Efficient Antennas for Wearable Wireless Sensor Nodes Author Vatankhah Varnoosfaderani, Mohammad Published 2016 Thesis Type Thesis (PhD Doctorate) School Griffith school of Engineering DOI https://doi.org/10.25904/1912/704 Copyright Statement The author owns the copyright in this thesis, unless stated otherwise. Downloaded from http://hdl.handle.net/10072/366335 Griffith Research Online https://research-repository.griffith.edu.au Efficient Antennas for Wearable Wireless Sensor Nodes Mr. Mohammad Vatankhah Varnoosfaderani BS, MS Griffith School of Engineering Griffith University Submitted in fulfilment of the requirements of the degree of Doctor of Philosophy March 2016 I Table of Contents 1 Chapter 1: Introduction....................................................................................................... 2 2 Chapter 2: Literature Review .............................................................................................. 7 2.1 Why and when the study on wearable antennas started? ................................................ 7 2.2 How does the body affect the performance of an antenna? ............................................. 7 2.3 What are the effects of the body on the performance of an antenna? ............................... 8 2.3.1 Resonant frequency shift...................................................................................... 8 2.3.2 Changing the radiation pattern of the antenna .......................................................10 2.3.3 Power absorption................................................................................................11 2.4 The criteria for a better performance ...........................................................................12 2.5 Solutions to improve the performance of an antenna next to human body ......................16 2.5.1 Using an antenna with a conducting ground plane.................................................16 2.5.2 Avoiding the shift in the resonant frequency of wearable antennas.........................17 2.5.3 Balanced versus unbalanced antennas ..................................................................18 2.5.4 EBG structures between the ground plane and antenna..........................................19 2.5.5 Photonic band-gap structures (PBG) ....................................................................20 2.5.6 Stacked antennas ................................................................................................21 2.5.7 Cavity backed substrate integrated waveguide (SIW) fabric antennas.....................22 2.5.8 Dielectric resonator antennas (DRA) ...................................................................23 2.5.9 Higher mode microstrip patch antennas (HMMPA) ..............................................24 2.5.10 Elevated patch antennas ......................................................................................26 2.6 Design steps for wearable antennas .............................................................................29 2.7 Conclusion ................................................................................................................31 3 Chapter 3: Using Electromagnetically Coupled External Parasitic Elements to Improve the Performance of Wearable Wireless Sensors................................................................................33 3.1 Parasitic element as a solution ....................................................................................33 3.2 What is a parasitic element? .......................................................................................33 3.3 Three element Yagi-Uda antenna can be a solution ......................................................34 3.4 Monopole antenna as the driver element of a parasitic element .....................................36 3.5 Simulation of the model using CST Microwave Studio ................................................39 3.6 Measurement methods and results...............................................................................48 3.6.1 Pattern measurement...........................................................................................49 II 3.6.2 Two ray ground reflection model.........................................................................51 4 Chapter 4: Slot antennas designed for wearable wireless sensors ..........................................58 4.1 Shaping the radiation pattern using a parasitic slot element...........................................58 4.2 The characteristics of a slotted cylinder parasitic element .............................................59 4.3 Implementing the parasitic element on the rectangular case a wearable wireless sensor ..67 5 Chapter 5: Elevated patch antennas with a capacitive feed ...................................................76 5.1 PIFA antennas are compacted and suitable for wearable applications ............................76 5.2 Increasing the bandwidth of PIFA using proximity feed structure .................................77 5.3 A compact capacitively fed PIFA antenna for wearable wireless sensors .......................80 5.3.1 Parametric study.................................................................................................81 5.3.2 Simulation and measurement results ....................................................................83 5.4 Conclusion ................................................................................................................85 6 Conclusion .......................................................................................................................88 6.1 Critical review and future work ..................................................................................89 References ...............................................................................................................................90 III Figure 1. (a) Balance feeding of a meandered loop antenna. (b) Unbalanced feeding of a meandered loop antenna [63]................................................................................................ 18 Figure 2. Measured current distribution on the ground plane of a PIFA antenna [64]. The radiating element is located in the top right corner of the ground plane in both cases. ....... 19 Figure 3. CPW fed antenna mounted on a uniform EBG structure [70]. The antenna is a meandered loop antenna fed with a coupled transmission line. ........................................... 20 Figure 4. A microstrip photonic band gap patch antenna on fabric was used to investigate the performance of PBG structures in the vicinity of a human body [73]............................ 21 Figure 5. A stacked patch antenna was designed to minimize the effects of the lossy materials on the performance of the antenna in harsh environments [39]............................ 22 Figure 6. Cavity backed slot antenna in conductor fabric(left) [81], SIW antenna with fabric substrate and Flectron conductive fabric as ground plane (right) [80]. ............................... 23 Figure 7. (a) HMMPA_5, (b) HMMPA_10, (c) monopole, (d) MPA-S, (e) MPA-F [87]. .. 25 Figure 8. Cross section and plan of dual-band metallic button antenna [89]. ...................... 27 Figure 9. Photograph of the dual band disk antenna prototype [91]. ................................... 28 Figure 10. Different solutions for designing the best wearable antenna. ............................. 30 Figure 11. Excitation of electric fields on a parasitic element to satisfy boundary conditions [93]........................................................................................................................................ 34 Figure 12. Three-element Yagi-Uda antenna consisting of a driver of length 0.47 λ, a reflector of length 0.482λ, and a director of length 0.422λ, spaced 0.2λ apart. The wire radius for all is 0.00425λ [93], W.L. Stutzman and G.A. Thiele, Antenna Theory and design. Wiley, 2012. ............................................................................................................. 35 Figure 13. z-core device with and without housing (left).Standard design monopole antenna (right). ................................................................................................................................... 36 Figure 14. Configuration of switched parasitic monopole antenna. ..................................... 37 Figure 15. Square conductor as a parasitic element next to a monopole antenna. ............... 37 Figure 16. Fabric armband and the method of installation of sensor (left) .The parasitic element which is added next to the antenna of the sensor (right)......................................... 38 Figure 17. Dimensions of the antenna and the optimized position of the parasitic element (mm).The red dashed lines show the step impedance parasitic element and the blue dashed lines show the straight line parasitic element. ...................................................................... 39 Figure 18. Cross section of the Z-core sensor showing the layers between the parasitic element and the meander line monopole antenna. ................................................................ 39 Figure 19. Simulated antenna next to the arm model in CST Microwave Studio showing the z-core box attached to an arm section by a fabric band........................................................ 40 Figure 20. Simulated total radiation efficiency of the antenna next to the arm model. Note the very significant decrease in efficiency when the sensor