Energy harvesting systems: overview, technologies and applications Luay Taha – University of Windsor taha1@uwindsor.ca

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 4/21/2019 Energy harvesting systems: overview, technologies and applications

Need of Energy harvesting The surrounding environment is a rich source of energy: solar, Wind , hydro, thermal, vibration, human body, RF radiation, ..etc. 4/21/2019 Energy harvesting systems: overview, technologies and applications

Example: Possible power recovery from body centred sources 4/21/2019 Energy harvesting systems: overview, technologies and applications

Applications The conversion of ambient energy into electrical energy found many applications in wireless sensor networks, monitoring systems, biomedical implants, wearable and portable devices. 4/21/2019 Energy harvesting systems: overview, technologies and applications

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.  4/21/2019 Energy harvesting systems: overview, technologies and applications

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. 4/21/2019 Energy harvesting systems: overview, technologies and applications

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 4/21/2019 Energy harvesting systems: overview, technologies and applications - Luay Taha

Energy harvesting Energy capture environment energy source converter Electricity 4/21/2019 Energy harvesting systems: overview, technologies and applications - Luay Taha

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. 4/21/2019 Energy harvesting systems: overview, technologies and applications

Example :Energy capturing- solar 4/21/2019 Energy harvesting systems: overview, technologies and applications

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 4/21/2019 Energy harvesting systems: overview, technologies and applications

Energy converters In this presentation I shall focus only on the three approaches. Piezoelectric Electrostatic Electromagnetic 4/21/2019 Energy harvesting systems: overview, technologies and applications

Piezoelectric Energy converter 4/21/2019 Energy harvesting systems: overview, technologies and applications

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. 4/21/2019 Energy harvesting systems: overview, technologies and applications

How to polarize the piezoelectric material? 4/21/2019 Energy harvesting systems: overview, technologies and applications

piezoelectric constitutive equations 4/21/2019 Energy harvesting systems: overview, technologies and applications

4/21/2019 Energy harvesting systems: overview, technologies and applications

Simplified Models of operation used in engineering application 4/21/2019 Energy harvesting systems: overview, technologies and applications

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 4/21/2019 Energy harvesting systems: overview, technologies and applications

4/21/2019 Energy harvesting systems: overview, technologies and applications

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  4/21/2019 Energy harvesting systems: overview, technologies and applications

Examples- close up of a d33-mode cantilever beam 4/21/2019 Energy harvesting systems: overview, technologies and applications

The two layer bending beam

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

The laminated type generator

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 4/21/2019 Energy harvesting systems: overview, technologies and applications

Piezoelectric transformer model 4/21/2019 Energy harvesting systems: overview, technologies and applications

New Piezoelectric model inner feedback loop model 4/21/2019 Energy harvesting systems: overview, technologies and applications

Piezoelectric generator Linear transfer function (33 mode) 4/21/2019 Energy harvesting systems: overview, technologies and applications

Simulation results/ voltage and power optimization 4/21/2019 Energy harvesting systems: overview, technologies and applications

Simulation results/ voltage and power optimization 4/21/2019 Energy harvesting systems: overview, technologies and applications

Experimental results / Impact force Resistive Inductive Capacitive Wein Bridge 4/21/2019 Energy harvesting systems: overview, technologies and applications

Piezoelectric pulse generator principle 4/21/2019 Energy harvesting systems: overview, technologies and applications

Electrostatic Energy converter 4/21/2019 Energy harvesting systems: overview, technologies and applications

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 4/21/2019 Energy harvesting systems: overview, technologies and applications

Constant voltage cycle 4/21/2019 Energy harvesting systems: overview, technologies and applications

Constant voltage 4/21/2019 Energy harvesting systems: overview, technologies and applications

Constant voltage- more details 4/21/2019 Energy harvesting systems: overview, technologies and applications

Constant Charge harvester 4/21/2019 Energy harvesting systems: overview, technologies and applications

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. 4/21/2019 Energy harvesting systems: overview, technologies and applications

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. 4/21/2019 Energy harvesting systems: overview, technologies and applications

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  4/21/2019 Energy harvesting systems: overview, technologies and applications

Block diagram of the harvester 4/21/2019 Energy harvesting systems: overview, technologies and applications

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. 4/21/2019 Energy harvesting systems: overview, technologies and applications

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.  4/21/2019 Energy harvesting systems: overview, technologies and applications

Energy transfer circuit 4/21/2019 Energy harvesting systems: overview, technologies and applications

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. 4/21/2019 Energy harvesting systems: overview, technologies and applications

Schematic diagram 4/21/2019 Energy harvesting systems: overview, technologies and applications

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 4/21/2019 Energy harvesting systems: overview, technologies and applications

4/21/2019 Energy harvesting systems: overview, technologies and applications

4/21/2019 Energy harvesting systems: overview, technologies and applications

4/21/2019 Energy harvesting systems: overview, technologies and applications

4/21/2019 Energy harvesting systems: overview, technologies and applications

Prototype testing & Results 4/21/2019 Energy harvesting systems: overview, technologies and applications

4/21/2019 Energy harvesting systems: overview, technologies and applications

4/21/2019 Energy harvesting systems: overview, technologies and applications

Fabrication of Electrostatic converters Thick film Thin film SOI-based surface micromachining Metal UMP process Note: Simple structure 4/21/2019 Energy harvesting systems: overview, technologies and applications

Micro machined variable capacitor 4/21/2019 Energy harvesting systems: overview, technologies and applications

MEMS variable capacitor 4/21/2019 Energy harvesting systems: overview, technologies and applications

Electromagnetic Energy converter 4/21/2019 Energy harvesting systems: overview, technologies and applications

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. 4/21/2019 Energy harvesting systems: overview, technologies and applications

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) 4/21/2019 Energy harvesting systems: overview, technologies and applications

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) 4/21/2019 Energy harvesting systems: overview, technologies and applications

Low frequency model (Rajeevan Amirtharajah) 4/21/2019 Energy harvesting systems: overview, technologies and applications

Generator output 4/21/2019 Energy harvesting systems: overview, technologies and applications

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 4/21/2019 Energy harvesting systems: overview, technologies and applications

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. 9/8/2005 MEMS micro generators// Luay Yassin Taha

Implementation 9/8/2005 MEMS micro generators// Luay Yassin Taha

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 4/21/2019 Energy harvesting systems: overview, technologies and applications

Laser micro machined 4/21/2019 Energy harvesting systems: overview, technologies and applications

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. 4/21/2019 Energy harvesting systems: overview, technologies and applications

Possible implementations Electromagnetic approach Electrostatic approach Piezoelectric approach 73 4/21/2019 Energy harvesting systems: overview, technologies and applications

Thank you Any Questions ?! 4/21/2019 Energy harvesting systems: overview, technologies and applications