Electromagnetic Radiation Energy Harvesting – The Rectenna Based Approach

Abstract

How much energy is available around us? Which use can we give to this energy? These are two questions to which answers had been changing over time. What would be our particular answer if a forefather or an ancestor would ask them to us? Some sources of energy like sun, wind or sea waves have been present unaltered since the prehistoric times and before to nowadays. Some others like oil and natural gas have been progressively reduced by the action of man. But it is interesting to notice that there are some other sources, which we can name as artificial sources, and that have emerged by man’s action, as a consequence of industrial and technological development. Such modern or artificial energy sources are directly connected to the energy harvesting technology since, for instance, most of the vibrations or temperature gradients are produced by machines and engines. Also in the electromagnetic spectrum, we can harvest energy not only from natural sun radiation, but also from all the artificial radio‐ frequency sources that are permanently increasing in number and which are a consequence of one of the last technological revolutions: the Information and Communications Technology (ICT) revolution. Although when we think about electromagnetic (EM) waves at present time, we probably tend to think about examples like radio, TV or cell phones, where the information part of the electromagnetic signal is the protagonist, we should bear in mind that those signals are in fact a combination of information and energy. In this chapter, we are not interested in describing how information can be transmitted through electromagnetic waves but how the energy of these waves is transmitted and collected to be harvested and used to supply ICT devices. In order to calculate how much energy can be associated to an electromagnetic wave, we have to consider the physical nature of these particular waves.