Optical sensors based on the NiPc-CoPc composite films deposited by drop casting and under the action of centrifugal force

In this study, solution processed composite films of nickel phthalocyanine（NiPc） and cobalt phthalocyanine（CoPc）are deposited by drop casting and under centrifugal force. The films are deposited on surface-type inter-digitated silver electrodes on ceramic alumina substrates. The effects of illumination on the impedance and capacitance of the NiPc–CoPc composite samples are investigated. The samples deposited under centrifugal force show better conductivity than the samples deposited by drop casting technique. In terms of impedance and capacitance sensitivities the samples fabricated under centrifugal force are more sensitive than the drop casting samples. The values of impedance sensitivity（Sz）are equal to（-1.83） MΩ·cm^2/mW and（-5.365） MΩ·cm^2/mW for the samples fabricated using drop casting and under centrifugal force, respectively. Similarly, the values of capacitance sensitivity（Sc） are equal to 0.083 pF·cm^2/mW and 0.185 pF·cm～2/mW for the samples fabricated by drop casting and under centrifugal force. The films deposited using the different procedures could potentially be viable for different operational modes（i.e., conductive or capacitive） of the optical sensors. Both experimental and simulated results are discussed.

Liquid Crystal Based Label-Free Optical Sensors forBiochemical Application

Biochemical sensors have important applications in biology,chemistry,and medicine.Nevertheless,many biochemical sensors are hampered by intricate techniques,cumbersome procedures,and the need for labeling.In the past two decades,it has been discovered that liquid crystals can be used to achieve the optical amplification of biological interactions.By modifying recognition molecules,a variety of label-free biochemical sensors can be created.Consequently,biochemical sensors based on the amplification of liquid crystals have become one of the most promising sensors.This paper describes in detail the optical sensing principle of liquid crystals,sensing devices,and optical detection technologies.Meanwhile,the latest research findings are elucidated.Finally,the challenges and future research directions are discussed.

Functional Optical Fiber Sensors Detecting Imperceptible Physical/Chemical Changes for Smart Batteries

The battery technology progress has been a contradictory process in which performance improvement and hidden risks coexist.Now the battery is still a“black box”,thus requiring a deep understanding of its internal state.The battery should“sense its internal physical/chemical conditions”,which puts strict requirements on embedded sensing parts.This paper summarizes the application of advanced optical fiber sensors in lithium-ion batteries and energy storage technologies that may be mass deployed,focuses on the insights of advanced optical fiber sensors into the processes of one-dimensional nano-micro-level battery material structural phase transition,electrolyte degradation,electrode-electrolyte interface dynamics to three-dimensional macro-safety evolution.The paper contributes to understanding how to use optical fiber sensors to achieve“real”and“embedded”monitoring.Through the inherent advantages of the advanced optical fiber sensor,it helps clarify the battery internal state and reaction mechanism,aiding in the establishment of more detailed models.These advancements can promote the development of smart batteries,with significant importance lying in essentially promoting the improvement of system consistency.Furthermore,with the help of smart batteries in the future,the importance of consistency can be weakened or even eliminated.The application of advanced optical fiber sensors helps comprehensively improve the battery quality,reliability,and life.

Quantitative Identification of Delamination Damage in Composite Structure Based on Distributed Optical Fiber Sensors and Model Updating

Delamination is a prevalent type of damage in composite laminate structures.Its accumulation degrades structural performance and threatens the safety and integrity of aircraft.This study presents a method for the quantitative identification of delamination identification in composite materials,leveraging distributed optical fiber sensors and a model updating approach.Initially,a numerical analysis is performed to establish a parameterized finite element model of the composite plate.Then,this model subsequently generates a database of strain responses corresponding to damage of varying sizes and locations.The radial basis function neural network surrogate model is then constructed based on the numerical simulation results and strain responses captured from the distributed fiber optic sensors.Finally,a multi-island genetic algorithm is employed for global optimization to identify the size and location of the damage.The efficacy of the proposed method is validated through numerical examples and experiment studies,examining the correlations between damage location,damage size,and strain responses.The findings confirm that the model updating technique,in conjunction with distributed fiber optic sensors,can precisely identify delamination in composite structures.

Distributed fiber optic sensors for tunnel monitoring:A state-of-the-art review

Distributed fiber optic sensors(DFOSs)possess the capability to measure strain and temperature variations over long distances,demonstrating outstanding potential for monitoring underground infrastructure.This study presents a state-of-the-art review of the DFOS applications for monitoring and assessing the deformation behavior of typical tunnel infrastructure,including bored tunnels,conventional tunnels,as well as immersed and cut-and-cover tunnels.DFOS systems based on Brillouin and Rayleigh scattering principles are both considered.When implementing DFOS monitoring,the fiber optic cable can be primarily installed along transverse and longitudinal directions to(1)measure distributed strains by continuously adhering the fiber to the structure’s surface or embedding it in the lining,or(2)measure point displacements by spot-anchoring it on the lining surface.There are four critical aspects of DFOS monitoring,including proper selection of the sensing fiber,selection of the measuring principle for the specific application,design of an effective sensor layout,and establishment of robust field sensor instrumentation.These four issues are comprehensively discussed,and practical suggestions are provided for the implementation of DFOS in tunnel infrastructure monitoring.

A Modified Principal Component Analysis Method for Honeycomb Sandwich Panel Debonding Recognition Based on Distributed Optical Fiber Sensing Signals

The safety and integrity requirements of aerospace composite structures necessitate real-time health monitoring throughout their service life.To this end,distributed optical fiber sensors utilizing back Rayleigh scattering have been extensively deployed in structural health monitoring due to their advantages,such as lightweight and ease of embedding.However,identifying the precise location of damage from the optical fiber signals remains a critical challenge.In this paper,a novel approach which namely Modified Sliding Window Principal Component Analysis(MSWPCA)was proposed to facilitate automatic damage identification and localization via distributed optical fiber sensors.The proposed method is able to extract signal characteristics interfered by measurement noise to improve the accuracy of damage detection.Specifically,we applied the MSWPCA method to monitor and analyze the debonding propagation process in honeycomb sandwich panel structures.Our findings demonstrate that the training model exhibits high precision in detecting the location and size of honeycomb debonding,thereby facilitating reliable and efficient online assessment of the structural health state.

Multifunctional flexible optical waveguide sensor: on the bioinspiration for ultrasensitive sensors development

This paper presents the development of a bioinspired multifunctional flexible optical sensor(BioMFOS)as an ultrasensitive tool for force(intensity and location)and orientation sensing.The sensor structure is bioinspired in orb webs,which are multifunctional devices for prey capturing and vibration transmission.The multifunctional feature of the structure is achieved by using transparent resins that present both mechanical and optical properties for structural integrity and strain/deflection transmission as well as the optical signal transmission properties with core/cladding configuration of a waveguide.In this case,photocurable and polydimethylsiloxane(PDMS)resins are used for the core and cladding,respectively.The optical transmission,tensile tests,and dynamic mechanical analysis are performed in the resins and show the possibility of light transmission at the visible wavelength range in conjunction with high flexibility and a dynamic range up to 150 Hz,suitable for wearable applications.The BioMFOS has small dimensions(around 2 cm)and lightweight(0.8 g),making it suitable for wearable application and clothing integration.Characterization tests are performed in the structure by means of applying forces at different locations of the structure.The results show an ultra-high sensitivity and resolution,where forces in theμN range can be detected and the location of the applied force can also be detected with a sub-millimeter spatial resolution.Then,the BioMFOS is tested on the orientation detection in 3D plane,where a correlation coefficient higher than 0.9 is obtained when compared with a gold-standard inertial measurement unit(IMU).Furthermore,the device also shows its capabilities on the movement analysis and classification in two protocols:finger position detection(with the BioMFOS positioned on the top of the hand)and trunk orientation assessment(with the sensor integrated on the clothing).In both cases,the sensor is able of classifying the movement,especially when analyzed in conjunction with preprocessing and clustering techniques.As another wearable application,the respiratory rate is successfully estimated with the BioMFOS integrated into the clothing.Thus,the proposed multifunctional device opens new avenues for novel bioinspired photonic devices and can be used in many applications of biomedical,biomechanics,and micro/nanotechnology.

Surface plasmon excitation in semitransparent inverted polymer photovoltaic devices and their applications as label-free optical sensors

Herein,we report on surface plasmon(SP)-sensitive semitransparent inverted polymer photovoltaic(PV)devices that are based on multilayered material systems consisting of poly(3-hexylthiophene):fullerene-derivative bulk-heterojunction PV layers and thin gold or silver anodes.We demonstrate that these PV devices allow the simultaneous generation of both electrical power and SPs on their anodes for photoexcitation just above the optical absorption edge of the PV layers,resulting not only in attenuated total reflection,but also in attenuated photocurrent generation(APG)under the SP resonance(SPR)condition.Moreover,we also confirm that the biomolecular interaction of biotin–streptavidin on the PV devices can be precisely detected via apparent SPR angle shifts in the APG spectra,even without the need for complex attenuated total reflection configurations.We highlight our view that APG measurements made using these PV devices show great potential for the development of future generations of compact and highly sensitive SPR-based optical sensors.

Asymmetric Fabry-Pérot interferometric cavity for fiber optical sensors

Good linearity and wide dynamic range are the advantages of asymmetric Fabry-Pérot （F-P） interferometric cavity, whose realization has been long for. Based on optical thin film characteristic matrix theory, an asymmetric F-P interferometric cavity with good linearity and wide dynamic range is designed. And by choosing the material of two different thin metallic layers, the asymmetric F-P interferometric cavity is successfully fabricated. The design theory and method of this asymmetric F-P interferometric cavity have been described in detailed. In this paper an asymmetric F-P interferometric cavity used in fiber optical sensor is reported.

Visualized optical sensors based on two/three-dimensional photonic crystals for biochemicals

Responsive photonic crystals(RPCs) constructed by periodic two/three-dimensional(2D/3D) photonic crystals(PCs) and responsive-material hosts,are important visualized optical sensors.Their optical diffraction color can be tuned reversibly by external stimuli,such as pH,metal ions,biomolecules,vapors and solvents,hence leading to wide applications as visualized sensors.This review introduces the recent progress of RPCs based on 2D/3D PCs for visual detection of chemical and biological analytes,including the preparation of 2D PCs,3D PCs films,3D PCs microbeads and their applications as visualized sensors.The different cases of detecting various chemical and biological analytes by naked eyes are presented.Emphasis is given to the description of their respective sensing mechanisms with the different systems for chemical and biological analytes.Compared with 3D RPCs sensors,2D RPCs sensors have shorter response time,better stabilization and higher production efficiency,however,the diffraction intensity of 2D RPCs based on monolayered 2D polystyrene(PS) microsphere array are weak.2D RPCs sensors based on 2D Au nanosphere can significantly improve the diffraction intensity compared with traditional 2D RPCs sensors based on monolayered PS microsphere array.The much higher scattering cross section of Au nanosphere leads to 2D Au nanosphere array with ultrahigh optical diffraction intensity,which are highly helpful for their practical application as visual sensors and further quantitative detection by monitoring the diffraction peak position and intensity.

Air-blast anti-fouling cleaning for aquatic optical sensors

In order to solve the problem of fouling of submerged optical instruments,an air-blast cleaning mechanism was integrated into an optical sensor used for measuring suspended sediment concentration(SSC)in natural waters.Laboratory experiments in a manually created fouling environment were conducted to observe the fouling process on sensor cases made of different materials,and to verify the effectiveness of air-blast cleaning in reducing fouling.Results indicated that sensors with an aluminum case experienced more serious bio-fouling than that with polyethylene case,and the air-blast cleaning mechanism was capable of reducing fouling effect on sensor signals.So the submerged optical instruments should avoid using metal materials.The duration and frequency of air-blast cleaning can be determined and adjusted depending on actual field conditions.

Sensors for control of water transparency in optical and microwave ranges

In the face of deteriorating environmental conditions in the world,water quality control is an urgent task.It can be solved by creating sensors with high accuracy and low cost,which requires the development of fundamentally new radiophysical methods that take advantage of the optical,microwave and millimeter wavelengths that have a significantly greater sensitivity to low concentrations of pollutants and a lower inertia.The article presents prototypes of measuring cells of the microwave and optical ranges as well as the results of an experimental study of water of various degrees of pollution with their help.The results show that the use of the highly sensitive method of capillary-waveguide resonance makes it possible to detect the presence of micro impurities in water with concentrations up to0.1%and to identify water even from sources of various natural origins.In addition,the use of measurements at several frequencies in the optical range will make it possible to solve the problem of creating water control sensors with high sensitivity to pollution and low cost.It can be concluded that the possibility of complex use of multiwave sensors(optical,infrared and microwave ranges)allows to increase the sensitivity and reliability of water quality assessment.

Feasibility and Application Study of Optical Voltage/Current Sensors Using FBG

This paper concludes the case study work on the optical sensor, which is a new method for voltage and current measurement. Fiber Bragg gratings (FBG) have been developed and used for decades in the telecommunication industry. In recent years, FBG sensors have found wide applications in monitoring strain, temperature, voltage and current across all industries. As the process of constructing a robust smart grid, thousands of miles of optical-fibers have been deployed along the power transmission lines for the purpose of power production communication. This paper focuses on using the power optical fiber as voltage/current sensors instead of those copper wired traditional current transformers. By using piezoelectric layers, the optical sensor is able to transform voltage/current magnitude into optical signal, as well as transmit the signal through the optical fiber. The application of using optical fiber will significantly reduce the cost of deploying traditional current transformers all around the power grid. Moreover, the optical sensor is more stable, more accurate and faster, with such characteristics, the smart grid monitoring system could be much better. The application of combining the optical composite low-voltage cable (OPLC) and the optical current sensor in the distribution network for smart distribution monitoring has been analyzed.

An Optical Fiber Sensor for Simultaneous Measurement of pO2 and pH

Whether in the monitoring of critically ill patients such as shock, respiratory failure, brain injury, or in major anesthesia surgeries, it is necessary to evaluate the patient’s pO2 and pH. An optical fiber sensor presented is capable of monitoring the presence of oxygen partial pressure (pO2) and pH in the real-time. The sensor is based on fluorescence sensing of polymer immobilized in the oxygen/pH-sensitive membranes and covalently attached to the optical fiber probe. The design of this sensor uses LED as light source, which is an excitation light source, inducing specific wavelengths of fluorescence on the oxygen/pH-sensitive membrane. The intensity and lifetime of fluorescence are related to the pO2 and pH. So the pO2 and pH can be measured by the relationship between the pO2/pH values and the intensity and lifetime of fluorescence. The signal conditioning system based on DSP and STM32 was used to store and process data, and display test values. The response of the sensor for pO2 and pH monitoring with nitrogen (N2) as a balancing gas in the laboratory was performed. Finally, the oxygen/pH sensing scheme presented in this work is intended for using in biological, medical and environmental applications.

Evaluation of excavation damaged zones(EDZs)in Horonobe Underground Research Laboratory(URL)

Excavation of underground caverns,such as mountain tunnels and energy-storage caverns,may cause the damages to the surrounding rock as a result of the stress redistribution.In this influenced zone,new cracks and discontinuities are created or propagate in the rock mass.Therefore,it is effective to measure and evaluate the acoustic emission(AE)events generated by the rocks,which is a small elastic vibration,and permeability change.The authors have developed a long-term measurement device that incorporates an optical AE(O-AE)sensor,an optical pore pressure sensor,and an optical temperature sensor in a single multi-optical measurement probe(MOP).Japan Atomic Energy Agency has been conducting R&D activities to enhance the reliability of high-level radioactive waste(HLW)deep geological disposal technology.In a high-level radioactive disposal project,one of the challenges is the development of methods for long-term monitoring of rock mass behavior.Therefore,in January 2014,the long-term measurements of the hydro-mechanical behavior of the rock mass were launched using the developed MOP in the vicinity of 350 m below the surface at the Horonobe Underground Research Center.The measurement results show that AEs occur frequently up to 1.5 m from the wall during excavation.In addition,hydraulic conductivity increased by 2e4 orders of magnitude.Elastoplastic analysis revealed that the hydraulic behavior of the rock mass affected the pore pressure fluctuations and caused micro-fractures.Based on this,a conceptual model is developed to represent the excavation damaged zone(EDZ),which contributes to the safe geological disposal of radioactive waste.

Temperature and Salinity Dual-parameter Sensing Based on Forward Brillouin Scattering in 1060-XP SMF

A novel temperature and salinity discriminative sensing method based on forward Brillouin scattering(FBS)in 1060-XP single-mode fiber(SMF)is proposed.The measured frequency shifts corresponding to different radial acoustic modes in 1060-XP SMF show different sensitivities to temperature and salinity.Based on the new phenomenon that different radial acoustic modes have different frequency shift-temperature and frequency shift-salinity coefficients,we propose a novel method for simultaneously measuring temperature and salinity by measuring the frequency shift changes of two FBS scattering peaks.In a proof-of-concept experiment,the temperature and salinity measurement errors are 0.12℃and 0.29%,respectively.The proposed method for simultaneously measuring temperature and salinity has the potential applications such as ocean surveying,food manufacturing and pharmaceutical engineering.

AN OPTICAL FIBER SENSOR TECHNIQUE BASED ON SLIGHT DISTURBANCE RADIATION LOSS OF STOCHASTIC WALL

This paper presents an optical sensor technique used in the damage evaluation which is formed by structurally integrated fiber optic reticulate sensors embedded in the composite materials. The fibers are processed by chemical method and their outsides are peeled to form particles of irregular distribution and they differ in size, so the slight disturbance range of stochastic wall are formed in fibers. According to the characteristics of power loss of waveguide mode caused by slight disturbance of stochastic wall and radiative mode transmission, the range of slight disturbance of stochastic wall may be served as the sensitive range of the sensor. On the basis of theory of slight disturbance of stochastic wall of planar optical waveguide, the relation between the corrosion time and the opposite power loss by experiments is investigated. In this paper, the measurement results of object of SIFORS are also presented. The results show that the optical sensor technique may be used in the damage evaluation of an aircraft.

New High Sensitivity Pressure Transducer with Optical Fibre Link

The principle of new optical fibre pressure transducer is analysed, and ingenious design scheme of this transducer is given. This new transducer specimen is provided with following characteristics: experimental transmitting distance is 20 m (actually up to 1 000 m ); system sensitivity is 0. 1 mV/Pa; power consumption of the probe is less than 125 μW. Finally, some points of the appraisement are given in this paper.

Metal–Organic Framework-Based Sensors for Environmental Contaminant Sensing

Increasing demand for timely and accurate environmental pollution monitoring and control requires new sensing techniques with outstanding performance, i.e.,high sensitivity, high selectivity, and reliability. Metal–organic frameworks(MOFs), also known as porous coordination polymers, are a fascinating class of highly ordered crystalline coordination polymers formed by the coordination of metal ions/clusters and organic bridging linkers/ligands. Owing to their unique structures and properties,i.e., high surface area, tailorable pore size, high density of active sites, and high catalytic activity, various MOF-based sensing platforms have been reported for environmental contaminant detection including anions, heavy metal ions,organic compounds, and gases. In this review, recent progress in MOF-based environmental sensors is introduced with a focus on optical, electrochemical, and field-effect transistor sensors. The sensors have shown unique and promising performance in water and gas contaminant sensing. Moreover, by incorporation with other functional materials, MOF-based composites can greatly improve the sensor performance. The current limitations and future directions of MOF-based sensors are also discussed.

Advances in phase-sensitive optical time-domain reflectometry

Phase-sensitive optical time-domain reflectometry(Φ-OTDR)has attracted numerous attention due to its superior performance in detecting the weak perturbations along the fiber.Relying on the ultra-sensitivity of light phase to the tiny deformation of optical fiber,Φ-OTDR has been treated as a powerful technique with a wide range of applications.It is fundamental to extract the phase of scattering light wave accurately and the methods include coherent detection,I/Q demodulation,3 by 3 coupler,dual probe pulses,and so on.Meanwhile,researchers have also made great efforts to improve the performance ofΦ-OTDR.The frequency response range,the measurement accuracy,the sensing distance,the spatial resolution,and the accuracy of event discrimination,all have been enhanced by various techniques.Furthermore,lots of researches on the applications in various kinds of fields have been carried out,where certain modifications and techniques have been developed.Therefore,Φ-OTDR remains as a booming technique in both researches and applications.