Practical Limitations in Achieving Shaped Modal Sensors With Induced Strain Materials

The purpose of this work is to explore practical limitations associated with the design of distributed modal sensors from induced strain materials for two-dimensional structures and illuminate difficulties associated with positioning sensors on structures in general. Results from this study indicate that a true modal sensor cannot be realized on a two-dimensional structure unless the boundary conditions are all pinned. This result stems from the fact that the sensor aperture must be orthogonal with respect to the structural mode (eigenfunction) and the curvature of the structural mode to render a distributed modal filter. The only class of functions satisfying this condition are sinusoidal functions. In addition, positioning of distributed strain sensing material is shown to be critical to the performance of the sensor over a specified bandwidth, specifically in the vicinity of structural resonances.