Environmental Engineering Reference
In-Depth Information
As seen in
Figure 3.12
, the sensor node's operation is comprised of (1)
sensing some external analog signals of sensors such as temperature and (2)
communicating and relaying the sensed information to the gateway node
every 5 s. On receiving the data at the base station, the collected data is then
postprocessed into usable information for any follow-up action. This duty-
cycling approach could significantly reduce the power consumption of the
energy-hungry radio module of the sensor node with a slower transmission
rate of every few seconds.
3.4 Experimental Results
The optimal TEH wireless sensor node has been successfully implemented in
a hardware prototype for laboratory testing. Several experimental tests have
been conducted to differentiate the performance of the TEH system and its
resistor emulation MPPT scheme in powering the connected load consisting
of a supercapacitor, control and PWM generation circuitries, and wireless
sensor node. The operation of the electrical load, as shown in
Figure 3.13
, is
first powered solely by its onboard supercapacitor and then the TEH system
with its integrated MPPT harvesting at a temperature difference of 20 K.
Referring to
Figure 3.13
, it can be observed that the supercapacitor voltage
V
o
keeps decreasing during the period of time when neither the TEH system
Main : 125 k
V
/
V
Powered by TEH
System with MPPT
6
Powered Solely by Supercapacitor
4.6 V
5
4.65 V
Supercapacitor Voltage (
V
o
)
4.5 V
4
3
I
/mA
20
2
Load Current (
I
o
)
1
10
0
0
0
50
100
150
200
250
300
350
400
Time/sec
FIGURE 3.13
Operation of a wireless sensor node.
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