Left-Handed Wave Propagation of a Coplanar Waveguide based on Split Ring Resonators
Due to the absence of LHMs in nature, a LHM medium has to be artificially fabricated. This can be achieved by micro-structuring a material in a length scale shorter than a wavelength, so that a continuous medium wth effectice permittivity and permeability is obtained. The famous concept of SRR is used here and is described in further detail in [1]. Various concepts are described and also measurement setups to operate in desired frequency bands. The measurement setup is modeled and simulated by CST MICROWAVE STUDIO® (CST MWS) : The model consists of a single SRR placed inside a circular aperture made in a metallic screen placed in a piece of recantangular waveguide as shown in Fig.1.
Figure 1: Model setup for simulating the SRRs magnetic polarizabilities
An edge-coupled SRR design was used in this simulation model and Fig. 2 presents a typical simulation result with a peak of S21 at the SRRs resonance.
Figure 2: A typical response of the S-parameters
The proposed implementation of a left-handed structure [2] is depicted in Fig.3: It consists of a host ordinary coplanar waveguide (CPW). SRRs are symmetrically placed in the back side of the substrate. Thin wires connect the signal-line to the grounded sidelines of the CPW at coincident positions with the SRR's centers, shown in Fig. 3.
Figure 3: CST-MWS Model of the SRR-based LH - CPW.
The dispersion relation given for a lumped element circuit model described in [2] forms a narrow pass band just above the resonant frequency of the rings. Since the wave propagation constant beta decreases with frequency, phase and group velocity are antiparallel. Therefore negative wave propagation occurs and the structure behaves as a narrow band left-handed material (LHM). Fig 4 shows the S-parameter response. In Figs. 5 and 6 an animated plot is shown for the magnetic fields at the center of the passband and outside of the passband, respectively.
Figure 4: Fig.4: S-Parameters for the LH SRR-CPW structure
Figure 5: Fig. 5: Propagation H-Field at the passband center. The port excitation incidents a propagating wave at the left side of the picture. Note the reversed propagation in the vicinity of the SRRs
Figure 6: Fig.6: H-Field at a vertical cutplane for a frequency above the passband
The current density of the SRRs can be seen in Fig 7.
Figure 7: Animated Current density plot. The phase propagation can nicely be seen travelling from right to left
If connecting wires are removed, effective permittivity is no longer negative and the passband behaviour is expected to change to a stop band. The pertinent CST MWS model and the S-parameters are shown in Figs. 8 and 9.
Figure 8: CPW Structure with wires removed
Figure 9: Simulated S-parameters for the model without connecting wires
Conclusion: LH- wave propagation in a CPW coupled to split ring resonators (SRR) and periodically loaded with signal-to-ground wires of the CPW acting as inductors has been shown. Since negative permeabiltiy and permittivity coexist only in the vicinity of the resonant frequency of the rings, signal propagation is limited to a narrow frequency band. The models were simulated with CST MWS and results agree very well with data given in [2].
References:
[1] R. Marques, F. Mesa, J. Martel,F. Medina: "Comparative Analysis of Edge- and Broadside coupled SRRs for meta material design - Theory and experiments", IEEE Trans. on Ant. and Prop. , Vol 51, No. 10, Oct 2003
[2] F. Martin, J. Bonache, F. Falcone, M. Sorolla, R. Marques: "Split-Ring Resonator-based left-handed coplanar waveguide", Applied Physics Letters, Vol. 83, No. 22, 1 Dec 2003
CST Article "Left-Handed Wave Propagation of a Coplanar Waveguide based on Split Ring Resonators"
last modified 15. Dec 2006 10:32
printed 12. Mar 2010 2:15, Article ID 246
URL:
All rights reserved.
Without prior written permission of CST, no part of this publication may be
reproduced by any method, be stored or transferred into an electronic data processing system, neither mechanical or by any other method.
Article ID: 246
Last modified: 15. Dec 2006 10:32
Other Articles
This article is concerned with the evaluation of the temperature distribution inside a human liver when a catheter is inserted. It summarises the simulations performed with the HUGO and University of L'Aquila's ALES anatomical models. The co-simulation procedure using both CST MICROWAVE STUDIO® (CST MWS) and CST EM STUDIO™ (CST EMS) is also described.
With permission and courtesy of the University of L'Aquila, Italy.
Read full article..
Nearly full-sized performance from a spherical coil only 1/6th as long in the E-plane normal direction as a half-wave dipole antenna.
Read full article..
The 3rd Dimension: This inductive, mostly planar structure contains an air bridge.
Read full article..
CST MICROWAVE STUDIO® (CST MWS) was used to aid in the computational investigation of the transverse B1-field homogeneity and SAR values in a 11.7 T / 500 MHz 4-port driven RF head coil loaded with a high-resolution human model (HUGO based on the Visible Human Project®).
The simulations show the expected enhancement of the B-field in the centre of the head compared with the unloaded case and no significant changes in the maximum 1g SAR values between 2-port linear and circular polarizations.
This work was carried out by CEA Saclay, France and is summarised in this article with the permssion and courtesy of Xavier Hanus and his colleagues.
Read full article..
The article presents an antenna-based approach to near-field imaging and spectroscopy, which can be used for both continuous-wave and pulsed broadband electromagnetic radiation from microwave to terahertz frequencies. CST MICROWAVE STUDIO® (CST MWS) was used to perform the simulations.
Read full article..