Progress in airborne ultrasonic data communications for indoor applications

Capacitive ultrasonic transducers are efficient transmitters and receivers for ultrasonic waves in air, making them ideal devices for signal transmissions in air. Ultrasonic signals are unregulated, difficult to intercept from outside the room, and interference free to most electronic devices. These high security features make ultrasonic communication systems an alternative to radio frequency (RF) based systems for indoor applications. This paper investigated a prototype ultrasonic communication system using a pair of commercially available capacitive ultrasonic transducers in an indoor laboratory environment. Multichannel On-OFF keying (OOK) and binary phase-shift keying (BPSK) modulation schemes were implemented successfully in the system with wireless synchronization, achieving an overall data rate of 60 kb/s using ultrasonic bands from 50 to 110 kHz. The results show that a reliable line-of-sight (LOS) link can be established for communications over distances of 10 and 11 m using multichannel OOK and BPSK, respectively.