Introduction - Energy Harvesting Autonomous Sensor Systems - page 30

Wind Generator

Li-Polymer
Battery
Eco
Sensor Node

Solar Panel

(a) AmbiMax hardware with a solar panel,
wind generator, lithium polymer battery,
and Eco Node

(b) Piezoelectric windmill prototype

(c) Optimized design of the small-scale windmill with an isometric view
and internal crankshaft structure exhibiting the translation mechanism

FIGURE 1.20
Examples of TEH systems.

Weimer et al. [60] presented an anemometer-based solution to perform the
WEH and sensing tasks, which are accomplished separately by two different
devices. The authors utilize the motion of the anemometer shaft to turn a
coupled alternator to generate electrical power for the sensor nodes. Although
the sensor nodes incorporating the harvesting solution have an increased
operational lifetime, this comes with the price of larger device size, higher
overall cost, and higher energy conversion loss.
In another WEH research work [61], Priya et al. designed a windmill that
uses piezoelectric elements to generate electricity from wind energy (see
Figure 1.20b ). An output power of 10.3 mW was harvested and reported
for a wind flow that leads to 6 rotations per minute. Subsequently, another
group of researchers, Myers et al. [62], developed an optimized small-scale
piezoelectric windmill as shown in Figure 1.20c . The whole structure of the
windmill is made of plastic, and it utilizes 18 piezoelectric bimorphs to con-
vert wind energy, hence vibration energy, into electrical energy. The windmill
was tested to provide 5 mW of continuous power at an average wind speed of