• Journal of electromagnetic engineering and science
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• v.2 no.1
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• pp.16-21
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• 2002

On the contrary to the progress of the electronic industry and radio communication technologies, many social problems such as EMI, due to unnecessary electromagnetic(EM) wave are serious with the increased use of EM wave. It is required that the absorbing capability of an EM wave absorber is more than 20 dB, the bandwidth of which is required from 30 MHz to 18 GHz to satisfy the international standard about an anechoic chamber for EMI/EMS measurement$^{[1]}$TEX>. However, the absorbing frequency band of the conventional EM wave absorbers satisfying more than 20 dB is very narrow, for examples, from 30 MHz to 400 MHz in ferrite tile type and from 30 MHz to 870 MHz in ferrite grid type, respectively. In this paper, we proposed and designed a new tripe absorber with broadband characteristics covering the frequency band from 30 MHz to 10 GHz by use of the equivalent material constants method (EMCM)$^{[2]~[4]}$TEX>.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.8
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• pp.1283-1291
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• 2002

In this paper, the PLL driven by the DDFS is designed on the schematic using the Q-logic cell based library and is implemented using FPGA QL32 x16B. The measurement results of the frequency synthesizer switching speed were agreement with a register. The simulated results show that the clock delay was generated after eleven clock and if input is random, It has influence on output DA converter has to be very extensive. Therefore, the DDFS used noise shaper to drive PLL by regular interval for input state. Also the bandwidth of DA converter very extensive, the simulation shows that the variation of small input control word is better than the switching speed of PLL.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.3
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• pp.311-317
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• 2014

In this paper, the flexible and reconfigurable frequency selective surface for C-band was designed using patch array and grid structure for radome and other curved surface applications. Frequency reconfigurability was obtained by varying the capacitance of varactor diode and flexibility is implemented by using flexible PCB. For the validity of the proposed structure, we fabricated the flexible and reconfigurable frequency selective structure and measured the frequency reconfigurability for different bias voltages and different curvature surfaces from the optimized design parameters. From the measurement results, we know that the proposed structure has the wideband reconfigurable frequency bandwidth of 6.05-7.08GHz. We can apply this proposed structure to the curved surface like as radome of aircraft or warship.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.2
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• pp.69-75
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• 2005

In order to improve the reliability of high voltage rotating machines and mold transformers, it is necessary to understand the breakdown mechanism and life assessment of the high voltage winding parts. Especially the on-line PD test provides the ability to monitor effects, such as slot discharge, internal discharge, and end-winding discharge without interrupting the electrical machines, this method has been proven the major testing technology. Capacitive couplers have been the most widely used sensors for the on-line partial discharge detection in rotating machines nowadays. This paper deals with the electrical characteristics and long-term reliability of a ceramic coupler(CC), which can be easily mounted into high voltage input terminal part, has been developed and tested to continuously measure PD activity during operating condition. This paper presents electrical characteristics (dielectric loss angle, capacitance, PD inception level, breakdown voltage, and frequency response bandwidth) and long-term life test result of the developed 6.6 kV class on-line ceramic coupling sensor. It was found that this sensor had good electrical characteristics to detect PD activity during the operating condition with its detection frequency band is between several and several tens MHz. Also, the voltage life of the 6.6kV class ceramic coupler was calculated over 60 years.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.12
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• pp.219-225
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• 2012

A low-power, low-noise pre-amplifier for digital hearing-aid application is designed. This pre-amplifier amplifies single-ended signal from an electret microphone, and produces differential output to be delivered to an ADC. It has a variable gain of 3.6, 7.2, 14.4 and 28.8 with a bandwidth between 100Hz~10kHzon. The measurement results show 85 dB of SNR, 0.05 % of harmonic distortion and $200{\mu}W$ of power consumption with 1.2V supply.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.89-90
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• 2008

We present an implementation and it's real-sea test of an underwater acoustic communication system, which allows the system to reduce complexity and increase robustness in time variant underwater environments. For easy adaptation to complicated and time-varying environments of the ocean, all-digital transmitter and receiver systems were implemented. For frame synchronization the CAZAC sequence was used, and QPSK modulation/demodulation method with carrier frequency of 25kHz and a bandwidth of 5kHz were applied to generate 10kbps transmission rate including overhead. To improve transmission quality, we used several techniques and algorithms such as adaptive beamforming, adaptive equalizer, and convolution coding/Viterbi decoding. For the verification of the system performance, measurement of BER has been done in a very shallow water with depth of 20m at JangMok, Geoje. During the experiment, image data were successfully transmitted up to about 9.6km.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.1
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• pp.71-76
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• 2004

A compact embedded tapped-line combline filter with interdigital capacitors using low temperature co-fired ceramic (LTCC) technology for wireless application is proposed. Also, in-situ measurement using T-pattern microstrip resonator was performed to acquire exact knowledge of electrical properties of the LTCC substrate. The proposed filter makes it possible to realize a relatively small size, 2.7mm${\times}$2.03mm. by employing interdigital and combline structure. It shows 1.8 ㏈ insertion loss, 37.6㏈ return loss, and 280 MHz bandwidth at the center frequency of 5.09 GHz. Its small size and simple structure make it a good candidate as an integrated filter for various LTCC substrates.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.10
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• pp.10-15
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• 1990

Theory and experimental results of measuring the microwave dielectric characteristics of low-loss materials by using dielectric rod resonator method are presented. The $TE_{011}$ mode resonance frequency was adapted to minimize the effect of the air gap between the rod and the conducting plates. The dielectric properties were computed from the resonance frequency, sample geometry and 3 dB bandwidth. The error of measurements was within ${\pm}3{\%}$ for dielectric constant and was within ${\pm}12{\%}$ for dielectric loss.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.1 s.104
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• pp.81-88
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• 2006

In this paper, spectrum use factor as the ratio between used spectrum bandwidth by the existing system and total spectrum resources at specific locations was derived and calculated. Spectrum use factor was also presented as a function of antenna patterns and transmitter power of existing systems. Real spectrum use factor was calculated for fixed radio station as a validity of this paper. With the results of this paper, we can use the spectrum more efficiently because the white space of spectrum space is replaced by the quantificated spectrum space.

• Proceedings of the KSMRM Conference
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• 2001.11a
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• pp.112-112
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• 2001

Purpose： We developed the software for diffusion tensor imaging and evaluated its feasibility in norm brains. Method： Five normal volunteers, aged from 25 to 29 years, were examined on a 1.5 T MR system. the diffusion tensor pulse sequence used a SE-EPI with 6 diffusion gradie directions of (1, 1, 0), (-1, 1,0), (1, 0, 1), (-1, 0, 1), (0, 1, 1), (0, 1, -1) and also with no diffusion gradient. A b-factor of 500 sec/mm2 was used. Measurement parameter were as follows； TR/TE=10000 ms/99 ms, FOV=240 mm, matrix=128$\times$128, slice thickness/gap=6 mm/0 mm, bandwidth=91 kHz and the number of total slices=20. Four repeated axial diffusion images were averaged for diffusion tensor imaging. A total scan 11 of 4 min 30 sec was used. Six full diffusion tensor components of Dxx, Dyy, Dzz, Dxy, Dxz and Dyz were obtained using two-point linear regression model from 7 diffusion-weight images at each pixel and fractional anisotropy and lattice index images was estimated fr their eigenvectors and eigenvalues. Our program was written on a platform of IDL. W evaluated the qualities of fractional anisotropy and lattice index images of normal brains a knew whether our software for diffusion tensor imaging may be feasible.