Earticle

본 논문에서는 항재밍 GPS(Global Positioning System) 시스템을 위한 선형 어레이 안테나(linear array antenna) 시뮬레이터 (simulator)를 설계하고 시뮬레이션을 통해 다양한 성능 평가를 수행하였다. 먼저 GPS 위성의 신호 구조 분석을 통해 모의 송신 신호를 발생시키고, 선형 어레이 안테나 고려시 잡음 환경하에서의 어레이 수에 따른 SNR(Signal to Noise power Ratio) 성능을 분석하였다. 또한 MMSE(Minimum Mean Square Error) 방식의 신호처리 시스템을 통해 재머(jammer) 수에 따른 항재밍 빔패턴 (beam pattern) 성능을 분석하였으며, 안테나 칼리브레이션(calibration) 문제를 고려하여 어레이간 지연이 존재하는 경우에서의 항 재밍 성능을 분석하였다.

In this paper, I design a linear array antenna simulator for anti-jamming GPS systems and perform various performance analysis by simulation. First, I generate simulated transmission signals through the analysis of GPS satellite signal structure, and analyze SNR(Signal to Noise power Ratio) performance of linear array antenna according to number of arrays under noise environments. In addition, I analyze the performance of the anti-jamming beam pattern using MMSE(Minimum Mean Square Error) signal processing method, and also analyze the anti-jamming performance considering antenna calibration problem when there are different delays between arrays.

본 연구에서는 ATS-539 다목적 초음파 팬텀을 이용하여 초음파 영상의 변조전달함수(Modulation-Transfer Function, MTF)를 분석하고, 임상 프리셋(THYROID, BREAST, APPE-L) 및 장비 설정 변수(Gain, Dynamic Range, Frame Average)의 변화가 영상의 공간 해상도에 미치는 영향을 정량적으로 평가하였다. 획득된 영상의 분석 결과, 중심 주파수가 높을수록 MTF 50% 값이 증가하여 세부 구조 재현성이 향상되는 경향을 보였다. 반면 Gain, DR, FA 변화에 따른 MTF 50% 값은 큰 차이를 나타나지 않았다. 또한 ATS-539 다목적 초음파 팬텀의 수직 방향 표적 분석 결과, 초점 영역이 형성된 근거리(상단) 위치에서 MTF 값이 높게 측정되어 깊이에 따른 공간 해상도 변화가 확인되었다. 이러한 결과는 초음파 영상 품질의 정량적 관리(Quality Assurance, QA) 및 장비 성능 검증의 표준화에 기여할 수 있으며, 초음파 영상의 진단적 품질 유지와 영상 최적화에 기여할 수 있을 것으로 기대된다.

In this study, the modulation transfer function (MTF) of ultrasound images was analyzed using the ATS-539 multi-purpose ultrasound phantom, and the effect of changes in clinical presets (THYROID, BREAST, APPE-L) and equipment setting variables (Gain, Dynamic Range, Frame Average) on the spatial resolution of images was quantitatively evaluated. As a result of analyzing the obtained images, the higher the center frequency, the higher the MTF 50% value, which tended to improve the detailed structure reproducibility. On the other hand, there was showed little variation in the MTF 50% value according to changes in Gain, DR, and FA. In addition, as a result of the vertical direction target analysis of the ATS-539 multi-purpose ultrasound phantom, the MTF value was measured high at the near (top) location where the focal area was formed, confirming the change in spatial resolution according to depth. These results are expected to contribute to the standardization of the quality assistance (QA) of ultrasound image quality and equipment performance verification, and to the maintenance of diagnostic quality of ultrasound images and image optimization.

This paper introduces a new efficient algorithm for mapping linear array into hex-cell network. The capability of mapping several topologies is considered as one of the most important features of the hex-cell interconnection network. This feature is strongly affecting the performance of parallel machines. In this paper, we present a new algorithm for mapping linear array topology into hex-cell network with dilation and congestion of one;which indicates that we have one-to-one mapping as a result of intercommunication among nodes.

Using color linear array CCD (Charge Coupled Device) to collect the information of image has an important meaning in the research of the machine vision processing. It now becomes the focus of study on CCD image acquisition using FPGA (Field Programmable Gate Array) to implement color linear array CCD-driven design. The image acquisition and processing of the rice color sorter as the research background in this paper, by using FPGA to achieve the color linear array CCD driven control, as well as simulated with Quartus II 8.0. In order to be able to extract the color linear array CCD output useful information of the color images, through study the RGB model and the HSI (Huge, Saturation, Intensity) model of color space model, the HSI space mode is selected as the color image processing space model, and design the suitable algorithm-FCM (Fuzzy C-Means) clustering algorithm in HSI space for color image segmentation, through a fuzzy Toolbox in MATLAB to accomplish the FCM algorithm, at the same time, through the simulation realized the FCM algorithm. The simulation shows that the algorithm can segment the image useful information well.

The excitations and locations of sensors in the non-uniformly spaced array affect the array performance such as sidelobe level and spatial resolution. Consequently, finding the optimal excitation coefficients and sensor positions of the array to produce a desired beam pattern with the smallest number of sensors is of great importance in practice. With the aim of reducing the number of the sensors in a linear antenna array, a novel method based on ℓp (0<p<1) norm minimization for optimizing both excitation coefficients and sensor locations of the array is proposed. Compared with the reweighted ℓ1 norm minimization (IRWL1) method, the proposed method can reduce more array sensors by optimizing the objective functions that include the measurements of peak sidelobe level (PSL) and array sparsity denoted by the ℓp norm of excitations. Numerical experiments have proved the effectiveness and advantages of the proposed method in the reduction of the number of the sensors of the linear antenna array.

In recent years, miniaturization has become the key factor in the development of mobile communication system. Portable communications and computing devices suffer from two conflicting requirements which are device size to be as small as possible and large, high resolution display. These problems can be solved by virtual display. Any display in which the user views an image through an optical system is a virtual display. It provides a display which is high resolution, appears large to the viewer and at the same time occupies little physical space. In this study, handhold units of mobile communication was investigated through use of the SLA(Scanned Linear Array). The basic SLA mechanism comprises a linear array of LED's, a magnifying lens, and a scan mirror. To optimize virtual image, we investigated optical system design and operating condition for each part.

In this study, a compact series-fed center-fed open-stub (SFCFOS) linear array antenna for K-band applications is presented. The antenna is composed of a single-line 10-element linear array. A symmetrical Chebyshev amplitude distribution (CAD) is used to obtain a low sidelobe characteristic against a uniform amplitude distribution (UAD). The amplitude is controlled by varying the width of the microstrip patch elements, and open-ended stubs are arranged next to the last antenna element to use the energy of the radiating signal more effectively. We insert a series-fed stub between two patches and obtain a low mutual coupling for a 4.28-mm center-to-center spacing ($0.7{\lambda}$ at 21 GHz). A prototype of the antenna is fabricated and tested. The overall size of the uniform linear array is $7.04{\times}1.05{\times}0.0563{\lambda}_g^3$ and that of the Chebyshev linear array is $9.92{\times}1.48{\times}0.0793{\lambda}_g^3$. The UAD array yields a ${\mid}S_{11}{\mid}$ < -10 dB bandwidth of 1.33% (20.912-21.192 GHz) and 1.45% (20.89-21.196 GHz) for the CAD. The uniform array design gives a -23 dB return loss, and the Chebyshev array achieves a -30.68 dB return loss at the center frequency with gains of 15.3 dBi and 17 dBi, respectively. The simulated and measured results are in good agreement.

본 논문에서는 particle swarm optimization (PSO)을 사용하여 가장 낮은 SLL같을 갖거나 가장 좁은 빔폭을 가지는 비균일 급전, 비균등 간격의 선형 어레이를 설계하였다. 어레이 소자의 급전 크기와 급전 소자간의 간격을 조절하기 위해 변수로 지정하였다. 두 가지 변수를 동시에 무작위로 조절하여 빔패턴을 최적화하였다. 빔패턴의 널 포인트를 기준으로 나누어 각각의 사이드로브에 가중치를 부여함으로써 적합도 함수의 성능을 향상시켰고, 이를 이용하여 최적의 빔패턴을 얻을 수 있었다. 이 때, 가중치 값과 빔패턴을 나누는 각은 여러 번의 시도를 통해 얻을 수 있었다. SLL 뿐만 아니라 빔폭까지 고려하기 위해 fitness function에 추가적인 항목 ${\beta}{\times}BW$을 첨가하였다. 이로써, 가장 낮은 SLL값을 갖거나 가장 좁은 빔폭을 갖는 빔패턴을 갖는 어레이를 설계하였다. 10개의 어레이 소자를 이용하여 최적화 하였을 때, 전자는 -43dB의 SLL값과 $32.2^{\circ}$의 빔폭을 가졌고, 후자는 -26dB의 SLL값과 $24.2^{\circ}$의 빔폭을 가졌다.

In this paper, we use particle swarm optimization (PSO) to design a randomly excited and randomly spaced linear array with either the lowest side lobe level (SLL) or the narrowest beamwidth. The positions and the excitation amplitudes of the array elements are considered as variables to be controlled. The beam pattern is optimized by controlling the two variables simultaneously and randomly. The best beam patterns are obtained using PSO in the fitness function where performance is improved by the random assignment of weight coefficients to each angular sector of the beam Pattern. The weight coefficients and angles are obtained through several trial runs. Also, an extra term, ${\beta}{\ast}BW$, is added to the fitness function to account for the beamwidth as well as the SLL. Is produces the best result for the beam pattern with either the lowest SLL or the narrowest beamwidth. In the former case, the SLL and beamwidth are about -43dB and $32.2^{\circ}$, respectively, with only 10 elements. In the latter case, the SLL and beamwidth are about -26dB and $24.2^{\circ}$, respectively.

본 논문에서는 LAROB상에서 이진영상을 사진트리로 변환하거나, 사진트리를 이진영상으로 변환하는 효율적인 알고리즘들을 제안한다. 이 알고리즘들은 영상의 화소 개수가 n $\times$ n일 때 n2 프로세서를 사용하며, $\theta$(1)의 시간 복잡도를 갖는다. 실행시간과 프로세서 수의 곱이 최적 순차 알고리즘의 실행시간인 $\theta$(n2)과 동일하므로, 여기서 제안한 알고리즘들은 최적 알고리즘이다.

We present efficient algorithms for transforming between binary images and quadtrees on the LABOR. For a binary image of size n ${\times}$ n, both algorithms run in $\theta$(1) time using n2 processors. These algorithms are optimal in the sense that the product of time and number of processors is asymptotically the same as the optimal sequential time which is $\theta$(n2).

A new class of data transformation matri is introduced for estimation of angles of arrivals by the rank reduction of multiple wideband sources. The proposed unitary focusing matri minimizes the average of the squared norm of focusing error over the angles of interest without a priori knowledge of source locations. The merit that result as a consequence is a lower resolution threshold. These matrices can be applied to the case of the multigroup sources. Simulations and the comparison of statistical performance are compared with the algorithms (especially, spatial resampling method) which does not require the pre-estimation.

최근 상시 진동 탐사법은 횡파 속도 구조의 규명을 위하며 이용되고 있다 상시 진동 탐사법 중 공간자기상관(SPAC)법은 적어도 3 혹은 4개의 수신기에서 동시에 기록된 자료를 이용한다. 2sSPAC과 선형 배열 상시 진동법과 같은 수정된 SPAC법은 2개의 수신기 자료만 이용하여 횡파 속도를 추정할 수 있지만, 1.0 Hz 이상의 주파수 대역에 대한 공간 자기상판 계수가 불안정해지는 문제점을 가지고 있다. 4개의 서로 다른 크기의 삼각형 배열과 4개의 같은 크기의 삼각형 및 선형 배열을 이용한 상시 진동 측정치에 근거하여, 2 Hz 에서 4 Hz 혹은 5 Hz주파수 대역에 대한 SPAC 계수의 안정성을 증명하였다. SPAC 계수를 Bessel 함수로 회귀하는 방식으로 획득되는 위상속도는 5 Hz까지 일관성을 보여주었다. 공간평균법을 이용한 선형배열의 경우를 제외하고, 모든 자료는 SPAC법으로 처리되었다. 평행탄성파법 자료가 있는 시추공 주변에서 상시 진동 배열을 순차적으로 다른 시간에 적용하였다. 자료의 품질을 나타내는 지시자로 SPAC 계수의 허수 성분을 이용하였다. 자기상관 스펙트럼의 변화량 (어떠한 경우에는 기록된 파동장에 대한 육안 검사)에 근거하여, 측정된 자료를 '신뢰성있는(reliable)'과 '신뢰성이 없는(unreliable)'로 구분하였다. 그 후, 'reliable'과 'unreliable'로 구분된 자료와 모든 자료에 대하여 SPAC 스펙트럼의 허수 성분을 계산하고 비교하였다. 측점의 방위각 분포가 불충분한 경우 (선형 배열), 허수 성분 곡선은 불안정한 형태를 나타내었고, 이러한 결과는 불충분한 공간평균의 지시자로 간주할 수 있음을 의미한다. 하지만, 측정된 파동장이 낮은 일관성을 나타낼 경우에도 허수성분 곡선은 주목할 만한 불안정성을 나타내지 않았다.

In recent years, microtremor array observations have been used for estimation of shear-wave velocity structures. One of the methods is the conventional spatial autocorrelation (SPAC) method, which requires simultaneous recording at least with three or four sensors. Modified SPAC methods such as 2sSPAC, and linear array methods, allow estimating shear-wave structures by using only two sensors, but suffer from instability of the spatial autocorrelation coefficient for frequency ranges higher than 1.0 Hz. Based on microtremor measurements from four different size triangular arrays and four same-size triangular and linear arrays, we have demonstrated the stability of SPAC coefficient for the frequency range from 2 to 4 or 5 Hz. The phase velocities, obtained by fitting the SPAC coefficients to the Bessel function, are also consistent up to the frequency 5 Hz. All data were processed by the SPAC method, with the exception of the spatial averaging for the linear array cases. The arrays were deployed sequentially at different times, near a site having existing Parallel Seismic (PS) borehole logging data. We also used the imaginary part of the SPAC coefficients as a data-quality indicator. Based on perturbations of the autocorrelation spectrum (and in some cases on visual examination of the record waveforms) we divided data into so-called 'reliable' and 'unreliable' categories. We then calculated the imaginary part of the SPAC spectrum for 'reliable', 'unreliable', and complete (i.e. 'reliable' and 'unreliable' datasets combined) datasets for each array, and compared the results. In the case of insufficient azimuthal distribution of the stations (the linear array) the imaginary curve shows some instability and can therefore be regarded as an indicator of insufficient spatial averaging. However, in the case of low coherency of the wavefield the imaginary curve does not show any significant instability.

Background/Aims: The optimal training mode for linear array endoscopic ultrasonography (EUS) has not been established. Prior radial-scanning EUS training seems to improve subsequent linear array EUS learning. The objective of this randomized controlled trial was to evaluate its value in linear array EUS training. Methods: In total, 18 freshman trainees conducted hands-on EUS operations on a live pig model. The training contents consisted of visualization and tracking of the pancreas and splanchnic vasculature and performing fine-needle aspiration of the body or tail of the pancreas and celiac plexus neurolysis through the stomach. The trainees were randomized into two groups: group A received linear array EUS training after receiving radial-scanning EUS training, whereas group B conducted linear array EUS training alone. Two teachers assessed the competence of each trainee using a scoring system and relevant parameters before and after the training process. Results: Groups A and B showed significant improvement between the pretests and posttests in terms of diagnostic and interventional procedures. There was no intergroup difference in terms of improvement. Conclusions: Prior radial-scanning EUS training did not contribute to subsequent linear array EUS study performance in the pig stomach model; thus, this training mode may need to be changed.

A linear detector array unit (LDAU) was proposed and designed for the high energy X-ray 2-D and 3-D imaging systems for industrial non-destructive test. Specially for 3-D imaging, a helical CT with a 15 MeV linear accelerator and a curved detector is proposed. The arc-shape detector can be formed by many LDAUs all of which are arranged to face the focal spot when the source-to-detector distance is fixed depending on the application. An LDAU is composed of 10 modules and each module has 48 channels of CdWO4 (CWO) blocks and Si PIN photodiodes with 0.4 mm pitch. This modular design was made for easy manufacturing and maintenance. Through the Monte Carlo simulation, the CWO detector thickness of 17 mm was optimally determined. The silicon PIN photodiodes were designed as 48 channel arrays and fabricated with NTD (neutron transmutation doping) wafers of high resistivity and showed excellent leakage current properties below 1 nA at 10 V reverse bias. To minimize the low-voltage breakdown, the edges of the active layer and the guard ring were designed as a curved shape. The data acquisition system was also designed and fabricated as three independent functional boards; a sensor board, a capture board and a communication board to a PC. This paper describes the design of the detectors (CWO blocks and Si PIN photodiodes) and the 3-board data acquisition system with their simulation results.

A multichannel optical detector system employing a self-scanning linear photodiode array has been developed. The photodiode array detector system is designed for various applications which require fast, multichannel detection of transient signals. The detector system consists of a controller which runs on an IBM personal computer and a detector head connected to the controller through a DB-15 cable. The entire scanning of 1024 detector elements is achieved in 20 ms. By using an on-board 16-bit counter/timer, the operational mode of the photodiode array detector is fully programmable by software. The design considerations and the performance of the photodiode array detector system is presented.

The 4 by 4 microstrip phased array antenna designed and radiation characteristics are studied. The design frequency was chosen to be 5.8GHz. Chebyshev ratio was achieved by unequal power divider and Wilkinson power divider. The ratio of current at each port is 1 : 2.6 : 2.6 : 1 and then side lobe level is less than -30 dB. It is shown that the radiation beam direction can be changed up to 30。 by control the phase at each port. The result can be used to design electrically controllable microwave scanning antennas.

We have developed a small bore x-ray CT for small animal imaging with a linear x-ray detector array and small-scale slip rings. The linear x-ray detector array consists of 1024 elements of 400□m×400□m with a gadolinium oxysulfide (GOS) scintillator on top of them. To avoid use of expensive large diameter slip rings for projection data transmission from the X­ray detector to the image reconstruction system, we used the wireless LAN technology. The projection data are temporally stored in the data acquisition system residing on the rotating gantry during the scan and they are transmitted to the image reconstruction system after the scan. With the wireless LAN technology, we only needed to use small-scale slip rings to deliver the AC electric power to the X-ray generator and the power supply on the rotating gantry. The performances of the small animal CT system, such as SNR, contrast, and spatial resolution, have been evaluated through experiments using various phantoms. It has been experimentally found that the SNR is almost linearly proportional to the tube current and tube voltage, and the minimum resolvable contrast is less than 30 CT numbers at 40kVp/3.0㎃. The spatial resolution of the small animal CT system has been found to be about 0.9Ip/㎜. Postmortem images of a piglet is also presented.

A general linearly constrained adaptive array is examined in the weight vector space to illustrate the array performance with respect to the gain factor. A narrowband linear adaptive array is implemented in a coherent signal environment. It is shown that the gain factor in the general linearly constrained adaptive array has an effect on the linear constraint gain of the conventional linearly constrained adaptive array. It is observed that a variation of the gain factor of the general linearly constrained adaptive array results in a variation of the distance between the constraint plane and the origin in the translated weight vector space. Simulation results are shown to demonstrate the effect of the gain factor on the nulling performance.