Cell miniaturization for x-band frequency selective surface

Abstract

Electromagnetic Interference (EMI) generated by wireless devices can cause disturbance to electrical circuits. In this thesis, the Frequency Selective Surface (FSS) is proposed as the EMI shield for the interference control as it eliminates the need for power supply and blocking only the unwanted signals without interrupting the operation of other wireless devices. The contribution of this thesis comprise of the miniaturization technique employed for the dimension reduction of the unit cell FSS and the evaluation of the bending effect of the conformal FSS based on the semi-infinite modeling technique. All the designs and simulation works are completed utilizing the Computer Simulation Technology (CST) Microwave Studio software. First, the FSS is developed on the FR-4 substrate to perform as the band-stop planar FSS which support the attenuation over the X-band signals ranging from 8 GHz to 12 GHz. The evaluation of the planar FSS is performed using the unit cell boundary modelling. The miniaturization of the ring loop FSS is performed by adding four stubs at each 90° angle of the ring loop and four cross-dipole are embedded into convoluted ring loop FSS to further reduce the unit cell dimension. All the proposed unit cell geometries are modeled to accomplish the excellent transmission frequency response for normal and oblique incidence up to 60° cases at Transverse Electric (TE) and Transverse Magnetic (TM) polarizations. In order to ensure the FSS is competent to be employed as the EMI shield for the conformal structure, the proposed design is developed onto the flexible Polyethylene Terephthalate (PET) substrate. To prove the conformal suitability of the proposed planar design, the bending effects of the conformal FSS are investigated. The semi-infinite modeling allows modelling of the finite and infinite array in curved and uncurved directions, respectively. With the employment of this technique, the bending effects toward the performance of the proposed FSS at the normal angle of incidence for TE and TM polarizations are obtainable. From the results obtained, the convoluted ring loop FSS is the most sensitive to the bending effect while the ring loop FSS is the least sensitive to the bending effect. All the proposed FSS geometries are fabricated using either photolithography or inkjet printing technique. The manufactured prototypes are measured experimentally using bi-static measurement technique. All the proposed FSS provides minimum attenuation of - 25 dB at 10 GHz. The measurement results are shown to be similar with the simulation results. Hence, the proposed FSS can be employed in both planar and conformal structure.