Search Results (188)

Silicon Photomultipliers (SiPMs) are optical sensors widely used in space applications due to their high photon detection efficiency, low power consumption, and robustness. However, in Low Earth Orbit (LEO), their performance degrades over time due to prolonged exposure to ionizing radiation, primarily from trapped protons and electrons. The dominant radiation-induced effect in SiPMs is an increase in dark current, which can compromise detector sensitivity. This study investigates the potential of thermal annealing as a mitigation strategy for radiation damage in SiPMs. We designed and tested PCB-integrated heaters to selectively heat irradiated SiPMs and induce recovery processes. A PID-controlled system was developed to stabilize the temperature at 100 °C, and a remotely controlled experimental setup was implemented to operate under irradiation conditions. Two SiPMs were simultaneously irradiated with 9 MeV protons at the EDRA facility, reaching a 1 MeV neutron equivalent cumulative fluence of (9.5 ± 0.2) × 10⁸ cm⁻². One sensor underwent thermal annealing between irradiation cycles, while the other served as a control. Throughout the experiment, dark current was continuously monitored using a source measure unit, and I–V curves were recorded before and after irradiation. A recovery of more than 39% was achieved after only 5 min of thermal cycling at 100 °C, supporting this recovery approach as a low-complexity strategy to mitigate radiation-induced damage in space-based SiPM applications and increase device lifetime in harsh environments. Full article

Stellar radiation simulation is critical in the space industry; however, with the current simulation methods, only a single color temperature and magnitude can be modulated at a time. Furthermore, star sensors rely on star observation tests for accurate calibration; this seriously restricts their development. This paper presents a novel star spectral information multi-partition mapping simulation method to closely simulate real sky star map information, thus replacing non-scenario-specific field stargazing experiments. First, using the stellar spectral simulation principle, a multi-partition mapping principle based on a digital micro-mirror device is proposed, and the theoretical basis of sub-region division is provided. Second, multi-component mapping simulation of stellar spectral information is expounded, and a general architecture for the same based on a double-prism symmetry structure is presented. Next, the influence of peak spectral half-peak width and peak interval on spectral simulation accuracy is analyzed, and a pre-collimated beam expansion system, multi-dimensional slit, and spectral splitting system are designed accordingly. Finally, a test platform is set up, and single-region simulation results and multi-region consistency experiments are conducted to verify the feasibility of the proposed method. Our method can realize high-precision simulation and independently control the output of various color temperatures and magnitudes. It provides a theoretical and technical basis for the development of star sensor ground calibration tests and space target detection light environment simulation. Full article

Millimeter-wave antennas have become more important recently due to the diversity of applications in 5G and upcoming 6G technologies, of which automotive systems constitute a significant part. Two crucial indices, detection range and angular resolution, are used to distinguish the performance of the automotive antenna. Strong gains and narrow beamwidths of highly directive radiation beams afford longer detection range and finer spatial selectivity. Although conventionally used, patch antennas suffer from intrinsic path losses that are much higher when compared to the waveguide antenna. Designed at 77 GHz, presented in this article is an 8-element slot array on the narrow side wall of a rectangular waveguide, thus being readily extendable to planar arrays by adding others alongside while maintaining the element spacing requirement for grating lobe avoidance. Comprising tilted Z-shaped slots for higher gain while keeping constrained within the narrow wall, adjacent ones separated by half the guided wavelength are inclined with reversed tilt angles for cross-polar cancelation. An open-ended external waveguide is placed over each slot for polarization purification. Equivalent circuit models of slotted waveguides aid the design. An approach for sidelobe suppression using the Chebyshev distribution is adopted. Four types of arrays are proposed, all of which show potential for different demands and applications in automotive radar. Prototypes based on designs by simulations were fabricated and measured. Full article

Seismic exploration is widely used in shallow engineering applications, yet extracting reflected wave information remains challenging due to contamination from Rayleigh waves. To overcome this, we propose a common shot point time-domain differential method that leverages the distinct velocity contrast between slow Rayleigh waves and faster P-wave reflections. These waves exhibit lower velocity and minimal dispersion in the radiation direction under the same seismic source excitation. This study establishes two closely spaced track records termed “far main and near slave” along the direction of the measurement line to counteract this interference. This method employs the difference in travel time between Rayleigh waves and subsurface interface reflection waves for time-domain differential analysis. The interference is minimized while preserving the reflected wave signal by conducting slight amplitude compensation on the far-field Rayleigh wave signal and subtracting the master and slave records. The application of time-domain differential detection technology in shallow engineering seismic exploration and marble plate thickness detection experiments demonstrated that this method effectively eliminates the influence of Rayleigh surface waves and enhances the resolution of reflection signals from anomalous bodies. Additionally, this study examines the impact of boundaries on time-domain differential technology. Without relying on long array shot records, this approach provides a promising result for Rayleigh wave suppression and offers broad potential in elastic wave exploration. Full article

Satellites traversing highly elliptical orbits (HEOs) encounter more severe radiation effects caused by the space particle environment, which are distinct from those in a low Earth orbit (LEO), medium Earth orbit (MEO), and geostationary orbit (GEO). This study proposed a space environment detection payload technology for assessing the particle radiation environment in HEOs. During ground tests, all technical indicators of the detection payload were calibrated and verified using reference signal sources, standard radioactive sources, and particle accelerators. The results indicate that the space environment detection payload can detect electrons and protons within the energy ranges of 30 keV to 2.0 MeV and 30 keV to 300 MeV, respectively, with an accuracy greater than 10%. The detection range of the surface potential spans from −11.571 kV to +1.414 kV, with a sensitivity greater than 50 V. Furthermore, the radiation dose detection range extends from 0 to 3.38 × 10⁶ rad (Si), with a sensitivity greater than 3 rad (Si). These indicators were also validated through an in-orbit flight. The observation of the particle radiation environment, radiation dose accumulation, and satellite surface potential variation in HEOs can cover space areas that have not been addressed before. This research helps fill the gaps in China’s space environment data and promotes the development of a space-based environment monitoring network. Full article

Space resources are of economic and strategic value. Infrared (IR) remote sensing, unaffected by geography and weather, is widely used in weather forecasting and defense. However, detecting small IR targets is challenging due to their small size and low signal-to-noise ratio, and the resulting low detection rates (DRs) and high false alarm rates (FRs). Existing algorithms struggle with complex backgrounds and clutter interference. This paper proposes an adaptive differential event detection method for space-based aerial target observation, tailored to the characteristics of target motion. The proposed IR differential event detection mechanism uses trigger rate feedback to dynamically adjust thresholds for strong, dynamic radiation backgrounds. To accurately extract targets from event frames, a lightweight target detection network is designed, incorporating an Event Conversion and Temporal Enhancement (ECTE) block, a Spatial-Frequency Domain Fusion (SFDF) block, and a Joint Spatial-Channel Attention (JSCA) block. Extensive experiments on simulated and real datasets demonstrate that the method outperforms state-of-the-art algorithms. To advance research on IR event frames, this paper introduces SITP-QLEF, the first remote-sensing IR event dataset designed for dim and moving target detection. The algorithm achieves an mAP@0.5 of 96.3%, an FR of 4.3 $\times {10}^{-5}$, and a DR of 97.5% on the SITP-QLEF dataset, proving the feasibility of event detection for small targets in strong background scenarios. Full article

Today’s highly complex and rapidly changing electromagnetic environment places higher demands on the precise localization of illegal radiation sources. In response to this, this paper innovatively proposes a multi-station fusion-based radiation source localization method, which leverages the frequency, field strength, bandwidth, and other characteristic information embedded in frequency band scanning data. The method thoroughly explores the energy characteristics of the detected radiation sources while closely integrating the objective laws of propagation attenuation in electromagnetic space. By employing an advanced, normalized power calculation technique, it successfully achieves high-precision localization of the radiation source. Through rigorous and thorough experimental validation, this method reduces localization errors by 25% and cuts the equivalent radiation power error by 30% compared to traditional localization methods. This achievement provides more reliable and accurate technical support for applications in the electromagnetic field, offering promising prospects for advancing and refining electromagnetic environment monitoring and management technologies. Full article

This paper presents a space-based limb-imaging spectrometer (LIS) for detecting atmospheric O₂ airglow; it scans the atmosphere with a vertical range of 10–100 km and has a vertical resolution of 2 km. The LIS’s detection performance needs to be examined before launch. A forward radiative transfer model (RTM) of airglow is studied to determine the airglow emission intensity. Spectral and radiation calibration is conducted to obtain the response parameters. Based on the airglow emission intensity, calibration results, and airglow spectral lines, the LIS’s simulated spectra are obtained, and then an optimal estimation inversion method for the LIS is studied. The results show that the LIS’s spectral range is 498.1 nm–802.3 nm, with a spectral resolution of 1.38 nm. Simulation results show that the LIS can detect airglow emission spectral lines, which characterize their dependence on temperature. The digital number response value is 20% to 50% of the saturation value. An inversion error analysis shows that, when the signal-to-noise ratio (SNR) of the LIS is 1000 and the prior temperature error is 10%, the inversion errors are 6.2 and 3 K at 63 and 77 km, respectively. This study shows that the LIS can achieve good SNR detection for airglow. Full article

With the rapid development of radio technology and its widespread application in the military field, the electromagnetic environment in which radar communication operates is becoming increasingly complex. Among them, human radio interference makes radar countermeasures increasingly fierce. This requires radar systems to have strong capabilities in resisting electronic interference, anti-radiation missiles, and radar detection. However, array antennas are one of the effective means to solve these problems. In recent years, array antennas have been extensively utilized in various fields, including radar, sonar, and wireless communication. Many evolutionary algorithms have been employed to optimize the size and phase of array elements, as well as adjust the spacing between them, to achieve the desired antenna pattern. The main objective is to enhance useful signals while suppressing interference signals. In this paper, we introduce the dandelion optimization (DO) algorithm, a newly developed swarm intelligence optimization algorithm that simulates the growth and reproduction of natural dandelions. To address the issues of low precision and slow convergence of the DO algorithm, we propose an improved version called the chaos exchange nonlinear dandelion optimization (CENDO) algorithm. The CENDO algorithm aims to optimize the spacing of antenna array elements in order to achieve a low sidelobe level (SLL) and deep nulls antenna pattern. In order to test the performance of the CENDO algorithm in solving the problem of comprehensive optimization of non-equidistant antenna array patterns, five experimental simulation examples are conducted. In Experiment Simulation Example 1, Experiment Simulation Example 2, and Experiment Simulation Example 3, the optimization objective is to reduce the SLL of non-equidistant arrays. The CENDO algorithm is compared with DO, particle swarm optimization (PSO), the quadratic penalty function method (QPM), based on hybrid particle swarm optimization and the gravity search algorithm (PSOGSA), the whale optimization algorithm (WOA), the grasshopper optimization algorithm (GOA), the sparrow search algorithm (SSA), the multi-objective sparrow search optimization algorithm (MSSA), the runner-root algorithm (RRA), and the cat swarm optimization (CSO) algorithms. In the three examples above, the SLLs obtained using the CENDO algorithm optimization are all the lowest. The above three examples all demonstrate that the improved CENDO algorithm performs better in reducing the SLL of non-equidistant antenna arrays. In Experiment Simulation Example 4 and In Experiment Simulation Example 5, the optimization objective is to reduce the SLL of a non-uniform array and generate some deep nulls in a specified direction. The CENDO algorithm is compared with the DO algorithm, PSO algorithm, CSO algorithm, pelican optimization algorithm (POA), and grey wolf optimizer (GWO) algorithm. In the two examples above, optimizing the antenna array using the CENDO algorithm not only results in the lowest SLL but also in the deepest zeros. The above examples both demonstrate that the improved CENDO algorithm has better optimization performance in simultaneously reducing the SLL of non-equidistant antenna arrays and reducing the null depth problem. In summary, the simulation results of five experiments show that the CENDO algorithm has better optimization ability in the comprehensive optimization problem of non-equidistant antenna array patterns than all the algorithms compared above. Therefore, it can be regarded as a strong candidate to solve problems in the field of electromagnetism. Full article

With the rapid advancement of infrared detection technology, the development of infrared stealth materials has become a pressing need. The study of optical micro/nano infrared stealth materials, which possess selective infrared radiation properties and precise structural features, is of significant importance. By integrating deep reinforcement learning with a multilayer perceptron, we have framed the design of radiation-selective films as a reinforcement learning problem. This approach led to the creation of a Ge/Ag/Ge/Ag multilayer micro/nano optical film that exhibits infrared stealth characteristics. During the design process, the agent continuously adjusts the thickness parameters of the optical film, exploring and learning within the defined design space. Upon completion of the training, the agent outputs the optimized thickness parameters. The results demonstrate that the film structure, optimized by the agent, exhibits a low average emissivities of 0.086 and 0.147 in the 3∼5 µm and 8∼14 µm atmospheric windows, respectively, meeting the infrared stealth requirements in terms of radiation characteristics. Additionally, the film demonstrates a high average emissivity of 0.75 in the 5∼8 µm range, making it effective for thermal radiation management. Furthermore, we coated the Si surface with the designed thin film and conducted experimental validation. The results show that the coated material exhibits excellent infrared stealth properties. Full article

Magnetic resonance imaging (MRI) currently serves as the primary diagnostic method for glioma detection and monitoring. The integration of neurosurgery, radiation therapy, pathology, and radiology in a multi-disciplinary approach has significantly advanced its diagnosis and treatment. However, the prognosis remains unfavorable due to treatment resistance, inconsistent response rates, and high recurrence rates after surgery. These factors are closely associated with the complex molecular characteristics of the tumors, the internal heterogeneity, and the relevant external microenvironment. The complete removal of gliomas presents challenges due to their infiltrative growth pattern along the white matter fibers and perivascular space. Therefore, it is crucial to comprehensively understand the molecular features of gliomas and analyze the internal tumor heterogeneity in order to accurately characterize and quantify the tumor invasion range. The multi-parameter quantitative MRI technique provides an opportunity to investigate the microenvironment and aggressiveness of glioma tumors at the cellular, blood perfusion, and cerebrovascular response levels. Therefore, this review examines the current applications of advanced multi-parameter quantitative MRI in glioma research and explores the prospects for future development. Full article

As an important target of space exploration, Mars has attracted a lot of attention due to its unique geographical and atmospheric conditions. The detection of the vertical profiles of Mars atmospheric parameters provides deeper insights into the structure and composition of the Martian atmosphere. Meanwhile, it holds significant importance for the design and execution of Mars exploration missions. This paper presents a detection method for the Martian atmosphere utilizing laser occultation technology based on a network of high-orbit and low-orbit satellites around Mars. The measurement principle of Mars laser occultation is first introduced, which is that the atmospheric temperature and pressure are measured by analyzing the absorption spectrum characteristics of infrared carbon dioxide. Then, a detailed simulation process is described, including the establishment and validation of both the radiation intensity calculation model for laser occultation signals and the method for retrieving atmospheric parameters. A set of satellite payload parameters is also designed. The simulation results reveal that this method can accurately measure temperature and pressure at a vertical resolution of 100 m from 5 km to 50 km altitude of the Martian atmosphere with deviations of 0.43 K and 1.06%, respectively. It is indicated that the proposed laser occultation method can achieve effective detection of temperature and pressure and provide a promising approach for high vertical resolution profile detection of the Martian atmosphere in the future. Full article

Background: The accurate diagnosis of degenerative joint diseases (DJDs) of the temporomandibular joint (TMJ) presents a significant clinical challenge due to their progressive nature and the complexity of associated structural changes. These conditions, characterized by cartilage degradation, subchondral bone remodeling, and eventual joint dysfunction, necessitate reliable and efficient imaging techniques for early detection and effective management. Cone-beam computed tomography (CBCT) is widely regarded as the gold standard for evaluating osseous changes in the TMJ, offering detailed visualization of bony structures. However, ultrasonography (US) has emerged as a promising alternative, offering a non-invasive and radiation-free option for assessing TMJ disorders. This study aims to evaluate the diagnostic accuracy of US in identifying degenerative changes in the TMJ, with CBCT serving as the definitive diagnostic reference. By analyzing the sensitivity, specificity, and predictive values of US in detecting key degenerative markers—such as subchondral erosion, osteophytes, and joint space narrowing—this investigation seeks to assess its utility as a screening tool and its potential integration into clinical workflows. Methods: Forty adult patients presenting temporomandibular joint disorders were included in our cross-sectional study. Each patient underwent a clinical examination and was subjected to cone-beam computed tomography (CBCT) and ultrasonography (US). A statistical analysis was performed to compare the imaging results from CBCT and US. Results: The results are summarized in three tables. The first table presents a comparative analysis of radiological outcomes in patients with temporomandibular joint disorders using different imaging techniques. CBCT demonstrated higher sensitivity in detecting osteophytes in the right mandibular head (27.50% vs. 7.50%, p = 0.027) and higher detection rates for erosions, though without a significant advantage over US. The second table analyzes the consistency of diagnostic results between CBCT and US. A moderate agreement was observed for detecting normal bone structures, with AC1 values of 0.58 for the right and 0.68 for the left mandibular head (p < 0.001). The third table evaluates the diagnostic accuracy of US compared to CBCT. US demonstrated a positive predictive value (PPV) of 90% for detecting normal conditions, indicating its high reliability as a screening tool for normal findings. US demonstrates higher effectiveness in ruling out certain issues due to its high specificity and negative predictive value. However, its lower sensitivity in detecting abnormalities may lead to both false-positive and false-negative results. Conclusions: US holds significant promise as a screening modality for detecting normal anatomical features of the temporomandibular joint, its limitations in identifying more complex degenerative changes necessitate a cautious and integrated approach to TMJ diagnostics. Full article

Nuclear power plant decommissioning requires the rapid and accurate classification of radioactive waste in narrow spaces and under time constraints. Photon-counting detector technology offers an effective solution for the quick classification and detection of radioactive hotspots in a decommissioning environment. This paper characterizes a 5 mm CdTe Timepix3 detector and evaluates its feasibility as a single-layer Compton camera. The sensor’s electron mobility–lifetime product and resistivity are studied across bias voltages ranging from −100 V to −3000 V, obtaining values of ${\mathrm{\mu }}_e{\tau }_e$ = (1.2 ± 0.1) × 10⁻³ cm²V⁻¹, and two linear regions with resistivities of ${\rho }_I=(5.8\pm 0.2) \mathrm{G}\Omega \mathrm{cm}$ and ${\rho }_{II}=(4.1\pm 0.1) \mathrm{G}\Omega \mathrm{cm}$. Additionally, two calibration methodologies are assessed to determine the most suitable for Compton applications, achieving an energy resolution of 16.3 $\mathrm{k}$$\mathrm{e}\mathrm{V}$ for the ¹³⁷Cs photopeak. The electron’s drift time in the sensor is estimated to be (122.3 ± 7.4) ns using cosmic muons. Finally, a Compton reconstruction of two simultaneous point-like sources is performed, demonstrating the detector’s capability to accurately locate radiation hotspots with a ∼51 cm resolution. Full article

This article introduces the design and development of a space environment monitoring unit embedded in the versatile experimental assembly for electronic components outside the China space station’s Wentian laboratory cabin module. A newly designed comprehensive detection system is being used for the first time in this kind of detector. The sensor head of the instrument includes a silicon telescope (composed of two silicon semiconductors) for measuring the LET spectrum and radiation dose rate, a typical chip for monitoring a single-event upset, and a CR-39 plastic nuclear track detector for detecting heavy ion tracks. The two silicon sensors stacked up and down are used for measuring the LET spectrum, which ranges from 0.001 to 100 MeV·cm²/mg. A sensor charge allocation method is adopted to divide the detection range into four cascaded levels, each achieving different detection ranges separately and then concatenated together, while traditional detection methods need multiple sets of probes to achieve the same dynamic range. At the same time, using the two sensors mentioned above, the silicon absorption dose rate under two different shielding thicknesses can be obtained through calculation, ranging from 10⁻⁵ to 10⁻¹ rad (Si)/h. Multiple calibration methods are applied on the ground. The preliminary in-orbit detection results are provided and compared with the simulation results obtained using the existing space environment model, and we analyze and discuss their differences. Full article