The preparation of good navigational synthetic aperture radar (SAR) reference image is critical to the SAR scene matching aided navigation system, especially for complex terrain. However, few papers discuss the problem, and almost none of the methods proposed by them are fully automatic. Based on the practical requirements, a fully automated method of SAR reference image preparation is introduced. Firstly, a number of distinctive control points (CP) in the simulated SAR image is detected based on a method of image segmentation and clustering. Then, the corresponding tie-points in the real SAR image are searched based on local similarity by means of template matching. To improve the accuracy of CP, a method for segmentation threshold calculation, outlier screening and sub-pixel location computation is presented. Finally, the real SAR image is warped to the simulated one, and then projected to the frame of digital elevation model (DEM) by the polynomial mapping function. Experimental results on real data sets demonstrate the accuracy and efficiency of the proposed method.
The paper studies boundary conditions in transformation-optics cloaking for two and three dimensional electromagnetic waves. Implicit boundary conditions for these two cases are derived, no matter if the source is placed in the interior or exterior of the cloak layer. More importantly, the two implicit boundary conditions are derived without solving Mie scattering problems, and these conditions are characteristics of the clock-air interface. In particular, the implicit boundary condition for two-dimensional electromagnetic wave case is reported for the first time. In addition, a sensor can be cloaked in two-dimensional electromagnetic waves, i.e., waves can penetrate into the interior of the cloak layer without exterior scattering.
We present a parallel implementation of the multilevel fast multipole algorithm (MLFMA) for fast and accurate solutions of electromagnetics problems involving homogeneous objects with diverse material properties. Problems are formulated rigorously with the electric and magnetic current combined-field integral equation~(JMCFIE) and solved iteratively using MLFMA parallelized with the hierarchical partitioning strategy. Accuracy and efficiency of the resulting implementation are demonstrated on canonical problems involving perfectly conducting, lossless dielectric, lossy dielectric, and double-negative spheres.
This paper deals with an analytical solution of the time domain Pocklington equation for a straight thin wire of finite length, buried in a lossy half-space and excited via the electromagnetic pulse (EMP) excitation. Presence of the earth-air interface is taken into account via the simplified reflection coefficient arising from the Modified Image Theory (MIT). The analytical solution is carried out using the Laplace transform and the Cauchy residue theorem. The EMP excitation is treated via numerical convolution. The obtained analytical results are compared to those calculated using the numerical solution of the frequency domain Pocklington equation combined with the Inverse Fast Fourier Transform (IFFT).
During Magnetic Resonance Imaging (MRI), the presence of an implant such as a Deep Brain Stimulation (DBS) lead in a patient's body can pose a significant risk. This is due to the fact that the MR radiofrequency (RF) field can achieve a very high strength around the DBS electrodes. Thus the specific absorption rate (SAR), which is proportional to the square of the magnitude of the RF electric field, can have a very high concentration in the near-field region of the electrodes. The resulting tissue heating can reach dangerous levels. The degree of heating depends on the level of SAR concentration. The effects can be severe, leading to tissue ablation and brain damage, and significant safety concerns arise whenever a patient with an implanted DBS lead is exposed to MR scanning. In this paper, SAR, electric field, and temperature rise distributions have been found around actual DBS electrodes. The magnitude and spatial distribution of the induced temperature rises are found to be a function of the length and structure of the lead device, tissue properties and the MR stimulation parameters.
On the basis of the extended Huygens-Fresnel principle, the cross-spectral density matrix (CSDM) of partially coherent Gaussian Schell-model (GSM) beams in the slant atmospheric turbulence is derived. Given that the light emitted from a transmitter is elliptically polarized light, the degree of polarization (DoP) of the partially coherent GSM beams is represented by Stokes parameters expressed by the elements of the CSDM. The expressions of the orientation angle, polarized light intensity in the major axis are derived and the numerical results are presented. Depolarization theory is studied using a Mueller matrix and the depolarization index (DI) is obtained to describe the depolarized state of the partially coherent GSM beams propagating in the slant atmospheric turbulence. Results show that the DOP and DI of the beam tend to their initial value in the long-range propagation.
In this work, we consider a waveguide composed of two periodic, perfectly conducting, one-dimensional rough surfaces. This periodic system has a band structure similar in some aspects to a one-dimensional photonic crystal. However, our system has some additional interesting features. We calculate the band structure and the reflectivity of a corresponding finite waveguide. We found that the variation of the roughness amplitude and the relative phases allow to control at a certain degree the band structure of the system. Particularly, wide gaps can be obtained. It is even possible to obtain discrete modes for some frequency range and then the periodic waveguide acts as an unimodal filter. The system considered constitutes itself a photonic crystal whose band structure corresponds in many ways to a conventional photonic crystal but using just a single material. The key properties of this system are that it really constitutes a waveguide whose optical response is similar to that of a one-dimensional photonic crystal.
By introducing bistatic geometry to near range microwave imaging systems, this paper proposes a near range three dimensional (3D) bistatic imaging geometry based on planar scanning aperture and establishes corresponding echo model. Then, the paper deduces the 3D bistatic Omega-K imaging algorithm based on implicit spectral decomposition, in which the impacts of residual phase, including position displacement, range, azimuth and elevation defocusing, are analyzed and compensated. Finally, the 3D bistatic imaging geometry and algorithm are investigated and verified via numerical simulations and experiments using a near range imaging system.
In this paper, time-domain physical optics (TDPO) method is extended to its iterative version (TDIPO) to consider the coupling effects between two regions, and the latter is employed to investigate electromagnetic scattering from three dimensional target half-buried by a two dimensional rough surface. By using iterative scheme, more accurate transient response reflected from combinative target with multi-scattering effects would be obtained than that by using TDPO alone. The TDIPO could also be enhanced by time-domain equivalent edge current (TDEEC) to further determine the far-field characteristics of the combinative target with rough surface. An accurate composite geometry model technique which combines 2D perfectly electrically conducting (PEC) rough surface and half-buried 3D PEC target is introduced and employed to assist the meshing work. The validity of the presented method is verified by comparing the scattering results for dihedral targets with those obtained through TDPO and finite difference in time domain (FDTD), as well as multi-level fast multiple algorithm (MLFMA). Then simulations of EM scattering from the target embedded in rough surface for different incidence directions are carried out to test the availability of TDIPO/EEC. Discussions on the effects of incidence direction and the presence of the target on the backscattering in far-zone are also given.
We propose a cylindrical invisibility cloak achieved utilizing two dimensional split-ring resonator structured metamaterials at microwave frequencies. The cloak has spatially uniform parameters in the axial direction, and can work very well even when the cloak shell is very thin compared with the concealed object and the working wavelength. Numerical simulation is performed to verify the functionality of the cloak, where the cloak layer is only around 1/4 of the operating wavelength. Our work provides a feasible solution to the experimental realization of cloaks with ideal parameters.
This paper presents two full differential bandpass filters with small occupied areas. Both filters are designed with the same basic structure which consists of two double coupled resonators with magnetic coupling. The resonators are stacked up and have the advantage of high coupling efficiency, reducing the area. Nevertheless, in the basic structure, the insertion loss in the high stopband is above -10 dB and therefore does not meet the requirement for bandpass filter design. Thus, two solutions are introduced to form the proposed filters. The first one integrates the ground plane, while the second one makes the use of an extra transmission zero. With the help of these solutions, two types of full differential bandpass filters are implemented on an FR4 using the embedded passive device technology, with the additional purpose of being designed for SiP applications. The passband of the filters conforms to the WLAN IEEE 802.11a (5 GHz) standard. Most importantly, the occupied areas of the two proposed bandpass filters are only 6 mm х 6.7 mm and 6.6 mm х 8.3 mm respectively. Compared with previous research, area reductions of up to 98.05% and 97.76% can be achieved.
A technical challenge in hyperthermia therapy is to locally heat the tumor region up to an appropriate temperature to destroy cancerous cells, without damaging the surrounding healthy tissue. Magnetic fluid hyperthermia (MFH) is a novel, minimally invasive therapy aiming at concentrating heat inside cancerous tissues. This therapy is based on the injection of different superparamagnetic nanoparticles inside the tumor. In our study, superparamagnetic nanoparticles, which we developed and characterized, consisted of iron oxide nanoparticles stabilized with polyethylene glycol. Moreover, a new technique for MFH using a specially designed external electromagnetic waveguide as applicator is presented. Three magnetite concentrations were used for making the tumor phantoms, which were embedded in muscle phantoms. The phantoms were radiated and located at three different distances from the applicator. Furthermore, two volumes of tumor (2.5 mL and 5.0 mL) were assayed. Heating curves, as a function of time, allowed the establishment of a more appropriate nanoparticle concentration for obtaining the temperature increase suitable for hyperthermia therapy. The results shown in this paper confirm the feasibility of using nanoparticles as agents to focus the energy over the tumor, without creating hot spots in healthy tissue. In addition, the experiments validated that by using this applicator in combination with nanoparticles, it is also possible to locally control the increments of temperature in tissues.
Cylindrical EBG structures excited by a Hertzian dipole source and TM polarized plane wave at oblique incidence are analyzed using a rigorous semi-analytical method based on the cylindrical Floquet mode expansion. Concentric and eccentric cylindrical EBG structures are investigated. Resonance and stopband characteristics in the transmission spectra of the cylindrical EBG structures, enhancement and shading effects in the excited fields, radiation patterns of Hertzian dipole located inside the cylindrical EBG structures in both H-plane and E-plane are numerically studied. Co-polarization and cross-polarizations scattering effects between the electric and magnetic fields are investigated at the oblique incidence of plane waves.
Aluminum conductor steel-reinforced (ACSR) cable is a specific type of stranded cable typically used for electrical power delivery. Steel strands in ACSR cable play a supportive role for overhead power line. Inspection timely is an important means to insure safety operation of power lines. As steel strands are wrapped in the center of ACSR cable, the common artificial inspection methods with optical instruments are limited to find inner flaws of power line. Recently, inspection of power line by robot with detectors is a method with good prospect. In this paper, the optimal design model of detector based on magnetic leakage flux (MLF) carried by robot for detecting broken steel strands in ACSR cables has been proposed. The optimal design model of MFL sensor is solved by niche genetic algorithm (NGA). Field experiment results show that the design method of the detector can be applied to different types of ACSR cables. The magnitude field induced by transmission current has nearly no influences on the detection of broken steel strands, and the developed detector carried by robot can identify broken steel strands with high reliability and sensitivity.
We present a numerical analysis of the interaction between novel scanning near field optical microscopy probes based on an asymmetric structure and a single fluorescent molecule. Our finite element analysis shows how such near field probes can be effectively used for high resolution detection of single molecules, in particular those with a longitudinal dipole moment. At the same time, fluorescent molecules can be exploited as point-like probes of the single vectorial components of the near field distribution at the probe apex, providing a powerful tool for near field probe characterization.
In this paper, a compact wideband high-rejection microstrip bandstop filter using two meandered parallel-coupled lines of different electrical lengths and characteristic impedances in shunt is presented. The transmission and reflection zeros of the filter can be controlled through analytical equations and rulers given. Using this signal interferences technology, this filter obtains a low insertion loss and sharp rejection. Bandwidth and rejection level of the filters of this bandstop filter can be designed by choosing different even- and odd-mode characteristic impedances values of the coupled lines. According to the transmission zeros number, two types of filters are shown in the paper. To validated this topology, a wideband bandstop filter with a 3 dB cutoff frequency bandwidth of 92% centered at 2.6 GHz with sharp rejection characteristics is built to verify the theoretical prediction. The measured frequency response of the filter agrees excellently with the predicted result.
In this paper, we present the space-domain integral-equation method for the analysis of frequency selective surfaces (FSS), consisting of an array of periodic metallic patches or a metal screens perforated periodically with arbitrarily shaped apertures. The computation of the spatial domain Green's function is accelerated by the Ewald transformation. The geometric model is simplified by the lattice symmetry, so that the unknowns are greatly reduced. Time of filling MOM matrix and solving linear system is dramatically reduced. Our technique shows much higher efficiency when compared with the available commercial software and the existing methods published.
Since its introduction in 1994 direct conversion six-port receivers have attracted a considerable attention at microwave frequencies, with most recent work focusing on the so called six-port receivers with analog $I/Q$ generation. Besides its applications at microwave frequencies, six-port receivers with I/Q regeneration play a crucial role in the optical communications field, as they are the most promising candidates for optical coherent receivers that are being developed for 100 Gigabit Ethernet transceivers. In this paper we analytically model the influence of six-port junction hardware impairments on receiver performance. New analytical expressions are developed which give geometrical interpretation of signal constellation distortion due to hardware impairments and allow for the definition of several interesting figures of merit. Closed formulas are also proposed to analytically calculate BER degradation, under AWGN conditions, from these figures of merit. Finally, the proposed formulas are validated by means of simulation, and it is shown that they can be of practical interest to set the specifications of the six-port junction components.
We have studied a new type of double-negative metamaterials (DNMs) composed of split ring resonators (SRRs) and wire strips with substrate teflon, suitable for generation of reversed Cherenkov radiation (RCR) which is TM radiation. We have experimentally observed a narrow pass band in a circular waveguide partially loaded with the DNMs and stop bands for SRRs-only with teflon and for wire strips-only with teflon, respectively. The experimental data show that the DNMs exhibit double-negative behavior over a frequency band of interest. This study provides a foundation for future experiment to observe RCR emitted by charged particles.
We investigated a dielectric resonator ceramic microstrip patch antenna. The antenna was formed using barium strontium titanate (BST), which has a dielectric constant of 15. A new approach, i.e., the use of a high temperature dielectric probe kit, was used to determine the dielectric constant of BST. A computer simulation technology (CST) microwave studio was used to simulate the BST array antennas, taking into consideration the dielectric constant. We also measured the gain of the antennas loaded with two-, four-, and six-element arrays of the BST antenna and found that the gain of a six-element BST array antenna was enhanced by a gain of about 1.6 dB over the four-element BST array antenna at 2.3 GHz. The impedance bandwidths of these BST array antennas for voltage standing wave ratio (VSWR) < 2 were in the application ranges, i.e., 2.30 to 2.50 GHz, established for Worldwide Interoperability for Microwave Access (WiMAX) and Wireless Local Area Network (WLAN). Compared with the conventional array antenna with the same aperture size, the performance of the antenna obviously was improved, and the design is suitable for array applications, including base stations, for example.
The monopoles are theoretically defined as charges which produce fields whose divergence is, obviously, different from zero. However, the entities which have been experimentally detected in the spin-ices, with mimetic behavior to that of the magnetic monopoles, generate magnetic fields which seem to be compatible with ∇·B = 0. This apparent contradiction can create confusion and therefore it requires explanation. In this paper we have carried out an analysis of the different electromagnetic fields in the spin-ices materials. We clarify the differences between the average fields of standard Maxwell equations with zero divergence even in spin-ices and the non macroscopic fields when there are magnetic monopoles in these materials. We give the molecular or local fields which allow us to determine the molecular polarizability. We combine the extended Clausius-Mossotti equations with the Lorentz-Drude model for obtaining the extended susceptibility and the optical conductivity which can be used for explaining the action of the electromagnetic fields in spin-ices.
A coplanar-strip dipole antenna with two enhanced features is presented for broadband circular polarization (CP) operation. The first feature of the proposed antenna is the replacement of a conventional thin dipole by a wide strip, resulting in two degenerated orthogonal modes to make CP operation possible. The second one is the use of two coplanar strips instead of two non-coplanar ones, thereby giving rise to the advantages of easy implement, good impedance matching, and wide axial ratio (AR) bandwidth. Two examples are given, one for the lower band around 1.8 GHz and the other for the ultra-wideband (UWB). For the lower band, the measured -10 dB return loss (RL) bandwidth is 119% (0.74 to 2.93 GHz), and the measured 3 dB AR bandwidth is 50% (1.45 to 2.41 GHz). As for UWB, the measured RL is below -10 dB between 2.1 to 10.1 GHz, and the measured AR is below 5 dB between 4.1 to 7.75 GHz.
A compact-size planar antenna with ultra-wideband (UWB) bandwidth and directional patterns is presented. The antenna can be fabricated on a printed circuit board (PCB). On one side of the PCB, it has a circular patch, and on the other side it has a slot-embedded ground plane with a fork-shaped feeding stub in the slot. Directional radiation is achieved by using a reflector below the antenna. To reduce the thickness of the antenna, a new low-profile antenna configuration is proposed. Three types of directional UWB antennas are analyzed. The distance between the antenna and the reflector is 12 mm (0.16 λ0, λ0 is the free space wavelength at the lowest frequency). In order to validate the design, a prototype is also fabricated and measured. Measured results agree well with the simulated ones. The measured results confirm that the proposed antenna features a reflection coefficient below -10 dB over the UWB range from 4.2 GHz to 8.5 GHz, a maximum gain around 9 dBi, a front-to-back ratio over 17 dB and pulse fidelity higher than 90% in the time domain. Thus it is promising for see-through-wall imaging applications.
In this paper, we present a novel approach for improving the bandwidth of a microstrip patch antenna using Jerusalem cross-shaped frequency selective surfaces (JC-FSSs) as an artificial magnetic ground plane. The invasive weed optimization (IWO) algorithm is employed to derive optimal dimensions of the patch antenna and JC-FSS element in order for the whole structure to work at 5.8 GHz with consideration of gain. For the most efficient design, the antenna and FSS ground plane are optimized together, rather than as separate components. Simulation results demonstrate that this optimum configuration (the microstrip patch antenna over the artificial magnetic ground plane) have a broad bandwidth of about 10.44%. This wide bandwidth is obtained while the thickness of the whole structure is limited to 0.1λ. Further more desirable radiation characteristics have been successfully realized for this structure. The radiation efficiency of the AMC antenna configuration was found to be greater than 85% over the entire bandwidth. In general by introducing this novel Jerusalem cross artificial magnetic conductor (JC-AMC) in lieu of the conventional perfect electric conductor (PEC) ground plane, the bandwidth enhancement of about 67% and a thinner and lighter weight design has been obtained. Sample antenna and EBG layer are also fabricated and tested, to verify the designs. It is shown that the simulation data in general agree with the measurement results for the patch antennas implemented with FSS ground plane.
Terahertz dielectric spectroscopy permits the study of biomolecular interactions. However, water induces high attenuation of electromagnetic waves in the THz frequency range, obscuring the response of biomolecules. The developed sensor overcomes this problem by concentrating the THz wave propagating in an integrated waveguide on a small liquid volume contained within a capillary tube. Detailed electromagnetic modeling shows effective interaction between the THz waves and liquids. Transmission measurement results for capillary tubes filled with water and methanol mixtures demonstrate a substantial increase in sensitivity to changes of liquid permittivity. The current integrated sensor facilitates THz spectroscopy of biological liquids: a case study on buffered human serum albumin solution demonstrates a great potential to complement biochemical analytical tools.
In this paper, an ultra high frequency (UHF) low-profile antenna is proposed; it is based on the discone antenna but with addition of a back cavity, a short-circuiting structure and a two-plate top structure in order to achieve both low-profile and wideband. It is simulated and prototyped. The test results show that the antenna has an omni-directional radiation pattern in the horizontal plane, is of low-profile, has a height of less than 0.1λmax, and is wideband with an impedance bandwidth of 65% from 430 MHz to 845MHz for VSWR < 2.5 and an impedance bandwidth of 43% from 440 MHz to 680 MHz for VSWR < 2.0. The proposed antenna can be easily flush-mounted on a planar surface and therefore has great potential for uses on aircrafts and high-speed trains due to its conformal capability.
Due to high-density routing under the CPU and DIMM areas, the original design of even and odd mode characteristic impedances changes. The occurrence of multi-drop problem between the CPU and memory chip causes over- and under-driven that reduce the eye opening. Furthermore, the different phase velocities of even- and odd-modes cause timing jitter at the receiver end. This paper proposes two steps to solve the complex issue of signal integrity for the multi-module memory bus. First, particle swarm optimization (PSO) is used to tune the characteristic impedance of the transmission line and on-die termination (ODT) values to improve transmission line impedance changes to obtain maximum power delivery. The fitness function of the algorithm is defined by selecting the minimum reflection coefficient at the driver side and maximum the transmission coefficient at the receiver side to reduce the over- and under-driven Second, the timing jitter can be reduced by placing a capacitor to compensate for the velocity difference caused by different propagation modes. Finally, signal integrity enhancements for the DDR3 are verified by measuring S parameters in the frequency domain and postprocessed eye diagrams in the time domain.
The effect of Kerr nonlinearity on a Lorentz beam is investigated by using the nonlinear Schrődinger (NLS) equation. Based on the variational method, the evolution of a Lorentz beam in a Kerr medium is demonstrated and the critical collapse powers of the Lorentz beam are derived. Numerical simulations of the propagation of a Lorentz beam in a Kerr medium show that the beam becomes quasi-circular in a very short distance. Although the beam width of the Lorentz beam broadens, the central part of the beam give rise to a partial collapse.
The novel TOPS mode can achieve wide swath imaging coverage at the cost of impaired azimuth resolution. MIMO-SAR systems combined with multi-channel SAR signal reconstruction in azimuth and digital beamforming (DBF) on receive in elevation can overcome the inherent contradiction between swath width and azimuth resolution of conventional SAR systems. This paper derives a novel spaceborne MIMO-TOPS mode for high-resolution ultra-wide-swath full polarimetric imaging. In such an imaging scheme, different polarimetric waveforms with different elevation beam pointing directions and short time delays are transmitted in a single pulse repetition interval (PRI) by different sub-aperture antennas in azimuth. Besides improving the desired signal-to-noise ratio (SNR) and suppressing ambiguous energy in elevation, a novel DBF on receive approach including two steps is adopted to separate different echoes corresponding to sub-pulses with different polarizations. The design example of a full polarimetric MIMO-TOPS SAR system, which allows for the imaging capacity to cover an ultra wide swath of 400 km with a high azimuth resolution of 3 m, is given to validate the proposed imaging scheme.
A new design for circularly polarized square slot antenna (CPSSA) is presented. The circular polarization operation in the proposed single-layer antenna is created through two equal sized crooked T-shape and an F-shape strips located on the patch. Compared to most of the previously reported CPSSA structures, the impedance bandwidth and the axial ratio bandwidth of the antenna are increased and also the size of the antenna becomes smaller. The presented CPSSA design has the compact dimensions of 40 x 40 x 0.8 mm3, total impedance matching bandwidth of 8.04 GHz and exhibiting a 28.03% (4.6-6.1 GHz) 3 dB axial ratio bandwidth. A prototype of the antenna is fabricated and tested, and a great agreement with simulated results is obtained.