• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.2
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• pp.413-421
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• 1990

Acoustic emission signals due to leak from circular holes of 0.4, 1, 2 and 4mm diameter and rectangular slits of different geometry having the same cross section as 4mm diameter hole was studied both analytically and experimentally. Acoustic emission signals from a wide-band type transducer were transformed to digital signals through a digital oscilloscope, and $V_{rms}$ and frequency spectrum were obtained by processing digital signals. Relationships between acoustic parameters and fluid mechanical parameters were derived analytically. A quadrapole aerodynamic model was applied in the analysis of leak from the circular holes and $V_{rms}$ was found to be proportional to the root square of leak rate through the circular hole. A modified model based on dipole source mechanism and laminar equivalent diameter was applied in the analysis of leak signals from the rectangular slits. In the case of constant pressure, $V_{rms}$ increased as the laminar equivalent diameter of slit decreased. In the case of constant laminar equivalent diameter, however the result was similar to that for leak from the circular hole. The frequency spectra of leak signals shows the same frequency characteristics irrespective of the pressure difference.rence.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.3
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• pp.173-179
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• 1999

The defects on the metal surface. such as the ended circular pressed hole. the penetrated circular drilled hole, and the linear hollow lanes have been investigated by means of the microwave. In this experiment, frequency was set at 9.2GHz with 3kHz modulation, and the methods of reflection, transmission, fixed carrier frequency, and mod-demodulated technique have been used for investigating defects. The magnitudes of the microwave signals have been changed at the ended circular pressed hole and the penetrated circular drilled hole. The defect sizes that were estimated from the reflected microwave signals had the dimensions enlarged by twice the original size of the penetrated circular drilled hole and 2.5 times the original size of the ended circular pressed hole. The magnitudes of the reflected microwave signals from the linear hollow lane have increased with expansion of the width of the notch. In the linear hollow lane with the depth of 2.4mm, the reflected microwave signals versus the defect widths had a maximum value at the defect width of 50mm, and in the linear hollow lanes with the depths of 1.2mm and 0.45mm, the reflected microwave signals versus the defects widths had the maximum values each at the defect depths of 55mm.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.1
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• pp.43-49
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• 2023

In modern wireless communication systems including beamformers or location-based services (LBS), which employ multiple antenna elements, estimating the number of signals is essential for accurately determining the quality of the communication service. Representative signal number estimation algorithms including the Akaike information criterion (AIC) and minimum description length (MDL) algorithms, which are information theoretical criterion models, determine the number of signals based on a reference value that minimizes each criterion. In general, increasing the number of elements mounted onto the array antenna enhances the performance of estimating the number of signals; however, it increases the computational complexity of the estimation algorithm. In addition, various configurations of array antennas for the increased number of antenna elements should be considered to efficiently utilize them in a limited location. In this paper, we introduce an efficient signal number estimation algorithm based on the beamspace based AIC and MDL techniques that reduce the computational complexity by reducing the dimension of a uniform circular array antenna. Since this algorithm is based on a uniform circular array antenna, it presents the advantages of a circular array antenna. The performance of the proposed signal number estimation algorithm is evaluated through computer simulation examples.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.2
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• pp.347-356
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• 1996

In this paper, we present the circular array structure for estimating the temporal and spatial specturm of multiple narrowband incoherent signals which have different frequencies. The conventional linear array is computationally demanding for simultaneously estimating the spatial and temporal spectrum since it requires the tapped delay line filer. The statistical performance of the circular array is never deteriorated eve though it requires much less computational load than the uniform linear array. Especially, it is shown that the circular array resolves the direction-of-arrivals of the multiple signals without the spatial and temporal aliasing the fundamental nonuniform-sampling property prossessed by it. Computer simulation results are shown to demonstrate the better performance achieved with the circular array geometry relative to that obtained with a uniform linear array with taps.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.1
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• pp.97-105
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• 2009

In this paper, the performance of AP(Alternating Projection) and EM(Expectation Maximization) algorithms is investigated in terms of detection of multiple signals, resolvability of coherent signals and the efficiency of sensor array processing. The basic idea of these algorithms is utilization of relaxation technique of successive 1D maximization to solve a direction finding problem by maximizing the multidimensional likelihood function. It means that the function is maximized over only for a single parameter while the other parameters are fixed at each step of the iteration. According to simulation results, the algorithms showed good performance for both incoherent and coherent multiple signals. Moreover, some advantages are identified for direction finding with very small samples and fast convergence. The performance of AP algorithm is compared with that of EM using multiple criteria such as the number of sensor, SNR, the number of samples, and convergence speed over uniform circular array. It is resulted AP algorithm is superior to EM overally except for one criterion, convergence speed. Especially, for EM algorithm there is no performance difference between incoherent and coherent case. In conclusion, AP and EM are viable and practical alternatives, which can be applied to a direction under due to the resolvability of multi-path signals, reliable performance and no troublesome eigen-decomposition of the sample-covariance matrix.

• Journal of the Korean Magnetics Society
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• v.13 no.2
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• pp.76-81
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• 2003

Non-linear anisotropic materials were used to simulate the effects of tensile stress in 3D finite element analysis (FEA). FEA was used to calculate the effects of far and near-side pit depth and tensile stress on magnetic flux leakage (MFL) signals. The axial and radial MFL signals were depended on far and near-side double circular pit depth and on the stress, but the circumferential MFL signal was not depended on them. The axial and radial MFL signals increased with greater pit depth and applied stress, but the circumferential MFL signal was scarcely changed.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.5
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• pp.845-852
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• 2019

The main goal of Signal Intelligence (SIGNT) based on a satellite is to collect valid and accurate data without the topographical constraints, but, due to the characteristics of the satellite communication, the collected signals are greatly vulnerable to the influence of interference and jamming signals because their power are very low. Therefore, the high performance techniques of estimating the angle of arrivals (AOAs) of the collected signals and suppressing interference signals are required for collecting various signals on the ground employing the satellite. In addition, the high quality of the transmission beam-forming technique is required for accurately transmitting the collected information to a ground control center. In this paper, we present a beam-forming satellite system based on a circular array antenna, considering the above techniques, and evaluate and analysis the performance of the presented beam-forming system through the computer simulation. The circular array antenna structure is expected to effectively employ for the SIGINT system based on a satellite, because it is suitable to be installed in the satellite.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.1
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• pp.59-65
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• 2023

A GNSS receiver must perform signal acquisition to estimate the code phase and Doppler frequency of the incoming satellite signals, which are essential information for baseband signal processing. Modernized GNSS signals have different modulation schemes and long PRN code lengths from legacy signals, which makes it difficult to acquire the signals and increases the computational complexity and time. This paper proposes a novel FFT/Inverse-FFT with baseband resampling to resolve the aforementioned challenges. The suggested algorithm uses a single block only for the FFT and thereby requires less hardware resources than conventional structures such as Double Block Zero Padding (DBZP). Experimental results based on a MATLAB simulation show this algorithm can successfully acquire GPS L1C/A, GPS L2C, Galileo E1OS, and GPS L5.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.7
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• pp.1534-1542
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• 1997

In this paper, we present a performance improvement method for the direction-of-arrival (DOA) estimation algorithm of the narrowband signals incident on a uniform circular array. It is very important to estimate the covariance matrix effectively because the performance of DOA algorithm mainly depends on the exactness of the sampel coveriance matrix which is computed from the received samples of signals. In case of uniform circular array with the even number sensors, the structure of the arrray has a useful geometrical property. Therefore we present the method which can estimate covariance matrix more effectively using this property. The simulation results are shown to demonstrate the superior perfodrmance obtained by the proposed covariance matrix estimation method relative to that of the conventional estimation method.

• ETRI Journal
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• v.46 no.3
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• pp.421-431
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• 2024

In this study, a direct position tracking method for non-circular (NC) signals using distributed passive arrays is proposed. First, we calculate the initial positions of sources using a direct position determination (DPD) approach; next, we transform the tracking into a compensation problem. The offsets of the adjacent time positions are calculated using a first-order Taylor expansion. The fusion calculation of the noise subspace is performed according to the NC characteristics. Because the proposed method uses the signal information from the previous iteration, it can realize automatic data associations. Compared with traditional DPD and two-step localization methods, our novel process has lower computational complexity and provides higher accuracy. Moreover, its performance is better than that of the traditional tracking methods. Numerous simulation results support the superiority of our proposed method.