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Tunable Negative Refractive Index Metamaterial

            There has been great interest in the development of metamaterial composites that possess negative dielectric (ε) and permeability (μ) constants coincident in frequency giving rise to a negative index of refraction (n). These constructs are generally referred to as negative index metamaterials or NIMs. Much of the fascination in NIMs arises from their unusual electromagnetic properties such as backward wave propagation and subwavelength resolution imaging that allow for several novel applications such as super lenses, leaky wave antennas, and miniature delay lines. Notable NIMs are resonant metamaterials, photonic crystals and planar periodic arrays of passive lumped circuit elements. These NIMs are limited by inherent narrow bandwidth and are not at all tunable. In order to obtain negative n at various frequencies, one would have to change the periodicity and size of the elements. Additionally, it is difficult to scale these materials to terahertz and visible frequencies as the magnetic plasma resonance cannot be achieved in nanoscale SRR that is necessary for optical implementation of the NIMs.

            We demonstrate a scheme by which continuous frequency tuning of the negative index is possible by using a YIG film or slab as shown in Fig. 1. The effect of the YIG film is to provide a tunable negative μ over a continuous range of frequencies on the high frequency side of the ferrimagnetic resonance. Complementary negative is achieved using a single periodic array of copper wires. As shown in Fig. 2, a negative refractive index region of 0.5GHz width is determined from the measurements. And it can be tuned by varying the bias magnetic field.

NIM
Figure 1. Schematic diagram of the NIM composite mounted in a K-band waveguide.
NIM
Figure 2. The calculated real part of refractive index from the transmission measurement of the NIM design

            Traditional ferrite phase shifters operate at frequencies away from the FMR in order to avoid absorption losses near the FMR frequency. As a result NIM is necessarily small. A tunable compact phase shifter utilizing negative refractive index metamaterial is demonstrated. It is the first application of its kind. Near ferrimagnetic resonance, a phase shift tuning of 160o/kOe is achieved at 24GHz as Fig. 4. The insertion loss varies from - 4dB/cm to -7dB/cm. Figure 3 shows the different working region relative to the permeability of the magnetic material.
NIM
Figure 3. The calculated complex permeability of high quality single crystal YIG films showing the different working frequency regions for traditional and NIM phase shifters.

NIM
Figure 4. The measured insertion phase shift and insertion loss (|S21|) vs. applied external magnetic field at 24GHz.

            At the same time, we are developing and testing planar designs of the tunable NIM and NIMs working at higher microwave frequency band using different magnetic materials. 

Reference:

  1. Y. He, P. He, S. D. Yoon, P.V. Parimi, F.J. Rachford, V.G. Harris and C. Vittoria: ‘Tunable negative index metamaterial using yttrium iron garnet,’ J. Magn. Magn. Mater., Vol.313, Issue 1, June 2007, Pages 187-191
  2. Y. He, P. He, V. G. Harris, and C. Vittoria: ‘Role of Ferrites in Negative Index Metamaterials’, IEEE Trans. Magnetics, Vol. 42 No 10
  3. P. He, P.V. Parimi, Y. He, V.G. Harris, and C. Vittoria:‘Tunable Negative Refractive Index Metamaterial Phase Shifter’, not published yet.

 

 

 

 


 

 
 
         
Maintained by Aria Yang, Last updated on Nov. 3, 2008