Fulya Bagci

Single and multi-band electromagnetic induced transparency-like metamaterials with coupled split ring resonators

We present a metamaterial configuration exhibiting single and multi-band electromagnetic induced transparency (EIT)-like properties. The unit cell of the single band EIT-like metamaterial consists of a multi-split ring resonator surrounded by a split ring resonator. The multi-split ring resonator acts as a quasi-dark or dark resonator, depending on the polarization of the incident wave, and the split ring resonator serves as the bright resonator. Combination of these two resonators results in a single band EIT-like transmission inside the stop band. EIT-like transmission phenomenon is also clearly observed in the measured transmission spectrum at almost the same frequencies for vertical and horizontal polarized waves, and the numerical results are verified for normal incidence. Moreover, multi-band transmission windows are created within a wide band by combining the two slightly different single band EIT-like metamaterial unit cells that exhibit two different coupling strengths inside a supercell configur...

Compact Balanced Dual-Band Bandpass Filter Based on Modified Coupled-Embedded Resonators

A new compact balanced dual-band bandpass filter based on coupled-embedded resonators with modified ground plane is presented in this work. Common-mode is rejected within the two differential passbands by symmetrically introducing four coupled U-shaped defected ground structures below the resonators. Common-mode rejection is significantly improved when compared with the standard (solid ground plane) filter with similar geometry thanks to the introduction of four extra transmission zeros. Due to the symmetry, the differential mode is not significantly affected by the presence of the U-shaped resonators. Circuit-model data, full-wave simulations and measurements are provided to verify the benefits of the proposed dual-band filter.

A polarization independent electromagnetically induced transparency-like metamaterial with large group delay and delay-bandwidth product

In this study, a classical analogue of electromagnetically induced transparency (EIT) that is completely independent of the polarization direction of the incident waves is numerically and experimentally demonstrated. The unit cell of the employed planar symmetric metamaterial structure consists of one square ring resonator and four split ring resonators (SRRs). Two different designs are implemented in order to achieve a narrow-band and wide-band EIT-like response. In the unit cell design, a square ring resonator is shown to serve as a bright resonator, whereas the SRRs behave as a quasi-dark resonator, for the narrow-band (0.55 GHz full-width at half-maximum bandwidth around 5 GHz) and wide-band (1.35 GHz full-width at half-maximum bandwidth around 5.7 GHz) EIT-like metamaterials. The observed EIT-like transmission phenomenon is theoretically explained by a coupled-oscillator model. Within the transmission window, steep changes of the phase result in high group delays and the delay-bandwidth products reach 0.45 for the wide-band EIT-like metamaterial. Furthermore, it has been demonstrated that the bandwidth and group delay of the EIT-like band can be controlled by changing the incidence angle of electromagnetic waves. These features enable the proposed metamaterials to achieve potential applications in filtering, switching, data storing, and sensing.

Optically transparent frequency selective surface for filtering 2.6 GHz LTE band

In this study, a frequency selective surface consisting of open ring resonator arrays on glass substrate is proposed for filtering TM-polarized 2.6 GHz frequency band by using equivalent inductance and capacitance expressions and full-wave electromagnetic simulation. The FSS is evaluated for different permittivity, strip and gap width as well as strip length and periodicity values and the transmission response is also verified experimentally.

Parametric analysis of different radii of concentric rings and substrates in frequency selective surfaces

In this study, the effects of the radii of the concentric rings and the substrate material on the spectral characteristics of the two concentric ring slot frequency selective surface structure are investigated by means of a finite integration technique and finite element technique based simulators. For the investigated dual band frequency selective surface structure, it has been demonstrated that the radius of the circular metallic patch and the inner ring slot affect only the resonance characteristics of the second stop band. However, the outer radius of the outer ring slot affects only the resonance characteristics of the first stop band. Tailoring the radius of the center metallic patch is found to be more useful for making fine adjustments in the spectral position of the second resonance band. The resonance frequencies of the stop bands can also be decreased if a substrate having a larger permittivity value is used.

A novel tunable metasurface for filtering the electromagnetic waves

In this study, a novel tunable metasurface is designed in order to filter the electromagnetic waves. The single-frequency window-shaped structure is enhanced to have dual-frequency by loading a gap in order to filter the electromagnetic waves. An epsilon-negative (ENG) unit cell is designed to form the metasurface. The parameter retrieval for the effective permittivity and permeability is performed using a version of the Nicholson-Ross-Weir (NRW) algorithm, which is improved by implementing the Kramers-Kronig relationship. The parametric analyses are also performed as regards the geometrical and material properties. The simulations are conducted via CST Microwave Studio, which is based on Finite Integration Method (FIM).

A 1x4 power-splitter based on photonic crystal Y-splitter and directional couplers

A 1×4 photonic crystal power splitter operating in the optical communication window is demonstrated by plane-wave expansion and finite-difference time-domain simulations. The device consists of one Y-junction and two directional couplers. Double 60o bends are formed at the exit of directional couplers to prevent crosstalk. The Y-junction, double bends and coupling holes at the directional couplers are optimized to increase the transmission efficiency at the output ports. The simulation results exhibit almost equal power splitting with low loss characteristic. The investigated design shows potential for optical switching and routing applications in optical communications.