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Sensors
(Chapter 2)
Sensor
chara
cte
ristics
Physic
al S
ensors
Resis
tive
Ca
pacitiv
e
Inductive
Pie
zoe
lectr
ic
Tem
pera
ture
Optical
Ch
em
ical
Bio
chem
ical
Sen
sor
is a
Tra
nsd
uce
r:
Wh
at i
s a
tran
sduce
r ?
A d
evic
e w
hic
h c
onver
ts o
ne
form
of
ener
gy t
o a
noth
er
Act
uat
ors
Sen
sors
Physi
cal
par
amet
er
Ele
ctri
cal
Outp
ut
Ele
ctri
cal
Input
Physi
cal
Outp
ut
e.g. P
iezo
elec
tric
:
Forc
e ->
volt
age
Volt
age-
> F
orc
e
=>
Ult
raso
und!
Sen
sor
Per
form
ance
Char
acte
rist
ics
Transfer Function:
Th
e fu
nct
ion
al r
elat
ion
ship
bet
wee
n p
hysi
cal
inp
ut
sig
nal
an
d e
lect
rica
l o
utp
ut
sig
nal
. U
sual
ly,
this
rel
atio
nsh
ip i
s re
pre
sen
ted
as
a g
rap
h s
ho
win
g t
he
rela
tio
nsh
ip b
etw
een
th
e in
pu
t an
d o
utp
ut
sig
nal
, an
d t
he
det
ails
of
this
rel
atio
nsh
ip m
ay c
on
stit
ute
a c
om
ple
te d
escr
ipti
on
of
the
sen
sor
char
acte
rist
ics.
Fo
r ex
pen
siv
e se
nso
rs w
hic
h a
re i
nd
ivid
ual
ly c
alib
rate
d,
this
mig
ht
tak
e th
e fo
rm
of
the
cert
ifie
d c
alib
rati
on
cu
rve.
Sensitivity:
Th
e se
nsi
tiv
ity i
s d
efin
ed i
n t
erm
s o
f th
e re
lati
onsh
ip b
etw
een
in
pu
t p
hysi
cal
sig
nal
an
d o
utp
ut
elec
tric
al s
ign
al.
Th
e se
nsi
tiv
ity
is
gen
eral
ly t
he
rati
o b
etw
een
a s
mal
l ch
ang
e in
ele
ctri
cal
sig
nal
to a
sm
all
chan
ge
in p
hysi
cal
sig
nal
. A
s su
ch, it
may
be
exp
ress
ed a
s th
e d
eriv
ativ
e o
f th
e tr
ansf
er
fun
ctio
n w
ith
res
pec
t to
ph
ysi
cal
sig
nal
. T
yp
ical
un
its
: Volts/Kelvin
. A
Th
erm
om
eter
wo
uld
hav
e "h
igh
sen
siti
vit
y"
if a
sm
all
tem
per
atu
re c
han
ge
resu
lted
in
a l
arg
e v
olt
age
chan
ge.
Span or Dynamic Range:
Th
e ra
ng
e o
f in
pu
t p
hysi
cal
sig
nal
s w
hic
h m
ay b
e co
nv
erte
d t
o e
lect
rica
l si
gn
als
by t
he
sen
sor.
Sig
nal
s o
uts
ide
of
this
ran
ge
are
exp
ecte
d t
o c
ause
un
acce
pta
bly
larg
e in
accu
racy
. T
his
sp
an o
r
dyn
am
ic r
ang
e is
usu
ally
sp
ecif
ied
by
th
e se
nso
r su
pp
lier
as
the
ran
ge
ov
er w
hic
h o
ther
per
form
ance
ch
arac
teri
stic
s d
escr
ibed
in
th
e d
ata
shee
ts a
re e
xp
ecte
d t
o a
pp
ly.
Sen
sor
Per
form
ance
Char
acte
rist
ics
Accuracy:
Gen
eral
ly d
efin
ed a
s th
e la
rges
t ex
pec
ted
err
or
bet
wee
n a
ctu
al a
nd
id
eal
ou
tpu
t si
gn
als.
Typ
ical
Un
its
: K
elv
in. S
om
etim
es t
his
is
qu
ote
d a
s a
frac
tio
n o
f th
e fu
ll s
cale
ou
tpu
t. F
or
exam
ple
, a
ther
mo
met
er m
igh
t b
e g
uar
ante
ed a
ccu
rate
to
wit
hin
5%
of
FS
O (
Fu
ll S
cale
Ou
tpu
t)
Hysteresis:
So
me
sen
sors
do
no
t re
turn
to
th
e sa
me
ou
tpu
t v
alu
e w
hen
th
e in
pu
t st
imu
lus
is c
ycl
ed u
p o
r
do
wn
. T
he
wid
th o
f th
e ex
pec
ted
err
or
in t
erm
s o
f th
e m
easu
red
qu
anti
ty i
s d
efin
ed a
s th
e
hyst
eres
is.
Typ
ical
un
its
: K
elv
in o
r %
of
FS
O
Nonlinearity (often called Linearity):
Th
e m
axim
um
dev
iati
on
fro
m a
lin
ear
tran
sfer
fu
nct
ion
ov
er t
he
spec
ifie
d d
yn
am
ic r
ang
e. T
her
e
are
sev
eral
mea
sure
s o
f th
is e
rro
r. T
he
mo
st c
om
mo
n c
om
par
es t
he
actu
al t
ran
sfer
fu
nct
ion
wit
h
the
`bes
t st
raig
ht
lin
e', w
hic
h l
ies
mid
way
bet
wee
n t
he
two
par
alle
l li
nes
wh
ich
en
com
pas
ses
the
enti
re t
ran
sfer
fu
nct
ion
ov
er t
he
spec
ifie
d d
yn
am
ic r
ang
e o
f th
ed
evic
e. T
his
ch
oic
e o
f
com
par
iso
n m
eth
od
is
po
pu
lar
bec
ause
it
mak
es m
ost
sen
sors
lo
ok
th
e b
est.
Sen
sor
Per
form
ance
Char
acte
rist
ics
Noise:
All
sen
sors
pro
du
ce s
om
e o
utp
ut
no
ise
in a
dd
itio
n t
o t
he
ou
tpu
t si
gn
al.
Th
e n
ois
e o
f th
e se
nso
r
lim
its
the
per
form
ance
of
the
syst
em
bas
ed o
n t
he
sen
sor.
No
ise
is g
ener
ally
dis
trib
ute
d a
cro
ss
the
freq
uen
cy s
pec
tru
m.
Man
y c
om
mo
n n
ois
e so
urc
es p
rod
uce
a w
hit
e n
ois
e d
istr
ibu
tio
n, w
hic
h
is t
o s
ay t
hat
th
e sp
ectr
al n
ois
e d
ensi
ty i
s th
e sa
me
at a
ll f
req
uen
cies
. S
ince
th
ere
is a
n i
nv
erse
rela
tio
nsh
ip b
etw
een
th
e b
and
wid
th a
nd
mea
sure
men
t ti
me,
it
can
be
said
th
at t
he
no
ise
dec
reas
es
wit
h t
he
squ
are
roo
t o
f th
e m
easu
rem
ent
tim
e.
Resolution:
Th
e re
solu
tio
n o
f a
sen
sor
is d
efin
ed a
s th
e m
inim
um
det
ecta
ble
sig
nal
flu
ctu
atio
n. S
ince
flu
ctu
atio
ns
are
tem
po
ral
ph
eno
men
a, t
her
e is
so
me
rela
tio
nsh
ip b
etw
een
th
e ti
mes
cale
fo
r th
e
flu
ctu
atio
n a
nd
th
e m
inim
um
det
ecta
ble
am
pli
tud
e. T
her
efo
re,
the
def
init
ion
of
reso
luti
on
mu
st
incl
ud
e so
me
info
rmat
ion
ab
ou
t th
e n
atu
re o
f th
e m
easu
rem
ent
bei
ng
car
ried
ou
t.
Bandwidth:
All
sen
sors
hav
e fi
nit
e re
spo
nse
tim
es
to a
n i
nst
anta
neo
us
chan
ge
in p
hysi
cal
sig
nal
. In
ad
dit
ion
,
man
y s
enso
rs h
ave
dec
ay t
imes
, w
hic
h w
ou
ld r
epre
sen
t th
e ti
me
afte
r a
step
ch
ang
e in
ph
ysi
cal
sig
nal
fo
r th
e se
nso
r o
utp
ut
to d
ecay
to
its
ori
gin
al v
alu
e. T
he
reci
pro
cal
of
thes
e ti
mes
corr
esp
on
d t
o t
he
up
per
an
d l
ow
er c
uto
ff f
req
uen
cies
, re
spec
tiv
ely.
Th
e b
and
wid
th o
f a
sen
sor
is
the
freq
uen
cy r
ang
e b
etw
een
th
ese
two
fre
qu
enci
es.
Ph
ysi
cal
Sen
sors
•B
lood f
low
/blo
od
pre
ssure
•Im
pac
t, a
ccel
erat
ion
•S
urg
ical
forc
eps
to
mea
sure
forc
e ap
pli
ed
•Air
bag
•B
ody
tem
per
ature
Bio
med
ical
Ph
ysi
cal
Sen
sors •P
acem
aker
•A
irbag
Res
isti
ve
Sen
sors
-P
ote
nti
om
eter
s
Translationaland Rotational
Potentiometers
Tra
nsl
atio
nal
or
ang
ula
r d
ispla
cem
ent
is p
rop
ort
ion
al t
o r
esis
tan
ce.
Tak
en f
rom
ww
w.f
ysl
ab.h
ut.
fi/k
urs
sit/
Tfy
-3.4
41
/lu
enn
ot/
Lu
ento
3.p
df
Res
isti
ve
Sen
sors
-S
trai
n G
uag
es
Res
ista
nce
is
rela
ted t
o l
ength
and a
rea
of
cross
-sec
tion o
f
the
resi
stor
and r
esis
tivit
yof
the
mat
eria
l as
By t
akin
g l
ogar
ithm
s an
d d
iffe
renti
atin
g b
oth
sid
es, th
e
equat
ion b
ecom
es
Dim
ensi
onal
pie
zore
sist
ance
Str
ain g
age
com
ponen
t ca
n b
e re
late
d b
y p
ois
son’s
rati
o a
s
Res
isti
ve
Sen
sors
-S
trai
n G
uag
es
Gage Factor of a strain gage
G i
s a
mea
sure
of
sensi
tiv
ity
Thin
k o
f th
is a
s a
Tra
nsf
er F
unct
ion!
⇒In
put
is s
trai
n
⇒O
utp
ut
is d
R
⇒P
ut
mer
cury
str
ain g
auge
around a
n a
rm o
r ch
est
to m
easu
re
forc
e of
musc
le c
ontr
acti
on o
r re
spir
atio
n, re
spec
tivel
y
⇒U
sed i
n p
rost
hes
is o
r neo
nat
al a
pnea
det
ecti
on, re
spec
tivel
y
Res
isti
ve
Sen
sors
-S
trai
n G
uag
es
Str
ain
gag
es a
re g
ener
ally
mo
unte
d o
n c
anti
lev
ers
and
dia
ph
rag
ms
and
mea
sure
th
e d
efle
ctio
n o
f th
ese.
More
th
an o
ne
stra
in g
age
is g
ener
ally
use
d a
nd t
he
read
ou
t g
ener
ally
emp
loys
a bri
dg
e ci
rcu
it.
Str
ain
Gag
e M
oun
tin
g
Tak
en f
rom
htt
p:/
/ww
w.o
meg
a.co
m/l
iter
ature
/tra
nsa
ctio
ns/
volu
me3
/str
ain3.h
tml
Appli
cati
ons!
⇒S
urg
ical
forc
eps
⇒B
lood p
ress
ure
tran
sduce
r (e
.g.
intr
acra
nia
l
pre
ssure
Bri
dg
e C
ircu
its
Wh
eats
ton
e’s
Bri
dg
e
R-d
RR
+dR
R
Rf
Vs
R
Vo
Rea
l C
ircu
it a
nd
Sen
sor
Inte
rfac
e
Induct
ive
Sen
sors
An i
nduct
or
is b
asic
ally
a
coil
of
wir
e over
a “
core
”
(usu
ally
fer
rous)
It r
esponds
to e
lect
ric
or
mag
net
ic f
ield
s
A t
ransf
orm
er i
s m
ade
of
at
leas
t tw
o c
oil
s w
ound o
ver
the
core
: one
is p
rim
ary a
nd
anoth
er i
s se
condar
y
Pri
mar
y S
econdar
yD
ispla
cem
ent
Sen
sor
Inductors and tranformers work only for ac signals
Induct
ive
Sen
sors
-L
VD
T
LV
DT
Lin
ear
Var
iable
Dif
fere
nti
al T
ran
sfo
rmer
Tak
en f
rom
htt
p:/
/ww
w.p
ages
.dre
xel
.edu/~
pyo22/m
em351-2
004/l
ectu
re04/p
p062-0
73lv
dt.
An L
VD
T i
s use
d a
s a
sensi
tive
dis
pla
cem
ent
senso
r: f
or
exam
ple
,in
a c
ardia
c as
sist
dev
ice
or
a bas
ic r
esea
rch p
roje
ct t
o s
tudy
dis
pla
cem
ent
pro
duce
d b
y a
contr
acti
ng m
usc
le.
Cap
acit
ive
Sen
sors e.
g. A
n e
lect
roly
tic
capac
itor
is m
ade
of
Alu
min
um
evap
ora
ted o
n
eith
er s
ide
of
a
ver
y t
hin
pla
stic
film
(or
elec
troly
te)
Ele
ctro
lyti
c or
cera
mic
cap
acit
ors
are
most
com
mon
Cap
acit
ive
Sen
sors
Other Configurations
c. D
iffe
ren
tial
Mo
de
b.
Var
iab
le D
iele
ctri
c M
ode
a. V
aria
ble
Are
a M
od
e
Pie
zoel
ectr
ic S
enso
rs
What is piezoelectricity ? Str
ain
cau
ses
a
red
istr
ibu
tio
n o
f ch
arg
es
and
res
ult
s in
a n
et
elec
tric
dip
ole
(a
dip
ole
is k
ind
of
a bat
tery
!)
A p
iezo
elec
tric
mat
eria
l
pro
du
ces
vo
ltag
e by
dis
trib
uti
ng
ch
arg
e
(un
der
mec
han
ical
stra
in/s
tres
s)
Dif
fere
nt
tran
sduce
r ap
pli
cati
ons:
⇒A
ccel
erom
eter
⇒M
icro
phone
Pie
zoel
ectr
ic S
enso
rs
Above
equat
ions
are
val
id w
hen
forc
e is
appli
ed i
n t
he
L,W
or
t dir
ecti
ons
resp
ecti
vel
y.
31
den
ote
s th
e
cryst
al a
xis
Pie
zoel
ectr
ic S
enso
rs -
Cir
cuit
ry
The Equivalent Circuit
Tak
en f
rom
Web
ster
, “M
edic
al I
nst
rum
enta
tion
”
Tem
per
atu
re S
enso
rs
1.
Res
ista
nce
bas
ed
a. R
esis
tance
Tem
per
ature
Dev
ices
(R
TD
s)
b. T
her
mis
tors
2.
Ther
moel
ectr
ic –
Ther
moco
uple
s
3.
Rad
iati
on T
her
mo
met
ry
4.
Fib
er O
pti
c S
enso
r
RT
Ds
RT
Ds
are
mad
e of
mat
eria
ls w
hose
res
ista
nce
chan
ges
in
acco
rdan
ce w
ith t
emper
ature
Met
als
such
as
pla
tinum
, nic
kel
and c
opper
are
com
monly
use
d.
They
exhib
it a
posi
tive
tem
per
ature
coef
fici
ent.
A c
om
mer
cial
Th
erm
oW
ork
s R
TD
pro
be
Th
erm
isto
rs
Ther
mis
tors
are
mad
e fr
om
sem
iconduct
or
mat
eria
l.
Gen
eral
ly, th
ey h
ave
a neg
ativ
e
tem
per
ature
coef
fici
ent
(NT
C),
that
is
NT
C
ther
mis
tors
are
most
com
monly
use
d.
Ro i
s th
e re
sist
ance
at
a re
fere
nce
poin
t (i
n t
he
lim
it, ab
solu
te 0
).
Th
erm
oco
up
les
Seebeck Effect
When
a p
air
of
dis
sim
ilar
met
als
are
join
ed a
t one
end, an
d t
her
e is
a
tem
per
ature
dif
fere
nce
bet
wee
n t
he
join
ed e
nds
and t
he
open
ends,
ther
mal
em
fis
gen
erat
ed, w
hic
h c
an b
e m
easu
red i
n t
he
open
ends.
This
form
s th
e bas
is o
f th
erm
oco
uple
s.
Th
erm
oco
up
les
Tak
en f
rom
Web
ster
, “M
edic
al I
nst
rum
enta
tion
”
Rad
iati
on T
her
mom
etry
Gover
ned
by W
ien’s
Dis
pla
cem
ent
Law
whic
h s
ays
that
at
the
pea
k o
f th
e em
itte
d r
adia
nt
flux p
er u
nit
are
a per
unit
wav
elen
gth
occ
urs
when
maxT=2.898x10-3m
oK
Tak
en f
rom
htt
p:/
/hy
per
phy
sics
.phy
-ast
r.gsu
.edu/h
bas
e/w
ien.h
tml#
c2
Fib
er O
pti
cs
A f
iber
opti
c ca
ble
Mo
st o
f th
e li
gh
t is
tra
pp
ed i
n t
he
core
, bu
t if
the
clad
din
g i
s te
mp
erat
ure
sen
siti
ve
(e.g
. d
ue
to e
xp
ansi
on),
it
mig
ht
allo
w s
om
e li
gh
t to
lea
k
thro
ug
h.
-> h
ence
th
e am
ou
nt
of
ligh
t tr
ansm
itte
d w
ou
ld
be
pro
po
rtio
nal
to t
emp
erat
ure
-> s
ince
you
are
mea
suri
ng
sm
all
chan
ges
in
ligh
t le
vel
, th
is s
enso
r is
exquis
itel
y s
ensi
tive.
Fib
er O
pti
csB
ased
on Total Internal Reflection
Tak
en f
rom
htt
p:/
/hyp
erp
hysi
cs.p
hy-a
str.
gsu
.ed
u/h
bas
e/p
hyo
pt/
toti
nt.
htm
l#c1
Fib
er O
pti
c T
emp
erat
ure
Sen
sors
Nort
ech's
fiber
-opti
c te
mper
ature
sen
sor
pro
be
consi
sts
of
a gal
lium
arse
nid
ecr
yst
al a
nd a
die
lect
ric
mir
ror
on o
ne
end o
f an
opti
cal
fiber
and a
sta
inle
ssst
eel
connec
tor
at t
he
oth
er e
nd.
Tak
en f
rom
htt
p:/
/ww
w.s
enso
rsm
ag.c
om
/art
icle
s/0
50
1/5
7/m
ain
.sh
tml
Oth
er P
hy
sica
l S
enso
rs
Photo
emis
sive
senso
rs
Photo
conduct
ive
senso
rs (
LD
Rs)
Photo
volt
aic
senso
rs
Ch
emic
al S
enso
rs (
Bio
senso
rs)
Bio
senso
rs p
roduce
an o
utp
ut
(ele
ctri
cal)
whic
h i
s pro
port
ional
to t
he
conce
ntr
atio
n o
f bio
logic
al a
nal
yte
s.
A t
ypic
al b
iose
nso
r
Sig
nal
Condit
ionin
gA
nal
yte
Bio
logic
al
Det
ecti
on
Agen
t
Tra
nsd
uce
r
Bio
sensi
ng
Pri
nci
ple
s
•E
lect
roch
emic
al
–P
ote
nti
om
etri
c
–A
mper
om
etri
c
–F
ET
bas
ed
–C
onduct
om
etri
c
•O
pti
cal
•P
iezo
elec
tric
•T
her
mal
=>
Neu
roch
emic
alse
nso
r fo
r D
op
amin
e, N
itri
c O
xid
e, e
tc.
=>
Pu
lse
ox
imet
er
=>
Acc
eler
om
eter
,
m
icro
phon
e
=>
Im
pla
nte
d r
ecta
l p
robe,
pac
emak
er
Bio
sensi
ng
Pri
nci
ple
s
Ele
ctro
chem
ical
Sen
sors
Potentiometric
: T
hese involv
e the m
easure
ment of th
eem
f(p
ote
ntial)
of
a c
ell
at zero
curr
ent. T
he
em
fis
pro
port
ional to
th
e logarith
m o
f th
e
concentr
ation o
f th
e s
ubsta
nce b
ein
g d
ete
rmin
ed.
Amperometric: A
n incre
asin
g (
decre
asin
g)
pote
ntial is
applie
d to the
cell
until oxid
ation (
reduction)
of th
e s
ubsta
nce to b
e a
naly
zed
occurs
and there
is a
sharp
ris
e (
fall)
in the c
urr
ent to
giv
e a
peak c
urr
ent. T
he
heig
ht of th
e p
eak c
urr
ent is
directly p
roport
ional to
the c
oncentr
ation o
f
the e
lectr
oactive
mate
rial. If th
e a
ppro
priate
oxid
ation (
reduction)
pote
ntial is
know
n, one m
ay s
tep the p
ote
ntial directly to that valu
e a
nd
observ
e the c
urr
ent.
Conductometric
. M
ost re
actions involv
e a
change in the c
om
positio
n o
f
the s
olu
tion. T
his
will
norm
ally
result in a
change
in the e
lectr
ical
conductivity o
f th
e s
olu
tion, w
hic
h c
an b
e m
easure
d e
lectr
ically
.
Blo
od
Gas
Mea
sure
men
t
Fas
t an
d a
ccura
te m
easu
rem
ents
of
the
blo
od l
evel
s of
the
par
tial
pre
ssure
s of
oxygen
(pO
2),
car
bon d
ioxid
e (p
CO
2)
as w
ell
as t
he
conce
ntr
atio
n o
f hydro
gen
ions
(pH
) ar
e vit
al i
n d
iagnosi
s.
Oxygen
is
mea
sure
d i
ndir
ectl
y a
s a
per
centa
ge
of
Hae
moglo
bin
whic
h i
s co
mbin
ed w
ith o
xygen
(sO
2)
[]
[]
sOHbO
Hb
2
2100
=×
pO
2ca
n a
lso p
rovid
e th
e ab
ove
val
ue
usi
ng t
he
oxyhae
moglo
bin
dis
soci
atio
n c
urv
e but
is a
poor
esti
mat
e.
pH
ele
ctro
de
Gover
nin
g e
quat
ion i
s th
e N
ernst
Equat
ion
[]
[]
ERT
nF
H HH
i
=
ln
0
pC
O2
Ele
ctro
de
The
mea
sure
men
t of
pC
O2
is b
ased
on i
ts l
inea
r re
lati
onsh
ip
wit
h p
H o
ver
the
range
of
10 t
o 9
0 m
m H
g.
HO
CO
HCO
HHCO
22
23
3+
⇔⇔
++
−
The
dis
soci
atio
n c
onst
ant
is g
iven
by
[] [
]k
HHCO
apCO
=⋅
+−
3
2
Tak
ing l
ogar
ithm
s
pH
= l
og[H
CO
3- ]
–lo
g k
–lo
g a
–lo
g p
CO
2
pO
2el
ectr
ode
The
pO
2el
ectr
ode
consi
sts
of
a pla
tinum
cat
hode
and a
Ag/A
gC
l re
fere
nce
ele
ctro
de.
Op
tica
l B
iose
nso
rs
Sensing Principle
They lin
k c
han
ges in lig
ht
inte
nsity to c
hang
es in m
ass
or
concentr
ation,
hence, fluore
scent
or
colo
rim
etr
ic
mole
cu
les m
ust
be p
resent.
Var
ious
pri
nci
ple
s
and m
ethods
are
use
d :
Optical fibre
s,
surf
ace
pla
sm
on
resona
nce,A
bsorb
ance,
Lum
inesce
nce
LE
D
Photo
det
ecto
r
Fin
ger
IR
light
Fib
er O
pti
c B
iose
nso
r
Bal
loon
Ther
mis
tor
Lig
ht
tran
smit
ter
Rec
eiver
/
refl
ecte
d
light
Intr
aven
tric
ula
r
Fib
er o
pti
c ca
thet
er
Ab
sorp
tion
/Flu
ore
scen
ce
Dif
fere
nt
dyes
show
pea
ks
of
dif
fere
nt
val
ues
at
dif
fere
nt
conce
ntr
atio
ns
when
the
abso
rban
ce o
r ex
cita
tion i
s plo
tted
agai
nst
wav
elen
gth
.
Phen
ol
Red
is
a pH
sen
siti
ve
rever
sible
dye
whose
rel
ativ
e
abso
rban
ce (
indic
ated
by r
atio
of
gre
en a
nd r
ed l
ight
tran
smit
ted)
is u
sed t
o m
easu
re p
H.
HP
TS
is
an i
rrev
ersi
ble
flu
ore
scen
t dye
use
d t
o m
easu
re p
H.
Sim
ilar
ly, th
ere
are
fluore
scen
t dyes
whic
h c
an b
e use
d t
o
mea
sure
O2
and C
O2
level
s.
Pu
lse
Ox
imet
ry
Tw
o w
avele
ngth
s o
f m
onochro
matic lig
ht
--re
d (
660 n
m)
and infr
are
d
(940 n
m)
--are
used t
o g
auge t
he p
resence o
f oxygenate
d a
nd r
educed
hem
oglo
bin
in b
lood. W
ith e
ach p
uls
e b
eat
the d
evic
e inte
rpre
ts t
he
ratio o
f th
e p
uls
e-a
dded r
ed a
bsorb
ance t
o t
he p
uls
e-a
dded infr
are
d
absorb
ance. The c
alc
ula
tion r
equires p
revio
usly
dete
rmin
ed c
alibra
tion
curv
es t
hat
rela
tetr
anscuta
neous
light
absorp
tion t
o s
O2.
The p
uls
eoxim
ete
ris
aspectr
ophoto
metr
icdevic
e
that
dete
cts
and c
alc
ula
tes
the d
iffe
rential absorp
tion
of light
by o
xygenate
d a
nd
reduced h
em
oglo
bin
to g
et
sO
2. A lig
ht
sourc
e a
nd a
photo
dete
cto
rare
conta
ined w
ithin
an e
ar
or
finger
pro
be for
easy
application.
Glu
cose
Sen
sors
Enzymatic Approach
Glu
eO
GluconicAcid
HO
Glu
eOxidase
cos
cos
+
→
+2
22
Mak
es u
se o
f ca
taly
tic
(enzy
mat
ic)
oxid
atio
n o
f glu
cose
The
setu
p c
onta
ins
an e
nzy
me
elec
trode
and a
n o
xygen
ele
ctro
de
and t
he
dif
fere
nce
in t
he
read
ings
indic
ates
the
glu
cose
lev
el.
The
enzy
me
elec
trode
has
glu
cose
oxid
ase
imm
obil
ized
on a
mem
bra
ne
or
a gel
mat
rix.
Platinum
electrode
Plastic
membrane
Glu
cose
O2G
luco
nic
acid Silver
anode
Glu
cose
Sen
sor
Affinity Approach
This
appro
ach i
s bas
ed o
n t
he
imm
obil
ized
com
pet
itiv
e
bin
din
g o
f a
par
ticu
lar
met
aboli
te (
glu
cose
) an
d i
ts
asso
ciat
ed f
luore
scen
t la
bel
wit
h r
ecep
tor
site
s sp
ecif
ic t
o
the
met
aboli
te (
glu
cose
) an
d
the
label
ed l
igan
d. T
his
chan
ge
in l
ight
inte
nsi
ty i
s
then
pic
ked
up.
3 m
m
0.3
mm
Holl
ow
dia
lysi
s fi
ber
Imm
obil
ized
Con A
Ex
cita
tati
on
Em
issi
on
Opti
cal
Fib
er
Glu
cose
Pro
ble
m (
1)
(a)
Des
crib
e a
senso
r or
a m
easu
rem
ent
syst
em i
n w
hic
h accuracy
is i
mp
ort
ant.
In
contr
ast,
des
crib
e a
sen
sor
or
a m
easu
rem
ent
in w
hic
h precision
is i
mpo
rtan
t.
(b)
A t
emp
erat
ure
sen
sor,
su
ch a
s a
ther
mis
tor
can
be
des
crib
ed b
y a
fir
st o
rder
syst
em. W
rite
dow
n t
he
gen
eral
equ
atio
n f
or
a fi
rst
ord
er s
yst
em(y
ou c
an w
rite
a
dif
fere
nti
al e
quat
ion
or
a tr
ansf
er f
un
ctio
n).
Plo
t th
e o
utp
ut
of
the
firs
t ord
er s
yst
em i
n r
espo
nse
to
a s
tep
ch
ang
e in
tem
per
ature
.
A b
loo
d p
ress
ure
sen
sor
is d
escr
ibed
by a
sec
ond
ord
er s
yst
em.
W
rite
do
wn
th
e
gen
eral
equ
atio
n f
or
a se
con
d o
rder
syst
em (
yo
u c
an w
rite
a d
iffe
ren
tial
equ
atio
n
or
a tr
ansf
er f
un
ctio
n).
Plo
t th
e o
utp
ut
of
the
seco
nd
ord
er underdamped
pre
ssure
syst
em i
n r
esp
on
se t
o
a b
loo
d p
ress
ure
sig
nal
.
Pro
ble
m (
2)
We
wou
ld l
ike
to m
easu
re s
mal
l
tem
per
ature
chan
ges
usi
ng
a t
her
mis
tor.
Th
erm
isto
ris
a r
esis
tor
wh
ich
ch
ang
es i
ts
resi
stan
ce i
n p
roport
ion t
o t
emp
erat
ure
. (i
)
Fir
st, su
gg
est
a su
itab
le b
iom
edic
al
appli
cati
on o
f th
e th
erm
isto
r. (
ii)
A u
sefu
l
des
ign
is
to p
ut
the
ther
mis
tor
in a
bri
dg
e
circ
uit
des
ign
. C
alcu
late
th
e ou
tpu
t of
the
foll
ow
ing
cir
cuit
for
a v
ery s
mal
l d
R
chan
ges
wit
h r
esp
ect
to t
he
R v
alu
es o
f
the
bri
dg
e el
emen
ts (
ther
e ar
e tw
o
senso
rs, o
ne’
s re
sist
ance
goes
up
wh
ile
the
oth
er g
oes
dow
n).
H
int:
Th
e o
utp
ut
sho
uld
be
a re
lati
on
ship
bet
wee
n V
s, R
,
dR
, R
fan
d V
o.
R-d
RR
+dR
R
Rf
Vs
R
Vo
Pro
ble
m (
3)
centr
al b
od
y t
emp
erat
ure
ver
y a
ccu
rate
ly. T
wo a
ppli
cati
ons
are
pro
pose
d:
ii)
mea
sure
the
tem
per
ature
ch
ang
e in
a r
ate
resp
onsi
ve
impla
nta
ble
pac
emak
er
(so
th
at e
xer
cise
dep
end
ent
chan
ges
in
th
e te
mp
erat
ure
can
be
use
d t
o a
lter
th
e
pac
ing r
ate)
.
the
ben
efit
s an
d p
rob
lem
s o
f yo
ur
des
ign
so
luti
on
. S
pec
ific
ally
, w
hy d
id y
ou
sel
ecte
d t
hat
par
ticu
lar
sen
sor,
wh
at s
hou
ld b
e it
s
per
form
ance
/sp
ecif
icat
ion
, an
d w
hat
are
its
ben
efit
s an
d d
isad
van
tag
es.
An
op
tica
l sy
stem
is
use
d i
n a
“sm
art
can
e”to
det
ect
and
war
n o
f an
ob
stac
le.
Dra
w t
he
CIR
CU
IT o
f a
light
sourc
e an
d a
pho
tod
etec
tor
for
this
pro
ject
.
Pro
ble
m (
4)
You
are
ask
ed t
o r
ecord
mag
net
ic f
ield
fro
m t
he
bra
in.
No
w,
bra
in’s
mag
net
ic f
ield
is
10
e-1
5 T
esla
as
oppo
sed
to
ear
th’s
fie
ld w
hic
h i
s 10
e-7
Tes
la. W
hat
kin
d o
f se
nso
r w
ould
you
use
to r
ecord
bra
in’s
mag
net
ic f
ield
(no
w, I
real
ize
that
th
is i
s a
lon
g s
hot
–b
ut
just
may
be,
you
co
uld
fig
ure
th
is
out)
? W
hat
pre
cau
tio
ns
wou
ld y
ou
tak
e to
rec
ord
this
ver
y s
mal
lm
agn
etic
fiel
d f
rom
th
e b
rain
in
pre
sence
of
oth
er i
nte
rfer
ence
?
Wh
at i
nst
rum
ent
is u
sed
to
mea
sure
th
e m
agn
etic
fie
ld f
rom
th
e bra
in? B
)
Wh
at a
re t
he
po
ssib
le a
dv
anta
ges
and
dis
advan
tag
es o
f th
e m
agn
etic
ver
sus
elec
tric
al m
easu
rem
ent?
C
) T
o y
our
kno
wle
dg
e, w
hat
bre
akth
rou
gh
s in
the
scie
nti
fic
worl
d t
hat
hav
e ar
e o
ccurr
ed (
or
ou
gh
t to
occ
ur?
) th
at w
ou
ld m
ake
mag
net
ic f
ield
mea
sure
men
t m
ore
fea
sib
le a
nd a
fford
able
? D
) If
yo
u h
ad a
chea
p m
agn
etic
fie
ld s
enso
r (w
ith a
rel
ativ
ely l
ow
er s
ensi
tiv
ity)
avai
lab
le
wh
at o
ther
bio
med
ical
app
lica
tion
wou
ld y
ou
th
ink o
f (o
ther
th
an
bio
po
ten
tial
mea
sure
men
ts).
Pro
ble
m (
5)
Des
crib
e on
e “i
nn
ov
ativ
e”se
nso
r an
d m
atch
ing
in
stru
men
tati
on
fo
r re
cord
ing
bre
athin
g o
r re
spir
atio
n. T
he
appli
cati
ons
mig
ht
be
resp
irom
etry
/sp
iro
met
ry,
ath
elet
sk
no
win
g w
hat
th
eir
hea
rt r
ate
is, p
aral
yze
d i
ndiv
idu
als
who
hav
e
dif
ficu
lty b
reat
hin
g n
eed
ing a
res
pir
atory
sen
sor
to s
tim
ula
te a
nd
co
ntr
ol
phre
nic
ner
ve.
Y
ou
may
sel
ect
on
e of
thes
e o
r oth
er a
pp
lica
tion
s, a
nd t
hen
iden
tify
a s
uit
able
sen
sor.
The
des
ign
(d
evel
op
su
itab
le c
ircu
it)
for
inte
rfac
ing
to t
he
sen
sor
to g
et r
espir
atory
sig
nal
.
Des
ign
and
dra
w a
sm
all
circ
uit
to
det
ect
the
hea
rt b
eat
pu
lse
(do
no
t dra
w o
r
des
ign
EC
G a
mp
lifi
er)
and
pu
lse
bas
ed o
xyg
enat
ion
. C
om
e up
wit
h a
su
itab
le
senso
r an
d i
nte
rfac
e el
ectr
on
ics.
Giv
e on
ly t
he
puls
e d
etec
tion
cir
cuit
. N
ow
,
sear
ch a
nd
rev
iew
a)
com
mer
cial
pu
lse
and o
xim
eter
des
ign
co
nce
pts
, b)
loca
te
som
e p
aten
ts,
and c
) p
ub
lica
tio
ns
in t
he
pas
t fe
w y
ear
on
the
subje
ct.
