Further investigation of the interference minimums in the low-frequency electromagnetic fields produced by a submerged vertical magnetic dipole

The quasi-static electromagnetic fields generated along the sea surface by a submerged vertical magnetic dipole are evaluated numerically using exact expressions and the results are plotted in a parametric form for source depths varying from 2 to 14 seawater skin depths δ. The curves show that there is a minimum in the amplitude of the vertical component of the magnetic field for horizontal distances from the source in the range 9–14δ and for dipole depths ranging from 2 to 8δ, with the deepest minimum occurring at a horizontal distance of pmin ≃ 11.07δ when the dipole is at a critical depth of dc ≃ 4.22δ. There also exists a similar minimum point in the variation along the surface of the amplitude of the total electric field for horizontal distances from the source in the range 10–20δ and dipole depths ranging from 4 to 23δ, with the deepest minimum occurring at a horizontal distance of pmin ≃ 12.95δ when the dipole is at a depth of dc ≃ 9.38δ. Both minimums are due to the strong destructive interference between the direct and the lateral wave components of the fields. No such minimum point exists for the variation of the amplitude of the horizontal component of the magnetic field.

[1]  Antony C. Fraser-Smith,et al.  ULF/ELF magnetic fields generated at the sea surface by submerged magnetic dipoles , 1976 .

[2]  P. K. Bhattacharya,et al.  Vertical Magnetic Dipole Buried Inside a Homogeneous Earth , 1966 .

[3]  Antony C. Fraser-Smith,et al.  ULF/ELF electromagnetic fields generated in a sea of finite depth by a submerged vertically‐directed harmonic magnetic dipole , 1978 .

[4]  H. B. Dwight,et al.  Tables of Integrals and Other Mathematical Data , 1934 .

[5]  James R. Wait,et al.  The fields of an oscillating magnetic dipole immersed in a semi‐infinite conducting medium , 1953 .

[6]  Seabed propagation of ULF/ELF electromagnetic fields from harmonic dipole sources located on the seafloor , 1988 .

[7]  M. Kraichman.  Handbook of electromagnetic propagation in conducting media , 1970 .

[8]  D. Staiman,et al.  Nature and optimisation of the ground (lateral) wave excited by submerged antennas , 1966 .

[9]  Ronold W. P. King,et al.  Electromagnetic surface waves: New formulas and applications , 1984 .

[10]  Herman H. Lowell.  Tables of the Bessel-Kelvin Functions Ber, Bei, Ker, Kei, and Their Derivatives for the Argument Range 0(0.01)107.50 , 1960 .

[11]  D. Bubenik.  A practical method for the numerical evaluation of Sommerfeld integrals , 1977 .

[12]  A. Fraser-Smith,et al.  Large-amplitude changes induced by a seabed in the sub-LF electromagnetic fields produced in, on, and above the sea by harmonic dipole sources , 1987 .

[13]  P. Bannister.  New simplified formulas for ELF subsurface-to-subsurface propagation , 1984 .

[14]  R.W.P. King,et al.  Lateral electromagnetic waves along plane boundaries: A summarizing approach , 1984, Proceedings of the IEEE.

[15]  A. Baños.  Dipole radiation in the presence of a conducting half-space , 1966 .