• Korean Journal of Optics and Photonics
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• v.8 no.2
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• pp.165-168
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• 1997

We have constructed a scanning confocal microscope using a 780 nm semiconductor laser, an actuator of a compact disk player and a quad-detector. This device detects heights and characteristics of a surface. The laser focus was located at the surface of a sample by using the error signal obtained by a quad-dector, and the current supplied to the actuator for lens was displayed as a height. The materials of a surface were classified according to reflected total intensities and was displayed by different color in a monitor. The device has very samll dimensions of 30 mm$\times$20 mm$\times$20 mm and scan field is 1.6 mm$\times$1.6mm. We obtained two images, one using only reflected light and the other using an error signal from a quad-detector and compared these two images.

• Proceedings of the KSRS Conference
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• 2009.03a
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• pp.147-150
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• 2009

본 논문에서는 해상 클러터를 고려하여 움직이는 물체의 SAR 원시 데이터를 생성하고, SAR 원시 데이터 중간 처리 결과인 range 압축 데이터의 azimuth 차분 신호로부터 물체의 속도를 측정하는 방법을 여러 가지 환경에 적용하여 그 정확도 및 적용 가능한 경우를 분석하였다. 움직이는 물체에 의한 도플러 중심 주파수의 변이가 azimuth 차분 신호에서 위상의 변화를 가져오므로, 이를 이용하여 움직이는 물체의 속도를 측정하는 알고리듬을 정리하였다. 이 알고리듬을 위에서 생성한 range 압축 데이터에 적용하여, 타깃이 되는 물체가 독립적으로 존재하는 경우, azimuth 상에 또 다른 속도를 가지는 산란체가 존재하는 경우, 그리고 높은 후방산란계수를 가지는 육지에 타깃이 되는 물체가 인접해 있는 경우를 가정하여 속도를 측정하였다. 그 결과, 타깃이 되는 물체가 SAR 영상에서 256 픽셀 범위 내에서 독립적으로 존재할 경우에는 높은 정확도로 물체의 속도를 측정할 수 있었으나, 128 픽셀 범위에 다른 움직이는 물체가 존재하거나, 높은 후방산란 계수를 갖는 육지와 인접해 있을 경우에는 최대 1m/s 의 오차를 나타냈다. 이는 주변 산란체의 영향에 의해 신호가 교란되어 목표물의 위치를 추정하는 과정에서 오차가 발생했기 때문이다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.8
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• pp.1777-1783
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• 2013

We do research on the simulation of Doppler effect from a target's moving under the sea by Transmission Line Matrix modeling which is one of numerical methods on time domain. To implement the effect, the input signal was entered at a moving node according to a moving target's moving speed. The result had maximum 2.47% error compared with the theoretical value. And from simulation results with speed control of a moving target, we could also obtain resonable results within 0.63% error range.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.1
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• pp.157-163
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• 1986

A method to improve the Finite Elements Model and to identify structure stiffness damages utilizing measured dynamic characteristics is suggested. In order to show the effectiveness of the proposed method, a sample structure is adopted and tested. It is found that; (1) the Finite Elements Model can be improved with experimentally obtained dynamic characteristics satisfactorily and (2) the test results are also very helpful to search the stiffness damaged part of the sample structure via plotting the error matrix[E], especially it is aboved that the weighted error matrix is very effective to detect even the stiffness changes are relatively small.

• Proceedings of the Korea Information Processing Society Conference
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• 2018.05a
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• pp.242-243
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• 2018

무선 통신기술이 발전함에 따라 위치기반 서비스에 대한 관심 또한 증가하고 있다. 그 중 저전력 블루투스 기술을 사용한 비콘(Beacon)은 실내 위치인식이 불가능한 GPS와 달리 실내에서도 측위가 가능하여 사용성이 주목 받고 있다. 그러나 비콘으로부터 수신되는 RSSI(Received Signal Strength Indication) 값은 여러 환경요소로부터 영향을 받기 때문에 RSSI값을 기반으로 한 거리측정이 실제거리와의 오차가 크게 나타난다. 이에 따른 문제를 해결하기 위한 기존의 연구들이 존재하지만 평균적으로 10m이하의 거리에서 2m의 오차를 나타내고 있다. 본 연구에서는 RSSI의 오차를 줄이기 위해 확장 칼만 필터와 신호 안정화 필터를 사용하여 Raw Data를 전처리 한 후 산출된 Cleaned Data를 기반으로 각 거리단위에 최적화된 ANN(Artificial Neural Network)모델을 생성하여 거리를 측정하는 기법을 제안한다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.11
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• pp.933-940
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• 2021

The space-borne SAR(Synthetic Aperture Radar) system radiates the microwave signal and receives the backscattered signal. The received signal is converted to digital at the Digital Receiver, which is implemented at the end of the SAR sensor receiving chain. The converted signal is formated after signal processing such as filtering and data compression. Two quantization are conducted in the Digital Receiver. One quantization is an analog to digital conversion at ADC(Analog-Digital Converter). Another quantization is the BAQ(Block Adaptive Quantization) for data compression. The quantization process is a conversion from a continuous or higher bit precision to a discrete or lower bit precision. As a result, a quantization noise is inevitably occurred. In this paper, the impact of two quantization processes are analyzed in a view of SNR degradation.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.1
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• pp.68-76
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• 2011

Acoustic emission(AE) has emerged as a powerful nondestructive tool to detect any further growth or expansion of preexisting defects or to characterize failure mechanisms. Recently, this kind of technique, that is an in-situ monitoring of inside damages of materials or structures, becomes increasingly popular for monitoring the integrity of large structures like a huge wind turbine blade. Therefore, it is required to find a symptom of damage propagation before catastrophic failure through a continuous monitoring. In this study, a new damage location method has been proposed by using signal mapping algorithm, and an experimental verification is conducted by using small wind turbine blade specimen; a part of 750 kW real blade. The results show that this new signal mapping method has high advantages such as a flexibility for sensor location, improved accuracy, high detectability. The newly proposed method was compared with traditional AE source location method based on arrival time difference.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.7
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• pp.643-649
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• 2013

In this paper, human heartbeat detection using signal reflected from the antenna which is varied reflection coefficient by near field variation of the antenna. For detection reflected signal from antenna, 20 dB directional coupler is used because of not affecting transmitting signal. Variance of reflection coefficient of dipole antenna is about 0.07 dB which is too small the distinction between heartbeat and noise. Sensitivity increasing method is applied and heartbeat is clearly detected. Due to phase and magnitude errors come from discrete value components, antenna is located some points in experiments ro find optimum sensitivity position. And providing verification of using communication signal, heartbeat detection when frequency modulated signal which have 4 MHz bandwidth is applied.

• The Journal of the Acoustical Society of Korea
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• v.26 no.1
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• pp.48-54
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• 2007

In this paper we have implemented a 3-D PL (Position Location) system to estimate the 3-dimensional position of a moving object in underwater environments. In this research, we let four sensors fixed in different Positions and moving sensorsto communicate with each other to find the 3-dementianal positions for both the fixed and moving objects. Using this we were also able to control the moving object remotely. When finding the position, we calculated the norm of the Jacobian matrix every iteration in the Newton algorithm. Also by using a different initial value for calculating the solution when the norm became higher than the critical value and the solution from the inverse matrix became unstable, we could find a more reliable position for the moving object. The proposed algorithm was used in implementing a DSP system capable of real-time position location. To verify the performance, experiments were done in a water tank. As a result we could see that our system could located the position of an object every 2 seconds with a error range of 5cm.

• Journal of Advanced Navigation Technology
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• v.20 no.1
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• pp.29-36
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• 2016

Accuracy of GPS (global positioning system) deteriorates dramatically or positioning is impossible in urban area occasionally since high-rise buildings and elevated roads make the reception of navigation signal very difficult so that number of visible satellites decreases. In these cases, vertical error usually becomes much larger than the horizontal error due to the intrinsic geometry of GPS satellites. To obtain more accurate and reliable height information, this paper proposes a hybrid method that combines GPS and a low-cost barometric altimeter. In the proposed method, the sea-level pressure and the sea-surface temperature are applied to the output of the altimeter. Next, the difference between the ellipsoid and the geoid is compensated. Finally, a simple Kalman filter combines the compensated barometric altitude and the GPS height. By static and car experiments, performance of the proposed method is evaluated. By the experiment results, it can be seen that the proposed method improves the altitude accuracy considerably.