In the military and civil fields, detecting small aircraft is of great significance. In recent years, the rapid development of LiDAR technology has made it possible to detect small aircraft at long distances. However, the scale change and attitude change make the detection difficult. Therefore, a detection network of multi-attitude small aircraft based on LiDAR anchorfree is proposed in this paper. The network structure is improved on the basis of the CenterNet network; using the encoder-decoder network structure, the extended convolutional module is designed to improve the receptive field and obtain the multi-scale information of the object. The IOU sensing branch is added to the detection header of the network to improve the localization accuracy of the object. The experimental results show that the detection accuracy of the improved network on the self-built simulation data set is 2.12% higher than that before the improvement and finally reaches 92.45%. Therefore, using this method can effectively improve the detection accuracy of the object.
A hybrid structure sensor is proposed for curvature and strain measurement. The sensor is fabricated by cascading the Michelson interferometer (MI) based on the up-taper and the Fabry-Perot interferometer (FPI) based on the air cavity. The MI is sensitive to curvature, and the FPI is sensitive to strain. Therefore, the cascade of sensing structures can realize the simultaneous measurement of curvature and strain. The curvature and strain sensitivity of the sensing structure are 2.59 nm/m-1 and 1.63 pm/με, respectively. The cascade of the FPI and the MI enables the end face of the MI to be effectively encapsulated, avoiding the crosstalk of external factors. The hybrid structure sensor has the advantages of simple structure, low cost, and easy preparation. The structure has the potential to be applied to structural health detection and biomedicine.
A vector curvature sensor based on a single fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The sensor is easily fabricated by encapsulating an FBG on a thin steel plate with ultraviolet glue. When the FBG deviates from the neutral plane, its effective refractive index and grating constant are changed by bending, therefore, the sensor can realize curvature measurement. Due to the opposite stress direction on the two sides of the neutral plane during bending, the sensor can realize vector measurement of curvature. The curvature sensitivity of the sensor in convex and concave bending is 558.42 pm/m-1 and -818.09 pm/m-1, respectively. This sensor has the advantage of simple structure, low cost, and easy industrial production. It has potential applications in engineering health monitoring and deformation measurement.
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