Strain-mediated magnetoelastic composite materials are being considered for communication in lossy environments. Their consideration is attributable to predictions stating order of magnitude improvements over current antenna technology. The magnetic antenna design considered herein consists of three layers: 1) a piezoelectric layer, 2) a linear elastic layer, and 3) a magnetoelastic layer. The antenna operates by mediating strain through the device in a resonant bending mode. The magnetoelastic layer is stressed which results in a changing magnetization ultimately leading to a changing magnetostatic field in free space which acts as a signal for information transfer. In order to prove the efficacy of this approach finite element models have been developed to aid in the design and optimization process. Where these models fall short is in their overall run-time to fully resolve the coupled dynamics. It is for this reason that the work presented in this thesis focuses on the development of a figure of merit capable of predicting optimal bias conditions and geometries needing only the data from a static bias study from FEA. The material level magnetomechanical coupling factor is chosen as the foundation for the figure of merit. The figure of merit is then augmented to include structure level information regarding the demagnetizing field and the non-uniform stress distribution. The main results presented are the effects of including demagnetization and stress distributions, and most importantly the ability of the metric to predict the change in magnetization of the device. It is shown that for aspect ratios greater than roughly 2.5 the metric trends the same as the change in magnetization predicted by finite element simulations. The region of disagreement between the metric and the fully resolved finite element simulation is explained by tying back to underlying assumptions made during the formulation of the magnetometric demagnetization factor used in the analysis. The case is made for the figure of merit to be included in the analysis of strain-mediated antennas for its ability to find optimum designs while reducing the overall simulation run-time by an order of magnitude. / Master of Science / Many communication devices are readily available however there are a few key gaps in communication technology that are yet to be filled. Notably, communication in lossy environments using small scale, low frequency, devices has proven difficult due to the fundamental limits of antennas (a cell phone cannot communicate into a mine shaft for search and rescue operations, nor can they communicate underwater to submarines or divers for instance). A promising new approach of communication using smart magnetic materials is under consideration in this thesis. Specifically, the goal herein is to develop an analysis tool capable of predicting device performance without having to run computationally expensive/time consuming finite element simulations. In this thesis it is shown that the analysis tool is capable of predicting device performance while reducing the necessary simulation run-time by an order of magnitude. Using this tool, researches will be able to design better prototypes; moving one step closer to portable communication in lossy environments.

abstract: There is an ever-growing need for broadband conformal antennas to not only reduce the number of antennas utilized to cover a broad range of frequencies (VHF-UHF) but also to reduce visual and RF signatures associated with communication systems. In many applications antennas needs to be very close to low-impedance mediums or embedded inside low-impedance mediums. However, for conventional metal and dielectric antennas to operate efficiently in such environments either a very narrow bandwidth must be tolerated, or enough loss added to expand the bandwidth, or they must be placed one quarter of a wavelength above the conducting surface. The latter is not always possible since in the HF through low UHF bands, critical to Military and Security functions, this quarter-wavelength requirement would result in impractically large antennas. Despite an error based on a false assumption in the 1950’s, which had severely underestimated the efficiency of magneto-dielectric antennas, recently demonstrated magnetic-antennas have been shown to exhibit extraordinary efficiency in conformal applications. Whereas conventional metal-and-dielectric antennas carrying radiating electric currents suffer a significant disadvantage when placed conformal to the conducting surface of a platform, because they induce opposing image currents in the surface, magnetic-antennas carrying magnetic radiating currents have no such limitation. Their magnetic currents produce co-linear image currents in electrically conducting surfaces. However, the permeable antennas built to date have not yet attained the wide bandwidth expected because the magnetic-flux-channels carrying the wave have not been designed to guide the wave near the speed of light at all frequencies. Instead, they tend to lose the wave by a leaky fast-wave mechanism at low frequencies or they over-bind a slow-wave at high frequencies. In this dissertation, we have studied magnetic antennas in detail and presented the design approach and apparatus required to implement a flux-channel carrying the magnetic current wave near the speed of light over a very broad frequency range which also makes the design of a frequency independent antenna (spiral) possible. We will learn how to construct extremely thin conformal antennas, frequency-independent permeable antennas, and even micron-sized antennas that can be embedded inside the brain without damaging the tissue. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017