized MIMO patch setup due to surface roughness of the gallery. In the linear polarization case, a signal degradation of more than 15 dB at the XP case is observed compared to the CP scenario. This signal loss that is due to depolarization is somewhat mitigated by the surface roughness.Due to its superior and stable performance, MIMO combined with circular polarization is better suited than a regular MIMO patch system for in-mine uses, especially in the applications where the transmitter may change direction with respect to the receiver.
Carbon fiber reinforced polymer (CFRP) is measured as reflector material for millimeter waves at 60 GHz. Reflectivity is measured to characterize material anisotropy in a mono-static setup. Disc shaped material samples are rotated in steps of one degree. Four commonly employed CFRP are investigated: unidirectional fibers, plain-weave, twill-weave and fiber shreds. Results show that the unidirectional CFRP and twill-weave CFRP are anisotropic, while the remaining materials are isotropic within measurement accuracy.