Applied Mechanics and Materials Vols. 128-129

Abstract: Ferromagnetic steel material is widely used as the bearing carrier in structure, whose stress would influence the entire security. As stress has a notable influence on magnetic characteristic parameters of steel material, with analysis of basic principles, a tubular type magnetic stress sensor is proposed in this paper. We verified the rationality of the magnetic path design with finite element analysis (In FLUX), and proposed a method combined with experiment and simulation to calibrate the output voltage of the sensor. With the comparison of the simulation and experimental results, feasibility of this means is proved, providing a high efficient calibration method of this kind of stress detection sensor, showing a promising marketing value.

Abstract: A fault diagnosis system based on the Client/Server mode is developed, which realizes the purpose of diagnosing the Telemetry Equipment placing on the station address through local or IP network. And the fault method uses the fault tree to describe the logic relation between fault nodes. And the fault tree is realized by virtual instrument. The signal acquisition module uses PXI architecture, the interactive user interface is develops under LabVIEW graphical software and the data storage uses SQL server database platform. The developed fault diagnosis system can realize the functions of information management on instrument and fault node, fault detection or location, and device remote control. Now this system is used in test area, which improves the telemetry equipment maintenance rate.

Abstract: In order to conquer the disadvantages of undetection, misjudgment and low-efficiency in ultrasonic A-scan testing for rotary parts, an ultrasonic automatic imaging system was developed, and automatic scan device was specially designed for rotary parts. Moreover, the testing software was programmed by LabWindows/CVI, which achieves the acquisition and processing of ultrasonic signals, and displays A, B, C, D and P-scan image. On the basis of storing A-scan data and transforming non-isotropic resolution B-scan image into isotropic one, P-scan imaging is realized. Medium filtering was applied to A-scan signal and C-scan image and the Signal-to-Noise is improved. The experimental results show that this system has well achieved numeralization, automatization and imaging of ultrasonic testing.

Abstract: In this paper, based on analysis of the near infrared spectral absorption of methane molecule and considering factors such as compatibility with the transmission characteristics of silica optical fiber and the price, using Fiber Bragg Grating (FBG) filters to replace the the traditional interference filter, a novel kind of all-fiber remote sensor utilizing FBG filters and 1.33μm high power light-emitting diode (LED) was developed for real time measurement of methane gas concentration. FBG has a low insert loss and can be produced easily compared with dielectric interference filters. Theory and experiment proved that the system has simple construct and high sensibility.

Abstract: Image motion and vibration are significant factors influencing image quality of satellite-based TDI camera. In order to learn their effect on TDICCD, motion degradation models at two directions were established. Based on the models, Line spread functions (LSF) for image motion of different types and strict expressions of MTF for abnormal linear image motion were deduced. Modulation transfer function (MTF) for sinusoidal image vibration was calculated through numerical integration. Geometric distortion was evaluated by linear part of phase transfer function (PTF). The results indicate that abnormal linear motion and high frequency vibration cause space-invariant image blur while low frequency vibration brings space-variant image blur and geometric distortion.

Abstract: Infrared and visible image fusion is an important precondition to realize target perception for unmanned aerial vehicles (UAV) based on which UAV can perform various missions. The details in visible images are abundant, while the target information is more outstanding in infrared images. However, the conventional fusion methods are mostly based on region segmentation, and then the fused image for target recognition can’t be actually acquired. In this paper, a novel fusion method of infrared and visible image based on target regions in discrete wavelet transform (DWT) domain is proposed, which can gain more target information and preserve the details. Experimental results show that our method can generate better fused image for target recognition.

Abstract: With the rapid development of interconnected power grid, the phenomenon of power system low-frequency oscillation appears unavoidably. Then, the appearance of wide-area measurement system provided a supporting technology for better scout low-frequency oscillation system and better recognize the oscillation mode . In this paper, the existing oscillation mode identifying methods are analyzed from the viewpoint of calculation speed, criterion, calculation accuracy, etc. Mainly compared the applicability of two methods, Prony and ESPRIT . Based on the above research, a new idea of monitoring power system low frequency oscillation based on WAMS is put forward in this paper.

Abstract: Since joint transform correlator (JTC) cannot directly detect the displacement between reference and target images without adequate exposure, an image displacement detection method using JTC based on log-Gabor wavelet denoising is proposed. The method uses a log-Gabor wavelet transform to denoise the reference and the target image obtained in the condition lack of enough exposure, preserving the phase information of them. Results show that the method can successfully accomplish the motion detection, RMSE of displacement measurement using JTC with wavelet denoising could be within 0.3 pixels under 1/80 of normal exposure. The method improved the detection ability of JTC in the condition of low illumination and low contrast, and has great application prospect under these circumstances.

Abstract: Mid-infrared lasers are very suitable for high-sensitive trace-gases detection for their wavelengths cover the fundamental absorption lines of most gases. Quantum-cascade (QC) lasers have been demonstrated to be ideal light sources with its special power, tuning and capability of operating in room-temperature. All these merits make it appropriate for the high resolution spectrum analysis. The absorption spectrum monitoring technology based on the QC laser pulsed operating in the room temperature, combining with the strong absorption of the gas molecule in the basic frequency, has become an effective way to monitor the trace gas with the characteristic of high sensitivity, good selectivity and fast response. In this paper, the inter-pulse spectroscopy based on a room-temperature distributed-feedback pulsed QC laser was introduced. Our approach to trace gas monitoring with QC lasers relies on short current pulses which are designed to produce even shorter light pulses. Each pulse corresponds to a single point in a spectrum. The N₂O absorption spectrum centered at 2178.2cm^-1 was also obtained.

Abstract: By using a four port Vector Network Analyzer (VNA), a caesium clock, a time-interval counter and a signal source to measure the delay of CEI system segmentally. Design measuring methods respectively for three segments of the circuit. When measure the delay, it is found that, delay of antenna’s amplifier output port to the input port of down converter (DC) is stable; the fluctuation of DC’s delay is less than 2ns; the cable delay’s standard deviation is stable at 0.1ns; we get a nanosecond accuracy for whole system. The methods of time delay measurement and the design of CEI system will provide a foundation and primary data for future deep space missions.