Presenter: Isaac Sorensen
Authors: Isaac Sorensen, Spencer Baker, Jacob Carter, Adam Bilodeau, David Fullwood, Anton Bowden
Faculty Advisor: David Fullwood
Institution: Brigham Young University
Piezoresistive polymeric sensors represent an important class of wide-range sensors – particularly for biomechanical applications. Previous characterization of sensor behavior has relied solely on tests in which the sensor is pulled to failure at a specified strain rate. However, these tests failed to simulate the real-world use of these sensors, namely, in their application to measure the back-and-forth stretching of the skin and muscles during various exercises. When tested with more complex and repetitive strain profiles, initial observations revealed that the sensor’s electrical response is not simply a function of sensor length. Rather, it appeared that transient effects in the electrical response were heavily correlated to the viscoelastic response of our polymer-based nano-composite sensors. Our current work has focused on estimating parameters for a 4-element viscoelastic model to capture the creep and stress relaxation behavior of the sensors. In creating a robust mechanical model of the sensor's stress-strain behavior, we hope to better model the associated electrical response. While many researchers have estimated model parameters for various viscoelastic polymers, the calculated models were based solely on one individual test. Hence, the model does not generalize well and fails to adequately predict stress-strain behavior for tests outside of the specific data used to fit the parameters. In our approach, we use data from both creep tests and stress relaxation tests, which allows us to estimate parameters with greater accuracy. Thus, we are able to develop an ‘average’ model that better predicts the sensor’s behavior for more complex strain-profiles. The methods we have developed also will help us to refine future mechanical and electrical models of the sensor’s behavior. These models will be absolutely vital to making these sensors useful and practical as skin-strain measurement devices.