SYSTEMATIC REVIEW OF SAR REDUCTION TECHNIQUES FOR MINIMIZING MOBILE PHONE RADIATION

4341 | P a g e S e p t e m b e r 2 0 1 6 w w w . c i r w o r l d . c o m SYSTEMATIC REVIEW OF SAR REDUCTION TECHNIQUES FOR MINIMIZING MOBILE PHONE RADIATION S.Palanivel Rajan, Dr.C.Vivek, 1 Assistant Professor, Department of Electronics and Communication Engineering, M.Kumarasamy College of Engineering, Karur, Tamilnadu, India. Email ID : palanivelrajanme@gmail.com 2 Associate Professor, Department of Electronics and Communication Engineering, M.Kumarasamy College of Engineering, Karur, Tamilnadu, India. Email ID : vivekc.phd@gmail.com ABSTRACT


INTRODUCTION
Within a short period of time, mobile phone has created a great impact on people all over the world [3]. According to the report of World Health Organization (WHO) about 4.6 billion of people around the world are using mobile phones. The radiation emitted from the mobile phone is transmitted in all the directions [5]. A part of the energy will incident on human head. The electromagnetic radiation interacts with human head and produce heat. This heat will be absorbed by the skin and by some other special tissues within our head [7]. Therefore, it can cause incurable diseases to human like brain tumor, cancer, etc. The objective of this paper is to limit the radiation level being emitted by the Planar Inverted F-Antenna (PIFA) by varying the antenna length placed inside the TEM cell using trial and error method. The simulation tool we are going to use is computer simulation technology(CST) microwave studio software from which we can find the characteristic impedance and VSWR.

EXISTING SYSTEM
Already a huge number of studies have been carried out for limiting the hazardous EM radiation from mobile antenna. But, still now no method has been proposed for completely eliminating the SAR [9]. The methods so far proposed have significantly limited the SAR within a specific value [10][11][12][13]. EBG structure can act as a perfect magnetic conductor surface which will reduce the radiation from mobile antenna by reducing the surface wave [1]. Metamaterials can be used to study the SAR reduction using finite-difference time-domain (FDTD) method [8]. By placing the Metamaterials between the human head and mobile antenna the SAR can be reduced [6]. Our work in this paper is to limit the EM radiation emitted from mobile antenna by varying the antenna length. Figure: 1(a) shows the scan image of a common human head before the usage of mobile phone [15]. From this image we can observe that the temperature of this human is within the range of standard temperature [17]. Figure: 1(b) shows the scan image of a common human after the usage of mobile phone for 15 minutes [19][20][21]. From this we can observe that heat generated inside the head is massive when compared to the previous image. This clearly shows that the interaction of EM radiation with human head is the fact behind the cause for this massive increase in temperature.  The rectangular TEM is broadly used for testing of emission from electronic devices [2]. The TEM cell is made up of a rectangular coaxial transmission section which is tapered at both sides with coaxial connector, as shown in Figure : 2. It consists of two conductors. The inner conductor which is also called as septum acts as the positive conductor or hot line [4]. The outer conductor acts as a ground. connected with a load of 50Ω [8]. The other end is connected to a HP 8791A network analyzer. The same experimental setup is used to measure VSWR. Figure 4 shows that the Planar Inverted Fractal Antenna (PIFA) which is a type of linear Inverted F-Antenna (IFA) [14]. PIFA is the widely used mobile antenna structure as it is widely used in most type of mobile phones due to its characteristics like low profile, small size, built-in structure, easy fabrication, low manufacturing cost and simple structure [16].

Characteristic Impedance and VSWR
There are large numbers of simulation tools available for designing mobile antenna. We have decided to use computer simulation technology (CST) microwave studio software due to its advantages such as multi-technology co design, high speed data link and easy integration to other components [18]. From the simulation result, we can observe the characteristic impedance and VSWR of PIFA.

Numerical Analysis
The SAR rating for various mobile phones can be defined using number of standards [25]. Here we have concentrated on American standard of SAR rating as it is being followed in many foreign countries as well as accepted by wide range of people all over the world.    Table : 2 we can infer about various R.F sources existing in India and their operating frequency range, transmission power as well as the availability of these sources [27]. The major sources of radio frequency in India are the transmitting towers such as AM/FM Tower, Cell Towers, Mobile Phones etc. emit EM radiation continuously. The EM radiation emitted from these sources has risen exponentially by rapid growth of wireless technology such as cell phones, Wireless Fidelity, Wi-max and other wireless devices [26].  The following ICNIRP guidelines have been adopted as standard by India for limiting the exposure to radio frequency energy produced by mobile phones . The SAR value from the Table : 4 has been averaged using 10g of average mass over a period of 6 minutes.

VSWR Measurement
The reduction in the length of PIFA will results in a very complicated structure. The length of PIFA is varied between 9.4 cm and 1 cm using trial and error method and the VSWR readings are summarized as follows. From the following Table : 5, we can infer that if the length of PIFA is reduced then the VSWR is also reduced considerably. This shows that VSWR is directly proportional to the length of PIFA.

Characteristic Impedance Measurement
Using trial and error method we have calculated characteristic impendence by varying the length of PIFA. From the following Table : 6 we can infer that if the length of PIFA is reduced then the Characteristics impedance(Ω) is also reduced considerably. Figure : 6 shows that Characteristics impedance (Ω) is directly proportional to the length of PIFA.

CONCLUSION
The progress in science and technology is a nonstop process. New things and new technology are being developed every now and then. The proposed work is based on investigating PIFA which is more reliable, compact and fewer complexes. Using the simulation tool, computer simulation technology (CST) microwave studio software the feasibility of the design has been studied. In future, this simulation result can be used to design low SAR PIFA.