Wind Energy Harvesting System - Energy Harvesting Autonomous Sensor Systems - page 64

2.2 Indirect WEH Approach Using Piezoelectric Material
With the great advancement of microelectronic technologies in many areas
such as integrated circuit (IC) designs, chip fabrications, and so on, the power
requirement for wireless sensor nodes continues to decrease from the milli-
watt to microwatt level. This paves the way for micro-WEH for some WSN
applications, whereby there is a need for the small-scale WEH system to
be as small as possible and highly portable so it does not interfere with
the normal operation of the deployment area. The direct WEH approach
using a wind turbine generator, as illustrated in Section 2.1, has been suc-
cessfully demonstrated in powering the miniaturized wireless sensor node.
However, there are certain limitations with this type of conventional wind
power generator, which uses a large rotational turbine of 3-cm blade ra-
dius to harvest energy from the wind flow. Limitations include: a large wind
front contact with the wind is required for good WEH, mechanical constraint
on the miniaturization of the electric generator and gearbox (if any), and
more.
The physical size of wind turbine generators that have been reported in
Section 2.1 as well as the academic literature is still relatively bulky com-
pared to the sensor node. Weimer et al. present a compact anemometer-based
solution [60] for remote area WEH; the space needed by the anemometer is still
relatively large compared to the miniature sensors. Another research study by
Priya et al. [61] describes the “piezoelectric windmill” that consists of several
piezoelectric actuators arranged along the circumference of the mill in the
cantilever form. The design of this windmill is very large and complex such
that the power generated, which is in the milliwatt range, exceeds the power
requirement of the ultralow-power sensor node. Hence, these large and bulky
WEH systems are not cost effective and appropriate for WSN applications,
which require miniaturized devices.
In this section, an indirect WEH approach using piezoelectric material is
proposed for powering a miniaturized wireless sensor node. The proposed
piezoelectric wind energy harvester is very different from the conventional
bladed wind turbine; a novel way of harvesting wind energy through the
piezoelectric effect is explored to address the limitations of the wind turbine
generator.

2.2.1 Vibration-Based Piezoelectric Wind Energy Harvester

A novel way of harvesting electrical energy from wind energy using bimorph
piezoelectric material is proposed here. The novel piezoelectric wind energy
harvester collects the vibration energy induced from the wind flow, and the
vibration creates stress on the piezoelectric material to generate electrical en-
ergy. The application of this novel piezoelectric-based wind energy harvester
is similar to the wind turbine research work, which is for a low-powered au-
tonomous wind speed sensor. The piezoelectric wind harvester is a unique