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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. 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. Applications • High Voltage Power Sources •Energy Harvesting •Sensors •Detection and Generation of Sonar Waves •Actuators •Piezoelectric Motors •Loudspeaker •AFM and STM •Inkjet Printers Piezo Systems Inc. Piezoelectric stacks are monolithic ceramic structures, constructed of many thin piezoceramic layers, electrically connected in parallel. The Principal Characteristics Part #:TSI8-H5-202 High Energy Conversion Efficiency Low Voltage Operation Large Force Low Motion Fast Response No Electromagnetic Interference Piezoelectric Pushbutton Igniter Energy Source Solar (direct and illuminated light) Performance 100mW/cm2 Thermoelectric 60μW/cm2 at 5°C gradient 0.93W at 100mmHg Blood Pressure Vibration Micro-Generators Piezoelectric Push Buttons 4μW/cm3 (Human Motion-Hz) 800μW/cm3 (Machines-kHz) 50μJ/N Notes Common polycrystalline cells are 16%-17% efficient, while monocrystalline cells approach 20% Efficiency ≤ 1% for ∆Ti40°C Generates μW when loaded continuously and mW when loaded intermittently Highly dependent on excitation, power tends to be proportional to ω and yo. Quoted at 3V DC for the MIT Media Lab Device. A look at Battery, Solar, and Vibration energy sources Operating at 10% mechanical-to-electrical efficiency, delivers 3mJ of energy per push. Actual Results I obtained 2% mechanical-to-electrical efficiency, delivering 0.6mJ of energy per push. Room To Improve RF Wireless Sensor *IEEE 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 Electric energy harvested was 67.61µJ, Allowing 2.5 digital words to be transmitted 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 Voltage Rectification AC - DC Lower voltage drop, allows less power loss Fast recovery time 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 0.3V at a forward current of 100mA Capacitor Schottky Diode Tantalum Electrolytic (2-3 Time More) Low equivalent parallel resistance Power does not dissipate as fast Equivalent series resistance ( 900mΩ ) Piezoelectric Element 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. Piezoelectric Element Voltage 15 Actual Pulse Voltage around 5kV (not to scale) 10 Volts (V) 1. Piezoelectric element in a voltage divider circuit. 5 0 -5 0 100 200 300 400 500 600 Time (us) 700 800 900 1000 0 100 200 300 400 500 600 Time (us) 700 800 900 1000 30 Zoomed in view of second voltage pulse 20 Volts (V) 2. 10 0 -10 Transformed Voltage 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. Transformer Output 1. Waveform Output from Transformer Volts (V) 40 20 0 -20 0 100 200 300 400 500 600 Time (us) 700 800 900 1000 0 100 200 300 400 500 600 Time (us) 700 800 900 1000 2. Zoomed in view Volts (V) 10 0 -10 -20 DC Voltage After Rectifier Full Wave Rectified Voltage 80 With Schottky Diodes 60 Volts (V) 1. Voltage of the Full Wave Rectifier 40 20 0 0 100 200 300 400 500 600 Time (us) 700 800 900 1000 0 100 200 300 400 500 600 Time (us) 700 800 900 1000 2. Zoomed in view Volts (V) 100 50 0 -50 Capacitor Voltage Capacitor Voltage 1. Voltage waveform of capacitor With LED circuit - drawing 10mA Volts (V) 4 2 0 -2 0 100 200 300 400 500 600 Time (us) 700 800 900 1000 0 100 200 300 400 500 600 Time (us) 700 800 900 1000 6 2. Zoomed in view Volts (V) 4 2 0 -2 New Capacitor Voltage Tantalum Capacitor - 15μF at 35V 2% Efficiency With One strike – Storage 0.6mJ at 9 V Capacitor Voltage 10 9 8 7 Volts (V) 6 5 4 3 2 1 0 -1 0 100 200 300 400 500 600 Time (us) 700 800 900 1000 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.