Electrical Power Transfer with “No Wires” - Energy Harvesting Autonomous Sensor Systems - page 183

are also widely used in the field of sensors. Yang et al. [160] explored the
concept of distributed sensing along power lines using sensor nets. Power
lines span long distances, and sensing from remote substations, as is cur-
rently done, provides poor resolution. Hence, distributed sensing along the
length of the power line with intelligent sensors powered by inductive cou-
pling would allow extraction of important local information from each sensor
for a long period of time. Many possibilities of incorporating inductive cou-
pling in medical applications as well are foreseen, for example, permanent
implants, supervising various parameters like the insulin rate for diabetics or
intraocular blood pressure, and excitation of a retina with defective photore-
ceptors [161].
Although many research works on inductive coupling power transfer (ICPT)
have been reported in the literature, such as by Boys et al. [162] and Kurs et al.
in [163], there are only a few research works on magnetic energy harvest-
ing for wireless sensor nodes, like the working Yang et al. [160]. They have
proposed the use of inductive coupling from high-power transmission and
distribution lines to power the sensor nets for power grid monitoring. In this
section, the proposed magnetic energy harvesting idea is different from what
Yang et al. have suggested. The main objective of this research work is to har-
vest the stray magnetic energy generated by electrical power cables deployed
around the residential, commercial, and industrial buildings. Through induc-
tive coupling, the stray magnetic energy is harvested to power the wireless
sensor nodes for condition-based maintenance of electrical energy systems,
and equipment.

6.1.1 Magnetic Energy Harvester

The research work on magnetic energy harvesting via inductive coupling uti-
lizes induction as the energy harvesting technology. It is based on the combi-
nation of the famous Ampere's law and Faraday's law of induction. Ampere's
law describes the magnetic flux density of the stray magnetic energy source
available for induction by the surge coil. Faraday's law of induction states
the induced electromotive force V emf in a surge coil is directly proportional
to the time rate of change of magnetic flux

through the winding loop. The
induced voltage V emf generated at the output of the surge coil is processed
by a power management unit and stored in an energy storage device (i.e.,
capacitor). This stored energy is then used to power up the operation of a
wireless sensor node.
In experimental tests, the characterization process of the magnetic energy
harvester was divided into two parts: (1) the magnetic energy source (i.e.,
magnetic field containing the magnetic energy governed by Ampere's law)
and (2) the magnetic energy harvester (i.e., toroid-based surge coil wound
with many turns of wires N as described by Faraday's law of induction).
The magnetic energy source is first characterized using the experimental
setup shown in Figure 6.1 . Since the magnetic flux density B along a current-
carrying electrical power cable is a function of the current I flowing through