1. Comparison of Energy Harvesting Systems for Wireless
Sensor Networks
2. A Quantitative Investigation of Inertial Power Harvesting
for Human-powered Devices
ENERGY HARVESTING &
STORAGE
Hyeon Joo
OUTLINE
 Power requirement
 Suitable scavenging energy source
 Energy conversion device
 Vibration
POWER REQUIREMENT
Power requirement
Power requirement
Actuator and
Communication
consumes a large
proportion of total
power
SUITABLE SCAVENGING
ENERGY SOURCE
Mechanical energy source
 Steady state mechanical source
 Steady state: wind, flow, current..
 Intermittent mechanical source
 Human activity(walking, typing.. 5.88J/2steps )
 Vehicles passing
 Vibration
 Energy depends on the amplitude and its freq.
 Mass of harvesting device relative to the vibrating
mass
Mechanical energy source
Typically vibration is made up of a
number of fundamental freq. and
their harmonic
ENERGY CONVERSION DEVICES
Vibration
m:
k:
u(t):
x(t):
b:
seismic mass
spring of stiffness
Position of case
Position of the seismic
Damping coefficient
Vibration
m:
k:
u(t):
x(t):
b:
seismic mass
spring of stiffness
Position of case
Position of the seismic
Damping coefficient
Mx’’(t) + Bx’(t) + Kx(t) = - Mu’’(t)
Vibration
m:
k:
u(t):
x(t):
b:

x (t ) 
(
k
m
2
 )  (
2
seismic mass
spring of stiffness
Position of case
Position of the seismic
Damping coefficient
2
b
m
U sin( t   )
)
2
Vibration
mx’’(t) + bx’(t) + kx(t) = - mu’’(t)
x ''( t ) 
b
x '( t ) 
m
S X (s) 
2
k
x ( t )   u ''( t )

m
bS
X (s) 
m
S 
2
(
X (s)   S U (s)
2
k
  )  j(
m
bS

m
k
U (s)
( j ) 
2
m
)
k
 )  (
2
2
b
U ( j )
)
2
m
U ( j )  U  sin( t ) e
 ( j )
b
U ( j )
2
m
m
S  j
X ( j ) 

(
b
m

2
2
2
m
S
X (s) 
k

 j t
dt
2
( j ) 
k
m
U ( j )

x (t ) 
(
k
m
2
 )  (
2
2
b
m
U sin( t   )
)
2
Vibration
ω : vibration freq
ωn : natural freq
T
: damping factor
ω =ωn => peak power
(resonant)
n 
k /m
m TY (
2
Pd 
[1  (

n

n
) 
2
) ]  [2  T (
2 2
3

n
)]
2
Vibration
ω : vibration freq
ωn : natural freq
Pd 
mA
2
T
: damping factor
4  n T
Increase the damping factor
Reducing the peak power,
 but increase bw
Pd 
mA
2
4  n T
Vibration
ω : vibration freq
ωn : natural freq
Pd 
mA
2
T
: damping factor
4  n T
Thus,
1) fixed freq => low d.f.
2) Various freq => high d.f.
Pd 
mA
2
4  n T
Vibration
Pe 
mAZ
m ax
n
4
proportional to the m
m d 
3
d  AZ
3
Pe 
m ax
n
4
Z
m ax
d
P e m ax  d  A n
4
m 
 Harvested energy is
d 
3
4
P e m ax  m 3 

1
3
A n
Vibration
 Piezoelectric conversion (pressure)
 Commonly used material: PZT, BaTiO3, PVDF
 Electrostatic conversion
 The formation of a parallel plate capacitor
 Electromagnetic conversion
 Magnetic and coil
E 
1
2
QV
Intermittent mechanical
conv.
 Piezoelectric conversion
 Electro-active polymers(EAP) conversion
 Electromagnetic conversion
ANY QUESTIONS?
OUTLINE
 Motivation
 Mobile device
 Energy harvesting model
 Data Analysis
 Power Estimation
Motivation
 Human motion energy harvesting
 Electronic devices
 Realistic experiment
 6 different parts of body
Mobile devices
Wearable device
Energy harvesting model
k: spring constant
m:proof mass
d: damping coefficient
y(t): generator displacement
z(t): generator’s motion
Zmax: interval travel limit
Energy harvesting model
 Loggers: 1GB SD
80HZ
Data Analysis
 3-aixs accelerometers (X,Y,Z)
 Harvest energy from daily human activities
using free motion
 Only kinetic energy from human body
 Zero-gravity for accuracy
 High-passed filtered with 0.05Hz cuffoff
Data Analysis
Data Analysis
Data Analysis
Ed 

z2
F dz
z1
F  Dz '
Ed 

z2
D z ' dz 
z1
P average 
1
T
Ed


T
t0
D
T

D
dz dz
dt dt
T
t0
z '' dt
dt  D 
T
t0
z '' dt
ANY QUESTIONS?