Information and communication technologies are developing rapidly as IC chip size becomes smaller and information processing becomes faster. With this development, digital circuit technology is being widely applied to mobile phones, wireless LANs, mobile terminals, and digital communications, in which high frequency range of GHz is used. In highdensity electronic circuits, issues of noise and EMC(Electro-Magnetic Compatibility) arising from cross talk between interconnects or devices should be solved. In this study, sheet-type electromagnetic wave absorbers that cause electromagnetic wave attenuation are fabricated using composites based on soft magnetic metal powder and silicon rubber to solve the problem of electromagnetic waves generated in wireless communication products operating at the frequency range of 2.4 GHz. Sendust(Fe-Si-Al) and carbonyl iron(Fe-C) were used as soft magnetic metals, and their concentrations and sheet thicknesses were varied. Using soft magnetic metal powder, a sheet is fabricated to exhibit maximum electromagnetic attenuation in the target frequency band, and a value of 34.2dB(99.9 % absorption) is achieved at the target frequency.

The recent development of information and communication technologies brings new changes to automobile traffic systems. The most typical example is the advancement of dedicated short range communication(DSRC). DSRC mainly consists of an intelligent transportation system(ITS), an electronic toll collection system(ETCS) and an advanced traveler information system(ATIS). These wireless communications often cause unnecessary electromagnetic waves, and these electromagnetic waves, in turn, cause frequent system malfunction. To solve this problem, an absorber of electromagnetic waves is suggested. In this research, various materials, such as powdered metal and iron oxides, are used to test the possibility for an effective absorption of the unnecessary electromagnetic waves. The various metal powders are made into a thin sheet form by compositing through processing. The electromagnetic characteristics(complex permittivity, complex permeability) of the fabricated sheet are measured. As a result, we achieve –6.5 dB at 940 MHz(77.6 % absorption rate) with a 1.0 mm-thickness electromagnet wave absorber, and –9.5 dB at 940 MHz(88.8 % absorption rate) with a 2.0 mm-thickness absorber.

Electromagnetic wave energies are consumed in the form of thermal energy, which is mainly caused by magnetic loss, dielectric loss and conductive loss. In this study, CNT was added to the nanocrystalline soft magnetic materials inducing a high magnetic loss, in order to improve the dielectric loss of the EM wave absorption sheet. Generally, the aspect ratio and the dispersion state of CNT can be changed by the pre-ball milling process, which affects the absorbing properties. After the various ball-milling processes, 1wt% of CNTs were mixed with the nanocrystalline base powder, and then further processed to make EM absorption sheets. As a result, the addition of CNT to Fe-based nanocrystalline materials improved the absorption properties. However, the increase of ball-milling time for more than 1h was not desirable for the powder mixture, because the ballmilling caused the shortening of CNT length and the agglomeration of the CNT flakes.

The electromagnetic wave absorption sheets were fabricated by mixing of nanocrystalline soft magnetic powder, charcoal powder and polymer based binder. The complex permittivity, complex permeability, and scattering parameter have been measured using a network analyzer in the frequency range of 10 MHz10 GHz. The results showed that complex permittivity of sheets was largely dependent on the frequency and the amount of charcoal powder : The permittivity was improved up to 100 MHz, however the value was decreased above 1 GHz. The power loss of electromagnetic wave absorption data showed almost the same tendency as the results of complex permittivity. However, the complex permeability was not largely affected by the frequency, and the values were decreased with the addition of charcoal powder. Based on the results, it can be summarized that the addition of charcoal powder was very effective to improve the EM wave absorption in the frequency range of 10 MHz1 GHz.

In this paper, we designed and fabricated the Electro-Magnetic (EM) wave absorber for wireless LAN by using Amorphous and CPE. The material constants and the absorption properties were measured for the samples containing 50 %, 60 %, and 70 % weight fraction of Amorphous. Moreover, the EM wave absorption abilities were simulated for the EM absorbers in different thicknesses by adopting the measured permittivity and permeability, and then the EM wave absorber was fabricated based on the simulated design values. As a result, the EM wave absorber with the composition ratio in Amorphous : CPE = 60 : 40 wt.% with the thickness of 4 mm has the absorption ability more than 35 dB at 2.4 GHz. Thus, it is expected the wireless LAN environment can be improved by using the developed absorber.

최근 빠르고 편리하게 데이터 송수신이 가능한 무선LAN은 가정, 사무실 등 다양한 장소에서 사용이 증가하고 있다. 그러나 실내에서 무선LAN을 사용할 경우 천장, 벽, 바닥, 책상 등에서의 반사파에 의한 다중반사가 발생하여 데이터 전송의 오류 및 성능 저하의 주된 원인이 된다. 이를 해결하기 위해 본 논문에서는 Graphite의 특성을 분석하고 최적의 조성비를 찾아내서 무선LAN 환경에 적합한 전파흡수체를 연구하였다. 먼저 Graphite와 지지재인 CPE(Chlorinated Polyethylene)를 이용하여 조성비별 전파흡수체 샘플을 제작하고, 각 샘플의 반사계수를 측정하였다. 측정된 데이터로부터 재료정수를 계산하고, 전파흡수체를 설계 및 제작하여 전파흡수능을 비교, 분석 하였다. 그 결과 조성비가 Graphite : CPE=50:50 wt%이고, 두께 1.7 mm 인 전파흡수체가 5.2 GHz에서 27 dB 이상의 전파흡수능을 가지는 우수한 전파흡수체를 개발하였다.

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 using measurement results of S-parameter. 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 consists of 1 mm 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 measured results showed a good agreement to the simulated ones. It is found toot 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.

천연세라믹, 옻칠, 그리고 고무의 전파흡수능을 조사하였다. 천연세라믹은 2.5GHz~4.5GHz의 주파수 범위에서 2.5dB이상의 전파흡수능을 나타내었으며 옻칠의 전파흡수능이 기존에 전파흡수체의 지지재로 이용되는 고무에 비해 우수한 전파흡수능을 갖고 있음을 확인하였다. 페라이트에 옻칠을 지지재로 이용한 전파흡수체에 대하여 시뮬레이션 한 결과 0.5GHz~10GHz의 주파수 범위에서 16dB 이상의 우수한 전파흡수능을 나타내었다. 따라서 기종에 지지재로 이용하던 고무대신 본 연구에서 새롭게 제안하는 옻칠을 전파흡수체의 지지재로 이용하는 것이 광대역에서 우수한 전파흡수체를 얻을 수 있을 것으로 예상된다.

Sheet형 전파흡수체를 제조하고 그들의 전자파 흡수 특성을 조사하였다. 제조된 ferrite 흡수체의 흡수특성은 2.4~3.2GHz의 주파수범위에서 입자크기의 감소에 따라 개선되었다.

With a rapid progress in electronic industry we enjoy various conveniences of life. As many kinds of information equipments are supplied even to most of individuals as to be called an information society, we are exchanging much information with one another surprisingly. Consequently the occupation density of microwave frequency band is highly increased, and electromagnetic environment is getting more seriously bad. It often gives fatal blow to even human life and thus becomes serious social problems. Electromagnetic wave absorbers for anechoic chamber are needed to broaden the effective frequency bandwidth, reduce the thickness, and decrease the weight. There are various absorbers proposed for the above conditions, but they could not decisively solve it the alone requirements. The Electromagnetic wave absorber made by a conventional ferrite tile has, for example, broadened the useful frequency bandwidth by the way of forming air layer(practically use urethane foam, etc.) on the ferrite tile. Therefore, an air layer is formed between a reflection plate and a sintered Ni-Zn ferrite tile of 7 mm in thickness, which has reflectivity less than -20 dB from 30 MHz to 400 MHz in bandwidth. Accordingly, in this paper, a broadened electromagnetic wave absorber are designed, which has the reflection characteristics less than -20 dB from 30 MHz to 6,000 MHz in the bandwidth. Then we achieved the goal by design the inserting square Ferrite Cylinders with the thickness less than 17.5 mm on existing grid type Ferrite absorber. The purpose of this research is on the development of very wide-band electromagnetic absorber for a universal anechoic chamber for measuring radiated electromagnetic wave or immunity of electronic equipments, GTEM-cell, wall material for preventing TV ghost, etc.

The super wideband electromagnetic wave absorber in RF-A-PF type has been proposed, which can be used for an anechoic chamber, wall material to prevent TV ghost, etc, In this paper, Nix-Mg0.1-Zn(1-x-0.1)·Fe2O4 Ferrite Powder has been fabricated. Using this, then, [Nix-Mg0.1-Zn(1-x-0.1)·Fe2O4-Rubber composite for RF-layer in the RF-A-PF type absorber has been fabricated and its characteristics has been analyzed. As a result, it has been shown that the Nix-Mg0.1-Zn(1-x-0.1)·Fe2O4-Rubber composit with the quantity x of Nix between 0.5 and 0.6 is suitable for the RF-layer in the case of which the grain size is sub-micrometer order.

According to the rapid development of the electric industry, the demand of the frequency allocation and the usage of electromagnetic wave are increased due to automation of modem society. Electromagnetic wave absorbers for anechoic chamber are needed to broaden the effective frequency bandwidth, reduce the thickness, and decrease the weight. There are various absorbers proposed for the above conditions, but they could not decisively solve the above requirements. The Electromagnetic wave absorber made by a conventional ferrite tile has, for example, broadened the effective frequency bandwidth by the way of forming air layer(practically in urethane foam, etc.) on the ferrite tile. Therefore, an air layer is formed between a reflection plate and a sintered Ni-Zn ferrite tile of 7 mm in thickness, which has reflectivity less than -20 dB from 30 MHz to 400 MHz in bandwidth. In this paper, a broadband electromagnetic wave absorber are designed, which has the reflection characteristics less than -20 dB from 30 MHz to 8,000 MHz in the bandwidth. A super broadband electromagnetic wave absorber is achieved by inserting square Ferrite Cylinders Type with the thickness less than 23.5 mm and with the frequency band from 30 MHz to 8,000 MHz under the above tolerance limits. The purpose of this research is on the development of a universal anechoic chamber for measuring radiated electromagnetic wave or immunity of electronic equipments, GTEM-cell and also a wall material for preventing TV ghost, etc.

A design method of an electromagnetic wave absorber with ferrite fins in the second layer, which has very wide band frequency characteristics, is proposed and discussed. A theoretical model using the equivalent material constants method is adopted, assessed for its accuracy by comparision with the Hashin-Shtrikman formulas and compared with the conventional absorbers. Based on the model, a wide band electromagnetic wave absorber with excellent reflectivity frequency characteristics in frequency range of 30MHZ to 3530MHZ has been designed.

A wide band design method of an electromagnetic wave absorber with square ferrite cylinders in the second layer, which has very wide band frequency characteristics, is proposed and discussed. A theoretical model using the equivalent material constants method is also evaluated and proposed for its accuracy by comparison with Hashin-Shtrikman formulas. Based on the developed model, wide band electromagnetic wave absorbers with excellent reflective frequency characteristics in the frequency range of 30MHz to 3, 690MHz were designed.

A wide band design method of an electromagnetic wave absorber using exponentially tapered ferrite, which has very wide band frequency characteristics, is proposed and discussed. The wide band electroma-gnetic wave absorber can be designed by the proposed equivalent material constants method for the re-gions varying spatially in the shape of ferrite. Futhermore, the wide band ferrite electromagnetic wave absorber with taper, which have not only exce-llent reflectivity frequency characteristics but also the band width of 30MHz to 2150 or 2450MHz under the tolerance limits of -20dB reflectivity, were designed.

Recently, according to the development of electromagnetic wave technique, more frequent and powerfull wave radiation becomes inevitable and so electromagnetic environments has become worse accordingly. Electromagnetic wave absorber is known the most effective preventive remedy to cope with the EMI/EMC problem. To realize broad-band electromagnetic wave absorber, triple layered structure where an air layer is interposed between a sintered ferrite layer and a ruber ferrite layer was adopted. Computer simulation for optimum design and evaluation of absorption characteristics has been made. The results shows that designed broad-band electromagnetic wave absorber can be useful for EMI/EMC problem, especially reducing TV ghosts in both VHF and UHF bands by additionally an air layer and a thin rubber ferrite layer on the surface of conventional ferrite, without replacing it.