Applied Mechanics and Materials Vols. 475-476

Abstract: A microscope to image weak magnetic fields using a low-temperature superconducting quantum interference device (SQUID) had developed with a liquid helium consumption rate of ~0.5L/hour. The gradient pickup coil is made by a low-temperature superconducting niobium wire with a diameter of 66 μm, which is coupled to the input circuit of the SQUID and is then enwound on the sapphire bobbin. Both of the pickup coil and the SQUID sensor are installed in a red copper cold finger, which is thermally anchored to the liquid helium evaporation platform in the vacuum space of the cryostat. To reduce the distance between the pickup coil and sample, a 100 μm thick sapphire window is nestled up to the bottom of the cryostat. A three-dimensional scanning stage platform with a 50 cm Teflon sample rack under the sapphire window had the precision of 10 μm. To test the fidelity of the new facility, the distribution of the magnetic field of basalt slice specimens was determined. Results show that the spatial resolution of the newly-designed facility is 500 μm with a gradient magnetic field sensitivity of 380 fT. This opens new opportunities in examining the distribution of magnetic assemblages in samples, which bear great geological and geophysical information.

Abstract: An on-line monitoring system was proposed to monitor lubrication oil real-time condition. Oil is the machine equipment blood, and its condition has very serious influence on machine running. Firstly, this paper expiated the research significance of on-line oil monitoring. Then the key problem of on-line oil monitoring was discussed and its goal was analyzed. Furthermore, basic research content and research thread were put forward. Based on the modern photoelectric detection, microscopic imaging and computer image processing technology, an on-line acquisition system of lubricating oil particle image was proposed. This work provides a new research idea for on-line monitoring system which is important to develop the technology of oil condition monitoring.

Abstract: The UHF radiation field generated by corona discharge of the two 500kV AC transmission lines was tested. The influencing factors of radiation field, including climate, bundle conductors number and test distance, were analyzed. Test results indicate that the field continuously arranges from 200MHz to 700MHz, mainly from 200MHz to 500MHz. The maximal measurement distance is 300 meters. The climate and bundled conductors number affect the radiation field obviously. The discharge will become intense when the temperature and humidity increase and bundle conductors number decays. The peak values of the electric field strength which decay rapidly with the distance increasing, can arrive several hundreds uV/m. The test results rich the UHF radiation field data and offer references to testing and evaluating the electromagnetic interference generated by corona discharge of ultra-high voltage transmission lines.

Abstract: In the electronic measurement field, how to measure the open-loop amplitude frequency characteristics of the amplifier automatically is a question to be overcame. And now , the system ,which under the integrated development environment that the virtual instrument software LabVIEW provides, to measure the open-loop amplitude frequency characteristics of the amplifier is developed by combining the modern electronic measurement technology and computer data processing technology. The virtual signal generator which is based on the data acquisition card, signal acquisition, correlation analysis, frequency response analysis, etc is included in the system. This design mainly includes the hardware circuit and the software program. The hardware circuit consists of the low noise preamplifier, measured operational amplifier, data acquisition card, power supply, computer, etc. Modular design is adopted in the software part, which includes the design of soft panel, signal generation, collection and analysis module. The advantages of the virtual instrument, such as the digital signal processing, waveform data automatic storage, graphical programming, are fully used in the modern electronic measurement. Simple structure, low cost, high level of test automation are its characteristics.

Abstract: In a probe calibration facility employing the TEM cell as the field generator, a method to calculate the net power delivered into the TEM cell is presented through monitoring the coupling power of the directional coupler. The new formula requires the effective reflection coefficient of the dual coupler and takes into consideration the directivity of the coupler, the mismatch between the coupler and the TEM cell, the mismatch between the power sensor and the coupling port of the coupler. The formula can provide sufficient accuracy in calibration purpose application using a TEM cell with a coupler combined with power sensors to monitor the net power.

Abstract: Identification of radar clutter model is one important step to choose optimum CFAR processor in radar signal detection, and Anderson-Darling (AD) goodness-of-fit test considered the practical and effective way under small sample size. As K distribution is a complex model providing suitable description for the amplitude of microwave sea clutter, the research on K distribution in AD test is useful but very difficult. Moment-based methods are widely used to estimate parameters of K distribution and comparison show that methods with lower moments are more accurate. Further in AD test, the influence of shape parameter on critical value (CV) for K distribution is presented. Taking it into account, tables of AD test results using varied critical value advanced in our study and fixed critical value proposed in previous research are shown based on Monte Carlo simulations.

Abstract: Marine underwater electromagnetic field plays an important role in the prediction of the marine disasters, such as earthquake and tsunami. A detection method for the weak marine electromagnetic anomalous signatures generated by the earthquake and tsunami is presented. In order to implement the anomalous signal detection, the ocean current meter and tidal wave meter are integrated into the marine environmental underwater electromagnetic field measurement system, and the electromagnetic field data and environmental data such as sea current and wave height can be measured synchronously. The measured environmental data should be used to construct the prediction model of marine underwater electromagnetic field induced by the sea motion. Based on the prediction model, the theoretical values of electromagnetic field induced by the sea motion are estimated. This real signature induced by the sea motion can be extracted from the measured underwater electromagnetic data by use of the coherent filter method, and the remaining anomalous signature can be used to analyze the earthquake and tsunami phenomenon.

Abstract: Drilling samples of lunar soil is an important and indispensable part of Chinas lunar exploration project. The drill bit temperature during the drilling process is one of the key concerns for scholars, especially for the hard lunar rock drilling in vacuum environment. In this article, a fiber grating temperature measurement system integrated with vacuum drilling system is established. Experiment on simulated lunar rock in atmospheric and vacuum environments is taken out and compared.

Abstract: The Yellow River is the muddiest major river in the world. It has thick bottom sediment and its water has low light transmittance, which can make sound signal, laser, radio waves through it attenuated and communication distance in its waters limited. So it is unable to meet the communication requirements of the underwater survey. In order to solve the problem, based on the electrical conductivity of water, an idea of underwater communication using current field was proposed, a model of underwater current field communication channel was also made according to electromagnetic field theory. The relationship among the received signal, transmitting voltage, communication distance and other parameters were analyzed. Underwater current field communication devices were then developed. It was proved by test that the bi-way underwater communication of such devices was correct, reliable, and easy to perform, thus a practical and feasible communication means for the underwater survey in the Yellow River silt layer was provided.