• Journal of Magnetics
• /
• 제17권1호
• /
• pp.42-45
• /
• 2012

We have developed an alternating magnetic field stimulation system consisting of a switched-mode power supply and a digital control circuit which modulates a duty ratio to maintain a magnetic field intensity of a few mT even while the frequency increases up to 4 kHz with a controllable coil temperature below $30^{\circ}C$ in air. This duty ratio modulation and water circulation are advantageous for cell culture under ac-magnetic field stimulation by preventing the incubator from exceeding a cell-viable temperature of $37^{\circ}C$. Although the temperature of the coil when subjected to a sinusoidal voltage rapidly increased, that of our system modulated by the duty factor did not change. This is a potentially valuable method to investigate the effects of intermediate frequency magnetic field stimulation on biological entities such as cells, tissues and organs.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2011년도 전력전자학술대회
• /
• pp.444-446
• /
• 2011

A bidirectional dual active converter with the power factor control capability is proposed as a battery charger. The source side half-bridge acts as a PWM converter that maintains the unity power factor. The battery side half-bridge converter acts as a dual active bridge (DAB) together shares the same DC link voltage with PWM converter. The imbalance voltage phenomenon is eliminated by employing asymmetric duty cycle technique. Simulation results are included to verify theoretical analysis.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2015년도 전력전자학술대회 논문집
• /
• pp.195-196
• /
• 2015

This paper investigates the design of coupled inductor for minimum inductor current ripple in rapid traction battery charger systems. Based on the general circuit model of coupled inductor together with the operating principles of dc-dc converter, the relationship between the ripple size of inductor current and the coupling factor is derived under the different duty ratio. The optimal coupling factor which corresponds to a minimum inductor ripple current becomes -0.5, i.e. a complete inverse coupling without leakage inductance, as the steady-state duty ratio operating point approaches 1/3 or 2/3. In an opposite manner, the optimal coupling factor value of zero, i.e. zero mutual inductance, is required when the steady-state duty ratio operating point approaches either zero or one. Coupled inductors having optimal coupling factor can minimize the ripple current of inductor and battery current resulting in a reliable and efficient operation of battery chargers.

• 한국생산제조학회지
• /
• 제24권3호
• /
• pp.314-319
• /
• 2015

Invar is a compound metal of Fe-Ni system contained 36.5% Ni. The characteristic of invar is that the coefficient of thermal expansion is $1.0{\times}10^{-6}cm/^{\circ}C$. It is approximately 10 times smaller than series of steel. Because of this low thermal expansion characteristic of Invar, it is used to shadow mask of display device such as UHDTV or OLED TV. In this study, pulse current from pulse generator instead of DC current is used to overcome the disadvantages of the conventional electrochemical machining. Pulsed current with different duty factor in PECM affect the precise geometry. Pulse electrochemical machining is conducted to machine the micro hole to the invar sheet with different duty factor. The machined shape and overcut of invar sheet with different duty factor is observed by optical microscope and scanning electron microscope (SEM).

• 한국정밀공학회지
• /
• 제14권9호
• /
• pp.80-89
• /
• 1997

Die sinking electrical discharge machining(EDM) was conducted for ceramic composite of 33 weight percent TiC based on AI$_{2}$O$_{3}$ ceramic matrix according to the change of current and duty factor(DF). Material removal rate(MRR) was increased as the current and the duty factor increased, but better surface mor-pholoty was obtained in the region of lower current and duty factor. From the scanning electron microscopy(SEM) photographs and the energy dispersive X-ray spectroscopy(EDX) of the EDMed surface, EDM trace formed by one discharge spark was analyzed. Although the bending strength after EDM was highly decreased, reliability obtained by weibull analysis was increased twice. The bending strength was recovered or more by barrel polishing after EDM. From the FEM analysis of temperature for one spark, the possible melting region of AI$_{2}$O$_{3}$and TiC was obtained.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1997년도 춘계학술대회 논문집
• /
• pp.827-831
• /
• 1997

Conductive veramic matrix composite(CMC) workpiece of TiC 33%/Al /sab 2/O /sab 3/ 66% Y /sab 2/ O /sab 3/ was machined by die sinking electrical discharge machining(EDM) according to different pulse duration and suty factor for reverse polarity of electrode. Material removal rate(MRR) was examined by process under various operating conditions. The surface morphology was evaluated by surface roughness values and scanning electron microscopy(SEM) research. The more MRR was obtained according to increase pulse duration and duty factor. Also the maximum surface roughness(Rmax) of EDMed surface was slightly changed with increased pulse duration and duty factor. The SEM photographs of EDMed surface showed wide recast wide recast distribution region of melting materials in purse duration 0.130(ms) than 0.048(ms).

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1996년도 춘계학술대회 논문집
• /
• pp.3-7
• /
• 1996

Metal Matrix Composite(MMC) material of 30% SiC particulate based on A1 matrix was machined by drilling and Electrical Discharge Machining (EDM) processes. When drilling process was executed, surface fracture due to brittle property near the bottom was found. It was also found the possiblity of difficult shape of EDM process for MMC material, but few the research about basic EDM characteristics. Material Removal Rate(MRR) was examined for different conditions and the surface morphology was evaluated by roughness values and Scanning Electron Microscopy(SEM) research. The higher the current is, the more MRR was obtained but the higher MRR was showed around 0.45 duty factor. The average roughness of EDMed surface was slightly changed with increased pulse current and increases with duty factor. The SEM photographs of EDMed surface showed recast region after melting.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2017년도 전력전자학술대회
• /
• pp.88-89
• /
• 2017

This paper investigates the design of multi-winding coupled inductor for minimum inductor current ripple in rapid traction battery charger systems. Based on the general circuit model of multi-winding coupled inductor together with the operating principles of dc-dc converter, the relationship between the ripple size of inductor current and the coupling factor is derived under the different duty ratio. The optimal coupling factor which corresponds to a minimum inductor ripple current becomes -(1/n-1), i.e. a complete inverse coupling without leakage inductance, as the steady-state duty ratio operating point approaches 1/n, 2/n, … or (n1)/n. In an opposite manner, the optimal coupling factor value of zero, i.e. zero mutual inductance, is required when the steady-state duty ratio operating point approaches either zero or one.

• 센서학회지
• /
• 제29권3호
• /
• pp.149-155
• /
• 2020

In this study, we employed Manchester code for illumination control and flicker prevention of the light-emitting diode (LED) used in a visible light communication (VLC) system. In the VLC transmitter, the duty factor of the Manchester code was utilized for illumination control; in the VLC receiver, the spike signal from an RC-high pass filter was utilized to recover the transmitted signal whilst suppressing the 120-Hz noise arising from adjacent lighting lamps. Instead of the clock being transmitted in a separate channel, a syncmark signal was transmitted in front of each data byte and used as the reference time for transforming the Manchester code to non-return-to-zero (NRZ) data in the receiver. In experiments, the LED illumination was controlled in the range of approximately 12-84% of the constant wave (CW) light via changing of the duty factor from 10% to 90%. This scheme is useful for constructing indoor wireless sensor networks using LED light that is flicker-free and presents capability for illumination control.

• 센서학회지
• /
• 제30권4호
• /
• pp.196-203
• /
• 2021

In this study, an optical identification system was developed, wherein visible light is used to transmit the interrogating signal, and infrared is used to send the response signal. In the reader, visible light from a light emitting diode (LED) array was modulated via modified pulse width modulation for flicker-free illumination and dimming control. Moreover, the duty factor of the dimming control time was employed to control the illumination from the LED. In the transponder, the spike signal in the output of the high-pass filter was utilized to recover the interrogating signal while preventing interference from the 120-Hz noise from adjacent lighting lamps. The illumination was controlled in 26-86% range of the constant wave LED illumination by changing the duty factor from 20% to 90%. This configuration is advantageous for the construction of optical identification systems for automatic security check and car fare calculation at toll gates or parking facilities.