Thermal Imaging Applications Research Articles

Multi-sensor spatial augmented reality for visualizing the invisible thermal information of 3D objects

In recent years, infrared imaging technology has been widely used to capture valuable thermal information of target objects for various applications such as construction engineering, advanced manufacturing, and medical diagnosis. However, it still remains a challenging task to visualize the invisible thermal information of three-dimensional objects for further evaluation and decision making. In this paper, we build a multi-sensor system consisting of a long-wave infrared camera, a RGBD camera, and a digital projector for multimodal data acquisition, real-time 3D thermographic reconstruction, and projector-based spatial augmented reality. We propose a hybrid method that combines the benefits of model-based ray casting and frame-based image warping to generate high-quality projected images with complete view coverage and abundant thermal details for visualizing the invisible thermal information on 3D objects. The effectiveness of the proposed method has been validated for two typical thermal imaging applications including human body temperature monitoring and non-destructive evaluation of composite materials.

Assessing and mapping vineyard water status using a ground mobile thermal imaging platform

Water status directly affects yield and crop quality in grapevines. Precision viticulture demands the application of new available technologies and methodologies for accurate irrigation management in vineyards. The objective of this work was the development of an on-the-go thermal imaging application for the assessment and mapping of vineyard water status, building a dataset from a commercial Tempranillo (Vitis vinifera L.) vineyard over two consecutive seasons and validating it in another commercial vineyard from a different winegrowing region. Thermal imaging was performed with a thermal camera mounted in an all-terrain vehicle, moving at 5 km/h and operating at a distance from the canopy of 1.20 m. Stem water potential (Ψstem) was used for validation as the grapevine water status reference method, using a Scholander pressure chamber. Crop Water Stress Index (CWSI) and Stomatal Conductance Index (Ig) from a 4-day dataset were computed and correlated with Ψstem, delivering significant (p < 0.0001) determination coefficients R2 up to 0.71. The prediction capability of this dataset was also validated in another commercial vineyard, achieving a prediction R2 up to 0.82 (RMSE of 0.123 MPa). The predicted values of both indices were thus employed for mapping vineyard water status in the second plot. These results evidence the potential applicability of on-the-go thermal imaging for assessing and mapping water status in commercial vineyards required for precision viticulture.

Guiding temperature waves with graded metamaterials

Temperature waves exist in many practical scenarios such as pulse heat sources and periodic temperature fluctuations, which have broad applications for thermal nondestructive detection. However, it is still challenging to guide temperature waves in irregularly shaped pipes because temperature waves might be strongly scattered. To solve the problem, we propose a scheme to guide temperature waves with graded metamaterials that have continuous parameter variations in space. Since graded metamaterials can ensure the same phases of thermal wavefronts despite different spatial distances, temperature waves can propagate in irregularly shaped pipes without scattering. We then demonstrate an elementary unit to realize the right-angle bending of temperature waves. Experimental suggestions are also provided to design the elementary unit with common materials and layered structures. We further combine the elementary units together to realize three practical functions including obstacle avoidance, thermal periscope, and reverse bending. These results have potential applications for thermal imaging and sensing in elbow pipes.

Ultrathin, broadband, omnidirectional, and polarization-independent infrared absorber using all-dielectric refractory materials

Abstract Broadband long-wavelength infrared (LWIR) optical absorbers have important applications in thermal emission and imaging, infrared camouflaging, and waste heat and biothermal energy utilization. However, the practical application of broadband LWIR optical absorbers requires low-cost and facile fabrication of large-area structures with limited thickness. This paper reports the design and fabrication of an ultrathin, broadband, omnidirectional, and polarization-independent LWIR optical absorber composed of anodized aluminum oxide and highly doped Si using the gradient refractive index strategy. The average absorption of the broadband optical absorber is higher than 95% in the 8–15 μm wavelength range, and it has wide incident angle and polarization tolerances. More than 95% of the optical energy in the wavelength range from 8 to 13 μm was absorbed within a depth of 8 μm, making this absorber the thinnest broadband LWIR dielectric absorber so far. The absorption remained above 90% after annealing at 800 °C in air. The infrared camouflage of the proposed absorber was successfully demonstrated with a human body background. With the advantages of facile fabrication, low-cost materials, restricted absorption thickness, and excellent thermal stability, the developed broadband LWIR optical absorber is very promising for the practical applications mentioned above.

Numerical investigation of polarization-insensitive multiband metamaterial for terahertz solar absorber

This study presents a nanostructured multiband metamaterial absorber for the optical regime application. The proposed structure is exhibited 0° to 90° polarization insensitivity and up to 45° angular stability with more than 90% peak absorption in between 300 THz800 THz frequency range. Proposed MMA structure is acquired perfect absorption of 99.99% at 571THz, 99.50% at 488.26 THz, 99.32% at 598 THz frequency by adjusting geometrical parameters. Due to perfect impedance matching with plasmonic resonance characteristics, these structures achieved an average absorption of 95.30%, 91.96%, 97.25%, 97.65%, 91%,90%,90.23% in between (337.5 THz-346.5 THz), (471 THz-478 THz), (497.5 THz-505 THz), (519 THz-530.5 THz), 564.5 THz-577 THz), (604 THz-673 THz), (686 THz-708 THz), respectively. The near field pattern of proposed MMA is used to explain the absorption mechanism at resonance frequency point and the geometric parameters are explored and analyzed to demonstrate the performance of the proposed structure. Moreover, CST-HFSS interference is validated the simulation data with the help of the finite element method (FEM). Polarization insensitivity and wide angular stability in terahertz (THz) frequency regime make this structure suitable for the application of magnetic resonance imaging (MRI), color images, thermal imaging and solar cell applications like exploitation of solar energy.

Controlling thermal waves of conduction and convection

Electromagnetic wave refractions have been widely explored due to their profound physics and practical applications, especially the negative refraction. However, the hyperbolic feature of the Maxwell equations makes it difficult to extend the related physics to the Fourier conduction because the Fourier equation is parabolic. To solve the problem, we study thermal waves of conduction and convection because convection can additionally introduce the hyperbolic feature to heat transfer. We further design convection-assisted metamaterials to realize the positive, vertical, and negative refractions of thermal waves, which have a phenomenal analog of electromagnetic wave refractions despite different mechanisms. The negative refraction of thermal waves means that the incident and refractive thermal waves are at the same side of the normal, but the wave vector and energy flow are still along the same direction. As a model application, we apply the refractive behaviors to design a thermal wave concentrator which can increase wave numbers and energy flows. This work provides insights into thermal wave manipulation, which may have potential applications in thermal wave imaging.

Assessment of temperature changes in carcasses in the early post-mortem period using the spectrum of a thermal imaging camera

Precise determination of the time of death of a human being or animal is extremely important for investigations by law enforcement agencies. The aim of the study was to use a thermal imaging camera for imaging of the cooling of dog carcasses in controlled conditions, as a practical application of thermal imaging in veterinary forensics for the purpose of establishing the time of death of an animal, as well as to compare the usefulness of this method with that of the currently used Henssge nomogram. A thermographic technique exploiting infrared radiation was used in the study. The research material was 10 dog carcasses (5 female and 5 male) aged 6 to 16 years, with body weight from 23 to 36 kg. Thermal imaging of a carcass in combination with other methods, such as measurement of internal body temperature and analysis of post-mortem changes, enables reliable determination of the time of death of an animal, which is often of fundamental importance in veterinary forensic practice.

Application of thermal imaging for detecting cold air leak location in cold storage

&lt;span&gt;Nowadays Cold storage has been playing an important role in preserving the perishable food products like fruits, vegetables, dairy products, fish, and meat etc. The major problem of cold storage is unwanted energy transmission during the operation. It is necessary to maintain the constant temperature during storing the products. There are different kinds of energy loss happening during the operation. One of the major causes is cold air leaking from the inside of the cold room to outside. It is due to poor insulation and improper maintenance of cold storage. It is very difficult to identify the exact location of the leak by the naked eye. In this research work, the cold storage was inspected with the thermal imaging system. Thermal cameras are highly sensitive to temperature and it can detect the variation of temperature ranging from 0.1°C. The measured temperatures are further converted into a colour based pattern. It is known as thermogram. These colour-based thermal patterns are further processed for identifying energy transmission location. It is done by applying various image processing methods such as histogram equalization, diffusion error, otsu thresholding and morphologic function. These techniques were applied to images of cold storages and exact cold air transmission locations were identified.&lt;/span&gt;

Nd3+ doped TiO2 nanocrystals as self-referenced optical nanothermometer operating within the biological windows

In this work, we report a potential optical nanothermometer (NTh) based on Nd3+ doped TiO2 nanocrystals, operating within the biological windows. The Nd3+ emissions at around 900, 1060, and 1340 nm were used upon excitation at 808 nm. The fluorescence intensity ratio (FIR) corresponding to the emissions at 1060 nm and 1340 nm (FIR = I1060 nm/I1340 nm) was investigated as a function of the temperature in the range of 300−343 K. In addition, the effect of the Nd3+ ions concentration and influence of the crystalline phase on the luminescence and the relative thermal sensitivity were presented. As a result, it was found that TiO2 nanocrystals doped with 10 wt% of Nd3+ ions and associated with the brookite phase has the highest luminescence emission and relative thermal sensitivity compared to other samples investigated here and in previous literature. The maximum value obtained to the relative thermal sensitivity was 0.86 % K−1, which is high comparatively with other ones of Nd3+ doped systems, and minimum thermal resolution of ∼1 K. This information together with the biocompatibility of TiO2 nanocrystals, and excitation and emissions wavelengths lying within the biological windows, favor potential applications in fluorescence and thermal imaging of biological systems.

Application of Acoustic Emission and Thermal Imaging to Test Oil Power Transformers

In this paper, the research methodology and the results of the analysis carried out using the acoustic emission (AE) and thermal imaging for a selected oil power transformer are presented. The basis for the research, by means of the AE method, was the author’s patented research method. The AE descriptor maps on the side walls of the tested transformer along with the location of areas with increased AE activity and an analysis of the properties of AE signals recorded at the measurement points located in these areas have been performed. The results showed no partial discharges that could threaten further operation of the tested transformer as well as three areas where increased magnetoacoustic emission occurred. Thermal imaging studies were carried out in the 7.5 μm &lt; λ &lt; 13 μm band. Three areas were located on the calculated thermograms: the entire upper surface of the transformer tank and two areas on the side walls of the tested transformer in which increased IR radiation occurred. The results of the analysis of the research results for the two methods correspond with each other, having a common part, and complement each other giving a broader description of studied phenomena.

Field identification of weed species and glyphosate-resistant weeds using high resolution imagery in early growing season

Accurate weed mapping in early growing season is an essential step in the site-specific weed management system. This study focuses on validating the potential application of high resolution multispectral and thermal UAS images in classification of weed species and glyphosate-resistant weeds at early phenological stages. A field experiment was conducted to evaluate supervised classification methods to identify three-weed species including waterhemp (Amaranthus rudis), kochia (Kochia scoparia), and ragweed (Ambrosia artemisiifolia L.). The accuracy of six classification algorithms namely Parallelepiped, Mahalanobis Distance, Maximum Likelihood, Spectral Angle Mapper, Support Vector Machine and Decision Tree implemented at pixel and object-based levels in weed species classification were evaluated. Thermal infrared imagery was also used to assess the canopy temperature variance within the weed species to identify the glyphosate-resistance status in detected weeds. The object-based algorithms developed with mosaicked imagery effectively classified weed species with the overall accuracy and Kappa coefficient values greater than 86% and 0.77, respectively. The lowest accuracy and Kappa coefficient (67% and 0.58) were observed for pixel-based Mahalanobis Distance algorithm. The canopy temperature-based classification of susceptible and resistant weeds resulted in the discrimination accuracies of 88%, 93% and 92% in glyphosate-resistant kochia, waterhemp and ragweed, respectively.

Resolution enhanced photothermal imaging by high-order correlation.

Laser scanning photothermal imaging offers a powerful non-destructive testing tool to visualize subsurface structures of opaque materials, but it suffers the resolution limit imposed by thermal diffusion. To overcome this physical obstacle, a tightly focused excitation beam with a high repetition rate is usually used to improve the spatial resolution. Here, we demonstrate that the resolution of photothermal imaging could be enhanced using the high-order correlation imaging method inspired by correlated optical imaging. By carefully designing the laser scanning and modulation behavior, we can individually control the statistical properties of isolated hotspots induced by lasers. Imaging reconstructions of subsurface structures are performed afterward by reading out time-fluctuated thermal images. Moreover, the resolution can be further enhanced by using the high-order correlation, which enables a new way for highly resolved thermal imaging and metrology applications.

Experimental verification of super-compact ultra-wideband (UWB) polarization and incident angle-independent metamaterial absorber

AbstractIn this paper, a super-compact ultra-wideband (UWB) metamaterial absorber (MMA) is presented. The absorber design consists of an inverted L-shaped structure and a diagonal rectangular-shaped structure. The capacitive coupling between these two structures not only provides UWB nature but also provides a super-compact absorber design. The dimension of the unit cell arrangement is 5 × 5 mm2 and printed on a low-cost FR-4 substrate of thickness 1.54 mm (0.061λlowest). The design absorber provides more than 97% absorptivity from 12 to 21 GHz for normal incidence electromagnetic (EM) wave. However, the proposed MMA has a full width at half maximum absorption bandwidth of 11.71 GHz from 10.34 to 22.05 GHz. Moreover, the surface current distributions have been analyzed to understand the absorption mechanism of the MMA. The stability of the proposed design is validated with different incident angles (for TE and TM modes) and different polarization angles. Finally, the absorber design is fabricated and verified experimentally. Furthermore, the UWB frequency range, high absorption, ease in design and fabrication, and cost-effective make it suitable for different quality applications in stealth technology, thermal imaging, radar detection, antenna systems, and other EM devices.

OBJECT DETECTION IN UAV-BORNE THERMAL IMAGES USING BOUNDARY-AWARE SALIENCY MAPS

Abstract. In this paper, we propose a method of object detection based on thermal images acquired from unmanned aerial vehicles (UAV). Compared with visible images, thermal images have lower requirements for illumination conditions, but they have some problems, such as blurred edges and low contrast. To address these problems, we propose to use the saliency map of thermal images for image enhancement as the attention mechanism of the object detector. In the paper, the YOLOv3 network is trained as a detection benchmark and BASNet is used to generate saliency maps from the thermal images. We fuse the thermal images with their corresponding saliency maps through the pixel-level weighted fusion method. Experiment results tested on real data have shown that the proposed method could realize the task of object detection in UAV-borne thermal images. The statistical results show that the average precisions (AP) of pedestrians and vehicles are increased by 4.5% and 2.6% respectively, compared with the benchmark of the YOLOv3 model trained on only the thermal images. The proposed model provides reliable technical support for the application of thermal images with UAV platforms.

Feasibility of Low-Cost Thermal Imaging for Monitoring Water Stress in Young and Mature Sweet Cherry Trees

Infrared thermography has been introduced as an affordable tool for plant water status monitoring, especially in regions where water availability is the main limiting factor in agricultural production. This paper outlines the potential applications of low-cost thermal imaging devices to evaluate the water status of young and mature sweet cherry trees (Prunus avium L.) submitted to water stress. Two treatments per plot were assayed: (i) a control treatment irrigated to ensure non-limiting soil water conditions; and (ii) a water-stress treatment. The seasonal evolution of the temperature of the canopy (Tc) and the difference between Tc and air temperature (ΔT) were compared and three thermal indices were calculated: crop water stress index (CWSI), degrees above control treatment (DAC) and degrees above non-water-stressed baseline (DANS). Midday stem water potential (Ψstem) was used as the reference indicator of water stress and linear relationships of Tc, ΔT, CWSI, DAC and DANS with Ψstem were discussed in order to assess their sensitivity to quantify water stress. CWSI and DANS exhibited strong relationships with Ψstem and two regression lines to young and mature trees were found. The promising results obtained highlight that using low-cost infrared thermal devices can be used to determine the plant water status in sweet cherry trees.

Kümeslerdeki ısı kayıplarının termal kamerayla izlenmesi

Buildings consume approximately 36% of the total energy overall in Turkey. Further, space heating and cooling in buildings accounts for more than one-third of the total energy consumed. Therefore, undesirable heat losses are one of the most significant problems in enhancing buildings’ energy efficiency. The most important issue in preventing heat losses in buildings is determining the areas that lead to loss, which can be detected with high-tech thermal cameras. The application of thermal imaging in poultry buildings is an innovative new technology that can help determine the performance of insulation applications. This study focused on applicability of thermal imaging to detect heat losses and gains because of structural problems in a poultry building. The findings indicate that thermal imaging technique can identify structural problems which lead to heat losses or gains and that these problems mostly arise from holes in windows and doors, insufficient insulation windows and doors frame, and cracks in sandwich panel structures.

Design and parametric analysis of a wide-angle polarization-insensitive metamaterial absorber with a star shape resonator for optical wavelength applications

Optical wavelengths considered as the key source of electromagnetic waves from the sun, and metamaterial absorber (MMA) enables various applications for this region like real invisible cloaks, color imaging, magnetic resonance imaging, light trapping, plasmonic sensor, light detector, and thermal imaging applications. Contemplated those applications, a new wide-angle, polarization-insensitive MMA is presented in this study. The absorber was formatted with three layers that consisted of a sandwiched metal-dielectric-metal structure. This formation of metamaterial absorber showed a good impedance match with plasmonic resonance characteristics. The structure was simulated using the FIT and validated with the FEM. A variety of parametric studies were performed with the design to gain best physical dimension. The mechanism of absorption also explained immensely by various significant analysis. The design had average 96.77% absorption from wavelengths of 389.34 nm to 697.19 nm and a near-perfect absorption of 99.99% at a wavelength of 545.73 nm for TEM mode. For an ultra-wide bandwidth of 102 nm, the design exhibited above 99% absorbance. The proposed is wide-angle independent up to 60° for both TE and TM mode, which is useful for solar energy harvesting, solar cell, and solar thermophotovoltaics (STPV). This MMA can be used for an optical sensor or as a light detector. Moreover, this proposed design can be employed in some applications mentioned above.

ZnO nanoparticles enhanced near-infrared photodetection in organic phototransistors based on narrow bandgap polymer

Highly sensitive near-infrared (NIR) photodetectors have attracted extensive attention due to their wide applications in thermal imaging, night vision and human health monitoring. Organic phototransistors (OPTs) are an important type of photodetector with three-terminal contact, which provides high sensitivity and tunable gain with an external quantum efficiency (EQE)>100% by controlling unbalanced charge transport through an optically controlled gate terminal. Thus, NIR OPTs are considered as a promising alternative NIR light detecting technology to conventional inorganic NIR phototransistors. The design and fabrication flexibility provided by the organic semiconductors and solution processes also have significant cost benefit, creating next-generation large-area, low-cost and flexible NIR photodetectors. However, now the performance of NIR-OPT is not high enough, which is still far from practical applications. Low field-effect mobility, limited exciton dissociation, and poor NIR light absorption are the main reasons to hamper the performance of NIR OPTs. A key technical development to circumvent this hurdle is to create an organic channel layer with ordered microstructure to provide high field-effect mobility and a smart device design to enhance exciton dissociation. In this work, an air stable conjugated semiconducting polymer of diketopyrrolopyrrole-dithienylthieno[3,2- b ]thiophene (DPP-DTT) with narrow band gap was selected as the NIR light response medium. The DPP-DTT nanowire network was obtained by a solution-processed and scalable approach called polymer-matrix-mediated molecular self-assembly. The matrix polymer of polystyrene (PS) was selectively removed from the resulted DPP-DTT:PS blend film, leaving the pristine DPP-DTT nanowire network thin film as the active channel layer for the NIR OPTs. The electrical properties and NIR response of the OPTs based on DPP-DTT nanowire network were studied. It is found that the pristine DPP-DTT nanowire network layer exhibited a typical p-type field-effect transport, showing the hole mobility of >1 cm2/(V s) and on/off ratio >106. These devices also showed sensitive NIR response with photoresponsivity ( R ) of 336 A/W and specific detectivity ( D *) of 5.6×1012 Jones under NIR light intensity of 8 μW/cm2. To further improve the NIR photodetection of the DPP-DTT nanowire network OPTs, zinc oxide (ZnO) nanoparticles were introduced into the devices as electron acceptor material. A small amount of ZnO nanoparticles (1.0 mg/mL) were spin coated onto the DPP-DTT nanowire network to increase the separation efficiency of photodenerated excitons and then capture the photogenerated electrons in trap sites, thereby minimizing the negative impact of photogenerated electrons on hole transport in the NIR OPTs. As a result, the NIR photodetection of the ZnO-modified OPTs was significantly improved. The photosensitivity of ZnO-modified devices reaches as high as 107, which is increased by about 4 to 5 orders of magnitude compared with the pristine DPP-DTT nanowire network NIR OPTs. Correspondingly, the R and D * of ZnO-modified NIR OPTs have been also enhanced. The maximum R value was increased to 721 A/W, which is more than twice the R value of the pristine DPP-DTT nanowire network NIR OPTs. It is noted that such a large R value has achieved the performance level of conventional inorganic NIR phototransistors. Moreover, the maximum D * of the ZnO-modified NIR OPTs reaches 1.3×1013 Jones under the NIR intensity of 8 μW/cm2. Therefore, this work provides a good idea for the structural design and device performance optimization of high-performance NIR OPTs.

Thermal imaging as a tool in food analysis

This Letter reviews the application of thermal imaging for food quality control. Thermal imaging uses a single, portable device, which provides a visible image of the invisible infrared radiation, and can be used for real-time monitoring at low cost compared to spectral imaging technology. To monitor the quality parameters of the sample, classification or regression models are constructed using multivariate analysis or chemometrics tools. Few studies have used thermography for the analysis of food to-date, so this Letter will only address thermal mapping, internal defect detection, adulteration detection and the prediction of compound concentration.

Free space super focusing using all dielectric hyperbolic metamaterial

Despite that Hyperbolic Metamaterial (HMM) has demonstrated sub-wavelength focusing inside of it, sub-wavelength imaging in free space of HMM is rarely introduced. The decay of hyperbolic momentum space outside the hyperbolic medium has hindered the realization of sub-wavelengh focusing in the near field of HMM. Furthermore, manipulating the negatively refracted waves exiting the HMM have addressed another major obstacle to realize free space sub-wavelength focusing. In this work, we report extended sub-wavelength focusing in free space based on negative refraction of light exiting the HMM. The proposed structure is composed of multilayers of doped InAs/intrinsic InAs integrated with metallic slit. We theoretically simulate the doped InAs/intrinsic InAs HMM and investigate the negative refraction behavior outside the HMM. We optimized the structure for achieving high resolution down to 0.2λ, extended to a distance of 3.2 µm in free space. Also, sub-wavelength focusing in free space has been studied at different doping concentrations showing that the small doping concentrations exhibit enhancement in resolution at short distances up to 600 nm away from the HMM. Extending the focusing distance is achieved up to distance 3.5 µm from the hyperbolic structure by manipulating the doping concentration. This proposed lens configuration is expected to find potential usage in mid IR thermal imaging and photolithography application.