Resistance compression networks (RCNs) have attracted special attention in the field of wireless power transmission (WPT) since they were put forward. A lot of research work has been done in rectifier basing on RCN for the purpose of increasing conversion efficiency. It is reported that many kinds of rectifiers containing RCN which operate in various circuit and physical forms are proposed. RCN and all kinds of modified versions are studied deeply in this paper, the rectifiers related to which are analyzed also. The results show that RCN only plays the role of bandpass filter (BPF) in the rectifying circuit, which does not reach the original idea of the first proposer. We have different understandings of the rectifying circuits presented in other papers.
Nebojsa Vojnovic, Lorenzo Crocco, Marija Nikolic Stevanovic
This paper presents a novel method for three-dimensional microwave imaging based on sparse processing. To enforce the sparsity of the unknown function, we take advantage of the fact that arbitrary three-dimensional electromagnetic fields can be decomposed into two components with respect to the radial direction: one with transverse-magnetic polarization and the other with transverse-electric polarization. Each component can be further expressed as a sum of spherical harmonics, which provide the dictionary exploited by the sparse processing algorithm. Our measurement model relates the data and the parameters of the spherical harmonics’ sources, which are uniformly distributed on a grid sampling the imaging domain. By relying on the theory of degrees of freedom of electromagnetic fields, it can be shown that only a few harmonics are sufficient to accurately represent the measured scattered field from objects whose diameter is of the order of the wavelength, thus allowing reducing the dimension of the adopted dictionary. We analyze several imaging scenarios to assess the algorithm’s performance, including different object shapes, sensor orientations, and signal-to-noise ratios. Moreover, we compare the obtained results with other state-of-the-art linear imaging techniques. Notably, thanks to the adopted dictionary, the proposed algorithm can yield accurate images of both convex and concave objects.
Deepa Thangarasu, Rama Rao Thipparaju, Sandeep Kumar Palaniswamy
et al.
With the promising developments in wearable communication technology, attention towards flexible electronics is increasing day-by-day. This study presents flexible low-profile ultra-wideband (UWB) antennas for wearable applications. The antenna comprised of a modified dewdrop-inspired radiator and a defected ground plane and has an impedance bandwidth of 3.1–10.6 GHz. The antenna flexibility is investigated using four different substrates (polyester, polyamide, denim, and Teslin) and tested on a cotton shirt and a high-end Res-Q jacket to evaluate their performance stability for body-worn applications. The fabricated planar dewdrop-shaped radiator (PDSR) antennas have a radiation efficiency of >90%, a gain of >4 dBi, and a group delay variation of fewer than 0.5 ns. The antenna conformability is measured by placing the fabricated antennas on various curved and nonplanar parts of the human body. The aforementioned antennas offer better flexibility for different bent conditions. The specific absorption rate (SAR) of the designed antennas is investigated to determine their wearability, and values are found to be less than 0.2 W/Kg. Also, the received signal strength (RSS) is discussed in order to analyze signal attenuation, and the performance analysis of the antennas is compared.
Suspense Averti IFO, Christophe Sannier, Gabriel Jaffrain
et al.
Des rapports précis et cohérents sur l'évolution de la superficie forestière et des changements d’occupation du sol sont importants dans le contexte de l’accord de Paris où les pays ont l’obligation de soumettre régulièrement leurs rapports sur le bilan émission absorption des gaz à effet de serre. Cette notification des changements peut avoir un impact direct sur les paiements par le biais de comparaisons avec les niveaux de référence (émissions) nationaux dans le cadre de la réduction des émissions dues à la déforestation et à la dégradation des forêts, notamment dans le cadre du processus REDD+. Cependant avant cela, les pays sont invités à renforcer leur système national de surveillance des forêts mais aussi de production des produits cartographiques qui respectent des règles robustes d’évaluation de l’incertitude des estimations de l’évolution de la superficie du couvert forestier prescrites par la CCNUCC. Dans cette étude, nous présentons les résultats de la précision des nombreuses cartes forestières dont le Congo dispose en utilisant l’approche assistée par modèle développée par Sannier et al, 2014, adaptée au contexte de la République du Congo. Les résultats de l’étude montrent une sous-estimation des près de 50% des pertes forestières dans la période entre 2000 et 2014 que ce soit par la méthode des estimations directes ou des estimations par régression. La comparaison des deux méthodes montre que les estimations des pertes de la couverture forestière par la méthode échantillons point sous-estime l’estimation des pertes sur la période 2000-2014 ainsi que sur la période 2014-2016. Nous concluons qu’il faut renforcer les équipes nationales en charge de l’élaboration des cartes forestières mais aussi que le pays doit s’approprier cette méthode de Sannier et al. 2014 pour l’évaluation de la précision.
Instruments and machines, Applied optics. Photonics
Jérémy Hyvernaud, Edson Martinod, Valérie Bertrand
et al.
In this paper, a high-power ultrawideband antenna is presented for the purpose of remotely neutralizing improvised explosive devices. The developed antenna has a bandwidth between 230 MHz and 2 GHz, as well as a maximum realized gain of 18.7 dB. The antenna structure incorporates a solid dielectric (HDPE 1000) so that it can be powered, without risk of a possible breakdown voltage, by a Marx generator which delivers a bipolar pulse with a peak amplitude of +/−250 kV, a rise time of 170 ps, and a duration of 1 ns. The radiated electric field obtained in simulation is, respectively, 1 MV/m peak and 126 kV/m peak at a distance of 1 m and 10 m.
Tristan Postadjian, Arnaud Le Bris, Hichem Sahbi
et al.
Les algorithmes de classification constituent un outil essentiel pour le calcul de cartes d'occupation des sols. Les récents progrès en apprentissage automatique ont montré les très grandes performances des réseaux de neurones convolutifs pour de nombreuses applications, y compris la classification d'images aériennes et satellites. Ce travail établit une stratégie quant à l'utilisation d'un réseau de neurone convolutif pour la classification d'images satellites à très haute résolution spatiale, couvrant de très larges régions géographiques, avec pour perspective future le calcul de cartes d'occupation des sols à l'échelle d'un pays.
Instruments and machines, Applied optics. Photonics
A novel planar Yagi antenna printed on a microwave substrate with dielectric constant of 3.55 for Ku band applications has been presented in this paper. The proposed antenna has been fed by the slow-wave half-mode substrate-integrated waveguide and has achieved good characteristics, such as reduced size, high gain, broadband, and low insertion loss. The proposed antenna has been fabricated by Rogers 4350 substrate with lengths of two arms for dipole 0.46 λ0. Measured results indicate that the impedance bandwidth (below −10 dB return loss) is from 15.4 GHz to 19.4 GHz with peak gain 7.49 dBi. Both simulations and experiments convince that the proposed antenna could have reliable applications for Ku band wireless communications.
Laurent Beaudoin, Antoine Gademer, Loïca Avanthey
et al.
L'étude de la biodiversité des écosystèmes et de leur dynamique est un enjeu majeur de notre siècle de transition climatique.
Pour cela, il est nécessaire de réaliser un suivi précis de l'évolution des populations, basé sur une cartographie
régulière et à haute résolution pour recueillir des informations à l'échelle des individus étudiés. Dans cet article, on s'intéresse
au potentiel de la télédétection basse altitude utilisant un prototype de micro-drone avec une charge cartographique
dédiée développés au laboratoire. Les retours d'expérience sur un site d'étude classé en zone Natura 2000 montrent un
potentiel très utile pour les gestionnaires de la réserve, tant du point de vue de l'exploitation des données brutes que des
nuages de points 3D générés à partir de celles-ci.
Instruments and machines, Applied optics. Photonics
In this paper, a new variant of flower pollination algorithm (FPA), namely, enhanced flower pollination algorithm (EFPA), has been proposed for the pattern synthesis of nonuniform linear antenna arrays (LAA). The proposed algorithm uses the concept of Cauchy mutation in global pollination and enhanced local search to improve the exploration and exploitation tendencies of FPA. It also uses dynamic switching to control the rate of exploration and exploitation. The algorithm is tested on standard benchmark problems and has been compared statistically with state of the art to prove its worthiness. LAA design is a tricky and difficult electromagnetic problem. Hence to check the efficacy of the proposed algorithm it has been used for synthesis of four different LAA with different sizes. Experimental results show that EFPA algorithm provides enhanced performance in terms of side lobe suppression and null control compared to FPA and other popular algorithms.
The conventional moving source localization methods are based on centralized sensors. This paper presents a moving source localization method for distributed passive sensors using TDOA and FDOA measurements. The novel method firstly uses the steepest descent algorithm to obtain a proper initial value of source position and velocity. Then, the coarse location estimation is obtained by maximum likelihood estimation (MLE). Finally, more accurate location estimation is achieved by subtracting theoretical bias, which is approximated by the actual bias using the estimated source location and noisy data measurement. Both theoretical analysis and simulations show that the theoretical bias always meets the actual bias when the noise level is small, and the proposed method can reduce the bias effectively while keeping the same root mean square error (RMSE) with the original MLE and Taylor-series method. Meanwhile, it is less sensitive to the initial guess and attains the CRLB under Gaussian TDOA and FDOA noise at a moderate noise level before the thresholding effect occurs.
This paper presents a new dual circularly polarized feed that provides good axial ratio over wide angles and low cross-polarized radiation in backward direction. A circular waveguide open end is fed with two orthogonally polarized waves in phase quadrature by a pair of printed crossed dipoles and a compact connectorized quadrature hybrid coupler. The waveguide aperture is loaded with a dielectric cylinder to reduce the cross-polarization beyond 90 degrees off the boresight. The fabricated feed has, at 5.5 GHz, 6.33-dBic copolarized gain, 3-dB beamwidth of 106°, 10-dB beamwidth of 195°, 3-dB axial ratio beamwidth of 215°, maximum cross-polarized gain of −21.4 dBic, and 27-dB port isolation. The reflection coefficient of the feed is less than −10 dB at 4.99–6.09 GHz.
Due to the variable curvature of the conformal carrier, the pattern of each element has a different direction. The traditional method of analyzing the conformal array is to use the Euler rotation angle and its matrix representation. However, it is computationally demanding especially for irregular array structures. In this paper, we present a novel algorithm by combining the geometric algebra with Multiple Signal Classification (MUSIC), termed as GA-MUSIC, to solve the direction of arrival (DOA) for cylindrical conformal array. And on this basis, we derive the pattern and array manifold. Compared with the existing algorithms, our proposed one avoids the cumbersome matrix transformations and largely decreases the computational complexity. The simulation results verify the effectiveness of the proposed method.
A procedure to synthesize asymmetrically shaped beam patterns is developed for planar antenna arrays. As it is based on the quasi-analytical method of collapsed distributions, the main advantage of this procedure is the ability to realize a shaped (null-free) region with very low ripple. Smooth and asymmetrically shaped regions can be used for Direction-of-Arrival estimation and subsequently for efficient tracking with a single output (fully analog) beamformer.
We propose to control the radiation patterns of a two-dimensional (2D) point source by using impedance metasurfaces. We show that the radiation patterns can be manipulated by altering the surface impedance of the metasurface. Full-wave simulation results are provided to validate the theoretical derivations. The proposed design enjoys novel properties of isotropy, homogeneity, low profile, and high selectivity of frequency, making it potentially applicable in many applications. We also point out that this design can be implemented with active metasurfaces and the surface impedance can be tuned by modulating the value of loaded elements, like resistors, inductors, and capacitors.
A compact patch antenna with stacked parasitic strips (SPSs) based on low temperature cofired ceramic (LTCC) technology is presented. By adding three pairs of SPSs above the traditional patch antenna, multiple resonant modes are excited to broaden the bandwidth. At the same time, the SPSs act as directors to guide the antenna radiation toward broadside direction to enhance the gain. The measured results show that the prototype antenna achieves an impedance bandwidth of 16% for S11<-10 dB (32.1–37.9 GHz) and a maximum gain of about 8 dBi at 35 GHz. Furthermore, the radiation patterns and gain are relatively stable within the operating bandwidth. The total volume of the antenna is only 8 × 8 × 1.1 mm3.
A plasma sheath enveloping a reentry vehicle would affect performances of on-board antenna greatly, especially the navigation antennas. This paper studies the effects of reentry plasma sheath on a GPS right-hand circularly polarized (RHCP) patch antenna polarization property during a typical reentry process. Utilizing the algorithm of finite integration technique, the polarization characteristic of a GPS antenna coated by a plasma sheath is obtained. Results show that the GPS RHCP patch antenna radiation pattern distortions as well as polarization deteriorations exist during the entire reentry process, and the worst polarization mismatch loss between a GPS antenna and RHCP GPS signal is nearly 3 dB. This paper also indicates that measures should be taken to alleviate the plasma sheath for maintaining the GPS communication during the reentry process.
A unidirectional dual-band coplanar waveguide fed antenna (DB-CPWFA) loaded with a reflector is presented in this paper. The reflector is made of an electric ground plane, a dielectric substrate, and artificial magnetic conductor (AMC) which shows an effective dual operational bandwidth. Then, the closely spaced AMC reflector is employed under the DB-DPWFA for performance improvement including unidirectional radiation, low profile, gain enhancement, and higher front-to-back (F/B) ratio. The final antenna design exhibits an 8% and 13% impedance bandwidths for 2.45 GHz and 5.8 GHz frequency regions, respectively. The overall gain enhancement of about 4 dB is achieved. The F/B ratio is approximate to 20 dB with a 16 dB improvement. The measured results are inconsistent with the numerical values. The presented design is a suitable candidate for radio frequency identification (RFID) reader application.
It is argued here that more accurate though more compute-intensive alternate algorithms to certain computational methods which are deemed too inefficient and wasteful when implemented within serial codes can be more efficient and cost-effective when implemented in parallel codes designed to run on today's multicore and many-core environments. This argument is most germane to methods that involve large data sets with relatively limited computational density—in other words, algorithms with small ratios of floating point operations to memory accesses. The examples chosen here to support this argument represent a variety of high-order finite-difference time-domain algorithms. It will be demonstrated that a three- to eightfold increase in floating-point operations due to higher-order finite-differences will translate to only two- to threefold increases in actual run times using either graphical or central processing units of today. It is hoped that this argument will convince researchers to revisit certain numerical techniques that have long been shelved and reevaluate them for multicore usability.