Design of integrated RF to DC power converters

A major problem in designing wireless sensor networks (WSN) is the very limited energy supply of its nodes. Although there are plenty of energy conservation protocols for these networks, the energy problem remains of paramount importance. Harvesting energy from the ambient environment is an approach that will solve the problem of powering these network nodes. Various sources of energy can be collected, such as solar radiation, vibrations - oscillations, heat, pressure variations, radiofrequency (RF) and other natural phenomena. Of course, harvesting energy from the environment typically changes over time with a non-deterministic manner and is characterized by randomness. The operation of a node which is powered by energy harvesting, generally is characterized by the fact that at any time, the total amount of energy required to operate normally, must be less than or equal to the sum of the energy that is already existed in the battery and total energy that can be harvested. Obviously, it is difficult to estimate the amount of harvesting energy, because is characterized by complete randomness thus is also difficult to achieve proper operation of the node. In a future “Internet of Things” where RFIDs (Radio Frequency IDentification) will be integrated with sensors or other devices (MEMS / Micro-Electro- Mechanical Systems or EnHANTs / Energy Harvesting Active Networked Tags) on everything and everywhere, these requirements are of crucial meaning. An energy harvesting system generally includes three parts, a microgenerator (rectifier, inverter etc.) which converts the energy of the environment into electric energy, a voltage amplifier (DC) to increase the DC voltage and a storage element (rechargeable battery or an electrolytic double layer EDLC (super)-capacitor). Although there are lots of alternative energy harvesting forms, we are initially focused on the electromagnetic radiofrequency energy harvesting (RF) which is present all around us as Background RF (radio, TV broadcasting, mobile phones and base stations, wireless networks etc.) or is specifically installed for this purpose (antenna transmitting power in a certain frequency to feed a network of sensors or RFIDs for their operation, without the necessity of energy source in their main bodies (passive tags)). Obviously, this research is focused on the radiofrequency energy harvesting and the conversion of the initial RF power to a DC one that can be implemented by a rectifier which is a nonlinear element such as diode (Schottky or MOS-diode).[...