A Micro-Fabricated Linear Array of Electrospray Emitters for Thruster Applications

Abstract

This paper reports the design, fabrication, and experimental characterization of an internally fed linear array of electrospray emitters intended for space propulsion applications. The engine uses doped formamide as propellant and operates in the single-Taylor-cone droplet emission regime. The engine implements the concept of hydraulic and electrodynamic flow rate matching to achieve electrical control. The engine uses a set of meso-scaled silicon deflection springs to assemble the hydraulics to the electrodes, allowing to decouple the corresponding process flows. The micro-fabrication of the engine is described and novel technologies that were developed are reported. Experimental results that demonstrate cumulative uniform and steady operation are provided. Current-flowrate characteristics of the engine are in agreement with a reduced-order model. Experimental data demonstrating the low divergence of electrospray emitter arrays operated in the single Taylor Cone is in qualitative agreement with a reduced-order mode that assumes the absence of a thermalized tail in the plume.[1420]Index Terms-Electrical flow control, electrospray array, propulsion, spring deflection system, three-dimensional (3-D).

Tailoring the hydraulic impedance of out-of-plane micromachined electrospray sources with integrated electrodes

“…͓DOI: 10.1063/1.3117191͔ Large arrays of nanoelectrospray emitters capable of operating in pure ionic mode using ionic liquids are of great interest for space micropropulsion and as ion sources for future focused ion beam applications. The feasibility of large arrays of microfabricated silicon out-of-plane arrays of capillaries has been shown previously, 1,2 but their operation has been difficult due to low hydraulic impedance, identified as a key parameter in the stability of electrosprays, [3][4][5] and as a key parameter in determining ion to droplet ratio when spraying ionic liquids. Recent studies with the ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate ͑EMI-BF 4 ͒ and 1-ethyl-3-methylimidazolium bis͑trifluorom-ethylsulfonyl͒imide ͑EMI-Tf 2 N, also referred to as EMI-Im͒, show that when sprayed from a capillary under vacuum conditions, a purely ionic regime ͑PIR͒ is only reached at low flow rates ͑Ӷ1 nL/ s͒ while at higher flow rates mixed droplet-ion emission is observed.…”

Precision Hand Assembly of MEMS Subsystems Using DRIE-Patterned Deflection Spring Structures: An Example of an Out-of-Plane Substrate Assembly

“…Fig. 6 shows one of the test structures implemented to analyze the spring assembly system of the electrospray linear array that we developed [21].…”

“…The emitted particles make a fan with a divergence angle due to the Coulomb repulsion of the particles. The semiangle of the emitted fan is estimated at 20 for formamide [21]. For an electrode 300 m wide separated 250 m from the emitter tips, the maximum tilting angle before particle interception is then about 10 .…”

“…16). A misalignment in this direction will produce a change in the emitter starting voltage because it has a dependence of the form [21] (7)…”

“…The working environment includes high vacuum and large temperature differences due to the day/light cycle of an object orbiting around the Earth. Also, these devices could see voltages up to 5000 V [21]. These devices require electrical integrity against ordinary breakdown at high voltage, and robustness against shorting via surface layers of contaminants.…”