• The Journal of the Acoustical Society of Korea
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• v.27 no.2
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• pp.57-65
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• 2008

Setting parameters of Ultrasonic scanners influence the quality of ultrasonic images. In order to obtain optimized images sonographers need to understand the effects of the setting parameters on ultrasonic images. The present study considered typical four parameters including TGC (Time Gain Control), Gain, Frequency, DR (Dynamic Range). LCS (low contrast sensitivity) was chosen to quantitatively compare the quality of the images. In the present experiment LCS targets of a standard ultrasonic test phantom (539, ATS, USA) were imaged using a clinical ultrasonic scanner (SA-9000 PRIME, Medison, Korea). Altering the settings in the parameters of the ultrasonic scanner, 6 LCS target images (+15 dB, +6 dB, +3 dB, -3 dB, -6 dB, -15 dB) to each setting were obtained, and their LCS values were calculated. The results show that the mean pixel value (LCS) is the highest at the max setting in TGC, mid to max in gain and pen mode in frequency and 40-66 dB in DR. Among all images, the image being the highest in LCS was obtained at the setting of DR 40 dB. It is expected that the results will be of use in setting the parameters when ultrasonically examining masses often clinically found In either solid lesions (similar to +15, +6, +3 dB targets) or cystic lesions (similar to -15, -6, -3 dB targets).

• Journal of the Korean Society of Combustion
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• v.22 no.2
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• pp.1-8
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• 2017

To evaluate the combustion instability of a gas turbine combustor, the DMD technique was applied. The mode frequency results for each fuel composition were compared with FFT(Fast Fourier Transform) results. The damping coefficient, which is a quantitative parameter for combustion instability, was evaluated for 5 experimental cases. The flame transfer function (FTF) was calculated in the most unstable test case. In deriving the FTF, gain and phase were calculated using DMD technique. As a result of the analysis of the OH radical perturbation of the DMD, the heat release fluctuation was the highest at 100 Hz, at which the highest value of gain is observed. The frequency of FFT and FTF were different. In order to clarify the reason for this, FTF for various resonance frequencies was performed and it shows that the pattern of gain was similar to FFT.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.479-483
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• 2006

As high-definition television(HDTV) broadcasting were generalized, there have been many researches and developments about large storage capacity and fast data transfer rate in optical disk drives(ODD). Pickup actuators must have high flexible mode frequencies and gain margins. Flexible modes are caused by the flexibility of moving parts in the actuator and a servo bandwidth is limited by them. As a result, the system becomes unstable for high-speed operations in high density reading and recording. In this paper, we suggest improved modeling method that considers the bonding layer. And, flexible mode frequency of actuator is improved by Design of Experiment of lens holder. Magnet circuit is designed considering the relation with moving part. Through improving yoke design, the magnetic flux is changed and DC tilt is reduced. Consequently, we designed actuator which has high flexible mode frequency and gain margins.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.3
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• pp.304-311
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• 2003

In this paper, we present the 2.4 ㎓ and 5 ㎓ dual band antenna fur access point of WLAN(Wireless Local Area Network). The proposed antenna must have equal gains in both frequency bands to accept two services. We proposed using collinear array to compensate gain difference for two different frequency bands. Simulation results using 3D simulation program, CST MWS(Microwave Studio), for dual band antenna with collinear away show that the maximum gain is about 4.7 dBi at 2.4 ㎓, 5.2 dBi at 5.7 ㎓. We got additional gain of about 2.1 ㏈ with collinear array for 2.4 ㎓ in measurement. Measured results for the dual band antenna with collinear array show applicable performances for access point of wireless LAN.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.1 s.94
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• pp.265-271
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• 1999

In the feed drive systems or the spindle systems of machine tools that consist of many mechanical components, a torsional vibration is often generated because of its elastic elements in torque transmission-Generally, the accuracy of motion control system is strongly influenced by the dynamic behavior of coupled transmission components Especially, a torsional vibration caused by the elasticity of mechanical elements might deteriorate the quick movement of system and lead to shorten the life time of the mechanical transmission elements. So, it is necessary to analyze the electromechanical system mathematically to optimize the dynamic characteristics of the feed m1d spindle system. In this paper, based on the DC motor model, a model of electro-drive system with motor has been developed and an optimal criterion for tuning the gain of speed controller is discussed. The frequency bandwidth of the system and the damping ratio in time domain are optimal design specifications for the gain adjustment speed controller. The gains of PI speed controller are then derived from the bandwidth and damping ratio, and those relationships have been classified.

• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1484-1494
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• 2017

We present a two-stage inverter with high step-up conversion ratio engaging modified finite-set Model Predictive Control (MPC) for utility-integrated photovoltaic (PV) applications. The anticipated arrangement is fit for low power PV uses, the calculated efficiency at 150 W input power and 19 times boosting ratio was around 94%. The suggested high-gain dc-dc converter based on Cockcroft-Walton multiplier constitutes the first-stage of the offered structure, due to its high step-up ability. It can boost the input voltage up to 20 times. The 3S current-source inverter constitutes the second-stage. The 3S current-source inverter hires three semiconductor switches, in which one is functioning at high-frequency and the others are operating at fundamental-frequency. The high-switching pulses are varied in the procedure of unidirectional sine-wave to engender a current coordinated with the utility-voltage. The unidirectional current is shaped into alternating current by the synchronized push-pull configuration. The MPC process are intended to control the scheme and achieve the subsequent tasks, take out the Maximum Power (MP) from the PV, step-up the PV voltage, and introduces low current with low Total Harmonic Distortion (THD) and with unity power factor with the grid voltage.

• Journal of the Korea Computer Industry Society
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• v.2 no.10
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• pp.1253-1260
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• 2001

In this paper, a new voltage-controlled tunable analog active element for low-voltage applications and information protection is proposed. The proposed active element is composed of the CMOS complementary cascode circuit which can extend transconductance of an element. Therefore, the unity gain frequency which is determined transconductance is increased than that of the conventional element. And then these results are verified by the $0.25\mutextrm{m}$ CMOS n-well parameter HSPICE simulation. As a result, the gain and the unity gain frequency are 42㏈ and 200MHz respectively in the element on 2V supply voltage. And power dissipation of the designed circuit is 0.32mW.

• Journal of information and communication convergence engineering
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• v.18 no.3
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• pp.162-166
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• 2020

The present paper presents an array antenna of a microstrip patch for 5G applications. Four rectangular microstrip patch elements are arranged in parallel and series to form an array antenna. Two insets are made on both sides of each patch element to achieve a wide frequency bandwidth of 23.97-31.60 GHz. To attain a high gain and wider bandwidth, the microstrip patch antenna is fed using series and corporate feeding networks. Further, three director elements on top of the top-most patch elements, and one reflector element at the open end of each patch element, are added. The addition of the Yagi elements improved the overall gain and acquired a higher radiation efficiency throughout the operating frequency bandwidth, with the array antenna achieving a maximum peak gain of 8.7 dB. The proposed antenna is built on a low-loss and low-cost substrate of FR4-eproxy. The proposed antenna design with a simple structure is suitable for Internet of Things and 5G applications.

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.215-218
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• 2006

In this paper, a small size, $7{\times}6mm^2$, Low Noise Amplifier(LNA) using LTCC process was fabricated with multi-layer structure for 2.4GHz wireless LAN. The measured results demonstrate that the bandwidth is 130 MHz, and the operating frequency is from 2.39GHz to 2.52GHz. The power gain is above 7.3 dB in the operating frequency range and the gain flatness is 0.5 dB. The maximum S11 is -4 dB and the maximum S22 is -7.5 dB. The noise figure is less than 1.83 dB. The measured power gain, S11 and S22 were had poorer performance than the simulation results. The reason for this discrepancy is that the input and output matching was not performed exactly. However, the noise figure of the LTCC low noise amplifier is better than simulation result. It is found that it is possible to fabricate a LTCC low noise amplifier in a small size.

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.1120-1122
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• 1999

In the design of vehicle glass antenna system, it is essential to use preamplifier between the glass antenna and the TV set, since glass antenna has low gain. In this paper, the preamplifier has been designed in the frequency range from 50MHz to 900MHz with the gam of 10dB. A negative feedback technique has been employed for the wideband characteristics of the amplifler. A DC block capacitor is also used to obtain flat gain response in the wide frequency range. The experimental result shows 1dB ripple in 9dB gain and 0.5dB ripple in 3dB noise figure. The test results were compared with those of the performed by the EEsof-touchstone.