Two-dimensional Electromagnetic Bandgap Research Articles

Design and SAR Analysis of a Dual Band Wearable Antenna for WLAN Applications

This paper presents the design of three types of dual band (2.5 & 5.2 GHz) wearable microstrip patch antennas. The first one is based on a conventional ground plane, whereas the other two antennas are based on two different types of two-dimensional electromagnetic band gap (EBG) structures. The design of these two different dual-band EBG structures using wearable substrates incorporates several factors in order to improve the performance of the proposed conventional ground plane (dual band) wearable antenna. The second EBG with plus-shaped slots is about 22.7% more compact in size relative to the designed mushroom-like EBG. Subsequently, we have demonstrated that the mushroom-like EBG and the EBG with plus-shaped slots improve the bandwidth by 5.2 MHz and 7.9 MHz at lower resonance frequencies and by 33.6 MHz and 16.7 MHz at higher resonance frequencies, respectively. Furthermore, improvements in gain of 4.33% and 16.5% at a frequency of 2.5 GHz and improvements in gain of 30.43% and 4.57% at 5.2 GHz have been achieved by using the mushroom-like EBG and EBG with plus-shaped slots, respectively. The operation of the conventional ground plane antenna is investigated under different bending conditions, such as wrapped around different rounded body parts. The proposed conventional ground plane antenna is placed over a three-layered (flat body phantom (chest)) and four-layered (rounded body parts) tissue models, and a thorough SAR analysis has been performed. It is concluded that the proposed antenna reduces SAR effects (<2 W/kg) on the human body, thereby making it useful for numerous critical wearable applications.

FERROELECTRIC THIN-FILM BASED TWO-DIMENSIONAL ELECTROMAGNETIC BANDGAP STRUCTURES

ABSTRACT A two-dimensional electromagnetic bandgap structure has been developed using ferroelectric thin-films. Using lumped inductors and parallel plate capacitors a planar structure is developed which creates a bandgap in the 20–40 GHz range, as demonstrated by experimental results. The ferroelectric material Ba0.6Sr0.4TiO3 (BST) is used in the form of a thin-film between patterned layers of gold to form capacitors on a 500 μm thick high-resistivity Si substrate. A meander line based design is used to form the two-dimensional surface which provides biasing pathways to the varactors. The concept is simulated and experimentally verified using a coplanar waveguide based device in which the EBG surface is used as the ground plane. Designs are also presented for the development of a biasing network to take advantage of the non-linear tunability of the BST dielectric constant in order to make the surface tunable. Experiments used both sputtered and PLD BST films with a maximum bandgap depth of 35 dB. Potential applications are in the area of frequency selective surfaces, and high-impedance ground planes.

On One- and Two-Dimensional Electromagnetic Band Gap Structures in Rectangular Waveguides at Microwave Frequencies

Electromagnetic band gap (EBG) structures of two different configurations implemented inside R120 rectangular waveguides (frequency range 10–15 GHz) are examined. The first configuration has a periodic, piecewise uniform variation of permittivity in the propagation direction. Two types of such one-dimensional (1D) EBG structures are analyzed, one with the unit cell comprising two dielectric layers, the other with three dielectric layers per unit cell. The second configuration is two-dimensional, with the unit cell along the propagation direction containing two sections, each of which is made of alternating pillars of two dielectric materials. The Bloch theorem is invoked for the ideal EBG structures, which are infinitely long in the propagation direction. The mode-matching method (MMM) is used for real 1D-EBG structures, which contain a finite number of unit cells, whereas a combination of the coupled-mode method (CMM) and the MMM is used for real 2D-EBG structures. Spectrums of the transmission coefficient of the fundamental mode for the 1D-EBG structures are computed and shown to compare favorably against experimental data. The effect of inserting a defect in 1D-EBG structures is demonstrated theoretically as well as experimentally. The band gaps computed for real and ideal 2D-EBG structures are compared as well.

Analysis of finite-size coated electromagnetic bandgap structure by an efficient scattering matrix method

This paper presents an efficient simulation algorithm-Scattering matrix method for investigation of the coated finite two-dimensional electromagnetic bandgap (EBG) structures. The method is derived to be capable to simulate the band properties of the coated cylinder photonic crystal with wave discontinuities. Numbers of photonic crystals with waveguide discontinuities are examined. The transmission characteristics of the EBG embedded with metal, dielectric, and various coated cylinders are analyzed. The results show that the tuned bandgap properties are able to provide an additional possibility to develop a novel device.

Mode excitation from sources in two-dimensional EBG waveguides using the array scanning method

An efficient semianalytical algorithm for the evaluation of the field and modal excitation by a line source in a two-dimensional electromagnetic bandgap (EBG) waveguide is presented. The method allows for an accurate and efficient calculation of the near field from the source inside the EBG waveguide, as well as the amplitude of the EBG waveguide mode that is excited. The same method can be applied to a wide variety of structures, as well as other types of sources and discontinuities.

Resonant and waveguiding defect modes in a two-dimensional electromagnetic band-gap slab structure for millimeter wave frequencies

In this article we report about the investigation of two-dimensional electromagnetic band-gap structures in a slab arrangement for millimeter wave frequencies made from high resistive silicon. We investigated both waveguiding modes of a line defect and resonant modes of a point defect with respect to a possible application as passive elements in millimeter wave integrated circuits. We found that a line defect can act as a broadband waveguide comprising low transmission losses and that localized point defect modes can be excited. In accordance with recent observations at optical frequencies, the quality factor of such a defect mode was found to be affected by the local displacement of certain lattice elements near the point defect.

Excitation of line and point defect modes in two-dimensional electromagnetic bandgap structures for microwave frequencies

We report on the controlled excitation of line and point defect modes in a two-dimensional hexagonal electromagnetic bandgap structure made of rods of dielectric material (aluminium oxide). We have investigated the coupling from external waveguides to line defects and subsequent coupling to resonant modes by numerical field simulations and experiments at microwave frequencies. We have demonstrated that an impedance matching to external transmission lines can be achieved for a line defect of a certain width. We have furthermore demonstrated that the excitation of localized defect resonances can be tuned by the variation of certain single lattice elements, affecting the transmission behaviour and quality factor of the resonant modes. Finally, the quality factors of the point defect modes are analysed and a possibility of creation of similar structures for the millimetre wave regime is shown.

Fractal Two-Dimensional Electromagnetic Bandgap Structures

Fractal two-dimensional electromagnetic bandgap (EBG) materials are proposed and studied by means of a full-wave method developed for diffraction gratings. Such technique allows us to characterize, In an accurate and rapidly convergent way, the transmission and reflection properties of periodic fractal structures with an arbitrary geometry in the unit cell. Both polarization cases can be treated. A validation of the employed method is performed through a comparison with theoretical results and experimental data taken from the literature; the convergence properties of our method when applied to fractal EBG materials are checked. In particular, three different fractal EBGs are considered here. Numerical results are reported for the transmission efficiency as a function of the frequency and the incidence angle. Typical effects due to the fractal geometry are observed, like multiband behavior and enlargement of stopbands.

Characterization and design of two-dimensional electromagnetic band-gap structures by use of a full-wave method for diffraction gratings

In this paper, an accurate and efficient characterization of a two-dimensional (2-D) electromagnetic band-gap (EBG) structures is performed, which exploits a full-wave diffraction theory developed for one-dimensional diffraction gratings. EBG materials constituted by 2-D arrays of dielectric rods with arbitrary shape and lattice configuration are analyzed, and the transmission and reflection efficiencies are determined. The high convergence rate of the proposed technique is demonstrated. Results are presented for both TE and TM polarizations, showing the efficiencies as a function of frequency and physical parameters. Comparisons with other theoretical results reported in the literature are shown with a very good agreement, and the authors' theory is also favorably compared with available experimental data. Useful design contour plots are reported by which a very immediate and accurate visualization of the band-gap configurations can be obtained, and design formulas are also included. Finally, the behavioral differences when a periodical defect is present are also highlighted.

Ceramic electromagnetic bandgap structures for microwave and millimetre wave applications

Abstract We have investigated defect resonances in two-dimensional electromagnetic bandgap structures made from sintered alumina ceramics. The particular emphasis of our studies was the analysis of quality factors of different types of defect resonances and the search for novel geometries aiming towards their controlled excitation. For the case of a two-dimensional hexagonal dielectric rod structure we have analysed the quality factors of resonant TM modes in an extended defect. We have identified modes with dielectric filling factor of less than thirty percent indicating the possibility of high Q values. In addition, we have demonstrated a defined excitation of such defect resonances by external waveguides. As a step toward a novel millimetre wave integrated circuit technology, we have demonstrated the defined excitation of 3D confined modes of a line defect in an air-suspended dielectric slab. Our results could pave the way to novel types of integrated millimetre circuits based either on LTCC or high temperature ceramics. Possible future applications are integrated low-phase noise oscillator circuits with potential use for optical communication networks, radar systems and point-to-multipoint communication links.