Two-element interferometer for millimeter-wave solar flare observations

In this paper, we present the design and implementation of a two-element interferometer working in the millimeter wave band (39.5 GHz - 40 GHz) for observing solar radio emissions through nulling interference. The system is composed of two 50 cm aperture Cassegrain antennas mounted on a common equatorial mount, with a separation of 230 wavelengths. The cross-correlation of the received signals effectively cancels the quiet solar component of the large flux density (~3000 sfu) that reduces the detection limit due to atmospheric fluctuations. The system performance is obtained as follows: the noise factor of the AFE in the observation band is less than 2.1 dB, system sensitivity is approximately 12.4 K (~34 sfu) with an integration time constant of 0.1 ms (default), the frequency resolution is 153 kHz, and the dynamic range is larger than 30 dB. Through actual testing, the nulling interferometer observes a quiet sun with a low level of output fluctuations (of up to 50 sfu) and has a significantly lower radiation flux variability (of up to 190 sfu) than an equivalent single-antenna system, even under thick cloud cover. As a result, this new design can effectively improve observation sensitivity by reducing the impact of atmospheric and system fluctuations during observation

Degradation of Two Anti-Corrosion and Anti-Fouling Coating Systems in Simulated Diurnal Cycling Immersion

The degradation process and the electrochemical behavior of two anti-corrosion and anti-fouling coating systems (FW-1 and FW-2) in a simulated diurnal cycling immersion environment (3.5% NaCl, 35 °C 12 h + 25 °C 12 h) were investigated by electrochemical impedance spectroscopy (EIS) technology. Combined with the coating gloss, color difference, adhesion strength and scanning electron microscopy (SEM) tests, the micro morphologies and the variations of the performance parameters were comparatively analyzed. The results showed that in the 160 days of immersion, with the hydrolysis of the FW-1 topcoat resin and some pigments dissolved and released, the surface micro-morphology of the coating changes from rough to smooth, thereby increasing the gloss. While, for the FW-2 topcoat, the occurrence of micro pores and tiny cracks results in an increase in the roughness and a decrease in the gloss. The release of the copper ion particles in the antifouling topcoat has an influence on the color, manifesting as obvious rise in the color difference of the coating. The low-frequency impedance (|Z|0.01 Hz) values of both coating samples decreases slowly and provides very good shielding to the carbon steel substrate. The self-polishing of the topcoat has no big effect on the electrochemical performance of the whole anti-corrosion and anti-fouling coating system; the protective performance of the coating system mainly depends on the integrity of the primer and the intermediate paint

The First Flare Observation with a New Solar Microwave Spectrometer Working in 35–40 GHz

The microwave spectrum contains valuable information about solar flares. Yet, the present spectral coverage is far from complete and broad data gaps exist above 20 GHz. Here we report the first flare (the X2.2 flare on 2022 April 20) observation of the newly built Chashan Broadband Solar millimeter spectrometer (CBS) working from 35 to 40 GHz. We use the CBS data of the new Moon to calibrate, and the simultaneous NoRP data at 35 GHz to cross-calibrate. The impulsive stage has three local peaks with the middle one being the strongest and the maximum flux density reaches ∼9300 solar flux unit at 35–40 GHz. The spectral index of the CBS data ( α _C ) for the major peak is mostly positive, indicating the gyrosynchrotron turnover frequency ( ν _t ) goes beyond 35–40 GHz. The frequency ν _t is smaller yet still larger than 20 GHz for most of the other two peaks according to the spectral fittings with NoRP-CBS data. The CBS index manifests the general rapid-hardening-then-softening trend for each peak and gradual hardening during the decay stage, agreeing with the fitted optically thin spectral index ( α _tn ) for ν _t < 35 GHz. In addition, the obtained turnover frequency ( ν _t ) during the whole impulsive stage correlates well with the corresponding intensity ( I _t ) according to a power-law dependence ( ${I}_{t}\propto {\nu }_{t}^{4.8}$ ) with a correlation coefficient of 0.82. This agrees with earlier studies on flares with low turnover frequency (≤17 GHz), yet it is being reported for the first time for events with a high turnover frequency (≥20 GHz)

Degradation of Two Anti-Corrosion and Anti-Fouling Coating Systems in Simulated Diurnal Cycling Immersion

The degradation process and the electrochemical behavior of two anti-corrosion and anti-fouling coating systems (FW-1 and FW-2) in a simulated diurnal cycling immersion environment (3.5% NaCl, 35 °C 12 h + 25 °C 12 h) were investigated by electrochemical impedance spectroscopy (EIS) technology. Combined with the coating gloss, color difference, adhesion strength and scanning electron microscopy (SEM) tests, the micro morphologies and the variations of the performance parameters were comparatively analyzed. The results showed that in the 160 days of immersion, with the hydrolysis of the FW-1 topcoat resin and some pigments dissolved and released, the surface micro-morphology of the coating changes from rough to smooth, thereby increasing the gloss. While, for the FW-2 topcoat, the occurrence of micro pores and tiny cracks results in an increase in the roughness and a decrease in the gloss. The release of the copper ion particles in the antifouling topcoat has an influence on the color, manifesting as obvious rise in the color difference of the coating. The low-frequency impedance (|Z|0.01 Hz) values of both coating samples decreases slowly, presenting a very good shielding to the carbon steel substrate. The self-polishing of the topcoat has no big effect on the electrochemical performance of the whole anti-corrosion and anti-fouling coating system; the protective performance of the coating system mainly depends on the integrity of the primer and the intermediate paint

Comparative Study on the Degradation of Two Self-Polishing Antifouling Coating Systems with Copper-Based Antifouling Agents

The degradation processes of two self-polishing antifouling coatings containing copper-based agents (CuSCN and Cu2O) in 3.5% NaCl solution and the protection effect of the coating systems were studied by electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM/EDS) methods. The results demonstrate that after immersion for 1525 d at room temperature, the two coating systems still have very good protection property for the 5083 Al alloy substrate, manifesting by the high value of the low-frequency impedance. Alternate high and low temperature immersion test (45 &deg;C 12 h + 25 &deg;C 12 h) leads to serious damage to the antifouling topcoat, and the failure is mainly manifested by many micro-pores and micro-cracks. Because the CuSCN antifouling agent particle has bigger diameter and slightly higher solubility than that of Cu2O agent, the micro-pores established after the agents dissolved and released during the hydrolysis process of the antifouling coating are relatively larger, which results in more decrease in the impedance and a worse protective property of the coating system for the substrate

A Dual-Band High-Gain Subwavelength Cavity Antenna with Artificial Magnetic Conductor Metamaterial Microstructures

This paper presents dual-band high-gain subwavelength cavity antennas with artificial magnetic conductor (AMC) metamaterial microstructures. We developed an AMC metamaterial plate that can be equivalent to mu-negative metamaterials (MNMs) at two frequencies using periodic microstructure unit cells. A cavity antenna was constructed using the dual-band AMC metamaterial plate as the covering layer and utilizing a feed patch antenna with slot loading as the radiation source. The antenna was fabricated with a printed circuit board (PCB) process and measured in an anechoic chamber. The |S11| of the antenna was −26.8 dB and −23.2 dB at 3.75 GHz and 5.66 GHz, respectively, and the realized gain was 15.2 dBi and 18.8 dBi at two resonant frequencies. The thickness of the cavity, a sub-wavelength thickness cavity, was 15 mm, less than one fifth of the long resonant wavelength and less than one third of the short resonant wavelength. This new antenna has the advantages of low profile, light weight, dual-frequency capability, high gain, and easy processing

Degradation of Carbon Fiber-Reinforced Polymer Composites in Salt Water and Rapid Evaluation by Electrochemical Impedance Spectroscopy

The electrochemical impedance spectroscopy and weight gain tests were performed on carbon fiber/vinyl ester and carbon fiber/bismaleimide composites in 3.5% NaCl solution to study the electrochemical and water absorption behaviors. The microstructure morphology and the flexural property of the composites in the long-term exposure process were analyzed with the scanning electron microscope and four-point bending tests. The results revealed that after long-time immersion (>200 d), the water absorption of the two composites is less than 0.5%. This has little effect on the microstructural integrity, only with slight damage on the fiber/resin interfaces, but results in a significant decrease (about 84%) in the composite flexural property. The variation of the water absorption percentage shows good consistency with that of the resin capacitance (Qc) and is negatively related to the variation of the resin resistance (Rpo) and the low-frequency impedance (|Z|0.01Hz) of the composites. A good linear relationship exists between the variations of phase angles in the middle-frequency range (0.1−10 Hz) and the |Z|0.01Hz. The phase angle at 10 Hz (θ10Hz) may be suggested as a suitable parameter to rapidly evaluate the performance of carbon fiber-reinforced polymer composites, just like for evaluating the protective performance of polymer-coated metals in the literature