Channel Capacity of Magnetic Communication in a General Medium Incorporating Full-Wave Analysis and High-Frequency Effects

Magnetic communication systems are most often analyzed assuming magnetoquasistatic (MQS) conditions, which neglect full-field terms and high-frequency (HF) effects in the transmitting and receiving coils. Such approximations may lead to nonoptimal designs in terms of operating frequency, size, and coil orientation. This paper presents an optimal design approach for maximizing the channel capacity, using both MQS analysis and full-wave (FW) analysis while incorporating HF effects, such as skin and proximity effects, radiation losses, and the self-resonance of coils. For a given medium and required transmission distance, the optimal operating frequency is such, for which the receiver is located in the radiative near field (NF) and not in the reactive NF. The optimal power allocation and the resulting channel capacity were obtained using a "water-filling" algorithm. The HF effects reduced the signal-to-noise ratio and limited the operating frequency and the coil size. This is especially true for short-distance transmission through low-loss media, where the optimal signal frequency is relatively high. In addition, FW analysis significantly improved potential data rates compared to the typical MQS approach. This improvement was achieved due to a higher operating frequency and sometimes a change of mutual orientation from coaxial to parallel. Electromagnetic simulations validated the primary effects presented here.