• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.1 s.104
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• pp.52-59
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• 2006

To construct its complex permittivity from the reflection coefficient of a thin film such as PCB substrate measured by open-ended coaxial probe, an integral equation is formulated using modal analysis and equivalent source. The accuracy of the conversion model based on the integral equation is confirmed in both cases of converted complex permittivities calculated from numerically computed and actually measured reflection coefficients. And the maximum valid frequency of open-ended coaxial probe is limited by the size of its flange.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.4
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• pp.54-59
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• 2003

In this paper, a cylindrical dielectric antenna with dielectric clad is designed and analyzed. Design parameters of a cylindrical dielectric resonator antenna are calculated from the wave equation of cylindrical dielectric. The variations of characteristics of the antenna are analyzed as varying the thickness and the relative permittivity of its clad. From the results, when the ratio of the outside radius of the dielectric clad to the radius of the cylindrical dielectric is 1.3 and the relative permittivity of the dielectric clad is one-third of the cylindrical dielectric resonator antenna, the relative bandwidth of the antenna is 49%, which is improved by 2.3 times than the cylindrical dielectric resonator antennas. However, the thickness and the relative permittivity of the dielectric clad have not effect on the radiation pattern, beamwidth and gain of the antenna.

• Proceedings of the KSEEG Conference
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• 1999.04a
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• pp.90-93
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• 1999

We present a high frequency electromagnetic (EM) inversion scheme for detecting and characterizing a fracture using single-hole data. At high frequencies, say above tens of mega-hertz, since displacement currents cannot be ignored, electrical permittivity as well as electrical conductivity is to be considered together for analyzing the EM scattering data. In this paper, we have developed a three-step inversion scheme to map the fracture and to evaluate its electrical conductivity and permittivity. We performed EM profiling along the z-axis using three-component receivers for each source. The model was excited by a vertical magnetic dipole and the resistant magnetic fields were inverted using the non-linear least-squares method. Background resistivity and permittivity were easily obtained using vertical magnetic fields below 1 MHz and above 10 MHz, respectively. Both the vertical and dipping sheets were successfully mapped using the phase difference between 40 and 41 MHz. The electrical property of the sheet was well resolved using the information obtained in the previous two steps and secondary magnetic fields. Our study shows the potential of imaging the fracture in single-hole survey environment using the high frequency EM method.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.16 no.3
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• pp.247-254
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• 1983

In previous paper (Lee and Kim, 1983) the effect of moisture level and frequency on dielectric properties of sardine starch paste was mentioned. The effect of temperature and starch content of the paste upon dielectric permittivity and activation energy was discussed in this report. Addition of starch affected on dielectric property. Increases of starch in the mixtures resulted in higher complex permittivity and lower critical moisture content (hc) as shown in the mixtures with $20\%$ and $50\%$ starch which were ${\varepsilon}^{\ast}=2.97+j0.36,\;hc=8.0\%;\;{\varepsilon}^{\ast}=3.54+j0.44,\;hc=7.8\%$, respectively while being ${\varepsilon}^{\ast}=2.73+j0.29,\;hc=8.4\%$ for the plain ground sardine meat. When temperature was raised the complex permittivity tended to increase at above the critical moisture content in all cases. The activation energies for plain ground meat and $30\%$ starch added mixture at below the critical moisture of $8.4\%$ were 15.44 kcal/mol and 13.86 kcal/mol while those at the moisture of $12.2\%$ were 10.27 kcal/mol and 9.31 kcal/mol, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.05c
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• pp.1-5
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• 2001

This paper describes the electrical characteristics of Nomex paper employed as an insulating material of distribution transformers. The relative permittivities(dielectric constants) and $tan{\delta}$(dielectric dissipation factors) were measured as a dielectric characteristic and the partial discharge inception voltages(PDIVs) and breakdown voltages were also measured as an electrical strength characteristic of Nomex paper. As a result, the permittivity and $tan{\delta}$ of Nomex paper showed temperature and frequency dependency. Especially, the permittivity of 0.18mm Nomex paper was 2.4 according to the ASTM condition. And the PDIVs and breakdown voltages were, almost linearly increased with the thickness of Nomex paper and its electrical strength was better than conventional kraft paper.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.297-300
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• 2006

In this paper, the EM wave absorbers were designed and fabricated for X-band sensors using Carbon of dielectric material with CPE. The complex relative permittivity of samples is calculated by the measured S-parameter data. We simulated the double-layered type EM wave absorber with broad bandwidth using the measured complex relative permittivity by changing the thickness and layer, which was fabricated based on the simulated design. The fabricated EM wave absorber consist of 1mm first layer sheet facing metal with Carbon composition ratio 70 vol% and 1.5 mm second layer sheet with Carbon composition ratio 60 vol%. The comparisons of simulated and measured results are good agreement. As a result, the optimized absorption ability of double-layered type EM wave absorber with thickness of 2.5 mm is higher than 10 dB from 7.8 GHz to 13.3 GHz.

• Journal of Powder Materials
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• v.14 no.4
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• pp.261-264
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• 2007

The electromagnetic wave (EM) absorption properties of various particle size have been investigated in a sheet-type absorber using the $Fe_{73}Si_{16}B_{7}Nb_{3}Cu_{1}$ alloy powder. With decreasing the average particle size, the complex permeability (${\mu}_{r}$) and permittivity (${\varepsilon}_{r}$) increased and the matching frequency is shifted toward lower frequency. The fabricated EM wave absorbers showed permeability $2{\sim}6$, permittivity $17{\sim}23$ for a $-325{\sim}+400$ mesh sample, and the calculated power absorption was as high as 80% in the frequency range over 2 GHz.

• Journal of Biosystems Engineering
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• v.32 no.4
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• pp.237-246
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• 2007

In this study, the microwave free-space transmission technique was used to measure the dielectric property of powdered food at microwave frequencies. The sample holder was designed and fabricated to transmit the microwave signals ranging from 1 to 15GHz. From the microwave propagation theory the equation expressing the dielectric property of powdered food was derived and validated by standard dielectrics. The dielectric property of powdered food such as wheat flour, coffee powder and milk powder was measured and analyzed. In the uniform range of bulk density of material, the real parts of permittivity of the food samples increased with the increase of moisture content, bulk density and temperature of the samples. The propagation properties such as attenuation and phase shift increased linearly as the moisture density of the food samples increased. As a measuring frequency of the moisture content, the X-band was recommended.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.5
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• pp.399-406
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• 2019

The variation of ground-penetrating radar(GPR) signal characteristics from dielectric-filled nonmetallic pipes buried in inhomogeneous ground are compared through a numerical simulation. The relative permittivity distribution of the ground is generated by using the continuous random media(CRM) technique. As a function of the relative permittivity of the material filling the nonmetallic pipe buried in the ground media, GPR signals are simulated by using the finite-difference time-domain(FDTD) method. We show that, unlike the case for homogeneous ground, the distortion characteristics of the reflected waves caused by the front convex surface and the rear concave surface of the pipe buried in inhomogeneous ground are different depending on the permittivity contrast between the inside and outside of the pipe.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.10
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• pp.971-981
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• 2002

An open-ended coaxial probe method has been considered as one of effective tools for measuring electrical properties of its contacted material without shaping and fitting. The measured reflection coefficient at the probe's end is able to convert into the corresponding complex permittivity by employing the improved version of virtual transmission-line model Presented by our lab already. But the error of complex permittivity converted by equivalent model increases as the operating frequency ascends high. The errors of complex permittivity in the open-ended coaxial probe can be yielded compositively by the imperfect contact or probe, manufacture error of probe and complex permittivity error of reference material etc. Therefore it is necessary to limit the problem to identify the error causes in high frequency. In this paper, the errors which are resulted from the measurement of reflection coefficient are removed by using the FDTD(Finite-Difference Time-Domain) method, the error causes are limited the conversion model problem. And the error study of the improved conversion model is performed from several viewpoints. At first, the local minimum of parameter to be calculated by the iteration method in the conversion model is checked. At second, the modeling of the equivalent model is checked in the frequency range. From this study, we know the valid range of the improved conversion model.