Frequency Selective Surfaces for Long Wavelengths

Lead Research Organisation: University of Kent
Department Name: Sch of Engineering & Digital Arts


Mobile communications and wireless computer networking are already enourmously popular with user numbers and system types set to continue increasing. Each system requires the use of certain transmission frequencies which must be separated in some way to avoid interference. OFCOM, the government body that licences the radio spectrum is beginning to deregulate the process of radio frequency usage and it is vital to devise a means of making the radio environment both more immune from interference and safe from eavesdropping. Also prisoners who should not be allowed access to telephones are using mobile phones smuggled into prisons. The phones are used to organise crime outside, smuggle in drugs and coordinate escapes and riots. This is of great concern to the prison authorities and the UK government as it is technically difficult to stop mobile phone communications without interfering with the phones of innocent users near the prisons. Parallel to the above issues is the fact that modern buildings are lined with a metallic layer for thermal insulation. This layer screens building interiors and can significantly reduce the strength of radio signals passing inside. This can reduce the coverage of radio systems used by the emergency services within buildings placing personnel at risk. This research seeks to create Frequency Selective Surfaces (FSS) to filter out radio signals at mobile frequencies while passing channels used by authorised services. The FSS designs will be convoluted and interweaved to compress their size and will be mounted in small apertures in metal screened walls. A specified isolation level will be aimed for and the performance will be made adaptable by integrating switching diodes to the design. Computer simulations will be made to predict the propagation of signals through the FSS and into rooms.


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Gu C (2017) 3-D Coverage Beam-Scanning Antenna Using Feed Array and Active Frequency-Selective Surface in IEEE Transactions on Antennas and Propagation

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Parker E (2008) Minimal size FSS for long wavelength operation in Electronics Letters

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Sanz-Izquierdo B (2011) Switchable Frequency Selective Slot Arrays in IEEE Transactions on Antennas and Propagation

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Sanz-Izquierdo B (2010) Tuning patch-form FSS in Electronics Letters

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Sanz-Izquierdo B (2010) Singly and Dual Polarized Convoluted Frequency Selective Structures in IEEE Transactions on Antennas and Propagation

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Sanz-Izquierdo B (2010) Dual-Band Tunable Screen Using Complementary Split Ring Resonators in IEEE Transactions on Antennas and Propagation

Description This project established that finite sized Frequency Selective (FSS) Panels may be introduced into apertures in metallic screens that are integrated into walls. FSS with highly convoluted and interwoven elements may be used to reduce overall panel size, to increase transmission bandwidths and to improve transmission response for incident rays at very oblique angles. Stop band performances can be achieved that will lead to a 3 times increase in the capacity of indoor wifi channels by introducing FSS screens to walls.
Exploitation Route Interest has arisen from Government agencies and architectural specialists (e.g. bids to fit buildings such as prisons and courtrooms where wireless access is prohibited or must be secure).
Sectors Digital/Communication/Information Technologies (including Software),Government, Democracy and Justice

Description we have worked with Dr Michael Neve of the University of Auckland to create an easily accessible interactive website: This website explains some of the problems encountered by signal propagation in the built environment and allows the user to manipulate wireless transmitters and receivers and view in 'real-time' the simulated effects of their actions - for instance the consequences of adding more transmitters, of increasing signal power, reusing channel frequencies and introducing signal attenuating walls between wireless devices. As the objective is public and interdisciplinary communication, the site is written to be understandable by a general audience rather than a communications specialist one. It was decided that interactive experimentation was the best method to allow non-specialist users to appreciate the issues concerned.
First Year Of Impact 2012
Sector Education,Electronics
Impact Types Societal,Policy & public services

Description International Travel Grant
Amount £17,971 (GBP)
Funding ID EP/I000941/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 04/2010 
End 04/2012
Description FSS at Aukland University, NZ and University of Kent, UK 
Organisation University of Auckland
Country New Zealand 
Sector Academic/University 
PI Contribution Kent designed FSS based on highly convoluted elements used in an office facility in the Engineering department at the University of Auckland to assess frequency dependent screening at long wavelengths. Two papers have been published. The FSS was designed and fabricated by staff at the University of Kent, despatched to Auckland and installed by technical staff there in a specially constructed screened office. Auckland's equipment characterized the frequency selective performance of the structure, the manpower including 2 Kent staff in addition to the NZ personnel. The outcomes were published in an Electronics Letter.
Collaborator Contribution In the period of this collaboration NZ staff (Williamson, Sowerby and Neve) have paid return visits to the Universities of Kent, Birmingham, Sheffield and Manchester. The Auckland partners have led authorship on several journal and conference papers with joint UK authorship, including the PI at Kent.
Impact Key outputs are journal and conference publications as listed in the project sections. Additionally, Auckland visitors have invited membership on the panel of the Wireless Friendly Buildings Forum, and have led the design of the user friendly wireless interference teaching tool mounted at:
Start Year 2006
Description Home Office Scientific Development Branch (HOSDB) 
Organisation Home Office
Department Home Office Scientific Development Branch
Country United Kingdom 
Sector Public 
PI Contribution The research team have engaged with the Prisons Project Manager at the HOSDB following an approach from Canterbury Prison to address the issue of illicit mobile phone use within prisons. The research team have communicated how the technologies proposed for development under ESPRC funding may help to address the issue of electromagnetic performance of both new build, and retrofitted prison buildings.
Collaborator Contribution The HOSDB partners provided information outlining the problem of illicit phone use and made available a report describing the issue at an international level.
Impact The investigators presented the approach and technologies developed in the project to a staff symposium hosted at HOSDB St Albans in 2009.
Start Year 2006
Description Police Information Technology Organisati 
Organisation National Policing Improvement Agency (NPIA)
Country United Kingdom 
Sector Public 
Start Year 2007
Description An electronically tuneable surface. The surface comprises: a conductive sheet comprising at least one opening; and a biasing circuit. The biasing circuit comprises first and second conductors, separated from the conductive sheet by a dielectric, and arranged at mutually opposing sides of the opening such that each conductor is capacitively coupled to the conductive sheet at the respective side of the opening. The conductors define a gap between them corresponding to the opening. The biasing circuit also comprises an electrical control element bridging the gap, connected to the first and second conductors. When the element is in a first state, the surface exhibits a first frequency transmission characteristic with respect to incident electromagnetic radiation, and when the element is in a second state, the surface exhibits a second, different characteristic. 
IP Reference WO2010092390 
Protection Patent granted
Year Protection Granted 2010
Licensed Yes
Impact N/A
Description Frequency Selective Surfaces Lunchtime Seminar 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact The application of Frequency Selective Surfaces to high tech buildings was described in an extensive powerpoint presentation to personnel at this company of civil engineers, Waterman Group PLC.

This presentation was delivered to an audience about 2 dozen people at Waterman Building Services, Versailles Court, 3 Paris Garden, London, SE1 8ND. As a contribution towards professional development, it was aimed at increasing awareness of the effect of building construction materials on internal wireless transmission and how FSS technology can mitigate and control propagation phenomina.

We made the issues and challenges of Electromagnetic Architecture clear to principal workers in a large Civil Consulting Partnership.
Year(s) Of Engagement Activity 2009
Description Smart Buiding Outreach talks to Kent schools 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact The talk provoked questions from interested pupils with several enquiring about further study in Engineering. One school requested a repeat of the talk for a larger audience.

One school requested a repeat of the talk for a larger audience. Another school reported that a pupil was disappointed to discover she could not continue to an Engineering degree as she had dropped maths.
Year(s) Of Engagement Activity 2007,2008,2009,2010,2011,2012