Electromagnetic Field in Air Produced by a Horizontal Magnetic Dipole Immersed in Sea: Theoretical Analysis and Experimental Results

In recent years, data transmission from seawater into air across the sea surface has attracted considerable interest and is essential for undersea sensing and networking applications. In particular, electromagnetic (EM) wave propagation across the sea surface via a seawater-air path has great potential for long-distance transmission, thus providing a possible solution for sensing and networking problems. However, current related theoretical analyses and experimental results are not sufficient to support research and development in the domain. Therefore, based on previous studies, this study theoretically and experimentally investigates EM wave propagation from a horizontal magnetic dipole (HMD), namely, a loop antenna immersed in seawater radiating into the air. A set of mathematical expressions is formulated for a model of three-layered conducting media on the basis of Maxwell's equations. In addition, a proof of concept measurement system was designed and built. A trial was conducted on the sea, and the results were in good agreement with the theoretical analysis. A horizontal transmission distance up to 574 m over the sea surface was achieved using a small loop antenna operated at 19 kHz and with an input power of less than 10 W. Therefore, the approach has been proven to be promising.