• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.8
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• pp.45-51
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• 2007

We designed and fabricated the planar graded-gap injector GaAs Gm diodes with $1.6{\mu}m$ active length for operation at 94 GHz. The fabrication of the Gunn diode is based on MESA etching, Ohmic metalization, and overlay metalization. The measured negative resistance characteristics of the graded-gap injector GaAs Gunn diodes are examined for two different device structures changing the distance between the cathode and the anode electrodes. Also, we discuss the DC results under the forward and the reverse biases concerning the role of the graded-gap injector. It is shown that the structure having the shorter distance between the cathode and the anode electrode has higher peak current, higher breakdown voltage, and lower threshold voltage than those of the larger distance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.12 s.91
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• pp.1190-1198
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• 2004

In this paper, meander-line planar monopole antenna mounted on PCS/IMT-2000/WLAN handset for SAR reduction is designed. Frequency characteristics and SAR value optimized with various design parameters are analyzed and designed. Designed internal monopole antenna mounted on the handset is simulated. The 1 g and 10 g peak average SARs of internal monopole antenna are 0.656 and 0.387 W/kg respectively. And internal monopole antenna and external monopole antenna attached on the handset are tested. As a result, internal monopole antenna 1 g and 10 g peak average SARs are 0.686 and 0.356 W/kg. And external monopole antenna's results are 1.33 and 0.812 W/kg, respectively. So internal monopole antenna has a about $50\%$ SAR reduction in comparison with external monopole antenna.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.8
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• pp.754-760
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• 2011

Reconfigurable beam steering using microstrippatch antenna with U-slot is proposed for wearable fabric applications. The proposed antenna is manufactured on a fabric substrate, and designed to steer the beam directions at the operation frequency of 6.0 GHz. The U-shaped slot and the indirect feeding-techniques are utilized in designing the proposed antenna. By the configuration of two artificial switches($S_0$, $S_1$, $S_2$) in between the indirect feed and the antenna patch, the antenna has three beam directions. The maximum beam directions are steerable in the yz-plane(${\theta}=0^{\circ}$, $30^{\circ}$, $331^{\circ}$), and the overall HPBW is $115^{\circ}$. The measured peak gains are 6.11~6.69 dBi.

• Smart Structures and Systems
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• v.21 no.5
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• pp.561-569
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• 2018

Ground vibration is one of the most undesirable effects induced by blast operation in mountain tunnels, which could cause negative impacts on the residents living nearby and adjacent structures. The ground vibration effects can be well represented by peak particle velocity (PPV) and corner frequency ($f_c$) on the ground. In this research, the PPV and the corner frequency of the mountain surface above the large-span tunnel of the new Badaling tunnel are observed by using the microseismic monitoring technique. A total of 53 sets of monitoring results caused by the blast inside tunnel are recorded. It is found that the measured values of PPV are lower than the allowable value. The measured values of corner frequency are greater than the natural frequencies of the Great Wall, which will not produce resonant vibration of the Great Wall. The vibration effects of associated parameters on the PPV and corner frequency which include blast charge, rock mass condition, and distance from the blast point to mountain surface, are studied by regression analysis. Empirical formulas are proposed to predict the PPV and the corner frequency of the Great Wall and surface structures due to blast, which can be used to determine the suitable blast charge inside the tunnel.

• Korean Journal of Veterinary Research
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• v.34 no.2
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• pp.407-415
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• 1994

Present experiments were undertaken in order to find out the most available diagnostic method for acute pancreatitis. Experimental dogs were divided into experimental group and control group. The experimental dogs were laparotomized and their pancreatic ducts were ligated for the induction of pancreatitis. The control dogs were laparotomized only for comparison. In addition to the complete blood count, serum amylase and lipase activities, serum glucose, total protein and albumin contents were measured daily for 11 days after the operation. Fecal fat droplet count by Sudan III staining and fecal trypsin activity examination by x-ray film digetion test were also undertaken daily. The results obtained were summarized as follows; 1. Serum amylase activities of the experimental group increased to peak on the third day and returned to the preoperative values on the eighth day. 2. Serum lipase activities of the experimental group increased to peak on the first day and returned to the preopertive values within six to eight days. 3. Serum glucose contents of the experimental group showed significant increse only on the first day. 4. Serum albumin contents of the experimental group decreased significantly during the experimental period. Whereas those of the control group significantly decreased only on the first day. 5. The experimental group showed marked leukocytosis, neutrophilia, and lymphopenia for the first 5 or 8 days. Whereas the control group showed only neutrophilia for the first 3 days. 6. The results of fecal fat droplet count showed some diagnostic value on the third and fourth day in only one experimental dog(No 1). No significant changes in the fecal trypsin activity were noticed in all dogs. 7. Histopathologically. all dogs of experimental group showed changes of pancreatitis. However the degree of the pancreatic lesion was not pararell to the degree of the serum amylase or lipase activity changes.

• Transactions of the Society of Information Storage Systems
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• v.1 no.2
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• pp.169-174
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• 2005

Current information storage devices read/write data on the rotating disk. The axial vibration of a rotating disk should be suppressed for the successful operation of the device. Information storage devices widely used in these days adopt relatively thick disk which is stiff enough to suppress axial vibration under allowable limit. However, the thickness of the disk is going to be thinner and thinner as the small form factor of the devices is getting preferred by the consumer. In this study, a stabilizer system, which is composed with 8 air bearings, is proposed for suppressing the axial vibration of a $95{\mu}m$ thick PC disk in a non-contacting manner. The performance of the stabilizer system is simulated by numerical computation and then confirmed its results through a series of experiment. A thin and flexible disk has various vibration modes when it rotates in high speed. The stabilizer system generates positive as well as negative pressure due to the rotation of flexible disk so that the force due to the pressure distribution pushes and pulls rotating disk in a non-contacting manner. The balance between positive and negative pressure forces can be obtained by adjusting the area and the slope of the air bearing surface. The axial vibration of the flexible disk of 120mm diameter is suppressed successfully from over $1000{\mu}m$ to $30{\mu}m$ peak-to-peak value at the rotational speed of 5,000rpm.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.4
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• pp.34-41
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• 2009

In this paper we propose a new image encryption method which utilizes Complemented MLCA(Complemented Maximum Length Cellular Automata) based on IBCA(Intermediate Boundary CA) and 2D CAT(Cellular Automata Transform). The encryption method is processed in the following order. First, Complemented MLCA is used to create a PN (pseudo noise) sequence, which matches the size of the original image. And, the original image goes through a XOR operation with the created sequence to convert the image into Complemented MLCA image. Then, the gateway value is set to produce a 2D CAT basis function. The produced basis function is multiplied by the encrypted MLCA image that has been converted to process the encipherment. Lastly, the stability analysis and PSNR(Peak Signal to Noise Ratio) verifies that the proposed method holds a high encryption quality status.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.294-299
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• 2004

An assessment of a novel laser-electric hybrid propulsion system was conducted, in which a laser-induced plasma was induced through laser beam irradiation onto a solid target and accelerated by electrical means instead of direct acceleration only by using a laser beam. A fundamental study of newly developed rectangular laser-assisted pulsed-plasma thruster (PPT) was conducted. On discharge characteristics and thrust performances with increased peak current compared to our previous study to increase effects of electromagnetic forces on plasma acceleration. Maximum peak current increased for our early study by increasing electromagnetic effects in a laser assisted PPT. At 8.65 J discharge energy, the maximum current reached about 8000 A. Plasma behaviors emitted from a thruster in various cases were observed with an ICCD camera. It was shown that the plasma behaviors were almost identical between low and high voltage cases in initial several hundred nanoseconds, however, plasma emission with longer duration was observed in higher voltage cases. Canted current sheet structures were also observed in the higher voltage cases using a larger capacitor. With a newly developed torsion-balance type thrust stand, thrust performances of laser assisted PPT could be estimated. The impulse bit and specific impulse linearly increased. On the other hand, coupling coefficient and the thrust efficiency did not increase linearly. The coupling coefficient decreased with energy showing maximum value (20.8 ？Nsec/J) at 0 J, or in a pure laser ablation cases. Thrust efficiency first decreased with energy from 0 to 1.4 J and then increased linearly with energy from 1.4 J to 8.6 J. At 8.65 J operation, impulse bit of 38.1 ？Nsec, specific impulse of 3791 sec, thrust efficiency of 8 %, and coupling coefficient of 4.3 ？Nsec/J were obtained.

• Korean Journal of Optics and Photonics
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• v.27 no.3
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• pp.95-100
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• 2016

High-power quasi-continuous-wave (qcw) operation in Yb-doped double-clad fiber lasers with near-diffraction-limited quality of the output beam is reported. Based on numerical simulation, we built a simple, all-fiberized Yb fiber laser, and a fiber-based master-oscillator power amplifier (MOPA). Both laser systems have successfully produced qcw output with average power greater than 150 W at 1080 nm and 10 ms pulse duration at 10 Hz repetition rate, corresponding to a peak power greater than 1.5 kW for 205 W of pump power at 976 nm. Laser performance, including beam quality and slope efficiency, was characterized in both configurations. Prospects for power scaling and applications are discussed.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.1
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• pp.94-101
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• 1999

In this paper the problems associated with the switching surge of PWM inverter devices were analysed. As the application of ASD for efficient speed control of AC rmtors is increased, so is the rrntor and ASD-related failure increased. In the industrial rmtor awlications, the introduction of PWM drives can sometmes cause insulation breakdown between the phase windings due to high transient voltage peak. The motor cable length combined with the high switching frequency becomes more sensitive issue for proper drive operation. Effects of the cable length and high switching frequency influence both on rmtor and inverter. When the insulation level of rmtor winding is low, the failure probability caused by high peak voltage and fast voltage rise times(dv/dt) is high. Voltage refloctions are simulated far rmtor capacities, ASD and rise times and are presented graphically. The filtering techniques are discussed to reduce the rmtor terminal overvoltage and dv/dt in inverter fed AC rrntor drive systems. We confirmed that the lower motar capacity and rmtar insulation level, the shorter switching time and cable length and the higrer the probability of insulation breakdown .kdown .