Tunable broadband absorber based on a layered resonant structure with a Dirac semimetal

A perfect ultra-wideband solar absorber with a multilayer stacked structure of Ti-SiO2-GaAs: structure and outstanding characteristics

In this paper, we introduce an entirely new solar absorber design-a multi-layer periodic stacked structure. Through coupling effects, this design has perfect ultra-wideband absorption characteristics. The absorber structure is composed of four absorption units with varying cycle lengths, which are cyclically stacked on the surface of the refractory metal Cr. Each cycle encompasses three-layer nanosheets of Ti-SiO2-GaAs. We verify through finite difference time domain method (FDTD) simulations that the absorber achieves an absorption efficiency of 97.8% within the wavelength range of 280 nm to 3000 nm, with an average efficiency of 96.6% under the AM1.5 standard solar spectrum. The absorber can achieve such a remarkable absorption effect because of surface plasmon resonance (SPR) and Fabry-Pérot resonance effects. At 1500 K, this structure exhibits a thermal radiation efficiency of up to 97.83%. Furthermore, the design is not affected by polarization and it is less affected by the incident angle of the light source. These absorption spectra remain consistent regardless of whether it is in the TE or TM mode. Even when the angle of incidence is increased to 60 degrees, the absorption efficiency remains high. Its unique structure and excellent performance characteristics provide higher solar energy efficiency. These outstanding features enable solar absorbers to have broad application potential in improving solar energy efficiency.

Theoretical research on a broadband terahertz absorber for thermally controlled radiation emission based on the epsilon-near-zero mode

In this paper, a tunable and ultra-broadband terahertz (THz) absorber is proposed. The absorber, which is built upon the conventional metal-dielectric-metal tri-layer configuration, incorporates a KCl thin film within the dielectric gap situated between the top resonator and the middle dielectric layer. The simulation indicates that the absorber effectively captures more than 90% of terahertz waves between 3.6 and 7.3 THz, achieving absorption of over 99% within the 5.8-6.9 THz range. This unique broadband absorber is enabled by the interaction of plasmon and epsilon-near-zero (ENZ) modes. Additionally, due to the utilization of VO2 in the top resonator, the designed absorber holds potential to function as a thermally controlled radiation emitter, exhibiting a high emissivity of 90.5% at high temperatures while maintaining a low emissivity of 8.2% at low temperatures. The absorber is uncomplicated and adjustable, offering great potential for use in thermal management, terahertz camouflage, and engineering insulation.

A Polarization-Insensitive and Highly Sensitive THz Metamaterial Multi-Band Perfect Absorber

In this article, we present a terahertz (THz) metamaterial absorber that blends two types of coordinated materials: Dirac semimetals and vanadium dioxide. Compared to other absorbers on the market, which are currently non-adjustable or have a single adjustment method, our absorber is superior because it has two coordinated modes with maximum adjustment ranges of 80.7% and 0.288 THz. The device contains four flawless absorption peaks (M1, M2, M3, and M4) spanning the frequency range of 2.0 THz to 6.0 THz, all with absorption rates greater than 99%. After calculation, the relative impedance of the device matches with that in free space, resulting in perfect absorption. In addition, our absorber has extremely excellent polarization insensitivity but is highly sensitive to changes in the environmental refractive index, with the highest environmental refractive index sensitivity of 716 GHz/RIU (gigahertz per refractive index unit). To sum up, the terahertz metamaterial absorber we showed has four perfect absorption peaks, high sensitivity, and stable polarization. This means it could be useful in areas like changing electromagnetic waves, making new sensors, and switching.

Three peak metamaterial broadband absorbing materials based on ZnSe-Cr-InAs stacked disk arrays

Metamaterial absorbers show great potential in many scientific and technological applications by virtue of their sub-wavelength and easy-to-adjust structure, with bandwidth as an important standard to measure the performance of the absorbers. In this study, our team designed a new broadband absorber, which consists of an indium arsenide (InAs) disk at the top, a zinc selenide (ZnSe)-chromium (Cr) stacked disk in the middle and a metal film at the bottom. Simulation results show that the absorber has remarkable absorptivity properties in the mid-long infrared band. In a wavelength range of 5.71-16.01 μm, the average absorptivity is higher than 90%. In the band of 5.86-15.49 μm, the absorptivity is higher than 95%. By simulating the electromagnetic field diagram at each resonant frequency, the reason for high broadband absorptivity is obtained. We also constructed Poynting vector diagrams to further elucidate this phenomenon. Next, we analyzed the influence of different materials and structural parameters on absorptivity properties and tested spectral response at different polarization angles and oblique incidence of the light source in the TM and TE modes. When the source is normally incident, the absorber shows polarization insensitivity. When the angle is 40°, absorptivity is still high, indicating that the absorber also possesses angle insensitivity. The broadband absorber proposed by us has good prospects in infrared detection and thermal radiators.

Temperature-tunable terahertz metamaterial device based on VO2 phase transition principle

Terahertz devices play an irreplaceable role in the development of terahertz technology. However, at present, it is difficult for most natural materials to respond in the terahertz band, making the devices made of them perform poorly. In order to realize the diversity and tunability of device functions, we designed a terahertz metamaterial device composed of the thermally-induced phase change material VO2. The device structure is composed of a Au bottom layer, a SiO2 dielectric layer and a VO2 top layer. Through software simulation, we found that when T = 313 K, the device has complete reflection ability in the whole terahertz band. When T = 342 K, the average absorptivity is above 95% in the ultra-wide band range of 4.71-9.41 THz, and the absorptivity reaches an amazing 0.99999 at 6.31 THz. Thus, the maximum thermal modulation range of the device is 0.001-0.99999. The Bruggeman effective medium theory clarifies the phase transition characteristics of vanadium dioxide. The Drude model establishes the functional relationship between the conductivity of vanadium dioxide and temperature. The basic principle of high absorption was described using the impedance matching theory. We also drew the electric field intensity diagram during the temperature rise of the device to further confirm the reason for the change in the device performance. In addition, the influence of the absence of different structural layers on the absorptivity was simulated, which reflected the role of each layer structure more intuitively. We also explored the influence of the geometric size of the device on the absorptivity, which provided a certain reference value for practical application. In short, we have designed a tunable terahertz device with simple structure, high absorptivity, and wide absorption bandwidth, which can be used in the fields of energy collection, electromagnetic stealth, and modulation.

Design and performance study of a multiband metamaterial tunable thermal switching absorption device based on AlCuFe and VO2

In this paper, we propose a multiband adjustable metamaterial absorption device based on a Dirac semimetal (BDS) AlCuFe and a thermally controlled phase-change material VO2. The absorption device has an axially symmetric structure, resulting in polarization-independent characteristics, and when VO2 is in a high-temperature metal state, ultra-high absorption rates and sensitives at frequencies of M1 = 2.89 THz, M2 = 7.53 THz, M3 = 7.97 THz, and M4 = 9.02 THz are achieved. Using a parameter inversion method, we calculated the impedance of the absorber, proving that it achieves impedance matching and produces perfect absorption in the resonance region. Additionally, we changed the physical and chemical parameters of the absorption device, demonstrating the device's excellent tunability and manufacturing tolerance. Furthermore, by lowering the temperature of VO2 to that of a low dielectric state, additional resonant peaks with ultra-high absorption rates at frequencies M5 = 5.62 THz, M6 = 7.16 THz, M7 = 7.64 THz, and M8 = 8.80 THz were obtained, broadening the absorption band of the device. Lastly, we investigated the detection sensitivity of the device by changing the external refractive index, resulting in a maximum sensitivity of 2229 GHz RIU-1. To sum up, the absorption device has great application potential in the fields of communication, sensing, temperature detection and photoelectric instruments.

Multilayer stacked ultra-wideband perfect solar absorber and thermal emitter based on SiO2-InAs-TiN nanofilm structure

In this paper, a broadband solar absorber is constructed and simulated based on the finite difference time domain method (FDTD). The modeled structure of the absorber consists of cyclic stacking of five absorber cells with different periods on refractory metal W, where a single absorber cell is composed of a three-layer SiO2-InAs-TiN square film. Due to the Fabry-Perot resonance and the surface plasmon resonance (SPR), an absorptivity greater than 90% within a bandwidth of 2599.5 nm was achieved for the absorber. Notably, one of these bands, 2001 nm, is a high-efficiency absorption with an absorption rate greater than 99%. The average absorption efficiency reaches 99.31% at an air mass of 1.5 (AM 1.5), and the thermal radiation efficiencies are 97.35% and 97.83% at 1000 K and 1200 K, respectively. At the same time, the structure of the absorber is also polarization-independent, and when the solar incidence angle is increased to 60°, it still achieves an average absorption of 90.83% over the entire wavelength band (280 nm to 3000 nm). The novelty of our work is to provide a design idea based on a unit structure with multiple cycles, which can effectively expand the absorption bandwidth of the absorber in the visible-near-infrared wavelengths. The excellent performances make the structure widely used in the field of solar energy absorption.

Tunable bandwidth terahertz perfect absorption device based on vanadium dioxide phase transition control

Utilizing the phase transition principle of VO2, this paper presents a tunable ultra-wideband terahertz perfect absorption device with simple structure and tunability. The proposed broadband terahertz perfect absorption device is a three-layer structure with a metal reflective layer, a silicon dioxide dielectric layer and a VO2 layer from bottom to top. It was found that the terahertz perfect absorption device's absorption could be dynamically adjusted from 1.2% to 99.9% when changing from an insulated to a metallic state. With the VO2 in the metallic state, the terahertz perfect absorption device has an absorption efficiency of more than 90% in 4.00 to 10.08 THz's ultra-broadband range and near-perfect absorption is achieved in the ranges of 4.71 THz to 5.16 THz and 7.74 THz to 8.06 THz. To explain the working principle of this terahertz perfect absorption device, this paper utilizes wave interference's principle, theory of impedance matching and electric field analysis. Compared to previously reported terahertz metamaterial devices, the vanadium dioxide device proposed in this paper is significantly optimized in terms of tunable range and absorption bandwidth. In addition, the terahertz perfect absorption device is polarization insensitive and maintains good absorptivity over a wide-angle incidence range. This tunable ultra-wideband terahertz perfect absorption device could have applications in the fields of modulation, stealth devices, and thermal emission devices.

Design and performance analysis of a mid-infrared broadband thermally tunable metamaterial absorption device based on the phase-change effect

We propose a structurally simple, innovative, and multifunctional mid-infrared broadband thermally tunable metamaterial absorption device. The absorption device consists of a three-layer structure, from bottom to top: Ti substrate, SiO2 dielectric layer, and patterned VO2 layer. Through temperature control, the average absorption intensity of the absorption device can vary between 0.08 and 0.94. The absorption device's absorption mechanism is rooted in the thermal phase-change characteristics exhibited by the topologically patterned VO2. When the temperature is below 340 K, VO2 is in a dielectric state, resulting in near-total reflection performance in the mid-infrared range. When the temperature is above 340 K, VO2 undergoes a dielectric-to-metal transition, enabling the absorption device to achieve an average absorption rate of 94.12% in the ultra-wideband range of 6.26 μm-20.96 μm in the mid-infrared. This absorption range completely covers the atmospheric window wavelengths of 8 μm-14 μm, demonstrating high practical value. We explain the working mechanism of the absorption device from the perspective of the electromagnetic field. Subsequently, we study the variations in the absorption curve of the absorption device at different temperatures of VO2 and use the changes in the electric field at the same wavelength under different temperatures to explain the variations in absorption. Compared to previous work, our structure has only three layers in a single unit, making it easy to process and produce. Additionally, the absorption device's operating bandwidth and average absorption rate in the mid-infrared range have been significantly improved. Furthermore, the absorption device exhibits substantial incident angle tolerance and polarization insensitivity. We believe that this design has broad application potential in future optothermal conversion, infrared stealth, and thermal radiation.

Tunable High-Sensitivity Four-Frequency Refractive Index Sensor Based on Graphene Metamaterial

As graphene-related technology advances, the benefits of graphene metamaterials become more apparent. In this study, a surface-isolated exciton-based absorber is built by running relevant simulations on graphene, which can achieve more than 98% perfect absorption at multiple frequencies in the MWIR (MediumWavelength Infra-Red (MWIR) band as compared to the typical absorber. The absorber consists of three layers: the bottom layer is gold, the middle layer is dielectric, and the top layer is patterned with graphene. Tunability was achieved by electrically altering graphene's Fermi energy, hence the position of the absorption peak. The influence of graphene's relaxation time on the sensor is discussed. Due to the symmetry of its structure, different angles of light source incidence have little effect on the absorption rate, leading to polarization insensitivity, especially for TE waves, and this absorber has polarization insensitivity at ultra-wide-angle degrees. The sensor is characterized by its tunability, polarisation insensitivity, and high sensitivity, with a sensitivity of up to 21.60 THz/refractive index unit (RIU). This paper demonstrates the feasibility of the multi-frequency sensor and provides a theoretical basis for the realization of the multi-frequency sensor. This makes it possible to apply it to high-sensitivity sensors.

Optimization of doping design for planar P-N homologous junction perovskite solar cells

In this study, we used the solar cell capacitance simulator (SCAPS) to analyse numerically the performance of perovskite solar cells (PSCs) containing CH3NH3PbI3. The findings indicate that P-N homologous junction processing based on traditional P-I-N PSCs can enhance the photoelectric conversion efficiency (PCE). Furthermore, the authors analyzed the effect of uniform P-N doping of CH3NH3PbI3, concluding that the photoelectric efficiency can be improved from 16.10% to 19.03% after doping. In addition, the optical properties of PSCs under solar irradiation are simulated using finite difference time-domain (FDTD) software under AM1.5. This method is applied to investigate the effect of the P-N uniform junction on the internal electric field generated within the cell. The generation of this electric field promotes carrier separation and transmission, ultimately increasing the open circuit voltage (VOC) of the solar cell from 1.03 to 1.12 V. The usage of P-N junctions enhances PSCs performance and exhibits vast potential for designing and developing PSCs.

Kinetics of extracting valuable components from Ti-bearing blast furnace slag by acidolysis with sulphuric acid

Ti-bearing blast furnace slag is a kind of solid waste produced by Pangang Group Company through the blast furnace smelting method. A variety of valuable components can be extracted from the Ti-bearing blast furnace slag after acidolysis with concentrated sulphuric acid. In order to study the kinetics of acidolysis, this paper investigated the effects of the acidolysis temperature, acid-slag ratio and raw material particle size on the overall extraction rate of Ti4+, Mg2+ and Al3+ components at different reaction times, and simulated the acidolysis process by using the unreacted shrinking core model. The results showed that the acidolysis process was controlled by internal diffusion with an apparent activation energy of 19.05 kJ mol-1 and the semi-empirical kinetic equation of the acidolysis process was obtained.

Actively Tunable "Single Peak/Broadband" Absorbent, Highly Sensitive Terahertz Smart Device Based on VO2

In recent years, the development of terahertz (THz) technology has attracted significant attention. Various tunable devices for THz waves (0.1 THz-10 THz) have been proposed, including devices that modulate the amplitude, polarization, phase, and absorption. Traditional metal materials are often faced with the problem of non-adjustment, so the designed terahertz devices play a single role and do not have multiple uses, which greatly limits their development. As an excellent phase change material, VO2's properties can be transformed by external temperature stimulation, which provides new inspiration for the development of terahertz devices. To address these issues, this study innovatively combines metamaterials with phase change materials, leveraging their design flexibility and temperature-induced phase transition characteristics. We have designed a THz intelligent absorber that not only enables flexible switching between multiple functionalities but also achieves precise performance tuning through temperature stimulation. Furthermore, we have taken into consideration factors such as the polarization mode, environmental temperature, structural parameters, and incident angle, ensuring the device's process tolerance and environmental adaptability. Additionally, by exploiting the principle of localized surface plasmon resonance (LSPR) accompanied by local field enhancement, we have monitored and analyzed the resonant process through electric field characterization. In summary, the innovative approach and superior performance of this structure provide broader insights and methods for THz device design, contributing to its theoretical research value. Moreover, the proposed absorber holds potential for practical applications in electromagnetic invisibility, shielding, modulation, and detection scenarios.

A tunable broadband terahertz MoS2 absorber using series-parallel hybrid network design

A method for designing a broadband absorber using a series-parallel hybrid network is proposed. The performance of the broadband absorber is improved by using frequency-selective surface patterns based on a series-parallel hybrid equivalent circuit. The results indicate that the tunable single-layered terahertz MoS2 absorber has excellent broadband characteristics. Between 0.84 and 2.34 THz, the absorption and relative absorption bandwidth exceed 90% and 94.3%, respectively. Also, the absorption level can be adjusted from 90% to 10% by applying a bias voltage on the electrodes. The effects of different types of MoS2 layers and surface fluctuations in monolayered MoS2 on the properties of the absorber are demonstrated. In the 60° (TM) and 50° (TE) ranges, the polarization of the terahertz absorber is insensitive to the incidence angle. Overall, this method enables the single-layered absorber to exhibit excellent broadband characteristics comparable to those of multilayered structures, as well as simplifies the structure. Consequently, this method significantly broadens the usefulness of tunable single-layered absorbers for radar stealth, terahertz imaging, and electrically tunable modulation.

Terahertz absorber based on vanadium dioxide with high sensitivity and switching capability between ultra-wideband and ultra-narrowband

The terahertz perfect absorber can be applied in the control, sensing and modulation of optical fields in micro- and nanostructures. However, they are only single function, complex device structure and low sensing sensitivity. Based on this, by introducing the bound state in the continuum (BIC) with infinite quality factor and field enhancement effect, and taking advantage of the phase transition characteristics of vanadium dioxide (VO2), we designed a terahertz perfect absorber device which can actively switch between ultra-wideband and ultra-narrowband. The absorption mechanism is explained by multipole analysis theory, impedance matching theory and electromagnetic field distribution. The broadband absorption is mainly due to the electric dipole resonance on metallic VO2 materials, and the absorption is more than 99% across 3.64-6.96 THz, and it has excellent characteristics such as robustness. Ultra-narrowband perfect absorption has a quality factor greater than 2200 due mainly to the implementation of symmetrically protected BIC with a sensing sensitivity of 2.575 THz per RIU. Therefore, this research could be widely used in the fields of integrated optical circuits, optoelectronic sensing and perceptual modulation of energy, as well as providing additional design ideas for the design of terahertz multifunctional devices.

Design of Plasmonic Photonic Crystal Fiber for Highly Sensitive Magnetic Field and Temperature Simultaneous Measurement

A high-sensitivity plasmonic photonic crystal fiber (PCF) sensor is designed and a metal thin film is embedded for achieving surface plasmon resonance (SPR), which can detect the magnetic field and temperature simultaneously. Within the plasmonic PCF sensor, the SPR sensing is accomplished by coating both the upper sensing channel (Ch1) and the lower sensing channel (Ch2) with gold film. In addition, the temperature-sensitive medium polydimethylsiloxane (PDMS) is chosen to fill in Ch1, allowing the sensor to respond to the temperature. The magnetic field-sensitive medium magnetic fluid (MF) is chosen to fill in Ch2, allowing this sensor to respond to the magnetic field. During these processes, this proposed SPR-PCF sensor can achieve dual-parameter sensing. The paper also investigates the electrical field characteristics, structural parameters and sensing performance using COMSOL. Finally, under the magnetic field range of 50-130 Oe, this sensor has magnetic field sensing sensitivities of 0 pm/Oe (Ch1) and 235 pm/Oe (Ch2). In addition, this paper also investigates the response of temperature. Under the temperature range of 20-40 °C, Ch1 and Ch2 have temperature sensitivities of -2000 pm/°C and 0 pm/°C, respectively. It is noteworthy that the two sensing channels respond to only a single physical parameter; this sensing performance is not common in dual-parameter sensing. Due to this sensing performance, it can be found that the magnetic field and temperature can be detected by this designed SPR-PCF sensor simultaneously without founding and calculating a sensing matrix. This sensing performance can solve the cross-sensitivity problem of magnetic field and temperature, thus reducing the measurement error. Since it can sense without a matrix, it further can solve the ill-conditioned matrix and nonlinear change in sensitivity problems in dual-parameter sensing. These excellent sensing capabilities are very important for carrying out multiparameter sensing in complicated environments.

High-transmission and large group delay terahertz triple-band electromagnetically induced transparency in a metal-perovskite hybrid metasurface

A high-transmission and large group delay terahertz triple-band electromagnetically induced transparency (EIT) effect is obtained in a metal-perovskite hybrid metasurface, which consists of a cross metal (CM), a pair of square metal frames (SMFs), and a pair of square split rings (SSRs). The results reveal that the transmission amplitudes of three transparent windows are 0.83, 0.9, and 0.89. The maximum values of group delays at three transparent windows are 7.64 ps, 4.07 ps, and 4.27 ps. The multipole scattering theory shows that the first and third transparent windows are created by the coupling between the electric dipole and toroidal dipole, and the second transparent window is created by the electric dipoles. The triple-band EIT effect can be dynamically controlled by adjusting the conductivity of perovskite while the modulation depths are 49.4%, 41%, and 31.5%. Moreover, the slow light effect can also be tunable by tuning the conductivity of perovskite while the modulation depths are 87.8%, 65.6%, and 68.4%. Our study puts forward a novel design concept for multi-band EIT effect and shows great prospects in the application of multi-band devices.

Ultra-Wideband High-Efficiency Solar Absorber and Thermal Emitter Based on Semiconductor InAs Microstructures

Since the use of chemical fuels is permanently damaging the environment, the need for new energy sources is urgent for mankind. Given that solar energy is a clean and sustainable energy source, this study investigates and proposes a six-layer composite ultra-wideband high-efficiency solar absorber with an annular microstructure. It achieves this by using a combination of the properties of metamaterials and the quantum confinement effects of semiconductor materials. The substrate is W-Ti-Al2O3, and the microstructure is an annular InAs-square InAs film-Ti film combination. We used Lumerical Solutions' FDTD solution program to simulate the absorber and calculate the model's absorption, field distribution, and thermal radiation efficiency (when it is used as a thermal emitter), and further explored the physical mechanism of the model's ultra-broadband absorption. Our model has an average absorption of 95.80% in the 283-3615 nm band, 95.66% in the 280-4000 nm band, and a weighted average absorption efficiency of 95.78% under AM1.5 illumination. Meanwhile, the reflectance of the model in the 5586-20,000 nm band is all higher than 80%, with an average reflectance of 94.52%, which has a good thermal infrared suppression performance. It is 95.42% under thermal radiation at 1000 K. It has outstanding performance when employed as a thermal emitter as well. Additionally, simulation results show that the absorber has good polarization and incidence angle insensitivity. The model may be applied to photodetection, thermophotovoltaics, bio-detection, imaging, thermal ion emission, and solar water evaporation for water purification.

Polarization-insensitive electromagnetically induced transparency and its sensing performance based on spoof localized surface plasmons in vanadium dioxide-based terahertz metasurfaces

The multi-layer terahertz metasurfaces are designed to achieve polarization-insensitive electromagnetically induced transparency (EIT) effect and its sensing performance based on spoof localized surface plasmons (S-LSPs). The unit cell of the proposed metasurfaces is comprised of a metallic spiral (MS) structure, square metal frame (SMF) structure, and vanadium dioxide (VO2) layer. The EIT effect is realized by the bright-bright coupling between spoof electric localized surface plasmons (S-ELSPs) and electric dipole, which can be proved by the multipole scattering theory. The maximum value of transmission amplitude at the transparent window is 0.91, and the modulation depth can reach 51% by adjusting the conductivity of VO2. The theoretical results based on the two-particle model show excellent agreement with the simulated results. Moreover, the change of polarization angle has little effect on the EIT effect and the proposed metasurfaces show polarization-insensitive characteristics. The slow light effect of the proposed metasurfaces can also be dynamically controlled by tuning the conductivity of VO2. Due to the high Q value of the transparent window, the proposed metasurfaces exhibit excellent sensing performance, and the sensitivity is 0.172 THz RIU-1. Our study provides a method for the fabrication of EIT metasurfaces and has a broad application prospect in slow light devices, sensors, and modulators.

Performance Analysis of an Aperture-Coupled THz Antenna for Diagnosing Breast Cancer

The most important technique for exposing early-stage breast cancer is terahertz imaging. It aids in lowering the number of breast cancer-related fatalities and enhancing the quality of life. An essential component of developing the THz imaging system for high-quality photos is choosing the right sensor. In this article, a wideband antenna for microwave imaging of breast tissue with an operating frequency of 30 GHz (107 GHz to 137 GHz) is constructed and analyzed. An aperture-coupled antenna with an optimized ground aperture is proposed and analyzed, which made it possible to obtain better and consistent impedance matching in the wideband spectrum. The variation of backscattered signal energy in body tissue is assessed with healthy breast tissue and in the presence of malignant cells. A significant difference in energy scattering is observed for both situations. The suggested antenna's linear and stable time domain characteristics make it an appropriate component for THz imaging technology.

Study on the Thermal Distribution Characteristics of a Molten Quartz Ceramic Surface under Quartz Lamp Radiation

More and more researchers are studying the heat transfer performance of aeronautical materials at high temperatures. In this paper, we use a quartz lamp to irradiate fused quartz ceramic materials, and the sample surface temperature and heat flux distribution were obtained at a heating power of 45~150 kW. Furthermore, the heat transfer properties of the material were analyzed using a finite element method and the effect of surface heat flow on the internal temperature field was investigated. The results show that the fiber skeleton structure has a significant effect on the thermal insulation performance of fiber-reinforced fused quartz ceramics and the longitudinal heat transfer along the rod fiber skeleton is slower. As time passes, the surface temperature distribution tends to stability and reaches an equilibrium state. The surface temperature of fused quartz ceramic increases with the increase in the radiant heat flux of the quartz lamp array. When the input power is 5 kW, the maximum surface temperature of the sample can reach 1153 °C. However, the non-uniformity of the sample surface temperature also increases, reaching a maximum uncertainty of 12.28%. The research in this paper provides important theoretical guidance for the heat insulation design of ultra-high acoustic velocity aircraft.

Ultra-Broadband Solar Absorber and High-Efficiency Thermal Emitter from UV to Mid-Infrared Spectrum

Solar energy is currently a very popular energy source because it is both clean and renewable. As a result, one of the main areas of research now is the investigation of solar absorbers with broad spectrum and high absorption efficiency. In this study, we create an absorber by superimposing three periodic Ti-Al₂O₃-Ti discs on a W-Ti-Al₂O₃ composite film structure. We evaluated the incident angle, structural components, and electromagnetic field distribution using the finite difference in time domain (FDTD) method in order to investigate the physical process by which the model achieves broadband absorption. We find that distinct wavelengths of tuned or resonant absorption may be produced by the Ti disk array and Al₂O₃ through near-field coupling, cavity-mode coupling, and plasmon resonance, all of which can effectively widen the absorption bandwidth. The findings indicate that the solar absorber's average absorption efficiency can range from 95.8% to 96% over the entire band range of 200 to 3100 nm, with the absorption bandwidth of 2811 nm (244-3055 nm) having the highest absorption rate. Additionally, the absorber only contains tungsten (W), titanium (Ti), and alumina (Al₂O₃), three materials with high melting points, which offers a strong assurance for the absorber's thermal stability. It also has a very high thermal radiation intensity, reaching a high radiation efficiency of 94.4% at 1000 K, and a weighted average absorption efficiency of 98.3% at AM1.5. Additionally, the incidence angle insensitivity of our suggested solar absorber is good (0-60°) and polarization independence is good (0-90°). These benefits enable a wide range of solar thermal photovoltaic applications for our absorber and offer numerous design options for the ideal absorber.

Triple-Band Surface Plasmon Resonance Metamaterial Absorber Based on Open-Ended Prohibited Sign Type Monolayer Graphene

This paper introduces a novel metamaterial absorber based on surface plasmon resonance (SPR). The absorber is capable of triple-mode perfect absorption, polarization independence, incident angle insensitivity, tunability, high sensitivity, and a high figure of merit (FOM). The structure of the absorber consists of a sandwiched stack: a top layer of single-layer graphene array with an open-ended prohibited sign type (OPST) pattern, a middle layer of thicker SiO₂, and a bottom layer of the gold metal mirror (Au). The simulation of COMSOL software suggests it achieves perfect absorption at frequencies of f_I = 4.04 THz, f_II = 6.76 THz, and f_III = 9.40 THz, with absorption peaks of 99.404%, 99.353%, and 99.146%, respectively. These three resonant frequencies and corresponding absorption rates can be regulated by controlling the patterned graphene's geometric parameters or just adjusting the Fermi level (E_F). Additionally, when the incident angle changes between 0~50°, the absorption peaks still reach 99% regardless of the kind of polarization. Finally, to test its refractive index sensing performance, this paper calculates the results of the structure under different environments which demonstrate maximum sensitivities in three modes: S_I = 0.875 THz/RIU, S_II = 1.250 THz/RIU, and S_III = 2.000 THz/RIU. The FOM can reach FOM_I = 3.74 RIU^-1, FOM_II = 6.08 RIU^-1, and FOM_III = 9.58 RIU^-1. In conclusion, we provide a new approach for designing a tunable multi-band SPR metamaterial absorber with potential applications in photodetectors, active optoelectronic devices, and chemical sensors.