• Korean Journal of Materials Research
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• v.17 no.7
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• pp.386-389
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• 2007

The dielectric properties of $(Ba_{0.5}Sr_{0.5})TiO_3$ ferroelectric thin films have been investigated according to the substrates in order to optimize the their properties. MgO, r-plane sapphire, and poly-crystalline sapphire (Alumina) substrates have been used to deposite $(Ba_{0.5}Sr_{0.5})TiO_3$ ferroelectric thin films by RF magnetron sputtering. The BST thin films deposited on the single crystal (100)MgO substrates have high tunability and low dielectric loss. These results are caused by a low misfit between the lattice parameters of the BST films and the substrate. The BST films deposited on r-plane sapphire have relatively high misfit, and the tunability of 17% and dielectric loss of 0.0007. To improve the dielectric properties of the BST films, the post-annealing methods has been introduced. The BST films deposited on (100)MgO, (1102)r-plane sapphire, and poly-crystalline sapphire substrates have best properties in post-annealing conditions of $1050^{\circ}C$, $1100^{\circ}C$, and $1150^{\circ}C$, respectively. The different optimal post-annealing conditions have been found according to the different misfits between the films and substrates, and thermal expansion coefficients. Moreover, the films deposited on alumina substrate which is relatively cheap have a good tunability properties of 23% by the post-annealing.

• Journal of Advanced Navigation Technology
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• v.10 no.3
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• pp.198-204
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• 2006

In this paper, TE(transverse electric) scattering problems by a resistive strip grating on a grounded dielectric plane according to the strip width and grating period, the relative permittivity and thickness of dielectric layer, and incident angles of a TE plane wave are analyzed by applying the FGMM(Fourier-Galerkin Moment Method) known as a numerical procedure. The induced surface current density is simply expanded in a Fourier series by using the exponential function as a simple function. The reflected power gets increased according as the relative permittivity and thickness of dielectric multilayers gets increased, the sharp variations of the reflected power are due to resonance effects were previously called wood's anomallies[7]. To verify the validity of the proposed method, the numerical results of normalized reflected power for the uniform resistivity R = 0 as a conductive strip case show in good agreement with those in the existing paper.

• Journal of Advanced Navigation Technology
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• v.15 no.3
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• pp.349-354
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• 2011

In this paper, H-polarized scattering problems by a resistive strip grating with zero resistivity at strip-edges over a grounded dielectric plane according to the strip width and grating period, the relative permittivity and thickness of a dielectric layer, and incident angles of a transverse electric (TE) plane wave are analyzed by applying the Fourier-Galerkin Moment Method (FGMM). The tapered resistivity of resistive strips has zero resistivity at strip edges, then the induced surface current density on the resistive strip is expanded in a series of Chebyshev polynomials of the second kind as a orthogonal ploynomials. The sharp variations of the reflected power are due to resonance effects were previously called wood's anomallies, the numerical results for the reflected power are compared with those of uniform resistivity in the existing papers.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.6
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• pp.91-98
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• 2004

This paper proposes a PCB plane model for generic SPICE circuit simulators. The proposed model reflects two frequency-dependent losses, namely skin and dielectric losses. After power/ground plane pair is divided into arrays of unit-cells, each unit-cell is modeled using a transmission line and two loss models. The loss model is composed of a resistor for DC loss, series HL ladder circuit for skin loss and series RC ladder circuit for dielectric loss. To verify the validity of the proposed model, it is compared with SPICE ac analysis using frequency-dependent resistors. Also, we show that the estimation results using the proposed model have a good correlation with that of VNA measurement for the typical PCB stack-up structure of general desktop PCs. With the proposed model, not only ac analysis but also transient analysis can be easily done for circuits including various non-linear/linear devices since the model consists of passive elements onl.

• Journal of Advanced Navigation Technology
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• v.15 no.4
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• pp.543-548
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• 2011

In this paper, H-polarized electromagnetic scattering problems by a resistive strip grating over a grounded dielectric plane according to the strip width and grating period, the relative permittivity and thickness of a dielectric layer, and incident angles of a TE (transverse electric) plane wave are analyzed by applying the FGMM (Fourier-Galerkin Moment Method). The tapered resistivity of resistive strips in this paper varies from finite resistivity at one edge to zero resistivity at the other edge, then the induced surface current density on the resistive strip is expanded in a series of Jacobi polynomials of the order ${\alpha}=1$, ${\beta}=0$ as a kind of orthogonal polynomials. The numerical results of the normalized reflected power show in good agreement with those of existing papers.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.5
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• pp.1005-1010
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• 2011

The accidents caused by dielectric instability have been increasing in power grid. It is important to enhance the dielectric reliability of a high voltage apparatus to reduce the damage from electrical hazards. To develop an electrically reliable high voltage apparatus, the experimental study on the electrical breakdown field strength is indispensable, as well as theoretical approach. In this paper, the lightning impulse breakdown characteristics considering utilization factors are studied for the establishment of insulation design criteria of an high voltage apparatus. The utilization factors are represented as the ratio of mean electric field to maximum electric field. Dielectric experiments are performed by using several kinds of sphere-plane electrode systems made of stainless steel. As a result, it is found that dielectric characteristics are affected by not only maximum electric field intensity but also utilization factors of electrode systems. The results are expected to be applicable to designing the air-insulated high voltage apparatuses.

• Journal of the Korean Ceramic Society
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• v.51 no.1
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• pp.32-36
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• 2014

The effects of an amphiphilic agent and the orientation of BN on the microwave dielectric properties of BN / polyvinyl butyral (PVB) composites were investigated as a function of the BN content in volume fractions from 0.1 to 0.5 ($V_f$). The plate-shaped BN samples were oriented in the PVB matrix by physical processes, in this case tape casting and laminate methods. With an increase in the BN content, the dielectric constant (K) increased because the K of BN was higher than that of the PVB. At the same BN content, composites with an in-plane orientation of the BN showed a higher dielectric constant than that of composites with a transverse orientation of the BN because the ceramics were oriented parallel to the electric field. All of the composites showed nearly constant K values ranging from 1 to 9.4 GHz, indicating good frequency stability over a wide frequency range. At the same frequency, the K values of the composites increased with an increase in the BN content.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2009.05a
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• pp.270-272
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• 2009

This paper presents a basic data of the surface discharge characteristics for solid dielectric under non-uniform field in $N_2/O_2$ mixture gas. Used electrodes are needle and plane. Used solid dielectric is expoxy resin. With the variation of the mixture rates of the gas by 80[%]:20[%], 60[%]:40[%] and 40[%]:60[%] in same condition, we can obtain different surface dielectric strength. Increased Pressure and thickness caused increased surface dielectric strength.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.648-651
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• 2004

Pb0.5Sr0.5TiO3(PST) thin films were deposited on the LaNiO3 (LNO(100))/Si and Pt/Ti/SiO2/Si substrates by the alkoxide-based sol-gel method. Structural and dielectric properties of PST thin films for the tunable microwave device applications were investigated. The PST films, which were directly grown on the Pt/Ti/SiO2/Si substrates showed the random orientation. For the LNO/Si substrates, the PST thin films exhibited highly (100) orientation. Compared with randomly oriented films, the highly (100)-oriented PST thin films showed better dielectric constant, tunability, and figure of merit (FOM). The dielectric constant, tunability, and FOM of the highly (100)-oriented PST thin film increased with increasing annealing temperature due to the decrease in lattice distortion. The differences in dielectric properties may be attributed to the change in the film stress and the in-plane oriented Polar axis depending on the substrate was used. The dielectric constants, dielectric loss and tunability of the PST thin films deposited on the LNO/Si substrates measured at 1 MHz were 483, 0.002, and 60.1%, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.3
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• pp.305-310
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• 2004

We have studied the optimal phase retardation value of a homogeneously aligned liquid crystal (LC) driven by fringe-field when using the LC with positive dielectric anisotropy. In general, the transmittance of a homogeneous aligned LC cell under crossed polarizer is maximum when a twist angle of LC by in-plane rotation is 45$^{\circ}$ with polarizer and the cell retardation becomes λ/2. However, the device using the LC with positive dielectric anisotropy does not follow this since the degree of rotation of the LC is dependent on electrode position and in addition the LCs tilt up along the fringe-field. At the center of common and pixel electrode, the LC is most twisted around a middle position of a cell whereas at the edge position of pixel electrode, the LC is most twisted near bottom surface of a cell. Consequently, the optimal phase retardation of the device becomes much larger than λ/2 and the transmittance can be described using the combination of the in-plane switching and twisted nematic mode.