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.
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,.
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.
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
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
Free space wavelength
Height of the antenna
Conductivity media of Graphene
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
Conductivity(?) in S/m
Mass density(?)in kg/ m3
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
10 gm mW/Kg
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
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.
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11 Monopole details,http://www.emss.de.