High-precision RCS measurement of aircraft’s weak scattering source

AbstractThe radar cross section (RCS) of weak scattering source on the surface of an aircraft is usually less than −40dBsm. How to accurately measure the RCS characteristics of weak scattering source is a technical challenge for the aircraft’s RCS measurement. This paper proposes separating and extracting the two-dimensional (2D) reflectivity distribution of the weak scattering source with the microwave imaging algorithm and spectral transform so as to enhance its measurement precision. Firstly, we performed the 2D microwave imaging of the target and then used the 2D gating function to separate and extract the reflectivity distribution of the weak scattering source. Secondly, we carried out the spectral transform of the reflectivity distribution and eventually obtained the RCS of the weak scattering source through calibration. The prototype experimental results and their analysis show that the measurement method is effective. The experiments on an aircraft’s low-scattering conformal antenna verify that the measurement method can eliminate the clutter on the surface of aircraft. The precision of measuring a −40dBsm target is 3–5dB better than the existing RCS measurement methods. The measurement method can more accurately obtain the weak scattering source’s RCS characteristics

Material and Energy Efficiency Analysis of Low Pressure Chemical Vapor Deposition of TiO2 Film

AbstractIn this paper, Low Pressure Chemical Vapor Deposition (LPCVD) of TiO2 thin film process is chosen as the research object to study the material and energy consumptions in this process. The material and energy utilization efficiencies have been calculated and compared under five different reaction conditions (623K, 500Pa; 673K, 500Pa; 723K, 500Pa; 673K, 400Pa; 673K, 300Pa). The material utilization efficiency result reveals that the material utilization in this process is rather low (less 1% in each condition) and increases with higher temperature and lower pressure. The energy analysis result shows that the energy efficiency is extremely low (less 0.1% in each condition) and increases with decreasing temperature and increasing pressure. The reaction condition (623K, 500Pa) is regarded as a satisfactory condition with the highest energy efficiency (0.083%) in spite of the lowest material utilization efficiency (0.5%). This research can lay a foundation for the future optimization work to improve the sustainability performance of LPCVD preparing thin films

Calculation of Differential Propagation Constant Determined by Plant Morphology Using Polarimetric Measurement

The morphology of vegetation greatly impacts propagation of polarized electromagnetic wave. In order to validate this phenomenon, the mathematical relation between the differential propagation constant of forest vegetation and of its polarized echo is quantitatively derived by using backscattering power profile. The fluctuation of differential propagation constant with frequency is analyzed by combining the morphological characteristics of vegetation. The accurate copolarized data of 3–10 GHz frequency-domain of small trees are obtained by indoor wideband polarimetric measurement system. The results show that morphological characteristics of vegetation at different frequencies can be obtained by the differential propagation constant of polarized electromagnetic wave. At low frequencies, the plants with structural features presented oriented distribution. However, the plants show random distribution of the echoes at higher frequencies, which is mainly from the canopy. The research provides important information to choose the coherence models employed in the parameters retrieval of vegetations

Climate and environment reconstruction during the Medieval Warm Period in Lop Nur of Xinjiang, China

We made multi-proxy analysis of C-14, grain size, microfossils, plant seeds, and geochemical elements on samples from a profile in the central West Lake of Lop Nur. The grain size suggests relatively stable sedimentary environment around the Medieval Warm Period (MWP) with weak storm effect, which is followed by frequent strong storm events. Abundant microfossils and plant seeds in this stage indicate a warm and humid fresh to brackish lake environment. C, N, and stable elements are high in content in the sediments while Rb/Sr, Ba/Sr, and Ti/Sr are in a steady low level. In addition, plenty of red willows lived here prior to about 700 a B.P., indicating a favorable environmental condition. The results indicate that the environment in Lop Nur and its west bank turned to be favorable at about 2200 a B.P., where the Loulan Culture began to thrive. Then the climate and environment came to be in the good condition in the Tang and Song Dynasties, when the storm effect became weaker, rainfall increased and the salty lake water turned to be brackish to fresh lake water. Hence, limnic biomass increased with higher species diversity

VHF/UHF band antenna measurement using return loss compensation

Abstract -VHF / UHF band antenna measurement is easily influenced by surroundings. Since the bandwidth of antenna is narrow, the corresponding time-domain resolution is low, so it is difficult to eliminate the effect of multipath signals by adding a time domain gating. This paper presents a method which uses the return loss of antennas to compensate the spectrum of signals. The method extends the test bandwidth of antenna and improves the time domain resolution of signals, thus multipath interference signals are more easily to separate. The experiment of a half wavelength dipole antenna is measured in an anechoic chamber, the results show that the method can eliminate the influence of multipath interference; the measured pattern is consistent with the theoretical value

Accumulation capacity of ions in cabbage (Brassica oleracea L.) supplied with sea water

Cabbage seedlings were grown hydroponically to study the effects of different concentrations of seawater on the seedling growth, ion content under one-fourth strength Hoagland's nutrient solution in the greenhouse. The biomass of various organs of cabbage seedlings as well as the whole plants was significantly higher in the treatments with 1 g and 2 g sea salt/L than the no-salt control, but the treatments with 4, 5 or 6 g sea salt/L caused a decrease in growth. Root/shoot ratio remained at the level of control regardless of the sea salt treatment. Na+ and Cl- concentration in different parts of cabbage seedlings increased significantly, whereas K+ and Ca2+ concentration generally increased at low concentrations of sea salt and then decreased with increasing seawater concentration. Sodium and K+ concentrations were significantly higher in the stems than roots and leaves regardless of the sea salt treatment. The sea salt treatment increased Mg2+ concentration in stems and leaves of cabbage seedlings. An increase in Na+ and Cl- concentration in roots, stems and leaves of cabbage seedlings was the main contributor to declining ratios of K+/Na+, Ca2+/Na+ and Mg2+/Na+. The obtained data suggest that cabbage seedlings have strong ability to sustain seawater stress by the regulation of transport and distribution of ions