Marten J. de Vries

Photoinduced grating-based optical fiber sensors for structural analysis and control

Optical fiber sensor-based instrumentation has been shown to be extremely attractive for the in situ health monitoring, diagnostics and control of civil infrastructure. This paper presents the design, fabrication and implementation of long-period grating (LPG) based optical fiber sensors for the nondestructive evaluation of smart structure systems. The LPG sensors, fabricated in standard SMF-28 Corning fiber, were attached to pieces of rebar and cyclically loaded from no-load through 35 kN loads; sensor performance was monitored using an optical spectrum analyzer. A mechanical extensometer was collocated with the LPG sensor for comparison. Short-period optical fiber Bragg grating (FBG) sensors were also tested under similar conditions. Sensor performance for both the LPG and the FBG was found to be consistent with strain measurements using the extensometer.

Analysis of the effect of imperfect fiber endfaces on the performance of extrinsic Fabry-Perot interferometric optical fiber sensors

A systematic theoretical analysis of the effect of imperfect fiber endface cleaves on the performance of extrinsic Fabry-Perot inter- ferometric (EFPI) optical fiber sensors is presented. This analysis allows the prediction of the dynamic range of a sensor with greater confidence, and gives the tolerances of the mechanical instrument required to pre- pare the fiber endfaces. Good correlation with preliminary experimental results is also shown.

Performance of fiber optic vehicle sensors for highway axle detection

An important part of traffic management and intelligent transportation systems is the availability of cost effective, reliable sensors for vehicle classification and traffic flow monitoring. Fiber optic sensors have numerous advantages over conventional sensors and are thus prime candidates for use in these traffic systems. In this paper, an optical fiber vehicle sensor is described for axle detection. Results from field tests are presented. The performance of the fiber optic vehicle sensor is evaluated and methods of vehicle weight-in-motion are also discussed.

Smart Structures and Materials

Introduction -- What are Smart Structures and Materials? Smart Structures -- The Instrumented Materials. Structural and Mesoscopic Materials. Molecular Materials -- An Engineering View. Nuclear Materials. Applications Examples. Scenario Building and the Future.

IMPLEMENTATION OF EFPI-BASED OPTICAL-FIBER SENSOR INSTRUMENTATION FOR THE NDE OF CONCRETE STRUCTURES

Abstract This paper reports on the design and implementation of an optical-fiber sensor based on the extrinsic Fabry-Perot interferometer (EFPI) for the non-destructive quantitative evaluation of advanced concrete-based civil structures. The performance of the EFPI sensor is demonstrated in two different applications. In the first implementation, performed with researchers in the Civil Engineering Department at the University of Southern California in Los Angeles, optical-fiber sensors were used to obtain quantitative strain information from reinforced concrete interior and exterior column-to-beam connections. The second implementation, performed in co-operation with researchers at the Turner Fairbanks Federal Highway Administration Center in McLean, Virginia, used optical-fiber sensors, attached to composite prestressing strands used for reinforcing concrete, to obtain absolute strain information. The paper is concluded with a discussion of practical considerations that need to be taken into account when implementing optical-fiber sensors in a concrete civil structure environment.

Completely embedded optical fiber sensors

Due to their small size, light weight, geometric flexibility, and their possible uses for monitoring various different physical parameters, optical fiber sensor technology offers numerous opportunities and advantages for instrumenting structures and materials for their analysis and control. While optical fiber sensors have advantages over conventional electric sensors, connectorization of optical fiber sensors to the supporting laser, detector, and electronics has proven to be difficult. In this paper we demonstrate the possibility of having an optical fiber sensor system that can be completely embedded within composite materials. The fiber sensor as well as the supporting opto-electronic components required to launch and receive light into and from the fiber could be embedded in a panel, avoiding connector problems. Interaction with the electronics to obtain strain and vibration measurements from the fiber sensor was made via external antenna coils.

Grating-based optical fiber sensors for structual analysis

Long-period gratings have recently gained popularity as versatile optical fiber sensing elements that are simple and economical to fabricate and demodulate. Long-period gratings are periodic photoinduced structures in fiber cores that couple light from guided to cladding modes. We discuss the applications of these devices to strain measurements in high-performance materials and structures. Experimental results from a preliminary loading test carried out on a reinforcing-bar commonly used in civil structures are presented. The temperature cross-sensitivity of long-period grating-based strain sensors is analyzed and two methods to overcome this limitation are presented. We also demonstrate that strain-insensitive long-period gratings can be fabricated in standard optical fibers. The application of such gratings to temperature measurements in the presence of actively varying axial strain is discussed. Preliminary results indicate that long-period gratings hold tremendous potential for health monitoring of advanced materials and structures.

Multimeasurand multiplexed extrinsic Fabry-Perot interferometric sensors

The commercialization of optical fiber sensors in smart structure applications largely depends on the development of a multi-sensor system, capable of simultaneously monitoring different optical fiber sensors. Efficient multi-sensor systems can be realized through multiplexing arrays of sensors within a system, reducing the number of input/output information channels between the support electronics and optical sensors. We demonstrate a sensor system, comprised of four multiplexed extrinsic Fabry-Perot interferometers, that uses a code division multiplexing technique to address each sensor. Qualitative measurements of strain and temperature, obtained with this multi-measurand multiplexing system, and an evaluation of crosstalk between sensors is presented.

Advances in optical fiber sensors for vehicle detection

THe primary objective for this project is the design of optical fiber-based sensor instrumentation for specific ITS applications. Specifically, this paper discusses research on optical fiber sensors that can be used for traffic monitoring and vehicle classification. This paper also discusses developments on the application of optical fiber sensor that can be used for monitoring visibility. This research is directly beneficial to the implementation of driver advisory and safety systems, traffic control system, and other ITS applications. This paper summarizes research performed on optical fiber sensors used for measuring traffic flow on highways and discusses progress on optical fiber sensors used for monitoring visibility.

Experimental study of embedded fiber optic strain gages in concrete structures

This paper reports the use of short gauge length optical fiber sensors for the quantitative measurement of strain in reinforced concrete and the direct comparison between the performance of these sensors and co-located foil strain gauges. Pairs of fiber sensor elements and reference foil gauges were mounted to specific rebar elements which together form the three-dimensional reinforcement cage in a cement cross-beam specimen. The geometry of the specimen sections, approximately 20 cm square and 2.5 meters along each axis, is intended to model typical construction of post and beam-reinforced concrete structures. The results of this work are that (1) the robust fiber sensors survived the embedding process, (2) their calibrated output signals accurately match with those of co-located reference foil strain gauges, (3) they may be used to extract quantitative strain information from a complicated reinforced concrete specimen, and (4) they may be used to monitor crack progression.