Multi-point Detection Research Articles

Research on Optical Fiber Sensor Localization Based on the Partial Discharge Ultrasonic Characteristics in Long-Distance XLPE Cables

To improve the safety and antielectromagnetic interference performance of partial discharge detection in high-voltage DC cables, partial discharge of cables is used as a criterion for characterizing insulation defects. An ultrasonic detection method for the partial discharge of optical fiber detection is carried out in a long-distance high-voltage DC operating environment. By analyzing the partial discharge mechanism and ultrasonic characteristics of DC cables, a correlation model between partial discharge ultrasonic waves and discharge quantity is established. The partial discharge charge of several common insulation defects is obtained experimentally, and an ultrasonic characteristic Sagnac fiber detection system is realized. Standard ultrasonic time domain signal detection and fiber-optic sensing probe directional experiments are performed. The influence of fiber sensing probes with different lengths on the sensitivity of partial discharge signals is investigated based on the frequency distribution characteristics of partial discharges. The ultrasonic wave is measured based on a fiber-optic probe and can perform multipoint detection, and the partial discharge of the ±320 kV flexible DC transmission system was tested based on the developed optical fiber sensing system. The experimental results show that the partial discharge signal detection of 6 km long cable can be realized, and the localization accuracy is less than ±80 m. It provides a practical monitoring method for the perception of long-distance transmission equipment operating states.

Multiplexing fiber-optic Fabry-Perot acoustic sensors using self-calibrating wavelength shifting interferometry.

Flexible and stable demodulation techniques of large-scale fiber-optic Fabry-Perot (FP) acoustic sensors are highly desirable for accelerating their industrial applications. In this paper, we report a novel self-calibrating wavelength shifting interferometry (WSI) technique that enables simultaneous multi-point acoustic detection using diaphragm based fiber-optic FP acoustic sensors. A widely tunable modulated grating Y-branch (MG-Y) laser (1527∼1567 nm) performs high-speed wavelength switching, introducing phase-shifts in the wavelength domain for real-time phase retrieval. The proposed self-calibrating WSI is easily extended for multiplexing FP acoustic sensors by calibrating the corresponding phase-shift step of each sensor probe. Based on a modified Hariharan 5-step phase shifting algorithm, the phase-shift step for each channel can be calibrated in real-time, making the system robust in applications involving large environmental perturbations. An all-optical multi-point acoustic detection system based on WSI is proposed and experimentally demonstrated for the first time. Sound source localization experiments show that the multi-point acoustic detection system works stably and the positioning accuracy is about 2.42 cm.

A multi-spot laser induced breakdown spectroscopy system based on diffraction beam splitter.

A quick simultaneous multispot laser induced breakdown spectroscopy (LIBS) system has been proposed. The basic idea is to combine the Diffraction Beam Splitter (DBS) with the linear-to-linear fiber bundle. The DBS divided the incident laser beam into five sub-beams, and then, a lens focused the incident sub-beam to produce a plasma array, where the distance between the neighbor subplasma was constant and the plasma emission was imaged on the fiber bundle. Each ablated spot on the sample generated the corresponding spectroscopy signals, which were collected by the defined fibers of the fiber bundle, propagated to the spectrograph slit, and then analyzed by the intensified charge-coupled device (ICCD) detector, where the two-dimensional capability of the charge-coupled device detectors was explored for the spectroscopy and position analyses. The five spectroscopy ribbon presented on the ICCD corresponded to the plasma radiation of the five ablated spots. The feasibility of a simultaneous multipoint spectroscopy detection at a single pulse ablation was confirmed by subjecting to the spectroscopy analyses of a copper plane, layered material, and magnesium-molybdenum mixture. The multispot LIBS system can be used in the ejecta research of detonation physics, fluid physics, and so on.

The Interface Behavior of Multiple Piezoelectric Films Attaching to a Finite-Thickness Gradient Substrate

Abstract The interface behavior of multiple piezoelectric films attaching to a gradient substrate under the action of electromechanical coupling is studied. The effect of neighboring films on the interface response is mainly concerned, including the interface stress, the stress intensity factors near both ends of piezoelectric films and the normal stress of films. In order to solve such a boundary value problem, Fourier transformation is used to achieve governing integro-differential equations, which could further demonstrate the interface behavior. The results show that, in comparison with the single-film model, both the interface stress and the normal stress of films are significantly affected by adjacent piezoelectric films. When the equivalent stiffness of the substrate or the distance between neighboring piezoelectric films becomes larger, the interaction between adjacent piezoelectric films gradually weakens. In addition, both shorter piezoelectric films and softer or thicker intermediate adhesive layers are beneficial to the interface property. The results should be helpful for the accurate measurement of surface sensors and the arrangement of multipoint health detection of gradient structures.

Multipoint-Detection Strain Sensor with a Single Electrode Using Optical Ultrasound Generated by Carbon Nanotubes.

With the development of wearable devices, strain sensors have attracted large interest for the detection of human motion, movement, and breathing. Various strain sensors consisting of stretchable conductive materials have been investigated based on resistance and capacitance differences according to the strain. However, this method requires multiple electrodes for multipoint detection. We propose a strain sensor capable of multipoint detection with a single electrode, based on the ultrasound pulse–echo method. It consists of several transmitters of carbon nanotubes (CNTs) and a single polyvinylidene fluoride receiver. The strain sensor was fabricated using CNTs embedded in stretchable polydimethylsiloxane. The received data are characterized by the different times of transmission from the CNTs of each point depending on the strain, i.e., the sensor can detect the positions of the CNTs. This study demonstrates the application of the multipoint strain sensor with a single electrode for measurements up to a strain of 30% (interval of 1%). We considered the optical and acoustic energy losses in the sensor design. In addition, to evaluate the utility of the sensor, finger bending with three-point CNTs and flexible phantom bending with six-point CNTs for the identification of an S-curve having mixed expansion and compression components were carried out.

Can Enhanced Flux Loading by High‐Speed Jets Lead to a Substorm? Multipoint Detection of the Christmas Day Substorm Onset at 08:17 UT, 2015

AbstractThis paper describes highly interesting observations of the 25 December 2015 substorm onset at 08:17 UT during northward interplanetary magnetic field (IMF) while magnetosheath contained several intervals of negative Bz. A unique alignment of several spacecraft near the Earth‐Sun line together with magnetohydrodynamic simulations, ground‐based magnetometer, and auroral observations allow a comprehensive timing analysis of the events leading to substorm onset. Perplexingly, prior to substorm onset Geotail measured for 26 min positive IMF Bz just upstream of the bow shock, while simultaneously MMS spacecraft measured several intervals of strong negative Bz in the dayside magnetosheath. These strong pulses of negative Bz in the magnetosheath were associated with high dynamic pressure magnetosheath jets, likely created by foreshock transients during strongly radial IMF interval. Multipoint plasma and magnetic field measurements from ARTEMIS and THEMIS spacecraft were used to determine tail reconnection time at 8:14 and location at x=−33RE. Ground‐based observations of Pi2 pulsations and auroral brightening, with observations of a dipolarization front by THEMIS spacecraft, allowed determination of substorm onset to be at ≈08:17. All MMS spacecraft detected the same magnetosheath jet structure with Bz=−25 nT at ∼08:00 while IMF was northward. Based on DMSP observations and timing analysis we propose that these jets produced magnetopause reconnection leading to final, critical flux enhancement in the midtail region, which may have triggered reconnection 12–14 min later after jet observations.

A Multi-Point Switchable and Self-Adaptive Ultrasonic Sensor Using Fiber Bragg Gratings in a Fiber Ring Laser

We propose and demonstrate a multi-point, self-adaptive fiber ultrasonic sensor based on fiber Bragg gratings (FBGs). The sensor is constructed from matched FBG pairs (FBGPs) and a tunable optical filter in a fiber ring laser. FBGPs with different Bragg wavelengths are used as both the comb filter to produce potential lasing lines and the ultrasonic sensing elements. The ultrasonic signal is directly detected by monitoring the intensity response at each laser channel to the cold-cavity loss modulation from the spectral shift of matched FBGPs. The laser channel between the FBGPs is actively switched using the tunable optical filter, thereby achieving multi-point and switchable detection yet avoiding mode competition in the lasers. Meanwhile, to achieve self-adaptability, the two FBGs of the FBGP are fixed side by side at the same location of the structure such that both FBGs respond similarly to static strain and temperature variation. The multi-point system is promising for the robustness in the practical applications because it is insensitive to static strain ranging over 1400 μ ϵ and temperature variation from 20 °C to 50 °C, respectively.

Research on multi-point temperature detection and time display system

For the industrial environment with complex application environment and large amount of information display, quadruple high-bright digital tubes, external perpetual calendar chip and multiple digital temperature sensors DS18B20 are used to design and manufacture system display, time function module and multi-point temperature detection function modules, they are integrated by the automatic control core IAP15F2K61S2 as the full-featured multi-point temperature detection and time display system. Based on the system time provided by the designed time system, it realizes single-point and multi-point high-precision detection of system temperature, statistics and record of the system key control parameters, real-time dynamic monitoring of the system’s key parameters through high-bright display and matrix keyboard with efficient human-computer interaction. The core control functions are encapsulated in a portable header file format, which can be used with other modules of the system to implement system function optimization and troubleshooting.

Tuning CdTe quantum dots reactivity for multipoint detection of mercury(II), silver(I) and copper(II)

In this work we tuned the surface chemistry of distinctly-sized CdTe quantum dots (QDs), by using a variety of capping ligands with distinctive functional moieties, and combined them in multi-QDs probing solutions for Hg2+, Cu2+ and Ag+. Upon the individual interaction of the distinctly-capped QDs with each of the abovementioned metal ions, several parameters such as Stern-Volmer constants, equilibrium binding constants, the red-shift magnitude and photoluminescence (PL) lifetime values were thoroughly evaluated.Due to their great reactivity, selectivity could become a major issue in the application of semiconductor quantum dots in chemical analysis. Therefore, the combination in the same analysis of multiple QDs, capped with distinct ligands and emitting at different wavelengths, was exploited to guarantee a specific analyte-response profile. When coupled with chemometrics, for data analysis and processing, the developed approach provided enhanced selectivity and accuracy. In fact, the obtained results of all the partial least squares (PLS) models coefficient of determination of cross-validation (R2CV) close to 1, root mean square error of calibration (RMSEC) and root mean square error of cross-validation (RMSECV) values ranging 0.0094–0.15 and 0.013–0.19 mg L−1, respectively. demonstrated the possibility to perform accurate predictions of Hg2+ and Cu2+. Additionally, the sensitivity of the developed models was also calculated and allowed us to conclude which combination of distinctly-capped QDs assured a more sensitive quantification of Cu2+ (sensitivity = 653 L−1 mg for 3-mercaptopropionic acid (MPA)/MPA conjugated probe) and Hg2+ (sensitivity = 14,017 L−1 mg for reduced glutathione (GSH)/MPA-conjugated probe).

Fiber optic multipoint remote methane sensing system based on pseudo differential detection

An all optical fiber multipoint methane sensing system based on a new pseudo differential detection technique, operating at the near-infrared wavelength of 1645.54 nm, is developed for continuous remote monitoring of methane gas concentration. A pseudo differential detection technique employing high frequency square modulation is applied to tunable diode laser absorption spectroscopy (TDLAS), and methane concentration is derived from the variation of square-wave amplitude. The efficacy of the new approach is analyzed theoretically and demonstrated experimentally. Test results show that the performance of the proposed simpler sensing system realizing multipoint remote detection is comparable with systems employing the second harmonic detection technique. The developed sensing system was deployed in a working underground utility tunnel in the Hengqin special district (Zhuhai, China) in April 2017, and has been functioning satisfactorily since.

Investigations on the Signal Recovery From the Non-Absorption Transmission Loss in Wavelength Modulation Spectroscopy

In practical applications, the signal-to-noise ratio (SNR), reliability, and the long-term stability of wavelength modulation spectroscopy (WMS) system is limited by the non-absorption transmission loss. In this investigation, we report on a signal recovery method to remove the impact of non-absorption transmission loss based on an automatic gain closed-loop control. The deviation of the WMS system with the introduced signal recovery method has been observed to be below 4.27% under the non-absorption transmission loss which varied from 0 dB to −6.02 dB, and is about 13 times lower than the ordinary system. The proposed method is suitable for promoting the reliability and stability of WMS system under rigorous circumstances. Besides, it has the potential value in the multi-point detection or to achieve a higher SNR.

Diaphragm-based optical fiber sensor array for multipoint acoustic detection.

Multipoint acoustic sensing system plays an important role in industrial applications. Here, a diaphragm based optical fiber sensor array is proposed, in which each sensor tip is made of 10-layer graphene diaphragm and optical fiber pigtail, with the compact size of about 2.5 mm in diameter. In particular, coherent phase detection is adopted to improve detection signal-to-noise ratio (SNR) and eliminate the demodulation dependence on structural parameters of sensor tips, and thus to achieve the multiplexing ability. Through time division multiplex (TDM), a multiplexing capacity up to 248 in theory can be realized, which is the first time to theoretically demonstrate large-scale acoustic sensor array for diaphragm based fiber sensor by phase detection, to the best of our knowledge. A prototype of 2 *2 sensor array is built to demonstrate the acoustic sensing performance. The field test results show excellent acoustic sensitivity of higher than -136 dB re 1 rad/μPa within the frequency range of 300 Hz~15 kHz, as well as the MDP of only 75 μPa/Hz1/2. Besides, good temperature stability and wide directivity are demonstrated. The proposed sensor array is promising in sound source localization, where the positioning accuracy of 3.55 cm is successfully realized.

Quasi-distributed multipoint laser methane detection system and its application in cable trench safety monitoring

A low power consumption, quasi-distributed, multi-point laser methane detection system incorporating a Vertical Cavity Surface Emitting Laser (VCSEL) has been designed and its performance discussed. Being based on the features of the methane absorption spectrum and adaptive tracking technology, the system can realize on-line methane monitoring across 14 channels of sensors, with the maximum transmission distance for each sensor being 10km. Working across a temperature range of 0°C-40°C, the measurement error was determined to be less than ±0.03% (of the gas concentration) when the methane volume concentration lies in the range up to 10% methane. The system has been tested in-the-field in a cable tunnel belonging to a power supply company in Jinan in China and the test results achieved show that the system has the high accuracy and good stability needed for use in industrial safety monitoring.

A New Resistive Belt Sensor for Multipoint Contact Detection of Robotic Wheels

In this paper, a new, simple and cheap sensor is proposed to detect the multipoint contact of a typical robotic wheel. The new sensor empowers a wheeled robot to scan the surface and to find stability margins during real-time locomotion without camera or laser sensors. Furthermore, it enhances the ability of the real-time solution of the dynamic equations. The new sensor is based on the total resistance of a circuit and can be classified into two types. In the first type, the resistive circuit includes a conductive path, a direct voltage source and some resistors by various values. The main advantage of this type of the new sensor is to determine the exact locations of multipoint contact only by means of an input data detecting the voltage of a resistor. The implementation of the new idea is easy to use and to be experimented. It can be used to improve the control process, especially on the rough surfaces and to enhance the locomotion stability. The second type of the new sensor contains a continuous resistive belt with higher accuracy than the first type. The algorithm of the multipoint contact detection is explained and the kinematics relations of the robot are obtained. The surface is scanned during the robot locomotion, and the error of the estimated surface profile is calculated. Finally, the static stability margins are extracted using the new sensor data.

Monitoring System of Shaft Based on ZigBee Wireless Sensor Network

Traditional shaft temperature and humidity detection system is wired mode, the transmission distance is limited. In order to overcome this shortcoming, this paper designed a detection system, which is based on ZigBee wireless sensor network and digital temperature-humidity sensor. In the system, the data’s acquisition and transmission of master-slave nodes is realized by the star network, and the data is displayed on the host computer through serial port. The system can realize multi-point detection and real-time monitoring.

Multiplexed analysis combining distinctly-sized CdTe-MPA quantum dots and chemometrics for multiple mutually interfering analyte determination

Semiconductor quantum dots (QDs) have demonstrated a great potential as fluorescent probes for heavy metals monitoring. However, their great reactivity, whose tunability could be difficult to attain, could impair selectivity yielding analytical results with poor accuracy. In this work, the combination in the same analysis of multiple QDs, each with a particular ability to interact with the analyte, assured a multi-point detection that was not only exploited for a more precise analyte discrimination but also for the simultaneous discrimination of multiple mutually interfering species, in the same sample. Three different MPA-CdTe QDs (2.5, 3.0 and 3.8nm) with a good size distribution, confirmed by the FWHM values of 48.6, 55.4 and 80.8nm, respectively, were used. Principal component analysis (PCA) and partial least squares regression (PLS) were used for fluorescence data analysis. Mixtures of two MPA-CdTe QDs, emitting at different wavelength namely 549/566, 549/634 and 566/634nm were assayed. The 549/634nm emitting QDs mixture provided the best results for the discrimination of distinct ions on binary and ternary mixtures. The obtained RMSECV and R2CV values for the binary mixture were good, namely, from 0.01 to 0.08mgL−1 and from 0.74 to 0.89, respectively. Regarding the ternary mixture the RMSECV and R2CV values were good for Hg(II) (0.06 and 0.73mgL−1, respectively) and Pb(II) (0.08 and 0.87mg L−1, respectively) and acceptable for Cu(II) (0.02 and 0.51mgL−1, respectively). In conclusion, the obtained results showed that the developed approach is capable of resolve binary and ternary mixtures of Pb (II), Hg (II) and Cu (II), providing accurate information about lead (II) and mercury (II) concentration and signaling the occurrence of Cu (II).

A Large-Area Nanoplasmonic Sensor Fabricated by Rapid Thermal Annealing Treatment for Label-Free and Multi-Point Immunoglobulin Sensing.

Immunoglobulins are important biomarkers to evaluate the immune status or development of infectious diseases. To provide timely clinical treatments, it is important to continuously monitor the level of multiple immunoglobulins. Localized surface plasmon resonance (LSPR)-based nanoplasmonic sensors have been demonstrated for multiplex immunoglobulins detection. However, the sensor fabrication process is usually slow and complicated, so it is not accessible for large-area and batch fabrication. Herein, we report a large-area (2 cm × 2 cm) nanofabrication method using physical vapor deposition followed by a rapid thermal annealing treatment. To optimize the sensor performance, we systematically characterized three fabrication conditions, including (1) the deposition thickness; (2) the maximum annealing temperature, and (3) the annealing time. The corresponding absorbance spectrum profile and surface morphology of the nanostructures were observed by a UV-VIS spectrometer and atomic force microscopy. We then tested the sensitivity of the sensor using a glucose solution at different concentrations. The results showed that the sensor with 10 nm gold deposition thickness under 5-min 900 °C rapid thermal annealing can achieve the highest sensitivity (189 nm RIU−1). Finally, we integrated this nanoplasmonic sensor with a microchannel and a motorized stage to perform a 10-spot immunoglobulin detection in 50 min. Based on its real-time, dynamic and multi-point analyte detection capability, the nanoplasmonic sensor has the potential to be applied in high-throughput or multiplex immunoassay analysis, which would be beneficial for disease diagnosis or biomedical research in a simple and cost-effective platform.

Optical Fiber Photoacoustic Gas Sensor With Graphene Nano-Mechanical Resonator as the Acoustic Detector

We report an all-optical fiber photoacoustic gas sensor with a graphene nano-mechanical resonator as the acoustic detector. The acoustic detector is a Fabry–Perot interferometer formed by attaching a 100-nm-thick, 2.5-mm-diameter multilayer graphene diaphragm to a hollow cavity at the end of a single-mode optical fiber. By operating at one of the mechanical resonances of the diaphragm, the sensitivity for acoustic detection is enhanced and a noise equivalent minimum detectable pressure of 2.11 μPa/Hz1/2 at 10.1 kHz is demonstrated. Detection of acetylene gas is demonstrated with a distributed feedback semiconductor laser tuned to the P(9) absorption line of acetylene and a lower detection limit of 119.8 parts-per-billion (ppb) is achieved with 123.9-mW pump power. Theoretical analysis shows that by increasing the Q-factor of the resonator, which may be achieved by operating at low gas pressures, ppb level gas detection is possible. The all-fiber photoacoustic gas sensor is immune to electromagnetic interference, safe in flammable and explosive environment, and would be ideally suited for remote, space-limited applications and for multipoint detection in a multiplexed fiber optic sensor network.

Grain bulk density measurement based on wireless network

To know the accurate quantity of stored grain, grain density sensors must be used to measure the grain’s bulk density. However, multi-sensors should be inserted into the storage facility, to quickly collect data during the inventory checking of stored grain. In this study, the ZigBee and Wi-Fi coexistence network’s ability to transmit data collected by density sensors was investigated. A system consisting of six sensor nodes, six router nodes, one gateway and one Android Pad was assembled to measure the grain’s bulk density and calculate its quantity. The CC2530 chip with ZigBee technology was considered as the core of the information processing, and wireless nodes detection in sensor, and router nodes. ZigBee worked in difference signal channel with Wi-Fi to avoid interferences and connected with Wi-Fi module by UART serial communications interfaces in gateway. The Android Pad received the measured data through the gateway and processed this data to calculate quantity. The system enabled multi-point and real-time parameter detection inside the grain storage. Results show that the system has characteristics of good expansibility, networking flexibility and convenience.

Multi-Point Disturbance Detection and High-Precision Positioning of Polarization-Sensitive Optical Time-Domain Reflectometry

Compared with its counterparts, polarization sensitive optical time-domain reflectometry (P-OTDR) has two typical problems in terms of multi-point disturbance detection and high precision positioning, which restrict its practical applications. In this paper, we propose a novel method by using two-dimensional (2-D) image processing and statistical clustering. In place of the traditional spatial or temporal signal analysis way, the idea employs the temporally and the spatially uneven/inconsistent evolving patterns induced by the multiple individual events, and the proposed method is carried out to accumulate the temporally differentiated OTDR traces and then build up a 2-D temporal-spatial evolving graph, by using edge detection and automatic clustering to distinguish different disturbing points with precise locations. Through series of multi-point disturbance tests, the proposed method has been proved to have better performance than the conventional direct differentiation method and the fast Fourier transform spectrum analysis.