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Recent Advances in Terahertz, Mid-Infrared, and Near-Infrared Sensing

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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: closed (5 June 2023) | Viewed by 10728

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Special Issue Editors

Dr. Xiaoqiong Qi

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Guest Editor

School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
Interests: semiconductor laser dynamics; terahertz quantum cascade lasers; laser feedback interferometry; terahertz sensing and imaging; skin cancer detection
Special Issues, Collections and Topics in MDPI journals

Dr. Cheng Wang

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Guest Editor

School of Information Science and Technology, ShanghaiTech University, Shanghai 201210, China
Interests: semiconductor optoelectronics; novel semiconductor lasers; laser dynamics; photonic integrated circuits, optical communication; optical neural networks

Special Issue Information

Dear Colleagues,

Recently, the development of laser sources and detection technologies at the terahertz, mid-, and near-infrared have greatly promoted sensing applications in these frequency bands. Novel light sources (represented by quantum cascade lasers and interband cascade lasers) and detection technology (such as laser feedback interferometry technology) have rapidly expanded the sensing applications in these fields. Some of the promising applications include biomedical sensing and imaging, trace gas spectrometry, industry monitoring, and security screening. This Special Issue encompasses a broad range of recent advances in terahertz, mid-, and near-infrared sensing technologies, including state-of-the-art technologies in sensing devices and systems. Both reviews and original research articles are very welcome. We look forward to your active participation in this Special Issue.

Dr. Xiaoqiong Qi
Dr. Cheng Wang
Guest Editors

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Keywords

optical sensing
vibrometry
velocimetry
THz sensing
biomedical sensing and imaging
trace gas spectroscopy
laser dynamics
integrated photonics
silicon photonics
nanoscale sensing

Published Papers (5 papers)

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Research

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18 pages, 4207 KiB

Open AccessArticle

Scaled-Model Radar Cross-Section Measurement: The Influence of the Scattered Field under Gaussian Beam Illumination—A Theoretical Analysis

by Yi Xuan Ang and Hoi-Shun Lui

Sensors 2023, 23(16), 7202; https://doi.org/10.3390/s23167202 - 16 Aug 2023

Viewed by 1789

Abstract

At microwave frequencies, radar cross-section (RCS) measurements are usually performed by placing the target in the far-field region of the antenna. The wavefront of the radiating field from the antenna can be approximated as planar, ensuring that the incident field and the power interact with the target independently of the antenna. However, for electrically large targets, the required distance becomes significant, posing challenges for implementation. Scaled-model RCS measurements offer an alternative solution. RCS measurements at terahertz and optical frequencies typically require a collimated beam as the source, where the intercepted power and RCS become dependent on the excitation. To address this dependency, researchers have proposed modifying the RCS definition to account for the intercepted power and to analytically formulate the scattering problem. However, such modifications require prior knowledge of the target’s geometry and material properties, which are often not readily available in practice. This also limits the study to only canonical targets. In this paper, we propose an alternative approach for modelling the intercepted power. The Gaussian beam is decomposed into a number of plane waves travelling to different directions using the theory of plane wave spectrum. The scattering problem is solved using the full-wave method of moment. Through theoretical proofs and numerical examples involving spheres and a non-canonical target, with a scaled-model aircraft, we demonstrate that the original RCS definition can serve as a good approximation for scaled measurements, provided that the beam waist is approximately four times the target’s dimensions. These findings provide valuable guidelines for radar engineers when performing scaled measurements using collimated beams. The results, which match those obtained from full-model measurements, enable us to predict the RCS of full-scale targets. This capability facilitates various target-related applications, such as target characterization, classification, detection, and even recognition. Full article

(This article belongs to the Special Issue Recent Advances in Terahertz, Mid-Infrared, and Near-Infrared Sensing)

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16 pages, 1887 KiB

Open AccessArticle

Determination of Sugars and Acids in Grape Must Using Miniaturized Near-Infrared Spectroscopy

by Lucie Cornehl, Julius Krause, Xiaorong Zheng, Pascal Gauweiler, Florian Schwander, Reinhard Töpfer, Robin Gruna and Anna Kicherer

Sensors 2023, 23(11), 5287; https://doi.org/10.3390/s23115287 - 2 Jun 2023

Viewed by 1598

Abstract

An automatic determination of grape must ingredients during the harvesting process would support cellar logistics and enables an early termination of the harvest if quality parameters are not met. One of the most important quality-determining characteristics of grape must is its sugar and acid content. Among others, the sugars in particular determine the quality of the must and wine. Chiefly in wine cooperatives, in which a third of all German winegrowers are organized, these quality characteristics serve as the basis for payment. They are acquired upon delivery at the cellar of the cooperative or the winery and result in the acceptance or rejection of grapes and must. The whole process is very time-consuming and expensive, and sometimes grapes that do not meet the quality requirements for sweetness, acidity, or healthiness are destroyed or not used at all, which leads to economic loss. Near-infrared spectroscopy is now a widely used technique to detect a wide variety of ingredients in biological samples. In this study, a miniaturized semi-automated prototype apparatus with a near-infrared sensor and a flow cell was used to acquire spectra (1100 nm to 1350 nm) of grape must at defined temperatures. Data of must samples from four different red and white Vitis vinifera (L.) varieties were recorded throughout the whole growing season of 2021 in Rhineland Palatinate, Germany. Each sample consisted of 100 randomly sampled berries from the entire vineyard. The contents of the main sugars (glucose and fructose) and acids (malic acid and tartaric acid) were determined with high-performance liquid chromatography. Chemometric methods, using partial least-square regression and leave-one-out cross-validation, provided good estimates of both sugars (RMSEP = 6.06 g/L, R² = 89.26%), as well as malic acid (RMSEP = 1.22 g/L, R² = 91.10%). The coefficient of determination (R²) was comparable for glucose and fructose with 89.45% compared to 89.08%, respectively. Although tartaric acid was predictable for only two of the four varieties using near-infrared spectroscopy, calibration and validation for malic acid were accurate for all varieties in an equal extent like the sugars. These high prediction accuracies for the main quality determining grape must ingredients using this miniaturized prototype apparatus might enable an installation on a grape harvester in the future. Full article

(This article belongs to the Special Issue Recent Advances in Terahertz, Mid-Infrared, and Near-Infrared Sensing)

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13 pages, 6136 KiB

Open AccessArticle

Comparison of Physical and System Factors Impacting Hydration Sensing in Leaves Using Terahertz Time-Domain and Quantum Cascade Laser Feedback Interferometry Imaging

by Khushboo Singh, Aparajita Bandyopadhyay, Karl Bertling, Yah Leng Lim, Tim Gillespie, Dragan Indjin, Lianhe Li, Edmund H. Linfield, A. Giles Davies, Paul Dean, Aleksandar D. Rakić and Amartya Sengupta

Sensors 2023, 23(5), 2721; https://doi.org/10.3390/s23052721 - 2 Mar 2023

Cited by 5 | Viewed by 1517

Abstract

To reduce the water footprint in agriculture, the recent push toward precision irrigation management has initiated a sharp rise in photonics-based hydration sensing in plants in a non-contact, non-invasive manner. Here, this aspect of sensing was employed in the terahertz (THz) range for mapping liquid water in the plucked leaves of Bambusa vulgaris and Celtis sinensis. Two complementary techniques, broadband THz time-domain spectroscopic imaging and THz quantum cascade laser-based imaging, were utilized. The resulting hydration maps capture the spatial variations within the leaves as well as the hydration dynamics in various time scales. Although both techniques employed raster scanning to acquire the THz image, the results provide very distinct and different information. Terahertz time-domain spectroscopy provides rich spectral and phase information detailing the dehydration effects on the leaf structure, while THz quantum cascade laser-based laser feedback interferometry gives insight into the fast dynamic variation in dehydration patterns. Full article

(This article belongs to the Special Issue Recent Advances in Terahertz, Mid-Infrared, and Near-Infrared Sensing)

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17 pages, 4191 KiB

Open AccessArticle

Single-Point and Surface Quality Assessment Algorithm in Continuous Production with the Use of 3D Laser Doppler Scanning Vibrometry System

by Lukasz Scislo

Sensors 2023, 23(3), 1263; https://doi.org/10.3390/s23031263 - 22 Jan 2023

Cited by 19 | Viewed by 2027

Abstract

In the current economic situation of many companies, the need to reduce production time is a critical element. However, this cannot usually be carried out with a decrease in the quality of the final product. This article presents a possible solution for reducing the time needed for quality management. With the use of modern solutions such as optical measurement systems, quality control can be performed without additional stoppage time. In the case of single-point measurement with the Laser Doppler Vibrometer, the measurement can be performed quickly in a matter of milliseconds for each product. This article presents an example of such quality assurance measurements, with the use of fully non-contact methods, together with a proposed evaluation criterion for quality assessment. The proposed quality assurance algorithm allows the comparison of each of the products’ modal responses with the ideal template and stores this information in the cloud, e.g., in the company’s supervisory system. This makes the presented 3D Laser Vibrometry System an advanced instrumentation and data acquisition system which is the perfect application in the case of a factory quality management system based on the Industry 4.0 concept. Full article

(This article belongs to the Special Issue Recent Advances in Terahertz, Mid-Infrared, and Near-Infrared Sensing)

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Review

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17 pages, 5627 KiB

Open AccessReview

Metasurface-Assisted Terahertz Sensing

by Qian Wang, Yuzi Chen, Jinxian Mao, Fengyuan Yang and Nan Wang

Sensors 2023, 23(13), 5902; https://doi.org/10.3390/s23135902 - 25 Jun 2023

Cited by 9 | Viewed by 3111

Abstract

Terahertz (THz) waves, which fall between microwaves and infrared bands, possess intriguing electromagnetic properties of non-ionizing radiation, low photon energy, being highly sensitive to weak resonances, and non-polar material penetrability. Therefore, THz waves are extremely suitable for sensing and detecting chemical, pharmaceutical, and biological molecules. However, the relatively long wavelength of THz waves (30~3000 μm) compared to the size of analytes (1~100 nm for biomolecules, <10 μm for microorganisms) constrains the development of THz-based sensors. To circumvent this problem, metasurface technology, by engineering subwavelength periodic resonators, has gained a great deal of attention to enhance the resonance response of THz waves. Those metasurface-based THz sensors exhibit high sensitivity for label-free sensing, making them appealing for a variety of applications in security, medical applications, and detection. The performance of metasurface-based THz sensors is controlled by geometric structure and material parameters. The operating mechanism is divided into two main categories, passive and active. To have a profound understanding of these metasurface-assisted THz sensing technologies, we review and categorize those THz sensors, based on their operating mechanisms, including resonators for frequency shift sensing, nanogaps for enhanced field confinement, chirality for handedness detection, and active elements (such as graphene and MEMS) for advanced tunable sensing. This comprehensive review can serve as a guideline for future metasurfaces design to assist THz sensing and detection. Full article

(This article belongs to the Special Issue Recent Advances in Terahertz, Mid-Infrared, and Near-Infrared Sensing)

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