M ultilayer Ionic T ransducers by B arbar J.A kle T hesis subm itted to the Faculty ofthe V irginia Polytechnic Institute and State U niversity in partialfulfillm ent ofthe requirem ents for the degree of M aster O f Science in M echanical E ngineering D onald J.Leo,C hair DanielInm an W illiam Saunders A pril2003 B lacksburg,V irginia K eyw ords: Ionic Polym er,M ultilayer,Sensor-actuator,M icro A ir Vehicle. C opyright by Barbar J.A kle 2003
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M ulti layer Ioni c Transducers
by
B arbar J.A kl e
Thesi ssubm itted to theFacul ty ofthe
V irgi nia Polytechni c Insti tute and StateUni versi ty
in parti alf ulfil lm entofthe requi rem entsf or the degreeof
M aster O fSci ence
in
M echanicalEngi neeri ng
Donald J.Leo,Chai rDanielInm an
W illiam Saunders
Apri l2003
Blacksburg,V i rgi nia
Keywords: Ioni cPolym er,M ul ti layer,Sensor- actuator,M i cro A i rVehi cl e.
Copyri ghtby BarbarJ.Akl e 2003
M ulti layer Ioni c Transducers
BarbarJ.Akl e,M S
V irgi nia Polytechni c Insti tute and StateUni versi ty,2003
Advisor:Donal d J.Leo
A bstract
A transducerconsi sti ngofm ul ti plelayersofi oni cpol ym erm ateri ali sdevel oped
for appl icati ons i n sensi ng,actuati on,and control . The transducer consi sts of two
to f our i ndi vi dual l ayers each approxi m atel y 200 m icrons thi ck. The transducers
are connected i n paral lel to m i nim ize the el ectri c fiel d requi rem ents f or actuati on.
The tradeoff i n deflecti on and f orce can be control led by control ling them echani cal
constrai ntat the i nterf ace.Packagi ng the transducer i n an outercoati ng producesa
hard constrai ntbetween l ayersand reducesthedeflecti on with a f orce that i ncreases
linearl y with thenum berofl ayers.Thi sconfigurati on al so i ncreasesthebandwi dth of
the transducer.Rem ovi ng the outerpackagi ng producesan actuator thatm ai ntai ns
the deflecti on ofa si ngl e layer but has an i ncreased f orce output. Thi s i s obtai ned
by al lowing the l ayers to sl ide rel ati ve to one another duri ng bendi ng. A Fi nite
Elem entAnal ysi s(FEA)m ethod capabl eofm odel ing thestructureofthem ul ti layer
transducers i s devel opped. It i s used to m odelthe i nterf aci alf ri cti on i n m ulti layer
transducers.
Experi m ents on transducers wi th one to three l ayers are perf orm ed and the
resul ts are com pared to Newbury’ s equi val ent ci rcui t m odel , whi ch was m odified
to accomm odate the m ul ti layer pol ym ers. The m odi ficati on wasperf orm ed on f our
di fferent boundary condi ti ons,two el ectri calthe seri es and the paral lelconnecti on,
and two m echani calthe zero i nterf aci alf ri cti on and the zero sl ip on the i nterf ace.
Resul tsdem onstratethatthel argestobstacl etoobtai ninggood perf orm ancei s
watertransportbetween the i ndi vi duall ayers.W atercrossoverproducesa nearshort
ci rcui t el ectri calcondi ti on and produces f eedthrough between actuati on layers and
sensi ng l ayers.El ectri calf eedthrough due to watercrossoverel im inatestheabi lity to
producea transducerthathascom bi ned sensi ng and actuati on properti es.El im inat-
ing water crossover through good i nsul ati on enabl es the devel opm ent ofa sm al l(5
mm x 30 mm )transducer thathassensi ng and actuati on bandwi dth on the orderof
100 Hz.
Due to the m echani calsi m ilari ti es of i oni c transducers to bi ologi calm uscl es
and thei r l arge flappi ng di spl acem ent capabi liti eswe are studyi ng the possi bi lity of
thei rusei n flappi ngM icroA i rVehi cl e(M AV)appl icati on,asengi nes,control lersand
sensors. The FEA m odel ing techni que capabl e isused to desi gn two i oni c pol ym ers
actuated flappi ng wings.
iii
To m y father,
Jawad Akl e,
m y m other,
Nazira Akl e,
and m y si sterand brothers,
Angele,Eti enne,and Si m on
A cknow l edgm ents
First Iwoul d l ike to thank m y advi sor,D r.Donal d J.Leo,f orhi shel p and pati ence
throughoutm y graduatestudi es.H i sgui danceand com pl etesupportm adem ywork-
ing and l earni ng experi ence,a very speci alone. A l so,Iwant to extend m y thanks
to D r.Dani elInm an and Dr.W i lliam Saundersf or thei rsupportand enthusi asm as
m embersofm y advi sory comm i ttee.
In addi ti on,Iwantto thankm ycol leaguesi n theCenterf orIntel ligentM ateri al
System sand Structures(CIM SS).Thegood hum orofeverybodym adei tan enj oyabl e
experi ence. A l so m y great thanks to m y research partnersM athi ew Bennet,K evi n
Fari nhol t,John Frankl in,and CurtCothera.Thei rgeneroushel p and f ri endshi p was
inval uabl e in assi sti ng m y research. Iappreci ate the support ofthe U. S.Arm y Re-
search Laboratory and theU . S.Arm y Research O ffi ce undercontract/grantnum ber
DAAD19-02-1-0275 M acrom ol ecul arA rchi tecture f orPerf orm ance (M AP)M URI.
Final ly, I woul d l ike to expressm y deep grati tude to the support I recei ved
from my fri ends at Em i lio’s and m y greatest appreci ati on to the l ove and support
provi ded bym y parentsand m y brothersand si sterduri ngm y yearsatV i rgi nia Tech.
5.2 Electri cali m pedancem odelpredi cti on versusexperi m entaldata . . . . . . 73
xi i
5.3 Sensi ti vi ty m odelpredi cti on versusexperi m entaldata . . . . . . . . . . . 73
5.4 Blocked f orcem odelpredi cti on versusexperi m entaldata . . . . . . . . . 73
5.5 M echanicali m pedancem odelpredi cti on versusexperi m entaldata . . . . . 74
6.1 The deflecti on col orm ap outputofthe FEA anal ysi softhe firstw i ng desi gn. 79
xi ii
C hapter 1
Introducti on
M ulti layered stacksofi oni ctransducershavebeen devel oped and characteri zed i n the
CenterofIntel ligentM ateri alsand Sm artStructures(CIM SS)Lab atV i rgi nia Tech.
They were configured as sensors,actuators,and combi ned sensor- actuators stacks.
They were connected i n seri es,and i n paral lel .The f ol lowing chaptersare rel ated to
the expl orati on ofthe stacki ng process,characteri zi ng i t,m odel ing i t,and studyi ng
itspossi ble appl icati ons.
1.1 P robl em Statem ent
Ioni c Polym ers are sof t transducers whi ch bel ong to the f am ily of El ectro- Acti ve
Polym ers(EAP).Theyhaveseverali nteresti ngm echani calproperti es,especi al ly thei r
large di spl acem ent,l arge sensi ti vi ty to m oti on,and l ow operati on vol tage. On the
otherhand,i oni c pol ym ers f ace severaldi sadvantages,especi al ly i n the sm al lf orces
they can generate.
In addi ti on to sm al lf orce output, i oni c pol ym ers exhi bit ‘ perm anent strai n’
effectsand rel axati on thati sdetri m entalto thei ruseasel ectrom echani calactuators.
Figure 1. 1 (a) i s an i llustrati on ofthe perm anent strai n effect. Thi s effect occurs
when thepol ym eri sexci ted wi th a step vol tageand then theel ectrodesarepl aced at
ground.The resul ti ng m oti on ofthem ateri alproducesa non- zero perm anentstrai n
that i sattri buted to perm anentcharge redi stri buti on withi n thepol ym er(Newbury,
1
Figure 1. 1: (a)A schem ati c draw i ng show i ng the hysteresesofpol ym ersduri ngoperati on and (b), the rel axati on.
2002). In addi ti on to perm anent strai n,severalresearchers have noted that certai n
ioni c pol ym er transducers exhi bi t a rel axati on phenom enon when subj ected to step
changes i n the vol tage (see Fi gure 1. 1). Thi s rel axati on phenom enon reduces the
quasi -stati c actuati on authori ty ofthe actuator.
Stacki ng techni quesweredevel oped i n orderto i ncrease thegenerated f orceof
ioni c pol ym eractuators. Ini ti al ly we started stacki ng the si ngl e-layer i oni c pol ym ers
electri cal ly i n seri es,whi ch i ssi m ply l ayi ng thestri psofpol ym erson top ofeach other
and appl y the el ectri c potenti alacross the whol e stack. Seri es stacki ng sol ved onl y
part of the probl em . It provi ded hi gher saturati on vol tage,but kept the f orce per
overal lvol tage approxi m atel y the sam e as the si ngle layer pol ym er. Theref ore the
seri esstack di d notperf orm better than the si ngle layerpol ym er i fwe com pl y with
the el ectrol ysi sstartvol tage. In orderto i ncrease the vol tageper l ayer,and i ncrease
the overal lgenerated f orce wi thout i ncreasi ng the vol tage per stack,we devel oped
paral lelstacks. Paral lelstacks are si ngl e layers i oni c pol ym ers overl aid on top of
each otherm echani cal ly,and connected i n paral lelel ectri cal ly. The resul t i sa stack
that generates l arger f orces wi thout exceedi ng the el ectrol ysi s l im it vol tage. Thi s
techni queworked properl y and encouraged usi nto f urther i nvesti gati ons.
Stacki ng ofi oni cpol ym ersnotonl y sol ved theprobl em ofsm al lf orcesbutal so
proved to resol ve theprobl em ofthecom pl ex non- uni form behavi or.Non- uni form i ty
2
in ioni cpol ym erscoul d bedefined ashysteresi s,rel axati on,and theperm anentstrai n
previ ousl y defined. It has been proven that those non- uni form behavi ors coul d be
sol ved usi ng feedback control(K othera,2002). In orderto accom pl ish f eedback con-
trol ,a sensor pol ym erwas i nserted i nsi de a stack ofseveralactuators. Thi s sensor
pol ym erwas i nsul ated,and connected to a sensi ng ci rcui tso i t f ed back them oti on.
Thisform ed thecombi ned sensor- actuatorstack.Resul tsdem onstratethatthel argest
obstacl etoobtai ninggood perf orm ancei swatertransportbetween thei ndi vi duall ay-
ers.W atercrossoverproducesa nearshort ci rcui tel ectri calcondi ti on and produces
feedthrough between actuati on layersand sensi ng l ayers.El ectri calf eedthrough due
to watercrossoverel im inates the abi lity to produce a transducer thathascombi ned
sensi ng and actuati on properti es. El im inati ng water crossover through good i nsul a-
ti on enabl es the devel opm ent ofa sm al ltransducer that has sensi ng and actuati on
capabi liti es. M oreover,f ordesi gn purposesa si m ulati on toolwasessenti alto m odel
al lthose stacki ng processes, theref ore Fi nite El em ent Anal ysi s (FEA)m ethod was
used and val idated by com pari ng i ts output to the experi m entalresul ts. The FEA
m ethod was abl e to m odelcom pl ex actuator geom etri es,but the anal ysi swas onl y
val id to the l ow frequency response. The l im itati onsofthe FEA m ethod m oti vated
us to adaptNewbury constui ti vem odelto handl e them ul ti layerstacks. Newbury’ s
m odel(Newbury,2002) i s capababl e ofm odel ing si m ple canti lever geom etry trans-
ducers,as sensors and actuators f or any type ofresponse. Fi nal ly al lthe tool s and
resul tswere used to set f orth f ora desi gn ofan Ioni cPolym erflappi ng M AV.
1.2 Li terature R evi ew
In thi s secti on,a bri efbackground i nform ati on on Ioni c Polym ers i s provi ded. The
revi ew hasstarted wi th thedefini ti on oftheEl ectro- Acti vePol ym ers.Nexta chrono-
logi calhi stori calbackground i sprovi ded and f ol lowed by abri efovervi ew on them an-
ufacturi ng techni queand theoperati onm echani sm .Fi nal ly,thei nteresti ngproperti es
and thepotenti alappl icati onsofi oni c pol ym ersare expl ored.
3
1.2.1 E lectro-A cti ve Pol ym ers (EA P )
Electroacti ve pol ym ers bel ong to the f am ily of acti ve m ateri als. Acti ve m ateri als
are defined asm ateri als that adapt to a change i n the physi calenvi ronm ent,such
as el ectri cal , therm al ,m agneti c,chem i cal ,pH ,or l ight envi ronm ent. They can be
used i n the f orm ofsensors,actuators,acti ve dam pers,and energy generators. (Leo
coursenotes,2001)EAP reactsto thechangei n theel ectri caldom ai n,l ikethewi del y
used and wel lknown el ectroacti ve m ateri als such as pi ezoel ectri c ceram i cs. Recent
devel opm ents i n the El ectroacti ve Pol ym ers (EAP) have l ead to i ncreasi ng interest
in them ,dueto thereflexi bi lity whi ch m akesthem si m ilarto bi ologi calm uscl es. (Bar-
Cohen et al .,1999) They are al so defined i n four categori es,gel s, i oni c pol ym ers,
conducti ng pol ym ers,and el ectrostri cti ve pol ym ers. In thi s thesi s the i nterest i s i n
ioni c pol ym ers.
1.2.2 H istori calB ackground of Ioni c pol ym ers
Polym er-m etalcom posi teswere devel oped asearl y as1930’ saspreci pitati on ofcol -
loidalSi lver on prepared substrates (Bar- Cohen,2001). In the earl y 1990’ s when
Sadeghi pour et al . were tryi ng to use i oni c pol ym ers as pressure transducers,they
found that they coul d act as vi brati on sensors. Ioni c pol ym ers were devel oped as
”sol id pol ym er el ectrol yte f uelcel lm embranes” (Bar- Cohen,2001). Later i n 1992
whileSadeghi pourand coworkersweregetti ng cl ose to di scoverthei ractuati on capa-
bi liti es,Oguro’ s group i n Japan descri bed the bendi ng ofthe i oni c pol ym ers under
the appl icati on ofa potenti alacross i ts thi ckness. Si nce than,severalgroups i n the
USA and acrosstheworl d areworki ngon i m provi ng them anuf acturi ngprocess,char-
acteri zi ng and m odel ing theperf orm ance,and searchi ng forappl icati onsf orthi snew
intel ligentm ateri al .
1.2.3 M anufacturi ng of Ioni c pol ym ers
Presented here i s the generalm ethod by whi ch i oni c pol ym ers are m anuf actured,
although severalvari ati ons i n thei rm anuf acturi ng have been reported (Bar- Cohen,
4
Figure 1. 2: Schem ati c ofan Ioni c Pol ym er.
2001).Asshown i n Figure 1. 2 ioni cpol ym ersconsi stofan Ioni cpol ym erm embrane
sandwi ched between two m etaloverl ayers.
Them ateri alsused i n m anufacturi ng ioni cpol ym ersarea strong aci d,am etal
sal t,a reduci ng chem icalsol uti on,and perfluori nated i onom erm embrane.A l though
they are not necessari ly the best m ateri al to be used i n ioni c pol ym ers,DuPont’ s
NafionTMproved to havethebestperf orm ancei n thecomm erci ali oni cpol ym ers.The
m anufacturi ng process i s usual ly com posed ofthree m ai n steps. A f ter cl eani ng the
pol ym erwi th a strong aci d such asH N O 3,a cl ean sheet ofpol yperfluoroethyl ene-
sul fonatem embrane (Nafion TM) i s soaked i n a m etalsal t sol uti on (P t(N H 3)C l 2) to
popul atei twi th a reduci blem etal(Bar- Cohen,2001).Duri ng thi sstep them etalsal t
willexchangehydrogen i on in thepol ym erbackbone.Than thi ssam ple issubm erged
in a chem icalreductantsuch asLi thi um Borohydri de(Li B H4),whi ch can’ tpenetrate
thei oni cpol ym er,thusthereducti on willoccuraccordi ng toequati ons(1. 1)and (1. 2)
onl y at the surf aceofthe pol ym er.
Li B H4 + 4[P t(N H 3)4]2+ + 8OH− −→ 4P t0(s)+ 16N H 3(g)+ Li BO2(sd)+ 6H 2O
(1. 1)
5
and
LiB H4 + 4H2O −→ 4H2(g)+ Li OH (Li + + OH− )+ B (OH ) 3(sd) (1. 2)
Equati on (1. 2)provi desthehydroxyli onsneeded i n equati on (1. 1),theref ore9
m olesofLi BH4arerequi red to reduce4m ol es[P t(N H 3)4]2+ .Noti cei n equati on (1. 1)
that the productsare pl ati num m etalswhich f orm the dendri ti c el ectrode. The am -
m onia gaswi llevaporate and theLi thi um Boroxi dewillpreci pitate.Asf orequati on
(1. 2),thehydrogen gaswi llevaporate theB (OH ) 3 preci pitate,thehydroxyli on will
reactaccordi ng to equati on (1. 1),whi le the Li thi um ion willchai n with thepol ym er
insi de the cl usters.
Currentl y several researchers are worki ng on opti m izi ng thi s process. The
surf aceconducti vi ty i sessenti ali n chargi ng them embrane(Bar- Cohen,2001).In the
CIM SS lab,M attBennett hasbeen worki ng on thi s probl em ,and f urther tryi ng to
incorporate i nexpensi vem etal ssuch ascopperi nto theconducti ng overl ayer.Fi nal ly
a thi rd m anuf acturi ng step m i ght be requi red to exchange the cati on with another
one (e. g. repl ace the Na+ wi th Li + ),whi ch willeffect the perf orm ance ofthe i oni c
pol ym eras i twi llbedescri bed l ater.
1.2.4 A ctuati on M echani sm
To date the physi calm echani sm sthatproduce actuati on are sti lluncertai n.Several
researchersaresuggesti ng di fferentactuati on m odels.The realactuati on m echani sm
coul d be one ofthose m odel s,or a combi nati on ofthem . A l lofthose m odel s con-
si der the pol ym er’ s i oni c m embrane as hydrophi lic cl usters i nsi de the hydrophobi c
fluorocarbon pol ym erbackbone.
The m ain assum pti on i s that ani ons i n the cl usters are attached to the fluo-
rocarbon backbone (Bar- Cohen,2001),whi le the f ree cati ons wi llm ove wi thi n the
water m edi um under the appl icati on of an el ectri c fiel d, causi ng them to m i grate
towards the cathode. Thi s redi stri buti on willcause som e changes i n the properti es
ofthe pol ym erm embraneat the anodeand cathode si des.Tabl e 1.1 del ineate those
changes.
6
Anode CathodeDecrease i n the effecti ve sti ffness Increase i n the effecti ve sti ffnessofthem embrane ofthem embraneGenerati on ofa repul si veel ectrostati c An increase i n the attracti ve f orces,force between the fixed ani onswhi ch holding the fixed ani onscl oserto eachincrease the cl ustersi ze i ncreasi ng othersdecreasi ng theentropy, and i ncreasi ngtheentropy,and rel ax thepre stretched theel asti c energy ofthe pol ym er.pol ym erchai nsdecreasi ng theel asti c energy.W ater i nsi de the cl usters,whi ch i sa On theCathode si de thi sdecrease i n thedielectri cm ateri al ,tendsto reori ent effecti veperm i tti vi ty ofthe cl usters,underthe appl icati on ofel ectri c fiel d; increase theel ectrostati c force betweendecreasi ng theeffecti ve perm i tti vi ty of the cati onsand theani ons.the cl usters,reduci ng theel ectrostati crepul si ve f orce between the fixed ani ons.Duri ng thei rm igrati on,the cati onswi ll This i ncrease i n water i nsi de the cl usterscarry som ewaterwi th them ,decreasi ng on theCathode si de,i ncrease the vol um ethe vol um eofthe cl usters ofthe cl usters.Decrease i n the osm oti c pressure i nsi de Increase i n the osm oti c pressure i nsi dethe cl usters the cl usters
Tabl e 1.1: C hangeson the cathode and the anode off our actuati on m echani sm s(B ar-C ohen,2001)
7
1.2.5 Interesti ng properti es of Ioni c pol ym ers
Ioni cPolym ersaresof tactuatorsthatperf orm largebendi ng and flappi ng deflecti ons
when a sm allvol tage i sappl ied acrossthei r thi ckness.Thedi spl acem entcapabi liti es
are i n the orderof2% -5% (com pared to 0. 1% -0.3% for the el ectroacti ve ceram i cs)
(Shahi npooretal .,1998).M oreoverthosem ateri alsaresof t,flexi ble,and m echani cal
parts f ree whi ch m akes them hi ghl y dexterous and robust. Fi nal ly i oni c pol ym ers
are abl e to operate i n harsh cryogeni c condi ti ons (sui tabl e for space appl icati ons,
where they operate on tem peratures are as l ow as -130c and pressure of f ew Tor-
res. )(Shahi npooretal .,1998). They are al so characteri zed by l ow actuati on vol tage
(el ectri c potenti al) i n the order of1 5V for the 0. 184 mm thickness pol ym ers. (Akl e
and Leo,2003)(sui tabl e lessthan 1. 23V in orderto avoi d electrol ysi s.) On theother
hand i oni c pol ym ers have a num ber ofdi sadvantages to overcom e. A m aj or prob-
lem developersf acesm ostofthe ti m ewhen dealing with i oni c pol ym ers i s that they
need to be hydrated al lthe ti m e to operate properl y (thi s m ight be an advantage
in case ofunderwater appl icati ons,or bi om edicalappl icati on in which they wi llbe
im plem ented i nsi de thehydrated hum i d hum an body. ) Furtherm ore,i oni cpol ym ers
rel axe af ter they bend due to a step response,and i t i s bel ieved that thi s i s due to
the back di ffusi on ofwater (Bar- Cohen,2001). Thi s property m akes i tm ore l ike a
vel oci ty actuator,rather than a posi ti on actuator,and the sam e appl ieswhen they
areused assensors(Thesensi ngsi gnalbehavesl ikean i m pulse,when astep deflecti on
is appl ied to the pol ym er. ) Fi nal ly they are non- linear i n there behavi or,and ti m e
vari ant,whi ch m akescharacteri zati on and controldi ffi cul t.
1.3 Ini ti alM oti vati on
The initi alf ocusofthe thesi swas to study the f easi bi lity ofusi ng ioni c pol ym ersas
flappi ng m echani sm s for flappi ng fli ght based M i cro A i r Vehi cl es (M AV).Fl appi ng
fli ghti sa very com pl ex aerodynam i cprobl em which i ssti llunderresearch.Theref ore
we deci ded to rel y on l iterature f or obtai ning som e rough numbers Ioni c Polym ers
has to m eet i n order to fly theM AV.A f ter an el aborate l iterature survey,a revi ew
8
paper f or W eiShyy et al . (1999) “Fl appi ng and flexi ble wings f or Bi ologi caland
m icro ai r vehi cl es” i n the Progress i n Aerospace Sci ences provi ded us wi th those
num bers. Com pari ng the aerodynam i c requi rem entswi th the experi m entaldata on
Ioni c Polym ers,we real ized that si ngle layer i oni c pol ym ersare f ar f rom bei ng abl e
to fly an M AV.Them aj ordi ffi cul ty wasthesm al lf orce Ioni cPolym erscan generate,
thusthe f ocuswenton i ncreasi ng i t.Atfirstweexpl ored thepossi bi lity ofi ncreasi ng
the actuati on vol tage.Thi sattem ptwent i n vei n af ter the i oni c pol ym ers reached a
saturati on vol tage and thi s i ncrease i n vol tage al so i nduced the el ectrol ysi sofwater
insi de the pol ym ers. Thus the opti on of i ncreasi ng the vol tage was el im inated f or
water based i oni c pol ym ers. Fi nal ly we were l eft wi th the opti on ofstacki ng ioni c
pol ym ers,whi ch proved effecti ve. Furtherm ore,m uti layer i oni c pol ym ers proved to
sol ve severalprobl em s rel ated to i oni c pol ym ers and thei r appl icati ons. Theref ore,
we changed the ai m ofthi s thesi s toward characteri zi ng and i m provi ng the stacki ng
ofi oni c pol ym ers.
1.3.1 Potenti alappl icati ons
A llthe i nteresti ng properti esm enti oned i n the previ oussecti on gi ves i oni c pol ym ers
a number ofpotenti alappl icati ons. Those appl icati ons can range f rom usi ng them
as sensors or as actuators. They coul d be used i n water subm erged appl icati ons,
or i n other envi ronm ents ei ther as packaged pol ym ers or i oni c l iquid sol vent based
pol ym ers (Bennett and Leo,2003). Ioni c pol ym ersare usual ly m ade in the f orm of
thi n plates (50 184 m i crom eter) enabl ing them to be use i n M EM S (M icro El ectro-
M echanicalSystem ).They m i ghtbe used assensors to createm i cro- accel erom eters,
or as actuators to create m i cro swi mm ing robots. Another i nteresti ng property of
ioni cpol ym ersi sthatthey arenottoxi c forhum an si nce they arem adeofNafion TM ,
nobl e m etal s (Pl ati num ,and Gol d for the coati ng),and LiorNa i ons. Thi sm akes
itpossi ble for them to be i m plem ented i nsi de the body.Appl icati on can range f rom
heal th m oni tori ng aspressure and pul se sensors,or as acti ve vei ns as actuators. A
currentappl icati on underresearch by ourgroup,i susi ng those transducersto detect
acousti c si gnal s generated by the turbul ance i nduced by a stenosi s (artery cl osure).
9
Detecti ng and characteri zi ng thi s turbul ance enabl es us to m easure the severi ty of
the cl osure. The end product of thi s research i s a non- invasi ve i oni c transducer
devi ce capabl e ofdetecti ng earl y stenosi s.AsactuatorsM attBennett i n ourteam i s
tryi ng to createan adapti vem irorf orouterspaceappl icati ons.Thepol ym erswi llbe
plated wi th a reflecti vem ateri al ,and thepotenti alappl ied acrossthetransducerswi ll
deform the shape ofthem i ror i ncreasi ng ordecreasi ng the convexi ty. Furtherm ore,
ioni c pol ym erm echani calproperti es are qui te si m ilar to the hum an muscl e,whi ch
rai se there potenti alofrepl aci ng Hum an muscle.Shahi npooretal .(1998).
Thei r hi gh dexteri ty m akes them perf ect f or roboti cs appl icati ons, they can
be used to bui ld end- effectors asdexterousas the hum an hand or as sof tm al leabl e
end-effectors
M oreover thi s thesi s has f ocused on two potenti alappl icati ons f or the i oni c
pol ym ers. Due to thei rm echani calsi m ilari ti es to bi ologi calm uscl esand thei r l arge
flappi ng di spl acem ent capabi liti es we were i nterested i n studyi ng the possi bi lity of
thei r use i n flappi ng M icro A i r Vehi cl e (M AV) appl icati on,as engi nes, control lers
and sensors.Asf or the combi ned sensors- actuatorsstack,wegaveattenti on to thei r
appl icati on assof t,l arge di spl acem entm i croposi ti oner.
1.4 O vervi ew ofT hesi s
1.4.1 R esearch O bj ecti ves
Theobj ecti ve ofthi s thesi s i s to bui ld and characteri zem ulti layer i oni c transducers.
Ioni cactuatorsgeneratesm al lf orceson theorderof0. 5m N fora 22mm *5mm *0.2mm
beam .Theoperati on ofthose transducersdependson them obi lity ofi onsi nsi de the
pol ym er cl usters. A sol vent i s requi red f or i ons to m ove,and those sol vents have a
certai n el ectri calstabi litywi ndow.Forwaterthi sstabi litywi ndow isaround 1. 2V ;the
vol tageatwhi ch waterstartsto decay i nto hydrogen and oxygen gases(el ectrol ysi s).
Paral lelm ul ti layerstacksare devel oped to m i nim ized the el ectri c fiel d requi rem ents
foractuati on,and therf ore i ncreasi ng thef orceperuni tvol tage.Them echani calcon-
10
strai nt at the i nterf ace i sproven to provi de a tradeoff between deflecti on and f orce.
Characteri zi ng thi si nterf aci alf ri cti on provi desdesi gnersa control lableparam eterf or
thei r appl icati on. In order to m odelthe i nterf aci alf ri cti on in m ulti layer transduc-
ers,a Fi nite El em entAnal ysi s (FEA)m ethod capabl e ofm odel ing thei rm echani cal
structure i sdevel oped.
M oreover,com bi nedm ulti layerstacksaredevel oped f orusei n feedbackcontrol .
They are f abri cated asan i oni c sensorem bedded i nsi de a multi layer i oni c actuator.
The combined m ulti layer transducers offers a com pact sensor- actuator that wi llbe
used i n preci si on appl icati ons.
Another obj ecti ve was to devel ope a m odel ing toolcapabl e of representi ng
m ulti layerpol ym ersas transducers. Newbury’ sequi val ent ci rcui tm odeli sm odified
to accomm odate the m ul ti layer pol ym ers. The m odi ficati on i s perf orm ed on f our
di fferentboundary condi ti ons,two el ectri cal :seri esand paral lelconnecti on;and two
m echanical :zero i nterf aci alf ri cti on and zero sl ip on the i nterf ace.
1.4.2 C ontri buti on
Them ain contri buti on ofthi s research i s the devel opm entand characteri zati on ofa
stacki ngprocessf ori oni cpol ym erm ateri als.In orderto characteri zethestacki ng,we
m easured thef reedi spl acem ent,bl ocked f orce,transf erf uncti on,resonancepeaks,and
thesensi ti vi ty f ordi fferentstacki ng techni quesand di fferentnum berofstacks.Duri ng
thecharacteri zati on processwereal ized thatthef reedi spl acem entcoul d becontrol led
by control ling the i nterf aci alsl ip between the i oni cpol ym erl ayers. Ifthere i sno sl ip
the stack wi llbehave as i f i t was one com pl ete bl ock,thus the naturalf requenci es
willi ncrease,whi le the f reedi spl acem entwi llbe reduced.On thecontrary i fthere i s
no fri cti on between the f aces,both thenaturalf requenci esand the f reedi spl acem ent
willbepreserved.Asf orthebl ocked f orce,i t i ncreased wi th thenumberofl ayersf or
the paral lelstacki ng,whi le i t rem ai ned approxi m atel y the sam e f or seri es stacki ng.
In sensi ng,i twas f ound that those pol ym ersactsascharge generatorsand si ncewe
were m easuri ng the short ci rcui t current am pl ifiers,we f ound that paral lelstacki ng
increases the sensi ti vi ty proporti onal to the num ber of stacks,whi le in the seri es
11
stacki ng i trem ai ned constant.Asf orthecom bi ned sensor- actuatorstack,them aj or
probl em was to el im inate the f eed- through. Feedthrough i s defined as the porti on
ofthe actuati ng si gnalofthe adj acent i oni c pol ym er that i s di rectl y fed through to
the output si gnalofthe sensor. The f eed- through wasm ai nly due the hum i dity i n
the gaps between stacks whi ch created a short- ci rcui t between the sensor and the
actuator(s).
Newbury’ s equi val ent ci rcui t representati on of i oni c pol ym ers was m odi fied
to accomm odate the m ul ti layer pol ym ers. The m odi ficati on wasperf orm ed on f our
di fferentboundary condi ti ons,two el ectri cal(seri esand theparal lelconnecti on)and
twom echani cal(zero i nterf aci alf ri cti on and zero sl ip on thei nterf ace).Thi sm odified
m odelhastheabi lity to m odelcanti leverm ul ti layeri oni c transducersassensorsand
actuators. It provi desa transf er f uncti on that coul d be used i n control ,and system
leveldesi gn ofi oni c transducerdevi ces.
By usi ng theFEA m ethod and stacki ng techni quewewereabl e to desi gn two
di fferentM AV wi ngs. The first wi ng was desi gn to be f ul ly m ade ofi oni c pol ym er
sheets. It was desi gned as a sem i ci rcul ar wi ng to m ake the best use of the area
covered (keepi ng the si ze oftheM AV assm al las possi ble). W hi le the second wi ng
wasdevel oped and wascom posed oftwodi fferentm ateri als:thepassi vel ightm ateri al
that f orm s thewi ng surf ace,and a stack of10 i oni c pol ym ersheetsof7 x 5 cm si ze
thatperf orm ed asm uscl esto actuate thewi ng.
Final ly thi swhole research coul d evol ve i nto a proj ect ofl arger scope to de-
vel op m icro- layered i oni c pol ym ersstacks,thatcoul d perf orm much better than the
si ngle ioni c pol ym erssheets.These stackswi llprovi de hi gher f orces,whi le thei r f ree
displ acem entand resonancecoul d becontrol led by them anuf acturi ng process,m ore-
overwem i ghtbe abl e to i ntegrate som e sensor l ayers f or f eedback control ,whi ch i n
turn wi llbeabl e to reduceorel im inate thesl ow rel axati on and hi gh overshootwhi ch
characteri ze i oni c pol ym ers.
12
1.4.3 A pproach
Chapter2 provi desan overvi ew forthefivedi fferentcharacteri zati on testsweperf orm
in order to characteri ze i oni c transducers. The output ofthose tests are descri bed,
and a descri pti on ofthe two testsetupswi th al lthere parts i spresented.
C hapter3 i s devoted f or the characteri zati on of Ioni c pol ym er stacks. At
firstan expl anati on oftheparal leland seri esstacki ng techni quesi spresented,and a
com pari son between them i sal so provi ded.Than both seri esand paral lelstacksare
characteri zed as sensor stacks and actuator stacks i n two di fferent secti ons. Char-
acteri zed was the f ree di spl acem entand bl ocked f orce,f ora step response,and asa
transf erf uncti on.Fi nal ly aFEA m ethod wasprovi ded,veri fied,and used to si m ulate
the behavi orofthe stacks.
C hapter4 i ntroduces the combi ned sensors- actuators,expl ores i ts potenti al
appl icati onsand i m portance.Thi schapterwi lldi scussthem anuf acturi ng techni ques,
which f ocuseson theel ectri calconnecti onsand i nsul ati ons. Ital so el aborateson the
si gnalf eed- through probl em .Fi nal ly i twi llexpl ore theLapl acedom ain m odelwhi ch
coul d beused i n controlappl icati ons.
C hapter5m odi fiesNewbury’ sm odeltoaccomm odatethem ul ti layerpol ym ers.
Them odificati on wasperf orm ed on f ourdi fferentboundary condi ti ons,two el ectri cal
theseri esand theparal lelconnecti on,and twom echani calthezero i nterf aci alf ri cti on
and the zero sl ip on the i nterf ace. Fi nal ly experi m entalresul tson transducerswi th
one to f our l ayers are perf orm ed and the resul ts are com pared to the new m odi fied
equi val entci rcui tm odel .
C hapter6 i s devoted to the finaldesi gn oftheM i cro A i rVehi cl e (M AV).It
illustrates the requi rem entsprovi ded by the revi ew paperprevi ousl y ci ted. Further-
m ore two Fi nite El em entdesi gnswi llbe dem onstrated and expl ained.And final ly a
summ ary with concl usi onsand proposi ti onsf orf uturework arepresented i n the l ast
secti on.
Atl ast,C hapter7 provi ded a bri efovervi ew ofthe thesi s. Ital so provi ded our
contri buti on to thefiel d,wi th concl usi onsbei ng drawn.And final ly,f uturework was
13
proposed.
14
C hapter 2
Experi m entalSetup
2.1 Introducti on
In thi s chapter a descri pti on of the i oni c pol ym er testi ng experi m ents wi th thei r
fixtures and ci rcui ts i s presented. Fi ve experi m ents are usual ly perf orm ed i n order
to f ul ly characteri ze the transducer. The experi m ents are the el ectri cali m pedance,
m echanicali m pedance,sensorsensi ti vi ty,bl ocked f orce,and f ree di spl acem ent tests.
Each experi m enti srun usi ng a step i nputora random i nput.Thefive testsarefirst
descri bed,wi th detai ls on the ci rcui try and equi pm entused. In the l ast secti on the
outputofthe experi m entsareel aborated.
2.2 Experi m ents O utput
Each experi m enti srun wi th two typesofi nputs,a step ora random i nput.Thestep
input i s used to determ i ne the l ow frequency response (DC) ofthe transducer. As
fortherandom i nput,i ti susual ly awhi tenoi sewith an evenl y di stri buted f requency
spectrum appl ied to thepol ym er.Thi stesti snotanal yzed i n theti m edom ain;rather
iti stransf orm ed to thef requency dom ai n usi ng theFouri ertransf orm ati on.Theout-
putofthi stesti sa FrequencyResponseFuncti on (FRF),whi ch i sthem agni tudeand
phaseoftheoutputasa f uncti on off requency.Thedurati on ofthe testi sa f uncti on
ofthreevari ables;i ti si nversel y proporti onalto thesam pl ing rate,proporti onalto the
15
num berofdata poi ntsperf ram e,and proporti onalto thenumberofaveragestaken.
The sam pling rate F s determ i nes the f requency range ofthe FRF.Ideal ly the range
oftheFRF extendsto Fs2 ,butdue to the i ncorporati on ofanti -al iasi ng fil tersaround
28% ofthi srangeareel im inated.Thenum berofpoi ntsperf ram eN p determ i nesthe
resol uti on oftheFRF whi ch i sequalto FsNp
.Severalf ram esofdata are gathered and
the resul ti ng FRFs are averaged to obtai n the finalFRF.The FRFs ofeach f ram e
are com pared together and a coherence f uncti on i s com puted. W hen the FRFsare
identi calthecoherence i sone,and i fthey are total ly di ssi m ilarthecoherence i szero.
Ideal ly for a causalsystem the coherence shoul d be one,but noi se and som e other
sam pling effects rui ns i t by i ntroduci ng random data to the output or i nput ofthe
system orboth.A l ow coherencem eansa sm al lsi gnalto noi se rati o.Fi nal ly a win-
dow functi on i susual ly m ulti pl ied by each f ram e forbef oreprocessi ng.In thi sthesi s
thepopul arHanni ng window wasused throughout.The rol eoftheHanni ng window
isto reducethel eakagedueto sam pl ing,reducetheeffectoftheuncorrel ated content
in the begi nning and theend ofthe f ram edue to phaseshi ft.
2.3 Types ofExperi m ents
The five di fferent experi m ents are expl ained i n thi s secti on. Both i m pedance tests
are conventi onalto any m ateri al ,whi le the el ectrom echani cal ly coupl ed experi m ents
are custom i zed f or i oni c pol ym ers.
2.3.1 E lectri calIm pedance
Electri cali m pedance i sdefined asel ectri calresi sti vi ty and capaci tance ofthe trans-
ducer.Theref oretheoutputofthi sexperi m enti sa tranf erf uncti on fortheresi stance
and capaci tanceofthe i oni c transducer.
Theexperi m entstartswi th appl yi ng a known vol tageacrossthe i oni cpol ym er
whilem easuri ng the open ci rcui tcurrent.The currentm easuri ng ci rcui t i sshown i n
Figure2. 1.Theel ectri cali m pedance i stheknown vol tage(V)appl ied di vi ded by the
16
Figure 2. 1: Schem ati c draw i ng show i ng the experi m entalsetup f or the bl ockedforce test.
currentsensed (I).
ZE =V
I(2. 1)
Theresi sti vi ty i stherealpartofthei m pedance,whi lethecapaci tancei sthei m aginary
part.
2.3.2 M echani calIm pedance
Ioni c pol ym ersare consi dered vi scoel asti cm ateri als thatarem odel ed usi ng two m e-
chani cali m pedance term s. The first term i s the stati c m odulus,whi le the second i s
a frequency dependent term .Newbury and Leo (2002)have used theGHM m ethod
to si m ulate the f requency dependent term .
A schem ati c ofthe setup used i n thi s experi m ent i s shown Fi gure 2. 2. The
shakerappl iesam echani caldef orm ati on while the l inearpotenti om eterm easuresthe
displ acem ent(D )and the l oad cel lm easuresf orce (F).Them echani cali m pedance i s
ZM =F
D(2. 2)
The testi ng configurati on used i n thi sfixture i sval id forl ow-frequency m easurem ent.
Thiswasshown by John Frankl in in theCIM SS,butthi sconfigurati on i shandf ulf or
the next test.
17
Figure 2. 2: Schem ati c draw i ng show i ng the experi m entalsetup f or the bl ockedforce test.
18
Figure 2. 3: Schem ati c draw i ng show i ng the experi m entalsetup f or the bl ockedforce test.
2.3.3 Sensor Sensi ti vi ty
Thesetup shown i n Figure 2. 2 isal so used to determ i ne thesensorsensi ti vi ty ofthe
ioni c transducers. The shaker i s appl yi ng the m echani caldef orm ati on,but i nstead
ofm easuri ng the l oad at the ti p a short ci rcui t current sensor i sm easuri ng current
form ed dueto theappl ied strai n.Thesensorsensi ti vi ty ofi oni cpol ym ersi sm easured
eitherasachargeoracurrent(S).A vol tagesensorprovi desl esssensi ti vi ty si ncethose
transducersare hi ghl y capaci ti ve (Newbury,2002).The sensi ti vi ty i sm easured as
Sensi ti vi ty =S
D(2. 3)
2.3.4 B locked Force
In thi s experi m ent the pol ym er i s connected to a power suppl y,and i t i s actuated
with a known appl ied vol tage (V) on the el ectrodes. On the other si de,a l oad cel l
is bl ocki ng the m oti on ofthe pol ym er and m easuri ng the f orce generated (F).The
setup i sshown i n Figure 2. 3.The bl ocked f orce i s them axi m um force thi spol ym er
19
Figure 2. 4: Schem ati c draw i ng show i ng the experi m entalsetup f or the bl ockedforce test.
can generate and com puted asf ol lows:
Blocked f orce=F
V(2. 4)
2.3.5 Free di spl acem ent
Thefreedi spl acem entexperi m enti sanotheractuati on experi m ent,buti tdi ffersf rom
thebl ocked f orce testby them echani calboundary condi ti on.
Theexperi m entalsetup i sshown i n Figure 2. 4.A known vol tage(V)i sappl ied
to the pol ym er,whi le a laservi brom eterm easures the transducers ti p di spl acem ent
(D )wi thoutaddi ng any obstacl e to the f reem oti on.The f reedi spl acem ent i s:
Freedi spl acem ent=D
V(2. 5)
20
Figure 2. 5: F ixture 1.
2.4 Equi pm ent D escri pti on
In thefiveprevi ousl y descri bed experi m entsi oni cpol ym erswerecl am ped atoneend
with two gol d electrodes. A l lthe experi m ents are conducted i n ai r,and dei oni zed
waterwasbrushed on pol ym erapproxi m atel y once a m i nute. Thi s i nsured that the
hydrati on leveli skeptwi thi n an acceptabl e range.W hen noti n use,the transducers
were stored i n dei oni zed water.
Two testfixtureswere used the experi m ents i n thi s thesi s. Fi xture 1 wasac-
qui red f rom previ ous researchers i n the CIM SS l ab Newbury (2002) and shown i n
Figure 2. 5. It i s com posed oftwo separate apparatus to perf orm al lthe five tests.
Thesensi ng and m odul ustestwasperf orm ed on thefixturewi th theAPS Dynam i cs
APS 113 long stroke shaker,whi ch provi des l arge di spl acem ent up to 50 Hz. The
displ acem ent i sm easured wi th a Novotechni k T25 Li nearpotenti om eterand an ap-
21
propri ate ci rcui t condi ti oning ci rcui t. The si gnalam pl ifiers used f or characteri zi ng
the perf orm ance ofthe stacks i s a current am pl ifier of10 5 V /am p sensi ti vi ty,wi th
the schem ati cs shown i n Figure 2. 2. M anuf acture’ s speci ficati ons of the l inear po-
tenti om eter i ndi cate a repeatabi lity of0. 002mm and a lineari ty of0. 06mm . For the
m odulus test a Transducer Techni quesGSO-10 10 gram l oad cel lwasm ounted on
the shaker arm ature and used to m easure the f orce due to the def orm ati on of the
pol ym er.Thi s l oad cel lwasused wi th a TM O-1 si gnalcondi ti oning ci rcui t. Itspre-
ci si on,repeatabi lity and l ineari ty were 0. 02m N.TheGSO-10 load cel lwasal so used
to m easure the bl ocked f orce on the actuati on apparatus. The actuati on apparatus
isshown i n Figure 2. 5 and i scom posed ofthe l oad cel lon a vari abl e cursorso that
it i seasy to change the boundary condi ti on f rom bl ocked f orce to f ree di spl acem ent.
For the f ree di spl acem enta Pol ytecOFV- 303 l aservi brom eterhead wi th OFV-3001
control lerand OVD-20 dem odulatorwasused.Theresol uti on ofthi ssetup was5µm .
The laser vi brom eterwasused f or f requency response,and sm al ldi spl acem ent step
responsesdue to i tshi gh resol uti on.But i n casea l arge ti p di spl acem enti sexpected
a RedLake i m aging M oti on Scope PCI2000 S hi gh f requency di gi talvi deo cam era
wasused to m easure the def orm ati on. Thi scam era coul d capture vi deo with a rate
up to 2000Hz.Im ageExpressM oti onTrace i m ageanalysi ssof twarewasused to track
the transducer’ sti p,and generatea ti p di spl acem entpl otasa f uncti on ofti m e.The
resol uti on ofthe trace sof tware depends on the i m age quality and the f ocall ength
used. Itcoul d locate a poi ntwi thi n a resol uti on ofa tenth ofa pi xel .A pi xeli n our
experi m entscorrespondsto approxi m atel y 0.1mm .
Thesecond fixturewasrecentl ybui ltbym embersoftheCIM SS l ab.Iti sshown
in Figure 2. 6with al lthecom ponents.Thel oad cel land thel inearpotenti om eterare
thesam eonesused i n theol d fixture.Thi sfixturei sbui ltto autom atef ourofthefive
experi m ents:bl ocked f orce,el ectri cali m pedance,m echani cali m pedance,and sensi ng
sensi ti vi ty. Those five experi m ents are suffi ci ent to f ul ly characteri ze the pol ym er.
The shakerused i n thi s fixture i sa Bruel& K j aer Instrum entsshaker,i t i s capabl e
ofhi gher f requenci es (up to 2- 3KHz) than the previ ous shakers. As f or the si gnal
processi ng,we used two di gitalsi gnalprocesses. The Tektroni x FFT anal yzerwi th
22
Figure 2. 6: A picture show i ng the new fixture w i th detai ls on the parts.
a si gnalgeneratorwasused f or the f requency response f uncti on. A dSpace DS1102
DSP wasused to m easure the step response.
23
C hapter 3
C haracteri zati on of Ioni c Pol ym er
Stacks
3.1 Introducti on
Asdefined i n the i ntroducti on,i oni c pol ym ersare sof t actuators thatperf orm large
Potent ial,and Chal lenges,SP IE P ress,Chap 6 pp.140—184,2001.
Akle,B.and Leo,D . ,M ul ti layer Ioni c Polym erTransducer,Subm i tted proceed-
ings of the SP IE Sm art M ateri al s and Structures C onf erence,2003.
Leo, D . , M E5984: Sm art St ruct ures/ Act ive M ateri al Syst em s, V i rgi ni a Tech
courses,2001.
Y .Bar- Cohen,S.Leary,M .Shahi npoor,J. O .Harri son,and J.Sm i th,El ect ro-Act ive
Polym er (EAP) act uators f or pl anet ary appl icat ions,P roceedi ng of the SP IE ,
Vol.3669,No.1,pp.57- 62,1999.
M .Shahi npoor, Y .Bar- Cohen,J. O .Sim pson and J.Sm i th,Ioni c Pol ym er-m etal
com posi tes (IPM C )as bi om im eti c sensors and actuators,Proceedi ng oft he
SPIE’ s5t hAnualSym posi oum on Sm artSt ruct uresandM at eri als,Vol .3324,No.27,
pp.1- 17,1998.
K .M .Newbury,Charact eri zat ion,M odel ing,and Cont rolofIoni c Polym er Trans-
ducers,P hD D i ssertati on,V i rgi ni a Tech,etd- 09182002- 081047,2002.
Piezo System s,Inc,URL: http://www. piezo. com /,Cambri dge,M assashusetts.
W .Shyy,M .Bergand D .Lj ungqvi st,Fl appi ngand Fl exi bleW ingsf orBi ologi caland
M icro Ai rVehi cles,P rogress i n A erospace Sci ences,Vol .35,No.1,pp.455- 505,
(1999).
87
K .M .Newbury,Leo,D .J. ,El ect ri cal ly i nduced perm anentst rai n in ioni c pol ym er-
m etal com posi te act uators, Sm art Structures and M ateri al s P roc. SP IE
Vol.4695,pp.67- 77,2002.
C.Kothera M i cro- M anipulation and Bandwi dth Charact eri zat ion ofIoni c Polym er
Actuators, M aster’ s T hesi s,V i rgi nia Tech, etd- 12062002- 110547,(2003).
M .BennettandD .Leo,Ioni c l iqui dsashyper-st ablesol vent sfori oni cpol ym ert rans-
ducers,Subm i tted to the Internati onalM echani calEngi neeri ng C ongress
and R & D Expo ,(2003).
J.Shi gley and C.M i schke,M echani calengi neeri ng desi gn,M cG R AW -H il lInter-
nati onalEdi ti onsFi fth edi ti on,M E seri es,1989.
88
V ita
Icom ef rom Zgharta,a town i n north LebanonwhereIl ived unti lIm oved toBei ruti n
1996tof urtherm yeducati on atTheAm eri canUni versi tyofBei rut,whereIgraduated
with di sti ncti on i n 2001. Ihol d a B.S in M echani calEngi neeri ng and i n the summ er
of2000 I di d an i nternshi p at Uni versi dad Carl os III de M adri d,where I desi gned
an industri alCori ol isEffectFl owM eterto beused i n hazardousl iquidsappl icati ons.
In August of2001,Im oved to V i rgi nia Tech to pursue m y M asters Degree. I am
currentl y worki ng in thearea ofm ul ti layeri oni c transducersactuatorswi th D r.Don
Leo at theCenter f or Intel ligentM ateri alSystem sand Structures
Perm anentAddress:300 Durham Hal l
Blacksburg,VA 24061
United StatesofAm eri ca
This thesi swastypesetwi th LATEX 2ε1 by theauthor.
1LATEX 2ε isan extensi on ofL ATEX .LATEX isa col lecti on ofm acrosf orT EX .T EX isa tradem arkofthe Am eri can M athem ati calSoci ety. Them acrosused i n form atti ng thi s thesi swere wri tten byG reg W alker,Departm entofM echani calEngi neeri ng,V i rgi nia Tech.