Abstract
Stretchable conductive materials are originally conceived as radio frequency (RF) and electromagnetic interference (EMI) shielding materials, and, under stretch, they generally function as distributed strain-gauges. These commercially available conductive elastomers have found their space in low power health monitoring systems, for example, to monitor respiratory and cardiac functions. Conductive elastomers do not behave linearly due to material constraints; hence, when used as a sensor, a full characterisation to identify ideal operating ranges are required. In this paper, we studied how the continuous stretch cycles affected the material electrical and physical properties in different embodiment impressed by bodily volume change. We simulated the stretch associated with breathing using a bespoke stress rig to ensure reproducibility of results. The stretch rig is capable of providing constant sinusoidal waves in the physiological ranges of extension and frequency. The material performances is evaluated assessing the total harmonic distortion (THD), signal-to-noise ratio (SNR), correlation coefficient, peak to peak (P-P) amplitude, accuracy, repeatability, hysteresis, delay, and washability. The results showed that, among the three controlled variables, stretch length, stretch frequency and fabric width, the most significant factor to the signal quality is the stretch length. The ideal working region is within 2% of the original length. The material cut in strips of >3 mm show more reliable to handle a variety of stretch parameter without losing its internal characteristics and electrical properties.
Highlights
Physiological monitoring and noninvasive sensing are paramount for the modern biomedical sensors industry
Total harmonic distortion: The total harmonic distortion analysed in our work focused only on first five harmonics produced by the band
We present experiments and calculations to evaluate performance of the stretchable conductive fabric using a mechanical stretchable rig and low power custom data acquisition system
Summary
Physiological monitoring and noninvasive sensing are paramount for the modern biomedical sensors industry. Recent technologies enable monitoring of vital physiological signals such as respiration, heart rate, electrocardiogram (ECG), and pulse velocity non-invasively. Non-invasive sensors enable comfortable yet accurate diagnosis and monitoring of sleep disordered breathing [1], peripheral vascular disease [2], and congestive heart failure [3], coronary artery disease [4], cardiopulmonary resuscitation [5] and cardiac arrhythmia [6]. Conventional portable monitoring sensors take advantage of recent advances of wireless networks technologies, mobile devices and cloud. Even with the current state-of-the-art technologies, end sensors remain moderately larger in size, cumbersome to use and unsuitable for long-term monitoring. Sleep studies are a good example scenario where long-term vital parameter monitoring is paramount
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