Two-Frequency Ultrasonic System with Direct Digital Frequency Synthesizers and Vernier Caliper Phase Meter for Measuring Air Temperature

Department of Electrical Engineering, National Cheng Kung University, No. 1, University Road, Tainan City 701, Taiwan, R.O.C. 1Department of Computer Science and Information Engineering, Cheng Shiu University, No. 840, Chengcing Rd., Niaosong Dist., Kaohsiung City 83347, Taiwan, R.O.C. 2Department of Electronic Engineering, I-Shou University, No. 1, Sec. 1, Syuecheng Rd., Dashu District, Kaohsiung City 84001, Taiwan, R.O.C. 3Department of Electronic Engineering, Cheng Shiu University, No. 840, Chengcing Rd., Niaosong Dist., Kaohsiung City 83347, Taiwan, R.O.C.