Wind Energy Harvesting System - Energy Harvesting Autonomous Sensor Systems - page 76

TABLE 2.2
Properties of Piezoelectric Material

Description of Properties Unit Symbol Value

Piezoelectric material Piezo systems PSI-5A4E Lead zirconate titanate

10 − 12 Piezoelectric strain/field

coefficient

Metres/volt d 33 390 ×

10 − 12 Piezoelectric charge

density/stress coefficient

Coulombs/newton d 31 − 190 ×

10 − 3 Piezoelectric strain/charge

density coefficient

Metres/coulomb metre g 33 24 ×

10 − 3

Piezoelectric field/stress
coefficient

Volt/newton metre g 31 − 11.6 ×

Coupling coefficient k 31 0.35

Newtons/metre 2 6.6x10 10 Elastic modulus Y E 1

generated by the vibration-based piezoelectric wind energy harvester can be
estimated based on the tip deflection y L of the piezoelectric generator, which
is expressed as

9 d 31 E y I

V oc =

33 L 3 wt 1

4

y L (2.32)

X

k 31 / 2 −

2.2.2 Characteristics and Performances of a Piezoelectric

Wind Energy Harvester

Wind flowing with a certain range of speeds is able to stir a certain amount of
vibration on the plastic flapper attached to the piezoelectric material, which
thus passes the vibrational energy to the piezoelectric material. The harvested
vibrational energy from the piezoelectric material would then be converted
into electrical energy at the output of the piezoelectric wind energy harvester.
The relationships between the harvested electrical energy and the incoming
wind depends on the orientations and rotating angles between the piezoelec-
tric wind energy harvester with respect to the directions of the incoming wind
flow as shown Figures 2.36 to 2.39 . Taking the concept about the flight dy-
namics of a vehicle rotating in three dimensions around its coordinate system
origin, the three rotating angles defined in this research work (

Z )
are equivalent to roll, pitch, and yaw angles, respectively. Experiments have
been conducted to find out the amount of electrical power that is generated by
the piezoelectric wind energy harvester when placed in different orientations.
Figures 2.37 , 2.38 , and 2.39 illustrate the power curves of the piezoelectric
wind energy harvester with different rotating angles

L , W , and

Z ranging
from 0 ◦ to 90 ◦ . Similar sets of experimental tests have been collected for the
rotating angles ranging from

L , W , and

90 ◦ to 0 ◦ , and the results are quite symmetrical.

−