Sensitive structures that retain stiffness by incorporating finite-length measurement paths

Frequently in designing a structure to incorporate integrated sensors the stiffness of the system is sacrificed to improve sensitivity. By incorporating finite length measurement paths that tessellate throughout the volume of a structure, a measurement's sensitivity can be optimized while retaining structural rigidity. Thus the transducer element can be utilized as a critical load-bearing structure. Within the framework of linear elastostatics, the normal, transverse, and shear components of strain along a path can be integrated over a finite length to separate and yield external loading components. These measurements over a long distance accommodate the use of fiber- optic displacement sensors. The use of interferometric sensors in contrast with electrical strain gauges allows the precision and range of the component measurements to scale with the geometry of the device rather than the maximum strain in the structure. It becomes possible by virtue of these scaling properties to construct a stiff yet sensitive device. The design of stiff structures that measure all six resultant-load-components using both piezo-resistive and interferometric sensors is described. An advanced torsion sensor and a linear acceleration transducer are also discussed. In addition, invariant paths have been found that allow the in-situ integrity of a structural volume to be monitored with a single pair of displacement sensors. Finally, practical considerations in the design of finite length sensor path transducers are noted.