Transient thermomechanical analysis of epidermal electronic devices on human skin

Abstract

Epidermal electronic devices (EEDs) have drawn much attention in human health monitoring due to their unique abilities to measure human vital signs continuously with high accuracy and without any invasion. Thermomechanical coupling between EED and skin is important since the temperature increase and the thermal strains/stresses from the Joule heating may cause human discomfort. In this paper, a three-dimensional transient analytical model is established to investigate thermomechanical behaviors of the EEDs/skin system based on the transfer matrix method. The combined Laplace and Fourier integral transformations are utilized to find the transfer equation for each layer of the system. The analytical predictions on the temperature increase and the maximum principal strain agree well with finite element analysis. The dynamic responses of cutaneous receptors (i.e., thermoreceptor and mechanoreceptor), which depend on the maximum temperature increase, the maximum rate of the principal strain and the maximum principal stress are obtained analytically. The influences of encapsulation and substrate thicknesses on the dynamic responses of cutaneous receptors are fully investigated. These results serve as the basis for the transient thermomechanical analysis of the EED/skin system and could provide design guidelines to minimize the adverse thermal effects in the EED/skin system.