In-Gon Lee

Design of Transparent Electromagnetic Absorbing Structure using Metal Grid Mesh Printing

ABSTRACT In this paper, we designed the transparent circuit analog radar absorbing structure using printed metal grid mesh for enhanced optical transmittance. To obtain wideband electromagnetic absorption and enhanced optical transparency at X-band, we proposed the resistive FSS(Frequency Selective Surface) using printed metal mesh pattern on transparent glass with PEC(Perfect Electric Conductor) plane using ITO(Indium Thin Oxide) coating. We then fabricated the proposed structure to verify the simulation results obtained from commercial EM simulator. The comparisons between the simulation and measured results show good agreements. The results also show that the proposed radar absorbing structure can provide wideband reflection as well as better optical transparency. We can apply this proposed structure to the canopy of stealth aircraft and other stealth and security applications for visible transparency.Key Words : Electromagnetic Absorbing Structure(전파 흡수구조), Frequency Selective Surface(주파수 선택표면구조), Metal mesh(메탈 메쉬), Optical Transmittance(광투과율)

Scalable Frequency Selective Surface with Stable Angles of Incidence on a Thin Flexible Substrate

A band-stop scalable frequency selective surface (FSS) structure that provides stability for an angle of incidence and polarization is designed using the repetitive arrangement of a unit structure miniaturized on a thin dielectric substrate. The designed miniaturized FSS has a hexagonal unit cell of a minimum size of 0.081 λ at 2.5 GHz in which a triangular loop is repeated. In addition to the frequency stability, the proposed structure reduces the design complexity that is the biggest shortcoming of the miniaturization techniques studied previously. A scalable FSS structure possessing stable frequency response characteristics over a wide band ranging from 2 to 8 GHz, which is achieved by the control of a single design variable, can be designed. For verification of the proposed structure, FSS structures that operate in the bands of 2.5 GHz, 5 GHz, and 8.2 GHz have been designed and fabricated on a very thin substrate. It has been confirmed that the results of the measurement and simulation correspond well with each other. The designed structures also demonstrate high stability for both the polarized wave and the incidence angle of the incident wave.

Design of Window Applicable Blind-type Frequency Selective Surface

In this paper, we presented the window applicable blind-type frequency selective surface to control the coverage area of wireless communication in secure building or conference room. The proposed frequency selective structure has the reconfigurable frequency range depends on its blind rotation angle. To verify the proposed structure, we fabricated the window blind-type frequency selective surface with four-legged loaded element and ring-type element as a unit cell and performed measurements of the transmission characteristics for different blind rotation angles to prove the feasibility. The measurement results show good agreements with the simulation results. One of the advantages is that the proposed structure does not need to have a bias circuit, so it is very easy to implement at low cost and also can be applied to any planar surface for wireless security applications.

Design of Active Frequency Selective Surface with Curved Composite Structures and Tunable Frequency Response

We present an active frequency selective surface (AFSS) consisting of a curved composite structure that provides structural stability and robustness. The proposed structure can operate on either the C-band (OFF state) or X-band (ON state) by controlling the PIN diode located between the cross-shaped loop and the inductive stub on the surface. Moreover, it minimizes parasitic couplings through grid-type on/off bias circuits and via holes. Thus, the AFSS guarantees isolation from the unit cell, which is a downside of a previous control technique called reconfigurable frequency selective surface. We analyzed the impact of composite structures and the three-dimensional shape on the AFSS transmission with a foam-core sandwich structure, which is light and mechanically strong, by considering conditions of a real application environment.

Design of a Patterned Soft Magnetic Structure to Reduce Magnetic Flux Leakage of Magnetic Induction Wireless Power Transfer Systems

A soft-magnetic-metal-based shield structure was designed to reduce magnetic flux leakage in magnetic-induction wireless power transfer systems. Soft magnetic metals have the advantages of high permeability and low magnetic loss, but have the disadvantage of high power loss owing to eddy current that is induced on the surface as a result of low-insulating characteristics. In order to solve this problem, a patterned soft magnetic metal was used to cut the route of the induced current. This decreases the power loss and reduces the leakage of magnetic field. A soft-magnetic-metal-based structure that has various patterns was designed to find the optimal structure for reducing the leaking magnetic field. By applying this structure to Wireless Power Consortium commercial A10 coil, the inductance, transfer efficiency, and magnetic flux leakage of the coil according to the material and the structure of the soft-magnetic-metal-based structure were observed. Fabrication and measurement tests were performed to verify the proposed structure, and it was found that the test results corresponded to the simulation results. It was confirmed that the proposed structure had a 84% thinner thickness compared with that of a conventional ferrite shield, an equivalent transfer efficiency of 74.5%, and a reduction in magnetic flux leakage of 20.9%.

Design of the Reconfigurable Frequency Selective Surface for X-Band Applications with Improved Isolation

This paper presents the design of reconfigurable frequency selective surfaces for X-band bandpass operation with improved isolation. The proposed reconfigurable FSS is composed of a four-legged loaded element, a inductive stub and a bias grid. The PIN diode is located between the four-legged loaded element and the stub, which can control the frequency response of reconfigurable FSS by ON/OFF state. By adjusting the length of the stub, the desired bandpass frequency and the improved isolation between ON and OFF state can be obtained. For validation of simulated results, we have carried out transmission characteristic measurements using rectangular waveguide of WR-90. The measured results are in good agreements with the simulated results.

Miniaturized Frequency Selective Surface with a Scalability of Operating Frequency

In this paper, a miniaturized frequency selective surface(FSS) for bandstop operation that provides stability for an angle of incidence and polarization is presented. The proposed miniaturized FSS has the unit cell of hexagonal structure with triangular loops and size of the unit cell is at 2.5 GHz operating frequency, which is very small compared to operating wavelength. In addition, unlike the conventional design, which requires complicated design parameters, the proposed FSS is easily expanded to the desired operating frequency for 2~8 GHz, by controlling the specific design parameters. To validate the simulation results, the FSS structures having different operating frequencies, 2.5 GHz, 5 GHz and 8.2 GHz were designed, fabricated and measured. The comparisons between the simulation and the measured results show good agreement. The proposed miniaturized FSS can provide better frequency stability for different incidence angles and polarizations.

Transmission Characteristics of Curved Reconfigurable Frequency Selective Structure

In this paper, the flexible and reconfigurable frequency selective surface for C-band was designed using patch array and grid structure for radome and other curved surface applications. Frequency reconfigurability was obtained by varying the capacitance of varactor diode and flexibility is implemented by using flexible PCB. For the validity of the proposed structure, we fabricated the flexible and reconfigurable frequency selective structure and measured the frequency reconfigurability for different bias voltages and different curvature surfaces from the optimized design parameters. From the measurement results, we know that the proposed structure has the wideband reconfigurable frequency bandwidth of 6.05-7.08GHz. We can apply this proposed structure to the curved surface like as radome of aircraft or warship.

Design of a film antenna using a cloverleaf-shaped monopole structure for WiBro and WLAN

This study designs a film monopole antenna for WiBro (wireless broadband internet, 2.3-2.4GHz) and WLAN (wireless local area network, 2.4-2.48GHz) bands. A variety of design parameters were used to optimize frequency properties, and radiating and grounding elements were placed on the same plane for maximized radiation efficiency. Cloverleaf-shaped radiating elements were used to induce a phase difference of 180 degrees and thus obtain improved bandwidth. This paper presents the possibility of realizing broadband by using parasitic elements. The antenna created in this study achieves a peak gain of up to 3.18dBi and satisfies WiBro (2.3-2.4GHz) and WLAN (2.4-2.48GHz) bands with a bandwidth of 2.30-2.54GHz (9.8%) at -10dB or lower.