NanoFET
Scalable Flat-Panel Nanoparticle Propulsion Technology for Space Exploration in the 21st Century Brian Gilchrist University of Michigan Ann Arbor, Michigan 2006 NIAC Annual Meeting Tucson, AZ October 18, 2006
NanoFET
Project Participants
• Extraction & Acceleration of Nanoparticles; Systems & Mission Design – Faculty Brian Gilchrist, Electrical Engineering & Space Systems Alec Gallimore, Aerospace Engineering & Applied Physics Michael Keidar, Aerospace Engineering – Students Thomas Liu, Aerospace Engineering Louis Musinski, Electrical Engineering Prashant Patel, Aerospace Engineering
• Storage & Transport of Nanoparticles – Faculty Mark Burns, Chemical & Biomedical Engineering Michael Solomon, Chemical Engineering & Macromolecular Science and Engineering Joanna Mirecki-Millunchick, Materials Science and Engineering – Students Deshpremy Mukhija, Chemical Engineering Kyung Sung, Chemical Engineering 2
NanoFET
Presentation Outline
• Electric propulsion systems • What is nanoFET? • Potential nanoFET advantages • Work-to-date – Particle charging, transport, extraction, and acceleration – Liquid surface instability
Acknowledgments • NASA Institute for Advanced Concepts • Matthew Forsyth & Bailo Ngom, University of Michigan • Robb Gillespie, University of Michigan
• Phase II work plan – Particle extraction and acceleration – Particle storage and transport – Systems and mission analysis 3
NanoFET
Electric Propulsion Systems
• The acceleration of charged gases or particles for propulsion by electrical heating and/or by electric and magnetic body forces • Advantages – High specific impulse possible – Low propellant cost compared to chemical rockets
1 q I sp = 2Vo g 0 m p
T 2 mp = P Vo q
1 2
1 2
• Disadvantages – Limited specific impulse range – Low efficiency when operating at low specific impulses – Charge exchange collisions (CEX) and hollow cathodes limit thruster lifetime
Source: PEPL
4
NanoFET
What is nanoFET?
• nanoparticle Field Extraction Thruster • Scalable arrays of micronsized emitters
Use MEMS/NEMS structures for propellant feed & acceleration
– thousands to millions of emitters possible – integrated MEMS/NEMS units
• In situ propellant manufacture?
45-nm dia. x 500-nm length
Source: N. Behan
– electrostatic charging and acceleration – great flexibility in controlling charge-to-mass ratio to tune performance
Use nanoparticles of various geometries and materials as propellant Source: Philips Electronics
• Nanoparticle propellant
100-nm dia.
5
NanoFET
Dielectric Liquid Configuration
• Low vapor pressure, dielectric liquid transports nanoparticles of specific geometry to extraction zones • Biased MEMS gate structures produce charging & accelerating electric fields • Charge neutralization can be achieved by other emitters operating at opposite polarity
Nanoparticle Accelerating Gate Dielectric Spacer
Dielectric Liquid Reservoir
Conducting & no liquid options possible
Charging Electrode 6
VN NanoFET
ur E
~1 Îźm
Conductor Conducting Grid
Dielectric
Conductor Conducting Grid
V2
Dielectric
ur E
V1
Charged Nanoparticles
Conductor Conducting Grid
Dielectric
Conductor Conducting Grid
ur E V0 Uncharged Nanoparticles
Liquid Reservoir
Liquid Flow
Liquid Flow
Stages of emitter operation 1. Transport to extraction zone via recirculating flow in microfluidic channel 2. Charging by contact with charging electrode 3. Lift-off from charging electrode & transit through liquid 4. Extraction from liquid surface 5. Acceleration through biased gate structures & ejection from emitter
Conducting Plate
7
NanoFET
nanoFET Advantages
• Decouples propulsion system design from spacecraft design – Geometrically scalable with power level – Plug-and-play approach
• Affords broader set of missions and mission phases with single engine type – Variable specific impulse over large range – High thrust-to-power with high efficiencies
• Both mission enhancing and mission enabling – Eliminates lifetime-limiting factors of existing EP systems – Lowers thruster specific mass
Flat-panel nanoFET architecture can be scaled for microsats to flagship missions Acceleration System
Gimbal Structure Prime Power PPU
10 kW 1 kW 10 W <1 W Particle Storage (Variable Depth)
Nanoparticle Emitters
Leveraging single engine type across broad range of missions lowers time for propulsion system development, testing, and qualification and thus cost
8
NanoFET
Compact & Scalable Design 3 cm
Individual nanoFET Emitters 2 Îźm
Emitter Array
Emission Sites
25 Îźm
Plug-and-play technology provides design flexibility, simplifies system integration, and lowers thruster specific mass 9
Large Isp Range Diameter [nm] 5 1 1 1
High efficiency
Specific Impulse (s)
With single engine type: â&#x20AC;˘ High Isp cruise to reduce propellant cost â&#x20AC;˘ Low Isp mode for greater thrust capability
Thrust-to-Power (mN/kW)
Internal Efficiency
NanoFET
Height [nm] 100 100 3500 400
Isp range [s] 100-500 500-2000 2000-10000 800-4000
High thrust-topower
Specific Impulse (s)
Wertz, 1999 10
• Variable-Isp engines – Consume less propellant than constant-Isp engines – Can optimize thrust profile in real time to accommodate missions with unplanned or unknown maneuvers – Enables propellant-time trade to be conducted
Normalized propellant cost
Greater Mission Flexibility Using Variable Isp
NanoFET
Variable Isp
Min Variable Isp
• Benefits
Max Variable Isp
Isp range (s)
– Wider margin to accommodate off-nominal mission scenarios – Improved capability for dynamic retasking and flight time adjustment
Constant Isp
Optimal constant Isp
Transfer time (min)
11
NanoFET
Summary of Work-to-Date
• Assessed significance of nanoFET as a propulsion system for space missions • Addressed fundamental physics questions regarding nanoFET’s feasibility – Demonstrated regime for particle extraction prior to liquid surface instability using scaled-up proof-ofconcept tests – Modeled nanoFET’s projected performance with decreased particle sizes
ln (4 A ) q (tex ) A2 exp ln mp l ln (4 A ) l A
12
NanoFET
Proof-of-Concept Experiments
• Understand how nanoFET works at scaled-up dimensions • Validate models of particle behavior and liquid surface instability • Experiments – Particle charging, transport, & lift-off – Particle extraction through liquid surface – Particle acceleration & ejection using multi-grid structure – Threshold for liquid surface instability
v E
Accelerating Grid
VN
Accelerating Grid
V2
Dielectric Accelerating Grid
V1
Dielectric
Charged Nanoparticle
v E
V0
Extraction Grid
Liquid Reservoir
Charging Grid
13
Particle Charging, Transport, and Lift-Off
NanoFET
• Demonstrate charging and transport of conducting particles in dielectric liquid with high electric fields • Particles: aluminum – Cylinders (300-μm dia. by 2.5-mm length – Spheres (800-μm dia.)
• Liquid: 100-cSt silicone oil
Experimental Setup: Liquid filled electrode gap with conducting particles Electrode
V
E-Fields
Gap Filled w/ Silicone Oil Conducting Particles
Electrode
Spherical Particles
Cylindrical Particles
5 mm 14
NanoFET
Particle Extraction & Acceleration Through Grid Particle charged on charging electrode Experimental Setup:
V2
E-Fields
Grid 2
Grid 2 Grid 1
Grid 1 E-Fields
V1
Particle
Liquid Surface
Conducting Particle
Charging Electrode
Charging Electrode
2 mm 15
Particle Extraction & Acceleration Through Grid
NanoFET
Particle extracted through liquid surface Charged particle is transported to and extracted through liquid surface by intense electric fields
(
)
dv dt = q(t)El + Fbuoyant W D Fsurface
mp + Kml
t q (t ) = q0 exp
l , =
l
Grid 2
Grid 1
Particle
Charging Electrode
Liquid Surface
2 mm
Particle appears to shift to left due to diffraction through test apparatus 16
NanoFET
Particle Extraction & Acceleration Through Grid Particle ejected from dual grid structure Grid 2
Particle is accelerated through the dual gird structure and finally ejected to provide thrust
Grid 1
Particle Liquid Surface
Charging Electrode
2 mm 17
NanoFET
1. 2.
Surface Instability & Taylor Cone Formation Electric field acts to pull free charge to liquid surface Cones form as a result of balancing surface tension and electric forces Electric field breaks cone off and accelerates charged liquid droplets
3.
1. Charges are pulled to surface
2. E-field pulls liquid up, surface tension pulls down
Electrode
3. Charged droplets are pulled off surface
Electrode
Electrode
E-Fields
V
V Electrode
V Electrode
Electrode
18
Surface Instability Threshold
NanoFET
â&#x20AC;˘ Charged liquid droplet emission degrades nanoFETâ&#x20AC;&#x2122;s performance by decreasing efficiency and controllability of charge-to-mass ratio â&#x20AC;˘ Does regime exist where particles are extracted without charged droplets?... 1 4
E0,min
â&#x20AC;˘ â&#x20AC;˘
â&#x20AC;˘
Spheres: â&#x20AC;&#x201C; 800 m dia. Cylinders â&#x20AC;&#x201C; 300 m dia. by 1.5 mm length Gap = 12.7 mm
2
4 g 0 l 0 = 1 + 2
0 l
1 2
Experimentally demonstrated regime where particles are extracted prior to liquid surface instabilities! 19
Phase II Work Plan
NanoFET
•
•
•
Increase physical understanding of particle charging, extraction, and acceleration as particle size is reduced from sub-millimeter scale down to micro- and nanometer scales Develop quantitative understanding of micro- and nanoparticle storage and transport to extraction zone Provide assessment of mission scenarios whose capabilities would be enabled or expanded by nanoFET
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NanoFET
Phase II: Nanoparticle Extraction & Acceleration
• How will particle extraction through liquid surface change as particle dimension decreases? – How does liquid wetting on the particle change? – What about liquid surface instability threshold under flow and zero-g conditions?
• How do particle charging properties change as size is reduced? – Does particle conductivity change when particle size is reduced to only several hundred atoms or less? – How will reducing contact area between particle and charging electrode affect charging process?
• Can common liquid and particles useful for extraction, transport, and storage be identified?
21
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• •
• •
Planned Experimental Work Verify accuracy and reliability of charge acquired by particles Extend particle charging, transport, and extraction experiments down to micro- and ultimately down to nano-scale Verify particle extraction behavior under vacuum is the same as in atmosphere Determine feasibility of particle charging, transport, and extraction from slightly conducting liquid Test prototype extractor & integrated feed system 22
Theoretical Work Refinements
NanoFET
• Electrohydrodynamic behavior and instability thresholds in zero-g • Particle effects at nanoscales • Particle extraction through liquid surface
Fluid level at specific test 4
– Particle wetting – Field enhancement effects
• Space charge current limitations due to viscous liquid 9 q Vl 2 j = l 8 dl 3
D v
1. Particle extraction (experiment) 2. Particle extraction (theory) 3. Feasible design space (theory) 4. Taylor cone formation (experiment and theory) 23
NanoFET
MEMS Gate Prototype Isometric
Top
1 cm Single-layer gate integrated with CNT substrate for field emission
Array of emission channels (2-Îźm diameter, 5-Îźm hole-to-hole spacing) 24
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Phase II: Nanoparticle Storage & Transport
â&#x20AC;˘ Under what conditions can nanoparticles be stored at high density and yet be transported as individual particles? â&#x20AC;˘ What are practical and future limits to nanoparticle fluxes when delivered in circulating channel networks? â&#x20AC;˘ How do nanoparticle properties, including size, shape, and material properties, affect transport and storage properties? 25
NanoFET
Microfluidic Feed System Profs. M. Solomon, M. Burns, & J. Mirecki-Millunchick
High density packing for low parasitic liquid mass
University of Michigan
Controlled displacement of individual particles
On-demand release of individual particles 26
NanoFET
Particle Control: Metering in Fluidic Channels
side view
valve
Particle properties: NIST polystyrene: 21±0.4 μm 10 μL of 0.01 wt% 2-valve PDMS device
fluid channel
Vanapalli, Sung, Mukhija 27
NanoFET
Particle Control: Transport in Fluidic Channels
1)
90 m
2)
90 m
3)
Sung, Vanapalli, Mukhija
90 m
Multi-channel pressure actuation used to move particles along complex trajectories (~ 20 Îźm particles) 28
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Reservoir for Particle Storage & Transport
• Transport 20 μm particles from storage area reservoir to thruster • Seek high reservoir loadings to minimize parasitic mass
Sung, Mukhija, Vanapalli 29
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Shape Effects on Particle Transport
Poly(methyl methacrylate) (PMMA) rods (length ~ 10 Îźm) with narrow polydispersity
PMMA rod (aspect ratio ~ 5) transport in fluidic channels Mukhija, Vanapalli, Sung 30
NanoFET
Phase II: nanoFET Systems & Mission Analysis – Particle & liquid properties – Geometric configurations – Current density limits
• System efficiency – Liquid drag & charge exchange – Particle impingement on gate – Beam defocusing
• Case studies of missions using nanoFET – Coupling between propulsion and power systems – Remote sensing near gravitational bodies – Variable-Isp to accommodate off-nominal conditions
Normalized Extraction Electric Field
• Performance optimization 3.0
r = 15 μm
2.5
At constant liquid thickness
r = 75 μm
2.0 r = 150 μm
1.5 1.0 0.5 0.0 1
10
100
Aspect Ratio
Low extraction electric field achieved by: high aspect ratio & reduced liquid thickness 31
NanoFET
Other nanoFET Applications Source: National Cancer Institute
Biomedical • targeted drug delivery to cells • cell tagging for diagnostics & tracking • cutting/dissection tool • subdermal implantation
nanoFET
More than just propulsion!
Cancer Cell
Material Substrate
Materials processing • implanting charged particles (doping & printing) • etching
32
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Conclusions
NanoFET
Backup Slides
34
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1. 2. 3. 4.
Particle Charging, Transport, & Lift-Off Particle in contact with bottom electrode in presence of electric field becomes charged Resulting Coulomb force on charged particle transports particle to top electrode At top electrode, particle becomes charged with opposite polarity but same magnitude Coulomb force pulls particle back down to bottom electrode and process repeats
1. Charged on bottom electrode (-)
2. Transported to top electrode
Electrode
V Electrode
l 2 l El = 2l ln 1 r 4. Transported to bottom electrode
Electrode
V Electrode
qcyl,vert
3. Charged on top electrode (+)
Electrode
V
qsph
2 3 2 = r l El 3
Electrode
V Electrode
Electrode
35
NanoFET
Particle Extraction Through Liquid Surface Experimental Setup: Partially liquid filled electrode gap with conducting particles
• Demonstrate – Use intense electric field to overcome surface tension forces and extract particles from liquid
Electrode E-Fields in Air gap
• Particles: aluminum – Spheres (800 and 1600 μm dia.) – Cylinders (300 μm dia. by 1.0 - 3.0 mm length)
• Liquid: 100 cSt silicone oil
V
Air gap
d Silicone Oil
E-Fields in liquid gap
Conducting Particles
dl
Electrode
36
NanoFET
Particle Extraction Through Liquid Surface
1
Liquid Surface
Cylindrical particles in oscillation – – – – –
Steel Electrodes
Particles 2
•
Liquid Surface
Steel Electrodes
diameter = 300 m length = 1.5 mm gap = 12.7 mm liquid height = 5 mm V ~ 14 kV
3
Particles
Liquid Surface
Steel Bottom Electrodes
Electrode
Particles
Particles 37
NanoFET
Particle Extraction Through Liquid Surface
1
Liquid Surface
Steel Electrodes
•
Required electric fields for particle extraction depends on – –
Particle size/shape Electric field strength
Particles 2
Liquid Surface
Steel Electrodes
3
Particles
Liquid Surface
Steel Bottom Electrodes
Electrode
Particles
Particles 38