Introduction - Energy Harvesting Autonomous Sensor Systems - page 31

4.5 m/s. Still, the physical size of the WEH systems are too large and bulky as
compared to the sensor node, and their harvested power exceeds the power
requirement of the sensor node. In addition, there is a lack of adequate power
management circuit to maximize electrical power transfer from the source to
the load.

1.4 Contribution of This Topic
As described in the literature survey on EH systems, there is no definite energy
source that is suitable for sustaining the operation of a wireless sensor node in
a different variety of applications. Hence, this topic aims to tell how to go about
the design, followed by some analysis for further optimization, and practical
implementation of the various types of EH autonomous sensor systems. In
many WSN applications, the environmental conditions of the sensed area,
where the sensor nodes are deployed, are often not consistent. The energy
sources are intermittent and fluctuating in nature, while the operations of the
wireless sensor nodes require a constant electrical power source. As such, one
of the main focuses of the topic is the adequate power management circuit
design to provide a proper match between the EH mechanism and the sensor
node. Other key contributions of the research works recorded in this topic are
as follows:

Tw o types of small-scale WEH systems have been proposed: (1) direct
WEH approach using a WTG and (2) indirect WEH approach using
piezoelectric material. Detailed analysis and characterisation of the
wind energy conversion mechanisms have been provided. Based on
the characteristics of the WEH mechanisms obtained, the power man-
agement unit is designed to take care of the dynamics of both the
WEH mechanisms subjected to environmental condition variation,
such as varying wind speeds and the wireless sensor node operating
in its WSN. Since most of the conventional MPPT algorithms are not
suitable for the WTG, a resistor emulation or impedance-matching
scheme has been introduced for MPPT. In addition, an alternating
current-direct current (AC-DC) active rectifier has been designed us-
ing MOSFETs (metal-oxide-semiconductor field-effect transitors) in
place of diodes for rectifying the low-amplitude AC voltage gener-
ated by the WTG under low wind conditions. Prototypes of the WEH
systems have been developed to validate the performance of the sys-
tems.

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In some places, a wind energy source might not be available; hence,
TEH has been investigated. The TEH mechanism, which houses a
miniaturized TEG, has been designed to harvest the thermal energy
from the heat source. An equivalent electrical circuit model of the TEH
mechanism has been developed. Based on this equivalent model, the

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