• 한국통신학회논문지
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• 제27권5C호
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• pp.506-511
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• 2002

본 논문에서는 널리 알려진 슬롯 라인-마이크로스트립 변환을 이용하여 Ka-band에서 동작하는 도파관 형태의 전력 결합기를 제안하였다. 입력이 구형 도파관이고 출력이 마이크로스트립인 전력 분배기는 구형 도파관-슬롯라인 변환, 슬롯라인-마이크로스트립 변환, 그리고, 임피던스 정합회로 등으로 구성되어 있다. 2-way 전력 결합기는 두개의 슬롯라인-마이크로스트립 변환을, 4-way는 2-way 전력 결합기 2개와 sloltline tee junction을 이용하여 개발되었다. 3차원 유한 요소법을 이용하여 제안된 구조를 수치 해석하여 최적의 특성이 나오도록 설계하였고, 손실이 작은 수정 기판을 사용하여 제작하였다. Back-to-back으로 연결된 전력 결합기를 측정한 결과, 공진 주파수를 제외하면, 2-way 전력 분배기는 25.7∼29.8 GHz에서 삽입손실은 1.0 dB 이하, 반사손실은 15 dB 이상이었고, 4-way의 경우는 26∼28.2GHz에서 삽입손실이 1.0 dB 이하, 반사손실이 15 dB 이상의 우수한 특성을 얻을 수 있었다.

• 한국전기전자재료학회논문지
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• 제15권10호
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• pp.889-895
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• 2002

Wafer level packaging is gain mote momentum as a low cost, high performance solution for RF-MEMS devices. In this work, the flip-chip method was used for the wafer level packaging of RF-MEMS devices on the quartz substrate with low losses. For analyzing the EM (electromagnetic) characteristic of proposed packaging structure, we got the 3D structure simulation using FEM (finite element method). The electric field distribution of CPW and hole feed-through at 3 GHz were concentrated on the hole and the CPW. The reflection loss of the package was totally below 23 dB and the insertion loss that presents the signal transmission characteristic is above 0.06 dB. The 4-inch Pyrex glass was used as a package substrate and it was punched with air-blast with 250${\mu}{\textrm}{m}$ diameter holes. We made the vortical feed-throughs to reduce the electric path length and parasitic parameters. The vias were filled with plating gold. The package substrate was bonded with the silicon substrate with the B-stage epoxy. The loss of the overall package structure was tested with a network analyzer and was within 0.05 dB. This structure can be used for wafer level packaging of not only the RF-MEMS devices but also the MEMS devices.

• 전기학회논문지
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• 제64권9호
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• pp.1330-1336
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• 2015

It is necessary to study on acoustic and vibratory response of a MEMS resonant accelerometer before applying to military applications. In this paper, we analyze why the resonant accelerometer reacts to an acoustic wave and a high frequency vibration. And we describe experimental results on acoustic and vibratory response of the accelerometer. The accelerometer consists of a proof mass and a dual ended tuning fork. It is a differential resonant accelerometer with arranging a pair of accelerometers. The mode shape was analyzed to find out the input mode frequency by using a FEM simulation. Some experiments regarding the acoustic noise was carried out by using a tweeter and a microphone in the anechoic room. Results showed that the accelerometer reacted to the acoustic wave and vibration which had the input mode frequency as we had expected. We showed experimentally not only that the susceptibility of the accelerometer to an acoustic wave was 70 dB but also that the effectiveness of applying an acoustic absorber and a metal case was 20 dB, respectively. Also, we could minimize the vibratory response property of the accelerometer by installing a IMU with a silicone rubber mount pad.

• 대한기계학회논문집A
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• 제20권11호
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• pp.3538-3548
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• 1996

In this study, as a part of basic study for developing the simulation program for the assemssment of reliability of electronic EMC packaging which covers from EMC mixing step to thermal analysis, comparison between a measured and predicted values of material properties of EMC and finitde element analysis of thermal stress are performed. For the experimental testing specimens of fifty, sixty hive and eighty percent filler($13\mu m$, spherical silica) weight fraction are fabricated using tranfer molding. Coefficient of thermal expansion, elastic modulus and thermla conductivity are measured using these specimens and then these measured values are compared with the predicted values by various equations ( such as dilute suspension method. self consistent method, generalized self consistent method, Hashin-Shtrikman's bounds. Shapery's bounds, Nielsen's method and others). Measured values are distributed within the upper and lower bounds of equations. Measured elastic modulus and coefficient of thermal expansion approaches closely the perdicted values with self consisten mehtod and upper bound of Shaperys equation respectively. However small differences of thermal conductivity between the different filler volume fraction are obserbed. FEM analysis indicates that firstly stress is concentrated at the corner section of EMC and secondly EMC with eighty percent filler weight fraction shows less thermal stress when package is cooling down and relatively high thermal stress when package is heating up.

• 전자공학회논문지D
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• 제36D권5호
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• pp.44-53
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• 1999

본 논문에서는 반도체 집적 회로의 다층 배선 인터커넥트 사이의 기생 캐패시턴스를 수치 해석적으로 계산하여 추출하는 새로운 방법과 그 적용 예를 보고한다. 기생 캐패시턴스를 시뮬레이션을 통해 추출하기 위하여, 복잡한 형태의 3차원 대층배선 구조물을 유한요소법을 이용하여 해석하였다. 캐패시턴스를 추출하기 위한 3차원 다층배선 구조물은 3차원 변환 정보를 가진 2차원 평면 마스크 레이아웃 데이터로부터 생성하였다. 시뮬레이션 결과의 정확도를 검증을 위하여 8.0×8.0×5.0㎛\sup 3\ 크기의 영역에 평행한 두 도전층이 상하로 교차한 구조에 대하여 실험치와 비교하였다. 3차원 다층배선 구조물의 기생 캐패시턴스 추출을 위해서, 유한 요소법 적용을 위한 1,960개의 노드와 8,892개의 사면체 메쉬를 생성하였으며, ULTRA SPARC 1 워크스테이션에 대해서 소요된 CPU 시간은 28초이었으며, 4.4 메가바이트의 메모리를 사용하였다.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.244-251
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• 2003

A two-dimensional BEM code, $FRACOD^{2D}$, was applied to simulate fracture initiation and propagation processes in a rock pillar during an in situ heater test of a rock pillar planned at the $\"{A}sp\"{o}$ Underground Rock laboratory of SKB, in Southern Sweden. To take the advantage of conventional BEM for simulating fracturing processes, but without efforts for domain integral transformation, a hybrid approach is developed to simulate the fracturing processes in rock pillar under coupled thermo-mechanical loading. The code FRACOD was used for simulating the fracture initiation and propagation processes with its boundary tractions reflecting the effects of the initial and redistributed thermomechanical stresses in the domain of interest at multiple excavation and heating steps were produced by a special algorithm of stress inversion, based on resultant thermo-mechanical stress fields at each excavation and heat loading step by a FEM code without considering fracturing processes. This hybrid approach can take the advantages of both types of numerical methods and avoids their shortcomings for fracturing process simulation and domain effects, respectively. In this paper, we present the hybrid approach for the stress, displacements, and fracturing processes at sequential excavation and heating steps of the in situ heater test as a predictive modelling, the formulation of the fracturing models and the predictive results. Two sections of borehole depth, 0.5 m and 1.5 m below the tunnel floor are considered. The pillar area is modelled with the FRACOD and the stress field produced by excavation and heating is transferred with corresponding boundary stresses. From the modelling results, the degree of fracturing and damage are evaluated for 120 days of heating. Dominated shear fracturing in the vicinity of the central pillar was observed from the models at both sections, but spalled area appears to be limited. Based on the modelling results, a sensitivity study for the effect of pre-existing fractures in the vicinity of the holes is also conducted, and the initiation and evolution of EDZ around the deposition holes are investigated using this particular numerical technique.

• 센서학회지
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• 제29권1호
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• pp.33-39
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• 2020

Typically, photoacoustic images are obtained in water or gelatin because the impedance of these mediums is similar to that of the human body. However, these acoustic mediums can have an additional mass effect that changes the resonance frequency of the transducer. The acoustic radiation impedance in air is negligible because it is very small compared to that of the transducer. However, the high acoustic impedance of mediums such as the human body and water is quite large compared to that of air, making it difficult to ignore. Specifically, in a case where the equivalent mass is very small, such as with a micro-machined ultrasound transducer, the additional mass effects of the acoustic medium should be considered for an accurate resonance frequency design. In this study, a piezoelectric micro-machined ultrasonic transducer (pMUT) was designed to have a resonance frequency of 10 MHz in the acoustic medium of water, which has similar impedance as the human body. At that time, the resonance frequency of the pMUT in air was calculated at 15.2 MHz. When measuring the center displacement of the manufactured pMUT using a laser vibrometer, the resonance frequencies were measured as 14.3-15.1 MHz, which is consistent with the finite element method (FEM) simulation results. Finally, photoacoustic images of human hair samples were successfully obtained using the fabricated pMUT.

• 비파괴검사학회지
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• 제35권2호
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• pp.134-140
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• 2015

전통적인 뜸 요법은 시술자의 주관적이고 정성적인 치료로 인해 환자의 피부에 강한 열 자극이 가해져 심한 통증을 주거나 화상을 입히는 문제점을 갖고 있다. 이러한 한계를 극복하기 위한 대안으로 객관성과 정량화가 가능한 초음파를 활용한 뜸 자극 치료기술이 주목받고 있다. 하지만, 초음파 에너지를 열에너지로 변환하기 위해서는 초음파 치료기기의 음향렌즈에 따른 초음파 집속 특성 분석이 필요하다. 따라서, 본 논문에서는 초음파 집속 특성에 영향을 주는 음향렌즈의 형태(오목렌즈, 계단형 렌즈)에 따른 집속 시뮬레이션을 통해 각 렌즈의 음압 분포, 음압의 크기, 초점의 위치를 계산하였으며, 설계한 렌즈를 제작하여 음압 측정 실험을 통해 음향렌즈의 집속 성능을 검증하였다.

• Ocean Systems Engineering
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• 제10권3호
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• pp.243-266
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• 2020

In-place analysis for offshore platforms is required to make proper design for new structures and true assessment for existing structures. In addition, ensure the structural integrity of platforms components under the maximum and minimum operating loads and environmental conditions. In-place analysis was carried out to verify the robustness and capability of structural members with all appurtenances to support the applied loads in either operating condition or storm conditions. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The SACS software is utilized to calculate the natural frequencies of the model and to obtain the response of platform joints according to in-place analysis then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have an important effect on the results of the in-place analysis behavior. The influence of the soil-structure interaction on the response of the jacket foundation predicts is necessary to estimate the loads of the offshore platform well and real simulation of offshore foundation for the in-place analysis. The result of the study shows that the in-place response investigation is quite crucial for safe design and operation of offshore platform against the variation of environmental loads.

• 한국항행학회논문지
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• 제9권2호
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• pp.147-155
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• 2005

본 논문에서는 기존 코플래나 웨이브가이드(CPW), 유한접지(FG) CPW, 그리고 접지(G) CPW와 같은 세 종류의 균일단면 구조의 CPW와 $TE_{01{\delta}}$ 모드 유전체공진기(DR : Dielectric Resonator)간의 결합 특성을 연구하고 마이크로스트립과 DR과의 결합과 같은 병렬 공진 특성을 보이는 CPW 와 DR간의 결합회로의 설계 방법을 제안한다. 결합 특성은 DR을 CPW의 접지와 신호선사이의 두 간격 중의 하나의 중심 상에 유전체 지지대(Support)를 이용하여 위치시키고 접지 방향으로 이동하면서 연구되었다. HFSS(High Frequency Structure Simulator : Finite Element Method Commercial Tool)의 시뮬레이션과 측정된 S-파라미터 값은 잘 일치했다. 마지막으로, 위에서 언급한 세 종류의 CPW와 DR과의 결합과 마이크로스트립라인과 DR과의 결합을 무부하 품질계수인 $Q_u$를 이용하여 비교하였다. 비교결과 CPW와 DR과의 결합은 마이크로스트립라인과 DR과의 결합보다 높은 $Q_u$ 값을 나타냈고 그 중에서 GCPW와 DR과의 결합이 가장 높은 $Q_u$를 보여줬다.