LWIR Range Research Articles

Optothermal characterization of vanadium dioxide films by Infrared Thermography

The thickness of vanadium dioxide (VO2) films is a crucial parameter for the study of their optical and thermal properties. In this paper we studied the effect of the film thickness on the thermal hysteresis loop during the phase transition of VO2 deposited on a sapphire substrate by pulsed laser deposition (PLD), by the application of the Infrared Thermography technique. We measure the main thermal hysteresis parameters of VO2 samples with different thicknesses in the LWIR range (8–14 μm) showing how the transition temperature during the heating and cooling cycles, and the width of the hysteresis loop, may change with thickness. We analyzed and compared the obtained results with, in situ Grazing Incidence X-Ray Diffraction (GI-XRD). A good agreement between the results obtained with the two techniques was found demonstrating the reliability of the IR Thermography as a quantitative characterization tool.The results show that the structural and IR emissivity properties of the VO2 layer exhibit a dynamic range dependent on the layer thickness due to a correlation with the crystalline grain size. This has important effects in view of a tailored energy management for the use of those materials as smart radiators or smart windows.

Longwave infrared multispectral image sensor system using aluminum-germanium plasmonic filter arrays

A multispectral camera records image data in various wavelengths across the electromagnetic spectrum to acquire additional information that a conventional camera fails to capture. With the advent of high-resolution image sensors and color filter technologies, multispectral imagers in the visible wavelengths have become popular with increasing commercial viability in the last decade. However, multispectral imaging in longwave infrared (LWIR, 8–14 μm) is still an emerging area due to the limited availability of optical materials, filter technologies, and high-resolution sensors. Images from LWIR multispectral cameras can capture emission spectra of objects to extract additional information that a human eye fails to capture and thus have important applications in precision agriculture, forestry, medicine, and object identification. In this work, we experimentally demonstrate an LWIR multispectral image sensor with three wavelength bands using optical elements made of an aluminum (Al)-based plasmonic filter array sandwiched in germanium (Ge). To realize the multispectral sensor, the filter arrays are then integrated into a three-dimensional (3D) printed wheel stacked on a low-resolution monochrome thermal sensor. Our prototype device is calibrated using a blackbody and its thermal output has been enhanced with computer vision methods. By applying a state-of-the-art deep learning method, we have also reconstructed multispectral images to a better spatial resolution. Scientifically, our work demonstrates a versatile spectral thermography technique for detecting target signatures in the LWIR range and other advanced spectral analyses.

Large-aperture, widely and linearly tunable, electromagnetically actuated MEMS Fabry-Perot filtering chips for longwave infrared spectral imaging.

Longwave infrared spectral imaging (LWIR-SI) has potential in many important civilian and military fields. However, conventional LWIR-SI systems based on traditional dispersion elements always suffer the problems of high cost, large volume and complicated system structure. Micro-electro-mechanical systems Fabry-Perot filtering chips (MEMS-FPFC) give a feasible way for realizing miniaturized, low cost and customizable LWIR-SI systems. The LWIR MEMS-FPFC ever reported can't meet the demands of the next-generation LWIR-SI systems, due to the limitation of small aperture size and nonlinear actuation. In this work, we propose a large-aperture, widely and linearly tunable electromagnetically actuated MEMS-FPFC for LWIR-SI. A multi-field coupling simulation model is built and the wafer-scale bulk-micromachining process is applied to realize the design and fabrication of the proposed MEMS-FPFC. Finally, with the rational structural design and fabrication process, the filtering chip after packaging has an aperture size of 10 mm, which is the largest aperture size of LWIR MEMS-FPFC ever reported. The fabricated electromagnetically actuated MEMS-FPFC can be tuned continuously across the entire LWIR range of 8.39-12.95 µm under ±100 mA driving current with a pretty good linear response of better than 98%. The developed electromagnetically actuated MEMS-FPFC can be directly used for constructing miniaturized LWIR-SI systems, aiming for such applications as military surveillance, gas sensing, and industry monitoring.

Simulation of the Operation of a Single Pixel Camera with Compressive Sensing in the Long-Wave Infrared

Imaging with the use of a single pixel camera and based on compressed sensing (CS) is a new and promising technology. The use of CS allows reconstruction of images in various spectrum ranges depending on the spectrum sensibility of the used detector. During the study image reconstruction was performed in the LWIR range based on a thermogram from a simulated single pixel camera. For needs of reconstruction CS was used. A case analysis showed that the CS method may be used for construction of infrared-based observation single pixel cameras. This solution may also be applied in measuring cameras. Yet the execution of a measurement of radiation temperature requires calibration of results obtained by CS reconstruction. In the study a calibration method of the infrared observation camera was proposed and studies were carried out of the impact exerted by the number of measurements made on the quality of reconstruction. Reconstructed thermograms were compared with reference images of infrared radiation. It has been ascertained that the reduction of the reconstruction error is not directly in proportion to the number of collected samples being collected. Based on a review of individual cases it has been ascertained that apart from the number of collected samples, an important factor that affects the reconstruction fidelity is the structure of the image as such. It has been proven that estimation of the error for reconstructed thermograms may not be based solely on the quantity of executed measurements.

The long-wave infrared (8-12 μm) spectral features of selected rare earth element—Bearing carbonate, phosphate and silicate minerals

Rare earth elements (REEs) are a group of metals essential to high technology industries. This high demand, combined with a high supply risk, has led to an understanding that REEs are critical to society. Despite the potential that hyperspectral imaging (HSI) data offers for a fast and non-invasive characterization of the REEs, it is still poorly understood whether REEs have some information in the long-wave infrared (LWIR; 8–12 μm) wavelength range that can be used for their identification. To partially fill this gap, we have investigated the spectroscopy of twelve REE-bearing mineral samples using relatively high spatial and spectral resolution LWIR hyperspectral imaging data. These samples were formerly characterized using electron probe microanalysis (EPMA), scanning electron microscopy (SEM), and hyperspectral imaging data acquired in the 0.4–2.5 μm wavelength range. Results from these analyses were compared to and used to guide the analysis of the HSI data recorded in the LWIR range. This information was further compared to a reference spectral library of rare earth oxides. Our findings suggest that the spectral features of the samples can generally be traced to the asymmetric degenerate stretching and bending modes of the X-O (X = C, Si, P) groups. Moreover and contrary to what has been observed in the shorter wavelengths, there are no definitive spectral features in the LWIR wavelength region that could be assigned to any specific REE.

1 Parametric Comparison of Selected Dual Elements PIR Sensors

Most of the warm blooded animals emanatethermal radiations in the MWIR to LWIR (Medium Wave toLong Wave Infrared) range from 3μm to 18μm. If the object iswarmer than the surroundings, its thermal radiation is shiftedtoward higher frequency within the band and the thermal fluxrate becomes stronger. To detect radiation in this band, singleand multi-elements pyroelectric sensors utilized in the scanningsystems to detect, with background contrast, the presence of stillor moving thermal objects emitting thermal flux in thebandwidth specified. PIR sensors are commonly used to detectthese radiation, their response is further processed by electronicsystems and generally analyzed by software embedded systems.Here we present a comparative study of commercially availablePIR sensors. In this study we evaluated dual element PIR sensorsfor their electrical and thermal parameters. Two types of testprocedures were used, which can be used for any type of PIRsensors.

Parametric Comparison of Selected Dual Elements PIR Sensors

Most of the warm blooded animals emanatethermal radiations in the MWIR to LWIR (Medium Wave toLong Wave Infrared) range from 3μm to 18μm. If the object iswarmer than the surroundings, its thermal radiation is shiftedtoward higher frequency within the band and the thermal fluxrate becomes stronger. To detect radiation in this band, singleand multi-elements pyroelectric sensors utilized in the scanningsystems to detect, with background contrast, the presence of stillor moving thermal objects emitting thermal flux in thebandwidth specified. PIR sensors are commonly used to detectthese radiation, their response is further processed by electronicsystems and generally analyzed by software embedded systems.Here we present a comparative study of commercially availablePIR sensors. In this study we evaluated dual element PIR sensorsfor their electrical and thermal parameters. Two types of testprocedures were used, which can be used for any type of PIRsensors.

Low-cost approach for integrated long-wavelength infrared sensor arrays

A new low-cost process for mid resolution FIR-Arrays for thermal imaging in the LWIR range (8- 14 μm) has been developed. Integrated array devices with 1k and 5k pixel array size have been designed and manufactured using this process which is fully compatible with semiconductor production. The devices are suitable to support detection of humans e.g. in security and automotive safety applications.

Infrared Detection Module for Free Space Optics

Free space optics (FSO) communication in LWIR range is less sensitive to atmosphere features. VIGO System S.A. — company from Poland — develops high performance detector module optimized for LWIR range. We present new detection module dedicated to open space optical communication optimized for 10μm. Module specification: Detector: PVI-2TE-10 photodiode with immersion lens, thermoelectrically cooled. Operating temperature range: −30 . . . + 60◦C. Detector temperature stabilization precision: 0.01◦C. Detector time constant: < 1 ns. Preamplifier bandwidth: 100 MHz. Input current noise: 5 pA/ √ Hz. Detector capacity < 5 pF. Detection module is based on PVI-2TE-10 HgCdTe photodiode, thermoelectrically cooled by two stage Peltier cooler. It is optimized for long wavelength — 10μm. TEC controller stabilizes detector temperature with high precision in wide ambient temperature range. Immersion lens enables optimization of the detector physical dimensions, decreasing detector capacity and time constant. Module parameters enables maximum transmission speed 100 Mb/s. Low bit error rate requires correct transmission with low and high signal level. Detector and preamplifier have wide linear working range, noise optimization provides module high detectivity. DC reverse bias increases dynamic resistance and improves frequency response.