Multiplexed electrospray emission on a porous wedge

Abstract

Linear porous wedge electrospray emitters exhibit a discrete number of emission sites that naturally form during operation. An analytical model is developed to examine the behavior and spacing of these emission sites via the pressure variation in the porous fluid flow associated with the flow focusing on each emission site, which is coupled with the local electric field. The solution for site spacing and current is informed by empirical results with support from electric field modeling and investigation of porous media parameters. Emission site currents of up to 500 nA and site spacings of roughly 50 µm–300 µm are predicted. Results from the model match well with experimental trends and provide further insights into the current and spacing of the discrete emission sites. These insights include the following: (1) for the investigated geometry, the total current can be estimated without taking into account the effects local to each emission site, (2) the wedge hydraulic resistance shows how the emitter output scales with emitter geometry and propellant properties, and (3) the emitted charge to mass ratio increases with the applied electric field. Last, we present a physical description of how specific charge increases with the restorative pressure from the reservoir.