The dipole is the fundamental elemental antenna. Moreover, the electric dipole and its monopole equivalent on a groundplane are widely used in practice. Despite the long history of dipole research, ...its complete impedance behaviour remains elusive. In numerical techniques, such as the method of moments, a gap voltage feed can be expected to give a well-defined radiation conductance but a susceptance which is dissimilar to that of a realized antenna, whereas an impressed current feed can give a well-defined radiation resistance, but dissimilar reactance. The reason is that neither of these feeds accurately model the input region of a practical dipole. Two analytic approaches to the dipole impedance are available - the wave structure method and the induced EMF method. The wave structure method does not lend itself to feed detail, but reveals the impact of dipole thickness and length on the impedance of dipoles which is not available from any other approach. It is reliable for short lengths but it remains restricted to an infinitesimal feed gap, i.e., different to a practical dipole antenna. The induced EMF method is accurate for short and impracticably thin antennas. Electromagnetic simulation techniques can be used for practical dipole thicknesses, but no theory is available to benchmark the results of the numerical experiments. The feed modeling remains a long standing problem in terms of accurately matching the complete impedance to physical experimental results. To make a theoretical start on the problem, the induced EMF method with finite feed gap is solved here and the impedance of the thin dipole is presented. The effect of feed gap size for the finite length wire, e.g. the dipole antenna, has not been studied before. From the induced EMF method, the lossless, thin dipole with finite gap turns out to have an extremely wide bandwidth when terminated with 50 or 75 ohms, a new and interesting result in antenna theory.
Neonatal skull is different from adults' skull. It is composed of ossified parts of flat bone and fontanels. Fontanels are fibrous membranes that at this stage of development connect the already ...ossified flat bones of the cranium. Since these two different tissue types have different electrical conductivities, it is important to model the geometry of the fontanels if one aims to solve the inverse problem as e.g. for source localization. In neonatal Computer Tomography (CT) images fontanels are identifiable as gaps between the bones forming the cranium. In this paper we propose an automatic method based on a level set algorithm with shape prior to segment skull and fontanels from neonatal CT images. Quantitative evaluation based on similarity between automatically and manually segmented skulls and fontanels using ten subjects show that the proposed method can appropriately segment skull and fontanels.
Physics-based simulation of radio channels offers a powerful technique for propagation analysis and even evaluation of antennas. In this paper, it is shown how the power delay profile (PDP) and its ...moment, the delay spread, can be evaluated from physics-based channel data. The situation is different to that of the measured channel. The simulated channel contains more information, including information that cannot be extracted from the measured channel. Different processing of this data gives different PDPs and moments, and some of the issues are presented here.
This paper presents a modeling technique for a faulty 3-phase Induction Motor (3-phase Induction Motor IM under open-phase fault). The developed model has the same structure of equations as the ...balanced 3-phase model. It is shown that the model can be utilized to estimate the speed of a faulty IM based on an Extended Kalman Filter (EKF) estimation technique, which was developed for a balanced 3-phase IM. Simulation and experimental results are presented to show the validity of the proposed techniques.
The newborn's skull is composed of already ossified parts of the flat bone connected by areas of fibrous membrane not yet ossified, which are called fontanels. At birth, an infant has six of such ...fontanels. These two different tissue types forming the outer part of the neuro-cranium have different electrical conductivities. Thus, it is important to determine the exact geometry of the fontanels if one aims to solve the inverse problem as e.g. for source localization. Computer Tomography (CT) imaging provides an excellent tool for the non-invasive study of bone which here can easily be identified due to its high contrast as compared to other tissue. Fontanels correspond to not yet ossified cartilage and give less contrast, thus they can be indirectly reconstructed by extrapolation for closing of the gaps between the flat bones forming the skull. In this paper, we propose an automatic model based method using level set to extract the fontanels from CT images. The automatically determined fontanels show good agreement with the manually extracted ones.
Bounds on Q for the short dipole Estarki, M. D.; Vaughan, R. G.
Proceedings of the 2012 IEEE International Symposium on Antennas and Propagation,
2012-July
Conference Proceeding
The quality factor (Q) relates to the theoretical impedance bandwidth of an antenna. Such a bandwidth could only be realized using an ideal (lossless, perfectly matched) network to interface the ...antenna to its terminating resistance. The Q is therefore particularly useful for deriving the limiting bandwidth of fixed, compact antennas. The Q factors of short dipoles - the most fundamental compact element - are calculated from different analytical and numerical methods. The lowest Q arises from the induced EMF method where a larger feed gap leads to a larger theoretical bandwidth for thin wire elements. This method is known to be rigorous but it is a challenge to check the result because no other theoretical or numerical methods are suitable for such thin structures, and it is difficult to realize this gap feed for a physical measurement. The results for thicker dipoles, from popular numerical solvers, are included.
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