Prof.황용하

Dept. of ElectroMechanical Systems Engineering

Korea University (Sejong Campus)

Rm.401, Science & Technology Bldg.1,

2511 Sejong-ro, Sejong, 30019, Republic of Korea

Office: (+82) 44-860-1442

Email: hwangyongha@korea.ac.kr

EDUCATION

Ph.D. in Electrical Engineering (Sep. 2008 – Dec. 2012)

Sensors and Technology Laboratory

Academic Advisor: Rob N. Candler, Ph.D.

Thesis: Micromechanical resonators with nanoporous materials for enhanced vapor sensing

M.S. in Electrical & Eletronics Engineering (Mar. 2004 – Feb. 2006)

Korea University, Seoul, Korea

Academic Advisor: James Jungho Pak, Ph.D.

Thesis: The research of the realization of a two-step micromirror array for the confocal microscope system

B.S. in Electrical Engineering (Mar. 1997 – Feb. 2004)

Korea University, Seoul, Korea

EXPERIENCES

Postdoctoral Researcher / Assistant Project Scientist (Dec. 2012-May 2015)

University of California, Los Angeles, California, USA

Sensors and Technology Laboratory, Electrical Engineering Department (PI: Rob N. Candler, Ph.D.)

Assistant Research Engineer (Feb. 2006 – Feb. 2007)

Samsung Electronics Co., Ltd., Gyeonggido, Korea

Technical Staff in process architecture team for the prototypes in Process Analysis and Control group / Semiconductor Business

Journal Publications

[19] K. Kang, S. Oh, H. Yi, S Han, and Y.H. Hwang, “Fabrication of truly 3D microfluidic channel using 3D-printed soluble mold,” Biomicrofluidics, Vol.12, No.1, 014105, Jan.5, 2018, DOI: 10.1063/1.5012548.

[18] D. Seo, S. Oh, M. Lee, Y.H. Hwang, and S. Seo, “A field-portable cell analyzer without a microscope and reagents,” Sensors, Vol.18, Issue1, 85, Jan. 2018, DOI:10.3390/s18010085.

[17] Y.H. Hwang, and R. Candler, “Non-planar PDMS microfluidic channels and actuators: a review,” Lab on a Chip, Vol.17, Issue 23, pp.3948–3959, 2017, DOI: 10.1039/C7LC00523G.

[16] H. Sohn, C. Liang, M. Nowakowski, Y.H. Hwang, S. Han, J. Bokor, G. Carman, and R. Candler, 'Deterministic multi-step rotation of magnetic single-domain state in Nickel nanodisks using multiferroic magnetoelastic coupling', Journal of Magnetism and Magnetic Materials, 439, pp.196–202, 2017, DOI: 10.1016/j.jmmm.2017.04.077. 

[15] Y.H. Hwang, D.M. Seo, M. Roy, E. Han, R.N. Candler, and S.K. Seo, ‘Capillary flow in PDMS cylindrical microfluidic channel using 3D printed mold’, Journal of Microelectromechanical Systems, Vol.25, No.2, pp.238-240, Mar 31, 2016, DOI: 10.1109/JMEMS.2016.2521858.

[14] M. Roy, G.S. Jin, J.H. Pan, D.M. Seo, Y.H. Hwang, S.W. Oh, M. Lee, Y.J. Kim, and S.K. Seo, ‘Staining-free cell viability measurement technique using lens-free shadow imaging platform’, Sensors and Actuators B: Chemical, Vol.224, pp.577-583, Oct.30, 2015, DOI: 10.1016/j.snb.2015.10.097.

[13] Y.H. Hwang, O. Paydar, and R.N. Candler, “Pneumatic microfinger with balloon fins for linear motion using 3D printed molds,” Sensors and Actuators A: Physical, Vol.234, pp.65-71, Oct.1, 2015, DOI:10.1016/j.sna.2015.08.008.

[12] Y.H. Hwang, O. Paydar, and R.N. Candler, “3D printed molds for non-planar PDMS microfluidic channels,” Sensors and Actuators A: Physical, Vol.226, pp.137-142, May 1, 2015, DOI: 10.1016/j.sna.2015.02.028.

[11] J. Harrison, Y.H. Hwang, O. Paydar, J. Wu, E. Threlkeld, J. Rosenzweig, P. Musumeci, and R. Candler, “High-gradient microelectromechanical system quadrupole electromagnets for particle beam focusing and steering,” Physical Review Special Topics-Accelerators and Beams, Vol.18, Issue 2, pp.023501-1, Feb.17, 2015, DOI: http://dx.doi.org/10.1103/PhysRevSTAB.18.023501.

[10] Y.H. Hwang, O.H. Paydar, M. Ho, J. B. Rosenzweig, and R.N. Candler, “Electrochemical macroporous silicon etching with current compensation,” Electronics Letters, Vol.50, No.19, pp.1373-1375, Sep.11, 2014, DOI: 10.1049/el.2014.1662.

[9] J. Harrison, O.Paydar, Y.H. Hwang, J. Wu, E. Threlkeld, P. Musumeci, and R.N. Candler, “Fabrication process for thick-film micromachined multi-pole electromagnets,” Journal of Microelectromechanical Systems, Vol.23, No.3, pp.505-507, May 29, 2014, DOI: 10.1109/JMEMS.2014.2315763.

[8] O.H. Paydar, C.N. Paredes, Y.H. Hwang, J. Paz, N.B. Shah, and R.N. Candler, “Characterization of 3D-printed microfluidic chip interconnects with integrated o-rings,” Sensors and Actuators A:Physical, Vol.205, pp.199-203, Jan.1, 2014, DOI: 10.1016/j.sna.2013.11.005.

[7] Y.H. Hwang, A. Phan, K. Galatsis, O.M. Yaghi, and R.N. Candler, “Zeolitic imidazolate framework-coupled resonators for enhanced gas detection,” Journal of Micromechanics and Microengineering, Vol.23, No.12, p.125027, Nov.14, 2013, DOI:10.1088/0960-1317/23/12/125027.

[6] Y.H. Hwang, H. Sohn, A. Phan, O.M. Yaghi, and R.N. Candler, “Dielectrophoresis-assembled zeolitic imidazolate framework nanoparticle-coupled resonators for highly sensitive and selective gas detection,” Nanoletters, Vol.13, Issue 11, pp.5271-5276, Oct.7, 2013, DOI: 10.1021/nl4027692.

[5] Y.H. Hwang, and Rob N. Candler, “Fabrication process for integrating nanoparticles with released structures using photoresist replacement of sublimated p-dichlorobenzene for temporary support,” Journal of Microelectromechanical Systems, Vol.21, No.6, pp.1282-1284, Nov.27, 2012, DOI: 10.1109/JMEMS.2012.2221160 .

[4] Y.H. Hwang, F. Gao, A.J. Hong, and R.N. Candler, “Porous silicon resonators for improved vapor detection,” Journal of Microelectromechanical Systems, Vol.21, No.1, pp.235-242, Feb.3, 2012, DOI: 10.1109/JMEMS.2011.2170819.

[3] S.M. Kim, E.B. Song, S. Seo, D.H. Seo, Y.H. Hwang, R. Candler, and K.L. Wang, “Suspended few-layer graphene beam electromechanical switch with abrupt on-off characteristics and minimal leakage current,” Applied Physics Letters, Vol.99, Issue 2, pp.023103, Jul.13, 2011, DOI: 10.1063/1.3610571.

[2] J.Y. Kim, A.J. Hong, S.M. Kim, K.S. Shin, E.B. Song, Y.H. Hwang, F. Xiu, K. Galatsis, C.O. Chui, R.N. Candler, S.Y. Choi, J.T. Moon, and K.L.Wang, “A stacked memory device on logic 3D technology for ultra high density data storage,” Nanotechnology, Vol.22, Issue 25, pp.254006-1, May 16, 2011, DOI: 10.1088/0957-4484/22/25/254006.

[1] Y.H. Hwang, S.O. Han, B.K. Lee, J.S. Kim, and J. Pak, "A two-step micromirror for low voltage operation," KIEE International Transactions on Electrophysics and Application, Vol.5-C, No.6, pp.270-275, Dec., 2005.

(1) 3D printed micro systems

- Microfluidic devices using 3D printed mold

The field of complex microfluidic channels is rapidly expanding toward channels with variable cross sections (i.e., beyond simple rounded channels with constant diameter), as well as channels whose trajectory can be outside of a single plane. This paper introduces the use of three-dimensional (3D) printed soluble wax as cast molds for rapid fabrication of truly arbitrary microfluidic polydimethylsiloxane (PDMS) channels that are not achieved through typical soft lithography. The molds are printed directly from computer-aided design (CAD) files, followed by simple dissolution using a solvent after molding PDMS, making rapid prototyping of microfluidic devices possible in hours. As part of the fabrication method, the solubility of several build materials in solvents and their effect on PDMS were investigated to remove the 3D-printed molds from inside the replicated PDMS microfluidic channels without damage. Technology limits, including surface roughness and resolution by comparing the designed channels with fabricated cylindrical channels with various diameters are also characterized. We reproduced a 3D image of an actual human cerebral artery as cerebral artery-shaped PDMS channels with 240 μm diameter to prove the developed fabrication technique. It was confirmed that the fabricated vascular channels were free from any leakage by observing the fluorescence fluid fill.

- Pneumatic balloon actuator

Polymer-based pneumatic balloon actuators consisting of novel trapezoidal vertical microballoon fins were fabricated by three-dimensional (3D) printed molds and validated experimentally. The introduction of 3D printed molds for pneumatic actuation provides additional freedom in the design of actuators, removing the limitation of extruded 2D shapes that is present with conventional microfabrication. Whereas conventional balloon actuators exhibit nonlinear response to applied pressure, the presence of balloon fins with 100s-mm width was shown to produce a linear change in bend angle with the injection of pressurized air. The balloon fins also mitigate stress concentrations that can lead to material failure. Static bending (exceeding 80° bend angle) and the mechanical force of the fabricated microfingers were tested and compared with analytical models. The expanded design space permitted by 3D printing allows actuator designs to achieve a given deflection with less stress in the material as compared to planar designs. Feasibility of this design flexibility and fast prototyping enabled by the 3D printed molding process was demonstrated by fabricating and testing various designs of microfingers. When grouped, the microfingers with balloon fins can successfully accomplish complex object transfer tasks (i.e., multi-directional actuation with independently controlled displacement).

(2) Mechanical resonator

- ZIF-coupled gas sensor

This work reports on zeolitic imidazolate framework (ZIF)-coupled microscale resonators for highly sensitive and selective gas detection. The combination of microscale resonators and nanoscale materials simultaneously permits the benefit of larger capture area for adsorption from the resonator and enhanced surface adsorption capacity from the nanoscale ZIF structure. Dielectrophoresis (DEP) was demonstrated as a novel method for directly assembling concentrated ZIF nanoparticles on targeted regions of silicon resonant sensors. As part of the dielectrophoretic assembly process, the first ever measurements of the Clausius-Mossotti factor for ZIFs were conducted to determine optimal conditions for DEP assembly. The first ever real-time adsorption measurements of ZIFs were also performed to investigate the possibility of inherent gas selectivity. The ZIF-coupled resonators demonstrated sensitivity improvement up to 150 times over a bare silicon resonator with identical dimensions, and real-time adsorption measurements of ZIFs revealed different adsorption time constants for IPA and CO2.

(3) Micro electromagnet

- High aspect ratio micro devices

Undergraduate students

강 윤(Yoon Kang)