Table of ContentsI. IntroductionII. S matrix and shielding effectivenessIII. Design ProcedureSummary — The frequency selective surface (FSS) is a repeated structure that transmits, reflects, or absorbs depending on the mode of interest using patches or slits. Patch and slot networks effectively create notch and bandpass filters. FSSs have potential applications in providing sufficient shielding in desired frequency ranges. The work proposed in this paper consists of studying and analyzing the structural requirements of FSS to protect against GSM band frequencies. People working near mobile towers are exposed to strong electromagnetic fields, especially near fields, so they must protect themselves against these fields. The concept of FSS is extended to print the structures on aircraft fabrics, and these can be worn by working personnel. The paper is mainly based on simulation analysis of fabrics designed using EM software tools. The simulation results are validated using experimental results. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essayKeywords: frequency selective surface, frequency selective fabric, shielding effectivenessI. IntroductionMobile phone technology has brought many changes in the telecommunication scenario in India. Cell phone technology has seen tremendous changes over the past decade. Currently, there are more cell phone users as well as cell towers to meet the communication demand. The number of mobile phones and relay antennas is increasing day by day without knowing the disadvantages. Cell tower antennas transmit in the frequency range of 869 to 894 MHz (CDMA), 935 to 960 MHz (GSM900), and 1810 to 1880 MHz (GSM1800). In addition, 3G whose base station antenna transmits in the frequency range of 2110 to 2170 MHz. Cell phone towers transmit 20 to 25 watts of power and the cell phone transmits 1 to 2 watts of power. Radiation from mobile phone and cell towers affects and poses a serious threat to human health due to electromagnetic field (EMF). Radiation from cell phone towers. and mobile handsets. An antenna is designed in such a way that the mobile phone must be able to transmit and receive a signal for proper communication up to a few kilometers. Most towers are mounted near residential and office buildings to provide good mobile phone coverage to users. These cell towers transmit radiation 24 hours a day, 7 days a week, so people living or working within 10 meters of the tower will receive a stronger signal than that required for mobile communications. In India, millions of people reside in these high radiation areas. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) studies the possible adverse effects on human health of exposure to non-ionizing radiation[1]-[2]. The main objective of ICNIRP is to disseminate information and advice on the potential health risks associated with exposure to non-ionizing radiation. In accordance with ICNIRP guidelines, the current limits/levels are detailed in the table below. Microwaves from cell phone towers can interfere with our body's EMFs, causing alteration of white blood cells inchildren; childhood leukemia, impaired motor function, headache, dizziness, fatigue, weakness, memory loss, birth defects, cancer and DNA damage, etc.[3]-[5]. Thus, developing a fabric with filtering properties in a specific frequency band of GSM -1800 is important for human health. GSM-1800 (Global System for Mobile Communications) uses the frequency 1810-1880 MHz to receive information from the mobile station to the base transceiver station (downlink). In recent years, various methods have been proposed to manufacture electromagnetic shielding textiles for protection against electromagnetic interference (EMI) waves [6]. In this area, customized, flexible, lightweight and porous conductive fabrics have been developed for either EM shielding or functional electronics applications by knife-on-roll coating [7]-[8]. In another study, co-woven, knitted, and woven conductive fabrics were produced with desirable properties of electromagnetic shielding effectiveness. The main goal of EMI shielding methods is to block electromagnetic radiation, so that the wave cannot pass through the blocking medium. EMI protective textiles refer to the manufacturing of fabrics from conductive and non-conductive materials using various processing methods. In all the conductive samples described above, these types of fabrics act as metal foils for EMI shielding [9]. Therefore, the problem with these fabrics is that they are unable to shield EM waves in a specific frequency band. Accordingly, frequency selective surface (FSS) technique is required to prepare a fabric with EM filtering properties in the GSM-1800 frequency band. Frequency selective surface (FSS) is a repetitive structure that acts as a filter and has a wide range of applications such as radomes, lenses, RFID, electromagnetic interference protection, medical and military sectors [10]. FSS can also stop unwanted mobile signals based on traditional FSS systems. Frequency selective fabrics are designed for filtering properties in the GSM-1800 band[11]-[13]. The FSS structure can be printed on flat fabrics to protect against the GSM frequency band. This fabric is useful to humans to protect themselves from strong radiation fields from cell phone towers.II. S-Matrix and Shielding EffectivenessThe S-matrix can play a very important role in filtering problems. The matrix S can be written as the linear relationship between the reflection wave b and the incident wave a, and it can be derived from the following formula (1) b1 = a1S11 + a2S12 b2 = a1S21 + a2S22 (1) Here , the matrix S is called the diffusion matrix of the two ports, and each of the four parameters S has a defined physical meaning. Specially, S21 is the transmission coefficient of port1 when port2 connects a matched load and it can be calculated from the formula (2)S21=b2/a1|a2=0 (2)The meaning of S21 is illustrated from of microwave transmission line theory, but in many cases the energy loss due to the difference between the EM impedance and the intrinsic impedance of the shielding material is more intuitive for designers who wish to characterize and evaluate the material. According to Schelkunoff's principle, for monolithic conductive materials without holes, the shielding efficiency can be calculated from the formula (3) SE=SEA+SER+SEM=10log (p1/p2) (3) Where SE represents shielding effectiveness, which means the degree of attenuation of the EM wave caused by shielding materials, and the unit is dB. SEA means loss.