A compact low-power underwater magneto-inductive modem

In this work, a magneto inductive (MI) link design is studied to achieve high speed transmission applied to a high density underwater network. For a small loop antenna, a design procedure is described to define the optimal operating frequency constrained on the system bandwidth and range. A coherent link is established between two nodes in a controlled underwater environment. For a small coil with radius of 5 cm, simulation results indicate that a range above 10 meters can be achieved in the low frequency spectrum spanning 10 kHz to 1 MHz. The design procedure is validated through measurements in seawater: a very high output SNR equal to 31.4 dB is realized at the output of the equalizer, and in these conditions a perfectly reliable 8-kbps link is demonstrated at a center frequency of 22.5 kHz.