Optically transparent microwave absorber based on water-based moth-eye structures.

We propose an approach to realize an optically transparent microwave absorber based on water-based moth-eye metamaterial structures. The absorber is made of a periodic array of properly shaped glass caps infiltrated with distilled water. Analytical calculations and numerical simulations show that the water-based metamaterial absorbs electromagnetic waves over a wide spectral band ranging from 4GHz to well above 120GHz, showing absorption levels close to 100% for incident radiation that ranges from normal to grazing angles, for both TE and TM polarizations. Yet, the structure is optically transparent, offering exciting opportunities in a variety of civil and military applications, such as for camouflage and shielding systems and in energy harvesting structures.

Nonlocal response of hyperbolic metasurfaces.

We analyze and model the nonlocal response of ultrathin hyperbolic metasurfaces (HMTSs) by applying an effective medium approach. We show that the intrinsic spatial dispersion in the materials employed to realize the metasurfaces imposes a wavenumber cutoff on the hyperbolic isofrequency contour, inversely proportional to the Fermi velocity, and we compare it with the cutoff arising from the structure granularity. In the particular case of HTMSs implemented by an array of graphene nanostrips, we find that graphene nonlocality can become the dominant mechanism that closes the hyperbolic contour - imposing a wavenumber cutoff at around 300k(0) - in realistic configurations with periodicity L<π/(300k(0)), thus providing a practical design rule to implement HMTSs at THz and infrared frequencies. In contrast, more common plasmonic materials, such as noble metals, operate at much higher frequencies, and therefore their intrinsic nonlocal response is mainly relevant in hyperbolic metasurfaces and metamaterials with periodicity below a few nm, being very weak in practical scenarios. In addition, we investigate how spatial dispersion affects the spontaneous emission rate of emitters located close to HMTSs. Our results establish an upper bound set by nonlocality to the maximum field confinement and light-matter interactions achievable in practical HMTSs, and may find application in the practical development of hyperlenses, sensors and on-chip networks.

Temporal soliton excitation in an ε-near-zero plasmonic metamaterial.

The excitation of temporal solitons in a metamaterial formed by an array of ε-near-zero (ENZ) plasmonic channels loaded with a material possessing a cubic (χ(3)) nonlinearity are theoretically explored. The unique interplay between the peculiar dispersion properties of ENZ channels and their enhanced effective nonlinearity conspires to yield low threshold intensities for the formation of slow group velocity solitons.

Thermal emission from a metamaterial wire medium slab.

We investigate thermal emission from a metamaterial wire medium embedded in a dielectric host and highlight two different regimes for efficient emission, respectively characterized by broadband emission near the effective plasma frequency of the metamaterial, and by narrow-band resonant emission at the band-edge in the Bragg scattering regime. We discuss how to control the spectral position and relative strength of these two emission mechanisms by varying the geometrical parameters of the proposed metamaterial and its temperature.

Topological phonon-polariton funneling in midinfrared metasurfaces.

Topological photonics offers enhanced control over electromagnetic fields by providing a platform for robust trapping and guiding of topological states of light. By combining the strong coupling between topological photons with phonons in hexagonal boron nitride (hBN), we demonstrate a platform to control and guide hybrid states of light and lattice vibrations. The observed topological edge states of phonon-polaritons are found to carry nonzero angular momentum locked to their propagation direction, which enables their robust transport. Thus, these topological quasiparticles enable the funneling of infrared phonons mediated by helical infrared photons along arbitrary pathways and across sharp bends, thereby offering opportunities for applications ranging from Raman and vibrational spectroscopy with structured phonon-polaritons to directional heat dissipation.

Coherent virtual absorption of elastodynamic waves.

Absorbers suppress reflection and scattering of an incident wave by dissipating its energy into heat. As material absorption goes to zero, the energy impinging on an object is necessarily transmitted or scattered away. Specific forms of temporal modulation of the impinging signal can suppress wave scattering and transmission in the transient regime, mimicking the response of a perfect absorber without relying on material loss. This virtual absorption can store energy with large efficiency in a lossless material and then release it on demand. Here, we extend this concept to elastodynamics and experimentally show that longitudinal motion can be perfectly absorbed using a lossless elastic cavity. This energy is then released symmetrically or asymmetrically by controlling the relative phase of the impinging signals. Our work opens previously unexplored pathways for elastodynamic wave control and energy storage, which may be translated to other phononic and photonic systems of technological relevance.

Acoustic Supercoupling in a Zero-Compressibility Waveguide.

Funneling acoustic waves through largely mismatched channels is of fundamental importance to tailor and transmit sound for a variety of applications. In electromagnetics, zero-permittivity metamaterials have been used to enhance the coupling of energy in and out of ultranarrow channels, based on a phenomenon known as supercoupling. These metamaterial channels can support total transmission and complete phase uniformity, independent of the channel length, despite being geometrically mismatched with their input and output ports. In the field of acoustics, this phenomenon is challenging to achieve, since it requires zero-density metamaterials, typically realized with waveguides periodically loaded with membranes or resonators. Compared to electromagnetics, the additional challenge is due to the fact that conventional acoustic waveguides do not support a cut-off for the dominant mode of propagation, and therefore zero-index can be achieved only based on a collective resonance of the loading elements. Here we propose and experimentally realize acoustic supercoupling in a dual regime, using a compressibility-near-zero acoustic channel. Rather than engineering the channel with subwavelength inclusions, we operate at the cut-off of a higher-order acoustic mode, demonstrating the realization and efficient excitation of a zero-compressibility waveguide with effective soft boundaries. We experimentally verify strong transmission through a largely mismatched channel and uniform phase distribution, independent of the channel length. Our results open interesting pathways towards the realization of extreme acoustic parameters and their implementation in relevant applications, such as ultrasound imaging, acoustic transduction and sensing, nondestructive evaluation, and sound communications.

Age-Related Effects of Lead Poisoning on Some Haematological Parameters in Adult Wistar Rats.

The World Health Organization (WHO) estimates that, about a quarter of the diseases facing mankind today occur due to prolonged exposure to environmental pollution, and that most of these environment-related diseases are however, not easily detected and may be acquired during childhood and manifested later in adulthood. The aim of this work was to evaluate sub-chronic effects of lead poisoning on haematological parameters and some sex hormones, as well as age-related changes on Wistar Rats. Thirty (30) of 3-, 5-, and 7-months old male Wistar rats, were divided into experimental (lead fed) and control (distil water) groups. Haematological parameters were determined, while blood lead concentration was determined using the method of Atomic Absorption Spectrophotometer. There was a significant (P< 0.05) increase (46.00, 46.75, 50.75 vs 14.56, 18.00, 17.60) in blood lead concentration with insignificant (P˃ 0.05) increase in the concentration of WBC counts (12.433, 13.000, 12.250 Vs 12.400, 10.000, 11.250) between the experimental and control groups. Significant decrease in Body Weight (77.43, 107.88, 134.35Vs 130.66, 150.60, 165.62), RBC counts (5.333, 7.000, 6.250 Vs 7.000, 7.500, 7.250), PCV (22.667, 40.00, 35.25 Vs 37.600, 45.5,43.25), Hb (10.000, 12.000, 10.75 Vs 13.200, 13.250, 12.50), MCV (45.333, 54.500, 55.750 Vs 55.400, 59.500, 58.250), MCH levels (15.00016.25016.500 Vs 18.400, 17.750, 17.000), as well as insignificant decrease in platelet counts(410, 373, 341 Vs 437, 313, 384), and MCHC (29.67, 29.75, 30.00 Vs 32.800, 30.25, 29.250). The effect of lead (Pb) on these parameters was observed to be more pronounced in younger animals (P≤0.05). It was concluded that, ingestion of lead acetate produces more physiological derangement in young Wistar Rats.

Effect of Caffeine on Serum Tumour Necrosis Factor Alpha and Lactate Dehydrogenase in Wistar Rats Exposed to Cerebral Ischaemia-reperfusion Injury.

Caffeine is known to confer neuro-protection via A1 and A2A adenosine receptor antagonism in which adenosine neuro-modulates excitotoxic release of glutamate. Currently, it is unclear whether caffeine modulates inflammation in ischaemic stroke model. The present study examined effects of caffeine following ischaemia-reperfusion injury on neuro-inflammatory tumour necrosis alpha (TNF-α), lactate dehydrogenase (LDH), as well as effect of caffeine against brain ischaemic damage on histology. Thirty three adult male Wistar rats (180-300 g) were used in this study. They were randomly divided into four groups (n=5 each): Group I (Control) that received neither the operation nor any treatment; Group II (Sham/Water) received a pseudo-ischaemic-reperfusion and 1ml water for injection; Group III (BCCO/Water) that received complete bilateral common carotid occlusion (BCCO) and 1ml water for injection; Group IV (BCCO/Caffeine) that received complete BCCO and caffeine solution intraperitoneally at a dose of 50% LD50 value (144mg/kg); and thirteen rats were used for LD50 assessment. Sensory and motor functions significantly (p<0.05) decreased in the rat following ischaemia-reperfusion injury when compared to pre-injury state on Garcia neurological score. Caffeine reduced brain ischaemic injury and significantly reduced (p<0.05) TNF-α activity. While no significant effects (p>0.05) of caffeine was observed on LDH activity. This study has shown neuro-protective roles of caffeine against ischaemia-reperfusion damage to brain tissue, inflammatory TNF-α activity, but not on LDH activity.

Negative effective permeability and left-handed materials at optical frequencies.

We present here the design of nano-inclusions made of properly arranged collections of plasmonic metallic nano-particles that may exhibit a resonant magnetic dipole collective response in the visible domain. When such inclusions are embedded in a host medium, they may provide metamaterials with negative effective permeability at optical frequencies. We also show how the same inclusions may provide resonant electric dipole response and, when combining the two effects at the same frequencies, left-handed materials with both negative effective permittivity and permeability may be synthesized in the optical domain with potential applications for imaging and nano-optics applications.

Cloaking through cancellation of diffusive wave scattering.

A new cloaking mechanism, which makes enclosed objects invisible to diffusive photon density waves, is proposed. First, diffusive scattering from a basic core-shell geometry, which represents the cloaked structure, is studied. The conditions of scattering cancellation in a quasi-static scattering regime are derived. These allow for tailoring the diffusivity constant of the shell enclosing the object so that the fields scattered from the shell and the object cancel each other. This means that the photon flow outside the cloak behaves as if the cloaked object were not present. Diffusive light invisibility may have potential applications in hiding hot spots in infrared thermography or tissue imaging.

Thermal invisibility based on scattering cancellation and mantle cloaking.

We theoretically and numerically analyze thermal invisibility based on the concept of scattering cancellation and mantle cloaking. We show that a small object can be made completely invisible to heat diffusion waves, by tailoring the heat conductivity of the spherical shell enclosing the object. This means that the thermal scattering from the object is suppressed, and the heat flow outside the object and the cloak made of these spherical shells behaves as if the object is not present. Thermal invisibility may open new vistas in hiding hot spots in infrared thermography, military furtivity, and electronics heating reduction.

Platonic scattering cancellation for bending waves in a thin plate.

We propose an ultra-thin elastic cloak to control the scattering of bending waves in isotropic heterogeneous thin plates. The cloak design makes use of the scattering cancellation technique applied, for the first time, to the biharmonic operator describing the propagation of bending waves in thin plates. We first analyze scattering from hard and soft cylindrical objects in the quasistatic limit, then we prove that the scattering of bending waves from an object in the near and far-field regions can be suppressed significantly by covering it with a suitably designed coating. Beyond camouflaging, these findings may have potential applications in protection of buildings from earthquakes and isolating structures from vibrations in the motor vehicle industry.

Layered plasmonic cloaks to tailor the optical scattering at the nanoscale.

We discuss the rich scattering features offered by thin and thick plasmonic layers covering dielectric nanoparticles and their potential optical applications. The frequency position of scattering dips and peaks may be controlled to a large degree using plasmonic layers, which may dramatically vary the total scattering signature in the frequency range of interest. We show that complex and exotic spectra may be obtained using a single composite nanosphere, including dipole-dipole Fano resonances and electromagnetic induced transparency effects. The described phenomena are observable at any angle of observation, in the total scattering cross section and for realistic plasmonic materials, since they are based on purely dipolar fields. Enhanced field amplitudes are associated with these anomalous scattering features, which may be used to efficiently boost weak optical nonlinear effects. Exciting applications of these nanostructures are envisioned, such as efficient and tunable sensors, all-optical switches and memories, optical tagging and biomolecular imaging.

Twisted optical metamaterials for planarized ultrathin broadband circular polarizers.

Optical metamaterials are usually based on planarized, complex-shaped, resonant nano-inclusions. Three-dimensional geometries may provide a wider set of functionalities, including broadband chirality to manipulate circular polarization at the nanoscale, but their fabrication becomes challenging as their dimensions get smaller. Here we introduce a new paradigm for the realization of optical metamaterials, showing that three-dimensional effects may be obtained without complicated inclusions, but instead by tailoring the relative orientation within the lattice. We apply this concept to realize planarized, broadband bianisotropic metamaterials as stacked nanorod arrays with a tailored rotational twist. Because of the coupling among closely spaced twisted plasmonic metasurfaces, metamaterials realized with conventional lithography may effectively operate as three-dimensional helical structures with broadband bianisotropic optical response. The proposed concept is also shown to relax alignment requirements common in three-dimensional metamaterial designs. The realized sample constitutes an ultrathin, broadband circular polarizer that may be directly integrated within nanophotonic systems.

Broadband metamaterial for nonresonant matching of acoustic waves.

Unity transmittance at an interface between bulk media is quite common for polarized electromagnetic waves incident at the Brewster angle, but it is rarely observed for sound waves at any angle of incidence. In the following, we theoretically and experimentally demonstrate an acoustic metamaterial possessing a Brewster-like angle that is completely transparent to sound waves over an ultra-broadband frequency range with >100% bandwidth. The metamaterial, consisting of a hard metal with subwavelength apertures, provides a surface impedance matching mechanism that can be arbitrarily tailored to specific media. The nonresonant nature of the impedance matching effectively decouples the front and back surfaces of the metamaterial allowing one to independently tailor the acoustic impedance at each interface. On the contrary, traditional methods for acoustic impedance matching, for example in medical imaging, rely on resonant tunneling through a thin antireflection layer, which is inherently narrowband and angle specific.

Plasmonic cloaking for irregular objects with anisotropic scattering properties.

Here we extend the plasmonic cloaking technique to irregularly shaped objects with anisotropic scattering response. The scattering-cancellation approach to cloaking [A. Alù and N. Engheta, Phys. Rev. E 72, 016623 (2005)] has been extensively applied in the past to symmetrical geometries and canonical shapes. However, recent papers have raised some doubts concerning the fact that its use may not be as effective when dealing with strongly anisotropic and noncanonical geometries. Our goal here is to extend the plasmonic cloaking technique to irregular obstacles and to show that proper cloak design may provide a significant and uniform scattering reduction, independent of angle of incidence, position, and polarization of the illumination. We investigate how the volumetric effect of scattering cancellation provided by plasmonic media may drastically suppress the scattering for these irregular geometries independent of the illumination angle, and we shed some light on the physical mechanisms and the design rules at the basis of this cloaking technique when applied to objects whose scattering properties are dependent upon polarization and angle of incidence.

Screening for coeliac disease in healthy blood donors at two immuno-transfusion centres in north-east Italy.

BACKGROUND AND AIMS: In the past, the reported prevalence of coeliac disease ranged from 1:1000 to 1:4000, whereas recent studies using serological screening methods have found a significantly higher prevalence. The aim of this study was to investigate the prevalence of coeliac disease in healthy blood donors in a North-eastern region of Italy. SUBJECTS: A total of 4000 healthy blood donors were studied from two immunotransfusion centres. METHODS: Serum IgA-antiendomysium antibodies were detected by indirect immunofluorescence using human umbilical cord vein sections, and positive sera were tested also on monkey oesophagus tissue. Intestinal biopsy was performed in all antiendomysium-positive subjects. RESULTS: Ten out of 4000 sera screened were found to be antiendomysium positive on human umbilical cord vein. All positive patients had flat mucosa on intestinal biopsy. Five subjects had coeliac disease-related clinical features (2 had a history of gastrointestinal symptoms, 1 a family history of IDDM, 1 sideropenic anaemia, and 1 IgA deficiency). One of the ten serum, antiendomysium positive on human umbilical cord vein, was found to be negative when tested on monkey oesophagus. CONCLUSIONS: These data confirm the high prevalence of undiagnosed silent coeliac disease in the healthy adult population. This is the first study where umbilical cord was used for screening coeliac disease in a large population. The human umbilical cord vein indirect immunofluorescence test is more specific for villous atrophy than conventional indirect immunofluorescence test on monkey oesophagus and is a reliable screening test for coeliac disease in an apparently healthy population.