An Electromagnetic Cloaking Scheme Using Magnetic Dipole Based Scattering Cancellation

This paper explores the possibility of creating a cylindrical electromagnetic cloaking scheme using resonant magnetic dipole excitation. Split-ring resonators are arranged around the cylindrical metal target to generate strong subwavelength resonant magnetic dipole moments to cancel far-field scattered power from the target. We used the multipole scattering theory to identify the actual reason behind scattering cancellation. The scattering from resonant circulating magnetic dipoles interferes destructively with that from the non-resonant electric dipole moments of the target resulting in a significant reduction in the Scattering Cross Section. The results are verified using full-wave simulation software and subsequently validated with backscattering measurements inside an anechoic chamber.

Measuring interstellar delays of PSR J0613−0200 over 7 yr, using the Large European Array for Pulsars

ABSTRACT Using data from the Large European Array for Pulsars, and the Effelsberg telescope, we study the scintillation parameters of the millisecond pulsar PSR J0613−0200 over a 7 yr timespan. The ‘secondary spectrum’ – the 2D power spectrum of scintillation – presents the scattered power as a function of time delay, and contains the relative velocities of the pulsar, observer, and scattering material. We detect a persistent parabolic scintillation arc, suggesting scattering is dominated by a thin, anisotropic region. The scattering is poorly described by a simple exponential tail, with excess power at high delays; we measure significant, detectable scattered power at times out to ${\sim}5 \, \mu {\rm s}$, and measure the bulk scattering delay to be between 50 to 200 ns with particularly strong scattering throughout 2013. These delays are too small to detect a change of the pulse profile shape, yet they would change the times of arrival as measured through pulsar timing. The arc curvature varies annually, and is well fitted by a one-dimensional scattering screen ${\sim}40{{\ \rm per\ cent}}$ of the way towards the pulsar, with a changing orientation during the increased scattering in 2013. Effects of uncorrected scattering will introduce time delays correlated over time in individual pulsars, and may need to be considered in gravitational wave analyses. Pulsar timing programmes would benefit from simultaneously recording in a way that scintillation can be resolved, in order to monitor the variable time delays caused by multipath propagation.

Full-wave electromagnetic modes and hybridization in nanoparticle dimers

The plasmon hybridization theory is based on a quasi-electrostatic approximation of the Maxwell’s equations. It does not take into account magnetic interactions, retardation effects, and radiation losses. Magnetic interactions play a dominant role in the scattering from dielectric nanoparticles. The retardation effects play a fundamental role in the coupling of the modes with the incident radiation and in determining their radiative strength; their exclusion may lead to erroneous predictions of the excited modes and of the scattered power spectra. Radiation losses may lead to a significant broadening of the scattering resonances. We propose a hybridization theory for non-Hermitian composite systems based on the full-Maxwell equations that, overcoming all the limitations of the plasmon hybridization theory, unlocks the description of dielectric dimers. As an example, we decompose the scattered field from silicon and silver dimers, under different excitation conditions and gap-sizes, in terms of dimer modes, pinpointing the hybridizing isolated-sphere modes behind them.

Produkowanie estetyk, produkowanie podmiotu. Początki odwilży i wolność twórcza w sztukach wizualnych na przykładzie wystawy w Arsenale

In Polish art history, there are two approaches to the “Arsenał” exhibition of August 1955. One, rooted in the debates around it, presents the “Arsenał” as the beginning of a political “thaw” – an act of emancipation, a demonstration of young artists who rebelled against the socialist realism. The other approach to the show or, rather, to the “thaw” as a whole, rejects an interpretation of artistic processes and choices as autonomous activities. Instead, with reference to the theory of Michel Foucault, the “Arsenał” is considered as a result of a reconfiguration of scattered power relations, stimulated by the changing strategies of the institutional power system. The present paper follows the latter approach. Foucault claims that power relations are combined with three interconnected types of human relations: defining the hierarchy of tasks and division of labor, compelling obedience, and performing “communicative binding,” i.e. purposeful action that affects the actors’ knowledge of the world and of themselves. After 1954, power relations in Poland were strategically changing: the system of labor division and the distribution of art, including all the related benefits, was still centralized, but the ineffective administrative control relaxed, while the production of meaning changed as well – the communist party modified its rhetoric referring to art and the range of artistic choice grew together with the options of communication. Still, the liberalization of the system and abandoning the Moscow version of the socialist realism in cultural policy did not mean any real increase of the freedom of choice. Using state exhibition institutions and the press, which was the main channel of communication between the authorities and the masses, the communist regime continued to control the aesthetic consciousness of the artists. An analysis of both printed and visual messages found in the press of the period, specialist periodicals and daily newspapers alike, has revealed a surprising similarity of the official discourse and the aesthetic choices made by the participants of the “Arsenał” – in particular those choices which were later interpreted as attempts to reject the socialist realism and launch a new beginning. It seems that the young artists were “positively censored,” i.e. the regime succeeded in creating an aesthetic reality which they accepted. What is more, they considered it subversive as an emanation of liberty. The selection of the aesthetic modes favored by the authorities took place in an unconscious way already at the stage of creation, before particular works of art were accepted by the ”Arsenał” jury and before they were actually controlled by the institutions of censorship.

Estimating Wave Direction Using Terrestrial GNSS Reflectometry

The signal-to-noise ratio (SNR) data are part of the global navigation satellite systems (GNSS) observables. In a marine environment, the oscillation of the SNR data can be used to derive reflector heights. Since the attenuation of the SNR oscillation is related to the roughness of the sea surface, the significant wave height (SWH) of the water surface can be calculated from the analysis of the attenuation. The attenuation depends additionally on the relation between the coherent and the incoherent part of the scattered power. The latter is a function of the correlation length of the surface waves. Since the correlation length changes with respect to the direction of the line of sight relative to the wave direction, the attenuation must show an anisotropic characteristic. In this work, we present a method to derive the wave direction from the anisotropy of the attenuation of the SNR data. The method is investigated based on simulated data, as well by the analysis of experimental data from a GNSS station in the North Sea.

Estimating Wave Direction by Using Terrestrial GNSS Reflectometry

The signal-to-noise ratio (SNR) data is part of the global navigation satellite systems (GNSS) observables. In a marine environment, the oscillation of the SNR data can be used to derive reflector heights. Since the attenuation of the SNR oscillation is related to the roughness of the sea surface, the significant wave height (SWH) of the water surface can be calculated from the analysis of the attenuation. The attenuation depends additionally on the relation between the coherent and the incoherent part of the scattered power. The latter is a function of the correlation length of the surface waves. Because the correlation length changes with respect to the direction of the line of sight relative to the wave direction, the attenuation must show an anisotropic characteristic. In this work, we present a method to derive the wave direction from the anisotropy of the attenuation of the SNR data. The method is investigated based on simulated data as well by the analysis of experimental data from a GNSS station in the North Sea.

Surface Plasmon Enhanced Light Scattering Biosensing: Size Dependence on the Gold Nanoparticle Tag

Surface plasmon enhanced light scattering (SP-LS) is a powerful new sensing SPR modality that yields excellent sensitivity in sandwich immunoassay using spherical gold nanoparticle (AuNP) tags. Towards further improving the performance of SP-LS, we systematically investigated the AuNP size effect. Simulation results indicated an AuNP size-dependent scattered power, and predicted the optimized AuNPs sizes (i.e., 100 and 130 nm) that afford extremely high signal enhancement in SP-LS. The maximum scattered power from a 130 nm AuNP is about 1700-fold higher than that obtained from a 17 nm AuNP. Experimentally, a bio-conjugation protocol was developed by coating the AuNPs with mixture of low and high molecular weight PEG molecules. Optimal IgG antibody bioconjugation conditions were identified using physicochemical characterization and a model dot-blot assay. Aggregation prevented the use of the larger AuNPs in SP-LS experiments. As predicted by simulation, AuNPs with diameters of 50 and 64 nm yielded significantly higher SP-LS signal enhancement in comparison to the smaller particles. Finally, we demonstrated the feasibility of a two-step SP-LS protocol based on a gold enhancement step, aimed at enlarging 36 nm AuNPs tags. This study provides a blue-print for the further development of SP-LS biosensing and its translation in the bioanalytical field.

An experimental realization of cylindrical cloaking using dogbone metamaterials

The quest for invisibility has inspired a deep ardour in the research community over the past decade. The invention of metamaterials has boosted the research on electromagnetic cloaking due to its unusual electromagnetic parameters under plane wave incidence. In this study, we propose a novel cloaking scheme, using dogbone metamaterials, for effectively routing the incident electromagnetic fields around a target metal cylinder under consideration. Notable reduction in the scattered power is observed from the target in comparison to an uncloaked target. Experiments and simulations validate an effective reduction in the scattering cross section of the target and effective guiding of the incident plane wave around the target.