This research explores the design of a secure electromagnetic building, focusing on buildings such as hospitals, embassies, cinemas and prisons. The novelty in this research was the investigation of a surface, which can be embedded into a wall or a window of a room/building, which is “smart”. In this case “smart” relates to the surfaces ability to reconfigure itself depending on the environment required for wireless signals that are present in the local surrounding area.
For the purpose of designing a “smart” surface, classical passive Frequency Selective Surface (FSS) designs attenuating more than 60dB being very difficult, due to this poor filtering obtained by current passive FSS designs with limited options to reconfigure it practically.
By introducing tuning elements, such as varactor diodes which are embedded into the FSS structure, vast improvements can be seen which can impair mobile phone signal without the need of greater attenuation levels. The outcome of this is a reconfigurable FSS, where the power transmitted through the FSS is a function of the bias voltage across the diodes. The reconfigurable nature of the FSS allows us to rapidly switch the complex transmission response such that the mobile phone signal passing through the FSS is corrupted. This is the first time that such a system has been tested against the GSM protocol.
Simulations and measurements of the system verified that this concept can achieve the required performance. To test the performance of the new FSS, state of the art signal generators and receivers were employed to evaluate the Bit Error Rate (BER), which is a measure of the quality of a communications signal. BER of greater than 35% were achieved, which is significantly higher than that needed to successfully receive a signal.
Original work has also been carried out investigating the diffraction effects of FSS for secure building applications in order to understand the practical implications of this technology. In summary all aspects of the design of a secure building have been investigated, from the FSS design and the scattering from the room/building which it is intended to be used in.
