Date of Award

Fall 2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical and Computer Engineering

First Advisor

Richie James

Second Advisor

Juan Luglio

Abstract

A wire mesh cage composed of thin conductive wires will influence the behavior of electromagnetic fields within it. Theory suggests that the cage will behave like a low Q cavity. Many researchers have investigated electromagnetic field behavior in solid walled cavities and waveguides, but little of this work has probed into the effects of a wire mesh. Additionally, few studies have investigated RF communication in these types of environments. The primary goal of this work is to research wireless communication inside a low Q wire mesh cavity in the 200-700 MHz range. Through simulated and experimental results, ideal antenna locations and behavior are described for simple antennas.

The Numerical Electromagnetics Code (NEC) is used to examine the electromagnetic field behavior inside a wire mesh rat cage. The code provides a foundation of theoretical results from which to base experimentation on. It is shown through simulations that dipole, loop, and monopole antennas are heavily affected by the cage. When placed inside, the antenna input impedance and current distribution are dramatically altered near cage resonance. Position of the antenna affects coupling to the mode and the changes in input impedance and current distribution.

Experimentally, monopole and loop antennas are evaluated inside the wire mesh animal cage. The monopole couples to the cage very well due to the impedance changing effects caused by the low Q cavity. The loop is shown to be resistant to same effects, and does not couple well. Due to the configuration of the first resonant mode, it is shown that coupling to the cage is best accomplished with an electric field dominant antenna.

RF communication is best accomplished with a receive monopole antenna located at the top center of the cage. The transmit antenna can move to any position without a significant loss of received power. This is a direct result of coupling to the first resonant mode. To construct a wireless communication system, the designer should consider coupling to the resonant modes and using a low Q cavity.