| Wearable electromechanical sensors transduce mechanical stimuli into readable electrical signals,their functionality and ease of integration have positioned them as desirable candidates for potential applications in human health.At the skin-device interface,physiological processes like sweat,metabolites,and secretion create a complex operational environment for bare pressure sensors that degrade their performance.Therefore,a soft,elastomeric encapsulation layer is typically used to mitigate the effects of skin physiological processes in the device,avoid erosion and pollution caused by the external environment,and isolate rigid electronic components from the external environmental stimuli.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 for the strain-and stress-isolation effects present in wearable devices with elastomeric encapsulation layers.A model of transversely isotropic is established to obtain transfer relations between state variables in various layers,and the strain-and stress-isolation effects are described using dimensionless parameters.The main research contents and conclusions are as follows:(1)For flexible wearable devices,the soft,elastomeric encapsulation layers and main electronic components layer are modeled as a three-layer structure,assuming that each layer is a transversely isotropic medium with an axisymmetric structure.Can be modeled using the theory of the plane linear elastic problems in cylindrical coordinates,First,starting from the stress equilibrium equations and the constitutive equations of the spatial axisymmetric problem,to establishing the state variable equation of the laminar structures,converting the state variable equation into a set of ordinary differential equations,and obtaining solutions in the Hankel transform space.Finally,the transfer matrix approach was used to develop the general analytical formula for the axisymmetric issue in the multi-layer medium space.(2)Based on the theoretical framework above,the actual signal received by the m ain layer was obtained by simulating the vertical vibration physiological signals from t he human body,and a strain-isolation index was defined.The results of finite element simulation are consistent with the theory.It shows that the strain isolation effect stron gly depends on the thickness,density,and elastic modulus of each layer.The strain-iso lation effects are larger for a multi-layered system as the thickness of layers increases,and the bottom encapsulation layer has the most significant effect on the strain-isolatio n effect.The results show that the strain-isolation effect can be reduced by increasing t he density of the bottom encapsulation layer and even further relieved by decreasing t he modulus of the main layer.(3)With the aid of the above theoretical model,the vertical uniform loading of ex ternal impact was analyzed,and the stress isolation index of the encapsulation layer w as obtained.The accuracy of the theory is further verified by finite element analysis.The results show that the effect of stress isolation depends on the thickness and elastic modulus of each layer.Indicating that the stress-isolation effect of the thicker elastic e ncapsulation layer and higher modulus ratio is more prominent,The better the protecti on of the device. |
