• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.4
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• pp.285-289
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• 2018

In this paper, we demonstrate electromagnetic wave focusing and rectification based on time reversal as a smart method for far-field wireless power transfer. Time reversal in a complex propagation environment allows for transmission of high peak power pulses by focusing the electromagnetic waves selectively regardless of the receiver position. We demonstrate wave focusing and radio frequency (RF) to direct current (DC) rectification via numerical simulation of a complex propagation environment. The results reveal that time reversal can ensure peak power up to 12 dB greater compared to a narrowband continuous wave signal, thereby enhancing the rectified DC voltage with better efficiency.

• The Journal of the Acoustical Society of Korea
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• v.25 no.5
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• pp.239-245
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• 2006

Time-reversal processing (TRP) has been shown as an effective way to focus in both time and space. The temporal focusing properties have been used extensively in underwater acoustics communications. Recently. adaptive time-reversal processing (ATRP) was applied to the simultaneous multiple focusing in an ocean waveguide. In this study. multiple focusing with ATRP is extended to the underwater acoustic communication algorithm for multiple receiving locations. The developed algorithm is applied to the underwater acoustic communication to show, via simulation and real data, that the simultaneous self-equalization at multiple receiving locations is achieved.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.241-241
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• 2016

반도체 선폭이 20 nm급까지 감소함에 따라 기존에 수율에 문제를 끼치던 공정 외부 유입 입자뿐만 아니라, 공정 도중에 발생하는 수~수십 나노의 작은 입자도 수율에 악영향을 끼치게 되었다. 이에 따라 저압, 극청정 조건에서 진행되는 공정 중 발생하는 입자를 실시간으로 모니터링 할 수 있는 장비에 대한 수요가 발생하고 있다. Particle beam mass spectrometer (PBMS)는 이러한 요구사항을 만족할 수 있는 장비로 100 mtorr의 공정 조건에서 5 nm 이상의 입자의 직경별 수농도를 측정할 수 있는 장비이다. PBMS로 입자의 수농도를 측정하기 위해서는 PBMS 전단에서 입자를 중앙으로 집속할 필요가 있다. 공기역학렌즈는 PBMS 전단에서 입자를 집속시키기 위해 일반적으로 널리 사용되고 있는 장비로 여러 개의 오리피스로 이루어져 있다. 공기역학렌즈를 지나는 수송 유체와 입자는 이러한 연속 오리피스를 거치면서 팽창과 수축을 반복하며, 관성력의 차이로 인해 입자가 중앙으로 집속된다. 그러나 기존 공기역학렌즈는 고정된 직경의 오리피스를 사용하기 때문에 설계된 공정조건 이외에는 입자의 집속효율이 감소한다는 단점을 지닌다. 따라서 공정조건이 바뀔 경우 공기역학렌즈를 교체해야 되며, 진공이라는 환경하에서 이러한 교체는 많은 시간과 노력을 요구로 한다. 본 연구에서는 이러한 공기역학렌즈의 문제점을 해결하기 위해 다양한 공정조건에서 교체 없이 사용할 수 있는 새로운 형태의 직경 가변형 공기역학렌즈인 조리개형 공기역학렌즈를 제안하였다. 기존 연구를 통해 조리개형 공기 역학 렌즈가 다양한 압력 범위 내에서 나노입자를 성공적으로 집속할 수 있음을 보였지만, 장비를 상용화하기 위해서는 사용자가 좀 더 쉽게 렌즈직경을 결정 할 수 있어야 한다. 이에 본 연구에서는 조리개형 렌즈의 중공 직경에 따른 입자 집속 특성을 평가하였으며, 최종적으로 압력과 집속하고자 하는 직경에 따라 렌즈 중공 직경을 결정할 수 있게 해주는 데이터 베이스를 제작하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.279.2-279.2
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• 2014

반도체 선폭이 20 nm급까지 감소함에 따라 기존에 수율에 문제를 끼치던 공정 외부 유입 입자뿐만 아니라, 공정 도중에 발생하는 수~수십 나노의 작은 입자도 수율에 악영향을 끼치게 되었다. 이에 따라 저압, 극청정 조건에서 진행되는 공정 중 발생하는 입자를 실시간으로 모니터링 할 수 있는 장비에 대한 수요가 발생하고 있다. Particle beam mass spectrometer (PBMS)는 이러한 요구사항을 만족할 수 있는 장비로 100 mtorr의 공정 조건에서 5 nm 이상의 입자의 직경별 수농도를 측정할 수 있는 장비이다. PBMS로 입자의 수농도를 측정하기 위해서는 PBMS 전단에서 입자를 중앙으로 집속할 필요가 있다. 공기역학렌즈는 PBMS 전단에서 입자를 집속시키기 위해 일반적으로 널리 사용되고 있는 장비로 여러 개의 오리피스로 이루어져 있다. 공기역학렌즈를 지나는 수송 유체와 입자는 이러한 연속 오리피스를 거치면서 팽창과 수축을 반복하며, 관성력의 차이로 인해 입자가 중앙으로 집속된다. 그러나 기존 공기역학렌즈는 고정된 직경의 오리피스를 사용하기 때문에 설계된 공정조건 이외에는 입자의 집속효율이 감소한다는 단점을 지닌다. 따라서 공정조건이 바뀔 경우 공기역학렌즈를 교체해야 되며, 진공이라는 환경하에서 이러한 교체는 많은 시간과 노력을 요구로 한다. 본 연구에서는 이러한 공기역학렌즈의 문제점을 해결하기 위해 다양한 공정조건에서 교체 없이 사용할 수 있는 새로운 형태의 공기역학렌즈인 조기래형 공기역학렌즈를 제안하였다. 각각의 오리피스가 중공의 직경을 변경할 수 있는 구조인 조리개의 형태로 설계되어 있어, 공정조건에 따라 중공의 직경을 변경함으로써 입자의 집속을 결정하는 요소인 Stokes number를 조절 할 수 있다. 이러한 조리개형 공기 역학 렌즈의 성능을 평가하기 위해 수치해석적인 방법을 이용하였다. 공기 역학 렌즈 전단의 압력을 0.1~10 torr까지 변화시켜가며 다양한 공정조건에서 오리피스의 직경만을 변경하여 입자 집속 가능 여부를 판단하였으며, 조리개 형태의 구조상 발생할 수 있는 leak로 인한 입자 집속 효율의 변화도 평가하였다.

• Journal of Biomedical Engineering Research
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• v.23 no.3
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• pp.243-251
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• 2002

Synthetic zinc wave employs Pulsed plane wave as transmit beam with linear time delay curve. The received echoes in different transmit directions at different transmit times are superposed at imaging Points with Proper time delay compensation using synthetic focusing scheme. This scheme. which uses full aperture in transmit, obtains a high SNR image, and also features high lateral resolution by using two way dynamic focusing at all imaging depths. In this Paper, we consider the Problems in realization of synthetic zinc wave. Also. we have applied the scheme to obtain phantom and in-vivo images using a linear array of 5 MHz. In phantom test. experimental images show high resolution over a more extended imaging depth than conventional fixed Point transmit and receive dynamic focusing schemes In-vivo images show that the resolution could not overcome conventional focusing systems because of motion blurring and(or) aberration of tissue. but the frame rate tan be increased by a factor of more than 5 compared to conventional focusing schemes. with competitive resolution at all imaging depths .

• Journal of the Korean Vacuum Society
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• v.22 no.5
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• pp.262-269
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• 2013

Though focused ion beam (FIB) is one of the candidates to fabricate the nanoscale patterns, precision milling of nanoscale structures is not straightforward. Thus this poses challenges for novice FIB users. Optimal determination in FIB parameters is a crucial step to fabricate a desired nanoscale pattern. There are two main FIB parameters to consider, beam current (beam size) and dose (beam duration) for optimizing the milling condition. After fixing the dose, the proper beam current can be chosen considering both total milling time and resolution of the pattern. Then, using the chosen beam current, the metal nano hole structure can be perforated to the required depth by varying the dose. In this experiment, we found the adequate condition of $0.1nC/{\mu}m^2$ dose at 1 pA Ga ion beam current for 100 nm thickness perforation. With this condition, we perforated the periodic square array of elliptical nano holes.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.9 no.1
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• pp.45-48
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• 2016

The treatment of obesity have been developed various devices for the treatment of obesity, the ultrasound is to be made after the state changes to become easy fat decomposition by heat and vibrations to facilitate the flow of blood and lymph fatty acid released into the blood. There is such ultrasonic transducer array is used in obesity therapy focusing angle of the transducer array and the frequency may have a significant impact on the degradation of fat. In this paper, we set the frequency that reaches the shortest time to a set temperature 27kHz, 1MHz, by applying a transducer with a diameter of 5mm, 10mm, 16mm for the frequency of 3MHz, obtain the wavelength and near the stomach in order to set the frequency of the transducer array, which was set to the focusing angle of the transducer with three contact surfaces. As a result, the time to reach the set temperature was short days when 3MHz frequency, the focusing angle is titrated is $40^{\circ}$.

• The Journal of the Acoustical Society of Korea
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• v.41 no.5
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• pp.525-533
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• 2022

We propose an effective method for suppressing both side and grating lobes by applying 2-dimensional Fourier Transform to the received channel data during the receive focusing process of an ultrasound imaging system. When the signal from the image point is focused, the channel signals have the same DC value across the channels. However, even after echoes from outside an imaging point are focused, they are manifested as having different spatial frequencies depending on their incident angles. Therefore, after the receive focusing delay time is applied, 2-D Fourier Transform is performed on the time-channel data to separate the DC component and other frequency components in the spectral domain, and the weighting value is defined using the ratio of the two values. The side lobe and grating lobe were suppressed by multiplying the ultrasound image by a weighting value. Ultrasound images with a frequency of 5 MHz were simulated in a 64-channel linear array. The grating lobe appearing in the ultrasound image was completely removed by applying the proposed method. In addition, the side lobe was reduced and the lateral resolution was greatly increased. Results of computer simulation on a human organ mimicking image show that the proposed method can aid in better lesion diagnosis by increasing the image contrast.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.1
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• pp.47-55
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• 2012

A structural health monitoring technique for locating impact position in a plate structure is presented in this paper. The method employs a single sensor and spatial focusing of time reversal (TR) acoustics. We first examine the TR focusing effect at the impact position and its surroundings through simulation and experiment. The imaging results of impact points show that the impact source location can be accurately estimated in any position of the plate. Compared to existing techniques for locating impact or acoustic emission source, the proposed method has the benefits of using a single sensor and not requiring material properties and geometry of structures. Furthermore, it does not depend on a particular mode of dispersive Lamb waves that is frequently used in other ultrasonic testings of plate-like structures.

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.203-213
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• 2023

In medical ultrasound imaging systems, Side lobes may appear if signals outside the imaging point are not completely removed during receive focusing. If the time signal of the side lobe overlaps with the time signal (main lobe) from the image point, it is difficult to completely remove it using filter processing in the time domain. However, In the receive focusing process, when time-channel signals are Fourier-transformed, the main lobe and side lobe signals are spatially separated in the spectral domain. Therefore, the side lobes can be suppressed by multiplying the image with magnitude weights, which are determined by the magnitudes of the main and side lobes calculated in the spectral domain. In addition, when the main lobe and the side lobe spectrum are adjacent, the distance weight was applied based on the distance between them. In a 5 MHz ultrasound imaging system using a 64-channel linear transducer, point reflector and speckle images with cysts of various brightness were synthesized and weights were applied to the ultrasound image. Using computer simulations, we confirmed that the side lobes were greatly reduced without affecting the spatial resolution in the point reflector image, and the contrast was significantly improved in the cyst image with computer simulations.