Seong Kwang Hong

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.

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 Optimization of PZT-Based Piezoelectric Cantilever Beam by Using Computational Experiments

Piezoelectric energy harvesting is gaining huge research interest since it provides high power density and has real-life applicability. However, investigative research for the mechanical–electrical coupling phenomenon remains challenging. Many researchers depend on physical experiments to choose devices with the best performance which meet design objectives through case analysis; this involves high design costs. This study aims to develop a practical model using computer simulations and to propose an optimized design for a lead zirconate titanate (PZT)-based piezoelectric cantilever beam which is widely used in energy harvesting. In this study, the commercial finite element (FE) software is used to predict the voltage generated from vibrations of the PZT-based piezoelectric cantilever beam. Because the initial FE model differs from physical experiments, the model is calibrated by multi-objective optimization to increase the accuracy of the predictions. We collect data from physical experiments using the cantilever beam and use these experimental results in the calibration process. Since dynamic analysis in the FE analysis of the piezoelectric cantilever beam with a dense step size is considerably time-consuming, a surrogate model is employed for efficient optimization. Through the design optimization of the PZT-based piezoelectric cantilever beam, a high-performance piezoelectric device was developed. The sensitivity of the variables at the optimum design is analyzed to suggest a further improved device.

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.

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.

Sustainable micro-power circuit for piezoelectric energy harvesting tile

ABSTRACT Piezoelectric energy harvesting tiles are used for converting the power of pedestrian footsteps in to electricity and can be used at the micro- and milli-watt level for storage and powering electronics devices. This paper effectively combines the systems and techniques for developing a sustainable circuit with the self-starting and self-power functions to efficiently store energy and drive low power consumption electronic devices from the piezoelectric energy harvester tile. The main part of the system is 80% efficient impedance matching converter with the self-starting and battery-less operation. The presented circuit has an overall efficiency of 63% and can power a wireless sensor node to transmit the information wirelessly.

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.