Transcript ENERGY HARVESTING USING MICRO AND NANO STRUCTURES

FALL 2008 MAE 589M FINAL PROJECT
KARTHIK TIRUTHANI
 Motivation
 Introduction
 Motion based energy conversion model
 Review
 Comparison of energy harvesting techniques
 Issues
 Existing solutions
 Proposed solution
 Analysis and Conclusion
 Increasingly intelligent
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systems
Complexity of wiring
Increased costs of wiring
Reduced costs of
embedded intelligence
Increasing popularity of
wireless networks
Limitations of batteries
Limitations of power
management techniques
Energy Harvesting Mechanisms
Properties of energy harvesting devices
 Ambient radiation sources
desired to power sensors
 Pyroelectric energy harvesting
 “Small”
 Photonic energy harvesting
 “Light weight”
 Energy harvesting using
 “Long life”
Electroactive Polymers
 “Inexpensive”
 Piezoelectric energy harvesting
 “Flexibility”
 Electrostatic energy harvesting
 “High power density”
 Electromagnetic energy
 “Easy fabrication”
harvesting
 Thermoelectric energy harvesting
 Magnetostrictive energy
harvesting
 “Easy implementation with
microelectronics”
 “Low wattage electronics without
parasitics”
 The equation for this
system is given by
 The solution for the
system is given by
 The power output is
Piezoelectric
Capacitive
Strain in piezoelectric material causes a
charge separation (voltage across capacitor)
Change in capacitance causes either
voltage or charge increase.
Piezoelectric generator
C Rs
Vs
Inductive
Magnetostrictive
Coil moves through magnetic field
causing voltage in wire through Faradays
Law
Strain induced on a MsM produces a
change in the magnetization of the
material(Villari Effect). Upon dynamic
or cyclic loading, this change in
magnetization is converted into
electrical energy using a pick-up coil
surrounding the magnetostrictive
layer. The constitutive equations are
and
Electromagnetic energy conversion device Amirtharajah et. al., 1998
MsM Energy harvesting device, Lei Wang 2007
Cross-Section of Micromachined Generator Williams et. al., 2001
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Seebeck effect describes the potential
generated when the junction of two
dissimilar metals experiences a
temperature difference
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Thermoelectric generators (TEGs) use
the Seebeck effect to harvest energy.
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ZT, called Figure of Merit is a very
convenient figure for comparing the
potential efficiency of different materials
for use in devices. Values of ZT=1 are
considered good.
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A simple charging circuit is shown
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Power output is calculated using
Seebeck Effect Illustration
Simple Charging Circuit
TYPE OF ENERGY HARVESTING
ADVANTAGES
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2.
THERMOELECTRIC
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4.
1.
ELECTROMAGNETIC
MAGNETOSTRICTIVE
ELECTROSTATIC
No moving parts allow continuous
operation for many years.
Thermoelectrics contain no materials
that must be replenished.
Heating and cooling can be reversed
No separate external voltage source is
needed
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No separate external voltage source is
needed
No mechanical stops are needed
No smart materials are needed
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2.
3.
4.
Maximum voltage obtained is only 0.1V
Bulky size
Difficult to integrate with microsystems
Difficulty in fabricating coil
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High Coupling coefficient
No depolarization occurs
High flexibility
Suitable for high frequency processes
1.
Easier to integrate with microsystems
and electronics.
Voltages of 2-10V are obtained
No smart material needed
1.
2.
3.
4.
1.
It is a non linear effect
Pick up coil is needed
Bias magnets are needed
Difficult to integrate with microsystems
Separate voltage source is sometimes
needed
Mechanical stops needed
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3.
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3.
1.
PIEZOELECTRIC
DISADVANTAGES
Thermoelectric energy conversion has
low efficiency for small thermal
gradients
Irreversible effects in thermoelectric
materials limit their efficiency and
economy for power generation
applications
Seebeck coefficient can currently not be
increased beyond a necessary limit
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Voltages of 2-10V are obtained
No mechanical stops needed
High energy density
No separate external energy source
needed
Compatible with microfabrication
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Capacitance causes damping which
needs to be reduces motion
Microfabrication process not compatible
with standard CMOS processes
Piezo thin films have poor coupling
coefficient
It has depolarization and ageing
problems
Charge Leakage and high output
impedance
PZT is brittle material
 Voltage required to be produced and energy density of the harvesting process for
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example as supply voltage for a sensor or to charge a battery or capacitor
Low wattage circuitry and eliminating parasitic
Size of the device
Ease of fabrication
Ease of implementation with CMOS processes and microelectronics
Flexibility
Adaptability and maximization of power (Resonance Tuning)
Performance Characteristics
 Synchronized switch
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harvesting on inductor
Adaptive control technique for
the dc–dc converter
DC-DC PWM Boost Converter
with feedforward and feedback
control
Piezoelectric nanogenerators
using aligned Zinc Oxide
nanowire (NW) arrays
Flexible Microfibre–nanowire
hybrid structures for energy
scavenging
Tunable nanoresonators
constructed from telescoping
nanotubes
Piezoelectric Nanogenerator
Flexible nanogenerators
Telescoping Nanotubes
 Multiple spring mass systems
 Tuning the effective non-linear stiffness by
particular design of the electrostatic drive
combs and mechanical springs
 Alter beam stiffness by changing the axial
preloads and causing buckling of beam
 The apparent stiffness of a beam is
dependent on both the elastic constant of
the material, and the electric field across
the material. The stiffness of a structure can
be varied by changing field
 Mass of the silicon structure
Wafer #1 Side and Top View
Wafer #2 Side and Top View
Wafer #3 Side View of
Microchannel
Assembled Microstructure
free to vibrate ~ 0.02 grams
(Assuming 2.33g/cc)
 Mass of fluid filled in the
enclosure ~ 0.28 g
(Assuming 4.95g/cc)
 Total proof mass can be
varied by varying the amount
of fluid in the enclosure
 If the initial quantity of fluid
is a quarter of the enclosure
then the frequency can be
tuned by 100%
Displacement Profile under loading
Stress distribution profile under loading
Factor of Safety plot under loading
 Minimum Factor of Safety for the design is 10.2
 Maximum stress occurs at beam supports and it has
factor of safety 12
 Designing the beams in a trapezoidal shape maximizes
the average strain on the beam thus increasing power
produced
 Future research could focus on improving the
efficiency, implementing microstructures with
microelectronics, developing nanostructures,
improving properties like ZT, piezoelectric and
magnetostrictive constants, factor of coupling, etc