Yoon-Pyo Lee

Modeling and Characterization of Piezoelectric

This paper presents the modeling, fabrication, and characterization of a piezoelectric microelectromechanical systems (MEMS) energy harvester using a d33 piezoelectric mode. A theoretical analysis and an analytical modeling for the d33-mode device were first performed to estimate the output power as a function of the material parameters and device geometry. A PbTiO3 seed layer was newly applied as an interlayer between the ZrO2 and Pb(Zr0.52Ti0.48)O3 (PZT) thin films to improve the piezoelectric property of the sol-gel spin-coated PZT thin film. The fabricated cantilever PZT film with an interdigital shaped electrode exhibited a remnant polarization of 18.5 C/cm2, a coercive field of less than 60 kV/cm, a relative dielectric constant of 1125.1, and a d33 piezoelectric constant of 50 pC/N. The fabricated energy-harvesting device generated an electrical power of 1.1 W for a load of 2.2 M with 4.4 Vpeak-to-peak from a vibration with an acceleration of 0.39 g at its resonant frequency of 528 Hz. The corresponding power density was 7.3 mW cm-3 · g-2. The experimental results were compared with those numerically calculated using the equations derived from the dynamic and analytical modeling. The fabricated device was also compared with other piezoelectric MEMS energy-harvesting devices.

d_{33}

A theoretical and experimental study was performed to examine the water spray evaporation method for ice particle production. The conditions for the formation of ice particles were investigated theoretically by the diffusion-controlled evaporation model. The prediction by the model was proved to agree relatively well with experiments. The production of cold storage heat will increase almost proportionally to the number of spray nozzles because no substantial difference was found in the mean droplet size of the overlapped sprays from twin nozzles. Finally, based on the results, the vacuum chamber was designed, and spherical ice particles of size below 300 μm were experimentally obtained by spraying water droplets of ambient temperature in the vacuum chamber where pressure is maintained below the freezing point of water. From the experiment for producing ice particles, it was found that the spray flow rate influences the performance of the system more than the position of spray nozzle.

-Mode MEMS Energy Harvester

Abstract A theoretical and experimental study was performed to examine the water spray method of ice slurry production. First, the conditions for the formation of ice particles were investigated theoretically by the diffusion-controlled evaporation model. The prediction of the model was proved to agree relatively well with experiments in which we examined the conditions for a droplet of initial temperature 20°C and size 50 μm to change into an ice particle in a chamber of height 1.33 m. Second, the production of cold storage heat will increase almost proportionally to the number of spray nozzles because no substantial difference was found in the Sauter Mean Diameter (SMD) of sprays from single and twin nozzle. Third, an ice slurry was experimentally obtained by spraying droplets of 7% ethylene glycol aqueous solution in a vacuum chamber where pressure is maintained below the freezing point of the solution. Finally, based on the theoretical and experimental results, we propose an optimizing chart for providing the operating conditions to make ice slurry using the relations of the staying time of the droplet in the chamber, the injection pressure, the spray droplet size and the chamber pressure.

Spherical-shaped ice particle production by spraying water in a vacuum chamber

A novel design method for a 2DOF energy harvesting device is studied. The energy harvesting device is modeled as a rigid body supported by two parallel sets of springs and dampers. The impedance expression for the model has been developed by utilizing the concept of the inerter. The proposed design method deals with tuning two resonant peaks and equalizing the harvested power at those frequencies. As a result, the proposed energy harvesting device is particularly effective at two frequencies and has increased bandwidth as well as reduced size and weight in comparison with previous SDOF devices. A numerical design example is provided to show effectiveness of the proposed method.

Study on ice slurry production by water spray

The tunable single-degree-of-freedom rotational energy harvester is proposed. The device is the combination of the rotational energy harvester and the suspended weight. Thus, it can harvest the electrical power from the translational base excitation associated with low frequency and large amplitude. Further, its natural frequency can be changeable by manipulating the size of the reel (i.e., geometrical tunability). The characteristics of the proposed device are investigated through numerical simulation and experimental test.

Design of a 2DOF Vibrational Energy Harvesting Device

In this paper, a MEMS energy harvester was investigated to scavenge power from ambient vibration source. It was designed to convert low level vibration to electrical power via the piezoelectric effect. The proposed energy harvester was fabricated by patterning Pt electrodes into inter-digital geometry on top of the sol-gel-spin coated Pb(Zr,Ti)O<inf>3</inf> thin film for d33 mode on silicon cantilever with proof mass. In order to obtain well grown PZT thin film, PbTiO3 seed-layer was newly applied as an inter-layer between PZT and ZrO<inf>2</inf> layer. The fabricated energy harvester generated 1.1uW of electrical power to 2.2MΩ of load with 4.4V<inf>peak-to-peak</inf> from a vibration of 0.39g acceleration at it resonant frequency of 528Hz. The corresponding power density was 2.8mW·cm^−3·g⁻¹.

A tunable rotational energy harvester for low frequency vibration

The district-cooling system (DCS) has been in service in Sang-am in Seoul, Korea since 2005. The capacity of the DCS facility in Sang-am was 111 Gcal/h in 2011, and an additional 63 Gcal/h capacity is planned for installation by 2025. However, the cooling demand has increased due to unexpected high-rise building blocks, and the required facility capacity is expected to be 101 Gcal/h. Adding a new building plan to the existing plant is difficult. This study centers on a feasibility study for the new requirement under the restrictions of existing pipelines, limited space and regulations on the use of electric-driven chillers in Korea, etc. The precise estimation of the diversity factor is essential to determine the required capacities. To this end, each building in the district area was categorized, and the cooling loads were measured for the summer seasons of 2010 and 2011. The large energy capacity of an ice-slurry can potentially increase the cooling capacity in existing plants while maintaining the same flow rate and pumping power. Thus introducing an ice-slurry is expected to be a potential solution to the significantly increased cooling load under the restriction of existing pipeline system without requiring increases in pipe size or system flow rates.

High performance piezoelectric MEMS energy harvester based on D33 mode of PZT thin film on buffer-layer with PBTIO3 inter-layer

The dynamic characteristics of a free-piston stirling engine(FPSE) with regard to the working frequency is investigated from theoretical and experimental studies. The FPSE is modeled as a two degree-of-freedom linear vibration system. A theoretical expression on the working frequency is derived from the instability condition for self-excitation based on the linear vibration model. A -type free-piston stirling engine is fabricated for experimental studies, and its working frequency is measured on various heater temperatures. Comparisons between the theoretical and experimental results reveal that the working frequency of the test FPSE depends on both the temperature of the compression space and the temperature difference between the expansion and compression spaces.

FEASIBILITY OF ICE-SLURRY APPLICATION TO THE DISTRICT COOLING SYSTEM IN KOREA

This study investigated on details of flow characteristics of a multi-blade fan for domestic ventilation. Experiments and analysis were carried out to describe on flow pattern with variations of cut-off angle near the scroll housing throat, which were performed by PIV measurement for the flow field and by total pressure probes. The stagnation point at cut-off region of the fan moves to the exit of the scroll housing as the cut-off angle increases. The movement of stagnation point and the variation of throat area of the scroll housing influence to the distribution of velocity magnitude at the exit of the fan. Furthermore, a large distortion of the velocity distribution at the scroll exit causes to increase mixing loss along the flow path.

Analyses on Working Frequency of A γ-type Free-piston Stirling Engine

The rise of a large gas bubble in a miniature two-phase closed thermosyphon with a thin wire insert has been analyzed by the potential flow theory. The effect of the interfacial surface tension is explicitly accounted for by the application of the Kelvin-Laplace equation and solved for the bubble shape. The solution is expressed in terms of the Stokes stream function which consists of an infinite series of Bessel functions. The conditions of the bubble movement in a miniature two-phase closed thermosyphon were theoretically ascertained. The analytical results were compared with the experimental results.