Wind Energy Harvesting System - Energy Harvesting Autonomous Sensor Systems - page 85

10 kS/s 100 ms/div

CH1
5.00
DC
CH2
2.00
DC
CH3
2.00
DC

100:1
V/div
Full
100:1
V/div
Full
1:1
V/div
Full

CH1
CH2
CH3

20.00 V
8.00 V
8.00 V

Main: 10 k

Expanded
View

-8.00 V
-8.00 V
-20.00 V

-500.0 ms 500.0 ms

20 ms/div

Channel 1: Output Voltage of Power Storage and
Supply

Channel 3: Output Voltage
of Linear Regulator

Channel 2: 12-Bit
Encoded Data Received
on RF Receiver Side

P-P
Max
Min
Avg

(C1)
(C1)
(C1)
(C1)

4.16667 V
8.75000 V
4.58333 V
6.91327 V

P-P
Max
Min
Max

(C2)
(C2)
(C2)
(C3)

4.66667 V
4.41667 V
-250.000 mV
3.41667 V

FIGURE 2.45
Waveforms collected at the RF receiver side to the display number of encoded data words received
using the harvested energy.

which means that a very minimal amount of energy would be consumed, so
it is reasonable to exclude the power being consumed by the RF load during
the idle time. By calculation, the average power and hence the energy con-
sumed by the RF transmitter are 13.2 mW and 132

J, respectively. Taking into
consideration the power loss in the voltage regulator, the total power required
for one digital 12-bit data word is 167 J. Based on the harvested electrical

energy of 917 J stored in the capacitor, five packets of 12-bit digital-encoded

data words (each packet consumes 167 J) can be transmitted. This is verified

by the five packets of digital-encoded data words received at the base station
shown in Figure 2.45 . Referring to Figure 2.45 , channels 1 and 3 exhibit the
output voltages of the storage capacitor and the voltage regulator; channel 2
shows the encoded data words received at the RF receiver end.
For the transmission of five packets of 12-bit encoded digital data words,
835 Jofelectrical energy is drawn from the bank (917 J) of electrical energy

stored in the capacitor. Of the 835 Jofelectrical energy drawn, the actual

useful energy being consumed by the RF transmitter is 660 J. Therefore, the

efficiency of the system is around 72%. Power loss is incurred in the power
management circuit. In addition, it can be observed in Figure 2.45 that during
the discharge period of 100 ms, as the capacitor voltage is decreasing from