Photovoltaics versus rectenna technologies Maxwell’s equations are summarized in Table 1.ġ.2. An EM wave can be described with these equations, which must be met for a set of particular boundary conditions. The set of equations which describe how electric and magnetic fields propagate, interact and how they are influenced by material properties are Maxwell’s equations. In most of materials, the direction of the EM wave propagation is perpendicular to the electric and magnetic fields, which are also oscillating in phase perpendicular to each other. Unlike what occurs in photovoltaics technology, where optical radiation energy is better accounted in terms of photon energy since there the conversion mechanism is based in photon-electron interactions, in rectenna technology it is more convenient to express the input EM radiation in terms of the power or the power density of the EM wave.Īn EM wave can be defined as a form of energy radiated by a source which results in a combination of oscillating electric and magnetic fields. A zoom detail of the optical part of the spectrum shows that light radiations is in the hundred nm and THz range of wavelengths and frequencies respectively. 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.ĭiagram of the electromagnetic spectrum with indications of the wavelength, λ, and frequency, ν, of the most representative radiations from shorter and most energetic, cosmic rays, to the longer and less energetic radiofrequencies. 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. Also in the electromagnetic spectrum, we can harvest energy not only from natural sun radiation, but also from all the artificial radiofrequency 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.Īlthough 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. 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. 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. Some others like oil and natural gas have been progressively reduced by the action of man. 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. 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. The energy available in the electromagnetic spectrum
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