• Interaction and multiscale mechanics
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• v.6 no.1
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• pp.15-29
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• 2013

Phononic system composed of periodical elastic structures exhibit band gap phenomenon, and all elastic wave cannot propagate within the band gap. In this article, we consider one-dimensional binary materials which are periodically arranged as a 20-layered medium instead of infinite layered system for phononic system. The layered medium with finite dimension is subjected to a uniformly distributed sinusoidal loading at the upper surface, and the bottom surface is assumed to be traction free. The transient wave propagation in the 20-layered medium is analyzed by Laplace transform technique. The analytical solutions are presented in the transform domain and the numerical Laplace inversion (Durbin's formula) is performed to obtain the transient response in time domain. The numerical results show that when a sinusoidal loading with a specific frequency within band gap is applied, stress response will be significantly decayed if the receiver is away from the source. However, when a sinusoidal force with frequency is out of band gap, the attenuation of the stress response is not obvious as that in the band gap.

• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.217-220
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• 2004

This paper presents design simulation, implementation, and measurement of a miniaturized GPS/K-PCS dual-band LTCC chip antenna for mobile communication handsets. The dimension of LTCC chip antenna is $9mm{\times}15mm{\times}1.2mm$. The lower meander type antenna is to be tuned to the lower frequency (GPS) band and the upper meander antenna with via hole connection is to contribute the higher frequency (K-PCS) band. In order to lowering the resonant frequency for GPS band, two printed modified meander antenna with gap stub is used to integrate with PCS band operation. The measured resonant frequency at GPS band shifts to lower frequency about 100MHz. The measured impedance bandwidth(VSWR $\leq$ 2) are 55MHz and 120MHz at the resonant frequency. respectively.

• Korean Journal of Materials Research
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• v.4 no.2
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• pp.227-232
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• 1994

Diamondlike carbon thin film has been fabricated with low discharging frequency, 450KHz by plasma enhanced chemical vapor deposition. Its physical properties such as optical band gap, microhardness and internal stress have been compared with 13.56MHz film. Optical band gap of 450KHz DLC thin film was less than 13.56MHz film and it was found that C-H bond concentration and total hydrogen contents in the film decreased greatly as the result of FT-IR and CHN analysis. Also, when DLC thin film was fabricated with low discharging frequency, it was expected that the adhesion of the film to the substrate was improved by the great decrease of internal stress without any considerable decrease of microhardness.

• Journal of electromagnetic engineering and science
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• v.15 no.2
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• pp.111-114
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• 2015

In this paper, we have proposed dual-band Phi-shaped slot gap filler antenna for satellite internet service applications. Some properties of the antenna such as return loss, radiation pattern, and gain have been simulated and measured. The proposed antenna has a Phi-shaped slot on the circular patch and is fabricated on the TLX-9 substrate. The radius of the circular patch is 25 mm, and it has a coaxial feeding structure. The dual-band Phi-shaped slot gap filler antenna has high-gain, small-size, simple-structure, and good radiation patterns at each band. The operating frequency band can be tuned by adjusting the length AL and FL of the Phi-shaped slot.

• Electrical & Electronic Materials
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• v.7 no.6
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• pp.490-495
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• 1994

We investigated photoreflectance of semi-insulating GaAs with respect to modulation sources, that is, modulation beam intensity, modulation frequency, temperature, and thickness of sample. PR spectra by each modulation source turned out to be signals of low electric field third differential, and band gap values of sample were fitted by least square root method for Aspnes' theoretical equation.

• Journal of Power Electronics
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• v.18 no.4
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• pp.985-996
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• 2018

The implementation and performance evaluation of an interleaved boundary conduction mode (BCM) boost power factor correction (PFC) converter is presented in this paper by employing three wide band-gap switching devices: a super junction silicon (Si) MOSFET, a silicon carbide (SiC) MOSFET and a gallium nitride (GaN) high electron mobility transistor (HEMT). The practical considerations for adopting wide band-gap switching devices to BCM boost PFC converters are also addressed. These considerations include the gate drive circuit design and the PCB layout technique for the reliable and efficient operation of a GaN HEMT. In this paper it will be shown that the GaN HEMT exhibits the superior switching characteristics and pronounces its merits at high-frequency operations. The efficiency improvement with the GaN HEMT and its application potentials for high power density/low profile BCM boost PFC converters are demonstrated.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.1
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• pp.13-19
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• 2004

This paper demonstrates the detailed study of a microstrip Yagi-Uda antenna with and without PBG structure at wireless LAN(5725∼5825 MHz) frequency band. The impedance bandwidth of the antenna with the PBG holes is greater than (about 30 MHz) that of its counter part without PBG holes. The measured gains of the antenna at the frequency band are 7 dB and 6 dB respectively for antenna with and without PBG. The improvement of gain of about 1 dB is likely due to the suppression of surface wave.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.10
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• pp.945-948
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• 2016

Recent premium smartphones commonly employ a metal frame and this trend is currently spreading over mid-range smartphones. However, the metal frame becomes a good coupling path of electromagnetic noises emitted from digital components in smartphones and then increases radio-frequency interference(RFI) to RF antennas located at top and bottom sides of smartphones. This paper proposed a metal frame with EBG(Electromagnetic Band Gap) structure to reduce the noise coupling to antenna by suppressing surface wave on the metal frame. By simulation, it is confirmed that the proposed metal frame with $7{\times}6$ mushroom-type EBG array pattern with multi-via can reduce the noise coupling to RF antenna by about 20 dB.

• Journal of information and communication convergence engineering
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• v.16 no.3
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• pp.197-202
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• 2018

This paper reveals the impact of the insertion of electromagnetic band gap (EBG) structures on the performance of circularly polarized (CP) patch-slot antenna with offset slot. Several optimizations are necessary to precise physical parameters in the aim to fix the resonance frequency at 3.2 GHz. The proposed antenna possesses lightweight, simplicity, low cost, and circular polarization ensured by two feeding sources to permit right-hand and left-hand circular polarization process (RHCP and LHCP). The measured results compared with simulation results of the proposed circularly polarized EBG antenna with offset slot show good band operations with –10 dB impedance bandwidths of 9.1% and 36.2% centered at 3.2 GHz, which cover weather radar, surface ship radar, and some communications satellites bands. Our investigation will confirm the simulation and experimental results of the EBG antenna involving new EBG structures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.195-198
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• 1999

A technique is investigated for achieving broadband properties by controlling the operation frequency of microstrip antennas. The control is achieved by applying DC bias to the microstrip antenna. Air gap antenna with PZT post is fabricated. by using in C-band. In the case of Air gap antenna, the variation of center frequency was about 16Mhz and the bandwidth was increased up to 123.3% at 15dB, 160.7% at 20dB than before applying DC bias respectively. The change property of frequency in air gap antenna is nearly the same the C-V property in PZT.