Numerical Analysis of Electrohydrodynamic Continuous Jet Printing for High-Precision Patterning of Wearable Sensor Elements

Non-invasive, wearable sensors for human health monitoring and motion detection have gained tremendous attention over the last years. Driven by cutting-edge printing technologies they are considered as next-generation devices for screening of biomarkers and physiological parameters. For the fabrication of wearable sensors highly precise and, at the same time, costefficient manufacturing approaches are mandatory. In this paper, the emerging electrohydrodynamic (EHD) printing technology is presented as promising candidate for patterning of microscaled sensor elements based on conductive silver nanoparticle inks. A numerical analysis to study the jetting behavior of this technique in its continuous jet mode is carried out in order to investigate the impact of ink properties and process parameters for the achievement of a stable jetting regime. The FEM simulation is implemented by means of COMSOL Multiphysics®, rests on the so-called Taylor-Melcher leaky dielectric model and utilizes the level set method for capturing the interface between the liquid and the gas phase. This way, the whole two-phase flow process is successfully simulated considering the Taylor-Cone formation and the transient jet ejection from a microscaled capillary nozzle initiated by an external electric field. Further numerical simulations are performed which reveal the dependence of the jet diameter on the applied electric potential, the stand-off-height and the nozzle diameter, respectively.