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Sensors and Actuators A 202 (2013) 147154
Contents lists available at ScienceDirect
Sensors and Actuators A: P!sical
" o u r n a l o # e $ a % e : & & & ' e l s e v i e r ' c o # l o c a t e s n a
ulti*sensor s!ste# &it +luetoot connectivit! ,or non*invasive
#easure#ents o, u#an bod! $!sical $ara#eters
A' De$ari- A' .la##ini- S' /inaldi- A' eoli
De$art#ent o, n,or#ation n%ineerin%- niversit! o, +rescia- ia +rane 3- 25123 +rescia- tal!
a r t i c l e i n , o
Article istor!:
/eceived 27 6ctober 2012
/eceived in revised ,or# 30A$ril 2013 Acce$ted 1 a!
2013
Available online 1 a! 2013
e!&ords:
Poto$let!s#o%ra$ic
sensor 8issue
i#$edance
#easure#ent 9ireless
sensor
Portable s#art
sensor on*
invasive
#easure#ent
a b s t r a c t
n te last ,e& !ears- te availabilit! o, $o&er,ul $ersonal co#$utin% devices- li;e
s#art$ones- as o$ened ne& scenarios to te so called $eri#ental caracteriation o, te $rotot!$e- $er,or#ed b!
usin% a s$eci,icall! desi%ned a$$lication ,or Android s#art$one s!ste#s- as
de#onstrated te validit! o, te $ro$osed a$$roac'
B 2013 lsevier +'' All ri%ts reserved'
1. Introduction
onitorin% $!sical data- $articularl! durin% s$ort
activities- can $rovide atletes &it use,ul in,or#ationabout te bod! res$onse to ,ati%ue' , te in,or#ation
&as %iven in real*ti#e- te atlete could i##ediatel!
reco%nie $otential serious aards ,or is ealt- ,or
e>a#$le due to overstrain- tus reducin% or inter*ru$tin%
te activit!' oreover- trainin% $ro%ra#s tailored to te
atlete caracteristics #a! ta;e advanta%e o, te real*
ti#e in,or*#ation- b! su%%estin% i# o& to ad"ust te
activit! in order to i#$rove is $er,or#ance' A s!ste#
able to ac@uire suc data ,ro# te u#an bod! #ust be
co#$act- li%t and $ortable- non*invasive and lo&*$o&er-
in order to be batter!*o$erated durin% outdoor use'
Several devices are toda! available on te #ar;et ,or
suc $ur*$oses ,or instance eart rate belts are used to
collect in,or#ation
; Corres$ondin% autor' 8el': 3 0303715 ,a>:3 03030014' *#ail address:alessandro'de$ariEin%'unibs'it (A' De$ari)'
024*4247F see ,ront #atter B 2013 lsevier +'' All
ri%ts reserved'
tt$:d>'doi'or%10'101G"'sna'2013'05'001
http://www.sciencedirect.com/science/journal/09244247mailto:[email protected]:[email protected]:[email protected]:[email protected]://var/www/apps/conversion/tmp/scratch_2/C:%5C%5CUsers%5C%5CSAMSUNG%5C%5CDownloads%5C%5Cdx.doi.org%5C%5C10.1016%5C%5Cj.sna.2013.05.001http://var/www/apps/conversion/tmp/scratch_2/C:%5C%5CUsers%5C%5CSAMSUNG%5C%5CDownloads%5C%5Cdx.doi.org%5C%5C10.1016%5C%5Cj.sna.2013.05.001mailto:[email protected]:[email protected]://var/www/apps/conversion/tmp/scratch_2/C:%5C%5CUsers%5C%5CSAMSUNG%5C%5CDownloads%5C%5Cdx.doi.org%5C%5C10.1016%5C%5Cj.sna.2013.05.001http://var/www/apps/conversion/tmp/scratch_2/C:%5C%5CUsers%5C%5CSAMSUNG%5C%5CDownloads%5C%5Cdx.doi.org%5C%5C10.1016%5C%5Cj.sna.2013.05.001http://www.sciencedirect.com/science/journal/09244247 -
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,ro# atlete bod! and to trans#it data to s#art$ones or
dedi*cated devices' ?o&ever- suc s!ste#s are usuall!
rater invasive and re@uire a care,ul $ositionin% o, te
sensitive ele#ents- in order to $rovide #eanin%,ul
results' n addition- te connection o, tese sensin%
devices to a s#art$one ,or data visualiation re@uires
te use o, e>ternal don%le- since t!$icall! teir
co##unication $ro*tocol is not nativel! su$$orted' n H1I-
a ne& a$$roac as been $ro$osed to i#$rove teco#,ort and te @ualit! o, te $rovided eart rate
#easure#ents' 8e sensor is $laced on te user earlobe
and te ac@uired data are trans#itted &it &ireless
tecnolo%! to an end*device ,or data $rocessin% and
visualiation' 8ere,ore- te co#$le>it! and te cost o,
te sensor a$$aratus can be #aintained lo&- &ereas
te $o&er consu#$tion is co#$arable to te one o, te
&ireless trans#ission unit' 8e $ur$ose o, te $resent
is to i#$rove te s!ste# in H1I- in order to collect
additional $!s*ical in,or#ation ,ro# te atleteJs bod! in
$articular- beside te $oto$let!s#o%ra$ic (PPK)
sensor o, H1I- te #easure#ent o, te earlobe tissue
i#$edance as been considered H2I' Data ,ro# botsensors are trans#itted b! te sa#e audio +luetoot
inter,ace-
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14 A' De$ari et al' Sensors and Actuators A 202 (2013) 147154
&itout te need ,or additional $rocessin% unit'
8e ai# is to use te audio si%nal to code-
tan;s to si#$le %lue lo%ic- t&o biolo%ical
si%nals' Since data collected ,ro# te sensors
ave not $articularl! $rivac! issues- codin%
and $rotection o, trans#itted data (li;e ,or
instance in H3I) ave not been considered'
8e PPK sensor is used to #onitor
#odi,ications in blood vol*u#e in te arteries-#easurin% te variation o, te li%t trou% te
tissues H4I' 8e ,re@uenc! o, te si%nal
$rovided b! te sen*sor is used to esti#ate
te eart beat rate and to %ater additional
in,or#ation ,ro# te caracteristics o, te
cardiac si%nal' .or e>a#*$le- b! anal!in% te
eart beat variabilit! H5-GI- it is $ossible to
detect events tat can seriousl! in"ure
atletes- suc as arr!t*#ias or arterial
stenosis and occlusions' 8e use o, a second
sensor- o$eratin% &it a di,,erent &avelen%t
or- si#ilarl!- a sin%le sen*sor e#$lo!in% t&o
di,,erent &avelen%ts- &ould #a;e $ossible
te esti#ation o, te o>!%en saturation inblood as &ell H7-I' 6n te oter and- te bio*
i#$edance #easure#ent is &ell*;no&n in lit*
erature HIto #onitor te can%es o, biolo%ical
tissue $ro$erties- li;e ,or e>a#$le ions
concentration due to $!sical e,,ort' 8e #on*
itorin% o, suc $ro$erties #a! el$ te atlete
to understand te bod! res$onse to te
current activit! and- in accordance- to ad"ust
is $!sical e,,ort' n te $resent - te
#easure#ent o, te earlobe tissue i#$edance
is acieved b! enca$sulatin% t&o elec*trodes
in te cli$ su$$ort o, te PPK sensor' +! doin%
tis- te sie and &ei%t o, te sensor unit
a$$lied on te atlete earlobe are not
substantiall! increased'
Data trans#ission ta;es advanta%e o, te
&ell*;no&n and &ides$read +luetoot &ireless
tecnolo%!- &ic is alread! used in several
a$$lications ,or collectin% sensor data H10-11I'
n ,act- +luetoot is nativel! available in al#ost
all $ortable devices- suc as s#art$ones and
tablets- &ic- in addition- are te best can*
didates ,or te data elaboration and
visualiation- tan;s to te $resence o,
relativel! i% co#$utational resources and o,
a touc screen ,or te user interaction' 6ter
co##unication tecnolo%ies t!$icall! ado$ted
to collect data ,ro# sensors- li;e 9i*.i H12Iand 02'15'4 H13I- $resent li#itations
re%ardin% te $o&er con*su#$tions (9i*.i)
and te su$$ort b! s#art$ones (
02'15'4)' 6ter interestin% a$$roaces- li;e
te one $ro$osed in H14I- are not suitable ,or
te $ro$osed a$$lication- since te sensors
are con*nected e>ternall! to te earlobe'
Latel!- +luetoot as been ado$ted ,or
data trans#ission also in sensor s!ste#s ,or
s$ort activities- tus #a;in% $ossible a direct
co##unication lin; &it te user s#art$one'
?o&ever- co#$at*ibilit! issues arise ,ro# tis
a$$roac in ,act- +luetoot standard de,ines a
broad set o, co##unication $ro,iles- oriented,or data as &ell as audio (strea#in%)
trans#ission- di,,erentl! su$$orted b! te #ost
&ides$read devices on te #ar;et (Android-
i6S- 9in*do&s Pone ter#inals)' Currentl!-
te onl! $ro,ile i#$le#ented b! all te devices
is te ?ands*.ree Pro,ile (?.P)- #ainl! used
,or co#*#unication &it co##ercial eadsets'
8e ?.P solution as been cosen ,or data
co##unication- to assure te ,ull co#$atibilit!
o, te $ro$osed sensor s!ste#s &it te #ost
available end*devices' 8is led to te need o,i#$le#entin% an e,,ective ,irst conditionin%
electronics ,or sensor data- &ic &ill be
dee$l! described in te ,ollo&in%'
.or de#onstrative $ur$oses- a data
ac@uisition and user inter*,ace $ro%ra##e as
been i#$le#ented in Android environ#ent'
?o&ever- bein% te $ro$osed solution
inde$endent o, te used end*device- te
develo$#ent o, a$$lications ,or oter ter#inals
e@ui$$ed &it di,,erent o$eratin% s!ste#s is
,acilitated H1I'
2. The proposed system
8e $ro$osed s!ste# is co#$osed o, tree
units- as illustrated in .i%' 1' 8e Sensor unit
includes te sensors a$$lied on te user
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Fig. 1. +loc; sce#e o, te overall s!ste# te circled
$art is te $ro$osed solution ,or data #easure#ent and
trans#ission'
earlobe ,or te $!sical data #easure#ent'
8e analo% ,ront*end $rovides $ro$er sensor
e>citation si%nals and i#$le#ents te ,irst
conditionin% electronics o, sensor data'
oreover- as detailed in te ,ollo&in%- it,urnises data to trans#it to te 8rans#ission
unit in a suitable ,or#at' 8e latter is devoted
to te +luetoot trans#ission o, data to s$eed
u$ te desi%n $rocess- a co##ercial
+luetoot ear$one- able to trans#it audio
data- as been used ,or tis $ur*$ose' 8e
batter! o, te ear$one is used to $o&er also
te oter t&o units o, te s!ste#'
8rans#itted data can be ac@uired b! an!
device &it +luetoot ca$abilities' n order to
de#onstrate te validit! o, te $ro$osed
sensor s!ste#- a s#art$one e@ui$$ed &it
Android as been used as te end*device' A
suitable so,t&are (A$$) as been develo$ed toso& te ac@uired data and to save te# as
an audio ,ile ,or ,ur*ter o,,*line anal!sis' n te
,ollo&in%- te tree units o, te sensor s!ste#
&ill be detailed- &ereas te s#art$one A$$
descri$tion &ill be included in Section 3'
2'1' Sensor unit
8e sensor unit consists o, an o$tical PPK
sensor and t&o elec*trodes ,or te i#$edance
#easure#ent' 8e utilied PPK sensor ado$ts
te trans#issive tecni@ue and tus it is
co#$osed o, a $ototransistor and a
$otodiode to be $laced ,ace*to*,ace- &it te
tar%et tissue in te #iddle' 8e $otodiodee#its an in,rared bea# &ic is detected b!
te $ototransistor once te li%t as crossed
te tar%et tissue' An increase o, blood volu#e
in te tissue deter#ines a decrease o, te li%t
received b! te $ototransistor tere,ore- an
electric si%nal ,ollo&in% te beaviour o, te
blood volu#e can be ac@uired' Several details
can be obtained b! usin% te
$oto$let!s#o%ra$ic &ave,or#' A sin%le
$eriod is co#$osed o, t&o $ea;s se$arated b!
a s#all di$- called Dicrotic otc it re$resents
te closure o, te aorta &it te end o, s!stole-
,ol*lo&ed b! te be%innin% o, te diastole' 8e
co#$lete cardiac c!cle can be used ,or te
eart beat rate esti#ation' oreover- recent
s H5-GI illustrate tat is $ossible to
evaluate te occurrence o, arr!t#ias or
arterial stenosis and occlusions ,ro# te eart
rate variabilit!' 8e t&o sensor co#$onents o,
te PPK- tat is te $ototransistor or
$otodiode- ave been $laced in te #iddle o,
t&o co$$er rin%s actin% as electrodes ,or te
i#$edance #easure*#ent' ac electrode as
te ,or# o, a circular rin% &it 1 ## tic;ness'
8e dia#eters o, te outer and inner
circu#,erences o, te rin%s are 10 ## and 5
##- res$ectivel!' lectrical connections o, te
PPK sensor are assured b! #eans o, suitable
ollo&s in te #etallic rin%s' 8e attraction,orce o, t&o #a%nets as been used to ;ee$
te rin%s in contact &it te t&o sides o, te
earlobe and to
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A' De$ari et al' Sensors and Actuators A202 (2013) 147154
Vcc
RD RC
PPG
(a)
RST
Ct
(Ctot) CSTFig. 2. 8e i#$le#ented $rotot!$e o, te Sensor unit'
(b)%uarantee a %ood ali%n#ent bet&een te t&o sensor co#$onents' Fig. 4. (a) 8e $olariation and ,irst conditionin% electronics ,or te PPK sensor' (b)8&o c!lindrical #a%nets &it circu#,erence e@ual to te electrode 8e i#$edance #easure#ent and #odulation circuits'outer one and tic;ness o, 2 ## ave been %lued to te rear o,
eac electrode te #a%net $ole orientation as been suitabl! co* analo% ,ront*end' 8e PPK sensor- as illustrated be,ore- is co#$osedsen to #a;e te rin%s attractin% eac oters &en te t&o PPKo, a $otodiode and a $ototransistor a si#$le $olariation circuitco#$onents are ,ace*to*,ace' A $icture o, te realied sensor unitis realied b! #eans o, te t&o resistors /Dand /C- as in .i%' 4(a)'$rotot!$e is so&n in .i%' 2' Co#$ared to te solution ado$ted
in H1I- &ere a cli$ as been used to sustain te PPK- te #a%* 8e eart beat &ave,or# C ,ro# te o$tical sensor as ver! lo&
net a$$roac #a;es te ali%n#ent o, te PPK sensor co#$onents a#$litude and it is rater nois!' 8e #a>i#u# a#$litude o, Cis
sli%tl! #ore critical neverteless- it %uarantees a #ore e,,ective on te order o, ,e& #illivolts and it as a DC o,,set' A ,ilterin% sta%e-
co#$osed o, a ,irst order i%*$ass ,ilter (/?P and C?P) is used toelectrode contact &it te tissue' asiness o, a$$lication on te
tar%et (e'%'- earlobe) and re#oval are o&ever assured' re#ove te DC o,,set- &ereas an a#$li,!in% sta%e- co#$osed o,
an active ,irst order lo&*$ass ,ilter (6A- /LP1- /LP1- and CLP- cut ,re*t sould be noticed tat te electrodes are in direct contact &it
te s;in and tere,ore an electric current can ,lo& trou% te tis* @uenc! o, about 5 ?)- as been used to $re$rocess C- obtainin%
sue' ?o&ever- bein% te s!ste# lo&*volta%e and batter!*o$erated- te PPKsi%nal'
tis does not re$resent a ris; ,or te u#an tar%et' .or i#$roved 8e circuit dedicated to te tissue i#$edance esti#ation- b!#eans o, te i#$le#ented electrodes- ta;es advanta%e o, te ,actsa,et!- te electrodes can be covered &it an insulatin% ,il#: t&otat te earlobe i#$edance can be a$$ro>i#ated as a $ure ca$ac*ca$acitive co#$onents 2Ci- due to te insulator- are introduced initive co#$onent- &en te o$eratin% ,re@uenc! is over a certainseries to te tissue i#$edance Mt- as so&n in .i%' 3' 8e overallvalue (about 20 ;?)' 8is consideration &ill be better detailede,,ect is a ca$acitive co#$onent Ciin series &it Mt- &ic #a;esin Section 3' 8ere,ore- te #easure#ent o, Mt (or Mtot- in case o,
te #easured i#$edance Mtotto be as described in (1)' insulatin% ,il#) #erel! beco#es te esti#ation o, te ca$acitive1 1
N /e(Mt) " #(Mt) O (1)co#$onent Ct(Ctot)- tus a si#$le ,irst conditionin% electronics can
MtotN Mt "2_,C 2_,C
i i be i#$le#ented' As stated be,ore- a co##ercial +luetoot device
Also in te case &en te insulator ,il# is a$$lied- te in,or#a* able to trans#it an audio si%nal &ill be used' .or tat reason- a
sin%le si%nal in te voice band&idt carr!in% bot te in,or#a*tion about te tissue i#$edance Mt can be neverteless obtainedtion related to te PPK and i#$edance sensor need to be $rovided
,ro# te esti#ation o, Mtotand te ;no&led%e o, Ci' to te 8rans#ission unit' n H1I- a si#$le #etod based on si%nal
2'2' Analo% ,ront*end#odulation &it a constant*,re@uenc! and s@uare &ave,or# car*rier as been used to si,t te PPK si%nal in te audio band&idt-
8e sensors need to be $ro$erl! e>cited and sensor out$ut si%* tus #a;in% it suitable ,or trans#ission &it te ado$ted +lue*
toot device' n tis - a si#ilar a$$roac as been ,ollo&ednals ave to be suitabl! conditioned be,ore trans#ission tesein ,act- in,or#ation about te tissue ca$acitance as been coded in
tas;s are $er,or#ed b! te electronic circuits i#$le#ented in te te #odulatin% carrier ,re@uenc!' n tis &a!- a sort o, co#bina*
tion bet&een a $ulse*,re@uenc! #odulation and $ulse*a#$litude
#odulation is obtained and in,or#ation related to bot sensors is
co#bined to create a sin%le audio si%nal'
An oscillator circuit based on a Sc#idt 8ri%%er lo%ic %ate is
used to %enerate te tissue*ca$acitance*de$endent s@uare &ave*
,or# S8- as so&n in .i%' 4(b)' 8e oscillator o$erates at a ,re@uenc!
%reater tan 20 ;?- in order to consider valid te a,ore#entioned
a$$ro>i#ation o, tar%et i#$edance as a $ure ca$acitive co#$o*
nent tis ,re@uenc! value is o&ever out o, te use,ul audio
band&idt' 8us- S8 is not a$$ro$riate to be directl! used as te
#odulation carrier- but it needs to be $rocessed b! a Prescaler- to
Fig. 3. 8e e@uivalent #odel o, te i#$edance sensor &en te electrodes are reduce te ,re@uenc! into te audio band' ventuall!- te PPK si%nal
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covered &it insulatin% ,il#s' #odulation is $er,or#ed b! #eans o, a co$$er circuit- consistin%
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150 A' De$ari et al' Sensors and Actuators A 202 (2013) 147154
o, te 6S transistor controlled b! te
s@uare &ave,or# Car ' /esu#in%- te
obtained sin%le si%nal +8 - &ic is in te
audio band and tus can be directl! ac@uiredb! te 8rans#ission unit- carries tein,or#ation about te PPK sensor in tea#$litude and data related to te tar%etca$acitance in te ,re@uenc!'
2'3' 8rans#ission unit
odern $ersonal devices- li;e
s#art$ones and tablets- are usu*all!
e@ui$$ed &it di,,erent co##unication
inter,aces- ,or instance S+- 9i*.i- and
+luetoot' n co#$arison &it oter
tecnolo%ies- +luetoot as several
advanta%es- suc as si#$le co##unication
stac;- sa,e co##unication cannel- and
availabilit! o, lo&*cost and lo&*$o&er devices
H1I' .or tese reasons- +luetoot is t!$*icall!
e#$lo!ed to $rovide co##unication &it add*
on devices- li;e ear$ones- eadsets- %a#edevices and #an! #ore' Latel!- a ne& release
o, +luetoot standard is available- te so
called +lue*toot Lo& ner%! (+L) H15I-
&ic is also ;no&n &it te na#e +luetoot
S#art' 8!$icall! tis $rotocol is ado$ted ,or te
devel*o$#ent o, sensors net H1GI- &ere
te $o&er consu#$tion is one o, te #ain
desi%n $ara#eters- li;e in #edical and ,itness
a$$liances H17I' everteless- des$ite its lo&
$o&er consu#$tion- co#$arable to oter ver!
lo& $o&er tecnolo%! li;e 02'15'a H1I-
tis solution cannot be e#$lo!ed in te
$ro$osed a$$roac- since a $ro,ile ,or te
continuous trans#ission o, data strea# is notavailable' n addition- onl! i%*end devices
are e@ui$$ed &it +L at $resent ti#e- li#itin%
its co#$atibilit!- &ic is one o, te #ain
advanta%es o, te $ro$osed a$$roac'
8ere are several +luetoot $ro,iles
available ,or data as &ell as audio
co##unication o&ever- not all o, te# are
i#$le#ented b! te o$eratin% s!ste#s
ado$ted in s#art$ones and tablets' .or
instance- Android su$$orts so#e o, te
$ro,iles (data and audio) $rovided b! te
standard- &ereas i6S i#$le#ents oter
$ro,iles (?.P 1'5- P+AP- A2DP- A/CP- PA-
?D) not co#$atible &it te $revious ones'
8e audio ?ands*.ree Pro,ile (?.P) as
been selected ,or te trans#ission o, te
sensor si%nal- because it is su$$orted b! te
#ost o, te devices on te #ar;et (included
Android- i6S s!s*te#s and 9indo&s Pone )
and due to te eas! recover! o, te
trans#itted sensor data at a$$lication level'
8e ?ands*.ree Pro,ile de,ines o& a eadset
(
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(a)5'00302
3'7502
Mag 2'5002
1'2502
0'0000
0 4000 000 12000
Frequency !z"
(b) 0
#hase *40
*0
0 4000 000 12000
Frequency !z"
Fig. $. 8e #a%nitude (a) and $ase (b) o, te earlobe
i#$edance Mt #easured &it te $ro$osed sensor
(&itout insulatin% ,il#) and ac@uired &it an i#$edance
anal!ser'
$ase o, te earlobe i#$edance #easured
&it te sensor a$$lied to a $erson in nor#alconditions are so&n' n tis case- te elec*trodes ave been a$$lied &itout teinsulatin% ,il#- tere,ore te %ra$s are related
to te actual tissue i#$edance Mt' t sould benoticed tat &en te ,re@uenc! increases- te
i#$edance $ase decreases to&ards O0Q -
tus indicatin% tat a ca$acitive co#$o*nent Ctis beco#in% #ore and #ore si%ni,icant' , te#easure#ent is $er,or#ed &it a ,re@uenc!%reater tan about 20 ;?- te tis*suei#$edance can be #odelled b! usin% onl! tei#a%inar! $art or- e@uivalentl!- b! utiliin% a
ca$acitive co#$onent Ct- as described in (2)'
MtN /e(Mt) "(#(Mt)) R "(#(Mt)) N O"
1
(2)2_,CtSi#ilarl!- &en te insulatin% ,il# is used
bet&een te tissue and te electrodes- tetotal i#$edance Mtotcan be #odelled b! usin%onl! te i#a%inar! $art- &ic is related to aca$acitive co#*$onent Ctot- de$endin% on Ctand Cias in (3) and (4)'
Mtot R "(#(Mtot)) N " #(Mt) O
1
2_,Ci1 1 1
N O" N O" (3)2_,Ct 2_,Ci 2_,Ctot
1 1 1 (4)
N Ctot Ct Ci
n .i%' G- te ac@uisition o, Mtot$er,or#ed&it te i#$edance anal!ser is so&n' t is&ort notin% tat te beaviour starts to besubstantiall! ca$acitive at o$eratin%,re@uencies lo&er tan in te $revious casetis is due to te $redo#inance o, te
ca$acitive e,,ect Cio, te insulator'n order not to lose sensitivit! in te
#easure#ent o, te tar%et i#$edance- it isi#$ortant to accuratel! select te #aterial ,orte insulator ,il# in $articular- esti#atedvalues &it te realied sen*sor $rotot!$e are
Ci R 10 $. and Ct R 1 $. &it o$eratin%
,re@uenc! o, about 100 ;?'A 8CM8020*PA/ device $roduced b!
isa! se#iconductor as been ado$ted as
te PPK sensor H20I' 8e #ain caracteris*tics
are: 50 n# bea# &avelen%t- G0 #A no#inal
current and
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A' De$ari et al' Sensors and Actuators A202 (2013) 147154 151
(a)1G0000
%&"
120000
Mag 0000
40000
0
0 4000 000 12000 1G000 20000
Frequency !z"
(b) 0
#hase'eg"
*40
*0tot
*120
0 4000 000 12000 1G000 20000
Frequency !z"
Fig. (. 8e #a%nitude (a) and $ase (b) o, te earlobe i#$edance Mtot #easured &it te $ro$osed sensor (&it
insulatin% ,il#) and ac@uired &it an i#$edance anal!ser'
1'25 ,or&ard volta%e o, in,rared led- 250 A current re@uired b! te $ototransistor' A di%ital sco$e
ac@uisition o, te non*,iltered sensor out$ut (Co, .i%' 4(a)) is so&n in .i%' 7 te si%nal is raternois!- even tou% te eart beat is alread! distin*%uisable' A di%ital sco$e ac@uisition o, te
obtained PPK ,iltered si%nal (PPKo, .i%' 4(a)) is so&n in .i%' ' .ro# PPK- in,or#a*tion aboutbeat rate- stee$ness o, s!stole $ase- its a#$litude and $eriod- localiation o, Dicrotic notc andte $resence o, te
diastole $ase can be easil! obtained' A lo&*$o&er o$erational a#$li,ier (8e>as nstru#ents
L35- &it su$$l! current o, about 5 A- at 3'3 ) as been used ,or te active ,ilter i#$le#enta*
tion'
8e oscillation ,re@uenc! o, te Sc#idt 8ri%%er circuit o, .i%' 4(b) as been tuned bet&een 70;? and 100 ;?- to o$erateinside te o$ti#al res$onse band&idt o, te tissue i#$edance' 8ePrescaler as been i#$le#ented b! usin% an *bit di%ital counter- lo&erin% te oscillator out$ut
S8,re@uenc! o, a ,actor o, 25G te ,inal ,re@uenc! value is bet&een about 270 ? and 400 ?- in
accordance &it te re@uired band ,or te audio si%nal to be trans#itted H1I' A detail o, PPKand
#odulated PPK si%nal (+8 o, .i%' 4(b)) is so&n in.i%' ' .or tis sta%e- a 74?C14 Sc#idt
8ri%%er inte%rated circuit and a 74?C33 counter- bot ,ro# 8e>as nstru*#ents and $o&ered at3'3 - ave been used' 8e #odulation is acieved b! a si#$le 27002 *6S transistor'
All te co#$onents ave been selected in order to reduce sie and $o&er consu#$tion- tus
obtainin% a co#$act and lo&*$o&er device- suitable ,or batter!*$o&ered o$erations' Kloball!- te
s!s*te# re@uires less tan 45 #A at 3'3 - al#ost e@uall! distributed bet&een te +luetoot
ear$one and te analo% ,ront*end' 8e ear*$one batter! as a ca$acit! o, 50 #A- tus te
c!cle batter! li,e o, te overall s!ste# is a$$ro>i#atel! 70 #in'
8o validate te $ro$osed a$$roac and to $rovide an e>a#$le o, a$$lication ,or a $ortable
device- a de#onstrative A$$ as been develo$ed ,or an Android s#art$one' 8e A$$ tas;s are to
ac@uire- store- elaborate- and so& te sensor si%nals' Data ac@uisition is si#$li,ied b! te use o,
te +luetoot inter,ace ,unctions $rovided b! te s#art$one o$eratin% s!ste# ten- ra& data are
saved as audio ,iles (&ave ,or#at) in te s#art$one #e#or!- ,or an o$tional o,,*line $ost
elaboration' 8e $rocessin% o, data includes te de#odulation o, te ac@uired audio si%nal- in
order to e>tract in,or#ation o, te PPK si%nal sa$e and to te carrier $eriod- &ic is related to
te tissue i#$edance' oreover- a si#$le evaluation o, te eart beat rate is $er,or#ed' 6btained
data are ten visual*ied on te s#art$one screen- as illustrated b! a screensot o, te
develo$ed A$$ in .i%' 10'
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Fig. ). Di%ital sco$e ac@uisition o, te non*,iltered PPK sensor out$ut (Co,.i%' 4(a))'
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Fig. +. Di%ital sco$e ac@uisition o, te ,iltered (PPKo,.i%' 4(a)) and #odulated (+8o,.i%' 4(b)) PPK sensor out$ut'
A' De$ari et al' Sensors and Actuators A202 (2013) 147154 153
Fig. 1,. Screenshot of the demo App implemented for an Androidsmartphone.
Fig. 11. O-line elaboration of an acquired le during a test of thesystem.
4. -onclusions
on*invasive and real*ti#e #easure#ent o, $!sical $ara#e*ters
re@uires a si#$le- $ortable and lo& cost s!ste# able to collect te
in,or#ation &itout inter,erin% &it atletic trainin%' A s!s*te#
co#$osed o, a +luetoot ear$one e@ui$$ed &it a PPK and tissue
i#$edance sensors- to be a$$lied on te earlobe o, te at*lete- as
been $ro$osed' 8an;s to an e,,ective $rocessin% o, te sensor data-
an audio si%nal- suitable to be trans#itted &it +lue*toot ear$ones
o$eratin% &it te standard ?ands*.ree $ro,ile- can be obtained'
8ere,ore- a broad ran%e o, $ortable devices- suc as s#art$ones
and tablets- can be used to ac@uire te sensor si%*nal- ,or real*ti#e
$rocessin%- data visualiation- and user inter,ace' Data obtained ,ro#
te esti#ation o, te eart beat rate and te earlobe i#$edance can
be used to $rovide to te atlete real*ti#e in,or#ation concernin% te
res$onse o, te bod! to te ,ati%ue- tus allo&in% te# to ad"ust is
activit!- avoidin% ealt ris;s and to i#$rove is $er,or#ance' 8e
#ulti*sensor $rotot!$e described
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and caracteried in te $a$er- alon% &it a de#o a$$lication ,or an
Android s#art$one- ave de#onstrated te ,easibilit! o, te $ro*
$osed a$$roac- #onitorin% te cardiac si%nal and te variations o,
u#an tissue i#$edance due to $!sical e,,ort'
e/erences
!1br0ken!! C.M. De Dominicis D. Ma!!otti M. "iccinelli S.#inaldi A. $e!!oli A. Depari %&aluation of bluetoothhands-free prolefor sensors applications in smart-phone platforms in' "roceedings of(%%% Sensors Applications Symposium )SAS* +,+ pp. +,+/.
!2br0ken!! A. Depari A. 0lammini S. #inaldi A. $e!!oli Aportable multi-sensor system for non-in&asi&e measurement ofbiometrical data in' "roceedings %ngineer-ing +1th %uropeanConference on Solid-State 2ransducers %3#OS%4SO# +,+ &ol. 567ra8o9 "oland September :+ +,+ pp. ;+;;+1http'L 0.. Eart %lectric properties of tis-sues Hiley
%ncyclopedia of iomedical %ngineering )+,,1* +http'
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154 A' De$ari et al' Sensors and Actuators A 202 (2013) 147154
lessandra Flammini &as born in +rescia- tal!- in 1G0'Se received te 'Sc'de%ree (&it onours) in $!sics,ro# te niversit! o, /o#e- /o#e- tal!- in 15' .ro#15 to 15- se &as involved &it industrial researcand develo$#ent on di%ital drive control' Currentl!- se is&it te De$art#ent o, n,or#ation n%ineer*in%-niversit! o, +rescia- +rescia- tal!- &ere se &as a/esearcer ,ro# 15 to 2002 and as been an
Associate Pro,essor since 2002' Se teaces severalcourses about #easure#ents in industrial environ#ents
and di%ital electronic s!ste#s' ?er #ain researc activit!includes e#bedded s!ste#s- #easure#entinstru#entation- sensor si%nal $rocessin%- s#artsensors- &ired and &ireless sensor netin%- s!n*croniation and s#art %rids'
Ste/ano inaldi &as born in Seriate- tal!- in 12' ?e
received te de%ree &it onours in electronics
en%ineerin% in 200G and te P'D' de%ree in electronic
instru#entation in 2010 ,ro# te niversit! o, +rescia-+rescia- tal!' ?is #ain researc activities are ,ocused on$er,or#ance anal!sis o, industrial net- &irelesssensor net- s#art sensors- real*ti#e ternet-,ieldbus a$$lications- s!ncroniation #etods- .PKASoC desi%n- and Linu>*e#bedded so,t&are devel*o$#ent'
ngelo ezzoli &as born in Ciari in 13' ?e %raduatedin lectronics n%ineerin% at niversit! o, +rescia in2010 &it a tesis titled