Sheet 1Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Micro Energy Harvesting
Power Supply for Distributed and Embedded Systems
Peter Woias
Albert-Ludwig-University of Freiburg
Department of Microsystems Engineering (IMTEK)
Laboratory for Design of Microsystems
Freiburg, Germany
Sheet 2Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Distributed MicroDistributed Micro--Embedded Systems (MES)Embedded Systems (MES)
wireless data link
micro-
sensor
wireless
transmitter
sensor input
micro-
controller
S TM
S TMS TM
S TM
S TM
S TMS TMS TMS TM
S TM S TM S TM
G
T
M
Sensor
Data processing
Communication
S
T
M
Gateway
S TMS TM
Fabrication and Transport
Building and Enviroment Medical
… power
supply ?
Automotive
Space, ….
Sheet 3Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Wire or battery Wire or battery …… or what ?or what ?
Sensors in redwood trees
© University of California
medical implants
© Vitatron
distributed and „embedded“ sensor
systems in greenhouses © Crossbow
tire pressure sensors
sensor
rope
battery service person
(vertigo-proof)
Sheet 4Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
energy
conversion
materials
and
energy
storage
energy and
system
management
Micro Energy Harvesting: The VisionMicro Energy Harvesting: The Vision
heat,
light
movement,
other bugs,…
Energy-Autonomous Embedded Systems
„always on“
no battery recharging or exchange
no power cords
easy to install …
… at numerous application sites
energy management
micro-
sensor
wireless
transmitter
sensor input
micro-
controller
wireless data link
generator energy storage
Sheet 5Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Micro energy harvesting Micro energy harvesting –– IMTEKIMTEK‘‘s PhD programs PhD program
Fact sheet
financed by DFG and industry
3 associated members
22+1 PhD scholarhips
start: October 2006
run-time: 4.5 years (1st phase)
Associated Members Members Sponsors
Research topics
energy conversion
materials for energy harvesting
energy storage and management
system considerations
Sheet 6Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
electromagnetic
field energy
Ambient energy and related conversion mechanismAmbient energy and related conversion mechanism
chemical
energy
electrical
energy
energy from
mechanical or
fluid motion
thermal
energy
piezoelectric
capacitive (electret)
inductive (P-magnet)
thermoelectric
fuel cells
electromagnetic,
capacitive,
EHD, MHD
(Carnot) cycle
optical
energy
photovoltaic
induction
Sheet 7Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Piezoelectric bending generators: Principle Piezoelectric bending generators: Principle
11,31 piezodq σ⋅=( )1131 σ⋅== dtd
d
td
qdI
Design challenges
homogeneous mechanical stress higher output power
tunable resonance frequency broader application range, more power
smart system integration cheaper, easier fabrication
Sheet 8Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Optimized vibrational piezo generator (2007)Optimized vibrational piezo generator (2007)
spectral output power (no seismic mass) influence of a seismic mass
E. Just et al., Proc. GMM-Workshop
“Energieautarke Mikrosysteme”, 2006
F. Goldschmidtböing, P. Woias,
Journ. Micromech. Microeng. 18, 2008, 104013
Sheet 9Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
FrequencyFrequency--tunable piezo generator (2008)tunable piezo generator (2008)
Principle
Actuation force in the „arms“ will
stiffen the resonating beam and
thus change its resonance frequency
high tuning range (22%)
loss of Q factor with
increasing force
C. Eichhorn et al., Proc. PowerMEMS 2008,
Sendai, Japan, 309-312.
force
Sheet 10Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Fabrication: PiezoFabrication: Piezo--PolymerPolymer--Composites (2003)Composites (2003)
vent
molding form
piezodisk
piezo disk cured polymer
molding form
liquidthermosettingpolymer
feed
Advantages
structure definition and piezo integration
in one single step
low-cost perspective via inject molding
extremely high design flexibility
actuators and generators in one single technology
20 mm
piezoceramic diskwith metal electrodes
electrical contact
polymer layer
mounting block
seismic mass
vibration
Sheet 11Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
ImpactImpact--type piezo generator (2005)type piezo generator (2005)
Advantages
stress-homogenized hinge design
for a maximal output power
non-resonant operation
high output power
high output voltage
stacked devices for power multiplication
6 mWp @ 36N pulse (100 ms)
Sheet 12Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Electromagnetic generators: Principle and examplesElectromagnetic generators: Principle and examples
multi-resonant generator
Univ. Hongkong, 2002
P = 800 µWtd
dNU
Φ⋅−=
rotatory generator of the
Seiko KineticTM wrist watch
P = 5 µW
rotor
generator
batteryelectromechanic
quartz clockwork
Properties
AC currents from motion or induced AC fields
bad to fair voltage range (mV…V)
moderate source impedance (<10 kΩ)
Sheet 13Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Electromagnetic generator in PCB technologyElectromagnetic generator in PCB technology
multi-resonant generator
Univ. Hongkong, 2002
lid
wire-wound
coil
permanent
magnet
spacer
mechanical
resonator22 mm
Properties
output power:
330 µW @ 102 Hz and 1G
no-load voltage: 210 mV
(improved via modified coil design)
E. Bouendeu, J. Kovink,
IMTEK – Laboratory for Simulation
Sheet 14Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Thermoelectric generators (TEG): PrincipleThermoelectric generators (TEG): Principle
relevant material combinations α [µV/K]
Al / p-Poly-Si 195
Al / n-Poly-Si 110
p-Poly-Si / n-Poly-Si 190...320
p-Bi0,5Sb1,5Te3 / n-Bi0,87Sb0,13 200...420
TU ∆⋅=∆ α
2TA
Pp electric
∆⋅=
Seebeck voltage
Specific output power
Sheet 15Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
3D micro3D micro--TEGTEG
Output power and no-load voltage @ 10K
measured: 1.612 µW
6 V
optimization potential: 36.3 µW
top heat conductor (gold)
bottom heat conductor
(silicon)
membrane with planar
thermocouples (Al-poly-Si)
thermal
insulator
(SU-8)
air chamber
for thermal
insulation
T. Huesgen et al., Sensors & Actuators A 145-146, 2008, 523-429.
10
mm
7500 thermocouples
Sheet 16Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Bio fuel cells: Principle and applicationBio fuel cells: Principle and application
direct-oxidizing
glucose fuel cell
S. Kerzenmacher et al., Journ. Power Sources, 2008
A. Kloke et al., Proc. Biosensors 2008, Shanghai
Properties
output power: 2.3 … 3.3 µW /cm²
open cell voltage: 0.5 … 0.3 V
power requirement of a pacemaker: 10 µW
0,0
0,2
0,4
0,6
0,8
1,0
1,2
0 5 10
Current density in µA cm-2
Cell
po
ten
tial
in V
0,0
0,5
1,0
1,5
2,0
2,5
3,0
Po
wer
den
sit
y i
n µ
W c
m-2
pacemaker
IMTEK – Laboratory for
MEMS Applications
Sheet 17Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Photovoltaic generatorsPhotovoltaic generators
Properties
delivers DC voltages
thickness: 0.3...0.6 mm
flexible and washable
effiziency: 3%
sunlight: ≈ 3.0 mW/cm²
in-door: ≈ 0.1 mW/cm²
flexible Si thin film cell
on a polymer carrier
© Flexcell
„Pico Beacon“ with rigid
Si thin film cell on glass
© UC Berkeley
Sheet 18Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Polymer PV cellsPolymer PV cells
0.0 0.2 0.4 0.6-8
-4
0
4
Voc
=0.58 V
Jsc
=7.34 mA/cm2
FF=0.54
η=2.28%
Cu
rre
nt d
en
sity (
mA
/cm
2)
Voltage (V)
AM 1.5G irradiation
CathodeCathode
AnodeAnodeActive area
0.08 cm2
Active area
0.08 cm2
300 400 500 600 7000
10
20
30
40
50
Exte
rna
l
Qu
an
tum
Effic
ien
cy (
%)
Wavelength (nm)
Cathode Al
CdSe QDs/P3HT
PEDOT:PSS
Anode ITO substrate
Sunlight
Y. Zhou, M. Krüger, G. Urban, IMTEK,
Laboratory of Sensors and FMF
Summer 2009: Highest reported
efficiency value* based on CdSe QDs!
Sheet 19Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Energy densities of various storage conceptsEnergy densities of various storage concepts
high storage density of H2 in MH
acceptable (and improving)
efficiency of H2 fuel cells
Would a „hydrogen battery“
make sense ?
0
20
40
60
80
100
Fa
rad
ay e
ffic
ien
cy [
%]
Gold
Cap
Ni-M
H
Li-I
on
H2 fu
el c
ell
Ele
ctro
lyze
r
Gold Cap
Lead Acid
Adenosine
Triphosphate
NiMH
Li-Ion
H2 in MH (< 2%)
H2 in MH (4%)
H2 in MH
(nanopowder) Methanol
Electrolyte Cap.
1
10
100
1.000
10.000
1 10 100 1.000 10.000
energy density in [Wh/kg]
en
erg
y d
en
sit
y i
n [
Wh
/l]
hydrogen in metal hydrides (MH)
batteries
capacitors
Refs: J. Brodd et al, J. Electrochem. Soc.,
151 (3), 2004, K1-K11 and HERA
Hydrogen Storage Solutions, Germany
Sheet 20Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
chip-integrated
fuel cell with Pd
storage
HydrogenHydrogen--based energy storagebased energy storage
G. Erdler, M. Frank, M. Lehmann, H. Reinecke, C. Mueller, Sensors & Actuators A 132/1
(2006), 331-336.
vo
ltag
e [
V]
current density [mA/cm²]
po
wer
den
sit
y [
mW
/cm
²]
0.5 mm thick fuel cell:
photograph (right) and
its electrical characteristics
6 mm6 mm
19 mm19 mm
Sheet 21Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Energy managementEnergy management
Requirements
start-up control
optimal impedance match between
generator, battery and load
voltage level transformation
active generator control
active rectification
supply voltage: < 1 V
power consumption: a few µW
Solutions, chips ? ….not
available today
(2004).
2163 µm
control ASIC for a capacitive
micro converter, Medinger,
Ph. D. thesis, MIT, and
Analog Devices, 1999
….eventually
coming along
(2007).
Solutions, microchips ?..... not available
today ( 2004).
Sheet 22Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Adaptive voltage converter for piezogeneratorsAdaptive voltage converter for piezogenerators
T. Hehn, Y. Manoli, IMTEK-
Laboratory of Microelectronics
Sheet 23Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
sensor system
Temperatur
e sensor
Micro-
controller
Energy management
and storage
RF
transmitte
r
Application szenario:
Remote temperature
sensing at „heavy“
machinery …
Demonstrator: Remote Temperature MonitoringDemonstrator: Remote Temperature Monitoring
Vibration
Temperature ?
Energy-
autonomous
Piezogenerator
RF
receiver
35,4 °C
35,4 °C
Sheet 24Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
System setSystem set--upup
Requirements
well-defined turn-on and turn-off
low-voltage operation
low-power operation
Sheet 25Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Stacked impactStacked impact--type piezogeneratortype piezogenerator
Technical data
maximum output power: 120 µW
optimal output voltage: 2.15 V
tolerance band: ± 0.2 V35 mm
Sheet 26Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Micro power managementMicro power management
A frequently used concept …
piezo-
generator storage load
(CMOS device)
… with inherent problems
overall bad efficiency
no safe start-up from zero power (danger of deadlock)
Solution: defined turn-on via power management
po
we
r d
raw
of
the
lo
ad
Sheet 27Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Why not buy Why not buy …… ??
Problems with today‘s ICs
no „real low voltage“
undefined sub-threshold
behaviour
limited functionality (not
specific for energy harvesting)
Sheet 28Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
LowLow--voltage regulator with sharp turnvoltage regulator with sharp turn--onon
Characteristics
mimimum transistor count (3)
safe-operation supply voltage: 0.4 V
max. power consumption: 25 µW
optimization potential:1…3 µW
Sheet 29Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Demonstration Demonstration
Sheet 30Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Conclusions Conclusions
Embedded systems are an essential part of our current and future living.
Their power supply can not be done by batteries and power grids alone.
We will depend on Energy Harvesting.
However, its successful application will require an optimum interplay of …
energy conversion
energy storage
energy management
system hardware and operation
… i.e. a thorough and application-specific system design.
Sheet 31Peter Woias, Hannover-Messe, IVAM-Workshop, 22.04.2010
Thank you very
much for your
attention !