Using Inductance as a Tuning Parameter for RF Meta-atoms

The resonant frequency of metamaterials structured with split ring resonator (SRR) meta-atoms is determined primarily through the capacitance and inductance of the individual meta-atoms. Two designs that vary inductance incrementally were modeled, simulated, fabricated, and tested to investigate the role inductance plays in metamaterial designs. The designs consisted of strategically adding sections to the SRR to increase the inductance, but in a manner that minimized capacitance variations. Each design showed a shift in resonant frequency that was proportional to the length of the added section. As the length of each section was increased, the resonant frequency shifted from 2.78 GHz to 2.18 GHz

Low-loss Meta-atom for Improved Resonance Response

Measurements of a meta-atom integrated with a low noise amplifier into the split-ring resonator are presented. A comparison is made between baseline meta-atoms and one integrated with a GaAs low noise amplifier. S-parameter measurements in a RF strip-line show the resonant frequency location. The resonance null is more prominent for the integrated meta-atom. Biasing the low noise amplifier from 0 to 7 VDC showed that the resonant null improved with biasing voltage. As the biasing voltage increases, the transmission null reduced from -11.82 to -23.21 dB for biases from 0 to 7 VDC at resonant frequency

Electrostatically Tunable Meta-Atoms Integrated With In Situ Fabricated MEMS Cantilever Beam Arrays

Two concentric split ring resonators (SRRs) or meta-atoms designed to have a resonant frequency of 14 GHz are integrated with microelectromechanical systems cantilever arrays to enable electrostatic tuning of the resonant frequency. The entire structure was fabricated monolithically to improve scalability and minimize losses from externally wire-bonded components. A cantilever array was fabricated in the gap of both the inner and outer SRRs and consisted of five evenly spaced beams with lengths ranging from 300 to 400 μm. The cantilevers pulled in between 15 and 24 V depending on the beam geometry. Each pulled-in beam increased the SRR gap capacitance resulting in an overall 1-GHz shift of the measured meta-atom resonant frequency

SRRs Embedded with MEMS Cantilevers to Enable Electrostatic Tuning of the Resonant Frequency

A microelectromechanical systems (MEMS) cantilever array was monolithically fabricated in the gap region of a split ring resonator (SRR) to enable electrostatic tuning of the resonant frequency. The design consisted of two concentric SRRs each with a set of cantilevers extending across the split region. The cantilever array consisted of five beams that varied in length from 300 to 400 μm, with each beam adding about 2 pF to the capacitance as it actuated. The entire structure was fabricated monolithically to reduce its size and minimize losses from externally wire bonded components. The beams actuate one at a time, longest to shortest with an applied voltage ranging from 30–60 V. The MEMS embedded SRRs displayed dual resonant frequencies at 7.3 and 14.2 GHz or 8.4 and 13.5 GHz depending on the design details. As the beams on the inner SRR actuated the 14.2 GHz resonance displayed tuning, while the cantilevers on the outer SRR tuned the 8.4 GHz resonance. The 14.2 GHz resonant frequency shifts 1.6 GHz to 12.6 GHz as all the cantilevers pulled-in. Only the first two beams on the outer cantilever array pulled-in, tuning the resonant frequency 0.4 GHz from 8.4 to 8.0 GHz

Mass Reduction Patterning of Silicon-on-oxide-based Micromirrors

It has long been recognized in the design of micromirror-based optical systems that balancing static flatness of the mirror surface through structural design with the system’s mechanical dynamic response is challenging. Although a variety of mass reduction approaches have been presented in the literature to address this performance trade, there has been little quantifiable comparison reported. In this work, different mass reduction approaches, some unique to the work, are quantifiably compared with solid plate thinning in both curvature and mass using commercial finite element simulation of a specific square silicon-on-insulator–based micromirror geometry. Other important considerations for micromirror surfaces, including surface profile and smoothness, are also discussed. Fabrication of one of these geometries, a two-dimensional tessellated square pattern, was performed in the presence of a 400-μm-tall central post structure using a simple single mask process. Limited experimental curvature measurements of fabricated samples are shown to correspond well with properly characterized simulation results and indicate ∼67% improvement in radius of curvature in comparison to a solid plate design of equivalent mass

The relationship between SF-6D utility scores and lifestyle factors across three life-stages: Evidence from the Australian Longitudinal Study on Women’s Health

Purpose: To investigate how SF-6D utility scores change with age between generations of women, and to quantify the relationship of SF-6D with lifestyle factors across life-stages. Methods: Up to seven waves of self-reported, longitudinal data were drawn for the 1973-78 (young, N=13772), 1946-51 (mid-age, N=12792), 1921-26 (older, N=9972) cohorts from the Australian Longitudinal Study on Women’s Health. Mixed effects models were employed for analysis. Results: Young and mid-age women had similar average SF-6D scores at baseline (0.63-0.64), which remained consistent over 16 year period. However, older women had lower scores at baseline at 0.57 which steadily declined over 15 years. Across cohorts, low education attainment, greater difficulty in managing on income, obesity, physical inactivity, heavy smoking, non-drinking and increasing stress levels were associated with lower SF-6D scores. The magnitude of effect varied between cohorts. SF-6D scores were lower amongst young women with high risk drinking behaviours than low-risk drinkers. Mid-age women who were underweight, never married, or underwent surgical menopause also reported lower SF-6D scores. Older women who lived in remote areas, who were ex-smokers, or were underweight reported lower SF-6D scores. Conclusion: The SF-6D utility score is sensitive to differences in lifestyle factors across adult lifestages. Gradual loss of physical functioning may explain the steady decline in health for older women. Key factors associated with SF-6D include physical activity, body mass index, menopause status, smoking, alcohol use and stress. Factors associated with poorer SF-6D scores vary in type and magnitude at different life stages

Scientific discovery as a combinatorial optimisation problem: How best to navigate the landscape of possible experiments?

A considerable number of areas of bioscience, including gene and drug discovery, metabolic engineering for the biotechnological improvement of organisms, and the processes of natural and directed evolution, are best viewed in terms of a ‘landscape’ representing a large search space of possible solutions or experiments populated by a considerably smaller number of actual solutions that then emerge. This is what makes these problems ‘hard’, but as such these are to be seen as combinatorial optimisation problems that are best attacked by heuristic methods known from that field. Such landscapes, which may also represent or include multiple objectives, are effectively modelled in silico, with modern active learning algorithms such as those based on Darwinian evolution providing guidance, using existing knowledge, as to what is the ‘best’ experiment to do next. An awareness, and the application, of these methods can thereby enhance the scientific discovery process considerably. This analysis fits comfortably with an emerging epistemology that sees scientific reasoning, the search for solutions, and scientific discovery as Bayesian processes

ISX-A Graphite Limiter Experiment

Graphite limiters were installed and tested in the ISX-A tokamak as part of the ISX-A surface physics program and the TFTR materials research program. The puropse of the experiment was to compare plasma performance using graphite limiters as opposed to the standard ISX-A stainless steel limiters. Heaters were installed in the graphite limiters so that the effects of operation at elevated temperatures could be evaluated

Financial considerations in the conduct of multi-centre randomised controlled trials: evidence from a qualitative study.

National Coordinating Centre for Research Methodology; Medical Research Council, UK Department of Health; Chief Scientist OfficeNot peer reviewedPublisher PD