MechE PhD Dissertation Defense: Ke Wu

TITLE: MAGNETIC FIELD ENHANCEMENT IN METAMATERIALS: FROM THEORY TO APPLICATION

ABSTRACT: Metamaterials, defined as artificially constructed materials composed of subwavelength meta-atoms, have emerged as a promising tool to manipulate electromagnetic (EM) waves due to their extraordinary responses to incident EM waves. Efforts in developing metamaterials have progressed from initial demonstrations of breaking the generalized limitations of refraction and reflection of natural materials, to their current use in facilitating a range of practical applications. One flourishing research direction is the applications of metamaterial in electromagnetic field enhancement. The enhanced magnetic fields are attractive for a variety of applications such as magnetic resonance imaging (MRI), wireless power transfer, and magnetic induction tomography, among others. The common thread across this dissertation is incorporating conventional and novel methods to create some functional magnetic metamaterials for field enhancement, considering the practical application scenarios. First, this dissertation investigates mechanically tunable metamaterials by integrating EM resonators with deployable auxetics. Aided by digital parametric design tools, the computationally designed metamaterials could conformably cover a person’s kneecap, ankle, head, or any part of the body in need of imaging, and meanwhile they are readily to be tuned for ensuring frequency match, making magnetic metamaterials more feasible in clinical scenarios. Second, this dissertation presents a flexible, smart metamaterial composed of an assembly of meta- atoms featuring a controlling circuit loaded spiral resonator (CCLSR) inductively coupled with a varactor-loaded ring resonator (VLRR). The reported metamaterial may not only be readily tuned to achieve precise frequency match with MRI by a controlling circuit, but is also capable of selectively amplifying the magnetic field by sensing excitation signal strength passively, thereby remaining ‘off’ during RF transmission and ensuring its optimal performance when applied to MRI. Third, this dissertation introduces a metamaterial- enhanced near-field readout platform for interrogating passive microsensor tags. With the unique evanescent wave amplification properties, the insertion of a metamaterial between the transmitter and receiver antennas could amplify the magnetic flux density and, thus, increase the coupling coefficient, ultimately improving the wireless power transfer efficiency. These functional metamaterials demonstrated in this thesis can be employed to construct application-oriented electromagnetic devices and facilitate metamaterial-based technologies.

COMMITTEE: ADVISOR Professor Xin Zhang, ME/ BME/ECE/MSE; CHAIR Professor Tom Bifano, ME/BME/ECE/MSE; Professor Chuanhua Duan, ME/MSE; Professor Lei Tian, ECE/BME; Professor Stephan Anderson, Radiology/BUSM/ME