This report presents a feasibility test of the distributed strain sensor based on plastic optical fiber (POF) for detecting
deformation of wooden structures. First, a simple method to fix POF cable onto wooden structures is developed, where
the dimensions of the fixing plate are determined so as to minimize the OTDR responses due to the fixing tool as well as
the slip between the POF cable and the structure. Second, the authors focus on a new function "memory effect" of the
POF-based strain sensor. The strain once applied to the POF cable is memorized through the plastic deformation of the
core material, and can be read out using OTDR even after the event. The characteristics of the memory effect and its
life are discussed experimentally for tensile strain. Third, in this report, we showed that a 5-point measurement with the
spatial resolution of around 5 m was possible for the axial elongation imposed on the POF. Then, we apply the present
method for detection of deformations of wooden frame structures. We try to detect the direction and magnitude of
deformations at four corners of a rectangular wooden frame using a POF cable and OTDR. The availability of the
memory effect in multipoint measurements on wooden structures is also discussed.
The authors have been investigating the sensing characteristics of plastic optical fiber (POF) using the optical
time-domain reflectometry (OTDR) for various kinds of mechanical disturbances such as bending, clamping,
twisting and stretching as well as the effects induced by temperature rise. In this report, methods to fix the
POF cable to wooden structures and their performances to detect the deformations are examined. The
dimensions of the fixing plate are changed to minimize the undesirable effect of the fixing on the OTDR
responses. Life of the memory effect also discussed through experiments. We can detect strain applied to the
POF after the event is over through the memory effect of POF, which is caused by the plastic deformation.
Our experiments show that the life of memory is over one month after the external force is released. Spatial
resolution along the POF is found to be 5 m, and 5-point detection experiments are carried out using a 100-m
POF. We discuss the memory effect in the case of multipoint measurements. Three types of POF cables are
compared in terms of the reflection and loss at the deformed point.