Different Angles Of Incidence Research Articles

In-plane omnidirectional magnetic field sensor based on Giant Magneto Impedance (GMI)

In this work the design and characterization of an omnidirectional in-plane magnetic field sensor are presented. The sensor is based on the Giant Magneto Impedance (GMI) effect in glass-coated amorphous microwires of composition (Fe6Co94)72.5Si12.5B15. For the first time, a circular loop made with a microwire is used for giving omnidirectional response. In order to estimate the GMI response of the circular loop we have used a theoretical model of GMI, determining the GMI response as the sum of longitudinal sections with different angles of incidence. As a consequence of the circular loop, the GMI ratio of the sensor is reduced to 15% instead of 100% for the axial GMI response of a microwire. The sensor response has been experimentally verified and the GMI response of the circular loop has been studied as function of the magnetic field, driven current, and frequency. First, we have measured the GMI response of a longitudinal microwire for different angles of incidence, covering the full range between the tangential and perpendicular directions to the microwire axis. Then, using these results, we have experimentally verified the decomposition of a microwire with circular shape as longitudinal segments with different angles of incidence. Finally, we have designed a signal conditioning circuit for the omnidirectional magnetic field sensor. The response of the sensor has been studied as a function of the amplitude of the incident magnetic field.

A Study on Seismic Response of an Irregular Structure with Different Angle of Incidence

A Study on Seismic Response of an Irregular Structure with Different Angle of Incidence

The film tells the story: Physical-chemical characteristics of IgG at the liquid-air interface.

The presence of liquid-air interfaces in protein pharmaceuticals is known to negatively impact product stability. Nevertheless, the mechanisms behind interface-related protein aggregation are not yet fully understood. Little is known about the physical-chemical behavior of proteins adsorbed to the interface. Therefore, the combinatorial use of appropriate surface-sensitive analytical methods such as Langmuir trough experiments, Infrared Reflection-Absorption Spectroscopy (IRRAS), Brewster Angle Microscopy (BAM), and Atomic Force Microscopy (AFM) is highly expedient to uncover structures and events at the liquid-air interface directly. Concentration-dependent adsorption of a human immunoglobulin G (IgG) and characteristic surface-pressure/area isotherms substantiated the amphiphilic nature of the protein molecules as well as the formation of a compressible protein film at the liquid-air interface. Upon compression, the IgG molecules do not readily desorb but form a highly compressible interfacial film. IRRA spectra proved not only the presence of the protein at the interface, but also showed that the secondary structure does not change considerably during adsorption or compression. IRRAS experiments at different angles of incidence indicated that the film thickness and/or packing density increases upon compression. Furthermore, BAM images exposed the presence of a coherent but heterogeneous distribution of the protein at the interface. Topographical differences within the protein film after adsorption, compression and decompression were revealed using underwater AFM. The combinatorial use of physical-chemical, spectroscopic and microscopic methods provided useful insights into the liquid-air interfacial protein behavior and revealed the formation of a continuous but inhomogeneous film of native-like protein molecules whose topographical appearance is affected by compressive forces.

Phononic crystal Luneburg lens for omnidirectional elastic wave focusing and energy harvesting

We explore a phononic crystal Luneburg lens through design, fabrication, and analysis for omnidirectional elastic wave focusing and enhanced energy harvesting both numerically and experimentally. The proposed lens is formed using hexagonal unit cells with blind holes of different diameters, which are determined according to the Luneburg lens refractive index distribution obtained by finite-element simulations of the lowest asymmetric mode Lamb wave band structure. Wave simulations are performed numerically under plane wave excitation from a line source, and focusing is observed at the opposite border of the lens with respect to the incident wave direction. Numerically simulated elastic wave focusing results are validated through a set of experiments. Omnidirectionality is demonstrated by testing the lens under plane wave excitation for different angles of incidence. With piezoelectric energy harvesters located at the boundary of the phononic crystal Luneburg lens, more than an order of magnitude larger power output can be extracted as compared to the baseline case of energy harvesting without the lens under the same plane wave excitation.

Iridescent Perfect Absorption in Critically-Coupled Acoustic Metamaterials Using the Transfer Matrix Method

The absorption performance of a locally-reacting acoustic metamaterial under oblique incidence is studied. The metamaterial is composed of a slotted panel, each slit being loaded by an array of Helmholtz resonators. The system is analytically studied using the transfer matrix method, accounting for the viscothermal losses both in the resonator elements and in the slits, allowing the representation of the reflection coefficient in the complex frequency plane. We show that by tuning the geometry of the metamaterial, perfect absorption peaks can be obtained on demand at selected frequencies and different angles of incidence. When tilting the incidence angle, the peaks of perfect absorption are shifted in frequency, producing an acoustic iridescence effect similar to the optic iridescence achieved by incomplete band gap. Effectively, we show that in this kind of locally-reacting metamaterial, perfect and omnidirectional absorption for a given frequency is impossible to achieve because the metamaterial impedance does not depend on the incidence angle (i.e., the impedance is a locally reacting one). The system is interpreted in the complex frequency plane by analysing the trajectories of the zeros of the reflection coefficient. We show that the trajectories of the zeros do not overlap under oblique incidence, preventing the observation of perfect and omnidirectional absorption in locally reacting metamaterials. Moreover, we show that for any locally resonant material, the absorption in diffuse field takes a maximal value of 0.951, which is achieved by a material showing perfect absorption for an incidence angle of 50.34 degrees.

Electron emission yield for low energy electrons: Monte Carlo simulation and experimental comparison for Al, Ag, and Si

The electron emission under electron impact between 10 eV and 2 keV is investigated with a Monte Carlo (MC) code in aluminum, silver, and silicon. The code is based on the complex dielectric function theory to describe the inelastic scattering and uses the Mott's model of partial waves to describe the elastic scattering. It takes into account both volume and surface plasmon excitations. The simulation results are compared with the experimental measurements of electron emission yields (EEY) and energy spectra of low energy electrons performed in ultrahigh vacuum on Ar-etched bulk samples. Our MC simulations at low energy are found to be in fairly good agreement with our experimental measurements. The peaks corresponding to the surface plasmon, the volume plasmon and its multiples and to the Auger transitions appear clearly on the energy loss spectra of aluminum, silver, and silicon. The simulated EEY are also in fairly good agreement with our measurements and with data from the literature. The EEY at normal incidence is studied for secondary and backscattered electrons. A focus is made for the EEY below 50 eV where a fairly good agreement is found with Bronstein and Fraiman's measurements on vacuum evaporated samples. Below 2 keV, for silver and aluminum, the total EEY is given for different angles of incidence θ. Some discrepancies are observed between our experimental measurements and our MC simulations for high angles of incidence. These discrepancies can be attributed to the modeling of surface plasmon excitations, surface oxidation, or roughness that occur during the Ar-etching process.

Realization of mode independent multichannel transmission filter by controlling the photon localization in symmetric cavities

Modern optical communication system requires multiple channel transmission in different spectral band for different applications. Here we are proposing a microresonator structure for closely spaced, mode independent multiple channel transmission in 3rd transmission window by controlling the localization of photons in its cavity. To design the proposed structure, the spectral filtering properties of a single cavity planar microresonator are studied initially. In conventional multilayer dielectric filter, the localization of light in the microcavity is generally controlled by controlling the number of layers. Here we have shown that application of electric field across the structure, designed with suitable materials can also affect the localization of light in the cavity as well as the Q values of the transmission spectra. The mode independent characteristic of the structure is found from the study of its transmittance characteristics at different angle of incidence of light. It is found that the results of single cavity structure hold well for multicavity resonator structure also, in the regime of optical communication wavelength range. A method to increase the number of transmission channels is also proposed here keeping the fabrication perspective in mind.

Study of the Omnidirectional Transmission Properties of a Three-Dimensional EBG Structure Fabricated with Titanium Dioxide Using 3-D Printing

The transmission properties of a three-dimensional electromagnetic bandgap (EBG) with a diamond structure made of titanium dioxide ceramic using three-dimensional (3-D) printing was studied. The experimental results show that EBG structures can form a wider bandgap with high-K materials for the standard direction, the standard direction, and the standard direction. This agrees well with the simulation using the plane-wave expansion method. However, the bandgap changes gradually when the EBG structure is rotated from one crystal orientation to another. It is also found that the position and the bandwidth associated with the bandgap differ for different angles of incidence, reaching the maximum bandwidth at 22.5°. The results of this study can help facilitate many applications with omnidirectional transmission properties of three-dimensional EBGs.

Ultrasonic measurements by means of continuous waves in a foam saturated with air

The study of porous materials has always been of great interest. Several characterization methods have been developed by means of ultrasonic waves, mainly because of their non-invasive behavior. A typical set-up involves transmission and reflection measurements through the test material using pulse signals. The received echoes are analyzed and compared with analytical models in order to estimate some specific acoustic properties of the sample itself. The main drawback of this approach is the low signal-to-noise ratio recorded when testing highly attenuating materials. This disadvantage is even more pronounced for measurements in air. The present work aims to overcome these limitations, replacing the excitation signals by continuous muti-harmonic waves. These signals have been developed by optimizing the phase of each harmonic, resulting in a low crest factor and consequently in a better signal-to-noise ratio Moreover their frequency content can be easily adapted to the different transducers used during the test. The method has been used to test a foam saturated with air, performing ultrasonic measurements in transmission/reflection, at different angles of incidence. The results show a significant improvement of the measurements, facilitating the estimation of the foam acoustics properties.

Angle-resolved and polarization-dependent investigation of cross-shaped frequency-selective surface terahertz filters

The spectral response of a terahertz (THz) filter is investigated in detail for different angles of incidence and polarization of the incoming THz wave. The filter is fabricated by patterning an aluminum frequency-selective surface of cross-shaped apertures on a thin foil of the low-loss cyclo-olefin polymer Zeonor. Two different types of resonances are observed, namely, a broadline resonance stemming from the transmittance of the slot apertures and a series of narrowline guided-mode resonances, with the latter being investigated by employing the grating theory. Numerical simulations of the filter transmittance based on the finite-element method agree with experimental measurements by means of THz time domain spectroscopy (THz-TDS). The results reveal extensive possibilities for tuning the guided-mode resonances by mechanically adjusting the incidence or polarization angle, while the fundamental broadline resonance is not significantly affected. Such filters are envisaged as functional elements in emerging THz systems for filtering or sensing applications.

Enhancement of the optical absorption in cholesteric liquid crystals due to photonic effects: an experimental study

ABSTRACTAn anomalous strong optical absorption was measured in a cholesteric liquid crystal (CLC) at both edges of its photonic band gap. The experiment was carried out by studying the luminescence generated by the CLC sample doped with a small amount of fluorescent dye. The material was excited with monochromatic light at different angles of incidence and polarisations. Clear peaks were found in the luminescence response at angles for which the pumping wavelength coincides with the positions of the gap edges. The effect is especially noticeable for excitation under circularly polarised light of the same handedness as that of the CLC helix, and it is the highest at the long-wavelength edge. The modification of the absorption is originated by the helicoidal (photonic) structure of the material, which drastically influences the propagation of electromagnetic waves at certain frequencies and polarisations. The results were analysed numerically using an extension of the Berreman method that incorporates absorption effects. Good agreement with the experiment was found.

McMC-based nonlinear EIVAZ inversion driven by rock physics

A single set of vertically aligned fractures embedded in a purely isotropic background medium may be considered as a long-wavelength effective transversely isotropic medium with a horizontal symmetry axis (HTI). The estimation of fracture weaknesses is essential for characterizing the anisotropy in HTI media. Using the fractured anisotropic rock-physics models and the wide-azimuth seismic data, elastic impedance inversion variation with incident angle and azimuth, or simply 'EIVAZ' for short, can be carried out for the estimation of the normal and tangential fracture weaknesses with the nonlinear Markov chain Monte Carlo (McMC) strategy. Firstly, an inversion method of nonlinear anisotropic elastic impedance (AEI) with the McMC algorithm was proposed, which is used for the inversion of nonlinear AEI information with different angles of incidence and azimuth. Then we extracted the normal and tangential fracture weaknesses directly using the ratio differences of inverted nonlinear AEI data. So we can eliminate the influence of the isotropic background elastic impedance on the anisotropic perturbation elastic impedance and obtain the normal and tangential fracture weaknesses more stably. A test on a 2D over-thrust model shows that the fracture weaknesses are still estimated reasonably with moderate noise. A test on a real data set demonstrates that the estimated results are in good agreement with the results of the well log interpretation, and our McMC-based nonlinear AEI approach appears to be a stable method for predicting fracture weaknesses.

The interaction of acoustic waves with a three-layer barrier at different angles of incidence

In this paper influence of the bubble layer on the transmission of the acoustic waves through the three-layer barrier placed in the water at various angles of incidence is investigated. Barrier consists of a layer of gel with polydispersed air bubbles limited polycarbonate layers. It is shown that the presence of bubbles in the layer substantially lowers the transmission of the acoustic waves through the multi-layer barrier for frequencies close to the resonant frequency of the bubbles. For these frequencies the values of the reflection and transmission coefficients are almost independent of the angle of incidence and determined by the parameters of the bubble gel.

Energy Absorption in Metallic Targets Subjected to Oblique Impact

The present study investigates mode of failure and energy absorption in impact of 1 mm thick Al 1100 H12 monolithic and double layered targets of 0.5 mm thickness in-contact with each other. The 255 mm span diameter circular targets were impacted by EN-24 steel ogive nosed projectile of 19 mm diameter and 52.5 g mass at different angles of incidence viz., 0o, 30o, 45o. Three dimensional modelling of targets and projectiles were carried out in ABAQUS/CAE module. The targets were modelled as a deformable body whereas, rigid body behavior was assumed for the projectiles due to negligible deformation observed in impact. ABAQUS/Explicit solver was used to simulate all the problems and results were discussed in terms of ballistic resistance, failure mode of the target and energy absorption during the impact.

An Investigation on Compact Ultra-Thin Triple Band Polarization Independent Metamaterial Absorber for Microwave Frequency Applications

This article claims, an investigation on compact ultrathin triple band polarization independent metamaterial absorber for microwave frequency applications. The proposed absorber unit cell consist of two resonators named as Structure-A and Structure-B. Both the resonators are printed on the upper surface of dual side copper coated FR-4 epoxy glass substrate of thickness 0.8 mm. The proposed absorber structure offers three distinct absorption peaks of 99.67%, 99.48%, and 99.42% with FWHM bandwidth of 170 MHz (4.11-4.28 GHz), 350 MHz (9.17–9.52 GHz), and 480 MHz (11.24–11.72 GHz) at 4.19 GHz, 9.34 GHz, and 11.48 GHz, respectively, under normal incidence. In addition to above, the four fold symmetry of proposed absorber structure make it polarization independent. Proposed absorber structure also offers more than 80% absorptivity at different angle of incidence (up to 60°) under transvers electric and transvers magnetic polarization states. The designed absorber unit cell has compactness of $0.11~\lambda _{0} \times 0.11~\lambda _{0}$ with ultra-thin thickness of $0.0111~\lambda _{0}$ , where $\lambda _{0}$ is the free space wavelength with respect to the lowest absorption peak of 4.19 GHz. Absorption mechanism of proposed unit cell has been discussed with the help of normalized input impedance, electric field distribution, and surface current density plots. In order to discuss the metamaterial property of proposed absorber unit cell dispersion diagram has been shown.

Numerically stable method for wave-field calculation and band-gap estimation in layered phononic crystals

High-frequency wave propagation in layered waveguides composed of periodic unit-cells is studied. Each unit-cell consists of a certain number of various elastic layers. Wave motion in the considered elastic structures (phononic crystals) is characterized by frequency bands, known as forbidden zones or band-gaps, where the full reflection of time-harmonic plane waves incident from an external half-space is observed. Using the transfer matrix method, the mathematical model of elastic wave propagation in anisotropic layered phononic crystals between two half-spaces is developed. A stable numerical algorithm for calculation of wave fields in the cells of phononic crystals is proposed. The amplitude coefficients of transmitted longitudinal and shear body waves are expressed in terms of transfer-matrix eigenvalues. A classification of band-gaps and pass-bands in layered anisotropic phononic crystals is proposed. It is based on the analysis of Bloch wavenumbers (expressed via the eigenvalues of the unit-cell transfer matrix) and the derived semi-analytical asymptotic expression of the transmission coefficients. Each Bloch wave has attenuation within the band-gaps of first kind. Waves propagating without attenuation are not excited within the band-gaps of second kind due to their specific polarization and boundary conditions at the interface between the multi-layered structure and the external half-space. By changing the parameters of the incident field, for instance, angles of incidence, band-gaps are converted into low transmission pass-bands where transmission coefficients are rather small. Therefore, a low transmission pass-band is similar to the traditional band-gap from an engineering point of view. The numerical results for energy transmission coefficient and Bloch waves are given at different angles of incidence; they demonstrate the formation of band-gaps in anisotropic phononic crystals.

Optical visible wavelength region selective reflector design for photovoltaic cells using photonic crystal

In this study, we have proposed an optical broadband angular reflector having a band selective feature and high reflectivity rate for photovoltaic implementations by using a photonic crystal structure made of two different dielectric layers. This paper presents new and useful information about a reflector that was designed by using a periodic structure composed of two Si based layers for the visible range in the solar spectrum region. The system has been adjusted in such a way that it could cover a wide wavelength area between the photonic band gaps at nearly λ ≈ 300-800 nm. We have tested the proposed reflector against different angles of incidence of the light. The reflectivity spectra of the optical structure have been calculated.

Preparation and Characterization of ITO Nanostructure by Oblique Angle Deposition

Indium doped tin oxide (ITO) nanostructured films were prepared by the electron-beam evaporation with the oblique-angle deposition (OAD) technique. The influence of the film thickness of the ITO nanostructures on the crystal structures, the physical morphologies, the optical properties, and the electrical attributes was investigated by grazing-incident X-ray diffraction (GIXRD), field-emission scanning electron microscopy (FE-SEM), UV-Vis spectrophotometry, four-point probe measurements, the respectively. The GIXRD analyses indicated that the ITO nanostructured films were mostly polycrystalline with the cubic bixbite structure. The FE-SEM micrographs clearly showed that the increased film thickness greatly affected the morphologies of the ITO nanostructures. The optical transmission spectra at the different angles of incidence clearly demonstrated the optimized results for the highest transmission in the visible region. The electrical resistivity of the ITO nanostructures was gradually decreased with the increased ITO thickness. Finally, the most optimized solar transmission with small light scattering and sheet resistance were discussed based on the anti-reflection performance of the ITO nanostructured films towards the solar cell applications.

Test method for characterising the thermal protective performance of fabrics exposed to flammable liquid fires

SummaryPeople, such as emergency service and military personnel, require protection from fires involving flammable liquids and liquefiable solids (Class B fires) in a number of situations. Fires involving flammable liquids typically reach higher temperatures sooner when compared to other types of fuel, yet there appears to be little literature that specifically investigates the protective performance of fabrics against such fires. Therefore, a new method was developed to enable the characterisation of the protective performance of fabrics when exposed to flammable liquid fires. Fabric samples were mounted on a sample plate inclined to three different angles of incidence. Known volumes of hydrocarbon fuel were pipetted into a fuel reservoir, ignited, then tipped onto fabric samples. Ten thermocouples embedded in the sample plate measured the resultant change in temperature at the technical rear of the fabric samples throughout the exposure. Significant differences were observed between fabrics for maximum temperature, time to maximum temperature, maximum heat flux, transferred energy and estimated burn risk. Therefore, this new methodology enabled discrimination among fabrics based on the protection they provide. Differences were also observed when the volume of fuel and the angle of incidence varied and, therefore, these device settings must be controlled for repeatable results. Copyright © 2016 John Wiley & Sons, Ltd.

Broadband Tunable Frequency Selective Surface for Steerable Antenna Applications

Resonant frequency tunable range is an important character for active frequency selective surfaces (AFSSs), especially when building electronically steerable antennas based on AFSS. In this communication, a broadband tunable bandpass AFSS is presented. The tunable ability is achieved by the varactors mounted on the surface. The proposed design has zigzag resonant current flows through multiple unit cells. Thus, the magnetic field coupling between unit cells is enhanced and the resonant frequency tunable range is extended. The measured resonant frequency tunable range is from 935 MHz to 2.405 GHz. Another advantage of this design is that no additional bias grid is required. Furthermore, this design has stable response under different angles of incidence because it has subwavelength dimensions.