Propagation characteristics of electromagnetic waves generated by an electric dipole are used for a variety of applications, including geological mapping of mineral deposits on the ocean floor, cellular or mobile communications, and detection of unexploded ordnance. Mapping of the regional geology in deep-ocean, near- bottom locations has led to discovery of poly- metallic sulfide mineral deposits in the vicinity of hydrothermal vents on mid-ocean ridges potentially worth billions of dollars.
Conventional frequency domain measurements are restricted in their applicability to working on the sea floor and, consequently, methods that measure the shape of the transient time domain response are under consideration as more effective techniques for detecting sea floor conductivity. In addition, studies of electric and magnetic field interaction with human tissue have suggested that exposure to continuous electromagnetic fields has a lesser effect than exposure to low-frequency transient fields.
To support exploration of the effects of electromagnetic waves produced by a transient pulse, AltaSim Technologies has developed computational approaches for treating the transient nature of a pulse with asymmetric, non-zero-rise and decay times. The shape of the current pulse applied to the electric dipole was represented by a heavy-side exponential function with independent, non-zero rise and decay times. The current pulse was integrated into COMSOL Multiphysics to provide solutions for the electric and magnetic response of an electric dipole.
To ensure accurate solutions, two critical aspects of the analysis were found to be significant: first, refinement of the analytical mesh to a critical level to ensure spatial resolution within the time transient of the current pulse; and secondly, settings of solver parameters were optimized to ensure solution time-stepping was maintained within the required time steps of the rise and decay times of the input current pulse.
Figure 1 compares the results for the normalized electric field in the x-direction as a function of time at a point 50 m from the dipole obtained by computational analyses, with those from published analytical results for a transient dipole in a conductive media. The width of the output pulse is a function of the conductivity of space and the time period of the input pulse. At zero conductivity, the time period of the pulse is the period of the input pulse; as the conductivity of the propagating medium increases, the time period increases from that of the input pulse and is defined by the conductivity of the medium. The spatial variation of the electric field is given in Figure 2.
Application of the solution methodology developed here has enabled wide-ranging studies to be performed to identify the electric and magnetic fields developed by a transient pulse electric dipole. The results of these analyses have shown that considerable differences in the surrounding environment are expected to arise in response to a transient pulse compared to that from a continuous applied current.
This work was performed by Dr. S.P. Yushanov, Dr. J.S. Crompton, and Dr. K.C. Koppenhoefer of AltaSim Technologies, LLC using COMSOL Multiphysics. For more information, visit http://info.hotims.com/22926-126.