[Encyclios]

Conversion modes

Energy conversion takes place in different modes depending on the environmental source.

• Spurious energy from radio and television transmissions or theoretically from any electromagnetic emission can be harvested. A typical use of this technique is used to power Radio Frequency Identification (RFID) identifiers.
• Conversion of mechanical motion can take place using piezoelectric crystals or special polymers, which when subjected to stress from mechanical deformation, generate small electrical potentials. One mode uses the kinetic energy of the motion of a magnetic pendulum within an electromagnetic winding. The originating forces can come from other periodically applied pressures, such as in shoes during a walk, or from mechanical vibrations from motors, or any low-frequency ambient sound or noise. In the case of fibers embedded in clothing fabrics, the very movement of the person produces electrical energy. Where there are air currents, even if inconstant, micro wind turbines are used.
• Solar energy is converted through photovoltaic cells, which lend themselves easily to be scaled in small sizes, an example is that of pocket calculators, or that of the garden step lamps.
• In the presence of thermal gradients, thermoelectric generators can be used, with a typical voltage of 0.1-0.2 mV/K. Useful potentials can also be obtained for direct use, simply by arranging several generators in series. The powers drawn are typically on the order of mW, and human and animal heat can also be exploited. They are often coupled to heat sinks to improve (increase) the temperature gradient. Alternatively, one can exploit the pyroelectric effect, another ferroelectric behavior. An advantage of pyroelectric materials over thermoelectric ones is their resistance up to 1200 °C or more, allowing energy to be gleaned even from high-temperature sources and thus with greater thermodynamic efficiency.