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11 pages, 3115 KiB

Open AccessArticle

Experimental Study on Deformation Monitoring of Bored Pile Based on BOTDR

by Lei Gao, Chuan Han, Zhongquan Xu, Yingjie Jin and Jianqiang Yan

Appl. Sci. 2019, 9(12), 2435; https://doi.org/10.3390/app9122435 - 14 Jun 2019

Cited by 30 | Viewed by 2835

Abstract

In order to study the deformation of bored pile, it is necessary to monitor the strain of the pile. The distributed optical fiber sensing technology realizes the integration of sensing and transmission, which is incomparable with traditional point monitoring method. In this paper, [...] Read more.

In order to study the deformation of bored pile, it is necessary to monitor the strain of the pile. The distributed optical fiber sensing technology realizes the integration of sensing and transmission, which is incomparable with traditional point monitoring method. In this paper, the Brillouin optical time domain reflectometer (BOTDR) distributed optical fiber sensing technology is used to monitor the deformation of the bored pile. The raw data monitored by BOTDR is processed by the wavelet basis function, that can perform noise removal processing. Three different methods of noise removal are chosen. Through the processing, the db5 wavelet is used to decompose the deformation data of bored pile monitored by BOTDR into two layers. The decomposed high-frequency signal is denoised by the Stein-based unbiased risk threshold, rigrsure. The decomposed data is smoothed by the translational mean method, and the final data after denoising and smoothing processing is real and reliable. The results of this study will provide data support for the deformation characteristics of bored pile, and also show the advantages of distributed optical fiber sensing technology. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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11 pages, 4700 KiB

Open AccessArticle

High Temperature (Up to 950 °C) Sensor Based on Micro Taper In-Line Fiber Mach–Zehnder Interferometer

by Yun-Cheng Liao, Bin Liu, Juan Liu, Sheng-Peng Wan, Xing-Dao He, Jinhui Yuan, Xinyu Fan and Qiang Wu

Appl. Sci. 2019, 9(12), 2394; https://doi.org/10.3390/app9122394 - 12 Jun 2019

Cited by 17 | Viewed by 3390

Abstract

A high temperature (up to 950 °C) sensor was proposed and demonstrated based on a micro taper in-line fiber Mach–Zehnder interferometer (MZI) structure. The fiber MZI structure comprises a single mode fiber (SMF) with two micro tapers along its longitudinal direction. An annealing [...] Read more.

A high temperature (up to 950 °C) sensor was proposed and demonstrated based on a micro taper in-line fiber Mach–Zehnder interferometer (MZI) structure. The fiber MZI structure comprises a single mode fiber (SMF) with two micro tapers along its longitudinal direction. An annealing at 1000 °C was applied to the fiber sensor to stabilize the temperature measurement. The experimental results showed that the sensitivity was 0.114 nm/°C and 0.116 nm/°C for the heating and cooling cycles, respectively, and, after two days, the sensor still had a sensitivity of 0.11 nm/°C, showing a good stability of the sensor. A probe-type fiber MZI was designed by cutting the sandwiched SMF, which has good linear temperature responses of 0.113 nm/°C over a large temperature range from 89 to 950 °C. The probe-type fiber MZI temperature sensor was independent to the surrounding refractive index (RI) and immune to strain. The developed sensor has a wide application prospect in the fields of high temperature hot gas flow, as well as oil and gas field development. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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Schematic diagram of the micro taper in-line fiber Mach–Zehnder interferometer (MZI). Full article ">Figure 2
(a) The simulated spectral response of the fiber MZI with arm lengths L of 1, 2, and 3 cm, respectively; (b) the corresponding spatial frequency; (c,d) the distributions of the optical field and the normalized optical intensity propagating along the MZI with an arm length of 3 cm at dip a 1571.2 nm and peak b 1578.8 nm. Full article ">Figure 3
(a) Schematic diagram of the micro taper structure fabrication process; (b) the photo under microscope; (c–e) the spectral responses with a sandwiched single mode fiber (SMF) length of 1, 2, and 3 cm, respectively; (f) the fast Fourier transform (FFT) spatial frequency spectra with arm lengths of 1, 2, and 3 cm, respectively. (g) The FFT spatial frequency spectra with waist diameters of 50, 60, and 80 μm, respectively. Full article ">Figure 4
Schematic diagram of experimental setup for temperature, strain, and refractive index (RI) measurements. Full article ">Figure 5
Wavelength shift versus temperature for the MZI-based sensor (L = 3 cm): (a) Wavelength shift of a sensor with no-annealing process. (b) The corresponding stability test in 3 h before and after the annealing process at 1000 °C. (c) The same dip was chosen for annealing processes and in the inset an example of the temperature shifting of the sensor after annealing at 1000 °C for 3 h. Full article ">Figure 6
(a) Relationship between micro-stain and wavelength. (b) Relationship between RI and wavelength. Full article ">Figure 7
(a) Schematic diagram of the probe-type MZI. (b) Experimental setup. The inset figure is the optical microscope image of the probe-type MZI. BBS: Broadband source; OSA: Optical spectrum analyzer; SMF: Single mode fiber. Full article ">Figure 8
The transmission spectra of the proposed probe-type MZI with different B (interference length); (a–d) are 1, 1.5, 2, and 3 cm, respectively. Full article ">Figure 9
(a) Probe-type MZI-based sensor (B = 2 cm) stability test; (b) wavelength shift of the sensor during the heating and cooling of the after annealing. The inset figure is the temperature response of interference spectra from 89 to 950 °C. Full article ">

18 pages, 7261 KiB

Open AccessArticle

Framework and Application of a Big Data Monitoring System for Mining with a Pillar-Free Self-Forming Roadway

by Zhigang Tao, Xiaohui Zheng, Chun Zhu, Haijiang Zhang and Xiulian Zhang

Appl. Sci. 2019, 9(10), 2111; https://doi.org/10.3390/app9102111 - 23 May 2019

Cited by 5 | Viewed by 2881

Abstract

The construction of a self-formed roadway without coal pillars is a new mining technology based on short-arm beam formation through roof cutting. With it, mining, tunneling and retaining roadway construction can be accomplished in a ‘three-in-one’ process that removes the need to dig [...] Read more.

The construction of a self-formed roadway without coal pillars is a new mining technology based on short-arm beam formation through roof cutting. With it, mining, tunneling and retaining roadway construction can be accomplished in a ‘three-in-one’ process that removes the need to dig in advance at the working face and to leave behind coal pillars. In order to realize real-time monitoring and warnings regarding rock pressure during this process, a big data monitoring system was developed based on quasi-distributed fiber Bragg grating (FBG) sensing technology and cloud technology. Firstly, real-time monitoring data on the stress and strain of the underground surrounding rock-support system are obtained by FBG sensor and transmitted to the main computer of the above-ground monitoring and early warning system by using an underground industrial ring network. These data are then sent to a big data remote online real-time monitoring system. Through the deployment of a cloud server, authorized users can observe changes in force and movement in the rock surrounding the supporting system during coal mining and roadway formation from anywhere and at any time. The successful application of the system in the S1201-II working face of the Ning Tiaota Mine shows that this remote real-time monitoring system can enable timely and accurate field data acquisition, feedback real-time production information and achieve good monitoring performance. This study thus provides a scientific basis for ensuring safe mining with the coal pillar-free self-forming roadway method. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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9 pages, 1666 KiB

Open AccessArticle

Hybrid Grating in Reduced-Diameter Fiber for Temperature-Calibrated High-Sensitivity Refractive Index Sensing

by Biqiang Jiang, Zhen Hao, Dingyi Feng, Kaiming Zhou, Lin Zhang and Jianlin Zhao

Appl. Sci. 2019, 9(9), 1923; https://doi.org/10.3390/app9091923 - 10 May 2019

Cited by 6 | Viewed by 2773

Abstract

We propose and experimentally demonstrate a hybrid grating, in which an excessively tilted fiber grating (Ex-TFG) and a fiber Bragg grating (FBG) were co-inscribed in a reduced-diameter fiber (RDF). The hybrid grating showed strong resonances due to coupling among core mode and a [...] Read more.

We propose and experimentally demonstrate a hybrid grating, in which an excessively tilted fiber grating (Ex-TFG) and a fiber Bragg grating (FBG) were co-inscribed in a reduced-diameter fiber (RDF). The hybrid grating showed strong resonances due to coupling among core mode and a set of polarization-dependent cladding modes. This coupling showed enhanced evanescent fields by the reduced cladding size, thus allowing stronger interaction with the surrounding medium. Moreover, the FBG’s Bragg resonance confined by the thick cladding was exempt from the change of the surrounding medium’s refractive index (RI), and then the FBG can work as a temperature compensator. As a result, the Ex-TFG in RDF promised a highly sensitive RI measurement, with a sensitivity up to ~1224 nm/RIU near the RI of 1.38. Through simultaneous measurement of temperature and RI, the temperature dependence of water’s RI is then determined. Therefore, the proposed hybrid grating with a spectrum of multi-peaks embedded with a sharp Bragg resonance is a promising alternative for the simultaneous measurement of multi-parameters for many RI-based sensing applications. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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10 pages, 2780 KiB

Open AccessArticle

Reflective Fiber Surface Plasmon Resonance Sensor for High-Sensitive Mercury Ion Detection

by Zhenlin Chen, Kunlin Han and Ya-Nan Zhang

Appl. Sci. 2019, 9(7), 1480; https://doi.org/10.3390/app9071480 - 9 Apr 2019

Cited by 32 | Viewed by 4044

Abstract

This paper proposes a reflective fiber mercury ion sensor based on the surface plasmon resonance (SPR) principle and chitosan (CS)/polyacrylic acid (PAA) multilayer sensitive film. By optimizing the coating parameters of the gold film, the refractive index (RI) sensitivity of the reflective SPR [...] Read more.

This paper proposes a reflective fiber mercury ion sensor based on the surface plasmon resonance (SPR) principle and chitosan (CS)/polyacrylic acid (PAA) multilayer sensitive film. By optimizing the coating parameters of the gold film, the refractive index (RI) sensitivity of the reflective SPR sensor is demonstrated to be 2110.33 nm/RIU. Then, a multi-layer CS/PAA film is fixed on the surface of the gold film as a mercury ion sensitive film to form a reflective SPR fiber mercury ion sensor. Experimental results demonstrate that the sensor can be used to detect different concentrations of mercury ions with a high sensitivity of 0.5586 nm/μM and good specificity and repeatability. Therefore, the reflective SPR fiber mercury ion sensor shows great promise for future applications of environmental monitoring and drinking water safety. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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Schematic diagram of the sensing principles. Full article ">Figure 2
Variation of the simulated SPR spectra along with the changes of the gold film length (a), gold film thickness (b), and surrounding refractive index (c). Full article ">Figure 3
Experimental SPR spectra when the Au film is coated with different coating currents (a) and coating times (b). Full article ">Figure 4
Optical fiber surface micrographs before and after Au film coating. Full article ">Figure 5
Coating process of the Hg2+ sensitive film. Full article ">Figure 6
Reflective fiber SPR Hg2+ measurement system. Full article ">Figure 7
Resonant spectra (a) and linear fitting result (b) of a reflective fiber SPR sensor in refractive index measurement. Full article ">Figure 8
Comparison of wavelength shifts for SPR sensors with different numbers of layers of sensitive film. Full article ">Figure 9
Resonant spectra (a) and linear fitting result (b) of the reflective fiber SPR sensor in the Hg2+ concentration measurement. Full article ">Figure 10
Resonant spectra (a) and wavelength shifts (b) of the reflective fiber SPR sensor in different metal ions. Full article ">Figure 11
Repetitive experiment of the SPR Hg2+ sensor in different Hg2+ concentrations (a) and the same Hg2+ concentration (b). Full article ">

15 pages, 5853 KiB

Open AccessArticle

Wing Load and Angle of Attack Identification by Integrating Optical Fiber Sensing and Neural Network Approach in Wind Tunnel Test

by Daichi Wada and Masato Tamayama

Appl. Sci. 2019, 9(7), 1461; https://doi.org/10.3390/app9071461 - 8 Apr 2019

Cited by 9 | Viewed by 3449

Abstract

The load and angle of attack (AoA) for wing structures are critical parameters to be monitored for efficient operation of an aircraft. This study presents wing load and AoA identification techniques by integrating an optical fiber sensing technique and a neural network approach. [...] Read more.

The load and angle of attack (AoA) for wing structures are critical parameters to be monitored for efficient operation of an aircraft. This study presents wing load and AoA identification techniques by integrating an optical fiber sensing technique and a neural network approach. We developed a 3.6-m semi-spanned wing model with eight flaps and bonded two optical fibers with 30 fiber Bragg gratings (FBGs) each along the main and aft spars. Using this model in a wind tunnel test, we demonstrate load and AoA identification through a neural network approach. We input the FBG data and the eight flap angles to a neural network and output estimated load distributions on the eight wing segments. Thereafter, we identify the AoA by using the estimated load distributions and the flap angles through another neural network. This multi-neural-network process requires only the FBG and flap angle data to be measured. We successfully identified the load distributions with an error range of −1.5–1.4 N and a standard deviation of 0.57 N. The AoA was also successfully identified with error ranges of −1.03–0.46° and a standard deviation of 0.38°. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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11 pages, 3080 KiB

Open AccessArticle

Optical Properties of Buffers and Cell Culture Media for Optofluidic and Sensing Applications

by Van Thuy Hoang, Grzegorz Stępniewski, Karolina H. Czarnecka, Rafał Kasztelanic, Van Cao Long, Khoa Dinh Xuan, Liyang Shao, Mateusz Śmietana and Ryszard Buczyński

Appl. Sci. 2019, 9(6), 1145; https://doi.org/10.3390/app9061145 - 18 Mar 2019

Cited by 46 | Viewed by 6813

Abstract

Interactions between light and various cells in cultures, such as bacteria or mammalian cells, are widely applied for optical sensors and optofluidic systems. These microorganisms need to be kept in proper aqueous media, referred to as buffers or cell culture media, that are [...] Read more.

Interactions between light and various cells in cultures, such as bacteria or mammalian cells, are widely applied for optical sensors and optofluidic systems. These microorganisms need to be kept in proper aqueous media, referred to as buffers or cell culture media, that are required, respectively, for stable storage or delivering biochemical nutrients for their growth. When experiments or numerical analyses on optical devices are performed, the properties of these media are usually considered to be similar to those of pure water, with negligible influence of biochemical compounds on the medium’s optical properties. In this work, we investigated the transmission, material dispersion, and scattering properties of selected and widely used buffers and cell culture media. We show that the optical properties of these media may significantly vary from those of water. Well-defined properties of buffers and cell culture media are essential for proper design of various optical sensing or future optofluidic systems dealing with biological structures. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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Scheme of the setup used for measuring (a) transmission and (b) material dispersion of the liquids. Full article ">Figure 2
Scheme of the setup used for measuring scattering properties. Full article ">Figure 3
The transmission of the investigated liquids measured in the 10-mm-long cuvette. Results for pure water are provided for reference. Legend: TBE—TRIS-Borate-EDTA Buffer; PBS—Dulbecco’s Phosphate Buffered Saline solution; EXPRESS 5—Cell culture medium Express Five™ SFM; DMEM—Cell culture medium Dulbecco’s Modified Eagle’s Medium. Full article ">Figure 4
The effect of long-term handling on transmission characteristics of (a) DMEM, (b) EXPRESS 5, (c) TBE, and (d) PBS. Legend: TBE—TRIS-Borate-EDTA Buffer; PBS—Dulbecco’s Phosphate Buffered Saline solution; EXPRESS 5—Cell culture medium Express Five™ SFM; DMEM—Cell culture medium Dulbecco’s Modified Eagle’s Medium. Full article ">Figure 5
(a) Group and (b) phase refractive indices measured for the investigated liquids. Legend: TBE—TRIS-Borate-EDTA Buffer; PBS—Dulbecco’s Phosphate Buffered Saline solution; EXPRESS 5—Cell culture medium Express Five™ SFM; DMEM—Cell culture medium Dulbecco’s Modified Eagle’s Medium. Full article ">Figure 6
Scattering properties of the investigated liquids. Legend: TBE—TRIS-Borate-EDTA Buffer; PBS—Dulbecco’s Phosphate Buffered Saline solution; EXPRESS 5—Cell culture medium Express Five™ SFM; DMEM—Cell culture medium Dulbecco’s Modified Eagle’s Medium. Full article ">Figure 7
Light scattering characteristics after 3- and 8-months-long storage time for (a) DMEM, (b) EXPRESS 5, (c) TBE, and (d) PBS. Legend: TBE—TRIS-Borate-EDTA Buffer; PBS—Dulbecco’s Phosphate Buffered Saline solution; EXPRESS 5—Cell culture medium Express Five™ SFM; DMEM—Cell culture medium Dulbecco’s Modified Eagle’s Medium. Full article ">

11 pages, 2479 KiB

Open AccessArticle

Influence of Initial Phase Modulation on the Sensitivity of the Optical Fiber Sagnac Acoustic Emission Sensor

by Zhuming Cheng, Jie Zeng, Dakai Liang, Chen Chang and Bing Wang

Appl. Sci. 2019, 9(5), 1018; https://doi.org/10.3390/app9051018 - 12 Mar 2019

Cited by 4 | Viewed by 3032

Abstract

Improving the phase sensitivity of the optical fiber Sagnac sensor is very important for accurately detecting weak signals of acoustic emission. Theoretical analysis shows that the initial phase of the sensor is π under ideal conditions, and the maximum phase sensitivity is obtained [...] Read more.

Improving the phase sensitivity of the optical fiber Sagnac sensor is very important for accurately detecting weak signals of acoustic emission. Theoretical analysis shows that the initial phase of the sensor is π under ideal conditions, and the maximum phase sensitivity is obtained when the bias phase is π/2. In this work, an experimental system was built with an aluminum alloy plate as the experimental object. The initial phase of the sensor was modulated by a Y-branch waveguide, and the fitting curve of the experimental data was in good agreement with the curve of the numerical simulation. Moreover, our experiments show there was a single value for the bias phase of π/2, which significantly deviated from the theoretical value. The results show that the greatest phase sensitivity of the sensor not only could be increased by nearly nine times through modulating the initial phase, but also could suppress the harmonic interferences in the sensing system. This study can provide a useful reference for improving the phase sensitivity of the optical fiber Sagnac AE sensor in practical applications. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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Principle of the optical fiber Sagnac acoustic emission (AE) sensor. Full article ">Figure 2
Ooutput voltage signal without phase modulation in the numerical simulation. (a) Output voltage waveform; (b) corresponding frequency spectrum. Full article ">Figure 3
Output voltage with a phase modulation of <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>ϕ</mi> <mo>=</mo> <mi mathvariant="sans-serif">π</mi> <mo>/</mo> <mn>2</mn> </mrow> </semantics></math> in the numerical simulation. (a) Output voltage waveform; (b) corresponding frequency spectrum. Full article ">Figure 4
Relationship between the amplitude of the output fundamental voltage and <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>ϕ</mi> </mrow> </semantics></math>. The red scatter points represent the simulative values, and the blue curve is the corresponding fitting curve. Full article ">Figure 5
Experimental system of the optical fiber Sagnac AE sensor. Full article ">Figure 6
Output voltage of the sensor without phase modulation in the experiments. (a) Output voltage waveform; (b) Corresponding frequency spectrum. Full article ">Figure 7
Output voltage of the sensor with a phase modulation of <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>ϕ</mi> <mo>=</mo> <mi mathvariant="sans-serif">π</mi> <mo>/</mo> <mn>2</mn> </mrow> </semantics></math> in the experiments. (a) Output voltage waveform; (b) Corresponding frequency spectrum. Full article ">Figure 8
Result of experimental fitting. The horizontal axis represents the amplitude of the modulation voltage, and the longitudinal axis represents the amplitude of the fundamental voltage. Full article ">

14 pages, 2784 KiB

Open AccessArticle

Fiber Optic Sensing for Geomechanical Monitoring: (2)- Distributed Strain Measurements at a Pumping Test and Geomechanical Modeling of Deformation of Reservoir Rocks

by Xinglin Lei, Ziqiu Xue and Tsutomu Hashimoto

Appl. Sci. 2019, 9(3), 417; https://doi.org/10.3390/app9030417 - 26 Jan 2019

Cited by 23 | Viewed by 4310

Abstract

In this study distributed fiber optic sensing has been used to measure strain along a vertical well of a depth of 300 m during a pumping test. The observed strain data has been used in geomechanical simulation, in which a combined analytical and [...] Read more.

In this study distributed fiber optic sensing has been used to measure strain along a vertical well of a depth of 300 m during a pumping test. The observed strain data has been used in geomechanical simulation, in which a combined analytical and numerical approach was applied in providing scaled-up formation properties. The outcomes of the field test have demonstrated the practical use of distributed fiber optic strain sensing for monitoring reservoir formation responses at different regions of sandstone–mudstone alternations along a continuous trajectory. It also demonstrated that sensitive and scaled rock properties, including the equivalent permeability and pore compressibility, can be well constrained by the combined use of water head and distributed strain data. In comparison with the conventional methods, fiber optic strain monitoring enables a lower number of short-term tests to be designed to calibrate the parameters used to model the rock properties. The obtained parameters can be directly used in long-term geomechanical simulation of deformation of reservoir rocks due to fluid injection or production at the CO₂ storage and oil and gas fields. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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15 pages, 4607 KiB

Open AccessArticle

Characteristic Analysis and Experiment of Adaptive Fiber Optic Current Sensor Technology

by Yansong Li, Weiwei Zhang, Xinying Liu and Jun Liu

Appl. Sci. 2019, 9(2), 333; https://doi.org/10.3390/app9020333 - 18 Jan 2019

Cited by 17 | Viewed by 4377

Abstract

The straight-through magneto-optical glass current sensor has desirable temperature properties, but it is vulnerable to magnetic interference. In contrast, a polarization-type fiber optic current sensor has poor temperature performance, but the magnetic anti-interference characteristic is very good. Aiming at the problem that the [...] Read more.

The straight-through magneto-optical glass current sensor has desirable temperature properties, but it is vulnerable to magnetic interference. In contrast, a polarization-type fiber optic current sensor has poor temperature performance, but the magnetic anti-interference characteristic is very good. Aiming at the problem that the accuracy of a fiber optic current sensor is susceptible to external disturbances and temperature fluctuations, we present an adaptive technology of a fiber optic current sensor that uses the magneto-optical output signal to correct the fiber output signal. The working principle of the improved method is introduced in this paper. The structure of the specific optical system and the signal processing system are presented. Temperature fluctuation and magnetic change detection units are included in the design in order to provide signal selection under different environmental fluctuations, thus stabilizing the output current data. The signal processing system was proved to be effective by building an experimental platform. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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19 pages, 6532 KiB

Open AccessArticle

Denoising of the Fiber Bragg Grating Deformation Spectrum Signal Using Variational Mode Decomposition Combined with Wavelet Thresholding

by Weifang Zhang, Meng Zhang, Yan Zhao, Bo Jin and Wei Dai

Appl. Sci. 2019, 9(1), 180; https://doi.org/10.3390/app9010180 - 6 Jan 2019

Cited by 16 | Viewed by 3261

Abstract

Damage detection using an FBG sensor is a critical process for an assessment of any inspection technology classified as structural health monitoring (SHM). FBG signals containing noise in experiments are developed to detect flaws. In this paper, we propose a novel signal denoising [...] Read more.

Damage detection using an FBG sensor is a critical process for an assessment of any inspection technology classified as structural health monitoring (SHM). FBG signals containing noise in experiments are developed to detect flaws. In this paper, we propose a novel signal denoising method that combines variational mode decomposition (VMD) and changed thresholding wavelets to denoise experimental and mixed signals. VMD is a recently introduced adaptive signal decomposition algorithm. Compared with traditional empirical mode decomposition (EMD), and it is well founded theoretically and more robust to noise samples. First, input signals were broken down into a given number of K band-limited intrinsic mode functions (BLIMFs) by VMD. For the purpose of avoiding the impact of overbinning or underbinning on VMD denoising, the mixed signals, which were obtained by adding different signal/noise ratio (SNR) noises to the experimental signals, were designed to select the best decomposition number K and data-fidelity constraint parameter α. After that, the realistic experimental signals were processed using four denoising algorithms to evaluate denoising performance. The results show that, upon adding additional noisy signals and realistic signals, the proposed algorithm delivers excellent performance over the EMD-based denoising method and discrete wavelet transform filtering. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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17 pages, 24586 KiB

Open AccessArticle

Use of Fiber-Optic Sensors for the Detection of the Rail Vehicles and Monitoring of the Rock Mass Dynamic Response Due to Railway Rolling Stock for the Civil Engineering Needs

by Jan Nedoma, Martin Stolarik, Marcel Fajkus, Miroslav Pinka and Stanislav Hejduk

Appl. Sci. 2019, 9(1), 134; https://doi.org/10.3390/app9010134 - 2 Jan 2019

Cited by 17 | Viewed by 4152

Abstract

The paper describes the original results of a comparative study of the standard seismic station vs. a novel interferometric sensor for civil engineering needs. The presented results showed that to implement seismic measurements using standard seismic stations, a method using a fiber optic [...] Read more.

The paper describes the original results of a comparative study of the standard seismic station vs. a novel interferometric sensor for civil engineering needs. The presented results showed that to implement seismic measurements using standard seismic stations, a method using a fiber optic interferometer may serve as an alternative. We presented time records and the frequency spectra obtained from experimental measurements of the dynamic response of the upper rock mass beneath passing tram vehicles (a total of 769 passes) over a period of five months of practical measurements under various climatic conditions. The fiber-optic sensor detected all phenomena at a 100% rate, and the recorded results were compared to the results from a standard seismic station. Both sets of results were recorded simultaneously and agreed significantly, especially in terms of frequency. With regard to time, all tram vehicle axles were detected in individual time records. With regard to frequency, the results detected in the bandwidth generally correlated to rail transport for individual types of tram vehicles. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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11 pages, 3007 KiB

Open AccessCommunication

Game Theory in Molecular Nanosensing System for Rapid Detection of Hg²⁺ in Aqueous Solutions

by Nan Fang Nie, Xin Xing Zhang, Chu Shan Fang, Qiu Yan Zhu, Jiao Yang Lu, Fu Rui Zhang, Qing Feng Yao, Wei Tao Huang, Xue Zhi Ding and Li Qiu Xia

Appl. Sci. 2018, 8(12), 2530; https://doi.org/10.3390/app8122530 - 7 Dec 2018

Cited by 5 | Viewed by 2875

Abstract

Game theory—the scientific study of interactive, rational decision making—describes the interaction of two or more players from macroscopic organisms to microscopic cellular and subcellular levels. Life based on molecules is the highest and most complex expression of molecular interactions. However, using simple molecules [...] Read more.

Game theory—the scientific study of interactive, rational decision making—describes the interaction of two or more players from macroscopic organisms to microscopic cellular and subcellular levels. Life based on molecules is the highest and most complex expression of molecular interactions. However, using simple molecules to expand game theory for molecular decision-making remains challenging. Herein, we demonstrate a proof-of-concept molecular game-theoretical system (molecular prisoner’s dilemma) that relies on formation of the thymine–Hg²⁺–thymine hairpin structure specifically induced by Hg²⁺ and fluorescence quenching and molecular adsorption capacities of cobalt oxyhydroxide (CoOOH) nanosheets, resulting in fluorescence intensity and distribution change of polythymine oligonucleotide 33-repeat thymines (T33). The “bait” molecule, T33, interacted with two molecular players, CoOOH and Hg²⁺, in different states (absence = silence and presence = betrayal), regarded as strategies. We created conflicts (sharing or self-interest) of fluorescence distribution of T33, quantifiable in a 2 × 2 payoff matrix. In addition, the molecular game-theoretical-system based on T33 and CoOOH was used for sensing Hg²⁺ over the range of 20 to 600 nM with the detection limit of 7.94 nM (3σ) and for determination of Hg²⁺ in pond water. Inspired by the proof-of-concept for molecular game theory, various molecular decision-making systems could be developed, which would help promote molecular information processing and generating novel molecular intelligent decision systems for environmental monitoring and molecular diagnosis and therapy. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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Graphical abstract

Graphical abstract
Full article ">Figure 1
Schematic illustration and fluorescence emission spectra change of an artificial molecular system based on molecular interactions among polythymine oligonucleotide T33, metal ions (Hg2+), CoOOH nanosheets. (a–c) the formation of T33–CoOOH (a); T–Hg2+–T pairs (b); T33–CoOOH–Hg2+ (c). T33: 100 nM, CoOOH nanosheets: 4.69 μg/mL, Hg2+: 10 μM. The excitation and emission wavelength are 485 and 520 nm. The fluorescence intensity is normalized. Buffer: 5 mM Tris-HCl buffer solution (pH 7.4); FAM: carboxyfluorescein; CoOOH: cobalt oxyhydroxide. Full article ">Figure 2
Representative atomic force microscopy (AFM) images and height analysis of (A) CoOOH; (B) T33–CoOOH; and (C) T33–CoOOH–Hg2+. Full article ">Figure 3
(A) Absorption response of T33 (a1, 1 μM) and T33–CoOOH (a2, 1 μM:46.9 μg/mL) on addition of Hg2+ ions; (B) CD spectra of T33 (b1, 5 μM) and T33–CoOOH (b2, 5 μM:234.5 μg/mL) on addition of Hg2+ ions. Buffer: 5 mM Tris-HCl, pH 7.4; (C) Fluorescence responses of the T33–CoOOH complex to T33’s fully complementary DNA A33. T33: 100 nM, CoOOH nanosheets: 4.69 μg/mL, A33: 300 nM. Full article ">Figure 4
(A) Generalized payoff matrix for prisoner’s dilemma where the two players are represented by red and black, and each player chooses to either silence or betrayal; (B) Realized payoff matrix for the molecular interaction of the bait molecule T33 with two molecular players, CoOOH and Hg2+, with different states (absence = silence and presence = betrayal) regarded as strategies, resulting in conflicts (sharing or self-interest) of fluorescence distribution change of T33, which conforms to the prisoner’s dilemma. Full article ">Figure 5
(A) Fluorescence emission spectra of T33–CoOOH complex (100 nM:4.69 µg/mL) upon addition of various concentrations of Hg2+ (from top to bottom: 0, 20, 80, 139, 198, 259, 320, 381, 441, 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800, and 2000 nM); (B) The dependence of the fluorescence intensity changes (F0 − F)/F0 at 520 nm on the concentration of Hg2+; (C) The linear relationship between (F0 − F)/F0 and the Hg2+ concentrations in the range from 20 to 600 nM; (D) The selectivity of the T33–CoOOH complex (100 nM:4.69 μg/mL) for Hg2+ assay (Hg2+: 600 nM, other metal ions: 1.2 μM). Buffer: 5 mM Tris-HCl, pH 7.4. Full article ">

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Open AccessReview

Reviews on Corrugated Diaphragms in Miniature Fiber-Optic Pressure Sensors

by Honglin Li, Hui Deng, Guangqi Zheng, Mingguang Shan, Zhi Zhong and Bin Liu

Appl. Sci. 2019, 9(11), 2241; https://doi.org/10.3390/app9112241 - 30 May 2019

Cited by 13 | Viewed by 5690

Abstract

Corrugated diaphragms (CDs) have been widely used in many fields because of their higher pressure sensitivity and wider linear range compared to flat diaphragms (FDs) in the same circumstances. Especially in the application of miniature fiber-optic pressure sensors, the introduction of the corrugated [...] Read more.

Corrugated diaphragms (CDs) have been widely used in many fields because of their higher pressure sensitivity and wider linear range compared to flat diaphragms (FDs) in the same circumstances. Especially in the application of miniature fiber-optic pressure sensors, the introduction of the corrugated structure gives the sensor high sensitivity, large dynamic range, good linearity, small hysteresis, good stability, and so on. Research on CD-based miniature fiber-optic pressure sensors has gradually attracted more attention in recent years. In this paper, the principles of operation of a miniature fiber-optic pressure sensor are briefly introduced, then the mechanical properties of FD and CD, as well as their influences on the performance of the sensor, are analyzed in detail. The application status of CDs in miniature fiber-optic pressure sensors is reviewed, and our conclusions and the prospects for the application of CDs in miniature fiber-optic pressure sensors are given finally. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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22 pages, 4394 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in Plasmonic Sensor-Based Fiber Optic Probes for Biological Applications

by M. S. Aruna Gandhi, Suoda Chu, K. Senthilnathan, P. Ramesh Babu, K. Nakkeeran and Qian Li

Appl. Sci. 2019, 9(5), 949; https://doi.org/10.3390/app9050949 - 6 Mar 2019

Cited by 119 | Viewed by 13753

Abstract

The survey focuses on the most significant contributions in the field of fiber optic plasmonic sensors (FOPS) in recent years. FOPSs are plasmonic sensor-based fiber optic probes that use an optical field to measure the biological agents. Owing to their high sensitivity, high [...] Read more.

The survey focuses on the most significant contributions in the field of fiber optic plasmonic sensors (FOPS) in recent years. FOPSs are plasmonic sensor-based fiber optic probes that use an optical field to measure the biological agents. Owing to their high sensitivity, high resolution, and low cost, FOPS turn out to be potential alternatives to conventional biological fiber optic sensors. FOPS use optical transduction mechanisms to enhance sensitivity and resolution. The optical transduction mechanisms of FOPS with different geometrical structures and the photonic properties of the geometries are discussed in detail. The studies of optical properties with a combination of suitable materials for testing the biosamples allow for diagnosing diseases in the medical field. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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Other

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7 pages, 2275 KiB

Open AccessLetter

Ultra-Small Fiber Bragg Grating Accelerometer

by Kuo Li, Guoyong Liu, Yuqing Li, Jun Yang and Wenlong Ma

Appl. Sci. 2019, 9(13), 2707; https://doi.org/10.3390/app9132707 - 3 Jul 2019

Cited by 10 | Viewed by 2388

Abstract

Reducing the size of an accelerometer overcomes the tradeoff between its sensitivity and resonant frequency, and the theoretical relationships are analyzed. A fiber Bragg grating (FBG) accelerometer with the shortest vibration arm, 7 mm, among FBG accelerometers using the optical fiber to hold [...] Read more.

Reducing the size of an accelerometer overcomes the tradeoff between its sensitivity and resonant frequency, and the theoretical relationships are analyzed. A fiber Bragg grating (FBG) accelerometer with the shortest vibration arm, 7 mm, among FBG accelerometers using the optical fiber to hold its inertial object is demonstrated here. The inertial object was 4.41 g. The experimental crest-to-trough sensitivity and resonant frequency, 244 pm/g and 90 Hz, disagree with the theoretical values, 633 pm/g and 67 Hz, perhaps due to the friction between the inertial object and shell. In order to find the theoretical values, a method to find the pre-stretch of the FBG is also presented here, based on the stretch of the FBG at equilibrium and the mass of the inertial object. The FFT program, experimental data and theoretical calculations are presented in detail in the ^{Supplementary Material}. Full article

(This article belongs to the Special Issue Recent Progress in Fiber Optic Sensors: Bringing Light to Measurement)

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