senso s
A icle
Measu emen s o Gene a ed Ene gy/Elec ical
Quan i ies om Locomo ion Ac i i ies Using
Piezoelec ic Wea able Senso s o Body Mo ion
Ene gy Ha es ing
An onino P o o 1,*, Ma ek Penhake 2, Daniele Bibbo 1, Da id Vala 2, Sil ia Con o o 1
and Mau izio Schmid 1
1Depa men o Enginee ing, Uni e si y o Roma T e, Via Vi o Vol e a, 62, Rome 00146, I aly;
[email p o ec ed] (D.B.); sil ia.con o o@uni oma3.i (S.C.); [email p o ec ed] (M.S.)
2Depa men o Cybe ne ics and Biomedical Enginee ing, VSB-Technical Uni e si y o Os a a,
17 Lis opadu 15, Os a a-Po uba 70833, Czech Republic; ma [email p o ec ed] (M.P.);
[email p o ec ed] (D.V.)
*Co espondence: an onino.p o o@uni oma3.i ; Tel.: +39-6-5733-7057; Fax: +39-6-5733-7026
Academic Edi o s: S e en Leonha d and Daniel Teichmann
Recei ed: 8 Ma ch 2016; Accep ed: 6 Ap il 2016; Published: 12 Ap il 2016
Abs ac :
In his pape , wo di e en piezoelec ic ansduce s—a ce amic piezoelec ic, lead zi cona e
i ana e (PZT), and a polyme ic piezoelec ic, poly inylidene luo ide (PVDF)—we e compa ed in
e ms o ene gy ha could be ha es ed du ing locomo ion ac i i ies. The ansduce s we e placed
in o a igh sui in p oximi y o he main body join s. Ini ial es ing was pe o med by placing
he ansduce s on he neck, shoulde , elbow, w is , hip, knee and ankle; hen, i e locomo ion
ac i i ies—walking, walking up and down s ai s, jogging and unning—we e chosen o he es s.
The alues o he powe ou pu measu ed du ing he i e ac i i ies we e in he ange 6
µ
W–74
µ
W
using bo h ansduce s o each join .
Keywo ds: piezoelec ic ansduce s; body mo ion ene gy ha es ing; elas ic ab ic
1. In oduc ion
Body mo ion ene gy ha es ing (BMEH) means eco e ing ene gy om body mo emen . BMEH
has been he objec o s udy by esea che s om a ound he wo ld o he pas wen y yea s.
S a ne [
1
], who is conside ed one o he i s esea che s who s udied ene gy ha es ing om
human mo ion, explo ed he possibili y o eco e ing he ene gy p oduced by body mo emen s,
du ing e e yday ac i i ies. He poin ed ou ha human beings p oduce he highes amoun o ene gy
du ing walking. Thus, Shenck and Pa adiso [
2
] de eloped an ene gy ha es ing sys em, moun ed on
he shoes, ha enables one o powe a wide ange o body-wo n de ices. Then, Gonzalez e al. [
3
] and
Niu e al. [
4
] analyzed he easibili y o using he ene gy ha es ed om he human body o powe
wea able senso s, which include he unc ions o da a p ocessing and wi eless communica ion [5,6].
Following he same logic, Rome e al. [
7
] de eloped a suspended-load backpack ha con e s
mechanical ene gy o he e ical mo emen o he ca ied load in o elec ical ene gy. In addi ion,
Donelan e al. [
8
] de eloped a biomechanical ene gy ha es e moun ed on he knee ha p o ides
powe gene a ion a he end o he swing phase, hus assis ing decele a ion o he knee join du ing
walking and jogging.
Mi cheson e al. [
9
] e iewed he p inciples in a mo ion-d i en minia u e ene gy ha es e
o in oduce he basis o a wea able and com o able body-wo n ene gy ha es ing sys em.
Vulle s e al.
[
10
] published a e iew dealing wi h he echniques o mic opowe ene gy ha es ing
Senso s 2016,16, 524; doi:10.3390/s16040524 www.mdpi.com/jou nal/senso s
Senso s 2016,16, 524 2 o 15
in o de o con i m he heo y, ea lie discussed by Huang e al. [
11
] and Hanson e al. [
12
], abou he
wi eless body senso ne wo k (WBSN), acco ding o which eliable ene gy ha es ing has now become
a eali y o human condi ions moni o ing.
Nowadays, BMEH sys ems a e becoming undamen al o spo s [
13
], medical [
14
] and
mili a y [
15
] applica ions. The esea ch end is o de elop sma clo hes wi h inco po a ed BMEH
sys ems. S oppa and Chiole io [
16
] p esen ed a pape on ecen p og ess in he ield o sma ex iles,
and Mis a e al. [
17
] p esen ed a pape on lexible echnologies ha enable ul a-long ba e y li e ime
and use com o .
Despi e a la ge body o li e a u e ocusing on he de elopmen and es ing o BMEH sys ems,
o he au ho s’ knowledge he e is a no able lack o s udies a ge ing he op imiza ion o ha es e
kinds, and hei placemen , o be used in e e yday li e ac i i ies.
To ill his gap, in his wo k, piezoelec ic ansduce s placed in a igh sui we e es ed and
compa ed o ind ou he bes loca ion whe e he BMEH sys em can be placed, o maximize ene gy
p oduc ion in e e yday li e. To his end, indi idual body mo emen s o single body join s we e es ed,
and hen i e di e en locomo ion ac i i ies we e chosen o es he senso s in eal-li e condi ions. The
posi ions o he BMEH sys ems we e chosen aking in o accoun he wea abili y o he ansduce s and
he use com o du ing exe cises, wi h he pe spec i e o inco po a ing hem in o sma clo hing.
2. Rele ance o he P oblem
BMEH is an ene gy ha es ing subca ego y ha is a pa o he b oade ca ego y o ene gy
ha es ing om en i onmen al ib a ions. While en i onmen al ib a ion ene gy ha es ing has been
ex ensi ely s udied ecen ly [9], BMEH is qui e a new esea ch ield o scien is s.
The mechanical ene gy om en i onmen al ib a ions can be con e ed in o elec ical ene gy
by elec omagne ic, elec os a ic, magne os ic i e and piezoelec ic ansduce s: in he s udied
li e a u e, he elec omagne ic, elec os a ic and piezoelec ic ansduce s domina e. The wo k
p esen ed by Roundy [
18
] p o ides a gene al heo y ha can be used o compa e hese di e en
ansduc ion app oaches.
In con en ional mac o-scale enginee ing, en i onmen al ib a ion ansduce s a e mos ly based
on he elec omagne ic echnique, while in small-scale ene gy ha es ing, elec os a ic and piezoelec ic
ansduce s a e mo e p ac ical and be e sui ed o mic oelec omechanical (MEMS) implemen a ion [
9
].
The main di e ence be ween piezoelec ic and elec os a ic ansduce s is ha he elec os a ic
ansduce mus be powe ed [
19
] o unc ion, and he e o e he piezoelec ic ansduce s we e chosen
o ou pu pose.
The mos common ypes o ma e ials o piezoelec ic ansduc ion a e lead zi cona e i ana e
(PZT) and poly inylidene luo ide (PVDF) [
20
]. O he piezoelec ic ma e ials a e ba ium i ana e
(BaTiO
3
) p esen ed by Koka e al. [
21
] and Zhang e al. [
22
], mic o- ibe composi es (MFC) illus a ed
by K anz e al. [
23
], and ac i e ibe composi es (AFC) discussed by Dü age [
24
]. In addi ion, lead
magnesium nioba e-lead i ana e (PMN-PT) p esen ed by Halim e al. [
25
] and zinc oxide nanowi es
(ZnO-NWs) p esen ed by Bai e al. [26] a e ma e ials wi h piezoelec ic physical p ope ies.
When compa ing he PZT and PVDF ansduce s [
27
], he o me is be e in e ms o ansduc ion
coe icien s, while he la e is less expensi e and mo e lexible, and i can add py oelec ic p ope ies.
PZT ansduce s can be di ided in o wo ca ego ies: ha d PZT and so PZT. Ha d PZT a e
gene ally no sui able o BMEH because hey a e no lexible enough o accommoda e body join
o a ions. Fo his pu pose, so PZT and PVDF ansduce s we e chosen o his wo k.
The undamen al pu pose in his pape is o quan i y he ene gy amoun ha can be eco e ed
om body mo emen s: o his end, he wea able piezoelec ic ansduce s we e inco po a ed in o
di e en slo s wi hin a igh body sui ; he measu emen s o ou pu ol age we e collec ed du ing he
execu ion o di e en ac i i ies, which will be speci ied in he ollowing pa ag aph.
Senso s 2016,16, 524 3 o 15
3. Ma e ials and Me hods
3.1. Piezoelec ic T ansduce s Chosen
Piezoelec ic ansduce s con e mechanical de o ma ions in o elec ical ene gy, i.e., di ec
piezoelec ic e ec . Thanks o his p ope y, he piezoelec ic ansduce s can p oduce elec ical
ene gy om he mo emen s o he body pa s o which hey adhe e. The P-876.A12 senso [
28
] and
he LDT4-028k senso [
29
] (Figu e 1) we e chosen o analyze he powe ou pu o a BMEH sys em,
espec i ely based on so PZT o on PVDF.
Senso s 2016, 16, 524 3 o 15
3. Ma e ials and Me hods
3.1. Piezoelec ic T ansduce s Chosen
Piezoelec ic ansduce s con e mechanical de o ma ions in o elec ical ene gy, i.e., di ec
piezoelec ic e ec . Thanks o his p ope y, he piezoelec ic ansduce s can p oduce elec ical
ene gy om he mo emen s o he body pa s o which hey adhe e. The P-876.A12 senso [28] and
he LDT4-028k senso [29] (Figu e 1) we e chosen o analyze he powe ou pu o a BMEH sys em,
espec i ely based on so PZT o on PVDF.
Figu e 1. The P-876.A12 senso [28] and LDT4-028k senso [29].
The ea u es o bo h P-876.A12 and LDT4-028k a e lis ed in Table 1.
While examining he piezoelec ic ansduce s beha io , unde condi ions o app oxima e an
open-ci cui ol age, he gene a ed ol age alue om piezoelec ic ansduce s is:
V=
εεd
Y
∆l
l (1)
In applica ions o BMEH, i is assumed ha he piezoelec ic ansduce is e ically suspended
o a suppo and ha a o ce, F, is ac ing on i s end. This o ce c ea es a a ia ion in he leng h l o he
senso , ∆l.
The ela ed applied s ess on he ansduce , X=Y∆
, is gi en by he o ce di ided by he c oss-
sec ional a ea, csa=w (whe e w is he wid h and is he hickness), so ha :
Y
∆l
l=F
w (2)
In his way, i is possible o w i e he equa ion o he gene a ed elec ical ene gy, U, in e ms
o he applied o ce [30]:
Ue=1
2ε0ε wl
V2=1
2ε0ε
l
w d31
2F2 (3)
Figu e 1. The P-876.A12 senso [28] and LDT4-028k senso [29].
The ea u es o bo h P-876.A12 and LDT4-028k a e lis ed in Table 1.
Table 1. P ope ies o he P-876.A12 and LDT4-028k ansduce s.
P ope ies P-876.A12 LDT4-028k
Densi y, ρ(g/cm3)7.8 1.8
Cu ié empe a u e, Tc(˝C) 350 100
Rela i e pe mi i i y, ε 1650–1750 12–13
Dielec ic loss ac o , σ0.02 0.02
Coupling ac o , k 0.47 0.14
Coupling ac o , k31 0.35 0.12
Coupling ac o , k33 0.69 -
Piezo cha ge coe icien , |d31| (10´12 C/N) 180 23
Piezo cha ge coe icien , |d33| (10´12 C/N) 400 33
Piezo ol age coe icien ,|g31| (10´3V m/N) 11.3 216
Piezo ol age coe icien ,|g33| (10´3V m/N) 25 330
Young’s modulus, Y (109N/m2)55.5 3.1
Minimum adius cu a u e, c(mm) 20 5
Ac i e ol. dimensions (l ˆwˆ ) (mm) (50 ˆ30 ˆ0.2) (156 ˆ19 ˆ0.028)
Elec ical capaci ance, C (10´9F) 90 12
Senso s 2016,16, 524 4 o 15
While examining he piezoelec ic ansduce s beha io , unde condi ions o app oxima e an
open-ci cui ol age, he gene a ed ol age alue om piezoelec ic ansduce s is:
V“
ε0ε d31Y∆l
l(1)
In applica ions o BMEH, i is assumed ha he piezoelec ic ansduce is e ically suspended o
a suppo and ha a o ce,
F
, is ac ing on i s end. This o ce c ea es a a ia ion in he leng h l o he
senso , ∆l.
The ela ed applied s ess on he ansduce ,
X“Y∆l
l
, is gi en by he o ce di ided by he
c oss-sec ional a ea, csa “w (whe e w is he wid h and is he hickness), so ha :
Y∆l
l“F
w (2)
In his way, i is possible o w i e he equa ion o he gene a ed elec ical ene gy,
Ue
, in e ms o
he applied o ce [30]:
Ue“1
2
ε0ε wl
V2“1
2ε0ε
l
w d2
31F2(3)
3.2. The Chosen Human Body Mo emen s
Se en body join s we e chosen in o de o ha es ene gy om body mo emen s. These join s
we e chosen in o de o measu e he mos common human body o a ions: neck, shoulde , elbow,
w is , hip, knee and ankle a e he join s a ound which he ansduce s we e placed.
The angle alues we e manually measu ed by a goniome e , o each ange o mo ion o he
pe o med es s. These esul s we e accep ed on he basis o he esul s p esen ed in he wo k o Reese
and Bandy [
31
]. In Table 2, he body join s, join mo emen s, ange o mo ion and he equencies o
mo ion a e summa ized.
Table 2. Body join s, body join mo emen s, ange o mo ion [31] and equency o es s.
Body Join Join Mo emen Range o Mo ion (˝) Mo ion F equency (Hz)
Neck lexion-ex ension 58 ˘12 1.40˘0.10
Shoulde adduc ion-abduc ion 140 ˘9 1.10 ˘0.10
Elbow lexion-ex ension 141 ˘8 1.25 ˘0.10
W is lexion-ex ension 129 ˘14 1.90 ˘0.10
Hip lexion-ex ension 138 ˘21 1.05 ˘0.10
Knee lexion-ex ension 135 ˘11 1.15 ˘0.10
Ankle plan a -do si lexion 66 ˘5 1.75 ˘0.10
3.3. The Chosen Human Body Ac i i y
Fi e common locomo ion ac i i ies we e chosen o ind ou i he wo piezoelec ic ansduce s
we e e icien enough o ha es ene gy om he body mo emen in p ac ice. The men ioned ac i i ies
we e walking, going down and up he s ai s, jogging and unning. The body join s chosen o he
compa ison o he wo piezoelec ic ansduce s we e a subse o he a o emen ioned ones: elbow,
ankle, knee, shoulde and hip. The lexion-ex ension o he w is and neck we e excluded om
he measu emen s because hese mo emen s we e deemed as mino in e ms o exe ed o ces
du ing he chosen locomo ion ac i i ies. In Table 3, he ac i i ies and hei co esponding equencies
a e summa ized.
Senso s 2016,16, 524 5 o 15
Table 3. Summa y o he common ac i i ies and hei equencies.
Common Ac i i y F equency o he Ac i i y (Hz)
Walking 1.15 ˘0.10
Walking downs ai s 1.65 ˘0.10
Walking ups ai s 1.05 ˘0.10
Jogging 1.60 ˘0.10
Running 2.10 ˘0.10
3.4. Elas ic Co on Fab ic o a Tigh Sui
Piezoelec ic ansduce s mus be placed di ec ly on o he skin o ansduce he mo emen s o he
join s in he mos app op ia e way. Thus, a igh elas ic co on sui was made. Elas ic co on ensu es
p ope adjacency o he body and com o , and i is easy o clean.
The piezoelec ic ansduce s we e placed in he pocke s o he sui , a ound each chosen join .
Figu e 2shows he blue sui wi h he g een pocke s, and a g een bel which was used o cap u e
ankle o a ions.
Senso s 2016, 16, 524 5 o 15
Table 3. Summa y o he common ac i i ies and hei equencies.
Common Ac i i y F equency o he Ac i i y (Hz)
Walking 1.15 ± 0.10
Walking downs ai s 1.65 ± 0.10
Walking ups ai s 1.05 ± 0.10
Jogging 1.60 ± 0.10
Running 2.10 ± 0.10
3.4. Elas ic Co on Fab ic o a Tigh Sui
Piezoelec ic ansduce s mus be placed di ec ly on o he skin o ansduce he mo emen s o
he join s in he mos app op ia e way. Thus, a igh elas ic co on sui was made. Elas ic co on
ensu es p ope adjacency o he body and com o , and i is easy o clean.
The piezoelec ic ansduce s we e placed in he pocke s o he sui , a ound each chosen join .
Figu e 2 shows he blue sui wi h he g een pocke s, and a g een bel which was used o cap u e
ankle o a ions.
Figu e 2. The blue sui wi h he g een pocke s and a g een bel (please see Table 4 o deno a ion).
The posi ions o he ansduce s on he sui we e chosen acco ding o he alue o hei olding
pa ame e , he minimum adius cu a u e. LDT4-028k is mo e lexible han P-876.A12, and he e o e
he o me one was placed in he inne pa s o he sui whe e he join s a e a he maximum bending
angle. The inne pa s o he sui ela e o he inne pa s o he elbow, knee and shoulde . Con e sely,
P-876.A12 ansduce s we e placed on he ou e pa s o hose join s. The posi ions o ansduce s
we e he same o he measu emen s o he w is , neck, ankle and hip join s. Table 4 shows he
e e ence posi ions o he ansduce s e e ing o he numbe s in Figu e 2.
Table 4. Posi ions o he ansduce s on he sui and on he bel .
Numbe s in Figu e 2 Join , T ansduce Re e ence Posi ion o he Measu emen s
1 W is , P-876.A12 Top o w is
2 W is , LDT4-028k Top o w is
3 Elbow, P-876.A12 Ou e elbow
4 Elbow, LDT4-028k Inne elbow
5 Neck, P-876.A12 Back o he neck
6 Neck, LDT4-028k Back o he neck
7 Knee, P-876.A12 Ou e knee
8 Knee, LDT4-028k Inne knee
9 Hip, P-876.A12 F on hip
10 Hip, LDT4-028k F on hip
11 Shoulde , P-876.A12 Ou e shoulde
12 Shoulde , LDT4-028k Inne shoulde
13 Ankle, P-876.A12 The ankle plan a
14 Ankle, LDT4-028k The ankle plan a
Figu e 2. The blue sui wi h he g een pocke s and a g een bel (please see Table 4 o deno a ion).
The posi ions o he ansduce s on he sui we e chosen acco ding o he alue o hei olding
pa ame e , he minimum adius cu a u e. LDT4-028k is mo e lexible han P-876.A12, and he e o e
he o me one was placed in he inne pa s o he sui whe e he join s a e a he maximum bending
angle. The inne pa s o he sui ela e o he inne pa s o he elbow, knee and shoulde . Con e sely,
P-876.A12 ansduce s we e placed on he ou e pa s o hose join s. The posi ions o ansduce s we e
he same o he measu emen s o he w is , neck, ankle and hip join s. Table 4shows he e e ence
posi ions o he ansduce s e e ing o he numbe s in Figu e 2.
Table 4. Posi ions o he ansduce s on he sui and on he bel .
Numbe s in Figu e 2Join , T ansduce Re e ence Posi ion o he Measu emen s
1 W is , P-876.A12 Top o w is
2 W is , LDT4-028k Top o w is
3 Elbow, P-876.A12 Ou e elbow
4 Elbow, LDT4-028k Inne elbow
5 Neck, P-876.A12 Back o he neck
6 Neck, LDT4-028k Back o he neck
7 Knee, P-876.A12 Ou e knee
8 Knee, LDT4-028k Inne knee
9 Hip, P-876.A12 F on hip
10 Hip, LDT4-028k F on hip
11 Shoulde , P-876.A12 Ou e shoulde
12 Shoulde , LDT4-028k Inne shoulde
13 Ankle, P-876.A12 The ankle plan a
14 Ankle, LDT4-028k The ankle plan a

Senso s 2016,16, 524 6 o 15
4. Expe imen al Sec ion
4.1. P elimina y Measu emen s
To ind ou he ol age ou pu , he ollowing measu emen ci cui (Figu e 3) was used, and he
alues o he ol age ou pu we e measu ed and acqui ed by he NI USB-6210 da a acquisi ion sys em
(DAQ), Na ional Ins umen s. A ol age di ide ci cui was used as he inpu s age o he NI USB-6210
DAQ in o de o a oid he p oblem o sa u a ion gi en by he ange o ol age alues a he inpu
s age o he DAQ.
Senso s 2016, 16, 524 6 o 15
4. Expe imen al Sec ion
4.1. P elimina y Measu emen s
To ind ou he ol age ou pu , he ollowing measu emen ci cui (Figu e 3) was used, and he
alues o he ol age ou pu we e measu ed and acqui ed by he NI USB-6210 da a acquisi ion sys em
(DAQ), Na ional Ins umen s. A ol age di ide ci cui was used as he inpu s age o he
NI USB-6210 DAQ in o de o a oid he p oblem o sa u a ion gi en by he ange o ol age alues
a he inpu s age o he DAQ.
Figu e 3. Measu emen ci cui .
The ol age ou pu o he ci cui in Figu e 3 is gi en by he ollowing Equa ion (4) [32]:
Vou =I Rload

1+󰇡2π CpRload󰇢2(4)
The powe alues, based on a ixed alue o he esis i e load, we e calcula ed. In o de o
op imize he powe ou pu , he anges o ixed alues o he esis o s we e ca e ully chosen based on
he ansduce s da ashee s [33,34] and on he mo ion equency o he join mo emen s, so ha he
ollowing ela ion is achie ed:
dP
dR =dV

R
dR =0⇔R =1
2π
C (5)
The ange alues o he esis o loads a e shown in Table 5.
Table 5. The chosen ixed alues o he esis o s.
Rload → P-876.A12 T ansduce Rload →LDT4-028k T ansduce
0.075 MΩ 1.865 MΩ
0.220 MΩ 3.715 MΩ
0.440 MΩ 5.745 MΩ
0.610 MΩ 7.100 MΩ
0.830 MΩ 8.530 MΩ
0.900 MΩ 10.545 MΩ
1.180 MΩ 13.180 MΩ
1.400 MΩ 14.930 MΩ
1.850 MΩ 17.215 MΩ
2.400 MΩ 18.775 MΩ
3.600 MΩ 22.340 MΩ
5.850 MΩ 25.175 MΩ
Figu e 3. Measu emen ci cui .
The ol age ou pu o he ci cui in Figu e 3is gi en by he ollowing Equa ion (4) [32]:
Vou “IRload
b1``2π CpRload˘2(4)
The powe alues, based on a ixed alue o he esis i e load, we e calcula ed. In o de o
op imize he powe ou pu , he anges o ixed alues o he esis o s we e ca e ully chosen based on
he ansduce s da ashee s [
33
,
34
] and on he mo ion equency o he join mo emen s, so ha he
ollowing ela ion is achie ed:
dPou
dRload “
d´V2
ou
Rload ¯
dRload “0ôRload “1
2π Cp(5)
The ange alues o he esis o loads a e shown in Table 5.
Table 5. The chosen ixed alues o he esis o s.
Rload ÑP-876.A12 T ansduce Rload ÑLDT4-028k T ansduce
0.075 MΩ1.865 MΩ
0.220 MΩ3.715 MΩ
0.440 MΩ5.745 MΩ
0.610 MΩ7.100 MΩ
0.830 MΩ8.530 MΩ
0.900 MΩ10.545 MΩ
1.180 MΩ13.180 MΩ
1.400 MΩ14.930 MΩ
1.850 MΩ17.215 MΩ
2.400 MΩ18.775 MΩ
3.600 MΩ22.340 MΩ
5.850 MΩ25.175 MΩ
To ensu e ha he P-876.A12 ansduce could be ben p ope ly, pe ec ly ollowing he whole
mo emen o he join s, i was necessa y o place an ex a elas ic band o e he sui , o make he
Senso s 2016,16, 524 7 o 15
ansduce s adhe e o he body pa du ing mo emen . Con e sely, he LDT4-028k ansduce s did
no need any addi ional suppo o secu e hei placemen , due o hei highe lexibili y and abili y o
ollow he join mo emen s.
To ob ain he oo mean squa e alues o he ol ages, cu en s and powe s, he measu ed alues
o he peak- o-peak ol age ou pu we e used in he ollowing Equa ion (6).
V ms “Vou
2?2ñI ms “V ms
R ixed ñP ms “V msI ms (6)
Equa ion (6) was used o ind he RMS alues om each pe o med mo emen epe i ion, shown
in Table 2. In he case o hese mo emen s, he na u e o he angula mo emen s could be oughly
app oxima ed o Equa ion (6), e en i i de ia es om a pu e sinusoidal one, as i is shown in Figu e 4.
Senso s 2016, 16, 524 7 o 15
To ensu e ha he P-876.A12 ansduce could be ben p ope ly, pe ec ly ollowing he whole
mo emen o he join s, i was necessa y o place an ex a elas ic band o e he sui , o make he
ansduce s adhe e o he body pa du ing mo emen . Con e sely, he LDT4-028k ansduce s did
no need any addi ional suppo o secu e hei placemen , due o hei highe lexibili y and abili y
o ollow he join mo emen s.
To ob ain he oo mean squa e alues o he ol ages, cu en s and powe s, he measu ed alues
o he peak- o-peak ol age ou pu we e used in he ollowing Equa ion (6).
V ms =Vou
2
√
2⇒I
ms =V ms
R ixed ⇒P
ms =V msI ms (6)
Equa ion (6) was used o ind he RMS alues om each pe o med mo emen epe i ion, shown
in Table 2. In he case o hese mo emen s, he na u e o he angula mo emen s could be oughly
app oxima ed o Equa ion (6), e en i i de ia es om a pu e sinusoidal one, as i is shown in Figu e 4.
Figu e 4. Sample o he signal o he ol age ou pu measu ed by using he LDT4-028k ansduce
placed on he elbow join o he mo emen o lexion-ex ension. The calcula ed RMS alue
co esponds o 13.78 V, sligh ly less han he alue ha could ha e been ob ained i Equa ion (6), o
sinusoidal wa es, had been applied (14.62 V).
Th ee heal hy male olun ee s (age: 34 ± 5 yea s; body weigh : 76 ± 4 kg; heigh : 175 ± 5 cm) we e
ec ui ed o pe o m he join mo emen s lis ed in Table 2. Each join mo emen was epea ed i e
imes, and he measu ing ime o each es was a ound en seconds.
Figu e 5 shows ou pu RMS powe alues coming om he body join s o each alue o he
esis i e load. Bo h ansduce s p oduce a signal ou pu p opo ional o he olding mo emen and
equency o he pe o med es . To ob ain he maximum alue o he powe ou pu , he mos
impo an pa ame e is he p ope posi ioning o he ansduce on he sui close o he skin, so ha
i can be ben as much as possible. The inhe en di e en na u e o he ansduce s makes i di icul
o use he same exac loca ion o bo h senso s, since he igidi y o he P-876.A12 ansduce makes
i necessa y o p o ide he use wi h a sus aining s uc u e and a di e en placemen as compa ed o
he LDT4-028k ansduce . This conside a ion makes i impossible o di ec ly compa e he powe
ou pu o ansduce s, bu since he ocus o he wo k is on he applicabili y o he ansduce s in
eal-li e condi ions, he compa ison be ween ansduce s needs o include he posi ioning choice,
as well.
In he P-876.A12 ansduce diag am (Figu e 5a), he powe ou pu s o he elbow join a e
highe han hose ob ained o he o he join s. In he g aph o he LDT4-028k ansduce (Figu e 5b),
he highes powe ou pu alues a e hose ela ed o w is , knee and hip join s. Fo bo h ansduce s,
he alues o he powe ou pu inc ease wi h he inc ease o R
load
o each a maximum alue, and
Figu e 4.
Sample o he signal o he ol age ou pu measu ed by using he LDT4-028k ansduce
placed on he elbow join o he mo emen o lexion-ex ension. The calcula ed RMS alue co esponds
o 13.78 V, sligh ly less han he alue ha could ha e been ob ained i Equa ion (6), o sinusoidal
wa es, had been applied (14.62 V).
Th ee heal hy male olun ee s (age: 34
˘
5 yea s; body weigh : 76
˘
4 kg; heigh : 175
˘
5 cm)
we e ec ui ed o pe o m he join mo emen s lis ed in Table 2. Each join mo emen was epea ed
i e imes, and he measu ing ime o each es was a ound en seconds.
Figu e 5shows ou pu RMS powe alues coming om he body join s o each alue o he
esis i e load. Bo h ansduce s p oduce a signal ou pu p opo ional o he olding mo emen and
equency o he pe o med es . To ob ain he maximum alue o he powe ou pu , he mos impo an
pa ame e is he p ope posi ioning o he ansduce on he sui close o he skin, so ha i can be
ben as much as possible. The inhe en di e en na u e o he ansduce s makes i di icul o use
he same exac loca ion o bo h senso s, since he igidi y o he P-876.A12 ansduce makes i
necessa y o p o ide he use wi h a sus aining s uc u e and a di e en placemen as compa ed o he
LDT4-028k ansduce . This conside a ion makes i impossible o di ec ly compa e he powe ou pu
o ansduce s, bu since he ocus o he wo k is on he applicabili y o he ansduce s in eal-li e
condi ions, he compa ison be ween ansduce s needs o include he posi ioning choice, as well.
In he P-876.A12 ansduce diag am (Figu e 5a), he powe ou pu s o he elbow join a e highe
han hose ob ained o he o he join s. In he g aph o he LDT4-028k ansduce (Figu e 5b), he
highes powe ou pu alues a e hose ela ed o w is , knee and hip join s. Fo bo h ansduce s, he
alues o he powe ou pu inc ease wi h he inc ease o R
load
o each a maximum alue, and hen,
hey g adually dec ease. Compa ing he g aphs in Figu e 5a,b, he maximum alues o he powe
ou pu o P-876.A12 on he elbow (49.1
µ
W), ankle (4.94
µ
W), w is (22.2
µ
W) and neck (7.68
µ
W)
Senso s 2016,16, 524 8 o 15
join s a e highe han hose ob ained by LDT4-028k on he same join s. Con e sely, he maximum
alues o he powe ou pu o LDT4-028k on he shoulde (12.3
µ
W), knee (15.9
µ
W) and hip (15.0
µ
W)
join s a e highe han hose appea ing o P-876.A12 placed on he same join s.
Senso s 2016, 16, 524 8 o 15
hen, hey g adually dec ease. Compa ing he g aphs in Figu e 5a,b, he maximum alues o he
powe ou pu o P-876.A12 on he elbow (49.1 µW), ankle (4.94 µW), w is (22.2 µW) and neck
(7.68 µW) join s a e highe han hose ob ained by LDT4-028k on he same join s. Con e sely, he
maximum alues o he powe ou pu o LDT4-028k on he shoulde (12.3 µW), knee (15.9 µW) and
hip (15.0 µW) join s a e highe han hose appea ing o P-876.A12 placed on he same join s.
(a)
(b)
Figu e 5. The calcula ed mean alues o he powe ou pu o each alue o he load esis o . E o
ba s ep esen s anda d de ia ions. (a) P-876.A12; (b) LDT4-028k.
4.2. Measu emen s o he Powe Ou pu du ing Locomo ion Ac i i ies
Fi e common ac i i ies we e chosen o es he wo piezoelec ic ansduce s. The common
ac i i ies we e walking, walking down and up he s ai s, jogging and unning, and he chosen join s
o he es s we e he shoulde , elbow, hip, knee and ankle. Fo each ac i i y, ol ages we e measu ed
and acqui ed by he NI USB-6210 DAQ, Na ional Ins umen s, while cu en and powe alues, based
on a ixed alue o he esis i e load, we e calcula ed using MATLAB so wa e. A ol age di ide
ci cui was used as he inpu s age o he NI USB-6210 DAQ o a oid sa u a ion gi en by he ange
Figu e 5.
The calcula ed mean alues o he powe ou pu o each alue o he load esis o . E o ba s
ep esen s anda d de ia ions. (a) P-876.A12; (b) LDT4-028k.
4.2. Measu emen s o he Powe Ou pu du ing Locomo ion Ac i i ies
Fi e common ac i i ies we e chosen o es he wo piezoelec ic ansduce s. The common
ac i i ies we e walking, walking down and up he s ai s, jogging and unning, and he chosen join s
o he es s we e he shoulde , elbow, hip, knee and ankle. Fo each ac i i y, ol ages we e measu ed
and acqui ed by he NI USB-6210 DAQ, Na ional Ins umen s, while cu en and powe alues, based
on a ixed alue o he esis i e load, we e calcula ed using MATLAB so wa e. A ol age di ide
ci cui was used as he inpu s age o he NI USB-6210 DAQ o a oid sa u a ion gi en by he ange
Senso s 2016,16, 524 9 o 15
o ol age alues a he inpu s age o he DAQ. The ixed alues o he esis i e load, based on he
p e ious measu emen s (Figu e 5), we e ca e ully chosen o each join , and hey a e shown in Table 6.
These alues we e ob ained h ough in e pola ion and app oxima ion o he disc e e alues es ed in
he i s expe imen a ion.
Table 6. The ixed alues o he esis o s o each join .
Join Rload ÑP-876.A12 Rload ÑLDT4-028k
Shoulde 2.000 MΩ8.880 MΩ
Elbow 0.952 MΩ7.880 MΩ
Hip 2.000 MΩ10.565 MΩ
Knee 1.430 MΩ10.565 MΩ
Ankle 0.952 MΩ7.080 MΩ
The es s we e epea ed o each epo ed esis ance alue, and hus, he alues o he powe
ou pu we e ob ained in s a is ical e ms as a e age alues ac oss mul iple epe i ions, o ake in o
accoun he inhe en a iabili y o ha ing di e en pa icipan popula ion samples epea ing he
men ioned ac i i ies.
Th ee heal hy male olun ee s (age: 34
˘
5 yea ; body weigh : 76
˘
4 kg; heigh : 175
˘
5 cm) we e
ec ui ed o pe o m he ac i i ies lis ed in Table 3. Each ask was epea ed ou imes. The measu ing
ime o walking and walking down and up he s ai s was one minu e o each es , while he measu ing
ime o he jogging ac i i y was wen y seconds and o he unning ac i i y eigh seconds.
Also o hese es s, he inhe en di e en na u e o he ansduce s makes i di icul o use
he same exac loca ion o bo h senso s, since he igidi y o he P-876.A12 ansduce makes i
necessa y o p o ide he use wi h a sus aining s uc u e and a di e en placemen as compa ed o he
LDT4-028k ansduce .
Figu e 6shows he measu emen s o he RMS powe ou pu alues o he body join s, o each
pe o med ac i i y. Locomo ion ac i i ies, such as walking and walking up s ai s, p oduce he lowes
alues o he powe ou pu o bo h ansduce s, while unning p oduces he highes alues o bo h
o hem, ollowed by powe ou pu alues o jogging and walking down s ai s.
As i can be clea ly seen in Figu e 6a, walking, walking up s ai s and walking down s ai s, o
P-876.A12, led o e y simila powe ou pu . Ou o hese h ee ac i i ies, he knee join p oduces he
highes alues o powe ou pu (2.21
µ
W) ollowed by he ankle (0.54
µ
W), elbow (0.41
µ
W), shoulde
(0.31
µ
W) and hip (0.20
µ
W) join s. As o he jogging ac i i y, he knee join p oduces he highes
alue o powe ou pu (5.98
µ
W) ollowed by he shoulde (2.24
µ
W), ankle (1.45
µ
W), elbow (0.60
µ
W)
and hip (0.31
µ
W) join s. As o unning, he knee join p oduces he highes alue o he powe ou pu
(23.70
µ
W) ollowed by hip (9.37
µ
W), elbow (8.16
µ
W), shoulde (3.12
µ
W) and ankle (1.65
µ
W) join s.
Simila conside a ions apply o he LDT4-028k ansduce (Figu e 6b), hough wi h lowe absolu e
alues. In all ac i i ies, excep unning and jogging, he knee join p oduces he highes alue o
powe ou pu (1.90
µ
W) ollowed by he hip (0.95
µ
W), ankle (0.67
µ
W), elbow (0.25
µ
W) and shoulde
(0.21
µ
W) join s. As o jogging, he knee join p oduces he highes alue o powe ou pu (3.71
µ
W)
ollowed by he ankle (2.88
µ
W), hip (2.43
µ
W), elbow (1.86
µ
W) and shoulde (4.46
µ
W) join s. As o
unning, he knee join p oduces he highes alue o powe ou pu (8.83
µ
W) ollowed by he shoulde
(5.16 µW), ankle (5.13 µW), elbow (4.83 µW) and hip (4.46 µW) join s.
Table 7b eaks down he compa ison be ween P-876.A12 (PZT) and LDT4-028k (PVDF) conside ing
all he locomo ion ac i i ies and all he join s, highligh ing which ansduce pe o med bes o each
ac i i y and join .