• Journal of Biomedical Engineering Research
• /
• v.23 no.1
• /
• pp.49-60
• /
• 2002

Receive dynamic focusing with an array transducer can provide near optimum resolution only in the vicinity of transmit focal depth. A customary method to increase the depth of field is to combine several beams with different focal depths, with an accompanying decrease in the frame rate. In this Paper. we Present a simultaneous multiple transmit focusing method in which chirp signals focused at different depths are transmitted at the same time. These chirp signals are mutually orthogonal in a sense that the autocorrelation function of each signal has a narrow mainlobe width and low sidelobe levels. and the crossorelation function of any Pair of the signals has values smaller than the sidelobe levels of each autocorrelation function. This means that each chirp signal can be separated from the combined received signals and compressed into a short pulse. which is then individually focused on a separate receive beamformer. Next. the individually focused beams are combined to form a frame of image. Theoretically, any two chirp signals defined over two nonoverlapped frequency bands are mutually orthogonal In the present work. however, a tractional overlap of adjacent frequency bands is permitted to design more chirp signals within a given transducer bandwidth. The elevation of the rosscorrelation values due to the frequency overlap could be reduced by alternating the direction of frequency sweep of the adjacent chirp signals We also observe that the Proposed method provides better images when the low frequency chirp is focused at a near Point and the high frequency chirp at a far point along the depth. better lateral resolution is obtained at the far field with reasonable SNR due to the SNR gain in Pulse compression Imaging .

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.4C
• /
• pp.230-238
• /
• 2005

An orthogonal frequency division multiplexing (OFDM) system consists of a number of independently modulated subcarriers and, thus, a high peak-to-average power ratio (PAR) can occur when the subcarriers are added coherently. The high PAR brings such disadvantages as an increased complexity of the analog-to-digital (ADC) and digital-to-analog (DAC) converters and a reduced efficiency of the radio frequency (RF) power amplifier. In this paper, we propose a novel PAR reduction scheme called selective mapping of partial tones (SMOPT). The SMOPT scheme has a reduced complexity, lower sensitivity to peak reduction tones (PRT) positions, and a shorter processing time as compared with the conventional tone reservation (TR) scheme. The performance of the SMOPT scheme is analyzed based on the IEEE 802.1la wireless local area network(WLAM) physical layer model. Numerical results show that the SMOPT scheme outperforms the TR scheme under various scenarios.

• Journal of Broadcast Engineering
• /
• v.19 no.2
• /
• pp.195-204
• /
• 2014

In this paper, we propose an automatic modulation classification method for ten digitally modulated baseband signals, such as 2-FSK, 4-FSK, 8-FSK, MSK, BPSK, QPSK, 8-PSK, 16-QAM, 32-QAM, and 64-QAM based on higher order statistics of cyclostationary process. The first order cyclic moments and higher order cyclic cumulants of the signal are used as features of the modulation signals. The proposed method consists of two stages. At the first stage, we classify modulation signals as M-FSK and non-FSK using peaks of the first order cyclic moment. At the next step, we apply the Gaussian mixture model-based classifier to classify non-FSK. Simulation results are demonstrated to evaluate the proposed scheme. The results show high probability of classification even in the presence of frequency and phase offsets.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.15 no.3
• /
• pp.242-250
• /
• 2004

In this thesis, a new broadband PIFA(Planar Inverted-F Antenna) for PCS and IMP-2000 applications is designed. The dual-L antenna structure is adopted in order to improve the characteristics of PIFA which usually has a narrow band. The height of the antenna is fixed 6 mm considering terminal's thickness and the structure is deformed into the folded radiation patches to minimize the size of the antenna. The bandwidth of a realized antenna is 1.66∼2.35 ㎓(34.5 %) fur return loss below -10 ㏈ which contain the required bandwidth of PCS and IMT-2000. And Monopole antenna with λ/4 length is designed and compared with dual-L with folded patch in SAR. 1 g and 10 g averaged peak SAR of PIFA are about 25.7 %, 30.3 % lower than those of monopole antenna respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.12
• /
• pp.1391-1401
• /
• 2007

This paper proposed a novel broadband printed monopole antenna for PCS/IMT-2000/WLAN terminals. Frequency characteristics are optimized with various design parameters. Two Z-shaped patchs were utilized in order to improve the characteristics of a printed monopole antenna which usually has a narrow bandwidth. The bandwidth of the realized antenna is $1.590{\sim}2.614$ GHz(48.43 %) below the return loss of -10 dB which contain the required bandwidth of PCS/IMT-2000/WLAN band. The simulated and measured values of 1 g and 10 g averaged peak SAR on human head caused by the proposed antenna on folder-type phone were analyzed and discussed. As a result, the measured 1 g peak SAR value is 0.794 W/kg and 10 g peak SAR value is 0.368 W/kg at 1.8 GHz. The results are smaller than the reference SAR limit values that are respectively 1.6 W/kg and 2 W/kg on 1 g and 10 g averaged SAR values.

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.49 no.1
• /
• pp.57-63
• /
• 2012

In this paper, a switch sizing method is proposed in order to prevent the cross-regulation in the TM type SIDO DC-DC buck converter. In TM type SIDO DC-DC buck converter, a DCM operation is required. In the DCM operation, the inductor peak current is larger than that in the CCM. Because of the larger inductor peak current and the added switch resistance, the voltage drop is increased, resulting in possible cross-regulation. To solve this problem, the switch resistance must be considered in sizing the switch. To simplify the calculation of the resistance, the inductor current was replaced by the average load current. Using the proposed method, TM type SIDO DC-DC buck converter for camera module was designed to provide two independent supply voltage(2.8 V and 1.8 V). The designed circuit was fabricated in a standard $0.35{\mu}m$ CMOS process. At a switching frequency of 1 MHz and a load current of 200 mA, a power effciency of 80.7% was achieved.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.27 no.12
• /
• pp.1097-1104
• /
• 2016

The infrared camera is difficult to satisfy the RE-102 specification of Mil-Std-461. Especially, in the case of UAV electronics, shielded cable is not used, so it is difficult to meet the electromagnetic compatibility standard. In the RE-102 test of the IR camera for UAV, radiated noise exceeding 30 dBuV/m was observed in the range of 50 MHz to 200 MHz. As a result of pcb em scan, peak noise which caused by the harmonic frequency of the digital control signal clock was observed. Radiated noise was reduced by up to 22.9 dBuV/m by applying the spread spectrum clock generator(SSCG) with 3 % down spreading method to the camera control clock.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.10 no.7
• /
• pp.985-997
• /
• 1999

In this paper, the detection of 1 g and 10 g averaged SAR on human head caused by PCS handheld phones is analyzed and discussed. Conventional monopole antenna and planar structured PIFA are used in the computational model to apply to the antennas mounted on handheld phone. These antennas are designed to operate in the near of frequency 1.8 GHz, human head model is sampled to have cell size 1.5 mm and sloped to front direction by 30$^{\circ}$. It is found that, when monopole antenna is applied, 1 g averaged SAR is 1.4 W/kg, 10 g averaged SAR is 0.7 W/kg, when PIFA is applied, for each case, SARs are 1.143 W/kg, 0.4866 W/kg. While the radiation pattern of the monopole antenna is symmetrical, that of planar structured antenna is asymmetrical and SAR caused by PIFA is less than SAR by the monopole antenna. The radiation efficiency of PIFA is 62.6%, which is higher than that of monopole, 53%.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.22 no.12
• /
• pp.29-35
• /
• 2008

In this paper, The author present a load current feed-forward compensator by method that improve voltage controller of Step-down Chopper to get stable output voltage to sudden change of load current. To confirm the characteristics of a presented load current feed-forward compensator compared each transfer function of whole system that load current feed-forward compensator is added with transfer function of whole system that existent voltage controller is included using Mason gains formula in Root locus and Bode diagram. As a result the pole of system is improved, extreme point of the wave and system improves, and size of peak value and phase margin of break frequency in resonance frequency confirmed that is good. Therefore, presented control technique could confirm that reduce influence by perturbation and improves stationary state and dynamic characteristics in output of Step-down Chopper.

• Proceedings of the Speleological Society Conference
• /
• 2001.06a
• /
• pp.3-29
• /
• 2001

파파리반딧불이(H papariensis)의 생태학적 특성을 규명하고자 서식처 환경, 개체군, 고도별 출현양상과 지역별 분포양상, 발광양상, 교미행동을 조사하였다. 춘천시 서면 지암리에서 H. papariensis 성충의 개체군 밀도를 1998년 5월부터 7월에 걸쳐 조사하였으며, 전체 채집 개체수는 703개체였다. 이중 수컷은 680개체, 암컷은 23개체를 채집하였다. 지암리에서 전체 출현기간은 50여 일로 추정되었다. 처음 출현한 날로부터 2주에서 3주 사이에 최대 정점을 나타내었으며, 이후 점진적으로 감소하는 출현양상을 나타내었다. 수컷 680개체중 47개체는 재 포획되었으며, 이로서 추정된 최대수명은 6일 이상, 평균수명은 3.26일로 나타났으며, 수컷과 암컷의 상대적인 성비는 27.5/l로 나타났다. 한국산 Hotaria속 반딧불이 2종의 고도별 출현 및 지역별 분포양상에 대하여 1999년 5월부터 7월까지 18개 지역을 선정하여 조사하였다. 전체 채집개체수는 1096개체였으며 이중 H. papariensis는 584개체, H unmunsana는 512개체였다 두 종은 제주도를 제외한 전 조사지역에서 공서 하고 있었으며 H. papariensis는 북쪽지역에 우세하게 분포하였고 H. unmunsana는 남쪽지역에 우세하게 분포하는 양상을 나타내었다. 성충 반딧불이의 최고 출현성기는 고도가 높아질수록 늦어지는 경향을 나타내었다. 고도별로 200m 이하 지역에서는 6월 초순에서 중순, 200-400m 지역에서는 6월 중순에서 말경, 400-600m 지역에서는 6월말 경부터 7월 초순, 600-800m 지역에서는 7월 초순부터 중순에 각각 최고 성기를 나타내었다. H. papariensis의 암컷과 수컷의 발광양상을 분석하고자 정지발광과 구애 발광을 구분하여 조사하였고 각각의 발광지속시간과 발광주기를 구분하여 측정하였다. 수컷의 발광지속시간은 정지발광(0.12초)보다 구애발광(0.17초)에서 1.4배 증가하였으며 암컷의 발광지속시간은 정지발광(0.15초)보다 구애발광(0.19초)에서 1.5배 증가하였다. 발광주기는 수컷에서 정지발광(1.26초)보다 구애발광(1.12초)에서 0.88배 감소하였고, 암컷에서 정지발광(2.99초)보다 구애발광(1.06초)에서 0.35배 감소하였다. 발광양상에서 발광주파수는 수짓의 정지발광에서 0.8 Hz, 수컷 구애발광에서 0.9 Hz, 암컷의 정지발광에서 0.3 Hz, 암컷의 구애발광에서 0.9 Hz로 각각 나타났다. H. papariensis의 발광파장영역은 400 nm에서 700 nm에 이르는 모든 영역에서 확인되었으며 가장 높은 첨두치는 600 nm에 있고 500에서 600 nm 사이의 파장대가 가장 두드러지게 나타났다. 발광양상과 어우러진 교미행동은 Hp system과 같은 결과를 얻었다.