Detection Of Thermal Radiation Research Articles

Ultrasensitive Flexible Temperature Sensors Based on Thermal-Mediated Ions Migration Dynamics in Asymmetrical Polymer Bilayers.

Accurately acquiring crucial data on the ambient surroundings and physiological processes delivered via subtle temperature fluctuation is vital for advancing artificial intelligence and personal healthcare techniques but is still challenging. Here, we introduce an electrically induced cation injection mechanism based on thermal-mediated ion migration dynamics in an asymmetrical polymer bilayer (APB) composed of nonionic polymer and polyelectrolyte layers, enabling the development of ultrasensitive flexible temperature sensors. The resulting optimized sensor achieves ultrahigh sensitivity, with a thermal index surpassing 10,000 K-1, which allows identifying temperature differences as small as 10 mK with a sensitivity that exceeds 1.5 mK. The mechanism also enables APB sensors to possess good insensitivity to various mechanical deformations─features essential for practical applications. As a proof of concept, we demonstrate the potential impact of APB sensors in various conceptual applications, such as mental tension evaluation, biomimetic thermal tactile, and thermal radiation detection.

Colored thermal camouflage and anti-counterfeiting with programmable In3SbTe2 platform

Abstract Camouflage is an important technology in various scenarios. Usually, this involves the visible compatibility of the background, which however is facile under infrared thermal radiation detection. The simultaneous visible and thermal camouflage are challenging because it requires full and decoupled manipulations of visible reflection and infrared emissivity using one single device, let alone to its adaptivity to complex environments. Here, we report a programmable, colored thermal camouflage at 3–5 μm and 8–14 μm based on mode coupling in phase-change In3SbTe2 materials. A series of industry-friendly colored multilayer thermal emitters are designed consisting of an anti-reflectance layer for structure coloration above a coupled nanocavity for IR modulation, which easily realizes the complete decoupled control of visible color and infrared emissivity. Our solution features independent structural visible colors in the full visible range and continuously programmable dual-band emissivity modulation with up to 90 % absolute tuning range. Our work facilitates near optimal camouflage and anti-counterfeiting solution for visible-infrared multi-band compatibility of complex environments under different temperatures and colored appearances.

Ultraviolet laser-driven ultra-high transverse voltage in Bi-2201 thin films

The development of high-performance optically induced voltage materials represents a significant challenge within the realm of optical detection. The constraints posed by low induced voltage and extended response times have impeded the practical applicability of optical and thermal radiation detectors. In this investigation, we propose the utilization of superconducting Bi2Sr2CuOy (Bi-2201) as a pulsed laser-induced voltage material, revealing the emergence of notable transverse voltage signals in tilted thin films. A noteworthy peak voltage of 25.12 V is attained upon exposure to ultraviolet pulsed laser (248 nm), with a rapid rise time of merely 60 ns. Furthermore, we establish an empirical equation specific to our laser detection heterostructure, serving as a benchmark for Bi-2201-based laser detection systems. These findings introduce a promising avenue for the expanded practical applications of high-temperature superconductors.

Infrared fiber bundle image super-resolved based on computational imaging

As the representative of flexibility in optical imaging media, in recent years, fiber bundles have emerged as a promising architecture in the development of compact visual systems. Dedicated to tackling the problems of universal honeycomb artifacts and low signal-to-noise ratio (SNR) imaging in fiber bundles, the iterative super-resolution reconstruction network based on a physical model is proposed. Under the constraint of solving the two subproblems of data fidelity and prior regular term alternately, the network can efficiently “regenerate” the lost spatial resolution with deep learning. By building and calibrating a dual-path imaging system, the real-world dataset where paired low resolution (LR) - high resolution (HR) images on the same scene can be obtained simultaneously. Numerical results on both USAF target and complex target objects demonstrate that the algorithm can restore high contrast images without pixilated noise. On the basis of super-resolution reconstruction, compound eye image composition based on fiber bundle is also realized in this paper for the actual imaging requirements. The proposed work is the first to apply a physical model-based network structure to fiber bundle imaging in the long-wave infrared band, effectively promoting the engineering application of thermal radiation detection.

Tunable and controllable multi-channel time-comb absorber based on continuous photonic time crystals.

To date there have been many studies on multi-channel absorbers for conventional photonic crystals (PCs). However, the number of absorption channels is small and uncontrollable, which cannot satisfy applications such as multispectral or quantitative narrowband selective filters. To address these issues, a tunable and controllable multi-channel time-comb absorber (TCA) based on continuous photonic time crystals (PTCs), is theoretically proposed. Compared with conventional PCs with fixed refractive index (RI), this system forms a stronger local electric field enhancement in the TCA by absorbing externally modulated energy, resulting in sharp multi-channel absorption peaks (APs). Tunability can be achieved by adjusting the RI, angle, and time period unit (T) of the PTCs. Diversified tunable methods allow the TCA to have more potential applications. In addition, changing T can adjust the number of multi-channels. More importantly, changing the primary term coefficient of n1(t) of PTC1 can control the number of time-comb absorption peaks (TCAPs) in multi-channels within a certain range, and the mathematical relationship between the coefficients and the number of multiple channels is summarized. This will have potential applications in the design of quantitative narrowband selective filters, thermal radiation detectors, optical detection instruments, etc.

Model-based deep learning for fiber bundle infrared image restoration

As the representative of flexibility in optical imaging media, in recent years, fiber bundles have emerged as a promising architecture in the development of compact visual systems. Dedicated to tackling the problems of universal honeycomb artifacts and low signal-to-noise ratio (SNR) imaging in fiber bundles, the iterative super-resolution reconstruction network based on a physical model is proposed. Under the constraint of solving the two subproblems of data fidelity and prior regularization term alternately, the network can efficiently “regenerate” the lost spatial resolution with deep learning. By building and calibrating a dual-path imaging system, the real-world dataset where paired low-resolution (LR) - high-resolution (HR) images on the same scene can be generated simultaneously. Numerical results on both the United States Air Force (USAF) resolution target and complex target objects demonstrate that the algorithm can restore high-contrast images without pixilated noise. On the basis of super-resolution reconstruction, compound eye image composition based on fiber bundle is also embedded in this paper for the actual imaging requirements. The proposed work is the first to apply a physical model-based deep learning network to fiber bundle imaging in the infrared band, effectively promoting the engineering application of thermal radiation detection.

Detection band expansion by independently tunable double resonances in a long-wavelength dual-color QWIP.

Multi-resonance light coupling management is a promising way to expand the operating spectral ranges of optoelectronic devices. The classical strategies are either lack of independent tunability for each resonance or involved with complex fabrication. Here, we propose a new scheme for expanding the operating spectral range of an optoelectronic device through a dual-color active material integrated with a simple resonant waveguide structure. The TM waveguide mode and the SPP mode of the resonant waveguide structure are regulated to match the two active regions of the dual-color material both spectrally and spatially. Applying this scheme to a long-wavelength infrared quantum well photodetector, the absorption efficiencies at the two peak detection wavelengths of the dual-color quantum wells are both enhanced by more than 10 times compared with the case of a standard 45° edge facet coupled device with the same detection material. The simple light coupling structure is easy to accomplish and compatible with focal plane arrays. For thermal radiation detection, the absorption efficiency of the 300 K blackbody radiation by our dual-color detector is 83.8% higher than that by a single-color detector with the optimized structural parameters. Moreover, either polarization sensitive or polarization insensitive detection could be achieved in this dual-color infrared quantum well photodetector by using anisotropic or isotropic gratings.

Wearable Ionogel-Based Fibers for Strain Sensors with Ultrawide Linear Response and Temperature Sensors Insensitive to Strain.

Fiber-shaped stretchable strain and temperature sensors are highly desirable for wearable electronics due to their excellent flexibility, comfort, air permeability, and easiness to be weaved into fabric. Herein, we prepare a smart ionogel-based fiber composed of thermoplastic polyurethane (TPU) and ionic liquid (IL) by the facile and scalable wet-spinning technique, which can serve as a wearable strain sensor with good linearity (a correlation coefficient of 0.997) in an ultrawide sensing range (up to 700%), ultralow-detection limit (0.05%), fast response (173 ms) and recovery (120 ms), and high reproducibility. Attributed to these outstanding strain sensing performances, the designed TPU/IL ionogel fiber-shaped sensor is able to monitor both subtle physiological activities and large human motions. More interestingly, because of the fast response and high resolution to strain, the fiber-shaped sensor can be sewn into the fabric to secretly encrypt and wirelessly translate message according to the principle of Morse code. More importantly, a wearable strain-insensitive temperature sensor can be obtained from the ionogel fiber if it is designed into an "S" shape, which can effectively eliminate the interference of strain on temperature sense. It is found that the inaccuracy of temperature sense is within 0.15 °C when the sensor is subjected to 30% tensile strain simultaneously. Moreover, this strain-insensitive temperature sensor shows a monotonic temperature response over a wide temperature range (-15 to 100 °C) with an ultrahigh detecting accuracy of 0.1 °C and good reliability, owing to the fast and stable thermal response of IL. This temperature sensor can realize the detection of thermal radiation, proximity, and respiration, exhibiting enormous potential in smart skin, personal healthcare, and wearable electronics. This work proposes a simple but effective strategy to realize the essential strain and temperature sensing capabilities of wearable electronics and smart fabrics without mutual interference.

Sensitivity and noise in THz electro-optic upconversion radiometers

This paper presents a study of noise in room-temperature THz radiometers that use THz-to-optical upconversion followed by optical detection of thermal radiation. Despite some undesired upconverted thermal noise, no noise is intrinsically introduced by efficient electro-optic modulation via a sum-frequency-generation process in high quality factor (Q) whispering-gallery mode (WGM) resonators. However, coherent and incoherent optical detection results in fundamentally different noise characteristics. The analysis shows that the upconversion receiver is quantum limited like conventional amplifiers and mixers, only when optical homodyne or heterodyne detection is performed. However, this type of receiver shows advantages as a THz photon counter, where counting is in the optical domain. Theoretical predictions show that upconversion-based room-temperature receivers can outperform state-of-the-art cooled and room-temperature THz receivers based on low-noise amplifiers and mixers, provided that a photon conversion efficiency greater than 1% is realized. Although the detection bandwidth is naturally narrow due to the highly resonant electro-optic modulator, it is not fundamentally limited and can be broadened by engineering selective optical coupling mechanisms to the resonator.

Flexible, double-sided broadband optical absorber based on tapered concave nanostructure

An optical absorber with the advantages of flexibility, broadband, insensitivity to incident angle and high efficiency in double-sided incidence is studied, realized and characterized. The absorber is composed of the tapered concave nanostructure covered with thin Ni-SiNx film. Simulation results show that there exist two different mechanisms in the absorptive behavior. The absorption is measured as 94.2% and 93.9% from 400 nm to 1600 nm in the front- and back-sided incidence, respectively. The absorber is fabricated by economic process, thus it can have a variety of potential applications, such as solar–thermal energy harvesting, thermal radiation detection, etc.

Comparative Study on Radiation Properties of Blackbody Cavity Model Based on Monte Carlo Method

In order to improve the absorption of stray radiation traps and thermal radiation detectors of blackbody radiators and enhance the thermal radiation transmission, large aperture and high-emissivity blackbody radiators or compact space-borne blackbody sources can be developed. The design of blackbody cavity with V-grooves is a method to change the effective emissivity of blackbody radiation source. At the design stage, the most important work is to evaluate its radiation characteristics in order to verify the effectiveness of this method. Two kinds of blackbody cavity models are designed in this paper. One is a cylindrical–conical blackbody cavity with a 2-mm deep 50° angle V-grooves (the cavity is 300 mm long and 80 mm in diameter, with a depth of 277 mm the cone part of the cavity is 23.09 mm long, the top angle of the cone is 120°, the wall thickness is 2 mm, and the surface will be painted with 0.95 emissivity coating). The other is the blackbody cavity model with the same structure and smooth inner wall. Using the special software based on Monte Carlo method, the radiation characteristics of the two blackbody cavity models are simulated under isothermal conditions. The average normal effective emissivity and right-conical effective emissivity of the blackbody cavity with different observation radius are obtained, respectively. The results show that the average normal effective emissivity and right-conical effective emissivity of the blackbody cavity with V-grooves on the inner wall are increased. In addition, the experimental results of radiative properties of the blackbody radiator having the V-grooved cavity measured by thermal cavity reflectometry method agree with the theoretical simulation results. Therefore, it is proved that the blackbody cavity with V-grooves on the inner wall (except for special angles) can be an effective way to improve the emissivity of the blackbody source.

Investigating the electronic and nonlinear optical properties of fullerene by substituting N, P, As, and Sb in the lattice structure: a DFT study

In this article, we used density functional theory (DFT) to investigate the structural, electronic and nonlinear optical properties of N, P, As and Sb doped fullerene. The average polarizability and hyperpolarizability is significantly improved when these impurities are substituted individually in the (C60) lattice structure. The maximum hyperpolarizability is calculated for N-doped fullerene (3541.27 au) followed by P-doped fullerene (259.71 au), As-doped fullerene (102.52 au) and Sb-doped fullerene (32.06 au). A similar trend is observed and the polarizability is found to decrease monotonically. Both the polarizability and hyperpolarizability values are found to decrease with an increasing energy gap of the doped fullerene. N-Doped fullerene has the lowest energy gap (1.28 eV) followed by P-doped fullerene (1.94 eV), As-doped fullerene (2.02 eV) and Sb-doped fullerene (2.10 eV). The lowest energy gap minimizes the excitation energy and thus improves the nonlinear optical response. From the calculation of time-dependent-DFT (TD-DFT), it is observed that the maximum absorption wavelength of N-doped fullerene, which is about 830 nm, is shifted towards the longer wavelength at the infrared region in the case of P, As, and Sb-doped fullerenes. The results obtained through this study will help encourage the potential utilization of the metal-free doped-fullerene systems as a form of unique optical devices, thermal radiation detector, etc.

Absorption Spectral Characteristics of Infrared Radiation in Silicon Dioxide Films for Thermal Radiation Detectors

The absorption spectral characteristics of silicon dioxide films in the IR range (λ = 8–14 µm) were studied to determine the optimal absorber thickness in the matrix structure of Golay microcells in order to design highly sensitive IR detectors. It is shown that the absorbance spectrum of SiO2 films deposited by electron-beam evaporation has a multipeak structure in the thickness range up to 2 µm and differs from the known absorption spectra of bulk silicon dioxide, which is apparently due to rearrangements in the film stoichiometry at the initial stages of film formation. Experiments have shown that the integrated absorption in deposited films in a given spectral range is close to a linear dependence on thickness and an order of magnitude smaller than the value obtained by calculation based on literature data for bulk SiO2.

A Novel Infrared Temperature Measurement with Dual Mode Modulation of Thermopile Sensor.

Superior to the traditional infrared temperature sensing architecture including infrared sensor and thermistor, we propose a novel sensing approach based on a single thermopile sensor with dual modes modulation. A switching and sensing circuit is proposed and realized with a chopper amplifier AD8551 and p-channel MOSFET (PMOS) for switching between detection of thermal radiation and the target and the ambient temperature for compensation. The error of target temperature after temperature compensation is estimated at less than 0.14 °C.

Thermoelectric radiation detector based on a superconductor-ferromagnet junction: Calorimetric regime

We study the use of a thermoelectric junction as a thermal radiation detector in the calorimetric regime, where single radiation bursts can be separated in time domain. We focus especially on the case of a large thermoelectric figure of merit ZT affecting significantly, for example, the relevant thermal time scales. This work is motivated by the use of hybrid superconductor/ferromagnet systems in creating an unprecedentedly high low-temperature ZT even exceeding unity. Besides constructing a very general noise model which takes into account cross correlations between charge and heat noise, we show how the detector signal can be efficiently multiplexed by the use of resonant LC circuits giving a fingerprint to each pixel. We show that for realistic detectors operating at temperatures around 100 to 200 mK, the energy resolution can be as low as 1 meV. This allows for a broadband single-photon resolution at photon frequencies of the order of or below 1 THz.

Infrared camera on a butterfly's wing.

Thermal cameras were constructed long ago, but working principles and complex technologies still limit their resolution, total number of pixels, and sensitivity. We address the problem of finding a new sensing mechanism surpassing existing limits of thermal radiation detection. Here we reveal the new mechanism on the butterfly wing, whose wing-scales act as pixels of an imaging array on a thermal detector. We observed that the tiniest features of a Morpho butterfly wing-scale match the mean free path of air molecules at atmospheric pressure - a condition when the radiation-induced heating produces an additional, thermophoretic force that deforms the wing-scales. The resulting deformation field was imaged holographically with mK temperature sensitivity and 200 Hz response speed. By imitating butterfly wing-scales, the effect can be further amplified through a suitable choice of material, working pressure, sensor design, and detection method. The technique is universally applicable to any nano-patterned, micro-scale system in other spectral ranges, such as UV and terahertz.

Modulation infrared thermometry of caloric effects at up to kHz frequencies.

We present a novel non-contact method for the direct measurement of caloric effects in low volume samples. The adiabatic temperature change ΔT of a magnetocaloric sample is very sensitively determined from thermal radiation. Rapid modulation of ΔT is induced by an oscillating external magnetic field. Detection of thermal radiation with a mercury-cadmium-telluride detector allows for measurements at field frequencies exceeding 1 kHz. In contrast to thermoacoustic methods, our method can be employed in vacuum which enhances adiabatic conditions especially in the case of small volume samples. Systematic measurements of the magnetocaloric effect as a function of temperature, magnetic field amplitude, and modulation frequency give a detailed picture of the thermal behavior of the sample. Highly sensitive measurements of the magnetocaloric effect are demonstrated on a 2 mm thick sample of gadolinium and a 60 μm thick Fe80B12Nb8 ribbon.

Control of microwave assisted macadamia drying

ABSTRACTWe studied the microwave-assisted macadamia drying, using surface temperature control and without surface temperature control as well as hot air drying, and assessed the drying time, drying rate, colour values, hardness and water activity of nuts and efficiency. The surface temperature of macadamia nuts was controlled between 60 and 80 °C using a thermal radiation detector. For drying without the surface temperature control, drying temperatures in the range of 40–60 °C and microwave power were controlled in the range of 1.6–4.4 Wg−1. We found that increase in microwave power and temperature had a positive effect with shorter drying time and increased drying rate. Microwave assisted hot air drying by surface temperature control led to a better quality product in respect of kernel brightness and suitable aw for storage, but a harder kernel. In addition, drying without surface temperature control had the highest energy efficiency followed by surface temperature control and hot air only. Considering quality, the recommended condition was drying by surface temperature control at 60 °C with 60 °C hot air combined with microwave.

Investigation on a laser-assisted radiation thermometry technique.

A laser-assisted radiation thermometry (LART) technique is proposed for the surface temperature measurement of objects at high temperatures, which obviates the need for the knowledge of specimen emissivity. It uses a modulated laser to excite a temperature rise at the specimen surface, which is remotely sensed through thermal radiation detection at two infrared wavelengths. The theoretical analysis indicates that the surface temperature of the specimen can be inferred from the detected signals, independently of specimen emissivity. Measurements were performed on an oxidized Inconel 600 sample over a temperature range of 1120-1265 K. Measured surface temperatures were compared with those deduced from thermocouple measurements made inside the sample, and indicated less than 3% differences between them for sample surface temperatures above 1200 K.

Three-dimensional integral imaging and object detection using long-wave infrared imaging.

We propose a passive three-dimensional (3D) imaging technique based on integral imaging using a long-wave infrared (LWIR) camera. 3D imaging can improve visualization and detection of objects in adverse environments, such as low light levels and the presence of partial occlusions, along with depth estimation by reconstructing the scene at the plane of the object. This is achieved by capturing multiple two-dimensional images, known as elemental images (EI), of a scene with each image having a unique perspective of the 3D objects. Moreover, LWIR imaging performs well in photon-limited environments due to detection of thermal radiation from an object rather than the reflected light. Once the EIs have been captured, image restoration is performed on the captured images. A 3D scene is then reconstructed and object detection using correlation filters and support vector machines is performed. Our experiments with human face detection show that 2D imaging may fail to detect occluded humans, whereas passive 3D imaging with LWIR could be successful. To the best of our knowledge, this is the first report of passive 3D integral imaging with LWIR for object detection, and in particular, in low light environments.