| In this era of telecommunications when most | | | | particular kind of waves. Therefore, the aim of |
| systems are being made wireless, the need for | | | | creating secure zones in buildings to avoid terrorist |
| security has increased tremendously because | | | | activities could be achieved through the |
| various signals need to be protected and isolated | | | | development of either of the following: |
| from each other. Meeting both these | | | | - A passive FSS, or; |
| requirements simultaneously can present a host | | | | - An active FSS. |
| of challenges. Currently, mobile communication and | | | | A passive FSS is the one in which some funny |
| Wireless Internet Local Area Network (WLAN) | | | | shapes are designed on a dielectric sheet for a |
| systems are being designed on the basis of a | | | | particular frequency to be passed or stopped. |
| detailed analysis of Radio Frequency (RF) | | | | Once this surface is fabricated, its properties |
| coverage and capacity requirements. Security and | | | | cannot be altered. The other basic point is that |
| privacy issues can be addressed through good | | | | they have to be relatively large enough to be |
| design but "eavesdropping" continues to be a real | | | | pasted on a large cross-section of the wall or |
| vulnerability. | | | | window. The advantage of this kind of FSS is that |
| A revolutionary technology, called Frequency | | | | they are easy to design and manufacture but the |
| Selective Surface (FSS), is increasingly being | | | | disadvantage is that they are not reconfigurable. |
| proposed and used as an answer to the | | | | On the other hand, active FSS is made up of the |
| deployment of secure wireless systems for | | | | same funny shapes with the incorporation of |
| indoor environments, taking advantage of | | | | some active electronic devices like gun diode, |
| innovative techniques in building design and the use | | | | varactor diode or capacitors. These active |
| of attenuating material. | | | | devices make the size of the FSS much smaller |
| Towards the end of the eighteenth century, the | | | | than a passive one and are reconfigurable. The |
| American physicist D. Rittenhouse discovered that | | | | only disadvantage is that the design and |
| some colours of a light spectrum were | | | | fabrication of such devices is very challenging. In |
| suppressed when a street lamp was observed | | | | both cases, FSS would help stop any cellphone |
| through a silk handkerchief. This was perhaps the | | | | signal coming into the security area, like airport |
| first "proof" that non-continuous surfaces can | | | | lounges, while other signals like those of the radio, |
| exhibit different transmission properties for | | | | TV or wireless would definitely come in. |
| different frequencies of incident wave. Hence, the | | | | An important area in human security is that |
| surfaces were called Frequency Selective | | | | overuse of cellphones can cause harm to the ear |
| Surfaces (FSS). | | | | and brain tissues with electromagnetic waves |
| Therefore, an FSS can be considered as a free | | | | going too frequently into the head. This has been |
| space filter which could be used to pass certain | | | | reported by people from around the world. |
| frequencies and stop others. These filters are | | | | This happens because in the recently developed |
| designed by fabricating some geometric metallic | | | | high-tech cellphones, the ground plane used behind |
| shapes on a dielectric material. The shapes could | | | | the antenna is usually a conductor which is not |
| be a circle, cross, square, ring or a tripole, as | | | | capable of stopping the electromagnetic radiations |
| shown. | | | | going past. Research is being carried out by |
| These geometric metallic shapes on a dielectric | | | | engineers and scientists to make a ground plane |
| material act like inductive and capacitive reactance | | | | of FSS which behaves as a perfect band stop |
| to the incident plane waves and hence, behave as | | | | filter to the incoming frequencies, hence eliminating |
| free space filters. The manufactured panels then | | | | the cause of backward radiations. |
| could be mounted on the walls of a building or | | | | Wireless internet |
| pasted on a window to get the desired band pass | | | | A certain type of frequency selective surfaces |
| or band stop results. | | | | has been designed in order to prevent Wireless |
| The design of FSS is basically obtained by putting | | | | Fidelity Local Area Network (WiFi LAN) signals |
| any of these shapes a half wavelength away | | | | from escaping a building without affecting |
| from each other in a periodic manner. The | | | | cellphone signals. The technology has been |
| wavelength is obtained by the frequency of | | | | designed to stop outsiders from gaining access to |
| operation. A very common example of FSS is the | | | | a secure network by using WiFi networks casually |
| front screen of a microwave oven, used in our | | | | set up by workers in the office or in a building. |
| houses or workplaces. You must have noticed a | | | | It only takes a moment for an employee to |
| periodic structure of hexagons or circles on the | | | | connect a paperback-sized WiFi base station to a |
| front glass. | | | | company network. That person can then wander |
| This is, in fact, an FSS which stops the | | | | around the office with his laptop while remaining |
| microwave frequency to come out of the oven, | | | | wirelessly connected to the internet. However, |
| since it is harmful to human beings. How and why | | | | the problem with this topology is that it gives a |
| do geometric shapes make an FSS act as a band | | | | chance to an outsider to breach that company's |
| pass or band stop filter? Well, it is very simple. | | | | computer security using the WiFi connection. |
| As an example, shown here is a cross geometry | | | | Unless the WiFi base station is protected by |
| and its equivalent circuit. It can easily be seen that | | | | security measures that most amateur users |
| when an incident wave impinges on this structure, | | | | would not bother to set up, it gives anyone up to |
| a small current flows in the material (mostly made | | | | 100 metres away, the chance to bypass the |
| up of copper) making it an equivalent series LC | | | | corporate firewall and wirelessly hack straight into |
| circuit (L= Inductor, C= Capacitor). Inductance is in | | | | the network. |
| the arms of each cross and capacitance in | | | | Until now, the only way to ensure that people are |
| between the adjacent edges due to currents | | | | not illicitly gaining access to company secrets has |
| produced in the structure as incident | | | | been to turn offices and buildings into a |
| electromagnetic waves strike, as shown in the | | | | signal-proof "Faraday cage," by lining the walls with |
| figure. At resonance frequency of LC circuit, the | | | | aluminum foil, and using glass that absorbs radio |
| signal would either pass or stop according to the | | | | waves in the windows. This ensures that all |
| design analogy and the form of incident wave | | | | electromagnetic emissions are absorbed, but it |
| impinging on the FSS. | | | | also means that no one can use a cellphone in the |
| In short, an FSS is not more than a parallel or | | | | building or office. |
| series LC circuit, to behave as a free space filter. | | | | Companies around the world have developed |
| Incorporating some active device(s) in between | | | | tunable frequency selective surfaces which can |
| these elements can make the FSS active, adding | | | | block WiFi at 2.4, 5 and 6 gigahertz, while letting |
| more functionality and configurability in design. | | | | through GSM and 3G cellphone signals, plus |
| An FSS could be used in many engineering | | | | emergency service calls. It means that FSS is |
| applications such as: | | | | now working as a band stop filter for 2.4, 5 and 6 |
| - Radio Frequency Identification (RFID) tags; | | | | gigahertz WiFi signals while acting as a band pass |
| - Collision avoidance; | | | | filter for GSM and 3G signals and other |
| - Radar cross-section augmentation; | | | | emergency service calls. |
| - Robotic guided paths; | | | | FSS can also provide the isolation between |
| - Electromagnetic interference protection; | | | | different standards of WiFi signals inside a building, |
| - Photonic band-gap structures; | | | | that is, between 2.4, 5 and 6 GHz systems. This |
| - Low probability of intercept systems (for | | | | isolation is very important otherwise interference |
| instance stealth); | | | | among these would cause a serious threat to |
| - Waveguide or cavity control coupling; | | | | data accessibility and security. For example, if an |
| - and, wireless security, etc. | | | | isolation is required between 2.4 and 5 GHz |
| It is not necessary for a reader without a | | | | system in a wireless network environment, an |
| scientific background to understand the | | | | FSS could be designed which could behave like a |
| terminologies given above, because my focus is | | | | band stop filter to either the frequencies and then |
| on the last application. This is because the use of | | | | fixed on a wall between the two WiFi networks. |
| wireless communication pertains to the masses. | | | | This would enable both networks to work |
| Therefore, the importance of FSS in the security | | | | separately in different locations, without any |
| of modern-day wireless technology will be | | | | interference. |
| discussed. | | | | As wireless communications evolve into a critical |
| Cellular communication | | | | business application, construction firms, landlords |
| Cellular phones cannot just be disruptive or | | | | and tenants should take a closer interest in RF |
| annoying, but on occasions, they can give rise to | | | | propagation. Engineers and designers will also need |
| security threats because they could be used to | | | | to familiarize themselves with a new breed of |
| set off a device. But the annoying sound of a | | | | building, fit-out and RF materials, especially FSSs, |
| cellphone ringing in the cinema or theatre could be | | | | as well as mastering the implementation of the |
| on the way out with the development of a | | | | latest wireless systems and intelligent antennas. |
| high-tech frequency selective surface that blocks | | | | Current developments in FSS point to a bright |
| their signals. | | | | future for the technology, with useful applications |
| Quiet zones could be created in hospitals, schools | | | | waiting to be exploited in a multitude of industries. |
| and airport lounges with the use of high-tech FSS. | | | | Pakistan, meanwhile, is on the verge of wireless |
| Also, the surface, made up of a metallic grid, | | | | age and soon there would be a great shift in data |
| could help foil terrorists. This type of security is | | | | communication from physical connections to |
| mostly needed in airports and other high-risk | | | | wireless connectivity. Wireless communication is |
| areas frequented by personnel belonging to the | | | | considered to be a clean form of networking |
| defence forces and security agencies. | | | | where no lengthy physical lines and network |
| The beauty in the design and development of an | | | | components are involved. That's why it could be |
| FSS is that it would only block a particular kind of | | | | inferred that more and more companies would |
| signals while other signals could be allowed to pass. | | | | turn towards this technology to save money and |
| In engineering terms, it would behave as a band | | | | to be efficient. |
| stop filter to the frequency to be blocked and a | | | | Therefore, we need experts in order to provide |
| band pass filter to the rest. | | | | security to the overall wireless networking. |
| It must be noted that before the advent of | | | | Moreover, with the development of a huge cellular |
| commercial FSS, large aluminum sheets were | | | | phone infrastructure in the country, we may at |
| incorporated in the walls of modern buildings to | | | | some point need to block signals in restricted |
| stop unwanted signals. A major problem with this | | | | areas like airports, hospitals and cinema halls. |
| technique was that besides blocking the desired | | | | Anyone interested in microwave and radio |
| frequency, it would stop other frequencies as well. | | | | frequency (RF) communication should choose FSS |
| However, with the commercial manufacturing of | | | | as a focal area for research because it carries a |
| frequency selective surfaces, it has now become | | | | lot of potential for the future, even in Pakistan. |
| possible to be selective - either to stop or pass a | | | | |