SAR Reduction In Mobile Phones

Using PIFA With EBG Structure

PRESENTED BY

Athira.D.Nair

S7 ECE

Roll No : 14

LBSITW

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OUTLINE

Introduction

SAR

PIFA

EBG Structure

Structure

Optimization

Characteristics (After optimization)

Return loss

Radiation pattern

Total Radiated power (TRP)

SAR

Conclusion

References

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INTRODUCTION Health risk in mobile usage

Need to reduce SAR

SAR (Specific Absorption Rate) Power absorbed per mass of the tissue (Unit :- W/kg)

Measurement – Taking average over small volume (1g/10g tissue)

σ – Sample electrical conductivity E - RMS electric field ρ - Sample density

Must not exceed exposure guidelines

Techniques to reduce SAR Optimizing antenna geometry Use of ferrite PIFA with EBG structure

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PIFA (Planar Inverted F – Antenna)

• Consists of :-

Ground plane

Top plate

Shorting strip

Feed wire

Features:-

Compact

Omni directional radiation pattern

High gain for both states of polarization

Reduced SAR

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Electromagnetic Band Gap (EBG) Structure

Small scale periodic structures

Prevent propagation of EM waves in specified frequency band

High surface impedance

Suppress propagation of surface waves

Stop band characteristics (in PCS): control radiation characteristics

Enhanced antenna performance

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PROPOSED STRUCTURE

• Consists of:-

Antenna (PIFA)

EBG cells

PCB layer

All connected to ground plane

Side view Top view

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PROPOSED STRUCTURE ….. cntd

Antenna (PIFA) :-

• Operate at PCS band (1.85 – 1.91GHz)

• Located on the underside of mobile phone

EBG Structure :-

Placed between PCB & PIFA

Control the radiations of EM waves towards body

Via – less EBG structure selected (simple & less SAR)

Consists of EBG unit cell

PCB:-

• Consists of active circuits, power lines, battery etc

• Eg:- FR4

EBG unit cell

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OPTIMIZATION

SIMULATION & MEASUREMENT

Simulation• Microwave studio based on 3-D FIT EM

simulator Measurement System

• MR900-W SAR

• Uses SAM head phantom• Consists of :

• Head equivalent liquid (Er = 40, σ = 1.4)

• Shell

• Test device (mobile) at distance 3mm

• Antenna location :

• X-Y plane, orientation – Z-axis

• Probe measures E–fields in head phantom

• Computer system calculates SAR values

Head Phantom

MR900-W SAR Measurement System

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OPTIMIZATION …. cntd

Parameter study of structure is done

Antenna bandwidth fixed under (-10dB) return loss

1. Vertical length (L) of EBG unit cell

• Vertical length (L) decreases Number of EBG cells increases

• More EBG cells in limited space SAR value reduced

• Optimized value of L= 3mm

SAR Values With Parameter L

EBG unit cell

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OPTIMIZATION …. cntd

2. Antenna height (Ha); Antenna position fixed

• Ha –> 3 – 3.5mm , SAR reduced

• Optimized value of Ha = 3.14mm

SAR values with Parameter Ha SAR Values With Parameter

Ha

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OPTIMIZATION …. cntd

3. Antenna position (T); Antenna height(Ha) fixed (3.14mm)

• Position between antenna & EBG structure asymmetrical

• Optimized value of T = 8mm

SAR Values With Parameter T

SAR values with parameter T

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CHARACTERISTICS Return loss :-

• Loss of signal power due to reflection

• RL(dB) = 20 log10(1 / )

• Less for proposed structure

• Satisfies PCS transmitting band for VSWR < 3

Return loss of the proposed antenna

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CHARACTERISTICS ….. cntd

Radiation pattern :-

• Spatial distribution of radiation as a function of angle

• Reduced radiation pattern in user’s direction

Simulated Radiation Pattern - Proposed Antenna Measured Radiation Pattern - Proposed Antenna

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CHARACTERISTICS ….. cntd

Total Radiated power (TRP) :-

• Power radiated by the antenna

• Should meet criteria of mobile communication service vendors

• Greater for proposed antenna (increased antenna gain)

TRP Values

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CHARACTERISTICS ….. cntd

SAR :-

• SAR reduced by 31% at center frequency

SAR Values

SAR DISTRIBUTION MAP

Conventional PIFA

Proposed PIFA

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CONCLUSION

Presented a novel scheme for SAR reduction

Radiation towards body reduced

Reduction in SAR value

Antenna performance maintained

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REFERENCES

Sang il Kwak, Dong-Uk Sim, and Jong Hwa Kwon, “Design of Optimized Multilayer PIFA With the EBG Structure for SAR Reduction in Mobile Applications,” IEEE Transactions On Electromagnetic Compatibility, Vol. 53, No. 2, May 2011.

Design of Multilayer PIFA based on an EBG structure for SAR reduction in mobile Applications - Sang il Kwak, Dong-Uk Sim, Jong Hwa Kwon and Je Hoon Yun.

D. Sivenpiper, L. Zhang, R. F. Broas, N. G. Alexopoulos, and E. Yablonovitch, “High-impedance electromagnetic surface with a forbidden frequency band,” IEEE Trans Microw. Theory Tech., vol. 47, no. 11, pp. 2059–2074, Nov. 1999.

Effects of Ferrite Sheet Attachment to Portable Telephone in Reducing Electromagnetic Absorption in Human Head - Jianqing Wangt Osamu F’ujiwarat Tasuku Takagi.

Z. Duan, D. Linton, W. Scanlon, and G. Conway, “Improving wearable slot antenna performance with EBG structures,” in Proc. Loughborough Antennas and Propag. Conf., Mar. 2008, pp. 173–176.

Thank You