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12 pages, 1752 KiB

Open AccessArticle

Time-Efficient SNR Optimization of WMS-Based Gas Sensor Using a Genetic Algorithm

by Filip Musiałek, Dariusz Szabra and Jacek Wojtas

Sensors 2024, 24(6), 1842; https://doi.org/10.3390/s24061842 - 13 Mar 2024

Viewed by 497

This paper presents the description of the wavelength modulation spectroscopy (WMS) experiment, the parameters of which were established by use of the Artificial Intelligence (AI) algorithm. As a result, a significant improvement in the signal power to noise power ratio (SNR) was achieved, [...] Read more.

This paper presents the description of the wavelength modulation spectroscopy (WMS) experiment, the parameters of which were established by use of the Artificial Intelligence (AI) algorithm. As a result, a significant improvement in the signal power to noise power ratio (SNR) was achieved, ranging from 1.6 to 6.5 times, depending on the harmonic. Typically, optimizing the operation conditions of WMS-based gas sensors is based on long-term simulations, complex mathematical model analysis, and iterative experimental trials. An innovative approach based on a biological-inspired genetic algorithm (GA) and custom-made electronics for laser control is proposed. The experimental setup was equipped with a 31.23 m Heriott multipass cell, software lock-in, and algorithms to control the modulation process of the quantum cascade laser (QCL) operating in the long-wavelength-infrared (LWIR) spectral range. The research results show that the applied evolutionary approach can efficiently and precisely explore a wide range of WMS parameter combinations, enabling researchers to dramatically reduce the time needed to identify optimal settings. It took only 300 s to test approximately 1.39 × 10³² combinations of parameters for key system components. Moreover, because the system is able to check all possible component settings, it is possible to unquestionably determine the operating conditions of WMS-based gas sensors for which the limit of detection (LOD) is the most favorable. Full article

(This article belongs to the Special Issue Towards Optoelectronic Technology: From Basic Research to Applications)

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14 pages, 5787 KiB

Open AccessArticle

Theoretical Analysis of GeSn Quantum Dots for Photodetection Applications

by Pin-Hao Lin, Soumava Ghosh and Guo-En Chang

Sensors 2024, 24(4), 1263; https://doi.org/10.3390/s24041263 - 16 Feb 2024

Viewed by 498

Abstract

GeSn alloys have recently emerged as complementary metal–oxide–semiconductor (CMOS)-compatible materials for optoelectronic applications. Although various photonic devices based on GeSn thin films have been developed, low-dimensional GeSn quantum structures with improved efficiencies hold great promise for optoelectronic applications. This study theoretically analyses Ge-capped [...] Read more.

GeSn alloys have recently emerged as complementary metal–oxide–semiconductor (CMOS)-compatible materials for optoelectronic applications. Although various photonic devices based on GeSn thin films have been developed, low-dimensional GeSn quantum structures with improved efficiencies hold great promise for optoelectronic applications. This study theoretically analyses Ge-capped GeSn pyramid quantum dots (QDs) on Ge substrates to explore their potential for such applications. Theoretical models are presented to calculate the effects of the Sn content and the sizes of the GeSn QDs on the strain distributions caused by lattice mismatch, the band structures, transition energies, wavefunctions of confined electrons and holes, and transition probabilities. The bandgap energies of the GeSn QDs decrease with the increasing Sn content, leading to higher band offsets and improved carrier confinement, in addition to electron–hole wavefunction overlap. The GeSn QDs on the Ge substrate provide crucial type–I alignment, but with a limited band offset, thereby decreasing carrier confinement. However, the GeSn QDs on the Ge substrate show a direct bandgap at higher Sn compositions and exhibit a ground-state transition energy of ~0.8 eV, rendering this system suitable for applications in the telecommunication window (1550 nm). These results provide important insights into the practical feasibility of GeSn QD systems for optoelectronic applications. Full article

(This article belongs to the Special Issue Towards Optoelectronic Technology: From Basic Research to Applications)

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12 pages, 5338 KiB

Open AccessArticle

Two-Channel Detecting Sensor with Signal Cross-Correlation for FTIR Instruments

by Krzysztof Achtenberg, Janusz Mikołajczyk and Zbigniew Bielecki

Sensors 2022, 22(22), 8919; https://doi.org/10.3390/s22228919 - 18 Nov 2022

Cited by 2 | Viewed by 1377

Abstract

This paper’s purpose was to demonstrate a performance of a novel approach in a low-noise optical sensor for an FTIR spectrometer. Methods: Compared to the standard FTIR detection setup, our sensor ensures a higher signal-to-noise ratio (SNR) and lower signal standard deviation by [...] Read more.

This paper’s purpose was to demonstrate a performance of a novel approach in a low-noise optical sensor for an FTIR spectrometer. Methods: Compared to the standard FTIR detection setup, our sensor ensures a higher signal-to-noise ratio (SNR) and lower signal standard deviation by reducing the uncorrelated noise components (e.g., thermal and 1/f noises of the detection module). Its construction is based on two-channel detection modules and a processing unit with implemented cross-correlation signal analyses. Each module was built of LWIR HgCdTe photodiodes and low-noise transimpedance amplifiers. Results: the experiments demonstrated a decrease in a signal standard deviation of about 1.7 times with a 10 dB-improvement in the SNR. Conclusion: this result indicates our sensor’s main benefit, especially in registered “weak” and noisy interferograms. Full article

(This article belongs to the Special Issue Towards Optoelectronic Technology: From Basic Research to Applications)

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16 pages, 4996 KiB

Open AccessArticle

Multi-Irradiance: A Method for Simultaneous Measurement of the Temperature and Spectral Emissivity of High-Temperature Targets in SWIR

by Yehan Sun, Jun Pan, Lijun Jiang, Libo Hao, Yu Cao and Helin Wang

Sensors 2022, 22(21), 8469; https://doi.org/10.3390/s22218469 - 03 Nov 2022

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Abstract

The currently used energy methods in spectral emissivity measurement are susceptible to the difference in temperature between the target and the reference blackbody. It is also limited by the state of the observation target and observation. This paper introduces the irradiance condition, while [...] Read more.

The currently used energy methods in spectral emissivity measurement are susceptible to the difference in temperature between the target and the reference blackbody. It is also limited by the state of the observation target and observation. This paper introduces the irradiance condition, while using the correlation between the information of emission energy and reflected energy of the high-temperature target. Based on the principle of radiative transmission and energy conservation, the relationship between the emissivity and bidirectional reflectance factor (BRF) was used to perform the retrieval of emissivity and temperature. An experimental device was designed, and graphite and rock were considered to verify the feasibility of the experimental scheme. The error of emissivity and temperature of both targets were, respectively, less than 5% and 0.5%, due to the Lambertian assumption, and the systematic errors had negligible impact on the retrieval. This verifies that the experimental observation method and scheme is reasonable. Full article

(This article belongs to the Special Issue Towards Optoelectronic Technology: From Basic Research to Applications)

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19 pages, 8613 KiB

Open AccessArticle

A Diagnostic Method Based on Active Thermography for the Degradation Assessment of Power Plant Boiler Tubes

by Sławomir Zator, Michał Tomaszewski and Mirosław Lasar

Sensors 2022, 22(21), 8401; https://doi.org/10.3390/s22218401 - 01 Nov 2022

Cited by 1 | Viewed by 1416

Abstract

Proper maintenance management of power infrastructure requires inspections, in order to gather knowledge about the facility’s current condition. For this purpose, periodic diagnostic tests are carried out, not only to determine the current state, but to also predict future conditions, and subsequently plan [...] Read more.

Proper maintenance management of power infrastructure requires inspections, in order to gather knowledge about the facility’s current condition. For this purpose, periodic diagnostic tests are carried out, not only to determine the current state, but to also predict future conditions, and subsequently plan for the scope of necessary repair work. Currently, in the case of heat screens of power boilers, the diagnostic process takes many days, is very expensive, and usually does not cover the entire screen area. Therefore, it is necessary to develop new, noninvasive diagnostic methods. This study presents the concept and research for an alternative method of locating places with excessive energy boiler screen degradation that require replacement. It was assumed that the new method should be fast, require no scaffolding assembly, and permit checking of the entire screen surface; this is unlike the methods used currently, which require manual checking of selected screen tubes. The proposed method is based on active thermography, in which heat flux is forced by the liquid flowing inside the screen. Tests were carried out based on a model of an axial-symmetric system in the form of a tube, with controlled reductions in the wall thickness. An experiment was carried out many times by recording the pipe surface temperature in many characteristic places (different thicknesses of the tube walls) with a thermal imaging camera. A temperature change was forced by a controlled flow of hot or cold water. The methods of analysis were proposed and verified, allowing firstly, detection of places with a reduced wall thickness, and secondly, estimations of the wall thickness (i.e., excessive degradation). For the best-proposed model (one of the four analyzed), all of the thickness changes were detected, and the limit error of thickness obtained was 0.3 mm. Full article

(This article belongs to the Special Issue Towards Optoelectronic Technology: From Basic Research to Applications)

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16 pages, 3618 KiB

Open AccessArticle

Polarization Calibration of a Microwave Polarimeter with Near-Infrared Up-Conversion for Optical Correlation and Detection

by Francisco J. Casas, Patricio Vielva, R. Belen Barreiro, Enrique Martínez-González and G. Pascual-Cisneros

Sensors 2022, 22(20), 8080; https://doi.org/10.3390/s22208080 - 21 Oct 2022

Cited by 4 | Viewed by 1329

Abstract

This paper presents a polarization calibration method applied to a microwave polarimeter demonstrator based on a near-infrared (NIR) frequency up-conversion stage that allows both optical correlation and signal detection at a wavelength of 1550 nm. The instrument was designed to measure the polarization [...] Read more.

This paper presents a polarization calibration method applied to a microwave polarimeter demonstrator based on a near-infrared (NIR) frequency up-conversion stage that allows both optical correlation and signal detection at a wavelength of 1550 nm. The instrument was designed to measure the polarization of cosmic microwave background (CMB) radiation from the sky, obtaining the Stokes parameters of the incoming signal simultaneously, in a frequency range from 10 to 20 GHz. A linearly polarized input signal with a variable polarization angle is used as excitation in the polarimeter calibration setup mounted in the laboratory. The polarimeter systematic errors can be corrected with the proposed calibration procedure, achieving high levels of polarization efficiency (low polarization percentage errors) and low polarization angle errors. The calibration method is based on the fitting of polarization errors by means of sinusoidal functions composed of additive or multiplicative terms. The accuracy of the fitting increases with the number of terms in such a way that the typical error levels required in low-frequency CMB experiments can be achieved with only a few terms in the fitting functions. On the other hand, assuming that the calibration signal is known with the required accuracy, additional terms can be calculated to reach the error levels needed in ultrasensitive B-mode polarization CMB experiments. Full article

(This article belongs to the Special Issue Towards Optoelectronic Technology: From Basic Research to Applications)

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14 pages, 5907 KiB

Open AccessArticle

A Reliable Method of Measuring the Conversion Degrees of Methacrylate Dental Resins

by Mirosław Kwaśny, Aneta Bombalska and Karolina Obroniecka

Sensors 2022, 22(6), 2170; https://doi.org/10.3390/s22062170 - 10 Mar 2022

Cited by 6 | Viewed by 1918

Abstract

The main aim of the study was to implement the most reliable method of measuring the degrees of conversion during photopolymerization of dental fillings. Contrary to the methods used so far, the method is based only on comparison with the monomer absorbance spectrum [...] Read more.

The main aim of the study was to implement the most reliable method of measuring the degrees of conversion during photopolymerization of dental fillings. Contrary to the methods used so far, the method is based only on comparison with the monomer absorbance spectrum without reference bands. Another aim of the study was to prepare a comparative analysis of the polymerization kinetics of dental resins under various light sources and different environmental conditions (irradiance, light dose, temperature), with estimation of the degrees of conversion (DC) of the resins being the main metric. HRi Universal Enamel (UE2) and HRi Universal Dentine (UD2) were examined under two different types of light sources used in dentistry, LED and halogen. DC was measured by Fourier transform infrared spectroscopy (FTIR) in transmission mode from 5 s up to 7 days. Spectra were recorded from the parallel optical layers of samples that were placed between the KBr crystals. The results are expressed by the changes in the absorbance spectrum during the polymerization and the calculated conversion rates. The results of each experiment were averaged from three separate measurements of three samples, during which the samples were illuminated under identical conditions. The data were analyzed by performing ANOVA test comparisons between sample groups at the significance level α = 0.05. The degree of conversion of the UD2 resin was higher than that of UE2 for each experimental condition, but there was no statistically significant difference between the DC of those materials (p > 0.05). There was statistically significant difference (p < 0.01) in the DC caused by LED and halogen light sources producing the same light doses (38 J/cm²). This was the result of different features of light transmission to the filler in the resin composite. The efficacy of the LED source is twice as high as that of the halogen light source. Maximal DC without any other differences in conditions, such as resin type or light source, reached around 70% for temperatures of 22–37 °C. For 37 °C, this took 24 h, which is a contrast to the 7 days it took for 23 °C. The influences of different conditions and factors on reaction kinetics are only strong in the early and the rapid stage of conversion. The optimal time of irradiance using either light source is 20 s for a monolayer, and its thickness should not exceed 2 mm. Full article

(This article belongs to the Special Issue Towards Optoelectronic Technology: From Basic Research to Applications)

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Review

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66 pages, 52190 KiB

Open AccessReview

Ultraviolet Photodetectors: From Photocathodes to Low-Dimensional Solids

by Antoni Rogalski, Zbigniew Bielecki, Janusz Mikołajczyk and Jacek Wojtas

Sensors 2023, 23(9), 4452; https://doi.org/10.3390/s23094452 - 02 May 2023

Cited by 10 | Viewed by 4385

Abstract

The paper presents the long-term evolution and recent development of ultraviolet photodetectors. First, the general theory of ultraviolet (UV) photodetectors is briefly described. Then the different types of detectors are presented, starting with the older photoemission detectors through photomultipliers and image intensifiers. More [...] Read more.

The paper presents the long-term evolution and recent development of ultraviolet photodetectors. First, the general theory of ultraviolet (UV) photodetectors is briefly described. Then the different types of detectors are presented, starting with the older photoemission detectors through photomultipliers and image intensifiers. More attention is paid to silicon and different types of wide band gap semiconductor photodetectors such as AlGaN, SiC-based, and diamond detectors. Additionally, Ga₂O₃ is considered a promising material for solar-blind photodetectors due to its excellent electrical properties and a large bandgap energy. The last part of the paper deals with new UV photodetector concepts inspired by new device architectures based on low-dimensional solid materials. It is shown that the evolution of the architecture has shifted device performance toward higher sensitivity, higher frequency response, lower noise, and higher gain-bandwidth products. Full article

(This article belongs to the Special Issue Towards Optoelectronic Technology: From Basic Research to Applications)

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