1. Energy harvesting systems: overview, technologies and applications
Luay Taha – University of Windsor

2. Aim of Presentation
To give an Overview of Energy harvesting systems: need of energy harvesting (EH) , definition of EH, block diagram, Energy converter classification and principle of operation with focused on piezoelectric, Electrostatic, and electromagnetic approaches.
To illustrate some technologies used for micro power and nano power applications
To highlight some applications
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Energy harvesting systems: overview, technologies and applications

3. Need of Energy harvesting
The surrounding environment is a rich source of energy: solar, Wind , hydro, thermal, vibration, human body, RF radiation, ..etc.
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Energy harvesting systems: overview, technologies and applications

4. Example: Possible power recovery from body centred sources
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Energy harvesting systems: overview, technologies and applications

5. Applications
The conversion of ambient energy into electrical energy found many applications in wireless sensor networks, monitoring systems, biomedical implants, wearable and portable devices.
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Energy harvesting systems: overview, technologies and applications

6. Need of Energy harvesting
To replace the battery (bulky, rechargeable, toxic).
To make use of the available energy at the environment. The target nowadays (especially in Wireless sensor networks- WSN) is :energy neutrality, i.e., finding a balance between the harvested energy and the consumed energy such that sustainable operation of WSN can be obtained. 
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Energy harvesting systems: overview, technologies and applications

7. Need of Energy harvesting
In Many Sensor applications, it is required to have a sensor with free power supply that is fabricated with the sensor in one IC.
In many MEMS applications the micro system needs to be embedded in the structure, with no physical connection to the outside word. Such a system requires its own power supply.
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Energy harvesting systems: overview, technologies and applications

8. Definition Energy harvesting
Energy harvesting (also known as power harvesting or energy scavenging) is the process in which energy is captured from a system's environment and converted into usable electric power
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Energy harvesting systems: overview, technologies and applications - Luay Taha

9. Energy harvesting Energy capture environment energy source converter
Electricity
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Energy harvesting systems: overview, technologies and applications - Luay Taha

10. Energy capturing Different approaches are possible:
Wind turbine: wind  angular kinetic energy 
Mass- Spring-Damper : vibration  kinetic energy
steam turbine in solar : pressure  angular kinetic energy
..etc. see example, next slide.
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Energy harvesting systems: overview, technologies and applications

11. Example :Energy capturing- solar
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Energy harvesting systems: overview, technologies and applications

12. Classifications of energy conversions
Vibration to electric:
Approaches:
Piezoelectric
Electrostatic
Electromagnetic
thermal to electric:
Thermophotovoltaic (TPV) approach
Thermoelectric (TE) approach
Flow to electric :
Approaches:
Piezoelectric
Electrostatic
Electromagnetic
Light /RF to electric
Direct using solar or photo cells
Indirect using TPV or TE
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Energy harvesting systems: overview, technologies and applications

13. Energy converters
In this presentation I shall focus only on the three approaches.
Piezoelectric
Electrostatic
Electromagnetic
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Energy harvesting systems: overview, technologies and applications

14. Piezoelectric Energy converter
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Energy harvesting systems: overview, technologies and applications

15. Piezoelectric Energy converter
This type of converter is based on the direct piezoelectric effect that occurs when a charge is generated due to a change in the dipole movement caused by the application of a mechanical stress to the crystal.
The converse piezoelectric effect occurs when a strain is generated on the crystal by the application of an electric field.
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Energy harvesting systems: overview, technologies and applications

16. How to polarize the piezoelectric material?
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Energy harvesting systems: overview, technologies and applications

17. piezoelectric constitutive equations
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Energy harvesting systems: overview, technologies and applications

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Energy harvesting systems: overview, technologies and applications

19. Simplified Models of operation used in engineering application
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Energy harvesting systems: overview, technologies and applications

20. Types of Piezoelectric material
Quartz
Polymers
Barium Titanate (Ba Ti O3),
Lead Titanate (Pb Ti O3),
Lead Zirconate Titanate (PZT)
and Lead Lanthanum Zirconate Titanate (PLZT)
ZNO
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Energy harvesting systems: overview, technologies and applications

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Energy harvesting systems: overview, technologies and applications

22. Construction of piezoelectric converters
The beam based method
The two layer bending element method
The thin film PZT
The unimorph strip method
The stave made from a multilayer laminate of PVDF foil method
Composite cantilever with nickel metal mass generator structure.
Harmonic steel cantilever with a piezoelectric element in thick-film form 
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Energy harvesting systems: overview, technologies and applications

23. Examples- close up of a d33-mode cantilever beam
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Energy harvesting systems: overview, technologies and applications

24. The two layer bending beam

25. The thin film lead zirconate titanate, Pb(Zr,Ti)O3 (PZT)

26. The laminated type generator

27. Fabrication of piezoelectric converters
Thick film
Thin film PZT
Sol–gel.
RIE dry etching
Wet chemical etching
UV-LIGA
Micromachining
Note- difficult to integrate in microsystems
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Energy harvesting systems: overview, technologies and applications

28. Piezoelectric transformer model
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Energy harvesting systems: overview, technologies and applications

29. New Piezoelectric model inner feedback loop model
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Energy harvesting systems: overview, technologies and applications

30. Piezoelectric generator Linear transfer function (33 mode)
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Energy harvesting systems: overview, technologies and applications

31. Simulation results/ voltage and power optimization
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Energy harvesting systems: overview, technologies and applications

32. Simulation results/ voltage and power optimization
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Energy harvesting systems: overview, technologies and applications

33. Experimental results / Impact force
Resistive
Inductive
Capacitive
Wein Bridge
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Energy harvesting systems: overview, technologies and applications

34. Piezoelectric pulse generator principle
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Energy harvesting systems: overview, technologies and applications

35. Electrostatic Energy converter
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Energy harvesting systems: overview, technologies and applications

36. Electrostatic Energy converter
Electrostatic converters use variable capacitor to converts mechanical energy to electrical energy.
The harvesting is based on :
Either Constant voltage
Or Constant charge
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Energy harvesting systems: overview, technologies and applications

37. Constant voltage cycle
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Energy harvesting systems: overview, technologies and applications

38. Constant voltage
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Energy harvesting systems: overview, technologies and applications

39. Constant voltage- more details
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Energy harvesting systems: overview, technologies and applications

40. Constant Charge harvester
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Energy harvesting systems: overview, technologies and applications

41. Comparison between Constant voltage and constant Charge harvester
Constant charge produces more energy than constant voltage. However, Vmax may exceed the CMOS switch rating so care should be taken while using constant charge approach.
Constant voltage does not have high voltage problem.
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Energy harvesting systems: overview, technologies and applications

42. Advantages of Electrostatic harvesters
Compact,
sensitive to low level mechanical energy,
easier to integrate in small scale systems,
not requiring smart materials,
simple to fabricate,
simply structured using less circuitry.
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Energy harvesting systems: overview, technologies and applications

43. Example: Electrostatic wind energy harvester with speed sensing
Consists of:
a micro wind turbine,
a multi-pole variable capacitor,
an LC to LC energy transfer circuit,
a controller with a capacitance sensing system 
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Energy harvesting systems: overview, technologies and applications

44. Block diagram of the harvester
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Energy harvesting systems: overview, technologies and applications

45. Variable capacitor
The capacitor used is a multi-pole capacitor made of two parallel plates: rotor and stator.
Each rotor and stator is divided into a number of poles. The number determines the amount of capacitance variation within a single rotation
It is compact, easily coupled with micro turbine system, has a simple structure, simple to fabricate, capacitance can be modified geometrically thus harvesting more energy per cycle.
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Energy harvesting systems: overview, technologies and applications

46. Energy transfer circuit
The energy transfer circuit is the LC to LC energy transfer circuit which is a simple structure with low energy losses and high energy harvesting efficiency
It uses the same storage device for pre-charging and storing of the harvested energy.
The main target of the energy transfer circuit is to deliver no more or less than the initial invested energy during the pre-charge phase. 
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Energy harvesting systems: overview, technologies and applications

47. Energy transfer circuit
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Energy harvesting systems: overview, technologies and applications

48. Controller/ Capacitance monitoring system
The controller is the key part of the harvester system. It is responsible for several functions.
It monitors maximum and minimum capacitance.
It sends control signals to operate the switching devices of the LC to LC circuit.
It sends information about harvesting time and wind speed to the RF transmitter.
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Energy harvesting systems: overview, technologies and applications

49. Schematic diagram
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Energy harvesting systems: overview, technologies and applications

50. Simulation Results VBat (V) L (mH) Cmax (nF) Cmin 7.4 100 2.5 0.6 0.18
VBat
(V) L
(mH)
Cmax
(nF)
Cmin
7.4
100
2.5
0.6
0.18
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Energy harvesting systems: overview, technologies and applications

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Energy harvesting systems: overview, technologies and applications

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Energy harvesting systems: overview, technologies and applications

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Energy harvesting systems: overview, technologies and applications

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Energy harvesting systems: overview, technologies and applications

55. Prototype testing & Results
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Energy harvesting systems: overview, technologies and applications

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Energy harvesting systems: overview, technologies and applications

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Energy harvesting systems: overview, technologies and applications

58. Fabrication of Electrostatic converters
Thick film
Thin film
SOI-based surface micromachining
Metal UMP process
Note: Simple structure
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Energy harvesting systems: overview, technologies and applications

59. Micro machined variable capacitor
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Energy harvesting systems: overview, technologies and applications

60. MEMS variable capacitor
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Energy harvesting systems: overview, technologies and applications

61. Electromagnetic Energy converter
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Energy harvesting systems: overview, technologies and applications

62. Electromagnetic Energy converter
Electrostatic converters are based on Farady’s law.
Any change in the magnetic environment of a coil of wire induces an electromotive force “e.m.f” in the coil.
The change could be produced by changing the magnetic field strength, moving a magnet toward or away from the coil, moving the coil into or out of the magnetic field and rotating the coil relative to the magnet.
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Energy harvesting systems: overview, technologies and applications

63. Electromagnetic Energy converter
The induced e.m.f is expressed by:-
where:
E.m.f = the electromotive force induced in the coil (V)
N = Number of turns
 = magnetic flux (Web)
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Energy harvesting systems: overview, technologies and applications

64. Electromagnetic Energy converter
The induced e.m.f is expressed by:-
where:
E.m.f = the electromotive force induced in the coil (V)
N = Number of turns
 = magnetic flux (Web)
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Energy harvesting systems: overview, technologies and applications

65. Low frequency model (Rajeevan Amirtharajah)
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Energy harvesting systems: overview, technologies and applications

66. Generator output
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Energy harvesting systems: overview, technologies and applications

67. Fabrication of electromagnetic converters
Variable micro fabrication techniques
Laser micromachining
SU-8 based electroplating technique
Thick parylene technology
Nano-imprint technology
Note:
Complicated 3D coil structure which is incompatible with the conventional MEMS technology
Planner inductor reduces the fabrication complexity
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Energy harvesting systems: overview, technologies and applications

68. The two bonded silicon wafers
The lower wafer has a deposited coil and an etched well in which the mass can move.
The upper wafer has a deposited membrane layer and an electroplated magnetic mass.
The silicon is etched through to the membrane forming a spring.
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MEMS micro generators// Luay Yassin Taha

69. Implementation
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MEMS micro generators// Luay Yassin Taha

70. Micro fabricated coil
Micro-coils are fabricated by building up layers of planar coils, with each layer typically consisting of a square or a circular spiral coil.
The technology which is used to fabricate the spiral coils generally limits the conductor thickness and the minimum spacing achievable between individual coil turns
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Energy harvesting systems: overview, technologies and applications

71. Laser micro machined
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Energy harvesting systems: overview, technologies and applications

72. Note The generated voltage is low (in mV).
There is a difficulty in fabrication the planner coil.
electromagnetic converters do not favourably scale down in size. Future applications for microscale vibration energy harvesters will be best served by piezoelectric and electrostatic transduction mechanisms that can more easily be realised using MEMS technology.
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Energy harvesting systems: overview, technologies and applications

73. Possible implementations
Electromagnetic
approach
Electrostatic
approach
Piezoelectric
approach 73
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Energy harvesting systems: overview, technologies and applications

74. Thank you Any Questions ?!
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Energy harvesting systems: overview, technologies and applications