Wavelength Selective Emitter Research Articles

Coordinated multi-band stealth based on phase change materials

With the integrated application of multiple detection technologies, multi-band compatible stealth is crucial to improve the counter-detection capability of targets. However, there are still significant challenges in achieving stealth that is compatible with different bands. This paper presents a wavelength-selective emitter with a structure consisting of a layer composed of a high-temperature-resistant material and a phase change material Ge2Sb2Te5 (GST), and an upper truncated pyramid array composed of TiO2. The structure can transition between “stealthy” and “non-stealthy” states by controlling the phase transition process of the GST. The structure in stealth mode has low reflectivity in the visible (VIS) region, low emissivity in the mid-wave infrared and long-wave infrared region. In addition, it has laser stealth at 1.06 μm and 1.54 μm, and provides radiative cooling in the non-atmospheric window (5–8 μm). The dipole resonance formed by TiO2 on the side gives the structure lower reflectivity in the VIS band and at two laser wavelengths. The high emission in the non-atmospheric window is mainly attributed to the Fabry-Perot resonance supported in the structure. In addition, the effects of incidence angle and temperature on the stealth performance of the structure are investigated. This research has promising applications in the field of multi-band compatible stealth.

Whole-infrared-band camouflage with dual-band radiative heat dissipation

Advanced multispectral detection technologies have emerged as a significant threat to objects, necessitating the use of multiband camouflage. However, achieving effective camouflage and thermal management across the entire infrared spectrum, especially the short-wave infrared (SWIR) band, remains challenging. This paper proposes a multilayer wavelength-selective emitter that achieves effective camouflage across the entire infrared spectrum, including the near-infrared (NIR), SWIR, mid-wave infrared (MWIR), and long-wave infrared (LWIR) bands, as well as the visible (VIS) band. Furthermore, the emitter enables radiative heat dissipation in two non-atmospheric windows (2.5–3 μm and 5–8 μm). The emitter’s properties are characterized by low emittance of 0.270/0.042/0.218 in the SWIR/MWIR/LWIR bands, and low reflectance of 0.129/0.281 in the VIS/NIR bands. Moreover, the high emittance of 0.742/0.473 in the two non-atmospheric windows ensures efficient radiative heat dissipation, which results in a temperature decrement of 14.4 °C compared to the Cr reference at 2000 W m−2 input power density. This work highlights the role of solar radiance in camouflage, and provides a comprehensive guideline for developing multiband camouflage compatible with radiative heat dissipation, from the visible to LWIR.

Multiband camouflage design with thermal management

Although the effective “stealth” of space vehicles is important, current camouflage designs are inadequate in meeting all application requirements. Here, a multilayer wavelength-selective emitter is demonstrated. It can realize visible light and dual-band mid-infrared camouflage with thermal control management in two application scenarios, with better effect and stronger radiation cooling capability, which can significantly improve the stealth and survivability of space vehicles in different environments. The selective emitter demonstrated in this paper has the advantages of simple structure, scalability, and ease of large-area fabrication, and has made a major breakthrough in driving multiband stealth technology from simulation research to physical verification and even practical application.

Design of a Hybrid Structure for Controlling Infrared Characteristic Based on Photonic Crystals with Active Thermal Management

Infrared Signature Tuning In article number 2200374, Qing Ai and co-workers propose and numerically investigate a hybrid structure for controlling the infrared (IR) characteristic combining a wavelength selective emitter, microchannel heat exchanger, and thermal barrier coating. The design can tune the surface infrared signature by active thermal management. The results indicates that the IR signal intensity of an object can be significantly reduced by simultaneously controlling the surface emittance and surface temperature.

Fabrication of highly lattice mismatched AlInSb diodes on GaAs substrates for thermophotovoltaic cells

We have fabricated and investigated the optical properties of highly lattice mismatched AlInSb thermophotovoltaic cells grown on GaAs substrates. Defects, such as dislocations and surface damage, were minimized by controlling the strain of the film structure and by using a silicon nitride passivation layer. An output power density of 9.7 mW cm−2 was achieved under 1000 °C blackbody radiation with an incident power density of 1.63 W cm−2, which gave a power conversion efficiency of 0.59 %. Optimal efficiency of above 5% was estimated by a simulation using recombination parameters obtained from electroluminescence analysis. Additionally, a six-fold increase in spectral efficiency was confirmed by using a 3.3 μm monochromatic light source, which indicated that a thermophotovoltaic cell with a high efficiency of more than 30% would be possible in combination with wavelength-selective emitter.

Theoretical and Numerical Analysis of Active Switching for Narrow-Band Thermal Emission with Graphene Ribbon Metasurface

Components smaller than the wavelength of electromagnetic waves are called meta-atoms. Thermal emission can be controlled by an artificial structure in which these meta-atoms are arranged on the surface. This artificial structure is called a metasurface, and its optical properties are determined by the materials and shapes of the meta-atoms. However, optical devices may require active control of thermal emission. In the present study, we theoretically and numerically analyze a wavelength-selective emitter using a graphene ribbon metasurface. The graphene ribbon metasurface consists of a graphene ribbon array, potassium bromide thin film, and silver substrate. The geometric parameters of the graphene metasurface are determined based on an equivalent circuit model that agrees well with the results of the electromagnetic field analysis (rigorous coupled-wave analysis). The proposed emitter causes impedance matching depending on the conductivity of the graphene ribbon in a very narrow wavelength range. The conductivity of graphene can be actively controlled by the gate voltage. Therefore, the proposed emitters may realize near-perfect emission with a high quality factor and active controllable switching for various wavelengths. In addition, the quality factor can be changed by adjusting the electron mobility of graphene. The proposed emitter can be used for optical devices such as thermophotovoltaic systems and biosensing.

A novel selective thermophotovoltaic emitter based on multipole resonances

Thermophotovoltaic systems can harvest electric energy from heat sources with a potential efficiency exceeding the Shockley–Queisser limit due to the selective emission of an elaborate thermal emitter. In this work, a two-dimensional nanodisks/thin-film metamaterial is proposed as a wavelength-selective emitter, which can coordinate well with the photovoltaic cell in a thermophotovoltaic system. Compared to conventional emitters based on surface plasmon polaritons, the emittance peaks of the proposed emitter are realized by the excitations of both electric dipole and anapole modes in silicon nanodisks, which can be easily tailored due to the non-dispersive optical constants of dielectric materials. Meanwhile, the effect of polarization and polar angle on the emittance spectra is also investigated, suggesting that the proposed emitter has high emittance and efficiency not only in the normal direction but also at large oblique angles. Electromagnetic field and current density distributions reveal that the coupling between multipole resonances and the bottom tungsten layer can induce a magnetic dipolar resonance. Therefore, the wavelengths of both emittance peaks are sensitive to the period paralleled to the incident electric field. Besides, the anapole-induced mode can couple with the lattice resonance, resulting in higher emittance. Moreover, the proposed emitter is successfully fabricated, and the measured spectra agree well with the theoretical results. The fundamental understanding and insights obtained here will facilitate the active design and application of novel multipole-based emitters in enhancing energy conversion.

High-Temperature Carbonized Ceria Thermophotovoltaic Emitter beyond Tungsten.

Thermophotovoltaics (TPVs) require emitters with a regulated radiation spectrum tailored to the spectral response of integrated photovoltaic cells. Such spectrally engineered emitters developed thus far are structurally too complicated to be scalable, are thermally unstable, or lack reliability in terms of temperature cycling. Herein, we report wafer-scale, thermal-stress-free, and wavelength-selective emitters that operate for high-temperature TPVs equipped with GaSb photovoltaic cells. One inch crystalline ceria wafers were prepared by sequentially pressing and annealing the pellets of ceria nanoparticles. The direct pyrolysis of citric acid mixed with ceria nanoparticles created agglomerated, pyrolytic carbon and ceria microscale dots, thus forming a carbonized film strongly adhering to a wafer surface. Depending on the thickness of the carbonized film that was readily tuned based on the amount of citric acid used in the reaction, the carbonized ceria emitter behaved as a tungsten-like emitter, a graphite-like emitter, or their hybrid in terms of the absorptivity spectrum. A properly synthesized carbonized ceria emitter produced a power density of 0.63 W/cm2 from the TPV system working at 900 °C, providing 13 and 9% enhancements compared to tungsten and graphite emitters, respectively. Furthermore, only the carbonized ceria emitter preserved its pristine absorptivity spectrum after a 48 h heating test at 1000 °C. The scalable and facile fabrication of thermostable emitters with a structured spectrum will prompt the emergence of thermal emission-harnessed energy devices.

A study on thermophotovoltaic system using wavelength-selective emitter

A study on thermophotovoltaic system using wavelength-selective emitter

Active thermal radiation control with nanoslit graphene metasurface

We propose a wavelength-selective emitter using nanoslit graphene metasurface. The nanoslit graphene metasurface consists of a graphene sheet, metallic slit, and dielectric layer for tailoring radiative properties. The utilization of rigorous electromagnetic simulation clarifies the mechanisms of thermal radiation. The proposed emitter shows high emissivity and a broad peak wavelength shift because of the electromagnetic resonances of graphene. This study may facilitate the initial design of wavelength-selective emitters using graphene metasurfaces.

Theoretical design of nanoparticle-based spectrally emitter for thermophotovoltaic applications

Wavelength-selective emitter is a critical component in thermophotovoltaic (TPV) systems. How to evaluate and further enhance TPV efficiency for different PV cells by designing selective emitter is still needed for realistic applications. Hence, the impact of the nanoparticle-based spectrally selective emitter on the TPV efficiency was investigated in this work. The nanoparticle material, radius, volume fraction and thickness of emitter was optimized based on the spectral cut-off efficiency ηs and effective emittance efficiency ηe for GaSb and InGaAsSb PV cells respectively. Results showed that W emitter achieved better TPV performance than Ti and Ni emitters. The maximized ηsηe achieved 0.415 and 0.535 for GaSb and InGaAsSb PV cells at 1200 °C, indicating that this nanoparticle-based structure emitter was more suitable for the InGaAsSb PV cell with the low bandgap. These results give valuable insights into design opportunity for the selective emitter in various TPV systems.

High-temperature infrared camouflage with efficient thermal management

High-temperature infrared (IR) camouflage is crucial to the effective concealment of high-temperature objects but remains a challenging issue, as the thermal radiation of an object is proportional to the fourth power of temperature (T4). Here, we experimentally demonstrate high-temperature IR camouflage with efficient thermal management. By combining a silica aerogel for thermal insulation and a Ge/ZnS multilayer wavelength-selective emitter for simultaneous radiative cooling (high emittance in the 5–8 μm non-atmospheric window) and IR camouflage (low emittance in the 8–14 μm atmospheric window), the surface temperature of an object is reduced from 873 to 410 K. The IR camouflage is demonstrated by indoor/outdoor (with/without earthshine) radiation temperatures of 310/248 K for an object at 873/623 K and a 78% reduction in with-earthshine lock-on range. This scheme may introduce opportunities for high-temperature thermal management and infrared signal processing.

A wavelength selective emitter design method using hyperbolic tangent level set-based shape optimization

A wavelength selective emitter is one of the key elements of the TPV generation system. Recently, a wavelength selective emitter with periodic microstructure on the surface has attracted attention. In this study, we propose a nonparametric design method of the wavelength selective emitter, which utilizes a shape optimization technique. The proposed method provides a design example of a 1D grating wavelength selective emitter that shows near unity emissivity at target wavelength. The obtained optimal configuration utilizes two physical mechanisms for the emissivity improvement: the excitation of the surface plasmon polariton and the cavity resonance. Furthermore, by considering multiple wavelengths, the proposed method can also provide an emitter configuration which has higher wavelength selectivity performance.

Wavelength-selective emitters with pyramid nanogratings enhanced by multiple resonance modes

Binary gratings with high or low metal filling ratios in a grating region have been demonstrated as successful candidates in enhancing the emittance of emitters for thermophotovoltaics since they could support surface plasmons (SPs), the Rayleigh–Wood anomaly (RWA), or cavity resonance (CR) within their geometries. This work shows that combining a tungsten binary grating with a low and high filling ratio to form a pyramid grating can significantly increase the emittance, which is nearly perfect in the wavelength region from 0.6 to 1.72 μm, while being 0.1 at wavelengths longer than 2.5 μm. Moreover, the emittance spectrum of the hybrid tungsten grating is insensitive to the angle of incidence. The enhancement demonstrated by magnetic field and Poynting vector patterns is due to the interplay between SPs and RWA modes at short wavelengths, and CR at long wavelengths. Furthermore, a combined grating made of nickel is also proposed providing enhanced emittance in a wide angle of incidence.

形状最適化に基づく波長選択放射体設計法

形状最適化に基づく波長選択放射体設計法

1D trilayer films grating with W/SiO2/W structure as a wavelength-selective emitter for thermophotovoltaic applications

Wavelength selectivity of emitters is of great importance for thermophotovoltaic applications. In this paper, a modified 1D trilayer films grating with a silica (SiO2) layer sandwiched between two tungsten (W) layers to form the W/SiO2/W structure is proposed to obtain high spectral selective emittance. High average emittance of 0.95 is obtained for TM waves from about 600nm to 1900nm, and a broadband emission peak with emittance close to unity occurs between 900nm and 1800nm. Simultaneously, the emittance decreases sharply when λ>1800nm, which can minimize the thermal loss. The finite-difference time-domain method (FDTD) is utilized to analyze the radiative properties of the grating. The inductance–capacitance (LC) circuit model for this trilayer grating structure is presented to predict the magnetic polaritons (MPs) resonance location compared with the results obtained by FDTD method. The effects of the geometric parameters and emission angles on the emittance of the proposed grating are also investigated. The broadband emittance peak is considered as the combined results of the surface plasmon polaritons (SPPs) and several fundamental modes of magnetic polaritons (MPs) resonance at neighboring wavelengths.

One-Dimensional Multilayer Microstructure Emitter for Thermophotovoltaic Applications

In this paper, a one-dimensional periodic multilayer is optimized for potential application as thermophotovoltaic (TPV) emitter. The proposed structure was prepared through a magnetron sputtering process. The influence of layers geometric parameters of the proposed structure on the spectral emittance is studied by using the rigorous coupled-wave analysis (RCWA).The emittance spectrum shows three close to unity emission peaks which are explained by the surface plasmon polaritons (SPPs), gap plasmon polaritons (GPPs) and magnetic polaritons (MPs) excitation. The results show that the geometric parameters are very sensitive and important parameter in the emitter fabrication. The normal emittance of the proposed structure is shown to be wavelength-selective and direction-insensitive. The proposed structure can be used as wavelength selective emitter with excellent performance in thermophotovoltaic systems.

Thermophotovoltaic emitters based on a two-dimensional grating/thin-film nanostructure

Thermophotovoltaic (TPV) devices can convert thermal radiation directly into electricity. To improve the efficiency of TPV systems, wavelength-selective emitters are designed to take thermal energy from various heat sources and then emit photons to the TPV cells. A two-dimensional grating/thin-film nanostructure is proposed as an efficient emitter, whose performance is enhanced by the excitations of both surface plasmon polaritons (SPPs) and magnetic polaritons (MPs). Rigorous coupled-wave analysis is used to predict the emittance as well as the electromagnetic field and current density distributions. The normal emittance of the proposed nanostructure is shown to be wavelength-selective and polarization-insensitive. The mechanisms of SPP and MP excitations in the nanostructure are elucidated for different polarizations. The current–density loop further confirms the existence of magnetic resonances. Furthermore, the effect of azimuthal and polar angles on the emittance spectra is also investigated, suggesting that the proposed structure has high emittance not only in the normal direction but also at large oblique angles.

Application of micro/nanoscale thermal radiation to thermophotovoltaic system

Thermophotovoltaic (TPV) system has been regarded as one promising means to alleviate current energy demand because it can directly generate electricity from radiation heat via photons. However, the presently available TPV systems suffer from low conversion efficiency and low throughput. A viable solution to increase their efficiency is to apply micro/nanoscale radiation principles in the design of different components to utilize the characteristics of thermal radiation at small distances and in microstructures. Several critical issues are reviewed, such as photovoltaic effect, quantum efficiency and efficiency of TPV system. Emphasis is given to the development of wavelength-selective emitters and filters and the aspects of micro/nanoscale heat transfer. Recent progress, along with the challenges and opportunities for future development of TPV systems are also outlined.

Infrared Radiative Properties of Heavily Doped Silicon at Room Temperature

This paper describes an experimental investigation on the infrared radiative properties of heavily doped Si at room temperature. Lightly doped Si wafers were ion-implanted with either boron or phosphorus atoms, with dosages corresponding to as-implanted peak doping concentrations of 1020 and 1021 cm−3; the peak doping concentrations after annealing are 3.1×1019 and 2.8×1020 cm−3, respectively. Rapid thermal annealing was performed to activate the implanted dopants. A Fourier-transform infrared spectrometer was employed to measure the transmittance and reflectance of the samples in the wavelength range from 2 μm to 20 μm. Accurate carrier mobility and ionization models were identified after carefully reviewing the available literature, and then incorporated into the Drude model to predict the dielectric function of doped Si. The radiative properties of doped Si samples were calculated by treating the doped region as multilayer thin films of different doping concentrations on a thick lightly doped Si substrate. The measured spectral transmittance and reflectance agree well with the model predictions. The knowledge gained from this study will aid future design and fabrication of doped Si microstructures as wavelength selective emitters and absorbers in the midinfrared region.