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Proceedings Paper

Hydrogel/fiber optic sensor for distributed measurement of humidity and pH value
Author(s): Alistair MacLean; W. Craig Michie; S. Gareth Pierce; Graham Thursby; Brian Culshaw; Chris Moran; Neil B. Graham
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Paper Abstract

The combination of chemically sensitive, swellable polymer materials with novel optical fiber cable designs to transduce the swelling activity into microbend loss enables a simple yet powerful sensor to be produced. Interrogating such cables with standard optical time domain reflectoctrometry (OTDR) instruments allows particular chemicals of interest to be detected and located along a cable which may extend to several kilometers. We report here on a sensor cable which uses a water swellable material, a hydrogel, to detect positions of water ingress, relative humidity level or pH value. In direct water ingress tests, wet sensor lengths as small as 5 cm in several hundreds of meters have been detected using conventional OTDRs. Following a review of the sensor design, we present the results of an investigation of the mechanical interaction between the hydrogel polymer and the optical fiber within the sensor. The behavior of the sensor is then characterized within environments of different relative humidity levels from 70 percent to 100 percent at temperatures ranging from 0 to 60 degrees C. The sensor was initially designed for applications within civil engineering but can be applied to a much broader range of measurement requirements, for example soil moisture measurement. We will report details on experimental observations on concrete cure within reinforcing tendon ducts and soil humidity measurements within different soil types.

Paper Details

Date Published: 21 July 1998
PDF: 11 pages
Proc. SPIE 3330, Smart Structures and Materials 1998: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, (21 July 1998); doi: 10.1117/12.316967
Show Author Affiliations
Alistair MacLean, Univ. of Strathclyde (United Kingdom)
W. Craig Michie, Univ. of Strathclyde (United Kingdom)
S. Gareth Pierce, Univ. of Strathclyde (United Kingdom)
Graham Thursby, Univ. of Strathclyde (United Kingdom)
Brian Culshaw, Univ. of Strathclyde (United Kingdom)
Chris Moran, Univ. of Strathclyde (United Kingdom)
Neil B. Graham, Univ. of Strathclyde (United Kingdom)

Published in SPIE Proceedings Vol. 3330:
Smart Structures and Materials 1998: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials
Richard O. Claus; William B. Spillman, Editor(s)

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