K.-H. Chang

Bio: K.-H. Chang is an academic researcher from National Taiwan Ocean University. The author has contributed to research in topics: Dielectric & Transverse plane. The author has an hindex of 1, co-authored 1 publications receiving 2 citations.

Transverse electric scattering by a dielectric biconvex cylinder loaded with a shallow circular trough in a ground plane

Abstract: The scattering problem of transverse electric wave from a dielectric biconvex cylinder buried in a shallow circular trough of a ground plane is investigated and a rigorous series solution is also derived. Based on the region-matching method, the analysed region is decomposed into two subregions by introducing a semi-circular auxiliary boundary. The magnetic field of each subregion is expressed in terms of cylindrical wave functions with unknown expansion coefficients. After imposing the matching conditions and the boundary condition on the trough surface with the aid of Graf's addition theorem, the unknown coefficients are determined. Comparisons with published data for a dielectric circular cylinder case show very good agreement. Visible effects of depth-to-half-width ratios of a dielectric biconvex cylinder on echo width, far-field pattern and near-field distribution are illustrated in graphical form.

Analysis of transient electromagnetic scattering from an overfilled cavity embedded in an impedance ground plane

Abstract: : We consider the transient, or time-domain, scattering problem of a two-dimensional overfilled cavity embedded in an impedance ground plane. This problem is a significant advancement from previous work where more simplified boundary conditions were used, which can limit the number of applications. This research supports a wide range of military applications such as the study of cavity-like structures on aircraft and vehicles. More importantly, this research helps detect the biggest threat on today's battlefield: improvised explosive devices. An important step in solving the problem is introducing an artificial boundary condition on a semicircle enclosing the cavity; this couples the fields from the infinite exterior domain to those fields inside. The problem is first discretized in time using the Newmark scheme, and at each time step, we derive the variational formulation and establish well-posedness of the problem. This sets the foundation for the finite element method used in the numerical analysis. Using both a planar and overfilled cavity model, we provide numerical results through the depictions of the scattered electric field and radar cross section of the cavities.

Electromagnetic plane-wave scattering from a sectorial groove in a perfectly conducting plane

Abstract: Scattering characteristics of plane waves by a sectorial groove in a perfectly conducting plane are investigated. Both the transverse magnetic (TM) and transverse electric (TE) polarizations of the incident wave are considered. Judicious use of the region-matching technique provides a rigorous series solution to the problem. The analyzed region is separated into two sub-regions by choosing a semi-circular auxiliary boundary. Thefield in each sub-region is expanded as a summationof proper wave functions with unknown coefficients. Enforcing the matching of conditions on the auxiliary boundary and of boundary condition on the circular-arc surface of the groove leads to a linear set of equations and the unknown coefficients are then determined. Numerical results demonstrate the influence of central angles of the sectorial groove on echo width, far-field pattern and near-field distribution. The presented geometry is easily applicable to the design and fabrication of a grating structure for optical switches and tunable filters.

Electromagnetic scattering by a circular cavity of arbitrary shape placed in a perfect electric conductor

Abstract: An efficient modal expansion technique for scattering by a circular cavity with an arbitrary arc in a perfect electric conductor is developed. In contrast to the existing methods proposed for a shallow or semi-circular cavity, the proposed method can be utilised for a circular cavity of arbitrary shape while is computationally efficient. The authors first introduce an auxiliary circular border that divides half-space above the cavity into two separate subregions. Then, the tangential fields in the two subregions, which satisfy the Helmholtz equation, are expanded in terms of an infinite series of radial wave functions. The fields are matched at the auxiliary border to construct three independent equations in two different coordinate systems. By employing the addition theorem, all equations are transferred into the same coordinate system. Finally, the equations are converted into a system of linear equations and then solved through regular matrix techniques for the expansion coefficients. The solution is verified by the Method of Moments used in FEKO electromagnetic simulation software. This method is employed to study the effects of cavity shape and incident wave polarisation on the scattering signature.