Fabrication and testing of an ionic electrospray propulsion system with a porous metal tip array

Li, H.Q.; Courtney, Daniel G.; Maqueo, Pablo Diaz Gomez; Lozano, Paulo

doi:10.1109/transducers.2011.5969199

Cited by 8 publications

(7 citation statements)

References 4 publications

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“…For the sparse emitters, symmetric emission is observed in both polarities with as much as 5 μA per emitter tip, more than five times higher than the best values previously reported in the literature for a plurality of electrospray emitters operating in parallel [6], [13], [16]. The operating voltages are lower for the array of 81 emitters than for the sparse emitter arrays, likely because the emitters in the array of 81 emitters are on average 50 μm taller than the emitters in the smaller arrays.…”

Section: Current-voltage Characteristicsmentioning

confidence: 82%

“…The objective of an optimized hydraulic impedance in an electrospray ion source is to set flow rates as close to Q min as possible without exceeding that value, in order to maximize the ionic emission current from each emission site without producing droplets. Recently, researchers have reported microfabrication approaches to create a high hydraulic impedance to each emitter of the array by filling-in capillary channels with silica microspheres [5], [22] or by electrochemically etching metallic emitter tips [6], [9], [16]; both approaches have demonstrated emission in the ionic regime. Drawbacks of these approaches include the limited degree to which the hydraulic impedance can be finely tuned, variation of the morphology of the porous material within each emitter and across the array, and the use of internal flow channels that are difficult to clean and can be prone to clogging, which can lead to device failure [9].…”

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confidence: 99%

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High-Throughput Ionic Liquid Ion Sources Using Arrays of Microfabricated Electrospray Emitters With Integrated Extractor Grid and Carbon Nanotube Flow Control Structures

Hill

Heubel

Leon

et al. 2014

J. Microelectromech. Syst.

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We report the design, fabrication, and experimental characterization of dense, monolithic, and planar arrays of externally-fed electrospray emitters with an integrated extractor grid and carbon nanotube flow control structures for low-voltage and high-throughput electrospray of the ionic liquid EMI-BF 4 in vacuum. Microfabricated arrays with as many as 1900 emitters in 1 cm 2 were fabricated and tested. Per-emitter currents as high as 5 µA in both polarities were measured, with start-up bias voltages as low as 470 V and extractor grid transmission as high as 80%. Maximum array emission currents of 1.35 mA (1.35 mA/cm 2 ) were measured using arrays of 1900 emitters in 1 cm 2 . A conformal carbon nanotube forest grown on the surface of the emitters acts as a wicking structure that transports liquid to the emitter tips, providing hydraulic impedance to regulate and uniformize the emission across the array. Mass spectrometry of the electrospray beam confirms that emission in both polarities is composed of solvated ions, and etching of the silicon collector electrode is observed. Collector imprints and per-emitter current-voltage characteristics for different emitter array sizes spanning three orders of magnitude show excellent emission uniformity across the array. Performance estimates of the devices as nanosatellite thrusters are provided.

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Section: Current-voltage Characteristicsmentioning

confidence: 82%

mentioning

confidence: 99%

High-Throughput Ionic Liquid Ion Sources Using Arrays of Microfabricated Electrospray Emitters With Integrated Extractor Grid and Carbon Nanotube Flow Control Structures

Hill

Heubel

Leon

et al. 2014

J. Microelectromech. Syst.

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“…In particular, this approach has been compatible with an overall MEMS thruster process flow [12], which includes the presented EMM methods as a step.…”

Section: Discussionmentioning

confidence: 99%

“…The electrochemical process presented here has been applied as a single step within a larger process designed by the authors [12] to fabricate porous ILIS thruster arrays as microelectromechanical systems (MEMS). Each thruster package consists of 480 porous ILIS within 1.5 cm 2 of total frontal area.…”

Section: Transport Limited Electrochemical Etchingmentioning

confidence: 99%

Electrochemical Micromachining on Porous Nickel for Arrays of Electrospray Ion Emitters

Courtney

Lozano

2013

J. Microelectromech. Syst.

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The emission of molecular ions from ionic liquid ion sources (ILIS) poses a number of advantages in applications from materials science to space propulsion. However, practical implementation of these field emitters requires their grouping into dense arrays of emitters to increase current throughput. A process to micromachine ILIS on porous metals is presented using a mixture of photolithographic and electrochemical etching techniques. It is found that emitter uniformity and pore integrity are achieved with pulsed voltage etching in a regime controlled by the thickness of the layer composed of products from the electrochemical dissolution process. Postetching in a presaturated solution is then applied to obtain a smooth rounded shape of porous metal emitters, which is adequate for ILIS operation. A prototype implementation is demonstrated in porous nickel with a mean pore size of 5 μm achieving uniform triangular arrays of 480 ILIS in a 1-cm 2 area mounted on a silicon frame. Each emitter is about 150-μm tall with a radius of curvature of about 15 μm at the tip.

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“…A third type of thruster array which does not cleanly fit into any of these groups is the porous tungsten and porous nickel planar arrays. [12][13][14][15] Regularly spaced peaks are etched into porous tungsten and nickel. The peaks provide the electric field enhancement so that Taylor cones form on the apex.…”

Section: Introductionmentioning

confidence: 99%

Electrospray from an Ionic Liquid Ferrofluid utilizing the Rosensweig Instability

Meyer

King

2013

49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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A new type of electrospray technology that could be used for space propulsion was developed at Michigan Technological University. This thruster utilized an ionic liquid ferrofluid that was synthesized by suspending magnetic nanoparticles in an ionic liquid carrier solution so that the resulting fluid is superparamagnetic. The magnetic properties of the fluid were exploited to create self-assembling static arrays of surface peaks which were then amplified with an applied electric field until ion current was emitted from the array. The current and voltage profile of the emitting array was measured and its ability to self-heal after a damaging event was observed. I. IntroductionTypical electrospray thruster concepts utilize linear "blade like" emitters, 2-D arrays of tips, or 2-D arrays of micro-capillaries to generate large electric fields and ion/droplet emission from an electrostatic Taylor cone. Linear arrays are manufactured from thin sheets of metal, such as porous tungsten, and sharp peaks are etched into the surface. The arrays are aligned with a slit in the extraction electrode and the propellant (ionic liquid) is passively pumped through the porous tungsten. 1, 2 This type of electrospray emitter can have good packing density along the length of the array, but leaves a sizeable gap between consecutive arrays. Legge and Lozano were able to demonstrate 2 tips per mm packing density along the length of the array. 2 A similar strategy is the tungsten crown emitter, which is a porous tungsten structure shaped like a king's crown with a circular array of 28 emitters. [3][4][5] The crown emitter used indium as its propellant.Two-dimensional arrays are typically etched from silicon with regularly spaced discrete needles. 6 For this type of arrangement, the propellant is typically externally applied to the surface of the silicon where capillary flow causes a uniform layer of propellant to coat the substrate and emitter tips. In order for the propellant to easily wet to the silicon surface, a surface treatment is usually necessary, such as making black silicon. 7 These arrays are then assembled with an extraction electrode and alignment/retention mechanisms. 8 The third type of electrospray thruster is the capillary thruster. These types of thrusters generally contain the fluid in a hollow tube or needle and the electric field is created at the exit of the capillary. 9 One such device is the capillary array of 19 emitters built by Krpoun and Shea. 10 In this device each of the capillaries are etched out of silicon and then filled with silica spheres to provide a more uniform hydraulic resistance within each emitter. A micromanufactured extraction electrode was placed and aligned using ruby balls for alignment and electrical isolation. Another version of a capillary thruster was developed by Busek. 11 Each of Busek's thruster heads contained an array of 9 individually manufactured emitters assembled into an array. A third type of thruster array which does not cleanly fit into any of these groups is the porous tungst...

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Fabrication and testing of an ionic electrospray propulsion system with a porous metal tip array

Cited by 8 publications

References 4 publications

High-Throughput Ionic Liquid Ion Sources Using Arrays of Microfabricated Electrospray Emitters With Integrated Extractor Grid and Carbon Nanotube Flow Control Structures

High-Throughput Ionic Liquid Ion Sources Using Arrays of Microfabricated Electrospray Emitters With Integrated Extractor Grid and Carbon Nanotube Flow Control Structures

Electrochemical Micromachining on Porous Nickel for Arrays of Electrospray Ion Emitters

Electrospray from an Ionic Liquid Ferrofluid utilizing the Rosensweig Instability

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