1. KKU-Seagate Cooperation Research Laboratory, Department of Electrical Engineering, Khon Kaen University, Khon Kaen 40002, Thailand
2. Department of Physics and Astronomy, MINT Center, University of Alabama, Tuscaloosa, Alabama 35487, USA
3. Faculty of Applied Science and Engineering, Khon Kaen University, Nong Khai Campus 43000, Thailand