In this era of communications, when most systems become wireless, the need for security increases significantly, since different signals need to be protected and isolated from each other. Meeting both of these requirements at the same time can present many problems. Currently, mobile communications and wireless local area network (WLAN) systems are being developed based on a detailed analysis of radio frequency (RF) requirements and power requirements. Security and privacy issues can be resolved with good design, but “eavesdropping” is still a real vulnerability.
The revolutionary technology, called frequency-selective surface (FSS), is increasingly being proposed and used as an answer to the deployment of secure wireless systems for indoor use, using innovative technologies in building design and the use of attenuating material.
At the end of the eighth century, the American physicist D. Rittenhouse discovered that certain colors of the light spectrum were suppressed when a street lamp was observed through a silk scarf. Perhaps this was the first "proof" of the fact that unstable surfaces may have different transmission properties for different frequencies of the incident wave. Here the surfaces were called frequency-selective surfaces (FSS).
Therefore, FSS can be considered as a free space filter that can be used to transmit certain vacancies and stop others. These filters are designed by making some geometric metallic shapes on a dielectric material. Forms can be a circle, a cross, a square, a ring, or a tripole, as shown.
These geometric metallic forms on a dielectric material act as an inductive and capacitive reaction to incident plane waves and, therefore, have free space as filters. Then, the fabricated panels can be mounted on the walls of a building or inserted into a window in order to obtain the desired strip pass or the results of stopping the tape.
The design of the FSS is mainly achieved by periodically setting any of these forms to half the wavelength of each other. The wavelength is obtained from the frequency of work. A very common example of FSS is the front panel of a microwave oven used in our homes or workplaces. You must have noticed the periodic structure of hexagons or circles on the windshield.
This is, in fact, the FSS, which stops the microwave frequency coming out of the oven because it is harmful to humans. How and why do geometric shapes do an FSS act as a strip pass or a strip stop filter? Well, it's very simple.
As an example, cross-geometry and its equivalent circuit is shown here. It is easy to see when a falling wave falls on this structure, a small current flows in the material (mainly copper), making it an equivalent LC circuit sequence (L = inductor, C = capacitor). The inductance is in the shoulders of each cross and the capacitance between the edges of the auxiliary element due to currents arising in the structure when the electromagnetic shock waves strike, as shown in the figure. At the resonant frequency of the LC circuit, the signal will either pass or stop in accordance with a constructive analogy and the shape of the incident wave incident on the FSS.
In short, an FSS is nothing more than a parallel or serial LC circuit to have free space as a filter. The inclusion of some active devices (s) between these elements can make the FSS active by adding more functionality and configuration to the design.
FSS can be used in many engineering applications, such as:
- radio frequency identification (RFID) tags;
- Avoidance of collision;
- increase the radar cross section;
- robotic guides;
- protection against electromagnetic interference;
- photonic zonal structures;
- low probability of interception systems (eg, secrecy);
- coupling to control the waveguide or resonator;
- and, wireless security, etc.
For a reader without a scientific background, there is no need to understand the terminology above, since my attention is focused on the last application. This is due to the fact that the use of wireless communication refers to the masses. Therefore, the importance of FSS in ensuring the security of modern wireless technologies will be discussed.
cellular
Cell phones can not be simply destructive or annoying, but in some cases they can cause security risks, as they could be used to send a device. But the annoying sound of a cell phone ringing in a movie theater or in a movie theater may be on its way to developing a high-tech frequency selective surface that blocks their signals.
Quiet zones can be created in hospitals, schools, and airport lounges using high-tech FSS. In addition, the surface, consisting of a metal grid, can help hide the terrorists. This type of security is mainly required at airports and other high-risk areas frequented by personnel associated with defense forces and security services.
The beauty in the design and development of the FSS is that it blocks only certain signals, while other signals can be passed through. In technical terms, it will have a passband filter for the frequency to be blocked, and a passband filter for the rest.
It should be noted that before the advent of commercial FSS, large aluminum sheets were laid in the walls of modern buildings to stop unwanted signals. The main problem with this method was that, in addition to blocking the desired frequency, it also stopped other frequencies.
However, in the commercial production of frequency selective surfaces, it became possible to be selective — either to stop or to miss a certain type of wave. Therefore, the goal of creating safe zones in buildings in order to avoid terrorist activities could be achieved by developing one of the following:
- passive FSS, Egypt;
- Active FSS.
Passive FSS is one in which some funny pieces are constructed on a dielectric sheet to transmit a specific frequency or stop. After this surface is made, its properties cannot be changed. Another key point is that they must be large enough so that they can be glued to a large cross-section of the wall or window. The advantage of this kind of FSS is that they are easy to design and produce, but the disadvantage is that they are not reconfigured.
On the other hand, an active FSS is composed of the same ridiculous forms with the inclusion of some active electronic devices, such as a diode diode, a varactor diode or capacitors. These active devices make the FSS size much smaller than the passive one and reconfigured. The only drawback is that the design and manufacture of such devices is very difficult. In both cases, the FSS will help stop any cell phone signal entering the security zone, for example, in airport lounges, while other signals, such as radio, television, or wireless, will be included.
An important area in the field of human security is that excessive use of cell phones can damage the ear and brain tissues, with electromagnetic waves too often entering the head. This is reported by people from all over the world.
This is because in recently developed high-tech cell phones, the ground plane used behind the antenna is usually a conductor that is not capable of stopping the passage of electromagnetic radiation. Engineers and scientists are doing research to make the ground plane FSS, which behaves like an ideal stop-band filter to incoming frequencies, therefore, eliminating the cause of the return radiation.
Wireless Internet
A certain type of frequency selective surfaces was designed to prevent wireless LAN signals from a wireless network from exiting the building without affecting cell phone signals. This technology was designed to prevent outsiders from gaining access to a secured network using wireless networks created outside the box by workers in an office or in a building.
For an employee, it only takes time to connect the WiFi base station in a paperback to the company's network. This person can roam the office with his laptop while remaining wirelessly connected to the Internet. However, the problem with this topology is that it allows an outsider to break the computer security of this company using a WiFi connection.
If the WiFi base station is not protected by security measures that most amateur users do not want to configure, it gives someone a distance of up to 100 meters, the ability to bypass the corporate firewall and wirelessly hack into the network.
Until now, the only way to ensure that people do not illegally gain access to company secrets was to turn offices and buildings into the Faraday signal box by lining the walls with aluminum foil and using radio-absorbing glass in the windows. This ensures that all electromagnetic emissions are absorbed, but it also means that no one can use a cell phone in a building or office.
Companies around the world have developed custom frequencies that select surfaces that can block WiFi at 2.4, 5, and 6 gigahertz, as well as transmit GSM and 3G cellular signals, as well as emergency calls. This means that the FSS now acts as a band stop filter for Wi-Fi 2.4, 5 and 6 GHz signals, acting as a band-pass filter for GSM and 3G signals and other emergency calls.
The FSS can also provide isolation between different WiFi signal standards within a building, that is, between 2.4, 5, and 6 GHz systems. This isolation is very important, and other interferences between them can be a serious threat to data access and security. For example, if isolation between a 2.4 and 5 GHz system is required in a wireless network environment, an FSS can be designed that can have a band stop filter at frequencies and then be fixed on the wall between two WiFi networks. This will allow both networks to work separately in different places without any interference.
As wireless is evolving into a critical business application, construction firms, landlords, and tenants should take a more keen interest in spreading radio frequencies. Engineers and designers will also need to familiarize themselves with the new breed of building, finishing and radio frequency materials, especially with the FSS, as well as master the introduction of the latest wireless systems and intelligent antennas. Current events at the FSS point to a bright future for technology, with useful applications awaiting use in a wide variety of industries.
Pakistan, meanwhile, is on the threshold of a wireless age, and soon there will be a big shift in the transmission of data from physical connections to wireless communications. Wireless communication is considered to be a pure form of network in which long physical lines and network components are not involved. This may be disturbed by the fact that more and more companies will turn to this technology to save money and be efficient.
Therefore, we need specialists to provide security for the entire wireless network. Moreover, with the development of a huge cellular phone infrastructure in the country, we can at some point block signals in areas such as airports, hospitals and cinemas.
Anyone interested in microwave and radio frequency (radiofrequency) communications should choose the FSS as the main area of research since it has great potential for the future, even in Pakistan.
