Furthering Electromagnetic Architecture of Buildings - An International Travel Application

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The electromagnetic spectrum is a finite resource and frequency reuse is essential particularly in the mobile communications bands. Signal propagation in the built environment is notoriously complex but buildings are an environment where measures can be implemented to modify their electromagnetic architecture. Multiple occupancy commercial buildings, partitioned into offices, can in principle be electromagnetically screened internally to assist frequency reuse, and large, more open structures such as theatres can be shielded by suitable construction of the outer walls. It is common practice now, particularly in new buildings, to install aluminium foil backed layers within walls, as a fire precaution measure or for insulation purposes. Suitable screening can greatly reduce co-channel interference and our colleagues in Auckland have pointed out that an increase in the signal-to-interference ratio of just 10 or 15dB can decrease outage probability by an order of magnitude or more. At other frequencies access through the screen is necessary, especially at the emergency services band - at 400MHz in the UK, but apparently as low as 75MHz in New Zealand. In a very successful project funded by EPSRC and the National Policing Improvement Agency, we have been focussing on the application of Frequency Selective Surfaces (FSS) to the built environment with the emphasis on operation at the long wavelengths used in mobile communications. For example, a long-wavelength FSS intended to provide this emergency access while employing a minimum number of array elements has been based on simple square loop slot elements. An alternative approach is to reduce the array unit cell size, and this concept has led to a close collaboration with the Radio Systems Group at the University of Auckland who have extensive experience measuring and modelling the propagation of signals in buildings. Although FSS is an established technology, it is not well understood at mobile frequencies where the arrays are finite, elements may well be highly convoluted, layer separations are electrically small and room dimensions are comparable to the operating wavelengths. FSS design is challenging at mobile bands as they are far apart in fractional ratio terms. We have already installed in an office-type test room in Auckland a novel two layer FSS composed of highly convoluted elements. This work is ongoing, building on the work previously funded by the EPSRC. This application is for funding to enable the investigators to travel to Auckland on two separate occassions to work on three related topics: 1. to study the effect of FSS when mounted in small apertures, 2. to characterise FSS performance for high angles of incidence, 3. to assess the effect of wall mounted FSS on Wireless Computer Network performance in a specially built office-type room.