• Proceedings of the IEEK Conference
• /
• 2002.07b
• /
• pp.735-738
• /
• 2002

This paper a new simple PWM (Pulse Width Modulation) signal generation based on modified relaxation oscillator is introduced. Its advantages of the proposed principle are that the precise PWM signal can be easily achieved with a high frequency range up to several megahertz and a low-voltage power supply. The proposed circuit can accept either voltage or current modulating signal. It is very suitable for developing into Integrated Circuits (ICs) form in communication applications. The simulation and experimental results are also depicted, they shown good agreement with theoretical anticipation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1997.11a
• /
• pp.177-181
• /
• 1997

A new piezoelectreic transformer is proposed as a key device for high power transimssion. The piezoelectric transformer made of lead titanate solid solution creamic is operated with a thickness extensional vibration mode. This transformer can operate at high frequency aver several megahertz with about 90% high efficiency.

• Journal of Power Electronics
• /
• v.9 no.2
• /
• pp.180-187
• /
• 2009

When converters operate in megahertz range, the passive components and magnetic devices generate high losses. However, the eddy current issues and choices of magnetic cores significantly affect on the design stage. Apart from that, the components' reduction, miniaturization technique and frequency scaling are required as well as improvement in thermal capability, integration technique, circuit topologies and PCB layout optimization. In transformer design, the winding and core losses give great attention to the design stage. From simulation work, it is found that E-25066 material manufactured by AVX could be the most suitable core for high frequency transformer design. By employing planar geometry topology, the material can generate significant power loss savings of more than 67% compared to other materials studied in this work. Furthermore, young researchers can use this information to develop new approaches based on concepts, issues and methodology in the design of magnetic components for high frequency applications.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.07a
• /
• pp.869-872
• /
• 2000

The aim of present work was to fabricate the piezoelectric composite materials of low megahertz applications such as non-destructive testing of materials. Among all the various composites, those with PZT rods embedded in Spurrs epoxy with regular periodicity (1-3 connectivity) was fabricated by dice and fill method. The fabricated size of the PZT cell were 0.18X0.18, 0.28X0.28mm$^2$, respectively. And the volume ratio of the PZT cell were 52, 64%, respectively. The resonant frequency and anti-resonant frequency of the composites were 3.5 MHz and 4.3MHz, respectively. The piezoelectric coupling coefficient were about 38 and 37% and the mechanical quality factor were about 12.7 and 22. These value were very different from these of bulk PZT Plate.

• Journal of the Korean institute of surface engineering
• /
• v.50 no.5
• /
• pp.392-397
• /
• 2017

The Young's modulus of a nanoscale titanium (Ti) thin-film was evaluated using a high-speed microcantilever resonating at the megahertz frequency in the present study. A 350 nm thick Ti film was deposited on the surface of a silicon microcantilever, and the morphology of the film was analyzed using the atomic force microscopy. The microcantilever was excited to resonate using an ultrasonic pulser that generates tone burst signals and the resonance frequency shift induced by the deposition of Ti was measured using a Michelson interferometer. The Young's modulus was determined through a modal analysis using the finite element method and the result was validated by the nanoindentation testing, showing good agreement within a relative error of 1.0%. The present study proposes a nanomechanical characterization technique with enhanced accuracy and sensitivity.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.41 no.6
• /
• pp.483-489
• /
• 2017

An ultrasonic technique was developed to characterize the resonance behavior of a microcantilever operating in a megahertz regime. A high-power ultrasonic pulser and a contact transducer were employed to excite the silicon microcantilever, and a Michelson interferometer was used to obtain the time domain waveform. The natural frequency of the microcantilever was evaluated through the fast Fourier transform of the signal, and a numerical analysis using the finite element method confirmed the measurement data. The present study proposes a novel and facile method to evaluate nanoscale materials and structures with high sensitivity compared to conventional approaches.