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Sustainable Energy Harvesting Technologies Past Present and Future Part 12

Tham khảo tài liệu 'sustainable energy harvesting technologies past present and future part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Energy Harvesting Technologies Thick-Film Piezoelectric Microgenerator 209 The dried paste is then co-fired in a nitrogen atmosphere. The nitrogen must be used because the filler must not be burnt out before the glass-ceramic has sintered. The process is repeated to form a multilayer composite film. Finally the composite film is co-fired in an air environment where the carbon filler acting as a sacrificial layer is burnt out without residues releasing a composite thick-film free-standing structure. The fabrication steps are shown in Figure 15. Similarly the proposed free-standing energy harvester structures as described in section 3.4 can be fabricated using this technique. 5. Energy harvesters performance comparison Over the years many micro-generator prototypes have been fabricated. The most common vibration energy harvester is based on an electromagnetic principle because at present the output powers produced by electromagnetic generators are greater than piezoelectric and electrostatic based generators. However with recent improvement in piezoelectric activity in PZT and the ability to be incorporated within simple cantilever structures which is relatively easy to be fabricated and integrated with microelectronic systems piezoelectric methods are an attractive alternative for future investigation. Each of the energy harvesters was being claimed to demonstrate better performance in one way than another. The most common comparison merit is the electrical output power density. Although power density comparison can give an idea of the performance of an energy harvester it does not explain the influence of the excitation source. As according to Equation 5 the output power of a resonant device is closely dependent on the amplitude of an excitation source. However to make the comparison meaningful all the energy harvesters have to be excited at a fixed vibration characteristic e.g. adjust acceleration level at resonant frequency of the tested devices to give a fixed .