Earticle

본 논문에서는 파라메트릭 어레이를 이용한 음향신호에 대한 수치 모델링 기법 및 분석 결과를 제시한다. 사용된 음성 파라메트릭 배열의 분석 수치모델은 KZK(Khokhlov-Zabolotskaya-Kuznetsov)로서 KZK수치모델은 시간영역의 차분방정식 알고리즘을 사용하며 파라메트릭배열의 정확한 응답특성이 분석이 가능하다. 시간영역기반의 KZK모델은 음원의 크기와 전송주파수의 영향을 받으며, 가청신호응답은 출력레벨과 빔폭의 크기를 포함한다. 음성신호에 대하여 파라메트릭 배열을 효율적으로 적용시키기 위해서는 고려해야할 요소는 표본화 주파수, 트랜스듀서의 반경 및 변조방식 파라미터 등이 있다. 본 논문에서는 다양한 요소 중 표본화 주파수에 따른 응답신호의 왜곡 분석 및 실험 결과를 시뮬레이션을 통해 제시하였다.

Parametric array for audio applications is analyzed by numerical modeling and analytical approximation. The nonlinear wave equations are used to provide design guidelines for the audio parametric array. A time domain finite difference code that accurately solves the KZK (Khokhlov-Zabolotskaya-Kuznetsov) nonlinear parabolic wave equation is used to predict the response of the parametric array. The time domain code relates the source size and the carrier frequency to the audible signal response including the output level and beamwidth to considering the implementation issues for audio applications of the parametric array, the emphasis is given to the frequency response and distortion. We use the time domain code to find out the optimal parameters that will help produce the parametric array with highest achievable output in terms of the average power within the demodulated signal. Parameters such as primary input frequency, audio source radius and the modulation method are given utmost importance. The output effect of those parameters are demonstrated through the numerical simulation.

The pull-out frequency of a second-order phase lock loop (PLL) is an important parameter that quantifies the loop's ability to stay frequency locked under abrupt changes in the reference input frequency. In most cases, this must be determined numerically or approximated using asymptotic techniques, both of which require special knowledge, skills, and tools. An approximating formula is derived analytically for computing the pull-out frequency for a second-order Type II PLL that employs a sinusoidal characteristic phase detector. The pull-out frequency of such PLLs can be easily approximated to satisfactory accuracy with this formula using a modern scientific calculator.

The relaxation time spectrum is a versatile parameter to calculate various polymer viscoelastic properties, such as the relaxation modulus (G(t)), dynamic modulus (G'(${\omega}$)) and loss modulus (G"(${\omega}$)). However, it cannot be measured experimentally. This study calculated the relaxation time spectrum using a calculation method based on Fusso-Kirkwood's theoretical research and using the empirical loss modulus formula. The calculated relaxation time spectrum and Rouse's model could describe the viscoelastic behavior of monodisperse polystyrene successfully. This analytical approximation of the relaxation time spectrum differed from experimental data in the intermediate region between the reputation and Rouse region. This may have resulted from a limitation of the molecular theory in the Rouse region.

The relaxation time spectrum is a very effective parameter for transforming material functions even with a limited amount of data. The spectrum also helps in understanding the relaxation behavior of polymers at the molecular scale. In this study, a relaxation time spectrum based on Marin-Graessley's dynamic compliance model was calculated using Fuosso-Kirkwood's complex analysis. The resulting model could successfully describe the viscoelastic behavior of mono-disperse polystyrene. However, it was clear that a more effective numerical analysis method was needed to obtain more accurate parameter values.

본 논문에서는 반응로 안에서 쌍극성 확산장의 거리 확장에 따르는 앞덮개(Presheath)영역에서의 효과를 고려하고, 앞덮개 영역 내에서 이온과 중성자간의 충돌을 고려한 입사각 분포에 따른 에너지 플럭스를 계산하였다. 이론의 각분포 현상과 에너지 플럭스 분포를 이온의 온도와 함께 앞덮개 효과를 고려된 새로운 근사 해석적 모델을 제시한다. 실제 식각 공정에 대한 실험결과 충돌이 없는 덮개에서도 이온의 입사각이 산란되는 현상이 나타난다. 이 현상은 이온의 앞덮개지역을 통과하면서 쌍극성 확산장(ambipolar diffusion field)에 의해 운동에너지를 얻게 되는데, 이때 얻어진 운동에너지가 가스 분자 충돌에 의해 변화는 효과 때문이라고 볼 수 있다. 제안된 근사적 해석모델을 이용하여 트렌치에서의 중착 형상을 모의실험 하였다.

In this work, we consider the effect of the presheath on the ion angular distribution. The recent shows the ion-neutral collision in the presheath and the calculated energy flux with the ion angular distribution at the presheath edge in plasma reactor. We also propose a new approximation analytical model for the ion angular distribution and the energy flux distribution with ion temperature. The ion passing the presheath region, Shows a ion scattering effect without ion-neutral collisions. This because the kinetic energy by the ambipolar diffusion field is changed by the gas collision,. Using the proposed approximation analytical model, we show the simulated results of a deposit profile on variable trench shape.

본 논문은 진성영역에서 공핍증 폭이 선형적으로 변화한다는 가정을 도입하고 전자이동도의 수평 및 수직 전계 이존성을 고려하여 단채널 MOSFET의 {{{{ { I-V }_{ } }}}} 특성에 대한 해석적 모형을 제시하였다. 이 모형으로부터 전 동작영역에 걸쳐 적용되는 문턱전압 방정식과 드레인전류 방정식을 도출하였다. 본 모형의 타당성을 검토하기 위하여 위 식들의 계산을 수행하였고, 그 결과 채널길이가 짧아짐에 따라 문턱전압이 지수함수적으로 감소하였으며, 아울러 채널길이변조, 채널이동로 열화 등을 본 모형에 의하여 일괄적으로 설명할 수 있었다.

By assuming a linearly graded depletion edge approximation in the intrinsic MOS region and by taking into account the mobility variation dependent on both lateral and vertical fields, a physics-based analytical model for a short-channel(n-channel) MOSFET is suggested. Derived expressions for the threshold voltage and the drain current of typical MOSFET is structures could be used in a unified manner for all operating range. The threshold voltage was calculated by changing following variables : channel length, drain-source voltage, source-substrate voltage, p-substrate doping level, and oxide thickness. It is shown that the threshold voltage decreases almost exponentially as the channel length decreases. In addition, the short-channel threshold voltage roll-off, the channel length modulation and the electron mobility degradation can be derived within a satisfactory accuracy.