Environmental Engineering Reference
In-Depth Information
Vo ltage Waveform of a Depressing Cycle
120
100
80
60
40
20
0
1.
2.
3.
0.50
0.70
0.90
1.10
1.30
1.50
Time/s
FIGURE 4.18
Voltage waveform of a depressing cycle of the prestressed piezoelectric diaphragm material.
the transducer to return to its equilibrium position via the opposite direc-
tion. The change in direction of displacement, and hence direction of stress,
causes a reverse in polarity, and an AC voltage is generated at the output
of the piezoelectric material. The impact-based energy harvesting process
seen in Figure 4.17 can be described as follows: Initially, at zero voltage state
labelled as 1, the piezoelectric material is not depressed, so it can be seen
from Figure 4.18 that no voltage is generated by the piezoelectric material.
On depressing the material, which is illustrated by the positive voltage state
labelled 2 in Figure 4.17 , the material is flattened, and the electrical voltage
developed across the material can be read from Figure 4.18 to be 110 V. Energy
accumulated in the piezoelectric material is available for harvesting by the
designed power management circuit and the connected wireless transmitter
load. Similarly, on releasing the material as illustrated by the negative volt-
age state labelled 3 in Figure 4.17 , the material bounces back to its original
prestressed state, a rectified electrical voltage of 110 V is developed across the
material, and energy is stored in the material for harvesting.
The natural bouncing characteristic and power generation ability of the
material has been utilized by this research to simplify the structure of the en-
ergy harvesting mechanism. By doing so, it is no longer necessary to have
any additional mechanical structure, like the LightningSwitch case shown
in Figure 4.14 , to translate the human pressing force into electrical energy.
This is a great advantage of this research over the commercial products avail-
able on the market. Without the need of an extra energy translation mech-
anism, this proposed impact-based energy harvesting mechanism using a
prestressed piezoelectric diaphragm material reduces the cost of manufactur-
ing the switch to lower than that of the more complicated LightningSwitch de-
sign. In summary, this research work, which uses a batteryless wireless control
switch and prestressed piezoelectric diaphragm material, is less complicated
to implement, is less susceptible to wear and tear due to less mechanical parts,
and enables more cost savings than similar products available in market.
To determine the characteristic of the prestressed piezoelectric diaphragm
material, different input forces—hard (
10 N), normal (
5 N), and light
 
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