• Journal of the Institute of Electronics Engineers of Korea SP
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• v.40 no.4
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• pp.292-302
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• 2003

We propose a new method to reduce the complexity of excitation codebook search. The preselected excitation pulses by the coarse search method can be updated to pulses with higher quality performance measure. The excitation pulses can arbitrarily be deleted and inserted among the searched pulses until the overall performance achieves. If we use this excitation pulse search method in AMR-WB, the complexity required for excitation codebook search can be reduced to half the original method while the output speech maintains equal speech quality to a conventional method.

• The Journal of the Acoustical Society of Korea
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• v.33 no.5
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• pp.300-308
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• 2014

Photoacoustic imaging is a useful tool for the diagnosis of atherosclerosis because it is capable of providing anatomical and pathological information at the same time. A photoacoustic signal detector is a pivotal element to achieve high spatial resolution, so that it should have broadband spectrum with a high center frequency. Since a photoacoustic imaging probe is directly inserted into blood vessel to diagnose atherosclerosis, the total size of the photoacoustic signal detector should be less than 1 mm. The main purpose of this paper is to demonstrate that PVDF can be used as an active material for the photoacoustic signal detector with a high frequency and broadband characteristic. The photoacoustic signal detector developed in this study was a single element ultrasound transducer with an aperture of $0.5{\times}0.5mm$ and the total size of 1 mm. In the design stage, the natural focal depth was adjusted for an effective focal area to cover the region of interest, i.e., 1~5 mm in depth. This was because geometrical focusing could not be used due to the small aperture. Through a pulse-echo test, it was ascertained that the developed photoacoustic signal detector has the -6 dB bandwidth ranging between 40.1 and 112.8 MHz and the center frequency of 76.83 MHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.4 s.119
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• pp.430-439
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• 2007

In this paper, we propose a broadband TEM horn antenna optimized using a genetic algorithm. The characteristics required for the TEM horn are the broad matching bandwidth from 2 GHz to 10 GHz and high gain in broadside with a small gain deviation within that bandwidth. In addition, a broadband balun is designed to improve the portability and to reduce the total size of the antenna. The measured return loss of the proposed TEM horn with the broadband balun is less than -10 dB(VSWR<2) from 2 GHz to 10 GHz. Compared to a conventional triangular type TEM horn, the proposed antenna shows about 80 % reduced volume and gives the broadside gain about 12 dBi with a gain deviation less than 6 dB from 2 GHz to 10 GHz. The time domain measurement shows less than 0.4 ns group delay and the pulse measurement using the transmitting signal with the rising time of 58.5 ps shows the received pulse with the rising time of 66.5 ps, which is less than 10 % rising time variation.

• Korean Journal of Environment and Ecology
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• v.23 no.6
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• pp.553-563
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• 2009

This study was conducted to analyze the changes in the echolocation of Pipistrellus abramus according to environmental characteristics. The survey was conducted in the day-roosting site of P. abramus located in Gyeongju City (North Gyeongsang Province) from April to August, 2009. The environmental characteristics during the research were classified in six categories: the emergence time after sunset moving time from day roost to feeding areas; rice fields; forest edges; open spaces; and residential areas. Analysis results showed that there are differences in environmental characteristics and also differences between the moving time to the habitat and the moving time to capture preys. At the emergence time from day roost, Pipistrellus abramus used a FM signal with a short pulse-duration. In open spaces, however, they used a CF signal with a long pulse-duration. In different environmental situations, they used both FM and CF signals, although the types of pulse which they used were different. Except pulse-duration, there were significant differences in pulse-interval, peak-frequency, starting-frequency and ending-frequency between the movement among habitats and the movement to capture preys. Except the emergence time from day-roost, they showed a narrow band FM signal and a long pulse-duration that are suitable to search for insects by sensing echoes of insects when they moved among their habitats. When they were out to capture their preys, they showed a broad band FM signal and a short pulse-duration which enabled them to widely search and accurately locate their preys.

• Korean Journal of Optics and Photonics
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• v.15 no.5
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• pp.455-460
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• 2004

We have developed a mode-locked ultra-short pulse C $r^{4+}$:YAG laser, as well as a continuous wave C $r^{4+}$:YAG laser. The laser was pumped by a Nd:YAG laser and its characteristics were investigated. In continuous wave mode, we obtained as much as 600 mW at 1.436 ${\mu}{\textrm}{m}$ with pumping power of 6 W, by using an output coupler with a reflectivity of 98%. The power slope efficiency was 10%, when the gain medium was cooled to 19$^{\circ}C$. The tuning range was varied from 1.39 ${\mu}{\textrm}{m}$ to 1.55 ${\mu}{\textrm}{m}$ and the maximum power was 400 mW at 1.492 ${\mu}{\textrm}{m}$ with a 3-plate birefringent filter. The C $r^{4+}$:YAG laser was mode-locked by a Kerr lens mode locking method. Mode locking at 1.436 ${\mu}{\textrm}{m}$was initiated by slightly rocking a mirror mount. But the pulses were very unstable because of the strong water absorption at this region. So we shifted the lasing wavelength to 1.492 ${\mu}{\textrm}{m}$ by using a 3-plate birefringent filter. Then we obtained stable state mode-locking with the maximum average power of 280 mW for a pumping power of 6 W. The pulse width of 43 fs was measured using an autocorrelator and the repetition rate was 104.5 MHz.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3A
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• pp.168-177
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• 2005

In this paper, we numerically investigated the optimum pump light power resulting best compensation of pulse distortion due to both chromatic dispersion and self phase modulation (SPM) in long-haul 3×40 Gbps wavelength division multiplexing (WDM) systems. We used mid-span spectral inversion (MSSI) method with path-averaged intensity approximation (PAIA) as compensation approach, which have highly nonlinear dispersion shifted fiber (HNL-DSF) as nonlinear medium of optical phase conjugator (OPC) in the mid-way of total transmission line. We confirmed that HNL-DSF is an useful nonlinear medium in OPC for wideband WDM transmission, and in order to achieve the excellent compensation the pump light power is selected to equal the conjugated light power into the latter half fiber section with the input light power of WDM channel depending on total transmission length. Also we confirmed that compensation degree of WDM channel with small conversion efficiency is improved by using pump light power increasing power conversion ratio upper than 1.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.2
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• pp.27-32
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• 2018

In this paper, W-band transceiver module for compact radar has been designed and fabricated. Utilizing proposed microstrip-to-waveguide transition, the error between design and implementation is reduced. The proposed transition provides less than 1 dB insertion loss per transition and reliability for fabrication. In order to apply compact radar with dual-polarized monopulse directly, W-band transmitter with 28 dBm output power is designed and developed. Also, 6 channels of receiver module with low noise figure 13.5 dB and maximum 17 dBm input P1dB is developed. Proposed W-band transceiver module is expected compact radar application for dual-polarized monopulse signal processing system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.8
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• pp.967-975
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• 2012

This paper presents a method to measure reflection coefficients of microwave devices or antennas based on time domain analysis with sampling oscilloscopes. The reflection coefficients were extracted by the Fourier transformation of echo pulses from devices with respect to the 20 GHz incident pulse signals. The three-error terms, which are commonly used for the correction of a microwave network, were determined using a 3.5 mm calibration kit. In addition, a modified error-correction model associated with a directional coupler for reflection coefficient measurements is introduced. The results were compared with those of measured with a commercial vector network analyzer.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.7
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• pp.1165-1172
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• 2008

In this paper, the scattering parameters of the metamaterial slab are obtained using the 2D FDTD(Finite-Difference Time-Domain) method. FDTD method is one of strongest electromagnetic numerical method which is widely used to analyze the metamaterial structure because of its simplicity. But it is very difficult to obtain frequency response of metamaterial itself because frequency dispersive model such as Lorentz, Drude model are used in FDTD. We used the well-known m-n-m cycle sine pulse to obtain the frequency response of the metamaterials. Comparisons between the wideband Gaussian input pulse and band-limited m-n-m cycle sine pulse are performed in this paper also. From the results, we concluded that the scattering parameters in frequency domain can be obtained using specific input pulse in FDTD even if the response has valid only for limited bandwidth.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.484-487
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• 2014

In this paper, We describe antenna characteristics for efficiently detecting human signs using small, planar and low power antenna. Then we can measure biological signals including respiration, heart rate, blood pressure, and blood sugar, using UWB (Ultra Wide Band) pulses, while does not contact the human body. The antenna need stable and wideband impedance characteristic, because it use gaussian pulse signal. Usually it has trade-off between wideband impedance and gain. But we don't considered array type antennas because we want to need small size. Generally the antennas that classified as frequency independent satisfy our requirements. Frequency independent antennas include spiral, log-periodic, sinuous, and etc. These antennas are possible to have shape planar type. In this paper, We tested these kind antenna's characteristics in center frequency 5 GHz, Especially circular patch and sinuous antenna designed and analyzed.