• Journal of the Korean Ceramic Society
• /
• v.40 no.8
• /
• pp.715-719
• /
• 2003

The Aerosol Deposition (AD) process will be proposed as a new fabrication technology for the integrated RF modules. $\alpha$-A1$_2$O$_3$ thick films were successfully grown on glass and Al substrates at room temperature by the AD process. Relative dielectric permittivity and loss tangent of the $Al_2$O$_3$ thick films on Al showed 9.5 and 0.005, respectively. To form microstrip lines on aerosol-deposited A1903 thick films, copper electroplating and lithography processes were employed, and the square-type cross section with sharp edges could be obtained. Low-pass LC filters with 10 GHz cutoff frequency were simulated by an electromagnetic analysis, exhibiting the validity of the AD process as a fabrication technology f3r integrated RF modules.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2005.03a
• /
• pp.499-506
• /
• 2005

지반오염조사에 대한 유전상수 측정기법의 적용성을 평가하기 위하여 중금속 오염도에 따른 흙의 유전특성 변화를 분석하였다. 유전상수의 실수부와 허수부 모두 체적함수비에 따른 증가경향을 나타내었으며, 특히 MHz 범위에서 유전상수 실수부는 쌍극자모멘트에 비례하기 때문에 흙의 유전상수는 체적함수비에 따른 선형적인 증가경향을 나타내었다. 중금속 용액은 50kHz 이하의 저주파영역에서 전극 분극효과에 의해 농도 증가에 따라 유전상수 실수부가 증가하는 경향을 나타내었으나, 고주파 영역에서는 이온의 수화작용에 의한 물분자의 배향분극 발현 감소로 인하여 유전상수 실수부가 감소하였다. 유전상수 허수부의 경우에는 모든 주파수 영역에서 중금속 농도 증가에 따른 전도손실에 의하여 증가하는 경향을 나타내었다. 흙과 중금속 혼합시료의 경우 함수비가 큰 시료에서는 중금속 용액 자체의 유전특성이 그대로 발현되었으나, 함수비가 작은 시료에서는 공간전하분극의 영향이 우세하여 유전상수 실수부가 10-20%정도 증가하는 경향을 나타내었다. 유전상수 허수부의 경우에는 중금속 농도 증가에 따른 뚜렷한 증가경향을 확인할 수 있었다. 본 연구의 결과에 의하면 중금속의 오염감지에 대해서는 유전상수 실수부보다는 허수부의 적용성이 높은 것으로 나타났으며, 현장에서의 정확한 오염도 평가를 위해서는 함수비에 대한 평가가 선행되어야 할 것으로 판단된다.

• Journal of the Korean Institute of Navigation
• /
• v.25 no.1
• /
• pp.53-60
• /
• 2001

This paper presents the fabrication of the LNA which is operating at 2.13 ~ 2.16 GHz for IMT-2000 front-end receiver using series feedback and resistive decoupling circuit. Series feedback added to the source lead of a GaAs FET keeps the low noise characteristics and drops the input reflection coefficient of a low noise amplifier simultaneously. Also, it increases the stability of the LNA. Resistive decoupling circuit is suitable for input stage matching because a signal at low frequency is dissipated by a resistor in the matching network. The amplifier consists of GaAs FET ATF-10136 for low noise stage and VNA-25 which is internally matched MMIC for high gain stage. The amplifier is fabricated with both the RF circuits and self bias circuit on the Teflon substrate with 3.5 permittivity. The measured results of the LNA which is fabricated using the above design technique are presented more than 30 dB in gain, PldB 17 dB and less than 0.7 dB in noise figure, 1.5 in inputㆍoutput SWR(Standing Wave Ratio).

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.10
• /
• pp.6839-6845
• /
• 2015

The optimization design method for the broadband operation of the sleeve monopole was proposed to unify the multiple antennas essential to the multi-functional broadband wireless communication systems into one antenna. The structure of the sleeve part was optimized to enhance the impedance matching characteristics based on the theoretical analysis that sleeve part can works as the open stub. The thick monopole was used for the broadband operation. The radius of the sleeve and the permittivity of the dielectric inside the sleeve was optimized to enhance the impedance matching characteristics for the broadband operation. The optimized sleeve monopole having thick monopole shows broadband characteristics over 3:1 bandwidth, from 0.8 to 2.43 GHz, which is suitable for the commercial wireless communication system. The proposed broadband sleeve monopole can reduce multiple antennas essential to the multi-functional broadband systems to one antenna.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.14 no.8
• /
• pp.884-890
• /
• 2003

In order to reduce the specific absorption rate(SAR) in a human head exposed to electromagnetic fields radiated by a cellular phone, we have analyzed an electromagnetic wave absorber attached to the handset. A manufactured electromagnetic wave absorber was composed of Mn - Zn, which had complex relative permittivity of 7.30-j0.05 and permeability of 2.20-i1.55. The SAR value from the electromagnetic wave absorber attachment was calculated by using the nonuniform finite difference time domain(FDTD) algorithm and measured by phantom model at 835 MHz. The SAR reduction due to the electromagnetic wave absorber are about 18 % at 835 MHz. The V.S.W.R and radiation pattern of antenna are good agreement with the normal antenna. The gain reduction due to the electromagnetic wave absorber are only 0.3 dB at 835 MHz. But the sensitivity of cellular phone generally improves about 1 dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.13 no.6
• /
• pp.566-573
• /
• 2002

In this paper, dielectric characteristics of pathological tissues cultivated using the xenograft method were analyzed. Since cancerous tissues were extracted from the nude mouse just before the measurements, they were maintained as fresh as living tissues in the measurements. This would be one of the advantages to get more accurate and reliable results. Dielectric properties of four cancerous tissues such as brain cancer, breast cancer, colon cancer and gastric carcinoma were measured in the frequency range between 45 MHz and 5 GHz. For the measurement of the dielectric properties, 58 xenografted samples were used. It was found that all of the cancerous tissues had the similar dielectric constant values. Comparing with the normal tissues, dielectric constant values of brain cancer, breast cancer and colon cancer were higher than those of the normal tissues except gastric carcinoma in the frequency range.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.10 no.2
• /
• pp.277-290
• /
• 1999

A simulation using the finite-difference time-domain method to analyze the electromagnetic interactions between a cellular phone and the human body was conducted, and a synthesis of a bone-equivalent material to make a human head phantom was performed. A test model of the cellular phone was fabricated to measure its reflection coefficient and radiation pattern in the free space. Various effects of the human body on the characteristics of the phone, such as input impedance, reflection coefficient, radiation pattern, and radiation efficiency are analyzed as the distance between the head and the phone antenna varies. When the phone was operated close to the head, the resonant frequency of the antenna decreased by up to 12%. With the output power of 0.6W, as long as the distance was larger than 30mm, the 1-g averaged peak SAR was below the ANSI/IEEE safety guideline, 1.6 W/kg. To synthesize the bone-equivalent material, an epoxy with hardener and a graphite powder were used as basis ingredients, and a small amount of a conducting epoxy was added to control the conductivity of the material. A material having a relative permittivity of 18.04 and a conductivity of 0.347, which are close to those of the bone at 850 MHz, was synthesized.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.9 no.5
• /
• pp.698-707
• /
• 1998

For inverse scattering problems reconstructing cross-sectional permittivity distributions of dielectric cylinders, the angular spectral inverse technique using the moment method with pulse basis function suffers from large reconstruction error even if very small noise due to requiring the higher spectral informations on the larger cross-section of the cylinder. To reduce the number of higher-order spectra, this paper presents an improved inverse technique in angular spectral domain applying the moment procedure with a series-expansion basis function for the induced field in each enlarged cross-sectional cell. By choosing adequate spectra and averaging over the enlarged cells with a suitable weighting function, the reconstruction profiles reveal fine enough to suppress the noise effect significantly.

• Journal of Ceramic Processing Research
• /
• v.19 no.6
• /
• pp.461-466
• /
• 2018

The effects of Ca/Sr ratio and the sintering temperature on the properties of $(Ca_xSr_{(1-x)})ZrO_3$ (CSZ) ceramics were investigated in this study. CSZ ceramics were prepared using solid-state reaction process, which were sintered in air at temperatures ranging from $1350^{\circ}C$ to $1450^{\circ}C$. Their structures were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The change in Ca/Sr ratio significantly affected the crystalline phase and the dielectric properties of the $(Ca_xSr_{(1-x)})ZrO_3$ ceramics. The secondary phase, $Ca_{0.15}Zr_{0.85}O_{1.85}$, was observed and increased correspondingly with the rising of sintering temperatures. In order to understand the effects of secondary phase on the dielectric properties of CSZ ceramics, the $Ca_{0.15}Zr_{0.85}O_{1.85}$ phase was prepared individually using solidstate method. The $Ca_{0.15}Zr_{0.85}O_{1.85}$ ceramics sintered at $1500^{\circ}C$ for 2 hours possessed a dielectric constant (${\varepsilon}_r$) of 21.7, a dielectric loss ($tan{\delta}$) of $49.510^{-4}$ and an Insulation Resistance (IR) of $2.1{\times}10^{10}{\Omega}$. The ($Ca_{0.7}Sr_{0.3})ZrO_3$ ceramics exhibited the best dielectric properties, with a permittivity of 29, a dielectric loss ($tan{\delta}$) of $2.7{\times}10^{-4}$, and an Insulation Resistance (IR) of $2.6{\times}10^{12}{\Omega}$.

• Proceedings of the International Microelectronics And Packaging Society Conference
• /
• 2005.09a
• /
• pp.201-212
• /
• 2005

[ $Epoxy/BaTiO_3$ ] composite embedded capacitor films (ECFs) were newly designed fur high dielectric constant and low tolerance (less than ${\pm}15\%$) embedded capacitor fabrication for organic substrates. In terms of material formulation, ECFs are composed of specially formulated epoxy resin and latent curing agent, and in terms of coating process, a comma roll coating method is used for uniform film thickness in large area. Dielectric constant of $BaTiO_3\;&\;SrTiO_3$ composite ECF is measured with MIM capacitor at 100 kHz using LCR meter. Dielectric constant of $BaTiO_3$ ECF is bigger than that of $SrTiO_3$ ECF, and it is due to difference of permittivity of $BaTiO_3\;and\;SrTiO_3$ particles. Dielectric constant of $BaTiO_3\;&\;SrTiO_3$ ECF in high frequency range $(0.5\~10GHz)$ is measured using cavity resonance method. In order to estimate dielectric constant, the reflection coefficient is measured with a network analyzer. Dielectric constant is calculated by observing the frequencies of the resonant cavity modes. About both powders, calculated dielectric constants in this frequency range are about 3/4 of the dielectric constants at 1 MHz. This difference is due to the decrease of the dielectric constant of epoxy matrix. For $BaTiO_3$ ECF, there is the dielectric relaxation at $5\~9GHz$. It is due to changing of polarization mode of $BaTiO_3$ powder. In the case of $SrTiO_3$ ECF, there is no relaxation up to 10GHz. Alternative material for embedded capacitor fabrication is $epoxy/BaTiO_3$ composite embedded capacitor paste (ECP). It uses similar materials formulation like ECF and a screen printing method for film coating. The screen printing method has the advantage of forming capacitor partially in desired part. But the screen printing makes surface irregularity during mask peel-off, Surface flatness is significantly improved by adding some additives and by applying pressure during curing. As a result, dielectric layer with improved thickness uniformity is successfully demonstrated. Using $epoxy/BaTiO_3$ composite ECP, dielectric constant of 63 and specific capacitance of 5.1nF/cm2 were achieved.