• Journal of Astronomy and Space Sciences
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• v.41 no.2
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• pp.87-106
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• 2024

The objective of this research is to address the issue of frozen orbits in charged satellites by incorporating geopotential zonal harmonics up to J6 and the initial tesseral harmonics. The employed model starts from the first normalized Hamiltonian to calculate specific sets of long-term frozen orbits for charged satellites. To explore the frozen orbits acquired, a MATHEMATICA CODE is developed. The investigation encompasses extensive variations in orbit altitudes by employing the orbital inclination and argument of periapsis as freezing parameters. The determined ranges ensuring frozen orbits are derived from the generated figures. Three-dimensional presentations illustrating the freezing inclination in relation to eccentricity, argument of periapsis, and semi-major axis parameters are presented. Additional three-dimensional representations of the phase space for the eccentricity vector and its projection onto the nonsingular plane are examined. In all investigated scenarios, the impacts of electromagnetic (EM) field perturbations on the freezing parameters of a charged satellite are demonstrated.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.1
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• pp.43-50
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• 2003

전자산업과 전파통신기술이 고도로 발전함에 따른 전파 이용의 증대로 인해 전자파환경 EMI/EMS이 사회적 문제를 야기하고 있다. 이에 따라, CISPR(Comite Internationale Special des Perturbations Radioelectrique), FCC (Federal Communications Commissions) ANSI (American National Standards Institute)등의 기구는 EMI/EMC 대책을 위해 전파환경의 규정을 제정하고 있다. 또한 EMI/EMC 측정을 위한 전파무향실(anechoic chamber)용 전파흡수체는 20 dB 이상의 전파흡수능이 요구된다. 종래의 EMI 측정 주파수 범위는 30 MHz～l,000 MHz 이었으나 1998년 11월, CISPR11은 1 GHz~18 GHz를 추가하는 안을 받아들였다. 본고는 새로운 형태의 다층형 페라이트 전파흡수체를 제안하고 등가재료정수법을 사용하여 광대역 설계를 시도한 것이다.

• Smart Structures and Systems
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• v.6 no.1
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• pp.29-38
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• 2010

An ElectroMagnetic Actuator (EMA) is designed and assessed numerically and experimentally. The EMA has the advantage to be without contact with the structure so it could be applied to light and small mechanism. Nevertheless, the open-loop instability and the nonlinear dynamic behavior with respect to the excitation frequency could limit its application field. The EMA is designed and dimensioned as a function of the experimental structure to be controlled. An inverse model of the EMA is proposed in order to implement a linear action block for the used frequency range. The control strategy is a fuzzy controller with displacements and velocities as inputs. A fuzzy controller of Takagi-Sugeno type is used. The air gap is estimated by using a modal approximation of the displacements issued from all measurements. Several configurations of control are assessed by using numerical simulations. The block diagram used for numerical simulations is implemented under Dspace$^{(R)}$ environment. The implemented controller was tested experimentally in the context of impact perturbations. The results obtained show the effectiveness of the developed procedures and the robustness of the implemented control.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2002.11a
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• pp.336-339
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• 2002

CISPR(Committee Internationale Special des Perturbations Radio Electriques) has proposed limits on the noises emitting from power lines and signal lines. But different measurement environment and different measurement methods are used in different countries. This difference causes much confusion in understanding the results measured by different test laboratories. In this paper, we measure EMI noise using the absorbing clamp method that takes short measurement time and is described in CISPR 13, 14-1, 16-2. We analyze the cause of the difference of measurement results.

• Bulletin of the Korean Chemical Society
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• v.6 no.5
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• pp.309-311
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• 1985

When a molecule is perturbed by an external field, the perturbed moecue can be described as a doubly perturbed system. Hartree-Fock operator in the absence of the field is the zeroth order Hamiltonian, and a correlation operator and the external field operator are perturbations. The effective Hamiltonian, which is a projection of the total Hamiltonian onto a small finite subspace (usually a valence space), has been formally derived. The influence of the external field to the molecular Hamiltonian itself has been examined within an effective Hamiltonian framework. The first order effective expectation values, for instance electromagnetic transition amplitudes, between valence states are found to be easily calculated - by simply taking matrix elements of the effective external field operator. Implications of the terms in perturbation expansion are discussed.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2001.11a
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• pp.343-343
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• 2001

최근 전자산업과 전파통신산업의 발달에 따라 불요전자파에 의한 전자파장해가 심각한 수 준에 이르게 되었다. 그 결과 국 . 내외 전자파환경은 나날이 악화되고 있으며, 이로 인한 사 회적 문제가 점차 증가되고 있는 실정이다. 이에 대한 대책으로 CISPR(Comite Internationale S Special des Perturbations Radioelectrique), FCC (Federal Communications Commissions) A ANSI(Amercian National Standards Institute) 둥이 주축이 되어 국제 규정이 제정되어 각종 전자기기들에 대해 방사(EMI) 및 내성(EMS)의 규제가 강화되고 있다. 그러나 국제규정이 요구하는(30 MHz - 18 GHz) 주파수 범위에서의 EMIjEMS 측정을 하기 위해 광대역(Broad-band) 전파무향실(Anechoic Chamber)이 필요하지만1 기존의 Ferrite T Tile 또는 그리드형 전파홉수체는 20 dB 이상 전파를 홉수할 수 잇는 주파수 대역이 30 M MHz - 400 MHz 또는 780 MHz에 불과하기 때문에 상기의 조건을 만족하는 전파무향실 을 구성하기에는 곤란한 실정이다. 본 논문에서는 국제 규격을 만족하는 전파무향실을 위한 광대역 전파홉수체를 개발하기 위해, 다충형으로 구성하고, 전파흡수체의 형상을 변화시켜 등가재료정수법을 사용하여 설계하고 그 특성을 평가함을 그 목적으로 하였다. 따라서 본 논문에서는 본 연구실에서 기폰에 제안한바 있는, 금속판 위에 타일형 페라이 트 충, 그 위에 원추절단형 페라이트 층과 원통형 페라이트 층을 적층시칸 형상의 전파홉수 체는 30 MHz - 6 GHz 정도까지 커버할 수 있으나, 1 GHz 부근의 주파수 대에서 16 dB 정도의 홉수능 밖에 가지지 못하였다. 이를 개선하기 위해, 금속판 위에 타일형 페라이트 층 을 형성하고 그 위에 원통형 페라이트 충, 원추절단형 페라이트 충I 원통형 페라이트 충, 타 원형 페라이트 충을 형성한 새로운 형태의 전파홉수체를 제안하였다. 본 논문에 제안한 새로운 형태의 전파흡수체의 시물레이션 결과 30 MHz - 20 GHz의 주파수 범위에서 전반적으로 25 dB이상의 전파흡수능을 가짐을 확인하였으며/ 특히 기폰에 제안한 전파홉수체와 비교하면,1GHz 부끈에서의 전파홉수능을 10 dB 이상 개선하였다. 나아가서/ 실재로 제작한 전파흡수체의 측정된 주파수특성이 시율레이션에 의한 이론치와 3 30 MHz - 6 GHz의 범위에서 잘 일치함을 확인하였다. 또한y 전파 홉수체의 전체 높이는 2 27 mm 밖에 되지 않으므로 본 연구에서 제안한 전파 홉수체를 사용할 경우 전파무향실의 유 효공간 확보에 매우 유리한 이점을 가진다

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.11
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• pp.1217-1224
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• 2009

This paper newly proposes a methodology towards computing antenna element weights which are satisfying asymmetric sidelobe levels(SLLs) specified arbitrarily on both sides of the main beam pattern, in the linear phased array antenna pattern synthesis problem. Opposite to the conventional methods in which the element weights are directly optimized from the array factor, this method is based on the optimum perturbations of complex roots inherent to the Schelkunoff's polynomial form which is described for the array factor. From the proposed methodology, the capability of nulling the directions of multiple jammers is also possible by independently perturbing only the complex roots corresponding to each jamming direction, hence allowing an enhancement of the simplicity of the numerical procedure by means of a proper reduction of the dimension of the solution space. The complex weights over the array are then easily computed by substituting the optimally perturbed complex roots to the Schelkunoff's polynomial. Some examples are examined and numerically verified by substituting the extracted weights into the array factor equation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.5
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• pp.556-561
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• 2008

The characteristics of microwave reflectometry, which is based on the technologies of FM radar and is applied as a non-invasive method to examine the properties including density distribution of inhomogeneous media, is investigated. The microwave reflectometry system requires not only an optimized system hardware but as well as the understanding of system response from the media under test in order to provide the system solution describing the object under test quantitatively. The introduction of microwave reflectometry especially in the area of applied plasma physics has been relatively new and the number of usage is found to be increasing gradually. The experimental method to characterize the microwave system as a device to examine the properties of plasma is explained. The microwave reflectometry signals consist of the cutoff signals which originate from the region where most of the reflected power comes from and the scattered signals which result as an interaction of the microwave and the density perturbations. This paper describes the experimental results of the scattered signal from the microwave reflectometry, such as the wavenumber dependence and the sensitivity on density perturbation, and the comparison of the characteristics with those from the numerical simulations and those from the cutoff signals.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.4
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• pp.505-513
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• 2000

This study suggests new antenna design for polarization diversity. For dual polarization, two port feeding lines are printed on two separate layers and cross-shaped aperture is located on ground between the substrates. For reducing back radiation, a reflector is attached around $\lambda$/4 behind feeding substrates. For wide bandwidth we use a perturbed patch with saw tooth shaped. This perturbation effect causes reduction of antenna size and also reduction of array size. With the antenna proposed here, $1\times4$ array dual polarization antenna for polarization diversity of PCS base station is built. One single element has as large as 10.3%, 11.3% bandwidths at each port, V.S.W.R less than 1.3 and the isolation is less than -40 dB, also array antenna has 13.2% 12.7% band bandwidth, V.S.W.R less than 1.3 the isolation below -36dB and the XPD of 10 dB.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2012.10a
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• pp.125-127
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• 2012

With the progress of electronics and radio communication technology, human enjoys greater freedom in communication. However, EMW (Electro-Magnetic wave) environments have became complicate and more difficult to control. Thus, international organizations, such as the American National Standard Institution (ANSI), Federal Communications Commission (FCC), the Comite Internationale Special des Perturbations Radio electrique (CISPR), etc, have provided standard for controlling the EM wave environments and for the countermeasure of the electromagnetic compatibility (EMC). In this paper, the status of EMW absorber and the goal of smart EMW absorber ifor the future were described. Furthermore, design method of the smart EM wave Absorber with heat radiating function was suggested. The designed smart EM wave Absorber has the absoption ability of more than 5 dB from 2 GHz to 2.45 GHz band, one optimum aperture (hole) size of which was 6 mm, 9 mm in adjacent hole space, and 6.5 mm in thickness, respectivly. Thus, it is repected that these results can be applied to various EMC devices in electronic, communication, and controlling systems.