Presentation on theme: "Jonathan T. Gold ECE499, EE Capstone Design Project Supervisor Professor James Hedrick February 28, 2009."— Presentation transcript:
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 SourcePerformanceNotes Solar (direct and illuminated light) 100mW/cm 2 Common polycrystalline cells are 16%-17% efficient, while mono- crystalline cells approach 20% Thermoelectric60μW/cm 2 at 5°C gradient Efficiency ≤ 1% for ∆T i 40°C Blood Pressure0.93W at 100mmHgGenerates μW when loaded continuously and mW when loaded intermittently Vibration Micro-Generators4μW/cm 3 (Human Motion-Hz) Highly dependent on excitation, power tends to be proportional to ω and y o. 800μW/cm 3 (Machines-kHz) Piezoelectric Push Buttons50μJ/NQuoted 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 Results I 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 )
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. 1. Piezoelectric element in a voltage divider circuit. Actual Pulse Voltage around 5kV (not to scale) 2. Zoomed in view of second voltage pulse
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. 1. Waveform Output from Transformer 2. Zoomed in view
DC Voltage After Rectifier 1. Voltage of the Full Wave Rectifier With Schottky Diodes 2. Zoomed in view
Capacitor Voltage 1. Voltage waveform of capacitor With LED circuit - drawing 10mA 2. Zoomed in view
New Capacitor Voltage Tantalum Capacitor - 15μF at 35V 2% Efficiency - With One strike – Storage 0.6mJ at 9 V
Holland, R. "Representation of dielectric, elastic, and piezoelectric losses by complex coefficients," IEEE Trans. Sonics Ultrason., SU-14, 18-20, Jan IEEE Standard on Piezoelectricity, IEEE ; Inst. Electrical, Electronics Engineers, New York, "Piezoelectricity." Wikipedia, The Free Encyclopedia. 29 May 2008, Wikimedia Foundation, Inc. 5 Jun 2008.http://en.wikipedia.org/w/index.php?title=Piezoelectricity&oldid= Joseph A. Paradiso and Mark Feldmeier, A compact, wireless, self-powered pushbutton controller, MIT Media Laboratory, W.G. Cady, Piezoelectricity, New York, McGraw-Hill Book Co. Inc., pp.2-8, K. Y. Hoe, An Investigation of Self Powered RF Wireless Sensors, National University of Singapore, 2006.