Optical Fiber Accelerometer System for Structural ... - IEEE Xplore

IEEE SENSORS JOURNAL, VOL. 9, NO. 11, NOVEMBER 2009

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Optical Fiber Accelerometer System for Structural Dynamic Monitoring Paulo Fernando da Costa Antunes, Hugo F. T. Lima, Nélia Jordão Alberto, Hugo Rodrigues, Pedro M. F. Pinto, João de Lemos Pinto, Rogerio N. Nogueira, Humberto Varum, Aníbal G. Costa, and Paulo Sérgio de Brito André, Member, IEEE

Abstract—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 São 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 10 5 . Index Terms—Accelerometer, fiber Bragg grating (FBG), optical sensor, structural health monitoring (SHM).

I. INTRODUCTION LL around the world, several major natural disasters, such as earthquakes or hurricanes, have occurred in the past decades. From those accidents, thousands of victims and a considerable monetary lost arouse due to the collapse or severe damage produced in the civil engineering structures. Therefore, the need to identify structural damage and to monitor its evolution imposes the development of structural health monitoring (SHM) techniques, which are useful tools for applications in civil engineering infrastructures and aeronautical platforms. The SHM techniques are supported by data related with the behavior and response of the structure, collected by a sensors network, providing indicators about eventual structure damage or anomalies, which adversely affect the structure integrity. The relevant data are collected in real-time conditions, being considered a wide group of parameters, including changes of

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Manuscript received February 24, 2009; accepted February 27, 2009. First published August 18, 2009; current version published September 23, 2009. The work of P. F. C. Antunes, H. F. T. Lima, and N. J. Alberto was supported by the Fundação para a Ciência e Tecnologia (FCT) under the Ph.D. Fellowships SFRH/BD/41077/2007, SFRH/BD/30295/2006, and SFRH/BD/30551/2006. The work of H. Rodrigues was supported by the University of Aveiro under the Ph.D. Fellowship. The associate editor coordinating the review of this paper and approving it for publication was Prof. Norbert Meyendorf. P. F. C. Antunes, N. J. Alberto, J. L. Pinto, and P. S. B. André are with the Instituto de Telecomunicações and the Departamento de Física da Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal (e-mail: [email protected]; [email protected]; [email protected]; [email protected]). H. F. T. Lima and P. M. F. Pinto are with the Departamento de Física da Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal (e-mail: [email protected]; [email protected]). H. Rodrigues, H. Varum, and A. G. Costa are with the Departamento de Engenharia Civil da Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal (e-mail: [email protected]; [email protected]; [email protected]). R. N. Nogueira is with the Instituto de Telecomunicações and the Departamento de Física da Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal, and also with the Instituto Politécnico de Saúde do Norte, 4585-116 Gandra, Portugal (e-mail: [email protected]). Digital Object Identifier 10.1109/JSEN.2009.2026548

chemical or electrical properties, corrosion, and fatigue. These parameters are related with the structure physical properties, such as strain, stress, acceleration, or crack. One approach to implement SHM strategies is based on the analyses of structural vibration, induced by instantaneous impacts or natural environmental actions, such as wind or traffic. The structures’ natural vibration frequencies are proportional to the structure stiffness, and often, the decrease of its value is understood as a damage progress [1]. In the present study, it is intended to develop, implement, and test an optical acceleration sensor able to collect vibration data to be used in SHM. The intrinsic characteristics of fiber Bragg gratings (FBGs) make them one of the most promising technologies to be used in SHM. The FBG-based sensors take advantage of some properties provided by optical fiber, namely low-loss transmission, immunity to electromagnetic interference, electrical isolation, and reduced weight and volume. These characteristics render them attractive for the use in hostile environments, where electrical currents might pose a hazard. Moreover, intrinsic advantages of FBG itself should also be considered. In particular, low noise, resulting from the information codification in the wavelength domain, and the possibility to multiplex a large number of FGB-based sensors (such as temperature, displacement, pressure, pH, humidity, high magnetic field, and acceleration) in the same optical fiber, reducing the need of multiple and heavy cabling used in traditional sensing [2], [3]. Nowadays, the main advantage of traditional sensors when compared with the optical ones is the reduced unitary price and the low complexity for the interrogation systems. In a near future, due to the maturity of FBG production and a cost reduction for the interrogation systems, this optical sensors technology will be widely commercialized for a large variety of applications, such as SHM. Moreover, in large infrastructures where a large number of different types of sensors is required, the utilization of several multiplexed types of FBG sensors may provide an effective solution to simultaneously measure static and dynamic parameters. Usually, the structural monitoring requires the analysis of the structure modal parameters obtained from the acceleration measurements, which can only be attained, with the required quality, by employing highly sensitive and low-noise accelerometers. While electronic accelerometers technology is deeply developed, FBG-based accelerometers are more sensitive, due to the higher SNR. These characteristics are relevant for some specific SHM, where highly sensitive accelerometers, with the capacity to sense low-amplitude vibrations, caused by environmental actions, such as those associated with wind loads or traffic, are required.

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The wavelength-encoded nature of the FBG sensors response must be converted into the electronic time domain before data processing. For this purpose, distinct interrogation systems have been reported. In literature, several techniques can be found, based on simple interferometry [4], Fabry--Perot filters [5], matched gratings [6], acoustic--optic tunable filters [7], long-period gratings [8], [9], Sagnac loops based on the chirped FBGs [10], and multiport fiber Mach--Zehnder interferometer for multisensors interrogation [11]. These solutions provide high resolution in the wavelength domain but are rather complex systems with high implementation costs. Several worldwide research groups have focused their activities in the application of FBG-based sensors for the measurements of acceleration values. The implemented systems are based on several technologies, such as the deformation of a semirigid metal plate, for seismic applications [12], the vibration of an end free cleaved FBG, for high acceleration values [13], or the more usual architecture, the vibration of a cantilever, monitored by an FBG [14], [15]. Zhu et al. have developed a sensor based on an FBG glued to a stainless steel beam, and the sensor response is codified in the grating optical bandwidth, which will increase due to the nonlinear deformation of the metallic beam. This solution presents low-temperature sensitivity, having the disadvantage of the nonlinearity of the response [15]. Li-Qun et al. proposed another solution to reduce the temperature sensitivity of the response, based on the differential response of two symmetric FBGs placed in a cantilever [14]. In this study, we report the development of a simple-solution single-axis accelerometer based on FBG technology, employed to monitor a footbridge. A suitable interrogation system providing a less expensive solution to the dynamic measurements of vibration is also presented. This study is organized as follows: after the introduction, the theoretical aspects related with optical FBGs, and the description of the optical accelerometer and the interrogation system are presented. The system calibration and characterization are presented in Section III. Section IV deals with the use of this optical solution to estimate the eigenfrequencies of a footbridge located in the Aveiro University Campus, in Portugal. Finally, the main conclusions are drawn in Section V. II. FBG-BASED ACCELEROMETER An FBG is a passive optical device based on the optical fiber core refractive index periodic modulation along the longitudinal axis. This index modulation is induced by exposing a photosensitive optical fiber to an UV radiation periodic pattern, created by a phase mask or using an interferometric process [16]. The optical fiber core refractive index modulation is equivalent to a set of light reflection planes, perpendicular to the longitudinal (propagation) axis of the fiber. When the FBG is illuminated by a broadband light source, the spectral components, which are centered in the wavelength that satisfies the Bragg condition, are reflected in the successive reflection planes, thus creating an intense reflection signal. , The first-order Bragg condition is given by is the center wavelength of the back-reflected light where is the fibers’ effective refractive index, (Bragg wavelength), is the periodicity of the refractive index modulation. and From this condition, it becomes clear that the wavelength of

the optical signal reflected by the Bragg grating is dependent on the FBG physical parameters. These parameters change if the grating is subjected to mechanical deformation or temperature variation. This influence of temperature and mechanical deformations on the Bragg wavelength value is given by

(1) The strain effect on the Bragg wavelength is represented by the first term in (1). This strain dependence can be expressed as follows: (2) where represents the silica Poisson ratio, and and are components of the strain-optic tensor. For typical germanosili, and values are 0.16, cate-core-doped optical fibers, , 0.113, and 0.252, respectively. Using these values in (2), a strain was achieved for a wavelength of sensitivity of 1.2 1550 nm [17]. The temperature dependence on the Bragg wavelength is represented by the second term in (1) and can also be expressed as (3) being the thermal expansion coefficient and the silica thermooptic coefficient. These terms could be considered conand 8.6 , respecstants and are equal to 0.55 tively. For a Bragg grating, written in a germanium-doped opis expected at tical fiber, a thermal sensitivity of 13 1550 nm [17]. The accelerometer sensor element is a Bragg grating, written in a photosensitive single-mode optical fiber, which was anchored in two points [A and B in Fig. 1(a)]. The structure of the accelerometer consists in an inertial mass, supported by a L-shaped aluminum cantilever beam, connected to the structure base by a steel leaf spring and an FBG element. When exposed to an external acceleration, the inertial mass moves in the vertical direction, imposing a contraction/expansion of the optical fiber. This deformation induces variations on the FBG Bragg wavelength. Since the vibration amplitude is small when compared with the cantilever dimensions, it can be considered that the movement of the inertial mass occurs only in the vertical direction. The use of a square-shaped leaf spring minimizes the cross-axis sensitivity and its dimensions determine the accelerometer dynamic range and sensitivity [18]. From the system work--energy concept analysis, the accan be celerometer undamped natural angular frequency written as [see the equivalent mechanical model scheme in Fig. 1(b)] (4) where and are the leaf spring and optical fiber elastic is the inertial mass, and is the constants, respectively, system equivalent elastic constant. The optical fiber elastic

ANTUNES et al.: OPTICAL FIBER ACCELEROMETER SYSTEM FOR STRUCTURAL DYNAMIC MONITORING

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Fig. 2. Scheme of the building blocks for the interrogation system. Fig. 1. FBG-based accelerometer: (a) diagram and (b) equivalent mechanical model.

TABLE I DIMENSION-RELATED PARAMETERS

constant was previously determined, thus yielding a value of 28249.33 [19]. The response of this accelerometer is based on the optical fiber strain imposed by the inertial mass displacement. The thermal effects also induce changes in the Bragg wavelength. However, this change occurs in a long time scale, and could be removed from the system response. and a Assuming an external acceleration damping factor , the motion equation for this system leads to a sensitivity of (5) The project of the optical accelerometer requires the initial specification of some dimensional-related parameters, the remaining being optimized in order to maximize the sensitivity. Since most civil infrastructures present the main fundamental eigenfrequencies in the 0--20 Hz range, the implemented accelerometer should present a natural frequency higher than this value, but lower enough to maximize its sensitivity and keep the noise minimized. The dimensions of the implemented unit are displayed in Table I. According to the accelerometer parameters presented in Table I, an undamped natural frequency [obtained from (4)] of 45.66 Hz is achieved.

To measure the response of this optical accelerometer, with a sampling rate compatible with the unit spectral response, the development of a low-cost and fast-interrogation unit was also required. The proposed interrogation system (see Fig. 2) is based on a bandpass optical filter, which presents a linear spectral transfer function in the tuning range of the Bragg grating. Due to the displacement of the accelerometer inertial mass, the grating Bragg wavelength changes, inducing variations in the optical power transmitted through the optical filter. This optical power variation, measured at the filter output, is related with the convolution of the filter transfer function and the FBG reflection spectrum. In the proposed interrogation system, the FBG is excited by a broad-band light source from Amonics, model ALS-CL-17-B-FA, emitting in the 1528--1608 nm spectral region, with an integrated optical power of 17 dBm. The FBG reflected signal, which carries the wavelength encoded accelerometer response, is divided in a 50/50 splitter. One of the splitter outputs is connected to the bandpass optical filter JDS Fitel (model DTB4500, tunable in a spectral range between 1530 and 1560 nm with a full-width at half-maximum (FWHM) of 1.2 nm). The signals at the filter and splitter outputs are then inserted in identical InGaAs photodetectors, at 1550 nm and a cutoff with a responsitivity of 0.84 frequency of 2 GHz. Both signals are amplified and converted to the digital domain by an analog-to-digital converter (ADC), National Instruments USB6008 acquisition board. This module samples per second, with an provides data acquisition at and a 12-bit resolution. input dynamic range of The digital signals are then processed in a laptop, by an application implemented in LabView. This scheme is able to operate at very high sampling rates, which are only limited by the photodetectors and remaining electronics frequency response or by the ADC sampling rate. III. SYSTEM CHARACTERIZATION AND CONCEPT PROOF For the systems’ static characterization, the accelerometer inertial mass was displaced from the equilibrium position, with

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Fig. 3. Acceleration measured with the optical and the reference electronic accelerometer for the rigid pendulum.

Fig. 4. Frequency spectra for the rigid pendulum, obtained with the optical and the reference electrical accelerometers.

external masses loading, which causes a controlled FBG contraction. This originates a blue shift in the Bragg wavelength, which could be monitored in an optical spectrum analyzer (OSA). Simultaneous measurements of the Bragg wavelength shift, with an Anritsu OSA (model MS9601A), and the electric voltage at the interrogator system output allowed the optical system response characterization. The measured value is for the relation between the interrogation system electric output voltage and the shift in Bragg was . wavelength. The estimated For the sensors’ quality assessment and comparative tests, an accelerometer from Crossbow Technology, model CLX02LF1Z (where stands (LF series), with a sensitivity of 0.997 ) was used. The elecfor the gravity acceleration tronic and the optical accelerometers were fixed to a rigid support, in order to expose both to the same external acceleration. The calibration of the optical sensor was made by fixing it to a rigid pendulum, which oscillated with a frequency of 1.21 Hz. After calibration, the optical system (optical accelerometer and interrogation system) presented a sensitivity equal to the elec). Fig. 3 shows the pendulum actronic system (0.997 celeration, measured with both accelerometers. The oscillations eigenfrequencies are obtained through the accelerogram time-domain data fast Fourier transform (FFT). The frequency spectrum allows the direct identification of the pendulum eigenfrequency, which corresponds to the oscillation frequency. In Fig. 4, the pendulum frequency spectra obtained from both accelerometers are observed.


Fig. 5. Accelerometer response. Dots represent the experimental values and the solid line represents the curve fitting results, extrapolated up to 60 Hz.

The system response was obtained for other frequencies than 1.21 Hz, recurring to a mechanical oscillator controlled by a signal generator from Metrizx model GX239. The accelerometer natural frequency and damping coefficient were also determined by observing the response to a step impulse, applied on the inertial mass. From the collected data, a and a damping coeffinatural frequency of were obtained. cient of Expression (5) was fitted to the experimental data values, considering the previous values and the cantilever dimensions to be must be considered fixed. A correction factor of for a real representation of the system transfer function, with a value of 7.4 . The need of this factor could reduced be related with the approximations of considering a negligible thickness cantilever and an inertial punctual mass. Fig. 5 displays the measured experimental values and the representation of the transfer function obtained from the fitted parameters, extrapolated to the frequency range up to 60 Hz. The measured sensitivity at 20 Hz is 26% higher than the value at 1.2 Hz. Although this variation is considerable, the previous knowledge of the real transfer function allows the implementation of a digital filter with a transfer function that compensates this sensitivity variation. In order to evaluate the performance of the implemented acceleration optical system, several comparative tests were carried out, taking the already used electronic accelerometer as reference from Crossbow Technology, and a seismograph from GeoSig (model AC-63). The first comparative test was carried out for measuring the vibrations of a steel plate with 120 mm 20 mm 4 mm, supported in the extremities. The vibrations on the steel plate were induced by small-amplitude mechanical impulses at the midspan of the plate. The accelerograms recorded, for the three sensors, are represented in Fig. 6. The data in Fig. 6 show an identical signal recorded at the optical accelerometer and at the two electronic devices. This similarity is noted in the signal amplitude and in the time-domain evolution. The root-mean-square error of the optical accelerometer data, when compared with the electronic accelerometer data , over the complete displayed time interval. In is 3.42 Figs. 6 and 7, the frequencies spectra for the data recorded are presented, allowing the identification of the steel plate eigenfrequency. The eigenfrequencies estimated from the signal ob-


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Fig. 6. Accelerograms for the steel plate vibration tests. Fig. 8. Steel footbridge over the Esteiro de São Pedro, University of Aveiro. (a) Photo (perspective). (b) Measuring point localization (plan).

Fig. 7. Frequency spectra for the steel plate vibration test. Fig. 9. Accelerograms recorded at the footbridge with the electronic accelerometer, the seismograph, and the optical accelerometer.

tained in all the sensors are similar. This steel plate vibration test confirms, in laboratorial environment, the performance of the implemented optical system. The main contributor to the disagreement between the accelerometer time-domain data arises from the system noise (accelerometer and interrogation unit). This is confirmed by the frequency spectra agreement, which is independent from the time-domain noise (if a white noise is assumed). The accuracy of the implemented solution sensibility, for all the measurement range is 0.27%, which correspond to an improvement to previously related solutions [20]. IV. STRUCTURAL MONITORING The developed accelerometer was tested in an existing footbridge to evaluate its performance in full-scale structures at real loading conditions. The structure selected is the footbridge over the “Esteiro de São Pedro,” located at the University of Aveiro (see Fig. 8). The footbridge was constructed in 2001 to connect the two Campus of the University site, over the Aveiro estuary branch “Esteiro de São Pedro.” The main structure is a straight continuous tubular steel truss, simply supported at the abutments at its ends and in eight intermediate steel piers. The nine spans of the bridge have an average length of 36 m, and the total length of the footbridge is 324 m. The bridge deck is a reinforced concrete slab connected to the steel tubular structure.

In this test, the implemented acceleration optical sensor was tested on a full-scale bridge structure, comparing the acceleration measured with two reference sensors already used in the previous tests, namely the electronic accelerometer and the seismograph. These three different sensing technologies have different intrinsic data sampling rates. However, in the processing stage, the signals were synchronized and the data points extrapolate to the same sampling rate. The tested sensors were attached to a heavy (5 kg) steel plate placed at the bridge over the measuring point [see Fig. 8(b)], assuming, therefore, that the steel plate and the footbridge, at the measuring point, have the same displacement and acceleration components. Fig. 9 shows the acceleration data collected by the optical accelerometer, the electronic accelerometer, and the seismograph during 40 s, in which two mechanical impulses were applied by the simultaneous impulsion of five persons over the footbridge at a point close to the measuring position. The root-mean-square error of the measured optical accelerometer data, when compared with the data from the . As in the previous electronic accelerometer, is 2.53 tests, this difference is related with the system noise. In Fig. 10, the acceleration evolutions recorded in a 10-s interval are plotted for a better visual comparison between the signals obtained from the three sensors. In Fig. 11, the frequencies

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frequencies higher than 30 Hz, an amplitude enhancement is obtained from the data recorded with the optical accelerometer, due to the proximity to the device natural frequency. From the data in Table II, it is possible to compare the eigenfrequencies obtained with the optical accelerometer and with the two electronic devices. The optical accelerometer allows the identification of the footbridge main eigenfrequencies with a maximum relative error of 0.6%, when compared with the values obtained with the seismograph data. V. CONCLUSION

Fig. 10. Accelerograms recorded at the footbridge (detail of Fig. 9—between 12 and 22 s).

In this study, we demonstrated the utilization of a low-cost optical accelerometer system, based on FBGs, to monitor the structural dynamic behavior of a footbridge. The implemented optical system allows the estimation of one footbridge eigenfrequencies, with very low relative error, when compared with other two sensing technologies. The maximum root-mean-square error of the data measured on the in situ tests, , relatively to that meawith the optical system, is 2.53 sured with a commercial electronic accelerometer. The maximum relative error in the identification of the eigenfrequencies was 0.6%, which confirms the expected high performance resulting from the introduction of the optical technology in the structures’ dynamic characterization. REFERENCES

Fig. 11. Footbridge frequencies spectra.

TABLE II EIGENFREQUENCIES ESTIMATED AND RELATIVE ERROR BETWEEN THE OPTICAL AND THE REFERENCE ELECTRONIC DATA

spectra obtained from the data recorded (see Fig. 10) are shown, thereby allowing the identification of the principal footbridge eigenfrequencies, which are summarily presented in Table II. The optical accelerometer spectrum is very similar to those obtained from the electronic devices in the 0--20 Hz range. For

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[13] S. Thériault, K. O. Hill, F. Bilodeau, D. C. Johnson, J. Albert, G. Drouin, and A. Béliveau, “High-g accelerometer based on an in-fiber Bragg grating sensor,” Opt. Rev., vol. 4, no. 1A, pp. 145–147, 1997. [14] S. Li-Qun, D. Bo, W. Yong-Xin, E. Lally, and W. An-Bo, “Temperature-insensitive fiber-optic acceleration sensor based on intensity-referenced fibre Bragg gratings,” Chin. Phys. Lett., vol. 25, no. 10, pp. 3593–3596, 2008. [15] Y. Zhu, P. Shum, C. Lu, B. M. Lacquet, P. L. Swart, and S. J. Spammer, “Temperature-insensitive fiber Bragg grating accelerometer,” IEEE Photon. Technol. Lett., vol. 15, pp. 1437–1439, 2003. [16] T. Erdogan, “Fiber grating spectra,” J. Lightw. Technol., vol. 15, pp. 1277–1294, 1997. [17] A. Othonos and K. Kalli, Fiber Bragg Gratings: Fundamentals and Applications in Telecommunications and Sensing. Norwood, MA: Artech House, 1999. [18] A. Mita and I. Yokoi, “Fiber Bragg grating accelerometer for structural health monitoring,” presented at the 5th Int. Conf. Motion Vibration Control (MOVIC 2000), Sydney, N.S.W., Australia, 2000. [19] P. Antunes, H. Lima, J. Monteiro, J. L. Pinto, and P. André, “Elastic constant measurement for standard and photosensitive single mode optical fibres,” Microw. Opt. Technol. Lett., vol. 50, no. 9, pp. 2467–2469, 2008. [20] A. Fender, W. N. MacPherson, R. R. J. Maier, J. S. Barton, D. S. George, R. I. Howden, G. W. Smith, B. J. S. Jones, S. McCulloch, X. Chen, R. Suo, L. Zhang, and I. Bennion, “Two-axis temperature-insensitive accelerometer based on multicore fiber Bragg gratings,” IEEE Sensors J., vol. 8, pp. 1292–1298, 2008.

Paulo Fernando da Costa Antunes was born in Mealhada, Portugal, in May 1977. He received the Degree in physics engineering and the M.Sc. degree in applied physics from the Universidade de Aveiro, Aveiro, Portugal, in 2005 and 2007, respectively. He is currently working towards the Ph.D. degree in the Departamento de Física and the Instituto de Telecomunicações, Aveiro. From 2005 to 2006, he was a Researcher with the Instituto de Telecomunicações-Aveiro, where he was engaged in the study and simulation of single photon sources and detectors. His current research interests include the study and simulation of fiber Bragg gratings and optical fiber sensors for static and dynamic measurements.

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Hugo Rodrigues graduated from the Universidade de Aveiro, Aveiro, Portugal, and received the M.Sc. degree in structures of civil engineering from the Faculty of Engineering, University of Porto, Porto, Portugal. He is currently working towards the Ph.D. degree from the Universidade de Aveiro. He is currently a civil engineer. His research interests include seismic engineering, structural analysis methods, and structural repair and maintenance of buildings.

Pedro M. F. Pinto was born in Aveiro, Portugal, in April 1985. He graduated in physics engineering in 2004/2005 from the Universidade de Aveiro, Aveiro, where he is currently working towards the Master’s degree in physics.

João de Lemos Pinto received the Ph.D. degree in applied physics from the University of Hull, Hull, U.K. Since 2000, he has been a Full Professor in the Departamento de Física da Universidade de Aveiro, Aveiro, Portugal, where he has been engaged in lecturing many different theoretical and practical courses, namely applied optics, optoelectronics and advanced topics in physics. He is currently leading the optics research group of the Institute of Nanostructures, Nanomodelling, and Nanofabrication (I3N-Aveiro), and the electronic and optoelectronic components research area of the Instituto de Telecomunicações (IT-Aveiro), Aveiro. His current research interests include optical communications, Bragg gratings systems, optical image processing, holography, and promotion of physics in society.

Hugo F. T. Lima graduated in physics and chemistry in 2005 and postgraduated in applied physics in 2006 from the Universidade de Aveiro, Aveiro, Portugal, where he is currently working towards the Ph.D. degree from the Departamento de Física. His current research interests include fiber grating sensors for study of materials and structural health monitoring, refractive index sensors, and novel sensors on optical fibers.

Rogerio N. Nogueira graduated in physics engineering and received the Ph.D. degree from the University of Aveiro, Aveiro, Portugal, in 1998 and 2005, respectively. He is currently an Assistant Research Fellow at the Instituto de Telecomunicações, where he has been engaged in the field of fiber optics since 1999, participating in several projects financed by national, E.U. organizations, and private companies. He is also an Assistant Professor at the Instituto Politécnico de Saúde do Norte, Gandra, Portugal. He is a coauthor of one book chapter, and has also authored or coauthored more than 30 papers published in international scientific journals and more than 100 papers presented at international conferences. His current research interests include design and production of optical components, fiber optical communication systems, and fiber optical sensors.

Nélia Jordão Alberto was born in Figueira da Foz, Portugal, in December 1981. She received the Licenciatura degree in physics and chemistry in 2005, and postgraduated in applied physics in 2006 from the Universidade de Aveiro, Aveiro, Portugal. She is currently working towards the Ph.D. degree in the Departamento de Física da Universidade de Aveiro and the Instituto de Telecomunicações, Aveiro. Her current research interests include the study and simulation of fiber Bragg gratings, and optical fiber sensors for biosensing applications.

Humberto Varum is an Assistant Professor at the Departamento de Engenharia Civil da Universidade de Aveiro, Aveiro, Portugal. He is engaged in large-scale experimental testing and nonlinear analytical modeling of structural systems. In his teaching, he has specialized in the computational methods of structural behavior, dynamic of structures, strength of materials and rehabilitation of structures. His current research interests include assessment, strengthening, and repair of existing structures, structural testing, and modeling, reliability of structures, earthquake engineering and structural dynamics, and earth construction.

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Aníbal G. Costa is currently a Full Professor at the Departamento de Engenharia Civil, Universidade de Aveiro, Aveiro, Portugal. He is engaged in the field of structural rehabilitation and reinforcement and seismic engineering. He is the Founder of the Conservation and Rehabilitation of Buildings and Patrimony Group, which is integrated in the Structure’s Section of the Engineering Faculty, University of Oporto Prof. Costa is the Vice-President of the Portuguese Society of Seismic Engineering.

Paulo Sérgio de Brito André (S’98–M’03) was born in Luanda, Angola, in April 1971. He received the degree in physics engineering and the Ph.D. degree in physics, both from the Universidade de Aveiro, Aveiro, Portugal, in 1996 and 2002, respectively. In 2002, he joined the Instituto de Telecomunicações, Aveiro, as a Researcher. He is also an Assistant Professor at the Universidade de Aveiro, where he is engaged in teaching physics. His current research interests include the study and simulation of optoelectronics components, fiber Bragg gratings, transparent performance monitoring, Raman amplification, multiwavelength optical communications systems, and networks. Dr. André is a member of the Portuguese Physics Society (SPF), the Portuguese Materials Society, and the Optical Society of America (OSA).