Electromagnetic coupling through apertures has been a subject of extensive electromagnetic (EM) research for many years and the coupling of electromagnetic energy from one region to another is an important problem in many areas of electromagnetic engineering. Some examples are leakage from microwave ovens, electromagnetic penetration into vehicles, and electromagnetic pulse interaction with shielded electronic equipment. Many specific applications, such as apertures in a conducting screen, waveguide-fed apertures, cavity-fed apertures, waveguide-to-waveguide coupling, waveguide-to-cavity coupling, cavity-to-cavity coupling, aperture-type antennas, frequency selective surfaces, and shielding enclosure have been investigated in the literature.
The problem of diffraction by a small aperture of circular or elliptic shape has been investigated by a rather large group of workers using a variety of different techniques. Most notable among these is Lord Rayleigh, who proposed a solution expressed as a series in ascending powers of the wave-number κ(=2/λ). Beth presented the results for the leading terms in the Rayleigh series expansion using a scalar potential fuction approach. Later, Bouwkamp investigated the same problem using a more complete set of coupled, integro-differential equations and pointed out some errors in Beth''s solution. It has been shown that an electrically small aperture in a perfectly conducting screen, when illuminated by an electromagnetic field, produces a perturbation of this field which can be described in terms of electric and magnetic dipole distributions induced in the aperture. Analytical expressions exist for the electric polarizability of a circular aperture and an elliptical aperture. At distances large compared with the dimensions of the aperture, the field due to the electric dipole can be expressed in terms of the aperture electric polarizability.
In chapter 2, multiple rectangular apertures (two-dimensional finite array) in a thick cinducting plane which is at zero potential is considered. Assume that a potential is normally-incident on multiple rectangular apertures from above. The scattered potential in terms of continuous and discrete modes is represented. In order to determine the discrete modal coefficients, the boundary conditions on the apertures and a conducting plane are used. The Fourier transform and the mode-matching technique are utilized to obtain the simultaneous equations for the discrete modal coefficients. The simultaneous equations for the modal coefficients are represented in rapidly convergent series which are amenable to numerical computations. The numerical computations are performed to illustrate the behaviors of the potential distribution through multiple apertures. The convergence rate of our series solutions are checked and it is confirmed that our solution gives accurate results. The potential distribution (or penetration) into multiple apertures is studied in terms of aperture shape, periodicity and thickness. It is also useful to introduce the concept of the electric polarizability and study its behavior. The characteristic of the electric polarizability are illustrated versus the thickness of the aperture. The presented theoretical study allows one to better understand the behavior of the electrostatic field penetration into multiple apertures often encountered in EMI/EMC problems.
In chapter 3, acoustic scattering from a rectangular aperture in a thick hard screen is examed. The Fourier transform is used to represent the scattered wave in the spectral domain and the boundary conditions are enforced to represent a solution in closed form. The solution is a simle, convergent series so that it is not only exact but also computationally very efficient. Numerical computations are preformed to illustrate the behavoir of the scattered wave from a thick rectangular aperture. Transmission loss(STL) of the rectangular aperture is calculated for various rectangular aperture geometry too. The solution is represented in series which are numerically efficient.
In chapter 4, electromagnetic wave scattering from multiple rectangular apertures in a conducting plane is studied by using the Fourier transform and the mode-matching technique to obtain simultaneous equations for the modal coefficients. The simultaneous equations are solved to represent the scattered and transmitted fields in series forms which are suitable for numerical computation. The numerical computations are performed to illustrate the aperture transmission and scattering behaviors in terms of aperture size, incident angle, and frequency. The effects of the finite number of apertures on the transmission characteristics are discussed.
In chapter 5, as application of chapter 4, electromagnetic penetration into a rectangular cavity through multiple apertures is studied by using the same method. The simultaneous equations are solved to represent the cavity field in series forms which are suitable for numerical computations Numerical computations are performed to investigate the field penetration into a cavity in terms of the shielding effectiveness(SE) for a various geometry.
