1. Division of Electronics and Informatics, Gunma University, 1-5-1 Tenjin-cho, Kiryu 376-8515, Gunma, Japan
2. Yangzhou Polytechnic Institute, No. 188 Huayangxilu, Yangzhou 225127, China
3. Sanki Engineering Co., Ltd., 7-10-1 Chuorinkan, Yamato 242-0007, Kanagawa, Japan