Dissertation for the degree of Doctor of Philosophy Self-powered Sensor Monitoring System in Industrial Internet of Things using Off-resonance Piezoelectric Energy Harvesting Techniques
by Jae Yong Cho
Graduate School of Hanyang University
February 2019
Department of Electrical Engineering
Graduate School of Hanyang University
ABSTRACT
The main keyword in the era of the fourth industrial revolution is IIoT (Industrial
Internet of Things) that enables the interactive network between devices, vehicles, home
appliances, and other items embedded with electronics, software, sensors, actuators and etc.
To realize IIoT world, there are key technologies; sensors, microcontroller, connectivity,
and energy management. Especially, in terms of energy management, many researches
have been carried out about self-powering, a battery-less device from energy harvesting.
At the center, there is piezoelectric energy harvesting technology, which converts
mechanical energy into electrical energy. Lots of researches about piezoelectric energy
harvesting have been carried about because piezoelectric material has relatively high power
density and is easily applicable to various infrastructures like road, building, and factory
close to our daily lives. Ultimately, the goal of this technology is heading for energy saving
and simple installation of sensors used for monitoring structural condition without
inconveniences such as the replacement of the batteries and the complexity of the cables.
In this dissertation, the research about design and fabrication of off-resonance type
piezoelectric energy harvesting systems for IIoT sensor was discussed. Because the actual
frequency environment in a real field is not geared to resonant frequencies, previous
piezoelectric energy harvesting systems were difficult to harvest ambient energy efficiently.
We developed the techniques for harvesting energy efficiently through new structures of
off-resonance piezoelectric energy harvesters according to various frequency environment.
As the final step, the demonstration study was conducted to illustrate IIoT platform as V2I
(Vehicle to Infrastructure) system from the piezoelectric energy harvesting techniques. The
developed harvester was fabricated and installed on the highway (Yeoju-si, Gyeonggi-do,
South Korea). As a result, self-powered temperature sensor monitoring system was
constructed using the energy harvester to be able to operate wireless temperature sensor
(eZ430-RF2500, Texas Instruments, USA) without battery. Finally, the system was
established to inform a driver of the freezing condition on the road in advance as V2I
system.
First, the design and fabrication of the resonance dependent type energy harvester
were conducted. We have developed the piezoelectric energy harvester using wind that is
dependent on the resonant frequency, which is a key component of piezoelectric power
generation. The experiment result showed that the difference in power generation
characteristics when and when not at resonant frequencies makes difficult for the energy
harvester to be applied to actual industrial environments where frequencies vary. Finally, it
is essential to develop energy harvesters considering these diverse frequency environments.
Second, the studies of energy harvesters optimized for different types of frequency
environments in industries were conducted. The frequency environment was divided in four
conditions (single frequency, multi frequency, random frequency, and intermittent
frequency). For single, multi and random frequency conditions, a magneto-mechanical
system was applied as the method of harvesting more energy utilizing magnetic forces. For
an intermittent condition, system design was conducted as the method to overcome the offresonance
region. In single frequency environment, conveyor belts within a smart factory
were presented as an experimental environment and the study was conducted to overcome
an environment using magnets on the core belt that is much lower than the resonant
frequencies of a typical piezoelectric device. In multi frequency environment, water pipes
located in plants or buildings were presented as an experimental environment, and to
harvest more energy, a hybrid system using piezoelectric energy harvester and
electromagnetic energy harvester was studied. In a random frequency environment, the
railway was proposed as experimental condition and the magnetic pendulum energy
harvester utilizing inertial moments was developed. The energy harvester for the
intermittent frequency environment was studied, taking into account the wireless switch
that is sometimes pressed by humans as one of the intermittent frequency environments.
Third, the research was carried out on the energy harvesting circuit, which is essential
for applying the energy harvester to the actual IIoT environment. Preferentially, equivalent
circuit modeling of piezoelectricity and impedance matching study was conducted to
deliver maximum power. The DC-DC converter study was also conducted to convert high
voltage of the piezoelectricity into low voltage so that actual sensor applications can be
self-driven by the energy harvester. Additionally, the research was conducted to create the
desired output voltage, and finally to establish the wireless communication interface.
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