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Simulation of a human head exposure to GSM/LTE/WLAN antenna radiation

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WEBINAR
Power-Handling of Electronic Products
Thursday, October 14, 2021
Time
SESSION 1
SESSION 2
CEST (GMT +2)
03:00 PM
08:00 PM
EDT (GMT -4)
09:00 AM
02:00 PM
View 3D results Gebrauchte Werkzeuge:

Introduction

Antennas used for mobile and smartphone applications have experienced big and rapid development to adapt to the progressive needs of wireless communication. These improvements are following the deployment of 3G, 4G and 5G technologies. On the other hand, more attention has been drawn to the adverse health effects of electromagnetic fields on human body. The safety of the radiated fields has been the concern of much debate and research.

The purpose of this analysis is to investigate the electromagnetic interaction between a printed mobile antenna for GSM/LTE/WLAN application and a human head tissue. The studied antenna [1] operates at a wide frequency band covering the LTE700/GSM850/GSM900 bands and the GSM1800/1900/LTE2300/2500 bands.

Antenna Geometry

The geometry of the presented planar antenna with with a T-shaped coupling feed and  an inductive shorting strip  is shown in Figure 1. It is printed on a 1.6mm FR4 substrate with length and width of 120mm and 36 mm, respectively. The active antenna part occupies a small size of 36mm x 20 mm which is printed on the top ungrounded portion of the circuit board and the rest used as a ground-plane with a size of 100 mm x 36 mm. The antenna is fed by a 50-ohm coaxial cable.

 a) 3D design and b)  front view of the studied antenna

Figure 1-  a) 3D design and b)  front view of the studied antenna 
              

Simulation Results

The Antenna solver of HFWorks is used for the working frequency range of 0.5 GHz – 3GHz. The properties of the used FR4 material are 4.4 for the relative permittivity and 0.02 for the dielectric loss tangent factor.

A mesh refinement is used for the port and conductor edges including the slot side to guarantee the accuracy of the results. After solving the study, the simulation revealed the following results.

Free Space Antenna Analysis

This first part is dedicated to the analysis of the antenna performance in free space.
Figure 2 shows the return loss results from which we can clearly observe that the studied antenna is capable of generating two different operating bands: the lower band with a band-width of 170 MHz (from 830 to 1000MHz) which covers the GSM850/GSM900 applications, while the upper band with a band-width of 570 MHz covering the LTE2300/LTE2500 and WLAN2400 applications.
 

2D Return loss plot versus frequency.

Figure 2: 2D Return loss plot versus frequency.
 

At 900 MHz, the antenna behaves with a good omnidirectional radiation pattern which confirms the stable radiation characteristic of the studied antenna over the lower band compared to the higher frequency band.
 

Gain radiation pattern for a)-900 MHz and b)- 2450 MHz

Figure 3: Gain radiation pattern for a)-900 MHz and b)- 2450 MHz
 

Near Head Antenna Analysis

The second part is studying the main purpose of this paper which is the effect of the electromagnetic radiation of the antenna on a human head tissue. For this reason, a human head phantom is added and placed near the antenna with a distance of 5mm. It is made of a single equivalent material defined by the material properties shown in Table 1.

3D design of the studied antenna near human head phantom

Figure 4: 3D design of the studied antenna near human head phantom
  
 
Material Relative permittivity Electrical conductivity (S/m) Thermal conductivity (W/m. K) Specific heat (J/Kg. K) Mass density (Kg/m cubed)
Human head equivalent material 42.61 1.48 0.48 3421 1030

Table 1: Material properties

After solving, the simulation revealed the S11 results versus frequency. We can notice the introduced curve shifting compared to the resonant frequencies of the free space antenna analysis.
 

 2D Return loss plot versus frequency.

Figure 5: 2D Return loss plot versus frequency.
 

For an input power of 24 dBm (250 mW) for the lower band frequency (900 MHz) and 21 dBm (125mW) for the higher band frequency (2450 MHz), the electric field and local SAR distribution results over the human head phantom for the low and high frequency bands are defined below: the first two plots (Figure 6) are showing the E-field distribution animation versus phase and the local SAR density, respectively, for the frequency of 900 MHz.

AS noticed, both characteristics are not exceeding the restricted limits defined by the FCC (Federal Communications Commission) and ICNIIRP (International Commission on Non-Ionizing Radiation Protection) [2]. For both frequencies, SAR value is highest around the human ear where it faces the maximum of incident waves.
 

3D plot of a)-Electric field animation versus phase and b)- SAR distribution at 900MHz
(a)
3D plot of a)-Electric field animation versus phase and b)- SAR distribution at 900MHz
(b)

Figure 6 - 3D plot of a) Electric field animation versus phase and b) SAR distribution at 900MHz
 

Same is noticed for the high band frequency and precisely for 2.45 GHz, local SAR inside the human head attained a maximum value of 2.95 W/Kg for a maximum E-field around 50 V/m inside the head tissue (Figure 7).

3D plot of a)-Electric field animation versus phase and b)- SAR distribution at 2450 MHz
(a)
3D plot of a)-Electric field animation versus phase and b)- SAR distribution at 2450 MHz

(b)
Figure 7 - 3D plot of a) Electric field animation versus phase and b)  SAR distribution at 2450 MHz
 

Figure 8 is showing the gain pattern for the frequency of 2.45GHz which attains a maximum gain of 3.81 dB near human head.

Gain radiation pattern ta 2.45 GHz Thermal Analysis

Figure 8 - Gain radiation pattern ta 2.45 GHz

Thermal Analysis

To check the thermal effect of the electromagnetic radiation on the human head tissue for a call duration of 10 min, transient thermal solver of HFWorks is used. For an input power of 24 dBm (250 mW) for the lower band frequency (900 MHz) and 21 dBm (125mW) for the higher band frequency (2450 MHz), the thermal simulation was performed.

As seen in Figure 9, a local temperature increase is obtained across the human head tissue near the cell phone antenna position. It increases by 0.25°C for 900MHz and by 0.14°C for 2.45GHz.

3D plot of temperature increase distribution for a) 900 MHz and b) 2450 MHz

Figure 9 - 3D plot of temperature increase distribution for a) 900 MHz and b) 2450 MHz
 

Conclusion

The aim of this article is to study the influence of mobile phone antenna radiation on the human head tissue. HFWorks software allowed us to investigate the performance and radiation behavior of mobile antenna in free space and the induced electromagnetic fields with their thermal effects side inside the biological human head tissue.

 

References

[1]. Belrhiti, Lakbir, et al. "Investigation of dosimetry in four human head models for planar monopole antenna with a coupling feed for LTE/WWAN/WLAN internal mobile phone." Journal of Microwaves, Optoelectronics and Electromagnetic Applications 16.2 (2017): 494-513.
[2]. https://www.icnirp.org/en/frequencies/radiofrequency/index.html

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