Next Generation Acoustic and Magnetic Devices for Radio Frequency Communication
This dissertation primarily focuses on utilizing low wave speed acoustic waves coupled with electromagnetics to increase performance of radio frequency front end architectures and reduce device dimensions. Chapter 1 begins with the history of communication technology beginning with Maxwell’s equations. Next brief introductions into the piezoelectricity, magnetism, and multiferroics are given to lay the groundwork for the following Chapters.
Chapter 2 of this dissertation aims at improving the capability of communicating in lossy RF-denied media such as seawater. First, magnetic antennas are theoretically analyzed and compared to electric antennas showing that magnetic antennas perform better when surrounded by lossy conductive media. Next, a prototype multiferroic antenna is developed that uses piezoelectric PZT and magnetostrictive FeGa. The PZT applies a time varying stress to the FeGa causing the FeGa’s internal flux density to dynamically vary resulting in a time-varying magnetic near field. Magnetic near field measurements are compared to an analytical model showing good agreement.
In Chapter 3 Lamb wave devices are investigated for filtering and frequency conversion applicationsin RF-front ends. Leveraging micro-fabrication techniques two Lamb wave delay lines are fabricated out of piezoelectric aluminum nitride (AlN). Interdigitated transducers (IDTs) are used to launch and receive Lamb waves as well as generate a time and space varying mechanical compliance. A circuit model is developed to compare to the experimental results and determine the magnitude of the compliance nonlinearity present in the AlN. Results show that acoustic devices can be developed that simultaneously filter and down-convert or up-convert a signal.
Chapter 4 numerically analyzes strain tunable magnetic filters for applications in software defined radio and cognitive radio. For these applications filters with a tunable bandpass are necessary. The design relies on two CoFeB ellipses deposited on piezoelectric PMN-PT. An electric field is applied through the thickness of the PMN-PT resulting in a strain applied to the CoFeB ellipses. The electric field can be applied to either strain one ellipse or both ellipses. Straining both ellipses results in a tunable susceptibility from 6 GHz to 8 GHz, while straining only one ellipse results in a broadening of the bandpass response. These results show a potential solution for dynamic filters for next generation communication architectures.