• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.11
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• pp.853-864
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• 2017

This paper proposes a false alarm rate reduction technique for detection of small targets in a terrestrial environment. CFAR algorithm is useful in homogeneous background, but it is not easy to detect targets in non-homogeneous background. In particular, when the clutter power is not significantly different from the target signal, it is difficult to detect the target due to high false alarm rate. To solve these difficulties, this study presents the false alarm rate reduction technique based on CFAR algorithm, matched filter and binary integration technique. The parameters are studied through the theoretical analysis and the validity of the proposed study is examined by the test results.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.1
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• pp.37-43
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• 1996

Breaking waves were generated in a 2-D flume. A piston-type wavemaker was operated in accordance with signals which consist of elementary harmonics with appropriate phase differences. These phase differences were estimated by using a linear wave theory so that wave crests were to be concentrated at the same position. The stroke of wavemaker was controlled to create plunging-type breaking waves. The signal with small amplitude could not generate breaking waves. In the case of moderate amplitudes, various breaking waves could be obtained. Most of breaking waves were spilling type. Only when the wavemaker was operated with appropriate amplitude, plunging-type breaking waves were generated. The parameters of breaking waves are the wave steepness and the frequency bandwidth. If the central frequency was low, breaking waves were not generated. Based on experimental data, we found that the wave height of breaking inception was H = 0.0113 gT$^2$. We also made computations by using a mixed Euler-Lagrangian scheme under the assumption of potential flow. The numerical results show good agreements with tank measurements.

• Journal of Power Electronics
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• v.18 no.1
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• pp.212-224
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• 2018

For maintaining a reliable and secure power system, this paper describes the design and implement of a single-phase grid-connected inverter with an enhanced phase-locked loop (PLL) and excellent power control performance. For designing the enhanced PLL and power regulator, a full-bridge voltage-controlled inverter (VCI) is investigated. When the grid frequency deviates from its reference values, the output frequency of the VCI is unstable with an oscillation of 2 doubling harmonics. The reason for this oscillation is analyzed mathematically. This oscillation leads to an injection of harmonics into the grid and even causes an output active power oscillation of the VCI. For eliminating the oscillation caused by a PLL, an oscillation compensation method is proposed. With the proposed method, the VCI maintains the original PLL control characteristics and improves the PLL robustness under grid frequency deviations. On the basis of the above analysis, a power regulator with the primary frequency and voltage modulation characteristics is analyzed and designed. Meanwhile, a small-signal model of the power loops is established to determine the control parameters. The VCI can accurately output target power and has primary frequency and voltage modulation characteristics that can provide active and reactive power compensation to the grid. Finally, simulation and experimental results are given to verify the idea.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.5
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• pp.927-934
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• 2019

Recently, mobile devices have evolved into small computers with various functions according to user requirements. Careful attention must be paid to the design of the power supply network for the stable operation of the application processor (AP), the wireless communication modem, the high performance camera, and the various interfaces of the mobile device to implement various functions of the mobile device. In this paper, we analyzed and verified the method of optimizing the design parameters such as the position, capacity, and number of decoupling capacitors to meet the target impedance required by the driver IC chip to ensure the stability of the power supply network of mobile devices that should be designed as wiring type due to mounting density limitation. The proposed wired power supply network design method can be applied to various applications including high-speed signal transmission line in addition to mobile applications.

• The Journal of the Acoustical Society of Korea
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• v.38 no.2
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• pp.231-239
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• 2019

In sonar systems, the passive ranging of a target is an active research area. This paper analyzed the performance of passive ranging based on an array invariant method for different environmental and sonar parameters. The array invariant developed for source range estimation in shallow water. The advantages of this method are that detailed environmental information is not required, and the real-time ranging is possible since the computational burden is very small. Simulation was performed to verify the algorithm. And this method is applied to sea-going experimental data in 2013 near Jinhae port. This study shows the performance of ranging for source orientation, transmission signal length, and length of a receiver through numerical simulation experiments. Also, the results using nested array and uniform line arrays are compared.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.5
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• pp.694-702
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• 2022

This paper shows a small and low-powered wireless communication system based on the ATSC broadcasting system using the ISM frequency band that can be used as a PBS(Personal Broadcasting System). It is designed to demonstrate a channel-adaptive CR(Cognitive Radio) system to provide a better service quality in the unlicensed band where co-channel interference exists. And it achieved very reliable communications by a closed-loop active phased array antenna. This ATSC-based personal broadcasting platform can be modified easily with given flexibility by using GNU Radio as an open-source signal processing platform based on USRP and implementing additional functions in FPGA. In addition, the chosen communication frequency resource can be managed and controlled by the return channel that transmits the channel status and communication parameters between transmission and reception in real-time.

• Journal of the Korean Magnetic Resonance Society
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• v.9 no.1
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• pp.48-60
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• 2005

Purpose: The purpose of this study was to design and build an optimized birdcage resonator configuration with a low pass filter, which would facilitate the acquisition of high-resolution 3D-image of small animals at 3T MRI system. Methods and Materials: The birdcage resonator with 12-element structures was built, in order to ensure B1 homogeneity over the image volume and maximum filling factor, and hence to maximize the signal to noise ratio (SNR) and resolution of the 3-dimensional images. The diameter and length of each element of a birdcage resonator were as follows: (1) diameter 13 cm, length 22 cm, (2) diameter 15 cm, length 22 cm, (3) diameter 17 cm, length 25 cm. Spin echo pulse sequence and fast spin echo pulse sequence were employed in obtaining MR images. The quality of the manufactured birdcage resonators wes evaluated on the basis of the return loss following matching and tuning process. Results: The experimental MR image of phantoms by the various manufactured birdcage resonators were obtained to compare the SNR in accordance with the size of objects. The size of an object to that of coil was identified by parameters that were estimated from the image of a phantom. First, the diameter of the birdcage resonator was 15cm, and the ratio of the tangerine to the birdcage resonator accounted for approximately 27%. The Q factor was 53.2 and the SNR was 150.7. Second, at the same birdcage resonator, the ratio of the orange was approximately 53%. The SNR and the Q parameter was 212.8 and 91.2, respectively. Conclusion: The present study demonstrated that if birdcage resonators have the same forms, SNR could be different depending on the size of an object, especially when the size of an object to that of coil is approximately 40~80%, the former is bigger than the latter. Therefore, when the size of an object to be observed is smaller than that of coil, the coil should be manufactured in accordance with the size of an object in order to obtain much more excellent images.

• Journal of the Microelectronics and Packaging Society
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• v.16 no.1
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• pp.13-19
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• 2009

A 440MHz wireless and passive surface acoustic wave (SAW) based chemical sensor was developed on a $41^{\circ}YX\;LiNbO_3$ piezoelectric substrate for simultaneous measurement of $CO_2$ gas and relative humidity (RH) using a reflective delay line pattern as the sensor element. The reflective delay line is composed of an interdigital transducer (IDT) and several shorted grating reflectors. A Teflon AF 2400 and a hydrophilic $SiO_2$ layer were used as $CO_2$ and water vapor sensitive films. The coupling of mode (COM) modeling was conducted to determine optimal device parameters prior to fabrication. According to simulation results, the device was fabricated and then wirelessly measured using the network analyzer. The measured reflective coefficient $S_{11}$ in the time domain showed high signal/noise (S/N) ratio, small signal attenuation, and few spurious peaks. In the $CO_2$ and humidity testing, high sensitivity ($2^{\circ}/ppm$ for $CO_2$ detection and $7.45^{\circ}/%$RH for humidity sensing), good linearity and repeatability were observed in the $CO_2$ concentration ranges of $75{\sim}375ppm$ and humidity levels of $20{\sim}80%$RH. Temperature and humidity compensations were also investigated during the sensitivity evaluation process.

• Geophysics and Geophysical Exploration
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• v.6 no.3
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• pp.126-133
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• 2003

High-resolution shallow marine seismic surveys have been carried out for the resources exploration, engineering applications and Quaternary mapping. To improve the resolution of subsurface structure image, multichannel digital technique has been applied. The quality of the image depends on the vertical and horizontal resolution and signal to noise (S/N) ratio which are associated with the data acquisition parameters such as sample interval, common midpoint (CMP) interval and CMP fold. To understand the effect of the acquisition parameters, a test survey was carried out off Yeosu and the acquired data were analyzed. A 30 $in^3$ small air gun was used as a seismic source and 8 channel streamer cable with a 5 m group interval was used as a receiver. The data were digitally recorded with a shot interval of 2 s and sample interval of 0.1 ms. The acquired data were resampled with various sample intervals, CMP intervals and CMP folds. The resampled data were processed, plotted as seismic sections and compared each other. The analysis results show that thin bed structure with ${\~}1m$ thickness and ${\~}6^{\circ}$ slope can be imaged with good resolution and continuity and low noise using the acquisition parameters with a sample interval shorter than 0.2 ms, CMP interval shorter than 2.5 m and CMP fold more than 4. Because seismic resolution is associated with the acquisition parameters, the quality of the subsurface structure can be imaged successfully using suitable and optimum acquisition parameters.

• Geophysics and Geophysical Exploration
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• v.2 no.1
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• pp.8-16
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• 1999

In terms of high resolution, seismic reflection survey is by far the most significant geophysical method applied to define subsurface structure. In shallow seismic reflection survey, it is, however, difficult to obtain high resolution image due to both the wave attenuation in the unconsolidated layer and the existence of source-generated surface waves Therefore, when collecting data, it is imperative to select proper equipments and choose optimum field data acquisition parameters for acquiring high S/N data. In this survey, a small size hammer was used as a low energy source and 40-Hz vertical geophones were used as receivers. Trigger signal was obtained from the hammer starter attached in the aluminum plate and thus it was possible to control the source onset time for the vertical stack. During the field work, a modified standard CMP technique was introduced to achieve the many-fold CMP data effectively. Data processing was conducted by the 'Seismic Unix' which is mounted on PC with a Linux operating system. The main distinctions were the emphasis and detail placed on near-surface velocity analysis and the extra care exercised in muting.