Se Bin Kim

Study on Application of Piezoelectricity to Korea Train eXpress (KTX)

In this study, we have investigated application of piezoelectricity to actual commercially operating high-speed Korean train. We recorded and analyzed the vibrations of commercial Korea Train eXpress (KTX). We experimented with different cantilever beam thicknesses (0.25 mm, 0.6 mm, and 1.0 mm) and different piezoelectric material dimensions (length × width × thickness, 10.0 mm × 10.0 mm × 0.5 mm, 20.0 mm × 10.0 mm × 0.5 mm, and 30.0 mm × 10.0 mm × 0.5 mm) on real data from recorded random frequencies and train vibration amplitudes. The addition of tip masses on the cantilever beam decreased the resonance frequency range when the vibrations were constant but not when they were random. The optimal condition was experimentally found, to involve decreasing the piezoelectric substrate beam thickness and increasing the piezoelectric substrate beam area rather than merely increasing the tip mass. The most effective method to improve the operational sensitivity was combination of decreasing the resonance frequency by adding tip masses, decreasing beam thicknesses, and increasing beam areas.

Design of a New Piezoelectric Energy Harvester Based on Secondary Impact

Two models for an energy harvester imparting rotational energy to piezoelectric materials are presented, in order to compare the effects of applying identical amounts of energy to a cantilever beam by changing the total displacement per unit time, and applying a secondary impact. For a piezoelectric energy harvester given a high total impulse per unit time with low total displacement per unit time, higher power outputs were generated at lower resistive loads. Conversely, for a harvester given high total displacement per unit time with low total impulse per unit time, power output was higher at high resistive loads. At matched impedance, the secondary-impact-type piezoelectric energy harvester generated higher power output than the hitting-type piezoelectric energy harvester did at low resistive load. Optimized response of secondary-impact-type piezoelectric energy harvester was obtained at a frequency of 60 Hz with a low resistive load of 1 kΩ. The generated output power was measured as 124 mW, which corresponds to power density of 140 mW/cm3 for the entire cantilever beam, and a power density of 342 mW/cm3 for only the piezoelectric material volume (including sliver paste volume). For a harvester without a secondary impulse at low resistive loads (1 kΩ), the optimizing frequency was between 20 and 30 Hz, with an output power of 22 mW, which corresponds to a 25 mW/cm3 power density for entire cantilever beam and power density of 60 mW/cm3 for only the piezoelectric material volume(including sliver paste volume).

Study of Charging Efficiency of a Piezoelectric Energy Harvesting System Using Rectifier and Array Configuration

This paper suggests the design in rectifier and array configuration for an impact-based piezoelectric energy harvesting (PEH) system, to investigate the charging efficiency. In the design of the rectifier, it is suggested that rectifying the signal from each piezoelectric module separately generates more electrical energy and charges a capacitor faster than using a single rectifier for all modules connected in series. In the structural design, the array was designed into two conditions: impacted simultaneously and impacted sequentially with a phase difference (30°, 60°, 90°, 120°, 150° and 180°). We show that when impacted sequentially with a phase difference, this allows faster charging rates of energy harvesting. Additionally, distribution of the torque required to transform the piezoelectric modules was found to be another advantage from this condition. These results could be used in the design of more-efficiently-charging impact-based PEH system.

Feasibility study on application of piezoelectricity to convert vibrations of Korea Train eXpress

In this study, we have investigated the feasibility of applying piezoelectricity to convert the mechanical vibrations of an operating commercial high-speed Korean train to useful electricity. We recorded and analyzed the vibrations of Korea Train eXpress (KTX). We experimented with different cantilever beam thicknesses (0.25, 0.6, and 1.0 mm) and different piezoelectric material dimensions (10.0 × 10.0 × 0.5 mm3, 20.0 × 10.0 × 0.5 mm3, and 30.0 × 10.0 × 0.5 mm3) on real data from recorded random frequencies and train vibration amplitudes. The addition of tip masses on the cantilever beam decreased the natural resonance frequency range when the vibrations were constant but not when they were random. The optimal condition was experimentally found, to involve decreasing the beam thickness and increasing the beam area rather than merely increasing the tip mass. The most effective method to improve the operational sensitivity was to decrease the resonance frequency by adding tip masses, decreasing beam thicknesses, and increasing beam areas.

Stress Distribution Design of Additional Substrate for Piezoelectricity

This study was conducted to analyze a relationship between deformation degree curvature and output voltage of piezoelectric system, as well as to interpret the calculated and experimented data. Basically, the experiment was conducted by using tip masses of 10, 20, and 30 g to two different thicknesses of piezoelectric materials (0.15 mm and 0.2 mm). With this approach, the result showed that the lowest average Ix value had the highest voltage, 26.12 V m/s2 when the vibration acceleration was 4 m/s2. On the other hand, the lowest standard deviation of curvature ratio, ρ, had highest voltage, 58.98 V when the vibration acceleration was of 40 m/s2. Overall, this study demonstrates that the deformation degree and curvature ratio are related and proves they can be controlled.

Rectifier and structural design for efficient energy harvesting system from impact-based piezoelectric array

This paper describes an efficient method for piezoelectric energy harvesting (PEH) system from impact forces using an array of piezoelectric modules. Specifically, the rectifier circuit and array configuration are considered. It is shown that rectifying the signal from each piezoelectric module separately generates more energy and charges a capacitor faster than using a single rectifier for all modules connected in series. In addition, the array can be designed such that the modules are impacted simultaneously or sequentially with a phase difference. We show that the latter allows faster energy harvesting. These results could be used in the design of efficient impact-based PEH system.

Design and optimization of secondary shock type piezoelectric system

Two models for energy harvesting system imparting rotational energy to piezoelectric materials are presented in order to compare the effects of applying identical amounts of energy to a cantilever beam by strain-changing and shock application. For a piezoelectric system given a high impulse with low displacement, higher power outputs were generated at lower resistive loads. Conversely, for a system with high displacement at a low impulse, power output was higher at high resistive loads. At matched impedance, the secondary shock system generated higher power output than the hitting system did at low resistive load. Optimized response of secondary shock system was obtained at a frequency of 60 Hz with a low resistive load of 1 k Ω. The generated output power was measured 124 mW, which corresponds to power density of 140 mW/cm3 for entire cantilever beam and power density of 342 mW/cm3 for only piezoelectric material volume. For a system without a secondary impulse at low resistive loads (1 k Ω), the optimizing frequency was between 20 and 30 Hz, with an output power of 22 mW, which corresponds to a 25 mW/cm3 power density for entire cantilever beam and power density of 60 mW/ cm3 for only piezoelectric material volume.

Design of supplemental plate for piezoelectric system to distribute impact force

The relationship between deformation degree and curvature to the output voltage of piezoelectric system was analyzed. The calculated data and experimental data were compared. The experiment was held by using tip mass of 10 g, 20 g, and 30 g for the various thickness of piezoelectric material as 0.15 mm and 0.2 mm for various type design of supplemental plate. As results, at the vibration acceleration of 4 m/s2, the lowest average Ix value was resulted the highest voltage of 26.12 V. However, when the vibration acceleration of 40 m/s2, the lowest standard deviation of curvature ratio, ρ, and resulted the highest voltage of 58.98 V. This study proves that the deformation degree and curvature ration can be controlled.

Enforcement of Levitation Force by Capturing Magnetic Flux between YBa2Cu3O7-x Superconductor Bulk and Permanent Magnet

An iron block was placed on a permanent magnet (PM) as a path to capture the magnetic flux between a high-temperature superconductor (HTS) bulk and a PM. The effects of the magnetic flux for different iron block thicknesses (0, 2, 4, and 6 mm), configurations, and dimensions were experimentally determined. The optimal conditions for increasing the levitation force, which increased with decreasing air gap between the iron block and the PM, and with increasing iron block thickness, were determined. As the area of the iron block decreased, the levitation force increased, reaching a saturation point. Some iron block configurations acted as a path to capture the magnetic flux, and a higher levitation force was observed for a certain gap distance. Software simulation results support the obtained experimental results.