Distributed-effect modal domain optical fiber sensors for flexible structure control

Abstract

Recently, a new class of sensors has emerged which have scalar outputs derived from distributed measurements over a significant gauge length; these sensors are known as distributed-effect sensors. The most familiar example of a distributed-effect sensor is the piezoelectric laminate PVDF film; other examples include holographic sensors and modal domain optical fiber sensors. Optical fiber sensors are particularly attractive for smart structure and materials applications because they have low mass, are flexible, and can be easily embedded in a variety of materials.

Distributed-effect sensors can be fabricated with spatially varying sensitivity to the distributed measurand and act as spatial filters. The spatial variation in the sensor sensitivity, known as the sensor's weighting function, determines the measurement provided by the spatial filter. Spatial filters can be configured to measure a variety of structural parameters, such as modal amplitudes and traveling waves, that can not be measured directly using point sensors. The mathematical model of the sensor is described and incorporated into a state-space model of a flexible structure. Several criteria are described in this dissertation for selecting the weighting functions of distributed-effect sensors for structural control laws.

The weighting function realized in the fabrication of a distributed-effect sensor may differ from the desired weighting function, causing the output of the manufactured sensor to differ from the desired measurement. In order to design reliable structural control laws, the nature and effects of errors in the implemented weighting functions of distributed-effect sensors must be understood. This dissertation describes several causes of errors in distributed-effect sensor weighting functions. Errors in the weighting functions of distributed-effect sensors are integrated into the mathematical models of the sensors, and the effects of these errors on the sensor outputs are examined.