A new method for defect recognition of foam sandwich structure composites based on morphological filtering is proposed in this paper. Firstly, the terahertz frequency modulated radar imaging system is used to detect the foam sandwich structure composites to obtain the original detection signal, and the original detection image is obtained by using amplitude imaging method. Secondly, the original detection images are transformed to binary images by setting threshold values. Thirdly, based on the morphological filtering theory we carry out closing operation to fill the inner tiny holes in the binary images, and connect the discontinuous adjacent targets. Finally, the opening operation is used to remove the redundant small objects in the image, and obtain the final detection result image. In this paper, the imaging detection of polymethacrylimide foam sandwich structure composites is carried out, and the original detection signal is processed by using the above method, the resulting images with the prefabricated defect effectively recognized is obtained.The accuracy of the proposed method for defect recognition is evaluated by calculating and comparing the error ratio of the defect area in the processed image and the original detection image relative to the actual defect area.The results show that the proposed method can effectively recognized the prefabricated defects in foam sandwich structure composites and optimize the size of the defects to be close to the actual defects, which is conducive to the further application of terahertz nondestructive testing technology in foam sandwich structure composites.
A recently developed 220GHz incoherent radar has potential for remote sensing of low reflectivity atmosphere targets in
Cloud Chamber. Stepped frequency system is used and bandwidth 10GHz. Preliminary reflectivity measurements of
clouds for ranges between 0.2m~4m in narrow Cloud Chamber. The instrument is briefly described. Highlighting
uncertainties due to highly variable attenuation and signal interference. Then the results of investigations of the
transmitter, receiver, Antennas, as well as the atmospheric Propagation Effects are presented. The results of this effort
demonstrate that the radar is a stable, sensitive, system capable of providing accurate power for clouds.
Stepped frequency pulses can be applied in Terahertz radar system, which has been proven by simulation.
The stepped frequency THz radar can provide centimeter accuracy. The theory of stepped frequency pulse
imaging is introduced, and the model is set up. According to the range-doppler algorithm, some results can
be got. At last, The THz imaging system is designed.
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