Chang-hyun Ji
Ewha Womans University
研究室紹介
Professor Chang-hyun Ji's research lab specializes in microelectromechanical systems (MEMS) and piezoelectric energy harvesting, focusing on innovative designs for vibration energy harvesters and gyroscopes. The lab develops advanced equivalent circuit models to accurately predict the dynamic behavior of impact-based energy harvesters under real-world, unpredictable vibrational conditions. Key research directions include frequency-up-conversion mechanisms, dual-mass vibratory gyroscopes for wideband stability, and the integration of macro-fiber composites (MFCs) for efficient power generation from low-frequency ambient vibrations. The lab emphasizes both theoretical modeling and experimental validation to advance energy harvesting and sensing technologies for portable and wearable electronics.
Research Overview
Research Output Trend
Figures are computed from collected data and may differ slightly.
Selected Papers
3A vibration-based energy harvester and its equivalent circuit models have been reported. Most models predict voltage signals at harmonic excitation. However, vibrations in a natural environment are unpredictable in frequency and amplitude. In this paper, we propose a realistic equivalent circuit model of a frequency-up-converting impact-based piezoelectric energy harvester. It can describe the behavior of the harvester in a real environment where the frequency and the amplitude of the excitation
In this research, a MEMS vibratory gyroscope with dual-mass system in the sensing mode has been proposed to increase the stability of the device using wide bandwidth. A wide flat region between the two resonance peaks of the dual-mass system removes the need for a frequency matching typically required for single mass vibratory gyroscopes. Bandwidth, mass ratio, spring constant, and frequency response of the dual-mass system have been analyzed with MATLAB and ANSYS simulation. Designed first and
This paper presents an impact-based piezoelectric vibration energy harvester using a freely movable metal sphere and a piezoceramic fiber-based MFC (Macro Fiber Composite) as piezoelectric cantilever. The free motion of the metal sphere, which impacts both ends of the cavity in an aluminum housing, generates power across a cantilever-type MFC beam in response to low frequency vibration such as human-body-induced motion. Impacting force of the spherical proof mass is transformed into the vibratio