Prof. YoungPak Lee
Hanyang University, Korea/ Fudan University, China
Title: Advanced ultra-broadband and shorter-wavelength perfect-absorption metamaterials, made and controlled easy
Abstract:
Recently, flexible and ultrathin wide-band
MM absorbers were suggested and demonstrated in the MHz/GHz/THz-frequency
range. The experimental absorption band over 97% was 0.87-6.11 GHz, for example.
Furthermore, the dielectric substrate of some MM absorbers was replaced with
flexible substrate in order to have the flexibility and the broadband
absorption properties. This innovation is expected to contribute to the
flexible microwave/electronic devices in the near future, and offers a
different approach to realize the potential wearable meta-devices by using
these ultrathin broadband MM absorbers.
We also suggest a plasmonic metasurface structure that was
simply fabricated using the standard printed circuit board
technique but provided a high absorption above 90%, also covering a broadband frequency range from 12.30 to 14.80 GHz.
This plasmonic metasurface consisted of structural unit cells
composed of multiple split rings connected by a copper bar, which
induced a broadband absorption by using a planar resistive interation in the
pattern without real resistive component there. Analysis, simulation, and measurement results showed that the
metasurface also showed polarization- and incident
angle-insensitive properties. The suggested plasmonic metasurface is a
fundamental design that can also be used to design the
absorber in different frequency ranges and is able to adapt well to being fabricated at various scales.
In addition, we developed a broadband
metamaterial absorber capable of optical switching between high- and
low-absorbing states. The proposed metasurface exhibits a wide absorption
bandwidth ranging from 13 to 17.3 GHz, maintaining a high absorption for wide
incidence angles and polarization-insensitively. The metasurface is composed of
periodically arranged unit cells integrated with photoresistors that enable
tunable electrical resistance under optical illumination. This optically
controllable behavior provides a simple and efficient approach for realizing
dynamically reconfigurable metamaterial absorbers, offering potential
applications in adaptive stealth technology, electromagnetic shielding, and
tunable sensing systems.
We also introduce a VO2-integrated broadband metamaterial
absorber designed for the THz frequency range. The simulation results
demonstrate a wide 90% absorption bandwidth of 8.23 THz, corresponding to a fractional
bandwidth of 89.5%. By leveraging the phase-transition properties of VO2,
the absorber demonstrated dynamic adjustability by modulating the absorption
from 3% to 98.74%. The absorption mechanism was analyzed to be magnetic
resonance and interference. Furthermore, machine learning algorithms were applied
to accelerate and optimize the design process.
Biography:
YoungPak Lee received his B. S. degree from Seoul National University, Korea, in 1975, and the Ph. D. degree in experimental condensed-matter physics in 1987 from Iowa State University, U. S. A. His research involved study on magneto-optical, magnetic, optical and transport properties, and electronic structures of thin films and nanostructures, characterization of the surfaces and interfaces of thin films including multilayers, vacuum science, and so forth since his Ph. D. degree. After many careers in U. S. A., Japan, Germany and Korea, he is now former President of the Korean Physical Society, former President of the Korean Federation of Basic-science, Distinguished Professor, Physics Department of Hanyang University, and Director of Quantum Photonic Science Research Center, Seoul, Korea, which exploited the convergence research of magnetism and optical science. Prof. Lee is also Member of Korea Academy of Science and Technology, Council of Association of Asia-Pacific Physical Societies, Honorary Member of National Academy of Sciences of Ukraine, Distinguished Visiting Professor of Aix-Marseille Univ. (France) and Edith Cowan Univ. (Australia), Guest Distinguished Professor / Professor of 7 Chinese Universities and Institutes, Scientific Advisor of Scientific Council of Materials Science of Vietnamese Academy of Science and Technology. His current investigations include metamaterials and spin-photonic crystals, nanoscopic investigation of morphology and magnetic domain, and magnetic semiconductors based on oxides. He has published 640 SCI papers (the total published number of papers : 750 papers) as of December 2014. Because of these achievements, he has received many kinds of awards (48 awards as of December 2014), including the highest-level Award from the Korean Physical Society (2014), Award by the Korean Minister of Education, Science and Technology (2009), Award by the Korean Minister of Science and Technology (1992), and various academic-paper awards and academic-achievement awards. Based on these recognitions, he was also selected as one of the 'Korean Scientists for the 21st Century' by a main national broadcasting company in 2007. He has led the globalization of Korean physics, based on the leadership in the research on quantum photonic science. So far, he has established the global collaboration network with 42 organizations in 15 countries, including the U. S. A. and China.