Waveband Range Research Articles

Nondestructively Determining Soluble Solids Content of Blueberries Using Reflection Hyperspectral Imaging Technique

Effectively detecting the quality of blueberries is crucial for ensuring that high-quality products are supplied to the fresh market. This study developed a nondestructive method for determining the soluble solids content (SSC) of blueberry fruit by using a near-infrared hyperspectral imaging technique. The reflection hyperspectral images in the 900–1700 nm waveband range were collected from 480 fresh blueberry samples. An image analysis pipeline was developed to extract the spectrums of blueberries from the hyperspectral images. A regression model for quantifying SSC values was successfully established based on the full range of wavebands, achieving the highest RP2 of 0.8655 and the lowest RMSEP value of 0.4431 °Brix. Furthermore, three variable selection methods, namely the Successive Projections Algorithm (SPA), interval PLS (iPLS), and Genetic Algorithm (GA), were utilized to identify the feature wavebands for modeling. The models calibrated from feature wavebands generated an RMSEP of 0.4643 °Brix, 0.4791 °Brix, and 0.4764 °Brix, as well as the RP2 of 0.8507, 0.8397, and 0.8420 for SPA, iPLS, and GA, respectively. Furthermore, a pseudo-color distribution diagram of the SSC values within blueberries was successfully generated based on established models. This study demonstrated a novel approach for blueberry quality detection and inspection by jointly using hyperspectral imaging and machine learning methodologies. It can serve as a valuable reference for the development of grading equipment systems and portable testing devices for fruit quality assurance.

Fabrication of Tb/Eu co-doped borosilicate glasses for white-light LED and broadband photodetection

We successfully prepared a series of rare-earth doped borosilicate glasses using the melt-quenching method, and carefully investigated the luminescent properties and the spectral modulation of Tb/Eu-cdoped borosilicate glasses under UV (200–400 nm) excitation. The results show that the prepared samples have the characteristics of broadband response, excellent transparency and tunable luminescence. By adjusting the excitation wavelength, the emissions of Tb3+, Eu2+ and Eu3+ ions are observed, which exhibit yellow-green, blue, red color and multi-color even white emissions, respectively. Moreover, the energy transfer between Tb3+ and Eu3+ ions in the codoped glasses is confirmed. Tb3+ absorbs a large number of solar-blind light, transfers to Eu3+ and results in intense visible emission in a wide waveband range. This makes the Tb/Eu codoped glass a desirable candidate for solar-blind light detections. The photodetection system was built and shows a strong and stable response to the UV light of 210–400 nm. Due to broad detection range, high sensitivity and stability, our results offer strong implications for the development of photodetection device for diverse applications.

Thermal infrared spectrum variation and waveband features of loaded rocks with different mineral components during the fracture evolution process

Previous studies focused mainly on temporal-spatial analyses of thermal infrared radiant temperature variations based on statistical parameters for rocks. These spectral analyses indicated that the thermal infrared radiance variation during the rock loading and fracturing process was a combined effect of the changes in both temperature and emissivity variation. The spectral features and mechanisms responsible for the thermal infrared spectral radiance changes in the fracturing stage and the relationship to the lithology remain poorly understood. In this paper, three types of typical rocks on the earth ground surface with different mineral components, i.e., sandstone, granite, and marble, were selected to investigate the thermal infrared spectrum (8.0–13.0 µm) waveband regulation during the loading process in the outdoor condition. The experiment yielded the following results: (1) The advantageous waveband corresponded to the reststrahlen feature (RF) waveband of the static emissivity spectrum, which was in the 8.2–9.4 μm, 8.4–10.3 μm and 11.1–11.4 μm range for sandstone, granite, and marble, respectively. There is a significant influence on the thermal infrared radiance variation caused by the waveband range. (2) The emissivity changes during the fracturing stage were the main factors causing the spectral radiance change, with opposite waveband features of the temperature change leading to an overall increase in amplitude. (3) The combination of spectral features in the advantageous waveband was more conducive to the analysis of the temporal-spatial-strength evolution of the thermal infrared radiation (TIR) temperature field on the loading rock surface. These results provide a scientific basis for thermal infrared remote sensing satellite loading design and waveband optimization and combination configuration.

Synthesis and Characterization of Schiff Base Polymers via Metal Coordination and Its Application in Infrared Stealth Coating.

In order to reduce the infrared emissivity to meet the requirements of modern warfare for infrared stealth materials, we prepared the polymers containing Schiff base moieties using polyetheramine and 2,6-pyridinedicarboxaldehyde by solution polycondensation and coordinated with Ni2+, Cu2+, and Sm3+ ions to prepare organic coatings. The structure and the thermal and mechanical properties of the coatings were studied in detail. Meanwhile, the effect of the conductivity change of coordination polymers on infrared emissivity was studied systematically. The results showed the polymer coordinated with Sm3+ ions had the lowest energy band gap, which was 2.99 eV, and the best electrical conductivity of 3.54 × 10-4 S/cm compared with Ni2+ and Cu2+ coordination polymers. The infrared emissivity was the lowest in the 2-22 μm infrared waveband range, which reached 0.58, suggesting the polymers containing Schiff base moieties and their coordination polymers may have a great potential to be applied as infrared stealth materials in military applications.

Study on the origin of linear deviation with the Beer-Lambert law in absorption spectroscopy by measuring sulfur dioxide

In accordance with the Beer-Lambert law, absorbance is proportional to concentration and optical path length of the absorbers in the sample, and in a linear relationship with total column concentration (product of concentration and optical path length) at a single wavelength. However, limitation of spectral resolution will result in linear deviation with the Beer-Lambert law in actual measurement. Regarding additivity of polychromatic light intensity as the theoretical basis, this paper attributed linear deviation with the Beer-Lambert law to spectral resolution, concentration and light intensity, and verified this explanation by measuring sulfur dioxide at various total column concentrations using spectrometers with different spectral resolutions in the waveband range of 216–230 nm. It was found that linear deviation with the Beer-Lambert law was in negative correlation with spectral resolution, and in positive correlation with total column concentration, and absorbance could be considered to be linear with total column concentration (below 171.4 mg/m2) of sulfur dioxide in the wavelength range of 216–230 nm. In addition, it was also proved that linear deviation increases with decreasing light intensity at a fixed sulfur dioxide column concentration.

Passively Q-switched Tm:YAP laser with a tantalum aluminum carbide saturable absorber.

Tantalum aluminum carbide (Ta4AlC3) phase ceramic (MAX) material has attracted much attention because of its high conductivity, high strength, corrosion resistance, and good optical properties. However, there are too few reports on lasers with Ta4AlC3-based saturable absorbers (SAs). We prepared and characterized a Ta4AlC3-based SA whose nonlinear absorption performances were achieved at a 2 µm waveband range and which was used in a passively Q-switched (PQS) Tm:YAP laser. In the PQS mode, a maximum average output power of 0.78 W was achieved with the central output wavelength of 1991.86 nm from a PQS Tm:YAP laser, corresponding to a pulse duration of 926 ns at 143.8 kHz.

Ultra-broadband mid-infrared TE01 vector mode selector based on ring-core few-mode photonic crystal fiber

A mid-infrared TE01 vector mode selector based on chalcogenide ring-core few-mode fiber is proposed and investigated numerically by the finite element method (FEM). By embedding metal composite nanowire in the PCF core to generate surface plasmon resonance, TE01 vector mode could propagate due to low loss transmission, whereas the fundamental mode, TM01 and HE21 modes could hardly be maintained due to high loss. The effects of structural parameters on mode transmission characteristics and mode loss in photonic crystal fibers in the mid-infrared wavelength range are investigated. Under the optimal structural parameters, the loss ratios of each mode to TE01 mode are more than 50 in the waveband range from 2 to 3 μm, which means the TE01 single-mode transmission can be maintained in ultra-wide mid-infrared band. The designed fiber can be connected with the mid-infrared laser as a vector mode selection device to efficiently output pure TE01 mode cylindrical vector beam, which makes preferable application in mid-infrared optical communication, optical capture, super-resolution imaging, biochemical sensing and other fields.

Electrospun bifunctional MXene-based electronic skins with high performance electromagnetic shielding and pressure sensing

With the rapid development of intelligent wearable electronics, flexible shielding electronic skin is highly desired to monitor physiological signals and protect human beings from electromagnetic radiation. One primary concern is the synergetic improvement of electromagnetic interference (EMI) shielding effectiveness and piezoresistive sensitivity that meet the demands above. Here, we report a bifunctional electrospun nanofiber membrane decorated with MXene nanosheets and Fe3O4 nanoparticles (NPs) that possess desired properties. Notably, this electrospun composite membrane (thicknesses of 33 μm) demonstrates excellent specific shielding effectiveness (SSE/t) of 9212.1 dB cm2 g−1 in a broad waveband range (8–26.5 GHz), owing to the combined effects of favorable porous structure, magnetic loss from Fe3O4 NPs and dielectric loss from MXene. The bifunctional membrane exhibited high sensitivity of 5.53 kPa−1 in a broad pressure regime (0–2.5 kPa), with a rapid response time and long-term stability. This pressure sensor can achieve noninvasive health monitoring of pulse, laryngeal movement, and other physiological signals. This work provides a new avenue toward wearable electromagnetic wave protection and human-machine interfaces.

Simultaneous low reflection in near-infrared range and low emission in long-wave infrared properties of Al/Bi2O3 composites

In this work, flaky aluminum was coated with bismuth oxide to obtain low reflection in near-infrared range and low emission in long-wave infrared stealth material. The composites were prepared through coprecipitation method, characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and measured by ultraviolet spectrophotometer and dual band infrared emissometer. The morphology and microstructure show that the flaky aluminum was coated by bismuth oxide nanoparticles. The optimal reaction temperature was 50 °C, and the optimized amount of Al was 20 wt%. Meanwhile, the infrared emissivity in 8–14 μm infrared waveband range was 0.462 and the reflectivity was 39.1% at wavelength of 1.064 μm. In addition, it could also achieve good thermal insulation in a thinner thickness. When the temperature of heating platform reached 100 °C, the temperature of the disk with 0.30 mm thickness was 26.9 °C which was only 2.7 °C higher than that of the disk with 0.94 mm thickness. It may shed light on a new material design orientation to obtain high performance infrared and laser compatible stealth materials.

Mid-infrared spectroscopy of hemispherical water droplets

As an important component of atmospheric aerosols, water is profoundly related with aerosol hygroscopicity and provides a medium for atmospheric heterogeneous reactions. The quantitative analysis of water content in aerosol droplets is instrumental to understanding atmospheric chemistry, as well as to addressing the related environmental issues, such as air pollution and climate change. Fourier transform infrared (FTIR) spectroscopy has been widely adopted to quantify the amount of water content in atmospheric aerosols, which is based on the absorbance of OH functional group in proportion to water content. However, in the OH stretching vibration band around 3400 cm−1, spectral distortions may occur, making a quantitative analysis impossible. In addressing this issue, here we put forth a model to simulate the FTIR absorption of hemispherical water droplets, along with a quantitative description of the spectral distortion. Our model prediction was benchmarked with the microscopic-FTIR experiments conducted on sodium sulfate droplets, and good agreements between theoretical and experimental results were found. We observed that the absorbance spanning across the mid-wavenumber infrared region increases with water absorption coefficients; while such an increasing trend was not seen in the 3400 cm−1 band. We speculate that the spectral saturated absorption is related to the absorption coefficient of water and the ratio of the projected area of droplets to the aperture area. In addition, the effects of droplet size and number density on the absorption spectra were investigated. The waveband range of the saturated absorption broadens with an increase in droplet radius. On the other hand, as the number density of water droplets increases, the absorption at 3400 cm−1 is enhanced, and the characteristic peak of condensed water becomes increasingly sharper, asymptotic to the typical infrared spectra of water collected by the pressing method.

Measurement of liquid thermo-optical coefficient based on all-fiber hybrid FPI-SPR sensor

This paper proposes and demonstrates an integrated optical fiber sensor, which combines Fabry-Perot interference (FPI) and surface plasmon resonance (SPR) to measure the thermo-optical coefficient of liquid samples. SPR is excited by the total reflection of light on the capillary fiber wall and the reflected light on the two reflective surfaces of the Fabry-Perot (FP) cavity to produce FPI. Two sensing units measure temperature and refractive index (RI), respectively. This sensor not only separates two sensing wavebands but also solves the inherent cross-sensitivity problems. The SPR sensing unit has a sensitivity of 2565.4 nm/RIU, and its sensing waveband range is 500−900 nm. The FPI sensing unit has a sensitivity of 394.3 pm/°C, and its sensing waveband range is 1500−1600 nm. The measurement range of RI is 1.333–1.393, and the measurement range of temperature is 20 °C–80 °C. We verify the feasibility of the sensor in various liquid samples. The experimental results indicate that the measured value of the thermo-optical coefficient agrees with the theoretical value. The measurement error of the thermo-optical coefficient of absolute ethanol is about 0.51 %. This research provides a novel insight into solving the inherent cross-sensitivity problems and how to separate the sensing wavebands.

Detection of Leek Rust Disease under Field Conditions Using Hyperspectral Proximal Sensing and Machine Learning

Rust disease is an important problem for leek cultivation worldwide. It reduces market value and in extreme cases destroys the entire harvest. Farmers have to resort to periodical full-field fungicide applications to prevent the spread of disease, once every 1 to 5 weeks, depending on the cultivar and weather conditions. This implies an economic cost for the farmer and an environmental cost for society. Hyperspectral sensors have been extensively used to address this issue in research, but their application in the field has been limited to a relatively low number of crops, excluding leek, due to the high investment costs and complex data gathering and analysis associated with these sensors. To fill this gap, a methodology was developed for detecting leek rust disease using hyperspectral proximal sensing data combined with supervised machine learning. First, a hyperspectral library was constructed containing 43,416 spectra with a waveband range of 400–1000 nm, measured under field conditions. Then, an extensive evaluation of 11 common classifiers was performed using the scikit-learn machine learning library in Python, combined with a variety of wavelength selection techniques and preprocessing strategies. The best performing model was a (linear) logistic regression model that was able to correctly classify rust disease with an accuracy of 98.14%, using reflectance values at 556 and 661 nm, combined with the value of the first derivative at 511 nm. This model was used to classify unlabelled hyperspectral images, confirming that the model was able to accurately classify leek rust disease symptoms. It can be concluded that the results in this work are an important step towards the mapping of leek rust disease, and that future research is needed to overcome certain challenges before variable rate fungicide applications can be adopted against leek rust disease.

Sun Exposure and Vitamin D.

Vitamin D is generally accepted in its importance on the regulation of calcium homeostasis and bone metabolism. Moreover, further health effects due to vitamin D are under discussion. In its effect, vitamin D is more like a hormone. In the classic view, a vitamin is an essential nutrient, which cannot be synthesized independently in the body. Besides nutrition, vitamin D will be produced in the body itself. The skin contains the provitamin D3 7-dehydrocholesterol, a precursor of vitamin D. Provitamin D3 will be photoconverted to previtamin D3 by UVB radiation that penetrates the skin superficially. In this way, the vitamin D metabolism will be started independent of the nutrition. In everyday life, this photosynthesis will be carried out due to the solar UVB radiation penetrating the uncovered skin. In the same spectral waveband range of UVB radiation, which causes the beneficial health effect of starting the vitamin D metabolism, the UVB radiation causes simultaneously acute and chronic harmful health effects as UV erythema (sunburn), skin aging and skin cancer. There is no vitamin D production in the skin without simultaneous DNA damage in the skin. Against this background, risks and benefits have to be balanced carefully.

Impact of the Structural Parameters on the Photoresponse of Terahertz Blocked-Impurity-Band Detectors With Planar Structure

We fabricate germanium-based blocked-impurity-band (BIB) terahertz detectors with the same planar structure but different structural parameters. The photoresponse waveband range is about 40-130 μm. The best detectivity of these detectors reaches as high as 1.3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> Jones at 2.6 V and 4 K. The impact of the structural parameters, including the length of the absorbing layer and blocking layer (BL) on the performance of detectors, is investigated. It is concluded that there is an optimum BL length, enabling the fabricated BIB detectors to achieve the highest sensitivity. This work highlights the importance of the optimized structural parameters and their influence on the performance of the detectors.

Quantitative analysis and hyperspectral remote sensing of the nitrogen nutrition index in winter wheat

ABSTRACTThe nitrogen nutrition index (NNI) is a quantitative and reliable indicator of the nitrogen nutrition distribution or status of crops. The timely and accurate estimation of the NNI is crucial in agriculture management. In this study, the quantitative analysis and hyperspectral remote sensing modelling of the NNI were conducted, in which the hyperspectral remote sensing data and NNI data at different growth stages of winter wheat were measured using ground and unmanned aerial vehicle (UAV) carrying high spectrometer equipment. First, the NNIs of the four growth stages of winter wheat were calculated and statistically analyzed. Then, the hyperspectral characteristics at different growth stages and various NNIs were examined. Second, the representation wavebands of the hyperspectral data, which were sensitive to the NNI of winter wheat, were acquired and evaluated. In addition, hyperspectral models were established and comparatively assessed for the NNI estimation. Finally, the hyperspectral characteristics and the remote sensing estimation of the NNIs were determined on the basis of UAV-based hyperspectral data. The results are as follows. (1) As the NNIs of winter wheat changed, the characteristic of the red shift, the variations in the red edge position, and the near-infrared waveband range of the hyperspectral data became apparent. (2) The green band, red edge, and near-infrared were sensitive to the NNIs of winter wheat, and they could be effectively used for estimating the NNI. Moreover, the multiple statistical regression models, which were based on representative wavebands, performed well in estimating the NNI results for the different growth stages of winter wheat.

Laser absorption and infrared stealth properties of Al/ATO composites

Abstract In this work, an Al powder was coated with antimony-doped tin oxide (ATO) to obtain an infrared-laser compatible stealth material. The composites are prepared via a coprecipitation method, characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and measured by ultraviolet spectrophotometer and dual band infrared emissometer. The morphology and microstructure show that the flaky Al powder was coated by the ATO nanoparticles and doped into the SnO2 rutile structure by an Sb5+ ion. The optimal Al content was 20%, and the optimized Sn/Sb molar ratio was 10: 1. Meanwhile, the reflectivity of the composites was 43.454%, and the infrared emissivity in 8–14 μm far infrared waveband range was 0.708. It may shed light on a new material design orientation to obtain high performance laser-infrared compatible stealth materials.

Al2O3/reduced graphene oxide double-layer radiative coating for efficient heat dissipation

In this work, a double-layer radiative coating was designed, and its radiative heat dissipation performance was studied theoretically and experimentally. The duplex coating was fabricated by assembling reduced graphene oxide (rGO) on Al2O3 bottom layer. The effects of Al2O3/rGO coatings on thermal radiation, heat dissipation and anti-corrosion properties of light emitting diode (LED) were investigated. The Al2O3/rGO radiative coating promoted the infrared emissivity value from 0.1 (bare aluminum radiator) to 0.57 at 3–8 μm and 0.83 at 8–20 μm waveband range, respectively. The double-layer coated aluminum alloy with high emissivity value enabled a significant 1 W LED temperature drop by 5.6 °C, which was coincident with the result by simulation (1 W). More remarkable, the temperature drop further decreases to 14.0 °C for 5 W LED chip. In addition, the Al2O3/rGO duplex coating exhibited superior hydrophobic and anti-corrosion properties, which is expected to be a promising candidate for heat dissipation of electronic products serving in oceans and humid ambient.

Identification of Adulterated and Non-adulterated Norwegian Salmon Using FTIR and an Improved PLS-DA Method

Norwegian salmon is often adulterated with Heilongjiang salmon at local fish markets. To promote fair price competition at fish markets and protect consumer rights, we developed a quick and accurate identification method to distinguish adulterated and non-adulterated Norwegian salmon using a Fourier transform infrared spectroscopy (FTIR). In this study, Norwegian and Heilongjiang salmon could be readily distinguished using partial least squares discriminant analysis (PLS-DA), but it failed to detect the accurate level of 20 to 80% of adulterated Norwegian salmon samples. In order to improve the PLS-DA model, several pre-processing methods, including standard normal variate (SNV), multiplicative scatter correction (MSC), and normalization, were used to evaluate individually to select the most appropriate correction method. Characteristics of the spectra within the waveband range covering 450 to 4000 cm−1 were also analyzed to determine the optimum sub-waveband range to improve the accuracy of the model. The results of the study showed that using FTIR and the improved PLS-DA model established in this study, the adulterated and non-adulterated Norwegian salmon could be completely distinguished. The accuracy of the adulteration level and the prediction accuracy of the model were also significantly improved when normalization method was used at 450 to 1790 cm−1 sub-wavebands. For the calibration and cross-validation sample sets, the determination coefficients of the improved PLS-DA model were at 0.99 and 0.98, respectively. The mean square errors were 2.3 and 4%, resulting in a 90% accuracy of validation sample sets. This technology should provide fish markets an easy and reliable way to distinguish the adulterated and non-adulterated salmon.

Potential impact of colors of filters used in sunglasses on the melatonin suppression process

In this article the methods for determining spectral transmittance of optical radiation in the visible waveband range through selected materials used as optical filters against solar glare were described. Transmittance coefficients specified for the fraction of light passing through tested filters, taking into account the mechanism of eye adaptation to daylight and night vision and the melatonin suppression process were compared for 4 dyed sunglass filters. The values of transmittance coefficients specified for wavelength bands, 380-780 nm (for visible range) and 425-560 nm (for blue light range affecting the melatonin suppression process) were determined. The use of sunglasses with different color filters modifies the spectral characteristics of transmittance (spectrum) of visible light reaching the eye (including blue radiation) in such a way that it may have a potential impact on the melatonin suppression process. Med Pr 2017;68(5):629-637.

Preparation, Microwave Absorption and Infrared Emissivity of Ni-doped ZnO/Al Powders by Coprecipitation Method in the GHz Range

In this work, Ni-doped ZnO/Al composites were prepared by a facile chemical co-precipitation method. The morphology and structure of the as-prepared composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. It was found that the flake-like Al powders were successfully coated by Ni-doped ZnO nanoparticles with slight aggregation and Ni[Formula: see text] was successfully doped into the crystal lattice of ZnO. Moreover, the effects of ZnO concentration and doped Ni concentration on the infrared emissivity of ZnO/Al composites at the waveband range of 8–14[Formula: see text][Formula: see text]m were studied. The results showed that the ZnO/Al composites exhibited the lowest infrared emissivity of 0.34 with 50[Formula: see text]wt.% ZnO concentration. Meanwhile, the electromagnetic parameters and microwave absorbing properties of Ni-doped ZnO/Al composites in the frequency range of 2–18[Formula: see text]GHz were explored. Significantly, 12[Formula: see text]mol.% Ni-doped ZnO/Al composites presented the lowest infrared emissivity of 0.37 and the maximum reflection loss reached [Formula: see text]32.5[Formula: see text]dB at 13.6[Formula: see text]GHz with a thickness of 4.5[Formula: see text]mm. The excellent microwave absorbing properties could be attributed to the good impedance match, crystal lattice defects and interfacial polarization. It was believed that the Ni-doped ZnO/Al composites could be used as potential infrared-microwave compatible stealth materials.