Reconfigurable Frequency Selective Surface Research Articles

Microelectromechanical Systems Tunable Frequency-Selective Surfaces and Electromagnetic-Bandgap Structures on Rigid-Flex Substrates

A novel microelectromechanical systems (MEMS) process is developed to fabricate large numbers of high-performance MEMS devices monolithically integrated onto a rigid-flex organic substrate using low-temperature processes. The rigid-flex substrate is all dielectric, which is amenable to low-loss electromagnetic structures. The substrate provides mechanical support to the MEMS devices while maintaining overall flexibility. The newly developed process is used to fabricate a MEMS reconfigurable frequency-selective surface (FSS). A practical bias network is incorporated into the structure design to ensure that all devices are actuated simultaneously. A detailed parametric sensitivity analysis establishes the robustness of the FSS design with respect to fabrication process variations. FSS structures operating in the Ku- and Ka-bands are fabricated and tested with good correlation between simulated and measured results. The newly developed MEMS process is also used to fabricate a reconfigurable electromagnetic-bandgap (EBG) structure. An EBG structure operating in the Ka -band is fabricated and tested to verify the validity of the proposed concept.

A novel concept for reconfigurable frequency selective surfaces based on silicon switches

AbstractThe authors describe a novel concept for reconfigurable frequency selective surfaces based on metallic dipole and cross‐dipole elements connected by switches on an exposed silicon substrate. As the conductivity of silicon can be varied over a large dynamic range by photonic excitation, it represents a good candidate substrate material for producing effective switches. The genetic algorithm was used to obtain optimal performance of the switch with respect to variations of the geometric and electrical parameters of the design for desired excitation frequencies. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 109–114, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22041

Magnetic MEMS Reconfigurable Frequency-Selective Surfaces

A reconfigurable frequency-selective electromagnetic filter implemented by integrating hard magnetic materials with microelectromechanical systems (MEMS) provides a new variation of reconfigurable frequency-selective surfaces (FSS). By incorporating magnetically actuated dipole elements that are capable of being tilted away from the supporting surface, we can tune the FSSs operating frequency without having to physically alter the dimensions of the dipole elements. The 25/spl times/25 array of microactuators used in this work each consist of a 896/spl times/168/spl times/30 /spl mu/m/sup 3/ ferromagnetic plate made of 40Co-60Ni, layered with a 1-/spl mu/m-thick conductor (Au), attached to a pair of 400/spl times/10/spl times/1 /spl mu/m/sup 3/ polysilicon torsion beams, suspended just above the supporting substrate. The high remanent magnetization of the ferromagnetic material allows for relatively small magnetic fields (/spl sim/2.1 kA/m) to induce significant angular deflections (/spl sim/45/spl deg/). This innovative reconfigurable FSS design has successfully demonstrated electromagnetic-signal diplexing and tuning its resonant frequency over a bandwidth of 2.7 GHz at a frequency of 85 GHz.

A Model-Based Parameter Estimation Technique for Wide-Band Interpolation of Periodic Moment Method Impedance Matrices With Application to Genetic Algorithm Optimization of Frequency Selective Surfaces

A model-based parameter estimation (MBPE) technique is introduced in this paper for efficiently interpolating periodic moment method (PMM) impedance matrices over a wide frequency band. In the model, only the Floquet harmonics that strongly affect the frequency band of interest are employed to approximate the matrix elements, while the contributions from all other higher-order harmonics are compactly represented by two additional terms. The derivation of the model is physics-based, and the objective is to find the coefficients of the terms in the model by utilizing the values of the impedance matrix elements calculated via PMM at only a few frequency points. The number and position of these fitting points can be pre-determined from the cutoff frequencies of the Floquet harmonics, which allows the MBPE interpolation process in this case to be completely automated. In other words, the number and position of the sampling points are only dictated by the periodicity of the frequency selective surface (FSS) structure and the frequency range of interest. Unlike many of the other scattering parameter-based techniques, the shape and the resonances in the response of the FSS do not have any impact on the construction of the interpolation model. This makes it particularly useful in genetic algorithm (GA) aided FSS design, since for a fixed periodicity and frequency range the MBPE interpolation is independent of the scattering response of candidate FSS designs. Several examples of the new PMM-MBPE approach are presented including one in which it is used to considerably speed up the GA-based design process for a reconfigurable FSS.

A novel design methodology for reconfigurable frequency selective surfaces using genetic algorithms

In this paper, a new reconfigurable frequency selective surface (RFSS) design concept is introduced. A grid of simple metallic patches interconnected by a matrix of switches is proposed as the unit cell of an RFSS. The switches are independently addressable and provide significant transmission and reflection flexibility over a large range of frequencies. This flexibility is exploited by optimizing the switch settings using a genetic algorithm to produce a desired frequency response. The versatility of the design technique is demonstrated by presenting several examples of genetically optimized RFSS. The first example to be considered is a linearly polarized FSS that can be reconfigured for either single-, dual-, or tri-band operation. An RFSS design is also introduced that can be optimized to have a frequency response that is polarization independent in one state (i.e., for one combination of switch settings) and polarization dependent in another state.

Reconfigurable MEMS-enabled frequency selective surfaces

A technique for designing reconfigurable frequency selective surfaces using microelectromechanical systems (MEMS) technology is presented. A method of moments simulation technique for analysing these periodic structures has been used to predict the tunability using this technique. Fabricated and measured results verify the concept of tunability.

Reconfigurable FSS response from two layers of slotteddipole arrays

Two layer frequency selective surfaces (FSS) comprised of aperture elements on a single dielectric substrate are used to produce extremely narrow and angularly stable passband transmission responses. Experimental results are compared with predictions to verify a computer model which is based on solving a pair of coupled aperture integral equations. Reductions in bandwidth of up to a factor of seven have been achieved.

Coupled dipole arrays as reconfigurable frequencyselectivesurfaces

A technique for reconfiguring in situ the plane wave transmission response of frequency selective surfaces is explained. An experimental prototype, consisting of arrays of dipole elements, has been assessed and frequency responses are presented at normal incidence. Reflection resonances are dynamically shifted achieving maximum frequency shift ratios of 2:1.