Abstract
Elastomeric encapsulation layers are widely used in soft, wearable devices to physically isolate rigid electronic components from external environmental stimuli (e.g., stress) and facilitate device sterilization for reusability. In devices experiencing large deformations, the stress-isolation effect of the top encapsulation layer can eliminate the damage to the electronic components caused by external forces. However, for health monitoring and sensing applications, the strain-isolation effect of the bottom encapsulation layer can partially block the physiological signals of interest and degrade the measurement accuracy. Here, an analytic model is developed for the strain- and stress-isolation effects present in wearable devices with elastomeric encapsulation layers. The soft, elastomeric encapsulation layers and main electronic components layer are modeled as transversely isotropic-elastic mediums and the strain- and stress-isolation effects are described using isolation indexes. The analysis and results show that the isolation effects strongly depend on the thickness, density, and elastic modulus of both the elastomeric encapsulation layers and the main electronic component layer. These findings, combined with the flexible mechanics design strategies of wearable devices, provide new design guidelines for future wearable devices to protect them from external forces while capturing the relevant physiological signals underneath the skin.
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This work was supported by the National Natural Science Foundation of China (Grant Nos. 12172319, 11872326, and 12072057), the Natural Science Foundation of Hunan Province (Grant Nos. 2021JJ30648, and 2021JJ30641), the Furong Scholars Programme of Hunan Province, the LiaoNing Revitalization Talents Program (Grant No. XLYC2007196), the Fundamental Research Funds for the Central Universities (Grant No. DUT20RC(3)032), the National Science Foundation Graduate Research Fellowship (Grant No. 1842165) and the Ford Foundation Predoctoral Fellowship.
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Wang, X., Huang, J., Liu, Y. et al. Design of protective and high sensitivity encapsulation layers in wearable devices. Sci. China Technol. Sci. 66, 223–232 (2023). https://doi.org/10.1007/s11431-022-2034-y
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DOI: https://doi.org/10.1007/s11431-022-2034-y