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Sökning: L773:1070 4698 OR L773:1559 8985

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1.
  • Cai, Fuhong, et al. (författare)
  • Exploratory Study on Light-Sheet Based Three-Dimensional Surface Topography
  • 2018
  • Ingår i: Progress In Electromagnetics Research. - : EMW PUBLISHING. - 1070-4698 .- 1559-8985. ; 161, s. 11-18
  • Tidskriftsartikel (refereegranskat)abstract
    • Light-sheet microscopy has attracted considerable attention because it is a fluorescence imaging technique with rapid optical sectioning capability for transparent samples. In this study, we report a new application based on light-sheet microscopy for exploratory investigation of three-dimensional surface topography of opaque objects. Instead of using inelastic scattering fluorescent signals, our method utilizes the elastic scattering of light from the surface of opaque samples, which are illuminated by a light sheet generated by a cylindrical lens. Through a simple structural modification by removing the fluorescent filter, the orthogonal imaging module can capture the elastically-scattered image. As the opaque object is scanned by a motorized stage, the light-sheet microscope acquires a series of sectional images, which can be stitched into a three-dimensional surface topography image. This method also offers the opportunity to visualize a 3D fingerprint at micron-level resolution. Therefore, this technique may be used in industry and the biomedical field for the measurement of surface microstructure. To our best knowledge, this is the first time a light-sheet microscopy is utilized to perform surface topography measurement.
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2.
  • Cai, F., et al. (författare)
  • Vectorial electric field Monte Caro simulations for focused laser beams (800 nm-2220 nm) in a biological sample
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 142, s. 667-681
  • Tidskriftsartikel (refereegranskat)abstract
    • Here we develop a method that combines vectorial electric field Monte Carlo simulation with Huygens-Fresnel principle theory to determine the intensity distribution of a focused laser beam in a biological sample. The proper wavelengths for deep tissue imaging can be determined by utilizing our method. Furthermore, effects of anisotropic factor, scattering and absorption coeffcients on the focal spots are analyzed. Finally, the focal beams formed by objective lenses with different values of numerical aperture are also simulated to study the focal intensity in the biological sample.
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3.
  • Cheng, Hao, et al. (författare)
  • Nanoparticles with aggregation-induced emission for monitoring long time cell membrane interactions
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 140, s. 313-325
  • Tidskriftsartikel (refereegranskat)abstract
    • We perform the long time monitoring of nanoparticle-cell membrane interaction with high spatial and temporal resolution. The 2, 3-bis(4-(pheny1(4-(1, 2, 2-triphenylvinyl) phenyl)amino)phenyl) fumaronitrile (TPE-TPA-FN) is doped in organically modified silica (ORMOSIL) to be a biocompatible nanoprobe, which displays an aggregation-induced emission (ATE) effect. Photobleaching resistance of this synthesized nanoparticle is tested and compared with its similar counterpart, which proves its superiority and capability of long term fluorescence emission. We utilize the objective-based total internal reflection microscopy combined with the living cell incubation platform to investigate the cell uptake process of this nanoparticle in real time.
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4.
  • Dai, Daoxin, et al. (författare)
  • Silicon Multimode Photonic Integrated Devices For On-Chip Mode-Division-Multiplexed Optical Interconnects
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 143, s. 773-819
  • Tidskriftsartikel (refereegranskat)abstract
    • Multimode spatial-division multiplexing (SDM) technology has attracted much attention for its potential to enhance the capacity of an optical-interconnect link with a single wavelength carrier. For a mode-multiplexed optical-interconnect link, the functional elements are quite different from the conventional ones as multiple modes are involved. In this paper we give a review and discussion on multimode photonic integrated devices for mode-multiplexed optical-interconnects. Light propagation and mode conversion in tapered waveguides as well as bent waveguides are discussed first. Recent progress on mode converter-(de)multiplexers is then reviewed. The demands of some functional devices used for mode-multiplexed optical-interconnects are also discussed. In particular, the fabrication tolerance is analyzed in detail for our hybrid demultiplexer, which enables mode-/polarization-division-(de)multiplexing simultaneously.
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5.
  • Dalarsson, Mariana, et al. (författare)
  • Arbitrary Loss Factors In The Wave Propagation Between RHM And LHM Media With Constant Impedance Throughout The Structure
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 137, s. 527-538
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the wave propagation properties in lossy structures with graded permittivity and permeability involving left-handed metamaterials. An exact analytic solution to Helmholtz' equation for a lossy case with both real and imaginary parts of permittivity and permeability profile, changing according to a hyperbolic tangent function along the direction of propagation, is obtained. It allows for different loss factors in RHM and LHM media. Thereafter, the corresponding numerical solution for the field intensity along the composite structure is obtained by means of a dispersive numerical model of lossy metamaterials that uses a transmission line matrix method based on Z-transforms. We present the expressions and graphical results for the field intensity along the composite structure and compare the analytic and numerical solutions, showing that there is an excellent agreement between them.
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6.
  • Dalarsson, Mariana, et al. (författare)
  • Exact Analytical Solution for Fields in a Lossy Cylindrical Structure with Linear Gradient Index Metamaterials
  • 2015
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 151, s. 109-117
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the electromagnetic wave propagation across a finite inhomogeneous and anisotropic cylindrical metamaterial composite containing both positive and negative effective refractive index parts with linear spatial gradient. Exact analytical solutions for the electric and magnetic field distributions are obtained for a linear variation of effective refractive index across the structure. The exact analytical results for the electric and magnetic fields are compared to the numerical results obtained using the numerical simulation software HFSS. The model allows for general temporal dispersion and uniform losses within the composite.
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7.
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8.
  • Gomes, Chandima, et al. (författare)
  • Vertical electric fields and field change parameters due to partly inclined lightning leader channels
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 135, s. 55-80
  • Tidskriftsartikel (refereegranskat)abstract
    • Vertical electric ¯elds generated by lightning leaderchannels, the total leader ¯eld change and the total leader ¯eld changeto the total return stroke ¯eld change ratio, at a certain distance, weretheoretically analysed by varying the angle of orientation of a segmentof upper part. Ground was treated as a perfectly conducting horizontalplane. Results were able to discern signi¯cantly large di®erences in thestatic ¯eld due to leader channels which have the same total lengthbut a certain channel segment is oriented at di®erent angles. Theoutcome of our calculations consistently explains the scatter of thetotal leader ¯eld observed in previous studies. Without consideringsuch channel segment orientation, one has to assume unrealistic chargesource heights or unreasonable charge densities to calculate matchingvalues for many observed total leader ¯elds and leader ¯eld to returnstroke ¯led ratios, labelled as anomalous observations in the literature.In some cases, irrespective of the charge source height and the chargedensity, one cannot ¯nd a suitable ¯t for the observed ¯elds with thestraight channel model.
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9.
  • Guo, Zefei, et al. (författare)
  • Optimization For Brain Activity Monitoring With Near Infrared Light In A Four-Layered Model Of The Human Head
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 140, s. 277-295
  • Tidskriftsartikel (refereegranskat)abstract
    • We describe a four-layered model for near infrared light propagation in a human head based on the Monte Carlo method. With the use of three-dimensional voxel-based media discretization, photon migration in the brain is analyzed by both the time-of-flight measurement and the spatial sensitivity profile. In the measurement of brain activity, the selection of light wavelength and the distance between the source and the detector have a great influence on the detected signal. In this study, we compare the detected signals from the detectors with different source-detector spacing at wavelengths of 690 nm, 800 nm and 1300 nm, and find that in our model, the wavelength of 1300 nm is more appropriate for the measurement of brain activity because the signals at 1300 nm get better detection sensitivity and spatial resolution. Source-detector spacing is also optimized.
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10.
  • Gustafsson, Mats, et al. (författare)
  • Stored electromagnetic energy and antenna Q
  • 2015
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 150, s. 13-27
  • Tidskriftsartikel (refereegranskat)abstract
    • Decomposition of the electromagnetic energy into its stored and radiated parts is instrumental in the evaluation of antenna Q and the corresponding fundamental limitations on antennas. This decomposition is not unique and there are several proposals in the literature. Here, it is shown that stored energy defined from the difference between the energy density and the far field energy equals the energy expressions proposed by Vandenbosch for many but not all cases. This also explains the observed cases with negative stored energy and suggests a possible remedy to them. The results are compared with the classical explicit expressions for spherical regions where the results only differ by the electrical size ka that is interpreted as the far-field energy in the interior of the sphere.
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11.
  • He, Sailing, et al. (författare)
  • Can Maxwell’s fish eye lens really give perfect imaging? : Part III. A careful reconsideration of the “evidence for subwavelength imaging with positive refraction”
  • 2015
  • Ingår i: Progress In Electromagnetics Research. - : Electromagnetics Academy. - 1070-4698 .- 1559-8985. ; 152, s. 1-15
  • Tidskriftsartikel (refereegranskat)abstract
    • Many scientists do not believe that Maxwell’s fish eye mirror (MFEM) can provide perfect imaging even if there is a drain array around the imaging points. However, one microwave experiment found a case where a 0.2λ resolution could be achieved in an MFEM experiment [1]. In this paper, we show that the MFEM cannot resolve two imaging points at such a subwavelength resolution in most cases even in the presence of a drain array, and an extraordinary case of subwavelength imaging requires a particular phase difference between two coherent sources. Both numerical simulations and experimental results show that the phase difference of two subwavelength-distanced coherent sources greatly influences the field distribution around the drain array. In very few cases (when the phase difference of the two sources is chosen to be a very specific value), we might resolve the image points in the drain array under the assumption that the power absorbed by the scanning cable on the left side of the drain array should be symmetric to that on the right side of the drain array [1]. However, in most cases, we cannot obtain a super-resolution imaging, as other drains around the image points will greatly influence the imaging. We also note that the experiment assumed that the power absorbed by the scanning cable on the left and the right sides of the drain array is symmetric is not correct for the experiment reported in [1], as the drain array itself is not symmetric. The highly non-symmetric distribution of the absorbed power is also verified by our simulation and experimental results. The experimental “result” of resolving two image peaks could potentially be recovered using only a single image peak, which demonstrates the wrong assumption of mirror symmetry. Comparisons and comments on perfect passive drains, “super-resolution” in a spherical geodesic waveguide, and time reverse imaging are also given.
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12.
  • He, Sailing, et al. (författare)
  • Light absorber with an ultra-broad flat band based on multi-sized slow-wave hyperbolic metamaterial thin-films
  • 2014
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 147, s. 69-79
  • Tidskriftsartikel (refereegranskat)abstract
    • Here we realize a broadband absorber by using a hyperbolic metamaterial composed of alternating aluminum-alumina thin films 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 (500-2500 nm) 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 2300 nm. The proposed absorbers open an avenue towards realizing thermal emission and energy- harvesting materials.
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13.
  • He, Sailing, et al. (författare)
  • On the possibility of a perfect power combiner
  • 2017
  • Ingår i: Progress In Electromagnetics Research. - : Electromagnetics Academy. - 1070-4698 .- 1559-8985. ; 158, s. 1-6
  • Tidskriftsartikel (refereegranskat)abstract
    • By reductio ad absurdum, we show that a perfect power combiner of single-mode waveguides is impossible for incoherent input waves of the same frequency and same polarization as it is against the law of conservation of energy. The inevitable 3 dB loss of a three-port power combiner is explained physically. An incoherent power combiner of nearly 100% efficiency can be realized only if the two input fields have different wavelengths, have different polarizations, or are of orthogonal modes.
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14.
  • Hu, Zhipeng, et al. (författare)
  • Wideband High-Reflection Chiral Dielectric Metasurface
  • 2021
  • Ingår i: Progress In Electromagnetics Research. - : EMW PUBLISHING. - 1070-4698 .- 1559-8985. ; 172, s. 51-60
  • Tidskriftsartikel (refereegranskat)abstract
    • Compared to natural materials, artificial subwavelength structures can enhance chiroptical effects in a stronger way, and the requirement of low material loss and wideband operation is desired in many situations. Here, we propose an all-dielectric chiral metasurface as a periodic array of centrosymmetric staggered silicon cuboid pairs to achieve strong circular dichroism in a wide band. As a demonstration, the designed chiral metasurface may strongly reflect the chosen circularly polarized light with the spin preserved in the operating wavelength range of 1.51 ti 1.60 mu m while highly transmit (with an efficiency greater than 95%) the opposite circularly polarized light with the spin flipped. Then, two application cases are given for the designed chiral metasurface. A flat chiral meta-lens is constructed to produce wideband focusing in the transmission/reflection side while the disturbing from the opposite circular polarization is well blocked by high reflection/transmission. A chiral Fabry-Perot cavity is also constructed, which has an extremely high quality factor (2.1E4). The proposed method provides an efficient way to produce strong chiroptical effects and has a promising potential for various applications such as signal processing, sensing, radiation and detection.
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15.
  • Lin, Xian Qi, et al. (författare)
  • Understand and realize an "invisible gateway" in a classical way
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 141, s. 739-749
  • Tidskriftsartikel (refereegranskat)abstract
    • We create an invisible gateway simply by putting electric and magnetic superscatterers in a metallic waveguide. The characteristics of the electric and magnetic resonators are analyzed in a metallic hollow waveguide, and the dual-mode superscattering property is discussed in detail to broaden the bandwidth of the invisible gateway. Good agreement is achieved between the simulation and measurement for such an invisible gateway. The present work help readers understand easily how an invisible gateway works (or makes sense) in a classical way without using any complex metamaterial or complicated method of transformation optics.
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16.
  • Liu, Kexin, et al. (författare)
  • Experimental Realization of Strong DC Magnetic Enhancement with Transformation Optics
  • 2014
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 146, s. 187-194
  • Tidskriftsartikel (refereegranskat)abstract
    • A passive DC magnetic concentrator is designed with transformation optics (TO) and realized by meta-materials. The passive DC magnetic concentrator based on space compression transformation can greatly enhance the magnetic field in a free space region and can be used for e.g., improving the sensitivity of magnetic sensors and increasing the efficiency of wireless energy transmission. The magnetic property of the medium obtained by TO is extremely anisotropic. To solve this, we use magnetic metamaterials made of alternated high-permeability ferromagnetic (HPF) materials and high-temperature superconductor (HTS) materials. We optimize our structure by conducting simulations using the finite element method (FEM) and experimentally demonstrate a strong, 4.74-time enhancement of the DC magnetic field by our meta-material magnetic concentrator. We also demonstrate that a simplified structure with only HPF materials working at room temperature can still gives 3.84-time enhancement of the DC magnetic field. The experimental results are in good agreement with the numerical simulations based on FEM.
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17.
  • Ma, Tengfei, et al. (författare)
  • Distinguishing Bipolar Depression from Major Depressive Disorder Using fNIRS and Deep Neural Network
  • 2020
  • Ingår i: Progress In Electromagnetics Research. - : The Electromagnetics Academy. - 1070-4698 .- 1559-8985. ; 169, s. 73-86
  • Tidskriftsartikel (refereegranskat)abstract
    • A variety of psychological scales are utilized at present as the most important basis for clinical diagnosis of mood disorders. An experienced psychiatrist assesses and diagnoses mood disorders based on clinical symptoms and relevant assessment scores. This symptom based clinical criterion is limited by the psychiatrist's experience. In practice, it is difficult to distinguish the patients with bipolar disorder with depression episode (bipolar depression, BD) from those with major depressive disorder (MDD). The functional near-infrared spectroscopy (fNIRS) technology is commonly used to perceive the emotions of a human. It measures the hemodynamic parameters of the brain, which correlate with cerebral activation. Here, we propose a machine learning classification method based on deep neural network for the brain activations of mood disorders. Large time scale connectivity is determined using an attention long short term memory neural network and short-time feature information are considered using the InceptionTime neural network in this method. Our combined method is referred to as AttentionLSTM-InceptionTime (ALSTMIT). We collected fNIRS data of 36 MDD patients and 48 BD patients who were in the depressed state. All the patients were monitored by fNIRS during conducting the verbal fluency task (VFT). We trained the model with the ALSTMIT network. The algorithm can distinguish the two types of patients effectively: the average accuracy of classification on the test set can reach 96.2% stably. The classification can provide an objective diagnosis tool for clinicians, and this algorithm may be critical for the early detection and precise treatment for the patients with mood disorders.
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18.
  • Pan, Jing, et al. (författare)
  • Optically Transparent and Mechanically Flexible Coplanar Waveguide-Fed Wideband Antenna Based on Sub-Micron Thick Micro-Metallic Meshes
  • 2023
  • Ingår i: Progress In Electromagnetics Research. - : EMW PUBLISHING. - 1070-4698 .- 1559-8985. ; 176, s. 11-23
  • Tidskriftsartikel (refereegranskat)abstract
    • optically transparent and flexible coplanar waveguide (CPW)-fed wideband antenna is proposed and demonstrated experimentally based on sub-micron thick micro-metallic meshes (mu-MMs). Due to the high visible transmittance (83.1%) and low sheet resistance (1.75 & OHM;/sq) of the silver mu-MM with thickness of only 190 nm, the transparent CPW has very low insertion loss and provides a good feed to the high-performance transparent antenna. The measured S11 spectrum of our antenna matches well with that of the opaque counterpart. The measured fractional bandwidth is 22% from 3.4 to 4.25 GHz. Based on numerical modeling, whose accuracy is experimentally verified, the radiation efficiency and peak gain of our transparent antenna at 3.45 GHz are calculated to be 89.7% and 3.03 dBi, respectively. Besides the good optical and electromagnetic properties, our transparent antenna is also highly flexible. Despite the sub-micron thick mu-MMs, the transparency, radiation efficiency, and mechanical properties of our transparent antenna are obviously superior to those of the transparent antennas reported previously, and the overall size and radiation gain are also comparable. Therefore, our transparent antenna has an excellent comprehensive performance, showing great potential for practical applications as well as the emerging applications in the field of flexible and wearable electronics.
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19.
  • Ramprecht, Jörgen, et al. (författare)
  • Biased magnetic materials in RAM applications
  • 2007
  • Ingår i: Progress in Electromagnetics Research. - 1559-8985 .- 1070-4698. ; 75, s. 85-117
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetization of a ferro- or ferri-magnetic material has been modeled with the Landau-Lifshitz-Gilbert (LLG) equation. In this model demagnetization effects are included. By applying a linearized small signal model of the LLG equation, it was found that the material can be described by an effective permeability and with the aid of a static external biasing field, the material can be switched between a Lorentz-like material and a material that exhibits a magnetic conductivity. Furthermore, the reflection coefficient for normally impinging waves on a PEC covered with a ferro/ferri-magnetic material, biased in the normal direction, is calculated. When the material is switched into the resonance mode, two distinct resonance frequencies in the reflection coefficient were found, one associated with the precession frequency of the magnetization and the other associated with the thickness of the layer. The former of these resonance frequencies can be controlled by the bias field and for a bias field strength close to the saturation magnetization, where the material starts to exhibit a magnetic conductivity, low reflection ( around - 20 dB) for a quite large bandwidth ( more than two decades) can be achieved.
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20.
  • Shen, Jianqi (författare)
  • A dressed-state assisted left-handed coherent medium for high-gain optical amplification
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 143, s. 263-284
  • Tidskriftsartikel (refereegranskat)abstract
    • A scheme of double-negative left-handed atomic vapor medium based on dressed-state assisted simultaneous electric and magnetic resonances is suggested. In this mechanism, simultaneous electric-and magnetic-dipole allowed transitions of atoms are driven by an optical wave by taking full advantage of both mixed-parity dressed-state assisted resonance and incoherent population pumping in a quantum-coherent atomic medium (e.g., alkali-metal atomic vapor). Since the simultaneously negative permittivity and permeability can be achieved in a same frequency band, such an atomic vapor will exhibit an incoherent-gain double-negative refractive index that is three-dimensionally isotropic and homogeneous. The imaginary part of the negative refractive index of the present atomic vapor would be drastically suppressed or would become negative because of loss compensation through incoherent population transfer. The quantum-coherent left-handed atomic vapor presented here will have four characteristics: i) three-dimensionally isotropic and homogeneous negative refractive index, ii) double-negative atomic medium at visible (and infrared) wavelengths, iii) tunable negative refractive index based on dressed-state quantum coherence, and iv) high gain due to incoherent pumping action.
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21.
  • Skobelev, S. P., et al. (författare)
  • A new type of the quasi-TEM eigenmodes in a rectangular waveguide with one corrugated hard wall
  • 2010
  • Ingår i: Progress in Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 102, s. 143-157
  • Tidskriftsartikel (refereegranskat)abstract
    • The problem of determining the eigenmodes of a rectangular waveguide with one hard wall formed by longitudinal corrugations with grooves filled with dielectric is considered. The characteristic equation is derived by using the asymptotic boundary conditions for corrugated surfaces. It is shown analytically that if the groove depth is equal to the value 0.25 lambda/(epsilon - 1)(1/2) corresponding to the hard wall condition, the TE eigenmode spectrum of the waveguide contains an infinite set of new non-uniform quasi-TEM modes with different transverse propagation constants in the empty part and identical longitudinal propagation constants equal to the wavenumber k. Analytical solution for the case of excitation of the waveguide by a specified source is given, and an example of forming local quasi-TEM waves is considered and discussed.
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22.
  • Sun, Fei, et al. (författare)
  • A General Method for Designing a Radome to Enhance the Scanning Angle of a Phased Array Antenna
  • 2014
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 145, s. 203-212
  • Tidskriftsartikel (refereegranskat)abstract
    • We propose a general method to design an arbitrarily shaped radome which can extend the scanning angle of a phased array antenna through finite embedded transformation (FET). The main advantage of our method is that the relationship between the incident angle and steered output angle of the radome can be designed in advance (e.g., a linear relation can be achieved). Unlike a traditional FET, which is often applied onto a slab region, we first apply FET onto an arbitrarily shaped region to bestow the desired radome with an arbitrary shape. Two specific examples have been given to demonstrate our method. Numerical simulations show good performance of our radome.
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23.
  • Sun, Fei, et al. (författare)
  • A Third Way to Cloak an Object : Cover-up with a Background Object
  • 2014
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 149, s. 173-182
  • Tidskriftsartikel (refereegranskat)abstract
    • Based on a space folding transformation, we propose a new way to hide an object in full space, namely, to cover-up the scattering of the hidden object with the scattering of a background object so that only the scattering of the background object can be detected by an outside observer and the hidden object disappears electromagnetically (a very weak "ghost image" or perturbation may appear inside the strong background object image in an experiment). The present method is essentially different from previous methods of cloaking an object, namely, the optically isolated cloak and the scattering cancellation cloak, and thus provide a third way to cloak an object. Unlike all the previous methods of cloaking, the present full-space omni-directional invisibility simultaneously has the following features: (i) the hidden object can "see" the outside world without being detected; (H) the cloak can still work when some characteristics (e.g., shape and medium) of the hidden object change; and (Hi) there is no need to know the information of the incident wave in advance. The present work furthers efforts to achieve invisibility and conceal an object in a real environment in full space.
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24.
  • Sun, Fei, et al. (författare)
  • Create a uniform static magnetic field over 50 t in a large free space region
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 137, s. 149-157
  • Tidskriftsartikel (refereegranskat)abstract
    • We propose a compact passive device as a super-concentrator to create an extremely high uniform static magnetic field over 50 T in a large two-dimensional free space from a weak background magnetic field. Such an amazing thing becomes possible for the first time, thanks to space-folded transformation and metamaterials for static magnetic fields. Finite element method (FEM) is utilized to verify the performance of the proposed device.
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25.
  • Sun, Fei, et al. (författare)
  • DC magnetic concentrator and omnidirectional cascaded cloak by using only one or two homogeneous anisotropic materials of positive permeability
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 142, s. 683-699
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel concentrator for static magnetic field enhancement is proposed and designed utilizing transformation optics. Compared with other devices for static magnetic field enhancement, our device has many good features: first, our concentrator can achieve a DC magnetic field enhancement in a relatively large free space with high uniformity. Secondly, our concentrator is composed by only one or two homogenous anisotropic materials with principal value greater than zero (without any infinitely large or zero value), which can be achieved by using currently available materials. Thirdly, the geometrical shape of the proposed device determines the enhancement factor and the permeability of the device. After choosing suitable geometrical parameters, we can obtain a concentration with a suitable enhancement factor and a material requirement that is easily achievable. The proposed concentrator will have many important applications in many areas (e.g., magnetic resonance imaging and magnetic sensors). Based on the same theoretical model, we also proposed a cascaded shielding device cloak for static magnetic fields. The proposed DC magnetic shielding device can be realized without using any material of zero permeability, and will have potential applications in, e.g., hiding a metallic object from being detected by a metal locator.
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26.
  • Sun, Fei, et al. (författare)
  • Homogenous Optic-Null Medium Performs as Optical Surface Transformation
  • 2015
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 151, s. 169-173
  • Tidskriftsartikel (refereegranskat)abstract
    • An optical surface transformation (OST) method is proposed briefly in this short paper. Compared with Transformation Optics (TO), we do not need to consider what kinds of coordinate transformation should be used when designing a novel device, but only need to choose the shapes of two end surfaces (namely, the input and output surfaces of the device), which are linked by an optic-null medium (ONM) that is a highly anisotropic homogeneous medium. All devices designed by OST can be realized by some ONM. The design process of an optical device with some pre-designed function can be converted to the simple choice of the shape and size of the optical surfaces with the OST, which will become a simple and yet innovative way to design electromagnetic/optical devices.
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27.
  • Sun, Fei, et al. (författare)
  • Static magnetic field concentration and enhancement using magnetic materials with positive permeability
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 142, s. 579-590
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper a novel compressor for static magnetic fields is proposed based on finite embedded transformation optics. When the DC magnetic field passes through the designed device, the magnetic field can be compressed inside the device. After it passes through the device, one can obtain an enhanced static magnetic field behind the output surface of the device (in a free space region). We can also combine our compressor with some other structures to get a higher static magnetic field enhancement in a free space region. In contrast with other devices based on transformation optics for enhancing static magnetic fields, our device is not a closed structure and thus has some special applications (e.g., for controlling magnetic nano-particles for gene and drug delivery). The designed compressor can be constructed by using currently available materials or DC meta-materials with positive permeability. Numerical simulation verifies good performance of our device.
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28.
  • Sun, Fei, et al. (författare)
  • Transformation inside a Null-Space Region and a DC Magnetic Funnel for Achieving an Enhanced Magnetic Flux with a Large Gradient
  • 2014
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 146, s. 143-153
  • Tidskriftsartikel (refereegranskat)abstract
    • The idea of transformation inside a null-space region is introduced for the first time, and used to design a novel DC magnetic compressor that concentrates DC magnetic flux greatly and behaves as a DC magnetic funnel. The proposed device can be used as a passive DC magnetic lens to achieve an enhanced DC magnetic field (e.g., 7.9 times or more depending on the size and other parameters of the compressor) with a large gradient (e.g., 450 T/m or more) in free space. After some theoretical approximation, the proposed device can be easily constructed by using a combination of superconductors and ferromagnetic materials. Numerical simulations are given to verify the performance of our device. The proposed method (use a null-space region as the reference space) can be extended to reduce the material requirement when designing other devices with transformation optics.
  •  
29.
  • Wang, Binhao, et al. (författare)
  • DETECTION OF GAS CONCENTRATION BY CORRELATION SPECTROSCOPY USING A MULTI-WAVELENGTH FIBER LASER
  • 2011
  • Ingår i: PROGRESS IN ELECTROMAGNETICS RESEARCH-PIER. - 1559-8985 .- 1070-4698. ; 114, s. 469-479
  • Tidskriftsartikel (refereegranskat)abstract
    • A correlation spectroscopy (COSPEC) based on a multi-wavelength fiber laser is first proposed for the detection of gas concentration. The lasing wavelengths are selected to match several characteristic absorption peaks of the gas under test, and the gas concentration is easily measured by correlating it with the reference gas. The present method is immune from the instability of the light source and the influence of other gases. The concentration measurement of C2H2 is demonstrated in the experiment in its near-infrared dominant absorption region. The technique has prospects for simultaneous detection of multiple gases, and the measurement of mixed gases of C2H2 and CO2 is also analyzed.
  •  
30.
  • Wang, N., et al. (författare)
  • A Simple Graphic Method for Analyzing the Polarization State of an Optical System with a Fixed Polarizer and a Rotating Elliptical Retarder
  • 2022
  • Ingår i: Progress In Electromagnetics Research. - : The Electromagnetics Academy. - 1070-4698 .- 1559-8985. ; 174, s. 107-114
  • Tidskriftsartikel (refereegranskat)abstract
    • The trajectory of the polarization state of a monochromatic beam passing through a fixed linear polarizer and a rotating elliptical retarder on the Poincaré sphere is found to be a three-dimensional 8-shaped contour, which is determined as the line of intersection of a right-circular cylinder with the Poincaré sphere. The cylinder is parallel to the S3 axis, and the projection of the contour on the S1 S2 plane is a circle whose center and radius are determined. A method of projecting the three-dimensional geometric relationships to the two-dimensional S1 S2 plane to locate the position of the polarization state of the emerging beam on the Poincaré sphere for a given azimuth of the elliptical retarder is presented, and applied to solve a problem of polarization optics. The proposed graphic method substantially simplifies the polarization state analysis involving elliptical retarders.
  •  
31.
  • Xiaoming, Chen, 1983 (författare)
  • Measurements and evaluations of multi-element antennas based on limited channel samples in a reverberation chamber
  • 2012
  • Ingår i: Progress in Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 131, s. 45-62
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, evaluations of diversity gains and capacities of multi-element antenna based on limited channel samples in a reverberation chamber (RC) are studied. It is shown that, for a large antenna array, the classical sample estimation based on finite channel samples tends to underestimate its diversity gain and capacity. An improved (yet slightly more complicated) eigenvalue estimation method is applied in both diversity gain and capacity calculations, which effectively alleviates the estimation bias. The findings of the present paper are applicable for measurements where the maximum independent channel samples per antenna element are limited. Apart from simulations, we also evaluate the performances of the classical and improved eigenvalue estimators based on measurements in a RC. Based on the results of this paper, the performance of the RC measurement (with limited samples) for multi-element antennas can be readily enhanced.
  •  
32.
  • Yaghjian, A. D., et al. (författare)
  • Minimum Q for lossy and lossless electrically small dipole antennas
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 143, s. 641-673
  • Tidskriftsartikel (refereegranskat)abstract
    • General expressions for the quality factor (Q) of antennas are minimized to obtain lower-bound formulas for the Q of electrically small, lossy or lossless, combined electric and magnetic dipole antennas confined to an arbitrarily shaped volume. The lowerbound formulas for Q are derived for dipole antennas with specified electric and magnetic dipole moments excited by both electric and magnetic surface currents as well as by electric surface currents alone. With either excitation, separate formulas are found for the dipole antennas containing only lossless or nondispersive-conductivity material and for the dipole antennas containing highly dispersive lossy material. The formulas involve the quasi-static electric and magnetic polarizabilities of the associated perfectly conducting volume of the antenna, the ratio of the powers radiated by the specified electric and magnetic dipole moments, and the efficiency of the antenna.
  •  
33.
  • Yao, Xinli, et al. (författare)
  • Dual-Mode Hyperspectral Bio-Imager with a Conjugated Camera for Quick Object-Selection and Focusing
  • 2020
  • Ingår i: Progress In Electromagnetics Research. - : The Electromagnetics Academy. - 1070-4698 .- 1559-8985. ; 168, s. 133-143
  • Tidskriftsartikel (refereegranskat)abstract
    • A dual-mode hyperspectral imager using field of view scanning needs no moving macro parts. It could work in dual-mode (macro imaging and micro imaging) and is equipped with a conjugated camera for quick object-selection and focusing. By adjusting the imaging lens and achieving the image clarity on the conjugated camera, we could find the correct location and focusing of the ROIs simultaneously instead of inefficiently checking the hyperspectral image after the whole scanning process. The whole system was applied to the study of spectral characteristics of blood oxygen in human hands and the microscopic identification of algae, showing a great potential of clinical and marine applications of our system.
  •  
34.
  • Yong, Zhengdong, et al. (författare)
  • Broadband Nanoantennas for Plasmon Enhanced Fluorescence and Raman Spectroscopies
  • 2015
  • Ingår i: Progress In Electromagnetics Research. - : EMW Publishing. - 1070-4698 .- 1559-8985. ; 153, s. 123-131
  • Tidskriftsartikel (refereegranskat)abstract
    • We propose a novel design of broadband plasmonic nanoantenna that is suitable for fluorescence and Raman enhancement. The structure consists of a gold nanoring and bowties at the center. We numerically investigate the near field and far field performance by employing the finite-difference time-domain method. High Purcell enhancement and large SERS are demonstrated in a record wide spectral bandwidth of 700 nm based on a single emitter-antenna configuration. Moreover, unlike a traditional antenna design, the proposed nanoantenna has low heat generation and high field enhancement at the gap simultaneously when operating off resonance.
  •  
35.
  • Zhan, Qiuqiang, et al. (författare)
  • Two-Photon Luminescence and Second Harmonic Generation of Single Layer Molybdenum Disulphide Nanoprobe for Nonbleaching and Nonblinking Optical Bioimaging
  • 2019
  • Ingår i: Progress In Electromagnetics Research. - : EMW PUBLISHING. - 1070-4698 .- 1559-8985. ; 166, s. 107-117
  • Tidskriftsartikel (refereegranskat)abstract
    • Layered molybdenum disulphide (MoS2) can efficiently emit photoluminescence (PL) excited by visible light. However, one-photon PL of MoS2 for bioimaging purposes suffers from strong autofluorescence and ion-induced PL quenching. Herein, we report single layer chitosan decorated MoS2 nanosheets as nonbleaching and nonblinking optical nanoprobes under near infrared femtosecond laser excitation and their applications for two photon luminescence (TPL) and second harmonic generation (SHG) bioimaging. The TPL can resist the ion-induced quenching by the cellular membrane. The proposed TPL and SHG of single layer MoS2 show great potential for real-time, deep and multiphoton bioimaging.
  •  
36.
  • Zhang, Shuai, et al. (författare)
  • MIMO Reference Antennas with Controllable Correlations and Total Efficiencies
  • 2014
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 145, s. 115-121
  • Tidskriftsartikel (refereegranskat)abstract
    • MIMO reference antennas are proposed for over the air (OTA) measurement applications. The reference antennas could get rid of feeding cable interference and control envelope correlation coefficients (ECC) continuously by only changing the length of an etched slot on a dual-feed PIFA. If only the ECC is investigated, the MIMO reference antenna is optimized to have a small variation of total efficiency from 70% to 50% when the ECC increases from 0.1 to 0.88. The prototypes are fabricated and measured in a scattered field chamber (SFC). Measurements agree well with the simulations. If the MIMO performance is studied, the MIMO reference antenna is proposed to own a large variation of total efficiencies from 90% to 47% while the ECC increases from 0 to 0.98. The bandwidth of the proposed reference antennas depend on the size of the antennas. This method is valid for all the frequencies.
  •  
37.
  • Zhang, Xi, et al. (författare)
  • Optimal design of a silicon-on-insulator nanowire waveguide for broadband wavelength conversion
  • 2009
  • Ingår i: Progress In Electromagnetics Research. - : The Electromagnetics Academy. - 1070-4698 .- 1559-8985. ; 89, s. 183-198
  • Tidskriftsartikel (refereegranskat)abstract
    • The broadband wavelength conversion based on four-wave mixing in a silicon nanowire waveguide is theoretically investigated by taking into account the influence of the waveguide loss and free-carrier absorption on the phase-matched condition. The lossy wavelength conversion is compared with the lossless one in terms of conversion efficiency and bandwidth. The size of the silicon-on-insulator nanowire waveguide is optimized to be 400nm x 269nm for broadband wavelength conversion by realizing a flattened dispersion. The pump wavelength is also optimized to 1538.7nm in order to further enhance the conversion bandwidth. A 3-dB conversion bandwidth of over 280 nm is achieved in the optimized waveguide with the optimized pump wavelength.
  •  
38.
  • Zhang, Yuan, et al. (författare)
  • super/zero scattering characteristics of circular srr arrays
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 137, s. 513-526
  • Tidskriftsartikel (refereegranskat)abstract
    • The ability to control the scattering property of an object is important in many applications. In this paper, we propose and study the scattering characteristics of a circular array of split-ring resonators (SRRs). By calculating the scattered energy spectrum, we show that the proposed structure has a localized surface plasmon resonance like behavior, which makes it useful as a super scatterer. Furthermore, in a special case, the proposed structure exhibits transparency to the illuminated waves, i.e., it does not scatter any energy at all and thus acts as a zero electromagnetic scattering object.
  •  
39.
  • Zhao, Kun, et al. (författare)
  • Reduce The Hand-Effect Body Loss For Lte Mobile Antenna In Ctia Talking And Data Modes
  • 2013
  • Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 137, s. 73-85
  • Tidskriftsartikel (refereegranskat)abstract
    • The reduction in the radiation efficiency of an antenna in a mobile handset due to user's hand effects in the talking and data modes is studied. A parameter called "body loss" is defined to evaluate the degradation of the radiation efficiency. A C-fed on-ground (OG) PIFA antenna, which can cover two typical LTE bands of 0.75 GHz-0.96 GHz and 1.7 GHz-2.1 GHz, is used to study the property of the hand-effect body loss in two CITA test positions: the talking and data modes. Three different positions of the proposed antenna in the talking mode are compared, and the position with the antenna located on the bottom of the mobile handset and facing the head is recommended for minimal body loss. A modified design with a smaller antenna width is proposed to reduce further the hand-effect body loss in the talking and data modes.
  •  
40.
  • Amin, Yasar, et al. (författare)
  • Design and Fabrication of Wideband Archimedean Spiral Antenna Based Ultra-Low Cost "Green" Modules for RFID Sensing and Wireless Applications
  • 2012
  • Ingår i: Progress In Electromagnetics Research-PIER. - 1559-8985. ; 130, s. 241-256
  • Tidskriftsartikel (refereegranskat)abstract
    • A parametric analysis is performed for a wideband Archimedean spiral antenna in recognition of an emerging concept to integrate RFID along with several applications by using a single antenna. The antenna is fabricated using state-of-the-art inkjet printing technology on various commercially available paper substrates to provide the low-cost, flexible RF modules for the next generation of "green" electronics. The effects on electromagnetic characteristics of the planar Archimedean spiral antenna, due to the use of paper are investigated besides other parameters. The proposed antenna is evaluated and optimized for operational range from 0.8-3.0GHz. It exhibits exceptional coverage throughout numerous RFID ISM bands so do for other wireless applications.
  •  
41.
  • Amin, Yasar, et al. (författare)
  • Development and Analysis of Flexible UHF RFID Antennas For "Green" Electronics
  • 2012
  • Ingår i: Progress In Electromagnetics Research-PIER. - 1070-4698. ; 130, s. 1-15
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, novel Bowtie antennas which cover complete UHF RFID band (860-960MHz), fabricated on various ultra-low-cost substrates using state-of-the-art printing technologies are investigated as an approach that aims to accommodate the antenna during the package printing process whilst faster production on commercially available paper. The proposed antenna structures are evaluated in reference to circuit and field concepts, to exhibit extreme degree of functional versatility. These antennas are developed to cater the variations which appear in electromagnetic properties and thickness of paper substrate due to various environmental effects. Computed (simulated) and well-agreed measurement results confirm a superior performance of the tag modules while stepping towards next generation of "green" tags.
  •  
42.
  • Amin, Yasar, et al. (författare)
  • Performance-Optimized Quadrate Bowtie RFID Antennas For Cost-Effective and Eco-Friendly Industrial Applications
  • 2012
  • Ingår i: Progress in Electromagnetics Research-PIER. - : EMW Publishing. - 1559-8985. ; 126, s. 49-64
  • Tidskriftsartikel (refereegranskat)abstract
    • Fully integrated printed RFID antennas show potential solution for item level labeling applications. In order to accommodate the antenna during the package printing process, it is vastly preferred that antenna structures are printed on paper substrates. However, the electromagnetic properties and thickness of paper substrates are susceptible to change due to various environmental effects. Thus, adequately consistent in performance and material insensitive printed Quadrate Bowtie RFID antennas are proposed. This paper presents an in-depth efficient optimization for high performance tag antenna designs for operability in frequencies 866-868MHz & 902-928MHz. It is demonstrated that the proposed antennas can tolerate a considerable variation in the permittivity on thin paper substrates, and present benchmarking results when n across metal and water containing objects.
  •  
43.
  • Björkberg, Jonas, et al. (författare)
  • Three-dimensional subterranean target identification by use of optimization techniques
  • 1997
  • Ingår i: Progress in Electromagnetics Research PIER. - 1070-4698. ; 15, s. 141-164
  • Tidskriftsartikel (refereegranskat)abstract
    • The identification of a subterranean metallic ore from scattering experiments, conducted on the surface of the ground or in a bore hole, is a classic geophysical problem. In general this problem is not well-posed. However, a priori information about the shape of the target provides enough regularization to make the problem numerically stable. The problem is solved by minimizing the mean-square error between an eleven parameter model, based on the null field approach, and the data. The optimization is done with a Newton technique in which a singular value decomposition of the model Jacobian is employed. The algorithm is very stable to noise and makes good reconstructions from feasible starting guesses, for realistically noise contaminated data.
  •  
44.
  •  
45.
  • Brydegaard, Mikkel, et al. (författare)
  • Super Resolution Laser Radar with Blinking Atmospheric Particles - Application to Interacting Flying Insects
  • 2014
  • Ingår i: Progress in Electromagnetics Research-Pier. - 1070-4698. ; 147, s. 141-151
  • Tidskriftsartikel (refereegranskat)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.
  •  
46.
  • Bukhsh, Waqquas Ahmed, et al. (författare)
  • Element position perturbation for a narrow spot beam with applications to satellite communication antennas
  • 2010
  • Ingår i: PROGRESS IN ELECTROMAGNETICS RESEARCH-PIER. - 1559-8985. ; 104, s. 283-295
  • Tidskriftsartikel (refereegranskat)abstract
    • Design of array antennas for satellite applications is always a trade-off between physical constrains and pattern requirements. In this paper, the focus is on the design of a large array antenna for earth coverage applications using spot beams. The array antenna has a diameter of 1 m and consists of circular polarized horn antennas positioned in a non-uniform grid. By using a binary coded genetic algorithm (BCGA) the desired element positions and their excitations are optimized to fulfill the pattern requirements. In addition thinning has been used to study the possibility of maintaining good antenna performance when reducing the number of elements. The proposed antenna design has robust side lobe level, beam width and gain; all remain virtually unchanged under a change of operating frequency +/- 7% and under lobe steering over earth +/- 8.8 degrees.
  •  
47.
  • Chedid, Michel, 1977-, et al. (författare)
  • Electromagnetic Coupling To a Wearable Application Based On Coaxial Cable Architecture
  • 2006
  • Ingår i: Progress In Electromagnetics Research, PIER. - 1070-4698. ; 56, s. 109-128
  • Tidskriftsartikel (refereegranskat)abstract
    • A radiated susceptibility problem has been identified and solved by means of simulations for a wearable computer system in the frequency range 30 MHz – 1 GHz. Simulation strategy is presented for analyzing the effects induced by an electromagnetic plane wave within the system comprising infra-red sensors connected by coaxial cables. A procedure of creating a TLM model of the coaxial cable with controlled electromagnetic coupling characteristics on a coarse grid is proposed. Results are verified by means of theoretical calculations. Different sensor enclosures and filtering circuits are analyzed and implemented to meet the hard electromagnetic compatibility requirements while not interfering with the functionality of the wearable application.
  •  
48.
  • Cooray, Gerald, et al. (författare)
  • Electromagnetic fields of a short electric dipole in free space - revisited
  • 2012
  • Ingår i: PROG ELECTROMAGN RES. - 1559-8985. ; 131, s. 357-373
  • Tidskriftsartikel (refereegranskat)abstract
    • Maxwell's equations specify that electromagnetic radiation fields are generated by accelerating charges. However, the electromagnetic radiation fields of an accelerating charge are seldom used to derive the electromagnetic fields of radiating systems. In this paper, the equations pertinent to the electromagnetic fields generated by accelerating charges are utilized to evaluate the electromagnetic fields of a current path of length l for the case when a pulse of current propagates with constant velocity. According to these equations, radiation is generated only at the end points of the channel where charges are being accelerated or decelerated. The electromagnetic fields of a short dipole are extracted from these equations when r >> l, where r is the distance to the point of observation. The speed of propagation of the pulse enters into the electromagnetic fields only in the terms that are second order in l and they can be neglected in the dipole approximation. The results illustrate how the radiation fields emanating from the two ends of the dipole give rise to field terms varying as 1/r and 1/r(2), while the time-variant stationary charges at the ends of the dipole contribute to field terms varying as 1/r(2) and 1/r(3).
  •  
49.
  • Fuks, Peter, et al. (författare)
  • Permittivity profile reconstructions using transient electromagnetic reflection data
  • 1997
  • Ingår i: Progress in Electromagnetics Research PIER. - 1070-4698. ; 17, s. 265-303
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • This paper is concerned with the permittivity reconstruction of inhomogeneous dielectric media. The method applies to profiles that vary with depth only, i.e. it provides a one-dimensional profile reconstruction. The data are collected and analyzed in the time domain. In the first part of the paper the theory of the method is reviewed. It is showed that a finite time trace of reflection data suffices to uniquely reconstruct the permittivity profile of the medium. The latter part of the paper presents the experimental set-up and contains also a thorough discussion of the errors that affect the measurements. The inverse scattering algorithm that is used is either based upon an imbedding procedure or on a Green functions approach. The input to either of these algorithms is the reflection kernel or the impulse response of the medium, i.e. the delta function response of the medium. Therefore, a deconvolution of the the measured reflected field and the incident field must be performed. This deconvolution problem is also addressed briefly in this paper.
  •  
50.
  • Gomes, C., et al. (författare)
  • Electromagnetic transients in radio/microwave bands and surge protection devices
  • 2010
  • Ingår i: PIER - Progress in Electromagnetics Research. - 1559-8985. ; 108, s. 101-130
  • Tidskriftsartikel (refereegranskat)abstract
    • A comprehensive review has been done on the types of electromagnetic transients that may affect low voltage electrical systems. The paper discusses various characteristics of lightning, swithcing, nuclear and intentional microwave impulses giving special attention to their impact on equipment and systems. The analysis shows that transients have a wide range of rise time, half peak width, action integral etc, with respect to both source and coupling mechanism. Hence, transient protection technology should be more specific with regard to the capabilities of the protection devices. Furthermore, we discuss the components and techniques available for the protection of low voltage systems from lightning generated electrical transients and the adequacy of International Standards in addressing the transient protection issues. The outcome of our analysis questions the suitability of 8/20 mu s test current impulse in representing characteristics such as the time derivative and the energy content of lightning impulses. The 10/350 mu s test current impulse better represents the integrated effects of the energy content of impulse component and long continuing current. A new waveform is required to be specified for testing the ability of protective devices to respond to the fast leading edges of subsequent strokes that may appear 100s of millisecond after the preceding stroke. The test voltage waveform 1.2/50 mu s should also be modified to evaluate the response of protective devices for fast leading edges of induced voltage transients. A surge protective device that is tested for lightning transients may not be able to provide defense against other transients.
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