XV Workshop Iberchip, Buenos Aires - Argentina, 25 - 27 de Marzo de 2009
Metamaterial-MEMS Reconfigurable Transmission Line Georgina Rosas-Guevara, Roberto Murphy-Arteaga, Alonso Corona-Chávez National Institute of Astrophysics, Optics and Electronics, Luis Enrique Erro #1, Tonanzintla, Puebla. 72840, México E-mail:
[email protected],
[email protected],
[email protected] II. DESIGN AND CIRCUIT MODEL
Abstract ² This article presents a broadband (BB) metamaterial (MTM) reconfigurable transmission line (TL) controllable by means of a MEMS capacitor. The device is based on coplanar waveguide (CPW) technology and operates at a central frequency of 5 GHz for a beam steering system. A design method for the transmission line, CRLH-MTMMEMS, which consists of a mixed approach using the developed circuit model and full-wave simulations, is herein presented.
A. CRLH-MTM MEMS Transmission Line The parameters of a composite structure righ/left handed Metamaterial CRLH-MTM are determined (LR, CR, LL, CL) using the following equations, developed by Caloz and Itoh [5]
Index Terms ² MTM metamaterial, TL transmission line, CPW coplanar waveguide, CRLH composite right/ left handed, MEMS micro-electro-mechanical systems.
LR
I. INTRODUCTION
LL
CR
Metamaterials are new, man made materials which present unique electromagnetic properties that are readily controllable. Research in this field opens up new ways for innovation in communications, based on original designs that exploit the principal properties of metamaterials, such as simultaneous negative permittivity (H) and permeability (μ), with anti-parallel group (vg) and phase velocities (vp), and a negative refractive index (n) [1-2]. These unique characteristics make them appropriate for RF and microwave applications [3-5].
CL
Z C [IRH ILH ] 2 NZ0 [I RH ILH ] 2 NZ C Z0
(1)
(2) (3)
2 NZ C
Z0 [I RH I LH ] 2N Z0 Z C [I RH I LH ]
(4)
where Z0 is the center angular frequency; ZC is the coupling impedance; N the number of cells; and the RH/LH phases are MRH and MLH. A LH Transmission Line is an artificial structure created with a series capacitance CL and a shunt inductance LL. Since there are always parasitic elements present, a purely LH structure cannot exist physically. These parasitic elements, CR and LR, are shown in Figure 1. Thus, we need to work with a composite RLH model, which represents the most general MTM structure possible, as shown in Figure 1 [5-6].
Through this article, we introduce a Transmission Line CRLH-MTM-MEMS cell, which using MEMS technology can be reconfigurable by moving elements (variable capacitors). In particular, for antenna applications, this reconfigurable metamaterial structure offers multiband operation, beamwith tuning, high directivity and small size.
Z se
The structures were simulated in Ansoft HFSS version10, using a high resistivity silicon substrate, and a gold conducting layer with a thickness of 4μm to reduce losses, and the insulating layer is made of BenzoCyclobutene (BCB). With these considerations, a basic cell with dimensions of 1.654 mm x 3.06 mm was designed to demonstrate the reconfigurability of a basic CRLH-TL MTM-MEMS cell. The design methodology is presented in detail, and the results of full-wave simulations are shown.
Zsh
Fig. 1. Equivalent Circuit Model of a cell CRLH LT-MTM.
The series resonant frequency and shunt resonant frequency are given by [5]:
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XV Workshop Iberchip, Buenos Aires - Argentina, 25 - 27 de Marzo de 2009
Z se
1 LR C L
(5)
Z sh
1 LL C R
(6)
presents excellent linearity. The main disadvantages are the limited actuation margin and the difficulty of encapsulation; this is a common problem to all MEMS devices [7]. The capacitance between parallel plates is determined from:
Theoretically, a CRLH TL has two operating regions, corresponding to the RH mode (E>0) and to the LH mode (E
