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
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.
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.
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.
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 1 1.1. Overview of Mobile Phone History 1 1.2. Electromagnetic Radiation from Mobile Phones 4 1.3. Evaluation of Human Safety in Electromagnetic Radiation 5 1.4. Overview of Pervious Research 7 1.5. Objectives and Organization of the Thesis 11 Chapter 2 Feasibility Study of Using Fractional Phantom Head Models on SAR Evaluation 13 2.1. Introduction 13 2.2. Numerical Modeling 14 2.2.1. Monopole Antenna and Mobile Phone Casing Modeling 14 2.2.2. Phantom Head Modeling 15 2.3. Numerical Simulation 18 2.4. Results and Discussion 21 2.4.1. Comparison of Phantom Head Models 22 2.4.2. Fractional Cubical Phantom Head Models 29 2.4.3. Fractional Spherical Phantom Head Models 32 2.4.4. Fractional Realistic Phantom Head Models 36 2.4.5. Computational Requirement 41 2.5. Summary 45 Chapter 3 Investigation of SAR and Antenna Performance of External Mobile Antenna with Factional Phantom Head Models 46 3.1. Introduction 46 3.2. Numerical Modeling 47 3.2.1. External Helical Antenna and Mobile Phone Casing Modeling 47
vii 3.2.2. Phantom Head Modeling 49 3.3. Numerical Simulation 49 3.4. Results and Discussion 51 3.4.1. Comparison of Phantom Head Models 51 3.4.2. Fractional Cubical Phantom Head Models 58 3.4.3. Fractional Spherical Phantom Head Models 61 3.4.4. Fractional Realistic Phantom Head Models 65 3.4.5. Computational Requirement 70 3.5. Summary 75 Chapter 4 Investigation of SAR and Antenna Performance of Internal Mobile Antenna with Fractional Phantom Head Models 76 4.1. Introduction 76 4.2. Numerical Modeling 77 4.2.1. Internal Patch Antenna Modeling 77 4.2.2. Phantom Head Modeling 79 4.3. Numerical Simulation 79 4.4. Results and Discussion 81 4.4.1. Comparison of Phantom Head Models 81 4.4.2. Fractional Cubical Phantom Head Models 88 4.4.3. Fractional Spherical Phantom Head Models 91 4.4.4. Fractional Realistic Phantom Head Models 95 4.4.5. Computational Requirement 99 4.5. Summary 104 Chapter 5 Experimental Verification of SAR due to Mobile Antennas with Fractional Phantom Head Models 105 5.1. Introduction 105 5.2. Antenna Configuration 106 5.3. Measurement Setup 107 5.4. Numerical Modeling 112 5.5. Results and Discussion 115 5.5.1. Return Loss 116 5.5.2. Specific Absorption Rate 125 5.5.3. Computational Requirement 129 5.6. Summary 132 Chapter 6 Effect of the Mobile Patch Antenna Ground Plane on SAR 133
viii 6.1. Introduction 133 6.2. Patch Antenna Ground Plane and Phantom Head Modeling 134 6.2.1. Patch Antenna Ground Plane Modeling 134 6.2.1.1. Length of the Ground Plane 136 6.2.1.2. Width of the Ground Plane 136 6.2.1.3. Addition of Vertical Sidewall on Ground Plane 137 6.2.2. Phantom Head Modeling 138 6.3. Numerical Simulation 139 6.4. Results and Discussion 140 6.4.1. Length of the Ground Plane 140 6.4.2. Width of the Ground Plane 147 6.4.3. Additional of Vertical Sidewall on Ground Plane 153 6.5. Summary 159 Chapter 7 Conclusion 160 References 163 Research Papers Published by the Author 170
ix List of Tables 1.1. Frequency bands and the maximum output power for 1G/2G/3G mobile phone systems in Hong Kong 5 2.1. Dielectric properties of the materials 18 2.2. Total number of grids used for different types of phantom head models in the FDTD numerical modeling 21 2.3. Simulated maximum averaged SAR over 1g and 10g of tissue for 900 MHz and 1.8 GHz monopole antennas with different phantom head models 27 2.4. Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional cubical head models 32 2.5. Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional spherical head models 36 2.6. Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional realistic head models 40 2.7. Total number of grids employed for the monopole antenna with the presence of different fractional cubical phantoms in the FDTD numerical modeling 42 2.8. Total number of grids employed for the monopole antenna with the presence of different fractional spherical phantoms in the FDTD numerical modeling 42 2.9. Total number of grids employed for the monopole antenna with the presence of different fractional realistic phantoms in the FDTD numerical modeling 43 2.10. Simulation time (in seconds) of monopole antenna with the presence of different fractional phantom models in the FDTD modeling 43
x 2.11. Time reduction of monopole antenna with the presence of different fractional phantom models in the FDTD modeling 43 3.1. Dielectric properties of the materials 49 3.2. Total number of grids used for different phantom head models in the FDTD numerical modeling 50 3.3. Simulated maximum averaged SAR over 1g and 10g of tissue for 900 MHz and 1.8 GHz helical antennas with different phantom head models 56 3.4. Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional cubical head models 61 3.5. Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional spherical head models 65 3.6. Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional realistic head models 69 3.7. Total number of grids employed for the helical antenna with the presence of different fractional cubical phantoms in the FDTD numerical modeling 71 3.8. Total number of grids employed for the helical antenna with the presence of different fractional spherical phantoms in the FDTD numerical modeling 71 3.9. Total number of grids employed for the helical antenna with the presence of different fractional realistic phantoms in the FDTD numerical modeling 72 3.10. Simulation time (in seconds) of helical antenna with the presence of different fractional phantom models in the FDTD modeling 73 3.11. Time reduction of helical antenna with the presence of different fractional phantom models in the FDTD modeling 73 4.1. Dielectric properties of the materials 79 4.2. Total number of grids used for different types of phantom head models in
xi the FDTD numerical modeling 80 4.3. Simulated maximum averaged SAR over 1g and 10g of tissue for 900 MHz and 1.8 GHz patch antennas with different phantom head models 86 4.4. Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional cubical head models 91 4.5. Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional spherical head models 95 4.6. Simulated maximum averaged SAR over 1g and 10g of tissue induced in different fractional realistic head models 99 4.7. Total number of grids employed for the patch antenna with the presence of different fractional cubical phantoms in the FDTD numerical modeling 100 4.8. Total number of grids employed for the patch antenna with the presence of different fractional spherical phantoms in the FDTD numerical modeling 101 4.9. Total number of grids employed for the patch antenna with the presence of different fractional realistic phantoms in the FDTD numerical modeling 101 4.10. Simulation time (in seconds) of patch antenna with the presence of different fractional phantom models in the FDTD modeling 102 4.11. Time reduction of patch antenna with the presence of different fractional phantom models in the FDTD modeling 103 5.1. Dielectric properties of the materials 115 5.2. Total number of grids used in each type of mobile antennas with the 100% phantom head model 115 5.3. Simulated and measured SAR over 1g and 10g of tissue of 100% phantom head models due to different mobile phone antenna 126 5.4. Total simulation time (in seconds) used for fractional phantom head models 130
xii 5.5. Total number of grids used for fractional phantom head models 130 6.1. Dielectric properties of the materials 134 6.2. Total number of grids used for the phantom head models in the FDTD numerical modeling 140 6.3. 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 145 6.4. 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 145 6.5. 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 151 6.6. 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 151 6.7. 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 157 6.8. 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
xiii List of Figures 2.1. Configuration of mobile phones installed with monopole antennas 14 2.2. Three different types of phantom head models 16 2.3. Different types of fractional phantom head models 17 2.4. Diagram of a typical simulation model 19 2.5. Simulated return loss at 900 MHz and 1.8 GHz monopole antennas due to the presence of different full phantom head models 24 2.6. Simulated far-field radiation pattern of 900 MHz monopole antenna due to the presence of different full phantom head models 25 2.7. Simulated far-field radiation pattern of 1.8 GHz monopole antenna due to the presence of different full phantom head models 26 2.8. SAR distribution for the three different phantom head models 28 2.9. Simulated return loss at 900 MHz and 1.8 GHz monopole antennas due to the presence of different cubical phantom heads 30 2.10. Simulated far-field radiation pattern of 900 MHz and 1.8 GHz monopole antennas due to the presence of different cubical phantom head models 31 2.11. Simulated return loss at 900 MHz and 1.8 GHz monopole antennas due to the presence of different spherical phantom head models 34 2.12. Simulated far-field radiation pattern of 900 MHz and 1.8 GHz monopole antennas due to the presence of different spherical phantom head models 35 2.13. Simulated return loss at 900 MHz and 1.8 GHz monopole antennas due to the presence of different realistic phantom head models 38
xiv 2.14. Simulated far-field radiation pattern of 900 MHz and 1.8 GHz monopole antennas due to the presence of different realistic phantom head models 39 2.15. Comparison of saved simulation time, saved computational resource and SAR variation for monopole antenna with the presence of different fractional head models 44 3.1. Configuration of mobile phones installed with 900 MHz helical antenna 48 3.2. Configuration of mobile phones installed with 1.8 GHz helical antenna 48 3.3. Simplified diagram of typical simulation model 50 3.4. Simulated return loss at 900 MHz and 1.8 GHz mobile phone helical antennas due to the presence of different full phantom head models 53 3.5. Simulated far-field radiation pattern of 900 MHz helical antenna due to the presence of different full phantom head models 54 3.6. Simulated far-field radiation pattern of 1.8 GHz helical antenna due to the presence of different full phantom head models 55 3.7. SAR distribution for the three different phantom head models 57 3.8. Simulated return loss at 900 MHz and 1.8 GHz helical antennas due to the presence of different cubical phantom head models 59 3.9. Simulated far-field radiation pattern of 900 MHz and 1.8 GHz helical antennas due to the presence of different cubical phantom head models 60 3.10. Simulated return loss at 900 MHz and 1.8 GHz helical antennas due to the presence of different spherical phantom head models 63 3.11. Simulated far-field radiation pattern of 900 MHz and 1.8 GHz helical antennas due to the presence of different spherical phantom head models 64 3.12. Simulated return loss at 900 MHz and 1.8 GHz helical antennas due to the presence of different realistic phantom head models 67
xv 3.13. Simulated far-field radiation pattern of 900 MHz and 1.8 GHz helical antennas due to the presence of different realistic phantom head models 68 3.14. Comparison of saved simulation time, saved computational resource and SAR variation for helical antenna with the presence of different fractional head models 74 4.1. Configuration of a 900 MHz patch antenna 77 4.2. Configuration of a 1.8 GHz patch antenna 78 4.3. Simplified diagram of typical simulation model 80 4.4. Simulated return loss at 900 MHz and 1.8 GHz mobile phone patch antennas due to the presence of different full phantom head models 83 4.5. Simulated far-field radiation pattern of 900 MHz patch antenna due to the presence of different full phantom head models 84 4.6. Simulated far-field radiation pattern of 1.8 GHz patch antenna due to the presence of different full phantom head models 85 4.7. SAR distribution for the three different phantom head models 87 4.8. Simulated return loss at 900 MHz and 1.8 GHz patch antennas due to the presence of different cubical phantom head models 89 4.9. Simulated far-field radiation pattern of 900 MHz and 1.8 GHz patch antennas due to the presence of different cubical phantom head models 90 4.10. Simulated return loss at 900 MHz and 1.8 GHz patch antennas due to the presence of different spherical phantom head models 93 4.11. Simulated far-field radiation pattern of 900 MHz and 1.8 GHz patch antennas due to the presence of different spherical phantom head models 94 4.12. Simulated return loss at 900 MHz and 1.8 GHz patch antennas due to the presence of different realistic phantom head models 97
xvi 4.13. Simulated far-field radiation pattern of 900 MHz and 1.8 GHz patch antennas due to the presence of different realistic phantom head models 98 4.14. Comparison of saved simulation time, saved computational resource and SAR variation for patch antenna with the presence of different fractional head models 103 5.1. Fabricated monopole, helical, and patch antennas for SAR evaluation 106 5.2. A simplified diagram and photo of the pre-compliance SAR measurement system 109 5.3. A typical setup and photo of modified SAR measurement system for 50% fractional phantom head model 110 5.4. Typical measurement setup of return loss measurement for antenna with the presence of MapSAR system 111 5.5. Simplified diagram of typical simulation model 113 5.6. Modeling of phantom head model used in simulation 113 5.7. Fractional phantom head models used in simulation 114 5.8. Simulated and measured return loss of 900 MHz monopole antenna with different fractional phantom head models 118 5.9. Simulated and measured return loss of 1.8 GHz monopole antenna with different fractional phantom head models 119 5.10. Simulated and measured return loss of 900 MHz helical antenna with different fractional phantom head models 120 5.11. Simulated and measured return loss of 1.8 GHz helical antenna with different fractional phantom head models 121 5.12. Simulated and measured return loss of 900 MHz patch antenna with different fractional phantom head models 122
xvii 5.13. Simulated and measured return loss of 1.8 GHz patch antenna with different fractional phantom head models 123 5.14. Variation of resonant frequency due to different fractional phantom head models in simulation and measurement 124 5.15. Simulated SAR variation over 1g and 10g tissue for different mobile phone antennas with different fractional head models 127 5.16. Measured SAR variation over 1g and 10g tissue for different mobile phone antennas with different fractional head models 128 5.17. Comparison of saved simulation time, saved computational resource, and SAR variation by using fractional head models 131 6.1. Dimensions (in mm) of a typical PIFA dual-band internal antenna 135 6.2. Length extension of internal antenna ground plane 136 6.3. Width extension of internal antenna ground plane 136 6.4. Configuration of the original PIFA antenna, and 7 cases of addition of vertical sidewall 133 6.5. Configuration of phantom head models 138 6.6. Simplified diagram of a typical simulation model 139 6.7. Return loss of the PIFA antenna with different lengths of ground plane due to the presence of phantom head models 142 6.8. 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 143 6.9. SAR value of PIFA antenna ground plane with length extension 146 6.10. Return loss of the PIFA antenna with different widths of ground plane due to the presence of phantom head models 148
xviii 6.11. 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 149 6.12. SAR value of PIFA antenna ground plane with width extension 152 6.13. 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 154 6.14. 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 155 6.15. SAR value of PIFA antenna with different cases of addition of vertical sidewall on antenna ground plane 158