CITY UNIVERSITY OF HONG KONG. A Study of Electromagnetic Radiation and Specific Absorption Rate of Mobile Phones with Fractional Human Head Models

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1 CITY UNIVERSITY OF HONG KONG A Study of Electromagnetic Radiation and Specific Absorption Rate of Mobile Phones with Fractional Human Head Models Submitted to Department of Electronic Engineering in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy by Chan Kwok Hung March 2008

2 i A Study of Electromagnetic Radiation and Specific Absorption Rate of Mobile Phones with Fractional Human Head Models by CHAN Kwok Hung Submitted to the Department of Electronic Engineering in partial fulfillment of the requirements for the Degree of Doctor of Philosophy Abstract The specific absorption rate (SAR) value is a key parameter in defining the energy absorbed by the human head and body under electromagnetic (EM) radiation. It is known that the complex configuration of the mobile phone antenna with the human head modeling makes the evaluation of the SAR extremely complicated; this result in requiring high computational resource and long simulation time in numerical modeling. The theme of this thesis is to examine the electromagnetic radiation and SAR of mobile phones with fractional human head models.

3 ii The evaluation of SAR induced in the head models in this thesis starts off with a simple monopole antennae using finite-difference time-domain (FDTD) method. This numerical analysis on the EM radiation and the SAR due to the monopole antenna installed on the mobile phone casing with the presence of fractional human head models is presented aiming at reducing the simulation computational time in the numerical analysis. Initial results have indicated that the idea of using fractional phantom head model can be used for an efficient SAR analysis. The common antenna in modern mobile communication applications falls into two categories - the external helical antenna and the internal patch antenna. Helical antenna consists of a small wire spring, and the patch antenna mainly consists of a patch and a ground plane. These antennas have been commonly adopted in the mobile applications in recent years. The numerical investigation of the EM radiation and the SAR induced in the human head because of both antennas together with various fractional phantom head models is also presented in this thesis. Results have indicated the feasibility of the fractional phantom head model for the SAR evaluation in most common types of mobile antennas. Measurements have also been carried out, and the MapSAR measurement system is used to verify the SAR value induced in the fractional phantom head models. Three types of antennas including the monopole, helical, and patch antenna are examined. The comparison of the measured and simulated SAR value on the fractional spherical phantom due to these antennas is presented. Both simulation and measurement results have shown a good agreement on the SAR analysis.

4 iii Finally, the fractional head model is also examined in the mobile antenna design s applications, the relationship between various ground plane configurations of mobile patch antennas and the SAR value are studied. It is found that the SAR value is sensitive to the size of the antenna ground plane; it can be summarized that the fractional phantom head model can be adopted in the mobile phone design analysis. In general, a study of the EM radiation and the SAR of mobile phones with different numerical human head models, including different shapes and different fractional models, are examined in this thesis. It is summarized that the fractional phantom model can be considered as an alternative phantom head model in the SAR analysis.

5 vi Table of Contents Abstract Certification of Approval by the Panel of Examiners Acknowledgements Table of Contents List of Tables List of Figures i iv v vi ix xiii Chapter 1 Introduction Overview of Mobile Phone History Electromagnetic Radiation from Mobile Phones Evaluation of Human Safety in Electromagnetic Radiation Overview of Pervious Research Objectives and Organization of the Thesis 11 Chapter 2 Feasibility Study of Using Fractional Phantom Head Models on SAR Evaluation Introduction Numerical Modeling Monopole Antenna and Mobile Phone Casing Modeling Phantom Head Modeling Numerical Simulation Results and Discussion Comparison of Phantom Head Models Fractional Cubical Phantom Head Models Fractional Spherical Phantom Head Models Fractional Realistic Phantom Head Models Computational Requirement Summary 45 Chapter 3 Investigation of SAR and Antenna Performance of External Mobile Antenna with Factional Phantom Head Models Introduction Numerical Modeling External Helical Antenna and Mobile Phone Casing Modeling 47

6 vii Phantom Head Modeling Numerical Simulation Results and Discussion Comparison of Phantom Head Models Fractional Cubical Phantom Head Models Fractional Spherical Phantom Head Models Fractional Realistic Phantom Head Models Computational Requirement Summary 75 Chapter 4 Investigation of SAR and Antenna Performance of Internal Mobile Antenna with Fractional Phantom Head Models Introduction Numerical Modeling Internal Patch Antenna Modeling Phantom Head Modeling Numerical Simulation Results and Discussion Comparison of Phantom Head Models Fractional Cubical Phantom Head Models Fractional Spherical Phantom Head Models Fractional Realistic Phantom Head Models Computational Requirement Summary 104 Chapter 5 Experimental Verification of SAR due to Mobile Antennas with Fractional Phantom Head Models Introduction Antenna Configuration Measurement Setup Numerical Modeling Results and Discussion Return Loss Specific Absorption Rate Computational Requirement Summary 132 Chapter 6 Effect of the Mobile Patch Antenna Ground Plane on SAR 133

7 viii 6.1. Introduction Patch Antenna Ground Plane and Phantom Head Modeling Patch Antenna Ground Plane Modeling Length of the Ground Plane Width of the Ground Plane Addition of Vertical Sidewall on Ground Plane Phantom Head Modeling Numerical Simulation Results and Discussion Length of the Ground Plane Width of the Ground Plane Additional of Vertical Sidewall on Ground Plane Summary 159 Chapter 7 Conclusion 160 References 163 Research Papers Published by the Author 170

8 ix List of Tables 1.1. Frequency bands and the maximum output power for 1G/2G/3G mobile phone systems in Hong Kong Dielectric properties of the materials Total number of grids used for different types of phantom head models in the FDTD numerical modeling Simulated maximum averaged SAR over 1g and 10g of tissue for 900 MHz and 1.8 GHz monopole antennas with different phantom head models Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional cubical head models Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional spherical head models Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional realistic head models Total number of grids employed for the monopole antenna with the presence of different fractional cubical phantoms in the FDTD numerical modeling Total number of grids employed for the monopole antenna with the presence of different fractional spherical phantoms in the FDTD numerical modeling Total number of grids employed for the monopole antenna with the presence of different fractional realistic phantoms in the FDTD numerical modeling Simulation time (in seconds) of monopole antenna with the presence of different fractional phantom models in the FDTD modeling 43

9 x Time reduction of monopole antenna with the presence of different fractional phantom models in the FDTD modeling Dielectric properties of the materials Total number of grids used for different phantom head models in the FDTD numerical modeling Simulated maximum averaged SAR over 1g and 10g of tissue for 900 MHz and 1.8 GHz helical antennas with different phantom head models Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional cubical head models Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional spherical head models Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional realistic head models Total number of grids employed for the helical antenna with the presence of different fractional cubical phantoms in the FDTD numerical modeling Total number of grids employed for the helical antenna with the presence of different fractional spherical phantoms in the FDTD numerical modeling Total number of grids employed for the helical antenna with the presence of different fractional realistic phantoms in the FDTD numerical modeling Simulation time (in seconds) of helical antenna with the presence of different fractional phantom models in the FDTD modeling Time reduction of helical antenna with the presence of different fractional phantom models in the FDTD modeling Dielectric properties of the materials Total number of grids used for different types of phantom head models in

10 xi the FDTD numerical modeling Simulated maximum averaged SAR over 1g and 10g of tissue for 900 MHz and 1.8 GHz patch antennas with different phantom head models Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional cubical head models Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional spherical head models Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional realistic head models Total number of grids employed for the patch antenna with the presence of different fractional cubical phantoms in the FDTD numerical modeling Total number of grids employed for the patch antenna with the presence of different fractional spherical phantoms in the FDTD numerical modeling Total number of grids employed for the patch antenna with the presence of different fractional realistic phantoms in the FDTD numerical modeling Simulation time (in seconds) of patch antenna with the presence of different fractional phantom models in the FDTD modeling Time reduction of patch antenna with the presence of different fractional phantom models in the FDTD modeling Dielectric properties of the materials Total number of grids used in each type of mobile antennas with the 100% phantom head model Simulated and measured SAR over 1g and 10g of tissue of 100% phantom head models due to different mobile phone antenna Total simulation time (in seconds) used for fractional phantom head models 130

11 xii 5.5. Total number of grids used for fractional phantom head models Dielectric properties of the materials Total number of grids used for the phantom head models in the FDTD numerical modeling Maximum averaged SAR over 1g and 10g of tissue for dual-band PIFA antenna operated at 930 MHz with different lengths of antenna ground plane Maximum averaged SAR over 1g and 10g of tissue for dual-band PIFA antenna operated at 1.75 GHz with different lengths of antenna ground plane Maximum averaged SAR over 1g and 10g of tissue for dual-band PIFA antenna operated at 930 MHz with different widths of antenna ground plane Maximum averaged SAR over 1g and 10g of tissue for dual-band PIFA antenna operated at 1.75 GHz with different widths of antenna ground plane Maximum averaged SAR over 1g and 10g of tissue for dual-band PIFA antenna operated at 930 MHz with different cases of additional vertical sidewalls on antenna ground plane Maximum averaged SAR over 1g and 10g of tissue for dual-band PIFA antenna operated at 1.75 GHz with different cases of additional vertical sidewalls on antenna ground plane 157

12 xiii List of Figures 2.1. Configuration of mobile phones installed with monopole antennas Three different types of phantom head models Different types of fractional phantom head models Diagram of a typical simulation model Simulated return loss at 900 MHz and 1.8 GHz monopole antennas due to the presence of different full phantom head models Simulated far-field radiation pattern of 900 MHz monopole antenna due to the presence of different full phantom head models Simulated far-field radiation pattern of 1.8 GHz monopole antenna due to the presence of different full phantom head models SAR distribution for the three different phantom head models Simulated return loss at 900 MHz and 1.8 GHz monopole antennas due to the presence of different cubical phantom heads Simulated far-field radiation pattern of 900 MHz and 1.8 GHz monopole antennas due to the presence of different cubical phantom head models Simulated return loss at 900 MHz and 1.8 GHz monopole antennas due to the presence of different spherical phantom head models Simulated far-field radiation pattern of 900 MHz and 1.8 GHz monopole antennas due to the presence of different spherical phantom head models Simulated return loss at 900 MHz and 1.8 GHz monopole antennas due to the presence of different realistic phantom head models 38

13 xiv Simulated far-field radiation pattern of 900 MHz and 1.8 GHz monopole antennas due to the presence of different realistic phantom head models Comparison of saved simulation time, saved computational resource and SAR variation for monopole antenna with the presence of different fractional head models Configuration of mobile phones installed with 900 MHz helical antenna Configuration of mobile phones installed with 1.8 GHz helical antenna Simplified diagram of typical simulation model Simulated return loss at 900 MHz and 1.8 GHz mobile phone helical antennas due to the presence of different full phantom head models Simulated far-field radiation pattern of 900 MHz helical antenna due to the presence of different full phantom head models Simulated far-field radiation pattern of 1.8 GHz helical antenna due to the presence of different full phantom head models SAR distribution for the three different phantom head models Simulated return loss at 900 MHz and 1.8 GHz helical antennas due to the presence of different cubical phantom head models Simulated far-field radiation pattern of 900 MHz and 1.8 GHz helical antennas due to the presence of different cubical phantom head models Simulated return loss at 900 MHz and 1.8 GHz helical antennas due to the presence of different spherical phantom head models Simulated far-field radiation pattern of 900 MHz and 1.8 GHz helical antennas due to the presence of different spherical phantom head models Simulated return loss at 900 MHz and 1.8 GHz helical antennas due to the presence of different realistic phantom head models 67

14 xv Simulated far-field radiation pattern of 900 MHz and 1.8 GHz helical antennas due to the presence of different realistic phantom head models Comparison of saved simulation time, saved computational resource and SAR variation for helical antenna with the presence of different fractional head models Configuration of a 900 MHz patch antenna Configuration of a 1.8 GHz patch antenna Simplified diagram of typical simulation model Simulated return loss at 900 MHz and 1.8 GHz mobile phone patch antennas due to the presence of different full phantom head models Simulated far-field radiation pattern of 900 MHz patch antenna due to the presence of different full phantom head models Simulated far-field radiation pattern of 1.8 GHz patch antenna due to the presence of different full phantom head models SAR distribution for the three different phantom head models Simulated return loss at 900 MHz and 1.8 GHz patch antennas due to the presence of different cubical phantom head models Simulated far-field radiation pattern of 900 MHz and 1.8 GHz patch antennas due to the presence of different cubical phantom head models Simulated return loss at 900 MHz and 1.8 GHz patch antennas due to the presence of different spherical phantom head models Simulated far-field radiation pattern of 900 MHz and 1.8 GHz patch antennas due to the presence of different spherical phantom head models Simulated return loss at 900 MHz and 1.8 GHz patch antennas due to the presence of different realistic phantom head models 97

15 xvi Simulated far-field radiation pattern of 900 MHz and 1.8 GHz patch antennas due to the presence of different realistic phantom head models Comparison of saved simulation time, saved computational resource and SAR variation for patch antenna with the presence of different fractional head models Fabricated monopole, helical, and patch antennas for SAR evaluation A simplified diagram and photo of the pre-compliance SAR measurement system A typical setup and photo of modified SAR measurement system for 50% fractional phantom head model Typical measurement setup of return loss measurement for antenna with the presence of MapSAR system Simplified diagram of typical simulation model Modeling of phantom head model used in simulation Fractional phantom head models used in simulation Simulated and measured return loss of 900 MHz monopole antenna with different fractional phantom head models Simulated and measured return loss of 1.8 GHz monopole antenna with different fractional phantom head models Simulated and measured return loss of 900 MHz helical antenna with different fractional phantom head models Simulated and measured return loss of 1.8 GHz helical antenna with different fractional phantom head models Simulated and measured return loss of 900 MHz patch antenna with different fractional phantom head models 122

16 xvii Simulated and measured return loss of 1.8 GHz patch antenna with different fractional phantom head models Variation of resonant frequency due to different fractional phantom head models in simulation and measurement Simulated SAR variation over 1g and 10g tissue for different mobile phone antennas with different fractional head models Measured SAR variation over 1g and 10g tissue for different mobile phone antennas with different fractional head models Comparison of saved simulation time, saved computational resource, and SAR variation by using fractional head models Dimensions (in mm) of a typical PIFA dual-band internal antenna Length extension of internal antenna ground plane Width extension of internal antenna ground plane Configuration of the original PIFA antenna, and 7 cases of addition of vertical sidewall Configuration of phantom head models Simplified diagram of a typical simulation model Return loss of the PIFA antenna with different lengths of ground plane due to the presence of phantom head models Far-field radiation patterns of the original PIFA antenna (l = 80 mm) and case of extended length (l = 150 mm) of antenna ground plane due to the presence of phantom head models SAR value of PIFA antenna ground plane with length extension Return loss of the PIFA antenna with different widths of ground plane due to the presence of phantom head models 148

17 xviii Far-field radiation patterns of the original PIFA antenna (w = 40 mm) and case of extended width (w = 80 mm) of antenna ground plane due to the presence of phantom head models SAR value of PIFA antenna ground plane with width extension Return loss of the PIFA antenna with different cases of additional vertical sidewall on the ground plane due to the presence of phantom head models Far-field radiation patterns of the original PIFA antenna and the case of additional 4 vertical sidewalls on the ground plane due to the presence of phantom head models SAR value of PIFA antenna with different cases of addition of vertical sidewall on antenna ground plane 158