Environmental Engineering Reference
In-Depth Information
system that combines the concept of wind and piezoelectric effect. Making
use of the force generated by the flow of wind to vibrate the piezoelectric ma-
terial, the mechanical energy harvested from the vibration of the piezoelectric
material is converted into electrical energy. The advantages of the piezoelec-
tric wind energy harvester are that it is compact and sensitive to low-speed
wind. Although the amount of energy that can be harvested is quite limited, it
is shown experimentally in the section that the piezoelectric energy harvester
is sufficient to power the wireless electronic circuits to transmit five digital
12-bit signals to the remote base station. Once the trigger signal is received,
the warning siren would be activated.
Figure 2.27 illustrates the power conversion process of the proposed
vibration-based piezoelectric wind energy harvester, starting from the in-
coming wind flow v to the output electrical power generation P elec . The
power conversion process can be divided into three main stages: aerody-
namic stage (Section 2.2.1.1), cantilever bending beam stage (Section 2.2.1.2),
and piezoelectric stage (Section 2.2.1.3). Referring Figure 2.27 , it can be seen
that each of these power conversion stages has its own set of representa-
tive analytical models, which are elaborated in detail in subsequent sec-
tions. Before that, the operating principle of the vibration-based piezoelectric
wind energy harvester, as illustrated in Figure 2.27 , is first discussed and
explained:
Difference in wind speeds above v a and below v b the airfoil/blade
creates a net pressure P that results in a lift force F at the tip of
the blade. This phenomenon can be explained based on Bernoulli's
principle.
Net pressure P is applied at the tip ( x
L )ofthe piezoelectric wind
energy harvester, which is free to vibrate, and its other end is fixed
with a clamp ( x
=
0). Due to the wind v flowing across the piezo-
electric wind energy harvester, the tip of the harvester deflects up
and down (
=
L ); hence, vibration is generated on the piezoelectric ma-
terial. This phenomenon can be explained with the Euler-Bernoulli
cantilever beam theory.
As the blade of the harvester swings, the piezoelectric material, which
is bonded to the blade, experiences the mechanical stress
of the
generated vibration. Electrical AC power is thus harvested from the
vibration-based piezoelectric wind energy harvester. This phenomenon
can be explained using piezoelectricity theory.
2.2.1.1 Aerodynamic Theory
The aerodynamic effect of airflow on the piezoelectric wind energy harvester
is described based on a well-known fluid mechanic principle: Bernoulli's
principle. Bernoulli's principle states that in fluid flow, an increase in velocity
occurs simultaneously with a decrease in pressure. This principle is a simplifi-
cation of Bernoulli's equation, which states that the sum of all forms of energy
in a fluid flowing along an enclosed path is the same at any two points in that
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