Zhanxiong Wei

High-sensitivity fiber Bragg grating pressure sensor using metal bellows

A novel structure of an optical fiber pressure sensor based on a fiber Bragg grating (FBG) and metal bellows is presented. Due to the novel structure, the sensitivity is improved to 48 pm/kPa. The relationship between Bragg wavelength and the applied pressure is derived. Experimental data indicates that there is a good linear relation between the Bragg wavelength shift and the applied pressure. This sensor can be utilized in low-pressure measurement.

High Pressure Sensor Based on Fiber Bragg Grating and Carbon Fiber Laminated Composite

A simple anisotropic structure made by carbon fiber laminated composite for fabricating a high pressure sensor is reported. A pressure sensor with good sensitivity over a broad measurement range is fabricated by using fiber Bragg grating and the anisotropic carbon fiber laminated composite structure. The characteristic responses of pressure and temperature of the new pressure sensor are analyzed. Experimental data show that when the pressure changes from 0 to 70 MPa, the wavelength shift of the fiber Bragg grating pressure sensor is up to 7 nm, corresponding to a sensitivity of 10 kPa/pm.

Liquid-level sensor using a fiber Bragg grating and carbon fiber composite diaphragm

ABSTRACT A novel liquid-level sensor based on fiber Bragg grating and carbon fiber composite diaphragm is proposed and demonstrated. The sensing principle and fi nite element analysis result are described. From the experimental result, this sensor shows high sensitivity and good repeatability. This sensor can find applications in the area of the liquid level sensing. Keywords : liquid-level sensor, fiber Bragg grating, carbon fiber composite diaphragm 1 INTRODUCTION Liquid-level measurement is important in modern industry such as water level monitor, fuel storage in a tank, and other applications. Various kinds of liquid-level sensing methods based on mechanical, electrical, and optical techniques have been proposed. Electrical liquid-level sensors are widely utilized. However, their applications are limited if the temperature of the monitored liquid is too high, conductive, potentially explosive or corrosive. Due to the inherent advantages of electrically passive operation, dielectric and im munity to the electromagnetic interference, high sensitivity and multiplexing capabilities, fiber Bragg grating sensors have attracted more interests. In the past few years, several optical fiber liquid-level sensors have been developed. These include sensors based on the photoelastic effect[1], multiple micro-bending sensor[2], liquid-level sensor based on the refractive index sensitivity of a long period grating [3], an intensity modulation approach using a pair of optical fibers to transmit the source light and receive the light partially reflected by the liquid surface through a glass prism[4], FBG sensors based on bending cantilever beam[5], FBG sensors consisting of diaphragm and Bourdon tube[6], liquid-level sensor based on etched Bragg grating[7]. For practical application, the above mentioned methods are limited due to the complicated sensor structure or the repeatability issue. In this paper, a novel method based on carbon fiber composite diaphragm and fiber Bragg grating and is proposed. It is well known that carbon fiber reinforced composite materials are an important class of engineering materials. They offer outstanding properties such as unique flexibility in design capabilities, ease of fabrication and also the advantages of light weight, corrosion resistance, impact resistance, excellent fatigue strength and good repeatability. In [8] we have previously reported an accurate high pressure sensor of 70Mpa which is based on FBG and carbon fiber laminate composite material. In this paper, to our knowledge, it is the first time that the carbon fiber composite diaphragm is proposed to be used as a sensing elemen t and experimental results are presented in detail.

Fiber-Bragg-grating-based weigh-in-motion system using fiber-reinforced composites as the load-supporting material

A novel fiber Bragg grating (FBG)-based weigh-in-motion (WIM) system is introduced in order to achieve a better performance compared with the existing WIM systems. This novel WIM system uses the fiber-reinforced composite (FRC) as the load-supporting material in combination with the FBG technology. The sensor is designed as a multiply FRC laminate with the FBG embedded inside it. A theoretical model is developed to analyze the mechanism of this WIM system. Both static and dynamic tests are conducted to verify the system performance. With the extraordinary mechanical properties of the FRC, this novel WIM system has achieved larger dynamic range and higher sensitivity than prior works. The simple design of the system also reduces the engineering difficulties and overall costs.

High-sensitivity pressure sensor based on fiber Bragg grating and metal bellows

An optical fiber pressure sensor based on fiber Bragg grating (FBG) and metal bellows is presented in this paper. Due to the lower spring rate of metal bellows, the sensitivity is improved to 48pm/kPa. The relationship between Bragg wavelength and the applied pressure is derived. Experimental data indicates that there is good linear relation between the Bragg wavelength shift and the applied pressure. This sensor can be utilized in low pressure measurement.

High speed, high performance, portable, dual-channel, optical fiber Bragg grating (FBG) demodulator

A high speed, high performance, portable, dual-channel, optical Fiber Bragg Grating demodulator based on fiber Fabry- Pérot tunable filter (FFP-FT) is reported in this paper. The high speed demodulation can be achieved to detect the dynamical loads of vehicles with speed of 15 mph. However, the drifts of piezoelectric transducer (PZT) in the cavity of FFP-FT dramatically degrade the stability of system. Two schemes are implemented to improve the stability of system. Firstly, a temperature control system is installed to effectively remove the thermal drifts of PZT. Secondly, a scheme of changing the bias voltage of FFP-FT to restrain non-thermal drifts has been realized at lab and will be further developed to an automatic control system based on microcontroller. Although this demodulator is originally used in Weight-In- Motion (WIM) sensing system, it can be extended into other aspects and the schemes presented in this paper will be useful in many applications.

Applications of Fiber Optic Bragg Grating Sensing Technology in a Forked Tunnel Model

Optical fiber Bragg gratings-based strain sensor modules were designed, fabricated, and embedded in a three-dimensional geo-mechanical model of a forked tunnel. These sensors recorded in-situ the strains of the embedded pots in the process of digging the tunnel. These results were compared with those of conventional strain gauges and of predictions from a detailed numerical analysis. The results indicate that the three sets of data (from the fiber Bragg grating strain sensors, the strain gauges and the numerical simulation) follow essentially the same trends and are basically consistent with one another. However, the fiber Bragg grating strain sensors recorded data that are much closer to those predicted with an accurate numerical model, compared with data recorded by the conventional strain gauges. The present experiment provided convincing evidence that the fiber Bragg grating strain sensors have much higher reliability and are more effective than the traditional strain sensors. As such, they are potentially strong candidates for applications in the long-term structural health monitoring of large-scale geotechnical engineering projects.

Monitoring the gaps between the platform screen doors and the doors of subway train based on optical time domain reflectrometer

Recently, many accidents were reported that some passengers were unfortunately restrained and killed at the gaps between the Platform Screen Doors (PSDs) and the doors of the subway trains. In this paper, one proposal of real time monitoring system based on optical time domain reflectrometer (OTDR) to detect the intrusions at these gaps is presented. In this method the locations and weight of intrusions can be obtained by detecting the abrupt power loss of backscattering light caused by the weight of intrusions upon the microbending sensor heads. This method can be easily multiplexed and extended into a multi-function sensing system, such as monitoring the temperature, smoking and the strains in the tracks, or applied in other fields, such as escalators, board gates for ferries or planes.

Liquid-level sensor based on fiber Bragg grating and carbon fiber composite diaphragm

A novel liquid-level sensor based on fiber Bragg grating and carbon fiber composite diaphragm is proposed and demonstrated. The sensing principle and finite element analysis result are described. From the experimental result, this sensor shows high sensitivity and good repeatability. This sensor can find applications in the area of the liquid level sensing.

Real-time highway pull-over vehicle monitoring using fiber microbending-loss reflectometry

This paper introduces a novel application of fiber microbending sensor to monitor the highway vehicles, i.e. overtime pull-over vehicles. Precise locations and durations of the overtime pull-over vehicles can be detected and alarms can be sent to highway administrators. Highway administrators can use these data to maintain the traffic order, secure the passengers and enforce the law. The sensor is designed based on fiber microbending effect and optical time-domain reflectometry method is utilized to generate, collect and process the optical signals. The experiment is designed to simulate the highway shoulder with vehicle parking on it. Different vehicle weight-induced fiber microbending losses are detected and measured. By the optical time domain reflectometry technique, the precise locations of pull-over vehicles have been obtained.