Microbend Sensor Research Articles

Vital Sign Monitoring for Cancer Patients Based on Dual-Path Sensor and Divided-Frequency-CNN Model.

Monitoring vital signs is a key part of standard medical care for cancer patients. However, the traditional methods have instability especially when big fluctuations of signals happen, while the deep-learning-based methods lack pertinence to the sensors. A dual-path micro-bend optical fiber sensor and a targeted model based on the Divided-Frequency-CNN (DFC) are developed in this paper to measure the heart rate (HR) and respiratory rate (RR). For each path, features of frequency division based on the mechanism of signal periodicity cooperate with the operation of stable phase extraction to reduce the interference of body movements for monitoring. Then, the DFC model is designed to learn the inner information from the features robustly. Lastly, a weighted strategy is used to estimate the HR and RR via dual paths to increase the anti-interference for errors from one source. The experiments were carried out on the actual clinical data of cancer patients by a hospital. The results show that the proposed method has good performance in error (3.51 (4.51 %) and 2.53 (3.28 %) beats per minute (bpm) for cancer patients with pain and without pain respectively), relevance, and consistency with the values from hospital equipment. Besides, the proposed method significantly improved the ability in the report time interval (30 to 9 min), and mean / confidential interval (3.60/[-22.61,29.81] to -0.64 / [-9.21,7.92] for patients with pain and 1.87 / [-5.49,9.23] to -0.16 / [-6.21,5.89] for patients without pain) compared with our previous work.

A Wearable Sandwich Heterostructure Multimode Fiber Optic Microbend Sensor for Vital Signal Monitoring.

This work proposes a highly sensitive sandwich heterostructure multimode optical fiber microbend sensor for heart rate (HR), respiratory rate (RR), and ballistocardiography (BCG) monitoring, which is fabricated by combining a sandwich heterostructure multimode fiber Mach-Zehnder interferometer (SHMF-MZI) with a microbend deformer. The parameters of the SHMF-MZI sensor and the microbend deformer were analyzed and optimized in detail, and then the new encapsulated method of the wearable device was put forward. The proposed wearable sensor could greatly enhance the response to the HR signal. The performances for HR, RR, and BCG monitoring were as good as those of the medically approved commercial monitors. The sensor has the advantages of high sensitivity, easy fabrication, and good stability, providing the potential for application in the field of daily supervision and health monitoring.

Evaluation of recycled concrete aggregate in reinforced concrete elements under simulated corrosion conditions utilising diverse non-destructive methods

ABSTRACT In this study, the performance of recycled concrete aggregate (RCA/RSA) available in Agartala, Tripura (north-eastern regions of India), was studied in reinforced concrete members subjected to a severe artificially induced corrosive environment. The performance test was based on the non-destructive and destructive parameters of concrete. Due to the scarcity of normal stone aggregate (NSA) in this region, studying the effect of using such type of aggregate in reinforced concrete members help not only to mitigate the demand but also assists in waste management. The study also presents an innovative application of micro-bend opticalfibre sensors for corrosion monitoring and validated using other non-destructive instruments. The study presents an effective application of the micro-bend optical fibre sensor to predict the initiation of corrosion (de-passivation) and initiation of cracking (critical stress) due to corrosion in reinforced concrete specimens. Later, the results were validated using half-cell potentiometer and electrical strain gauge values. The specimen also presented different mechanical and durability properties with varying RCA percentages. A regression model to predict mechanical properties and corrosion amount (hoop strain) in reinforcement for different RCA-replaced concrete has been presented. The sorptivity and other porosity-related results were also presented for different RCA replacement percentage specimens.

Combined application of an optical sensor and a common non-destructive instrument for corrosion monitoring in reinforced concrete members

The reliable monitoring of the progression or extent of pitting-type corrosion in reinforced concrete members requires great effort due to non-uniformity. This paper presents a new approach for measuring the progression and extent of pitting-type (non-uniform) corrosion in reinforced concrete members by combining both non-destructive testing with optical fibre sensing results. Accelerated corrosion on the reinforcement (rebar) of the specimen was produced artificially using an alternate wetting and drying process in sodium chloride solution with 7.5% and 10% concentrations. The multimode optical fibre patch cords were attached to the reinforcement in three different arrangements in a single specimen (normal optical patch cord and loose and firm microbend patch cords). Intensity loss in a propagating light travelling inside an optical fibre takes place due to the development of pressure from surrounding concrete on the fibre from rust formation (corrosion). The study also describes the effect of corrosion in half-cell potentiometer, chloride ion resistivity and indirect pulse velocity readings obtained from the specimen. A later study found that the use of an optical microbend sensor is an effective alternate method for determining the starting time of initial depassivation in the reinforcement and validates it using half-cell potentiometer values. The study also developed models to predict overall mass loss in the rebar due to corrosion using combined non-destructive testing methods.

Low-cost real-time fiber optic sensor for intrusion detection

PurposeThe purpose of this paper is to introduce a novel intensity-modulated fiber optic sensor for real-time intrusion detection using a fiber-optic microbend sensor and an optical time-domain reflectometer (OTDR).Design/methodology/approachThe proposed system is tested using different scenarios using person/car as intruders. Experiments are conducted in the lab and in the field. In the beginning, the OTDR trace is obtained and recorded as a reference signal without intrusion events. The second step is to capture the OTDR trace with intrusion events in one or multiple sectors. This measured signal is then compared to the reference signal and processed by matrix laboratory to determine the intruded sector. Information of the intrusion is displayed on an interactive screen implemented by Visual basic. The deformer is designed and implemented using SOLIDWORKS three-dimensional computer aided design Software.FindingsThe system is tested for intrusions by performing two experiments. The first experiment is performed for both persons (>50 kg) in the lab and cars in an open field with a car moving at 60 km/h using two optical fiber sectors of lengths 200 and 500 m. For test purposes, the deformer length used in the experiment is 2 m. The used signal processing technique in the first experiment has some limitations and its accuracy is 70% after measuring and recording 100 observations. To overcome these limitations, a second experiment with another technique of signal processing is performed.Research limitations/implicationsThe system can perfectly display consecutive intrusions of the sectors, but in case of simultaneous intrusions of different sectors, which is difficult to take place in real situations, there will be the ambiguity of the number of intruders and the intruded sector. This will be addressed in future work. Suitable and stable laser power is required to get a suitable level of backscattered power. Optimization of the deformer is required to enhance the sensitivity and reliability of the sensor.Practical implicationsThe proposed work enables us to benefit from the ease of implementation and the reduced cost of the intensity-modulated fiber optic sensors because it overcomes the constraints that prevent using the intensity-modulated fiber optic sensors for intrusion detection.Originality/valueThe proposed system is the first time long-range intensity-modulated fiber optic sensor for intrusion detection.

Two-dimensional microbend sensor based on the 2-core fiber with hump-shaped taper fiber structure

Abstract A novel two-dimensional bending vector sensor formed by cascading two hump-shaped tapers (HSTs) in a segment of 2-core fiber (2CF) is proposed and fabricated, in which the HSTs serve as the mode splitting and coupling. Several modes are excited at the first HSTs, where a part of the light energy is propagated within the center core of the 2CF, and the other part is coupled to the external core. Due to the effective refractive index difference between these core modes, they are recoupled into the lead-out single-mode fiber (SMF) at the second HSTs and interfere with each other. The bulge of the HSTs and two cores of the 2CF are distributed in a triangle. Owing to the asymmetric structure, the sensor can distinguish multiple bending directions. In addition, the linear spectral responses for bending and temperature are observed experimentally. The proposed sensor has many advantages, including compact, inexpensive, and high directional resolution ratio. Experiment results show that the sensor can distinguish bending directions and experience a maximum sensitivity of −6.182 nm/m−1 with a bending range of 0–0.98 m−1 without dead zone.

Micro-bending sensor made from polydimethylsiloxane

W artykule opisano konstrukcje czujnika ugiecia wykonanego z polydimethylsiloxanu. Zbadano trzy alternatywne konstrukcje i określono mase obliczeniowoą przy zalozeniu ze poziom tlumienia jest znany. Zbadano tez praktyczne zastosowanie czujnika jako detektora krokow.

Designing and Constructing the Strain Sensor Using Microbend Multimode Fiber

The microbend sensor is designed to experience a light loss when force is applied to the sensor. The periodic microbends cause propagating light to couple into higher order modes, the existing higher order modes become unguided modes. Three models of deform cells are fabricated at (3, 5, 8) mm pitchand tested by using MMF and laser source at 850 nm. The maximum output power of (8, 5, 3)mm model is (3, 2.7, 2.55)nW respectively at applied force 5N and the minimum value is (1.9, 1.65, 1.5)nW respectively at 60N.The strain is calculated at different microbend cells ,and the best sensitivity of this sensor for cell 8mm is equal to 0.6nW/N.

Designing and Constructing the Strain Sensor Using Microbend Multimode Fiber

The microbend sensor is designed to experience a light loss when force is applied to the sensor. The periodic microbends cause propagating light to couple into higher order modes, the existing higher order modes become unguided modes. Three models of deform cells are fabricated at (3, 5, 8) mm pitchand tested by using MMF and laser source at 850 nm. The maximum output power of (8, 5, 3)mm model is (3, 2.7, 2.55)nW respectively at applied force 5N and the minimum value is (1.9, 1.65, 1.5)nW respectively at 60N.The strain is calculated at different microbend cells ,and the best sensitivity of this sensor for cell 8mm is equal to 0.6nW/N.

Two-dimensional microbend sensor based on long-period fiber gratings in an isosceles triangle arrangement three-core fiber.

To realize the 2D microbend sensor, we design and fabricate two non-orthogonal long-period fiber gratings (LPFGs) in an isosceles triangle arrangement three-core optical fiber which is made in our lab, making an isosceles triangle arrangement three-core optical fiber. To mark two directions without crosstalk, we write two different periods of LPFG in each of the two external cores and the central core, which induces a strong asymmetric refractive index arrangement in the fiber cross section. Theoretical analysis and experimental results verify that the resonant wavelength originates from the tunneling between the LP01 core mode in the center core and the external core. In the confirmation experiments, the proposed sensor can distinguish multiple bending directions and experiences a maximum sensitivity of 3.234 nm/m-1 with a bending range of 0-0.588 m-1.

Fiber loop ring down for static ice pressure detection

Abstract We studied static ice pressure detection of hydraulic structures based on fiber loop ring down technology. Our detection system consists of a mode-locked laser, two 2 × 1 optical fiber couplers, a piece of single-mode fiber, the on-line micro-bend fiber sensor and a photo-detector. The static ice pressure was monitored based on measuring the change of the ring down time induced by external ice pressure on on-line micro-bend fiber sensor. We monitored the static ice pressure during ice growth and melting from −10 °C to 6 °C. The detection sensitivity is 0.00998/(μs·kPa). The proposed pressure sensing method has many advantages such as free from the fluctuation of the light power, simple structure, fast response and high sensitivity.

Study of Wavelength-Dependent Bend Loss in Step-Index Multimode Fiber-Optic Microbend Displacement Sensor

In this article, the wavelength dependence of bend loss in a step-index multimode optical fiber (100 µm core diameter; fused silica) was investigated for fiber bend radii ranging between 2.0 and 4.5 mm using six excitation wavelengths, namely, 337.1, 470, 590, 632.8, 750 and 810 nm. The results obtained from fitting the bend loss measurements to Kao's model and utilizing MATLAB indicate that bend loss is wavelength dependent and transmission loss in multimode optical fibers increases with the decrease in the fiber bend radius. Furthermore, the response of a microbend fiber optic displacement sensor was characterized at 337.1, 470, 632.8, 750 and 810 nm. Measurements obtained from the microbend sensor indicate that the sensor output power is linear with the applied displacement and the sensor output is wavelength dependent.

IMPROVING OPTICAL FIBER SENSING BY MIMO SIGNAL PROCESSING

Optical fiber sensors have reached a high state of maturity. Besides the high number of sensor groups, multi-mode fiber evanescent field sensors can be found in a lot of applications. Here, the signal source commonly excites many optical modes under steady-state conditions. Perturbations of the fiber then produce leaky modes. Thus, a simple intensity detector measures the degree of perturbation. In some cases also restricted mode launching conditions have been applied. They resulted in higher sensitivity but showed a narrower measurement range. Considering the individual modes as carriers of information we adapted multiple-input multiple-output (MIMO) signal processing which is well studied in the telecommunications community, for improvements on both the sensor sensitivity and its measurement range. In this paper MIMO signal processing is investigated for fiber optic sensor applications. A (2x2) MIMO implementation is realized by using lower-order and higher-order mode groups of a gradient-index multi-mode fiber as separate transmission channels. A micro-bending pressure sensor changes these separate transmission characteristics and introduces additional crosstalk. By observing the layer specific weight-factors of the MIMO system the amount of load applied was determined. Experiments verified a good correlation between the change of the MIMO weight coefficients and the load applied to the sensor and thus verified that MIMO signal processing can beneficially be used for fiber optic sensor applications. The experimental results also verified the superior sensitivity and measurement range when MIMO signal processing is utilized.

Sensor data quality processing for vital signs with opportunistic ambient sensing.

Opportunistic ambient sensing involves placement of sensors appropriately so that intermittent contact can be made unobtrusively for gathering physiological signals for vital signs. In this paper, we discuss the results of our quality processing system used to extract heart rate from ballisto-cardiogram signals obtained from a micro-bending fiber optic sensor pressure mat. Visual inspection is used to label data into informative and non-informative classes based on their heart rate information. Five classifiers are employed for the classification process, i.e., random forest, support vector machine, multilayer, feedforward neural network, linear discriminant analysis, and decision tree. To compute the overall effectiveness of quality processing, the informative signals are processed to estimate interbeat intervals. The system was used to process, data collected from 50 human subjects sitting in a massage chair while performing different activities. Opportunistically collected data was obtained from the fiber optic sensor mat placed on the headrest of the massage chair. Using our classification approach, 57.37% of the dataset was able to provide informative signals. On the informative signals, random forest classifier achieves the best classification accuracy with a mean accuracy of 98.99%. The average of the mean absolute error between the estimated heart rate and the reference ECG is reduced from 13.2 to 8.47. Therefore, the proposed system shows a good robustness for opportunistic ambient sensing.

Micro-bending vector sensor based on six-air-hole grapefruit microstructure fiber using lateral offset splicing.

A one-dimensional micro-bending vector sensor based on two-mode interference has been introduced. This device was fabricated by lateral offset splicing a piece of six-air-hole grapefruit microstructure fiber (GMF) with single mode fiber (SMF). Variation of effective mode index occurred by micro-bending was investigated in simulation and experiment. This device exhibits micro-bending sensitivities of 0.441 nm/m(-1) and -0.754 nm/m(-1) at 0° and 180° bending orientations, respectively. Moreover, this sensor is immune to surrounding refractive index (SRI) and presents a low crosstalk of temperature.

Textile Fiber Optic Microbend Sensor Used for Heartbeat and Respiration Monitoring

This paper reports on a textile fiber optic microbend sensor for heartbeat and respiration monitoring. A section of multimode optical fiber sandwiched between parallel strips acting as a microbender is being integrated onto an elastic substrate. Its design is based on fiber microbending effects. The textile sensor can be used to measure heartbeat and respiration rate simultaneously during standing and sitting position. The detected heart rates from our sensor are in good agreement with that from the commercial SpO2, whereas the respiration rate is verified by counting the breathing manually. We characterize the frequency response of the sensor with a simulation setup and find that the sensitivity of the sensor is large enough at 105 r/min although it decreases with the increase of the motor speed. The textile fiber optic sensor is very comfortable to wear due to the elastic nature of the substrate.

Incomplete coupling triple-core photonic crystal fiber sensors for micro-bending angle detection

We demonstrate a flexible, high-sensitivity and low-cost optical fiber transducer to detect the micro-bending angle. The sensor uses a triple-core photonic crystal fiber. Based on a traditional triple-core photonic crystal fiber, large air holes are placed in the left and right cores around the central core, which causes the power among the three cores be incompletely coupled. Beams with a wavelength of 1550 nm are launched into the two side cores simultaneously. The optical power difference between the two side cores changes with the micro-bending angle. Coupling characteristic and beam propagation analysis of the micro-bending sensor are performed. The simulation results show that the optical power difference has a good linear relationship with the micro-bending angle in the range from 0° to 0.4°, and this sensor allows highly accurate micro-bending angle detection. The sensitivity of the micro-bending angle sensor can reach 0.421 62 W/deg.

Application of Improved BP Neural Networks Based on LM Algorithm in Characteristic Curve Fitting of Fiber-Optic Micro-Bend Sensor

As a key factor in a testing system, sensor nonlinearity has always been the study focus in the field of engineering and techniques. In order to accurately reflect the practical characteristics of a fiber-optic micro-bend sensor, Levenberg-Marguardt (LM) algorithm is used to optimize the correction of the weight values of standard back propagation neural network (BPNN). The learning process of improved BPNN based on LM algorithm (LM-BPNN) is also illustrated mathematically, and LM-BPNN is applied in fitting the input and output characteristic curve of a fiber-optic micro-bend sensor. The simulation results show that LM-BPNN is superior both in its convergence rate and fitting precision over standard BPNN.

Application of General Regression Neural Network in Characteristic Curve Fitting of Optical Fiber Micro-Bend Sensor

In order to reflect the input and output features of an optical fiber micro-bend sensor, a new method using general regression neural network (GRNN) to fit the characteristic curve is proposed in this paper. First, the measuring principle of optical fiber micro-bend sensor and the principle of GRNN are introduced. Then, to verify the feasibility and effectiveness of this new method, a comparison between two kinds of fitting methods is done. One is based on GRNN, the other is based on Levenberg-Marquart improved BPNN. The results of the simulation experiment show that with the same number of training samples and for small scale to medium scale networks, compared with BPNN, GRNN has smaller error, faster convergence speed and higher fitting accuracy. So the method discussed in this paper provides a reliable basis for the nonlinear compensation problem of optical fiber micro-bend sensor.

Mode couplings and elasto-optic effects study in a proposed mechanical microperturbed multimode optical fiber sensor

A step index multimode optical fiber with a perturbation on a micrometer scale, inducing a periodic deformation of the fiber section along its propagation axis, is theoretically investigated. The studied microperturbation is mechanically achieved using two microstructured jaws squeezing the straight fiber. As opposed to optical fiber microbend sensors, the optical axis of the proposed transducer is not bended; only the optical fiber section is deformed. Further, the strain applied on the fiber produces a periodical elliptical modification of the core and a modulation of the index of refraction. As a consequence of the micrometer scale perturbation period, the resulting mode coupling occurs directly between guided and radiated modes. To simulate the transmission induced by these kinds of perturbations, simplified models considering only total mode couplings are often used. In order to investigate the range of validity of this approximation, results are compared to the electromagnetic mode couplings rigorously computed for the first time, to our knowledge, with a large multimode fiber (more than 6000 linear polarized modes) using the Marcuse model. In addition, in order to have a more complete modeling of the proposed transducer, the anisotropic elasto-optic effects in the stressed multimode fiber are considered. In this way, the transmission of the microperturbed optical fiber transmission and, therefore, the behavior of the transducer are physically explained and its applications as a future stretching sensor are discussed.