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We predict that photonic moiré patterns created by two mutually twisted periodic sublattices in quadratic nonlinear media allow the formation of parametric solitons under conditions that are strongly impacted by the geometry of the pattern. The question addressed here is how the geometry affects the joint trapping of multiple parametrically coupled waves into a single soliton state. We show that above the localization-delocalization transition the threshold power for soliton excitation is drastically reduced relative to uniform media. Also, the geometry of the moiré pattern shifts the condition for phase matching between the waves to the value that matches the edges of the eigenmode bands, thereby shifting the properties of all soliton families. Moreover, the phase-mismatch bandwidth for soliton generation is dramatically broadened in the moiré patterns relative to latticeless structures. V. V. K. acknowledges financial support from the Portuguese Foundation for Science and Technology (FCT) under Contracts No. PTDC/FIS-OUT/3882/2020 and No. UIDB/00618/2020. Y. V. K. and L. T. acknowledge support from the Government of Spain (Severo Ochoa CEX2019-000910-S), Fundació Cellex, Fundació Mir-Puig, Generalitat de Catalunya (CERCA). F. Y. acknowledges support from the NSFC (No. 91950120), Scientific Funding of Shanghai (No. 9ZR1424400), and Shanghai Outstanding Academic Leaders Plan (No. 20XD1402000).

This article presents the results of a series of measurements of multistatic radar signatures of small UAVs at L‐ and X‐bands. The system employed was the multistatic multiband radar system, NeXtRAD, consisting of one monostatic transmitter‐receiver and two bistatic receivers. NeXtRAD is capable of recording simultaneous bistatic and monostatic data with baselines and two‐way bistatic range of the order of a few kilometres. The paper presents an empirical analysis with range‐time plots and micro‐Doppler signatures of UAVs and birds of opportunity recorded at several hundred metres of distance. A quantitative analysis of the overall signal‐to‐noise ratio is presented along with a comparison between the power of the signal scattered from the drone body and blades. A simple study with empirically obtained features and four supervised‐learning classifiers for binary drone versus non‐drone separation is also presented. The results are encouraging with classification accuracy consistently above 90% using very simple features and classification algorithms.

In order to further improve positioning accuracy, this paper proposes an indoor vision/INS integrated mobile robot navigation method using multimodel-based multifrequency Kalman filter. Firstly, to overcome the insufficient accuracy of visual data when a robot turns, a novel multimodel integrated scheme has been investigated for the mobile robots with Mecanum wheels which can make fixed point angled turns. Secondly, a multifrequency Kalman filter has been used to fuse the position information from both the inertial navigation system and the visual navigation system, which overcomes the problem that the filtering period of the integrated navigation system is too long. The proposed multimodel multifrequency Kalman filter gives the root mean square error (RMSE) of 0.0184 m in the direction of east and 0.0977 m in north, respectively. The RMSE of visual navigation system is 0.8925 m in the direction of east and 0.9539 m in north, respectively. Experimental results show that the proposed method is effective. © 2021 Yuan Xu et al. open access

In this work, we propose a novel classification approach based on dual-band one-dimensional Convolutional Neural Networks (1D-CNNs) for classification of multifrequency polarimetric SAR (PolSAR) data. The proposed approach can jointly learn from C- and L-band data and improve the single band classification accuracy. To the best of our knowledge, this is the first study that introduces 1D-CNNs to land use/land cover classification domain using PolSAR data. The proposed approach aims to achieve maximum classification accuracy by one-time training over multiple frequency bands with limited labelled data. Moreover, the proposed dual-band 1D-CNN approach yields a superior computational efficiency compared to the deep 2D-CNN based approaches. The performed experiments using AIRSAR PolSAR image over San Diego region at C- and L-bands have shown that the proposed approach is able to simultaneously learn from the C- and L-band SAR data and achieves an elegant classification performance with minimal complexity. acceptedVersion

There is a growing pressure on antenna designers to provide ever increasing operating bandwidth, efficiency, and flexibility. Emerging communications standards are requiring operation over wide frequency ranges, often with multiple, separated bands of operation. This communication proposes and demonstrates an optically tunable cavity backed slot antenna. Through the incorporation of four silicon bridging pieces and a fiber coupled laser, the operating frequency can be tuned between 4.2 and 6 GHz. Antenna efficiency has been measured and ranges between 36% and 62% depending upon the combination of frequency and tuning state, with the gain taking values between 4.3 and 6.9 dBi. An effective fabrication process for the incorporation of silicon into the antenna has been described, as well as methods for effectively simulating the optically generated conductivity. Simulations and measurements show good agreement, and several proposed improvements are proposed for this novel and flexible tuning technology.

We provide an approach to reformulate the problem of extracting the information on scatterers in inverse problems. The approach is based on the recently introduced concept of singular value optimization and exploits the single scattering hypothesis of the Born approximation. A two-dimensional geometry with multifrequency/single-view plane wave illumination and TM polarization with near-field acquisitions is considered. Numerical results show how it is possible to dramatically reduce the number of near-field samples against the canonical ${{\rm{\lambda }}_{{\rm{min}}}}{\rm{/2}}$ criterion.

Local electromechanical (EM) measurements were performed in Pr doped BiFeO3 (BPFO) ceramics via piezoresponse force microscopy (PFM). The results revealed that local EM response was different from the macroscopic one due to the large contribution of the leakage current. The locally measured response was used to evaluate effective piezoelectric coefficient d33 of the material. The multi-frequency PFM mode with additional compensation of the cantilever-surface Coulomb interaction under application of the external DC bias provided the most accurate values of the effective d33 coefficient and allowed studying its surface distribution and residual depolarization field distribution across the surface of BPFO ceramics. © 2018 Taylor & Francis Group, LLC.

Since the very first studies, polarimetric synthetic aperture radars (Pol-SARs) revealed a great potential for the study of glaciers and ice sheets. Besides the high spatial resolution and all-weather all-season operability inherited from conventional SAR systems, they can provide information about the dielectric and geometric properties of surface as well as near-surface layers as a result of the penetration capability of microwaves into dry snow and ice. Despite most of the works performed over glaciated areas is focused on the amplitude (or intensity) of the backscattered signal at different polarizations, recent studies have shown that also the coherent nature of the polarimetric signature is essential. In particular, it has been shown that polarimetric phase differences between the co-polarized (co-pol) channels HH and VV can reveal details of the microstructure of snow and firn layers [1],[2]. Such information is relevant for the derivation of glaciological parameters like accumulation rate and surface mass balance [3] and its inversion from polarimetric data requires appropriate coherent models. However, the fact that the various ice zones are characterized by different subsurface structures hampers the generalization of such models and results. In this paper, a multi-frequency study of polarimetric signatures over the different ice zones of the Greenland ice sheet is performed. The goal is to evaluate the validity of coherent scattering models across different glacier zones at different frequencies. For this, dedicated scattering components are considered according to the main scattering mechanisms expected in each zone [4]. Finally the potential of such models to identify the individual glacier zones and to invert glaciological parameters from PolSAR data is assessed. The study is conducted on multi-frequency (P-, L-, S-, C- and X- band) airborne Pol-SAR dataset acquired in May 2015, during the ARCTIC15 campaign, over five test sites located in the percolation zone and in the ablation zone of Greenland. The investigation is supported by available GPR measurements and existing literature. [1] Leinss S., Parrella G. and Hajnsek I.: Snow height determination by polarimetric phase differences in X-band SAR data, JSTARS, vol. 7, no. 9, pp. 3794-3810, 2014. [2] Parrella G., Hajnsek I. and Papathanassiou K.: On the interpretation of polarimetric phase differences in SAR data over land ice, GRSL, vol. 13, no. 2, pp. 192-196, 2016. [3] Paterson W.S.B., The Physics of Glaciers, 3rd ed. Pergamon Press, 1994. [4] Parrella G., Hajnsek I. and Papathanassiou K.: Polarimetric decomposition of L-band PolSAR backscattering over the Austfonna ice cap, TGRS, vol. 54, no. 3, pp. 1267-1281, 2016.

This thesis contains two different subjects. In first part, two cases are considered. One is the thin plate spline smoother model and the other one is the elliptic boundary equations with uncertain boundary data. In this part, stochastic convergences of the finite element methods are proved for each problem.In second part, we provide a mathematical analysis of the linearized inverse problem in multifrequency electrical impedance tomography. We present a mathematical and numerical framework for a procedure of imaging anisotropic electrical conductivity tensor using a novel technique called Diffusion Tensor Magneto-acoustography and propose an optimal control approach for reconstructing the cross-property factor relating the diffusion tensor to the anisotropic electrical conductivity tensor. We prove convergence and Lipschitz type stability of the algorithm and present numerical examples to illustrate its accuracy. The cell model for Electropermeabilization is demonstrated. We study effective parameters in a homogenization model. We demonstrate numerically the sensitivity of these effective parameters to critical microscopic parameters governing electropermeabilization.., Cette thèse contient deux matières différentes. Dans la première partie, deux cas sont considérés. L'un est le modèle plus lisse de la plaque mince et l'autre est les équations des limites elliptiques avec des données limites incertaines. Dans cette partie, les convergences stochastiques des méthodes des éléments finis sont prouvées pour chaque problème.Dans la deuxième partie, nous fournissons une analyse mathématique du problème inverse linéarisé dans la tomographie d'impédance électrique multifréquence. Nous présentons un cadre mathématique et numérique pour une procédure d'imagerie du tenseur de conductivité électrique anisotrope en utilisant une nouvelle technique appelée Tentomètre de diffusion Magnéto-acoustographie et proposons une approche de contrôle optimale pour reconstruire le facteur de propriété intrinsèque reliant le tenseur de diffusion au tenseur de conductivité électrique anisotrope. Nous démontrons la convergence et la stabilité du type Lipschitz de l'algorithme et présente des exemples numériques pour illustrer sa précision. Le modèle cellulaire pour Electropermécanisme est démontré. Nous étudions les paramètres efficaces dans un modèle d'homogénéisation. Nous démontrons numériquement la sensibilité de ces paramètres efficaces aux paramètres microscopiques critiques régissant l'électropermécanisme.

The proper understanding of blazar variability at the various electromagnetic spectral bands is one goal of multifrequency astrophysics. In this frame a peculiar and controversial phenomenology is the periodicity, postulated for long-term radio or optical flux light curves of about a dozen of blazars. The well-known BL Lac object OJ 287 (PKS 0851+202, S3 0851+20, PG 0851+202, z = 0.306) is not only a high-variable, peculiar, extragalactic source with hints for approximatively cyclical optical outbursts, but it also represents a case of substantial intensive and extensive (long-term) multifrequency observations. This rich database allow us a deeper analysis based on a wide range of variability timescales with some recent results that are highlighted here. © Copyright owned by the author(s).

Overhauser-DNP-enhanced homonuclear 2D 19F correlation spectroscopy with diagonal suppression is presented for small molecules in the solution state at moderate fields. Multi-frequency, multi-radical studies demonstrate that these relatively low-field experiments may be operated with sensitivity rivalling that of standard 200-1000MHz NMR spectroscopy. Structural information is accessible without a sensitivity penalty, and diagonal suppressed 2D NMR correlations emerge despite the general lack of multiplet resolution in the 1D ODNP spectra. This powerful general approach avoids the rather stiff excitation, detection, and other special requirements of high-field 19FNMR spectroscopy. � 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In this paper we describe a method to monitor for a difference in the ionospheric delay observed by a ground station of a Ground Based Augmentation System (GBAS) and an airborne user. In case of detection the affected satellite can be excluded or a switch to an ionospheric free processing mode can be triggered. As it is not possible to estimate the absolute ionospheric delay at the ground station from the transmitted corrections directly, we compare a pseudo-ionospheric delay estimate from the corrections with an ionospheric estimate after removing biases. We then show the performance of the proposed monitoring architecture in flight trials from our GBAS test environment for different scenarios. In order to obtain results for a full constellation we considered an L1/L2 dual frequency combination where the expected noise and multipath is larger than in the L1/L5 case which will be used in an operational GBAS. Results show that even with the larger test statistic and in the single constellation case the monitor is feasible and provides good results. Furthermore, we also show results using the available L5/E5a signals collected during flight tests. Also in this case the performance is good and the threshold was not exceeded despite the low threshold of the monitor due to the marginal geometry. In order to test the reaction of the monitor to ionospheric gradients we injected a simulated error into the airborne measurements. As the monitoring threshold depends on the satellite geometry we show some exemplary results of the impact of different gradient slopes on the test statistic of the affected satellites.

International audience; In a recent communication, we presented a compact multi-frequency meander antenna [1]. This structure has a potential to be reconfigurable by using varactor diode. We plan to present this study in a future conference. In this paper, we present a mechanically tunable meander antenna by adjusting a floating ground plane placed under the meander structure. the use of mechanical tunable technique is very interesting because it provides a very simple handling of the power, no risk of nonlinearity and a continuous tunable capability. We present in this paper two possibilities of tunable device, one with the displacement of the floating ground plane and the second with the use of moving copper wires. Simulated and measured results are presented and discussed. © 2016 European Association of Antennas and Propagation.

In this paper, we describe the results of dual frequency Ground Based Augmentation System (GBAS) performance using data from DLR’s experimental GBAS testbed and flight trials carried out at the research airport in Braunschweig, Germany. We show the results of noise and multipath evaluation of the new L5 signals from the GPS Block IIF satellites and their application in our experimental GBAS ground station. Results show that, due to the long smoothing time in GBAS processing, there is no clearly visible improvement in terms of , despite the fact that noise and multipath is significantly lower on the raw (unsmoothed) L5 signals compared to the currently used L1 signals. Two proposed dual-frequency smoothing techniques (Divergence Free and Ionosphere Free) are implemented in the ground and airborne subsystems and tested in comparison with single frequency GBAS performance. During the flight trials, no ionosphere anomaly was observed, thus nominal behavior is presented. In offline analysis, we injected a simulated ionospheric gradient into these raw measurements to compare and evaluate the dual frequency and single frequency techniques and the output of the relevant monitors.

The timing service of Global Navigation Satellite Systems (GNSS) is being steadily improved. Generally, this fact traces back to increasing accuracy of the provided ephemeris data, improvements in Precise Point Positioning, continuous refinement of time transfer techniques, the utilization of modern signals, the use of wider bandwidth, and a growing number of available satellites—the latter particularly due to the coexistence of an increasing number of independent GNSSs available. The accuracy achievable by the GNSS common view time transfer method is within range of nanoseconds. In particular the upcoming Galileo in combination with the Global Positioning System is expected to improve that accuracy even further. In this paper, we present results for an approach for absolute calibration of Galileo timing receivers operating in the L1BC and E5 signal bands. The internal receiver delays for Galileo E1 and GPS L1 signals of the institute’s Septentrio PolaRx4 TR PRO are assessed. The approach utilizes a hardware simulator, which is an expanded version of a GSS7790 GNSS simulator from Spirent Communications. The simulator, the receiver under test, as well as the utilized measurement equipment use the 10 MHz signal from the same cesium clock as reference.

MR Elastography (MRE) is a relatively novel imaging technique using conventional MRI methods to assess the mechanical properties of tissues. In time-harmonic MRE, a Rayleigh, or proportional, Damping (RD) model incorporates attenuation behavior proportionally related to both elastic and inertial forces, thus providing a more sophisticated description of the elastic energy dissipation occurring in the biological tissue. The overall damping ratio can be extracted from the combined effect of these two components, while an additional measure, called Rayleigh Composition, can be calculated by the ratio between the two components. Thus, RD elastography is capable of not only reconstructing the viscoelastic properties of the material, but also providing additional information about damping behavior and structure. A 3D subzone based reconstruction algorithm using a RD material model has been developed and optimized to reconstruct the viscoelastic properties, damping behavior and elastic energy attenuation mechanism of tissue-simulating damping phantoms across multiple frequencies. Results have shown that all three iterative reconstructed parameters are in relatively close agreement for both the tofu and gelatin materials in both phantom configurations across the frequency range. Preliminary results from in-vivo healthy brain are also presented and discussed., 34th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), August 28-September 1, 2012, San Diego, CA, USA, Series: Engineering in Medicine and Biology Society, Conference proceedings. Annual International Conference of the IEEE

Multifrequency atomic force microscopy holds promise as a method to provide qualitative and quantitative information about samples with high spatial resolution. Here, we provide experimental evidence of the excitation of subharmonics in ambient conditions in the regions where capillary interactions are predicted to be the mechanism of excitation. We also experimentally decouple a second mechanism for subharmonic excitation that is highly independent of environmental conditions such as relative humidity. This implies that material properties could be mapped. Subharmonic excitation could lead to experimental determination of surface water affinity in the nanoscale whenever water interactions are the mechanism of excitation.

We report on a multifrequency radio study of the supernova remnant (SNR) G338.3-0.0, in positional coincidence with the TeV source HESS J1640-465. To carry out this research we observed the SNR G338.3-0.0 using the Giant Metrewave Radio Telescope (GMRT) at 235, 610, and 1280 MHz. We also reprocessed archival data from the Australia Telescope Compact Array (ATCA) at 1290 and 2300 MHz. Also we conducted a search for radio pulsations towards a central point-like source, using the GMRT antennas at 610 and 1280 MHz. The molecular material in the region of the SNR was investigated based on observations made with the NANTEN telescope in the 12^CO (J=1-0) emission line. The new radio observations revealed a remnant with a bilateral morphology, which at 235 MHz has the western wing completely attenuated because of absorption due to foreground ionized gas. The quality of the new images allows us to provide accurate estimates for the total radio flux density of the whole SNR at different radio frequencies. From the new and existing flux density estimates between 235 and 5000 MHz we derived for the whole remnant a spectral index alpha=-0.51 +/-0.06 with a local free-free continuum optical depth at 235 MHz tau_{235}=0.9+/-0.3. No radio pulsations were detected towards the only radio point-like source within the HESS error circle. We derived upper limits of 2.0 and 1.0 mJy at 610 and 1280 MHz, respectively, for the pulsed flux towards this source. No radio counterpart was found for the pulsar wind nebula discovered in X-rays. The inspection of the interstellar molecular gas towards G338.3-0.0 and surroundings revealed that there is not any associated dense cloud that might explain a hadronic origin for the TeV detection., 7 pages, 4 figures. Accepted for publication in A&A

Material parameter characteristics of a photonic multi-band-gap structure, relying on strip-line technology, is presented. Two layers of dielectric fill the space between two metallic planes and surround a periodic 2D lattice of rectangular metallic patches connected to the ground plane through metallic vias. The variations of the dispersion diagrams with the dielectric constant of one of the layers as parameters are calculated by electromagnetic simulation. Due to the large number of band-gaps the structure presents in the microwave range, it may find applications in multifrequency filter design and enhanced sensibility sensor construction.

The mutual coupling between elements of a multifrequency dipole antenna array is experimentally investigated by S-parameter measurements and planar near-field scanning of the radiated field. A multifrequency array with six dipoles is analyzed. In order to reduce the coupling between dipoles, a planar metasurface is placed atop the array acting as superstrate. The mutual coupling of the antenna elements in the absence and presence of the superstrate is presented comparatively. Between 3 and 20 dB mutual coupling reduction is achieved when the superstrate is used. By scanning the field radiated by the antennas and far-field measurements of the radiation pattern, it is observed that the superstrate confines the radiated power, increases the boresight radiation, and reduces the endfire radiation., European Council; Spanish Government; Scientific and Technological Research Council of Turkey (TÜBİTAK)

Cataloged from PDF version of article. Strong reduction of the scattering cross section is obtained for subwavelength dielectric and conducting cylinders without any magnetism for both TE and TM polarizations. The suggested approach is based on the use of Fabry-Perot type radial resonances, which can appear in single-layer, high-ε, isotropic, and homogeneous shells with the properly chosen parameters. Frequencies of the minima of the scattering cross section, which are associated with the cloaking, typically depend on whether TE or TM polarization is considered. In some cases, large-positive-ε and largenegative-e objects can be cloaked. In other cases, non-ideal multifrequency cloaking can be realized. ©2009 Optical Society of America.

Part VI: Haptics Applications; International audience; This paper presents a real-time physically based platform for multi-sensory interactive simulation. It is centred on high quality dynamic requirements driven by the concept of instrumental interaction and is able to render a wide variety of physical phenomena : from very rigid interactions to large and complex phenomena such pastes or plastic soils. The platform consists in a precisely synchronized multiprocessor architecture extended with a DSP board used for the simulation of very reactive models. It aims for obtain simulation rate necessary for rigid object (1KHz and more) in the context of 6 Degree of Freedom.

ENACTIVE / 07 Papers; International audience; This paper presents a real-time physically based platform for multi-sensory interactive simulation. This platform is centred on high quality dynamic requirements driven by the concept of instrumental in- teraction. It is oriented towards the simulation of " vis- a-vis "human- object interactive simulation for a broad range of physical phenomena, with a speci c focus on simulations with demanding capacities regarding dynamics such as tool use, object manipulation, music instrument playing, etc. The platform consists in a precisely synchronized multipro- cessor architecture extended with a DSP board used for the simulation of very reactive models. Two versions have been implemented correspon ding to specific simulation requirements : (1) a highly reactive simulator for models with strong dynamical requirements but low computation needs, such as sounding instruments ; (2) a 64 bit oating point multiprocessor architecture for large 3D models with complex interactions such as fluids, smoke, crowds.