Like any wave, ultrasound may be modulated to carry information. Whilst techniques are well-established in underwater applications, few applications exist for air-coupled ultrasonic communication due to the inherent difficulties of generating and propagating ultrasound in air.
Recent work by the Ultrasonics Research Group has demonstrated the feasibility of transmitting data over short distances in air using high-frequency ultrasound, at rates of up to 80kb/sec, using various modulation schemes including amplitude shift keying (ASK) and orthogonal frequency division multiplexing (OFDM).
The image below shows an 8-bit word '11110000' transmitted over 4 channels, with (a) the 4-channel OFDM representation, (b) the transmitted AM modulation at 250kHz, (c) the received ultrasonic signal and (d) the demodulated received OFDM representation.
- W. M. D. Wright, O. M. Doyle and C. T. Foley, "Multi-channel data transfer using air-coupled capacitive ultrasonic transducers”, Proc. 2006 IEEE Ultrasonics Symposium, pp. 1805-1808 (2006)