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A symmetry relation of the integral operators in a layered medium proved by the reciprocal theory can be applied to improve the accuracy of the magnetic-field integral equation (MFIE). Based on the symmetric layered medium Green’s function, the normal vector can be transferred into the inner integral to keep the field integral as the inner integral of the elements in the impedance matrix. When discretized by the divergence-conforming function, this field-extracted scheme shows better performance than the classic expression in accuracy. Meanwhile, this form of expression can be applied in the combined-field integral equation (CFIE). Several numerical results are provided to validate the formulation of the symmetry relations from the layered medium Green’s function to the impedance matrices and to reveal its advantages in enhancing the accuracy of the field-extracted form of MFIE. [ABSTRACT FROM AUTHOR]

Spoof surface plasmons (SSP) on the corrugated metal surfaces have been widely studied over the past decade in both microwave and Terahertz (THz) band. Previous studies show that SSP mode on the metal grating suffers from high dissipative losses in high THz band especially near asymptotic frequency which may limit its real applications. The issue can be addressed by utilizing long-range SSP mode (LRSSP). LRSSP is a special low-loss symmetric propagating surface wave mode along double-layer corrugated metallic waveguides. In this paper, the asymmetric double metal gratings are proposed to support LRSSP which can significantly reduce the damping losses of the other short-range SSP mode (SRSSP) on the conventional doubly-corrugated metallic surfaces, thus enabling new possibilities to utilizing this SRSSP mode within long-range manner. According to our dispersion theory and the numerical calculations, the propagation loss of LRSSP is still lower than that of SRSSP within asymmetric regime, which demonstrates good tolerance to the asymmetry of the double-layer corrugated structure. However, its long-range propagation superiority of LRSSP vanishes gradually as the degree of asymmetry is enlarged. This work provides an alternative approach to increase the propagation length of SRSSP mode on the doubly-corrugated metallic surfaces and can open up new avenues to develop some novel LRSSP-based plasmonic devices such as waveguides, filters, sensors and active powerful radiation sources induced by energy beam below optical spectrum. [ABSTRACT FROM AUTHOR]

In this article, the famous Sommerfeld integrals (SIs) have been revisited by assuming that the approximation of $\gamma _{0}\approx {\mathrm{ i}}\lambda $ is valid for the near-field propagation of low frequencies over a plane conducting ground. A deduction from that is proposed and adopted in the present study, which is defined by $|\gamma _{0}\gamma _{1}|\gg k_{0}^{2}$ , extending to cover a magnetic dipole source in air-to-undersea communications. The focus is on deriving complete and effective solutions in air and seawater regions under the cylindrical coordinates for the electromagnetic near-field, which is generated by a vertical magnetic dipole above sea surface. The resulting formulas can be given by a few summands in closed form as the well-known Fourier–Bessel integrals. It is believed to go a step further by relaxing the reliance on various distance conditions and replacing the integrands by simple, exact integrated terms which are usable at the frequencies of interest for any distance from the source. Computations and discussions are carried out by comparing with related works and late experiments, including the field components and Poynting vectors. It is verified that the derived formulas can be degenerated into some simplified forms which are in accord with those obtained by a “quasi-static” treatment. [ABSTRACT FROM AUTHOR]