Monte Carlo method for the reduction of measurement errors in the material parameter estimation with cavities

The quantitative determination of material parameter distributions in resonant cavities is a relatively new method for the real-time monitoring of chemical processes. For this purpose, electromagnetic resonances of the cavity resonator are used as input data for the reverse calculation (inversion). However, the reverse calculation algorithm is sensitive to disturbances of the input data, which produces measurement errors and tends to diverge, which leads to no measurement result at all. In this work a correction algorithm based on the Monte Carlo method is presented which ensures a convergent behavior of the reverse calculation algorithm.

Homodyne vector network analysis as a tool for the real-time measurement of electrical material parameter distributions in the field

The spatial distribution of electrical material parameters (e. g. permittivity and conductivity) can be a valuable indicator of the state of a chemical process or the condition of the processing system. Unfortunately, there are very few measurement systems that could handle this task in the field at low cost and with small shape factors. A potential solution currently under research for the determination of material parameter distributions is based on electromagnetic resonances inside chemical reactors. In the laboratory, vector network analyzers (VNA) and personal computers are used, which is expensive. This contribution reports on an application-specific stand-alone homodyne VNA with integrated data processing as an effort to transfer the laboratory-proven method to the field. The quality of the approach, validated by comparison with commercial VNAs, is shown to suffice for typical field applications.

Schumann resonance intensity as a precursor for warm ENSO episodes

<p>Schumann resonances (SR) are the global electromagnetic resonances of the Earth-ionosphere cavity and constitute the extremely low frequency (< 100 Hz) radiation of the worldwide lightning activity (Schumann, 1952). The recording of SR intensity at a few distant SR stations is an efficient tool to monitor the global lightning. We present the variations of SR intensity in the transition months preceding the warm ENSO episodes for the two super El Niño events in 1997/98 and 2015/16 as well as for the two medium size El Niño periods in 2001/02 and 2008/09  based on SR observations at multiple locations.: Nagycenk, Hungary (47.6N, 16.7E);  Hornsund, Svalbard (77.0N, 15.6E);  Eskdalemuir, UK (55.3N, 3.2W);  Alberta, Canada (51.9N, 111.5W);  Boulder Creek, USA (37.2N, 122.1W).</p><p>A remarkable increase in SR intensity is documented two-three months before or just at the beginning of El Niño episodes as compared with the SR intensity in the same months of the preceding La Niña (or non-ENSO) phase for all cases studied here. The percentage increase in SR intensity depends on the amplitude of the warm ENSO period, and is consistently higher for the two super El Niño events. The enhanced SR intensity indicates a worldwide response of global lightning activity. Increased atmospheric instability due to the land-ocean thermal interaction during the transition interval could be responsible for the intensification of lightning activity. This systematic behavior may have been overlooked in earlier studies that compared lightning activity in the integrated ‘cold’ and the ‘warm’ phases, but without exploring the transitional variation. Our results suggest that the SR intensity variation on the interannual time scale acts a precursor for the occurrence of warm ENSO episode.</p>

High-Efficiency Metasurfaces with 2π Phase Control Based on Aperiodic Dielectric Nanoarrays

In this study, the high-efficiency phase control Si metasurfaces are investigated based on aperiodic nanoarrays unlike widely-used period structures, the aperiodicity of which providing additional freedom to improve metasurfaces’ performance. Firstly, the phase control mechanism of Huygens nanoblocks is demonstrated, particularly the internal electromagnetic resonances and the manipulation of effective electrical/magnetic polarizabilities. Then, a group of high-transmission Si nanoblocks with 2π phase control is sought by sweeping the geometrical parameters. Finally, several metasurfaces, such as grating and parabolic lens, are numerically realized by the nanostructures with high efficiency. The conversion efficiency of the grating reaches 80%, and the focusing conversion efficiency of the metalens is 99.3%. The results show that the high-efficiency phase control metasurfaces can be realized based on aperiodic nanoarrays, i.e., additional design freedom.

Influence of Resonances on the Noise Performance of SQUID Susceptometers

Scanning Superconducting Quantum Interference Device (SQUID) Susceptometry simultaneously images the local magnetic fields and susceptibilities above a sample with sub-micron spatial resolution. Further development of this technique requires a thorough understanding of the current, voltage, and flux ( I V Φ ) characteristics of scanning SQUID susceptometers. These sensors often have striking anomalies in their current–voltage characteristics, which we believe to be due to electromagnetic resonances. The effect of these resonances on the performance of these SQUIDs is unknown. To explore the origin and impact of the resonances, we develop a model that qualitatively reproduces the experimentally-determined I V Φ characteristics of our scanning SQUID susceptometers. We use this model to calculate the noise characteristics of SQUIDs of different designs. We find that the calculated ultimate flux noise is better in susceptometers with damping resistors that diminish the resonances than in susceptometers without damping resistors. Such calculations will enable the optimization of the signal-to-noise characteristics of scanning SQUID susceptometers.