Radio Frequency Superconducting Quantum Interference Device Meta-atoms and Metamaterials: Experiment, Theory, and Analysis

Metamamterials are 1D, 2D or 3D arrays of articial atoms. The articial atoms, called "meta-atoms", can be any component with tailorable electromagnetic properties, such as resonators, LC circuits, nano particles, and so on. By designing the properties of individual meta-atoms and the interaction created by putting them in a lattice, one can create a metamaterial with intriguing properties not found in nature. My Ph. D. work examines the meta-atoms based on radio frequency superconducting quantum interference devices (rf-SQUIDs); their tunability with dc magnetic field, rf magnetic field, and temperature are studied. The rf-SQUIDs are superconducting split ring resonators in which the usual capacitance is supplemented with a Josephson junction, which introduces strong nonlinearity in the rf properties. At relatively low rf magnetic field, a magnetic field tunability of the resonant frequency of up to 80 THz/Gauss by dc magnetic field is observed, and a total frequency tunability of 100% is achieved. The macroscopic quantum superconducting metamaterial also shows manipulative self-induced broadband transparency due to a qualitatively novel nonlinear mechanism that is different from conventional electromagnetically induced transparency (EIT) or its classical analogs. A near complete disappearance of resonant absorption under a range of applied rf flux is observed experimentally and explained theoretically. The transparency comes from the intrinsic bi-stability and can be tuned on/ off easily by altering rf and dc magnetic fields, temperature and history. Hysteretic in situ 100% tunability of transparency paves the way for auto-cloaking metamaterials, intensity dependent filters, and fast-tunable power limiters. An rf-SQUID metamaterial is shown to have qualitatively the same behavior as a single rf-SQUID with regards to dc flux, rf flux and temperature tuning. The two-tone response of self-resonant rf-SQUID meta-atoms and metamaterials is then studied here via intermodulation (IM) measurement over a broad range of tone frequencies and tone powers. A sharp onset followed by a surprising strongly suppressed IM region near the resonance is observed. This behavior can be understood employing methods in nonlinear dynamics; the sharp onset, and the gap of IM, are due to sudden state jumps during a beat of the two-tone sum input signal. The theory predicts that the IM can be manipulated with tone power, center frequency, frequency difference between the two tones, and temperature. This quantitative understanding potentially allows for the design of rf-SQUID metamaterials with either very low or very high IM response.

FOLLOWING THE TRAIL OF THE SNAKE: A LIFE HISTORY OF COBRA MANSA "COBRINHA" MESTRE OF CAPOEIRA

This dissertation is a cultural biography of Mestre Cobra Mansa, a mestre of the Afro-Brazilian martial art of capoeira angola. The intention of this work is to track Mestre Cobrinha's life history and accomplishments from his beginning as an impoverished child in Rio to becoming a mestre of the tradition-its movements, music, history, ritual and philosophy. A highly skilled performer and researcher, he has become a cultural ambassador of the tradition in Brazil and abroad. Following the Trail of the Snake is an interdisciplinary work that integrates the research methods of ethnomusicology (oral history, interview, participant observation, musical and performance analysis and transcription) with a revised life history methodology to uncover the multiple cultures that inform the life of a mestre of capoeira. A reflexive auto-ethnography of the author opens a dialog between the experiences and developmental steps of both research partners' lives. Written in the intersection of ethnomusicology, studies of capoeira, social studies and music education, the academic dissertation format is performed as a roda of capoeira aiming to be respectful of the original context of performance. The result is a provocative ethnographic narrative that includes visual texts from the performative aspects of the tradition (music and movement), aural transcriptions of Mestre Cobra Mansa's storytelling and a myriad of writing techniques to accompany the reader in a multi-dimensional journey of multicultural understanding. The study follows Cinezio Feliciano Pe anha in his childhood struggle for survival as a street performer in Rio de Janeiro. Several key moves provided him with the opportunity to rebuild his life and to grow into a recognized mestre of the capoeira angola martial art as Mestre Cobra Mansa ("Tame Snake" in Portuguese). His dedicated work enabled him to contribute to the revival of the capoeira angola tradition during the 1980's in Bahia. After his move to the United States in the early 1990's, Mestre Cobrinha founded the International Capoeira Angola Foundation, which today has expanded to 28 groups around the world. Mestre Cobra returned home to Brazil to initiate projects that seek to develop a new sense of community from all that he has learned and been able to accomplish in his life through the performance and study of capoeira angola.