Chang-Mook Choi

A Study on the Improvement of EM Wave Absorption Properties with Al(OH) 3

In this paper, we investigated how to improve the EM wave absorption properties with Al(OH)3. Where we compared results for the case of the absorption properties of samples containing 0 wt%, 1 wt%, 3 wt%, 5 wt%, and 7 wt% of Al(OH)3. The absorption property curve just has the tendency to improve the characteristics at 5 wt% of Al(OH)3 at Sendust, and at 3 wt% of Al(OH)3 at Carbon. As a result, the optimized composition ratio of Al(OH)3 is 5 wt% at Sendust and 3 wt% at Carbon. Al(OH)3 is an important material to increase EM wave absorption in Sendust or Carbon EM wave absorbers.

Mathematical Algorithms for Two-Dimensional Positioning Based on GPS Pseudorange Technique

Recently, one has realized that the threedimensional positioning technique used in GPS can be effectively applied to the modern two-dimensional positioning. Such a technique might has applied to the twodimensional positioning in fields of the mobile communication, eLORAN and the GPS jamming/ electronic warfare system. In the paper, we have studied on algorithms for two-dimensional positioning based on GPS Pseudorange Technique. The main works and results are summarized below. First, the linearized state equation was mathematically derived based on GPS pseudorange technique. Second, the geometry model with respect to triangles formed using unit-vectors were proposed for investigation of land-based radio positioning. Finally, the corresponding mathematical formulations for DOP values and covariance matrix were designed for two-dimensional positioning.

A Study on Development of EM Wave Absorber Using TiO₂ for Automotive Radar in Cars

In this paper, we designed and fabricated an electromagnetic(EM) wave absorber for automotive radar in cars using TiO₂ as a dielectric material and chlorinated polyethylene(CPE) as a binder. First of all, we confirmed that the optimum composition ratio of TiO₂ was about 70 wt.%. The complex relative permittivity of a sample containing TiO₂: CPE=70:30 wt.% was calculated from S-parameter. The EM wave absorption abilities were simulated for the EM wave absorbers of different thickness using the calculated relative permittivity, and the EM wave absorber was manufactured based on the simulated design. A comparison of simulated and measured results is in good agreement. Measurement shows that a 1.85 ㎜ thick absorber has absorption ability higher than 20 ㏈ in the frequency range of 76～77 ㎓ for automotive radars.

A Study on the EM Wave Absorber for the Electromagnetic Environment of Indoor Wireless LAN

Recently, wireless LAN are often applied in home or office because of its various of convenience. Frequency rage of wireless LAN specified by IEEE 802.11a is at 5.2 GHz and IEEE 802.11b is 2.4 GHz. But in offices with wireless LAN devices, reflection of waves against walls, ceilings, floors and desks made of metal creates multipath problems that reduce communication speed and lose data. These problems can be solved by using EM wave absorber. In this paper, we designed and fabricated EM wave absorbers using MnZn-ferrite, sendust, carbon and CPE(Chlorinated Polyethylene). The EM wave absorber with the ratio of MnZn-Ferrite : sendust : CPE

A Study on Electromagnetic Wave Absorber for W-Band Radars Using Permalloy

In this paper, we use Permalloy and CPE (Permalloy: CPE=70:30 wt.%) to fabricate the electromagnetic (EM) wave absorber for W-band radars. The EM wave absorption abilities at different thicknesses were simulated using material properties of the EM wave absotber, and an EM wave absorber was manufactured based on the simulated design. The comparisons of simulated and measured results show good agreement. Measurements show that a 1.15 mm thick EM wave absorber has absorption ability higher than 18 dB at 94 GHz for missile guidance radars, and a 1.4 mm EM wave absorber has absorption ability higher than 20 dB at 76 GHz for collision-avoidance radars.

A Study on Non-acoustic Stealth Techniques of Submarine

The submarines reach their weakest point when they sail on the surface to operate snorkel and periscope. At this period, however, there lies a high possibility that the submarines are detected by non-acoustic sensors such as radars, IR signatures, and human observations. In this paper, the non-acoustic stealth was adopted on the mast and periscope of submarines so as to overcome their vulnerability of being easily detected in this given situation. First of all, the non-acoustic detection sensors were investigated and the stealth methods were analyzed. And multi-layered structures consisting of RAM layer, IR layer, and Camouflage layer were proposed on the surface of the submarine. As a results, multi-layered structure was suggested with 3~5 mm of a magnetic material such as ferrite for RAM layer, 1~2 mm of ceramic or nickel for IR layer, and sea-blue paint for Camouflage layer.

A Study on Absorption Properties of the EM Wave Absorber Using TiO 2 in W-band

In this paper, the electromagnetic (EM) wave absorbers using TiO2 as a dielectric material with chlorinated polyethylene (CPE) were investigated in W-band radio frequencies. We compared the relative permittivity with reflectionless curve and the absorption properties of samples containing 40 wt.%, 50 wt.%, 60 wt.%, 70 wt.%, and 80 wt.% TiO2. It is possible to realize a complex relative permittivity satisfying the reflectionless condition by choosing composition ratio of TiO2. The optimized composition ratio of TiO2 for the maximum absorption property is about 70 wt.%. As a result, we have confirmed the realization of an EM wave absorber with a high absorption property in W-band radio frequencies.

Development of the EM Wave Absorber for Preventing RFID Reader Interference in UHF band

In this paper, the EM wave absorber was designed and fabricated for preventing Reader Interference of RFID communication system in UHF band We fabricated several samples in different composition ratios of Amorphous and CPE(Chlorinated Polyethylene). Absorption abilities were simulated in accordance with different thicknesses of the prepared absorbers and changed complex relative permittivity and permeability due to composition ratio. The mixing ratio of Amorphous and CPE was searched as 80 : 20 wt.% by experiments and simulation. Then the EM wave absorber was fabricated and tested using the simulated data. As a result, the developed EM wave absorber has a thickness of 4 mm and absorption ability was over 20 dB in frequency range of . Therefore, it was confirmed that the developed absorber can be used for suppressing RFID reader interference in UHF band.

Analysis on the Characteristics of the EM Wave Absorber Using Sendust-Al(OH) 3

In this paper, we designed and fabricated EM wave absorbers using Sendust, and CPE(Chlorinated Polyethylene). We compared the absorption properties of samples containing 0 wt.%, 3 wt.%, 5 wt.%, 7 wt.% of . The optimized composition ratio of is 5 wt.%, and the absorption property curve just has the tendency to improve at 5 wt.% of . And we used this characteristics to design the double-layered EM wave absorber. The double-layered EM wave absorber has thickness of 2 mm and has absorption ability more than 18.5 dB at a wireless LAN frequency band using 2.4 GHz.

Development of the EM Wave Absorber Using MnZn-Ferrite and Sendust for Wireless LAN at 2.4 GHz

Recently, wireless LANs are often applied in home or office because of its various of convenience. Frequency range of wireless LANs specified by IEEE 802.11b is at 2.4 GHz. The bluetooth, the microwave oven, and the PDA(Personal Digital Assistants) uses, however, the same frequency band. So problems will be produced in these environments, such as multi-pass interference and system-to-system interference. These problems can be eliminated by using EM wave absorber. In this paper, we designed and fabricated EM wave absorber using MnZn-Ferrite, Sendust, and CPE( Chlorinated Polyethylene). The EM wave absorber with the ratio of material (MnZn-Ferrite : Sendust : CPE