There is a significant body of work that addresses the use of rod-core antennas as receiver coils. However, research on the use of rod-core antennas as transmitters is limited since high-permeability core materials are nonlinear at high-drive levels. This paper analyzes weight, power and volume efficiencies of rod cores constructed from six different materials: two types of ferrite toroids; black-oxide, low-carbon-steel wire; two types of Metglas foil tapes; and Nanocrystalline material foil tape. Weight efficiency is defined as the ratio of the antenna's magnetic moment to the sum of the antenna's core, wire and battery weights. Likewise, power efficiency is defined as the ratio of the antenna's magnetic moment and the antenna's resistive power losses, and volume efficiency is defined as the ratio of the antenna's magnetic moment and the antenna's volume.
The magnetic moment, core-series-loss-resistance, and inductance were measured at various magnetic core flux densities. These data were then modified to simulate the effects of changing the wire gauge and number of turns to determine the optimum drive level and coil design for a specific rod core. Furthermore, we compare the results to an air-core loop whose length of one side is comparable to the length of the constructed rod antennas. It is shown that rod-core antennas possess significant advantages over air-core transmitters in weight, power and volume efficiency for the types of antennas investigated here. Specifically, at 100 Hz, the maximum weight efficiency for a 0.50-m long rod antenna made from Metglas was found to be 310% larger than a 0.50-m air-core antenna. The power efficiencies associated with the maximum weight efficiencies for these two cases differ by 420%. The volume efficiency of the Metglas rod antenna was calculated as about 500% larger than the 0.5-m air-core antenna.