Document Type

Dissertation

Date of Degree

Summer 2015

Degree Name

PhD (Doctor of Philosophy)

Degree In

Electrical and Computer Engineering

First Advisor

Anton Kruger

Abstract

We developed curved spiral antennas for use in underwater (freshwater) communications. Specifically, these antennas will be integrated in so-called mussel backpacks. Backpacks are compact electronics that incorporate sensors and a small radio that operate around 300 MHz. Researchers attach these backpacks in their freshwater mussel related research. The antennas must be small, lightweight, and form-fit the mussel. Additionally, since the mussel orientation is unknown, the antennas must have broad radiation patterns. Further, the electromagnetic environment changes significantly as the mussels burrow into the river bottom. Broadband antennas, such a spiral antennas, will perform better in this instance. While spiral antennas are well established, there has been little work on their performance in freshwater. Additionally, there has been some work on curved spiral antennas, but this work focused on curving in one dimension, namely curving around a cylinder. In this thesis we develop spiral antennas that curve in two dimensions in order to conform the contour of a mussel's shell.

Our research has three components, namely (a) an investigation of the relevant theoretical underpinning of spiral antennas, (b) extensive computer simulations using state-of-the art computational electromagnetics (CEM) simulation software, and (c) experimental validation. The experimental validation was performed in a large tank in a laboratory setting. We also validated some designs in a pool (∼300,000 liters of water and ∼410 squared-meter dive pool) with the aid of a certified diver.

To use CEM software and perform successful antenna-related experiments require careful attention to many details. The mathematical description of radiation from an antenna, antenna input impedance and so on, is inherently complex. Engineers often make simplifying assumptions such as assuming no reflections, or an isotropic propagation environment, or operation in the antenna far field, and so on. This makes experiments on antennas challenging since it often quite difficult to replicate the simplifying assumptions in an experimental setting.

Still, with careful consideration of the important factors and careful experimental design it is possible to perform successful experiments. For example, antenna measurements are often performed in anechoic chambers. For our research we used a large swimming pool to mimic an underwater anechoic chamber. Our CEM simulations and experimental results are in most cases congruent. We are confident that we can design formfitting, compact (spiral) antennas that one could deploy on mussels. This will greatly enhance the mussel backpacks that are used by researchers at the University of Iowa.

Public Abstract

Researchers at the University of Iowa are developing so-called mussel backpacks. These backpacks contain sensors, a microcontroller, and a small radio to transmit data from the sensors to an on-shore receiver, or to other backpacks in the vicinity. Backpacks are attached to freshwater mussels that can then be deployed in their natural habitat or in a laboratory-based habitat. Typical sensors measure mussel heartrate and mussel gape (the rhythmic opening and closing of their valves). The backpacks will aid several ongoing freshwater mussel research efforts. The underwater radio propagation environment is complex and reliable data transmission requires a specialized antenna. It is the antenna design that is the focus of this thesis.

We identified spiral antennas as suitable for this application. They are broadband and compact. Conventional spiral antennas are flat. In this thesis we explore curved spiral antennas. Curving is required so that the antenna snuggly fit the mussel shell, so as to not impede its motion. We have developed procedure to design curved spiral antennas. The design starts from the well-known flat spiral antenna, and then we project it onto the mussel shell. This projection disturbs the intrinsic properties of the flat spiral antenna. In the second step, we apply a correction.

Our investigation has three components, namely a study of the existing spiral antennas, computer simulations, and finally an experimental verification. The experimental verification was performing in a large tank in a laboratory as well as a large diving pool. Our results indicate that our spiral antennas will work well in the mussel backpack application. We have developed the engineering CAD model for the antenna housing using 3D-printed techniques.

Keywords

publicabstract, Biosensors, Broadband Antennas, Environmental Monitoring, Remote Monitoring, Spiral Antennas, Underwater Communication

Pages

xvi, 116 pages

Bibliography

Includes bibliographical references (pages 112-116).

Copyright

Copyright 2015 Ruben A. Llamas

Share

COinS