INVESTIGATION OF ANTENNAS AND ENERGY HARVESTING METHODS FOR USE WITH A UHF MICROTRANSCEIVER IN A BIOSENSOR NETWORK by AMELIA LYNN HODGES B.S., Kansas State University, 2010 A THESIS submitted in partial fulfillment of the requirements for the degree MASTER OF SCIENCE Department of Electrical and Computer Engineering College of Engineering KANSAS STATE UNIVERSITY Manhattan, Kansas 2013 Approved by: Major Professor William B. Kuhn Copyright AMELIA LYNN HODGES 2013 Abstract This work was a part of NASA EPSCoR Project NNX11AM05A: Biosensor Networks and Telecommunication Subsystems for Long Duration Missions, EVA Suits, and Robotic Precursor Scout Missions. The project’s main goal is the development of a wireless sensor network inside an astronaut’s spacesuit. Antennas are essential components in a wireless network. Since this antenna will be used inside the spacesuit it is important to consider both the physical size limitations and the desired antenna polarization. After exploring the WWVB radio station antenna which provides the preferred vertical polarization and has a suitable aspect ratio, the top hat antenna seemed promising for intrasuit communication. The design of a top hat antenna is outlined. Then, the antennas were tested using 433 MHz radios in a full scale model spacesuit. This spacesuit was designed specifically to model the behavior of aluminized mylar in the real suit. Test results support the feasibility of an intrasuit wireless network. If a gateway radio is placed on the chest or back, a sensor could be placed anywhere on the body and provide an adequate signal. These initial tests did not include a matching network, but the additional link- margin afforded by a matching network, even an imperfect match, is considered. Energy harvesting is explored as an alternative to batteries powering the intrasuit radio. In the oxygen rich environment of a spacesuit, even the smallest spark can be catastrophic. A variety of energy harvesting options are explored with a focus on thermal energy harvesting. The temperature difference between the human skin and the astronaut’s Liquid Cooling and Ventilation Garment can be used to produce a small voltage. To increase the voltage a step-up converter is implemented. Final integration of the two systems with a biosensor is left for on- going work in the three year NASA project. Table of Contents List of Figures ............................................................................................................................... vii List of Tables .................................................................................................................................. x Acknowledgements ........................................................................................................................ xi Dedication ..................................................................................................................................... xii Chapter 1 - Introduction .................................................................................................................. 1 1.1 NASA EPSCoR Project NNX11AM05A ............................................................................. 1 1.2 Thesis Goals and Motivation ................................................................................................ 1 Chapter 2 - Designing an Antenna and Matching Network ............................................................ 3 2.1 Background Study of Antennas ............................................................................................ 3 2.1.1 Antennas Options ........................................................................................................... 3 2.1.2 Requirements of In-Suit Antennas ................................................................................. 4 2.1.2 WWVB Antenna ............................................................................................................ 5 2.2 Designing the Top Hat Antenna ........................................................................................... 6 2.2.1 Components of Top Hat Antennas ................................................................................. 6 2.2.2 Procedure for Simulation ............................................................................................... 7 2.2.3 Understanding Each Components’ Role ........................................................................ 7 2.2.3.1 Adjusting Post Height ............................................................................................. 8 2.2.3.2 Adjusting Post Diameter ....................................................................................... 10 2.2.3.3 Adjusting Top Hat Diameter ................................................................................. 13 2.2.4 Final Design ................................................................................................................. 15 2.3 Determining Matching Network Parameters ...................................................................... 17 2.3.1 Initial Measurements .................................................................................................... 18 2.3.2 Problems in Antenna Measurements ........................................................................... 21 2.3.3 Correcting Initial Measurements .................................................................................. 22 2.3.4 Conclusions on Matching Networks ............................................................................ 23 Chapter 3 - Testing the Antenna in Space Suit Models ................................................................ 26 3.1 Physical Models of the Spacesuit ....................................................................................... 26 3.1.1 The Need for a Physical Model.................................................................................... 26 3.1.2 The Models .................................................................................................................. 26 iv 3.2 Testing in Full Scale Model Suit ........................................................................................ 27 3.2.1 Initial Pre-suit Test ....................................................................................................... 27 3.2.2 Coupling Issues ............................................................................................................ 28 3.2.2.1 A First Look at the Coupling Issue ....................................................................... 29 3.2.2.2 A Second Look at the Coupling Issue................................................................... 30 3.2.3 Solution to Coupling and Intra-Suit Measurement Problems ...................................... 32 3.2.4 Implementing an Audio Oscillator ............................................................................... 34 3.2.4.1 Received Power to Audio Frequency Mapping .................................................... 35 3.2.5 In-Suit Test Set Up ....................................................................................................... 36 3.2.6 In-Suit Test Findings .................................................................................................... 41 Chapter 4 - Exploring Energy Harvesting .................................................................................... 44 4.1 Background Study of Energy Harvesting ........................................................................... 44 4.1.1 What is Energy Harvesting .......................................................................................... 44 4.1.2 Previous Energy Harvesting Work at K-State ............................................................. 45 4.2 Selecting a Focus Area ....................................................................................................... 45 4.2.1 Infeasible Options for Use in a Space Suit .................................................................. 45 4.2.2 Down Selecting Feasible Options to One Area ........................................................... 46 4.3 Thermal Energy Harvesting ................................................................................................ 47 4.3.1 Basic Concept .............................................................................................................. 47 4.3.2 A Concept for In-Suit Application ............................................................................... 47 4.3.3 Surveying Available Products ...................................................................................... 49 4.3.4 Initial Functional Evaluation ........................................................................................ 49 4.3.5 Thermal Model of TEG in Spacesuit ........................................................................... 51 4.4 Testing the Thermoelectric Generators ............................................................................... 52 4.4.1 Test Setup and Procedures ........................................................................................... 52 4.4.2 Test Results .................................................................................................................. 54 4.5 Energy Harvesting Low Voltage and Power Output Problem. ........................................... 56 4.5.1 Understanding the Problem .......................................................................................... 56 4.5.2 Finding a Solution .......................................................................................................