Extremely-broad band metamaterial absorber for solar energy harvesting based on star shaped resonator

A new metamaterial absorber (MA) is investigated and shown numerically for solar energy harvesting for future solar cell applications. The structure consists of two metals and one dielectric layer having different thicknesses. Owing to this combination, the structure exhibits plasmonic resonance characteristics. In the entire spectrum of visible frequency region, the obtained results show that investigated structure has perfect absorptivity which is above 91.8%. Proposed structure also has 99.87% absorption at 613.94 THz and 99% absorption between 548 and 669 THz. The proposed structure also shows both polarization and angle independency for the entire visible region. The MA based solar cell proposes high absorption with an upper ratio of 90% in the widest range of visible spectrum comparing to the studies in literature. Hence, the proposed metamaterial absorber solar cells can be used for invisibility in entire spectrum of visible light. The absorption characteristics of the solar absorber are also investigated for infrared and ultraviolet region. The enhancement of absorption of the structure will provide new type of sensors in these frequency ranges.     

A spectral isoperimetric inequality for cones

In this note, we investigate three-dimensional Schrödinger operators with \(\delta \)-interactions supported on \(C^2\)-smooth cones, both finite and infinite. Our main results concern a Faber–Krahn-type inequality for the principal eigenvalue of these operators. The proofs rely on the Birman-Schwinger principle and on the fact that circles are unique minimizers for a class of energy functionals. The main novel idea consists in the way of constructing test functions for the Birman-Schwinger principle.     

Smart inverters with broadband light absorption enhancement of nanostructure plasmonic solar absorber using PSO algorithms and FDTD method

Optical Review - Solar plasmonics absorbers have received outstanding interest from nanotechnology. However, they have small efficiency. To overcome this challenge, we have used two ways in this...     

New criterion for optimization of solar selective absorber coatings

We discuss a merit function F as judgment of photo-thermal conversion efficiency instead of two indepen- dent parameters： solar absorptance α and thermal emittance ε. The merit function F is developed using Essential Macleod software to optimize the photo-thermal conversion efficiency of solar selective coating. Bruggeman and Maxwell-Garnett models are used to calculate the dielectric function of composite cermet film. Mo, W, V, and Pd are used as metallic component as well as infrared （IR） refector materials, and SiO2, A1203, A1N, and TiO2 are used for dielectric component or antireflection （AR） layer materials. The layer structure can be described as substrate （Sub）/IR reflector/ high-metal-volume fraction （HMVF）/ low-metal-volume fraction （LMVF）/AR. Results show that Mo-Al2O3, Mo-AlN, W-SiO2, W-A12O3, V- SiO2, and V-A1203 double-cermet coatings have high conversion efficiency which is greater than 86%. The best among above is Mo-SiO2 with α=0.94, e=0.05 at 450℃, f= 89.9%. Some selective coatings with different layer thicknesses have been successfully optimized for different solar irradiations （air mass （AM0）, AM1.5D, and AM1.5G spectra） and different operating temperatures （300, 450, and 600 ℃）, respectively. However, the optical constants for calculation are from the software, most datum are measured for bulk materials. Therefore. results are more useful to indicate the trend than the exact values.     

太赫兹频域的强双带特异材料吸收体(英文)

We report the design and simulation of a dual-band perfect terahertz absorber which is composed of an electric Split-Resonance-Ring(eSRR) layer, polyimide spacer and a metal plate layer. The absorber has two near-unity absorptions near 0.502 THz and 0.942 THz and both are related to the LC resonance of the eSRR. The results show that the designed terahertz absorber is an excellent electromagnetic wave concentrator. The electromagnetic waves are firstly converged into the spacer and the eSRR layer and are th...     

Engineering the electronic band structure for multiband solar cells

Using the unique features of the electronic band structure of GaN(x)As(1-x) alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the band anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.     

Optical communications in the mid-wave IR spectral band

The mid-wave IR (MWIR) spectral band extending from 3 to 5 microns is considered to be a low loss atmospheric window. The MWIR wavelengths are eye safe and are attractive for several free-space applications including remote sensing of chemical and biological species, hard target imaging, range finding, target illumination, and free-space communications. Due to the nature of light-matter interaction characteristics, MWIR wavelength based systems can provide unique advantages over other spectral bands for these applications. The MWIR wavelengths are found to effectively penetrate natural and anthropogenic obscurants. Consequently, MWIR systems offer increased range performance at reduced power levels. Free-space, line-of-sight optical communication links for terrestrial as well as space based platforms using MWIR wavelengths can be designed to operate under low visibility conditions. Combined with high-bandwidth, eye-safe, covert and jam proof features, a MWIR wavelength based optical communication link could play a vital role in hostile environments. A free-space optical communication link basically consists of a transmitter, a receiver and a scheme for directing the beam towards a target. Coherent radiation in the MWIR spectral band can be generated using various types of lasers and nonlinear optical devices. Traditional modulation techniques are applicable to these optical sources. Novel detector and other subcomponent technologies with enhanced characteristics for a MWIR based system are advancing. Depending on the transmitter beam characteristics, atmospheric conditions may adversely influence the beam propagation and thereby increasing the bit error rate. For satisfactory transmission over a given range, the influence of atmosphere on beam propagation has to be analyzed. In this chapter, salient features of atmospheric modeling required for wavelength selection and performance prediction is presented. Potential optical sources and detectors for building a practical MWIR communication link are surveyed. As an illustration, the design configuration and experimental results of a recently demonstrated free-space, obscurant penetrating optical data communication link suitable for battlefield applications is discussed. In this case, the MWIR wavelength was derived using an all solid-state, compact, optical parametric oscillator device. With this device, weapon codes pertaining to small and large weapon platforms were transmitted over a range of 5 km. Furthermore, image transmission through light fog, accomplished using this hardware, is also presented. Advances in source and detector technologies are contributing to the development of cost effective systems compatible with various platforms requirements. In coming years, MWIR wavelengths are anticipated to play a vital role in various human endeavors.     

Intermediate band insertion by group-IIIA elements alloying in a low cost solar cell absorber CuYSe2: A first-principles study

By using first-principles calculations based on HSE06 hybrid functional, the structural, electronic, and optical properties of CuYSe₂ as a low cost absorber material have been studied. Our results show that CuYSe₂ is a semiconductor with indirect band gap of 1.46 eV and optical band gap of 2.00 eV. Especially, an intermediate band has been found in Ga and In alloyed CuYSe₂, respectively, which can be served as a stepping stone to optical absorption on low energy photons. Therefore, Ga and In alloyed CuYSe₂ with an intermediate band as a new absorber material have been proposed.     

太赫兹波段电磁超材料吸波器折射率传感特性

太赫兹超材料吸波器作为一类重要的超材料功能器件,除了可以实现对入射太赫兹波的完美吸收外,还可以作为折射率传感器实现对周围环境信息变化的捕捉与监测.通常从优化表面金属谐振单元结构和改变介质层材料和形态两个方面出发,改善太赫兹超材料吸波器的传感特性.为深入研究中间介质层对太赫兹超材料吸波器传感特性的影响,本文基于金属开口谐...     

Optimization of concentric array resonators for wide band noise reduction

In air duct noise control, Helmholtz resonators (HR) are considered as narrow band attenuators. For some applications they can be combined in line to form a wide band silencer. This study investigates the role of distance between HR side branch openings on the whole array attenuation. In the case of two resonators with same performance, the optimal distance can be calculated and corresponds to the quarter wave of HR mean frequency. On three or more HR arrays, relationships between resonators parameters and optimal lengths are much more complex. Tuning of such a device requires taking many geometrically coupled parameters into account; hence, design has to be automated. To operate this process, a 2D FEM COMSOL model has been coupled to a global MATLAB optimization solver. Among different types of constructions, arrays made of concentric resonators with transversal openings offers the most efficient and flexible design to optimize distance between openings. This methodology was applied to an existing turbo compressor silencer. Modifying openings and chambers arrangement, using the proposed approach increased the attenuation band by 10%. Another application concerning an air box for a two stroke engine was also investigated. This resulted in a 16L two chambers concept, being replaced by a more compact and more efficient, 8.3L wide band silencer, made of 8 resonators. With this approach it therefore becomes possible to handle available space and required noise attenuation on a required frequency band, all in one process.     

Measurement setup for differential spectral responsivity of solar cells

Optical Review - We have developed a setup for measuring differential spectral responsivities of unifacial and bifacial solar cells under bias light conditions. The setup uses 30 high-brightness...     

光电列阵元件光谱响应的整体测试法

本文针对列阵元件的特点,提出了对其光谱响应进行整体测试的方法。实测结果与误差分析计算表明,整体测试法是一种准确稳定和易行的方法。     

ALIS: An efficient method to compute high spectral resolution polarized solar radiances using the Monte Carlo approach

An efficient method to compute accurate polarized solar radiance spectra using the (3D) Monte Carlo model MYSTIC has been developed. Such high resolution spectra are measured by various satellite instruments for remote sensing of atmospheric trace gases. ALIS (Absorption Lines Importance Sampling) allows the calculation of spectra by tracing photons at only one wavelength. In order to take into account the spectral dependence of the absorption coefficient a spectral absorption weight is calculated for each photon path. At each scattering event the local estimate method is combined with an importance sampling method to take into account the spectral dependence of the scattering coefficient. Since each wavelength grid point is computed based on the same set of random photon paths, the statistical error is almost same for all wavelengths and hence the simulated spectrum is not noisy. The statistical error mainly results in a small relative deviation which is independent of wavelength and can be neglected for those remote sensing applications, where differential absorption features are of interest.Two example applications are presented: The simulation of shortwave-infrared polarized spectra as measured by GOSAT from which CO₂ is retrieved, and the simulation of the differential optical thickness in the visible spectral range which is derived from SCIAMACHY measurements to retrieve NO₂. The computational speed of ALIS (for 1D or 3D atmospheres) is of the order of or even faster than that of one-dimensional discrete ordinate methods, in particular when polarization is considered.     

Evolution of the spectral parameters of quasiparticles in an open symmetrical three-barrier resonant tunneling nanostructure

The spectral parameters (resonance energies and resonance widths) of quasi-stationary states in an open symmetrical three-barrier resonant tunneling nanostructure have been theoretically calculated in terms of the model of spatially dependent effective masses and rectangular potentials of quasiparticles (electrons, holes, excitons) by using the methods of transmission coefficient, scattering matrix, and probability distribution function. The evolution of the spectral parameters of quasi-stationary states of quasiparticles as a function of the variation in the geometric sizes of the nanosystem has been calculated and analyzed for the open three-barrier resonant tunneling structure consisting of three barriers (GaAs) and two wells (In_0.25Ga_0.75As) as an example. It has been established that the experimental and theoretical results are in satisfactory agreement for the model without fitting parameters in the case of a heavy exciton.     

Polarization sensitivity contributes to multiple band spectra of one mid-infrared absorber

The emerging perfect-absorber metamaterials （PAMs） provide an alternative material approach for the next generation of electromagnetic detection at any frequency band of interest. One type of dual cross-shaped PAMs is developed to obtain multiplex-band spectrum absorption at mid-infrared region. Three distinct absorption peaks are attributed to the polarization sensitivity excitation of the plasmonic resonance. The charge density distributions, which are excited by resonant electromagnetic waves passing through the PAMs medium, provide insights into the observed absorption behavior. We find that the retrieved optical properties of the PAMs including permittivity and permeability are still consistent with the sum of the Drude and Lorentz type models at wavelengths ranging from 2.0 to 10.0μm. Such multiplex-band absorption properties enable the proposed PAMs a powerful tool for the direct detection of multiple molecular vibrational structures, and for multiple spectra infrared detection.     

Effects of controlled surface treatment on titanium dioxide electrode nanostructure for dye-sensitized solar cells

A stable surface treatment for the nanoporous TiO₂ electrode of dye-sensitized solar cells (DSCs) has been developed via sol-gel processing of titanium(IV) isopropoxide (TiP), enabling controllable performance improvements, which has been hitherto unachievable. A systematic study of the electrode chemistry and morphology was performed to examine the mechanisms by which the treatment contributes to enhancement in DSC performance. The electrode exhibited a linear increase in mass with TiP concentration and a corresponding reduction in porosity. The increase in nanoparticle diameter resulted in the increase in surface area without altering the surface chemistry, leading to an increase in dye loading. Current–voltage characteristics and incident photon-to-electron conversion efficiencies (IPCE) were analyzed. A linear increase in the short-circuit photocurrent was measured with TiP concentration, increasing by 30 % for a 4 mM TiP treatment, which resulted in a corresponding efficiency gain of 23 %. This was found to primarily result from a controllable increase in the charge collection efficiency, via a 30 % faster electron transport time and a 19 % increase in the electron lifetime. The results elucidate the underlying physical mechanisms for improvement in DSC performance by surface treatment.     

Non-LTE spectral absorption coefficients for electronic band systems of diatomic molecules

Analytical expressions have been derived for the average non-LTE spectral absorption coefficients and the associated spontaneous spectral emission coefficients for electronic bands of anharmonic oscillators. Relatively simple differential expressions are provided for the important practical conditions under which the smeared-rotational-line approximation is applicable and for which individual rotational temperatures exist for the populations in each pair of the vibrational levels of interest. Further simplifications are given for the cases in which also vibrational temperatures exist for the populations of the two electronic states considered and in which the displacement of the band-heads from the band-centers can be neglected.