The multi-peak point phenomenon of broadband microwave reflection caused by inhomogeneous plasma

During spacecraft re-entry,the challenge of measuring plasma sheath parameters directly contributes to difficulties in addressing communication blackout.In this work,we have discovered a phenomenon of multiple peaks in reflection data caused by the inhomogeneous plasma.Simulation results show that the multi-peak points fade away as the characteristic frequency is approached,resembling a series of gradually decreasing peaks.The positions and quantities of these points are positively correlated with electron density,yet they show no relation to collision frequency.This phenomenon is of significant reference value for future studies on the spatial distribution of plasmas,particularly for using microwave reflection signals in diagnosing the plasma sheath.

Analyzing Bandwidth on the Microwave Absorber by the Interface Reflection Model

Metallic flaky sendust particles are prepared for use as fillers in electromagnetic attenuation composites. We report the interface reflection model to divide the broad bandwidth into electromagnetic loss and quarter-wavelength （λ/4） cancelation. Combining with the face reflection calculation, we identify the electromagnetic loss originated from skin effect, which is used to explain over half of the absorbed energy in high frequency band. Most impor- tantly, the unique electromagnetic loss cannot generate the reflection loss （RL） peak. Using the phase relation of face reflection, we show evidence that the λ/4 cancelation is vital to generate the RL peak. The calculated energy loss agrees well with the experimental data and lays the foundation for further research.

Microwave Reflectometry on HL-2A Tokamak

One of the most important electron density diagnostics, microwave reflectometry, has been developed on many large and medium nuclear fusion devices in recent years . Not only the electron density profiles with high temporal and spatial resolutions, but also the profiles of plasma rotation and turbulence can be obtained with this diagnostic system.

Single-layer broadband planar antenna using ultrathin high-efficiency focusing metasurfaces

Phase gradient metasurfaces（PGMS） offer a fascinating ability to control the amplitude and phase of the electromagnetic（EM） waves on a subwavelength scale, resulting in new applications of designing novel microwave devices with improved performances. In this paper, a reflective symmetrical element, consisting of orthogonally I-shaped structures, has been demonstrated with an approximately parallel phase response from 15 GHz to 22 GHz, which results in an interesting wideband property. For practical design, a planar antenna is implemented by a well-optimized focusing metasurface and excited by a self-designed Vivaldi antenna at the focus. Numerical and experimental results coincide well. The planar antenna has a series of merits such as a wide 3-d B gain bandwidth of 15–22 GHz, an average gain enhancement of 16 d B, a comparable aperture efficiency of better than 45% at 18 GHz, and also a simple fabrication process. The proposed reflective metasurface opens up a new avenue to design wideband microwave devices.

An Emerging Testing Method for Metallics Based on NV Center in the Diamond

Metal substance detection plays an extremely important role in daily life,industrial manufacturing and even industrial security.The traditional methods include optical detection,X-ray detection,microwave detection and ultrasonic detection.These methods,playing a vital role in the field of non-destructive testing,can not only judge the presence or absence of metal,but also accurately detect the type and size of metal defects.For microwave detection,the detection efficiency of metal materials is limited by the response sensitivity of the detector to microwaves.In recent years,scientists have discovered a quantum sensing system based on the diamond nitrogen-vacancy(NV)color center.The system obtains optical detection magnetic resonance(ODMR)fluorescence spectra under the combined action of a 532nm laser and a certain frequency band of microwaves,and the signal contrast changes significantly with the microwave power.Based on the NV color center quantum sensing system,this paper studies its application in the field of metal detection,and takes steel detection as an example to detect the size of steel bars according to the changes in the spectral line,providing a new method for non-destructive testing such as metal substance detection.

LABORATORY STUDY ON MICROWAVE REMOTE SENSING OF GROUND TRUTH

In order to improve the interpretation of the earth system microwave remote sensing, the research of microwave spectrum characteristics of the ground truth (earth objects) was carried out in laboratory. A laboratory for microwave remote sensing of the earth objects has been constructed to improve the remote sensing level, the laboratory consists of four parts: the measuring system of dielectric constants, the microwave emissivity meter, the microwave reflectometer and the microwave remote sensing simulation experiment in field. In this paper, the principle of measurement, the correction of near field process, the structure of instrument, the calibration method and the measurement of the earth substances, including soil, water and oil, are discussed. The labora- tory may supply the condition for measuring the parameters of thc earth substance remote sensing and help to interpret the remote sensing data.