• International Journal of Highway Engineering
• /
• v.2 no.4 s.6
• /
• pp.101-109
• /
• 2000

This study was performed to estimate fatigue life of polymer-modified and reinforced overlay asphalt mixtures with respect to reflection cracking in asphalt overlay pavement. In order to achieve the goal, the expedited reflection cracking test method was developed and applied to various mixtures and the results were compared one another with respect to the resistant characteristics of reflection cracking. The theoretical prediction equation of fatigue life for each mixture was suggested based on statistical analysis of experimental test results in the flexural failure mode. Since coefficients of correlation between estimated values and measured values were very high ($r^2=0.95$ or higher), the prediction model can be used for relative comparison of various pavement overlay choices to be used in the field.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.6 s.121
• /
• pp.620-628
• /
• 2007

An H-sector horn antenna has a constant beam coverage characteristic and it can be useful for application to a wide band phased array antenna system. In this paper, we designed a broadband E-plane H-sector horn phased-array antenna, which has a 3:1 bandwidth and ${\pm}60^{\circ}$ beam steering capability. An H-sector hem antenna was designed to have $30{\sim}50^{\circ}$ half-power beam width in the principal H-plane. The active reflection coefficient including mutual coupling was calculated using a waveguide simulator, and the active reflection characteristic was improved by mutual coupling over wide frequency range. Using these results, an $8{\times}1$ H-sector phased array antenna was fabricated. The measurement results for the half-power beam width in the principal H-plane and the active reflection coefficient showed a good agreement with the simulation results. The peak-value pattern in the steered radiation beams also agreed well with the active element pattern. The measured active reflection coefficients within the beam steering range are mostly less than 0.3 over the 3:1 frequency range.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.04a
• /
• pp.21-24
• /
• 2008

This study proposes a optimized shape of diffuser profile through investigating the scattering and diffusion characteristics of diffusers. The scattering coefficient according to ISO 17497-1 evaluates uniformity of reverberant sound field of late reflections, while the diffusion coefficient according to AES-4id-2001 evaluates polar response of early reflections. Thus both scattering and diffusion characteristics should contribute to design shape of diffusers to maximize physical performance. To find out design method, the previous results on hemisphere diffusers are reviewed. The frequency characteristics of scattering coefficients depended on the structural height of the diffusers, while amount of scattering coefficients depended on the surface coverage density of the diffusers. However absorptive properties also increased with augment of surface coverage density, thus optimum coverage density should be considered. For the directional diffuser, three types of 2D-diffusers are proposed; semicylinder of h=5mm, semi-truncated cone of h=5-25mm and semicylinder of h=25mm. As results, diffusers with the maximum height of 25mm show the highest scattering coefficients, while diffuser of h=5mm shows high scattering coefficients only at the high-frequency bands. Diffusion coefficient will be investigated for diffusive properties of the early reflection.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.19 no.2
• /
• pp.331-337
• /
• 1994

The scatting problem by E-polarized plane wave with obique incidence on a tapered resistive strip grating with zero resistivity(perfectly conducting) at strip-edges is analyzed by the method of moments in the spectral domain. Then the induced surface current density on the strip is expanded in a series of Chebyshev polynomials of the second kind. The expasion coefficients are calculated numerically in the spectral domain, the numerical results of the geometric-optical reflection coefficient for the tapered resistivity in this paper are compared with those for the existing uniform resistivity. And the position of sharp variation points in the magnitude of the geometric-optical reflection coefficient can be moved by varying the incident angle and the strip spacing, It is found out that these sparp variation points are due to the transition of higher mode between the propagation mode and the evanescent mode.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.4
• /
• pp.1455-1462
• /
• 2013

This study examines the reflection of a partially perforated wall with single chamber by 2D and 3D hydraulic experiments. The effects of slit shape on the front wall, relative chamber width and wave steepness were discussed. For the normal incident wave condition, the reflections of horizontal slit case were lower than that of the vertical slit with the similar porosity, but the differences are not significant. When the wave steepness is relatively small, the reflection coefficients are large. In the oblique incidence, the normalized wave heights along a perforated wall with similar porosity are almost same for the vertical and horizontal slit walls and therefore the difference by slit shape can be ignored.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.25 no.1
• /
• pp.108-113
• /
• 2014

This paper presents the influence on the transmission characteristics of swelling in rectangular waveguides for Q-band. We derived the Green's functions of the waveguide with eigenfunction expansion method. The reflection coefficient of the waveguide with a swelling is calculated by using internal impedance in order to investigate the influence of swelling in the waveguide. In order to check the validity of the theoretical analysis, the calculated reflection coefficients are compared with the measured results.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.37 no.5
• /
• pp.17-24
• /
• 2000

Complex permittivity of dry sand is measured by using an open-ended coaxial probe, which was self-designed and manufactured. As a simple calibration scheme of the probe, the phase difference between the measured and the calculated reflection coefficients of pure water is subtracted from the phase of the measured reflection coefficient for dry sand. And then the complex permittivity of dry sand is reconstructed by applying its measured reflection coefficient into an improved imaginary transmission-line model. The accuracy of our measurement scheme is verified by showing that its reconstructed complex permittivity approaches the precise value of dry sand.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.24 no.7
• /
• pp.722-729
• /
• 2013

This paper presents the influence on the transmission characteristics of dimensional tolerances of rectangular waveguides usually used as a low-loss transmission line in the millimeter-wave band. We derived the Green's functions of the waveguide with eigenfunction expansion method. The reflection coefficient of the waveguide with a post is calculated by using internal impedance in order to investigate the influence of dimensional tolerances of the waveguide. In order to check the validity of the theoretical analysis, the calculated reflection coefficients are compared with the measured results.

• Structural Engineering and Mechanics
• /
• v.77 no.4
• /
• pp.473-479
• /
• 2021

The propagation of plane waves in a linear, homogeneous and isotropic nonlocal generalized thermoelastic solid medium is considered in the framework of Lord and Shulman generalization. The governing field equations are formulated and specialized in a plane. Plane wave solutions of governing equations show that there exists three plane waves, namely, P, thermal and SV waves which propagate with distinct speeds. Reflection of P and SV waves from thermally insulated or isothermal boundary of a half-space is considered. The relevant boundary conditions are applied at stress free boundary and a non-homogeneous system of three equations in reflection coefficients is obtained. For incidence of both P and SV waves, the expressions for energy ratios of reflected P, thermal and SV waves are also obtained. The speeds and energy ratios of reflected waves are computed for relevant physical constants of a thermoelastic material. The speeds of plane waves are plotted against nonlocal parameter and frequency. The energy ratios of reflected waves are also plotted against the angle of incidence of P wave at a thermally insulated stress-free surface. The effect of nonlocal parameter is shown graphically on the speeds and energy ratios of reflected waves.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.4B
• /
• pp.377-384
• /
• 2009

In order to reduce computing time significantly for a large matrix in EFEM of linear waves propagation over ripple beds, each of which is approximated to a multi-step topography, a partition method is presented to calculate reflection coefficients. By use of 10 evanescent modes in the model, the most accurate numerical solutions have been obtained up to date, which show different behaviors of computed reflection coefficient in some cases against the existing results. Both computing time and memory of the present partition model for solving a large matrix are still so much demanding that it is needed to develop an efficient method.