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Infrared and THz Sensing and Imaging

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A special issue of Sensors (ISSN 1424-8220).

Deadline for manuscript submissions: closed (30 April 2016) | Viewed by 241061

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Special Issue Editors

Prof. Dr. Vincenzo Luigi Spagnolo

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Guest Editor

Dipartimento Interateneo di Fisica (Department of Physics) Politecnico di Bari, Via Edoardo Orabona n. 4, 70125 Bari, Italy
Interests: optoacoustic gas sensing; quantum cascade lasers; spectroscopic techniques for real-time device monitoring; thermal modeling of optoelectronic devices
Special Issues, Collections and Topics in MDPI journals

Dr. Dragan Indjin

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Guest Editor

Optoelectronics and Nanoscale Electronics, Pollard Institute, School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
Interests: optical absorption; semiconductor lasers; mid-infrared and terahertz lasers and detectors; quantum-cascade lasers; infrared and terahertz sensing and imaging, medical sensing and imaging
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The recent advance in IR and Terahertz optical sources and detectors has opened up new opportunities for sensing and imaging techniques and applications. This Special Issue of Sensors, entitled “IR and THz sensing and imaging”, will focus on all aspects of the research and development related to these areas. Original research papers that focus on the design and experimental verification of new sensors and imaging system operating in these spectral ranges, as well as papers that focus on their field-testing, are welcome. Both reviews and original research articles will be published. Reviews should provide an up-to-date, well-balanced overview of the current state-of-the-art in a particular application and include main results from other groups. We look forward to, and welcome, your participation in this Special Issue.

Prof. Dr. Vincenzo Spagnolo
Dr. Dragan Indjin
Guest Editors

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

sensing mechanisms
gas and liquid sensor
fiber optic sensor
chemical sensors
bio-medical sensors
physical sensors
imaging
spectral imaging
multispectral imaging
chemical imaging
imaging spectroscopy
medical imaging

Published Papers (35 papers)

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8776 KiB

Open AccessArticle

A Novel Gradient Vector Flow Snake Model Based on Convex Function for Infrared Image Segmentation

by Rui Zhang, Shiping Zhu and Qin Zhou

Sensors 2016, 16(10), 1756; https://doi.org/10.3390/s16101756 - 21 Oct 2016

Cited by 20 | Viewed by 6746

Infrared image segmentation is a challenging topic because infrared images are characterized by high noise, low contrast, and weak edges. Active contour models, especially gradient vector flow, have several advantages in terms of infrared image segmentation. However, the GVF (Gradient Vector Flow) model [...] Read more.

Infrared image segmentation is a challenging topic because infrared images are characterized by high noise, low contrast, and weak edges. Active contour models, especially gradient vector flow, have several advantages in terms of infrared image segmentation. However, the GVF (Gradient Vector Flow) model also has some drawbacks including a dilemma between noise smoothing and weak edge protection, which decrease the effect of infrared image segmentation significantly. In order to solve this problem, we propose a novel generalized gradient vector flow snakes model combining GGVF (Generic Gradient Vector Flow) and NBGVF (Normally Biased Gradient Vector Flow) models. We also adopt a new type of coefficients setting in the form of convex function to improve the ability of protecting weak edges while smoothing noises. Experimental results and comparisons against other methods indicate that our proposed snakes model owns better ability in terms of infrared image segmentation than other snakes models. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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2730 KiB

Open AccessArticle

A Ground-Based Near Infrared Camera Array System for UAV Auto-Landing in GPS-Denied Environment

by Tao Yang, Guangpo Li, Jing Li, Yanning Zhang, Xiaoqiang Zhang, Zhuoyue Zhang and Zhi Li

Sensors 2016, 16(9), 1393; https://doi.org/10.3390/s16091393 - 30 Aug 2016

Cited by 48 | Viewed by 10401

This paper proposes a novel infrared camera array guidance system with capability to track and provide real time position and speed of a fixed-wing Unmanned air vehicle (UAV) during a landing process. The system mainly include three novel parts: (1) Infrared camera array [...] Read more.

This paper proposes a novel infrared camera array guidance system with capability to track and provide real time position and speed of a fixed-wing Unmanned air vehicle (UAV) during a landing process. The system mainly include three novel parts: (1) Infrared camera array and near infrared laser lamp based cooperative long range optical imaging module; (2) Large scale outdoor camera array calibration module; and (3) Laser marker detection and 3D tracking module. Extensive automatic landing experiments with fixed-wing flight demonstrate that our infrared camera array system has the unique ability to guide the UAV landing safely and accurately in real time. Moreover, the measurement and control distance of our system is more than 1000 m. The experimental results also demonstrate that our system can be used for UAV automatic accurate landing in Global Position System (GPS)-denied environments. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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6516 KiB

Open AccessArticle

A High Precision Terahertz Wave Image Reconstruction Algorithm

by Qijia Guo, Tianying Chang, Guoshuai Geng, Chengyan Jia and Hong-Liang Cui

Sensors 2016, 16(7), 1139; https://doi.org/10.3390/s16071139 - 22 Jul 2016

Cited by 16 | Viewed by 5571

With the development of terahertz (THz) technology, the applications of this spectrum have become increasingly wide-ranging, in areas such as non-destructive testing, security applications and medical scanning, in which one of the most important methods is imaging. Unlike remote sensing applications, THz imaging [...] Read more.

With the development of terahertz (THz) technology, the applications of this spectrum have become increasingly wide-ranging, in areas such as non-destructive testing, security applications and medical scanning, in which one of the most important methods is imaging. Unlike remote sensing applications, THz imaging features sources of array elements that are almost always supposed to be spherical wave radiators, including single antennae. As such, well-developed methodologies such as Range-Doppler Algorithm (RDA) are not directly applicable in such near-range situations. The Back Projection Algorithm (BPA) can provide products of high precision at the the cost of a high computational burden, while the Range Migration Algorithm (RMA) sacrifices the quality of images for efficiency. The Phase-shift Migration Algorithm (PMA) is a good alternative, the features of which combine both of the classical algorithms mentioned above. In this research, it is used for mechanical scanning, and is extended to array imaging for the first time. In addition, the performances of PMA are studied in detail in contrast to BPA and RMA. It is demonstrated in our simulations and experiments described herein that the algorithm can reconstruct images with high precision. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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3560 KiB

Open AccessArticle

Modeling and Compensating Temperature-Dependent Non-Uniformity Noise in IR Microbolometer Cameras

by Alejandro Wolf, Jorge E. Pezoa and Miguel Figueroa

Sensors 2016, 16(7), 1121; https://doi.org/10.3390/s16071121 - 19 Jul 2016

Cited by 26 | Viewed by 8828

Images rendered by uncooled microbolometer-based infrared (IR) cameras are severely degraded by the spatial non-uniformity (NU) noise. The NU noise imposes a fixed-pattern over the true images, and the intensity of the pattern changes with time due to the temperature instability of such [...] Read more.

Images rendered by uncooled microbolometer-based infrared (IR) cameras are severely degraded by the spatial non-uniformity (NU) noise. The NU noise imposes a fixed-pattern over the true images, and the intensity of the pattern changes with time due to the temperature instability of such cameras. In this paper, we present a novel model and a compensation algorithm for the spatial NU noise and its temperature-dependent variations. The model separates the NU noise into two components: a constant term, which corresponds to a set of NU parameters determining the spatial structure of the noise, and a dynamic term, which scales linearly with the fluctuations of the temperature surrounding the array of microbolometers. We use a black-body radiator and samples of the temperature surrounding the IR array to offline characterize both the constant and the temperature-dependent NU noise parameters. Next, the temperature-dependent variations are estimated online using both a spatially uniform Hammerstein-Wiener estimator and a pixelwise least mean squares (LMS) estimator. We compensate for the NU noise in IR images from two long-wave IR cameras. Results show an excellent NU correction performance and a root mean square error of less than 0.25

^{\circ}

C, when the array’s temperature varies by approximately 15

^{\circ}

C. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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7005 KiB

Open AccessArticle

Spectral Characterization of a Prototype SFA Camera for Joint Visible and NIR Acquisition

by Jean-Baptiste Thomas, Pierre-Jean Lapray, Pierre Gouton and Cédric Clerc

Sensors 2016, 16(7), 993; https://doi.org/10.3390/s16070993 - 28 Jun 2016

Cited by 49 | Viewed by 9026

Multispectral acquisition improves machine vision since it permits capturing more information on object surface properties than color imaging. The concept of spectral filter arrays has been developed recently and allows multispectral single shot acquisition with a compact camera design. Due to filter manufacturing [...] Read more.

Multispectral acquisition improves machine vision since it permits capturing more information on object surface properties than color imaging. The concept of spectral filter arrays has been developed recently and allows multispectral single shot acquisition with a compact camera design. Due to filter manufacturing difficulties, there was, up to recently, no system available for a large span of spectrum, i.e., visible and Near Infra-Red acquisition. This article presents the achievement of a prototype of camera that captures seven visible and one near infra-red bands on the same sensor chip. A calibration is proposed to characterize the sensor, and images are captured. Data are provided as supplementary material for further analysis and simulations. This opens a new range of applications in security, robotics, automotive and medical fields. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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2331 KiB

Open AccessArticle

Planar Laser-Based QEPAS Trace Gas Sensor

by Yufei Ma, Ying He, Cheng Chen, Xin Yu, Jingbo Zhang, Jiangbo Peng, Rui Sun and Frank K. Tittel

Sensors 2016, 16(7), 989; https://doi.org/10.3390/s16070989 - 28 Jun 2016

Cited by 11 | Viewed by 6083

A novel quartz enhanced photoacoustic spectroscopy (QEPAS) trace gas detection scheme is reported in this paper. A cylindrical lens was employed for near-infrared laser focusing. The laser beam was shaped as a planar line laser between the gap of the quartz tuning fork [...] Read more.

A novel quartz enhanced photoacoustic spectroscopy (QEPAS) trace gas detection scheme is reported in this paper. A cylindrical lens was employed for near-infrared laser focusing. The laser beam was shaped as a planar line laser between the gap of the quartz tuning fork (QTF) prongs. Compared with a spherical lens-based QEPAS sensor, the cylindrical lens-based QEPAS sensor has the advantages of easier laser beam alignment and a reduction of stringent stability requirements. Therefore, the reported approach is useful in long-term and continuous sensor operation. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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9132 KiB

Open AccessArticle

Nondestructive Evaluation of Carbon Fiber Reinforced Polymer Composites Using Reflective Terahertz Imaging

by Jin Zhang, Wei Li, Hong-Liang Cui, Changcheng Shi, Xiaohui Han, Yuting Ma, Jiandong Chen, Tianying Chang, Dongshan Wei, Yumin Zhang and Yufeng Zhou

Sensors 2016, 16(6), 875; https://doi.org/10.3390/s16060875 - 14 Jun 2016

Cited by 38 | Viewed by 7114

Terahertz (THz) time-domain spectroscopy (TDS) imaging is considered a nondestructive evaluation method for composite materials used for examining various defects of carbon fiber reinforced polymer (CFRP) composites and fire-retardant coatings in the reflective imaging modality. We demonstrate that hidden defects simulated by Teflon [...] Read more.

Terahertz (THz) time-domain spectroscopy (TDS) imaging is considered a nondestructive evaluation method for composite materials used for examining various defects of carbon fiber reinforced polymer (CFRP) composites and fire-retardant coatings in the reflective imaging modality. We demonstrate that hidden defects simulated by Teflon artificial inserts are imaged clearly in the perpendicular polarization mode. The THz TDS technique is also used to measure the thickness of thin fire-retardant coatings on CFRP composites with a typical accuracy of about 10 micrometers. In addition, coating debonding is successfully imaged based on the time-delay difference of the time-domain waveforms between closely adhered and debonded sample locations. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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33297 KiB

Open AccessArticle

Wavelet-Based Visible and Infrared Image Fusion: A Comparative Study

by Angel D. Sappa, Juan A. Carvajal, Cristhian A. Aguilera, Miguel Oliveira, Dennis Romero and Boris X. Vintimilla

Sensors 2016, 16(6), 861; https://doi.org/10.3390/s16060861 - 10 Jun 2016

Cited by 40 | Viewed by 7059

This paper evaluates different wavelet-based cross-spectral image fusion strategies adopted to merge visible and infrared images. The objective is to find the best setup independently of the evaluation metric used to measure the performance. Quantitative performance results are obtained with state of the [...] Read more.

This paper evaluates different wavelet-based cross-spectral image fusion strategies adopted to merge visible and infrared images. The objective is to find the best setup independently of the evaluation metric used to measure the performance. Quantitative performance results are obtained with state of the art approaches together with adaptations proposed in the current work. The options evaluated in the current work result from the combination of different setups in the wavelet image decomposition stage together with different fusion strategies for the final merging stage that generates the resulting representation. Most of the approaches evaluate results according to the application for which they are intended for. Sometimes a human observer is selected to judge the quality of the obtained results. In the current work, quantitative values are considered in order to find correlations between setups and performance of obtained results; these correlations can be used to define a criteria for selecting the best fusion strategy for a given pair of cross-spectral images. The whole procedure is evaluated with a large set of correctly registered visible and infrared image pairs, including both Near InfraRed (NIR) and Long Wave InfraRed (LWIR). Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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4608 KiB

Open AccessArticle

Experimental Evaluation of Pulsed Thermography, Lock-in Thermography and Vibrothermography on Foreign Object Defect (FOD) in CFRP

by Bin Liu, Hai Zhang, Henrique Fernandes and Xavier Maldague

Sensors 2016, 16(5), 743; https://doi.org/10.3390/s16050743 - 21 May 2016

Cited by 40 | Viewed by 5924 | Correction

In this article, optical excitation thermographic techniques, including pulsed thermography and lock-in thermography, were used to detect foreign object defect (FOD) and delamination in CFRP. Then, vibrothermography as an ultrasonic excitation technique was used to detect these defects for the comparative purposes. Different [...] Read more.

In this article, optical excitation thermographic techniques, including pulsed thermography and lock-in thermography, were used to detect foreign object defect (FOD) and delamination in CFRP. Then, vibrothermography as an ultrasonic excitation technique was used to detect these defects for the comparative purposes. Different image processing methods, including cold image subtraction (CIS), principal component thermography (PCT), thermographic signal reconstruction (TSR) and Fourier transform (FT), were performed. Finally, a comparison of optical excitation thermography and vibrothermography was conducted, and a thermographic probability of detection was given. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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3453 KiB

Open AccessArticle

Current Developments on Optical Feedback Interferometry as an All-Optical Sensor for Biomedical Applications

by Julien Perchoux, Adam Quotb, Reza Atashkhooei, Francisco J. Azcona, Evelio E. Ramírez-Miquet, Olivier Bernal, Ajit Jha, Antonio Luna-Arriaga, Carlos Yanez, Jesus Caum, Thierry Bosch and Santiago Royo

Sensors 2016, 16(5), 694; https://doi.org/10.3390/s16050694 - 13 May 2016

Cited by 43 | Viewed by 7247

Optical feedback interferometry (OFI) sensors are experiencing a consistent increase in their applications to biosensing due to their contactless nature, low cost and compactness, features that fit very well with current biophotonics research and market trends. The present paper is a review of [...] Read more.

Optical feedback interferometry (OFI) sensors are experiencing a consistent increase in their applications to biosensing due to their contactless nature, low cost and compactness, features that fit very well with current biophotonics research and market trends. The present paper is a review of the work in progress at UPC-CD6 and LAAS-CNRS related to the application of OFI to different aspects of biosensing, both in vivo and ex vivo. This work is intended to present the variety of opportunities and potential applications related to OFI that are available in the field. The activities presented are divided into two main sensing strategies: The measurement of optical path changes and the monitoring of flows, which correspond to sensing strategies linked to the reconstruction of changes of amplitude from the interferometric signal, and to classical Doppler frequency measurements, respectively. For optical path change measurements, measurements of transient pulses, usual in biosensing, together with the measurement of large displacements applied to designing palliative care instrumentation for Parkinson disease are discussed. Regarding the Doppler-based approach, progress in flow-related signal processing and applications in real-time monitoring of non-steady flows, human blood flow monitoring and OFI pressure myograph sensing will be presented. In all cases, experimental setups are discussed and results presented, showing the versatility of the technique. The described applications show the wide capabilities in biosensing of the OFI sensor, showing it as an enabler of low-cost, all-optical, high accuracy biomedical applications. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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9094 KiB

Open AccessArticle

Interferometric Sensor of Wavelength Detuning Using a Liquid Crystalline Polymer Waveplate

by Paweł Wierzba

Sensors 2016, 16(5), 633; https://doi.org/10.3390/s16050633 - 09 May 2016

Cited by 3 | Viewed by 4267

Operation of a polarization interferometer for measurement of the wavelength changes of a tunable semiconductor laser was investigated. A λ/8 waveplate made from liquid crystalline polymer is placed in one of interferometers’ arms in order to generate two output signals in quadrature. [...] Read more.

Operation of a polarization interferometer for measurement of the wavelength changes of a tunable semiconductor laser was investigated. A λ/8 waveplate made from liquid crystalline polymer is placed in one of interferometers’ arms in order to generate two output signals in quadrature. Wavelength was measured with resolution of 2 pm in the wavelength range 628–635 nm. Drift of the interferometer, measured in the period of 500 s, was 8 nm, which corresponded to the change in the wavelength of 1.3 pm. If needed, wavelength-dependent Heydemann correction can be used to expand the range of operation of such interferometer. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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3951 KiB

Open AccessArticle

A Practical and Portable Solids-State Electronic Terahertz Imaging System

by Ken Smart, Jia Du, Li Li, David Wang, Keith Leslie, Fan Ji, Xiang Dong Li and Da Zhang Zeng

Sensors 2016, 16(4), 579; https://doi.org/10.3390/s16040579 - 22 Apr 2016

Cited by 6 | Viewed by 6470

A practical compact solid-state terahertz imaging system is presented. Various beam guiding architectures were explored and hardware performance assessed to improve its compactness, robustness, multi-functionality and simplicity of operation. The system performance in terms of image resolution, signal-to-noise ratio, the electronic signal modulation [...] Read more.

A practical compact solid-state terahertz imaging system is presented. Various beam guiding architectures were explored and hardware performance assessed to improve its compactness, robustness, multi-functionality and simplicity of operation. The system performance in terms of image resolution, signal-to-noise ratio, the electronic signal modulation versus optical chopper, is evaluated and discussed. The system can be conveniently switched between transmission and reflection mode according to the application. A range of imaging application scenarios was explored and images of high visual quality were obtained in both transmission and reflection mode. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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2248 KiB

Open AccessArticle

Reconstructing Face Image from the Thermal Infrared Spectrum to the Visible Spectrum

by Brahmastro Kresnaraman, Daisuke Deguchi, Tomokazu Takahashi, Yoshito Mekada, Ichiro Ide and Hiroshi Murase

Sensors 2016, 16(4), 568; https://doi.org/10.3390/s16040568 - 21 Apr 2016

Cited by 4 | Viewed by 6713

During the night or in poorly lit areas, thermal cameras are a better choice instead of normal cameras for security surveillance because they do not rely on illumination. A thermal camera is able to detect a person within its view, but identification from [...] Read more.

During the night or in poorly lit areas, thermal cameras are a better choice instead of normal cameras for security surveillance because they do not rely on illumination. A thermal camera is able to detect a person within its view, but identification from only thermal information is not an easy task. The purpose of this paper is to reconstruct the face image of a person from the thermal spectrum to the visible spectrum. After the reconstruction, further image processing can be employed, including identification/recognition. Concretely, we propose a two-step thermal-to-visible-spectrum reconstruction method based on Canonical Correlation Analysis (CCA). The reconstruction is done by utilizing the relationship between images in both thermal infrared and visible spectra obtained by CCA. The whole image is processed in the first step while the second step processes patches in an image. Results show that the proposed method gives satisfying results with the two-step approach and outperforms comparative methods in both quality and recognition evaluations. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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2873 KiB

Open AccessArticle

Low-Loss Coupling of Quantum Cascade Lasers into Hollow-Core Waveguides with Single-Mode Output in the 3.7–7.6 μm Spectral Range

by Pietro Patimisco, Angelo Sampaolo, Laura Mihai, Marilena Giglio, Jason Kriesel, Dan Sporea, Gaetano Scamarcio, Frank K. Tittel and Vincenzo Spagnolo

Sensors 2016, 16(4), 533; https://doi.org/10.3390/s16040533 - 13 Apr 2016

Cited by 24 | Viewed by 7019

We demonstrated low-loss and single-mode laser beam delivery through hollow-core waveguides (HCWs) operating in the 3.7–7.6 μm spectral range. The employed HCWs have a circular cross section with a bore diameter of 200 μm and metallic/dielectric internal coatings deposited inside a glass capillary [...] Read more.

We demonstrated low-loss and single-mode laser beam delivery through hollow-core waveguides (HCWs) operating in the 3.7–7.6 μm spectral range. The employed HCWs have a circular cross section with a bore diameter of 200 μm and metallic/dielectric internal coatings deposited inside a glass capillary tube. The internal coatings have been produced to enhance the spectral response of the HCWs in the range 3.5–12 µm. We demonstrated Gaussian-like outputs throughout the 4.5–7.6 µm spectral range. A quasi single-mode output beam with only small beam distortions was achieved when the wavelength was reduced to 3.7 μm. With a 15-cm-long HCW and optimized coupling conditions, we measured coupling efficiencies of >88% and transmission losses of <1 dB in the investigated infrared spectral range. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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3398 KiB

Open AccessArticle

Essential Limitations of the Standard THz TDS Method for Substance Detection and Identification and a Way of Overcoming Them

by Vyacheslav A. Trofimov and Svetlana A. Varentsova

Sensors 2016, 16(4), 502; https://doi.org/10.3390/s16040502 - 08 Apr 2016

Cited by 21 | Viewed by 5166

Low efficiency of the standard THz TDS method of the detection and identification of substances based on a comparison of the spectrum for the signal under investigation with a standard signal spectrum is demonstrated using the physical experiments conducted under real conditions with [...] Read more.

Low efficiency of the standard THz TDS method of the detection and identification of substances based on a comparison of the spectrum for the signal under investigation with a standard signal spectrum is demonstrated using the physical experiments conducted under real conditions with a thick paper bag as well as with Si-based semiconductors under laboratory conditions. In fact, standard THz spectroscopy leads to false detection of hazardous substances in neutral samples, which do not contain them. This disadvantage of the THz TDS method can be overcome by using time-dependent THz pulse spectrum analysis. For a quality assessment of the standard substance spectral features presence in the signal under analysis, one may use time-dependent integral correlation criteria. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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4068 KiB

Open AccessArticle

Microfluidic Devices for Terahertz Spectroscopy of Live Cells Toward Lab-on-a-Chip Applications

by Qi Tang, Min Liang, Yi Lu, Pak Kin Wong, Gerald J. Wilmink, Donna D. Zhang and Hao Xin

Sensors 2016, 16(4), 476; https://doi.org/10.3390/s16040476 - 04 Apr 2016

Cited by 43 | Viewed by 7513

THz spectroscopy is an emerging technique for studying the dynamics and interactions of cells and biomolecules, but many practical challenges still remain in experimental studies. We present a prototype of simple and inexpensive cell-trapping microfluidic chip for THz spectroscopic study of live cells. [...] Read more.

THz spectroscopy is an emerging technique for studying the dynamics and interactions of cells and biomolecules, but many practical challenges still remain in experimental studies. We present a prototype of simple and inexpensive cell-trapping microfluidic chip for THz spectroscopic study of live cells. Cells are transported, trapped and concentrated into the THz exposure region by applying an AC bias signal while the chip maintains a steady temperature at 37 °C by resistive heating. We conduct some preliminary experiments on E. coli and T-cell solution and compare the transmission spectra of empty channels, channels filled with aqueous media only, and channels filled with aqueous media with un-concentrated and concentrated cells. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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22718 KiB

Open AccessArticle

Human Detection Based on the Generation of a Background Image and Fuzzy System by Using a Thermal Camera

by Eun Som Jeon, Jong Hyun Kim, Hyung Gil Hong, Ganbayar Batchuluun and Kang Ryoung Park

Sensors 2016, 16(4), 453; https://doi.org/10.3390/s16040453 - 30 Mar 2016

Cited by 23 | Viewed by 7121

Recently, human detection has been used in various applications. Although visible light cameras are usually employed for this purpose, human detection based on visible light cameras has limitations due to darkness, shadows, sunlight, etc. An approach using a thermal (far infrared light) [...] Read more.

Recently, human detection has been used in various applications. Although visible light cameras are usually employed for this purpose, human detection based on visible light cameras has limitations due to darkness, shadows, sunlight, etc. An approach using a thermal (far infrared light) camera has been studied as an alternative for human detection, however, the performance of human detection by thermal cameras is degraded in case of low temperature differences between humans and background. To overcome these drawbacks, we propose a new method for human detection by using thermal camera images. The main contribution of our research is that the thresholds for creating the binarized difference image between the input and background (reference) images can be adaptively determined based on fuzzy systems by using the information derived from the background image and difference values between background and input image. By using our method, human area can be correctly detected irrespective of the various conditions of input and background (reference) images. For the performance evaluation of the proposed method, experiments were performed with the 15 datasets captured under different weather and light conditions. In addition, the experiments with an open database were also performed. The experimental results confirm that the proposed method can robustly detect human shapes in various environments. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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2082 KiB

Open AccessArticle

Improved Tuning Fork for Terahertz Quartz-Enhanced Photoacoustic Spectroscopy

by Angelo Sampaolo, Pietro Patimisco, Marilena Giglio, Miriam S. Vitiello, Harvey E. Beere, David A. Ritchie, Gaetano Scamarcio, Frank K. Tittel and Vincenzo Spagnolo

Sensors 2016, 16(4), 439; https://doi.org/10.3390/s16040439 - 25 Mar 2016

Cited by 59 | Viewed by 6332

We report on a quartz-enhanced photoacoustic (QEPAS) sensor for methanol (CH₃OH) detection employing a novel quartz tuning fork (QTF), specifically designed to enhance the QEPAS sensing performance in the terahertz (THz) spectral range. A discussion of the QTF properties in terms [...] Read more.

We report on a quartz-enhanced photoacoustic (QEPAS) sensor for methanol (CH₃OH) detection employing a novel quartz tuning fork (QTF), specifically designed to enhance the QEPAS sensing performance in the terahertz (THz) spectral range. A discussion of the QTF properties in terms of resonance frequency, quality factor and acousto-electric transduction efficiency as a function of prong sizes and spacing between the QTF prongs is presented. The QTF was employed in a QEPAS sensor system using a 3.93 THz quantum cascade laser as the excitation source in resonance with a CH₃OH rotational absorption line located at 131.054 cm⁻¹. A minimum detection limit of 160 ppb in 30 s integration time, corresponding to a normalized noise equivalent absorption NNEA = 3.75 × 10⁻¹¹ cm⁻¹W/Hz^½, was achieved, representing a nearly one-order-of-magnitude improvement with respect to previous reports. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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8608 KiB

Open AccessArticle

Spectroscopic Terahertz Imaging at Room Temperature Employing Microbolometer Terahertz Sensors and Its Application to the Study of Carcinoma Tissues

by Irmantas Kašalynas, Rimvydas Venckevičius, Linas Minkevičius, Aleksander Sešek, Faustino Wahaia, Vincas Tamošiūnas, Bogdan Voisiat, Dalius Seliuta, Gintaras Valušis, Andrej Švigelj and Janez Trontelj

Sensors 2016, 16(4), 432; https://doi.org/10.3390/s16040432 - 25 Mar 2016

Cited by 73 | Viewed by 9200

A terahertz (THz) imaging system based on narrow band microbolometer sensors (NBMS) and a novel diffractive lens was developed for spectroscopic microscopy applications. The frequency response characteristics of the THz antenna-coupled NBMS were determined employing Fourier transform spectroscopy. The NBMS was found to [...] Read more.

A terahertz (THz) imaging system based on narrow band microbolometer sensors (NBMS) and a novel diffractive lens was developed for spectroscopic microscopy applications. The frequency response characteristics of the THz antenna-coupled NBMS were determined employing Fourier transform spectroscopy. The NBMS was found to be a very sensitive frequency selective sensor which was used to develop a compact all-electronic system for multispectral THz measurements. This system was successfully applied for principal components analysis of optically opaque packed samples. A thin diffractive lens with a numerical aperture of 0.62 was proposed for the reduction of system dimensions. The THz imaging system enhanced with novel optics was used to image for the first time non-neoplastic and neoplastic human colon tissues with close to wavelength-limited spatial resolution at 584 GHz frequency. The results demonstrated the new potential of compact RT THz imaging systems in the fields of spectroscopic analysis of materials and medical diagnostics. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Open AccessArticle

Application of Thin ZnO ALD Layers in Fiber-Optic Fabry-Pérot Sensing Interferometers

by Daria Majchrowicz, Marzena Hirsch, Paweł Wierzba, Michael Bechelany, Roman Viter and Małgorzata Jędrzejewska‑Szczerska

Sensors 2016, 16(3), 416; https://doi.org/10.3390/s16030416 - 22 Mar 2016

Cited by 46 | Viewed by 8015

In this paper we investigated the response of a fiber-optic Fabry-Pérot sensing interferometer with thin ZnO layers deposited on the end faces of the optical fibers forming the cavity. Standard telecommunication single-mode optical fiber (SMF-28) segments were used with the thin ZnO layers [...] Read more.

In this paper we investigated the response of a fiber-optic Fabry-Pérot sensing interferometer with thin ZnO layers deposited on the end faces of the optical fibers forming the cavity. Standard telecommunication single-mode optical fiber (SMF-28) segments were used with the thin ZnO layers deposited by Atomic Layer Deposition (ALD). Measurements were performed with the interferometer illuminated by two broadband sources operating at 1300 nm and 1550 nm. Reflected interference signal was acquired by an optical spectrum analyzer while the length of the air cavity was varied. Thickness of the ZnO layers used in the experiments was 50 nm, 100 nm, and 200 nm. Uncoated SMF-28 fiber was also used as a reference. Based on the results of measurements, the thickness of the ZnO layers and the length of the cavity were selected in order to achieve good visibility. Following, the interferometer was used to determine the refractive index of selected liquids. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Open AccessArticle

Laser Feedback Interferometry as a Tool for Analysis of Granular Materials at Terahertz Frequencies: Towards Imaging and Identification of Plastic Explosives

by She Han, Karl Bertling, Paul Dean, James Keeley, Andrew D. Burnett, Yah Leng Lim, Suraj P. Khanna, Alexander Valavanis, Edmund H. Linfield, A. Giles Davies, Dragan Indjin, Thomas Taimre and Aleksandar D. Rakić

Sensors 2016, 16(3), 352; https://doi.org/10.3390/s16030352 - 09 Mar 2016

Cited by 28 | Viewed by 6125

We propose a self-consistent method for the analysis of granular materials at terahertz (THz) frequencies using a quantum cascade laser. The method is designed for signals acquired from a laser feedback interferometer, and applied to non-contact reflection-mode sensing. Our technique is demonstrated using [...] Read more.

We propose a self-consistent method for the analysis of granular materials at terahertz (THz) frequencies using a quantum cascade laser. The method is designed for signals acquired from a laser feedback interferometer, and applied to non-contact reflection-mode sensing. Our technique is demonstrated using three plastic explosives, achieving good agreement with reference measurements obtained by THz time-domain spectroscopy in transmission geometry. The technique described in this study is readily scalable: replacing a single laser with a small laser array, with individual lasers operating at different frequencies will enable unambiguous identification of select materials. This paves the way towards non-contact, reflection-mode analysis and identification of granular materials at THz frequencies using quantum cascade lasers. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Open AccessArticle

A Low-Noise CMOS THz Imager Based on Source Modulation and an In-Pixel High-Q Passive Switched-Capacitor N-Path Filter

by Assim Boukhayma, Antoine Dupret, Jean-Pierre Rostaing and Christian Enz

Sensors 2016, 16(3), 325; https://doi.org/10.3390/s16030325 - 03 Mar 2016

Cited by 35 | Viewed by 8710

This paper presents the first low noise complementary metal oxide semiconductor (CMOS) terahertz (THz) imager based on source modulation and in-pixel high-Q filtering. The 31 × 31 focal plane array has been fully integrated in a 0 . 13 μ m standard CMOS [...] Read more.

This paper presents the first low noise complementary metal oxide semiconductor (CMOS) terahertz (THz) imager based on source modulation and in-pixel high-Q filtering. The 31 × 31 focal plane array has been fully integrated in a 0 . 13 μ m standard CMOS process. The sensitivity has been improved significantly by modulating the active THz source that lights the scene and performing on-chip high-Q filtering. Each pixel encompass a broadband bow tie antenna coupled to an N-type metal-oxide-semiconductor (NMOS) detector that shifts the THz radiation, a low noise adjustable gain amplifier and a high-Q filter centered at the modulation frequency. The filter is based on a passive switched-capacitor (SC) N-path filter combined with a continuous-time broad-band G_m-C filter. A simplified analysis that helps in designing and tuning the passive SC N-path filter is provided. The characterization of the readout chain shows that a Q factor of 100 has been achieved for the filter with a good matching between the analytical calculation and the measurement results. An input-referred noise of 0 . 2 μ V RMS has been measured. Characterization of the chip with different THz wavelengths confirms the broadband feature of the antenna and shows that this THz imager reaches a total noise equivalent power of 0 . 6 nW at 270 GHz and 0 . 8 nW at 600 GHz. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Open AccessArticle

Signal-Conditioning Block of a 1 × 200 CMOS Detector Array for a Terahertz Real-Time Imaging System

by Jong-Ryul Yang, Woo-Jae Lee and Seong-Tae Han

Sensors 2016, 16(3), 319; https://doi.org/10.3390/s16030319 - 02 Mar 2016

Cited by 14 | Viewed by 6862

A signal conditioning block of a 1 × 200 Complementary Metal-Oxide-Semiconductor (CMOS) detector array is proposed to be employed with a real-time 0.2 THz imaging system for inspecting large areas. The plasmonic CMOS detector array whose pixel size including an integrated antenna is [...] Read more.

A signal conditioning block of a 1 × 200 Complementary Metal-Oxide-Semiconductor (CMOS) detector array is proposed to be employed with a real-time 0.2 THz imaging system for inspecting large areas. The plasmonic CMOS detector array whose pixel size including an integrated antenna is comparable to the wavelength of the THz wave for the imaging system, inevitably carries wide pixel-to-pixel variation. To make the variant outputs from the array uniform, the proposed signal conditioning block calibrates the responsivity of each pixel by controlling the gate bias of each detector and the voltage gain of the lock-in amplifiers in the block. The gate bias of each detector is modulated to 1 MHz to improve the signal-to-noise ratio of the imaging system via the electrical modulation by the conditioning block. In addition, direct current (DC) offsets of the detectors in the array are cancelled by initializing the output voltage level from the block. Real-time imaging using the proposed signal conditioning block is demonstrated by obtaining images at the rate of 19.2 frame-per-sec of an object moving on the conveyor belt with a scan width of 20 cm and a scan speed of 25 cm/s. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Open AccessArticle

Advancement of an Infra-Red Technique for Whole-Field Concentration Measurements in Fluidized Beds

by Jose A. Medrano, Niek C. A. De Nooijer, Fausto Gallucci and Martin Van Sint Annaland

Sensors 2016, 16(3), 300; https://doi.org/10.3390/s16030300 - 27 Feb 2016

Cited by 6 | Viewed by 4660

For a better understanding and description of the mass transport phenomena in dense multiphase gas-solids systems such as fluidized bed reactors, detailed and quantitative experimental data on the concentration profiles is required, which demands advanced non-invasive concentration monitoring techniques with a high spatial [...] Read more.

For a better understanding and description of the mass transport phenomena in dense multiphase gas-solids systems such as fluidized bed reactors, detailed and quantitative experimental data on the concentration profiles is required, which demands advanced non-invasive concentration monitoring techniques with a high spatial and temporal resolution. A novel technique based on the selective detection of a gas component in a gas mixture using infra-red properties has been further developed. The first stage development was carried out using a very small sapphire reactor and CO₂ as tracer gas. Although the measuring principle was demonstrated, the real application was hindered by the small reactor dimensions related to the high costs and difficult handling of large sapphire plates. In this study, a new system has been developed, that allows working at much larger scales and yet with higher resolution. In the new system, propane is used as tracer gas and quartz as reactor material. In this study, a thorough optimization and calibration of the technique is presented which is subsequently applied for whole-field measurements with high temporal resolution. The developed technique allows the use of a relatively inexpensive configuration for the measurement of detailed concentration fields and can be applied to a large variety of important chemical engineering topics. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Open AccessArticle

Analysis of Forensic Casework Utilizing Infrared Spectroscopic Imaging

by Adam Lanzarotta

Sensors 2016, 16(3), 278; https://doi.org/10.3390/s16030278 - 24 Feb 2016

Cited by 6 | Viewed by 5566

A search of the current scientific literature yields a limited number of studies that describe the use of Fourier transform infrared (FT-IR) spectroscopic imaging for the analysis of forensic casework, which is likely due to the fact that these instruments are fairly new [...] Read more.

A search of the current scientific literature yields a limited number of studies that describe the use of Fourier transform infrared (FT-IR) spectroscopic imaging for the analysis of forensic casework, which is likely due to the fact that these instruments are fairly new commodities to the field of analytical chemistry and are therefore not yet commonplace in forensic laboratories. This report describes recent forensic case studies that have used the technique for determining the composition of a wide variety of multi-component sample types, including animal tissue sections for toxic inclusions, drugs/dietary supplements, an antibiotic with an active pharmaceutical ingredient (API) present as several different salt forms, an adulterated bulk API, unknown trace powders for illicit drugs and an ophthalmic solution suspected of being adulterated with bleach. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Open AccessArticle

Improved Sensitivity MEMS Cantilever Sensor for Terahertz Photoacoustic Spectroscopy

by Ronald A. Coutu, Ivan R. Medvedev and Douglas T. Petkie

Sensors 2016, 16(2), 251; https://doi.org/10.3390/s16020251 - 19 Feb 2016

Cited by 18 | Viewed by 7564

In this paper, a microelectromechanical system (MEMS) cantilever sensor was designed, modeled and fabricated to measure the terahertz (THz) radiation induced photoacoustic (PA) response of gases under low vacuum conditions. This work vastly improves cantilever sensitivity over previous efforts, by reducing internal beam [...] Read more.

In this paper, a microelectromechanical system (MEMS) cantilever sensor was designed, modeled and fabricated to measure the terahertz (THz) radiation induced photoacoustic (PA) response of gases under low vacuum conditions. This work vastly improves cantilever sensitivity over previous efforts, by reducing internal beam stresses, minimizing out of plane beam curvature and optimizing beam damping. In addition, fabrication yield was improved by approximately 50% by filleting the cantilever’s anchor and free end to help reduce high stress areas that occurred during device fabrication and processing. All of the cantilever sensors were fabricated using silicon-on-insulator (SOI) wafers and tested in a custom built, low-volume, vacuum chamber. The resulting cantilever sensors exhibited improved signal to noise ratios, sensitivities and normalized noise equivalent absorption (NNEA) coefficients of approximately 4.28 × 10⁻¹⁰ cm⁻¹·WHz^−1/2. This reported NNEA represents approximately a 70% improvement over previously fabricated and tested SOI cantilever sensors for THz PA spectroscopy. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Open AccessArticle

Tunable Microcavity-Stabilized Quantum Cascade Laser for Mid-IR High-Resolution Spectroscopy and Sensing

by Simone Borri, Mario Siciliani de Cumis, Giacomo Insero, Saverio Bartalini, Pablo Cancio Pastor, Davide Mazzotti, Iacopo Galli, Giovanni Giusfredi, Gabriele Santambrogio, Anatoliy Savchenkov, Danny Eliyahu, Vladimir Ilchenko, Naota Akikusa, Andrey Matsko, Lute Maleki and Paolo De Natale

Sensors 2016, 16(2), 238; https://doi.org/10.3390/s16020238 - 17 Feb 2016

Cited by 20 | Viewed by 6100

The need for highly performing and stable methods for mid-IR molecular sensing and metrology pushes towards the development of more and more compact and robust systems. Among the innovative solutions aimed at answering the need for stable mid-IR references are crystalline microresonators, which [...] Read more.

The need for highly performing and stable methods for mid-IR molecular sensing and metrology pushes towards the development of more and more compact and robust systems. Among the innovative solutions aimed at answering the need for stable mid-IR references are crystalline microresonators, which have recently shown excellent capabilities for frequency stabilization and linewidth narrowing of quantum cascade lasers with compact setups. In this work, we report on the first system for mid-IR high-resolution spectroscopy based on a quantum cascade laser locked to a CaF₂ microresonator. Electronic locking narrows the laser linewidth by one order of magnitude and guarantees good stability over long timescales, allowing, at the same time, an easy way for finely tuning the laser frequency over the molecular absorption line. Improvements in terms of resolution and frequency stability of the source are demonstrated by direct sub-Doppler recording of a molecular line. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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A Quantum Cascade Laser-Based Optical Sensor for Continuous Monitoring of Environmental Methane in Dunkirk (France)

by Rabih Maamary, Xiaojuan Cui, Eric Fertein, Patrick Augustin, Marc Fourmentin, Dorothée Dewaele, Fabrice Cazier, Laurence Guinet and Weidong Chen

Sensors 2016, 16(2), 224; https://doi.org/10.3390/s16020224 - 08 Feb 2016

Cited by 19 | Viewed by 6531

A room-temperature continuous-wave (CW) quantum cascade laser (QCL)-based methane (CH₄) sensor operating in the mid-infrared near 8 μm was developed for continuous measurement of CH₄ concentrations in ambient air. The well-isolated absorption line (7F_2,4 ← 8F_1,2) of [...] Read more.

A room-temperature continuous-wave (CW) quantum cascade laser (QCL)-based methane (CH₄) sensor operating in the mid-infrared near 8 μm was developed for continuous measurement of CH₄ concentrations in ambient air. The well-isolated absorption line (7F_2,4 ← 8F_1,2) of the ν₄ fundamental band of CH₄ located at 1255.0004 cm⁻¹ was used for optical measurement of CH₄ concentration by direct absorption in a White-type multipass cell with an effective path-length of 175 m. A 1σ (SNR = 1) detection limit of 33.3 ppb in 218 s was achieved with a measurement precision of 1.13%. The developed sensor was deployed in a campaign of measurements of time series CH₄ concentration on a site near a suburban traffic road in Dunkirk (France) from 9th to 22nd January 2013. An episode of high CH₄ concentration of up to ~3 ppm has been observed and analyzed with the help of meteorological parameters combined with back trajectory calculation using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model of NOAA. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Open AccessArticle

Comparison of Thermal Detector Arrays for Off-Axis THz Holography and Real-Time THz Imaging

by Erwin Hack, Lorenzo Valzania, Gregory Gäumann, Mostafa Shalaby, Christoph P. Hauri and Peter Zolliker

Sensors 2016, 16(2), 221; https://doi.org/10.3390/s16020221 - 06 Feb 2016

Cited by 43 | Viewed by 8079

In terahertz (THz) materials science, imaging by scanning prevails when low power THz sources are used. However, the application of array detectors operating with high power THz sources is increasingly reported. We compare the imaging properties of four different array detectors that are [...] Read more.

In terahertz (THz) materials science, imaging by scanning prevails when low power THz sources are used. However, the application of array detectors operating with high power THz sources is increasingly reported. We compare the imaging properties of four different array detectors that are able to record THz radiation directly. Two micro-bolometer arrays are designed for infrared imaging in the 8–14 μm wavelength range, but are based on different absorber materials (i) vanadium oxide; (ii) amorphous silicon; (iii) a micro-bolometer array optimized for recording THz radiation based on silicon nitride; and (iv) a pyroelectric array detector for THz beam profile measurements. THz wavelengths of 96.5 μm, 118.8 μm, and 393.6 μm from a powerful far infrared laser were used to assess the technical performance in terms of signal to noise ratio, detector response and detectivity. The usefulness of the detectors for beam profiling and digital holography is assessed. Finally, the potential and limitation for real-time digital holography are discussed. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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3279 KiB

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Impact of Humidity on Quartz-Enhanced Photoacoustic Spectroscopy Based CO Detection Using a Near-IR Telecommunication Diode Laser

by Xukun Yin, Lei Dong, Huadan Zheng, Xiaoli Liu, Hongpeng Wu, Yanfang Yang, Weiguang Ma, Lei Zhang, Wangbao Yin, Liantuan Xiao and Suotang Jia

Sensors 2016, 16(2), 162; https://doi.org/10.3390/s16020162 - 27 Jan 2016

Cited by 60 | Viewed by 6706

A near-IR CO trace gas sensor based on quartz-enhanced photoacoustic spectroscopy (QEPAS) is evaluated using humidified nitrogen samples. Relaxation processes in the CO-N₂-H₂O system are investigated. A simple kinetic model is used to predict the sensor performance at different [...] Read more.

A near-IR CO trace gas sensor based on quartz-enhanced photoacoustic spectroscopy (QEPAS) is evaluated using humidified nitrogen samples. Relaxation processes in the CO-N₂-H₂O system are investigated. A simple kinetic model is used to predict the sensor performance at different gas pressures. The results show that CO has a ~3 and ~5 times slower relaxation time constant than CH₄ and HCN, respectively, under dry conditions. However, with the presence of water, its relaxation time constant can be improved by three orders of magnitude. The experimentally determined normalized detection sensitivity for CO in humid gas is 1.556 × 10 − 8 W ⋅ cm − 1 / Hz 1 / 2 . Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Open AccessArticle

EMD-Based Symbolic Dynamic Analysis for the Recognition of Human and Nonhuman Pyroelectric Infrared Signals

by Jiaduo Zhao, Weiguo Gong, Yuzhen Tang and Weihong Li

Sensors 2016, 16(1), 126; https://doi.org/10.3390/s16010126 - 20 Jan 2016

Cited by 11 | Viewed by 6225

In this paper, we propose an effective human and nonhuman pyroelectric infrared (PIR) signal recognition method to reduce PIR detector false alarms. First, using the mathematical model of the PIR detector, we analyze the physical characteristics of the human and nonhuman PIR signals; [...] Read more.

In this paper, we propose an effective human and nonhuman pyroelectric infrared (PIR) signal recognition method to reduce PIR detector false alarms. First, using the mathematical model of the PIR detector, we analyze the physical characteristics of the human and nonhuman PIR signals; second, based on the analysis results, we propose an empirical mode decomposition (EMD)-based symbolic dynamic analysis method for the recognition of human and nonhuman PIR signals. In the proposed method, first, we extract the detailed features of a PIR signal into five symbol sequences using an EMD-based symbolization method, then, we generate five feature descriptors for each PIR signal through constructing five probabilistic finite state automata with the symbol sequences. Finally, we use a weighted voting classification strategy to classify the PIR signals with their feature descriptors. Comparative experiments show that the proposed method can effectively classify the human and nonhuman PIR signals and reduce PIR detector’s false alarms. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Labeled RFS-Based Track-Before-Detect for Multiple Maneuvering Targets in the Infrared Focal Plane Array

by Miao Li, Jun Li and Yiyu Zhou

Sensors 2015, 15(12), 30839-30855; https://doi.org/10.3390/s151229829 - 08 Dec 2015

Cited by 4 | Viewed by 5153

The problem of jointly detecting and tracking multiple targets from the raw observations of an infrared focal plane array is a challenging task, especially for the case with uncertain target dynamics. In this paper a multi-model labeled multi-Bernoulli (MM-LMB) track-before-detect method is proposed [...] Read more.

The problem of jointly detecting and tracking multiple targets from the raw observations of an infrared focal plane array is a challenging task, especially for the case with uncertain target dynamics. In this paper a multi-model labeled multi-Bernoulli (MM-LMB) track-before-detect method is proposed within the labeled random finite sets (RFS) framework. The proposed track-before-detect method consists of two parts—MM-LMB filter and MM-LMB smoother. For the MM-LMB filter, original LMB filter is applied to track-before-detect based on target and measurement models, and is integrated with the interacting multiple models (IMM) approach to accommodate the uncertainty of target dynamics. For the MM-LMB smoother, taking advantage of the track labels and posterior model transition probability, the single-model single-target smoother is extended to a multi-model multi-target smoother. A Sequential Monte Carlo approach is also presented to implement the proposed method. Simulation results show the proposed method can effectively achieve tracking continuity for multiple maneuvering targets. In addition, compared with the forward filtering alone, our method is more robust due to its combination of forward filtering and backward smoothing. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Open AccessArticle

Sea-Based Infrared Scene Interpretation by Background Type Classification and Coastal Region Detection for Small Target Detection

by Sungho Kim

Sensors 2015, 15(9), 24487-24513; https://doi.org/10.3390/s150924487 - 23 Sep 2015

Cited by 14 | Viewed by 9438

Sea-based infrared search and track (IRST) is important for homeland security by detecting missiles and asymmetric boats. This paper proposes a novel scheme to interpret various infrared scenes by classifying the infrared background types and detecting the coastal regions in omni-directional images. The [...] Read more.

Sea-based infrared search and track (IRST) is important for homeland security by detecting missiles and asymmetric boats. This paper proposes a novel scheme to interpret various infrared scenes by classifying the infrared background types and detecting the coastal regions in omni-directional images. The background type or region-selective small infrared target detector should be deployed to maximize the detection rate and to minimize the number of false alarms. A spatial filter-based small target detector is suitable for identifying stationary incoming targets in remote sea areas with sky only. Many false detections can occur if there is an image sector containing a coastal region, due to ground clutter and the difficulty in finding true targets using the same spatial filter-based detector. A temporal filter-based detector was used to handle these problems. Therefore, the scene type and coastal region information is critical to the success of IRST in real-world applications. In this paper, the infrared scene type was determined using the relationships between the sensor line-of-sight (LOS) and a horizontal line in an image. The proposed coastal region detector can be activated if the background type of the probing sector is determined to be a coastal region. Coastal regions can be detected by fusing the region map and curve map. The experimental results on real infrared images highlight the feasibility of the proposed sea-based scene interpretation. In addition, the effects of the proposed scheme were analyzed further by applying region-adaptive small target detection. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Study of QCL Laser Sources for the Realization of Advanced Sensors

by Giuseppe De Risi, Lorenzo Luigi Columbo and Massimo Brambilla

Sensors 2015, 15(8), 19140-19156; https://doi.org/10.3390/s150819140 - 05 Aug 2015

Cited by 5 | Viewed by 4598

We study the nonlinear dynamics of a quantum cascade laser (QCL) with a strong reinjection provided by the feedback from two external targets in a double cavity configuration. The nonlinear coupling of interferometric signals from the two targets allows us to propose a [...] Read more.

We study the nonlinear dynamics of a quantum cascade laser (QCL) with a strong reinjection provided by the feedback from two external targets in a double cavity configuration. The nonlinear coupling of interferometric signals from the two targets allows us to propose a displacement sensor with nanometric resolution. The system exploits the ultra-stability of QCLs in self-mixing configuration to access the intrinsic nonlinearity of the laser, described by the Lang–Kobayashi model, and it relies on a stroboscopic-like effect in the voltage signal registered at the QCL terminals that relates the “slow” target motion to the “fast” target one. Full article

(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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Correction: Liu, B., et al. Quantitative Evaluation of Pulsed Thermography, Lock-In Thermography and Vibrothermography on Foreign Object Defect (FOD) in CFRP. Sensors 2016, 16, doi:10.3390/s16050743

by Bin Liu, Hai Zhang, Henrique Fernandes and Xavier Maldague

Sensors 2017, 17(1), 195; https://doi.org/10.3390/s17010195 - 20 Jan 2017

Viewed by 4776

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(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)

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