In this paper we present an alternative approach to addressing the problem of scattering reduction for radar targets, which have recently been dealt with by using the Transformation Optics (TO) algorithm which typically calls for the use of Metamaterials (MTMs) that are inherently narrowband, dispersive and highly sensitive to polarization as well as to the incident angle. The present design utilizes realistic lossy materials that can be conveniently fabricated in the laboratory, and are wideband as well as relatively insensitive to polarization and incident angle of the incoming wave. A modified interpretation of the TO algorithm is presented and is employed the design of RCS-reducing absorbers for arbitrarily shaped targets, and not just for canonical shapes, e.g., cylinders, for which cloaks have been designed by using the TO. The paper also briefly examines the topic of performance enhancement of absorbers by using graphene materials and embedded Frequency Structure Surfaces (FSSs). We begin by presenting the design procedure for planar absorbers, and then examine how well those designs perform for arbitrarily-shaped objects. Finally, we discuss how the planar design can be modified by tailoring the material parameters of the coating for specific object shapes. A number of test cases are included as examples to illustrate the application of the proposed design methodology, which is a modification of the classical TO paradigm.

A new very compact open slot antenna for wireless communication systems application has been designed and fabricated. With antenna overall dimension of 9.2 x 9.8 mm², the proposed design can be used in many modern communication devices with size constraints. Experimental measurements have also been performed to validate the performance of the proposed antenna. The measured results show that the antenna provides a wide bandwidth of 48% (5-8.17 GHz) with an average size reduction of about 88% with respect to a conventional microstrip patch antenna.

This paper deals with the magnet pole shape design for the minimization of cogging torque in permanent magnet synchronous machines (PMSM). New shapes of permanent magnet are proposed. The magnet shape is modeled analytically by a set of stacked and well dimensioned layers relatively to the height and opening angle. The final shape of magnet is configured by using three models in view of obtaining lower magnitude of cogging torque. A 2-D exact analytical solution of magnetic field distribution taking into account the shape of magnet, the irregular mechanical thickness of air-gap and semi-closed stator slots is established. The influence of motor's parameters such as the number of stator slots per pole and per phase and PM's magnetization on cogging torque is discussed. Analytical results are validated by the static finite-element method (FEM).

A one-dimensional, dual frequency, active retrodirective array is proposed for wireless power transfer applications. Microstrip circular patch antennas with four shorting pins are used as array elements to suppress surface waves. The proposed design eliminates undesired coupling between array elements due to surface waves present in conventional microstrip antenna arrays in order to improve array performance. The antenna array uses circularly polarized microstrip elements with higher gain than conventional microstrip antennas. The proposed retrodirective array operates at 2.4GHz for the interrogating signal and 5.8GHz for the retransmitted signal, using up-converting mixers. The beam scanning inherent in retrodirective arrays ensures a constant power level available to the charging devices, regardless of their location within an angular sector over which retrodirectivity is achieved. A two-element experimental prototype provided uniform power density within a 60° angular sector. The Design procedure, simulation results and experimental measurements are presented.

In modeling electromagnetic phenomena randomness of the propagation medium and of the dielectric object should be taken up in the model. The usually applied Monte-Carlo based methods reveal true characteristics of the random electromagnetic field at the expense of large computation time and computer memory. Use of expansion based methods and their resulting algorithm is an efficient alternative. In this paper the focus is on characteristics of electromagnetic fields that satisfy integral equations where the integral kernel has a random component, typically, electromagnetic fields that describe scattering due to dielectric objects with an inhomogeneous random contrast field. The assumption is that the contrast is affinely related to a random variable. The integral equation is of second kind Fredholm type so that its solutions are determined by the resolvent, a random operator field. The key idea is to expand that operator field with respect to orthogonal polynomials defined by the probability measure on the underlying sample space and to derive the properties of the solution from that expansion. Two types of illustration are presented: an inhomogeneous dielectric slab and a 2D dielectric grating with 1D periodicity.

A wideband planar inverted-F MIMO antenna with high isolation is proposed in this letter. The proposed MIMO antenna consists of two back-to-back planar inverted-F antennas and a fork-shaped de-coupling stub. The two planar inverted-F antennas are merged together with a shorting strip connected to the ground plane. In order to enhance the isolation, a fork-shaped decoupling stub connected to the ground plane through shorting pins is introduced, and the impedance matching is significantly improved simulta-neously. The proposed antenna prototype is fabricated and measured, and a compact size of 28×26 mm² makes the proposed antenna be easily integrated in a MIMO system. Measured results show that the measured bandwidth for |S₁₁| less than -10 dB covers from 5.05 GHz to 6.23 GHz, and the measured isolation is higher than 20 dB in the whole working frequency band.

The resolution of a frequency diverse compressive metamaterial aperture imager is investigated. The aperture consists of a parallel plate waveguide, in which an array of complementary, resonant metamaterial elements is patterned into one of the plates. Microwaves injected into the waveguide leak out through the resonant metamaterial elements, forming a spatially diverse waveform at the scene. As the frequency is scanned, the waveforms change, such that scene information can be encoded onto a set of frequency measurements. The compressive nature of the metamaterial imager enables image reconstruction from significantly reduced number of measurements. We characterize the resolution of this complex aperture by studying the simulated point spread function (PSF) computed using different image reconstruction techniques. We compare the imaging performance of the system with that expected from synthetic aperture radar (SAR) limits.

This paper presents a wide upper stopband dual-band bandpass filter (BPF) with controllable passband frequencies and bandwidths as well as a high out-of-band rejection level. The proposed filter is realized by utilizing a novel stepped impedance stub-loaded quad-mode resonator. All the four-mode equivalent circuits of the resonator are quarter-wavelength stepped impedance resonators (SIRs), and their fundamental resonance frequencies are used to form the passbands, so the designed filter has a compact circuit size. By controlling the impedance and length ratios of the stubs of the resonator, wide upper stopband performance is obtained. Hook-shape feed-lines and source-load coupling are applied to provide appropriate external coupling and generate three extra transmission zeros, which greatly improve the selectivity of the proposed filter. An experimental filter operating at 1.5 and 3.5 GHz is designed, fabricated, and measured for validation. The measured results have good agreement with the simulated ones.

Workers using an implantable cardioverter defibrillator (ICD) are classified by European Directive 2013/35/EU as being at particular risk because of the potential interference between implanted medical devices and electromagnetic fields. The aim of the study was to investigate ICD function using a human-shaped phantom in high magnetic fields of a shunt reactor at a 400 kV substation. We used the phantom in the following experiment periods: isolated from the ground, grounded by a foot, or grounded by a hand. We performed five ICD tests using five different ICD devices. In experiment place A, the magnetic field was over 1000 μT, and in experiment place B, the exposure was over 600 μT. We did not find any disturbances in the ICDs. However, we conducted only 5 ICD experiments in real exposure situations at 400 kV substations. Although it is not possible to draw a strong conclusion regarding risk level, the risk of such ICD disturbances from magnetic field exposure at 400 kV substations does not appear to be high.

A novel dual-band unidirectional circularly polarized (CP) antenna fed by coplanar waveguide (CPW) for wireless applications is proposed. The antenna configuration consists of a ring-shaped ground, an F-shaped central strip, and a spherical cap reflector. The longer and shorter branches of the F-shaped central strip help to produce radiant waves at lower and higher frequencies. The CP characteristics are achieved through adding two solid arcs and a grounded tuning stub. Both simulated and measured results are given and analyzed. Measurement results show a 10 dB return loss with a bandwidth of 56% (2.15 GHz-3.83 GHz) at 2.45 GHz (ISM), and a bandwidth of 42.6% (4.67 GHz-7.2 GHz) at 5.8 GHz (HiperLAN), a 3 dB axial ratio bandwidth of 15.1% (2.25 GHz-2.62 GHz), 4.1% (5.67 GHz-5.91 GHz). The maximum gain within the two CP bands are 8.7 dBic and 10.2 dBic, respectively.

An omnidirectional low-profile multiband antenna is designed and fabricated for vehicular telecommunication applications. The fabricated antenna with a radiator patch size of 0.26λ_L×0.3λ_L has a low-profile of 0.022λ_L and shows multiple resonant frequencies at 1.14, 1.91, and 2.45 GHz. Omnidirectional radiation patterns in the azimuth plane and vertical polarization at all operating frequency bands were obtained. Antenna gains greater than 1.7 dBi were obtained at the three operating frequencies, and the antenna height is 6 mm. Therefore, the proposed antenna is applicable to the vehicular telecommunication system.

Many government-led wind farms are being constructed in Korea as sources of clean and renewable energy. However, construction of these wind farms is continuously opposed by nearby military bases that operate X-band tracking radar because the amplitude and phase of the electromagnetic waves reflected from the wind turbines may interfere with tracking radars installed along the coastline of the Korean peninsula. This paper proposes a method to analyze the effect of a wind farm on tracking radar, and presents the results of using the radar cross section of the blade of a real turbine predicted by the method of physical optics. Simulation results using various flight scenarios demonstrate that the tracking accuracy may be considerably degraded; thus appropriate action is required to eliminate this effect.

Fundamental properties of carbon nanotube antenna are firstly investigated to predict the antenna bundle response. The carbon nanotube effects are mathematically introduced via a quantum mechanical conductivity. This paper presents a new formulation based on integral equations system to study the coupled carbon nanotube antennas. The proposed integral equations system is numerically solved by the moments method. Each dipole antenna is excited at its center by a gap voltage source. The aim of the developed method is to investigate the antennas interaction effects for any coupling distance. The obtained input impedances, the current distributions and the antenna radiation patterns are in agreement with those obtained by the effective conductivity method or by the array factor method, according to the coupling distances.

Transponders (also known as polarimetric active radar calibrators or PARCs) are commonly used for radiometric calibration of synthetic aperture radars (SARs). Currently three methods for the determination of a transponder's frequency-dependent radar cross section (RCS) are used in practice. These require either to measure disassembled transponder components, or a separate radiometric measurement standard (like a flat, metallic plate or a corner reflector), leading to additional uncertainty contributions for the calibration result. In this paper, a novel method is introduced which neither requires disassembly nor an additional radiometric reference. Instead, the measurement results can be directly traced back to a realization of the meter, lowering total measurement uncertainties. The method is similar in approach to the well known three-antenna method, but is based on the radar equation instead of Friis transmission formula. The suitability of the method is demonstrated by a measurement campaign for DLR's three new Kalibri C-band transponders, completed by an uncertainty analysis. The method is not universally applicable for all transponder calibrations because (a) three devices are necessary (instead of only one for the known methods), and (b) the transponders must provide certain additional features. Nevertheless, these features have become standard in modern SAR calibration transponder designs. The novel, potentially more accurate three transponder method is thus a viable alternative for transponder RCS calibration, ultimately contributing to synthetic aperture radars with a reduced radiometric measurement uncertainty.

We report, for the first time, a study on the biocompatibility of the poly(ethylene glycol)-thiol (PEG)-coated Au/Ag alloyed nanobox (PC-ANB) particles in zebrafish. We measured the mortality rate and the hatch rate of the zebrafish embryos injected with the PC-ANB particles and observed the distribution of the PC-ANB particles in the zebrafish embryos at different stages of growth development. The results show that the PC-ANB particles have negligible toxicity to the zebrafish embryos even at extra-high concentration (1.2 mg ml^-1), while uncoated Ag nanoparticles, used in the form of nanospheres or nanoplates, were found to cause embryo deformation or even death. Additionally, we have investigated the distribution of the PC-ANB particles within the zebrafish in the interest of studying their behavior in the zebrafish using imaging. For this, we used the three-photon luminescence imaging technique and it has been found that the PC-ANB particles mainly assemble in the backside muscle tissues of the zebrafish, suggesting that the PC-ANB particles are mostly metabolized out after about 96 hours of growth development.

In a previous paper, we have introduced an innovative approach called the self-adaptive correlation method (SACM). It consists in treating the reflectogram in order to amplify the signatures of soft defects and make them more easily detectable. This method allows to highlight the soft defect while attenuating the noise present on the reflectogram and has the advantage of reducing the computational complexity compared to the state of the art. We drew attention to the sensitivity of the performance of this method to noise. In this paper, we propose a solution for the pre-denoising of reflectogram before applying the SACM. This solution consists of an adapted version of the empirical mode decomposition algorithm, we called MEMD for Modified Empirical Mode Decomposition which bypasses some limitations of the conventional EMD.

A novel surface plasmon based square-shaped ring resonator with bending metaldielectric-metal input/output (I/O) waveguide at optical spectral range is investigated. The influence of various geometric parameters is studied in detail, with parallel finite difference time domain method. The results validate that vertical coupling disturbance can be efficiently suppressed by employing the modified I/O structure. The transmittance performance has all the resonant frequencies workable with better extinction ratios, higher finesse and higher Q-factors compared to the original plasmonic micro-ring resonator. From these analyses, it is found that the proposed waveguide is outstanding in aspects of the total field extinction and frequency selectivity characteristic.

In performing the experiments, the interference source has the form of a hollow PVC tube wrapped with a current-carrying coil, while the detector has the form of a PIN (Positive-Intrinsic-Negative) photodiode. The experimental results show that the electromagnetic disturbance (EMD) signal effect is dependent on the number of turns, the direction of the electromagnetic field, and the frequency and amplitude of the interference voltage. Specifically, it is shown that when the electromagnetic field acts in the opposite direction to that of the laser beam, the intensity and optical power of the detected signal decrease with an increasing interference frequency or amplitude. By contrast, when the electromagnetic field acts in the same direction as that of the laser beam, the intensity and optical power increase with an increasing interference frequency or amplitude. In addition, it is shown that the effect of EMD on the intensity of the laser beam increases with an increasing laser beam dispersion (i.e., an increasing distance from the laser source).

This paper proposes an imaging method of multi-direction swath and digital beamforming (DBF) in elevation for spaceborne Hybrid Phased-MIMO SAR that combines traditional phased-array radar with a new technique for multiple-input multiple-output (MIMO) radar to achieve multifunctional synthetic aperture radar (SAR). At first, we build a signal model and derive a virtual control matrix of the Hybrid Phased-MIMO SAR. Furthermore, considering the image overlap and range ambiguity caused by multiple direction imaging, we present adaptive Digital Beamforming based on Linearly Constrained Minimum Variance (LCMV). In this approach, the first constraint is dedicated to make the overall beamformer response equal the quiescent response in the desired signal region so that the signal is not cancelled when it is present, and additional constraints are included to assure proper reception of the desired signal and form nulls in the direction of interference at the same time. The diagonal loading method is combined with this method to reduce small eigenvalue interference for its eigenvector, which improves the convergence speed in sidelobe. The substantial improvements offered by the proposed adaptive Digital Beamforming technique as compared to previous techniques are demonstrated analytically and by simulations through analysis of the corresponding range compression results and achievable output performance of interference suppression. Simulation results validate the effectiveness of the adaptive DBF.

In the hyperthermia therapy, multiple microwave sources can be arranged with appropriate spacing around the tissue containing tumor by using left-handed material (LHM) lenses. We employ some low loss LHM lenses schemes for an effective non-invasive microwave hyperthermia treatment of large tumors up to several centimeters of depth inside the biological tissues. Different configurations of LHM lenses are proposed and compared in order to assess the efficiency of hyperthermia treatment. High-resolution focusing of microwave radiation can be achieved by joint heating of several microwave antennas behind a conformal flat LHM lens. We show that a microwave radiation can be effectively focused in a 1.2 cm diameter tumor located within a lossy breast tissue. The results show that hyperthermia (temperature over 42°) is reached and then maintained for one hour without involving the surrounding healthy tissues. Lastly, the heating area is adjusted in both lateral and longitudinal directions changing the position of the microwave sources or selecting LHM lenses with different thickness. This approach confirms that the conformal four-lens system is more efficient to achieve microwave tumor hyperthermia than single- and double-lens schemes.