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Nano-
FET
Scalable Flat-Panel NanoparticlePropulsion Technology for SpaceExploration in the 21st Century
Brian Gilchrist
University of Michigan
Ann Arbor, Michigan
2006 NIAC Annual Meeting
Tucson, AZ
October 18, 2006
2
Nano-
FET Project Participants
• Extraction & Acceleration ofNanoparticles; Systems &Mission Design
– Faculty
Brian Gilchrist, ElectricalEngineering & SpaceSystems
Alec Gallimore, AerospaceEngineering & AppliedPhysics
Michael Keidar, AerospaceEngineering
– Students
Thomas Liu, AerospaceEngineering
Louis Musinski, ElectricalEngineering
Prashant Patel, AerospaceEngineering
• Storage & Transport ofNanoparticles
– Faculty
Mark Burns, Chemical &Biomedical Engineering
Michael Solomon, ChemicalEngineering &Macromolecular Science andEngineering
Joanna Mirecki-Millunchick,Materials Science andEngineering
– Students
Deshpremy Mukhija,Chemical Engineering
Kyung Sung, ChemicalEngineering
3
Nano-
FET Presentation Outline
• Electric propulsionsystems
• What is nanoFET?
• Potential nanoFETadvantages
• Work-to-date– Particle charging, transport,
extraction, and acceleration
– Liquid surface instability
• Phase II work plan– Particle extraction and
acceleration
– Particle storage and transport
– Systems and mission analysis
Acknowledgments
• NASA Institute for AdvancedConcepts
• Matthew Forsyth & Bailo Ngom,University of Michigan
• Robb Gillespie, University ofMichigan
4
Nano-
FET Electric Propulsion Systems
• The acceleration of chargedgases or particles for propulsionby electrical heating and/or byelectric and magnetic body forces
• Advantages– High specific impulse possible
– Low propellant cost compared tochemical rockets
• Disadvantages– Limited specific impulse range
– Low efficiency when operating at lowspecific impulses
– Charge exchange collisions (CEX)and hollow cathodes limit thrusterlifetime
1
2
sp
0
12
o
p
q
mI V
g=
1
22
o
pm
q
T
P V=
Source: PEPL
5
Nano-
FET What is nanoFET?
• nanoparticle FieldExtraction Thruster
• Scalable arrays of micron-sized emitters
– thousands to millions ofemitters possible
– integrated MEMS/NEMS units
• Nanoparticle propellant– electrostatic charging and
acceleration
– great flexibility in controllingcharge-to-mass ratio to tuneperformance
• In situ propellantmanufacture?
Use MEMS/NEMS structures forpropellant feed & acceleration
100-nm dia.45-nm dia. x 500-nm length
Use nanoparticles of variousgeometries and materials as
propellant
Sour
ce: P
hilip
s E
lect
roni
cs
Sour
ce: N
. Beh
an
6
Nano-
FET
Dielectric LiquidConfiguration
• Low vapor pressure,dielectric liquid transportsnanoparticles of specificgeometry to extractionzones
• Biased MEMS gatestructures producecharging & acceleratingelectric fields
• Charge neutralization canbe achieved by otheremitters operating atopposite polarity
Nanoparticle
Accelerating
Gate
Dielectric
Spacer
Dielectric
Liquid
Reservoir
Charging ElectrodeConducting & no liquid options possible
7
Nano-
FET Stages of emitter operation
1. Transport to extraction zonevia recirculating flow inmicrofluidic channel
2. Charging by contact withcharging electrode
3. Lift-off from chargingelectrode & transit throughliquid
4. Extraction from liquidsurface
5. Acceleration through biasedgate structures & ejectionfrom emitter
2 V
0V
N V
Conducting Grid
Conducting Grid
Conducting Grid
Conducting Grid
~1 μm
1 V
Dielectric
Conducting Plate
Charged
Nanoparticles
Dielectric
Dielectric
E
ur
Liquid
ReservoirUncharged
Nanoparticles
Liquid FlowLiquid Flow
Conductor
Conductor
Conductor
Conductor
E
ur
E
ur
8
Nano-
FET nanoFET Advantages
• Decouples propulsion systemdesign from spacecraft design
– Geometrically scalable with powerlevel
– Plug-and-play approach
• Affords broader set of missions andmission phases with single enginetype
– Variable specific impulse over largerange
– High thrust-to-power with highefficiencies
• Both mission enhancing andmission enabling
– Eliminates lifetime-limiting factors ofexisting EP systems
– Lowers thruster specific mass
Flat-panel nanoFET architecturecan be scaled for microsats to
flagship missions
Nanoparticle
Emitters
PPU
Acceleration
SystemPrime
Power
Particle Storage
(Variable Depth)
10 W
1 kW
10 kW
<1 W
Gimbal
Structure
Leveraging single engine typeacross broad range of missions
lowers time for propulsion systemdevelopment, testing, andqualification and thus cost
9
Nano-
FET Compact & Scalable Design
25 μm
Emission Sites
2 μm
Individual nanoFET Emitters3 cm
Emitter Array
Plug-and-play technology
provides design flexibility,
simplifies system integration, and
lowers thruster specific mass
10
Nano-
FET Large Isp Range
Diameter [nm] Height [nm] Isp range [s]
5 100 100-500
1 100 500-2000
1 3500 2000-10000
1 400 800-4000
High thrust-to-
power
High efficiency
Wertz, 1999
With single engine type:
• High Isp cruise to reducepropellant cost
• Low Isp mode for greater thrustcapability Specific Impulse (s)
Specific Impulse (s)
Inte
rnal
Effi
cien
cy
Th
rust
-to-
Pow
er (m
N/k
W)
11
Nano-
FET
Greater Mission FlexibilityUsing Variable Isp
• Variable-Isp engines– Consume less propellant than
constant-Isp engines
– Can optimize thrust profile inreal time to accommodatemissions with unplanned orunknown maneuvers
– Enables propellant-time trade tobe conducted
• Benefits– Wider margin to accommodate
off-nominal mission scenarios
– Improved capability for dynamicretasking and flight timeadjustment
Nor
mal
ized
pro
pel
lan
t cos
t
Transfer time (min)
Isp
ran
ge (s
)
Constant Isp
Variable Isp
Min Variable Isp
Max Variable Isp
Optimal constant Isp
12
Nano-
FET Summary of Work-to-Date
• Assessed significance ofnanoFET as a propulsionsystem for space missions
• Addressed fundamentalphysics questions regardingnanoFET’s feasibility
– Demonstrated regime for particleextraction prior to liquid surfaceinstability using scaled-up proof-of-concept tests
– Modeled nanoFET’s projectedperformance with decreased particlesizes
( )
( )2
exln 4( )
expln 4 ln
p
Aq t A
m l A l A
13
Nano-
FET
Proof-of-ConceptExperiments
• Understand how nanoFETworks at scaled-updimensions
• Validate models of particlebehavior and liquid surfaceinstability
• Experiments– Particle charging, transport, &
lift-off
– Particle extraction throughliquid surface
– Particle acceleration & ejectionusing multi-grid structure
– Threshold for liquid surfaceinstability
0V
NV
1V
Liquid
Reservoir
Charging Grid
2V Dielectric
Dielectric
Accelerating
Grid
Extraction
Grid
Accelerating
Grid
Accelerating
GridEv
Ev
Charged
Nanoparticle
14
Nano-
FET
Particle Charging, Transport,and Lift-Off
• Demonstrate charging andtransport of conductingparticles in dielectric liquid withhigh electric fields
• Particles: aluminum
– Cylinders (300-μm dia. by 2.5-mmlength
– Spheres (800-μm dia.)
• Liquid: 100-cSt silicone oil
CylindricalParticles
SphericalParticles
V
Electrode
Electrode
Gap Filled w/
Silicone OilE-Fields
Conducting
Particles
Experimental Setup:
Liquid filled electrode gapwith conducting particles
5 mm
15
Nano-
FET
Particle Extraction &Acceleration Through Grid
Particle charged on charging electrode
V1
Charging Electrode
E-Fields
Conducting
Particle
Experimental Setup:
V2
E-Fields
Grid 1
Grid 2
Charging Electrode
Grid 1
Grid 2
2 mm
Liquid Surface
Particle
16
Nano-
FET
Particle Extraction &Acceleration Through Grid
Particle extracted through liquid surface
Particle appears to shift to left due to diffraction through test apparatus
Charging Electrode
Liquid Surface
Grid 1
Grid 2
2 mm
Particle
Charged particle istransported to andextracted through liquidsurface by intense electricfields
mp
+ Kml( ) dv
dt
= q(t)El+ F
buoyantW D F
surface
0( ) exp ,
l
l
tq t q= =
17
Nano-
FET
Particle Extraction &Acceleration Through Grid
Particle ejected from dual grid structure
Particle is accelerated
through the dual gird
structure and finally
ejected to provide thrust
Charging Electrode
Grid 1
Grid 2
2 mm
Liquid Surface
Particle
18
Nano-
FET
V
Electrode
Electrode
1. Charges are
pulled to surface
E-Fields
V
Electrode
Electrode
2. E-field pulls
liquid up, surface
tension pulls down
V
Electrode
Electrode
3. Charged
droplets are pulled
off surface
1. Electric field acts to pull free charge to liquid surface
2. Cones form as a result of balancing surface tension and electricforces
3. Electric field breaks cone off and accelerates charged liquiddroplets
Surface Instability & TaylorCone Formation
19
Nano-
FET Surface Instability Threshold
• Charged liquid droplet emission degrades nanoFET’s performance bydecreasing efficiency and controllability of charge-to-mass ratio
• Does regime exist where particles are extracted without chargeddroplets?...
• Spheres:
– 800 m dia.
• Cylinders
– 300 m dia.by 1.5 mmlength
• Gap = 12.7 mm
Experimentally
demonstrated regime
where particles are
extracted prior to liquid
surface instabilities!
11
2 24
0 0
0,min 2
0
41
l
l
gE = +
20
Nano-
FET Phase II Work Plan
• Increase physical understanding of particlecharging, extraction, and acceleration as particlesize is reduced from sub-millimeter scale down tomicro- and nanometer scales
• Develop quantitative understanding of micro- andnanoparticle storage and transport to extractionzone
• Provide assessment of mission scenarios whosecapabilities would be enabled or expanded bynanoFET
21
Nano-
FET
Phase II: NanoparticleExtraction & Acceleration
• How will particle extraction through liquid surface changeas particle dimension decreases?
– How does liquid wetting on the particle change?
– What about liquid surface instability threshold under flow andzero-g conditions?
• How do particle charging properties change as size isreduced?
– Does particle conductivity change when particle size is reducedto only several hundred atoms or less?
– How will reducing contact area between particle and chargingelectrode affect charging process?
• Can common liquid and particles useful for extraction,transport, and storage be identified?
22
Nano-
FET Planned Experimental Work
• Verify accuracy and reliability ofcharge acquired by particles
• Extend particle charging,transport, and extractionexperiments down to micro- andultimately down to nano-scale
• Verify particle extraction behaviorunder vacuum is the same as inatmosphere
• Determine feasibility of particlecharging, transport, andextraction from slightlyconducting liquid
Test prototype extractor &
integrated feed system
23
Nano-
FET
Theoretical WorkRefinements
• Electrohydrodynamicbehavior and instabilitythresholds in zero-g
• Particle effects atnanoscales
• Particle extraction throughliquid surface
– Particle wetting
– Field enhancement effects
• Space charge currentlimitations due to viscousliquid
2
3
9
8
l
l
l
Vq Dj
d v=
1. Particle extraction (experiment)
2. Particle extraction (theory)
3. Feasible design space (theory)
4. Taylor cone formation (experiment and theory)
4
Fluid level at
specific test
24
Nano-
FET MEMS Gate Prototype
1 cm
Single-layer gate integrated with
CNT substrate for field emission
Array of emission channels (2-μm
diameter, 5-μm hole-to-hole
spacing)
Top
Isometric
25
Nano-
FET
Phase II: NanoparticleStorage & Transport
• Under what conditions can nanoparticles be stored athigh density and yet be transported as individualparticles?
• What are practical and future limits to nanoparticle fluxeswhen delivered in circulating channel networks?
• How do nanoparticle properties, including size, shape,and material properties, affect transport and storageproperties?
26
Nano-
FET Microfluidic Feed System
High
density
packing for
low
parasitic
liquid mass
Controlled
displacement
of individual
particles
Profs. M. Solomon, M. Burns,& J. Mirecki-Millunchick
University of Michigan
On-demand
release of
individual
particles
27
Nano-
FET
Particle Control: Metering inFluidic Channels
Particle properties:
NIST polystyrene:21±0.4 μm
10 μL of 0.01 wt%
2-valve PDMS device
Vanapalli, Sung,
Mukhija
sideview
valve
fluid channel
28
Nano-
FET
Particle Control: Transportin Fluidic Channels
90 m
90 m
90 m
1)
2)
3)
Multi-channel pressure actuation used to move particlesalong complex trajectories (~ 20 μm particles)
Sung, Vanapalli, Mukhija
29
Nano-
FET
Reservoir for ParticleStorage & Transport
• Transport 20 μm
particles from
storage area
reservoir to thruster
• Seek high reservoir
loadings to minimize
parasitic mass
Sung, Mukhija, Vanapalli
30
Nano-
FET
Shape Effects on ParticleTransport
Mukhija, Vanapalli, Sung
Poly(methyl methacrylate)(PMMA) rods (length ~ 10 μm)
with narrow polydispersity
PMMA rod (aspect
ratio ~ 5) transport in
fluidic channels
31
Nano-
FET
Phase II: nanoFET Systems& Mission Analysis
• Performance optimization– Particle & liquid properties
– Geometric configurations
– Current density limits
• System efficiency– Liquid drag & charge exchange
– Particle impingement on gate
– Beam defocusing
• Case studies of missionsusing nanoFET
– Coupling between propulsionand power systems
– Remote sensing neargravitational bodies
– Variable-Isp to accommodateoff-nominal conditions
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1 10 100
Aspect RatioN
orm
alized
Extr
acti
on
Ele
ctr
ic F
ield r = 15 μm
r = 150 μm
r = 75 μm At constant liquidthickness
Low extraction electric
field achieved by: high
aspect ratio & reduced
liquid thickness
32
Nano-
FET Other nanoFET Applications
Biomedical
• targeted drug delivery to cells
• cell tagging for diagnostics &tracking
• cutting/dissection tool
• subdermal implantation
More than just propulsion!
Materials processing
• implanting chargedparticles (doping &printing)
• etching
Source: National Cancer Institute
nanoFET
Cancer Cell
Material Substrate
Nano-
FET Conclusions
34
Nano-
FET Backup Slides
35
Nano-
FET
1. Particle in contact with bottom electrode inpresence of electric field becomes charged
2. Resulting Coulomb force on charged particletransports particle to top electrode
3. At top electrode, particle becomes chargedwith opposite polarity but same magnitude
4. Coulomb force pulls particle back down tobottom electrode and process repeats
V
Electrode
Electrode
1. Charged on
bottom electrode (-)
V
Electrode
Electrode
2. Transported to top
electrode
V
Electrode
Electrode
3. Charged on top
electrode (+)
V
Electrode
Electrode
4. Transported to
bottom electrode
llErqsph
2
3
3
2=
qcyl ,vert =l2
lE
l
ln2l
r1
Particle Charging, Transport,& Lift-Off
36
Nano-
FETParticle Extraction Through
Liquid Surface
• Demonstrate
– Use intense electric field toovercome surface tensionforces and extract particlesfrom liquid
• Particles: aluminum
– Spheres (800 and 1600 μmdia.)
– Cylinders (300 μm dia. by1.0 - 3.0 mm length)
• Liquid: 100 cSt silicone oil
Experimental Setup:
Partially liquid filled electrodegap with conducting
particles
Electrode
Electrode
Air gapE-Fields
in Air gap
Conducting
Particles
E-Fields in
liquid gap
Silicone Oil
dl
d
V
37
Nano-
FET
• Cylindrical particles inoscillation
– diameter = 300 m
– length = 1.5 mm
– gap = 12.7 mm
– liquid height = 5 mm
– V ~ 14 kV
1
Steel
Electrodes
Liquid
Surface
Particles
2
Steel
Electrodes
Liquid
Surface
Particles
Bottom
Electrode
Particles3
Steel
Electrodes
Liquid
Surface
Particles
Particle Extraction ThroughLiquid Surface
38
Nano-
FET
• Required electric fieldsfor particle extractiondepends on
– Particle size/shape
– Electric field strength
1
Steel
Electrodes
Liquid
Surface
Particles
2
Steel
Electrodes
Liquid
Surface
Particles
Bottom
Electrode
Particles3
Steel
Electrodes
Liquid
Surface
Particles
Particle Extraction ThroughLiquid Surface