Thermal Emission Signals Research Articles

Kinetics of Laser-Induced Thermal Emission of Porous Carbon Materials: Dependence on Laser Wavelength

For the porous carbon material excited by the first and second harmonics of a neodymium laser, the shape of pulsed signals of laser-induced thermal emission is investigated. It is found that the duration of thermal emission pulses significantly depends on the wavelength of the laser excitation, which is caused by the differences in the depth of penetration of laser radiation into the surface layer. The mentioned effect is actual, if the penetration depth of laser radiation exceeds the length of thermal diffusion in the studied material for a time of the order of the laser pulse duration. The computer modeling is carried out for the processes of pulsed laser heating and formation of thermal emission signal. The simulation results showed satisfactory agreement with the measurement results.

56 Monitoring Diesel Exhaust Particles by Lock-in Thermography

Abstract Diesel exhaust particles (DEPs) can deposit onto the respiratory epithelial surface upon inhalation. In vitro exposures of various lung models to DEPs have been performed under the air-liquid interface (ALI) conditions in previous studies, however, methods to quantify DEPs onto/into cells during and after exposure are still challenging and not well established. In our study, a new particle detection system, i.e. lock-in thermography (LIT), was explored. LIT is a heat- sensitive imaging method that applies the light illumination to induce the heat of carbon-based particles for detection. By testing a standard DEPs sample (SRM2975), a positive linear relationship (R2 = 0.98) was established between the thermal emission signals and DEPs levels ranging from 0 to 30 µg/mL, with limit of detection (LOD) at 1.00 µg/mL. Moreover, phototoxicity tests showed that no cytotoxic effects were observed on human lung epithelial (A549) cells upon excitation light wavelength of 525 and 660 nm for 1 – 2 mins. Taken together, it suggests that the LIT can be used for detecting DEPs exposed with A549 cells at the relatively low concentration. Further improvement and optimization of the LIT system are ongoing to evaluate DEPs exposed lung cells.

Cooling and Crack Suppression of Bone Material Drilling Based on Microtextured Bit Modeled on Dung Beetle

In recent years, the number of patients with orthopedic diseases such as cervical spondylosis has increased, resulting in an increase in the demand for orthopedic surgery. However, thermal necrosis and bone cracks caused by surgery severely restrict the development and progression of orthopedic surgery. For the material of cutting tool processing bone in bone surgery of drilling high temperature lead to cell death, easy to produce the problem such as crack cause secondary damage effects to restore, in this paper, a bionic drill was designed based on the micro-structure of the dung beetle’s head and back. The microstructure configuration parameters were optimized by numerical analysis, and making use of the optical fiber laser marking machine preparation of bionic bit; through drilling test, the mathematical model of drilling temperature and crack generation based on micro-structure characteristic parameters was established by infrared thermal imaging technology and acoustic emission signal technology, and the cooling mechanism and crack suppression strategy were studied. The experimental results show that when the speed is 60 m/min, the cooling effects of the bionic bit T1 and T2 are 15.31% and 19.78%, respectively, and both kinds of bits show obvious crack suppression effect. The research in this paper provides a new idea for precision and efficient machining of bone materials, and the research results will help to improve the design and manufacturing technology and theoretical research level in the field of bone drilling tools.

Potentially underestimated gas flaring activities—a new approach to detect combustion using machine learning and NASA’s Black Marble product suite

Monitoring changes in greenhouse gas (GHG) emission is critical for assessing climate mitigation efforts towards the Paris Agreement goal. A crucial aspect of science-based GHG monitoring is to provide objective information for quality assurance and uncertainty assessment of the reported emissions. Emission estimates from combustion events (gas flaring and biomass burning) are often calculated based on activity data (AD) from satellite observations, such as those detected from the visible infrared imaging radiometer suite (VIIRS) onboard the Suomi-NPP and NOAA-20 satellites. These estimates are often incorporated into carbon models for calculating emissions and removals. Consequently, errors and uncertainties associated with AD propagate into these models and impact emission estimates. Deriving uncertainty of AD is therefore crucial for transparency of emission estimates but remains a challenge due to the lack of evaluation data or alternate estimates. This work proposes a new approach using machine learning (ML) for combustion detection from NASA’s Black Marble product suite and explores the assessment of potential uncertainties through comparison with existing detections. We jointly characterize combustion using thermal and light emission signals, with the latter improving detection of probable weaker combustion with less distinct thermal signatures. Being methodologically independent, the differences in ML-derived estimates with existing approaches can indicate the potential uncertainties in detection. The approach was applied to detect gas flares over the Eagle Ford Shale, Texas. We analyzed the spatio-temporal variations in detections and found that approximately 79.04% and 72.14% of the light emission-based detections are missed by ML-derived detections from VIIRS thermal bands and existing datasets, respectively. This improvement in combustion detection and scope for uncertainty assessment is essential for comprehensive monitoring of resulting emissions and we discuss the steps for extending this globally.

Correcting thermal-emission-induced detector saturation in infrared spectroscopy.

We found that temperature-dependent infrared spectroscopy measurements (i.e., reflectance or transmittance) using a Fourier-transform spectrometer can have substantial errors, especially for elevated sample temperatures and collection using an objective lens. These errors can arise as a result of partial detector saturation due to thermal emission from the measured sample reaching the detector, resulting in nonphysical apparent reduction of reflectance or transmittance with increasing sample temperature. Here, we demonstrate that these temperature-dependent errors can be corrected by implementing several levels of optical attenuation that enable convergence testing of the measured reflectance or transmittance as the thermal-emission signal is reduced, or by applying correction factors that can be inferred by looking at the spectral regions where the sample is not expected to have a substantial temperature dependence.

Dilepton signature of a first-order phase transition

The search for a first-order phase transition in strongly interacting matter is one of the major objectives in the exploration of the phase diagram of Quantum Chromodynamics (QCD). In the present work we investigate dilepton radiation from the hot and dense fireballs created in Au-Au collisions at projectile energies of 1-2 $A$GeV for potential signatures of a first-order transition. Toward this end, we employ a hydrodynamic simulation with two different equations of state, with and without a phase transition. The latter is constrained by susceptibilities at vanishing chemical potential from lattice-QCD as well as neutron star properties, while the former is implemented via modification of the mean-fields in the quark phase. We find that the latent heat involved in the first-order transition leads to a substantial increase in the low-mass thermal emission signal, by about a factor of two above the cross-over scenario.

Statistical Approach to Spectrogram Analysis for Radio-Frequency Interference Detection and Mitigation in an L-Band Microwave Radiometer.

For the elimination of radio-frequency interference (RFI) in a passive microwave radiometer, the threshold level is generally calculated from the mean value and standard deviation. However, a serious problem that can arise is an error in the retrieved brightness temperature from a higher threshold level owing to the presence of RFI. In this paper, we propose a method to detect and mitigate RFI contamination using the threshold level from statistical criteria based on a spectrogram technique. Mean and skewness spectrograms are created from a brightness temperature spectrogram by shifting the 2-D window to discriminate the form of the symmetric distribution as a natural thermal emission signal. From the remaining bins of the mean spectrogram eliminated by RFI-flagged bins in the skewness spectrogram for data captured at 0.1-s intervals, two distribution sides are identically created from the left side of the distribution by changing the standard position of the distribution. Simultaneously, kurtosis calculations from these bins for each symmetric distribution are repeatedly performed to determine the retrieved brightness temperature corresponding to the closest kurtosis value of three. The performance is evaluated using experimental data, and the maximum error and root-mean-square error (RMSE) in the retrieved brightness temperature are served to be less than approximately 3 K and 1.7 K, respectively, from a window with a size of 100 × 100 time–frequency bins according to the RFI levels and cases.

The Lassell massif—A silicic lunar volcano

Lunar surface volcanic processes are dominated by mare-producing basaltic extrusions. However, spectral anomalies, landform morphology, and granitic or rhyolitic components found in the Apollo sample suites indicate limited occurrences of non-mare, geochemically evolved (Si-enriched) volcanic deposits. Recent thermal infrared spectroscopy, high-resolution imagery, and topographic data from the Lunar Reconnaissance Orbiter (LRO) show that most of the historic “red spots” and other, less well-known locations on the Moon, are indeed silica rich (relative to basalt). Here we present a geologic investigation of the Lassell massif (14.65°S, 350.96°E) near the center of Alphonsus A basin in Mare Nubium, where high-silica thermal emission signals correspond with morphological indications of viscous (possibly also explosive) extrusion, and small-scale, low-reflectance deposits occur in a variety of stratigraphic relationships. Multiple layers with stair-step lobate forms suggest different eruption events or pulsing within a single eruption. Absolute model ages derived from crater size-frequency distributions (CSFDs) indicate that the northern parts of the massif were emplaced at ∼4Ga, before the surrounding mare. However, CSFDs also indicate the possibility of more recent resurfacing events. The complex resurfacing history might be explained by either continuous resurfacing due to mass wasting and/or the emplacement of pyroclastics. Relatively low-reflectance deposits are visible at meter-scale resolutions (below detection limits for compositional analysis) at multiple locations across the massif, suggestive of pyroclastic activity, a quenched flow surface, or late-stage mafic materials. Compositional evidence from 7-band UV/VIS spectral data at the kilometer-scale and morphologic evidence for possible caldera collapse and/or explosive venting support the interpretation of a complex volcanic history for the Lassell massif.

Damage Observation of Glass Fiber/Epoxy Composites Using Thermography and Supported by Acoustic Emission

This work presents an experimental study to monitor the damage propagation of composite material by non destructive testing (NDT) method. In order to achieve this, an open hole condition of glass fiber/epoxy composite has been used as the specimen test under static tensile loading and observed using two different real-time monitoring techniques of NDT namely infra-red (IR) camera and supported by Acoustic Emission. The results show that the thermal response and acoustic emission signals give a good detection on damage appearance and damage propagation of glass fiber/epoxy composite under static tensile loading conditions.

Design of process diagnostics for excimer laser irradiation of oxide thin films

The authors have developed an in situ excimer laser irradiation system that can monitor the temperature field of oxide thin films through thermal radiation produced upon a pulsed ultraviolet laser irradiation. Thermal emission signals from a Si single crystal obtained using with this system agreed well with a numerical simulation result, validating the time constant of the measurement system. The time-dependent transient temperature profile of tin-doped indium oxide thin films, which was converted from thermal emission signals, clearly showed a recalescence behavior in its cooling curve. The transmittance data of the laser-irradiated indium oxide thin films suggested that the transmittance monitoring at near-infrared and ultraviolet–visible regions could be useful in monitoring the dopant levels and laser processing conditions, respectively.

Application of infrared lock-in thermography for the quantitative evaluation of bruises on pears

An infrared lock-in thermography technique was adjusted for the detection of early bruises on pears. This mechanical damage is usually difficult to detect in the early stage after harvested using conventional visual sorting or CCD sensor-based imaging processing methods. We measured the thermal emission signals from pears using a highly sensitive mid-infrared thermal camera. These images were post-processed using a lock-in method that utilized the periodic thermal energy input to the pear. By applying the lock-in method to infrared thermography, the detection sensitivity and signal to noise ratio were enhanced because of the phase-sensitive narrow-band filtering effect. It was also found that the phase information of thermal emission from pears provides good metrics with which to identify quantitative information about both damage size and damage depth for pears. Additionally, a photothermal model was implemented to investigate the behavior of thermal waves on pears under convective conditions. Theoretical results were compared to experimental results. These results suggested that the proposed lock-in thermography technique and resultant phase information can be used to detect mechanical damage to fruit, especially in the early stage of bruising.

In situ monitoring of excimer laser annealing of tin-doped indium oxide films for the development of a low-temperature fabrication process

In this paper, in situ monitoring of excimer laser irradiation processing is examined for application to the production of thin films of transparent conductive oxides (TCOs) such as tin-doped indium oxide (ITO). Numerical simulations reveal that differences in the thin film state, for example, in the dopant levels, could greatly affect the proper laser fluence, suggesting the importance of in situ monitoring of the excimer laser processing. The thermal emission signals of ITO thin films under irradiation by a pulsed ultraviolet laser were successfully detected in situ with a near-infrared sensor on a nanosecond timescale. Non-monotonic decay of the thermal radiation from the ITO thin films was observed under XeCl laser irradiation above a certain fluence. At this fluence, the surface morphology of the ITO thin films observed by atomic force microscopy changed to a microstructure reflecting melting and solidification. This correspondence between the thermal radiation and morphology suggests that the observed non-monotonic decay was caused by recalescence upon solidification and that the in situ monitoring technique can be used to detect such phase changes.

Health condition monitoring with multiple physical signals in tensile test for double-material friction welding

The manifold physical signals including micro resistance, infrared thermal signal and acoustic emission signal in the tensile test for double-material friction welding normative samples were monitored and collected dynamically by TH2512 micro resistance measuring apparatus, flir infrared thermal camera and acoustic emission equipment which possesses 18 bit PCI-2 data acquisition board. Applied acoustic emission and thermal infrared NDT (non-destructive testing) means were used to verify the feasibility of using resistance method and to monitor dynamic damage of the samples. The research of the dynamic monitoring system was carried out with multi-information fusion including resistance, infrared and acoustic emission. The results show that the resistance signal, infrared signal and acoustic emission signal collected synchronously in the injury process of samples have a good mapping. Electrical, thermal and acoustic signals can more accurately capture initiation and development of micro-defects in the sample. Using dynamic micro-resistance method to monitor damage is possible. The method of multi-information fusion monitoring damage possesses higher reliability, which makes the establishing of health condition diagnosing and early warning platform with multiple physical information monitoring possible.

Photo-Thermal Spectroscopic Imaging of MEMS Structures with Sub-Micron Spatial Resolution

ABSTRACTWe are developing a new non-contact and non-destructive imaging technique which requires no sample preparation and provides similar content information as FTIR or Raman spectroscopy while being immune to fluorescence and offers a potentially faster scan rate and/or higher spatial resolution. It utilizes photo-thermal heating of the sample with a quantum cascade laser (or other suitable infrared laser) and measuring the resulting increase in thermal emissions by either an infrared (IR) detector or a laser probe consisting of a visible laser reflected from the sample. The latter case allows for further increases in the spatial resolution from ∼10 μm to ∼1 μm or better, with suitable experimental conditions. Since the thermal emission signal is proportional to the absorption coefficient, by tuning the wavelength of the IR laser we can directly measure the IR spectrum of the sample. By raster scanning over the surface of the sample we can obtain maps of the chemical composition of the sample surface. We demonstrate this technique by imaging the surface of a micro-fabricated flow-through chemical vapor preconcentrator consisting of a silicon frame and a suspended-perforated polyimide membrane with a pair of platinum heater traces, coated with a custom sorbent polymer for selective sorption of analyte. We measure the spatial resolution of our photo-thermal imaging system as well as discuss the conditions under which the spatial resolution can be further increased from the far-field diffraction limited resolution given by the combination of the imaging optic and IR excitation laser wavelength.

Remote Explosives Detection (RED) by Infrared Photothermal Imaging

ABSTRACTRED is a technique we have developed for stand-off detection of trace explosives using infrared (IR) photo-thermal imaging [1,2,3]. RED incorporates compact IR quantum cascade lasers tuned to strong characteristic absorption bands and may be used to illuminate explosives present as particles on a surface. An IR focal plane array is used to image the surface and detect any small increase in the thermal emission upon laser illumination. We have previously demonstrated the technique at several meters to 10’s of meters of stand-off distance indoors and in field tests [4,5], while operating the lasers below the eye-safe intensity limit (100 mWcm2) [6]. Sensitivity to traces of explosives as small as a nanogram has been demonstrated. By varying the incident wavelength slightly, we can readily show selectivity between individual explosives such as TNT and RDX. Using a sequence of lasers at different wavelengths, we increase both sensitivity and selectivity. A complete detection protocol can be performed in a sub-second time domain. More recently, RED has been used to emphasize measurements with cooled detectors in addition to examining the utility of filtering the collected thermal emission signal which is rich in analyte-specific spectroscopic information. A next generation RED system and detection algorithm is being developed to take advantage of these more powerful features. This manuscript will include an overview of the approach and recent experimental results.

Use of thermal emission signals to characterize the impact of fully and partially molten plasma-sprayed zirconia particles on glass surfaces

Plasma-sprayed yttria-stabilized zirconia particles (∼ 40 µm diameter) were photographed during impact (velocity ∼ 200 m/s) on glass surfaces that were maintained at either room temperature or 400 °C. A droplet that approached the surface was sensed using a photodetector and after a known delay, a light source was triggered to illuminate the particle in order to photograph it with a charge-coupled device (CCD) camera. A rapid two-color pyrometer was used to collect the thermal radiation from the particles to follow the evolution of their temperature and size, in-flight and after impact. The fully molten particles spread into a thin liquid splat after impacting the surfaces. The partially molten particles disintegrated into small satellite fragments immediately upon impact. The surface area, as indicated by the pyrometric signals, of the partially molten particles during spreading was almost an order of magnitude smaller than that of the fully molten droplets. The pyrometric signals of partially molten zirconia showed significant fluctuations, lower maximum voltages, and were wider than those of fully molten zirconia. These signals, characteristic of the impact of partially molten zirconia, provide a novel method of identifying partially molten ceramic particles after impact on a flat surface.

Sensitivity of the Kurtosis Statistic as a Detector of Pulsed Sinusoidal RFI

A new type of microwave radiometer detector that is capable of identifying low-level pulsed radio frequency interference (RFI) has been developed. The Agile Digital Detector can discriminate between RFI and natural thermal emission signals by directly measuring other moments of the signal than the variance that is traditionally measured. The kurtosis is the ratio of the fourth central moment of the predetected voltage to the square of the second central moment. It can be an excellent indicator of the presence of RFI. A number of issues that are related to the proper calculation of the kurtosis are addressed. The mean and standard deviation of the kurtosis, in both the absence and the presence of pulsed sinusoidal RFI, are derived. The kurtosis is much more sensitive to short-pulsed RFI-such as from radars-than to continuous-wave RFI. The minimum detectable power for pulsed sinusoidal RFI is found to be proportional to ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> ) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1/4</sup> , where <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> is the number of independent samples and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> is the number of frequency subbands in the receiver.

RFI detection and mitigation for microwave radiometry with an agile digital detector

A new type of microwave radiometer detector has been developed that is capable of identifying high and low levels of radio-frequency interference (RFI) and of reducing or eliminating its effect on the measured brightness temperatures. High-level, localized RFI can be easily identified by its unnatural appearance in brightness temperature imagery. Low-level or persistent RFI can be much more difficult to identify and filter out. The agile digital detector (ADD) can discriminate between RFI and natural thermal emission signals by directly measuring higher order moments of the signal than the variance that is traditionally measured. After detection, the ADD then uses spectral filtering methods to selectively remove the RFI. ADD performance is experimentally verified in controlled laboratory tests and in the field near a commercial air traffic control radar. High-level RFI is easily identified and removed. Very low level RFI contamination, with power levels as low as the radiometric measurement uncertainty of the radiometer, is also shown to be reliably detected and removed.

Emissivity-correcting near-UV pyrometry for group-III nitride OMVPE

We developed a pyrometer that operates near the high-temperature bandgap of GaN, thus solving the transparency problem once a ∼1 μm thick GaN epilayer has been established. The system collects radiation in the near-UV (380–415 nm) and has an effective detection wavelength of ∼405 nm. By simultaneously measuring reflectance we also correct for emissivity changes when films of differing optical properties (e.g. AlGaN) are deposited on the GaN template. We recently modified the pyrometer hardware and software to enable measurements in a multiwafer Veeco D-125 OMVPE system. A method of synchronizing and indexing the detection system with the wafer platen was developed; so signals only from the desired wafer(s) could be measured, while rejecting thermal emission signals from the platen. Despite losses in optical throughput and duty cycle we are able to maintain adequate performance from 700 to 1100 °C.

Exogenous and endogenous growth of the Unzen lava dome examined by satellite infrared image analysis

Phase 1 of the most recent eruption of Unzen volcano (Japan) occurred between 1991 and 1993 and involved the endogenous and exogenous addition of magma to a growing summit lava dome. The temporal variation between endogenous and exogenous styles of dome growth has an important bearing on the hazard posed by dome collapse and explosive events. However, such data are difficult to acquire and have previously only been obtained in a fully quantitative manner for the Mount St. Helens dome, in that case using detailed photogrammetry. Here we investigate these competing dome growth processes at Unzen via analysis of their thermal emission signals present in shortwave infrared (SWIR) satellite imagery. We find that both the endogenous and exogenous growth styles exhibit identifiable SWIR signatures whose magnitude can be related to their respective magma supply rates. We find that the SWIR radiant area corresponding to endogenous growth is around four times larger than that corresponding to exogenous growth at the same magma discharge rate. Analysis of time series imagery indicates that, like Mount St. Helens, Unzen experienced a temporally decreasing magma discharge rate during phase 1. As time progressed and the discharge rate fell, the growth style of the Unzen dome changed from ‘exogenous only’, through ‘exogenous decreasing and endogenous increasing’ to ‘endogenous only’. Thus relative growth rates at the endogenous and exogenous areas of the Unzen dome appear to be at least partly controlled by the overall magma discharge rate. As with Mount St. Helens, the cause of this relationship was most likely the formation and strengthening of a brittle crust at the surface vent, which impeded exogenous growth more effectively as time elapsed and the discharge rate fell. These results suggest the similarity of the processes operating at the Unzen and Mount St. Helens domes, though important differences remain in that dome growth was basically continuous at Unzen, whilst at Mount St. Helens growth episodes were interspersed by significant periods of repose.