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6393 KiB

Open AccessArticle

A Simplified, Light Emitting Diode (LED) Based, Modular System to be Used for the Rapid Evaluation of Fruit and Vegetable Quality: Development and Validation on Dye Solutions

by Raffaele Civelli, Valentina Giovenzana, Roberto Beghi, Ezio Naldi, Riccardo Guidetti and Roberto Oberti

Sensors 2015, 15(9), 22705-22723; https://doi.org/10.3390/s150922705 - 8 Sep 2015

Cited by 30 | Viewed by 5448

Abstract

NIR spectroscopy has proven to be one of the most efficient and ready to transfer tools to monitor product’s quality. Portable VIS/NIR instruments are particularly versatile and suitable for field use to monitor the ripening process or quality parameters. The aim of this [...] Read more.

NIR spectroscopy has proven to be one of the most efficient and ready to transfer tools to monitor product’s quality. Portable VIS/NIR instruments are particularly versatile and suitable for field use to monitor the ripening process or quality parameters. The aim of this work is to develop and evaluate a new simplified optoelectronic system for potential measurements on fruit and vegetables directly in the field. The development, characterization and validation of an operative prototype is discussed. LED technology was chosen for the design, and spectral acquisition at four specific wavelengths (630, 690, 750 and 850 nm) was proposed. Nevertheless, attention was given to the modularity and versatility of the system. Indeed, the possibility to change the light sources module with other wavelengths allows one to adapt the use of the same device for different foreseeable applications and objectives, e.g., ripeness evaluation, detection of particular diseases and disorders, chemical and physical property prediction, shelf life analysis, as well as for different natures of products (berry, leaf or liquid). Validation tests on blue dye water solutions have shown the capability of the system of discriminating low levels of reflectance, with a repeatability characterized by a standard deviation proportional to the measured intensity and in general limited to 2%–4%. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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2968 KiB

Open AccessArticle

Designing a Microfluidic Device with Integrated Ratiometric Oxygen Sensors for the Long-Term Control and Monitoring of Chronic and Cyclic Hypoxia

by Samantha M. Grist, Jonathan C. Schmok, Meng-Chi (Andy) Liu, Lukas Chrostowski and Karen C. Cheung

Sensors 2015, 15(8), 20030-20052; https://doi.org/10.3390/s150820030 - 14 Aug 2015

Cited by 36 | Viewed by 10058

Abstract

Control of oxygen over cell cultures in vitro is a topic of considerable interest, as chronic and cyclic hypoxia can alter cell behaviour. Both static and transient hypoxic levels have been found to affect tumour cell behaviour; it is potentially valuable to include [...] Read more.

Control of oxygen over cell cultures in vitro is a topic of considerable interest, as chronic and cyclic hypoxia can alter cell behaviour. Both static and transient hypoxic levels have been found to affect tumour cell behaviour; it is potentially valuable to include these effects in early, in vitro stages of drug screening. A barrier to their inclusion is that rates of transient hypoxia can be a few cycles/hour, which is difficult to reproduce in traditional in vitro cell culture environments due to long diffusion distances from control gases to the cells. We use a gas-permeable three-layer microfluidic device to achieve spatial and temporal oxygen control with biologically-relevant switching times. We measure the oxygen profiles with integrated, ratiometric optical oxygen sensors, demonstrate sensor and system stability over multi-day experiments, and characterize a pre-bleaching process to improve sensor stability. We show, with both finite-element modelling and experimental data, excellent control over the oxygen levels by the device, independent of fluid flow rate and oxygenation for the operating flow regime. We measure equilibration times of approximately 10 min, generate complex, time-varying oxygen profiles, and study the effects of oxygenated media flow rates on the measured oxygen levels. This device could form a useful tool for future long-term studies of cell behaviour under hypoxia. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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9951 KiB

Open AccessArticle

Suppression of Systematic Errors of Electronic Distance Meters for Measurement of Short Distances

by Jaroslav Braun, Martin Štroner, Rudolf Urban and Filip Dvořáček

Sensors 2015, 15(8), 19264-19301; https://doi.org/10.3390/s150819264 - 6 Aug 2015

Cited by 20 | Viewed by 9064

Abstract

In modern industrial geodesy, high demands are placed on the final accuracy, with expectations currently falling below 1 mm. The measurement methodology and surveying instruments used have to be adjusted to meet these stringent requirements, especially the total stations as the most often [...] Read more.

In modern industrial geodesy, high demands are placed on the final accuracy, with expectations currently falling below 1 mm. The measurement methodology and surveying instruments used have to be adjusted to meet these stringent requirements, especially the total stations as the most often used instruments. A standard deviation of the measured distance is the accuracy parameter, commonly between 1 and 2 mm. This parameter is often discussed in conjunction with the determination of the real accuracy of measurements at very short distances (5–50 m) because it is generally known that this accuracy cannot be increased by simply repeating the measurement because a considerable part of the error is systematic. This article describes the detailed testing of electronic distance meters to determine the absolute size of their systematic errors, their stability over time, their repeatability and the real accuracy of their distance measurement. Twenty instruments (total stations) have been tested, and more than 60,000 distances in total were measured to determine the accuracy and precision parameters of the distance meters. Based on the experiments’ results, calibration procedures were designed, including a special correction function for each instrument, whose usage reduces the standard deviation of the measurement of distance by at least 50%. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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766 KiB

Open AccessArticle

A Time Difference Method for Measurement of Phase Shift between Distributed Feedback Laser Diode (DFB-LD) Output Wavelength and Intensity

by Yongning Liu, Jun Chang, Jie Lian, Zhaojun Liu, Qiang Wang and Cunguang Zhu

Sensors 2015, 15(7), 16153-16161; https://doi.org/10.3390/s150716153 - 6 Jul 2015

Cited by 9 | Viewed by 6731

Abstract

A time difference method to conveniently measure the phase shift between output wavelength and intensity of distributed feedback laser diodes (DFB-LDs) was proposed. This approach takes advantage of asymmetric absorption positions at the same wavelength during wavelength increase and decrease tuning processes in [...] Read more.

A time difference method to conveniently measure the phase shift between output wavelength and intensity of distributed feedback laser diodes (DFB-LDs) was proposed. This approach takes advantage of asymmetric absorption positions at the same wavelength during wavelength increase and decrease tuning processes in the intensity-time curve by current modulation. For its practical implementation, a measurement example of phase shift was demonstrated by measuring a time difference between the first time and the second time attendances of the same gas absorption line in the intensity-time curve during one sine or triangle modulation circle. The phase shifts at modulation frequencies ranging from 50 Hz to 50 kHz were measured with a resolution of 0.001π. As the modulation frequency increased the shift value increased with a slowed growth rate. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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2670 KiB

Open AccessArticle

Estimation of Prestress Force Distribution in the Multi-Strand System of Prestressed Concrete Structures

by Keunhee Cho, Sung Yong Park, Jeong-Rae Cho, Sung Tae Kim and Young-Hwan Park

Sensors 2015, 15(6), 14079-14092; https://doi.org/10.3390/s150614079 - 15 Jun 2015

Cited by 18 | Viewed by 6408

Abstract

Prestressed concrete (PSC) is one of the most reliable, durable and widely used construction materials, which overcomes the weakness of concrete in tension by the introduction of a prestress force. Smart strands enabling measurement of the prestress force have recently been developed to [...] Read more.

Prestressed concrete (PSC) is one of the most reliable, durable and widely used construction materials, which overcomes the weakness of concrete in tension by the introduction of a prestress force. Smart strands enabling measurement of the prestress force have recently been developed to maintain PSC structures throughout their lifetime. However, the smart strand cannot give a representative indication of the whole prestress force when used in multi-strand systems since each strand sustains a different prestress force. In this paper, the actual distribution of the prestress force in a multi-strand system is examined using elastomagnetic (EM) sensors to develop a method for tracking representative indicators of the prestress force using smart strands. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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3392 KiB

Open AccessArticle

A Rapid Method to Achieve Aero-Engine Blade Form Detection

by Bin Sun and Bing Li

Sensors 2015, 15(6), 12782-12801; https://doi.org/10.3390/s150612782 - 1 Jun 2015

Cited by 42 | Viewed by 7303

Abstract

This paper proposes a rapid method to detect aero-engine blade form, according to the characteristics of an aero-engine blade surface. This method first deduces an inclination error model in free-form surface measurements based on the non-contact laser triangulation principle. Then a four-coordinate measuring [...] Read more.

This paper proposes a rapid method to detect aero-engine blade form, according to the characteristics of an aero-engine blade surface. This method first deduces an inclination error model in free-form surface measurements based on the non-contact laser triangulation principle. Then a four-coordinate measuring system was independently developed, a special fixture was designed according to the blade shape features, and a fast measurement of the blade features path was planned. Finally, by using the inclination error model for correction of acquired data, the measurement error that was caused by tilt form is compensated. As a result the measurement accuracy of the Laser Displacement Sensor was less than 10 μm. After the experimental verification, this method makes full use of optical non-contact measurement fast speed, high precision and wide measuring range of features. Using a standard gauge block as a measurement reference, the coordinate system conversion data is simple and practical. It not only improves the measurement accuracy of the blade surface, but also its measurement efficiency. Therefore, this method increases the value of the measurement of complex surfaces. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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1678 KiB

Open AccessArticle

Optical Detection of Paraoxon Using Single-Walled Carbon Nanotube Films with Attached Organophosphorus Hydrolase-Expressed Escherichia coli

by Intae Kim, Geon Hwee Kim, Chang Sup Kim, Hyung Joon Cha and Geunbae Lim

Sensors 2015, 15(6), 12513-12525; https://doi.org/10.3390/s150612513 - 27 May 2015

Cited by 16 | Viewed by 7317

Abstract

In whole-cell based biosensors, spectrophotometry is one of the most commonly used methods for detecting organophosphates due to its simplicity and reliability. The sensor performance is directly affected by the cell immobilization method because it determines the amount of cells, the mass transfer [...] Read more.

In whole-cell based biosensors, spectrophotometry is one of the most commonly used methods for detecting organophosphates due to its simplicity and reliability. The sensor performance is directly affected by the cell immobilization method because it determines the amount of cells, the mass transfer rate, and the stability. In this study, we demonstrated that our previously-reported microbe immobilization method, a microbe-attached single-walled carbon nanotube film, can be applied to whole-cell-based organophosphate sensors. This method has many advantages over other whole-cell organophosphate sensors, including high specific activity, quick cell immobilization, and excellent stability. A device with circular electrodes was fabricated for an enlarged cell-immobilization area. Escherichia coli expressing organophosphorus hydrolase in the periplasmic space and single-walled carbon nanotubes were attached to the device by our method. Paraoxon was hydrolyzed using this device, and detected by measuring the concentration of the enzymatic reaction product, p-nitrophenol. The specific activity of our device was calculated, and was shown to be over 2.5 times that reported previously for other whole-cell organophosphate sensors. Thus, this method for generation of whole-cell-based OP biosensors might be optimal, as it overcomes many of the caveats that prevent the widespread use of other such devices. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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1186 KiB

Open AccessArticle

Photonic Crystal Fiber-Based Surface Plasmon Resonance Sensor with Selective Analyte Channels and Graphene-Silver Deposited Core

by Ahmmed A. Rifat, G. Amouzad Mahdiraji, Desmond M. Chow, Yu Gang Shee, Rajib Ahmed and Faisal Rafiq Mahamd Adikan

Sensors 2015, 15(5), 11499-11510; https://doi.org/10.3390/s150511499 - 19 May 2015

Cited by 288 | Viewed by 13567

Abstract

We propose a surface plasmon resonance (SPR) sensor based on photonic crystal fiber (PCF) with selectively filled analyte channels. Silver is used as the plasmonic material to accurately detect the analytes and is coated with a thin graphene layer to prevent oxidation. The [...] Read more.

We propose a surface plasmon resonance (SPR) sensor based on photonic crystal fiber (PCF) with selectively filled analyte channels. Silver is used as the plasmonic material to accurately detect the analytes and is coated with a thin graphene layer to prevent oxidation. The liquid-filled cores are placed near to the metallic channel for easy excitation of free electrons to produce surface plasmon waves (SPWs). Surface plasmons along the metal surface are excited with a leaky Gaussian-like core guided mode. Numerical investigations of the fiber’s properties and sensing performance are performed using the finite element method (FEM). The proposed sensor shows maximum amplitude sensitivity of 418 Refractive Index Units (RIU⁻¹) with resolution as high as 2.4 × 10⁻⁵ RIU. Using the wavelength interrogation method, a maximum refractive index (RI) sensitivity of 3000 nm/RIU in the sensing range of 1.46–1.49 is achieved. The proposed sensor is suitable for detecting various high RI chemicals, biochemical and organic chemical analytes. Additionally, the effects of fiber structural parameters on the properties of plasmonic excitation are investigated and optimized for sensing performance as well as reducing the sensor’s footprint. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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871 KiB

Open AccessArticle

Immunity to Laser Power Variation in a DFB Diode Laser Based Optical Gas Sensor Using a Division Process

by Hengtai Chang, Jun Chang, Qingjie Huang, Qiang Wang, Changbin Tian, Wei Wei and Yuanyuan Liu

Sensors 2015, 15(4), 9582-9591; https://doi.org/10.3390/s150409582 - 22 Apr 2015

Cited by 3 | Viewed by 6488

Abstract

The division process used in a DFB diode laser-based optical gas sensor was studied to improve the immunity to laser power variation. Residual amplitude modulation (RAM) in wavelength modulation spectroscopy (WMS) detection was eliminated by intensity normalization using a division process. As a [...] Read more.

The division process used in a DFB diode laser-based optical gas sensor was studied to improve the immunity to laser power variation. Residual amplitude modulation (RAM) in wavelength modulation spectroscopy (WMS) detection was eliminated by intensity normalization using a division process. As a result the detected harmonic signals showed a significant improvement in line shape. For the first harmonic (1f) signal, Bias was improved from 38.7% to 1.2%; Baseline Difference was improved from 2.7% to 0.69% and Asymmetry was improved from 15.4% to 0.22%. For the second harmonic (2f) signal, the Asymmetry Coefficient was improved from 103% to 5.1%. Moreover the division process can further suppress the influence of unstable laser power. As a result, for the 1f signal, stable detection with a variation coefficient of 0.59% was obtained over a wide dynamic range (0.38–8.1 mW). For the 2f signal, stable detection with a variation coefficient of 0.53% was obtained from 0.64 mW to 8.27 mW. The test results showed a good agreement with the theoretical analysis and the proposed method has considerable potential application in gas sensing. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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610 KiB

Open AccessArticle

Development and Beam-Shape Analysis of an Integrated Fiber-Optic Confocal Probe for High-Precision Central Thickness Measurement of Small-Radius Lenses

by Boonsong Sutapun, Armote Somboonkaew, Ratthasart Amarit and Sataporn Chanhorm

Sensors 2015, 15(4), 8512-8526; https://doi.org/10.3390/s150408512 - 13 Apr 2015

Cited by 1 | Viewed by 6601

Abstract

This work describes a new design of a fiber-optic confocal probe suitable for measuring the central thicknesses of small-radius optical lenses or similar objects. The proposed confocal probe utilizes an integrated camera that functions as a shape-encoded position-sensing device. The confocal signal for [...] Read more.

This work describes a new design of a fiber-optic confocal probe suitable for measuring the central thicknesses of small-radius optical lenses or similar objects. The proposed confocal probe utilizes an integrated camera that functions as a shape-encoded position-sensing device. The confocal signal for thickness measurement and beam-shape data for off-axis measurement can be simultaneously acquired using the proposed probe. Placing the probe’s focal point off-center relative to a sample’s vertex produces a non-circular image at the camera’s image plane that closely resembles an ellipse for small displacements. We were able to precisely position the confocal probe’s focal point relative to the vertex point of a ball lens with a radius of 2.5 mm, with a lateral resolution of 1.2 µm. The reflected beam shape based on partial blocking by an aperture was analyzed and verified experimentally. The proposed confocal probe offers a low-cost, high-precision technique, an alternative to a high-cost three-dimensional surface profiler, for tight quality control of small optical lenses during the manufacturing process. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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904 KiB

Open AccessArticle

Monitoring of Low Levels of Furfural in Power Transformer Oil with a Sensor System Based on a POF-MIP Platform

by Nunzio Cennamo, Letizia De Maria, Girolamo D'Agostino, Luigi Zeni and Maria Pesavento

Sensors 2015, 15(4), 8499-8511; https://doi.org/10.3390/s150408499 - 13 Apr 2015

Cited by 82 | Viewed by 9002

Abstract

In this work an innovative, miniaturized and low cost optical chemical sensor (POF-MIP platform), based on a molecular imprinted polymer (MIP) and surface plasmon resonance in a plastic optical fiber (POF), is presented and preliminarily tested for monitoring of furfural (furan-2-carbaldehyde) in transformer [...] Read more.

In this work an innovative, miniaturized and low cost optical chemical sensor (POF-MIP platform), based on a molecular imprinted polymer (MIP) and surface plasmon resonance in a plastic optical fiber (POF), is presented and preliminarily tested for monitoring of furfural (furan-2-carbaldehyde) in transformer oil. To this end, the optical platform was coupled to an MIP layer, highly selective for furfural. The ability of the developed sensor to directly detect furfural in the insulating oil was investigated. The detection limit of the sensor has been found to be 9 ppb, with a linear response up to about 30 ppb. However there is a sensible response up to 0.15 ppm. Because of the small linearity range, the Hill equation is suggested for the quantification. The sensor has been effectively tested in real oil samples collected from aged electrical equipment removed from service. The assessed concentration of furfural is in good agreement with that evaluated by a high pressure liquid chromatography (HLPC) method, confirming the good selectivity of the proposed sensor. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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744 KiB

Open AccessArticle

Noninvasive and Real-Time Plasmon Waveguide Resonance Thermometry

by Pengfei Zhang, Le Liu, Yonghong He, Yanfei Zhou, Yanhong Ji and Hui Ma

Sensors 2015, 15(4), 8481-8498; https://doi.org/10.3390/s150408481 - 13 Apr 2015

Cited by 7 | Viewed by 6030

Abstract

In this paper, the noninvasive and real-time plasmon waveguide resonance (PWR) thermometry is reported theoretically and demonstrated experimentally. Owing to the enhanced evanescent field and thermal shield effect of its dielectric layer, a PWR thermometer permits accurate temperature sensing and has a wide [...] Read more.

In this paper, the noninvasive and real-time plasmon waveguide resonance (PWR) thermometry is reported theoretically and demonstrated experimentally. Owing to the enhanced evanescent field and thermal shield effect of its dielectric layer, a PWR thermometer permits accurate temperature sensing and has a wide dynamic range. A temperature measurement sensitivity of 9.4 × 10⁻³ °C is achieved and the thermo optic coefficient nonlinearity is measured in the experiment. The measurement of water cooling processes distributed in one dimension reveals that a PWR thermometer allows real-time temperature sensing and has potential to be applied for thermal gradient analysis. Apart from this, the PWR thermometer has the advantages of low cost and simple structure, since our transduction scheme can be constructed with conventional optical components and commercial coating techniques. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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1378 KiB

Open AccessArticle

Quartz Enhanced Photoacoustic Spectroscopy Based Trace Gas Sensors Using Different Quartz Tuning Forks

by Yufei Ma, Guang Yu, Jingbo Zhang, Xin Yu, Rui Sun and Frank K. Tittel

Sensors 2015, 15(4), 7596-7604; https://doi.org/10.3390/s150407596 - 27 Mar 2015

Cited by 37 | Viewed by 7247

Abstract

A sensitive trace gas sensor platform based on quartz-enhanced photoacoustic spectroscopy (QEPAS) is reported. A 1.395 μm continuous wave (CW), distributed feedback pigtailed diode laser was used as the excitation source and H₂O was selected as the target analyte. Two kinds [...] Read more.

A sensitive trace gas sensor platform based on quartz-enhanced photoacoustic spectroscopy (QEPAS) is reported. A 1.395 μm continuous wave (CW), distributed feedback pigtailed diode laser was used as the excitation source and H₂O was selected as the target analyte. Two kinds of quartz tuning forks (QTFs) with a resonant frequency (f₀) of 30.72 kHz and 38 kHz were employed for the first time as an acoustic wave transducer, respectively for QEPAS instead of a standard QTF with a f₀ of 32.768 kHz. The QEPAS sensor performance using the three different QTFs was experimentally investigated and theoretically analyzed. A minimum detection limit of 5.9 ppmv and 4.3 ppmv was achieved for f₀ of 32.768 kHz and 30.72 kHz, respectively. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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2502 KiB

Open AccessArticle

Bio-Optics Based Sensation Imaging for Breast Tumor Detection Using Tissue Characterization

by Jong-Ha Lee, Yoon Nyun Kim and Hee-Jun Park

Sensors 2015, 15(3), 6306-6323; https://doi.org/10.3390/s150306306 - 16 Mar 2015

Cited by 6 | Viewed by 5657

Abstract

The tissue inclusion parameter estimation method is proposed to measure the stiffness as well as geometric parameters. The estimation is performed based on the tactile data obtained at the surface of the tissue using an optical tactile sensation imaging system (TSIS). A forward [...] Read more.

The tissue inclusion parameter estimation method is proposed to measure the stiffness as well as geometric parameters. The estimation is performed based on the tactile data obtained at the surface of the tissue using an optical tactile sensation imaging system (TSIS). A forward algorithm is designed to comprehensively predict the tactile data based on the mechanical properties of tissue inclusion using finite element modeling (FEM). This forward information is used to develop an inversion algorithm that will be used to extract the size, depth, and Young's modulus of a tissue inclusion from the tactile data. We utilize the artificial neural network (ANN) for the inversion algorithm. The proposed estimation method was validated by a realistic tissue phantom with stiff inclusions. The experimental results showed that the proposed estimation method can measure the size, depth, and Young's modulus of a tissue inclusion with 0.58%, 3.82%, and 2.51% relative errors, respectively. The obtained results prove that the proposed method has potential to become a useful screening and diagnostic method for breast cancer. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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429 KiB

Open AccessArticle

Simultaneous 2D Strain Sensing Using Polymer Planar Bragg Gratings

by Manuel Rosenberger, Waltraud Eisenbeil, Bernhard Schmauss and Ralf Hellmann

Sensors 2015, 15(2), 4264-4272; https://doi.org/10.3390/s150204264 - 12 Feb 2015

Cited by 30 | Viewed by 7051

Abstract

We demonstrate the application of polymer planar Bragg gratings for multi-axial strain sensing and particularly highlight simultaneous 2D strain measurement. A polymer planar Bragg grating (PPBG) fabricated with a single writing step in bulk polymethylmethacrylate is used for measuring both tensile and compressive [...] Read more.

We demonstrate the application of polymer planar Bragg gratings for multi-axial strain sensing and particularly highlight simultaneous 2D strain measurement. A polymer planar Bragg grating (PPBG) fabricated with a single writing step in bulk polymethylmethacrylate is used for measuring both tensile and compressive strain at various angles. It is shown that the sensitivity of the PPBG strongly depends on the angle between the optical waveguide into which the grating is inscribed and the direction along which the mechanical load is applied. Additionally, a 2D PPBG fabricated by writing two Bragg gratings angularly displaced from each other into a single polymer platelet is bonded to a stainless steel plate. The two reflected wavelengths exhibit different sensitivities while tested toward tensile and compressive strain. These characteristics make 2D PPBG suitable for measuring multi-axial tensile and compressive strain. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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2801 KiB

Open AccessArticle

Spatial and Temporal Characteristics of Insulator Contaminations Revealed by Daily Observations of Equivalent Salt Deposit Density

by Ling Ruan, Ge Han, Zhongmin Zhu, Miao Zhang and Wei Gong

Sensors 2015, 15(2), 3023-3040; https://doi.org/10.3390/s150203023 - 29 Jan 2015

Cited by 5 | Viewed by 5686

Abstract

The accurate estimation of deposits adhering on insulators is of great significance to prevent pollution flashovers which cause huge costs worldwide. Researchers have developed sensors using different technologies to monitor insulator contamination on a fine time scale. However, there is lack of analysis [...] Read more.

The accurate estimation of deposits adhering on insulators is of great significance to prevent pollution flashovers which cause huge costs worldwide. Researchers have developed sensors using different technologies to monitor insulator contamination on a fine time scale. However, there is lack of analysis of these data to reveal spatial and temporal characteristics of insulator contamination, and as a result the scheduling of periodical maintenance of power facilities is highly dependent on personal experience. Owing to the deployment of novel sensors, daily Equivalent Salt Deposit Density (ESDD) observations of over two years were collected and analyzed for the first time. Results from 16 sites distributed in four regions of Hubei demonstrated that spatial heterogeneity can be seen at both the fine and coarse geographical scales, suggesting that current polluted area maps are necessary but are not sufficient conditions to guide the maintenance of power facilities. Both the local emission and the regional air pollution condition exert evident influences on deposit accumulation. A relationship between ESDD and PM₁₀ was revealed by using regression analysis, proving that air pollution exerts influence on pollution accumulations on insulators. Moreover, the seasonality of ESDD was discovered for the first time by means of time series analysis, which could help engineers select appropriate times to clean the contamination. Besides, the trend component shows that the ESDD increases in a negative exponential fashion with the accumulation date (ESDD = a − b × exp(−time)) at a long time scale in real environments. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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2313 KiB

Open AccessArticle

Frequency Noise Suppression of a Single Mode Laser with an Unbalanced Fiber Interferometer for Subnanometer Interferometry

by Radek Šmíd, Martin Čížek, Břetislav Mikel and Ondřej Číp

Sensors 2015, 15(1), 1342-1353; https://doi.org/10.3390/s150101342 - 12 Jan 2015

Cited by 11 | Viewed by 7070

Abstract

We present a method of noise suppression of laser diodes by an unbalanced Michelson fiber interferometer. The unstabilized laser source is represented by compact planar waveguide external cavity laser module, ORIONTM (Redfern Integrated Optics, Inc.), working at 1540.57 nm with a 1.5-kHz linewidth. [...] Read more.

We present a method of noise suppression of laser diodes by an unbalanced Michelson fiber interferometer. The unstabilized laser source is represented by compact planar waveguide external cavity laser module, ORIONTM (Redfern Integrated Optics, Inc.), working at 1540.57 nm with a 1.5-kHz linewidth. We built up the unbalanced Michelson interferometer with a 2.09 km-long arm based on the standard telecommunication single-mode fiber (SMF-28) spool to suppress the frequency noise by the servo-loop control by 20 dB to 40 dB within the Fourier frequency range, remaining the tuning range of the laser frequency. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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5048 KiB

Open AccessArticle

A Sensor-Type PC Strand with an Embedded FBG Sensor for Monitoring Prestress Forces

by Sung Tae Kim, YoungHwan Park, Sung Yong Park, Keunhee Cho and Jeong-Rae Cho

Sensors 2015, 15(1), 1060-1070; https://doi.org/10.3390/s150101060 - 8 Jan 2015

Cited by 66 | Viewed by 7091

Abstract

Prestressed Concrete Wire and Strand (PC) strands are the most used materials to introduce prestress in a Pre-Stressed Concrete (PSC) structure. However, it is difficult to evaluate the final prestress force of the PC strand after prestressing or its residual prestress force after [...] Read more.

Prestressed Concrete Wire and Strand (PC) strands are the most used materials to introduce prestress in a Pre-Stressed Concrete (PSC) structure. However, it is difficult to evaluate the final prestress force of the PC strand after prestressing or its residual prestress force after completion of the structure on site. This impossibility to assess eventual loss of prestress of the PC strand has resulted in a number of serious accidents and even in the collapse of several structures. This situation stresses the necessity to maintain the prestress force residual or after prestressing for the evaluation of the health of the concrete structure throughout its lifespan. Recently, several researchers have studied methods enabling one to verify the prestress force by inserting an optical fiber sensor inside the strand but failed to provide simple techniques for the fabrication of these devices to fulfill measurement performance from the design prestress to failure. Moreover, these methods require the additional installation of electrical resistance strain gages, displacement sensors and load cells on the outer surface of the structure for long-term precise measurement. This paper proposes a method enabling one to evaluate precisely and effectively the prestress force of the PC strand and intends to verify the applicability of the proposed method on actual concrete structures. To that end, an innovative PC strand is developed by embedding a Fiber Bragg Grating (FBG) sensor in the core wire of the PC strand so as to enable short term as well as long term monitoring. The measurement performance of the developed strand is then evaluated experimentally and the reliability of the monitoring data is assessed. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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1392 KiB

Open AccessArticle

All-Optical Graphene Oxide Humidity Sensors

by Weng Hong Lim, Yuen Kiat Yap, Wu Yi Chong and Harith Ahmad

Sensors 2014, 14(12), 24329-24337; https://doi.org/10.3390/s141224329 - 17 Dec 2014

Cited by 63 | Viewed by 7826

Abstract

The optical characteristics of graphene oxide (GO) were explored to design and fabricate a GO-based optical humidity sensor. GO film was coated onto a SU8 polymer channel waveguide using the drop-casting technique. The proposed sensor shows a high TE-mode absorption at 1550 nm. [...] Read more.

The optical characteristics of graphene oxide (GO) were explored to design and fabricate a GO-based optical humidity sensor. GO film was coated onto a SU8 polymer channel waveguide using the drop-casting technique. The proposed sensor shows a high TE-mode absorption at 1550 nm. Due to the dependence of the dielectric properties of the GO film on water content, this high TE-mode absorption decreases when the ambient relative humidity increases. The proposed sensor shows a rapid response (<1 s) to periodically interrupted humid air flow. The transmission of the proposed sensor shows a linear response of 0.553 dB/% RH in the range of 60% to 100% RH. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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2394 KiB

Open AccessArticle

A High Sensitivity and Wide Dynamic Range Fiber-Optic Sensor for Low-Concentration VOC Gas Detection

by Md. Rajibur Rahaman Khan and Shin-Won Kang

Sensors 2014, 14(12), 23321-23336; https://doi.org/10.3390/s141223321 - 5 Dec 2014

Cited by 31 | Viewed by 10411

Abstract

In this paper, we propose a volatile organic compound (VOC) gas sensing system with high sensitivity and a wide dynamic range that is based on the principle of the heterodyne frequency modulation method. According to this method, the time period of the sensing [...] Read more.

In this paper, we propose a volatile organic compound (VOC) gas sensing system with high sensitivity and a wide dynamic range that is based on the principle of the heterodyne frequency modulation method. According to this method, the time period of the sensing signal shift when Nile Red containing a VOC-sensitive membrane of a fiber-optic sensing element comes into contact with a VOC. This sensing membrane produces strong, fast and reversible signals when exposed to VOC gases. The response and recovery times of the proposed sensing system were less than 35 s, and good reproducibility and accuracy were obtained. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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Review of Trackside Monitoring Solutions: From Strain Gages to Optical Fibre Sensors

by Georges Kouroussis, Christophe Caucheteur, Damien Kinet, Georgios Alexandrou, Olivier Verlinden and Véronique Moeyaert

Sensors 2015, 15(8), 20115-20139; https://doi.org/10.3390/s150820115 - 14 Aug 2015

Cited by 105 | Viewed by 13677

Abstract

A review of recent research on structural monitoring in railway industry is proposed in this paper, with a special focus on stress-based solutions. After a brief analysis of the mechanical behaviour of ballasted railway tracks, an overview of the most common monitoring techniques [...] Read more.

A review of recent research on structural monitoring in railway industry is proposed in this paper, with a special focus on stress-based solutions. After a brief analysis of the mechanical behaviour of ballasted railway tracks, an overview of the most common monitoring techniques is presented. A special attention is paid on strain gages and accelerometers for which the accurate mounting position on the track is requisite. These types of solution are then compared to another modern approach based on the use of optical fibres. Besides, an in-depth discussion is made on the evolution of numerical models that investigate the interaction between railway vehicles and tracks. These models are used to validate experimental devices and to predict the best location(s) of the sensors. It is hoped that this review article will stimulate further research activities in this continuously expanding field. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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Fibre Optic Sensors for Structural Health Monitoring of Aircraft Composite Structures: Recent Advances and Applications

by Raffaella Di Sante

Sensors 2015, 15(8), 18666-18713; https://doi.org/10.3390/s150818666 - 30 Jul 2015

Cited by 582 | Viewed by 40650

Abstract

In-service structural health monitoring of composite aircraft structures plays a key role in the assessment of their performance and integrity. In recent years, Fibre Optic Sensors (FOS) have proved to be a potentially excellent technique for real-time in-situ monitoring of these structures due [...] Read more.

In-service structural health monitoring of composite aircraft structures plays a key role in the assessment of their performance and integrity. In recent years, Fibre Optic Sensors (FOS) have proved to be a potentially excellent technique for real-time in-situ monitoring of these structures due to their numerous advantages, such as immunity to electromagnetic interference, small size, light weight, durability, and high bandwidth, which allows a great number of sensors to operate in the same system, and the possibility to be integrated within the material. However, more effort is still needed to bring the technology to a fully mature readiness level. In this paper, recent research and applications in structural health monitoring of composite aircraft structures using FOS have been critically reviewed, considering both the multi-point and distributed sensing techniques. Full article

(This article belongs to the Special Issue Optical Sensors for Chemical, Biological and Industrial Applications)

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