Abstract
Wearable electronics are recognized as a vital tool for gathering in situ kinematic information of human body movements. In this paper, we describe the production of a core–sheath fiber strain sensor from readily available materials in a one-step dip-coating process, and demonstrate the development of a smart sleeveless shirt for measuring the kinematic angles of the trunk relative to the pelvis in complicated three-dimensional movements. The sensor’s piezoresistive properties and characteristics were studied with respect to the type of core material used. Sensor performance was optimized by straining above the intended working region to increase the consistency and accuracy of the piezoresistive sensor. The accuracy of the sensor when tracking random movements was tested using a rigorous 4-h random wave pattern to mimic what would be required for satisfactory use in prototype devices. By processing the raw signal with a machine learning algorithm, we were able to track a strain of random wave patterns to a normalized root mean square error of 1.6%, highlighting the consistency and reproducible behavior of the relatively simple sensor. Then, we evaluated the performance of these sensors in a prototype motion capture shirt, in a study with 12 participants performing a set of eight different types of uniaxial and multiaxial movements. A machine learning random forest regressor model estimated the trunk flexion, lateral bending, and rotation angles with errors of 4.26°, 3.53°, and 3.44° respectively. These results demonstrate the feasibility of using smart textiles for capturing complicated movements and a solution for the real-time monitoring of daily activities.
Highlights
Wearable electronics have become increasingly popular with the advancement of materials and electronics over the past two decades, producing more flexible and integrated functional materials
Using the strain patterns by Mattmann et al as a starting point and conducting further empirical for trunk twisting and lateral bending [64,65]. This placement resulted in more sensitivity to rotation sensor placement tests, we found the placements shown in Figure 2 to provide the best strain and lateral bending movements, which were isolated patterns for trunk twisting and lateral bending [64,65]
The maximum strain and pre-strain that the fiber sensor would be exposed to during use was analyzed using a motion capture system. This analysis determined that the sensor was strained approximately 5% when the garment was worn without any movement, which we have defined as pre-strain (Figure 1b,d)
Summary
Wearable electronics have become increasingly popular with the advancement of materials and electronics over the past two decades, producing more flexible and integrated functional materials. Wearable electronics span a wide variety of applications such as biomedical monitoring (i.e., body vitals), motion tracking, and integrated personal electronics [1]. While there are non-wearable technologies that are able to track movement accurately. Flexible fiber strain sensors have the potential for seamless integration into textiles and clothing creating wearable systems for in situ tracking of movements and further quantitative physical exposure measurement for injury risk assessment, with increased mobility and comfort, and without spatial restrictions—such as those with motion capture systems
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