Stretchable piezoresistive vs. capacitive silicon sensors integrated into ski base layer pants for measuring the knee fl
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TECHNICAL NOTE
Stretchable piezoresistive vs. capacitive silicon sensors integrated into ski base layer pants for measuring the knee flexion angle Aljoscha Hermann1 · Julius Ostarhild1 · Yakira Mirabito2 · Nicole Bauer1 · Veit Senner1 Accepted: 23 October 2020 / Published online: 18 November 2020 © The Author(s) 2020
Abstract The knee is the most often injured body part in alpine skiing. The loads on different structures of the knee, and thus the risk of injury, is influenced by the flexion angle of the knee joint. A mechatronic ski binding continuously supplied with information about the knee joint’s flexion angle could adjust its release settings to react to the situation appropriately. In this study, a silicon-based piezoresistive sensor fibre and capacitive silicon sensor were compared with respect to their ability to measure the knee flexion angle. Each sensor type was incorporated in base layer compression pants. These sensor-underwear-systems were validated using a flexion test rig and in a human subject test (n = 20). The pants with capacitive sensors performed better, as they were more accurate (e.g. mean error 3.4° ± 5.1° of the capacitive sensor vs. 10.6° ± 7.5° of the resistive sensor in the human subject test) and had fewer hysteresis effects. Flexible sensors integrated into compression underwear can provide valuable data of the knee angles for performance measurements in sports or safety systems, and thus may help to reduce knee injuries. Keywords Knee flexion sensor · Piezoresistive fibre · Capacitive sensor · Mechatronic ski binding · Technical textile
1 Introduction The injury rate in skiing is about three injuries per 1,000 skiing days [1, 2]. Over a third of all injuries are related to the knee [3, 4], which may result in lifelong mobility issues Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12283-020-00336-9) contains supplementary material, which is available to authorized users. * Aljoscha Hermann [email protected] Julius Ostarhild [email protected] Yakira Mirabito [email protected] Nicole Bauer [email protected] Veit Senner [email protected] 1
Sport Equipment and Materials, Technical University of Munich, 85748 Garching, Germany
Materials Science and Engineering, Northwestern University, Evanston 60201, USA
2
and pain. Current ski bindings do not always protect the knee from non-physiological loads [5, 6]. Complex physiological and biomechanical mechanisms are causes of injury [1, 7]. Besides external/internal knee rotation and abduction, the knee flexion angle influences the loads acting on the knee and its structures [8]. A promising concept to reduce knee injuries in alpine skiing is a mechatronic ski binding [9–11]. The mechatronic system could use information about the knee flexion angle (KFA) to predict the risk of injury and react by releasing the ski or adjusting the binding setting. For such a mechatronic binding, sensors are needed, which measure the KFA reliably. The sensor
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