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An Electromagnetic Vibration Energy Harvester
With Strong Electro-mechanical Coupling
○Takahiro Sato,
Hajime Igarashi
Hokkaido University:
1. Introduction
2. Vibration energy harvester with magnetic core
3. Measurement
4. Conclusion
2
Background: What is vibration energy harvester ?
Low-power electronic devices
for wireless sensing
3
If we can use low-power sensor ICs without
battery, various new WSN systems will be
realized !
e.g., motioning the “health” of bridges and
tunnelsZigbee, RFIF, etc,...
Vibration energy harvester
Vibration is generated from the traffic on bridges.
If we can harvest the small electric power
form this vibration, the sensor ICs can work
without any batteries.
Vibration energy harvester is the device to
produce the power from vibration.
Electromagnetic Vibration Energy Harvester
4
Electromagnetic vibration energy harvester (VEH) transforms
vibration energy to electric energy through magnetic induction.
Cantilever
beam
Magnets
Coil
ambient vibration
Magnetic flux across the
coil temporally changes.
When ambient vibration is applied to base (coil), the cantilever
is oscillated.
As a result, electromotive force is induced in the coil.
0
1
2
3
4
5
20 30 40 50 60 70
出力
(μW)
入力周波数 (Hz)frequency(Hz)
freq
uen
cy(H
z)
Electromagnetic Vibration Energy Harvester
5
Electromagnetic vibration energy harvester (VEH) transforms
vibration energy to electric energy through magnetic induction.
Cantilever
beam
Magnets
Coil
ambient vibration
Conventional VEHs produce the electrical energy
through linear spring-damper oscillations.
The output power is generated only around the
natural frequencies of VEHs.
m
Ambient
vibration
effective
stiffness
effective
damping
mass on
cantilever
k cm
Electromagnetic Vibration Energy Harvester
6
In the real-world, vibration has wide frequency
spectrum.
The operation bandwidth of VEH must be improved.
Higher output
Broader bandwidth
In case of zigbee, about 2mW is necessary.
VEHs must be produce the power from wider frequency range.
We propose a new harvester by
introducing magnetic materials
For real-world application...
1. Introduction
2. Vibration energy harvester with magnetic
core
3. Measurement
4. Conclusion
7
Concepts for improvement of performance
8
For Higher output,
Electro-mechanical coupling can be increased by forming
appropriate magnetic circuits.
＜with magnetic circuit and two magnets pairs＞ ＜ without magnetic circuit ＞
SD
D
D
Dd
tN
tNV
S
s
iB
The electromotive force is equal to the time derivative of the
magnetic flux across the coil Φ.
0
1
2
3
4
5
20 30 40 50 60 70
出力
(μW)
入力周波数 (Hz)frequency(Hz)
freq
uen
cy(H
z)
Concepts for improvement of performance
9
For Higher output,
For wider bandwidth,
appropriate magnetic circuits should be designed.
nonlinear phenomena is used.
＜with magnetic circuit and two magnets pairs＞ ＜ without magnetic circuit ＞
-0.6
-0.3
0
0.3
0.6
-0.8
-0.4
0
0.4
0.8
0.2 0.4 0.6
vo
ltage
(V)
z(m
m)
time (s)
z V
entrainment,
hysteresis,
chaotic,
etc.....
Our previous work
10
Based on the mentioned concepts, we have developed a
harvester with nonlinear oscillations.[1,2]
[1]: T. Sato, H. Igarashi, “A New Wideband Electromagnetic Vibration Energy Harvester with Chaotic Oscillation”, Proc. of
PowerMEMS2013, pp. 622-626, 2013.
[2]: T.Sato, H. Igarashi, “A Chaotic Vibration Energy Harvester Using Magnetic Material,” submitted to Smart. Mater. Struct.
A soft-magnetic composite core (SMC core) is introduced to form
a magneticc circuit.
Our previous work
11
[1]: T. Sato, H. Igarashi, “A New Wideband Electromagnetic Vibration Energy Harvester with Chaotic Oscillation”, Proc. of
PowerMEMS2013, pp. 622-626, 2013.
[2]: T.Sato, H. Igarashi, “A Chaotic Vibration Energy Harvester Using Magnetic Material,” submitted to Smart. Mater. Struct.
The harvester has wide bandwidth.
The oscillator has a complicated
(chaotic) motion.
0
0.05
0.1
0.15
0.2
20 30 40 50 60 70 80 90
load
vo
ltag
e (V
rms)
input frequency (Hz)
-0.4
-0.2
0
0.2
0.4
-1.2
-0.6
0
0.6
1.2
0 0.1 0.2 0.3
load
vo
ltag
e (V
)
dis
pla
cem
ent
(mm
)
time (s)
displacement voltage
-0.6
-0.3
0
0.3
0.6
-1.2
-0.6
0
0.6
1.2
0 0.1 0.2 0.3
load
vo
ltag
e (V
)
dis
pla
cem
ent
(mm
)
time (s)
displacement voltage
-0.2
-0.1
0
0.1
0.2
0
0.2
0.4
0.6
0.8
0 0.1 0.2 0.3
load
vo
ltag
e (V
)
dis
pla
cem
ent
(mm
)
time (s)
displacement voltage
<Output power >
Our previous work
12
Although the harvester has a wide bandwidth, the
maximum voltage is under 0.2VRMS.
To connect rectifier circuits to the harvester, over 0.2VRMS
is necessary.
0
0.05
0.1
0.15
0.2
20 30 40 50 60 70 80 90
load
vo
ltag
e (V
rms)
input frequency (Hz)-0.4
-0.2
0
0.2
0.4
-1.2
-0.6
0
0.6
1.2
0 0.1 0.2 0.3
load
vo
ltag
e (V
)
dis
pla
cem
ent
(mm
)
time (s)
displacement voltage
In this work, we enhance this harvester model
to increase the output and bandwidth.
Nonlinear VEH with magnetic cores
13
A harvester with silicon steel sheets is presented.
The silicon steel sheets form a closed
magnetic circuit to increase the flux
linkage with the coils.
As a result, electro-mechanical
coupling will be increased.
Nonlinear VEH with magnetic cores
14
Attraction magnetic force is generated between
magnets and the cores.
The magnetic force is nonlinear with respect to
displacement, which gives rise to nonlinearity.
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
-2 -1 0 1 2forc
e (N
)
displacement (mm)
magnetic
spring
＜Magnetic and spring forces＞
By forming magnetic circuits,
• higher output
• wider bandwidth
would be simultaneously realized.
magnetic core
magnets
flux
Electromotive force
15
The effect of the introduction of the steel iron
sheet is evaluated by FEM.
It is clear that the silicon steel sheets can
effectively increase electromotive force.
0
0.3
0.6
0.9
1.2
0 0.5 1 1.5 2 2.5
elec
tro
mo
tiv
e fo
rce
(V)
displacement (mm)
with iron sheet
without iron sheet
＜Electromotive force when magnets moving at 0.15m/s.＞
Potential energy
16
We now consider potential energy of VEH, E.
,2
1 2kXXEXE mag Emag：magnetic energy
k：spring constant
It can be found that the potential profile depends on by
k.
28.4
28.6
28.8
29
-1.5 -1 -0.5 0 0.5 1 1.5
po
ten
tial
en
erg
y (
mJ)
displacement (mm)
k=1000 k=2000
＜Potential energy＞
Potential energy
17
When k is large, the VEH system
would be near to linear.28.4
28.6
28.8
29
-1.5 -1 -0.5 0 0.5 1 1.5
po
ten
tial
en
erg
y (
mJ)
displacement (mm)
k=1000 k=2000
axFAXXE 2
[*]：R. L. Harne, K. W. Wang, 2013, A review of the recent research on vibration energy harvesting via bistable systems, Smart.
Mater. Struct., vol. 22, no. 2, 023001.
When setting proper k, bistable potential structure* is realized.
As for the bistable VEHs, the inertial mass of VEH transits between
two potential wells if the oscillator can overcome the potential barrier
by the vibrations regardless of frequency.
It has been shown that bistable VEHs can harvest electrical power
under noise excitations.
19.3
19.32
19.34
19.36
19.38
-1.2 -0.6 0 0.6 1.2
po
ten
tial
en
erg
y (
mJ)
displacement (mm)
19.3
19.32
19.34
19.36
19.38
-1.2 -0.6 0 0.6 1.2
po
ten
tial
en
erg
y (
mJ)
displacement (mm)
19.3
19.32
19.34
19.36
19.38
-1.2 -0.6 0 0.6 1.2
po
ten
tial
en
erg
y (
mJ)
displacement (mm)
-1.2
-0.8
-0.4
0
0.4
0.8
1.2
1 1.2 1.4 1.6
dis
pla
cem
ent
(mm
)
time (s)
behavior of bistable harvester
18
Bistable harvester has three behavior modes
＜mode1＞
Transit two wells regularly.
interwell oscilaltion
(In general, mode2 is chaotic)
＜mode2＞
Transit two wells irregularly.
＜mode3＞
Trapped one well.
intrawell oscillation
-1.2
-0.8
-0.4
0
0.4
0.8
1.2
0.5 0.7 0.9 1.1
dis
pla
cem
ent
(mm
)
time (s)-1.2
-0.8
-0.4
0
0.4
0.8
0.5 0.6 0.7 0.8
dis
pla
cem
ent
(mm
)
time (s)
1. Introduction
2. Vibration energy harvester with magnetic core
3. Measurement
4. Conclusion
19
Experiments
20
The proposed harvester was manufactured.
The output power was measured.
37mm
30mm
18mm
Coils and steel irons are inside.
Magnets are inside.
Fig. 4. Manufactured Harvester.
Experiments
21
Sinusoidal vibration is applied to the harvester.
37mm
30mm
18mm
Coils and steel irons are inside.
Magnets are inside.
oscilloscope
vibrator
VEH
position
sensor
resistive load
Load voltage is measured by oscilloscope.
Aresistive load,460Ω, is connected to the coil.
The input acceleration is fixed to 1.0G for all the frequencies.
Experiments
22
Experimental results: k=2000
23
The maximum output power is obtained at 60Hz.
The maximum voltage is about 0.7V, which is sufficiently higher than the
threshold of diodes which are included in the rectifiers connected to the
harvester.
The frequency characteristic is well similar to the linear oscillation.
Fig. 1. Load voltage Fig. 2. Output power
0
0.2
0.4
0.6
0.8
30 40 50 60 70 80 90
load
vo
ltag
e (V
RM
S)
input frequency (Hz)
0
0.4
0.8
1.2
30 40 50 60 70 80 90
ou
tpu
t p
ow
er (
mW
)
input frequency (Hz)
24
The maximum output power is obtained at 40Hz.
The output is increased with frequency, then drops at about 45Hz.
Fig. 3. Load voltage Fig. 4. Output power
Experimental results: k=1000
0
0.2
0.4
0.6
0.8
20 30 40 50 60 70 80
load
vo
ltag
e (V
RM
S)
input frequency (Hz)
0
0.4
0.8
1.2
20 30 40 50 60 70 80
ou
tpu
t p
ow
er (
mW
)
input frequency (Hz)
25
As expected, when k=2000, the frequency-response is seemed to be
linear.
When k=1000, the operational bandwidth is not effectively improved.
Fig. 5. Output power
Experimental results
0
0.4
0.8
1.2
20 30 40 50 60 70 80
ou
tpu
t p
ow
er (
mW
)
input frequency (Hz)
k=2000 k=100028.4
28.6
28.8
29
-1.5 -1 -0.5 0 0.5 1 1.5
po
ten
tial
en
erg
y (
mJ)
displacement (mm)
k=1000 k=2000
0
0.4
0.8
1.2
20 30 40 50 60 70 80 90 100
ou
tpu
t p
ow
er (
mW
)
input frequency (Hz)
k=2000 k=1000
26
In linear system, the resonant frequency is given by
Fig. 5. Output power
Discussion1: when k=2000
m
kn
When k=2000, the natural frequency is about 90Hz.
However, the measured natural frequency is 60Hz.
Original resonant point: 90Hz
27
The total force acting on the harvester when k=2000 is shown in Fig. 6.
The initial gradient of the total force is about 900N/m, which can be
assumed to effective spring constant.
In case of k=900, the resonant point is 60Hz.
Fig. 6. effective total force when k=2000
Effective spring constant when k=2000
-3.5
-2.5
-1.5
-0.5
0.5
1.5
0 0.5 1 1.5 2
Fo
rce
acti
ng
on
osc
illa
tor
(N)
displacement (mm)
magnetic force
spring force
total force
: x
: F
N/m900 effkdx
dF
Discussion2: behavior modes when k=1000
28
From the potential energy, when k=1000, the
system has bistable property, by which the
operational bandwidth is improved.
However, the bandwidth of the harvester is not
improved.
The time-variations of displacement and
voltage is shown in Fig. 7, which shows that
the harvester has two behavior modes.
-1
-0.5
0
0.5
1
-1.5
-1
-0.5
0
0.5
1
1.5
0 0.1 0.2 0.3
load
vo
ltag
e (V
)
dis
pla
cem
ent
(mm
)
time (s)
displacement load voltage
-1
-0.5
0
0.5
1
-1.5
-1
-0.5
0
0.5
1
1.5
0 0.1 0.2 0.3
load
vo
ltag
e (V
)
dis
pla
cem
ent
(mm
)
time (s)
displacement load voltage
(a): 35Hz
Fig. 7 Time-variations of displacement and voltage.
(b): 50Hz
0
0.4
0.8
1.2
20 30 40 50 60 70 80
ou
tpu
t p
ow
er (
mW
)
input frequency (Hz)
28.4
28.6
28.8
29
-1.5 -1 -0.5 0 0.5 1 1.5
po
ten
tial
en
erg
y (
mJ)
displacement (mm)
k=1000 k=2000
-1.2
-0.8
-0.4
0
0.4
0.8
1.2
1 1.2 1.4 1.6
dis
pla
cem
ent
(mm
)
time (s)
Discussion2: behavior modes when k=1000
29
？
-1.2
-0.8
-0.4
0
0.4
0.8
1.2
0.5 0.7 0.9 1.1
dis
pla
cem
ent
(mm
)
time (s)-1.2
-0.8
-0.4
0
0.4
0.8
0.5 0.6 0.7 0.8
dis
pla
cem
ent
(mm
)
time (s)
-1
-0.5
0
0.5
1
-1.5
-1
-0.5
0
0.5
1
1.5
0 0.1 0.2 0.3
load
vo
ltag
e (V
)
dis
pla
cem
ent
(mm
)
time (s)
displacement load voltage
-1
-0.5
0
0.5
1
-1.5
-1
-0.5
0
0.5
1
1.5
0 0.1 0.2 0.3
load
vo
ltag
e (V
)
dis
pla
cem
ent
(mm
)
time (s)
displacement load voltage
ideal bistable structure
manufactured harvester
As mentioned before, the bistable harvester has three
behavior modes.
However, the manufactured harvester has two modes.
Experimental results
30
The reason why the measured output does not agree with the analysis results
would be due to the manufacturing error.
Bistable VEH with low potential barrier easily looses the double-well potential
due to manufacturing errors.
28
29
30
-1.8 -1.2 -0.6 0 0.6 1.2 1.8
po
ten
tial
en
erg
y (
mJ)
displacement (mm)
28.4
28.6
28.8
29
-1.5 -1 -0.5 0 0.5 1 1.5
po
ten
tial
en
erg
y (
mJ)
displacement (mm)
k=800 k=1100 k=1600
misaligned
1. Introduction
2. Bistable harvester with magnetic core
3. Simulation and Measurement
4. Conclusion
31
Conclusion
32
For high output and wider bandwidth, a harvester with silicon iron
sheets has been presented.
The proposed harvester has the closed magnetic circuit which is
formed by the silicon iron sheets.
When k is large, the frequency response is almost linear.
When k is appropriately small, the harvester has bistable property
in the ideal case. It has suggested that the bistable property is
disappeared due to manufacturing error.
Future works
Precise harvester will be manufactured.
A new harvester model which is robust against
manufacturing errors will be considered.
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