• Journal of Welding and Joining
• /
• v.23 no.2
• /
• pp.81-89
• /
• 2005

A numerical model for multiple reflection effects of a polarized beam on laser grooving has been developed. The surface of the treated material is assumed to reflect laser irradiation in a fully specular fashion. Combining electromagnetic wave theory with Fresnel's relation, the reflective behavior of a groove surface can be obtained as well as the change of the polarization status in the reflected wave field. The material surface is divided into a number of rectangular patches using a bicubic surface representation method. The net radiative flux far these patch elements is obtained by standard ray tracing methods. The changing state of polarization of the electric field after reflection was included in the ray tracing method. The resulting radiative flux is combined with a set of three-dimensional conduction equations governing conduction losses into the medium, and the resulting groove shape and depth are found through iterative procedures. It is observed that reflections of a polarized beam play an important role not only in increasing the material removal rate but also in forming different final groove shapes. Comparison with available experimental results for silicon nitride shows good agreement for the qualitative trends of the dependence of groove shapes on the electric field vector orientation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.16 no.2 s.93
• /
• pp.228-234
• /
• 2005

A magnetic composite as noise absorber of quasi-microwave band was developed. The Fe-Si-Al alloy powder were forged by attrition mill to get flaky shape. The magnetic composite sheet was fabricated in which powders are dispersed in polymer and aligned in the direction perpendicular to electromagnetic wave propagation. The permittivity of magnetic composite is increased as forging time increasing, while the permeability is decreased slightly. The maximum attenuation peak of reflection loss is shifted to lower fiequency range as milling time increasing, and the value of maximum attenuation peak is to get smaller gradually. From these result, we could designed a noise absorber sheet (t=1.0 mm) for quasi-microwave band, which is impedance matched at 1.4 GHz with respect to -8.2 dB reflection 1055.

• Journal of the Korea Institute of Building Construction
• /
• v.19 no.3
• /
• pp.209-217
• /
• 2019

EMP (Electromagnetic Pulse) usually means High Power Electromagnetic Wave (HPEM). In the case of the shielding plate against the EMP, there is a possibility of deterioration of the electromagnetic wave shielding performance due to the skill of the constructor, bad construction, deformation of the shielding plate at the connection portion (joint portion). The inefficient use of space due to the separation distance is also pointed out as a problem. Therefore, this study aims to derive the optimum electromagnetic shielding condition by applying ATMSM to concrete as a part of securing electromagnetic wave shielding performance with reflection loss against concrete wall. Experimental parameters included concrete wall thickness and application of Zn-Al ATMSM. For the concrete wall, the wall thickness was 100 to 300mm, which is generally applied, and experimental parameters were set for the application of Zn-Al metal spraying method to evaluate electromagnetic shielding performance. Experimental results showed that as the thickness increases, the electromagnetic shielding performance increases due to the increase of absorption loss. In addition, after the application of Zn-Al ATMSM, the average shielding performance increased by 56.68 dB on average, which is considered to be increased by the reflection loss of the ATMSM. In addition, it is considered that the shielding performance will be better than that when the conductive mixed material and the ATMSM are simultaneously applied.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 1993.10b
• /
• pp.53-64
• /
• 1993

This study aims to measure the reflection loss and the material constants of the fabricated samples for electromagnectic wave absorber precisely and easily by using 20mm$\Phi$coaxial tube with the end-short-type. The authors have estabilished the extraction algorithm of material constants by one port method and proved that the results of the experiments coincided with the calculated ones. On the basis of the above results the validity of the proposed measuring method is confirmed. This measurement method could be used effectively for the design of microwave absorbe and for its evaluation.

• Composites Research
• /
• v.17 no.5
• /
• pp.68-77
• /
• 2004

The electromagnetic (EM) absorption or shielding characteristics of a material is an important issue not only for military purpose but also for commercial purposes such as radar, electric or telecommunication devices. In order to design the effective electromagnetic wave absorber, the electromagnetic characteristics of the constituents of the material should be available in target frequency band. Also, it must be possible to predict the electromagnetic properties of absorbers with respect to the content of lossy ingredients. In this study, the dielectric properties of unsaturated polyester resins containing nano-size conductive carbon black powder were measured with a free space method in the X-band frequency range and analyzed with respect to the content of carbon black. Finally, the method for estimating the dielectric properties of polymeric resin containing conductive carbon black with respect to the EM frequency was developed and verified.

• Korean Journal of Materials Research
• /
• v.9 no.9
• /
• pp.913-918
• /
• 1999

As an alternative evaluation method of electromagnetic shielding properties, the material parameters are considered in determining the qualitative value of shielding effectiveness. The specimens are metallized nylon fabrics with the thickness of about 0.1 mm and the electrical conductivities in the range from 6.4$\times$10~2.4$\times$10(sup)5 mhos/m. On the basis of shielding theory, the shielding effectiveness (which is a sum of reflection loss and absorption loss) has been determined from the material parameters of the barrier sheets. For the conductive fabrics, the dominant shield mechanism is predicted to be reflection loss, which shows an increasing function of electrical conductivity. Comparing these theoretical value with the directly measured surface impedances, the error range is found to be within 10 dB, which demonstrates that the proposed material-parameters method can be a convenient way to determine the electromagnetic shielding properties.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.27 no.1
• /
• pp.15-23
• /
• 2024

In order to avoid the high observability due to the cavity resonance or electromagnetic wave leakages from the bridge of a battleship or the cockpit of an aircraft, this paper presents a transparent conductive oxide coated structure to prevent the incoming/outgoing electromagnetic waves. Currently, most of the RCS reduction technologies were focused on radar absorbing material such as paints based on conductive or magnetic materials in the fuselage, and there is not much research on countermeasures for achieving the low observability of materials that required optical transparency in actual weapon systems. In this study, the transmission/reflection and absorption performance of the ITO coated structure according to the change of the surface resistance of the transparent conductor were analyzed. Finally, the relationship between the electromagnetic and optical characteristics was established through fabrication and measurement.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
• /
• v.5 no.4
• /
• pp.40-46
• /
• 1994

Design and microwave absorbing properties of ferrite plate are investigated for the application to the radiowave absorbers used in anechoic chamber. The required frequency-dependence of complex permeability is determined on the basis of wave-impedance-matching relationship. The plate thickness and matchingfrequency are determined from the complex permeability and dielectric constant, and then compared with the directly measured reflection loss. A systematic variation of material constants and their influence on the microwave absorbing properties are demonstrated.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 1999.05a
• /
• pp.47-49
• /
• 1999

The air and impurity gaps generated by a defect in homogeneous material have a difference index of refraction compare to the homogeneous material. Therefore an electromagnetic wave has a multiple reflection between the two indices of refraction. If the gap has a small thickness, it is difficult to know the gap in time domain. However, the presence of the gaps can be known in frequency domain by total transmission and phase difference. Also, the thickness and index of refraction can be measured by well known Febry-Perot theory.

• Applied Chemistry for Engineering
• /
• v.10 no.5
• /
• pp.778-783
• /
• 1999

The effect of carbon fiber orientation on the tribological properties of carbon fiber/epoxy composites used as a reflecting material for the electromagnetic wave has been investigated. It was found that the carbon fiber/epoxy composite which slides normal to prepreg lay-up direction had less friction and wear that those slides parallel to prepreg fiber lay-up direction due to the increase of delamination between carbon fiber and epoxy. Composite with unidirectional orientation($0/0^{\circ}$) had higher tribological properties than those with multidirectional orientation($0/45/90/-45^{\circ}$ and $0/90^{\circ}$) when the sliding direction was normal to prepreg lay-up direction. This was caused by the debonding between carbon fiber and epoxy which is proportional to contact area between the sliding surface and carbon fiber. Opposite results have been found when the sliding direction was parallel to prepreg lay-up direction due tot he tensile force applied on carbon fiber. In addition, it was shown that wear factor increased with increasing sliding velocity but the friction coefficient did not depend upon the sliding velocity.