Liquid Pressure Sensor Based on Fiber Bragg Grating with an Adjustable Structure.

In this paper, a fiber-optic liquid pressure sensor is designed and developed by encapsulating the fiber Bragg grating (FBG) inside the adjustable double-flange cylinder rigid structure with flexible polymer polydimethylsiloxane (PDMS). Within the elastic deformation range of the PDMS, the proposed adjustable FBG-based liquid pressure sensor is proven to change its measuring range while maintaining high measurement sensitivity by simply adjusting the structure, that is, the sensor can achieve high measurement sensitivity in various liquid levels. In addition, the simulation and experimental results show that the sensor sensitivity can be enhanced by the proper changes of the structural parameters, such as the inner diameter, etc. The proposed sensor has shown that it has good linearity and stability, which provides a new opportunity for the monitoring of liquid pressure in oceans, dams and other environments.

Fault reconstruction and resilient control for discrete-time stochastic systems.

In this paper, a novel resilient control technique is proposed for discrete-time stochastic Brownian systems with simultaneous unknown inputs and unexpected faults. Prior to previous work, the stochastic Brownian system under consideration is quite general, where stochastic perturbations exist in states, control inputs, uncertainties, and faults. Moreover, the unknown input uncertainties concerned cannot be fully decoupled. Innovative observer by employing augmented system approach, decomposition observer, and optimization algorithms is proposed to achieve simultaneous estimates of both states and faults. Furthermore, fault reconstruction-based signal compensation is formulated to alleviate the effects from actuator faults and sensor faults. An observer-based controller is eventually constructed to enhance the stability and robustness of the closed-loop dynamic system. The integrated resilient control technique can ensure the system has reliable output even under faults. Both linear systems and Lipschitz nonlinear systems are investigated and the design procedures are addressed, respectively. Finally, the proposed resilient control techniques are validated via an electromechanical servo-system, and an aircraft system.

Opto-Microfluidic Fabry-Perot Sensor with Extended Air Cavity and Enhanced Pressure Sensitivity.

An opto-microfluidic static pressure sensor based on a fiber Fabry-Perot Interferometer (FPI) with extended air cavity for enhancing the measuring sensitivity is proposed. The FPI is constructed in a microfluidic channel by the combination of the fixed fiber-end reflection and floating liquid surface reflection faces. A change of the aquatic pressure will cause a drift of the liquid surface and the pressure can be measured by detecting the shift of the FPI spectrum. Sensitivity of the sensor structure can be enhanced significantly by extending the air region of the FPI. The structure is manufactured by using a common single-mode optical fiber, and a silica capillary with the inner wall coated with a hydrophobic film. A sample with 3500 µm air cavity length has demonstrated the pressure sensitivity of about 32.4 µm/kPa, and the temperature cross-sensitivity of about 0.33 kPa/K.

Wearable Physiological Monitoring System Based on Electrocardiography and Electromyography for Upper Limb Rehabilitation Training.

Secondary injuries are common during upper limb rehabilitation training because of uncontrollable physical force and overexciting activities, and long-time training may cause fatigue and reduce the training effect. This study proposes a wearable monitoring device for upper limb rehabilitation by integrating electrocardiogram and electromyogram (ECG/EMG) sensors and using data acquisition boards to obtain accurate signals during robotic glove assisting training. The collected ECG/EMG signals were filtered, amplified, digitized, and then transmitted to a remote receiver (smart phone or laptop) via a low-energy Bluetooth module. A software platform was developed for data analysis to visualize ECG/EMG information, and integrated into the robotic glove control module. In the training progress, various hand activities (i.e., hand closing, forearm pronation, finger flexion, and wrist extension) were monitored by the EMG sensor, and the changes in the physiological status of people (from excited to fatigue) were monitored by the ECG sensor. The functionality and feasibility of the developed physiological monitoring system was demonstrated by the assisting robotic glove with an adaptive strategy for upper limb rehabilitation training improvement. The feasible results provided a novel technique to monitor individual ECG and EMG information holistically and practically, and a technical reference to improve upper limb rehabilitation according to specific treatment conditions and the users' demands. On the basis of this wearable monitoring system prototype for upper limb rehabilitation, many ECG-/EMG-based mobile healthcare applications could be built avoiding some complicated implementation issues such as sensors management and feature extraction.

Multifunctional Textile Platform for Fiber Optic Wearable Temperature-Monitoring Application.

Wearable sensing technologies have been developed rapidly in the last decades for physiological and biomechanical signal monitoring. Much attention has been paid to functions of wearable applications, but comfort parameters have been overlooked. This research presents a developed fabric temperature sensor by adopting fiber Bragg grating (FBG) sensors and processing via a textile platform. This FBG-based quasi-distributed sensing system demonstrated a sensitivity of 10.61 ± 0.08 pm/°C with high stability in various temperature environments. No obvious wavelength shift occurred under the curvatures varying from 0 to 50.48 m-1 and in different integration methods with textiles. The temperature distribution monitored by the developed textile sensor in a complex environment with multiple heat sources was deduced using MATLAB to present a real-time dynamic temperature distribution in the wearing environment. This novel fabric temperature sensor shows high sensitivity, stability, and usability with comfort textile properties that are of great potential in wearable applications.

Wearable Fiber Optic Technology Based on Smart Textile: A Review.

Emerging smart textiles have enriched a variety of wearable technologies, including fiber optic technology. Optic fibers are widely applied in communication, sensing, and healthcare, and smart textiles enable fiber optic technology to be worn close to soft and curved human body parts for personalized functions. This review briefly introduces wearable fiber optic applications with various functions, including fashion and esthetics, vital signal monitoring, and disease treatment. The main working principles of side emission, wavelength modulation, and intensity modulation are summarized. In addition, textile fabrication techniques, including weaving and knitting, are discussed and illustrated as combination methods of embedding fiber optic technology into textile fabric. In conclusion, the combination of optical fibers and textiles has drawn considerable interest and developed rapidly. This work provides an overview of textile-based wearable fiber optic technology and discusses potential textile fabrication techniques for further improvement of wearable fiber optic applications.

Kayaking paddle blade compression load distribution sensing system based on optical fiber with a polydimethylsiloxane membrane.

This paper proposed a novel real-time compression load measurement system for a kayaking paddle based on optical fiber technology. The optical fiber sensor, fiber Bragg grating, is embedded in a 2 mm polydimethylsiloxane membrane, which serves as a pressure mat that can be easily attached/detached to/from the kayaking paddle. The proposed system is proposed for measuring and evaluating both handgrip loading and paddle blade load distribution during on-water kayaking, e.g., peak compression load distribution pattern and duration of the paddle blade in real time. Both indoor prototype experiment results and on-water experimental data on an expert paddler were presented to demonstrate the application potential of the proposed system.

Chitosan-nickel film based interferometric optical fiber sensor for label-free detection of histidine tagged proteins.

An interferometric fiber sensor for detection of hexa-histidine tagged microcin (His-MccS) is reported and experimentally demonstrated. This intermodal fiber sensor is implemented by a no-core fiber (NCF) functionalized with chitosan (CS)-nickel (Ni) film for direct detection of small peptide: microcin. The fiber intermodal sensor relies on the refractive index modulations due to selective adsorption event at the chitosan (CS)-nickel (Ni) film. Owing to the strong affinity between Ni2+ ions and histidine, the immobilized Ni2+ ions in the chitosan film were utilized as binding agents for the direct detection of hexa-histidine tagged microcin. A comparative study in relation to different target size was conducted: full proteins trypsin, bovine serum albumin (BSA) and human serum albumin (HSA), with high histidine content on their surface and His-MccS (peptide, 11.6kDa), have been employed for sensor evaluation. Results have shown selectivity for His-MccS relative to trypsin, BSA and HSA. The most telling contribution of this study is the fast detection of small biomolecule His-MccS compared to standard detection procedures like SDS-PAGE and western blot. The proposed sensor exhibits His-MccS detection sensitivity of 0.0308nm/(ng/ml) in the range of (0-78) ng/ml with concentration detection limit of 0.8368ng/ml.

Three-dimensional navigation-guided percutaneous screw fixation for nondisplaced and displaced pelvi-acetabular fractures in a major trauma centre.

BACKGROUND: Navigation assisted minimally invasive percutaneous screw fixation (MIS) for pelvi-acetabular fracture was recently advocated. METHODS: We report 38 consecutive cases of pelvi-acetabular fractures treated with 3D navigation-guided MIS from 2015 to 2016. Ohe hundred and forty-three screws were inserted (59 sacroiliac, 45 retrograde anterior column, 34 supra-acetabular, three antegrade posterior-column and two subcristal). Navigation planning was mainly performed pre-operatively. RESULTS: The mean operative blood loss and time was 179 ml and 141 mins, respectively. The distance (deviation) between the planned and executed screw entry and tip measured by the navigation computer were 1.91 and 1.94 mm, respectively. There were no immediate or early surgical complications. Patients were followed for at least 6 month; 79% had fracture healing at 4.3 months on average, and 53% walked unaided by the six month follow-up. The average visual analogue scale for pain was 2.69. CONCLUSION: We believe 3D navigation-guided MIS is a safe and effective surgical alternative in most pelvi-acetabular fractures.

PDMS-coated fiber volatile organic compounds sensors.

The functionality of poly(dimethylsiloxane) (PDMS)-based interferometric fiber sensors for volatile organic compounds (VOCs) detection is investigated and experimentally demonstrated. Two interferometric configurations are considered in this work, namely Fabry-Perot (FP) and Sagnac interferometers (SI). Both sensors are functionalized with a thin layer of VOC-sensitive polymer: PDMS, whose degree of swelling varies as a function of VOC concentrations. This swelling effect will result in an optical path length and birefringence modulation for FP and SI sensors, respectively. In this paper, the two common VOCs, ethanol and 2-propanol, were detected by the proposed sensor and the inverse matrix method was used to differentiate the VOC in gas mixture.

Miniature temperature sensor with germania-core optical fiber.

A miniature all-fiber temperature sensor is demonstrated by using a Michelson interferometer formed with a short length of Germania-core, silica-cladding optical fiber (Ge-fiber) fusion-spliced to a conventional single-mode fiber (SMF). Thanks to the large differential refractive index of the Ge-fiber sensing element, a reasonably small free spectral range (FSR) of 18.6 nm is achieved even with an as short as 0.9 mm Ge-fiber that may help us increase the measurement accuracy especially in point sensing applications and, at the same time, keep large measurement temperature range without overlapping reading problem. Experimental results show that high sensitivity of 89.0 pm/°C is achieved and the highest measurement temperature is up to 500°C.

Photonic crystal fiber interferometric pH sensor based on polyvinyl alcohol/polyacrylic acid hydrogel coating.

We present a simple photonic crystal fiber interferometer (PCFI) that operates in reflection mode for pH measurement. The sensor is made by coating polyvinyl alcohol/polyacrylic acid (PVA/PAA) hydrogel onto the surface of the PCFI, constructed by splicing a stub of PCF at the distal end of a single-mode fiber with its free end airhole collapsed. The experimental results demonstrate a high average sensitivity of 0.9 nm/pH unit for the 11 wt.% PVA/PAA coated sensor in the pH range from 2.5 to 6.5. The sensor also displays high repeatability and stability and low cross-sensitivity to temperature. Fast, reversible rise and fall times of 12 s and 18 s, respectively, are achieved for the sensor time response.

In-fiber photo-immobilization of a bioactive surface.

We demonstrate the first in-fiber light-induced bioactive biotin-functionalization via photobleaching fluorophore-conjugated biotin. Photobleaching the fluorophores generated free radicals that bind to the albumin-passivated inner surface of pure silica photonic crystal fiber. The subsequent attachment of dye-conjugated streptavidin to the bound biotin qualified the photo-immobilization process and demonstrated a potential for the construction of in-fiber macromolecular assemblies or multiplexes. Compared with other in-fiber bioactive coating methods, the proposed light-induced technique requires only a low-power light source, without the need for additional preactivation steps or toxic chemical reagents. This method, hence, enables a simple and compact implementation for potential biomedical applications.

In-fiber fluorospectroscopy based on a spectral decomposition method.

We report a simplified model for the computation of light-fluorescence interactions within photonic crystal fibers (PCFs). It involved the plotting of ray trajectories confined by total internal reflection within a geometrically simplified PCF core. This was followed by the calculation of absorption and fluorescence emission at each point of reflection, which were subsequently summed and averaged over all the launched rays. The computation of these components for two specified wavelengths (peak excitation and emission) produced a dimensionless ratiometric relationship for varying concentrations of fluorescence dye. This hence eliminated the need for optical filters and minimized the effects of intensity fluctuations. Modeled results were demonstrated to concur well with that obtained experimentally for two PCFs with different microstructured cores.

Double-pass Mach-Zehnder fiber interferometer pH sensor.

A biocompatible fiber-optic pH sensor based on a unique double-pass Mach-Zehnder interferometer is proposed. pH responsive poly(2-hydroxyethyl methacrylate-co-2-(dimethylamino)ethyl methacrylate) hydrogel coating on the fiber swells/deswells in response to local pH, leading to refractive index changes that manifest as shifting of interference dips in the optical spectrum. The pH sensor is tested in spiked phosphate buffer saline and demonstrates high sensitivity of 1.71 nm/pH, pH 0.004 limit of detection with good responsiveness, repeatability, and stability. The proposed sensor has been successfully applied in monitoring the media pH in cell culture experiments to investigate the relationship between pH and cancer cell growth.

Magnetic field sensor using tilted fiber grating interacting with magnetic fluid.

A novel magnetic field sensor using tilted fiber Bragg grating (TFBG) interacting with magnetic fluid is proposed and experimentally demonstrated. The TFBG is surrounded by magnetic fluid whose complex refractive index changes with external magnetic field. The guiding properties of cladding modes excited by the TFBG are therefore modulated by the external magnetic field. As a result, the magnetic field strength measurement is successfully achieved within a range up to 196 Gauss by monitoring extinction ratio of cladding mode resonance. Furthermore, temperature variation can be obtained simultaneously from the wavelength shift of the TFBG transmission spectrum.

Magneto-optical fiber sensor based on magnetic fluid.

A novel magnetic field fiber sensor based on magnetic fluid is proposed. The sensor is configured as a Sagnac interferometer structure with a magnetic fluid film and a section of polarization maintaining fiber inserted into the fiber loop to produce a sinusoidal interference spectrum for measurement. The output interference spectrum is shifted as the change of the applied magnetic field strength with a sensitivity of 16.7 pm/Oe and a resolution of 0.60 Oe. The output optical power is varied with the change of the applied magnetic field strength with a sensitivity of 0.3998 dB/Oe.

Polyvinyl alcohol-coated hybrid fiber grating for relative humidity sensing.

A relative humidity (RH) sensor based on a hybrid fiber grating coated with polyvinyl alcohol is proposed and demonstrated experimentally. The hybrid fiber grating is formed by superimposing a normal fiber Bragg grating (FBG) and a tilted-FBG around the same position of a single-mode fiber so that it can work in the reflection mode. Optical power of the reflected signal changes with the refractive index of the moisture sensitive polyvinyl alcohol, and humidity measurement can be realized. Experimental results show that the measurement range is 30 to 95% with the maximum sensitivity of 0.737 nW∕% RH. The average response time is ∼2 s and the measurement is nearly insensitive to temperature. Compared with the wavelength detection method used in normal FBG-based relative humidity sensors, the intensity demodulation method in this report is simpler and more cost-efficient.

Partially liquid-filled hollow-core photonic crystal fiber polarizer.

A compact fiber polarizer is demonstrated by the filling of selected air holes of a hollow-core photonic crystal fiber (PCF) with a liquid. The liquid-filling results in an asymmetric waveguide structure, leading to a large polarization dependent loss. A 6 mm long ethanol-filled PCF exhibits a polarization extinction ratio of ∼18 dB over a wavelength range from 1480 nm to 1600 nm.

Highly sensitive fiber loop ringdown strain sensor using photonic crystal fiber interferometer.

A highly sensitive strain sensor is demonstrated by introducing a photonic crystal fiber (PCF) Mach-Zehnder interferometer (MZI) in a cavity ringdown fiber loop as a sensing element. The MZI is fabricated by splicing a short length of PCF between two single-mode fibers with collapsed air holes over a short region at two splicing points, which allows coupling between core and cladding modes inside the PCF. By measuring the decay constants of the fiber ringdown loop under different applied strains, a high strain sensitivity of ~0.21 µs⁻¹/εm and a minimum detectable strain of ~3.6 µÎµ are obtained. As a benefit from the ultralow thermal dependence of PCF, the maximum temperature-induced measurement error could be reduced to ~0.24 µÎµ.