Multi-point Detection Research Articles

Development of an antenna coil type sensor device for hydrogen leakage detection

An antenna coil type hydrogen gas sensor device was fabricated and evaluated for applying to radio frequency identification (RFID) tag which can easily realize highly reliable and multipoint hydrogen leakage detection system. An antenna coil composed of platinum thin film was formed by photolithography onto a quartz-glass substrate. Then, a platinum-supported tungsten trioxide thin film was deposited on that coil by spin coating method. A frequency dependence of electrical properties (S-parameters) of the sensor device in air and in 4vol.% hydrogen balanced with nitrogen gas was investigated in the range from 300kHz to 3GHz. The considerably change in frequency dependence of S11 with the exposure to hydrogen gas was observed. The result indicated high sensitivity of this sensor device and the possibility of wireless transmission of the information about hydrogen leakage. The 90% response time was about 3s at 188MHz. The sensitivity to hydrogen in air was lower than that in nitrogen atmosphere. It could result from the competitive oxidation reaction of tungsten bronze by oxygen. However, the sensor device was able to detect hydrogen gas in concentration range below lower explosion limit. In addition, the change in S21 between the sensor device and a conventional antenna coil was also demonstrated.

The Design and Realization of Intelligent Control System in Temperature and Humidity of Tea Intelligent Fixation

Aiming at the difficulty in control in tea fixation process, the intelligent control technology is adopted in the research which is for the core to the C8051F340 SCM and adopts the multi-point detection system to collect the temperature and humidity data. Besides, the data transmission with the epistemic machine can be realized by the I2C Bus, SPI and so on while the control rules and parameters of the controller can be intended. Thus it can be seen that the multi-parameter control of the temperature and humidity can be realized in tea green removing technology. The bunk watchdog circuit is adopted in hardware design to repair the systems bug automatically and safeguard the control system operate stably for a long time in this research. Additionally, the PID control algorithm is applied in software design to control systemic error less than 2%. Practical application indicates that this system is with simple structure, high reliability and good scalability, and it also can reduce the amount of labor and improve the teas quality.

Design of Temperature Control System in Incubator

To realize the real-time temperature measure and control rapidly and accurately in the incubator, a temperature measurement, control and display system is designed in the paper by using of the smart temperature sensor DS18B20 and the microcontroller AT89S52. The output mode of DS18B20 is serial in one-way, and its main function is to transform the temperature into the digital data and store the control word of the output conversion accuracy, which is available for data processing of single-chip microcomputer. In the actual temperature measurement it doesnt require any extra components including backup power supply, and the user can also choose the resolution. It is easy to realize multi-point measurement, connect and extend the real-time measure data. The system circuit can be applied to any field which needs multi-point measurement and real-time detection.

Multi-point accelerometric detection and principal component analysis of heart sounds

Heart sounds are a fundamental physiological variable that provide a unique insight into cardiac semiotics. However a deterministic and unambiguous association between noises in cardiac dynamics is far from being accomplished yet due to many and different overlapping events which contribute to the acoustic emission. The current computer-based capacities in terms of signal detection and processing allow one to move from the standard cardiac auscultation, even in its improved forms like electronic stethoscopes or hi-tech phonocardiography, to the extraction of information on the cardiac activity previously unexplored. In this report, we present a new equipment for the detection of heart sounds, based on a set of accelerometric sensors placed in contact with the chest skin on the precordial area, and are able to measure simultaneously the vibration induced on the chest surface by the heart's mechanical activity. By utilizing advanced algorithms for the data treatment, such as wavelet decomposition and principal component analysis, we are able to condense the spatially extended acoustic information and to provide a synthetical representation of the heart activity. We applied our approach to 30 adults, mixed per gender, age and healthiness, and correlated our results with standard echocardiographic examinations. We obtained a 93% concordance rate with echocardiography between healthy and unhealthy hearts, including minor abnormalities such as mitral valve prolapse.

Miniature fiber-tip photoacoustic spectrometer for trace gas detection

We demonstrate a fiber-tip photoacoustic spectrometric sensor for trace gas detection. The sensor head is a miniature fiber-tip hollow-cavity with a deflectable polymer diaphragm. Periodic light absorption of gas molecules within the cavity generates an acoustic pressure wave, which causes deflection of the diaphragm. The hollow cavity also is a Fabry-Perot interferometer with which the diaphragm deflection is detected with high sensitivity. Experimental test around the P(9) absorption line of C(2)H(2) achieved a minimum detectable gas concentration of 4.3 ppm with an excitation laser power of 8 mW. The miniature sensor head and fiber optic detection system make this type of spectrometers ideally suited for remote and space-limited applications as well as for multipoint detection in a multiplexed fiber optic sensor network.

多通道光纤法-珀解调系统分析与实验

A multi-channel optical fiber Fabry-Perot demodulation system based on non-scanning correlation demodulation combining with white light interfered Fabry-Perot sensor is designed.Utilizing cylindrical lens collecting and focusing light as linear light spot and get equivalent inverted image at 2times focal length plane,the corresponding optical model is set up;the optical characteristic analysis and parameter optimization is carried on;and the optical system and embedded demodulation system is designed.A Butterworth filter is used to filter out the background noise on the correlation signal effectively.Experiments based on the prototype demodulator show that the stability is up to 7nm,at the measuring range of 10~40μm,with the resolution of 8nm.The experimental results indicate that the system can achieve real-time measurement,high measurement accuracy,stability and consistency,and can realize multi-point detection and improve the multiplexing capacity.

Comb Filter-Based Fiber-Optic Methane Sensor System With Mitigation of Cross Gas Sensitivity

A remote fiber-optic methane gas sensor system is proposed and demonstrated with accurate gas concentration measurement and good mitigation of cross gas sensitivity. We use a polarization-maintaining photonic crystal fiber (PM-PCF)-based Sagnac loop filter to slice the spectrum of a broadband light source so as to precisely match several absorption lines of the methane gas within the near-infrared band. Meanwhile, a compact and cost-effective gas cell with multiple reflections is designed to enhance the interaction between the light beam and the methane gas to be detected, which also subsequently increase the system sensitivity. Due to the insensitive temperature dependence of the PM-PCF-based comb filter, we can obtain gas concentration measurement with a sensitivity of ~410 ppm. Moreover, by intentionally pumping the acetylene gas into the gas cell during the methane gas concentration measurement, the power variation caused by the interfering gas with 100% concentration is only equals to 0.7% of the power variation induced by the 100% concentration methane gas. Thus, effective mitigation of cross gas sensitivity is experimentally verified. The proposed fiber-optic methane gas sensor system is verified with low cost, compact size, potential capability of multipoint detection, and high sensitivity.

Backmixing Characterization of a Bubble Column with Short Venturi Throats by Multipoint Internal Tracer Injections

In reduction of liquid backmixing in bubble columns, Wu et al. [Wu, Y; Cheng, Z. M.; Huang, Z. B. Backmixing reduction of a bubble column by interruption of the global liquid circulation. Ind. Eng. Chem. Res.2009, 48, 6558–6563] have shown that the backmixing could be substantially reduced by interrupting the global liquid circulation using four identical short Venturi throats (SVTs). Considering the advantages of such structures, it is necessary to further investigate the backmixing characteristics of a bubble column with SVTs. In the present work, a multipoint tracer injection and detection device was employed to enhance the insight into where and how the liquid tracer was backmixed in different stages of a 50-cm diameter column. Tracer response profiles were measured to track the liquid backmixing trajectory in different stages at various operating conditions. The results showed that the backmixing of the column was sensitive to the throat diameter of SVTs. Based on the observed physical phenomena, a tanks-in-series with backflow (TISB) model was adopted to interpret the tracer experiment data, which shows an excellent agreement between the prediction and experimental measurements.

Determination of Liquid Multiscale Circulation Structure in a Bubble Column by Tracing the Liquid Flowing Trajectory

To identify the liquid circulation flow structure in a bubble column, a set of multipoint tracer injection and detection device was developed for a systematic study in a bubble column of 550 cm in height and 50 cm in diameter. Tracer response profiles were measured to track the liquid flowing trajectory under various flow conditions in the column with and without draft tubes. They showed that only when the draft tube length was greater than 3 m could the tracer response exhibit obvious periodicity. To resolve the liquid circulation flow structure in the time and frequency domain, wavelet multiresolution analysis was adopted. The results showed that the liquid circulation frequency increased with superficial gas velocity, which is in agreement with the published literature. It was also found that the macroscale, mesoscale, and microscale circulation loops coexisted in the bubble column.

Amperometric detection of DNA hybridization using a multi-point, addressable electrochemical device

A novel device was designed for the multipoint addressable detection of DNA hybridization. Row and column electrodes array were orthogonally arranged, and the microwells were assembled on the crossing points of the row/column electrodes to form a 4 × 4 microwell array. Amperometric signals at the individual microwells could be detected separately on the basis of redox cycling of localized electroactive species occurring between the electrodes. Immobilization and hybridization of DNA could block the redox cycling of Fe(CN) 6 4−/Fe(CN) 6 3− at the designated microwells, resulting in the reduction of current response. This device had been used to detect DNA hybridization with excellent sensitivity (0.03 μM) and selectivity. The device can be applied to comprehensive and high-throughput detection and imaging of biochemical species.

Design of multiplexed fiber optic chemical sensing system using clad-removable optical fibers

To prevent possible threats to public safety and economic loss from chemical leakage accidents, novel chemical sensing techniques for regular monitoring and leakage detection have been developed for various fields. We propose a fiber optic liquid chemical sensor (FOCS) system using specialty optical fibers and an optical time domain reflectometer (OTDR), and is based on the leaky wave mode sensing principle. OTDR enables simple multiplexing where individual sensor nodes along the fiber length could be interrogated by a common OTDR. The sensor node in the optical fiber is prepared by removing the desired length of a protective layer using mechanical stripping and chemical etching techniques. A novel laser stripping technique with superior capability to fabricate quasi-distributed dense sensor nodes is devised as well. The FOCS system is further analyzed to characterize the sensor response behavior in relation to the sensor node length and possible environmental and chemical temperature effect. Under the condition satisfying the leaky wave mode principle and within the minimum acceptable refractive index (RI) range by the system, this FOCS system could monitor numerous liquid chemicals with variable refractive indices and has been tested with positive results. In addition, the system shows the possibility for multi-point detection and is further expanded into a hybrid technique capable of estimating the refractive index range of the detected chemical.

The Study of the Internal Curing Technology of Filament Wound Composite Based on Fiber Bragg Grating Detection

At present, only the temperature of external surface of the filament wound composite and the core mode can be detected in the curing process which is developed by experiencing many times, and the change of the internal parameters is not available. Based on the glass fiber pipe production line as the experimental platform, the paper suggests that the fiber grating sensors be embedded fiber composite materials at different levels when winding and the multipoint detection be performed in the internal curing process. The comparison analysis of the plotted curves for data collected from different points shows that the method is reliable to improve production efficiency and promote the automation of intelligent control.

Research on Multi-Mode Driver Fatigue Detection System

This paper presented a multi-mode fatigue detection system. It included visual detection, multi-point pressure detection and physiological signal detection. Visual detection mainly carried out on eyes and mouth feature extraction and the states detection. First, skin color detection was used into face image extraction,and then one-dimensional wavelet transform and gray integral projection were used to detect the eye and mouth in human face image. Finally, the status of the eyes and mouth were detected to judge fatigue. The principle of multi-point pressure detection was that during fatigue state period, the body and the back will be still in a long time. So we can use sensors to detect pressure points to judge fatigue. Physiological signal detection was detected by the speed of the human wrist pulse signal. The paper mainly presented visual detection that used the camera to capture face images. The algorithm has advantages of low computation complexity, high speed and better detection effect.

Fabry−Pérot Cavity Sensors for Multipoint On-Column Micro Gas Chromatography Detection

We developed and characterized a Fabry-Pérot (FP) sensor module based micro gas chromatography (microGC) detector for multipoint on-column detection. The FP sensor was fabricated by depositing a thin layer of metal and a layer of gas-sensitive polymer consecutively on the endface of an optical fiber, which formed the FP cavity. Light partially reflected from the metal layer and the polymer-air interface generated an interference spectrum, which shifted as the polymer layer absorbed the gas analyte. The FP sensor module was then assembled by inserting the FP sensor into a hole drilled in the wall of a fused-silica capillary, which can be easily connected to the conventional gas chromatography (GC) column through a universal quick seal column connector, thus enabling on-column real-time detection. We characterized the FP sensor module based microGC detector. Sensitive detection of various gas analytes was achieved with subnanogram detection limits. The rapid separation capability of the FP sensor module assembled with both single- and tandem-column systems was demonstrated, in which gas analytes having a wide range of polarities and volatilities were well-resolved. The tandem-column system obtained increased sensitivity and selectivity by employing two FP sensor modules coated with different polymers, showing great system versatility.

Rapid tandem-column micro-gas chromatography based on optofluidic ring resonators with multi-point on-column detection

We demonstrated a novel tandem-column micro-gas chromatography (microGC) based on optofluidic ring resonator (OFRR). The OFRR is a thin-walled fused silica capillary whose interior surface is coated with a polymeric stationary phase. The circular cross section of the OFRR forms the micro-ring resonator and supports whispering gallery modes (WGMs). Via tapered optical fibers in contact with the OFRR, the WGM can be excited externally at any positions along the OFRR capillary, thus enabling multi-point, on-column, real-time detection of vapor molecules flowing through the OFRR. In the present OFRR-based tandem-column-based microGC implementation, a 180 cm long conventional GC column coated with a nonpolar stationary phase was followed by a relatively short OFRR column coated with a polar phase. Two detection positions, one at the inlet of the OFRR and the other a few centimeters downstream, were used to monitor the separation achieved by the first and the second column, respectively. Owing to the multi-point on-column detection that provides complementary retention time information on each chemical compound, co-eluted analytes can be well separated and identified on at least one detection channel and no modulation is needed at the interface of tandem columns. Separation and detection of twelve analytes with various volatilities and polarities within four minutes were demonstrated. In addition, the chromatograms obtained from three different locations along the OFRR column demonstrated the system's capability of on-column monitoring of the separation process for the target analyte in a vapor mixture. Our results will lead to the development of a rapid, simple, and portable microGC system with significantly improved selectivity and chemical identification capabilities.

Fine positioning of a poloidal probe array

Multipoint detection is an essential requirement for investigating plasma turbulence which is a highly nonlinear phenomenon in space and time. We have fabricated an array of 64-channel poloidal probes surrounding the linear cylindrical plasma named LMD-U in order to study turbulence properties, particularly the nonlinear mode couplings, in the domain of poloidal wave number and frequency. However, misalignments of probe tips produce spurious modes, which do not exist in the real plasma, to distort the precise wave number measurements. The paper presents the description of the 64-channel poloidal probe array with means to adjust the probe positions, with discussion on the effects of the misalignments on the wave number measurements.

Microfluidic chip‐based cell electrophoresis with multipoint laser‐induced fluorescence detection system

In this work, the electrophoretic mobility (EPM) measurement of individual cells was investigated by a simple on-chip electrophoresis system with LIF multipoint detection. The system enabled the characterization of cell electrophoresis behavior as well as the fluorescence signal from individual cells simultaneously. The measurement yielded the electropherograms of a large number of cells labeled with dye, in which the migration time and migration distance could be obtained easily. The EPM has been demonstrated to be different between the K562 cells and K562 cells treated with anticancer drug arsenic trioxide (As2O3). The K562 cells were found to exhibit a lower EPM compared to the cells after drug addition with different concentration. In this preliminary study, over 300 cells could be analyzed within 2 h, demonstrated a much higher analysis throughput compared with traditional methods. The established system is simple and fast, which is expected to be a promising method for evaluating cell surface properties and to be useful in clinical and pharmaceutical applications.

Active Fiber Bragg Grating Hydrogen Sensors for All-Temperature Operation

The use of liquid hydrogen as a fuel requires low-cost multipoint sensing of hydrogen gas for leak detection and location well below the 4% explosion limit of hydrogen. Herein is presented a multipoint in-fiber hydrogen sensor capable of hydrogen detection below 0.5% concentration with a response time of less than 10 s. Our solution entails use of a fiber Bragg grating (FBG) coated with a layer of hydrogen-absorbing palladium which, in turn, induces strain in the FBG in the presence of hydrogen. Infrared power laser light is used to induce heating in the palladium coating which dramatically decreases sensor response time and increases the sensor's sensitivity at low temperatures. This technology promises an inexpensive fiber solution for a multipoint hydrogen detection array with only one fiber feed-through

Wavelength Division Multiplexed Fiber Bragg Grating Vibration Sensor Array with Temperature Compensation

We have developed a novel method of wavelength division multiplexed operation of thermally stabilized fiber Bragg grating (FBG) vibration sensors in that simultaneous multipoint vibration detection with a temperature-insensitive operation can be achieved. One of the sensing elements of the arrayed sensors consists of a pair of FBGs, one is used for providing a narrow-spectrum light from a broad-spectrum incoherent optical source and the other is used for vibration sensing. The paired FBG configuration enables us to compensate the temperature effects that are commonly applied to the FBGs used. In the experiment, two sensing elements are arranged in tandem and the detection of simultaneous two-point multiple vibrations and the measurement of an elastic wave propagating in a metal bar are demonstrated.

Fiber Bragg Grating Hydrophone Array using Feedback Control Circuit: Time-division Multiplexed and Thermally Stabilized Operation

A novel fiber Bragg grating (FBG) hydrophone array has been proposed in order to realize multipoint underwater sound detection with thermal stabilization. The interrogation technique of the FBG hydrophone to be arrayed is based on an intensity-modulation scheme, in which a tunable laser is used for an optical source with its oscillation wavelength tuned to a slope of the reflection spectrum curve of the FBG. The partially reflected light from the FBG is modulated by an acoustic wave and offers a sensor output. For fabricating the FBG hydrophone array, an optical switch and a specially designed feedback circuit have been employed. The arrayed FBG hydrophones are connected in parallel with the output ports of the optical switch so that the time-division multiplexed (TDM) operation is performed by selecting the optical paths to the hydrophones. In the TDM operation, the feedback circuit enables us to control the oscillation wavelength automatically in accordance with the reflection spectrum for the selected FBG hydrophone. In addition, the automatic wavelength control allows the stabilization of the sensor output against temperature variations. In the experiment, two-point TDM sound detection with a thermally stabilized operation has been successfully demonstrated.