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Session: Wearable
Session starts: Friday 27 January, 11:30
Presentation starts: 11:45
Room: Room 531

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Nick Willemstein (University of Twente)
Ali Sadeghi (University of Twente)
Herman van der Kooij (University of Twente)

Abstract:
Wearable sensors are a useful tool for monitoring a wide variety of parameters during motion such as force distribution during walking. Sensors for such applications must be non-intrusive and comfortable to wear. These aspects are essential to minimize the impact on the measurand and foster acceptance by patients. One interesting candidate for this application are soft sensors. These sensors can measure parameters such as pressure, force, and strain while their inherent flexibility allows for comfortable interaction with the user. An example of such soft sensors are porous (foam-like) sensors that can adapt to the user’s body, are lightweight, and can be mechanically programmed (i.e. stiffness can be adjusted). Such porous sensors can be 3D printed through our InFoam printing method [1]. The 3D printing of foam-like structures allows for the fabrication of strain and force sensors in a myriad of geometries, which can be useful for customized sensors. The focus was on investigating the effect of porosity gradient/magnitude on the 1) Stress/strain sensitivity 2) Range (i.e. minimum and maximum) stress/strain 3) Repeatability of the sensor A set of cubes with a carbon black-filled thermoplastic elastomer were printed using our InFoam method with different levels of porosity (gradients). Two experiments were conducted on these samples: 1) Compression tests by a tensile tester for stress/strain behavior 2) Walking test on a force plate with a cube embedded in an insole During all these experiments an Arduino was used to record the electrical resistance of the cube. Subsequently, MATLAB was used to identify and evaluate models. Current results indicate that these porous sensors can be used to estimate the compressive stress and strain quite accurately (>75% fits) yet are still very soft (< 5 megapascals). Whereas the magnitude of stress ranged from a few - >200 kilopascal. In addition, changing the porosity enabled the programming of the strain/stress sensitivity. Thus, soft 3D-printed porous sensors are interesting to provide both stress/strain estimation. In future work, these sensors will need to be tested in a more challenging environment such as with a patient. In addition, multi-modal sensing could be investigated for other loads beside compression.