Development and validation of a low‐frequency modeling code for high‐moment transmitter rod antennas

Abstract

[1] The goal of this research is to develop and validate a low-frequency modeling code for high-moment transmitter rod antennas to aid in the design of future low-frequency TX antennas with high magnetic moments. To accomplish this goal, a quasi-static modeling algorithm was developed to simulate finite-length, permeable-core, rod antennas. This quasi-static analysis is applicable for low frequencies where eddy currents are negligible, and it can handle solid or hollow cores with winding insulation thickness between the antenna's windings and its core. The theory was programmed in Matlab, and the modeling code has the ability to predict the TX antenna's gain, maximum magnetic moment, saturation current, series inductance, and core series loss resistance, provided the user enters the corresponding complex permeability for the desired core magnetic flux density. In order to utilize the linear modeling code to model the effects of nonlinear core materials, it is necessary to use the correct complex permeability for a specific core magnetic flux density. In order to test the modeling code, we demonstrated that it can accurately predict changes in the electrical parameters associated with variations in the rod length and the core thickness for antennas made out of low carbon steel wire. These tests demonstrate that the modeling code was successful in predicting the changes in the rod antenna characteristics under high-current nonlinear conditions due to changes in the physical dimensions of the rod provided that the flux density in the core was held constant in order to keep the complex permeability from changing.

The use of modified scaling factors in the design of high-power, non-linear, transmitting rod-core antennas

“…Here we determine the effects of scaling all physical dimensions of the rod antenna by a factor p, except for the cross-sectional area of the individual wires or strips that are used to construct the core. Since the complex permeability and electrical conductivity vary with frequency, we will use the same frequency for the rods by using the simple and analytical expressions for an air-core antenna and expressions that were derived in the prolate spheroidal analysis [Jordan, 2008]. From this, we found the modified scaling factors for air-core and rod-core antennas that are shown in Table 1.…”

“…The trade off for using more turns and less drive current to reach the desired magnetic flux density is an increase in both inductance and core series loss resistance by a factor of N 2 . Refer to Jordan (2008) to see this N turns 2 dependence and the direct tradeoff between the current and the number of turns which was obtained by investigating the tangential magnetic field coefficients in the prolate spheroidal series expansions.…”

“…Saturation curves for two black oxide, low-carbon steel (BOLCS) rod antennas, at a frequency of 100 Hz and a magnetic flux density of 0.8 T, are presented in Jordan et al (2009) , Fig. 8.…”

“…The modified scale factors in Table 1 were checked using both theory and numerical simulations (Jordan, 2008). The drive current was modified to produce a constant B-field within the core.…”

“…In order to model a finite-length rod-core antenna, a prolate spheroidal rod antenna was analyzed in Jordan (2008), Fig. 1.…”