Hetero-core Fiber Optic Sensor Research Articles

Lipid-coated hetero-core optical fiber sensor for wide-range chemical detection

We developed a chemical sensor based on a hetero-core optical fiber structure where lipid films coat a cylindrical cladding. Two lipids were applied to the fiber surface: oleic acid and phosphoric acid di(2-ethylhexyl) ester. Experiments were performed to observe the differential optical loss spectra over the measured spectral region in response to each chemical substance. The oleic acid- and PAEE-coated sensors induced optical losses of approximately 0.4 and 0.2 dB, respectively, for a refractive index difference of 0.0008 between water and quinine. Compared with a conventional hetero-core optical fiber sensor based on surface plasmon resonance, which uses double-layer films of gold and lipid, the proposed sensors scheme showed the different sensitivity to chemical substances and could detect a wide range of chemical substances such as quinine. The response of the proposed sensor was reproducible at concentrations of >0.01 mM. Changing the type of lipid in the film controls the selectivity of chemical substances. The proposed sensor works based on hydrocarbon groups of fatty acids or carboxyl groups that form self-assembled monolayers on the fiber. The exposure of carboxyl groups at the surface of the fatty acids may be involved in the sensor response.

Cantilever Type Accelerometer Based on a Mirror-Terminated Hetero-Core Optical Fiber

This paper describes a novel cantilever type accelerometer using a mirror-terminated hetero-core optical fiber for fault diagnosis of machinery. Hetero-core optical fiber sensors are suitable for long-term measurement in on-site fields with attractive advantages of robustness to environmental disturbances such as electromagnetic interference, chemical corrosion, and temperature fluctuation. Moreover, the proposed sensor contained a mirror termination on the hetero-core fiber in order to form a compact and cantilever-shaped structure. It was experimentally found that the mirror-terminated hetero-core fiber worked as Mach-Zehnder interferometry having interference fringes in transmission spectrum, in which linear changes in peak intensities enabled to detect the deflection of fiber beam using a cost-effective LED/PD measurement instrument. For the vibration response characteristics, the sensor reproduced the waveforms of input vibrations to optical loss changes when sinusoidal vibration was applied. Furthermore, the sensitivities were stable in the range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.4\times10^{3}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.3\times10^{2}$ </tex-math></inline-formula> dB/g for the frequency ranges less than 620–130 Hz, when setting a fiber beam length by 6–13 mm. Additionally, finite element simulations indicated that the frequency response characteristics were well correlated with the vibration characteristics of the cantilever-shaped fiber beam, which implied that the sensor performance can be optimized with respects to the sensitivity and the measurable frequency range by changing the fiber beam length.

Optical Strain Gauge-Based on a Hetero-Core Fiber Macro-Bending Sensor

This paper describes a novel approach for optical strain sensing based on a hetero-core fiber optic macro-bending sensor. A gauge substrate for the proposed sensor was designed to transduce the tensile and compression strain by changing to a gentle bending curvature on the fiber; thus, the hetero-core fiber detects the strain on the substrate as the transmitted light lost. Because optical fibers perform as a flexible structure in a buckling scheme owing to their slenderness, the mechanical properties of the proposed sensor can be widely tuned by the shape and mechanical properties of the gauge substrate. Experiments demonstrated that the proposed strain gauge with a spring-structured substrate made of SUS304 showed a strain applied within $\pm 3100~\mu \epsilon $ with a sensitivity of up to $- 9.14\times 10^{-4}$ dB/ $\mu \epsilon $ , and responded to temperature changes from 0 °C to 60 °C with $- 1.10\times 10^{-2}$ dB/°C owing to the thermal expansion of the substrate. Furthermore, both the strain and temperature sensitivities are tunable by changing the geometrical parameters of the gauge substrate.

U-Shaped Polymer Cladding and Hetero-Core Fiber Optic Sensors for Monitoring Scale Formation in Geothermal Brine

In the development of fiber optic sensors for monitoring scale formation in geothermal brine, high sensitivity and easy handling are desirable features. These characteristics have already been successfully enhanced for U-shaped sensors with other applications. In this work, U-shaped fiber optic sensors for scale formation are reported. The sensors were easily fabricated by bending the exposed core of a multimode fiber optic. Two types of fiber optics, i.e., a polymer cladding silica fiber and a hetero-core structure fiber, were used in preparing the U-shaped sensors. The percentage of total internal reflection between water and the fiber core is affected by the high refractive index of the CaCO3 scale formed on the surface. For laboratory measurements, the optical responses of the U-shaped fiber sensors with respect to calcium carbonate formation were investigated in a mixture of calcium chloride dehydrate and sodium hydrogen carbonate using a white-light source and a spectroscopic detector. The U-shaped fiber sensors were responsive to calcium carbonate formation on the sensor surface. Almost no change in the sensitivity was detected when comparing the U-shaped sensors with their straight counterparts. The transmittance changes were independent of the bending radius. Finally, the U-shaped polymer cladding fiber sensor was used to monitor the silica scale formation in geothermal brine at the Takigami geothermal plant.

Localized Surface Plasmon Resonance Based Hetero-Core Optical Fiber Sensor Structure for the Detection of L-Cysteine

In this article, a hetero-core optical fiber sensor structure is developed for the diagnosis of L-Cysteine content in human urine. The hetero-core structure is created by sequentially cascading the single mode-multimode-single mode fibers using thermal fusion splicing. The multimode section of fiber probe is etched out and coated with synthesized gold nanoparticles (AuNPs), polyvinyl alcohol stabilized silver nanoparticles (PVA-AgNPs) and graphene oxide (GO). The AuNPs and PVA-AgNPs are used to initiate the localized surface plasmon resonance (LSPR) phenomenon on the application of exponentially decaying evanescent waves. The layer of GO is used to provide the larger surface area and binding sites for the L-Cysteine (L-Cys) molecules. Based on the combination of NPs, two different configurations of sensor probes are developed. In first one, a layer of AuNPs is deposited over fiber surface and further followed by the coating of GO, and named Probe I. In the second one, a layer of PVA-AgNPs is sandwiched between the fiber surface and GO layer and termed as Probe II. The characterization of synthesized NPs and GO solutions, and developed sensor probes are done by using UV-Vis spectrophotometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). To authenticate the biocompatibility of developed sensor probes, the artificial aqueous samples of L-Cys ranges from 0 μM to 1 mM are tested. To determine the stability of L-Cys, a pH level based study is also carried out to ensure the good stability of analyte in aqueous samples. From the results, it was ascertained that the response of Probe II is better in terms of attained limit of detection and sensitivity that is 126.6 μM and 0.0009 nm/μM, respectively.

Effective modes investigation of transmitted and reflective heterocore optical fiber surface plasmon resonance sensors

Two unexpected experimental phenomena in transmitted and reflective heterocore optical fiber sensors are observed. The surface plasmon resonance (SPR) wavelength of the reflective SPR (R-SPR) sensor redshifts about 100nm to the transmitted SPR (T-SPR) sensor. The maximal extinction ratio is 0.60 for the T-SPR sensor and reaches 0.77 for the R-SPR sensor. For a further understanding of the generation mechanism of SPR in both sensors, the finite-element method is employed to calculate distributions of the electric fields. Accompanied with experiments, modal energy coupling among the modes as light transmits through the multimode-single-mode-multimode fiber sensor is demonstrated, and the length of the single-mode fiber (SMF) is the focus of interest. The initial dissipated energy of the higher-order TM modes breaks the dynamic coupling balance of modal energy in the SMF when SPR takes place as a significant perturbation. With increasing SMF length, extra energy couples from lower-order modes to higher-order modes, from TE modes to TM modes as well, which results in a deeper trough and a longer SPR wavelength and thus a more sensitive device. The results are promising for various applications of a broader spectrum, such as modulators and sensors.

Nursing Movement Monitoring System Utilizing Hetero-core Fiber Optic Sensors Embedded in Medical Thin Films

Nursing Movement Monitoring System Utilizing Hetero-core Fiber Optic Sensors Embedded in Medical Thin Films

Fundamental Experiment to Verify the Resolution of Hetero-core Fiber Optic Sensor for the Prestress Measurement

Fundamental Experiment to Verify the Resolution of Hetero-core Fiber Optic Sensor for the Prestress Measurement

Pendulum-Type Hetero-Core Fiber Optic Accelerometer for Low-Frequency Vibration Monitoring

In this paper, a novel pendulum-type accelerometer based on hetero-core fiber optics has been proposed for structural health monitoring targeting large-scale civil infrastructures. Vibration measurement is a non-destructive method for diagnosing the failure of structures by assessing natural frequencies and other vibration patterns. The hetero-core fiber optic sensor utilized in the proposed accelerometer can serve as a displacement sensor with robustness to temperature changes, in addition to immunity to electromagnetic interference and chemical corrosions. Thus, the hetero-core sensor inside the accelerometer measures applied acceleration by detecting the rotation of an internal pendulum. A series of experiments showed that the hetero-core fiber sensor linearly responded to the rotation angle of the pendulum ranging within (−6°, 4°), and furthermore the proposed accelerometer could reproduce the waveform of input vibration in a frequency band of several Hz order.

Smart Textile Using Hetero-Core Optical Fiber for Heartbeat and Respiration Monitoring

This paper aims to describe a novel smart textile that uses a single-mode hetero-core optical fiber sensor for monitoring heartbeat and respiration. The smart textile was designed by weaving hetero-core optical fibers together with the wool fabric. This novel textile that can detect variations in shapes can be incorporated into clothes. Such clothes can offer comfort to the wearer. To simultaneously monitor heartbeat and respiration, the proposed textile is sewn on to the clothes to be able to sense minute load changes produced by chest movements. The vital signs, which were calculated from the heartbeat and respiration frequency of a healthy adult, while sitting, were in agreement with those verified using commercial monitoring devices. In addition, to confirm the capability of monitoring vital signs, seven monitoring trials were performed in which the subjects were asked to wear and take off the smart cloth. The vital signs rates were successfully extracted within the four beats per minute error by the fiber optic sensor system. The proposed smart textile in clothes can monitor vital signs in daily life activities, such as sitting and standing.

Behavior Monitoring Based on Intensity Matrix Distribution in Output Plane of Single-Mode Fiber Bundle

A smart structure using intensity-based optical fiber sensors has the potential to be a simple and low-cost system. In this paper, a novel fiber-optic smart structure system using a complementary metal–oxide–semiconductor (CMOS) is demonstrated that simultaneously monitors a number of hetero-core optical fiber bending sensors. The proposed system can integrate a number of optical fiber transmission lines. Therefore, the system does not require a number of photodetectors, which is different from conventional techniques. To simultaneously measure optical intensity, we coupled a number of hetero-core optical fiber sensors to a CMOS camera. The optical fiber sensor can detect macrobending to the optical light intensity. The output images comprise luminance spots distribution directly representing the sensor arrangements in the smart structure. A template matching technique based on the sum of absolute differences was introduced to distinguish between the overall behaviors of structures. A recognition experiment for object shapes was performed with a smart pressure sheet in which hetero-core optical fiber sensors are embedded as a simple case. In addition, a real-time human body posture recognition application was implemented using a fiber-optic smart clothing to apply the proposed system. Recognition results show that all images comprising luminance spots distribution were matched with the correct template images, with an error rate of 0% for 15 trials.

A Fiber-Optic Mechanoreceptor in a Finger-Shaped End Effector for Human-Like Tactile Sensing

An artificial mechanoreceptor based on a hetero-core fiber-optic sensor has been developed using a reflective-type sensor element for realizing human-like sensations for multiple tactile information on artificial structures. The proposed mechanoreceptor is embedded in a finger-shaped end effector as a pseudoartificial finger in order to evaluate how the end effector responds to a variety of tactile information. The end effector can detect contact forces in the range of 0.02–4 N with a maximum force sensitivity of 3.23 dB/N and is sensitive in a local area contact within 2 mm, which is comparable with the spatial resolution of human fingertips. The end effector can also detect vibrations at frequencies up to 1 kHz. The developed end effector is also tested in assessing the hardness of a soft resin material in the range of 5°–80° on the Shore A hardness scale, and in discriminating surface conditions when scanned across a surface.

Unconstrained pulse pressure monitoring for health management using hetero-core fiber optic sensor.

In this paper, we present a pulse pressure waveform sensor that does not constrain a wearer's daily activity; the sensor uses hetero-core fiber optics. Hetero-core fiber sensors have been found to be sensitive to moderate bending. To detect minute pulse pressure changes from the radial artery at the wrist, we devised a fiber sensor arrangement using three-point bending supports. We analyzed and evaluated the measurement validity using wavelet transformation, which is well-suited for biological signal processing. It was confirmed that the detected pulse waveform had a fundamental mode frequency of around 1.25 Hz over the time-varying waveform. A band-pass filter with a range of frequencies from 0.85 to 1.7 Hz was used to pick up the fundamental mode. In addition, a high-pass filter with 0.85 Hz frequency eliminated arm motion artifacts; consequently, we achieved high signal-to-noise ratio. For unrestricted daily health management, it is desirable that pulse pressure monitoring can be achieved by simply placing a device on the hand without the sensor being noticed. Two types of arrangements were developed and demonstrated in which the pulse sensors were either embedded in a base, such as an armrest, or in a wearable device. A wearable device without cuff pressure using a sensitivity-enhanced fiber sensor was successfully achieved with a sensitivity of 0.07-0.3 dB with a noise floor lower than 0.01 dB for multiple subjects.

Frequency characteristics of hetero-core fiber optics sensor for mechanical vibration

In this paper, we present characteristics of a hetero-core fiber optic sensor in mechanical vibration based on rigid supported beam property for vibration monitoring in fault diagnosis of the industrial equipments. A first configuration of the hetero-core fiber optic vibration sensor was rigidly supported at two fixed ends as curved setting without tension to the fiber. In order to tune the range of the detectable frequencies to be higher of the vibration sensor, a second configuration was evaluated, in which the hetero-core fiber optics was linearly-arranged with tension to the fiber. As a result, the both types of the proposed hetero-core fiber optic vibration sensors could pick up the free vibration from an impact force. Analytical natural frequencies were calculated based on an FEM fiber beam model. It was indicated that the natural frequencies from the experimental results of the 1st configuration were appropriate to the FEM results and a typical beam property, and could be tuned by the length between two fixed ends. Additionally, the 2nd configuration of the vibration sensor with tension to the fiber enabled its detectable frequencies to be dramatically higher than without tension.

Monitoring of Plantar Pressure in Gait Based on Hetero-core Optical Fiber Sensor

In this paper, a sensitive shoe for gait evaluation is described, in which hetero-core optical fiber sensors are embedded in the insole for detecting plantar pressure. The sensitive shoe can obtain important factors indicative of weight shift and foot rolling for gait evaluation by monitoring plantar pressure without constraint to walking. The hetero-core optical fiber sensor has been proposed to have many advantages which are high sensitivity to macro-bending, lightweight, independent on temperature fluctuations, and no electric contact. Gait of three subjects has been monitored who wear the sensitive shoe in walking on the treadmill. As a result, the proposed sensitive shoe could successfully detect different gait characteristics.

A Motion Monitor Using Hetero-Core Optical Fiber Sensors Sewed in Sportswear to Trace Trunk Motion

In this paper, a cameraless motion monitor has been described by introducing very thin sensor modules into sportswear, in which a single-mode hetero-core optical fiber sensor is fabricated. An elbow joint motion and a trunk motion are monitored by a sportswear on which the hetero-core optical fiber sensor modules are sewed so as to be sensitive to stretch on the wear. In order to get rid of the restriction to the human body, a two-plane model has been proposed in which only two sets of sensors simplify three kinds of motions at the trunk, which are anteflexion, lateral bending, and rotation. Additionally, the real-time monitoring system has been tested when golf swing motion is performed. As a result, it has been indicated that the motion, which consists of a composite of three motions, can be significantly analyzed by means of the two sensors. The developed system is viable to an unconstrained motion capture system intended for a teaching device in sports and rehabilitation fields.

Real-time measurement of multipoint hetero-core fiber optic binary sensors based on optical pulse loss change

Hetero-core fiber optic sensors can transmit sensing and communication signals on a single fiber optic transmission line and have numerous advantages for environmental information monitoring such as home security. Moreover, these sensors are cost effective due to their temperature independence and light-intensity-based measurements. We have previously developed a hetero-core fiber optic binary sensor that can be connected in series to detect the number of doors and windows that are opened or closed. In this paper, we propose an improved method for using hetero-core fiber optic binary sensors that are connected in series, which are referred to as binary switches. A unique pulse loss change enables the states of the connected switches to be identified. As a result, the total optical loss in the transmission line is reduced. Therefore, the number of binary switches connected in series can be increased on a single transmission line. The unique pulse loss peaks can be controlled by the action of a flat spring and by adjusting the position of the flat spring inside the binary switch module. Typical pulse peaks of each binary switch are from 0.13 to 0.75 dB in the positive direction and from −0.47 to −0.03 dB in the negative direction, while the typical insertion loss is from 2.23 to 2.61 dB, depending on the position of the hetero-core segment within the binary switch module. The connection of two binary switches in series is successfully demonstrated for monitoring the optical loss change on a single transmission line. The results of the present study show that the number of binary switches connected in series can be increased significantly on a single transmission line.

Respiration and body movement analysis during sleep in bed using hetero-core fiber optic pressure sensors without constraint to human activity

We describe respiration monitoring in sleep using hetero-core fiber optic pressure sensors. The proposed hetero-core fiber optic sensor is highly sensitive to macrobending as a result of the core diameter difference due to stable single-mode transmission. Pressure sensors based on hetero-core fiber optics were fabricated to have a high sensitivity to small pressure changes resulting from minute body motions, such as respiration, during sleep and large pressure changes, such as those caused by a rollover. The sensors are installed in a conventional bed. The pressure characteristic performance of all the fabricated hetero-core fiber optic pressure sensors is found to show a monotonic response with weight changes. A respiration monitoring test in seven subjects efficiently demonstrates the effective use of eight hetero-core pressure sensors installed in a bed. Additionally, even in the case of different body postures, such as lying on one's side, a slight body movement due to respiration is detected by the hetero-core pressure sensors.

ヘテロコア型光ファイバセンサを用いた土壌重力水の検出

ヘテロコア型光ファイバセンサを用いた土壌重力水の検出

Surface plasmon resonances of a curved hetero-core optical fiber sensor

In this work, a novel characterization of surface plasmon resonance (SPR) is described on using a curved hetero-core optical fiber sensor that can flexibly change the radius of curvature of the sensor probe. It has been found that the decrease in the radius of curvature resulted in a 2.8 fold increase in the SPR (loss) spectrum peak with a decrease in spectral bandwidth by 75% and an additional 9-nm shift in the SPR resonant wavelength, compared with the straight case. To discuss the experimental results, the power distribution in the hetero-core region was investigated by using uncoated hetero-core fibers. It was found that the power distribution was shifted to the critical angle by bending, the discussion of which successfully explained the observed bending effect of SPR.