TELK
OMNIKA
Indonesian
Journal
of
Electrical
Engineering
V
ol.
12,
No
.
10,
October
l
2014,
pp
.
7214
7222
DOI:
10.11591/telk
omnika.v12.i10.6576
7214
Loc
k-in
Amplifier
as
a
Sensitive
Instrument
f
or
Biomedical
Measurement
:
Anal
ysis
and
Implementation
Y
.Abd
Dja
wad*
1
,
J
.
Kiel
y
2
,
P
.
Wraith
2
,
and
R.
Luxton
2
1
State
Univ
ersity
of
Makassar
,
Indonesia
2
Univ
ersity
of
the
W
est
of
England,
United
Kingdom
Jl.
AP
P
ettar
ani,
Makassar
,
Indonesia,
telp:0411-865894
*Corresponding
author
,
e-mail:
y
asser
.dja
w
ad@unm.ac.id
Abstract
A
measur
ing
instr
ument
pla
ys
impor
tant
role
in
the
biomedical
measurement
since
the
biological
process
in
living
organism
gener
ates
v
er
y
w
eak
signal.
Theref
ore
,
a
reliab
le
and
sensitiv
e
measur
ing
in-
str
ument
is
needed.
In
this
study
,
a
loc
k-in
amplifier
w
as
analysed
and
tested.
This
paper
presents
an
e
xper
iment
to
in
v
estigate
the
loc
k-in
amplifier
f
or
biomedical
measurement.
An
e
xper
im
ent
using
RC
(re-
sistor
capacitor)
tissue
model
to
measure
the
v
oltage
cha
nge
related
to
impedance
change
w
as
perf
or
med
using
a
loc
k-in
amplifier
to
e
v
aluate
the
accur
acy
of
the
loc
k-in
amplifier
.
Three
diff
erent
v
alues
of
the
capac-
itor
in
the
RC
tissue
model
w
ere
applied
regarding
to
sim
ulate
small
impedance
changes
.
The
measurement
results
w
ere
compared
with
the
theoretical
calculation
and
an
impedance
measurement
system.
An
error
analysis
w
as
conducted
to
in
v
estigate
the
accur
acy
of
the
measurement.
The
compar
ison
result
sho
w
ed
that
impedance
measurement
usin
g
loc
k-in
amplifier
is
an
eff
ectiv
e
technique
,
which
could
ab
le
to
measure
v
er
y
small
v
oltage
regarding
impedance
change
in
the
RC
tissue
model.
K
e
yw
or
ds:
biomedical,
RC
tissue
model,
impedance
measurement,
loc
k-in
amplifier
Cop
yright
c
2014
Institute
of
Ad
v
anced
Engineering
and
Science
.
All
rights
reser
v
ed.
1.
Intr
oduction
A
Loc
k-in
Amplifier
(LIA)
is
a
measur
ing
instr
ument
that
measures
a
signal
which
has
similar
frequency
and
phase
as
the
ref
erence
signal.
The
LIA
can
be
used
to
measure
a
v
er
y
small
signal
(nano
v
olts)
and
is
ab
le
to
ignore
an
y
signals
that
are
not
synchroniz
ed
with
it,
which
ma
y
be
a
thousand
times
larger
.
The
LIA
consists
of
5
b
loc
ks;
a
signal
amplifier
,
a
p
hase
shifter
to
pro
vide
a
ref
er
ence
signal,
a
phase
sensitiv
e
detector
(PSD)
or
m
ultiplier
,
a
lo
w
pass
filter
(LPF)
and
a
DC
amplifier
,
as
sho
wn
in
Figure
1.
An
input
signal
is
connected
to
the
amplifier
.
A
second
signal
is
connected
to
the
phase
shifter
as
a
ref
erence
signal.
The
output
is
a
DC
v
oltage
which
is
propor
tional
to
the
amplitude
of
the
signal
being
measured.
The
ref
erence
signal
m
ust
be
similar
to
the
source
signal
to
”loc
k”
the
signal
to
the
frequency
of
interest.
The
LIA
has
been
used
in
man
y
applications
such
as
measurement
of
signal
to
noise
r
atio
of
photother
mal
signals
[1],
chem-
istr
y
e
xper
iments
using
diode
laser
[2],
in
a
r
ing
laser
gyroscope
[3]
and
nanoelectromechanical
systems
[4].
In
biomedical
resea
rch,
the
LIA
is
usually
used
in
Impedance
spectroscop
y
(IS)
technique
.
IS
is
a
char
acter
ization
method
of
mater
ials
to
obtain
its
electr
ical
proper
ties
using
electrodes
[5].
IS
can
be
divided
into
tw
o
categor
ies
,
electrochemical
impedance
spectrosco
p
y
(EIS)
and
other
techniques
.
EIS
engages
measurement
and
analysis
of
ionic
conduction
in
the
mater
ial.
EIS
is
used
also
to
study
of
fuel
cells
,
rechargeab
le
batter
ies
,
and
corrosion.
The
resting
categor
y
of
impedance
spectroscop
y
is
applied
to
study
electr
ical
char
acter
istic
of
die
lectr
ic
mater
ial,
solid
or
liquid
non
conductors
,
in
which
electr
onic
conduction
strongly
in
the
major
ity[6].
IS
has
been
also
applied
in
biomedical
research
areas
[7,
8,
9,
10,
11].
IS
nor
mally
in
v
olv
es
tw
o
electrodes
,
counter
electrode
(CE)
and
detecting
electrode
(DE).
The
sensor
detects
the
chang
e
of
resistance
Receiv
ed
J
une
19,
2014;
Re
vised
A
ugust
3,
2014;
Accepted
A
ugust
18,
2014
Evaluation Warning : The document was created with Spire.PDF for Python.
TELK
OMNIKA
ISSN:
2302-4046
7215
hi
gh
p
ass
filter
ph
ase
sh
ift
e
r
A
C am
p
li
f
i
er
P
S
D
lo
w pa
ss
filter
DC
a
m
pl
ifie
r
V
in
(t)
V
r
ef
(t)
V
ac(
t)
V
psd
(t)
V
out
(t)
Figure
1.
Bloc
k
diag
r
am
of
loc
k-in
amplifier
that
consists
of
signal
amplifier
,
phase
shifter
,
PSD
and
lo
w
pass
filter
and
capacitance
of
the
mater
ial
abo
v
e
or
betw
een
the
sensor
.
The
basic
idea
is
to
apply
an
input
signal
via
CE
and
gather
the
result
on
DE.
These
tw
o
electrodes
with
cer
tain
dista
nce
beha
v
es
lik
e
a
capacitor
when
small
A
C
v
oltage
applied
to
the
sensor
.
Signals
with
a
r
ange
frequency
are
applied
to
the
circuit
to
analyse
the
char
acter
istics
of
the
mater
ial.
An
e
xample
of
de
v
eloped
of
IS
technique
is
Electr
ic
Cell-substr
ate
Impedance
Sensing
(ECIS).
The
technique
pro
vides
a
v
er
y
useful
and
elegant
approach
f
or
the
study
of
cell
spreading,
mor
phology
and
micromotion.
Thef
ore
,
ECIS
could
be
used
f
or
dr
ug
screening
and
to
xicology
studies
in
the
animal
testing
[12].
The
pr
inciple
of
ECIS
is
based
on
Ohm’
s
la
w
that
the
adhered
cell
can
be
treated
as
an
equiv
alent
of
an
RC
circuit.
ECIS
uses
electrodes
that
are
coated
b
y
protein
to
pro
vide
a
surf
ace
f
or
cell
attachment
and
spreading.
When
t
he
cells
begin
to
spread
on
the
electrode
surf
ace
,
the
cell
la
y
er
star
ts
to
aff
ect
the
electromagnetic
field
betw
een
the
tw
o
electrodes
since
the
adhere
d
cells
beha
v
e
lik
e
insulating
par
ticles
due
to
their
plasma
membr
ane
[13].
This
small
electromagnetic
field
change
on
the
electrode
surf
ace
modifies
the
impedance
of
the
capacitance
component.
Theref
ore
,
se
v
er
al
rese
archers
[12,
14,
15]
ha
v
e
used
ECIS
to
predict
the
impedance
of
the
cells
and
enab
le
direct
monitor
ing
of
impedance
changing
of
the
cells
using
the
LIA
as
measur
ing
instr
ument.
In
this
study
the
LIA
has
been
choosen
since
it
has
some
adv
antages
lik
e
it
can
be
b
uild
with
lo
w
cost,
v
er
y
sensitiv
e
and
can
remo
v
e
noise
.
A
RC
tissue
model
w
as
used
to
replace
the
or
iginal
cell
tissue
.
The
measurement
w
as
perf
or
med
b
y
connecting
the
LIA
par
allel
with
the
RC
tissue
model.
This
RC
tissue
model
is
based
on
an
appro
ximation
of
RC
v
alues
of
human
er
y-
throcyte
[16].
Rd
char
acter
iz
es
the
dielectr
ic
of
the
electrode/electrolyte
.
Rc
is
the
cell
resistance
and
t
he
capacitor
C
in
this
circuit
represents
the
cell
tissue
.
The
LIA
output
w
as
read
b
y
a
PC
Oscilloscope
and
the
man
ual
impedance
calculation
w
as
conducted
based
on
the
LIA
v
oltage
output.
2.
Resear
c
h
Methodology
2.1.
A
trigonometr
y
per
spective
of
the
LIA
Presumab
ly
a
signal
with
a
frequency
f
1
and
phase
of
1
is
applied
to
input
channel.
It
is
assumed
that
signal
has
a
v
er
y
lo
w
amplitude
and
it
m
ust
be
amplified
with
gain
G
ac
.
The
output
of
the
amplifier
is
a
signal
with
a
specific
gain,namely
:
V
ac
(
t
)
=
G
ac
V
o
cos
(
w
1
t
+
1
)
(1)
In
addition,
a
ref
erence
signal
that
has
a
frequency
f
2
and
2
is
giv
en
as
a
m
ultiplicand
of
the
output
signal
from
amplifier
,
the
signal
is
:
V
r
ef
(
t
)
=
E
o
cos
(
w
2
t
+
2
)
(2)
The
product
result
of
the
amplifier
output
signal
and
the
ref
erence
signal
is
an
identity
product
of
these
tw
o
signals
and
can
be
e
xpressed
as
:
Title
of
man
uscr
ipt
is
shor
t
and
clear
,
implies
research
results
(First
A
uthor)
Evaluation Warning : The document was created with Spire.PDF for Python.
7216
ISSN:
2302-4046
V
psd
(
t
)
=
1
2
G
ac
V
o
E
o
(
cos
[(
w
1
+
w
2
)
t
+
(
1
+
2
)]+
cos
[(
w
1
w
2
)
t
+
(
1
2
)])
(3)
Equation
3
sho
ws
that
the
product
of
tw
o
sin
usoidal
signals
,
which
ha
v
e
diff
erent
frequen-
cies
,
produces
tw
o
sin
usoidal
signals
with
diff
erent
frequencies
.
V
psd
1
(
t
)
=
1
2
G
ac
V
o
E
o
(
cos
[(
w
1
+
w
2
)
t
+
(
1
+
2
)])
(4)
V
psd
2
(
t
)
=
1
2
G
ac
V
o
E
o
(
cos
[(
w
1
w
2
)
t
+
(
1
2
)])
(5)
If
Equation
3
is
applied
to
a
LPF
that
has
a
frequency
cut
off
smaller
than
(
w
1
+
w
2
)
,
the
high
frequency
component
(Equation
4)
is
atten
uated
and
the
lo
w
frequency
component
(Equation
5)
is
passed
the
LPF
and
the
final
result
is
sum
of
tw
o
sin
usoidal
signals
wit
h
diff
erent
frequencies
.
When
the
frequency
and
phase
of
the
input
signal
and
the
ref
erence
signal
are
similar
,
the
Equation
3
becomes
:
V
psd
(
t
)
=
1
2
G
ac
V
o
E
o
[1
+
cos
(2
w
t
+
2
)]
(6)
F
rom
Equation
6,
it
re
v
eals
that
there
a
re
tw
o
signal
components
,
A
C
and
DC
.
The
ampli-
tude
of
the
output
signal
is
a
half
of
the
input
signal
and
the
frequency
of
A
C
component
is
twice
of
the
amplified
input
signal.
When
a
LPF
which
has
frequency
cut
off
smaller
than
frequency
of
A
C
signal
is
applied
to
the
Equation
6,
the
A
C
signal
is
atten
uated
b
y
the
LPF
.
The
result
is
the
sum
of
the
DC
signal
and
the
atten
uated
A
C
signal
which
is
a
r
ipple
DC
signal.
Equation
3
demonstr
ates
that
if
the
frequencies
and
the
phases
of
the
input
and
ref
er-
ence
signal
are
equal,
the
DC
component
is
maxim
um
since
it
produces
z
ero
phase
diff
erent.
If
the
input
signal
and
the
ref
erence
signal
ha
v
e
diff
erent
phase
,
the
output
signal
does
not
reach
maxim
um
output
which
half
of
the
amplified
input
signal.
It
concludes
that
the
LIA
only
measures
signals
that
ha
v
e
same
frequency
and
phase
as
ref
erence
signal.
2.2.
Instrumentation
F
or
testing
the
LIA,
a
RC
tissue
model
w
as
used
as
sho
wn
in
Figure
2.
The
RC
tissue
model
consists
of
tw
o
fix
ed
carbon
resist
ors
22
Ohm
and
a
cer
amic
capacitor
as
a
cell
tissue
which
has
three
v
alues
0.01
F
,
0.1
F
and
1
F
.
These
v
alues
of
capacitor
w
ere
chosen
to
analyse
the
accur
acy
of
the
LIA
when
small
impedance
of
the
RC
tissue
model
is
changed.
T
o
conduct
the
impedance
measurement,
the
LIA
w
as
used.
The
high-pass
filter
(HPF)
w
as
set
to
ha
v
e
a
frequency
cut
off
0.7
Hz
and
the
lo
w
pass
filter
(LPF)
w
as
set
to
ha
v
e
a
frequency
cut
off
16
Hz.
The
HPF
w
as
used
to
remo
v
e
the
DC
offset
of
the
sensor
.
This
a
v
oids
DC
offset
dr
iving
the
chip
into
satur
ation
mode
.
while
the
LPF
w
as
used
to
remo
v
e
the
noise
and
suppressed
the
A
C
component
of
the
output
signal.
The
f
requency
cut-off
w
as
chosen
based
on
the
interest
of
the
signal.
A
frequency
cut-off
of
0.7
Hz
w
as
selected
as
this
is
sufficiently
high
to
remo
v
e
the
DC
component
of
the
input
signal.
A
frequency
cut-off
of
16
Hz
w
as
chosen
based
on
the
obser
v
ation
dur
ing
e
xper
iment,
since
it
pro
vides
smoothest
output
of
DC
signal.
T
o
constr
uct
a
v
oltage
divider
,
the
RC
tissue
model
w
as
co
nnected
in
ser
ies
with
a
1.5
K
Ohm
resistor
.
The
1.5
K
Ohm
resistor
w
as
designated
to
allo
w
the
major
ity
of
the
v
oltage
to
be
dropped
across
it
and
lea
v
e
only
v
er
y
small
por
tion
of
v
oltage
to
be
dropped
across
the
RC
tissue
model.
An
A
C
v
oltage
with
amplitude
of
250
mV
,
from
PICOScope
(PICOScope
is
a
real
time
PC-based
digital
oscilloscope
,
which
has
function
of
digital
stor
age
oscilloscope
,
meter
and
data
logger
,
spectr
um
analyser
and
signal
gener
ator),
and
ref
erence
signal
of
the
LIA
with
frequency
r
ange
from
10
Hz
-
1
MHz
w
ere
applied
to
the
circuit.
The
LIA
w
as
connected
par
allel
with
the
RC
tissue
model
to
detect
small
v
oltage
drop
across
the
RC
tissue
model.
LIA
o
utput
w
as
measured
b
y
PicoScope
.
At
a
specific
frequency
v
alue
,
the
output
amplitude
of
the
LIA
w
as
recorded
and
the
impedance
TELK
OMNIKA
V
ol.
12,
No
.
10,
October
l
2014
:
7214
7222
Evaluation Warning : The document was created with Spire.PDF for Python.
TELK
OMNIKA
ISSN:
2302-4046
7217
w
as
cal
c
u
lated
to
allo
w
a
compar
ison
betw
een
theoretical
v
alues
and
C60
(impedance
measur
ing
instr
ument
made
b
y
Cypher
instr
uments
Ltd)
output.
C
Ro = 1.5 K
Rd = 22
Rc= 22
cel
l m
od
el
= Ze
q
Vi
Vo
LIA
PICO
scope
out
PC
US
B
Figure
2.
The
circuit
diag
r
am
of
measurement
system
with
the
RC
tissue
model
3.
Result
and
Anal
ysis
3.1.
Experimental
Results
Theoretically
,
the
cell
impedance
can
be
defined
b
y
f
ollo
wing
equations
:
Z
eq
=
R
d
+
R
c
1
+
j
!
R
c
C
Z
eq
=
R
d
+
R
c
1
+
j
!
R
c
C
:
1
j
!
R
c
C
1
j
!
R
c
C
Z
eq
=
R
d
+
R
c
j
!
R
2
c
C
1
+
!
2
R
2
c
C
2
(7)
and
can
be
represented
in
the
rectangular
f
or
m
as
:
Z
eq
=
R
d
+
R
c
1
+
(
!
C
R
c
)
2
j
!
C
R
2
c
1
+
(
!
C
R
c
)
2
(8)
in
the
polar
f
or
m
can
be
represented
as
f
ollo
w
:
Magnitude
:
Z
eq
=
p
(
R
d
+
R
c
+
!
2
R
2
c
R
d
C
2
)
2
+
(
!
R
2
c
C
)
2
1
+
(
!
C
R
c
)
2
(9)
Phase:
=
ar
ctan
!
C
R
2
c
R
d
+
R
c
+
!
2
R
2
c
R
d
C
2
(10)
When
the
frequency
is
v
er
y
lo
w
,
the
imaginar
y
par
t
of
Equation
8
is
relativ
ely
lo
w
.
As
the
imaginar
y
par
t
of
cell
impedances
retains
only
a
minor
v
alue
,
the
impedance
of
the
cell
model
is
appro
ximately
equal
to
Rc+Rd.
When
the
frequency
g
r
adually
increases
,
the
imaginar
y
par
t
also
slo
wly
increases
until
reaching
a
maxim
um
at
a
specific
frequency
and
then
steadily
decreases
to
z
ero
again.
Thus
,
the
v
alues
of
the
RC
tissue
model
pro
vide
v
er
y
small
eff
ect
to
the
whole
impedance
as
sho
wn
in
Figure
3.
Figure
4
sho
ws
the
impedance
change
when
the
capacitor
is
changed.
It
sho
ws
that
the
impedance
change
is
relativ
e
ly
small.
The
g
r
aph
re
v
ealed
that
the
impedance
change
betw
een
Title
of
man
uscr
ipt
is
shor
t
and
clear
,
implies
research
results
(First
A
uthor)
Evaluation Warning : The document was created with Spire.PDF for Python.
7218
ISSN:
2302-4046
Figure
3.
Contr
ib
ution
of
imaginar
y
par
t
to
the
impedance
of
the
RC
tissue
model
with
the
capac-
itor
of
1
F
capacitor
0.01
F
and
0.1
F
is
v
er
y
small
which
is
less
than
0.1
Ohm.
While
the
impedance
change
f
or
capacitors
0.1
F
and
1
F
is
e
xponentially
increased.
Similar
result
is
happened
with
capacito
r
v
alues
of
0.01
F
and
1
F
.
The
compar
ison
of
impedance
change
w
as
limited
until
frequency
around
3.3
kHz
since
this
is
the
smallest
frequency
cut
off
among
three
v
alues
of
capacitor
.
Abo
v
e
this
frequency
,
the
impedance
change
increased
because
the
smaller
the
capacitor
v
alue
the
bigger
the
frequency
cut
off
.
Figure
4.
Impedance
change
as
the
capacitor
v
alues
change
un
til
frequency
cut
off
around
3.3
kHz
Using
the
LIA
v
oltage
output,
the
impedance
calculati
on
is
perf
or
med
across
a
v
oltage
divider
as
f
ollo
ws
:
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7219
(a)
(b)
(c)
Figure
5.
Compar
ison
of
the
impedance
measurement
of
the
RC
tissue
model
with
capacitor
of
(a)
0.01
F
(b)
0.1
F
(c)
1
F
Title
of
man
uscr
ipt
is
shor
t
and
clear
,
implies
research
results
(First
A
uthor)
Evaluation Warning : The document was created with Spire.PDF for Python.
7220
ISSN:
2302-4046
Z
eq
=
V
o
R
o
V
i
V
o
(11)
F
rom
Figure
5,
it
sho
ws
that
the
LIA
perf
or
ms
adequate
measurement
compared
with
theoretical
calculation
and
measure
ment
using
the
C60
impedance
measur
ing
inst
r
ument.
It
also
demonstr
ates
that
the
LIA
has
limited
measurement
of
appro
ximately
210
KHz,
as
be
y
ond
this
frequency
the
v
oltage
decreases
r
apidly
and
pro
vides
less
accur
ate
results
.
The
figures
illustr
ate
that
the
measurement
of
the
LIA
pro
vides
results
close
to
the
theoretical
and
the
C60
output
in
the
frequency
r
ange
from
10
Hz
-
100
Hz.
Abo
v
e
this
frequency
,
the
impedance
is
slightly
increased.
Meanwhile
at
the
slope
,
the
measurements
from
the
LIA
pro
vides
impro
v
ed
outcome
.
It
also
can
be
obser
v
ed
that
when
the
capacitor
v
alues
are
increase
10
times
,
the
frequency
cut
off
decreased
appro
ximately
10
times
compared
with
pre
vious
frequency
cut-off
.
3.2.
Err
or
anal
ysis
In
this
study
,
an
error
analysis
w
as
perf
or
med.
The
error
analysis
w
as
conducted
in
the
r
ange
frequency
of
0
-
210
kHz
since
this
r
ange
is
the
limited
frequency
r
ange
of
the
LIA.
Be
y
ond
this
frequency
r
ange
the
measurement
pro
vide
unacceptab
le
results
.
In
the
error
analysis
,
the
relativ
e
error
and
standard
error
w
ere
used
and
defined
as
f
ollo
ws
:
=
x
o
x
x
(12)
=
S
D
p
N
(13)
Where
x
o
is
t
he
measurement
v
alue
,
x
is
the
theoretical
v
alue
,
S
D
is
the
standard
de
via-
tion
of
measurement
and
N
is
the
n
umber
of
data
in
the
measurement.
Figure
6a
illustr
ates
the
relativ
e
error
g
r
aph
of
the
LIA.
It
sho
ws
that
relativ
e
errors
of
measurement
using
capacitor
0.01
F
are
linear
ly
increased
from
4%
until
100
kHz
and
steadily
decreases
until
frequency
210
kHz.
While
measurement
using
capacitor
0.1
F
,
the
g
r
aph
sho
ws
that
the
relati
v
e
errors
are
almost
constant
until
frequency
30
kHz
and
at
this
point
the
v
alues
are
decreased
linear
ly
until
frequency
100
kHz
and
almost
constant
abo
v
e
100
kHz.
Diff
erent
result
sho
w
ed
b
y
the
measurement
of
1
F
.
A
spik
e
of
relativ
e
error
sho
w
ed
at
frequency
1.5
kHz.
Abo
v
e
this
frequency
,
the
measurement
sho
w
ed
constant
v
alues
and
increased
until
210
kHz.
While
,
Figure
6b
depicted
the
relativ
e
er-
ror
g
r
aph
of
C60
measurement.
The
g
r
aph
sho
ws
constant
relativ
e
error
f
or
measurement
using
capacitor
0.01
F
until
around
60
kHz.
The
error
r
ises
abo
v
e
60
kHz
and
almost
constant
abo
v
e
100
kHz
which
is
around
2%.
The
measurement
using
capacitor
0.1
F
pro
vided
better
relativ
e
error
which
around
2%
belo
w
50
kHz
and
constantly
0.5%
abo
v
e
50
kHz.
Similar
with
the
LIA
measurement,
the
result
of
using
capacitor
1
F
pro
vides
a
spik
e
of
relativ
e
error
sho
w
ed
at
1.5
kHz
and
decreased
slo
wly
until
50
kHz
an
d
after
this
frequency
the
result
slo
wly
r
ises
until
210
kHz.
The
relativ
e
errors
of
bot
h
measurements
presented
v
ar
ying
relativ
e
error
.
The
g
r
aphs
depicted
that
relativ
e
error
mean
of
C60
is
slightly
better
than
the
LIA,
where
the
diff
erences
about
1-3%.
Ho
w
e
v
er
,
T
ab
le
1
descr
ibes
the
standard
error
of
tw
o
measurements
.
It
can
be
seen
from
T
ab
le
1,
that
both
mea
s
u
rement
results
pro
vide
similar
trend
which
as
the
capacitor
v
alue
is
increased
the
standard
error
is
also
r
ise
.
The
error
r
ises
with
margin
about
1.5
as
the
capacitor
v
alue
increases
10
times
.
T
ab
le
1.
Standard
error
of
measurement
0.01uF
0.1uF
1uF
LIA
0.34
1.85
3.01
C60
0.10
1.61
3.00
TELK
OMNIKA
V
ol.
12,
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.
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l
2014
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7214
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TELK
OMNIKA
ISSN:
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7221
(a)
(b)
Figure
6.
Standard
error
of
measurement
using
(a)
the
LIA
(b)
C60.
Dotted
lines
are
mean
of
the
standard
error
4.
Conc
lusion
The
theor
y
of
loc
k-in
amplifier
has
been
re
vie
w
ed
and
an
e
xper
iment
to
measure
the
RC
tissuel
model
using
the
LIA
has
been
perf
or
med.
The
main
idea
of
the
LIA
w
as
descr
ibed
mathe-
matically
to
gain
deep
understanding
about
ho
w
the
LIA
w
or
ks
and
to
obser
v
e
the
char
acter
istics
of
the
circuit.
An
e
xper
iment
of
impedance
measurement
of
RC
tissue
model
using
diff
erence
v
alues
of
capacitor
has
been
perf
or
med.
The
e
xper
iment
re
v
ealed
that
the
LIA
w
as
ab
le
to
detect
small
v
oltage
change
in
the
RC
tissue
model
as
the
impedance
change
.
The
compar
ison
of
the
LIA
with
theoretical
calculation
and
impedance
measurement
(C60
)
sho
w
ed
that
measurement
using
the
LIA
pro
vides
an
accur
ate
measurement
result
which
ab
le
to
detect
small
impedance
change
.
This
ability
is
sho
wn
b
y
the
error
analysis
,
where
the
relativ
e
error
of
the
LIA
measure-
ment
is
relativ
ely
small.
Theref
ore
,
this
study
sho
w
ed
that
LIA
can
be
used
as
an
alter
nativ
e
lo
w
cost
and
an
eff
ectiv
e
measur
ing
instr
ument
f
or
biomedical
measurement.
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erences
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ybr
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Title
of
man
uscr
ipt
is
shor
t
and
clear
,
implies
research
results
(First
A
uthor)
Evaluation Warning : The document was created with Spire.PDF for Python.
7222
ISSN:
2302-4046
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requency
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TELK
OMNIKA
V
ol.
12,
No
.
10,
October
l
2014
:
7214
7222
Evaluation Warning : The document was created with Spire.PDF for Python.