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Transcript of Fourier Series. Introduction Decompose a periodic input signal into primitive periodic components. A...
Introduction
• Decompose a periodic input signal into primitive periodic components.
A periodic sequenceA periodic sequence
T 2T 3T
t
f(t)
Synthesis
T
ntb
T
nta
atf
nn
nn
2sin
2cos
2)(
11
0
DC Part Even Part Odd Part
T is a period of all the above signals
)sin()cos(2
)( 01
01
0 tnbtnaa
tfn
nn
n
Let 0=2/T.
Decomposition
dttfT
aTt
t
0
0
)(2
0
,2,1 cos)(2
0
0
0
ntdtntfT
aTt
tn
,2,1 sin)(2
0
0
0
ntdtntfT
bTt
tn
)sin()cos(2
)( 01
01
0 tnbtnaa
tfn
nn
n
Example (Square Wave)
112
200
dta
,2,1 0sin1
cos2
200
nntn
ntdtan
,6,4,20
,5,3,1/2)1cos(
1 cos
1sin
2
200
n
nnn
nnt
nntdtbn
2 3 4 5--2-3-4-5-6
f(t)1
Harmonics
T
ntb
T
nta
atf
nn
nn
2sin
2cos
2)(
11
0
DC Part Even Part Odd Part
T is a period of all the above signals
)sin()cos(2
)( 01
01
0 tnbtnaa
tfn
nn
n
Harmonics
tnbtnaa
tfn
nn
n 01
01
0 sincos2
)(
Tf
22 00Define , called the fundamental angular frequency.
0 nnDefine , called the n-th harmonic of the periodic function.
tbtaa
tf nn
nnn
n
sincos2
)(11
0
Harmonics
tbtaa
tf nn
nnn
n
sincos2
)(11
0
)sincos(2 1
0 tbtaa
nnnn
n
12222
220 sincos2 n
n
nn
nn
nn
nnn t
ba
bt
ba
aba
a
1
220 sinsincoscos2 n
nnnnnn ttbaa
)cos(1
0 nn
nn tCC
Amplitudes and Phase Angles
)cos()(1
0 nn
nn tCCtf
20
0
aC
22nnn baC
n
nn a
b1tan
harmonic amplitude phase angle
Complex Exponentials
tnjtne tjn00 sincos0
tjntjn eetn 00
2
1cos 0
tnjtne tjn00 sincos0
tjntjntjntjn eej
eej
tn 0000
22
1sin 0
Complex Form of the Fourier Series
tnbtnaa
tfn
nn
n 01
01
0 sincos2
)(
tjntjn
nn
tjntjn
nn eeb
jeea
a0000
11
0
22
1
2
1
0 00 )(2
1)(
2
1
2 n
tjnnn
tjnnn ejbaejba
a
1
000
n
tjnn
tjnn ececc
Complex Form of the Fourier Series
1
000)(
n
tjnn
tjnn ececctf
1
10
00
n
tjnn
n
tjnn ececc
n
tjnnec 0
)(2
1
)(2
12
00
nnn
nnn
jbac
jbac
ac
)(
2
1
)(2
12
00
nnn
nnn
jbac
jbac
ac
Complex Form of the Fourier Series
2/
2/
00 )(
1
2
T
Tdttf
T
ac
)(2
1nnn jbac
2/
2/ 0
2/
2/ 0 sin)(cos)(1 T
T
T
Ttdtntfjtdtntf
T
2/
2/ 00 )sin)(cos(1 T
Tdttnjtntf
T
2/
2/
0)(1 T
T
tjn dtetfT
2/
2/
0)(1
)(2
1 T
T
tjnnnn dtetf
Tjbac
Complex Form of the Fourier Series
n
tjnnectf 0)(
n
tjnnectf 0)(
dtetfT
cT
T
tjnn
2/
2/
0)(1 dtetf
Tc
T
T
tjnn
2/
2/
0)(1
)(2
1
)(2
12
00
nnn
nnn
jbac
jbac
ac
)(
2
1
)(2
12
00
nnn
nnn
jbac
jbac
ac
If f(t) is real,*nn cc
nn jnnn
jnn ecccecc
|| ,|| *
22
2
1|||| nnnn bacc
n
nn a
b1tan
,3,2,1 n
00 2
1ac
Example
2
T
2
T TT
2
d
t
f(t)
A
2
d
dteT
Ac
d
d
tjnn
2/
2/
0
2/
2/0
01
d
d
tjnejnT
A
2/
0
2/
0
0011 djndjn ejn
ejnT
A
)2/sin2(1
00
dnjjnT
A
2/sin1
002
1dn
nT
A
TdnT
dn
T
Adsin
TdnT
dn
T
Adcn
sin
82
5
1
T ,
4
1 ,
20
1
0
T
dTd
Example
40 80 120-40 0-120 -80
A/5
50 100 150-50-100-150
TdnT
dn
T
Adcn
sin
42
5
1
T ,
2
1 ,
20
1
0
T
dTd
Example
40 80 120-40 0-120 -80
A/10
100 200 300-100-200-300
Example
dteT
Ac
d tjnn
0
0
d
tjnejnT
A
00
01
00
110
jne
jnT
A djn
)1(1
0
0
djnejnT
A
2/0
sindjne
TdnT
dn
T
Ad
TT d
t
f(t)
A
0
)(1 2/2/2/
0
000 djndjndjn eeejnT
A
Decomposition
• Any function f(t) can be expressed as the sum of an even function fe(t) and an odd function fo(t).
)()()( tftftf oe
)]()([)( 21 tftftfe
)]()([)( 21 tftftfo
Even Part
Odd Part
Hidden Symmetry
• The following is a asymmetry periodic function:
Adding a constant to get symmetry property.
A
TT
A/2
A/2
TT
Fourier Coefficients of Symmetrical Waveforms
• The use of symmetry properties simplifies the calculation of Fourier coefficients.– Even Functions– Odd Functions– Half-Wave– Even Quarter-Wave– Odd Quarter-Wave– Hidden
Fourier Coefficients of Even Functions
)()( tftf
tnaa
tfn
n 01
0 cos2
)(
2/
0 0 )cos()(4 T
n dttntfT
a
Fourier Coefficients for Half-Wave Symmetry
)()( Ttftf and 2/)( Ttftf
TT/2T/2
The Fourier series contains only odd harmonics.The Fourier series contains only odd harmonics.
Fourier Coefficients for Half-Wave Symmetry
)()( Ttftf and 2/)( Ttftf
)sincos()(1
00
n
nn tnbtnatf
odd for )cos()(4
even for 02/
0 0 ndttntfT
na T
n
odd for )sin()(4
even for 02/
0 0 ndttntfT
nb T
n
Fourier Coefficients forEven Quarter-Wave Symmetry
TT/2T/2
])12cos[()( 01
12 tnatfn
n
4/
0 012 ])12cos[()(8 T
n dttntfT
a
Fourier Coefficients forOdd Quarter-Wave Symmetry
])12sin[()( 01
12 tnbtfn
n
4/
0 012 ])12sin[()(8 T
n dttntfT
b
T
T/2T/2
Example
Even Quarter-Wave Symmetry
4/
0 012 ])12cos[()(8 T
n dttntfT
a 4/
0 0 ])12cos[(8 T
dttnT
4/
0
00
])12sin[()12(
8T
tnTn
)12(
4)1( 1
nn
TT/2T/2
1
1T T/4T/4
Example
Even Quarter-Wave Symmetry
4/
0 012 ])12cos[()(8 T
n dttntfT
a 4/
0 0 ])12cos[(8 T
dttnT
4/
0
00
])12sin[()12(
8T
tnTn
)12(
4)1( 1
nn
TT/2T/2
1
1T T/4T/4
Example
TT/2T/2
1
1
T T/4T/4
Odd Quarter-Wave Symmetry
4/
0 012 ])12sin[()(8 T
n dttntfT
b 4/
0 0 ])12sin[(8 T
dttnT
4/
0
00
])12cos[()12(
8T
tnTn
)12(
4
n
Example
TT/2T/2
1
1
T T/4T/4
Odd Quarter-Wave Symmetry
4/
0 012 ])12sin[()(8 T
n dttntfT
b 4/
0 0 ])12sin[(8 T
dttnT
4/
0
00
])12cos[()12(
8T
tnTn
)12(
4
n
Dirichlet ConditionsDirichlet Conditions
• A periodic signal x(t), has a Fourier series if it satisfies the following conditions:
1. x(t) is absolutely integrableabsolutely integrable over any period, namely
2. x(t) has only a finite number of maxima finite number of maxima and minima and minima over any period
3. x(t) has only a finite number of finite number of discontinuities discontinuities over any period
| ( ) | ,a T
a
x t dt a
• We have seen that periodic signals can be represented with the Fourier series
• Can aperiodic signalsaperiodic signals be analyzed in terms of frequency components?
• Yes, and the Fourier transform provides the tool for this analysis
• The major difference w.r.t. the line spectra of periodic signals is that the spectra of spectra of aperiodic signalsaperiodic signals are defined for all real values of the frequency variable not just for a discrete set of values
Fourier TransformFourier Transform
• Given a signal x(t), its Fourier transform Fourier transform is defined as
• A signal x(t) is said to have a Fourier transform in the ordinary sense if the above integral converges
The Fourier Transform in the General Case
The Fourier Transform in the General Case
( )X
( ) ( ) ,j tX x t e dt
• The integral does converge if1. the signal x(t) is “well-behavedwell-behaved” 2. and x(t) is absolutely integrableabsolutely integrable, namely,
• Note: well behavedwell behaved means that the signal has a finite number of discontinuities, maxima, and minima within any finite time interval
The Fourier Transform in the General Case – Cont’d
The Fourier Transform in the General Case – Cont’d
| ( ) |x t dt
• Consider
• Since in general is a complex function, by using Euler’s formula
Rectangular Form of the Fourier Transform
Rectangular Form of the Fourier Transform
( ) ( ) ,j tX x t e dt
( )X
( ) ( )
( ) ( )cos( ) ( )sin( )
R I
X x t t dt j x t t dt
( ) ( ) ( )X R jI
• can be expressed in a polar form as
where
Polar Form of the Fourier TransformPolar Form of the Fourier Transform
( ) | ( ) | exp( arg( ( )))X X j X
( ) ( ) ( )X R jI
2 2| ( ) | ( ) ( )X R I
( )arg( ( )) arctan
( )
IX
R
• If x(t) is real-valued, it is
• Moreover
whence
Fourier Transform of Real-Valued Signals
Fourier Transform of Real-Valued Signals
( ) ( )X X
( ) | ( ) | exp( arg( ( )))X X j X
| ( ) | | ( ) | and
arg( ( )) arg( ( ))
X X
X X
Hermitian Hermitian symmetrysymmetry
• Consider the even signal
• It is
Example: Fourier Transform of the Rectangular Pulse
Example: Fourier Transform of the Rectangular Pulse
/ 2
/ 2
00
2 2( ) 2 (1)cos( ) sin( ) sin
2
sinc2
t
tX t dt t
Example: Fourier Transform of the Rectangular Pulse – Cont’d
Example: Fourier Transform of the Rectangular Pulse – Cont’d
( ) sinc2
X
Example: Fourier Transform of the Rectangular Pulse – Cont’d
Example: Fourier Transform of the Rectangular Pulse – Cont’d
amplitude amplitude spectrumspectrum
phase phase spectrumspectrum
• A signal x(t) is said to be bandlimitedbandlimited if its Fourier transform is zero for all where BB is some positive number, called the bandwidth bandwidth of the signalof the signal
• It turns out that any bandlimited signal must have an infinite duration in time, i.e., bandlimited signals cannot be time limited
Bandlimited SignalsBandlimited Signals
( )X B
• If a signal x(t) is not bandlimited, it is said to have infinite bandwidthinfinite bandwidth or an infinite infinite spectrumspectrum
• Time-limited signals cannot be bandlimited and thus all time-limited signals have infinite bandwidth
• However, for any well-behaved signal x(t) it can be proven that whence it can be assumed that
Bandlimited Signals – Cont’dBandlimited Signals – Cont’d
lim ( ) 0X
| ( ) | 0X B B being a convenient large number
• Given a signal x(t) with Fourier transform , x(t) can be recomputed from
by applying the inverse Fourier transforminverse Fourier transform given by
• Transform pairTransform pair
Inverse Fourier TransformInverse Fourier Transform
( )X ( )X
1( ) ( ) ,
2j tx t X e d t
( ) ( )x t X
Properties of the Fourier Transform Properties of the Fourier Transform
• Linearity:Linearity:
• Left or Right Shift in Time:Left or Right Shift in Time:
• Time Scaling:Time Scaling:
( ) ( )x t X ( ) ( )y t Y
( ) ( ) ( ) ( )x t y t X Y
00( ) ( ) j tx t t X e
1( )x at X
a a
Properties of the Fourier Transform Properties of the Fourier Transform
• Time Reversal:Time Reversal:
• Multiplication by a Power of t:Multiplication by a Power of t:
• Multiplication by a Complex Exponential:Multiplication by a Complex Exponential:
( ) ( )x t X
( ) ( ) ( )n
n nn
dt x t j X
d
00( ) ( )j tx t e X
Properties of the Fourier Transform Properties of the Fourier Transform
• Multiplication by a Sinusoid (Modulation):Multiplication by a Sinusoid (Modulation):
• Differentiation in the Time Domain:Differentiation in the Time Domain:
0 0 0( )sin( ) ( ) ( )2
jx t t X X
0 0 0
1( )cos( ) ( ) ( )
2x t t X X
( ) ( ) ( )n
nn
dx t j X
dt
Properties of the Fourier Transform Properties of the Fourier Transform
• Integration in the Time Domain:Integration in the Time Domain:
• Convolution in the Time Domain:Convolution in the Time Domain:
• Multiplication in the Time Domain:Multiplication in the Time Domain:
1( ) ( ) (0) ( )
t
x d X Xj
( ) ( ) ( ) ( )x t y t X Y
( ) ( ) ( ) ( )x t y t X Y
Properties of the Fourier Transform Properties of the Fourier Transform
• Parseval’s Theorem:Parseval’s Theorem:
• Duality:Duality:
1( ) ( ) ( ) ( )
2x t y t dt X Y d
2 21| ( ) | | ( ) |
2x t dt X d
( ) ( )y t x tif
( ) 2 ( )X t x
Example: Time ScalingExample: Time Scaling
2 ( )p t
2 (2 )p t
2sinc
sinc2
time compression frequency expansiontime expansion frequency compression
1a 0 1a
Example: Multiplication in TimeExample: Multiplication in Time
2( ) ( )x t tp t
2
sin cos sin( ) 2sinc 2 2
d dX j j j
d d
Example: Multiplication by a SinusoidExample: Multiplication by a Sinusoid
0( ) ( )cos( )x t p t t sinusoidal burst
0 01 ( ) ( )( ) sinc sinc
2 2 2X
Example: Multiplication by a Sinusoid – Cont’d
Example: Multiplication by a Sinusoid – Cont’d
0 01 ( ) ( )( ) sinc sinc
2 2 2X
0 60 / sec
0.5
rad
Example: Multiplication in TimeExample: Multiplication in Time
2( ) ( )x t tp t
2
sin cos sin( ) 2sinc 2 2
d dX j j j
d d
Example: Multiplication by a SinusoidExample: Multiplication by a Sinusoid
0( ) ( )cos( )x t p t t sinusoidal burst
0 01 ( ) ( )( ) sinc sinc
2 2 2X
Example: Multiplication by a Sinusoid – Cont’d
Example: Multiplication by a Sinusoid – Cont’d
0 01 ( ) ( )( ) sinc sinc
2 2 2X
0 60 / sec
0.5
rad
Example: Integration in the Time Domain
Example: Integration in the Time Domain
2 | |( ) 1 ( )
tv t p t
( )( )
dv tx t
dt
Example: Integration in the Time Domain – Cont’d
Example: Integration in the Time Domain – Cont’d
• The Fourier transform of x(t) can be easily found to be
• Now, by using the integration property, it is
( ) sinc 2sin4 4
X j
21( ) ( ) (0) ( ) sinc
2 4V X X
j
Example: Integration in the Time Domain – Cont’d
Example: Integration in the Time Domain – Cont’d
2( ) sinc2 4
V
• Fourier transform of
• Applying the duality property
Generalized Fourier TransformGeneralized Fourier Transform
( )t
( ) 1j tt e dt
( ) 1t
( ) 1, 2 ( )x t t
generalized Fourier transformgeneralized Fourier transform of the constant signal ( ) 1,x t t
Generalized Fourier Transform of Sinusoidal Signals
Generalized Fourier Transform of Sinusoidal Signals
0 0 0cos( ) ( ) ( )t
0 0 0sin( ) ( ) ( )t j
Fourier Transform of Periodic SignalsFourier Transform of Periodic Signals
• Let x(t) be a periodic signal with period T; as such, it can be represented with its Fourier transform
• Since , it is002 ( )j te
0( ) jk tk
k
x t c e
0 2 /T
0( ) 2 ( )kk
X c k
• Since
using the integration property, it is
Fourier Transform of the Unit-Step FunctionFourier Transform of
the Unit-Step Function
( ) ( )t
u t d
1( ) ( ) ( )
t
u t dj
Why use Laplace Transforms?
• Find solution to differential equation using algebra
• Relationship to Fourier Transform allows easy way to characterize systems
• No need for convolution of input and differential equation solution
• Useful with multiple processes in system
How to use Laplace
• Find differential equations that describe system
• Obtain Laplace transform• Perform algebra to solve for output or
variable of interest• Apply inverse transform to find solution
How to use Laplace
• Find differential equations that describe system
• Obtain Laplace transform• Perform algebra to solve for output or
variable of interest• Apply inverse transform to find solution
What are Laplace transforms?
j
j
st
st
dsesFj
sFLtf
dtetftfLsF
)(
2
1)}({)(
)()}({)(
1
0
• t is real, s is complex!• Inverse requires complex analysis to solve• Note “transform”: f(t) F(s), where t is integrated and s is
variable• Conversely F(s) f(t), t is variable and s is integrated• Assumes f(t) = 0 for all t < 0
Evaluating F(s) = L{f(t)}
• Hard Way – do the integral
0
0 0
)(
0
)sin()(
sin)(
1)(
)(
1)10(
1)(
1)(
dttesF
ttf
asdtedteesF
etf
ssdtesF
tf
st
tasstat
at
stlet
let
let
Evaluating F(s)=L{f(t)}- Hard Way
remember vduuvudv
)tcos(v,dt)tsin(dv
dtsedu,eu stst
0
stst
0 0
st
0
stst
dt)tcos(es)1(e
dt)tcos(es)tcos(e[dt)tsin(e ]
)tsin(v,dt)tcos(dv
dtsedu,eu stst
0
stst
0
st
0
st
0
st
dt)tsin(es)0(edt)tsin(es)tsin(e[
dt)tcos(e
]
20
st
0
st2
0 0
st2st
s1
1dt)tsin(e
1dt)tsin(e)s1(
dt)tsin(es1dt)tsin(se
let
let
Substituting, we get:
It only gets worse…
Table of selected Laplace Transforms
1s
1)s(F)t(u)tsin()t(f
1s
s)s(F)t(u)tcos()t(f
as
1)s(F)t(ue)t(f
s
1)s(F)t(u)t(f
2
2
at
More transforms
1nn
s
!n)s(F)t(ut)t(f
665
2
1
s
120
s
!5)s(F)t(ut)t(f,5n
s
!1)s(F)t(tu)t(f,1n
s
1
s
!0)s(F)t(u)t(f,0n
1)s(F)t()t(f
Note on step functions in Laplace
0
stdte)t(f)}t(f{L
0t,0)t(u
0t,1)t(u
• Unit step function definition:
• Used in conjunction with f(t) f(t)u(t) because of Laplace integral limits:
Properties of Laplace Transforms
• Linearity• Scaling in time• Time shift• “frequency” or s-plane shift• Multiplication by tn
• Integration• Differentiation
Properties of Laplace Transforms
• Linearity• Scaling in time• Time shift• “frequency” or s-plane shift• Multiplication by tn
• Integration• Differentiation
Properties: Linearity
)()()}()({ 22112211 sFcsFctfctfcL Example :
1s
1)
1s
)1s()1s((
2
1
)1s
1
1s
1(
2
1
}e{L2
1}e{L
2
1
}e2
1e
2
1{y
)}t{sinh(L
22
tt
tt
Proof :
)s(Fc)s(Fc
dte)t(fcdte)t(fc
dte)]t(fc)t(fc[
)}t(fc)t(fc{L
2211
0
st22
0
st11
st22
0
11
2211
)a
s(F
a
1)}at(f{L
Example :
22
22
2
2
s
)s
(1
)1)s(
1(
1
)}t{sin(L
Proof :
)a
s(F
a
1
due)u(fa
1
dua
1dt,
a
ut,atu
dte)at(f
)}at(f{L
a
0
u)a
s(
0
st
let
Properties: Scaling in Time
Properties: Time Shift
)s(Fe)}tt(u)tt(f{L 0st00
Example :
as
e
)}10t(ue{Ls10
)10t(a
Proof :
)s(Fedue)u(fe
due)u(f
tut,ttu
dte)tt(f
dte)tt(u)tt(f
)}tt(u)tt(f{L
00
0
0
0
st
0
sust
t
0
)tu(s
00
t
st0
0
st00
00
let
Properties: S-plane (frequency) shift
)as(F)}t(fe{L at
Example :
22
at
)as(
)}tsin(e{L
Proof :
)as(F
dte)t(f
dte)t(fe
)}t(fe{L
0
t)as(
0
stat
at
Properties: Multiplication by tn
)s(Fds
d)1()}t(ft{L
n
nnn
Example :
1n
n
nn
n
s
!n
)s
1(
ds
d)1(
)}t(ut{L
Proof :
)s(Fs
)1(dte)t(fs
)1(
dtes
)t(f)1(
dtet)t(f
dte)t(ft)}t(ft{L
n
nn
0
stn
nn
0
stn
nn
0
stn
0
stnn
The “D” Operator
1. Differentiation shorthand
2. Integration shorthand)t(f
dt
d)t(fD
dt
)t(df)t(Df
2
22
)t(f)t(Dg
dt)t(f)t(gt
)t(fD)t(g
dt)t(f)t(g
1a
t
a
if
then then
if
Properties: Integrals
s
)s(F)}t(fD{L 1
0
Example :
)}t{sin(L1s
1)
1s
s)(
s
1(
)}tcos(D{L
22
10
Proof :
let
stst
0
st
10
es
1v,dtedv
dt)t(fdu),t(gu
dte)t(g)}t{sin(L
)t(fD)t(g
t
0
st0
st
dt)t(f)t(g
s
)s(Fdte)t(f
s
1]e)t(g
s
1[
0
)()( dtetft st If t=0, g(t)=0
for so
slower than
0
)()( tgdttf 0 ste
Properties: Derivatives(this is the big one)
)0(f)s(sF)}t(Df{L Example :
)}tsin({L1s
11s
)1s(s
11s
s
)0(f1s
s
)}tcos(D{L
2
2
22
2
2
2
2
Proof :
)s(sF)0(f
dte)t(fs)]t(fe[
)t(fv,dt)t(fdt
ddv
sedu,eu
dte)t(fdt
d)}t(Df{L
0
st0
st
stst
0
st
let
Inverse Laplace Transforms
Background:
To find the inverse Laplace transform we use transform pairsalong with partial fraction expansion:
F(s) can be written as;
)(
)()(
sQ
sPsF
Where P(s) & Q(s) are polynomials in the Laplace variable, s.We assume the order of Q(s) P(s), in order to be in properform. If F(s) is not in proper form we use long division and divide Q(s) into P(s) until we get a remaining ratio of polynomialsthat are in proper form.
Inverse Laplace Transforms
Background:There are three cases to consider in doing the partial fraction expansion of F(s).
Case 1: F(s) has all non repeated simple roots.
n
n
ps
k
ps
k
ps
ksF
...)(
2
2
1
1
Case 2: F(s) has complex poles:
...)))()((
)()(
*11
1
1
js
k
js
k
jsjssQ
sPsF
Case 3: F(s) has repeated poles.
)(
)(...
)(...
)())((
)()(
1
1
1
12
1
12
1
11
11
1
sQ
sP
ps
k
ps
k
ps
k
pssQ
sPsF
rr
r
(expanded)
(expanded)
Inverse Laplace Transforms
Case 1: Illustration:
Given:
)10()4()1()10)(4)(1(
)2(4)( 321
s
A
s
A
s
A
sss
ssF
274)10)(4)(1(
)2(4)1(| 11
ssss
ssA 94
)10)(4)(1(
)2(4)4(| 42
ssss
ssA
2716)10)(4)(1(
)2(4)10(| 103
ssss
ssA
)()2716()94()274()( 104 tueeetf ttt
Find A1, A2, A3 from Heavyside
Inverse Laplace Transforms
Case 3: Repeated roots.
When we have repeated roots we find the coefficients of the terms as follows:
|111
)()(1 psr
sFpsds
dk r
|121
)()(!2 12
2
psrsFps
ds
dk r
|11
)()()!( 1 psj
sFpsdsjr
dk r
jr
jr
Inverse Laplace Transforms
Case 3: Repeated roots. Example
2
1
1
2211
2 )3()3()3(
)1()(
K
K
A
s
K
s
K
s
A
ss
ssF
)(____________________)( 33 tuteetf tt ? ? ?
Inverse Laplace Transforms
Complex Roots: An Example.
For the given F(s) find f(t)
o
jj
j
jss
sK
ss
sA
js
K
js
K
s
AsF
jsjss
s
sss
ssF
js
s
10832.0)2)(2(
12
)2(
)1(
5
1
)54(
)1(
22)(
)2)(2(
)1(
)54(
)1()(
|
|
2|1
0|
11
2
2
*