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Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications

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

Deadline for manuscript submissions: closed (31 August 2022) | Viewed by 67928

Special Issue Editors

Department of Photonic Engineering, Chosun University, 309 Pilmun-daero, Dong-gu, Gwangju 61452, Korea
Interests: Optical metrology; dimensional metrology; precision measurement; optical imaging; optical interferometry; ultrafast measurement

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Guest Editor
Department of Aerospace Engineering, Texas A&M University, College Station, TX 77843, USA
Interests: Gravitational Wave Observatories: LIGO and LISA, Optomechanical inertial sensing technologies: accelerometry, force sensing and navigation, Optical metrology, precision measurements, and space technologies, Optical, optomechanical and atom-interferometric sensing systems for applications in geophysics: gravimetry, gravity gradiometry and seismometry

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Guest Editor
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea
Interests: advancing ultra-precision light source technology from an IR to an EUV regime using the optical comb of the femtosecond pulse laser, and its interdisciplinary applications including precision spectroscopy, time/frequency standards, precision laser ranging, optical metrology, and nano/micro material processing
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear colleagues,

Optical sensors have been widely used to observe natural phenomena in the macroscopic or microscopic environment, and the importance of their roles has rapidly increased in science and industry.

This Special Issue, entitled “Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications”, focuses on collecting and discussing novel and advanced research works in various fields of optical sensors, especially opto-mechanical and opto-electronic sensors.

It pursues recent developments and new applications of optical sensors, but is not limited to fully novel optical devices only. Significant improvements on sensitivity, precision, accuracy, measurement speed, miniaturization of systems, and optical integration to optimize systems are also welcome topics for this issue. Moreover, innovative designs of optical sensors for novel and specific applications are sought to increase the value of discussion. As well as original research papers, there is also scope for review articles to summarize the technical developments and provide challenging themes.

We expect many colleagues in the field of optical sensors to contribute to this Special Issue.

Dr. Ki-Nam Joo
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • optical sensors
  • opto-mechanical sensors
  • opto-electronic sensors
  • sensor design
  • precise measurement
  • optical sensor applications

Published Papers (20 papers)

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Research

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14 pages, 10076 KiB  
Article
Design of a Concentric Multi-Scale Zoom Optical System Based on Wide Object Distance and High-Precision Imaging
by Kun Zhang, Zheng Qu, Jingchen Li, Jian Wang, Si Sun and Fan Yang
Sensors 2022, 22(19), 7356; https://doi.org/10.3390/s22197356 - 28 Sep 2022
Viewed by 1582
Abstract
To effectively balance the trade-off between a large field of view (FOV) and high resolution of an optical system, as well as to solve the problem of image stitching misalignment after focusing, firstly, this paper conducts a theoretical analysis of the design principle [...] Read more.
To effectively balance the trade-off between a large field of view (FOV) and high resolution of an optical system, as well as to solve the problem of image stitching misalignment after focusing, firstly, this paper conducts a theoretical analysis of the design principle of the concentric multi-scale optical system and the causes of image stitching misalignment after focusing. Secondly, the design idea of using a combination structure of a two-layer front concentric imaging group and an image-space telecentric relay imaging array and then a joint full-motion zoom relay imaging system is proposed. Finally, an image-space telecentric two-step zoom concentric multi-scale optical system with a 7 × 7 relay imaging array is designed. The FOV of this optical system is 60° × 45°; the focal lengths are 50 mm and 100 mm for the center channel and 50 mm for the other channels. This concentric multi-scale zoom system has the advantages of both high-precision imaging stitching with a wide object distance and high-resolution imaging, which makes up for the defects of the conventional concentric multi-scale optical system, making it a promising application in the fields of aviation and security. Full article
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12 pages, 4711 KiB  
Communication
Design of a Multimodal Oculometric Sensor Contact Lens
by Jean-Louis de Bougrenet de la Tocnaye, Vincent Nourrit and Cyril Lahuec
Sensors 2022, 22(18), 6731; https://doi.org/10.3390/s22186731 - 6 Sep 2022
Cited by 1 | Viewed by 1512
Abstract
Oculometric data, such as gaze direction, pupil size and accommodative change, play a key role nowadays in the analysis of cognitive load and attentional activities, in particular with the development of Integrated Visual Augmentation Systems in many application domains, such as health, defense [...] Read more.
Oculometric data, such as gaze direction, pupil size and accommodative change, play a key role nowadays in the analysis of cognitive load and attentional activities, in particular with the development of Integrated Visual Augmentation Systems in many application domains, such as health, defense and industry. Such measurements are most frequently obtained by different devices, most of them requiring steady eye and body positions and controlled lighting conditions. Recent advances in smart contact lens (SCL) technology have demonstrated the ability to achieve highly reliable and accurate measurements, preserving user mobility, for instance in measuring gaze direction. In this paper, we discuss how these three key functions can be implemented and combined in the same SCL, considering the limited volume and energy consumption constraints. Some technical options are discussed and compared in terms of their ability to be implemented, taking advantage of recent developments in the field. Full article
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12 pages, 2661 KiB  
Communication
High-Speed Infrared Radiation Thermometer for the Investigation of Early Stage Explosive Development and Fireball Expansion
by Matthew J. Hobbs, Andrew Barr, Scott Woolford, Dain Farrimond, Sam D. Clarke, Andrew Tyas and Jon R. Willmott
Sensors 2022, 22(16), 6143; https://doi.org/10.3390/s22166143 - 17 Aug 2022
Cited by 7 | Viewed by 5964
Abstract
The understanding of blast loads is critical for the development of infrastructure that protects against explosions. However, the lack of high-quality experimental work on the characterisation of such loads prevents a better understanding of many scenarios. Blast loads are typically characterised by use [...] Read more.
The understanding of blast loads is critical for the development of infrastructure that protects against explosions. However, the lack of high-quality experimental work on the characterisation of such loads prevents a better understanding of many scenarios. Blast loads are typically characterised by use of some form of pressure gauge, from which the temperature can be inferred from a pressure measurement. However, such an approach to temperature measurement is limited; it assumes ideal gas laws apply throughout, which may not be the case for high temperature and pressure scenarios. In contrast, infrared radiation thermometers (IRTs) perform a measurement of temperature based upon the emitted radiance from the target object. The IRTs can measure fast changes in transient temperature, making them seemingly ideal for the measurement of a fireball’s temperature. In this work, we present the use of a high-speed IRT for the measurement of early-stage explosive development and fireball expansion within a confined blast, with the temperature of the explosive fireball measured from its emitted radiance. The temperature measured by the IRT was corroborated against the temperature inferred from a pressure gauge measurement; both instruments measured the same temperature from the quasi-static pressure (QSP) point onwards. Before the QSP point, it is deduced that the IRT measures the average temperature of the fireball over a wide field-of-view (FOV), as opposed to that inferred from the singular shocks detected by the pressure gauge. Therefore, use of an IRT, in tandem with a pressure gauge, provides a potential invaluable measurement technique for the characterisation the early stages of a fireball as it develops and expands. Full article
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19 pages, 2366 KiB  
Article
Doppler Measurement of Modulated Light for High Speed Vehicles
by Kookjin Sung and Manoranjan Majji
Sensors 2022, 22(4), 1444; https://doi.org/10.3390/s22041444 - 13 Feb 2022
Cited by 2 | Viewed by 2569
Abstract
Technical details associated with a novel relative motion sensor system are elaborated in the paper. By utilizing the Doppler effect, the optical sensor system estimates the relative motion rates between the sensor and the moving object equipped with modulating light sources and relatively [...] Read more.
Technical details associated with a novel relative motion sensor system are elaborated in the paper. By utilizing the Doppler effect, the optical sensor system estimates the relative motion rates between the sensor and the moving object equipped with modulating light sources and relatively inexpensive electrical components. A transimpedance amplifier (TIA) sensing circuit is employed to measure the Doppler shift exhibited by the amplitude modulated light sources on the moving platform. Implementation details associated with the amplitude modulation and photo-detection processes are discussed using representative hardware elements. A heterodyne mixing process with a reference signal is shown to improve the signal-to-noise ratios of the Doppler shift estimation processing pipeline. Benchtop prototype experiments are used to demonstrate the utility of the proposed technology for relative motion estimation applications. Full article
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16 pages, 468 KiB  
Article
Estimation and Error Analysis for Optomechanical Inertial Sensors
by Patrick Kelly, Manoranjan Majji and Felipe Guzmán
Sensors 2021, 21(18), 6101; https://doi.org/10.3390/s21186101 - 11 Sep 2021
Viewed by 1723
Abstract
A sensor model and methodology to estimate the forcing accelerations measured using a novel optomechanical inertial sensor with the inclusion of stochastic bias and measurement noise processes is presented. A Kalman filter for the estimation of instantaneous sensor bias is developed; the outputs [...] Read more.
A sensor model and methodology to estimate the forcing accelerations measured using a novel optomechanical inertial sensor with the inclusion of stochastic bias and measurement noise processes is presented. A Kalman filter for the estimation of instantaneous sensor bias is developed; the outputs from this calibration step are then employed in two different approaches for the estimation of external accelerations applied to the sensor. The performance of the system is demonstrated using simulated measurements and representative values corresponding to a bench-tested 3.76 Hz oscillator. It is shown that the developed methods produce accurate estimates of the bias over a short calibration step. This information enables precise estimates of acceleration over an extended operation period. These results establish the feasibility of reliably precise acceleration estimates using the presented methods in conjunction with state of the art optomechanical sensing technology. Full article
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19 pages, 2204 KiB  
Article
Feasibility of Novel Rear-Side Mirage Deflection Method for Thermal Conductivity Measurements
by Gwantaek Kim, Moojoong Kim and Hyunjung Kim
Sensors 2021, 21(17), 5971; https://doi.org/10.3390/s21175971 - 6 Sep 2021
Viewed by 1879
Abstract
Among the noncontact measurement technologies used to acquire thermal property information, those that use the photothermal effect are attracting attention. However, it is difficult to perform measurements for new materials with different optical and thermal properties, owing to limitations of existing thermal conductivity [...] Read more.
Among the noncontact measurement technologies used to acquire thermal property information, those that use the photothermal effect are attracting attention. However, it is difficult to perform measurements for new materials with different optical and thermal properties, owing to limitations of existing thermal conductivity measurement methods using the photothermal effect. To address this problem, this study aimed to develop a rear-side mirage deflection method capable of measuring thermal conductivity regardless of the material characteristics based on the photothermal effect. A thin copper film (of 20 µm thickness) was formed on the surfaces of the target materials so that measurements could not be affected by the characteristics of the target materials. In addition, phase delay signals were acquired from the rear sides of the target materials to exclude the influence of the pump beam, which is a problem in existing thermal conductivity measurement methods that use the photothermal effect. To verify the feasibility of the proposed measurement technique, thermal conductivity was measured for copper, aluminum, and stainless steel samples with a 250 µm thickness. The results were compared with literature values and showed good agreement with relative errors equal to or less than 0.2%. Full article
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18 pages, 2386 KiB  
Article
Investigation and Mitigation of Noise Contributions in a Compact Heterodyne Interferometer
by Yanqi Zhang, Adam S. Hines, Guillermo Valdes and Felipe Guzman
Sensors 2021, 21(17), 5788; https://doi.org/10.3390/s21175788 - 28 Aug 2021
Cited by 22 | Viewed by 2610
Abstract
We present a noise estimation and subtraction algorithm capable of increasing the sensitivity of heterodyne laser interferometers by one order of magnitude. The heterodyne interferometer is specially designed for dynamic measurements of a test mass in the application of sub-Hz inertial sensing. A [...] Read more.
We present a noise estimation and subtraction algorithm capable of increasing the sensitivity of heterodyne laser interferometers by one order of magnitude. The heterodyne interferometer is specially designed for dynamic measurements of a test mass in the application of sub-Hz inertial sensing. A noise floor of 3.31×1011m/Hz at 100 mHz is achieved after applying our noise subtraction algorithm to a benchtop prototype interferometer that showed a noise level of 2.76×1010m/Hz at 100 mHz when tested in vacuum at levels of 3×105 Torr. Based on the previous results, we investigated noise estimation and subtraction techniques of non-linear optical pathlength noise, laser frequency noise, and temperature fluctuations in heterodyne laser interferometers. For each noise source, we identified its contribution and removed it from the measurement by linear fitting or a spectral analysis algorithm. The noise correction algorithm we present in this article can be generally applied to heterodyne laser interferometers. Full article
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14 pages, 4185 KiB  
Article
On-Board Monitoring of SO2 Ship Emissions Using Resonant Photoacoustic Gas Detection in the UV Range
by Mahmoud El-Safoury, Miguel Dufner, Christian Weber, Katrin Schmitt, Hans-Fridtjof Pernau, Bert Willing and Jürgen Wöllenstein
Sensors 2021, 21(13), 4468; https://doi.org/10.3390/s21134468 - 29 Jun 2021
Cited by 12 | Viewed by 3138
Abstract
A photoacoustic gas detector for SO2 was developed for ship exhaust gas emission monitoring. The basic measurement setup is based on the absorption of electromagnetic radiation of SO2 at 285 nm wavelength. A commercially available ultraviolet (UV) light-emitting diode (LED) is [...] Read more.
A photoacoustic gas detector for SO2 was developed for ship exhaust gas emission monitoring. The basic measurement setup is based on the absorption of electromagnetic radiation of SO2 at 285 nm wavelength. A commercially available ultraviolet (UV) light-emitting diode (LED) is used as the light source and a micro-electro-mechanical system (MEMS) microphone as the detector. In order to achieve the required detection limits in marine applications, a measuring cell which allows an acoustically resonant amplification of the photoacoustic signal was developed and characterized. A limit of detection of 1 ppm was achieved in lab conditions during continuous gas flow. Long-term measurements on a container ship demonstrated the application relevance of the developed system. Full article
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15 pages, 7276 KiB  
Article
Motionless Polarizing Structured Illumination Microscopy
by Hyo Mi Park and Ki-Nam Joo
Sensors 2021, 21(8), 2837; https://doi.org/10.3390/s21082837 - 17 Apr 2021
Cited by 2 | Viewed by 3697
Abstract
In this investigation, we propose a motionless polarizing structured illumination microscopy as an axially sectioning and reflective-type device to measure the 3D surface profiles of specimens. Based on the spatial phase-shifting technique to obtain the visibility of the illumination pattern. Instead of using [...] Read more.
In this investigation, we propose a motionless polarizing structured illumination microscopy as an axially sectioning and reflective-type device to measure the 3D surface profiles of specimens. Based on the spatial phase-shifting technique to obtain the visibility of the illumination pattern. Instead of using a grid, a Wollaston prism is used to generate the light pattern by the stable interference of two beams. As the polarization states of two beams are orthogonal with each other, a polarization pixelated CMOS camera can simultaneously obtain four phase-shifted patterns with the beams after passing through a quarter wave plate based on the spatial phase-shifting technique with polarization. In addition, a focus tunable lens is used to eliminate a mechanical moving part for the axial scanning of the specimen. In the experimental result, a step height sample and a concave mirror were measured with 0.05 µm and 0.2 mm repeatabilities of step height and the radius of curvature, respectively. Full article
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19 pages, 6144 KiB  
Article
Development of a Compound Speckle Interferometer for Precision Three-Degree-of-Freedom Displacement Measurement
by Hung-Lin Hsieh and Bo-Yen Sun
Sensors 2021, 21(5), 1828; https://doi.org/10.3390/s21051828 - 5 Mar 2021
Cited by 1 | Viewed by 2313
Abstract
In this study, a compound speckle interferometer for measuring three-degree-of-freedom (3-DOF) displacement is proposed. The system, which combines heterodyne interferometry, speckle interferometry and beam splitting techniques, can perform precision 3-DOF displacement measurements, while still having the advantages of high resolution and a relatively [...] Read more.
In this study, a compound speckle interferometer for measuring three-degree-of-freedom (3-DOF) displacement is proposed. The system, which combines heterodyne interferometry, speckle interferometry and beam splitting techniques, can perform precision 3-DOF displacement measurements, while still having the advantages of high resolution and a relatively simple configuration. The incorporation of speckle interferometry allows for non-contact displacement measurements by detecting the phase of the speckle interference pattern formed from the convergence of laser beams on the measured rough surface. Experiments were conducted to verify the measurement capabilities of the system, and the results show that the proposed system has excellent measurement capabilities suitable for future real-world applications. Full article
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16 pages, 1181 KiB  
Article
Ghost Beam Suppression in Deep Frequency Modulation Interferometry for Compact On-Axis Optical Heads
by Oliver Gerberding and Katharina-Sophie Isleif
Sensors 2021, 21(5), 1708; https://doi.org/10.3390/s21051708 - 2 Mar 2021
Cited by 6 | Viewed by 2802
Abstract
We present a compact optical head design for wide-range and low noise displacement sensing using deep frequency modulation interferometry (DFMI). The on-axis beam topology is realised in a quasi-monolithic component and relies on cube beamsplitters and beam transmission through perpendicular surfaces to keep [...] Read more.
We present a compact optical head design for wide-range and low noise displacement sensing using deep frequency modulation interferometry (DFMI). The on-axis beam topology is realised in a quasi-monolithic component and relies on cube beamsplitters and beam transmission through perpendicular surfaces to keep angular alignment constant when operating in air or in a vacuum, which leads to the generation of ghost beams that can limit the phase readout linearity. We investigated the coupling of these beams into the non-linear phase readout scheme of DFMI and implemented adjustments of the phase estimation algorithm to reduce this effect. This was done through a combination of balanced detection and the inherent orthogonality of beat signals with different relative time-delays in deep frequency modulation interferometry, which is a unique feature not available for heterodyne, quadrature or homodyne interferometry. Full article
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16 pages, 5322 KiB  
Article
Improved Self-Calibration of a Multilateration System Based on Absolute Distance Measurement
by Quoc Khanh Nguyen, Seungman Kim, Seong-Heum Han, Seung-Kook Ro, Seung-Woo Kim, Young-Jin Kim, Wooram Kim and Jeong Seok Oh
Sensors 2020, 20(24), 7288; https://doi.org/10.3390/s20247288 - 18 Dec 2020
Cited by 5 | Viewed by 2438
Abstract
Multilateration tracking systems (MLTSs) are used in industrial three-dimensional (3D) coordinate measuring applications. For high-precision measurement, system parameters must be calibrated properly in advance. For an MLTS using absolute distance measurement (ADM), the conventional self-calibration method significantly reduces estimation efficiency because all system [...] Read more.
Multilateration tracking systems (MLTSs) are used in industrial three-dimensional (3D) coordinate measuring applications. For high-precision measurement, system parameters must be calibrated properly in advance. For an MLTS using absolute distance measurement (ADM), the conventional self-calibration method significantly reduces estimation efficiency because all system parameters are estimated simultaneously using a complicated residual function. This paper presents a novel self-calibration method that optimizes ADM to reduce the number of system parameters via highly precise and separate estimations of dead paths. Therefore, the residual function to estimate the tracking station locations can be simplified. By applying a suitable mathematical procedure and solving the initial guess problem without the aid of an external device, estimation accuracy of the system parameters is significantly improved. In three self-calibration experiments, with ADM repeatability of approximately 3.4 µm, the maximum deviation of the system parameters estimated by the proposed self-calibration method was 68.6 µm, while the maximum deviation estimated by the conventional self-calibration method was 711.9 µm. Validation of 3D coordinate measurements in a 1000 mm × 1000 mm × 1000 mm volume showed good agreement between the proposed ADM-based MLTS and a commercial laser tracker, where the maximum difference based on the standard deviation was 17.7 µm. Conversely, the maximum difference was 98.8 µm using the conventional self-calibration method. These results confirmed the efficiency and feasibility of the proposed self-calibration method. Full article
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21 pages, 4659 KiB  
Article
Multi-Camera-Based Universal Measurement Method for 6-DOF of Rigid Bodies in World Coordinate System
by Zuoxi Zhao, Yuchang Zhu, Yuanhong Li, Zhi Qiu, Yangfan Luo, Chaoshi Xie and Zhuangzhuang Zhang
Sensors 2020, 20(19), 5547; https://doi.org/10.3390/s20195547 - 28 Sep 2020
Cited by 8 | Viewed by 3754
Abstract
The measurement of six-degrees-of-freedom (6-DOF) of rigid bodies plays an important role in many industries, but it often requires the use of professional instruments and software, or has limitations on the shape of measured objects. In this paper, a 6-DOF measurement method based [...] Read more.
The measurement of six-degrees-of-freedom (6-DOF) of rigid bodies plays an important role in many industries, but it often requires the use of professional instruments and software, or has limitations on the shape of measured objects. In this paper, a 6-DOF measurement method based on multi-camera is proposed, which is accomplished using at least two ordinary cameras and is made available for most morphological rigid bodies. First, multi-camera calibration based on Zhang Zhengyou’s calibration method is introduced. In addition to the intrinsic and extrinsic parameters of cameras, the pose relationship between the camera coordinate system and the world coordinate system can also be obtained. Secondly, the 6-DOF calculation model of proposed method is gradually analyzed by the matrix analysis method. With the help of control points arranged on the rigid body, the 6-DOF of the rigid body can be calculated by the least square method. Finally, the Phantom 3D high-speed photogrammetry system (P3HPS) with an accuracy of 0.1 mm/m was used to evaluate this method. The experiment results show that the average error of the rotational degrees of freedom (DOF) measurement is less than 1.1 deg, and the average error of the movement DOF measurement is less than 0.007 m. In conclusion, the accuracy of the proposed method meets the requirements. Full article
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17 pages, 1503 KiB  
Article
Single-Element Dual-Interferometer for Precision Inertial Sensing
by Yichao Yang, Kohei Yamamoto, Victor Huarcaya, Christoph Vorndamme, Daniel Penkert, Germán Fernández Barranco, Thomas S. Schwarze, Moritz Mehmet, Juan Jose Esteban Delgado, Jianjun Jia, Gerhard Heinzel and Miguel Dovale Álvarez
Sensors 2020, 20(17), 4986; https://doi.org/10.3390/s20174986 - 3 Sep 2020
Cited by 4 | Viewed by 3570
Abstract
Tracking moving masses in several degrees of freedom with high precision and large dynamic range is a central aspect in many current and future gravitational physics experiments. Laser interferometers have been established as one of the tools of choice for such measurement schemes. [...] Read more.
Tracking moving masses in several degrees of freedom with high precision and large dynamic range is a central aspect in many current and future gravitational physics experiments. Laser interferometers have been established as one of the tools of choice for such measurement schemes. Using sinusoidal phase modulation homodyne interferometry allows a drastic reduction of the complexity of the optical setup, a key limitation of multi-channel interferometry. By shifting the complexity of the setup to the signal processing stage, these methods enable devices with a size and weight not feasible using conventional techniques. In this paper we present the design of a novel sensor topology based on deep frequency modulation interferometry: the self-referenced single-element dual-interferometer (SEDI) inertial sensor, which takes simplification one step further by accommodating two interferometers in one optic. Using a combination of computer models and analytical methods we show that an inertial sensor with sub-picometer precision for frequencies above 10 mHz, in a package of a few cubic inches, seems feasible with our approach. Moreover we show that by combining two of these devices it is possible to reach sub-picometer precision down to 2 mHz. In combination with the given compactness, this makes the SEDI sensor a promising approach for applications in high precision inertial sensing for both next-generation space-based gravity missions employing drag-free control, and ground-based experiments employing inertial isolation systems with optical readout. Full article
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18 pages, 6167 KiB  
Article
A Combined Measurement Method for Large-Size Aerospace Components
by Zhilong Zhou, Wei Liu, Qiong Wu, Yuxin Wang, Binchao Yu, Yi Yue and Jiabo Zhang
Sensors 2020, 20(17), 4843; https://doi.org/10.3390/s20174843 - 27 Aug 2020
Cited by 16 | Viewed by 2984
Abstract
Automated and high-accuracy three-dimensional (3D) shape measurement is required in quality control of large-size components for the aerospace industry. To eliminate the contradiction between global measurement and local precision measurement control in 3D digitalization for the key local features of the large-size components, [...] Read more.
Automated and high-accuracy three-dimensional (3D) shape measurement is required in quality control of large-size components for the aerospace industry. To eliminate the contradiction between global measurement and local precision measurement control in 3D digitalization for the key local features of the large-size components, a combined measurement method is proposed, including a 3D scanner, a laser tracker, and an industrial robot used as an orienting device, to achieve high-accuracy measurement. As for improving the overall measurement accuracy, an accurate calibration method based on coordinate optimization of common points (COCP) and coordinate optimization of global control points (COGP) is proposed to determine the coordinate systems. Firstly, a coordinate optimization method of common points (COCP) is recommended. Then, a coordinate optimization method of global control points (COGP) based on the angular constraint is proposed for minimizing the measurement errors and improving the measurement accuracy of the position and orientation of the 3D scanner. Finally, a combined measurement system is established, and validation experiments are carried out in laboratory within a distance of 4 m. The calibration experiment results demonstrate that the max and mean errors of the coordinate transformation have been reduced from 0.037 and 0.022 mm to 0.021 and 0.0122 mm. Additionally, the measurement experiment results also show that the combined measurement system features high accuracy. Full article
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21 pages, 6571 KiB  
Article
Multiple Optical Sensor Fusion for Mineral Mapping of Core Samples
by Behnood Rasti, Pedram Ghamisi, Peter Seidel, Sandra Lorenz and Richard Gloaguen
Sensors 2020, 20(13), 3766; https://doi.org/10.3390/s20133766 - 5 Jul 2020
Cited by 5 | Viewed by 3052
Abstract
Geological objects are characterized by a high complexity inherent to a strong compositional variability at all scales and usually unclear class boundaries. Therefore, dedicated processing schemes are required for the analysis of such data for mineralogical mapping. On the other hand, the variety [...] Read more.
Geological objects are characterized by a high complexity inherent to a strong compositional variability at all scales and usually unclear class boundaries. Therefore, dedicated processing schemes are required for the analysis of such data for mineralogical mapping. On the other hand, the variety of optical sensing technology reveals different data attributes and therefore multi-sensor approaches are adapted to solve such complicated mapping problems. In this paper, we devise an adapted multi-optical sensor fusion (MOSFus) workflow which takes the geological characteristics into account. The proposed processing chain exhaustively covers all relevant stages, including data acquisition, preprocessing, feature fusion, and mineralogical mapping. The concept includes (i) a spatial feature extraction based on morphological profiles on RGB data with high spatial resolution, (ii) a specific noise reduction applied on the hyperspectral data that assumes mixed sparse and Gaussian contamination, and (iii) a subsequent dimensionality reduction using a sparse and smooth low rank analysis. The feature extraction approach allows one to fuse heterogeneous data at variable resolutions, scales, and spectral ranges and improve classification substantially. The last step of the approach, an SVM classifier, is robust to unbalanced and sparse training sets and is particularly efficient with complex imaging data. We evaluate the performance of the procedure with two different multi-optical sensor datasets. The results demonstrate the superiority of this dedicated approach over common strategies. Full article
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11 pages, 4171 KiB  
Article
Anomaly Detection Neural Network with Dual Auto-Encoders GAN and Its Industrial Inspection Applications
by Ta-Wei Tang, Wei-Han Kuo, Jauh-Hsiang Lan, Chien-Fang Ding, Hakiem Hsu and Hong-Tsu Young
Sensors 2020, 20(12), 3336; https://doi.org/10.3390/s20123336 - 12 Jun 2020
Cited by 77 | Viewed by 8500
Abstract
Recently, researchers have been studying methods to introduce deep learning into automated optical inspection (AOI) systems to reduce labor costs. However, the integration of deep learning in the industry may encounter major challenges such as sample imbalance (defective products that only account for [...] Read more.
Recently, researchers have been studying methods to introduce deep learning into automated optical inspection (AOI) systems to reduce labor costs. However, the integration of deep learning in the industry may encounter major challenges such as sample imbalance (defective products that only account for a small proportion). Therefore, in this study, an anomaly detection neural network, dual auto-encoder generative adversarial network (DAGAN), was developed to solve the problem of sample imbalance. With skip-connection and dual auto-encoder architecture, the proposed method exhibited excellent image reconstruction ability and training stability. Three datasets, namely public industrial detection training set, MVTec AD, with mobile phone screen glass and wood defect detection datasets, were used to verify the inspection ability of DAGAN. In addition, training with a limited amount of data was proposed to verify its detection ability. The results demonstrated that the areas under the curve (AUCs) of DAGAN were better than previous generative adversarial network-based anomaly detection models in 13 out of 17 categories in these datasets, especially in categories with high variability or noise. The maximum AUC improvement was 0.250 (toothbrush). Moreover, the proposed method exhibited better detection ability than the U-Net auto-encoder, which indicates the function of discriminator in this application. Furthermore, the proposed method had a high level of AUCs when using only a small amount of training data. DAGAN can significantly reduce the time and cost of collecting and labeling data when it is applied to industrial detection. Full article
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Review

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33 pages, 5564 KiB  
Review
Optical Fibre-Based Sensors for Oil and Gas Applications
by Jincy Johny, Solomon Amos and Radhakrishna Prabhu
Sensors 2021, 21(18), 6047; https://doi.org/10.3390/s21186047 - 9 Sep 2021
Cited by 31 | Viewed by 5020
Abstract
Oil and gas (O&G) explorations moving into deeper zones for enhanced oil and gas recovery are causing serious safety concerns across the world. The sensing of critical multiple parameters like high pressure, high temperature (HPHT), chemicals, etc., are required at longer distances in [...] Read more.
Oil and gas (O&G) explorations moving into deeper zones for enhanced oil and gas recovery are causing serious safety concerns across the world. The sensing of critical multiple parameters like high pressure, high temperature (HPHT), chemicals, etc., are required at longer distances in real-time. Traditional electrical sensors operate less effectively under these extreme environmental conditions and are susceptible to electromagnetic interference (EMI). Hence, there is a growing demand for improved sensors with enhanced measurement capabilities and also sensors that generates reliable data for enhanced oil and gas production. In addition to enhanced oil and gas recovery, the sensing technology should also be capable of monitoring the well bore integrity and safety. The sensing requirements of the O&G industry for improved sensing in deeper zones include increased transmission length, improved spatial coverage and integration of multiple sensors with multimodal sensing capability. This imposes problems like signal attenuation, crosstalks and cross sensitivities. Optical fibre-based sensors are expected to provide superior sensing capabilities compared to electrical sensors. This review paper covers a detailed review of different fibre-optic sensing technologies to identify a feasible sensing solution for the O&G industry. Full article
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10 pages, 1806 KiB  
Letter
High-Performance Ultra-Thin Spectrometer Optical Design Based on Coddington’s Equations
by Zhiwei Feng, Guo Xia, Rongsheng Lu, Xiaobo Cai, Hao Cui and Mingyong Hu
Sensors 2021, 21(2), 323; https://doi.org/10.3390/s21020323 - 6 Jan 2021
Cited by 11 | Viewed by 4177
Abstract
A unique method to design a high-throughput and high-resolution ultrathin Czerny–Turner (UTCT) spectrometer is proposed. This paper reveals an infrequent design process of spectrometers based on Coddington’s equations, which will lead us to develop a high-performance spectrometer from scratch. The spectrometer is composed [...] Read more.
A unique method to design a high-throughput and high-resolution ultrathin Czerny–Turner (UTCT) spectrometer is proposed. This paper reveals an infrequent design process of spectrometers based on Coddington’s equations, which will lead us to develop a high-performance spectrometer from scratch. The spectrometer is composed of cylindrical elements except a planar grating. In the simulation design, spot radius is sub-pixel size, which means that almost all of the energy is collected by the detector. The spectral resolution is 0.4 nm at central wavelength and 0.75 nm at edge wavelength when the width of slit is chosen to be 25 μm and the groove density is 900 lines/mm. Full article
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11 pages, 3030 KiB  
Letter
Applying Differential Wave-Front Sensing and Differential Power Sensing for Simultaneous Precise and Wide-Range Test-Mass Rotation Measurements
by Neda Meshksar, Moritz Mehmet, Katharina-Sophie Isleif and Gerhard Heinzel
Sensors 2021, 21(1), 164; https://doi.org/10.3390/s21010164 - 29 Dec 2020
Cited by 6 | Viewed by 2551
Abstract
We propose to combine differential wave-front sensing (DWS) and differential power sensing (DPS) in a Mach-Zehnder type interferometer for measuring the rotational dynamics of a test-mass. Using the DWS method, a high sensitive measurement of 6 nrad Hz−1/2 in sub-Hz frequencies can [...] Read more.
We propose to combine differential wave-front sensing (DWS) and differential power sensing (DPS) in a Mach-Zehnder type interferometer for measuring the rotational dynamics of a test-mass. Using the DWS method, a high sensitive measurement of 6 nrad Hz−1/2 in sub-Hz frequencies can be provided around the test-mass nominal position (±0.11 mrad), whereas the measurement of a wide rotation range (±5 mrad) is realized by the DPS method. The interferometer can be combined with deep frequency modulation (DFM) interferometry for measurement of the test-mass translational dynamics. The setup and the resulting interferometric signals are verified by simulations. An optimization algorithm is applied to find suitable positions of the lenses and the waist size of the input laser in order to determine the best trade of between the slope of DWS, dynamic range of DPS, and the interferometric contrast. Our simulation further allows to investigate the layout for robustness and design tolerances. We compare our device with a recent experimental realization of a DFM interferometer and find that a practical implementation of the interferometer proposed here has the potential to provide translational and rotational test-mass tracking with state-of-the-art sensitivity. The simple and compact design, and especially the capability of sensing the test-mass rotation in a wide range and simultaneously providing a high-precision measurement close to the test-mass nominal position makes the design especially suitable for example for employment in torsion pendulum setups. Full article
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