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Issue 7 ， 2022
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Fiber Bragg grating probe system with picometer-level micro-displacement signal processing resolution
Abstract：To measure micro-displacement with ultra-high resolution， a high sensitivity probe system based on fiber Bragg grating（FBG） sensing was established and static phase-locked amplification was studied. According to the principle of FBG sensing， the structure of a dual grating self-compensating demodulation system was designed for high sensitivity. Then， based on the signal characteristics， the static phase-locked amplification technique was studied for real-time detection and processing of weak measurement signals. Finally， the system performance parameters including sensitivity and resolution were obtained through the performance experiment. The experimental results show that the micro-displacement measurement range of the probe system in the contact region is approximately 1 μm， the sensitivity is -15.33 mV/nm， the mean value of the short-term noise range is 0.83 mV， the standard deviation is 0.32 mV， the signal processing resolution is approximately 0.06 nm（60 pm），and the standard deviation is 0.02 nm（20 pm）. Hence， the micro-displacement signal processing resolution of this FBG system reaches the picometer level. In addition， the system meets the requirements of strong anti-interference， good repeatability， and low cost.Keywords：Fiber Bragg Grating（FBG）;Micro-displacement measurement;signal processing resolution;picometers level;high-sensitivity probe system;static phase-locked amplification- 259
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Published：2022-04-22 -
Calibration of VUV spectroradiometers for space exploration
Abstract：The calibration method used for spectral radiance of the vacuum ultraviolet band （115-200 nm） was studied to calibrate the radiation parameter of VUV radiometer at 115 nm. Two calibration methods were designed to solve the following problems： low uniformity of calibration source， long value transfer chain， and insufficient lower limit of calibration band. In the method based on standard diffuse reflectors， the VUV bidirectional reflectance distribution function/bidirectional transmittance distribution function （BRDF/BTDF） measurement standard component was developed to measure the lowest wave band at 115 nm. In the method based on standard radiometer， the standard design method of spectral radiance transfer was proposed， and the experimental verification was completed with a field angle of 2°. A new preparation method of a standard vacuum ultraviolet diffuse transmitter was proposed and its measurement was carried out， revealing good Lambert characteristics in the range of ±10°. The calibration devices were developed and the value transfer chain and measurement uncertainty were analyzed， revealing a reduced BRDF measurement uncertainty component with better measurement uncertainty. A calibration test of payload on FY satellite was carried out using the calibration device. The uncertainty of spectral radiance measurement in the range of 115-200 nm is 12%（k=2）， and the payload runs well in orbit. This research on the calibration method and VUV spectroradiometer is of great significance to the research and application of VUV space exploration technology.Keywords：ultraviolet remote sensing;vacuum ultraviolet;spectral radiance;diffuse transmission;calibration;uncertainty of measurement- 131
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Published：2022-04-22 -
Broadband frequency selective surface based on composite coupling structure
Abstract：To meet the requirements of low profile and broadband frequency selective surface （FSS） structure with stable transmission characteristics， a novel broadband FSS based on composite coupling structure was proposed. Based on the phase-amplitude modulation between adjacent periodic sub-units， a novel broadband FSS model was established. Subsequently， its electromagnetic transmission characteristics and the influence of the scanning angle on its electromagnetic transmission characteristics were calculated using full-wave numerical simulations. Finally， an FSS prototype of 500 mm× 500 mm was fabricated using the printed circuit board （PCB） technology and tested using the free space method. The experimental results show that the proposed FSS structure has stable broadband characteristics， and its bandwidth at -3 dB is 8.85 GHz. The top of the stopband is flat and its edge is steep. The FSS also shows good incident angle stability. Based on phase-amplitude modulation theory， a novel method to broaden the working bandwidth of FSS is proposed. The novel broadband FSS structure designed by this method has potential engineering significance.Keywords：Frequency Selective Surfaces（FSS）;composite coupling;wide stopband;electromagnetic transmission characteristic- 96
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Published：2022-04-22
Modern Applied Optics
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Development of rotating magnetic field device for vector atomic magnetometers
Abstract：The working principle and system composition of a vector atomic magnetometer was introduced， which was based on the magnetic field rotation modulation method and a pump-probe atomic magnetometer， and the technical requirements of such a system was dicussed. According to the identified technical requirements， a technical scheme for the rotating magnetic field was proposed. In this scheme， phase compensation and precise regulation between sinusoidal signals were realized based on DDS phase synchronization technology. The theoretical design value of the phase regulation accuracy is 0.022°. By establishing the corresponding circuit model and performing simulation analysis and research on the coupling relationship of multiple modules， a current regulation module based on multi-module cooperative control was designed for precise control and adjustment of the current of the coil driving circuit. When the rotating magnetic field is 500 nT， the adjustment accuracy of the magnetic intensity is greater than 5 nT. The above design enables the rotating magnetic field generator to achieve precise control and adjustment of the intensity， trajectory， and direction of the rotating magnetic field. The rotating magnetic field generator provides a technical foundation for the research and development research of vector atomic magnetometers. At the same time， the rotating magnetic field generator also has important application value in metallurgy， life science， and basic physics research.Keywords：Vector atomic magnetometer;rotating magnetic field generator;precise regulation of magnetic field;DDS phase synchronization- 141
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Published：2022-04-22 -
Acceleration and deceleration combined with look-ahead control of laser processing machine tools for engine connecting rod cracking groove
Abstract：To improve the processing efficiency of laser processing machine tools for engine connecting rod cracking grooves， a method of combining the look-ahead control algorithm with the S-curve acceleration and deceleration of the CNC system was proposed. Through the introduction of the commonly used S-curve acceleration and deceleration algorithm for high-end CNC systems， the original seven-stage process was simplified into five stages. Next， the look-ahead control theory was introduced and applied to the S-curve acceleration and deceleration algorithm. The theory was used to plan the speed in advance before the speed change point， and the displacement， speed， and acceleration in the S-curve acceleration and deceleration algorithm were all transformed into discrete changes in cycles. Finally， the improved algorithm was transferred to the CNC system. The simulation results show that the application of the improved algorithm shortens the time for the system to reach a steady state after changing speed by 0.4 s， and the maximum overshoot is only 80% of the original. The experimental results show that， for various types of connecting rods， the depth of the cracking grooves are approximately the same （the groove depth tolerance of each point on the cracking groove is ±0.02 mm） and there is no overcut or residue， indicating that this method considerably improves the stability， speed and precision of the laser processing machine tools.Keywords：laser processing;connecting rod;cracking groove;S-type curve acceleration and deceleration;look-ahead algorithm- 94
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Published：2022-04-22 -
Computer-aided alignment for large-aperture off-axis three mirrors optical system with artificially random air flow
Abstract：Airflow disturbance becomes critical to wavefront measurements in large-aperture and long focal length optical systems. Hence， airflow disturbances have significant impact on the efficiency and quality of optical alignment. To solve this problem， a method based on an active random air supply is proposed to suppress the influence of air flow disturbances on wavefront measurements. The experimental results show that the standard deviations of the obtained Zernike coefficients are reduced to below 0.01 from 0.04 due to the active random air supply. Furthermore， an off-axis three-mirror anastigmat telescope whose clear aperture is 0.5 m and focal length is 6 m is aligned when random air is actively supplied. After two rounds of computer-aided alignment， the mean RMS of the wavefront error of the optical system is reduced to 0.086λ from 0.49λ， which meets the requirements of the system image quality index. Evidently， the influences of airflow disturbance on wavefront measurements in large aperture and long focal length optical systems can be effectively suppressed by an active random air supply， which is critical to optical alignment in terms of efficiency and quality. This study is of great significance for developing large aperture optical systems.Keywords：computer-aided alignment;off-axis three-mirror optical system;active random air supply;optical system with large aperture;airflow disturbance- 142
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Published：2022-04-22 -
Single point diamond turning and compensation for micro-lens array
Abstract：To improve the efficiency and consistency of machining micro-lens arrays using single point diamond turning， a theoretical model of surface residuals was proposed in this study. A compensation method for the model was then studied. The micro-lens array was regarded as a freeform surface. The radius of curvature at each cutting point along the cutting direction was calculated by establishing an slow slide servo （SSS） cutting model. Combined with the tool equivalent tilt angle and lathe delay models， the theoretical surface residuals of the freeform array in SSS were obtained. Subsequently， the actual surface residuals were measured and processed using in situ measurement. The theoretical and measured surface residuals were then compared and the surface residuals were compensated for in the machining program. The theoretical surface residuals are consistent with the actual ones， with an error range of ［-0.7 μm，0.3 μm］. The peak to valley （PV） value is reduced from 5.4 μm to 0.6 μm after compensation. Therefore， the single point diamond turning and compensation method presented in this study is able to predict the surface residuals and significantly improve machining accuracy and consistency.Keywords：ultra-precision fabrication;micro-lens array;single diamond turning;slow slide servo;in situ measurement;machining compensation- 157
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Published：2022-04-22
Micro/Nano Technology and Fine Mechanics
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Extraction method for fluorescence information from droplet digital PCR images
Abstract：Droplet digital polymerase chain reaction （ddPCR） is one of the main methods used in nucleic acid detection. Counting the droplets in ddPCR experiments can be difficult if the number of droplets is too high or low， the fluorescence intensity is uneven， or the droplets are too closely arranged. We propose an image analysis method in which the image information is collected via the gray traversal method and droplets are classified and counted by differential analysis. Noise is removed from the image using the convolution algorithm， and the gray contrast of the image is enhanced by gray distribution equalization. The image is then converted to binary form by the gray traversal method with the geometric conditions taken as screening conditions， and the number of droplets is counted by differential analysis. Experiments with human gDNA （genomic DNA） as a detection sample， with approximately 20 000 droplets， showed an average detection accuracy of 99.36 % as compared to those conducted using commercial instrument algorithms or similar， with an average improvement of 2.24 % and 2.53 %， respectively， in the detection accuracy. The developed method can therefore be considered to provide reliable results and is suitable for use in ddPCR experiments.Keywords：fluorescent spot detection;droplet digital PCR;nucleic acid detection;image processing;image analysis- 275
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Published：2022-04-22 -
Stereo matching based on urban satellite remote sensing image pair
Abstract：To solve the problem of poor stereo matching effect owing to numerous shadows and disparity step regions in urban satellite remote sensing images， a stereo matching algorithm suitable for urban remote sensing image pairs was proposed. The matching cost function， cost aggregation method， disparity， and optimization method used by the algorithm were investigated. First， the matching cost function was improved and the multi-order weighted census algorithm was used to reduce the influence of noise and other factors. Subsequently， the constraints of the building edge information were added to the cost aggregation. Finally， regarding disparity refinement， the disparity map was optimized by fully considering the characteristics of urban building morphology. The experimental results show that on the Middlebury dataset， the accuracy of this algorithm is 4.54% higher than that of the classic SGM algorithm. On the WorldView-2 stereo image pair in the urban area， the variance of the building roof elevation is 0.71. The requirements to obtain high-precision disparity maps are met based on urban satellite remote sensing images and good conditions for urban three-dimensional reconstruction are provided.Keywords：satellite remote sensing;urban remote sensing image;census transform;edge constraint;disparity optimization;stereo matching- 135
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Published：2022-04-22 -
Semantic segmentation of 3D point cloud based on self-attention feature fusion group convolutional neural network
Abstract：The existing algorithms ignore the profound relationship between global single point features and local geometric features. This results in the lack of discriminative captured local geometric information and increases the difficulty of effectively identifying complex shape categories. This paper proposes a semantic segmentation algorithm for three-dimensional point clouds based on a self-attention feature fusion group convolutional neural network. First， the proxy point graph convolution of lightweight network is designed to extract the local geometric features of the point cloud. Then， the group convolution operation is added to reduce the amount of calculation and complexity and enhance the richness of features with less redundant information. Second， the feature information exchange between different branches is carried out through the Transformer module to ensure mutual compensation between the global and local geometric features and to enhance the completeness of features. Then， the underlying semantic features of the point cloud are fused with the original point cloud to expand the local neighborhood perception field and obtain high-level context semantic information. Finally， the features are input into the segmentation module to complete fine-grained semantic segmentation. The experimental results show that the segmentation accuracy reaches 79.3% and 56.6% in the S3DIS and SemanticKITTI datasets， respectively. This algorithm can extract the key feature information from a 3D point cloud using fewer network parameters and exhibits high robustness of semantic segmentation.Keywords：three-dimensional point cloud;semantic segmentation;graph convolution;group convolution- 169
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Published：2022-04-22 -
Vehicle pressure line detection based on improved Mask R-CNN + LaneNet
Abstract：To address the problem of vehicle pressure line detection of on-board images in the field of assisted or automatic driving， as well as the problem of missed and false detection caused by underexposure， shadow， or solid occlusion in the detection process， a vehicle pressure line detection algorithm based on improved Mask R-CNN and LaneNet was proposed. In terms of network optimization， based on the Mask R-CNN network， the image scaling algorithm （bilinear interpolation） of the ROI alignment layer was improved to bicubic interpolation， and the convoluted VGG16 network of a full connection layer was replaced by LaneNet's E-Net shared decoder. For image enhancement， the Gamma correction algorithm was improved to realize the automatic correction of underexposed images. In terms of training data， the vehicle target in the Tusimple data set was marked， and the data were enhanced in the network training process， based on the improved random erasing algorithm. The experimental results show that while the vehicle detection speed remains unchanged， the lane line detection speed is increased by 28%， and the vehicle missed and false detection rate are reduced by 38.93% and 89.04%， respectively. Further， the lane line missed and false detection rate are reduced by 67.21% and 87.05%， respectively. The achieved performance index can meet the requirements of vehicle line pressing judgement method.Keywords：image correction;instance segmentation;lane line detection;data enhancement;line pressing detection- 151
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Published：2022-04-22 -
Infrared small target detection using tri-layer template local difference measure
Abstract：Current algorithms suffer from high false alarm rates and poor real-time performance in complex backgrounds. Therefore， a single-frame infrared small target detection algorithm based on the tri-layer template local difference measure was proposed. A tri-layer template was constructed. Then， by making full use of the disparity in grayscale distribution between different layers， a tri-layer template local difference measure combining the grayscale difference and grayscale variance measures was proposed， which simultaneously achieved target enhancement and background suppression. Finally， an adaptive threshold segmentation method was applied to extract the targets from the saliency map. The experimental results show that the proposed algorithm only needs to traverse the image by a fixed-scale tri-layer template to detect targets with different sizes. This not only avoided the increase in complexity caused by multi-scale operation， but also prevented missed detection caused by regional overlap. Eight methods were operated on the public dataset SIRST. The experimental results show that the signal to clutter gain and background suppression factor of the proposed algorithm are improved by 7.7 times and 3.9 times on average， respectively. In addition， the proposed algorithm achieves better real-time performance compared to existing algorithms.Keywords：target detection;infrared small target;regional overlap;tri-layer template;local difference measure- 192
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Published：2022-04-22
Information Sciences
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