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