Electrical Power Transfer with “No Wires” - Energy Harvesting Autonomous Sensor Systems - page 206

Eciency vs. Load

80.00%

70.00%

60.00%

50.00%

1.44 Amplitude
1.8 Amplitude
2.2 Amplitude

40.00%

30.00%

20.00%

10.00%

0.00%

0 5000 10000 15000

Load Resistance (ohms)

FIGURE 6.22
Experimental efficiency of a WPT under different loading conditions.

6.2.4 Experimental Results

The experimental setup of the WPT system, as shown in Figure 6.23 , consisted
of a high-power, high-frequency AC source; a set of source, transmitting, re-
ceiving, and load coils; electrical testing loads; and an oscilloscope. To achieve
both high-power and high-frequency electrical supply from the AC source
is very challenging, but it has been successfully implemented using a low-
power, high-frequency signal generator capable of generating an AC signal
up to 500 MHz, and a high-power amplifier. The high-frequency AC signal
generated by the signal generator was channelled to the power amplifier for
amplification.

6.2.4.1 WPT System Powering Electrical Load(s)
The designed WPT system was experimentally tested with an electrical ap-
pliance as the system load instead of a resistor to demonstrate and determine
the wireless power capability of the system. To add a physical perspective to
the WPT research work, a 12-V lightbulb was used. Figure 6.24 shows a 12-V
lightbulb lit at a distance of 20 cm between the transmitting and receiving
coils.
Based on the experimental results, the WPT system shown in Figure 6.24
was able to transmit an electrical output power of 1 W over a distance of
20 cm to the lightbulb with an efficiency of around 51%. During the experi-
ment, whenever the coil separation distance was beyond the limit of 20 cm,
the brightness of the lightbulb diminished quickly. This phenomenon was
due to the low efficiency of the WPT system with weak coupling between the
coils. The same experiment was conducted for different lightbulbs of 2.4, 3.6,
and 7.2 V as well, and their experimental results, which include input power