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Spectral Detection Technology, Sensors and Instruments

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Optical Sensors".

Deadline for manuscript submissions: 15 May 2024 | Viewed by 16143

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Special Issue Editors

Dr. Qing Yu

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Guest Editor

Fujian Key Laboratory of Green Intelligent Drive and Transmission for Mobile Machinery, Huaqiao University, Xiamen 361021, China
Interests: multispectral detection; confocal measurement

Dr. Ran Tu

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Guest Editor

College of Mechanical Engineering and Automation, Huaqiao University, Xiamen 361021, China
Interests: hazard detection and diagnosis; safety engineering

Dr. Ting Liu

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Guest Editor

College of Mechanical Engineering and Automation, Huaqiao University, Xiamen 361021, China
Interests: optical fiber sensing; spectral detection and micro-nano photonics

Dr. Lina Li

E-Mail Website
Guest Editor

College of Mechanical Engineering and Automation, Huaqiao University, Xiamen 361021, China
Interests: spectral analysis technology; biomedical photoelectric testing instrument

Special Issue Information

Dear Colleagues,

Spectral detection technology has always been a research hotspot in the field of precision measurement. It can not only obtain the spectral characteristics of the measured object, but also obtain the topography of samples through hyperspectral and multispectral. It is widely used in national defense, space remote sensing, biomedicine, disaster monitoring, and many engineering fields. In recent years, with the development of technology, intelligent manufacturing and environmental protection have attracted worldwide attention, which extends the application of spectral detection technology to new dimensions. Therefore, a Special Issue about "Spectral Detection Technology, Sensors and Instruments" is set up, in which we want to find innovative research work by scientists around the world in the following areas, but not limited to:

Multispectral detection technology;
Spectral analysis technology;
Spectral imaging processing;
Spectral-based hazard analysis and diagnosis;
Spectral-based environmental detecting and monitoring;
Medical detection based on spectrum;
Optical fiber spectral sensing technology.

Dr. Qing Yu
Dr. Ran Tu
Dr. Ting Liu
Dr. Lina Li
Guest Editors

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Published Papers (11 papers)

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Research

16 pages, 9595 KiB

Open AccessArticle

Impact of Reducing Statistically Small Population Sampling on Threshold Detection in FBG Optical Sensing

by Gabriel Cibira, Ivan Glesk, Jozef Dubovan and Daniel Benedikovič

Sensors 2024, 24(7), 2285; https://0-doi-org.brum.beds.ac.uk/10.3390/s24072285 - 03 Apr 2024

Viewed by 467

Abstract

Many techniques have been studied for recovering information from shared media such as optical fiber that carries different types of communication, sensing, and data streaming. This article focuses on a simple method for retrieving the targeted information with the least necessary number of significant samples when using statistical population sampling. Here, the focus is on the statistical denoising and detection of the fiber Bragg grating (FBG) power spectra. The impact of the two-sided and one-sided sliding window technique is investigated. The size of the window is varied up to one-half of the symmetrical FBG power spectra bandwidth. Both, two- and one-sided small population sampling techniques were experimentally investigated. We found that the shorter sliding window delivered less processing latency, which would benefit real-time applications. The calculated detection thresholds were used for in-depth analysis of the data we obtained. It was found that the normality three-sigma rule does not need to be followed when a small population sampling is used. Experimental demonstrations and analyses also showed that novel denoising and statistical threshold detection do not depend on prior knowledge of the probability distribution functions that describe the FBG power spectra peaks and background noise. We have demonstrated that the detection thresholds’ adaptability strongly depends on the mean and standard deviation values of the small population sampling. Full article

(This article belongs to the Special Issue Spectral Detection Technology, Sensors and Instruments)

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22 pages, 15334 KiB

Open AccessArticle

Raw Spectral Filter Array Imaging for Scene Recognition

by Hassan Askary, Jon Yngve Hardeberg and Jean-Baptiste Thomas

Sensors 2024, 24(6), 1961; https://0-doi-org.brum.beds.ac.uk/10.3390/s24061961 - 19 Mar 2024

Viewed by 461

Abstract

Scene recognition is the task of identifying the environment shown in an image. Spectral filter array cameras allow for fast capture of multispectral images. Scene recognition in multispectral images is usually performed after demosaicing the raw image. Along with adding latency, this makes the classification algorithm limited by the artifacts produced by the demosaicing process. This work explores scene recognition performed on raw spectral filter array images using convolutional neural networks. For this purpose, a new raw image dataset is collected for scene recognition with a spectral filter array camera. The classification is performed using a model constructed based on the pretrained Places-CNN. This model utilizes all nine channels of spectral information in the images. A label mapping scheme is also applied to classify the new dataset. Experiments are conducted with different pre-processing steps applied on the raw images and the results are compared. Higher-resolution images are found to perform better even if they contain mosaic patterns. Full article

(This article belongs to the Special Issue Spectral Detection Technology, Sensors and Instruments)

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13 pages, 4532 KiB

Open AccessArticle

A Microlens Array Grating for Miniature Multi-Channel Spectrometers

by Shuonan Shan, Jingwen Li, Peiyuan Liu, Qiaolin Li, Xiaohao Wang and Xinghui Li

Sensors 2023, 23(20), 8381; https://0-doi-org.brum.beds.ac.uk/10.3390/s23208381 - 11 Oct 2023

Cited by 1 | Viewed by 1191

Abstract

Most existing multi-channel spectrometers are constructed by physically stacking single-channel spectrometers, resulting in their large size, high weight, and limited number of channels. Therefore, their miniaturization is urgently needed. In this paper, a microlens array grating is designed for miniature multi-channel spectrometers. A transmissive element integrating microlens arrays and gratings, the MLAG, enables simultaneous focusing and dispersion. Using soft lithography, the MLAG was fabricated with a deviation of less than 2.2%. The dimensions are 10 mm × 10 mm × 4 mm with over 2000 available units. The MLAG spectrometer operates in the 400–700 nm wavelength range with a resolution of 6 nm. Additionally, the designed MLAG multi-channel spectrometer is experimentally verified to have independently valid cells that can be used in multichannel spectrometers. The wavelength position repeatability deviation of each cell is about 0.5 nm, and the repeatability of displacement measurements by the chromatic confocal sensor with the designed MLAG multi-channel spectrometer is less than 0.5 μm. Full article

(This article belongs to the Special Issue Spectral Detection Technology, Sensors and Instruments)

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12 pages, 18467 KiB

Open AccessArticle

Gaussian Decomposition vs. Semiclassical Quantum Simulation: Obtaining the High-Order Derivatives of a Spectrum in the Case of Photosynthetic Pigment Optical Properties Studying

by Andrei P. Razjivin, Vladimir S. Kozlovsky, Aleksandr A. Ashikhmin and Roman Y. Pishchalnikov

Sensors 2023, 23(19), 8248; https://0-doi-org.brum.beds.ac.uk/10.3390/s23198248 - 05 Oct 2023

Viewed by 728

Abstract

In this paper, a procedure for obtaining undistorted high derivatives (up to the eighth order) of the optical absorption spectra of biomolecule pigments has been developed. To assess the effectiveness of the procedure, the theoretical spectra of bacteriochlorophyll a, chlorophyll a, spheroidene, and spheroidenone were simulated by fitting the experimental spectra using the differential evolution algorithm. The experimental spectra were also approximated using sets of Gaussians to calculate the model absorption spectra. Theoretical and model spectra can be differentiated without smoothing (high-frequency noise filtering) to obtain high derivatives. Superimposition of the noise track on the model spectra allows us to obtain test spectra similar to the experimental ones. Comparison of the high derivatives of the model spectra with those of the test spectra allows us to find the optimal parameters of the filter, the application of which leads to minimal differences between the high derivatives of the model and test spectra. For all four studied pigments, it was shown that smoothing the experimental spectra with optimal filters makes it possible to obtain the eighth derivatives of the experimental spectra, which were close to the eighth derivatives of their theoretical spectra. Full article

(This article belongs to the Special Issue Spectral Detection Technology, Sensors and Instruments)

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23 pages, 11783 KiB

Open AccessArticle

A Spectral Encoding Simulator for Broadband Active Illumination and Reconstruction-Based Spectral Measurement

by Peng Jiang, Xiaoxu Wang, Zihui Zhang, Guochao Gu, Jifeng Li, Heng Wu, Limin He and Guanyu Lin

Sensors 2023, 23(10), 4608; https://0-doi-org.brum.beds.ac.uk/10.3390/s23104608 - 10 May 2023

Viewed by 1594

Abstract

Spectral reflectance or transmittance measurements provide intrinsic information on the material of an object and are widely used in remote sensing, agriculture, diagnostic medicine, etc. Most reconstruction-based spectral reflectance or transmittance measurement methods based on broadband active illumination use narrow-band LEDs or lamps combined with specific filters as spectral encoding light sources. These light sources cannot achieve the designed spectral encoding with a high resolution and accuracy due to their low degree of freedom for adjustment, leading to inaccurate spectral measurements. To address this issue, we designed a spectral encoding simulator for active illumination. The simulator is composed of a prismatic spectral imaging system and a digital micromirror device. The spectral wavelengths and intensity are adjusted by switching the micromirrors. We used it to simulate spectral encodings according to the spectral distribution on micromirrors and solved the DMD patterns corresponding to the spectral encodings with a convex optimization algorithm. To verify the applicability of the simulator for spectral measurements based on active illumination, we used it to numerically simulate existing spectral encodings. We also numerically simulated a high-resolution Gaussian random measurement encoding for compressed sensing and measured the spectral reflectance of one vegetation type and two minerals through numerical simulations. We reconstructed the spectral transmittance of a calibrated filter through an experiment. The results show that the simulator can measure the spectral reflectance or transmittance with a high resolution and accuracy. Full article

(This article belongs to the Special Issue Spectral Detection Technology, Sensors and Instruments)

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11 pages, 2135 KiB

Open AccessArticle

Performance-Enhanced Static Modulated Fourier Transform Spectrometer with a Spectral Reconstruction

by Ju Yong Cho, Seunghoon Lee and Won Kweon Jang

Sensors 2023, 23(5), 2603; https://0-doi-org.brum.beds.ac.uk/10.3390/s23052603 - 27 Feb 2023

Cited by 1 | Viewed by 1231

Abstract

A static modulated Fourier transform spectrometer has been noted to be a compact and fast evaluation tool for spectroscopic inspection, and many novel structures have been reported to support its performance. However, it still suffers from poor spectral resolution due to the limited sampling data points, which marks its intrinsic drawback. In this paper, we outline the enhanced performance of a static modulated Fourier transform spectrometer with a spectral reconstruction method that can compensate for the insufficient data points. An enhanced spectrum can be reconstructed by applying a linear regression method to a measured interferogram. We obtain the transfer function of a spectrometer by analyzing what interferogram can be detected with different values of parameters such as focal length of the Fourier lens, mirror displacement, and wavenumber range, instead of direct measurement of the transfer function. Additionally, the optimal experimental conditions for the narrowest spectral width are investigated. Application of the spectral reconstruction method achieves an improved spectral resolution from 74 cm⁻¹ when spectral reconstruction is not applied to 8.9 cm⁻¹, and a narrowed spectral width from 414 cm⁻¹ to 371 cm⁻¹, which are close to the values of the spectral reference. In conclusion, the spectral reconstruction method in a compact static modulated Fourier transform spectrometer effectively enhances its performance without any additional optic in the structure. Full article

(This article belongs to the Special Issue Spectral Detection Technology, Sensors and Instruments)

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18 pages, 6151 KiB

Open AccessArticle

Design and Research of Chromatic Confocal System for Parallel Non-Coaxial Illumination Based on Optical Fiber Bundle

by Yali Zhang, Qing Yu, Chong Wang, Yaozu Zhang, Fang Cheng, Yin Wang, Tianliang Lin, Ting Liu and Lin Xi

Sensors 2022, 22(24), 9596; https://0-doi-org.brum.beds.ac.uk/10.3390/s22249596 - 07 Dec 2022

Cited by 2 | Viewed by 2079

Abstract

Conventional chromatic confocal systems are mostly single-point coaxial illumination systems with a low signal-to-noise ratio, light energy utility and measurement efficiency. To overcome the above shortcomings, we propose a parallel non-coaxial-illumination chromatic-confocal-measurement system based on an optical fiber bundle. Based on the existing single-point non-coaxial-illumination system, the optical fiber bundle is used as the optical beam splitter to achieve parallel measurements. Thus, the system can yield measurements through line scanning, which greatly improves measurement efficiency. To verify the measurement performance of the system, based on the calibration experiment, the system realizes the measurement of the height of the step, the thickness of the transparent specimen and the reconstruction of the three-dimensional topography of the surface of the step and coin. The experimental results show that the measuring range of the system is 200 μm. The measurement accurcy can reach micron level, and the system can realize a good three-dimensional topography reconstruction effect. Full article

(This article belongs to the Special Issue Spectral Detection Technology, Sensors and Instruments)

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25 pages, 9952 KiB

Open AccessArticle

Characterisation and Quenching Correction for an Al₂O₃:C Optical Fibre Real Time System in Therapeutic Proton, Helium, and Carbon-Charged Beams

by Luana de Freitas Nascimento, Paul Leblans, Brent van der Heyden, Mark Akselrod, Jo Goossens, Luis Enrique Correa Rocha, Ana Vaniqui and Dirk Verellen

Sensors 2022, 22(23), 9178; https://0-doi-org.brum.beds.ac.uk/10.3390/s22239178 - 25 Nov 2022

Cited by 3 | Viewed by 1254

Abstract

Real time radioluminescence fibre-based detectors were investigated for application in proton, helium, and carbon therapy dosimetry. The Al₂O₃:C probes are made of one single crystal (1 mm) and two droplets of micro powder in two sizes (38 μm and 4 μm) mixed with a water-equivalent binder. The fibres were irradiated behind different thicknesses of solid slabs, and the Bragg curves presented a quenching effect attributed to the nonlinear response of the radioluminescence (RL) signal as a function of linear energy transfer (LET). Experimental data and Monte Carlo simulations were utilised to acquire a quenching correction method, adapted from Birks’ formulation, to restore the linear dose–response for particle therapy beams. The method for quenching correction was applied and yielded the best results for the ‘4 μm’ optical fibre probe, with an agreement at the Bragg peak of 1.4% (160 MeV), and 1.5% (230 MeV) for proton-charged particles; 2.4% (150 MeV/u) for helium-charged particles and of 4.8% (290 MeV/u) and 2.9% (400 MeV/u) for the carbon-charged particles. The most substantial deviations for the ‘4 μm’ optical fibre probe were found at the falloff regions, with ~3% (protons), ~5% (helium) and 6% (carbon). Full article

(This article belongs to the Special Issue Spectral Detection Technology, Sensors and Instruments)

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13 pages, 5764 KiB

Open AccessArticle

Location of Latent Forensic Traces Using Multispectral Bands

by Samuel Miralles-Mosquera, Bernardo Alarcos and Alfredo Gardel

Sensors 2022, 22(23), 9142; https://0-doi-org.brum.beds.ac.uk/10.3390/s22239142 - 25 Nov 2022

Viewed by 1782

Abstract

In this paper, a conventional camera modified to capture multispectral images, has been used to locate latent forensic traces with a smart combination of wavelength filters, capturing angle, and illumination sources. There are commercial multispectral capture devices adapted to the specific tasks of the police, but due to their high cost and operation not well adapted to the field work in a crime scene, they are not currently used by forensic units. In our work, we have used a digital SLR camera modified to obtain a nominal sensitivity beyond the visible spectrum. The goal is to obtain forensic evidences from a crime scene using the multispectral camera by an expert in the field knowing which wavelength filters and correct illumination sources should be used, making visible latent evidences hidden from the human-eye. In this paper, we show a procedure to retrieve from latent forensic traces, showing the validity of the system in different real cases (blood stains, hidden/erased tattoos, unlocking patterns on mobile devices). This work opens the possibility of applying multispectral inspections in the forensic field specially for operational units for the location of latent through non-invasive optical procedures. Full article

(This article belongs to the Special Issue Spectral Detection Technology, Sensors and Instruments)

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14 pages, 4718 KiB

Open AccessArticle

Development and Validation of a Tunable Diode Laser Absorption Spectroscopy System for Hot Gas Flow and Small-Scale Flame Measurement

by Ran Tu, Junqing Gu, Yi Zeng, Xuejin Zhou, Kai Yang, Jiaojiao Jing, Zhihong Miao and Jianhong Yang

Sensors 2022, 22(17), 6707; https://0-doi-org.brum.beds.ac.uk/10.3390/s22176707 - 05 Sep 2022

Cited by 4 | Viewed by 2002

Abstract

TDLAS (tunable diode laser absorption spectroscopy) is an important gas analysis method that can be employed to obtain characteristic parameters non-invasively by the infrared absorption spectra of tracer molecules such as CH₄, H₂O and O₂. In this study, a portable H₂O-based TDLAS system with a dual optical path was developed with the aim of assessing the combustion characteristics of flammable gases. Firstly, a calculation method of gas characteristics including temperature and velocity combining absorption spectra and a HITRAN database was provided. Secondly, to calibrate and validate this TDLAS system precisely, a pressure vessel and a shock tube were introduced innovatively to generate static or steady flow fields with preset constant temperatures, pressures, or velocities. Static tests within environment pressures up to 2 MPa and steady flow field tests with temperatures up to 1600 K and flow velocities up to 950 m/s were performed for verification. It was proved that this system can provide an accurate values for high temperature and velocity gas flows. Finally, an experimental investigation of CH₄/air flames was conducted to test the effectiveness of the system when applied to small diffusion flames. This TDLAS system gave satisfactory flame temperature and velocity data owing to the dual optical path design and high frequency scanning, which compensated for scale effects and pulsation of the flame. This work demonstrates a valuable new approach to thermal hazard analysis in specific environments. Full article

(This article belongs to the Special Issue Spectral Detection Technology, Sensors and Instruments)

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18 pages, 4513 KiB

Open AccessArticle

Detection of Water pH Using Visible Near-Infrared Spectroscopy and One-Dimensional Convolutional Neural Network

by Dengshan Li and Lina Li

Sensors 2022, 22(15), 5809; https://0-doi-org.brum.beds.ac.uk/10.3390/s22155809 - 03 Aug 2022

Cited by 6 | Viewed by 1938

Abstract

pH is an important parameter for water quality detection. This study proposed a novel calibration regression strategy based on a one-dimensional convolutional neural network (1D-CNN) for water pH detection using visible near-infrared (Vis-NIR) spectroscopy. Two groups of Vis-NIR spectral analysis experiments of water pH detection were employed to evaluate the performance of 1D-CNN. Two conventional multivariate regression calibration methods, including partial least squares (PLS) and least squares support vector machine (LS-SVM), were introduced for comparative analysis with 1D-CNN. The successive projections algorithm (SPA) was adopted to select the feature variables. In addition, the learning mechanism of 1D-CNN was interpreted through visual feature maps by convolutional layers. The results showed that the 1D-CNN models obtained the highest prediction accuracy based on full spectra for the two experiments. For the spectrophotometer experiment, the root mean square error of prediction (RMSEP) was 0.7925, and the determination coefficient of prediction (

R_{p}^{2}

) was 0.8515. For the grating spectrograph experiment, the RMSEP was 0.5128 and the

R_{p}^{2}

was 0.9273. The convolutional layers could automatically preprocess the spectra and effectively extract the spectra features. Compared with the traditional regression methods, 1D-CNN does not need complex spectra pretreatment and variable selection. Therefore, 1D-CNN is a promising regression approach, with higher prediction accuracy and better modeling convenience for rapid water pH detection using Vis-NIR spectroscopy. Full article

(This article belongs to the Special Issue Spectral Detection Technology, Sensors and Instruments)

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