STUDY OF DUAL BAND WEARABLE ANTENNAS USING COMMONLY WORN FABRIC MATERIALS By DIPEN KUMAR DAS Bachelor of Science in Electronics and Telecommunication Engineering North South University Bangladesh 2012 Submitted to the Faculty of the Graduate College of the Oklahoma State University in partial fulfillment of the requirements for the Degree of MASTER OF SCIENCE May, 2017 STUDY OF DUAL BAND WEARABLE ANTENNAS USING COMMONLY WORN FABRIC MATERIALS Thesis Approved: Charles F. Bunting, Ph.D. Thesis Adviser George Scheets, Ph.D. Committee Member Sabit Ekin, Ph.D. Committee Member ii ACKNOWLEDGEMENTS To my Dad and Mom for their love and support throughout my life. My friends who have stood by my side in down time of my life without judging me. I would like to show my special gratitude to Dr. Mary Ruppert-Stroescu for her unconditional support throughout my work. My advisor Dr. Charles F. Bunting, who has supported me all through my journey at Oklahoma State University. His guidance have been pivotal in the success of my thesis. I am grateful for everything you did. Last but not the least, the faculty and students of EM group – my honest gratitude for nurturing me in this excellent research environment. iii Acknowledgements reflect the views of the author and are not endorsed by committee members or Oklahoma State University. Name: DIPEN KUMAR DAS Date of Degree: MAY, 2017 Title of Study: STUDY OF DUAL BAND WEARABLE ANTENNAS USING COMMONLY WORN FABRIC MATERIALS Major Field: ELECTRICAL ENGINEERING Abstract: In recent years, body-centric communication has become one of the most attractive fields of study. The versatile applications of body-centric communication not only being used for health monitoring, but also for real-time communication purposes in special occupations. They are important for supporting a population with increasing life expectancy and increase the probability of survival for the people suffering from chronic illness. For both wearable and implantable form of body-centric communication, characterizing the system electromagnetically is very important. Given the constraints in power, size, weight and conformity, one of the most challenging parts become the designing antenna for such communication systems. Wearable antennas are the most popular option regarding these issues. Wearable antennas are easier and simpler to mount on clothing when they are made of textile materials. In the process of designing a textile antenna, the availability of the fabrics is pivotal to mount on regularly worn clothes. In this report, several designs of a co-planar waveguide microstrip patch antenna are presented. Instead of felt fabric, the antenna was modified using 100% polyester and cotton fabric for the substrate material. A parasitic patch slot was created on the co-planar ground plane to achieve the dual band resonance frequencies at 2.4 GHz and 5.15 GHz. The geometrical modifications of the antennas were described and their performances were analyzed. The antenna achieved resonating frequency with a thinner substrate as the dielectric constant went higher for the fabrics. The design with different fabric materials was first simulated in CST Microwave Studio, then fabricated and measured in regular environment. They were also mounted on a 3-D printed human body model to analyze the bending effect. The design of the antennas shows satisfactory performance with a good -10dB bandwidth for both the lower and higher desired resonating frequency band. iv TABLE OF CONTENTS Chapter Page I. INTRODUCTION ......................................................................................................1 1.1 Research Objectives ...........................................................................................4 1.2 Thesis Organization ...........................................................................................5 II. BODY-CENTRIC WIRELESS COMMUNICATION .............................................6 2.1 Body-centric communication system .................................................................7 2.1.1 Off-body Communication ........................................................................9 2.1.2 On-body Communication .......................................................................12 2.1.3 In-body Communication .........................................................................13 2.2 Overview of Systems .......................................................................................15 2.2.1 Narrowband Systems ..............................................................................17 2.2.2 Wideband Systems ..................................................................................18 2.3 mmWave Wireless Body-centric Communication ..........................................20 2.4 Applications of Body-centric Communication Systems……………………..22 III. HUMAN BODY MODELING AND NUMERICAL METHODS FOR BODY- CENTRIC COMMUNICATION...........................................................................25 3.1 Electromagnetic Characteristics of Human Body Tissue ................................26 3.1.1 Overview of EM Wave Propagation .......................................................27 3.1.2 Dielectric Properties of Human Body Tissue .........................................29 3.2 Physical Body Phantom ...................................................................................30 3.3 Numerical Phantoms ........................................................................................31 3.3.1 Theoretical Phantoms..............................................................................31 3.3.2 Voxel Phantoms ......................................................................................32 3.4 CST Body Phantoms .........................................................................................34 3.5 Numerical Techniques for Body-centric Communication ................................37 3.5.1 Method of Moments (MoM) ....................................................................38 3.5.2 Finite Element Method (FEM).................................................................39 3.5.3 Finite-Difference Time-Domain Method (FDTD)...................................40 3.6 Numerical Methods in CST Microwave Studio...............................................42 v Chapter Page IV. BODY-CENTRIC WIRELESS COMMUNICATION: WEARABLE ANTENNAS ................................................................................................................................44 4.1 Wearable Antennas ..........................................................................................46 4.2 Designing Textile Antennas .............................................................................49 4.3 Textile Materials and Their EM Characterization ...........................................51 4.3.1 Dielectric Fabrics ....................................................................................51 4.3.2 Conductive Fabrics .................................................................................53 4.4 Wearable Antenna Performance: In Close Proximity of Human Body ...........54 4.4.1 Bending Effect ........................................................................................55 4.4.2 Crumpling Effect ....................................................................................56 4.4.3 Specific Absorption Rate (SAR) .............................................................56 4.5 Wearable Antenna Performance: Effects of Nature .........................................57 V. DUAL BAND TEXTILE ANTENNA DESIGNING ............................................59 5.1 Background Study ............................................................................................60 5.2 Fabric Selection and Their Characterization ....................................................61 5.2.1 Dielectric Fabric ......................................................................................61 5.2.2 Conductive Fabric ...................................................................................62 5.3 Antenna Design ................................................................................................63 5.3.1 Design I ...................................................................................................63 5.3.2 Design II..................................................................................................66 VI. DUAL BAND TEXTILE ANTENNA: FABRICATION AND MEASUREMENTS ....................................................................................................................70 6.1 Fabrication of Dual Band Antenna ..................................................................69 6.2 Feeding the Antenna ........................................................................................72 6.3 Antenna Measurements ....................................................................................72 6.3.1 Prototype I ...............................................................................................72 6.3.2 Prototype II .............................................................................................74 6.3.3 Prototype III ............................................................................................76 6.3.4 Prototype IV ............................................................................................78 6.3.5 Prototype V .............................................................................................79 6.4 Antennas on Body Phantom.............................................................................81