Fábio V. de Nazaré

Tapered plastic optical fiber-based biosensor – Tests and application

Cells detection is crucial in microbiological analysis of clinical, food, water or environmental samples. However, currently employed methods are time consuming. Plastic optical fiber (POF) biosensors consist in a viable alternative for rapid and inexpensive scheme for detection. In order to study the sensitivity of tapers for microbiological detection, geometric parameters are studied, such as the taper waist diameter since the formation of taper regions are the key sensing element in this particular type of sensors. In this study, a series of POF taper sensors were prepared using a specially developed tapering machine, and the dispersion of geometric dimensions is evaluated, aiming to achieve the best tapering characteristics which will provide a better sensitivity on the sensor response. The fiber tapers that presented the finest results were those constructed in U-shaped (bended) configurations, with taper waist diameters ranging from 0.40 mm up to 0.50 mm. These fiber tapers were used as the main section of the monitoring device, and when chemically treated as immunosensors for the detection of bacteria, yeast and erythrocytes.

A Guide to Fiber Bragg Grating Sensors

Optical fiber sensors (OFS) appeared just after the invention of the practical optical fiber by Corning Glass Works in 1970, now Corning Incorporated, that produced the first fiber with losses below 20 dB/km. At the beginning of this era, optical devices such as laser, photodetectors and the optical fibers were very expensive, afforded only by telecom companies to circumvent the old saturated copper telephone network. With the great diffusion of the optical fiber technology during the 1980’s and on, optoelectronic devices became less expensive, what favored their use in OFS.

Detection and Monitoring of Leakage Currents in Power Transmission Insulators

An optoelectronic sensor for real-time leakage current monitoring on high-voltage (500 kV) and medium-voltage (13.8 kV) power line insulators was developed. The leakage current drives an ultrabright light-emitting diode producing an amplitude modulated light signal. The optically intensity-encoded signal is coupled to a plastic optical fiber cable and transmitted from the high potential measurement point to the remote unit in ground potential. After the demodulation, the leakage current root mean square values are concentrated in a data logger and sent to a remote station 150-km away by general packet radio service technology. Field tests at real operational conditions on coastal regions have been performed; all data collected are stored in a structured database, which can be consulted from the Internet, while a serially produced head was developed and the sensor is ready for commercialization. Since leakage current on high-voltage insulators depends on local air pollution and microclimate changes, several sensors have to be used to cover the region monitored. For this reason, research has been conducted to determine the sensor representativeness, i.e., the actual area, which can be covered by only one sensor.

Compact Optomagnetic Bragg-Grating-Based Current Sensor for Transmission Lines

A compact and practical optomagnetic current sensor intended to be used in power transmission lines is proposed in this paper. The novel sensor is able to retrieve the complete sinusoidal current signal, which is being carried by the line conductor through a fiber Bragg grating, which is attached to a magnetostrictive rod setup excited by dc and AC magnetic fields: a DC magnetic field created by a designed magnetic circuit in order to make the magnetostrictive material operate in its linear region; and an AC magnetic field generated by the current being monitored. Design stages and the proposed sensor configuration are showed in detail, and the assembled sensor head is tested using a power setup exclusively developed to simulate current magnitude levels in a transmission line. Measurement results are compared with those provided by a reference commercial probe, attesting the effectiveness of the novel current sensor, especially in terms of waveform distortion.

Enhanced plastic optical fiber sensor for refractometry based on amplitude modulation

The authors characterize four U-shaped plastic optical fiber sensors, manufactured with a particularly developed simple mechanical scheme, which are characterized and implemented as refractometry sensors. The enhanced measurement set-up consists of an LED and a photodiode connected to the ends of the fiber, while the signal is detected by a Lock-in amplifier implemented in Matlab. The calibration process led to the evaluation of the sensitivity, accuracy and repeatability by using solutions of sucrose for obtaining refractive indexes in the range of 1.33 - 1.39.

Detection and monitoring of leakage currents in distribution line insulators

An optoelectronic sensor for real time leakage current monitoring on high-voltage (13.8 kV) power line insulators was developed. The leakage current drives an ultra-bright green LED producing an AM light signal. The optically intensity-encoded signal is coupled to a 1-mm plastic optical fiber and transmitted from the high potential measurement point to the Remote Unit in ground potential. After the demodulation, the leakage current values are concentrated in a data logger and sent to a remote station 150 km away by GPRS technology.

Application of Fiber Bragg Grating Sensors in Power Industry

With the idea of decreasing the number of copper wires and consequently decreasing installation and operation costs, we designed a fiber optic temperature sensor for application in large generators. The objective of the system is to cover all temperature monitoring needs of an HEP that would also overcome some of the disadvantages presented by the conventional RTD (resistive temperature detector) network.

Towards a hybrid current monitoring system: Nickel and GMM comparison as magnetostrictive transducers

In this paper, the magnetostrictive aspects of nickel and Terfenol-D are compared, in order to carry out the development of magneto-optical current sensing devices. The design and construction of the transducers are described, whereas their response when submitted to magnetic fields, with and without temperature compensation, is evaluated.

Geometric aspects in a novel plastic optical fiber biosensor system

Cells detection plays a crucial role in clinical specimens analysis and in food and water microbiological quality control. However, current employed methods demand time and material, raising the analysis procedure costs. Plastic Optical Fiber (POF) biosensors consist in a viable alternative for rapid and inexpensive scheme for detection. In this study, a series of optical fiber taper sensors were prepared using a proprietary tapering machine, and the obtained geometric dimensions dispersion is evaluated, aiming to achieve the best tapering characteristics which will provide a better sensor response — in other words, an increased sensitivity.

Efficient magnetic biasing scheme for a Bragg-grating-based magnetostrictive alternating current sensor

In this work, the authors describe in detail the development of an efficient magnetic biasing scheme for FBG-based magnetostrictive current transducers intended to be used in innovative transmission line monitoring systems. A Fiber Bragg grating is attached to a giant magnetostrictive rod, and a DC magnetic field is created by a magnetic circuit in order to enable the magnetostrictive material operate in its linear region. Design stages, including simulations using the Finite Element Method, and the proposed sensor configuration are presented. The sensor prototype, which is assembled in laboratory, is tested by employing an arrangement built to simulate the current in a transmission line, showing the efficiency of the proposed magnetic biasing set-up.