P2I-9 Multi-Channel Data Transfer Using Air-Coupled Capacitive Ultrasonic Transducers

In some situations, wireless data transfer using radio waves or microwaves is not permitted as it may interfere with other sensitive electronic equipment. Optical beam modulation methods may also be unsuitable due to the presence of atmospheric contamination. The feasibility of using air-coupled ultrasound to transmit binary data at practical rates has been investigated. A prototype system was constructed using a single pair of broadband capacitive ultrasonic transducers (CUTs) with a central frequency of 250 kHz and a 300 kHz bandwidth. Two transmission schemes for sending ASCII data across short distances were investigated. Amplitude Shift Key (ASK) modulation was successfully implemented using 8 separate data channels at frequencies from 215 kHz to 320 kHz with a channel spacing of 15 kHz, allowing 8-bit data packets to be sent in parallel. Orthogonal Frequency Division Multiplexing (OFDM) was also implemented successfully, using 32 parallel 1 kHz channels and a 250 kHz carrier frequency to send 32-bit data packets. Data transfer rates of up to 80 kbit/sec were achieved over distances of up to 0.5 m with direct line-of-sight between the transmitter and receiver. Higher transfer rates should also be possible, and over greater distances