• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.1
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• pp.68-72
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• 2004

The integrated voltage-controlled-oscillator(VOC) operating at 1.75 ㎓ is designed using the InGaP/GaAs HBT process. The proposed noise removal circuit and FR-4 substrate structure in this letter show the better characteristic of the phase noise and reduce the size of the VCO. The frequency tuning range of the VCO is about 200 ㎒ and the phase noise at 120 ㎑ offset is -119.3 ㏈c/㎐. The power consumption of the VCO core is 11.2 ㎽ at 2.8 V supply voltage and the output power is -2 ㏈m. The calculated figure of merit(FOM) is 191.7, which shows the best performance compared with the previous FET or HBT VCO.

• Carbon letters
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• v.27
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• pp.90-97
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• 2018

Electromagnetic interference (EMI) shielding is an important issue in modern daily life due to the increasing prevalence of electronic devices and their compact design. This study estimated EMI-shielding effect (EMI-SE) of small ($8-14{\times}17mm$) Hanji (Korean traditional paper) doped with carbon nanotubes (CNTs) and compared to Hanji without CNT using $^2H$ (92.1 MHz) and $^{23}Na$ (158.7 MHz) nuclear magnetic resonance (NMR) peak area data obtained from 1 M NaCl in $D_2O$ samples in capillary tubes that were wrapped in the Hanji samples. The simpler method of using the variation of reflected power and tuning frequency by inserting the sample into an NMR coil was also tested at 242.9, 158.7, and 92.1 MHz. Overall, EMI shielding was relatively more effective at the higher frequencies. Our results validated that NMR methods to be useful to evaluate EMI-SE, particularly for small, flexible shielding materials, and demonstrated that EMI shielding by absorption is dominant in Hanji mixed with CNT.

• Journal of information and communication convergence engineering
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• v.11 no.1
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• pp.56-61
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• 2013

Modern integrated circuits (ICs) are becoming an integrated parts of analog, digital, and radio frequency (RF) circuits. Testing these RF circuits on a chip is an important task, not only for fabrication quality control but also for tuning RF circuit elements to fit multi-standard wireless systems. In this paper, RF test circuits suitable for embedded testing are introduced: RF power detectors, power control circuits, directional couplers, and six-port reflectometers. Various types of embedded RF power detectors are reviewed. The conventional approach and our approach for the RF power control circuits are compared. Also, embedded tunable active directional couplers are presented. Then, six-port reflectometers for embedded RF testing are introduced including a 77-GHz six-port reflectometer circuit in a 130 nm process. This circuit demonstrates successful calibrated reflection coefficient simulation results for 37 well distributed samples in a Smith chart. The details including the theory, calibration, circuit design techniques, and simulations of the 77-GHz six-port reflectometer are presented in this paper.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.358-361
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• 2004

This paper describes the development process of high stiffness body for ride and handling performance. High stiffness and light weight vehicle is a major target in the refinement of passenger cars to meet customers' contradictable requirements between ride and handling performance and fuel economy. This paper describes the analysis approach process for high stiffness body through the data level of body stiffness. According to the frequency band, we can suggest the design guideline about Is cornering static stiffness, torsional and lateral stiffness, body attachment stiffness. The ride and handling characteristic of a vehicle is significantly affected by vibration transferred to the body through the chassis mounting points from front and rear suspension. It is known that body attachment stiffness is an important factor of ride and handling performance improvement. And high stiffness helps to improve the flexibility of bushing rate tuning between Handling and road noise. It makes it possible to design the good handling performance vehicle at initial design stage and save vehicles to be used in tests by using mother car at initial design stage. These improvements can lead to shortening the time needed to develop better vehicles.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.11
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• pp.5306-5313
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• 2011

Most previous studies for finding optimal design parameters of a tuned mass damper(TMD) have been focused on the harmonic excited single-degree-of freedom system. In this study, optimal values of damping ratio and tuning frequency ratio of a TMD applied to control a seismically excited structure are investigated through numerical analyses. Considering that the structural responses due to earthquake loads are strongly dependent on the soil condition, the site effects on the optimal parameters of the TMD are studied and compared to those presented by previous studies. Numerical analyses results indicate that better control performance can be obtained by using the parameters proposed by this study in the seismic application of the TMD.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.16-23
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• 2012

3-D linear acoustic analysis has been performed to elucidate damping characteristics of large Helmholtz acoustic cavities in FASTRAC combustor. Acoustic impedance concept has been introduced to quantify combustion stabilization capacity. For a given acoustic cavity, sonic velocity in cavity to achieve an optimal tuning has been determined and satisfactory agreement with the previous results has been obtained. Feasible estimation of sonic velocity in acoustic cavity has been devised. Results show similar trends without significant deviations, which can be used in the procedure of design and verification of acoustic cavity. From the satisfactory results, investigation of other combustors with acoustic cavities which have shown combustion instabilities will be done as future works.

• Journal of Power Electronics
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• v.19 no.4
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• pp.1000-1010
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• 2019

The use of internal-model-based linear controller, such as resonant controller, is a well-established technique for the current control of grid-connected systems. Attractive properties for resonant controllers include their two-sequence tracking ability, the simple control structure, and the reduced computational burden. However, in the case of continuous-designed resonant controller, the transient performance is inevitably degraded at a low switching frequency. Moreover, available design methods for resonant controller is not able to realize the direct design of transient performances, and the anticipated transient performance is mainly achieved through trial and error. To address these problems, the zero-order-hold (ZOH) characteristic and inherent time delay in digital control systems are considered comprehensively in the design, and a corresponding hold-equivalent discrete model of the grid-connected converter is then established. The relationship between the placement of closed-loop poles and the corresponding transient performance is comprehensively investigated to realize the direct mapping relationship between the control gain and the transient response time. For the benefit of automatic tuning and real-time adaption, analytical expressions for controller gains are derived in detail using the required transient response time and system parameters. Simulation and experimental results demonstrate the validity of the proposed method.

• Smart Structures and Systems
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• v.24 no.1
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• pp.1-14
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• 2019

Transmission tower-line system is one of most critical lifeline systems to cities. However, it is found that the transmission tower-line system is prone to be damaged by earthquakes in past decades. To mitigate seismic demands, this study introduces a tuned-mass damper (TMD) using superelastic shape memory alloy (SMA) spring for the system. In addition, considering the dynamic characteristics of both tower-line system and SMA are affected by temperature change. Particular attention is paid on the effect of temperature variation on seismic behavior. In doing so, the SMA-TMD is installed into the system, and its properties are optimized through parametric analyses. The considered temperature range is from -40 to $40^{\circ}C$. The seismic control effect of using SMA-TMD is investigated under the considered temperatures. Interested seismic performance indices include peak displacement and peak acceleration at the tower top and the height-wise deformation. Parametric analyses on seismic intensity and frequency ratio were carried out as well. This study indicates that the nonlinear behavior of SMA-TMD is critical to the control effect, and proper tuning before application is advisable. Seismic demand mitigation is always achieved in this wide temperature range, and the control effect is increased at high temperatures.

• Journal of Sensor Science and Technology
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• v.31 no.2
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• pp.115-119
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• 2022

A readout circuit for a mercury-cadmium-telluride (MCT)-amplified mid-wave infrared (IR) photodetector was realized and applied to noncontact chemical agent detectors based on a quantum cascade laser (QCL). The QCL emitted 250 times for each wavelength in 0.2-㎛ steps from 8 to 12 ㎛ with a frequency of 100 kHz and duty ratio of 10%. Because of the nonconstant QCL emission power during on-duty, averaging the photodetector signals is essential. Averaging can be performed in digital back-end processing through a high-speed analog-to-digital converter (ADC) or in analog front-end processing through an integrator circuit. In addition, it should be considered that the 250 IR data points should be completely transferred to a PC during each wavelength tuning period of the QCL. To average and minimize the IR data, we designed a readout circuit using the analog front-end processing method. The proposed readout circuit consisted of a switched-capacitor integrator, voltage level shifter, relatively low-speed analog-to-digital converter, and micro-control unit. We confirmed that the MCT photodetector signal according to the QCL source can be accurately read and transferred to the PC without omissions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.4A
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• pp.586-591
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• 2000

In this paper, a PLHRO(Phase Locked Hair-pin Resonator Oscillator) for K-band is designed with the feedback property of PLL(Phase Locked Loop) using a new tuning mechanism. The proposed PLHRO generates the output power of -0.6 dBm at 24.42 GHz, and has the phase noise of -86.6 dBc/Hz at 100 KHz and -76.5 dBc/Hz at 10KHz offset from carrier frequency, and has suppression characteristics of -23 dBc and spurious noise of -65 dBc. Buffered 24.42 GHz PLHRO generates the output power of 5.6 dBm at 24.42 GHz and has the of a phase noise of -77.34 dBc/Hz at 100 KHz and -72 dBc/Hz at 100 KHz offset from carrier frequency.