An Improved Differential Evolution (IDE) algorithm is proposed for optimization problems. With the novel mutant operation adopting sub-optimal individual, the convergence of Differential Evolution (DE) algorithm is accelerated without increasing the risk of premature. Five typical test functions are minimized using DE and IDE algorithms, and the results show the superior performance of IDE algorithm. Furthermore, the algorithm is applied to pattern synthesis of two antenna arrays. Broad nulls are formed in radiation pattern of a linear array to suppress broad-band interferences. In a microstrip patch array, the sidelobe level of array is decreased about 12.9 dB and the mainlobe can scan to the desired angle.
The considerable overlap in the dielectric properties of benign and malignant tissue at microwave frequencies means that breast tumour classification using traditional UWB Radar imaging algorithms could be very problematic. Several studies have examined the possibility of using the Radar Target Signature (RTS) of a tumour to classify the tumour as either benign or malignant, since the RTS has been shown to be influenced by the size, shape and surface texture of tumours. The main weakness of existing studies is that they mainly consider tumours in a 3D dielectrically homogenous or 2D heterogeneous breast model. In this paper, the effects of dielectric heterogeneity on a novel Spiking Neural Network (SNN) classifier are examined in terms of both sensitivity and specificity, using a 3D dielectrically heterogeneous breast model. The performance of the SNN classifier is compared to an existing LDA classifier. The effect of combining conflicting classification readings in a multi-antenna system is also considered. Finally and importantly, misclassified tumours are analysed and suggestions for future work are discussed.
An efficient double superimposition model (DSM) is proposed to generate two-dimensional (2-D) ocean surface waves. On the basis of this efficient model, a modulated slope-deterministic facet model (MSDFM) is developed to compute the radar cross section (RCS) of synthetic aperture radar (SAR) for the generated ocean surface. Then, the properties of the SAR imaging mechanism for wind seas are discussed from a combination of SAR and ocean wave parameters. Furthermore, a hybrid facet scheme, which is the combination of physical theory of diffraction equivalent edge currents (PTDEEC) and physical optics (PO) method, is introduced to analyze the high frequency scattering characteristics of large ship target. Finally, this hybrid facet scheme combines with the four-path model and MSDFM to investigate SAR imaging for the composite model of ship on dynamic ocean scene. The resolution degradation of ship-ocean model arising from different facet velocities within a SAR resolution cell and the range migration caused by coupling scattering are investigated in this paper. SAR imagery simulations of marine scene are illustrated, proving the validity and practicability of the presented algorithms.
A new design of microwave band pass filter design is presented using metamaterial-inspired Epsilon Near Zero (ENZ) and Mu Near Zero (MNZ) behaviors. These filters are based on waveguide technology. The proposed structure allows us to reduce the number of tunnels normally used for passband filter design by reducing its size. It is also incorporated the half mode concept to the tunnels leading a greater miniaturization. Two Chebyshev filters with two and four-poles were designed, fabricated and measured showing good agreement between simulated and experimental results.
A planar array composed of 41 parasitic dipoles, above a ground plane, fed by an active dipole at 5 GHz, was designed to obtain a pencil beam pattern with a moderate gain and bandwidth. Experimental results are in good agreement with the theory and show a pattern with an 18.78 dB gain, a sidelobe level (SLL) of -15 dB, an impedance bandwidth of 16.53% (the frequency range over which the value of S11 is below -10 dB) and a 2.7% bandwidth that is achieved within 1 dB gain variations.
This paper presents a novel permanent-magnet (PM) machine for wind power generation. In order to achieve high power/torque density as well as get rid of the nuisances aroused by the mechanical gearbox, a coaxial magnetic gear (CMG) is engaged. Different from the existing integrated machine in which armature windings are deployed in the inner bore of the CMG as an individual part, stator windings are directly inserted among the slots between the ferromagnetic segments in this proposed machine. Thus, it can offer several merits, such as simpler mechanical structure, better utilization of PM materials and lower manufacturing cost. Moreover, by artfully designing the connection of the armature windings, the electromagnetic coupling between the windings and the outer rotor PMs can be dramatically decreased, and the electromechanical energy conversion can be achieved by the field interaction between the inner rotor PMs and the armature windings. This machine adopts an outer-rotor topology, for compact design, the wind blades are directly mounted on the outer rotor of the machine, while the fairing is equipped on the front end of the stator. The design details and operating principle are elaborated. By using the time-stepping finite element method (TSFEM), the electromagnetic characteristics of the proposed machine are analyzed. The results verify the validity of the proposed machine.
This study investigates possible lightning threats to naval crafts, especially those sailing in the shallow waters of tropical oceans where thunderstorms prevail throughout the year and Far-East Asian region where dangerous positive lightning is a significant characteristic in winter thunderstorms. It is empathized that sea water acts as nearly a perfect conductor thus lightning electromagnetic transients propagate over the sea with almost zero attenuation of amplitude and high frequency components intact. The ratio between the peak electric fields at 5 km from the lightning channel, after fields propagate over dry soil and over sea water is 0.75. The ratio between the peak electric field derivatives under the same conditions is 0.1. Such small ratios are observed in the magnetic fields and their time derivatives as well. Apart from the conductivity, the topological irregularities of the plane over which propagation takes place also contribute to further attenuation of fields and their time derivatives. This makes marine naval systems more vulnerable to lightning induced effects than their ground-based counterparts. The paper discusses in detail the lapses of existing naval standards in the defense of electrical and electronic systems against both direct lightning currents and induced effects of nearby lightning. Consequently we propose the development of a dedicated standard for the lightning protection of naval systems, with the inclusion of several significant recommendations specified in this paper.
A multimode Brillouin Erbium Fiber Laser BEFL, at 1550 nm band, with in-cavity intensity modulation is demonstrated. The output of the laser is in the form of nanosecond pulses. The longitudinal mode separation is increased, which results in both reducing the number of oscillation modes and, at the same time, changing the output pulses repetition rate to be multiples of the round trip cavity frequency. It is also demonstrated that the number of modes is greatly reduced by the combination of active mode locking and the group velocity dispersion arising from the change in the refractive index at each mode due to the change in its gain within the Brillouin gain bandwidth. A case of a quasi single mode is reached where the output is nearly CW with very low sinusoidal modulation index.
This paper presents a high speed configurable FPGA-based wideband channel sounder with signal bandwidths up to 200 MHz and results of a study of dynamic urban picocell channel. The use of FPGA allows the sounder to be adaptable for measurements in different scenarios. Adaptable options include changes to the waveform, bandwidth, channel sampling rate and real-time averaging to improve signal-to-noise ratio in weak signal conditions. The implemented architecture has led to a 70% reduction in size and weight compared to sounders in use elsewhere making it ideal for mobile channel measurements. The study of an urban picocell channel has shown that dynamic variation due to automotive traffic introduces average signal strength fades of up to 5 dB but causes frequency selective fading with depths of up to 40 dB. Existing channel models assume antenna heights of more than 6 m and path lengths of more than 30 m. Therefore there is a need for shorter path models and this paper proposes a linear picocell channel model for static and dynamic urban environment.
In this paper, the application of compact non-uniform transmission line transformers (NTLTs) in suppressing and controlling the odd harmonics of the fundamental frequency is presented. A design example showing the complete suppression of the odd harmonics of the fundamental frequency is given. In addition, several compact NTLTs are designed showing the possibility of controlling the existence of a fundamental frequency's odd harmonics. Moreover, multi-band operation using NTLTs is investigated. Specifically, a design example of a miniaturized triple-frequency NTLT is introduced. Based on these compact NTLTs, a 3-way triple-frequency modified Bagley power divider (BPD) with a size reduction of 50%, and a 5-way modified BPD with harmonics suppression and size reduction of 34%, are designed. For verification purposes, both dividers are simulated using the two full-wave simulators IE3D and HFSS. Moreover, the modified 5-way BPD with harmonics suppression is fabricated and measured. Both the simulation and measurement results validate the design approach.
In this study, a very compact, second-order, full differential bandpass filter is presented. To achieve compact circuit area and system-in-package (SiP) applications, the transformer structure is integrated using integrated passive device (IPD) technology on a glass substrate. The coupled resonator synthesis method is used to achieve the bandpass filter design and suitably adjust the tapped feed-lines to obtain good impedance match at all ports. The area (1.27 mm×1.27 mm) of the bandpass filter is effectively reduced, and the performance, as measured by insertion loss (2.5 dB) and CMRR (>30 dB), is still acceptable with such a compact area. Most importantly, this full differential bandpass filter is also suitable for SiP applications, as other studies implemented using glass IPD technology have demonstrated.
We analyze the transverse-electric wave propagation through lossless trilayer stacks containing single-negative (SNG) materials in which only one of the two material constants, permittivity (epsilon) or permeability (mu), is negative. We consider the following combinations: ENG/MNG/ENG, ENG/DPS/MNG, DPS/ENG/DPS, and ENG/DPS/ENG, where ENG refers to epsilon-negative, MNG to mu-negative, and DPS to double-positive media. The transfer matrix formalism is applied. Although the waves are evanescent in the SNG media, combining the SNG layers or the SNG and DPS layers, leads to some unusual features, such as the complete tunneling. Since the symmetrical trilayer is equivalent to a single homogeneous layer, the complete tunneling conditions are easily predicted analytically for the trilayer stacks, and we show that in most of cases, they are rather well applicable to the respective bilayer stacks. The field and the Poynting vector distributions are studied in different trilayers and, in some cases, in the respective bilayers. In particular, we show that the complete tunneling is facilitated theoretically in the electrically thin stacks. Similar results could be obtained for the transverse-magnetic waves and the respective dual combinations by using the duality principle.
We numerically demonstrate that the transmission through a deep subwavelength (λ0/20) aperture in a metal plate could be greatly enhanced owing to the resonance effects of a high permittivity (κ) dielectric cube tightly coupled to the aperture. The transmission enhancement originates from the confinement and re-radiation of the electromagnetic energy impinging onto the high κ cube which operates in the 1st Mie resonance mode, and behaves as an ultra-small magnetic dipole antenna. The complex permittivity of the cube governs the operating frequency and the enhancement in terms of bandwidth and transmissivity maximum. Additionally, based on the isotropic response of the high κ cube with dimensions comparable to the aperture size, the almost independence of the enhancement properties on the illumination polarization and incidence angle was assessed.
Frequency-dependent admittance (J-) inverter is incorporated in synthesis of microstrip trisection filters to achieve a quasi-elliptic function response. In the admittance matrix of the lowpass prototype, certain coupling is modeled by a constant J-inverter multiplied by the complex frequency variable s. Direct synthesis of three lowpass prototypes is presented. Based on the standard lowpass to bandpass transformation, coupled microstrip resonators with both electric and magnetic coupling are devised to implement the J-inverter with desired frequency-dependent characteristics. Tapped-line input/output is used and several transmission zeros can be created in the upper and lower rejection bands. In experiments, a third-order filter with four zeros, a fourth-order circuit with three zeros, and a fourth-order filter with five zeros are designed and fabricated. Measured results are compared with the simulation responses to validate the theory.
Highly dense two-dimensional periodic arrays of nano-scaled silicon pillars present interesting photonic band gaps and the capacity to act as photonic crystals which can mould, manipulate and guide light. We demonstrate finite element modelling of silicon pillars based photonic crystals and their effective use in applications like waveguides, optical power dividers, multiplexers and switches. The optical wave propagation through these structures was thoroughly simulated and analysed, confirming their high efficiency. The band gaps studied through the plane wave expansion method are also presented. Later the fabrication of highly periodic two-dimensional arrays of silicon pillars through the process of etching is also explained. The arrays with pillar radius of 50 nm and lattice constant of 400 nm were successfully utilised as photonic crystal waveguides and their measured results are reported. Moreover, the silicon nanopillars sputtered with noble metals can also display artificial optical properties and act as metamaterials due to the mutual plasmonic coupling effects. We report the theoretical results for the silicon nanopillars based metamaterial high-pass filter.
We propose two metamaterials with sub-wavelength double-slots --- single-side double-slot metamaterial and double-side double-slot metamaterial. The dependence of the electromagnetic resonances and local intensity enhancements on the structural parameters is studied by the finite-difference time-domain technique and the finite element method. Results show that the central-arm of a double-slot structure strongly influences frequency and local intensities at both high- and low-frequency resonances. Very strong field localization can be achieved at the high-frequency resonance and its particular distribution can be well controlled by the width of the central-arm. A double-side double-slot structure can be utilized to separately enhance the high-frequency resonance, while suppressing the low-frequency resonance. The simulation results are discussed in terms of plasmon resonances.
A system has been developed for measuring the complex permittivity of low loss materials at frequencies from 500 MHz to 7 GHz and over a temperature range up to 1500°C using stripline resonator cavity method. Details of the design and fabrication of the cavity were discussed. Particular features related to high-temperature operation were described. An improved resonance method at high temperature for determining complex dielectric properties of low-loss materials was developed. The calculation process was given by a physical model of the stripline resonator cavity at high temperature. The paper brought forward the method of segmentation calculation according to the temperature changes over the cavity, which matched the actual situation of high temperature measurements. We have verified the proposed method from measurements of some typical samples with the available reference data in the literature.
In this paper, a novel technique is proposed to solve the electromagnetic scattering by large finite arrays by combining the tangential equivalence principle algorithm (T-EPA) with multilevel fast multipole algorithm (MLFMA). The equivalence principle algorithm (EPA) is a kind of domain decomposition scheme for the electromagnetic scattering and radiation problems based on integral equation (IE). For the array with same elements, only one scattering matrix needs to be constructed and stored. T-EPA has better accuracy than the original EPA. But the calculating for the impedance matrix in T-EPA is still time consuming. MLFMA is proposed to speed up the matrix-vector multiplication in T-EPA. Numerical results are shown to demonstrate the accuracy and efficiency of the proposed technique.
A synthesis procedure is developed in this paper for the design of N-step coplanar waveguide-to-microstrip transitions. An equivalent circuit approach is adopted to model the structure in terms of N cascaded ABCD matrices relative to the N coplanar waveguide sections forming the transition. A constrained optimization problem is formulated as the minimum finding of a proper functional to accurately determine the transition dimensions by imposing an upper bound to the return loss within a prescribed frequency band. An iterative N-step procedure is developed to find the optimization problem solution. Numerical results on millimeter-wave transition configurations are provided to demonstrate the effectiveness of the proposed synthesis method. A back-to-back transition prototype with N=3 sections is then fabricated and characterized in terms of measured S-parameters to experimentally demonstrate a return loss better than 10 dB in the frequency range from 1 GHz up to 40 GHz.
The design and realization of a multi-band and polarization insensitive metamaterial absorber is presented. The structure with thickness 1.1 mm consists of six close rings which distribute in two metallic layers separated by FR4 substrates. Experimental results show that over 93.3% absorption can be achieved in this metamaterial absorber at multiple frequency bands (more than two). Due to the rotational symmetric pattern of the metamaterial, the performance of the absorber is insensitive to the polarization of the incident waves, indicating the superiority of the structure in the application.
In spaces with Finslerian geometry, the metric tensor depends on the directional variable, which leads to a dependence on this variable of the electromagnetic tensor and of the 4-potential. In this paper, we investigate some of the consequences of this fact, regarding the basic notions and equations of classical electromagnetic field theory.
In this paper, we will propose a new structure of the socket contactor, which is applied to the lead-frame test board. This structure contains a variable open stub to suffice for matching the impedance between the package and the load board. Its electrical property is considered superior to a conventional spring probe's especially when it is applied to a QFP device. In the following paragraphs, we will present its equivalent model and go into details. Note that the transmission-line model is a substitute for a physical structure at this point. First of all, its RLC model will be constructed after we demonstrate its simulation and test data. Finally, we will use the so-called MonteCarlo Method to analyze the inaccurate length in manufacturing to see how this new structure works.
In this paper a novel approach to design multifrequency self-diplexed single patch antennas is proposed. This approach is based on a square microstrip patch antenna loaded with split ring resonators (SRRs). The working frequencies can be arbitrarily chosen and frequency ratios lower than 1.07 have been achieved. In addition self-diplexing characteristics are also achieved between transmitting and receiving ports by including SRRs in the feeding lines. Several prototypes have been manufactured and measured in the X-band showing good performance.
Passive source localization has wide applications in array signal processing. In the practical applications, the observations collected by an array may be ``arbitrary"-field signals, i.e., which are either mixed near-field and far-field signals or multiple near-field signals or multiple far-field signals. With a cross array, a two-stage separated steering vector-based algorithm is developed to localize ``arbitrary"-field narrowband sources in the spherical coordinates. The key points of this paper are: i) different physical steering vectors of near-field and far-field sources are transformed into the virtual ones with the same form, thus linearizing the quadratic phases of near-field sources and allowing the same operations for near-field and far-field sources; ii) the virtual steering vector is separated into two parts and restored by introducing a special phase angle, and thus it is used to estimate the azimuth-elevation arrival-angles of ``arbitrary"-field sources; and iii) special Hermitian matrices are constructed using the separated physical steering vector and their eigenvalue decomposition (EVD) are performed, thus the ranges of near-field sources are easily obtained from the eigenvector being corresponding to the smallest eigenvalue. The proposed algorithm can localize ``arbitrary"-field sources without pairing parameters and multidimensional search. Simulation results are provided to validate the performance of the proposed method.
The T-match feed is a useful impedance matching tool for dipole antennas, especially for electrically short dipoles with capacitive loads. The Uda model has been extensively tested for accuracy in the literature for the special case of the folded dipole, but not for the more general T-match dipole, which is often used for RFID antenna design. We investigate the accuracy of the Uda model for this more general case and show that aspects of the model become inaccurate for a number of practical scenarios. Nevertheless, we show that the model can still be used as a guide to T-match dipole designs.
Submit
