title: Pulsed time-of-flight radar for fiber-optic strain sensing.
abstract: This article describes a fiber-optic interrogation device based on the pulsed time-of-flight technique. The apparatus is capable of measuring time delays between wideband reflectors, such as connectors, along a fiber path with a precision of about 280 fs (rms value) and a spatial resolution of about 3 ns (0.30 m) in a measurement time of 25 ms. Potential application areas include measuring integral strain and its derivatives such as cracks, deflections, and displacements, particularly in large civil engineering and composite structures. The operation and basic blocks of the measurement system are presented in detail together with measurement results obtained in laboratory and field conditions. It is shown that by using a fiber loop sensor with a reference fiber, it is possible to achieve a strain precision below 1 microstrain and a measurement frequency of 4 Hz. System performance proved adequate for the study of both static and dynamic phenomena in a bridge deck.
authors.affiliation: Electronics Laboratory, Department of Electrical and Information Engineering and Infotech Oulu, Erkki Koiso-Kanttilankatu 3, 90014 University of Oulu, Finland.
authors.forename: Veijo
authors.initials: V
authors.lastname: Lyöri
authors.forename: Ari
authors.initials: A
authors.lastname: Kilpelä
authors.forename: Guoyong
authors.initials: G
authors.lastname: Duan
authors.forename: Antti
authors.initials: A
authors.lastname: Mäntyniemi
authors.forename: Juha
authors.initials: J
authors.lastname: Kostamovaara