Metamaterials Research
Metamaterials are artificial electromagnetic materials that contain structure which is small compared to the wavelength of operation. They can be designed to have an electrical or a magnetic response (i.e. an effective permittivity, e, and permeability, µ) that can be large or small, positive, negative or even zero at any selected frequency. The engineered response of such artificially constructed metamaterials has had a dramatic impact on the physics, optics, and engineering communities, because metamaterials can offer electromagnetic properties that are difficult or impossible to achieve with conventional, naturally occurring materials.
Artificial magnetic materials based on non-magnetic conducting elements, which can provide a designed magnetic response at RF frequencies, are a natural match for magnetic resonance (MR) applications. For operation in the RF regime, we have developed the Swiss Roll metamaterial design (see Fig. 1), which is manufactured by rolling an insulated metallic sheet around a cylinder, and stacking many of these cylinders together.
This metamaterial can be applied in the MRI environment as a flux duct, linking the imaged region to the detector. In an early demonstration (Fig. 2), we performed an MRI experiment in which the metamaterial was used as a flux guide, transporting image information from the object (a thumb) to the detector coil. Without the metamaterial, no image could be seen; with the material in place, the signal was ducted to the detector, revealing the structure of the thumb.
More recently, we have built a prism composed of high performance Swiss Rolls (Fig. 3) which behaves as a magnetic faceplate, transferring a magnetic field distribution faithfully from the input to the output face.
Metamaterials can be used to manipulate RF flux in a variety of ways, and we have also explored the construction of an RF yoke for directing and concentrating magnetic flux. This could provide enhanced sensitivity, permit the use of a remote detector (possibly cooled), or allow the applied RF field distributions to be tailored to particular requirements.
Contact
For more information contact Mike Wiltshire.
Useful Links
http://www.sst.ph.ic.ac.uk/photonics/
http://www.ee.duke.edu/~drsmith/
Recent Publications
D R Smith, J B Pendry and M C K Wiltshire, “Metamaterials and Negative Refractive Index”, Science 305, 788 - 792 (2004)
M C K Wiltshire, E Shamonina, I R Young and L Solymar, “An experimental and theoretical study of magneto-inductive waves supported by one-dimensional arrays of ‘Swiss Rolls’ ”, J. Appl. Phys. 95, 4488 - 4493 (2004)
S Anantha Ramakrishna, J B Pendry, M C K Wiltshire and W J Stewart, “Imaging the near field”, J Modern Optics 50, 1419 - 1430 (2003)
M C K Wiltshire, E Shamonina, I R Young, and L Solymar, “Dispersion characteristics of magneto-inductive waves: comparison between theory and experiment”, Electron. Lett. 39, 215 - 217 (2003)
M C K Wiltshire, J B Pendry, J V Hajnal, D J Edwards and C J Stevens, “A metamaterial endoscope for magnetic field transfer: near field imaging with magnetic wires”, Optics Express 11, 709 - 715 (2003)
M C K Wiltshire, “Bending Light the Wrong Way”, Science 292, 60 - 1 (2001)
M C K Wiltshire, J B Pendry, I R Young, D J Larkman, D J Gilderdale and J V Hajnal, “Microstructured Magnetic Materials for RF Flux Guides in Magnetic Resonance Imaging”, Science 291, 849 - 851 (2001)
