Introduction - Energy Harvesting Autonomous Sensor Systems - page 33

storage device, and wireless sensor node (load), have been proposed,
investigated, and analyzed. These EH systems have been designed
and optimized to suit the target applications (i.e., ambient conditions
and event/task requirements) and then implemented into hardware
prototypes for proof of concept.
1.5 Organization of the Topic
Chapter 1 has introduced the background of the research works recorded in
the topic. Motivation for this research has been stated. The problems in pow-
ering the wireless sensor nodes have been identified. To overcome these prob-
lems, an overview of the EH solution and its system design were described.
A brief review of past works on various EH systems has been provided to
show the state of the art. Contributions of the research works recorded in the
book have been listed.
Chapter 2 discusses WEH research. Two types of WEH approaches based
on WTG and piezoelectric wind energy harvester have been explored. For the
first approach, the issues of small-scale WEH using a WTG for sustaining the
operation of a wireless sensor node are discussed. To resolve the problems,
an ultralow-power management circuit consisting of a resistance emulator
and an active rectifier is specially designed to optimize the WEH system.
Detailed analysis of the WEH system is provided and then validated by the
experimental results. For space constraint applications, a conventional WTG
is not suitable. In the second part of Chapter 2 , a novel method to harvest
wind energy using piezoelectric material (PZT) is proposed. Energy harvested
from the piezoelectric-based wind energy harvester is first accumulated and
stored in a capacitor until sufficient energy is harvested; a trigger signal is then
initiated to release the stored energy in the capacitor to power an autonomous
wind speed sensor node. Experimental results are provided to verify the novel
method proposed in this work.
Chapter 3 discusses TEH from ambient heat sources with low temperature
differences. TEH has recently received great attention but is impeded by the
challenges of low energy conversion efficiency, inconsistency, and low out-
put power due to temperature fluctuation and higher cost. To supplement the
TEH scheme in sustaining the operation of a wireless sensor node, this chap-
ter presents a DC-DC buck converter with resistor emulation-based MPPT.
The resistance emulator approach uses a specially designed ultralow-power
management circuit to perform close impedance matching between the ther-
mal energy harvester and the sensor node to achieve MPPT under varying
thermal conditions. Detailed design steps are provided for obtaining various
parameters of the resistance emulator used in this work. Experimental results
validate the performance of the optimized TEH system.
Like any of the commonly available renewable energy sources, vibration is
another type of energy source. Human activity can be the source of vibrational