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Showing papers in "Progress in Electromagnetics Research-pier in 2014"


Journal ArticleDOI
TL;DR: The photoacoustic tomography (PAT) is an emerging imaging modality that shows great potential for preclinical research and clinical practice as mentioned in this paper, which is based on the acoustic detection of optical absorption from either endogenous chromophores, such as oxy-hemoglobin and deoxy-hemoglobaloglobin, or exogenous contrast agents such as organic dyes and nanoparticles.
Abstract: Photoacoustic tomography (PAT) is an emerging imaging modality that shows great potential for preclinical research and clinical practice. As a hybrid technique, PAT is based on the acoustic detection of optical absorption from either endogenous chromophores, such as oxy-hemoglobin and deoxy-hemoglobin, or exogenous contrast agents, such as organic dyes and nanoparticles. Because ultrasound scatters much less than light in tissue, PAT generates high-resolution images in both the optical ballistic and diffusive regimes. Over the past decade, the photoacoustic technique has been evolving rapidly, leading to a variety of exciting discoveries and applications. This review covers the basic principles of PAT and its different implementations. Strengths of PAT are highlighted, along with the most recent imaging results.

368 citations


Journal ArticleDOI
TL;DR: The results show that the proposed kSVM-DT achieves 80% classiflcation accuracy, better than 74% of the method without kernel, and the PSO exceeds the random selection method in choosing the parameters of the classifler.
Abstract: In this paper we proposed a novel classiflcation system to distinguish among elderly subjects with Alzheimer's disease (AD), mild cognitive impairment (MCI), and normal controls (NC). The method employed the magnetic resonance imaging (MRI) data of 178 subjects consisting of 97NCs, 57MCIs, and 24ADs. First, all these three dimensional (3D) MRI images were preprocessed with atlas-registered normalization. Then, gray matter images were extracted and the 3D images were under-sampled. Afterwards, principle component analysis was applied for feature extraction. In total, 20 principal components (PC) were extracted from 3D MRI data using singular value decomposition (SVD) algorithm, and 2 PCs were extracted from additional information (consisting of demographics, clinical examination, and derived anatomic volumes) using alternating least squares (ALS). On the basic of the 22 features, we constructed a kernel support vector machine decision tree (kSVM-DT). The error penalty parameter C and kernel parameter ae were determined by Particle Swarm Optimization (PSO). The weights ! and biases b were still obtained by quadratic programming method. 5-fold cross validation was employed to obtain the out-of-sample estimate. The results show that the proposed kSVM-DT achieves 80% classiflcation accuracy, better than 74% of the method without kernel. Besides, the PSO exceeds the random selection method in choosing the parameters of the classifler. The computation time to predict a new patient is only 0.022s.

181 citations


Journal ArticleDOI
TL;DR: In this paper, a generalized gauge is proposed for solving electromagnetics problems in inhomogeneous media that can be extended to the anistropic case, and the matrix representation of the integral equation for a PEC (perfect electric conductor) scatterer is given.
Abstract: The mixed vector and scalar potential formulation is valid from quantum theory to classical electromagnetics. The present rapid development in quantum optics applications calls for electromagnetic solutions that straddle both the quantum and classical physics regimes. The vector potential formulation using A and ' (or A-' formulation) is a good candidate to bridge these two regimes. Hence, there is a need to generalize this formulation to inhomogeneous media. A generalized gauge is suggested for solving electromagnetics problems in inhomogenous media that can be extended to the anistropic case. An advantage of the resulting equations is their absence of catastrophic breakdown at low-frequencies. Hence, the usual difierential equation solvers can be used to solve them over a wide range of scales and bandwidth. It is shown that the interface boundary conditions from the resulting equations reduce to those of classical Maxwell's equations. Also, the classical Green's theorem can be extended to such a formulation, resulting in an extinction theorem and a surface equivalence principle similar to the classical case. Moreover, surface integral equation formulations can be derived for piecewise homogeneous scatterers. Furthermore, the integral equations neither exhibit the low-frequency catastrophe nor the frequency imbalance observed in the classical formulation using E-H flelds. The matrix representation of the integral equation for a PEC (perfect electric conductor) scatterer is given.

138 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a new approach to generate a non-zero OAM fleld through a single patch antenna, which can be used as compact and low-cost generators of electromagnetic flelds carrying OAM.
Abstract: The recent extension of the orbital angular momentum (OAM) concept from optical to microwave frequencies has led some researchers to explore how well established antenna techniques can be used to radiate a non-zero OAM electromagnetic fleld. In this frame, the aim of the present paper is to propose a new approach to generate a non-zero OAM fleld through a single patch antenna. Using the cavity model, we flrst analyze the radiated fleld by a standard circular patch and show that a circular polarized (CP) TMnm mode excited by using two coaxial cables generates an electromagnetic fleld with an OAM of order §(ni1). Then, in order to obtain a simpler structure with a single feed, we design an elliptical patch antenna working on the right-handed (RH) CP TM21 mode. Using full-wave simulations and experiments on a fabricated prototype, we show that the proposed antenna efiectively radiates an electromagnetic fleld with a flrst order OAM. Such results prove that properly designed patch antennas can be used as compact and low-cost generators of electromagnetic flelds carrying OAM.

132 citations


Journal ArticleDOI
TL;DR: In this article, the state-of-the-art in the science of invisibility for electromagnetic waves, and examine the different available technical concepts and experimental investigations, focusing on the underlying physics and the basic scientific concepts.
Abstract: Invisibility has been a tantalizing concept for mankind over several centuries. With recent developments in metamaterial science and nanotechnology, the possibility of cloaking objects to incoming electromagnetic radiation has been escaping the realm of science fiction to become a technological reality. In this article, we review the state-of-the-art in the science of invisibility for electromagnetic waves, and examine the different available technical concepts and experimental investigations, focusing on the underlying physics and the basic scientific concepts. We discuss the available cloaking methods, including transformation optics, plasmonic and mantle cloaking, transmission-line networks, parallel-plate cloaking, anomalous resonance methods, hybrid methods and active schemes, and give our perspective on the subject and its future. We also draw a parallel with cloaking research for acoustic and elastodynamic waves, liquid waves, matter waves and thermal flux, demonstrating how ideas initiated in the field of electromagnetism have been able to open ground breaking venues in a variety of other scientific fields. Finally, applications of cloaking to non-invasive sensing are discussed and reviewed.

103 citations


Journal ArticleDOI
TL;DR: In this paper, a laser-radar system for field entomology based on the so-called Scheimpflug principle and a continuous-wave laser was developed, where the sample-rate of this method is unconstrained by the roundtrip time of the light, and the method allows assessment of the fast oscillatory insect wing-beats and harmonics over kilometers range, e.g., for species identification and relating abundances to the topography.
Abstract: Assessment of biodiversity of pollinators on the landscape scale or estimation of fluxes of disease-transmitting biting midges constitutes a major technical challenge today. We have developed a laser-radar system for field entomology based on the so called Scheimpflug principle and a continuouswave laser. The sample-rate of this method is unconstrained by the round-trip time of the light, and the method allows assessment of the fast oscillatory insect wing-beats and harmonics over kilometers range, e.g., for species identification and relating abundances to the topography. Whereas range resolution in conventional lidars is limited by the pulse duration, systems of the Scheimpflug type are limited by the diffraction of the telescopes. However, in the case of sparse occurrence of the atmospheric insects, where the optical cross-section oscillates, estimation of the range and spacing between individuals with a precision beyond the diffraction limit is now demonstrated. This enables studies of insect interaction processes in-situ.

99 citations


Journal ArticleDOI
TL;DR: In this paper, a new kind of metamaterial (MTM) absorber was proposed for the solar cell applications, which is particularly presented in a range of the solar spectrum in order to utilize the solar energy efficiently.
Abstract: We design, characterize, and analyze a new kind of metamaterial (MTM) absorber (MA) in difierent frequency regions for the solar cell applications. This MTM based structure is particularly presented in a range of the solar spectrum in order to utilize the solar energy efiectively. The proposed MTM based solar cell provides perfect absorption for both infrared and visible frequency ranges and can be used for the realization of more e-cient new solar cells. The structure is also tested in terms of the polarization angle independency. The suggested MA has a simple conflguration which introduces ∞exibility to adjust its MTM properties to be used in solar cells and can easily be re-scaled for other frequency ranges. Our experimental results in microwave frequencies conflrm the perfect absorption for the resonance frequency and agree with the simulation results. This means that the developed MA for solar cells will ofier perfect absorption in infrared and even in visible frequencies.

97 citations


Journal ArticleDOI
TL;DR: In this paper, a dual-band metamaterial-based absorber (MA) is designed and constructed, which is based on isotropic ring resonator with gaps and octa-star strip.
Abstract: Polarization and incident angle independent metamaterial-based absorber (MA) which acts as a strong dual-band resonator is designed and constructed. Besides, a method to design single/dual- band MA is presented in detail. The proposed model is based on isotropic ring resonator with gaps and octa-star strip (OSS) which allows maximization in the absorption because of the characteristic features of the structure. Re∞ection and absorption responses are obtained both numerically and experimentally and compared to each other. Two maxima in the absorption are experimentally obtained around 90% at 4:42GHz for the flrst band and 99:7% at 5:62GHz for the second band which are in good agreement with the numerical simulations (95:6% and 99:9%, respectively). The numerical studies verify that the dual-band MA can provide perfect absorption at wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves. The proposed model can easily be used in many potential application areas such as security systems, sensors, medical imaging technology.

75 citations


Journal ArticleDOI
TL;DR: In this article, a frequency reconfigurable slot-patch antenna with reflector at the back of an antenna is presented, which is capable to reconfigure up to six different frequency bands from 1.7 GHz to 3.5 GHz.
Abstract: In this paper, frequency reconfigurable slot-patch antenna with reflector at the back of an antenna is presented. The proposed antenna consists of a microstrip patch antenna and a microstrip slot antenna where the slot antenna is positioned at the ground plane underneath the patch. Three switches are placed in the slot. The antenna is capable to reconfigure up to six different frequency bands from 1.7 GHz to 3.5 GHz. The microstrip patch antenna produces three different frequency bands with directional radiation pattern while the microstrip slot antenna produces another three frequency bands with bidirectional radiation pattern. Due to the reflector placed at the back of the antenna, the radiation pattern is directional at all frequency bands. Simulated and measured results are used to demonstrate the performance of the antenna. The simulated and measured reflection coefficients and radiation patterns are presented and compared.

75 citations


Journal ArticleDOI
TL;DR: In this article, the surface and volume integral equation methods for finding time-harmonic solutions of the full-wave solutions of MaxMax's equations are discussed, and the main focus is on advanced techniques that would enable accurate, stable and scalable solutions on a wide range of material parameters, frequencies and applications.
Abstract: During the last two-three decades the importance of computer simulations based on numerical full-wave solutions of Maxwell's has continuously increased in electrical engineering. Software products based on integral equation methods have an unquestionable importance in the frequency domain electromagnetic analysis and design of open-region problems. This paper deals with the surface and volume integral equation methods for finding time-harmonic solutions of Maxwell's equations. First a review of classical integral equation representations and formulations is given. Thereafter we briefly overview the mathematical background of integral operators and equations and their discretization with the method of moments. The main focus is on advanced techniques that would enable accurate, stable, and scalable solutions on a wide range of material parameters, frequencies and applications. Finally, future perspectives of the integral equation methods for solving Maxwell's equations are discussed.

65 citations



Journal ArticleDOI
TL;DR: In this article, a hyperbolic metamaterial composed of alternating aluminum-alumina thin fllms based on superposition of multiple slow-wave modes was used to realize a broadband absorber.
Abstract: Here we realize a broadband absorber by using a hyperbolic metamaterial composed of alternating aluminum-alumina thin fllms based on superposition of multiple slow-wave modes. Our super absorber ensures broadband and polarization-insensitive light absorption over almost the entire solar spectrum, near-infrared and short-wavelength infrared regime (500{2500nm) with a simulated absorption of over 90%. The designed structure is fabricated and the measured results are given. This absorber yields an average measured absorption of 85% in the spectrum ranging from 500nm to 2300nm. The proposed absorbers open an avenue towards realizing thermal emission and energy- harvesting materials.

Journal ArticleDOI
Chen Jie, Qiang Cheng1, Zhao Jie, Di Sha Dong, and Tie-Jun Cui 
TL;DR: In this article, a metasurface for Radar Cross Section (RCS) reduction is proposed, which is composed of the same type of metamaterial units with different geometric dimensions, leading to various re∞ection phases under the incidence of plane waves.
Abstract: A metasurface for Radar Cross Section (RCS) reduction is proposed. The surface is composed of the same type of metamaterial units with difierent geometric dimensions, leading to various re∞ection phases under the incidence of plane waves. By carefully choosing the phase distributions, difiusion will be produced for the re∞ected waves which may redistribute the scattering energy from the surface toward all the directions, and hence it can be applied as the coating of metallic targets with ultra-low RCS. Both the simulated and experimental results have validated the proposed method.

Journal ArticleDOI
TL;DR: In this article, the design, simulation, and measurement of a compact flltering microstrip antenna is presented, where a feed line, two hairpin resonators and a rectangular patch are integrated to form the antenna.
Abstract: Design, simulation, and measurement of a compact flltering microstrip antenna is presented. A feed line, two hairpin resonators, and a rectangular patch are integrated to form the flltering antenna. The elements together function as a third order bandpass fllter with Chebyshev equal ripple response of 0.043dB at midband frequency of 2.0GHz. The rectangular patch acts not only as a radiating element, but also as the last resonator of the bandpass fllter. The proposed flltering antenna exhibits good out-of- band gain suppression, ∞at in-band gain response, good selectivity at the band edges, and well-shaped radiation pattern.

Journal ArticleDOI
TL;DR: In this article, a chiral metamaterial based on split ring resonators with double splits (SRDS) is demonstrated both theoretically and experimentally in X band range, based on transmission measurements and simulations monitoring the resonance frequency changes with respect to the thickness of the sensing layer and permittivity values.
Abstract: In this work, sensor abilities of a chiral metamaterial based on split ring resonators with double splits (SRDS) are demonstrated both theoretically and experimentally in X band range. This study is based on transmission measurements and simulations monitoring the resonance frequency changes with respect to the thickness of the sensing layer and permittivity values. Experimental and simulated results show that the resonance frequency of the chiral metamaterial based SRDS sensor is linearly related to the permittivity and the thickness of the sensor layer which creates a suitable approach for sensing environment and organic parameters. When the sensor layer filled with the related material, changes in the tissue temperature, sand humidity and calcium chloride density lead to resonance frequency changes. The physical mechanisms are explained by using both equivalent circuit model and the fundamental sensitivity theorem of chiral sensors. This is the first study investigating a sensing mechanism based on the chiral metamaterials in X band range.

Journal ArticleDOI
TL;DR: Numerical results obtained with the novel combined algorithmic approach, based on synthetically generated breast phantoms, show significant improvement in image quality.
Abstract: Microwave tomography (MWT) and a radar-based region estimation technique are combined to create a novel algorithm for biomedical imaging with a focus on breast cancer detection and monitoring. The region estimation approach is used to generate a patient-specific spatial map of the breast anatomy that includes skin, adipose and fibroglandular regions, as well as their average dielectric properties. This map is incorporated as a numerical inhomogeneous background into an MWT algorithm based on the finite element contrast source inversion (FEM-CSI) method. The combined approach reconstructs finer structural details of the breast and better estimates the dielectric properties than either technique used separately. Numerical results obtained with the novel combined algorithmic approach, based on synthetically generated breast phantoms, show significant improvement in image quality.

Journal ArticleDOI
TL;DR: In this article, a 3D metamaterial stacked array for the conversion of electromagnetic waves energy into AC was proposed. But the authors considered an operating frequency of 5:8GHz and showed that using stacked arrays can signiflcantly improve the efficiency of the harvesting system in comparison to a 2-D array.
Abstract: We present the design of 3-D metamaterial stacked arrays for e-cient conversion of electromagnetic waves energy into AC. The design consists of several vertically stacked arrays where each array is comprised of multiple Split-Ring Resonators. The achieved conversion e-ciency is validated by calculating the power dissipated in a resistive load connected across the gap of each resonator. Numerical simulations show that using stacked arrays can signiflcantly improve the e-ciency of the harvesting system in comparison to a ∞at 2-D array. In fact, the per-unit-area e-ciency of the 3-D design can reach up to 4.8 times the case of the 2-D array. Without loss of generalization, the designs presented in this work considered an operating frequency of 5:8GHz.

Journal ArticleDOI
TL;DR: In this article, the authors investigated periodic structures in antenna design for wireless applications and compared the CRLH miniaturization method with EBG ground, metamaterial substrate or EBG/AMC structure.
Abstract: In this paper, periodic structures are investigated in antenna design for wireless applications. These antennas were compared with CRLH miniaturization method. Three difierent models of patch antenna with coaxial feed on EBG ground, metamaterial substrate or EBG/AMC structure have been presented here. Also two compact dual-band antennas have been designed and fabricated based on CRLH techniques for wireless and GSM applications. The flrst antenna has directional pattern and operates at 1760, 2550 and 3850MHz (three-band antenna) with gain 2.1, i3:9 and 2.5dBi, and it is dual polarized. The size of prototype patch antenna is 20 £ 20mm 2 which is reduced about 47% in comparison to conventional patch antenna at 2.5GHz. The second antenna is designed by the use of interdigital capacitor and spiral inductor. Dimensions of antenna are 15:5£12mm 2 , so the size is reduced about 69% in comparison to conventional microstrip patch antennas at 1.8GHz. The second tri-band antenna operates at 1060MHz, 1800MHz and 2500MHz in which two frequencies (1.8 and 2.5GHz) are suitable for GMS and WLAN applications. Both structures have been designed and fabricated on FR4 low cost substrate with "r = 4:4 and thickness of 1.6mm. All simulations are done with CST and HFSS. Equivalent circuit and experimental results are also presented and compared.

Journal ArticleDOI
Guolong He1, Yafeng Zhan, Ge Ning, Yukui Pei, Bin Wu, Yuan Zhao 
TL;DR: In this article, the authors used computational ∞uid dynamics (CFD) technique, Demetriades's plasma turbulence model and flnite-difierence time-domain (FDTD) algorithm, amplitude variation and phase ∞uctuation induced by plasma electron density turbulence are obtained, and their statistical properties are analyzed and characterized.
Abstract: Efiects on the communication signals caused by the time-varying plasma sheath surrounding hypersonic vehicles are investigated. Using computational ∞uid dynamics (CFD) technique, Demetriades's plasma turbulence model and flnite-difierence time-domain (FDTD) algorithm, amplitude variation and phase ∞uctuation induced by plasma electron density turbulence are obtained, and their statistical properties are analyzed and characterized. Furthermore, a flnite-state Markov channel (FSMC) model is proposed, to represent the dynamical efiects on electromagnetic wave propagation through plasma sheath. With high accuracy and greatly reduced complexity, the FMSC model could be very useful to develop novel communication techniques for alleviating the radio blackout problem.

Journal ArticleDOI
TL;DR: In this article, an ultra-thin triple-band metamaterial absorber (MA) is proposed in the microwave region, which is composed of a periodic array of three rotated square rings (RSRs) and a continuous metal fllm separated by only 1mm dielectric substrate.
Abstract: An ultra-thin triple-band metamaterial absorber (MA) is proposed in the microwave region, which is composed of a periodic array of three rotated square rings (RSRs) and a continuous metal fllm separated by only 1mm dielectric substrate. The fabricated MA exhibits three experimental absorption peaks at 4.88GHz, 7.88GHz, and 11.32GHz with the corresponding absorption rates of 98.8%, 96.5%, and 95.9%, which shows an excellent agreement with the simulated results. The triple-band MA is polarization-insensitive at the normal incidence. Finally, the multi-re∞ection interference theory is introduced to interpretate the absorption mechanism. The calculated absorption rates of the improved unit cell for the strongly coupled MA coincide well with the simulated results at wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves.

Journal ArticleDOI
TL;DR: In this article, a multi-color STED ∞uorescence microscope is presented for biomedical research, providing far-fleld optical resolution down to 20nm for imaging at sub-difiraction length scales.
Abstract: We present a multi-color STED ∞uorescence microscope providing far-fleld optical resolution down to 20nm for biomedical research. The optical design comprises flber lasers, beam scanners, and a set of active and passive polarizing elements that cooperatively yield an optically robust system for routinely imaging samples at subdifiraction length scales.

Journal ArticleDOI
TL;DR: The proposed imaging technique difiers from conventional microwave imaging methods in that it does not require the direct measurement of the complex fleld scattered from the imaged object but mathematically recovers it from intensity-only scalar microwave measurements.
Abstract: In this paper, indirect microwave holographic imaging of concealed ordnance is demonstrated. The proposed imaging technique difiers from conventional microwave imaging methods in that it does not require the direct measurement of the complex fleld scattered from the imaged object but mathematically recovers it from intensity-only scalar microwave measurements. This brings the advantages of simplifying the hardware implementation and signiflcantly reducing the cost of the imaging system. In order to demonstrate the ability of the proposed technique to reconstruct good quality images of concealed ordnance, indirect microwave holographic imaging of a metallic gun concealed in a pouch is carried out for airport security imaging applications. It is demonstrated that good resolution amplitude and phase images of concealed objects can be recovered when back-propagation is applied.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a dual-access rectenna with two dc-recombined rectifiers and a cross-slot coupled square patch antenna fed by a microstrip line to minimize the RF power imbalance between accesses caused by multipath effects and consequently arbitrary polarized incident waves.
Abstract: This paper reports a 2.45 GHz, low power dual circularly polarized (DCP) and dual access rectenna. It contains two dc-recombined rectifiers and a cross-slot coupled square patch antenna fed by a microstrip line. A judicious dc recombination scheme allows to minimize the RF power imbalance between accesses caused by multipath effects and consequently arbitrary polarized incident waves. The proposed rectenna is then able to harvest linearly polarized, right-hand circularly polarized (RHCP) and left-hand circularly polarized (LHCP) electromagnetic waves, with nearly stable performances. The rectenna has been optimized at -15 dBm per access and dedicated to remote and contactless supply low consumption sensors. It has been experimentally tested with very low power densities from 0.057 μW/cm2 (Erms=0.46 V/m) to 2.3 μW/cm2 (Erms=2.95 V/m). At 1.49 μW/cm2 (-15 dBm on each rectifier), the structure exhibits an output dc voltage and a global efficiency of 189 mV and 37.7%, respectively when the azimuthal angle (Φ) of the incident field is equal to 0°. Due to the nearly constant total gain of the DCP antenna and an appropriate dc recombination of the two rectifiers, the global efficiency slightly varies between 37.7% and 41.4% when the azimuthal angle (Φ) varies between -90 and 90°.

Journal ArticleDOI
TL;DR: This paper attempts to develop an accurate model accounting for the key contributions to the Doppler signature for the human motion in a forest environment and combines analytical techniques with full wave numerical methods to achieve a realistic representation of the signature from the scene.
Abstract: Automatic detection of human motion is important for security and surveillance applications. Compared to other sensors, radar sensors present advantages for human motion detection and identiflcation because of their all-weather and day-and-night capabilities, as well as the fact that they detect targets at a long range. This is particularly advantageous in the case of remote and highly cluttered radar scenes. The objective of this paper is to investigate human motion in highly cluttered forest medium to observe the characteristics of the received Doppler signature from the scene. For this purpose we attempt to develop an accurate model accounting for the key contributions to the Doppler signature for the human motion in a forest environment. Analytical techniques are combined with full wave numerical methods such as Method of Moments (MoM) enhanced with Fast Multipole Method (FMM) to achieve a realistic representation of the signature from the scene. Mutual interactions between the forest and the human as well as the attenuation due to the vegetation are accounted for. Due to the large problem size, parallel programming techniques that utilize a Graphics Processing Unit (GPU) based cluster are used.

Journal ArticleDOI
TL;DR: In this article, a novel frequency reconfigurable 4G MIMO handset antenna is presented and verified with experimental results, where frequency tuning is used to minimize the antenna volume and to compensate for the losses related to user-originated impedance detuning.
Abstract: A novel frequency reconfigurable 4G Multiple-Input Multiple-Output (MIMO) handset antenna is presented and verified with experimental results. Frequency tuning is used to minimize the antenna volume and to compensate for the losses related to user-originated impedance detuning. Both antenna elements are independently frequency reconfigurable and can cover most of the LTE-A bands. The study compares the losses of CMOS- and MEMS-based digitally tunable capacitors (DTC). In addition, two prototypes with total antenna volumes of 1170 and 3900 mm 3 have been studied. The results show that the larger antenna structure operates with an efficiency better than 49% across the frequencies of 698-960 MHz and better than 56% across the frequencies of 1430-2690 MHz, when a MEMS-based DTC is used. In addition, a new method is introduced to estimate the suitability of the antenna geometry for frequency tunable antennas.

Journal ArticleDOI
TL;DR: The proposed MFPDV upwrap phase images better than conventional PDV map, and I2L2 and TSGS are e-cient strategies to reduce computation time.
Abstract: An improved method of quality guided phase unwrapping (QGPU) is proposed in this work. It extracts the quality map via a median flltered phase derivative variance (MFPDV) that applies a two-dimensional median fllter on the phase derivative variance (PDV) map, in order to reduce the efiect of noise in the background area. In addition, we employed the Indexed Interwoven Linked List (I2L2) structure to store the orderly adjoin list more e-ciently and the Two Section Guided Strategy (TSGS) to reduce comparison frequency. The experiments demonstrate that the normalized L1 norm of MFPDV of a brain MR image is only 0.0827, less than that of PDV method at 0.0923. Besides, the computation time of QGPU with I2L2 technique is only 30% of that with sequence structure, and the computation time of QGPU with TSGS is only 65% of that without TSGS. In total, the proposed MFPDV upwrap phase images better than conventional PDV map, and I2L2 and TSGS are e-cient strategies to reduce computation time.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the detection and estimation of surface snowfall using NASA's CloudSat through the first evaluation of its newly released 2C-SNOW-PROFILE products using the National Mosaic and Multisensor QPE System (NMQ) snowfall products.
Abstract: This study investigates snowfall detectability and snowfall rate estimation with NASA's CloudSat through the flrst evaluation of its newly released 2C-SNOW-PROFILE products using the National Mosaic and Multisensor QPE System (NMQ) snowfall products. The primary focus is on the detection and estimation of surface snowfall. The results show that the CloudSat product has good detectability of light snow (snow water equivalent less than 1mm/h) but degrades in moderate and heavy snow (heavier than 1mm/h). The analysis suggests that the new 2C-SNOW-PROFILE algorithm is insu-cient in correcting signal losses due to attenuation. Its underestimation is well correlated to snowfall intensity. Issues of sensitivity and data sampling with ground radars, which may afiect the interpretation of the results, are also discussed. This evaluation of the new 2C-SNOW-PROFILE algorithm provides guidance for applications of the product and identifles particular error sources that can be addressed in future versions of the CloudSat snowfall algorithm.

Journal ArticleDOI
TL;DR: This work examines the use of classiflcation algorithms for early- stage tumor detection with an experimental time-domain microwave breast screening system, and investigates a method for detecting the tumors within the breast but without the usual complexity inherent to image-generation methods.
Abstract: In this work we examine, for the flrst time, the use of classiflcation algorithms for early- stage tumor detection with an experimental time-domain microwave breast screening system. The experimental system contains a 16-element antenna array, and testing is done on breast phantoms that mimic breast tissue dielectric properties. We obtain experimental data from multiple breast phantoms with two possible tumor locations. In this work, we investigate a method for detecting the tumors within the breast but without the usual complexity inherent to image-generation methods, and conflrm its feasibility on experimental data. The proposed method uses machine learning techniques, namely Support Vector Machines (SVM) and Linear Discriminant Analysis (LDA), to determine whether the current breast being scanned is tumor-free. Our results show that both SVM and LDA methods have promise as algorithms supporting early breast cancer microwave screening.

Journal ArticleDOI
TL;DR: In this article, the authors derived analytic expressions for induced total axial current in the body and associated flelds in the vicinity of the body when an imperfectly conducting cylindrical antenna model of the human body is illuminated by a vertically polarized plane wave within the 1{200MHz frequency range.
Abstract: Human body communication (HBC) is a promising wireless technology that uses the human body as part of the communication channel. HBC operates in the near-fleld of the high frequency (HF) band and in the lower frequencies of the very high frequency (VHF) band, where the electromagnetic fleld has the tendency to be conflned inside the human body. Electromagnetic interference poses a serious reliability issue in HBC; consequently, it has been given increasing attention in regard to adapting techniques to curtail its degrading efiect. Nevertheless, there is a gap in knowledge on the mechanism of HBC interference that is prompted when the human body is exposed to electromagnetic flelds as well as the efiect of the human body as an antenna on HBC. This paper narrows the gap by introducing the mechanisms of HBC interference caused by electromagnetic fleld exposure of human body. We derived analytic expressions for induced total axial current in the body and associated flelds in the vicinity of the body when an imperfectly conducting cylindrical antenna model of the human body is illuminated by a vertically polarized plane wave within the 1{200MHz frequency range. Also, flelds in the vicinity of the human body model from an on-body HBC transmitter are calculated. Furthermore, conducted electromagnetic interference on externally embedded HBC receivers is also addressed. The results show that the maximum HBC gain near 50MHz is due to whole-body resonance, and the maximum at 80MHz is due to the resonance of the arm. Similarly, the results also suggest that the magnitude of induced axial current in the body due to electromagnetic fleld exposure of human body is higher near 50MHz.

Journal ArticleDOI
TL;DR: In this article, a wave-guided metamaterial (WG-MTM) was employed to suppress mutual coupling between adjacent elements in a densely packed microstrip array, where the edge-to-edge separation between elements was kept at only 0.093λ0.
Abstract: In this paper, suppression of mutual coupling is achieved using compact waveguided metamaterials (WG-MTMs) in between elements of a densely packed microstrip array. Both the E-plane internally folded complementary split ring resonator and the H-plane internally folded complementary split ring resonator are employed to reduce the mutual coupling between adjacent elements. Coupling suppression of 18 dB and 9 dB, for elements in the E-plane and H-plane, respectively, is demonstrated. Due to the compact size of the waveguided metamaterials, the edge-to-edge separation between elements is kept at only 0.093λ0. With the same element spacing, a 2 × 2 array is also simulated with compact WG-MTMs. The proposed structure reduces the array size and enables the implementation of compact Multiple-Input-Multiple-Output systems.