Mechanical and electrical characterization of printed flexible electronics deformed over complex surfaces

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Bower, Isaac Andrew
Sitaraman, Suresh K.
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In many different applications, substrates with flexible electronics are bent or adhered to complex curved surfaces. Therefore, it is vital to understand how the performance of these flexible electronics changes, when the substrates with flexible electronics are deformed over these complex surfaces. In this thesis, tests were developed for characterizing the mechanical and electrical performance of printed sensors and antennas deformed over various surfaces such as a spherical dome and a saddle. The sensors and the antennas were fabricated by inkjet printing silver nanoparticle ink on flexible polymer substrates such as polyethylene terephthalate (PET), polyimide, and liquid crystal polymer (LCP). Test fixtures were designed for attaching to a universal test machine, and were fabricated using 3D printing of PolyLactic Acid (PLA). These fixtures were used to test the printed sensors and antennas under monotonic and cyclic loadings. The electrical performance and the fatigue behavior of the printed structures were monitored in situ during the tests. Scanning Electron Microscopy (SEM) imaging was used to examine the effect of the deformations on the ink microstructure. In addition to the physical testing, simulations of the various deformation cycles were conducted on the sensors and antennas. Through simulations, the stress and strain distributions were examined in the deformed structures, and the changes in electrical characteristics with deformed shapes were determined through experiments. Also, relationships between the change in electrical resistance and the applied strain were determined. This work provides both a test methodology for deforming flexible electronics on complex surfaces as well as a better understanding of how printed silver inks will perform under such deformations.
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