Energy scavenging for wireless sensor nodes with a focus on vibration to electricity conversion

The vast reduction in size and power consumption of CMOS circuitry has led to a large research effort based around the vision of ubiquitous networks of wireless communication nodes. The wireless devices are usually designed to run on batteries. However, as the networks increase in number and the devices decrease in size, the replacement of depleted batteries is not practical. Furthermore, a battery that is large enough to last the lifetime of the device would dominate the overall system size, and thus is not very attractive. Methods of scavenging ambient power for use by low power wireless electronic devices have been explored in an effort to make the wireless nodes and resulting wireless sensor network indefinitely self-contained.; A broad survey of potential energy scavenging methods has been performed in order to determine likely power densities and how these densities compare with current battery technology. A power density of 100 μW/cm3 was established as a practical target from both a power consumption and power production point of view. Based on the results of the survey, the conversion of ambient vibrations to electricity was chosen as a method for further research. Solar powered systems also appear attractive and have been developed for purposes of comparison.; A wide variety of vibration sources have been considered and measured in common environments including buildings and manufacturing spaces. Virtually all vibrations measured had a dominant frequency component somewhere between 75 Hz and 200 Hz. The magnitude of the vibrations varied from about 0.1 m/s 2 to about 10 m/s2. An average value of 2.25 m/s 2 at 120 Hz was chosen as a baseline on which to base power generation calculations and tests.; Three methods of coupling mechanical kinetic energy to electrical energy were evaluated as technologies on which to base vibration to electricity converters. These are electromagnetic, electrostatic, and piezoelectric. After an initial investigation, electromagnetic conversion was dropped because of the very low AC voltages generated (tens of millivolts). Both piezoelectric converters and electrostatic (or capacitive) converters based on MEMS technology were further pursued.; Both piezoelectric and MEMS electrostatic converters were carefully modeled. Designs were optimized based on the models developed within in total size constraint of 1 cm3. Test results from the piezoelectric converters demonstrate power densities of about 200 μW/cm3 from the baseline input vibrations. (Abstract shortened by UMI.)...