• Journal of electromagnetic engineering and science
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• v.4 no.3
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• pp.107-112
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• 2004

In this paper, the phase noise of 900 MHz VCO is improved using modified strip line square ring resonator. In order to demonstrate the phase noise improvement of the proposed VCO, the same circuit was manufactured using shorted-circuit resonator. In condition of the same bias current, the phase noise of the proposed VCO with modified square ring resonator is suppressed by 7 dB as - 103 dBc/Hz at 100 kHz offset compared to the conventional VCO with short-circuit resonator. From the proposed VCO, we achieved output power of - 4.8 dBm, harmonics suppression of 16 dB, and tuning bandwidth of 100 MHz. The proposed VCO consumed 5 mA at 3 V, and its size is 1.2 cm ${\times}$ 1.0 cm.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.297-300
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• 2002

In this study, the deformation of the free surface motion of a magnetic fluid for the change in electromagnetic force is discussed and carried out theoretically and experimentally on the basis of Rosensweig Ferrohydrodynamic Bernoulli Equation. While applied magnetic fields are induced by 4$\times$4 electromagnet located under the magnetic fluid, the surface of the magnetic fluid is formed the balance of surface force, gravity, pressure difference, magnetic normal pressure and magnetic body farce. In case, magnetic fluid in characteristics of fluid adjusted to the opposite direction of the gravity direction. thus, the device of a magnetic fluid proposed the surface actuator. The device of surface deformation as well comparison between numerical simulation and experiments as will be presented.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2002.11a
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• pp.182-185
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• 2002

A RE predistorted asymmetric Doherty amplifier for CDMA IS-95 signal has been fabricated using GaAs FETs. The Doherty amplifier used a Class AB main device and a Class C auxiliary device. At 6 ㏈ back-of from Pl ㏈ of 34 ㏈m, PAE of 27% was measured. This Doherty amplifier has higher PAE than Class AB for over 20 dB range of pout power. A RF predistortion linearizer is applied to the Doherty amplifier to improve the IMD cancellation performance. The 3rd order IMD cancellation of 12.2 ㏈ was achieved at output power of 18 ㏈m.

• Journal of electromagnetic engineering and science
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• v.9 no.1
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• pp.32-37
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• 2009

Various Class-E CMOS power amplifiers for GSM applications are presented. A stage-convertible transformer for a dual mode power amplifier is proposed to increase efficiency in the low-output power region. An integrated passive device(IPD) process is used to reduce combiner losses. A split secondary 1:2 transformer with IPD process is designed to obtain efficient and symmetric power combining. A quasi-four-pair structure of CMOS PA is also proposed to overcome the complexities of power combining.

• Journal of electromagnetic engineering and science
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• v.8 no.1
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• pp.17-22
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• 2008

It is presented that sampling rates for behavioral modeling of quasi-memory less nonlinear devices can be far less than the Nyquist rate of the input signal. Although it has been believed that the sampling rate of nonlinear device modeling should be at least the Nyquist rate of the output signal, this paper suggests that far less than the Nyquist rate of the input signal can be applied to the modeling of quasi-memoryless nonlinear devices, such as frequency multipliers. To verify, a QPSK signal at 820 MHz were applied to a frequency tripler, whereby the device can be utilized as an up-converting mixer into 2.46 GHz with the aid of digital predistortion. AM-AM, AM-PM and PM-PM can be successfully measured regardless of sampling rates.

• Journal of Power Electronics
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• v.19 no.3
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• pp.744-750
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• 2019

A new type of auto-rotary PM mechanical flux-varying PM machine (ARPMMFVPMM) is proposed in this paper, which can overcome the problem where the air-gap magnetic field of a PM machine is difficult to freely adjust. The topology structures of the machine and the mechanical flux-adjusting device are given. In addition, the operation principle of flux-adjusting is analyzed in detail. Furthermore, the deformation of a spring with the speed variation is obtained by virtual prototype technology. Electromagnetic characteristics including the flux distribution, air gap flux density, flux linkage, electromagnetic-magnetic-force (EMF), and flux weakening ability are computed by 2D finite element method (FEM). Results show that the machine has some advantages such as the good field control ability.

• Journal of Korea Foundry Society
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• v.25 no.4
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• pp.156-160
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• 2005

There are many factors that influence solidification behavior during continuous casting, e.g. include superheat, casting speed, cooling rate and holding time. However, when melt is stirred by electromagnetic force, there would be some changes in its solidification behavior compared to that of the ordinary casting process. In this study, the billets of A356 alloy with a diameter of 3 inch were fabricated with electromagnetic stirring under various conditions of superheat, casting speed and input voltage of electro magnetic stirring (EMS) device. The microstructure was also investigated under the various casting conditions and electromagnetic input voltages. When increase in input voltage, the microstructure was changed from dendritic to rosette type and finally to spheroidal. With pouring temperature, casting speed and electromagnetic input voltage were $650^{\circ}C$, 100 mm/min and 140 V, respectively, the billet with a diameter of 3 inch, which has a uniform dispersed spheroidal particles in the whole area of billet except for the surface area, was manufactured.

• Journal of electromagnetic engineering and science
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• v.13 no.1
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• pp.54-61
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• 2013

An equivalent model has been developed to estimate the electromagnetic immunity for integrated circuits under a complex electromagnetic environment. The complete model is based on the characteristics of the equipment and physical configuration of the device under test (DUT) and describes the measurement setup as well as the target integrated circuits under test, the corresponding package, and a specially designed printed circuit board. The advantage of the proposed model is that it can be applied to a SPICE-like simulator and the immunity of the integrated circuits can be easily achieved without costly and time-consuming measurements. After simulation, measurements were performed to verify the accuracy of the equivalent model for immunity prediction. The improvement of measurement accuracy due to the added effect of a bi-directional coupler in the test setup is also addressed.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1140-1143
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• 2009

Organic Vapor Phase Deposition (OVPD) equipment enables the accurate and simultaneous control of deposition rates of multiple materials as well as their homogenous mixing in the gas phase. Graded or even cross-faded layers by varying carrier gas flow are options to improve OLED performances. As example, we will show how the efficacies of standard red phosphorescent OLEDs with sharp interfaces can be increased from 18.8 cd/A and 14.1 lm/W (1,000 cd/$m^2$) to 36.5 cd/A (+94 %, 18 % EQE) and 33.7 lm/W (+139 %) by the introduction of cross-fading, which is a controlled composition variation in the organic film.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.835-837
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• 2002

This paper presents a shape optimization algorithm of electromagnetic devices using the design sensitivity analysis with FEM. The design sensitivity and adjoint variable formulas are derived for the 3D FEM with edge element. This algorithm is applied to 3D electro-magnet pole shape optimization problem to make a uniform flux density at the target region.