Multiple Internal Reflections Research Articles

Particle identification with DIRCs at PANDA

The DIRC technology (Detection of Internally Reflected Cherenkov light) offers an excellent possibility to minimize the form factor of Cherenkov detectors in hermetic high energy detectors. The PANDA experiment at FAIR in Germany will combine a barrel-shaped DIRC with a disc-shaped DIRC to cover an angular range of 5 to 140 degrees. Particle identification for pions and kaons with a separation power of 3 standard deviations or more will be provided for momenta between 0.5 GeV/c and 3.5 GeV in the barrel region and up to 4 GeV/c in the forward region. Even though the concept is simple, the design and construction of a DIRC is challenging. High precision optics and mechanics are required to maintain the angular information of the Cherenkov photons during multiple internal reflections and to focus the individual photons onto position sensitive photon detectors. These sensors must combine high efficiencies for single photons with low dark count rates and good timing resolution at high rates. The choice of radiation hard fused silica for the optical material and of MCP-PMT photon sensors is essential for DIRC detectors to survive in an environment of radiation and strong magnetic field. The two DIRC detectors differ in the focusing optics, in the treatment of chromatic dispersion and in the electronic readout systems. The technical design of the two DIRC detectors and their validation by testing prototypes in a mixed particle beam at CERN are presented.

Electromagnetic wave trapping in NiFe2O4 nano-hollow spheres: An efficient microwave absorber

Abstract In search of lightweight, broadband and stable microwave absorbing material, here we have presented a morphology dependent study of microwave properties on Nickel Ferrite (NFO). A comparative study of permittivity (e), permeability (μ), Reflection Loss (RL) and Shielding efficiency (SE) on NFO nano hollow spheres (NHS) with its nano particles (NPs) and bulk counterpart has been performed for widely used X-Band (8–12 GHz) on composites filled (25 wt% and thickness of 2 mm) with each sample. Interestingly, NFO nano hollow spheres (NHS) are found to be highly efficient material towards microwave attenuation. An optimal RL of ∼−59.2 dB is obtained for frequency ∼11.7 GHz with a broad band-width (W) of ∼(9.18–12) GHz having RL 90%). Hollow cavity of NHS leads to a lower density (∼3.91 g/cc) as well as multiple internal reflections, which enhances wave absorption. Excellent impedance matching with free space, accompanied by proper dielectric and magnetic loss contributes towards maximization of RL for NHS. These properties enhance the potentiality of NFO NHS as an efficient microwave absorbing material suitable in various microwave devices.

PVC bead assisted selective dispersion of MWCNT for designing efficient electromagnetic interference shielding PVC/MWCNT nanocomposite with very low percolation threshold

The present study describes the electromagnetic interference shielding effectiveness (EMI SE) of poly (vinyl chloride) (PVC)/MWCNT nanocomposites prepared by solution blending in the presence of PVC beads and their corresponding electrically conductivity. Commercial PVC beads were added to the high viscous media of solution blended PVC-MWCNT during solvent evaporation of the prepared PVC/MWCNT nanocomposite. Addition of PVC beads increased the EMI SE and electrical conductivity values of the nanocomposite compared to the PVC/MWCNT nanocomposite without any PVC beads. Additionally, both EMI SE and electrical conductivity were also increased with increasing content of PVC bead at constant MWCNT loading in the nanocomposite. The insulating PVC bead regions are free from any MWCNT and acts as dispersed domains (excluded volume) which enhances effective concentration of MWCNT in the continuous PVC phase of the nanocomposites, and thus, play the key role to lower the percolation threshold, enhance the EMI SE and electrical conductivity values of the nanocomposite. The nonconductive PVC bead region in the nanocomposite acts as excluded volume that attenuates the microwave energy through multiple internal reflections by creating an impedance mismatch in the nanocomposites.

Multi-layered stack consisting of PVDF nanocomposites with flow-induced oriented MWCNT structure can supress electromagnetic radiation

Polymeric nanocomposites have emerged as a potential material in the electronic world owing to its numerous advantages like ease of processing, design flexibility, light-weight, ease of embedding and integrating with the existing production line. Given the surge in electronic components, electromagnetic interference, which severely impairs the reliability of precise electronic devices, has emerged as a new challenge. Hence, technologically, viable design is the need of the day. However, the high concentration of fillers required to achieve the desired properties still remains a challenge with respect to the design of functional polymeric nanocomposites. In this context herein, we report as to how flow induced distribution of multi-walled carbon nanotubes (MWCNT) in poly-vinylidene (PVDF) matrix during mechanical rolling influence the texture, polymorphism and electromagnetic shielding properties. We demonstrate the flow induced orientation of MWCNT, polymorphism in PVDF and composites shielding performance by TEM, crystallographic texture and shielding effectiveness measurements, respectively. Further, mechanical and thermal properties of as pressed and mechanically rolled samples were investigated by DMA and DSC. TEM analysis revealed that MWCNT form small aggregate, however were aligned along the rolling direction. This observation is in sharp contrast to the random distribution for as pressed samples. Quantitatively, a strong texture was observed for rolled samples as compared to as pressed samples. Absorption of EM waves is the major shielding mechanism which is mechanistically discussed here through associated dielectric loss parameters. Interactions, alignment of MWCNTs, and polymorphism influence the shielding efficiency in these composites. In addition, stacking of such nanocomposite layers further enhances the overall shielding efficiency by absorption (up to 72%) due to the polarization, multiple internal reflections and interlayer charge storing capacity. A Bluetooth module was employed to successfully demonstrate the efficacy of this approach in supressing unwanted EM interference. This study comprehensively guides researchers as to how processing or flow-induced changes alter the distribution of MWCNTs in polymer composites and how this influences the overall shielding behaviour.

Visualizing Light Rays Using Fluorescence

We present a simple and effective experimental setup to help students visualize light rays in optics experiments. When illuminated by a blue-violet laser pointer (typical wavelength [Formula: see text][Formula: see text]nm), tonic water and phosphorescent paper show fluorescence which allows the laser beam to be clearly seen by a large audience under normal ambient lighting. The setup is particularly useful for conducting classroom demonstrations on the reflection, refraction and diffraction of light. Quantitative measurement is also possible, e.g. students can attach a transparent scale to the phosphorescent paper or container holding the tonic water, and perform a quick verification of Snell’s law and the diffraction formula [Formula: see text]. The appeal of the visualization of light beams in multiple total internal reflections and retroreflection could help teachers introduce technological applications such as optical fibers and retroreflectors in road signs. A simple but interesting experiment of scattering laser light to form a light cone in a medium is shown using the fluorescence method. Redoing or modifying other innovative optics experiments using the fluorescence method is also discussed.

Free-surface and internal multiple elimination in one step without adaptive subtraction

We have derived a scheme for retrieving the primary reflections from the acoustic surface-reflection response by eliminating the free-surface and internal multiple reflections in one step. This scheme does not require model information and adaptive subtraction. It consists only of the reflection response as a correlation and convolution operator that acts on an intermediate wavefield from which we compute and capture the primary reflections. For each time instant, we keep one value for each source-receiver pair and store it in the new data set. The resulting data set contains only primary reflections, and from this data set, a better velocity model can be built than from the original data set. A conventional migration scheme can then be used to compute an artifact-free image of the medium. We evaluated the success of the method with a 2D numerical example. The method can have a wide range of applications in 3D strongly scattering media that are accessible from one side only.

Facile fabrication of sponge-like hierarchically porous Ni,La–SrTiO3 templated by in situ generated carbon deposits and the enhanced visible-light photocatalytic activity

Hierarchical pore-induced multiple internal reflections and/or scattering of light improves the capability of light trapping and thus photocatalytic efficiency.

Surface Texturing of Silicon {100} in an Extremely Low Concentration TMAH for Minimized Reflectivity

Micro-texturing of silicon front surface which consists of geometrical array of structures is needed to reduce the overall reflectance and to increase light trapping by multiple internal reflections of incident light for solar cell application. A wet anisotropic etching technique based on the alkaline solution is widely used to form micro-sized pyramidal structures on the silicon surface. In this work, an extremely low concentration tetramethylammonium hydroxide (TMAH) is employed for texturing the surface of {100} oriented monocrystalline silicon without adding any additive and agitation during etching to investigate the surface roughness and thereby reflectance. TMAH concentration is varied from 1.0-0.1 wt% in a step of 0.1 wt%. For each concentration, time of etching is also varied from 20–100 min with an interval of 20 min at a fixed temperature of 70°C. Surface morphology and surface roughness for as-textured silicon surfaces are analyzed by scanning electron microscope (SEM) and 3D laser scanning microscope, respectively. SEM images of etched silicon surface with 0.5 wt% TMAH confirm uniform and dense pyramidal structures. As measured by UV-Vis spectrometer using integrating sphere mode, we were able to achieve the lowest reflectance of 8.3% at 570 nm and solar weighted reflectance (RSW) of 9.7% in visible range after 80 min of etching in 0.5 wt% TMAH solution at 70°C.

New ellipsometric approach for determining small light ellipticities

Control of the coherent light polarization is always one of the important topics in laser physics and engineering. We propose an exact ellipsometric method for investigation of coherent light with small ellipticity. Using compensators with phase retardations providing maximum measurement accuracy for the selected ellipticity range is suggested. The method allows us to avoid taking into account the interference of multiple internal reflections of coherent light. The accuracy of the method increases with decreasing of the compensator phase retardation. Using light with a given ellipticity, we have measured the ellipticity of the light in the range of 3.5×10−4 to 5.0×10−3. The relative error of the ellipticity measuring in the range of 8.0×10−4 to 5.0×10−3 turns out does not exceed 0.02.

Microporous and Flexible Framework Acoustic Metamaterials for Sound Attenuation and Contrast Agent Applications.

The low-frequency (100-1250 Hz) acoustic properties of metal-organic framework (MOF) materials were examined in impedance tube experiments. The anomalously high sound transmission loss of HKUST-1, FeBTC, and MIL-53(Al) quantitatively demonstrated that these prototypical MOFs are absorptive acoustic metamaterials. To the best of our knowledge, this is the first example of MOFs that have been demonstrated to be acoustic metamaterials. Low-frequency acoustic dampening by subwavelength MOF metamaterials is likely due to sound dissipation and absorption facilitated by multiple internal reflections within the microporous framework structure. Modification of MIL-53(Al) with flexible organic linkers clarified that acoustic signatures of the MOFs may be tailored to add or alter certain diagnostic acoustic signatures. These results may be applied to the rational design of lightweight sound-insulating construction materials and acoustic contrast agents for subsurface mapping and monitoring applications at low frequency (100-1250 Hz).

Impact of Al2O3, TiO2, ZnO and BaTiO3 on the microwave absorption properties of exfoliated graphite/epoxy composites at X-band frequencies

Bi-filler composites composed of exfoliated graphite (EG) and any one of Al2O3, BaTiO3, ZnO and TiO2 metallic oxides are fabricated in epoxy matrix to improve microwave absorption properties exclusively in X band. These composites are characterized for their morphology and compositional studies using SEM, Raman spectroscopy and X-rays photoelectron spectroscopy. The strong reflection loss values of −43 dB (99.995% absorption), −25.7 dB (99.731% absorption), −33.9 dB (99.959% absorption) and −46.0 (99.997% absorption) with wide effective bandwidths are successfully achieved by the EG/epoxy composites containing 40 wt% Al2O3, 30 wt% BaTiO3, 30 wt% TiO2 and 20 wt% ZnO when the thicknesses are 1.8, 1.6, 1.4 and 1.8 mm, respectively. These absorption performances are attributed to the perfect matching conditions, multiple internal reflections, interface polarizations and defect polarizations. The incorporation of metallic oxides demonstrated improved adhesion and reinforcement efficiency factors, as well as uplifted the values of flexural strength and thermal conductivity of EG/epoxy composites. These properties justifies the potential future of metallic oxide/EG/epoxy composite in microwave absorption applications.

Breakthrough and significance of technology on internal multiple recognition and suppression: A case study of Sinian Dengying Formation in Central Sichuan Basin, SW China

Abstract Aimed at the serious mismatch between the synthetic seismogram and the real data of the Sinian Dengying Formation and the Lower Cambrian Qiongzhusi Formation in the GS1 well area, Sichuan Basin, four aspects of internal multiples identification and suppression were studied. Firstly, a forward modeling method of internal multiple based on reflectivity method was developed. Through eight means such as post-stack and pre-stack forward modeling of internal multiple, and combined with VSP data, it was demonstrated that well-seismic mismatching in this area is mainly caused by the internal multiples. Secondly, the simulation results of internal multiple forward modeling using the stripping method combined with the internal multiple periodicity analysis showed that four groups of overburden layers with velocity inversion were the main sources of the internal multiples. Thirdly, by identifying internal multiples accurately and using suppression technology based on pattern recognition, an effective and replicable suppression scheme suitable for these formations was established, overcoming the difficulty of the small speed difference between internal multiple and primary reflection wave which makes the current methods ineffective. Fourthly, an evaluation index of internal multiple intensity was proposed, and the internal multiple intensity distribution diagram of the fourth member of Dengying Formation (Deng-4 Member) in Gaoshiti-Moxi area was compiled. This scheme greatly improved the well-seismic match, and the strata sedimentary features are clearer on the new seismic profiles with higher lateral resolution, with which smaller faults and geological anomalies can be identified and a series of the bead reflections in the Dengying Formation are first discovered. The coincidence rate of reservoir prediction based on seismic waveform classification was increased from 60% to 90%, and that of hydrocarbon detection based on dual phase medium theory was increased from 70% to 100%.

Multiple Elimination and Transmission Compensation in Primary Reflections in Data Domain

We retrieve transmission compensated subsurface primary reflections from the reflection response measured at the surface. This is achieved by filtering the reflection response. The application of this scheme does not require model information. In this process, the reflection response is convolved and correlated with itself. The result after each convolution and correlation is truncated in the time domain. Free-surface and internal multiple reflections are removed and the two-way transmission effects in the primary reflections are compensated for in one step. The output of this scheme is a data set that contains only transmission compensated primary reflections. The obtained data set can be used as input to retrieve an artefact-free image of the medium. We illustrate the method with a two-dimensional example that shows how free-surface and internal multiple reflections are removed and transmission loss in primary reflections are compensated for. The method can have a wide range of applications in 3D strongly scattering media that are accessible from one side only.

Uncertain Analysis of a Stationary Solar Compound Parabolic Concentrator PV Collector System Using Fuzzy Set Theory

The uncertain analysis of fixed solar compound parabolic concentrator (CPC) collector system is investigated for use in combination with solar PV cells. Within solar CPC PV collector systems, any radiation within the collector acceptance angle enters through the aperture and finds its way to the absorber surface by multiple internal reflections. It is essential that the design of any solar collector aims to maximize PV performance since this will elicit a higher collection of solar radiation. In order to analyze uncertainty of the solar CPC collector system in the optimization problem formulation, three objectives are outlined. Seasonal demands are considered for maximizing two of these objectives, the annual average incident solar energy and the lowest month incident solar energy during winter; the lowest cost of the CPC collector system is approached as a third objective. This study investigates uncertain analysis of a solar CPC PV collector system using fuzzy set theory. The fuzzy analysis methodology is suitable for ambiguous problems to predict variations. Uncertain parameters are treated as random variables or uncertain inputs to predict performance. The fuzzy membership functions are used for modeling uncertain or imprecise design parameters of a solar PV collector system. Triangular membership functions are used to represent the uncertain parameters as fuzzy quantities. A fuzzy set analysis methodology is used for analyzing the three objective constrained optimization problems.

Marchenko scheme based internal multiple reflection elimination in acoustic wavefield

Marchenko imaging is a methodology to image the subsurface with two important properties: (1)accurate amplitude and (2)free from free-surface and internal multiple artefacts. It requires an estimate of the first arrival of the focusing function which is commonly obtained from a macro velocity model. Inspired by this limitation, a projected Marchenko scheme has been introduced from which an internal multiple reflection elimination scheme has been derived. This internal multiple reflection elimination scheme requires an estimate of the two-way travel time surface of a selected horizon in the subsurface instead of a macro model. In order to make it totally model free we have rewritten the scheme by replacing the estimate of the two-way travel time surface by a fixed truncation for all traces. The output of the current scheme contains primary reflections without contamination from internal multiple reflections. We apply this scheme to a 2D numerical example to illustrate the procedure of this method and show how the internal multiple reflection eliminated data set can be retrieved and the migration image is improved.

Frequency domain scanning acoustic microscopy for power electronics: Physics-based feature identification and selectivity

In the evaluation of power electronic components non-destructive test methods (NDT) such as scanning acoustic microscopy (SAM) are valuable tools in packaging and failure analysis. As power modules become more compact and power devices thinner, echo overlap and interference can hamper the imaging capability and analysis of the conventional SAM time domain-based imaging techniques. Frequency domain analysis offers increased resolution and contrast but the interpretation and feature identification of waveforms is less obvious and interpretation guidelines have received little attention. In this paper a physics-based analysis of the frequency domain response is presented in a power module case study. The analysis is used to demonstrate physics-based feature selective contrast in such systems and offers guidelines for feature prediction. The approach is verified on full scan datasets from acoustic scans of a hybrid multilayer stack. Distinct features in the echo frequency domain are identified as resonances associated with multiple internal reflections in the layer structure. Where such features may hamper analysis in the conventional approach these can, if properly assigned, be exploited to yield selective and improved contrasts and allow accurate structural and material analysis.

Artifact-free reverse time migration

We have derived an improved reverse time migration (RTM) scheme to image the medium without artifacts arising from internal multiple reflections. This is based on a revised implementation of Marchenko redatuming using a new time-truncation operator. Because of the new truncation operator, we can use the time-reversed version of the standard wavefield-extrapolation operator as initial estimate for retrieving the upgoing focusing function. Then, the retrieved upgoing focusing function can be used to directly image the medium by correlating it with the standard wavefield-extrapolation operator. This imaging scheme can be seen as an artifact-free RTM scheme with two terms. The first term gives the conventional RTM image with the wrong amplitude and artifacts due to internal multiple reflections. The second term gives a correction image that can be used to correct the amplitude and remove artifacts in the image generated by the first term. We evaluated the success of the method with a 2D numerical example.

Note: Elastic wave velocity measurement using ultrasonic system with two-reflectors

We report an experiment protocol for ultrasonic velocity measurements carried out in a synchrotron-based multi-anvil high-pressure apparatus. By adding a second reflector in the cell assembly, ultrasonic signals are significantly stabilized for experiments where samples experience structural changes such as phase transition or partial melting. Features of the elastic wave can be calculated from acoustic impedance allowing us to evaluate the possible interference between the sample reflection and other internal multiple reflections. This new protocol allows various forms of samples including cold-pressed powder samples, for which grain size and porosity can be monitored and controlled in situ during the annealing process.

Microwave absorption properties of single- and double-layer coatings based on strontium hexaferrite and graphite nanocomposite

The microwave absorption properties of single- and double-layer doped strontium hexaferrite (SrCoZnFe16O27) and graphite nanocomposite were investigated. W-type SrCoZnFe16O27 nanoparticles was prepared via solid state reaction using high energy ball milling and sintered at different sintering temperatures. Microwave absorption properties of single- and double-layer structures of different thicknesses were investigated in the frequency range of 8–18 GHz using a network analyzer, and their behavior analyzed based on electromagnetic transmission line theory. The results show that double-layer absorbing material showed better microwave absorption properties than single-layer. Double-layer absorbing material which consisted of graphite as the matching layer and SrCoZnFe16O27 as the absorbing layer demonstrated higher reflection loss values of − 19.5 dB when both layers were 1 mm thick. The bandwidth corresponding to the reflection loss below − 10 dB (i.e. 90% absorption) was 3.8 GHz (11.0–14.8 GHz). The excellent microwave absorption properties of double-layer structures were influenced by good impedance match, multiple internal reflections and coupling interactions between the matching and absorbing layers.

Omnidirectional Reflector based on Transparent Oxide Materials for Light Extraction Enhancement of Organic and Inorganic Solid-state Light Emitting Devices

High performance reflector is significant structure for efficiency improvement of organic and inorganic solid-state light emitting devices because a large difference in the refractive index between the light source and air leads to multiple internal reflections at the reflector. Then we focused on wide angular light incidence and designed a total internal omnidirectional reflector (TI-ODR) based on transparent oxide layers. The simulation results showed that light extraction structure with TI-ODR gives 17% and 4% efficiency enhancement compared to typical Ag based mirror for organic LED (n=1.8) and inorganic LED (n=2.4), respectively. Then the TI-ODR on blue LED structure was fabricated and that showed enhancement effect of about 8%. The layers are composed of conductive layer for current distribution, low-index thick layer for total internal reflection (TIR) of wide angular light, and high-index layer for the reinforcement of adhesion of layers.