Electromagnetic Components Research Articles

Permanent-magnet quadrupoles for an interdigital H -mode drift tube linear accelerator: Optimization code and adjustable magnet design

Magnets to be used for the internal quadrupoles of an interdigital $H$-mode drift tube linear accelerator (IH-DTL) using KONUS beam dynamics should be both compact in size and high in focusing field gradient. Permanent magnets are an attractive solution, but then the ability to adjust the field strength is lost. We investigated two different solutions to this problem: the first using external adjustable electromagnets; the second using internal adjustable permanent magnets. The first method moves the variability out of the resonant cavity, using adjustable electromagnet quadrupole doublets before entry into the IH-DTL to compensate for the lack of internal variability. We carried out optimization simulations with custom code that ran many instances of the lorasr beam dynamics simulation software, using different values of field strength for the external doublets. By optimizing the magnet settings for different values of input current, we were able to compensate for the space-charge forces involved in accelerating a high-intensity continuous-wave (CW) deuteron beam. Second, we designed some novel adjustable permanent-magnet quadrupoles to be used inside the cavity, which combine the advantages of small cross-section and variable field gradient. This allows much more control over the beam, and even other ion species with differing charge-to-mass ratios can be accommodated within the same accelerator design. We developed two adjustable permanent-magnet designs: one with an electromagnetic component, and the other with two concentric moving rings of Halbach-array quadrupoles.

IDENTIFICATION OF AIR RADAR TARGETS USING THE DOPPLER EFFECT FROM A HEATED JET ENGINE

ObjectivesThe aim of the study is to develop a methodology for identifyingaircraft by the deflections of an electromagnetic radar beam by a heated jet engine. MethodsAtoms of the crystal lattice of the metallic parts of the operating jet engine will be in a state of chaotic Brownian motion due to heating. The electromagnetic beam, falling on these atoms, will change its frequency in accordance with the Doppler effect, by means of which the spectral electromagnetic radiation component will expand in direct proportion to the magnitude of the engine temperature. When determining the width of the spectral line of the direction-finding radio emission, it is possible to accurately identify the temperature of the aircraft in order to avoid false targets.ResultsWhen locating aircraft having a working jet engine, it is possible not only to determine the coordinates of the target, but also to identify the heated engine. Due to the use of high-precision methods for identifying heated sections, the direction-finding targets may be classified, the spatial orientation of both the aircraft itself and its control planes to be determinedand the direction of the thrust vector control of the jet engine calculated.ConclusionThe application of an innovative technique for direction-finding air targets will allow the radar targets to be identified with high accuracy against the background of active and passive interferences. In addition, when analysing the information on the magnitude and direction of the jet engine thrust and the position of the aircraft controls, it is possible to determine not only the coordinates of the direction-finding object, but also to proactively identify the manoeuvres to be performed.

Class Regular–Increased– and Class Iso–Toxicity, the two clearly defined and recognisable forms of the phenomenon. A developed Köln–Model (Hydractinia echinata Test–System. V.) study

According to the currently developed Köln–Model based on Hydractinia echinata Test–System (HeTS), the methodical toxicity investigations conducted with amphiphilic and non–amphiphilic singular derivatives with homo– and heteronomous segmentation from 20 different classes, reveals that the effectiveness noted M (mol/L) are characteristic for the Aromatic Basis of Toxicity (ABT) model, for the Class Regular–Increased Toxicity (CRIT) and for Class Iso–Toxicity (CIT), respectively. The phenomenon of toxicity is the result of monovalent interaction between the larval cellular receptor (R) of the marine colonial hydroid H. echinata organism and the xenobiotic substrate (SbX) with the molecular aggregate transitional–complex (RSbX) formation and the information–signal generation (SI), according to the Dual Causality Principle that biological phenomena are simultaneously determined by genetic programs and physics laws. The SI consists of chemical (SIch) and electromagnetic (SIem) components, and is directly responsible for the simultaneous onset of the metamorphosis quantified by the M toxicity values and the metabolizing process of the SbX, with the formation of the reaction products (P). The CRIT, respectively CIT approach was also successfully applied to published data obtained with the ciliate protozoan Tetrahymena pyriformis (T. pyriformis), the freshwater fish Pimephales promelas (P. promelas), the freshwater crustacean Daphnia magna (D. magna) and the marine bacterium Vibrio fischeri (name Aliivibrio fischeri) test–systems (TS’s).

Factors of Solar Activity Enhance Locomotor and Exploratory Behavior in Rats

According to the literature, solar activity affects the functioning of the human brain. However, its effect has not been studied on experimental animals. The purpose of this study was to investigate whether factors of solar activity influence the behavior of rats. From October 26 to December 24, 2011, the behavior of individual rats or small groups of them (N = 19) was recorded in an open field test and operant food-uptake behavior test. Parameters of solar activity were obtained from public databases on the Internet. Results of the correlation analysis have demonstrated that the number of sectors travelled by the rats in the open field test, number of holes they investigated, and number of food pellets they earned while learning a food-uptake task were positively associated with solar activity on the day of the study and in the days before and after that. Such associations were revealed for the number of sunspots, the intensity of solar radiation in the radio range, and number of solar flares in the X-ray and Hα ranges. Factor analysis made it possible to distinguish two factors positively associated with the behavior of rats. One of them closely correlated with the solar radio flux and can therefore be presumably attributed to its electromagnetic component. The other is closely related to the 3-h planetary index of oscillations of the Earth’s magnetic field K, and this indicates its corpuscular nature. These results correspond to the literature data on the association between the parameters of solar and geomagnetic activity and the characteristics of electrical activity of the brain of humans and animals. The behavior of rats is associated most closely with the number of sunspots on the day of the study, the parameter of which significantly correlates with both factors of solar activity. Therefore, this index can be used to consider the influence of solar activity on the behavior of rats in experimental practice.

Fundamental Examination of Multiple Potential Passive Component Technologies for Future Power Electronics

Efficient and compact high-power high-frequency passive energy storage components are required for miniaturization of power converters and remain a challenging obstacle in power electronics. In this paper, multiple energy storage mechanisms are analyzed on an order-of-magnitude basis to identify potential alternatives for conventional passive components, especially magnetics, which have frequency-dependent power losses. The high energy density of mechanical storage methods provides an attractive alternative to the widely used LC resonance. Piezoelectric transduction is explored, and the performance of a piezoelectric resonator is compared to that of an LC resonator in terms of efficiency and power handling capabilities in a resonant switched-capacitor-type circuit. The analysis provides a basis for exploring potential passive energy storage component technologies and comparing their performance limits with those of electromagnetic passive components. The analysis shows that both electromagnetic and mechanical resonance, in the ideal scenarios, can offer much better performance than do passive component technologies in use today. A prototype resonator is built with off-the-shelf C0G capacitors to confirm the low loss and high power predicted by the model. The resulting resonator has an effective resistance of 2.76 $\text{m}{\Omega }$ at 2.70 MHz in 1 ${\text{cm}^{3}}$ volume and can handle 7.42 kW within the rated temperature.

A Theoretical Analysis of Pulsating Torque Components in AC Machines With Variable Frequency Drives and Dynamic Mechanical Loads

This paper analytically investigates expressions of an oscillating motor's air-gap torque resulting simultaneously from dynamic electromagnetic and dynamic mechanical components. The electromagnetic torque is generated in the air gap when the motor is supplied by variable frequency drives (VFDs), such as pulsewidth modulated voltage source inverters or load commutated inverters. Whereas, the mechanical torque components might result from dynamic mechanical processes, such as wind turbine blades, oil and gas fluid fluctuation, and, for emulating dynamic mechanical loads, a load-side VFD. Simple and straightforward analytical relationships between electrical and mechanical harmonics are developed to understand the propagation of mechanical dynamics to the electric side and vice versa. Intensive numerical simulations have been carried out to support the theoretical analysis. Time and frequency domain results confirm the robustness of the proposed relationships. Finally, laboratory experimental test results also confirm the accuracy of the proposed relationships.

EEG Resting-State Networks Responsible for Gait Disturbance Features in Idiopathic Normal Pressure Hydrocephalus.

Idiopathic normal pressure hydrocephalus (iNPH) is a neuropsychiatric disease characterized by gait disturbance, cognitive dysfunction, and urinary incontinence that affects a large population of elderly people. These symptoms, especially gait disturbance, can potentially be improved by cerebrospinal fluid (CSF) drainage, which is more effective if performed at an early stage of the disease. However, the neurophysiological mechanisms of these symptoms and their recovery by CSF drainage are poorly understood. In this study, using exact low-resolution brain electromagnetic tomography-independent component analysis (eLORETA-ICA) with electroencephalography (EEG) data, we assessed activities of five EEG resting-state networks (EEG-RSNs) in 58 iNPH patients before and after drainage of CSF by lumbar puncture (CSF tapping). In addition, we assessed correlations of changes in these five EEG-RSNs activities with CSF tapping-induced changes in iNPH symptoms. The results reveal that compared with 80 healthy controls, iNPH patients had significantly decreased activities in the occipital alpha rhythm, visual perception network, and self-referential network before CSF tapping. Furthermore, CSF tapping-induced changes in occipital alpha activity correlated with changes in postural sway and frontal lobe function. Changes in visual perception network activity correlated with changes in gait speed. In addition, changes in memory perception network activity correlated with changes in Parkinsonian gait features. These results indicate a recruitment of cognitive networks in gait control, and involvement of the occipital alpha activity in cognitive dysfunction in iNPH patients. Based on these findings, eLORETA-ICA with EEG data can be considered a noninvasive, useful tool for detection of EEG-RSN activities and for understanding the neurophysiological mechanisms underlying this disease.

Modelling of heat transfer in low‐power IPM synchronous motors

This study presents results of modelling of heat transfer in low-power synchronous motors with internal permanent magnets (IPM). The analysis is conducted on the basis of equivalent thermal network as well as the magnetostatic finite element analysis for determination of usual electromagnetic loss components. The approach which consistently combines the two mentioned models allows for effective analysis of heat transfer in the machine at the designing stage. Special attention is focused on the method for homogenisation of a mush-wound winding and sheet stack. The results of computer simulations are positively verified by measurements carried out on the physical motor.

Research of frequency characteristics of hybrid inductive-capacitive converters

Current stabilization systems require stable operation when the magnitude and nature of the load resistance changes. From this point of view, the most optimal solutions are circuit ones containing inductive-capacitive converters (ICC). The main disadvantages of ICC are large mass and dimensions. These disadvantages are eliminated by increasing the conversion frequency and hybrid execution of electromagnetic elements that perform the ICC function. An effective way to improve the mass-dimension parameters of ICC is the use of multifunctional integrated electromagnetic components (MIEC). In this article, the authors conducted the research of the frequency and energy characteristics of ICC based on a single-section MIEC. The parameters characterizing the ICC as a current stabilizer are estimated. The experimental confirmation of the adequacy of the developed mathematical models for calculating and constructing the MIEC frequency characteristics and estimating the ICC stabilization properties is carried out. The obtained results allow us to conclude that the use of the calculation method using the integrated parameters of MIEC is possible for the analysis of more complex MIEC schemes (two-section, three-section, three-electrodes) and electrotechnical devices based on them. The description of the electromagnetic processes by the system of differential equations leads to rather cumbersome mathematical derivations.

Influence of switching processes on effective operation modes of mixed load with complex waveform current supply

Currently, the development of effective modes of mixed-load with a complex waveform current supply is relevant. In the article by the example of the physical model of a low-voltage electrode water heater and an energy-saving lamp, the work of mixed load after switching in the network is investigated.The purpose of the work is the processes research of heating in the electrode water heater and lighting characteristics of an energy-saving lamp with the complex waveform current supply. This was made to select the efficient mixed-load modes in a steady-state mode after commutation in the power node. This required the solution of scientific problems in the development of mixed-load research methods, obtaining regulatory characteristics, developing recommendations for the selection of effective operation modes necessary for the synthesis of the automatic control system algorithm.The decision of the task allowed us to determine the influence of the electromagnetic component along with the temperature on the processes of water heating and lighting parameters of the lamp. It is proved that the mixed load in a steady-state mode after commutation works in an efficient mode.

An approach for calculating arbitrary-order diffraction through hole-array based on thin microcavity theory

Abstract An approach for calculating the optical diffraction coefficients through a subwavelength hole-array embedded in a suspending thin metal layer is investigated based on the rigorous coupled wave analysis method and thin microcavity theory. In this approach, the electromagnetic field components in the reflected and transmitted regions and diffraction coefficients of arbitrary orders are derived, respectively, and some enhanced diffraction phenomena are discussed in detail, which are then verified via finite element (FE) simulation. Subsequently, the effects of structural and material parameters of holey thin film including film material, incident angle, hole geometry, and duty cycle of periodic array layer on the transmittance are analyzed. The relevant results show that the duty cycle is the main influence factor, and with the suitable duty cycle the optical transmittance through the free-standing metal layer can be enhanced as high as 0.8 in the visible region. All these findings may be utilized in the wavelength tuning of subwavelength optics.

An Analytical Expression for Magnet Shape Optimization in Surface-Mounted Permanent Magnet Machines

Surface-mounted permanent magnet machines are widely used in low and medium speed applications. Pulsating torque components is the most crucial challenge, especially in low-speed applications. Magnet pole shape optimization can be used to mitigate these components. In this research, an analytical model is proposed to calculate the magnetic vector potential in surface-mounted permanent magnet machines. A mathematical expression is also derived for optimal the magnet shape to reduce the cogging torque and electromagnetic torque components. The presented model is based on the resolution of the Laplace’s and Poisson’s equations in polar coordinates by using the subdomain method and applying hyperbolic functions. The proposed method is applied to the performance computation of a surface-mounted permanent magnet machine, i.e., a 3-phase 12S-10P motor. The analytical results are validated through the finite element analysis (FEA) method.

A New Low-Profile Electromagnetic-Pneumatic Actuator for High-Bandwidth Applications

This paper proposes a new electromagnetic-pneumatic actuator with high force density for wide bandwidth applications. The actuator includes an active electromagnetic actuator and a pneumatic spring, fused together into a hybrid design. The electromagnetic component acts as an active element, generating wide bandwidth high-density forces. It further provides a baseline stiffness, for the device, using its magnetic spring. The active electromagnetic actuator consists of a number of stacks positioned in a vertical arrangement. The modular design of the actuator, allows for reconfiguring the device with different number of stacks to adjust the strokes, depending on the target application. The pneumatic spring is then responsible for adding extra stiffness and support for heavy load masses. The added stiffness by the pneumatic spring can be easily adjusted by regulating the gas pressure. Based on the proposed active electromagnetic actuator, analytical and FEM models are developed, which are used for optimizing the design. The proposed actuator has a low-profile design, making it suitable for many applications with space limitations. The final design is prototyped, and experimentally tested. To evaluate the performance of the electromagnetic component, its force density (force to volume ratio) is compared with a voice coil actuator (that is widely used in both academic and industrial sectors). The FEM and experimental results confirmed the high force density of the electromagnetic component, comparing to a voice coil of similar size. The proposed design, with a diameter of $\sim {\text{125 mm}}$ and a height of $\sim {\text{60 mm}}$ , generates a force variation of $\sim {\text{318 N}}$ for the currents of $I=\pm {\text{2 A}}$ . Furthermore, it has small electromagnetic and electromechanical time constants of 5.2 and 10.5 $\text{ms}$ , respectively, with negligible eddy current effect. These findings make the actuator suitable for wide bandwidth applications.

Selective Attenuation of Lightning‐Generated Whistlers at Extralow Frequencies: DEMETER Spacecraft Observations

AbstractFrequency‐time spectrograms measured by the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) spacecraft (2004–2010, altitude about 700 km) at frequencies below 20 kHz sometimes contain lightning‐generated whistlers whose intensity is significantly reduced at specific frequencies. The frequencies of the reduced intensity vary smoothly over the event duration, forming apparent curves in frequency‐time spectrograms. Events at frequencies higher than the Earth‐ionosphere waveguide cutoff frequency were explained by the interference of the first few waveguide modes of lightning‐generated spherics propagating therein (Záhlava et al., 2015, https://doi.org/10.1002/2015JA021607. Here we present an analysis of events observed at frequencies lower than about 1 kHz. Altogether, we analyze 263 events identified at the times when DEMETER operated in the burst mode. The vast majority of the events (95%) took place during the nighttime, and they occurred more frequently during spring/autumn than during winter/summer. We present an overview of event properties. Moreover, measurements of all six electromagnetic field components performed by DEMETER allow us to perform a detailed wave analysis. It is shown that the emissions propagate with high wave normal angles inclined toward the Earth. We suggest that the events might be due to the wave propagation in the ionospheric waveguide formed around the refractive index maximum at the altitude of about 105 km.

Electrodynamic sensor for determining the state of water in biological objects

The distribution of free water and water associated with molecules of biological matter determines its state. The electrophysical properties of free and bound water are significantly different, and the relaxation frequency of molecules lies in the microwave range. Therefore, microwave methods of measurement are effective. The microwave sensor circuit is analyzed, for which it is possible to create a rigorous analytical model. The results of calculations of the electromagnetic field components and the transfer function of the sensor are discussed, and the dimensions of its working area are estimated.

A controllable-accuracy stochastic time-domain technique for randomly varying microwave applications

PurposeThis paper aims to introduce an efficient time-domain formulation of adjustable accuracy for a consistent and trustworthy computation of electromagnetic field characteristics in randomly varying configurations. The developed methodology is carefully certified via comprehensive comparisons with the corresponding outcomes obtained by the Monte Carlo approach.Design/methodology/approachThe presented methodology uses higher-order approximations of Taylor series expansions of stochastic multivariable functions for the rapid estimation of the electromagnetic field component mean value and confidence intervals of their variance. Toward this objective, new time-update equations for the mean value and the variance of the involved electromagnetic field are elaborately derived.FindingsThe featured technique presents an efficient alternative to the excessively resource-consuming Monte Carlo finite-difference time-domain (MC–FDTD) implementation, which requires an unduly number of realizations to achieve a satisfying convergence. The higher-order stochastic algorithm retrieves accurately the statistical properties of all electromagnetic field in a single simulation, presenting promising accuracy, stability and convergence.Originality/valueThe adjustable-accuracy higher-order scheme introduces a new framework for the derivation of the stochastic explicit time-update equations and precisely computes the required confidence intervals for the electromagnetic field variance instead of the variance itself, which can be deemed a key advantage over existing schemes. This fully controllable formulation results in significantly more accurate calculations of the electromagnetic field variance, especially for larger fluctuations of the involved electromagnetic media parameters.

Propagation Behavior Studies on Elliptically Polarized Wave within Chiral Negative Refraction Mediums

According to elementary transmission theories of electromagnetic wave and constitutive relation of mediums, the propagation behaviors are analyzed theoretically and numerically in detail when the elliptically polarized wave is incident upon the surface of a chiral negative refraction medium. The change rules of flux density of reflection and refraction with incident angle are given, which have distinct difference with conventional medium. It is also found that the left and right circularly polarized electromagnetic wave components have different propagation behaviors with the chiral negative refraction medium.

Breaking the mould

Researchers at the University of Oklahoma in the US have developed a method to rapidly produce metallic prototypes for radio and microwave applications. They reproduce a standard rectangular cavity resonator with a high quality factor and centre frequency within the desired range. These results demonstrate that the novel application of Lost-Shell Casting (LSC) techniques to electromagnetic component fabrication is a viable and cost-effective manufacturing method. LSC is the process of creating a metallic object in the space left by a 3D printed part that is burned away. The voided space is filled with metal as the printed part is burned. The “Shell” component of the name refers to the fact that the printed part is made with as little fill as possible, making it ideally just an outer shell, in order to minimise the amount of material used. Lost-Shell Casted cavity resonator immediately following production. Casting sand was used as the prototype moulding medium. LSC can be performed quickly with inexpensive materials, making it an ideal option for quickly fabricating and testing prototypes. While widely used in other fields, it has not been used in electromagnetic applications before this Letter. LSC is a useful technique for fabricating radio frequency (RF) components as it produces a completely metallic prototype in an overall time-span from design to final fabricated and tested prototype in only two or three days, depending on the size and complexity of the design. This process also leverages some of the benefits of 3D printing, allowing for significantly more complicated designs without the fabrication difficulties and limitations of other methods. The LSC process begins with a CAD design, which is then printed using a 3D Polylactic acid (PLA) printer. Next, the printed part is encased in a casting medium (casting sand in this Letter) inside a steel vessel. This entire vessel is then placed in a programmable oven with an aluminum ingot placed on top and heated such that the PLA will completely burn off and the aluminum will completely fill the void left by the burned PLA. After cooling, the casted part is collected and fitted with the appropriate connectors for testing. Other fabrication techniques for rapid prototyping that are based on similar 3D printing techniques will often create a component out of plastic or resin. Following the printing a thin conductive layer, such as copper plating or conductive paint, is applied. However, such coated components lack the structural integrity of metal and are not representative as prototypes of a finalised design. LSC, on the other hand, creates an entirely metallic component, but still maintains the design complexity of 3D printed parts. The resonator produced using LSC in this Letter possessed greater durability than those created by other 3D printing methods with high quality factor, and the desired prototype properties were verified in subsequent testing. “Metallurgical issues were the main challenge in this work” explains one of the authors David Mitchell, as “several aspects of the design do not affect the electrical performance of the part but had to be added in order to ensure quality”. The structures on either side of the cavity, shown in the Letter, are necessary to provide the excess liquid aluminum a place to flow as well as to allow the aluminum to shrink as it cools without affecting the electrically important area itself. Surface imperfections on the interior cavity prototype are due to gases released by the molten aluminum being unable to escape, which reduces the quality factor of the team's produced component. A potential solution would be to release these gases, but as this would involve direct handling of the molten metal, the team did not explore this in their Letter and remains a topic for future research. LSC could be widely used to develop more durable and more complex filter and antenna designs as a novel method for rapidly iterating on new designs. As the technique is refined and developed it has potential to become a widespread standard for creating complex, fully metallic components. The team have begun investigating other methods of rapid prototyping using 3D printing, and Mitchell has high hopes for the field, stating: “We have only just cracked the surface. Each method has design types for which it is best suited, but as these fabrication methods are combined and adapted previously unimaginable designs become possible.”

Вплив відхилення напруги на технологічні та енергетичні характеристики скреперних установок для прибирання гною

The voltage deviation from the normalized values has negative consequences, among which the most significant are the violation of the normal course of technological processes, simple enterprises and the issue of poor quality products, shortening the life of electrical equipment, increase in electricity losses in the elements of the power supply system. Economic losses, caused by low quality of electric energy, have two components: electromagnetic and technological. The electromagnetic component is determined mainly by the loss of active power and the change in the life of the electrical equipment. The technological component of losses is due to the influence of the quality of electricity on the productivity of technological installations and the cost of production. The purpose of the study is to determine the effect of voltage deviation on the technological and energy characteristics of scraper plants for cleaning manure. Due to the deviation of the voltage, the angular velocity of the motor changes, which, in turn, causes the change in the technological characteristics of the working machines. For steady-state installations, the change in angular velocity is inversely proportional to the square of the voltage deviation, and the output is directly proportional to the angular velocity of the electric motor .. When voltage decreases, the scraper speed and the performance of the scraper unit for manure removal increase indirectly. The law of the change of these values is determined by the law of changing the angular velocity of the engine when the voltage changes. The voltage deviation causes the loss of active power in the electric drive of the scraper unit. Variable power losses in the electric drive of the scraper installation are inversely proportional to the square of the voltage. When voltage increases, they decrease in comparison with nominal, and at decrease - increase Continuous power losses, on the contrary, when voltage decreases, decrease, and with increase - increase. Since permanent losses of power are less than variable losses, when the voltage decreases, the loss in the engine increases, and at increase - somewhat reduced. As a result of the conducted research it was established that when the voltage decreases by 20%, the efficiency of the scraper installation decreases by 4%, and the specific power consumption increases by 11%. Key words: scraper installation, electric drive, voltage deviation, productivity, scraper speed, technological characteristic, power characteristic

Near-field dynamics at a metallic transmission grating with femtosecond illumination: A theoretical study

This paper reports on the temporal and spectral light field evolution for two different types of metallic gratings after illumination with a near-infrared TM-polarized femtosecond pulse: a freestanding grating in air and a grating on a dielectric substrate. The electromagnetic field components are calculated numerically at various transverse locations of the gratings by use of a finite-difference time-domain model. The spectral dynamics are explained by the dynamics of surface plasmon polaritons (SPPs). Fano-like profiles are observed close to an SPP resonance in the calculated spectral curves, indicating a connection between the Rayleigh anomaly and a nearby SPP resonance. For the freestanding grating, only a single Fano-like profile close to the air/metal SPP resonance and, with the dielectric support, two Fano-type profiles are observed, one in the proximity of the air/metal SPP resonance, the other in the proximity of the substrate/metal resonance. Investigating the changes in the spectra for an increasing distance to the grating, it is found that with increasing distance, the spectral curves related to different transverse locations coincide almost completely, providing evidence that the near-field contributions disappeared.