In this work, we experimentally and theoretically explore voltage controlled oscillations occurri... more In this work, we experimentally and theoretically explore voltage controlled oscillations occurring in micro-beams of vanadium dioxide. These oscillations are a result of the reversible insulator to metal phase transition in vanadium dioxide. Examining the structure of the observed oscillations in detail, we propose a modified percolative-avalanche model which allows for voltage-triggering. This model captures the periodicity and waveshape of the oscillations as well as several other key features. Importantly, our modeling shows that while temperature plays a critical role in the vanadium dioxide phase transition, electrically induced heating cannot act as the primary instigator of the oscillations in this configuration. This realization leads us to identify electric field as the most likely candidate for driving the phase transition.
Tunable Metamaterials The electromagnetic response of metamaterials gives rise to exciting phenom... more Tunable Metamaterials The electromagnetic response of metamaterials gives rise to exciting phenomena such as cloaking, negative refraction, and perfect lensing. Their response, however, tends to depend strongly on resonant effects, thereby limiting the application bandwidth. Driscoll et al. (p. 1518 , published online 20 August) combine a split ring resonator array with the phase change material, VO 2 , to form a metamaterial in which the response can be tuned. The heat-induced phase change of VO 2 from an insulator to a metal alters the response of split-ring resonator, and, because it displays a hysteresis, the device can retain a “memory” of the induced change. The results may lead to a flexible method for achieving metamaterials operating over a wide bandwidth and to novel switching applications.
High-efficiency voltage oscillation in planer-type junctions with infinite negative differential ... more High-efficiency voltage oscillation in planer-type junctions with infinite negative differential resistance
Structures engineered to give a specific response to light are certainly nothing new. The long hi... more Structures engineered to give a specific response to light are certainly nothing new. The long history of engineering materials response to light encompasses seemingly disparate structures from antennas to stained glass, lighting rods to mirrors. It is only in the recent decade, however, that we have appreciated the full gamut of possibilities this field holds, and envisioned paths towards realizing these possibilities. The new field of electromagnetic metamaterials has given us the potential to create devices that manipulate light in nearly any way we can envision. The work of this thesis is involved principally with the study of metamaterials and their unique properties. Using a wide array of developed apparatus and techniques - spanning microwave frequencies through the infrared - we investigate metamaterial behavior, and the ways they differ from conventional materials. Applications are always kept in the forefront of thought. The demonstration of a graded negative-index lens, f...
Submitted for the MAR07 Meeting of The American Physical Society A spectroscopic multi-angle prob... more Submitted for the MAR07 Meeting of The American Physical Society A spectroscopic multi-angle probe of metamaterial permeability TOM DRISCOLL, Univsersity California San Diego, SABARNI PALIT, Duke University, WILLIE PADILLA, Los Alamos National Laboratory, TONG REN, JACK MOCK, Duke University, GREGORY ANDREEV, University California San Diego, SANG-YEON CHO, NAN MARIE JOKERST, DAVID SMITH, Duke University, DIMITRI BASOV, University California San Diego — We present spectroscopic data for acute-angle reflection and transmission of two planar metamaterial samples, one at microwave frequencies and one at far-infrared frequencies. We show that the observed evolution of the magnetic resonance with the increasing angle of incidence is in quantitative agreement with the Fresnel expressions. This finding uncovers a convenient approach towards the retrieval of optical constants of metamaterials by fitting the Fresnel theory to multiple angle-datasets simultaneously; thus obviating the need for...
Gradient Index (GRIN) metamaterials have been used to create devices inspired by, but often surpa... more Gradient Index (GRIN) metamaterials have been used to create devices inspired by, but often surpassing the potential of, conventional GRIN optics. The unit-cell nature of metamaterials presents the opportunity to exert much greater control over spatial gradients than is possible in ...
2019 Antenna Measurement Techniques Association Symposium (AMTA), 2019
Echodyne has recently completed and qualified a new millimeter-wave antenna measurement system fo... more Echodyne has recently completed and qualified a new millimeter-wave antenna measurement system for characterization of beam-steering antennas such as our Metamaterial Electronic Steering Arrays (MESAs). Unlike most far-field systems that employ a standard Phi/Theta or Az/El positioner, we use a six-axis industrial robot that can define an arbitrary AUT coordinate system and center of rotation. In different operational modes, the robot is used as an angular AUT positioner (e.g., Az/El) or configured for linear scan areas. This flexible positioning system allows us to characterize the range illumination and quiet zone reflections without modification to the measurement system. With minor modifications, the system could also be used in a planar-near field configuration. Range alignment can be easily performed by redefining the coordinate system of the AUT movement in software. The approximate 5.2-meter range length is within the radiating near-field of many arrays of interest, so we em...
We report on the nanoscale infrared response of a prototypical ferromagnetic semiconductor Ga1-xM... more We report on the nanoscale infrared response of a prototypical ferromagnetic semiconductor Ga1-xMnxAs at Mn doping fractions in the range of x=1.8-7.75 %. These studies have been carried out using an apertureless scattering Scanning Near field Infrared Microscope (s-SNIM) with a pseudoheterodyne detection scheme operating at the wavelength near 10 mum.. For samples with doping fractions below 7% we observe
Methods for real-time tuning (dynamic-tuning) of metamaterial electromagnetic response have recei... more Methods for real-time tuning (dynamic-tuning) of metamaterial electromagnetic response have received significant attention as a possible approach to alleviate limitations associated with bandwidth in metamaterials. In a dynamic-tuning configuration, an applied stimulus induces some ...
IEEE Transactions on Microwave Theory and Techniques
Dynamic metamaterial antennas (DMAs) offer the potential to generate diverse beam patterns with l... more Dynamic metamaterial antennas (DMAs) offer the potential to generate diverse beam patterns with less hardware complexity than traditional electronic beam steering arrays. This paper describes an enhanced resolution stripmap mode (ERSM) synthetic aperture radar (SAR) approach for 3-D imaging with DMAs, which achieves an improved resolution in all dimensions while maintaining a larger scene size than spotlight SAR approaches. Because 3-D ERSM SAR accumulates a large number of measurements, image reconstruction is a computationally complex process. GPU-accelerated partitioned inverse (PI) algorithms are extended to allow for the fast 3-D ERSM SAR image reconstruction. Laboratory experiments using a commercial prototype DMA are presented, which show an improvement of 26% and 42% in cross-range resolution and ground-range resolution, respectively, compared with standard SM SAR. Furthermore, the PI reconstruction results in a speedup of 23.5 versus the commonly used matched filter approach.
IEEE Antennas and Wireless Propagation Letters, 2015
We present the design of a tunable metamaterial element that can serve as the building block for ... more We present the design of a tunable metamaterial element that can serve as the building block for a dynamically reconfigurable aperture. The element-a complimentary electric-LC (cELC) resonator-is patterned into the upper conductor of a microstrip transmission line, providing both a means of exciting the radiating metamaterial element as well as independent access for biasing circuitry. PIN diodes are connected across the capacitive gaps of the cELC, and a dc bias current is used to switch the junction between conducting and insulating states. The leakage of RF signal through the bias line is mitigated by integration of a radial decoupling stub. The proposed design and operation of the element are demonstrated through full-wave electromagnetic simulations. We discuss the potential application of the cELC element as a building block for metamaterial apertures capable of dynamic beamforming, imaging, or security screening applications.
We have demonstrated the creation of spatial gradients in the optical properties of a metamateria... more We have demonstrated the creation of spatial gradients in the optical properties of a metamaterial device through tuning of a vanadium dioxide layer that interacts with an array of split ring resonators (SRR). Application of a transient electrical pulse across the metamaterial-VO2 system leaves persistent changes in the properties of the metamaterial due to the hysteresis of the insulator-to-metal transition in VO2. Through modification of contact geometry, pulse shape, and pulse duration, we have shown increased control over such devices allowing for independent tuning of individual sections of our hybrid VO2-SRR device through the application of several transient voltage pulses. The characteristics of the gradients resulting from the voltage pulses were measured using infrared transmission spectroscopy. We observed a 15% variation in the magnitude of transmission with spatial scales on the order of one wavelength at the resonance frequency. Thus we have demonstrated the viability ...
In this work, we experimentally and theoretically explore voltage controlled oscillations occurri... more In this work, we experimentally and theoretically explore voltage controlled oscillations occurring in micro-beams of vanadium dioxide. These oscillations are a result of the reversible insulator to metal phase transition in vanadium dioxide. Examining the structure of the observed oscillations in detail, we propose a modified percolative-avalanche model which allows for voltage-triggering. This model captures the periodicity and waveshape of the oscillations as well as several other key features. Importantly, our modeling shows that while temperature plays a critical role in the vanadium dioxide phase transition, electrically induced heating cannot act as the primary instigator of the oscillations in this configuration. This realization leads us to identify electric field as the most likely candidate for driving the phase transition.
Tunable Metamaterials The electromagnetic response of metamaterials gives rise to exciting phenom... more Tunable Metamaterials The electromagnetic response of metamaterials gives rise to exciting phenomena such as cloaking, negative refraction, and perfect lensing. Their response, however, tends to depend strongly on resonant effects, thereby limiting the application bandwidth. Driscoll et al. (p. 1518 , published online 20 August) combine a split ring resonator array with the phase change material, VO 2 , to form a metamaterial in which the response can be tuned. The heat-induced phase change of VO 2 from an insulator to a metal alters the response of split-ring resonator, and, because it displays a hysteresis, the device can retain a “memory” of the induced change. The results may lead to a flexible method for achieving metamaterials operating over a wide bandwidth and to novel switching applications.
High-efficiency voltage oscillation in planer-type junctions with infinite negative differential ... more High-efficiency voltage oscillation in planer-type junctions with infinite negative differential resistance
Structures engineered to give a specific response to light are certainly nothing new. The long hi... more Structures engineered to give a specific response to light are certainly nothing new. The long history of engineering materials response to light encompasses seemingly disparate structures from antennas to stained glass, lighting rods to mirrors. It is only in the recent decade, however, that we have appreciated the full gamut of possibilities this field holds, and envisioned paths towards realizing these possibilities. The new field of electromagnetic metamaterials has given us the potential to create devices that manipulate light in nearly any way we can envision. The work of this thesis is involved principally with the study of metamaterials and their unique properties. Using a wide array of developed apparatus and techniques - spanning microwave frequencies through the infrared - we investigate metamaterial behavior, and the ways they differ from conventional materials. Applications are always kept in the forefront of thought. The demonstration of a graded negative-index lens, f...
Submitted for the MAR07 Meeting of The American Physical Society A spectroscopic multi-angle prob... more Submitted for the MAR07 Meeting of The American Physical Society A spectroscopic multi-angle probe of metamaterial permeability TOM DRISCOLL, Univsersity California San Diego, SABARNI PALIT, Duke University, WILLIE PADILLA, Los Alamos National Laboratory, TONG REN, JACK MOCK, Duke University, GREGORY ANDREEV, University California San Diego, SANG-YEON CHO, NAN MARIE JOKERST, DAVID SMITH, Duke University, DIMITRI BASOV, University California San Diego — We present spectroscopic data for acute-angle reflection and transmission of two planar metamaterial samples, one at microwave frequencies and one at far-infrared frequencies. We show that the observed evolution of the magnetic resonance with the increasing angle of incidence is in quantitative agreement with the Fresnel expressions. This finding uncovers a convenient approach towards the retrieval of optical constants of metamaterials by fitting the Fresnel theory to multiple angle-datasets simultaneously; thus obviating the need for...
Gradient Index (GRIN) metamaterials have been used to create devices inspired by, but often surpa... more Gradient Index (GRIN) metamaterials have been used to create devices inspired by, but often surpassing the potential of, conventional GRIN optics. The unit-cell nature of metamaterials presents the opportunity to exert much greater control over spatial gradients than is possible in ...
2019 Antenna Measurement Techniques Association Symposium (AMTA), 2019
Echodyne has recently completed and qualified a new millimeter-wave antenna measurement system fo... more Echodyne has recently completed and qualified a new millimeter-wave antenna measurement system for characterization of beam-steering antennas such as our Metamaterial Electronic Steering Arrays (MESAs). Unlike most far-field systems that employ a standard Phi/Theta or Az/El positioner, we use a six-axis industrial robot that can define an arbitrary AUT coordinate system and center of rotation. In different operational modes, the robot is used as an angular AUT positioner (e.g., Az/El) or configured for linear scan areas. This flexible positioning system allows us to characterize the range illumination and quiet zone reflections without modification to the measurement system. With minor modifications, the system could also be used in a planar-near field configuration. Range alignment can be easily performed by redefining the coordinate system of the AUT movement in software. The approximate 5.2-meter range length is within the radiating near-field of many arrays of interest, so we em...
We report on the nanoscale infrared response of a prototypical ferromagnetic semiconductor Ga1-xM... more We report on the nanoscale infrared response of a prototypical ferromagnetic semiconductor Ga1-xMnxAs at Mn doping fractions in the range of x=1.8-7.75 %. These studies have been carried out using an apertureless scattering Scanning Near field Infrared Microscope (s-SNIM) with a pseudoheterodyne detection scheme operating at the wavelength near 10 mum.. For samples with doping fractions below 7% we observe
Methods for real-time tuning (dynamic-tuning) of metamaterial electromagnetic response have recei... more Methods for real-time tuning (dynamic-tuning) of metamaterial electromagnetic response have received significant attention as a possible approach to alleviate limitations associated with bandwidth in metamaterials. In a dynamic-tuning configuration, an applied stimulus induces some ...
IEEE Transactions on Microwave Theory and Techniques
Dynamic metamaterial antennas (DMAs) offer the potential to generate diverse beam patterns with l... more Dynamic metamaterial antennas (DMAs) offer the potential to generate diverse beam patterns with less hardware complexity than traditional electronic beam steering arrays. This paper describes an enhanced resolution stripmap mode (ERSM) synthetic aperture radar (SAR) approach for 3-D imaging with DMAs, which achieves an improved resolution in all dimensions while maintaining a larger scene size than spotlight SAR approaches. Because 3-D ERSM SAR accumulates a large number of measurements, image reconstruction is a computationally complex process. GPU-accelerated partitioned inverse (PI) algorithms are extended to allow for the fast 3-D ERSM SAR image reconstruction. Laboratory experiments using a commercial prototype DMA are presented, which show an improvement of 26% and 42% in cross-range resolution and ground-range resolution, respectively, compared with standard SM SAR. Furthermore, the PI reconstruction results in a speedup of 23.5 versus the commonly used matched filter approach.
IEEE Antennas and Wireless Propagation Letters, 2015
We present the design of a tunable metamaterial element that can serve as the building block for ... more We present the design of a tunable metamaterial element that can serve as the building block for a dynamically reconfigurable aperture. The element-a complimentary electric-LC (cELC) resonator-is patterned into the upper conductor of a microstrip transmission line, providing both a means of exciting the radiating metamaterial element as well as independent access for biasing circuitry. PIN diodes are connected across the capacitive gaps of the cELC, and a dc bias current is used to switch the junction between conducting and insulating states. The leakage of RF signal through the bias line is mitigated by integration of a radial decoupling stub. The proposed design and operation of the element are demonstrated through full-wave electromagnetic simulations. We discuss the potential application of the cELC element as a building block for metamaterial apertures capable of dynamic beamforming, imaging, or security screening applications.
We have demonstrated the creation of spatial gradients in the optical properties of a metamateria... more We have demonstrated the creation of spatial gradients in the optical properties of a metamaterial device through tuning of a vanadium dioxide layer that interacts with an array of split ring resonators (SRR). Application of a transient electrical pulse across the metamaterial-VO2 system leaves persistent changes in the properties of the metamaterial due to the hysteresis of the insulator-to-metal transition in VO2. Through modification of contact geometry, pulse shape, and pulse duration, we have shown increased control over such devices allowing for independent tuning of individual sections of our hybrid VO2-SRR device through the application of several transient voltage pulses. The characteristics of the gradients resulting from the voltage pulses were measured using infrared transmission spectroscopy. We observed a 15% variation in the magnitude of transmission with spatial scales on the order of one wavelength at the resonance frequency. Thus we have demonstrated the viability ...
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Papers by Tom Driscoll