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Senior Project – Electrical Engineering – 2009 The Use of Piezoelectrics as a Battery-less Power Source Jonathan T. Gold Senior Advisor: Professor James Hedrick Abstract Our landfills are full of toxic dead batteries from small handheld devices such as TV remote controls. In my presentation, I describe a method for harnessing the energy created from human activities to power handheld devices. For example, the force of pushing the button on a TV remote control could be used to power the remote, itself. In this project, I investigated a battery-less system, which generates its energy using a piezoelectric element combined with a spring-loaded hammer to strike the piezoelectric material one time. Piezoelectricity is the ability of some materials, notably crystals and certain ceramics, to generate an electric potential in response to an applied mechanical stress. An electric voltage results from a separation of electric charges across the elements crystal lattice. This is what allows piezoelectric materials to convert mechanical energy—you pushing on the TV remote button—and transform it into electrical energy. Implementation of a piezoelectric system in daily human activities, with applications of low voltage devices from an initialized applied force was investigated. The piezoelectric ‘pushbutton’ was adapted to matching circuitry, composed of voltage transformation with a step-down transformer and energy storage with a capacitor. In my presentation, I will be describing the design and implementation of this piezoelectric system, as well as the results I have achieved. Block Diagram Common Energy Sources Power Output Design Specifications Waveform Analysis Piezoelectric Element Piezoelectric Element •Piezoelectric Pushbutton Igniter •Transformation & Impedance Matching 15 10 Volts (V) •Mechanical resonance near 50kHz •Capacitance equal to 18pF Piezoelectric Element Voltage 5 •High voltage at low currents to Low voltage at high currents •Piezoelectric Output to Capacitor Input 0 -5 •Voltage Rectification 200 300 400 500 600 Time (us) 700 800 900 1000 0 100 200 300 400 500 600 Time (us) 700 800 900 1000 20 Volts (V) •Voltage is collected through a capacitor 100 30 •Converts AC to DC currents •Energy Storage 0 10 0 -10 The measurement of the piezoelectric voltage was achieved through the use of a voltage divider circuit. Bottom waveform is zoomed in view of the second voltage pulse (not to scale) NOTE: Actual Pulse Voltage around 5kV Capacitor Output Capacitor Voltage 10 9 8 7 Results Experimental results: From one pushbutton depression, averages a maximum force of 15N. Measured results from my test circuit indicated a stored energy of 0.6mJ in the capacitor at 9V. Volts (V) 6 5 4 3 2 1 0 -1 0 100 200 300 400 500 600 Time (us) 700 800 900 1000 The stored capacitor energy was recorded, the Tantalum Capacitor was a 15μF at 35V This shows that on one pushbutton compression the capacitor stores 9V NOTE: Capacitor is discharging 10mA to an LED