H. Lima

Optical Fiber Accelerometer System for Structural Dynamic Monitoring

In this study, the implementation of an optical accelerometer unit based on fiber Bragg gratings, suitable to monitor structures with frequencies up to 45 Hz, is reported. The developed optical system was used to estimate the structure eigenfrequencies of a steel footbridge, with a total length of 300 m, over the Sao Pedro Creek, located at University of Aveiro Campus, in Portugal. The acceleration records measured with this solution are compared with those obtained by traditional commercial electronic devices, revealing a root-mean-square error of 2.53 times 10-5 G.

Simultaneous Measurement of Strain and Temperature With a Single Fiber Bragg Grating Written in a Tapered Optical Fiber

A sensing head configuration and the necessary interrogation parameters to simultaneously measure strain and temperature using a single fiber Bragg grating (FBG) are presented and demonstrated. By writing the FBG in a linearly etched fiber, we were able to use the information encoded in the peak wavelength and in the spectral width of the FBG. The spectral width of the grating depends uniquely on the applied strain and is temperature independent. An uncertainty of ±15.26 ¿¿ and ±1.92°C was achieved in the experimental verification.

Feasibility studies of Bragg probe for noninvasive carotid pulse waveform assessment.

Abstract. The arterial stiffness evaluation is largely reported as an independent predictor of cardiovascular diseases. The central pulse waveform can provide important data about arterial health and has been studied in patients with several pathologies, such as diabetes mellitus, coronary artery disease and hypertension. The implementation and feasibility studies of a fiber Bragg grating probe for noninvasive monitoring of the carotid pulse are described based on fiber Bragg grating technology. Assessment tests were carried out in carotids of different volunteers and it was possible to detect the carotid pulse waveform in all subjects. In one of the subjects, the sensor was also tested in terms of repeatability. Although further tests will be required for clinical investigation, the first studies suggest that the developed sensor can be a valid alternative to electromechanical tonometers.

Optical Sensors Based on Fiber Bragg Gratings for Structural Health Monitoring

In this work we review the structural health monitoring techniques based on fiber Bragg gratings. The working principle of the fiber Bragg gratings sensors and the most common techniques to inscribe and interrogate these sensors are described. Several implemented examples are also presented, like the deformation monitoring of one historical building with reduced visual impact, the unidirectional acceleration measurements in a metallic bridge structure and the bidirectional acceleration monitoring in a 50 m mobile telecom tower. Finally, the implementation of an automated remote structural health monitoring system design to operate with optical sensors in a highway bridge is described.

Development of a FBG probe for non-invasive carotid pulse waveform assessment

One of the early predictors of cardiovascular diseases, with growing interest, is the arterial stiffness which is typically evaluated through the velocity and morphology of the arterial pressure wave. In each cardiac cycle the heart generates a pressure wave which propagates through the arterial tree. Along its path, the pressure wave interacts with the arterial walls and, consequently, the morphology of a local arterial pressure wave can be assessed by the arterial distention movement. Due to its superficiality, proximity of the heart and high probability of atherosclerosis development, the carotid artery has particular interest to be monitored. In this work, the development of a non-invasive fibre Bragg grating (FBG) probe for the acquisition of the arterial distention wave is presented. Comparing to traditional methods, optical FBG based sensors can offer many advantages, namely, compactness, immunity to electromagnetic interference, high sensitivity, low noise and immunity to light source intensity due to its codification in the wavelength domain. The arterial movements induce strain on a uniform FBG, with the arterial distention pattern. The carotid pulse wave was successful accessed in young human carotid artery, with an acquisition rate of 950 Hz, allowing a clear distinction of the carotid pulse identification points.

Static and dynamic structural monitoring based on optical fiber sensors

In this paper, we report the monitoring of an adobe structure with optical fiber sensors. Static and dynamic measurements were made during a destructive test on a full-scale wall, in which an in-plane cyclic force was imposed, by a hydraulic jack, until the wall collapse. An optical fiber accelerometer and a network of thirteen multiplexed displacement sensors were used to monitor the wall under test. The obtained results demonstrate that the optical fiber sensors had the capacity to monitor this large scale test, showing results similar, with a maximum relative error of 2.08 %, to the results obtained with electronic reference sensors.

Development and characterization of new sensors for hemodynamic evaluation: Fibre Bragg sensor for arterial pulse waveform acquisition

Cardiovascular diseases are the leading cause of death in the world, arising their early prediction as a key aspect. The analysis of pulse wave propagation characteristics, such as velocity and morphology, can give important data about arterial stiffness, a parameter with growing significance in cardiovascular events prediction. In this paper it is presented a new optical fibre sensor to assess the pressure waveform in the carotid artery. The optical sensor is based on fibre Bragg grating technology, increasingly applied in several fields, including biomedical sensing due to its advantageous features. The Bragg sensor was characterized and tested in human carotids. It is presented a case study showing the great potential of Bragg technology in the assessment of the pressure waveform.

Temperature and strain discrimination using a single fibre Bragg grating written in a tapered optical fibre

A sensing head configuration and the necessary interrogation parameters to simultaneously measure strain and temperature using a single FBG are presented and demonstrated. By writing the FBG in a linearly etched fibre, we were able to use the information encoded in the peak wavelength and in the spectral width of the fibre Bragg grating. The spectral width of the grating depends uniquely on the applied strain and is temperature independent. An uncertainty of ±15.26 με and ±1.92 ºC was obtained in the experimental verification.

Dual scale structural health monitoring system combining FBG sensors and laser scanning

This work reports a case study of a structural health monitoring (SHM) system combining large and micro scale measurements installed in a 16th Century Church in Aveiro. This dual scale SHM system relies on a network of 24 fibre Bragg grating (FBG) sensors to perform micro scale, high resolution displacement and temperature measurements in several key points of the structure, while the large scale measurements are ensured by a scanning laser range finder. The results demonstrate that the developed systems allow adequate monitoring of the evolution of deformation in buildings, in different scales, keeping the visual impact in the structure reduced to a minimum and contributing for the implementation of best practices for rehabilitation of historic and cultural heritage.