Ic-Pyo Hong

Fast Frequency Sweep Using Asymptotic Waveform Evaluation Technique and Thin Dielectric Sheet Approximation

The thin dielectric sheet (TDS) surface integral equation (SIE) combined with the asymptotic waveform evaluation (AWE) technique is proposed to efficiently analyze wideband properties of thin dielectric layers such as radome and composite materials. The TDS SIE is an efficient method for analyzing the thin dielectric layer because the number of unknowns of the TDS SIE is fewer than that of the volume integral equation (VIE) and the condition number of the TDS impedance matrix is small. In addition, the AWE technique based on a Taylor series and the Pade approximation is a well-known method for fast frequency sweep. Therefore, the combination of these two methods makes analysis of the thin dielectric layer efficient in the wide frequency region because the advantages of each method are shown at the same time. In order to determine the valid bandwidth of the approximated results for arbitrary problems using the TDS combined with the AWE, the bandwidth estimation approach for the AWE is applied. The results of the proposed method for closed and open structures agree very well with the exact solutions and reveal the capability for fast frequency sweep.

Paper-based frequency selective surface for stable angle of incidence

In this letter, a paper-based frequency selective surface (FSS) attachable to building walls using the ink-jet printing technique is presented using the novel type of FSS at Ku-band. The proposed paper-based FSS has frequency stability for different incidence angles and polarizations and wide band-stop bandwidth. Simulation was performed using a commercial EM software to obtain the transmission loss of the structure and then the measurement results of the fabricated one were compared. The comparisons between the simulation and measured results show good agreements.

Registration sensitivity study of double-layer FSS design for radome

Registration sensitivity study of double-layer cross FSS and 4-legged slot FSS designed for FSS radome was conducted in this paper. Transmission properties, from aligned structure to misaligned structure of half periodicity of unit cell between FSS layers, were discussed. Transmission properties such as center frequency, 3-dB bandwidth and specific characteristic of each misaligned double layer FSS are shown in the paper. The results show that each FSS structure had maximum center frequency transition of 2 GHz and 1.2 GHz and also bandwidth showed change.

Design of X-band Reconfigurable Frequency Selective Surface with High Isolation

In this paper, a bandpass reconfigurable frequency selective surface (FSS) with high isolation at passband, which can reconfigure the operating frequency by using a PIN diode for the X-band, was designed. The proposed surface is composed of four-legged loaded elements, inductance stubs, and a bias grid to supply power. By controlling the electrical length of the unit cell using the forward bias and zero bias of the PIN diode located between the cross-shaped pattern and the stub, the operating frequency can be reconfigured. By controlling the stub length, the switching range of the operating frequency can be controlled. Based on the design results, two types of reconfigurable FSS were constructed, and their measured transmission losses, obtained using the rectangular waveguides WR-75 and WR-90, were compared with simulation results. The comparison showed very similar results.

Investigation of the Finite Planar Frequency Selective Surface with Defect Patterns

In this paper, RCS characteristics on defect pattern of crossed dipole slot FSS having a finite size have been analyzed. To analyze RCS, we applied the electric field integral equation analysis which applies BiCGSTab algorithm with iterative method and uses RWG basis function. To verify the validity of this paper, RCS of PEC sphere has been compared to the theoretical results and FSSs with defect patterns are fabricated and measured. As defect patterns in FSS, missing one column, missing some elements, and discontinuity in surfaces are simulated and compared with the measurement results. Resonant frequency shifts in pass band and changes in bandwidth are observed. From the results, precisely predicting and designing frequency characteristics over defect patterns are essential when applying FSS structures such as FSS radomes.

Study on Thermal Residual Stresses and Transmission Characteristics in N-pole Type Frequency Selective Surface Embedded Composite Structures

In this paper, the delamination and failures in frequency selected surface(FSS) caused by residual stresses in the FSS embedded hybrid composites due to the difference between the coefficients of thermal expansion of components and the transmission characteristic changes due to deformation of FSS patterns by residual stresses were studied. FSS may have different electromagnetic characteristics depending on the type of element, design variables, and arrangement. Design variables of dipole FSS were determined using PSO(Particle Swarm Optimization) to obtain the transmission characteristic for the target resonant frequency. Subsequently, the design variables of other types of N-pole(tripole, cross dipole, and Jerusalem cross) were determined based on the dimensions of the dipole for the comparisons of residual stresses of FSS embedded composite structures and transmission characteristics. In addition, effects of FSS pattern, and stacking sequence of composite laminates were considered.

Design of Security Paper with Selective Frequency Reflection Characteristics

In this research, a security paper based on frequency selective structure technologies was designed and fabricated using selective wave reflection characteristics to prevent the offline leakage of confidential documents. Document leakage detection systems using security papers detect security papers using transceiving antenna gates. For the application of such systems, the structure must be designed with excellent reflection performance and stability at the angle of incidence. For this purpose, a loop and patch-type frequency selective structure based on a four-legged element structure was designed to have X-band frequency reflection characteristics. This design was based on optimized variables and was realized through the screen printing method using silver ink on A4 paper. It was verified that both the design and simulation results matched well. To verify its actual applicability, a detector module operable at 10 GHz was manufactured to observe both the security paper detection range in relation to distance with a signal strength of −10 dBm and the detection area in relation to the number of times that the security paper had been folded.

Security Paper Design with Frequency-Selective Structure for X-Band Electromagnetic Detection System

This study designed and fabricated a frequency-selective structure-based security paper for the electromagnetic detection system of a security gate, which aims to prevent leakage of confidential documents. When a functional paper embedded with a frequency-selective pattern that selectively reflects a specific frequency is being leaked out of a security zone, the electromagnetic detection system receives and detects the intensity of the electromagnetic wave reflected from the security paper passing through an antenna gate, which transmits/receives RF signals. A stable detection performance of the security paper can be ensured by improving the incidence angle stability for incident waves and reducing the reflection loss. This study designed a frequency-selective structure with stable frequency reflection properties at the X-band by utilizing a Jerusalem cross structure. The proposed design was realized using the screen printing technique, which could implement a circuit, to print silver ink on a plain paper. To verify the applicability of the frequency-selective structure-based security paper, an RF detection system with a multiple antenna array was constructed and the intensity of the received signals was measured. The measurement was performed for various scenarios, and the result showed that the proposed security paper was well detected.

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%.

Thermal residual stresses in FSS layer-embedded composite plates in co-cure bonding

The residual stresses occur in the frequency selective surface (FSS)-embedded composite structures after co-curing due to mismatch between the coefficient of thermal expansions between the FSS and composite materials. It is well known that residual stress has a great influence on the strength and fatigue life of the FSS-embedded composite structures. Numerous researches have been reported about residual stresses in the composite structures. However, studies on the residual stresses in the FSS-embedded composite structure have not been widely investigated. Therefore, in this study, the thermal residual stresses of FSS-embedded composite structures were analyzed using finite element analysis, with considering the effect of FSS pattern and size. Various FSS patterns, such as square loop, gridded square loop, and double square loop, are considered in the analysis. The effects of dimensional change of design parameters of FSS pattern on the residual stresses in the hybrid composites were also investigated.