Energy Harvesting For Embedded Systems Author: Srivanthi Chalsani & Dr. James M Conrad Presented by: Monil Neema Date : 04/14/2008

Introduction: What is the need for Power Harvesting? What is Power Harvesting? Sources: Wind, Water, Sun, Thermoelectricity, Photovoltaic cells, Piezoelectricity.

Solar Energy: Uses sunlight to get electrical energy Examples are roadway signs and marine locations. There are limitations to solar energy.

Example: Figure shows a current research going on at the University of California at Berkley, which uses Photovoltaic cells and is called as Smart Dust Program. Here instead of RF these motes communicate optically. Experiments have shown that the motes require 10 micro watts a day and if the sunlight is proper the solar cell is able to generate 1 Joule per day.

Thermo-electricity Thermoelectric phenomena and generation of thermoelectricity. Solid state thermoelectric generators are said to have long life, low maintenance, and high reliability. Typical experiments have shown that thermoelectric devices generate 10 to 100 micro watts of power.

Electromagnetic method (Induction method). Faradays law of electromagnetic induction. Electromagnetic energy harvesting can be achieved by changing the magnetic field around the conductor.

Piezoelectricity Generation of electric potential in response to mechanical stress applied (from pressure or vibration). Typical Piezoelectric devices such as lead zirconate titanate, polycrystalline ceramics generate power of order of mwatts which is too small for system applications but is good for hand held devices such as wristwatch.

Examples They are using pressure exerted in a heel strike to generate power. Power – milliwatts. Applications : Low power embedded devices. They used it for driving LCD and small loudspeakers.

Comparison Energy SourceEnergy earning under optimal conditions Space consumed Voltage versus Current Thermo elementLowVery LowV – Low C – Med. Solar cellVery highHighV – Low C – Med. Piezoelectric element Med.LowV – High C – Low Electromagnetic Method High V – Med. C - Low

References: A survey of energy harvesting systems for embedded systems. By Sravanthi Chalsani and Dr. James M. Conrad. Wikipedia Mobile Networking for Smart Dust by Joseph M Kahn, Randy Howart Katz, and Kristopher SJ Pister. Requirements for Battery free embedded systems. By Ulrich wagnerArmin Vaichtlbauer, and Eberhard Muller. Parasitic Power Harvesting in Shoes Physics and media group MIT laboratory.