• International Journal of Ocean System Engineering
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• v.3 no.1
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• pp.22-32
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• 2013

A heuristic physical theory of diffraction (PTD) for an acoustic impedance wedge is proposed. This method is based on Ufimtsev's three-dimensional PTD, which is derived for an acoustic soft or hard wedge. We modify the original PTD according to the process of physical optics (or the Kirchhoff approximation) to obtain a 3D heuristic diffraction model for an impedance wedge. In principle, our result is equivalent to Luebbers' model presented in electromagnetism. Moreover, our approach provides a useful insight into the theoretical basis of the existing heuristic diffraction methods. The derived heuristic PTD is applied to an arbitrary impedance polygon, and a simple PTD formula is derived as a supplement to the physical optics formula.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.2
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• pp.99-105
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• 2012

This paper deals with the experimental results of the frequency-dependent resultant ground impedance of vertical ground electrodes installed with a regular n-polygon. In order to propose an effective method of installing the vertically-driven multiple ground electrodes used to obtain the low ground impedance, the resultant ground impedance of ground electrodes installed with a regular n-polygon were measured as functions of the number of ground electrodes and the frequency of test currents and the results were discussed based on the potential interferences among ground electrodes. As a consequence, the effect of potential interference on the resultant ground impedance of vertical ground electrodes is frequency-dependent and it is significant in the low frequency of a few hundreds [Hz]. The resultant ground impedance of multiple vertical ground electrodes is not decreased in linearly proportion to the number of ground electrodes due to the overlapped potential interferences. Also the distributed-parameter circuit model considering the potential interference, the frequency-dependent relative permittivity and resistivity of soil was proposed. The simulated results of the frequency-dependent resultant ground impedance of multiple vertical ground electrodes are in good agreement with the measured data.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.49 no.5
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• pp.257-263
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• 2000

One of the basic assumptions in the static gait design for a walking robot is that the weight of leg should be negligible compared to that of body, so that the total gravity center is not affected by swing of a leg. Based on the ideal assumption of zero leg-weight, conventional static gait has been simply designed for the gravity center of body to be inside the support polygon, consisting of each support leg's tip position. In case that the weight of leg is relatively heavy, however, while the gravity center of body is kept inside the support polygon, the total gravity center of walking robot can be out of the polygon due to weight of a swinging leg, which causes instability in walking. Thus, it is necessary in the static gait design of a real robot a compensation scheme for the fluctuation in the gravity center. In this paper, a body impedance control is proposed to obtain the total gravity center based on foot forces measured from load cells of a real walking robot and to adjust its position to track the pre-designed trajectory of the corresponding ideal robot's body center. Therefore, the walking stability is secured even in case that the weight of leg has serious influence on the total gravity center of robot.

• Journal of Advanced Navigation Technology
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• v.15 no.5
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• pp.774-780
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• 2011

This paper presents a Bagley polygon and Gysel divider using open-stub loaded transmission line. The structure of slow-wave characteristic consists of small transmission line and shunt capacitive open stub that have reduced characteristic impedance and phase velocity, so we can implement the small circuit size. To validate the slow-wave characteristics, we are implemented the slow-wave characteristic of Bagley polygon and Gysel divider at center frequency 2.1 GHz. Its characteristics are same, but the circuit size is reduced above 15 % respectively.