Transmittance Band Gap Research Articles

Transmission and Reflection Properties of Iron Pyrite-Epoxy Resin Composite for Electromagnetic Applications.

This study examines the electromagnetic properties of a composite material composed of iron pyrite (FeS2) and epoxy resin, mixed in a 3:2 weight ratio to create a 10 cm3 cube. The research analyzes transmission and reflection coefficients and band gap parameters to determine its viability as an antenna substrate for electromagnetic wave applications. The composite displays a tunable band gap of 1.3 eV, enabling selective absorption and emission of electromagnetic radiation. The transmission coefficient achieved 90% throughout a frequency range of 1 GHz to 15 GHz, whilst the reflection coefficient was measured at 10%, significantly reducing reflecting losses. The epoxy resin binder was essential for preserving structural integrity and augmenting the dielectric characteristics of the composite, thereby raising transmission efficiency. UV-Vis spectroscopy showed an absorption value of 0.875% at the band gap, indicating efficient interaction with UV energy. The S21 transmission coefficient ranged from -10 dB to -80 dB, with a maximum of -40 dB at 6 GHz, indicating strong energy transfer capability for antenna applications. The S21 values exhibited negligible signal attenuation between 2 GHz and 7 GHz, indicating the material's exceptional suitability for antenna substrates necessitating dependable transmission. The S11 reflection coefficient varied from -5 dB to -55 dB, with substantial decreases between 4 GHz and 14 GHz, when reflection decreased to -45 dB, signifying little signal reflection at essential frequencies. The results underscore the composite's appropriateness for applications requiring high transmission efficiency, little reflection, and effective engagement with electromagnetic waves, especially as an antenna substrate. Measurements were performed using a vector network analyzer (VNA) to obtain the S11 and S21 characteristics, underscoring the material's potential in sophisticated electromagnetic applications.

Selective dynamic band gap tuning in metamaterials using graded photoresponsive resonator arrays.

The introduction of metamaterials has provided new possibilities to manipulate the propagation of waves in different fields of physics, ranging from electromagnetism to acoustics. However, despite the variety of configurations proposed so far, most solutions lack dynamic tunability, i.e. their functionality cannot be altered post-fabrication. Our work overcomes this limitation by employing a photo-responsive polymer to fabricate a simple metamaterial structure and enable tuning of its elastic properties using visible light. The structure of the metamaterial consists of graded resonators in the form of an array of pillars, each giving rise to different resonances and transmission band gaps. Selective laser illumination can then tune the resonances and their frequencies individually or collectively, thus yielding many degrees of freedom in the tunability of the filtered or transmitted wave frequencies, similar to playing a keyboard, where illuminating each pillar corresponds to playing a different note. This concept can be used to realize low-power active devices for elastic wave control, including beam splitters, switches and filters.This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 2)'.

Studies on the physico-chemical properties of semi-organic nonlinear optical (NLO) material: 2-CPPC [2-CNPyH][ClO4]

Semi-organic NLO single crystals 2-cyanopyridinium perchlorate (2-CPPC) were successfully grown by the method of slow evaporation of solvent at room temperature (27 °C) by using acetone as a solvent and of dimension 15×12×3mm3. The powder X-ray diffraction (XRD) of the grown crystal has been investigated. The UV–vis study estimates the transmission range, refractive index, extinction coefficient, band gap, and reflectance of the grown 2-CPPC crystal. The fluorescence spectra of the grown crystal were also recorded. The presence of different functional groups and the vibrational modes were confirmed by using FTIR analysis. The crystal's mechanical properties were studied by a Vickers microhardness tester. Single beam Z-scan technique using He–Ne laser is used to study the third-order NLO properties.

Bandgap tunability and impact mitigation enhancement of hybrid graded origami-inspired metamaterials with multiple resonators

Origami structure has become an important design source of metamaterials because of its extremely rich form and infinite design space. In order to improve the wave attenuation and impact mitigation ability of origami structure, a hybrid graded origami-inspired metamaterials with multiple resonators is proposed. The bandgap characteristics, transmission spectrum and impact resistance of the proposed metamaterials are analyzed in detail by numerical simulation. The results show that multiple local resonance mechanisms can open two new bandgaps compared to the single local resonance case, and the bandgap boundary is very sensitive to the dimension of resonance units. In particular, the resonance peaks of the origami metamaterials are substantially weakened due to the presence of dimensional gradients, which allows multiple bandgaps to merge into an ultra-wide bandgap (bandwidth up to 8.9 kHz), about five times than the original bandwidth. According to the time domain and frequency domain analysis results, it can be found that the amplitude of reaction force is significantly reduced in the bandgap range, and the ultra-wide frequency domain (2.9–10 kHz) with sustainable-low peak appears. Moreover, the asymmetry and graded design of unit-cell also affects the ability of dissipate and attenuate wave energy and delay the wave transmission time. In addition, the local-resonant origami metamaterials are fabricated by 3D printing technology, and the experimental results are in good agreement with the numerical simulation results. This study is expected to provide valuable ideas in crashworthiness design and impact wave protection of important equipments.

Experimental and theoretical studies on cobalt ruthenium phosphate structure optimization towards supercapacitor application

Recent studies have given indications that nanoarchitectured binary transition metal phosphates can act as potential supercapacitor (SC) electrode materials due to their exceptional energy storage capacity and remarkable electrochemical stability. However, the highly amorphous nature or broad X-ray diffraction peaks of metal phosphates put a limit on the structural optimization of these materials. We demonstrate a combined experimental and theoretical study leading to an optimized cobalt-ruthenium phosphate (CRP) structure for high-performance SC application. The material structure was optimized by detailed density functional theory (DFT) calculations, including the Bader charge analysis, DOS, and PDOS, revealed the lattice and volume expansion, reduced band gap, and improved conductivity of the cobalt phosphate lattice by including ruthenium in the cobalt phosphate. These predictions are verified with experimental band gap and high-resolution transmission electron microscope plane image indexing. Further, the CRP was developed by potentiostatic deposition onto the carbon cloth substrate. The flexible CRP electrode exhibited a high specific capacitance of 1258 F g−1 (943.5C g−1) in the aqueous 2 M KOH electrolyte. The asymmetric SC device (CRP//activated carbon) has exhibited an excellent specific energy of ∼59 Wh kg−1 at a specific power of ∼751 W kg−1.

Degradation of rhodamine B dye under visible and solar light on zinc oxide and nickel-doped zinc oxide thin films

The kinetic investigation of rhodamine B dye's photocatalytic degradation, chosen as a model pollutant, was conducted at room temperature using Zinc oxide (ZnO) and nickel-doped zinc oxide (Zn0.97Ni0.03O) photocatalysts synthesized through the spray pyrolysis method. XRD analysis confirmed the formation of hexagonal ZnO and Zn0.97Ni0.03O films, with crystallite sizes ranging from 19 to 29 nm and varying in mean average grain size from 72 nm to 88 nm. The surface morphology of the Ni-doped ZnO films was influenced by nickel doping, observed through SEM and TEM micrographs, revealing a dense structure of spherical-shaped crystals. Light transmission and optical band gap energy of the films ranged between specified values, ranging from 3.27 to 3.24 eV. The degradation process was assessed under various conditions, including different light sources (UV lamp and solar irradiation), pH levels, and substrate concentrations. Degradation followed a pseudo-first-order kinetic model, with rate constants (k) and half-life times (t1/2) calculated accordingly. The degradation efficiency of undoped ZnO and ZnO doped with nickel decreased with increasing concentration under UV irradiation from (0.1–0.5 M) under UV irradiation decreased from (34.29–45.02) (49.61–56.61), while under visible light are (40–45.07 %) (58.46–60.24 %), removal rates ranged within specific percentages. The porous Zn0.97Ni0.03O synthesized at 0.5 M exhibited the highest photocatalytic efficiency due to its enhanced crystallinity, resulting in degradation rates of 9.22 and 11.22 × 10−3 min−1 and half-life times of 75.18 and 61.77 min at 90 min specified for both UV and solar light irradiations, respectively. Acidification of the reaction medium accelerated the photocatalytic degradation kinetics, while alkalization slowed it down. These findings mark a significant advancement in the utilization of oxide semiconductors for water pollutant degradation under natural sunlight.

Band gap characteristics of bionic acoustic metamaterials based on spider web

For the purpose of low-frequency vibration isolation and noise reduction, combined with the nested mode of spider web, a new concave star bionic acoustic metamaterial was proposed in this paper. Based on the finite element method (FEM) and Bloch theory, the effects of vertex connection mode, nesting level (n), and rotation angle (α) on the band gap distribution, transmission spectrum, and isofrequency line of concave star structure were discussed. The results showed that the two-dimensional (2D) concave star structure had the lowest opening frequency of the first band gap when the vertices coincide and n = 3; when α = 45°, the three-dimensional (3D) concave star structure had the widest band gap distribution and the lowest first band gap in the frequency range within 1000 Hz. The correctness of the simulation results was verified by experiments. These findings can provide a new idea for low-frequency vibration isolation and noise reduction.

Low-Frequency Bandgap Characterization of a Locally Resonant Pentagonal Phononic Crystal Beam Structure.

This paper proposes a local resonance-type pentagonal phononic crystal beam structure for practical engineering applications to achieve better vibration and noise reduction. The energy band, transmission curve, and displacement field corresponding to the vibration modes of the structure are calculated based on the finite element method and Bloch-Floquet theorem. Furthermore, an analysis is conducted to understand the mechanism behind the generation of bandgaps. The numerical analysis indicates that the pentagonal unit oscillator creates a low-frequency bandgap between 60-70 Hz and 107-130 Hz. Additionally, the pentagonal phononic crystal double-layer beam structure exhibits excellent vibration damping, whereas the single-layer beam has poor vibration damping. The article comparatively analyzes the effects of different parameters on the bandgap range and transmission loss of a pentagonal phononic crystal beam. For instance, increasing the thickness of the lead layer leads to an increase in the width of the bandgap. Similarly, increasing the thickness of the rubber layer, intermediate plate, and total thickness of the phononic crystals results in a bandgap at lower frequencies. By adjusting the parameters, the beam can be optimized for practical engineering purposes.

A New Miniaturized Double Stop-band Frequency Selective Surface

A miniaturized double stop-band FSS for WLAN was proposed based on the structure of a ring patch with internal branches and a cross zigzag loaded line. This construction is obtained by using the multilayer connection method to paint the two layers of the patch that we designed on the top and bottom of the dielectric substrate to simulate the designed construction by using HFSS simulation. Analyzing the frequency response characteristics of the FSS indicates that the construction can generate two transmission band gaps at 1.92-2.17 GHz and 4.94-5.99 GHz in the WLAN wave. This construction has stronger polarization stability and angle stability when the incident electromagnetic wave is 0-60∘. It also has a simple construction, small size, and significant engineering applicationvalue.

Tailoring structure and nanoscale surface topography in Mg–N doped CuCrO[formula omitted] thin films via post deposition annealing for optothermoelectric application

In this study, we explored how varying the annealing temperature and the duration of post-annealing affect the structural, optical, and thermoelectric characteristics of thin films doped with Mg–N in CuCrO2. As the annealing time increased, we observed that all the annealed films exhibited enhanced conductivity at room temperature. Additionally, both the power factor and Seebeck coefficient also exhibited increases. The quantitative assessment of the nanometric dimensional surface roughness and the surface nano-texture of the deposited film was done by atomic force microscopy analysis. The spiky peaks and positive roughness skewness (Rsk) value made the two-hour annealed film suitable for energy harvesting. Wide band gap and high transmission of more than 60% were found by UV–Vis spectroscopic analysis and Fermi energy of 7 meV is calculated and determined the possibility of the film from being used in ohmic contact with delafossite to prevent Schottky barriers and track the work function of the material.

Topological Edge States on Different Domain Walls of Two Opposed Helical Waveguide Arrays

Floquet topological insulators (FTIs) have richer topological properties than static systems. In this work, we designed different domain wall (DW) structures consisting of a Floquet photonic lattice with opposite helical directions. We investigated the existence and types of edge states in three shared coupling structures and the impact of these shared coupling structures on edge states. When two opposite helical lattices share a straight waveguide array coupling, the edge states are localized on the straight waveguide. When two opposite helical lattices share a clockwise (or anticlockwise) helical waveguide array coupling, the DWs consist of zigzag and bearded edges, but the positions of the zigzag and bearded edges of the shared clockwise waveguide array are different from those of the shared anticlockwise waveguide array. The slope and transmission rate of the edge states both vary with the degree of coupling between the shared waveguides. The characteristics of these edge states, such as transmission speed and band gap width, are also affected by the incidence angle, modulation phase factor, and helical radii, and the methods for controlling the edge states in different shared coupling structures are provided. This will help deepen our understanding of how topological structures influence the electronic and photonic properties of materials. This could also lead to combining topology with metasurface-based structured light, which would highlight many novel properties with great application potential for various fields, such as imaging, metrology, communication, quantum information processing, and light–matter interaction.

Tunable bandstop filtering specialities in superconducting Thue–Morse photonic multilayers

We theoretically investigate wide and tunable bandstop filters based on one-dimensional superconducting photonic multilayers. These multilayers are composed of superconductors (Nb) and semiconductors (GaAs), arranged in accordance with the Thue–Morse sequence. The wide transmission bandgap of the multilayers can be utilized as a bandstop filter, with greater accuracy achieved by larger sequence number and thinner semiconductor. Our results demonstrate that both the bandwidth and center frequency decrease as the ambient temperature and semiconductor thickness increase. Especially, the stopband disappears when the temperature exceeds the critical temperature (Tc) of Nb. On the other hand, increasing hydrostatic pressure and superconductor thickness leads to monotonous increases in both the bandwidth and center frequency. Moreover, for thin superconductors or high temperatures close to Tc, the quality factor is high and tunable in a wide range. Our work presents a flexible solution for optical bandstop filters, which may also find potential applications in optical switching and modulating.

Nonlinear bandgap transmission with zero frequency in a cross-stitch lattice

We consider a model for a cross-stitch lattice with onsite nonlinearity. The linear analysis and the determination of the homoclinic threshold for this model are carried out theoretically. In the case of a self-focusing nonlinearity, we show that the traveling bandgap soliton is possible as a result from the periodic excitation of the edge of the chains. Contrary to the usual supratransmission phenomenon, the generation of traveling solitons is possible by driving the lattice with zero frequency and constant amplitude. In the case of defocusing nonlinearities, the heteroclinic orbit is obtained with the frequency within the phonon band. By exciting one component of complex waves, a traveling phonon kink is obtained. Meanwhile, in the case of the driving of two complex waves with zero phonon and nonzero phonon frequencies, respectively, the fly phonon breather is observed. The collision of the waves from the flat band and phonon band gives the traveling bright carry by the traveling kink. These results are obtained through computer simulations.

Integrated analysis of bandgap optimization regulation and wave propagation mechanism of hexagonal multi-ligament derived structures

In this paper, a new class of multi-ligament derived structures is proposed. Based on the finite element method and Bloch's theorem, the bandgap characteristics and transmission properties of different derived structures are comprehensively analyzed, and the bandgap opening and closing mechanism and the vibration and noise reduction capability of the structure are explained by stress cloud diagrams and vibration modes. Then, a better bandgap is obtained by structural optimization and active frequency modulation. Finally, the propagation characteristics of elastic waves in different derived structures are investigated separately. The results show that the multi-ligament derived structure has excellent bandgap performance and can obtain better vibration and noise reduction capability through bandgap adjustment and active strain modulation, which greatly improves its engineering practicality. The comprehensive analysis of wave propagation in this paper provides a theoretical basis and technical means for the improvement and design of metamaterials.

Fabrication and characterization of TiO2: ZnO thin films as electron transport material in perovskite solar cell (PSC)

In developing quicker, smaller, and more efficient optoelectronic devices, composite thin films are becoming progressively crucial. One reason for using composite thin films is to improve materials optical and electrical properties. Thermal Evaporation is a type of physical vapor deposition that can produce thin films with well-controlled nanostructures that are pure, homogeneous, and conformal. The prime focus of this study was to fabricate TiO2 and composite TiO2:ZnO thin films on ITO-coated glass substrates by thermal Evaporation. The goal of this study was to investigate the optical, structural, and electrical properties of deposited thin films. The optical properties were assessed using UV–Vis and Photoluminescence spectroscopy, and FTIR spectroscopy was used to identify the fingerprint of materials. The crystal structure of deposited thin films was investigated using X-ray diffraction. The changes in morphology induced by adding ZnO content to TiO2 were examined using optical microscopy. SEM investigation corroborated the granular-like structure of thin films, whereas EDX demonstrated the doping and composition of ZnO concentration in TiO2. The electrical measurements were performed using the Van der Pauw technique. Adding ZnO into TiO2 improved transmission, photoconductivity, and optical bandgap to generate a viable electron transport material (ETM) for efficient perovskite solar cells (PSC). XRD results revealed the grain size increase after adding ZnO into TiO2. The transmission was increased to 95%, while the bandgap was decreased from 3.8 eV to 3.68 eV. It was also revealed that after integrating ZnO into TiO2, the generated thin films have stronger visible photoluminescence peaks, and the material's conductivity has been improved. The results indicate that TiO2:ZnO could be employed as an ETM in PSC to improve productivity.

Effect of Annealing Temperature on Radio Frequency Sputtered p-Type Delafossite Copper Chromium Oxide (CuCrO2) Thin Films and Investigation of Diode Characteristics Forming Transparent pn-Heterojunction

For the first time, the deposition of CuCrO2 thin films was carried out using a dual-target RF magnetron sputtering technique using Cu2O and Cr2O3 targets. The deposited films were subsequently annealed in N2 ambiance from 600–900 °C. This work reports that the electrical, optical, structural, and morphological properties of CuCrO2 thin films are significantly affected due to the variation in the annealing temperature. XRD analysis confirms the presence of single-phase CuCrO2 in the films annealed at 650 °C. The presence of Cu in the 1+ oxidation state in the phase pure CuCrO2 thin films was confirmed through XPS analysis. Further, through XPS analysis, the oxidation states of Cu and Cr, the full-width half maximum (FWHM), the peak positions, and their respective binding energies have been elucidated. SEM analysis confirms the promotion of nanocrystalline growth in the thin films as the annealing temperature was increased from 600 °C. The average grain size increased from 40.22 nm to 105.31 nm as the annealing temperature was increased from 600 to 900 °C. Optical studies conducted in the wavelength range of 200 nm to 800 nm revealed a decrease in the optical transmission and optical bandgap with an increase in the annealing temperature. The highest optical transmission of ~81% and an optical bandgap of 3.21 eV were obtained for the films depicting the delafossite nature of CuCrO2. The optical bandgap was found to vary between 3.16 eV and 3.74 eV for the films studied in this research. The lowest resistivity of 0.652 Ω cm was obtained for the films annealed at 650 °C. Transparent heterojunction diodes involving p-type delafossite copper chromium oxide (CuCrO2) and n-type indium tin oxide (ITO) were fabricated. The best diode depicted a cut-in voltage of 0.85 V, a very low leakage current of 1.24 x 10-8, an ideality factor of 4.13, and a rectification ratio of 2375.

Low‐Frequency Vibration and Noise Reduction and Wave Propagation Properties of Hexagonal Hybrid Metamaterials with Local Resonance Strips

Based on the idea of local resonance, a class of hybrid acoustic metamaterials with interposed resonant strips is proposed in this article, and the bandgap characteristics and transmission properties are calculated by combining Bloch's theorem and lattice theory. The new structure is verified to have low‐frequency damping and noise reduction capability through the analysis of the stress cloud diagram at specific frequencies in the bandgap range. A comprehensive analysis of vibration modes, phase constant surfaces, group velocity, phase velocity, and wave propagation direction diagram is used to explore the wave propagation and bandgap opening mechanism, providing technical support and theoretical basis for subsequent bandgap optimization and structural improvement. The results show that this structure can open multiple bandgaps in the low‐frequency range below 500 Hz, and the stepped design of the single‐cell structure and the introduction of resonant strips provide a new design idea for low‐frequency vibration and noise reduction.

Novel meter-scale seismic metamaterial with low-frequency wide bandgap for Lamb waves

Seismic metamaterials (SMs) have attracted the attention of many researchers in the field of damping and elastic wave isolation because of their bandgap properties, i.e., attenuating elastic waves in the range of bandgaps. However, the dimension of these SMs often reaches the 10-meter scale, which impedes practical engineering application. To break through this bottleneck and achieve a smaller scale, a meter-scale novel SM composed of steel and rubber is proposed for attenuating ultra-low frequency seismic Lamb waves. Firstly, the finite element method is used to analyze the band structure of SMs and calculate the bandgaps. To explain the mechanism of bandgap, the vibration modes of the waves at the bandgap boundary frequency are further analyzed. Subsequently, the transmission spectrum of Lamb waves incidents on the finite SMs system is analyzed to prove the authenticity of the bandgaps. Finally, parameter analyses including the geometric variables, material properties, equivalent mass density, and structural matrix forms with identical equivalent mass density are investigated numerically. The results show that Lamb waves in the range of 0–20 Hz are significantly attenuated by SMs, and the aforementioned parameters are significant factors affecting the bandgap properties and transmission properties. The proposed SM has a smaller size while maintaining some wide bandgaps at 0–20 Hz for ultra-low frequencies. It is worth noting that the 2 Hz seismic peak spectrum causing the destruction of building structures is covered effectively.

Analytical dispersion curves and bandgap boundaries for quadrilateral lattices

The two-dimensional quadrilateral lattice structures are the most common periodic structures in industrial engineering application. This paper investigates the Bragg bandgap mechanism of classical quadrilateral periodic lattice structures. The explicit expressions of dispersion relations are obtained analytically and those with the eigenmodes corresponding to the same dispersion relation solution are connected to form the band structure. Unlike the existing works, it is the first to connect dispersion curves with the same eigenmodes, which explains the bandgap formation and transmission loss more reasonably. Four kinds of two-dimensional quadrilateral lattice structures are investigated to discuss the effects of shear force and mid-masses. The analytic expressions of bandgap boundaries are obtained and the influence of parameters including the mass ratio, tensile stiffness ratio and shear stiffness ratio on the bandgap boundaries is discussed.

Band gap transmission in a periodic network of coupled buckled beams

Wave propagation in a periodic network of coupled buckled beams, which represents a finite dissipative periodic structure with quadratic and cubic nonlinearities, is studied. The aforementioned structure is harmonically forced and parametrically excited at one end with forcing frequencies lying within its band gaps, one below and one above the pass band. Numerical simulations, supported by the analytical estimates using the method of multiple scales (MMS), show the occurrence of supratransmission which is a sudden increase in the energy transmitted across the finite structure due to a certain excitation amplitude. In essence, this nonlinear energy transmission across the discrete nonlinear periodic structure occurs due to the loss of stability of the periodic solutions which are initially localized to the driven end of the structure (nonlinear instability). Practical ways including damping ratio and coupling stiffness variations to alter the transmission threshold are assessed. In particular, it is found that the presence of parametric excitation can considerably lower the required threshold for the onset of energy transmission within the stop band. The presented results of this work may offer some insights to enhance the performance of acoustic and mechanical metamaterials.