Effect of SAR Impact on a Tissue Cube with Graphene-Dipole for 900MHz

  Jemima Priyadarshini.S                                                                      Dr.D.Jude Hemanth

   Research Scholar,                                                                            Associate Professor,

                 Department of Electronics and Communication                             Department of Electronics and Communication

                   Karunya Institute of Technology and Sciences                              Karunya Institute of Technology and Sciences

                              Coimbatore, Tamil Nadu, India.                                                       Coimbatore, Tamil Nadu, India.

                                      [email protected]                                                                    [email protected]

 

 

Abstract— Nano conductive antennas are the novel type of antennas used for research purposes. Graphene has its unique properties as a radiating structure and its characteristics towards EM interaction is to be studied. Human health concerns are pivotal in exposure analysis. Specific absorption rate parameter is  vital for measurement of absorption of radiation in exposure analysis. This paper intends to study the effect of SAR when a Graphene based dipole is radiated in GSM frequency of 900 MHz and then its placed near a cube with equivalent with muscle properties. The investigation is conducted to a varying frequency between 600MHz to 1200MHz. The 1g ,10g and Overall SAR parameters are estimated and analyzed.

Index Terms — Dielectric properties, SAR, G-Dipole ,MOM,.

                                                                         I. Introduction

 

There is always a constant interaction of Human with technology on a daily basis. The primary purpose of the investigation is to study the impact of the radiation exposure and the possibility of its reduction for the Human concern. SAR is a prominent parameter in the field of exposure analysis. Dipole antenna is considered for analysis due to its

simple design and used in many applications. Graphene properties such as conductivity and relative permeability is applied to the designed dipole. The Human models used for simulation are classified as homogeneous or heterogeneous. For this initial setup a homogenous cube model with tissue equivalent characteristics is considered for the evaluation. The simulation tool FEKO is used for the analysis and validation is done. The results are further discussed below.

                                                           II. Specific Absorption Rate

Specific absorption rate is measurable quantity that considers the rate at which energy is absorbed by the exposing body to a particular radio frequency (RF). It is defined as the power absorbed per mass of tissue and denoted in units of watts per kilogram (W/kg). The SAR is calculated based in the induced electric field E (V/m) and it is given by the following equation 1.

 

                                   

 

                        (1)      

 

Where the parameter E is the electric field (V/m), SAR units are represented in (W/kg), ? is the conductivity (S/m) of the exposed tissue and ? is the mass density of the exposed volume (kg/m3).

                                                                    III. Dipole Antenna

The half wave dipole antenna is type of antenna that has conductive wire that consist of half the length of the maximum wavelength. The antenna is designed to operate for a particular frequency from one end to another end. The radiating structure is a wire which is usually split in the middle of the length, and each are separated by an insulator at the center where the excitation is applied for the radiation . The separated wire is normally connected to 50-ohm coaxial cable at the ends of the center insulator closest to the middle of the antenna. It has two identical lengths of the conductor on each side of the center insulator. Radio frequency voltages are applied  at the designed GSM frequency of 900 MHz to dipole antennas at the center, between the two conductors shown in figure 112

 

Fig. 1.  Dipole Antenna

iv  Numerical modelling

A.  Modelling Background

The limitation of SAR computations on the anatomical real Human body is strictly limited due to safety concerns. The investigation is possible with calculations done on numerical field implying on several numerical models of the human body 2.

B.  Graphene based Dipole Antenna Design and Dimensions

G-Dipole is linear structure with the wire radiator element with its excitation in the centre.  

 

The design parameters are calculated using the below formulas

 

                                                                    (2)

                                                                      (3)

 

where (?) Lambda depends on the center frequency. In this case 900 MHz is considered as center frequency

h is the height of antenna and c is the constant.

The conductivity of the graphene of 10e8 is created as a metallic medium and applied on the radiating structure. The designed G-Dipole dimensions were listed in Table-1.

 

`

Fig. 2.  G-Dipole designed using FEKO

                                                                                                                                      Table I                 Design parameters of G-Dipole

Dipole Variables

Values(m)

Free space wavelength

0.32

Height of the antenna

0.16

Conductivity media of Graphene

10e8

C.    Cubic Tissue Model with Dielectric Properties of Human Head Tissue equivalent

The design of the cubic tissue model is considered for radius of 0.1 m. It is simulated with a  equivalent material of muscle properties with relative permittivity, conductivity and mass density for 900 MHz as in Fig.3.The muscle equivalent values of the tissues are obtained from databases.In the simulation setup the electromagnetic fields are simulated in human body, the parameters for the conductivity ?(S/m) and the relative permittivity ?, of different materials are that used for the calculation were set as in Table-26.

 

Table II. properties of Cube tissue used in the simulation at 900 MHz    

Properties of Tissue

At 900 MHz

Dielectric permittivity(?,)

45.8

Conductivity(?) in S/m

0.77

Mass density(?)in kg/ m3

1030

 IV. Feko Simulation and Validation

A.  Validation of Graphene Antenna

 

S11 parameters establishes the reflection coefficient of the antenna. The value obtained is 0.2 in the operating frequency of 900 MHz. Figure 3 shows the obtained value over the range of 0.6GHz to 1.2 GHz

 

 

Fig. 3.  Reflection coefficient of G-Dipole

Fairfield characteristics in polar and 3D is are given below in Figure 4.

 

 

 

Fig. 4.  Farfield characteristics

 

   Gain for the G-dipole is obtained 1.56 db. That lies within the gain of conventional dipole antenna which is less gain of 2dB.

 

A.  Free Space Condition

The spatial distance kept between the G-Dipole antenna and the Muscle Tissue is kept at a constant of 0.05m for proposed exposure analysis as shown in Fig.5

 

Fig. 5.        G-dipole antenna with Tissue cube

VI.  Result Analysis

On the consideration of constraints such as problem size and its complexity, the FEKO model is simulated using Method of Moments (MoM) based solving platform 7. The SAR values are shown in Table-3 and the values plotted are shown in Fig 6.  

Table III. SAR ESTIMATION

 

Frequency at
GHz

 1gm mW/Kg

 10  gm mW/Kg

 Overall    mW/Kg

0.6

0.316799

0.238158

0.00208

0.63

0.449345

0.34081

0.00294

0.66

0.652633

0.498905

0.04720

0.72

1.5683

1.20647

0.10240

0.78

4.72836

3.66487

0.31139

0.84

14.6271

11.45

0.99412

0.87

14.3397

11.2638

0.99630

0.9

9.07606

7.14275

0.64430

0.96

3.57713

2.77689

0.25800

1.02

1.92082

1.45268

0.13729

1.08

1.22972

0.920424

0.00873

1.14

0.89072

0.667897

0.00627

 

The SAR 1-gram equivalent is calculated by averaging the Local maximum SAR, adding the highest SAR volume in the tissue till a mass of 1 g of cube.  The estimated  SAR 10-grams is the maximum estimated SAR value which is  averaged on 10-gram  cube obtained by averaging the SAR around each point in the estimated volume, by adding the nearest points until an average mass of 10g is reached with a resulting indicated volume having the shape of a portion of cube 8.                                

Fig 6. Overall SAR value

The overall SAR Value with respect is to 1g, 10g and overall is compared over the varying frequencies at Fig.46 It is noted that there is a peak increase in value around 900MHz 9. The value is elevated up to 14m W/Kg for 1g equivalent exposure and 10 mW/Kg for 10 g exposure.

                                             Figure 7. Excitation

SAR2 is the 1 gram, SAR3 is  the 10 gram and SAR4 is overall SAR over the volume. The excitation is induced to an input voltage of 1 volt and 0 phase difference and is shown in a smith chart in Fig 7.The Near field region of an antenna is a region, is dependent on the distance between the structures .Near field is the main parameter for calculation of SAR10. Fig 8 shows the 3D radiation pattern at 900MHz.The spluttering of field radiation around the cube can be observed,

Fig 8. Simulated Radiation Pattern in 3D at  frequency 900 MHz

The Far Field Characteristics E and H plane represents the radiation properties and analysis over the Phi degree are obtained 11. The presence of Muscle tissue model affects the Far field and are represented below in Fig.9

Fig 9.Farfield with Tissue cube

VII. Conclusion.

 The paper performs Investigation examines the field distribution and validation of Graphene based dipole. The SAR is computed for the GSM frequency of 900 MHz over a range between 6 to 12 MHz. The performance of G-Dipole over the range is examined and found to be maximum for 1g then to 10g and minimum to overall peak SAR values. The gain in the experimental setup is between 1.5 to 1.75 dB the reflection coefficient is 0.3 and power used is 16 mW. These values are optimal for the performance of the G-Dipole and ideal for Human analysis and SAR computation. The homogenous cubic tissue model is designed with the tissue equivalent properties and with essential conductive and permittivity values for a particular frequency. SAR and the electric field parameters in 3D Far-field are calculated and plotted for extensive analysis. The localized peak SAR estimation interns of  1g, 10g and the whole-body average SAR induced in cubic model are respectively evaluated using MoM which is better than FDTD and other techniques 6.

The designed models have been executed and validated by FEKO EM software11, an ideal software for computation of electromagnetic with its unique features of  high Scalability and its reliability. SAR measurements of 1 gram and 10-gram cubes also has a  correlative ability over the operating frequency of 900 MHz9. This correlation can be observed in Fig 6. SAR absorption is extensively increased in when frequency reaches about 900MHz. This experiment can be further developed to specific human design or any other vital areas of human body. The further enhancement in the detailed investigation can help to analyze and reduce the exposure effects.

REFERENCES

1    Basic Standard for the Measurement of Specific Absorption Rate Related to Exposure to Electromagnetic Fields from Mobile Phones (300 MHz-3GHz). European Committee for Electrical Standardization (CENELEC), EN-50361.

2    0. S. Dautov, Russiaad, Elz Etne. M., Egypt “Application of FEKO Program to the analysis of SAR on Human Head modeling at 900 and 1800 MHz from a Handset Antenna” IEEE

3    Ignacio Llatser”Graphene-based nano-patch antenna for terahertz radiation “Photonics and Nanostructures – Fundamentals and ApplicationsVolume 10, Issue 4, October 2012, Pages 353-358

4    A. Y. Simba, T. Hikage, S. Watanabe and T. Nojima, “Specific Absorption Rates of Anatomically Realistic Human Models Exposed to Radiofrequency Electromagnetic Fields From Mobile Phones Used in Elevators,” IEEE Trans. Microwave. Theory Tech.,vol.57, no.5,pp.1250-1259, May.2009

5    P.-Y. Chen and A. Alu, “Atomically Thin Surface Cloak Using Graphene Monolayers,” 2011 ACS Nano, 5, 585-5863 IEEE Standard-1528, “IEEE Recommended Practice for Determining the Peak Spatial-Average Specific Absorption Rate (SAR) in the Human Head from Wireless Communications Devices: Measurement Techniques,” December 2003.

6    “Procedure to measure the Specific Absorption Rate (SAR) in the frequency range of 300MHz to 3 GHz—part 1: handheld mobile wireless communication devices,” International Electro technical Commission, committee draft for vote, IEC 62209.

7    M. Young “Specific Absorption Rate (SAR) Estimation for Cellular Phone,” Association of Radio Industries and businesses, ARIBSTD-T56,., The Technical Writer’s Handbook. Mill Valley, CA: University Science, 1989.

8    M. A. Jensen and Y. Rahmat-Samii, “EM interaction of handset antennas and a human in personal communications,” Proc. IEEE, vol. 83, pp.7-17, 1995.

9    Bineet Kaur , Sukhwinder Singh, Jagdish Kumar” A study of SAR pattern in biological tissues due to RF exposure” A study of SAR pattern in biological tissues due to RF exposure,IEEE explore 2015

10  FEKO software,http://www.feko.info/contact.htm

11  Monopole details,http://www.emss.de.

12  https://www.tutorialspoint.com/antenna_theory/antenna_theory_half_wave_folded_dipole.htm