Mr Miguel Camacho Aguilar
PhD ProjectThin metal multilayers for microwave applications
Prof. Alastair Hibbins and Prof. Roy Sambles
The use of structured metal surfaces to control the absorption and emission of microwave radiation is now well established with much original work by Sievenpiper  and also our group here at Exeter . However such structures use metal layers which are several microns thick and as such are much thicker than the microwave skin depth. Thus, as far as the microwaves are concerned they may just as well be infinitely thick. We have shown in recent work how to resonantly transmit microwaves through a thin metal  which would normally, because of the huge impedance mismatch (even though thinner than the skin depth) be impossible. Here we wish to extend this work to explore for the first time the microwave response of multilayer metal/dielectric stacks. Such stacks are likely to strongly absorb microwaves provided the impedance can be adjusted suitably to match that of air. This is a far from trivial task as modelling the electromagnetic field inside the thin metal layers is formidably difficult because of the massive (factor of over 10,000) scale factor change for the wavelengths of microwaves in the air and metal. This work will be a combination of such difficult modelling with sample fabrication and characterisation. Large area multilayer samples will also be a challenge experimentally although initially we shall be able to work with the thin metal layers found on aluminised mylar. The ultimate structures will contain multilayers with magnetic materials and conductive layers establishing underlying principles for the ‘onion skin’ microparticle structures which are currently of much interest to the magnetic Metamaterials community.
1. D Sievenpiper, L Zhang, RFJ Broas, NG Alexopolous, E Yablonovitch (1999) Microwave Theory and Techniques, IEEE Transactions on 47, 2059-2074 High-impedance electromagnetic surfaces with a forbidden frequency band
2. Butler C A M, Parsons J, Sambles J R, Hibbins A P and Hobson P A (2009) Appl Phys Lett, 95, 174101
Microwave transmissivity of a metamaterial-dielectric stack.
3. Edmunds J D, Lockyear M J, Hibbins A P, Sambles J R, and Youngs I J (2013) Appl Phys Lett, 102, 011120
Resonantly overcoming metal opacity.