Automated Design Optimisation and Simulation of Stitched Antennas for Textile Devices

AUTOMATED DESIGN OPTIMISATION AND SIMULATION OF STITCHED ANTENNAS FOR TEXTILE DEVICES By Abraham Torleele Wiri A Doctoral Thesis Submitted in Partial Fulfilment of the Requirements for the Award of Doctor of Philosophy of Loughborough University July 2019 © by Abraham Torleele Wiri Abstract This thesis describes a novel approach for designing 7-segment and 5-angle pocket and collar planar antennas (for operation at 900 MHz). The motivation for this work originates from the problem of security of children in rural Nigeria where there is risk of abduction. There is a strong potential benefit to be gained from hidden wireless tracking devices (and hence antennas) that can protect their security. An evolutionary method based on a genetic algorithm was used in conjunction with electromagnetic simulation. This method determines the segment length and angle between segments through several generations. The simulation of the antenna was implemented using heuristic crossover with non-uniform mutation. Antennas obtained from the algorithm were fabricated and measured to validate the proposed method. This first part of this research has been limited to linear wire antennas because of the wide range and flexibility of this class of antennas. Linear wire antennas are used for the design of high or low gain, broad or narrow band antennas. Wire antennas are easy and inexpensive to build. All the optimised linear wire antenna samples exhibit similar performances, most of the power is radiated within the 900 frequency band. The reflection coefficient (S11) is generally better than -10dB. The method of moment (MoM-NEC2) and FIT (CST Studio Suite 2015) solvers were used for this design. MATLAB is used to as an interface to control computational electromagnetic solvers for antenna designs and analysis. The genetic algorithm procedures were written in MATLAB. The second part of the work focuses on meshed ground planes for applications at 900 MHz global system for mobile communications (GSM), 2.45 Hz industrial, scientific, and medical (ISM) band and 5 Hz wearable wireless local area networks (WLAN) frequencies. Square ground planes were developed and designed using linear equations in MATLAB. The ground plane was stitched using embroidery machines. To examine the effect of meshing on the antenna performance and to normalise the meshed antenna to a reference, solid patch antenna was designed, fabricated on an FR4 substrate. A finite grid of resistors was created for numerical simulation in MATLAB. The resistance from the centre to any node of a finite grid of resistors are evaluated using nodal analysis. The probability that a node connects to each node in the grid was computed. The circuit model has been validated against the experimental model by measurement of the meshed ground plane. A set of measurement were collected from a meshed and compared with the numerical values, they show good agreement. Keywords- Linear wire antennas; Genetic algorithm; Reproduction operation; Stitched; Embroidery; Meshed ground plane i Acknowledgements I would like to express my heartfelt appreciation and gratitude to my supervisors: Dr. Robert D. Seager and Dr. James A. Flint, for their irreplaceable advice, guidance and shared knowledge throughout my PhD. I would also like to thank Dr. Will Whittow, Dr. Alford Chauraya and Dr. Shiyu Zhang for their shared experience and knowledge towards completing my thesis. To Prof M.J Ayotamuno, Dean Faculty of Engineering, Rivers State University, Port Harcourt, Nigeria for giving me this opportunity to do a PhD, I sincerely thank you. My deepest gratitude belongs to Precious my wife and my children; Zina, Barilunanee and Lenu for supporting me, your patient and understanding throughout the research years. Lastly to my mother; Mrs Baakoasae Stella Wiri for being my first teacher, who died in the middle of this study 2017. Thank you for your inspiration and care. ii Dedication To my wife Precious, for her unconditional support, love, encouragement and prayers of day and night make me able to get victory and honour. And, to my children, Zina, Barilunanee and Lenu who inspired me to be strong in spite of many challenges in life. Thank you, Jesus, for all. iii List of Abbreviations BW Bandwidth CST Computer Simulation Technology dB Decibels dBi Decibels compared to an isotropic radiator EBG Electromagnetic Band Gap EM Electromagnetic FBR Front to Back Ratio FR4 Flame Resistant 4, substrate LC Inductor Capacitor IBM International Business Machines MIDI Musical Instrument Digital Interface PCB Printed Circuit Board PET Polyester RF Radio Frequency RL Resistor Inductor RLC Resistor Inductor capacitor SMA Sub Miniature version A, connector TM Transverse Magnetic VNA Vector Network Analyser WLAN Wireless Local Area Network List of Symbols Symbol Meaning Unit Characteristic impedance 0 Real part of Characteristic impedance Ω 0 Imaginary part of Characteristic impedance Ω 0 Length Ω ∆ Resistivity . Conductivity Ω/ iv Skin depth Permeability of free space −/ 0 Relative permeability Permittivity of free space −/ 0 Relative permittivity tan Loss tangent − Wavelength Attenuation constant or −1 2 −1 Phase constant Wave number − Reflection Coefficient − Γ − List of Figures Figure 1.1 Multifunctional shirt integrated with wearable antennas………………………...1.3 Figure 1.2 Candidate space for hiding an antenna on garments……………………………..1.5 Figure 2.1 Antenna system....................................................………………………………. 2.2 Figure 2.2 Standard spherical coordinate system used in antenna measurements..................2.5 Figure 2.3. Positional axis for chamber measurements...........................................................2.5 Figure 2.4 Examples of early wearable applications.............................................................. 2.6 Figure 2.5 Functional chordingkeyboard embroidered into a jacket.......................................2.7 Figure 2.6 Commercial floating lifejacket............................................................................2.12 Figure 2.7 Fabricated textile patch antenna placed conformal on the human arm................2.13 Figure 2.8 Six e-textile complementary-8 antennas..............................................…………2.13 Figure 2.9 Brother Pr1000e embroidery machine.................................................................2.16 Figure 2.10 (a) Sketch of the lock stitches and (b) Bobbin with top thread and looper thread.............................................................................................…………………………2.17 Figure 2.11 Schematic of a woven textile with warp yarns in white and weft yarns in dark grey........................................................................................................................................2.18 Figure 2.12 (a) Weft knitted (on left) and warp knitted (on right). The blue yarns represent a particular row inside the fabric. (b) A fabric with knitted tubes...........................................2.19 v Figure 2.13 (a) Metal coated wire combined in iron tube; (b) Several diameter reductions of tube; (c) Bundling of tubes; (d) Leaching, realizing fibres...................................................2.21 Figure 2.14 Various conductive threads..........................………………………………….2.22 Figure 2.15 Standard design of copper yarn twisted with polyester fibres...........................2.23 Figure 2.16 Photographs of prototype evolved antennas......................................................2.26 Figure 3.1 Quarter-wavelength monopole on an infinite perfect electric conductor ………….......3.4 Figure 3.2 Vertical plane patterns of a monopole of 4 on infinite ground plane................3.5 Figure 3.3 Flowchart of Evolutionary Algorithm.......................................................................⁄ .3.7 Figure 3.4 Software flowchart showing the link between NEC and MATLAB in this thesis ……3.13 Figure 3. 5 Detailed process flowchart for the GA...........................................................................3.14 Figure 3.6 CAD design of linear wire antenna..................................................................................3.15 Figure 3.7 Antenna geometries...........................................................................................................3.18 Figure 3.8 Geometrical model (physical) of the wire antenna designs.................................3.25 Figure 3.9 Simulated S11 results of linear wire antenna sample in CST and NEC2.............3.26 Figure 3.10(a) GA-optimised solutions after 100 generations..............................................3.27 Figure 3.10(b) GA-optimised solutions after 100 generations.............................................3.28 Figure 3.11 Wire antennas on Shirt front pocket design.......................................................3.29 Figure 3.12 Geometry of pocket antennas.............................................................................3.31 Figure 3.13 Simulated S11 of Pocket A.................................................................................3.32 Figure 3.14 Simulated S11 of Pocket B.................................................................................3.32 Figure 3.15 Simulated S11 of Pocket C.................................................................................3.33 Figure 3.16 Simulated S11 of Pocket D.................................................................................3.33 Figure 3.17 Diagram of the antenna in a shirt collar showing..............................................3.34

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