As it was required to be able to control the quantity of energy available to the energy harvesters during the demonstration, controllable energy sources were provided for each of the four energy harvester types being utilized. The energy sources used are as follows:
• Solar energy harvester: For this module the ambient illumination was used, along with some paper clouds that could be used to partly or fully occlude the active face of the solar module and thus simulate variations in incident brightness.
• Vibration energy harvester: As the device used with this module is designed to operate from vibrations from machines powered by the mains electricity supply, a small mains-operated vacuum pump was used as the test source. This has a low level of operational vibration that can be perceived when the pump is touched but is not visible to the naked eye. The amount of vibration
produced can be varied by changing the loading of the pump by constricting the air inlet line.
• Thermal energy harvester: To provide heat to the hot side of the thermal energy harvester, a small adjustable hot plate was used. To aid the dissipation of heat from the cold side of the device, a multipin heat sink was attached and arranged so air could flow across it. To allow the measurement of the hot and cold side temperatures, two k-type bead thermistors were mounted with thermally conductive adhesive to the corresponding device faces.
• Wind energy harvester: Operation of the miniature wind turbine has been achieved either by simply blowing onto it or by directing the output from a standard small desk fan onto the blades.
The component modules used in the energy-aware, energy-harvesting node demonstration are shown in Figure 8.10. Interconnecting cables between the core node and the energy multiplexer subsystem, between the energy multiplexer subsystem and the energy modules, and between the energy harvesters and their corresponding modules are omitted for clarity. In addition, an energy bleed circuit was connected to the energy bus comprising of a low value resistor in series with a push switch, pressing the switch to make the circuit adds in a further energy drain for demonstration purposes.
