Quantifying the Contributing Factors toward Signal Fatigue in Nanocomposite Strain Sensors

Abstract

With unparalleled sensitivities, nanocomposites are believed to be key components in future bodily sensor and healthcare devices. However, there is a lack in understanding of how repeated strain cycles effect their electromechanical performance and what measures can be taken to accommodate changes in measurement using modelling and signal processing. Here, the author examines published cyclic data from a wide range of nanocomposite strain sensors. From the datasets, the author reports a near universal scaling in electromechanical signal with cycle number (C) as a result of the Mullin's effect.Using a modified model based on Basquin's law of fatigue, for all nanocomposites, signal was found to following a nearly identical C -0.1 power law scaling with cycle number. Using the presented model, the author demonstrated that a critical conditioning cycle number for a nanocomposite at which a steady state signal occurs, known as the endurance limit, can be predicted. Endurance limit was reported to be highly dependent on the scaling exponent noted in the cyclic data.

Approaching the Limit of Electromechanical Performance in Mixed-Phase Nanocomposites

“…4 Repeated cycles in this linear regime are reported to follow a regular and well-defined power law decay until a critical number of conditioning cycles, known as the endurance limit, is reached after which a steady state signal is observed. 9 Beyond the yield point and W, nanocomposites will undergo plastic deformation and their response will be non-linear due to the tunnelling distance between nanofillers changing. 4 From the right-hand side of eq 3, it can be seen that a non-linear, exponential increase in tunnelling resistance will occur with increasing tunnelling distance.…”

“…Below the yield point, changes in the distribution of d from eq due to the viscoplastic flow of nanofillers are minimized, leading to a linear electromechanical response dominated by changes in the nanofiller areal overlap. , The linear limit of a material’s response is set by the yield strain and can be described using the linear range metric, the working factor ( W ) . Repeated cycles in this linear regime are reported to follow a regular and well-defined power law decay until a critical number of conditioning cycles, known as the endurance limit, is reached after which a steady-state signal is observed . Beyond the yield point and W , nanocomposites will undergo plastic deformation and their response will be nonlinear because of the tunneling distance between nanofillers changing .…”

“…Many models exist that describe the response curve of nanocomposites but in most cases they are empirical and unique to that particular material. , Furthermore, past emphasis on fitting the whole response curve including the plastic regime, for the most part, is redundant as it is outside of the functional working range of a nanocomposite. Strains beyond W cannot be practically applied in applications that require repeatable measurement, as signal is reported to be highly irregular . Thus, a simple and more universal mode of modelling, which focuses on describing the linear regime and incorporating nanocomposite network properties to describe electromechanical performance, is required.…”

“…The approach for our model here is one that relies on an introspective, analytical methodology, which utilizes trends and results reported in literature data. In the past, such an approach has been successful in identifying critical intrinsic material properties that greatly influence a nanocomposite’s strain-sensing performance. , Furthermore, dissimilar to previous models, here, the ramifications of the nanocomposite functional application strain range are considered.…”

“…Strains beyond W cannot be practically applied in applications that require repeatable measurement, as signal is reported to be highly irregular. 9 Thus, a simple and more universal mode of modelling, which focuses on describing the linear regime and incorporating nanocomposite network properties to describe electromechanical performance, is required.…”