The omnipresence of electromagnetic fields is implied just by simple current flow. We are surrounded by electromagnetic fields which we are producing for information transfer or as a byproduct. Many of those fields are very capacitive and can be harvested with coils and high frequency diodes. Accordingly, I built special harvesting devices that are able to tap into several electromagnetic fields to exploit them. The energy is stored in an usual battery. So you can for example gain redundant energy from the power supply of a coffee machine, a cell phone or an overhead wire by holding the harvester directly into the electromagnetic field whose strength is indicated by a LED on the top of the harvester.
Depending on the strength of the electromagnetic field it is possible to charge a small battery within one day. The system is meant to be an option for granting access to already existing but unheeded energy sources. By exploring these sources it can create a new awareness of the invisible electromagnetic spaces while giving them a spatial dimension.
There are two types of harvester for different electromagnetic fields: a smaller harvester that is suitable for lower frequencies below 100Hz which you can find in the general mains (50/60Hz, 16,7Hz) and a bigger one that is suitable for lower and higher frequencies like radio broadcast (~100MHz), GSM (900/1800MHz) up to Bluetooth and WLAN (2,4GHz).