Ricardo M. Ribeiro

Development of an evanescent-field fibre optic sensor for Escherichia coli O157:H7

An intensity-modulated fibre optic sensor was developed for Escherichia coli O157:H7. The interaction between the whole natural bacteria and the guided lightwave was carried out by means of evanescent-field coupling. A correlation between optical response and the current number of bacteria was achieved. The device sensitivity had been calibrated for initial number of bacteria (N(0)) from 10-800. The sensor sensitivity was 0.016 (+/-0.001) dB/h/N(0). The sensing mechanism starts together with the log phase leading the present sensor response to be five to ten times faster than conventional bacteriological techniques.

Aerobiological pathogen detection by evanescent wave fibre optic sensor

An evanescent field fibre optic sensor was employed for detecting and monitoring aerobiological pathogen contamination in hospital environment. Measurements of methicillin-resistant Staphylococcus aureus (MRSA) and Streptococcus pneumoniae colonies were detected in 6 and 13 h, respectively, faster than those obtained by means of conventional techniques. All of the bacteria growth phases were clearly time resolved by means of the optical sensor. The 0.33 cm2 sensitive surface area fibre optic transducer also exhibited reproducibility, was of easy construction and low cost, which greatly enhances its potential and usefulness.

Wavelength demodulation of ultrabright green light-emitting diodes for electrical current sensing

We report on a novel electrical current-sensing principle based on wavelength-encoded modulation of the ultrabright green (at 525 nm) light-emitting diode (LED) transducers. It complies with the optical subsystem of a hybrid current transformer . Real-time wavelength demodulation is performed with the passive spectral edge filter OG 530. Linear calibration plots were achieved with -0.33 nm/mA for dc and +0.99 mA/sup -1/ for ac current sensitivity, respectively. A measurement accuracy of 1.3% for 28.4-mA ac peak current range is achieved. A simple theoretical model is outlined. Issues such as electronic and thermal effects on stability performance are also addressed.

An evanescent-coupling plastic optical fibre refractometer and absorptionmeter based on surface light scattering

To the best of our knowledge, an evanescent-coupling plastic optical fibre (POF) refractometer and absorptionmeter, based on surface light scattering, is described for the first time. The sensing elements were manufactured by machining random roughness, using side-polishing technique. Coarser polishing leads to stronger surface light scattering, allowing measurements of refraction index smaller than the fibre cladding value. The same device also works as an absorptionmeter, where refractive and absorptive mechanisms may compete with each other.

A Compositional Automata-based Approach for Model Checking Multi-Agent Systems

This paper addresses the issue of model checking knowledge in concurrent systems. The work benefits from many recent results on model checking and combined logics for time and knowledge, and focus on the way knowledge relations can be captured from automata-based system specifications. We present a formal language with compositional semantics and the corresponding Model Checking algorithms to model and verify Multi-Agent Systems (MAS) at the knowledge level, and a process for obtaining the global automaton for the concurrent system and the knowledge relations for each agent from a set of local automata that represents the behavior of each agent. Our aim is to describe a model suitable for model checking knowledge in a pre-defined way, but with the advantage that the knowledge relations for this would be extracted directly from the automata-based model.

A novel sensor to measure the concentration of nitrous oxide in anesthetic mixtures

Describes experimental results of a novel intrinsic gas sensor, based on plastic optical fiber (POF), to detect and to measure relative concentration of nitrous oxide in oxygen in anesthetic mixtures. The sensor was able to measure concentrations from zero to 100 V%, in a total flow of 10 l/min, with sensitivity around -2.32 10/sup -3/ dB/V%.

Fiber optic sensors and systems at the Federal University of Rio de Janeiro

As widely known, fiberoptics (FO) are being used in a large variety of sensors and systems particularly for their small dimensions and low cost, large bandwidth and favorable dielectric properties. These properties have allowed us to develop sensors and systems for general applications and, particularly, for biomedical engineering. The intravascular pressure sensor was designed for small dimensions and high bandwidth. The system is based on light-intensity modulation technique and uses a 2 mm-diameter elastomer membrane as the sensor element and a pigtailed laser as a light source. The optical power output curve was linear for pressures within the range of 0 to 300 mmHg. The real time optical biosensor uses the evanescent field technique for monitoring Escherichia coli growth in culture media. The optical biosensor monitors interactions between the analytic (bacteria) and the evanescent field of an optical fiber passing through it. The FO based high voltage and current sensor is a measuring system designed for monitoring voltage and current in high voltage transmission lines. The linearity of the system is better than 2% in both ranges of 0 to 25 kV and 0 to 1000 A. The optical flowmeter uses a cross-correlation technique that analyses two light beams crossing the flow separated by a fixed distance. The x-ray image sensor uses a scintillating FO array, one FO for each image pixel to form an image of the x-ray field. The systems described in these paper use general-purpose components including optical fibers and optoelectronic devices, which are readily available, and of low cost.