Daniel Song

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).

Effective Piezoelectric Area for Hitting-Type Piezoelectric Energy Harvesting System

The effective piezoelectric material area was determined by comparing data for different lengths of piezoelectric material on a substrate plate for a hitting-type piezoelectric module. Experimental results show that longer piezoelectric material lengths enable higher output power per unit volume. Further, as the piezoelectric material length increases, the maximum output power frequency increases and the matching impedance, or resistive load, decreases. In modeling the piezoelectric modules (cantilever beam), a UV resin coating was used to enhance the output power per unit volume in a hitting-type piezoelectric energy harvesting system. Comparison results of with UV and without UV coating showed that as the piezoelectric material length increases, UV coating has a greater effect on increasing the output power.

Restoration and Reinforcement Method for Damaged Piezoelectric Materials

This study investigated the effects of strain and crack formation on the performance of damaged piezoelectric materials as well as methods to restore damaged electrodes and reinforce the piezoelectric material. Specifically, this study investigated whether Ag paste (thickness: 0.1 mm) could restore electrical contact in damaged electrodes, and whether a coating of UV curable resin could provide reinforcement against crack formation. Experiments were conducted with a piezoelectric material on a steel cantilever substrate. The substrate was subjected to impact at various distances from the free end of the piezoelectric material to vary the applied strain. It was found that the output voltage increased with the strain (distance of impact from free end) until crack formation, which led to a large decrease in output. However, Ag paste could successfully restore electrical contact. Furthermore, before crack formation, coating with UV curable resin increased the maximum strain, and therefore, maximum electrical output, as well as cycle life.

Study on the Strain Effect of a Piezoelectric Energy Harvesting Module

In order to investigate the relationships among strain, frequency, and output power, a novel piezoelectric energy harvesting module with controllable strain was designed. Conventional vibration module can control over strain through variation in tip mass, but it is also affected by vibration frequency. In the contrast, the designed controllable strain module allows more accurate strain control at various frequencies through adjustment of the displacement of the free end of the cantilever from 5 mm to 45 mm. Experimental results proved that both types of modules exhibit an increase in open circuit output voltage with strain. But output voltage was decreased when the piezoelectric ceramic broke at severe strain. In addition, it was confirmed that the proposed module design can keep the strain constant, which allows investigation into the relationship between frequency and output power. At constant strain, the matching impedance was found to be low at high frequency. Thus, as effect of strain to the piezoelectric energy harvesting module, the optimum conditions for harvesting maximum power are found to be high frequency and the largest strain do not degrade the piezoelectric plate.

Design of Piezoelectric Energy Harvesting System by Magnetic Force–Controlled Resonance Frequency

We designed a piezoelectric energy harvesting system that can be controlled the resonance frequency to the frequency of external energy. A permanent magnet (10 mm × 10 mm × 5 mm) was affixed to the free end of cantilever, and a permanent magnet was affixed to each of the four faces of a rotor at 90° angles. The effect of the dimension of the permanent magnets (20 mm × 20 mm × 10 mm, 30 mm × 20 mm × 10 mm, and 40 mm × 20 mm × 10 mm) and the effect of the pole array (NNNN, SSSS, NSNS, and NNSS) were experimentally tested. The optimum conditions were selected by testing varied distances between the magnets at varied rpm. The experiments demonstrated that the maximum output voltage was generated for the largest magnet and the minimum distance. The most effective way to control the resonance frequency was to modify the pole arrays of magnets affixed to the rotor. Furthermore, the optimum conditions were determined at each distance by changing the pole array and rpm. Simulation software supports the experimental results.

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.

Design of an impact-type piezoelectric energy harvesting system for increasing power and durability of piezoelectric ceramics

The purpose of this study is to design a piezoelectric energy harvester (PEH) that not only resists damage but also generates a higher power when impact is applied. To increase the generated power and durability a PEH, in this study, we investigated a new model and carried out numerical simulations of and experiments on the PEH. The numerical simulation results show that the stress distribution of the proposed PEH is more uniform than that of a conventional impact-type PEH. Thus, the proposed PEH decreases its possibility of being damaged. Experimental results for power under a matched impedance condition show that the maximum RMS powers of the conventional impact-type and proposed PEHs were 0.69 mW at 16 kΩ and 3.97 mW at 7 kΩ, respectively. Furthermore, the peak power of the proposed PEH was 518 mW, which was 3,047% higher than that of the conventional impact-type PEH having a peak power of 17 mW.

Design of vibration exciter by using permanent magnets for application to piezoelectric energy harvesting

We designed a piezoelectric energy harvesting system that can shift the resonant frequency to match the fixed external energy frequency. A permanent magnet (10 × 10 × 5 mm3) was attached to the free end of a cantilever beam, and a permanent magnet was attached to each of the four faces of a rotor at 90° angles. The effect of the size of the permanent magnets (40 × 20 × 10 mm3, 30 × 20 × 10 mm3, and 20 × 20 × 10 mm3) and the effect of the pole array distribution (NNNN, SSSS, NSNS, and NNSS) were experimentally investigated. The optimum conditions were determined by testing various distances between the magnets at different rpms. The experiments showed that the maximum output power was generated for the minimum distance and largest magnet. The most effective approach to adjust the resonance frequency was to change the pole arrays of the magnets attached to the rotor. Furthermore, the optimum conditions were determined at each distance by changing the pole array and rpm. Software simulations support the experimental results.