Parameterizing Quasiperiodicity: Generalized Poisson Summation and Its Application to Modified-Fibonacci Antenna Arrays

The fairly recent discovery of "quasicrystals", whose X-ray diffraction patterns reveal certain peculiar features which do not conform with spatial periodicity, has motivated studies of the wave-dynamical implications of "aperiodic order". Within the context of the radiation properties of antenna arrays, an instructive novel (canonical) example of wave interactions with quasiperiodic order is illustrated here for one-dimensional (1-D) array configurations based on the "modified-Fibonacci" sequence, with utilization of a two-scale generalization of the standard Poisson summation formula for periodic arrays. This allows for a "quasi-Floquet" analytic parameterization of the radiated field, which provides instructive insights into some of the basic wave mechanisms associated with quasiperiodic order, highlighting similarities and differences with the periodic case. Examples are shown for quasiperiodic infinite and spatially-truncated arrays, with brief discussion of computational issues and potential applications.Comment: 29 pages, 10 figures. To be published in IEEE Trans. Antennas Propagat., vol. 53, No. 6, June 200

Short‐pulse radiation by a sequentially excited semi‐infinite periodic planar array of dipoles

This paper deals with the fourth in a sequence of canonical problems aimed toward an understanding of the time domain (TD) behavior of wideband-excited sequentially pulsed planar periodic finite arrays of dipoles, which play an important role in a variety of practical applications. The present investigation of sequentially pulsed semi-infinite planar dipole arrays extends our previous studies of sequentially pulsed infinite and semi-infinite line dipole arrays and of infinite planar dipole arrays. The discrete element-by-element radiations are converted collectively to radiations from a series of Floquet wave (FW)-modulated truncated smooth equivalent aperture distributions, and to corresponding FW-modulated edge diffraction. After a summary of necessary results from the earlier studies, emphasis is placed on the new truncation-induced TD results and interpretations, which are extracted via phenomenology-matched high-frequency asymptotics from rigorous frequency and time domain formulations parameterized in terms of the dispersive FW instantaneous frequencies and wave numbers. As in our previous studies, the outcome is a numerically efficient, physically incisive algorithm whose accuracy is verified preliminarily by application to a pulsed planar strip array of dipoles

Radiation and scattering of waves

This world-renowned classic by Professors Felsen and Marcuvitz continues to abound in timely and useful materialover 20 years after it was originally published. The book contains indispensable information that remains difficult to find anywhere else in the electromagnetics and acoustics literature, and it will be useful for many years to come. Of particular interest is Chapter 4, Asymptotic Evaluation of Integrals, which is appreciated and cited worldwide. It contains an in-depth description of asymptotic techniques and formulas useful to both engineers and physicists

Electromagnetic engineering in the 21st century: challenges and perspectives

This paper aims at a broad-brush look at certain technological and educational challenges that confront wave-oriented electromagnetic (EM) engineering in the 21st century, in a complex computer and technology-driven world with rapidly shifting societal and technical priorities. Simulation strategies for complex EM systems, both analytic and numerical, are reviewed and categorized, and are illustrated on selected practical complex multicomponent system scenarios currently under investigation in Turkey. Educational issues to ensure proper multidisciplinary exposure of new generations of computer-weaned students, who will have to deal with these problems, are touched upon as well

Maxillary distraction of cleft lip and palate patients by internal distractors

The excitation of various types of leaky waves in layered elastic media by beams incident from an exterior fluid at or near the leaky wave phase-matching angle is of interest for NDE applications. In particular, much attention has been given to the non-specular reflection of beams under such conditions of incidence. While various methods have been employed to study and clarify these phenomena for well collimated beams in plane layered environments [1–11], much less has been done on the corresponding effects when the incident beams are diverging and/or when the layers are curved. To extend the plane layer results to more general conditions, it is desirable to employ analytic modeling that adapts the wave phenomenology locally from planar to curved geometries. Because the phenomena occur in the range of high frequencies, ray field modeling affords an attractive option. By the complex-sourcepoint (CSP) technique, which places a radiating source at a complex coordinate location, a conventional line or point source excited field can be converted into a two-or three-dimensional quasi-Gaussian beam field that is an exact solution of the dynamical equations [12,13]. When the CSP field interacts with a plane or cylindrically layered elastic medium, the resulting internal and external fields can be expressed rigorously in terms of wavenumber spectral integrals [14]. Asymptotic reduction of these integrals, achieved by the method of saddle points applied to deformed contours in the complex spectral wavenumber plane, accounts for all relevant wave phenomena. For the reflected field, this yields explicit waveforms which are synthesized by interacting specularly reflected beam, leaky wave, and possible lateral wave contributions

Groundwave propagation modeling: problem-matched analytical formulations and direct numerical techniques

In this overview of groundwave propagation, we address a particular class of propagation scenarios in the presence of surface terrain and atmospheric refractivity. Beginning with idealized analytically solvable models over a smooth spherical Earth, we trace the progression toward more "reality" through physics-based numerical algorithms, operating in the frequency and short-pulse time domain, which take advantage of computational resources. An extensive sequence of simulations for various terrains and atmospheric refractivities, as well as different source-receiver arrangements and operating frequencies, serves to calibrate these algorithms one against the other, and establishes the range of problem parameters for which each is more effective.IEEE Antennas and Propagation Societ