Electrical Power Transfer with “No Wires” - Energy Harvesting Autonomous Sensor Systems - page 188

Power Line

Voltage
Doubler
(AC-DC
Rectifier)

Energy
Storage
and Supply
Circuit
Power Management Unit

Wireless
RF
Sensor
Node

Linear
Voltage
Regulator

Stray Magnetic Energy
Harvesting via Inductive Coupling

FIGURE 6.7
Block diagram of energy harvesting and a wireless RF transmitter system.

is inherently AC from the power supply along the power line, the induced
voltage V emf would appear as an alternative voltage source to the connected
load. However, the wireless sensor node (i.e., AM RF transmitter) requires a
DC source to operate; therefore, the induced voltage must be rectified to DC
and regulated prior to powering up the device. This is achieved by using a
voltage doubler instead of a standard diode-based full-wave rectifier, which
is capable of rectifying and amplifying the low AC voltage to a higher DC
voltage.
Referring to the power curve shown in Figure 6.6 , the amount of power
that is generated across the designed ferrite core wound with copper wires
is in the few milliwatt range. With the limited power generation level, it
is not feasible for the magnetic energy harvester to power the wireless RF
transmitter continuously. To overcome that, an effective energy storage and
supply circuit discussed by Tan et al. [166] was designed and inserted between
the energy source and the wireless load. This ensured that the electrical energy
was stored in the capacitor and the energy stored was sufficient to sustain the
operation of several RF transmissions. When the energy level of the storage
capacitor in the power management unit was sufficient for operations, the RF
transmitter would then start to transmit digital-encoded information to the
RF receiver located some distance away. The amount of energy consumed by
the transmitter was dependent on the number of 12-bit digital-encoded data
to be transmitted.
The design specifications of the experiments to be carried out in the re-
search work were defined according to the practical field condition. The
specifications were as follows: (1) source frequency of 50 Hz, which is the
operating frequency in the Singapore context; (2) electrical current flowing
in the mainstream power line set at 4 A; and (3) 500 turns in each winding.
The advantage of the magnetic energy harvester is that it provides flexibil-
ity in the design parameters, that is, N , , B , involved, which can be de-

signed accordingly to suit different operating conditions of the sensor node
in certain specific applications. The experimental setup of the entire mag-
netic energy harvesting system, which consists of the stray magnetic energy
harvester, power management unit, and wireless RF transmitter, is shown in
Figure 6.8 .