Multi-tone FSK for ultrasonic communication

Traditional radio frequency communication schemes are not capable of transmitting signals through metal enclosures. However, in some applications it is necessary to transmit information to/from devices located inside metal enclosures, e.g., a closed shipping container in transit. A conformal ultrasonic communication system based on multi-tone FSK (MFSK) has been developed and evaluated using steel corner posts from shipping containers as the communication medium. The communication system is configurable, consisting of two or more modules. A module is mounted to a metal surface and utilizes an inexpensive ultrasonic transducer to send and receive modulated signals through the metal channel. A module also makes use of an inexpensive DSP chip for modulating and demodulating MFSK signals. For the shipping container application, experiments were conducted that achieve data rates of approximately 800 bps. Experiments related to two scenarios for the shipping container application were investigated: (1) communicating through one container and (2) communication between stacked containers. For the second case, experiments were conducted with modules on two separate corner posts that are under compressive load.