Jonathan T. Gold

ECE499, EE Capstone Design Project

Supervisor Professor James Hedrick

February 28, 2009

Piezoelectricity: Refers to the force applied to a segment of material, leading to the appearance of an electrical charge on the surface of the segment. The source of this phenomenon is the specific distribution of electric charges in the unit cell of a crystal structure.

Applications• High Voltage Power Sources

•Energy Harvesting•Sensors

•Detection and Generation of Sonar Waves

•Actuators•Piezoelectric Motors•Loudspeaker•AFM and STM•Inkjet Printers

Motivation:•The idea of power a small device on the controlling gesture itself is amazing.•A remote for the TV you never have to change battery for.

The Principal Characteristics High Energy Conversion Efficiency Low Voltage Operation Large Force Low Motion Fast Response No Electromagnetic Interference

Part #:TSI8-H5-202

Piezoelectric Pushbutton Igniter

Piezo Systems Inc.

Piezoelectric stacks are monolithic ceramic structures, constructed of many thin piezoceramic layers, electrically connected in parallel.

A look at Battery, Solar, and Vibration energy sources

Energy Source Performance NotesSolar (direct and illuminated light)

100mW/cm2 Common polycrystalline cells are 16%-17% efficient, while mono-crystalline cells approach 20%

Thermoelectric 60μW/cm2 at 5°C gradient

Efficiency ≤ 1% for ∆Ti40°C

Blood Pressure 0.93W at 100mmHg Generates μW when loaded continuously and mW when loaded intermittently

Vibration Micro-Generators 4μW/cm3 (Human Motion-Hz)

Highly dependent on excitation, power tends to be proportional to ω and yo.

800μW/cm3 (Machines-kHz)

Piezoelectric Push Buttons 50μJ/N Quoted at 3V DC for the MIT Media Lab Device.

Room To Improve Piezoelectric Pushbutton

Reconfigure spring-loaded hammer to softer strikes

Transformer Design Redesign step down transformer (90:1)

This “LC” electrical resonance to equal the element’s mechanical resonance for optimum energy transfer.

Capacitor Choice Ultra-Capacitor, Tantalum Cap., or Regular

Operating at 10% mechanical-to-electrical efficiency, delivers 3mJ of energy per push.

RF Wireless Sensor *IEEE

Electric energy harvested was 67.61µJ,

Allowing 2.5 digital words to be transmitted

Actual ResultsI obtained 2% mechanical-to-electrical efficiency, delivering 0.6mJ of energy per push.

Piezoelectric Element Piezoelectric Pushbutton Igniter Mechanical resonance near 50kHz Capacitance of 18pF

Transformation & Impedance Matching High voltage at low currents to Lower voltage at high currents Matching resonance of element, for optimal power transfer

Voltage Rectification Convert active current (AC) to direct current (DC) Minimize power loss – used Schottky diodes

Energy Storage Voltage collection through selected capacitor

Piezoelectric Element Kinetic Energy Converted into Electrical

Energy

Impedance Matching (kV – V) Optimal Resonance Matching

Conserve power loss

Ferrite Core Working range of low frequencies 1 to 50 kHz Mixture of ferrite and ceramic minimal heat loss

Voltage Rectification AC - DC Schottky Diode

Lower voltage drop, allows less power loss Fast recovery time

0.3V at a forward current of 100mA

Capacitor Tantalum Electrolytic (2-3 Time More)

Low equivalent parallel resistance Power does not dissipate as fast

Equivalent series resistance ( 900mΩ )

When the hammer strikes the element, a pressure wave is generated. As a result , the pressure wave is reflected multiple times in both the element and the hammer. This creates a resonance in the piezoelectric element and is shown in the several AC voltage pulses in the top waveform.

1. Piezoelectric element in a voltage divider circuit.Actual Pulse Voltage around 5kV (not to scale)

2. Zoomed in view of second voltage pulse

0 100 200 300 400 500 600 700 800 900 1000-5

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15Piezoelectric Element Voltage

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Matching mechanical resonance of the Element’s resonance to optimize maximum power transfer. Used to couple the most energy when the tank circuit matched the elements frequency to allow the element to work as maximum efficiency.

1. Waveform Output from Transformer

2. Zoomed in view

0 100 200 300 400 500 600 700 800 900 1000-20

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40Transformer Output

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0 100 200 300 400 500 600 700 800 900 1000-20

-10

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1. Voltage of the Full Wave Rectifier

With Schottky Diodes

2. Zoomed in view

0 100 200 300 400 500 600 700 800 900 10000

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80Full Wave Rectified Voltage

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0 100 200 300 400 500 600 700 800 900 1000-50

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100V

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1. Voltage waveform of capacitor

With LED circuit - drawing 10mA

2. Zoomed in view

0 100 200 300 400 500 600 700 800 900 1000-2

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4Capacitor Voltage

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6V

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Tantalum Capacitor - 15μF at 35V

2% Efficiency -With One strike – Storage

0.6mJ at 9 V

0 100 200 300 400 500 600 700 800 900 1000-1

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Holland, R. "Representation of dielectric, elastic, and piezoelectric losses by complex coefficients," IEEE Trans. Sonics Ultrason., SU-14, 18-20, Jan. 1967.

IEEE Standard on Piezoelectricity, IEEE 176-1978; Inst. Electrical, Electronics Engineers, New York, 1978.

"Piezoelectricity." Wikipedia, The Free Encyclopedia. 29 May 2008, Wikimedia Foundation, Inc. 5 Jun 2008 <http://en.wikipedia.org/w/index.php?title=Piezoelectricity&oldid=215622383>.

Joseph A. Paradiso and Mark Feldmeier, A compact, wireless, self-powered pushbutton controller, MIT Media Laboratory, 2002.

W.G. Cady, Piezoelectricity, New York, McGraw-Hill Book Co. Inc., pp.2-8, 1946.

K. Y. Hoe, An Investigation of Self Powered RF Wireless Sensors, National University of Singapore, 2006.