UC San Diego

The performance of structural and human health systems deteriorates during their service life. If left unaddressed, catastrophic failures can occur. As a result, the field of structural and human health monitoring is seeking new sensing technologies for condition assessment. Most of the sensors available for structural response measurements are point-sensors and not suitable for spatial sensing. The complex geometries, complicated damage modes, and diverse operational conditions of the structural systems make the damage identification process more challenging. Earlier works on materials-based sensing have demonstrated its potential to solve the aforementioned challenges. However, time-, labor-, and cost-intensive materials fabrication process, contact-based measurement strategies, and surface-level inspections, among others, limit its practical applications.

This research aims to solve these engineering bottlenecks by integrating new generation multifunctional materials with structural systems and combining them with advanced soft-field tomographic imaging techniques. In particular, a piezoresistive multi-walled carbon nanotube (MWCNT)-based nanocomposite was fabricated through a scalable, and low-cost spray fabrication technique. This nanocomposite was used to engineer the cement-aggregate interface for encoding self-sensing property in the cementitious composites. An electrical impedance tomography (EIT) algorithm and measurement strategy were developed and implemented to capture spatially distributed damage in the self-sensing concrete. Furthermore, distributed strain filed monitoring was accomplished by combining an updated EIT algorithm with a highly piezoresistive graphene-based sensing mesh.

This dissertation also explored a noncontact, radiation-free, electrical permittivity mapping technique for osseointegrated prosthesis (OIP) monitoring. The design of the MWCNT-based thin film was modified in such a way that their electrical permittivity is sensitive to external stimuli. The imaging system was coupled with these nanocomposites for subcutaneous infection and strain sensing at the tissue-OIP interface. The imaging system was also employed for prosthesis loosening and bone-fracture monitoring. As a step forward, the geometry of the imaging system was conformed into a planar array to use it as a scanning tool for rapid assessment of the subsurface condition of composite structures. Unlike traditional sensors, the proposed sensing systems (i.e., nanocomposite sensors coupled with tomographic imaging) can directly detect spatially distributed damage in structural and human systems hence improving their safety and reliability.