Power Line Induction Energy Harvesting Powering Small Sensor Nodes

Abstract: This thesis is examining the possibility of powering small wireless sensor nodes using induction and magnetic fields, generated by alternating current in conductors. As more devices becomes online, powering them all using batteries is not a good enough solution. The application in this thesis is a current sensor mounted near the electric distribution boxwhere there are typically no power outlets, instead powered by an inductor. Two theoretical models are created. One basic, with calculations in 2d and one more complex in 3d. Experiments show that the 3d one is significantly more accurate and a goodway of estimating an inductor’s possible power output. Along with the theoretical models, an electric one is also created showing the performance to expect while connected to a load. The combination allows for estimation and optimization of the inductor output during the design process. A hardware prototype is then constructed and evaluated according to the requirements of a real world application, as a way of minimizing the number of battery changes of a small wireless sensor node. The results show that it would not be reasonable to use an inductor for charging batteries this way as it fails to reach the requirements in several areas. At reasonable sizes and weights it will not be able to produce enough power for the sensor’s needs. With an inductor big enough, the required output could be big enough. Although batteries of equal size would last for a very long time. These tests are performed with the Swedish power grid as the source conductor. The higher currents and frequencies of the American power grid shows a big increase in output power, as both parameters are squared in the equations. In Sweden the output power is only about 16 percent of what would have been possible in America. But even then the inductor would have to be placed in close proximity of the source conductor, as its output power is quickly decreasing with distance. The conclusion is that this way of powering electronics has very limited use. There are few situations where the load are close enough to conductors with strong alternating current and the size of the inductor required to power a minimal load makes it unpractical.