Vacuum cryogenic area source blackbody

Abstract

The application discloses a vacuum low-temperature surface source blackbody, a plurality of pyramid structures of polygonal pyramids are processed on the surface of a blackbody radiation panel, and a high-emissivity coating is matched, so that the surface source blackbody with micro-cavity structures is formed, and the effective emissivity of the vacuum low-temperature surface source blackbody is improved. In addition, the application adopts a reasonable liquid nitrogen pipeline and an I-shaped heat-conducting bridge to form a low-temperature module, and connects a uniform temperature plate to uniformly distribute cold energy, so that the radiation performance of the vacuum low-temperature surface source blackbody is ensured. The vacuum low-temperature surface source blackbody has the characteristics of high emissivity and uniform temperature field distribution. The application adopts a liquid nitrogen cooling mode, reduces the requirement on the use environment, can realize real-time calibration of a laboratory full aperture and full temperature range of an infrared detector, effectively improves calibration precision, and further improves the detection precision of the infrared detector.

Description

Technical Field

[0001] This invention relates to the field of infrared measurement technology, and specifically to a vacuum low-temperature surface source blackbody. Background Technology

[0002] With the rapid development of infrared technology, its applications have spread to various fields. Since the beginning of the 21st century, countries around the world have invested heavily in the aerospace field, launching satellites in orbit to achieve large-scale real-time monitoring of the Earth. Infrared remote sensing technology is an important observation method for space-based Earth observation systems, and infrared detection instruments, as key equipment, directly affect the accuracy of information acquisition.

[0003] Infrared detection instruments require precise measurement of the differences in radiation characteristics of different targets to detect various infrared targets. With the continuous increase in the aperture of optical systems, the imaging area and positional resolution of spaceborne infrared remote sensing are constantly improving. As infrared imaging instruments, they use focal plane array infrared detectors as signal receivers. Therefore, precise calibration of parameters such as detection sensitivity, linearity, spectral and temporal response, and non-uniformity of each unit detector in the focal plane array is necessary to ensure the detection accuracy of the instrument. This is achieved through full-field-of-view calibration using a large-aperture infrared calibration source (vacuum cryogenic blackbody radiation source). However, my country's current level of large-aperture calibration sources is not high, directly limiting the calibration level of infrared detection. Therefore, it is necessary to develop an ultra-large aperture uniform blackbody radiation source as a laboratory calibration blackbody for spaceborne infrared remote sensing payloads to improve the calibration level of infrared target detection in my country.

[0004] To balance factors such as radiation surface size, temperature uniformity, and blackbody volume, large-aperture blackbody radiation sources are currently mainly surface-type blackbody sources. This also leads to a disadvantage compared to cavity blackbody sources: their emissivity is limited.

[0005] Meanwhile, full-aperture calibration in the laboratory requires placing the infrared detection equipment and the surface source blackbody within a vacuum chamber simulating a low-temperature, high-vacuum space environment. Laboratory calibration of the infrared detector needs to achieve full-temperature range calibration, from low to high temperatures, as required. This necessitates that the vacuum low-temperature surface source blackbody can provide uniform, stable, and high-precision infrared radiation energy across all temperature ranges to ensure complete coverage of the infrared camera's field of view. Currently, domestic vacuum chambers simulating space environments typically use liquid nitrogen for cooling to achieve the required low temperatures. Furthermore, the reserved flange windows are small, making it difficult to accommodate the installation of a cooling system. Therefore, this necessitates using liquid nitrogen cooling for the blackbody to achieve low-temperature calibration. The use of liquid nitrogen cooling enhances the versatility of vacuum low-temperature surface source blackbody calibration. The flow rate of liquid nitrogen and the presence of the gas-liquid two-phase system have a significant impact on the temperature uniformity and stability of the blackbody. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a vacuum low-temperature surface source blackbody.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A vacuum cryogenic surface source blackbody includes a blackbody radiation source, comprising a radiation-proof shell and a blackbody radiation panel, a heating mechanism, a heat spreader, a fixing base, a heat insulation pad, a temperature sensor, a thermal bridge, a liquid nitrogen pipeline, and a pipeline back fixing mechanism fixed within the radiation-proof shell. One side of the heating mechanism is located on the back of the blackbody radiation panel, and its other side is connected to one side of the thermal bridge via the heat spreader. The other side of the thermal bridge is connected to the pipeline back fixing mechanism. The liquid nitrogen pipeline is located between the thermal bridge and the pipeline back fixing mechanism and is in contact with both. A heat insulation pad is provided between the thermal bridge and the radiation-proof shell. The temperature sensor is fixed to the blackbody radiation panel for measuring its temperature. The bottom of the radiation-proof shell is fixed to the fixing base.

[0009] Furthermore, the blackbody radiation source also includes a protective shell, the blackbody radiation panel, the heating mechanism and the heat spreader are all disposed inside the protective shell, a heat insulation block is provided between the outer wall of the blackbody radiation panel and the inner wall of the protective shell, and a heat insulation gasket is provided between the outer wall of the protective shell and the inner wall of the radiation shielding shell.

[0010] Furthermore, the front of the blackbody radiation panel is formed by an array of multiple square pyramids, and its surface is coated with high emissivity black paint.

[0011] Furthermore, the high emissivity black paint is Nextel Velvet Black 811-21 black paint.

[0012] Furthermore, the back of the blackbody radiation panel is uniformly arranged with multiple temperature measuring holes of the same depth in an array. One of the temperature measuring holes is located at the center of the back of the blackbody radiation panel, and the other temperature measuring holes are symmetrical about the center of the back of the blackbody radiation panel. Each temperature sensor is embedded in the corresponding temperature measuring hole through a countersunk hole and is close to the front of the blackbody radiation panel.

[0013] Furthermore, the heating mechanism includes multiple polyimide heating films; each polyimide heating film is attached to the corresponding heating area on the back of the blackbody radiation panel using thermal grease according to the distribution of the temperature sensors; wherein, one polyimide heating film is located in the central region of the back of the blackbody radiation panel, and the distribution of the other polyimide heating films is symmetrical about the center of the back of the blackbody radiation panel.

[0014] Furthermore, a high-purity indium sheet is bonded between the polyimide heating film and the heat spreader using thermal grease to ensure good contact and heat conduction.

[0015] Furthermore, the heat-conducting bridge is I-shaped, with one end having an arc surface to wrap around the liquid nitrogen pipeline, and the other end having a flat structure to connect with the heat spreader.

[0016] Furthermore, the liquid nitrogen pipeline includes a liquid nitrogen inlet pipe, a liquid nitrogen outlet pipe, and several liquid nitrogen flow pipes; the top end of each liquid nitrogen flow pipe is connected to the liquid nitrogen inlet pipe, and the bottom end is connected to the liquid nitrogen outlet pipe.

[0017] Furthermore, the vacuum cryogenic surface source blackbody also includes a control cabinet, a power supply system, a temperature control system, and a self-pressurizing liquid nitrogen tank; the temperature control system is connected to the control cabinet; the blackbody radiation source is located inside the vacuum chamber; the control cabinet, temperature control system, and power supply system are all located outside the vacuum chamber, and the control cabinet and temperature control system are powered by the power supply system; the leads of the temperature sensor are soldered to a multi-core aviation connector, which is connected to the temperature control system outside the vacuum chamber via an electrical flange; the liquid nitrogen pipeline is connected to the self-pressurizing liquid nitrogen tank via a control valve; the control valve, heating mechanism, and temperature control system are all connected to the control cabinet.

[0018] The beneficial effects of this invention are as follows: This invention processes a pyramidal structure with multiple facets on the surface of the blackbody radiation panel and combines it with a high emissivity coating to form a surface-source blackbody with a microcavity structure in the radiation surface, thereby improving the effective emissivity of the vacuum cryogenic surface-source blackbody. Furthermore, this invention employs a rational liquid nitrogen pipeline and an I-shaped heat-conducting bridge to construct a cryogenic module, connected to a vapor chamber to achieve uniform distribution of cooling, ensuring the radiation performance of the vacuum cryogenic surface-source blackbody. The vacuum cryogenic surface-source blackbody of this invention features high emissivity and a uniform temperature field distribution. Its use of liquid nitrogen cooling reduces the requirements of the operating environment, enabling real-time calibration of infrared detectors across the entire aperture and temperature range in the laboratory, effectively improving calibration accuracy and thus enhancing the detection accuracy of the infrared detector. Attached Figure Description

[0019] Figure 1 This is an exploded view of the blackbody radiation source in Embodiment 1 of the present invention;

[0020] Figure 2 This is a three-dimensional schematic diagram of the back of the blackbody radiation source in Embodiment 1 of the present invention;

[0021] Figure 3 This is a schematic diagram of the front structure of the blackbody radiation source in an embodiment of the present invention;

[0022] Figure 4 This is a schematic diagram of the front structure of the blackbody radiation panel in Embodiment 1 of the present invention;

[0023] Figure 5 This is a schematic diagram of the heat spreader in Embodiment 1 of the present invention;

[0024] Figure 6 This is a side view showing the connection between the heat-conducting bridge and the heat spreader in Embodiment 1 of the present invention;

[0025] Figure 7 This is a three-dimensional structural diagram of the thermal bridge in Embodiment 1 of the present invention;

[0026] Figure 8 This is a front view of the thermal bridge structure in Embodiment 1 of the present invention;

[0027] Figure 9 This is a schematic diagram of the temperature sensor distribution in Embodiment 1 of the present invention;

[0028] Figure 10 This is a schematic diagram of the overall blackbody system in Embodiment 1 of the present invention;

[0029] Figure 11 This is a schematic diagram of the simulation analysis mesh in Embodiment 2 of the present invention;

[0030] Figure 12 This is a graph showing the analysis results of liquid nitrogen flowing through 5 pipes in Example 2 of the present invention;

[0031] Figure 13 This is a graph showing the analysis results of liquid nitrogen flowing through 6 pipes in Example 2 of the present invention;

[0032] Figure 14 This is a diagram showing the analysis results of the copper liquid nitrogen pipeline in Embodiment 2 of the present invention;

[0033] Figure 15 The diagram shows the analysis results of the stainless steel liquid nitrogen pipeline in Embodiment 2 of the present invention.

[0034] Figure 16 This is a diagram showing the overall temperature distribution and the temperature distribution of the liquid nitrogen pipeline when the heating power is 2000W in Embodiment 2 of the present invention.

[0035] Figure 17 This is a schematic diagram of the temperature difference distribution on the radiating surface in Embodiment 2 of the present invention;

[0036] Figure 18 This is a diagram showing the centrally symmetrical heating zone distribution in Embodiment 2 of the present invention;

[0037] Figure 19 and Figure 20 These are schematic diagrams showing the temperature uniformity of the blackbody radiation surface before and after heating optimization in Embodiment 2 of the present invention.

[0038] Figure 21 This is a schematic diagram of 10 sets of original data recorded during the blackbody normal emissivity process in Embodiment 2 of the present invention;

[0039] Figure 22 This is a schematic diagram of the experimental results of the spectral emissivity of the vacuum surface source blackbody in 8-14 μm in Embodiment 2 of the present invention;

[0040] Figure 23 This is a schematic diagram of the temperature uniformity and stability test structure under atmospheric conditions in Embodiment 2 of the present invention;

[0041] Figure 24 This is a schematic diagram of the temperature uniformity and stability test state under vacuum environment in Embodiment 2 of the present invention;

[0042] Figure 25 and Figure 26 The temperature change trends over 30 minutes are shown for 100-150K and 160-360K under vacuum environment temperature uniformity and stability test in Example 2 of the present invention.

[0043] Figure 27 This is a schematic diagram of the measurement results of the radiance temperature of a blackbody in the 2.5μm-16μm range in Embodiment 2 of the present invention. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0045] Example 1

[0046] This invention provides a vacuum low-temperature surface source blackbody, such as... Figure 1-10 As shown, the device includes a blackbody radiation source, comprising a radiation shielding shell 1 and a blackbody radiation panel 2, a heating mechanism 3, a heat spreader 4, a fixing base 5, a heat insulation pad 7, a temperature sensor 8, a thermal bridge 9, a liquid nitrogen pipeline 10, and a pipeline back fixing mechanism 11, all fixed within the radiation shielding shell 1. One side of the heating mechanism 3 is located on the back of the blackbody radiation panel 2, and its other side is connected to one side of the thermal bridge 9 via the heat spreader 4. The other side of the thermal bridge 9 is connected to the pipeline back fixing mechanism 11. The liquid nitrogen pipeline 10 is located between the thermal bridge 9 and the pipeline back fixing mechanism 11 and is in contact with both. A heat insulation pad 9 is provided between the thermal bridge 9 and the radiation shielding shell 1. The temperature sensor 8 is fixed to the blackbody radiation panel 2 and is used to measure the temperature of the blackbody radiation panel 2. The bottom of the radiation shielding shell is fixed to the fixing base 5.

[0047] In this embodiment, the blackbody radiation source also includes a protective shell 6. The blackbody radiation panel 2, the heating mechanism 3, and the heat spreader 4 are all disposed inside the protective shell 6. A heat insulation block 12 is provided between the outer wall of the blackbody radiation panel 2 and the inner wall of the protective shell 6. A heat insulation pad 13 is provided between the outer wall of the protective shell 6 and the inner wall of the radiation shielding shell 1.

[0048] In this embodiment, the temperature sensor 8 is fixed to the blackbody radiation panel 2 by a fixing plate 14.

[0049] In this embodiment, the blackbody radiation panel 2 is made of aluminum, such as Figure 4 As shown, its front side is formed by an array of multiple square pyramids 15, and its surface is sprayed with high-emissivity black paint (Nextel Velvet Black 811-21 black paint is used in this embodiment). It is necessary to ensure that the coating is thin and uniform in order to reduce the wall temperature gradient and reduce the uncertainty caused by the coating.

[0050] It should be noted that the operating temperature of a vacuum low-temperature surface source blackbody is 120K-360K, with alternating high and low temperature cycles during operation. Simultaneously, the infrared equipment being measured is placed directly in front of the blackbody's radiation panel, making it susceptible to contamination by condensable volatiles released by the blackbody. Therefore, it is crucial to strictly control the total mass loss (TML) and condensable volatiles (CVCM) of the high-emissivity black paint and related materials. Nextel Velvet Black 811-21 black paint offers an emissivity superior to 0.965 in the 2.5-16μm wavelength range. Blackbodies coated with this black paint can operate within the 74K-360K temperature range, meeting the requirements for vacuum applications and suitable for coating the radiation surface of this surface source blackbody. Furthermore, the blackbody radiation panel can also be made of other metallic materials or non-metallic materials that have undergone vacuum performance testing, ensuring that the vacuum outgassing rate meets the requirements for optical system use.

[0051] It should be noted that the structure of the array of four-sided pyramids and the spraying of high-emissivity black paint can improve the emissivity of the vacuum low-temperature surface source blackbody. The four-sided pyramid structure of the blackbody radiation surface is obtained based on theoretical calculations, simulations and experiments, which meets the requirements of high emissivity.

[0052] It should be noted that the blackbody radiation panel 2 itself is large in size and weight, so it must be heat-treated before and after processing to avoid large thermal deformation caused by the blackbody during long-term cold and hot operation.

[0053] In this embodiment, the back of the blackbody radiation panel 2 is uniformly arrayed with multiple temperature measuring holes of the same depth. One temperature measuring hole is located at the center of the back of the blackbody radiation panel 2, and the other temperature measuring sensors are symmetrically arranged around the center of the back of the blackbody radiation panel 2. Each temperature sensor 8 is embedded in its corresponding temperature measuring hole through a countersunk hole, close to the front of the blackbody radiation panel. The uniform depth of the temperature measuring holes ensures consistent temperature acquisition. The temperature sensors should be as close as possible to the front of the blackbody radiation panel to make the acquired temperature value closer to the temperature value of the blackbody radiation panel. In this embodiment, as... Figure 9 As shown, the blackbody radiation panel 2 is equipped with nine temperature sensors 8, and the distance between each temperature sensor is equal.

[0054] More specifically, the temperature sensor 8 is a high-precision PT100 sensor with a measurement uncertainty of 0.01-0.05K. Each temperature sensor has calibration data that is traceable to the temperature standard of the National Institute of Metrology of China, ensuring the accuracy of blackbody temperature measurement.

[0055] In this embodiment, the heating mechanism 3 includes multiple polyimide heating films. Each polyimide heating film is attached to the corresponding heating area on the back of the blackbody radiation panel 2 using thermal grease, according to the distribution of the temperature sensors. The polyimide heating film is located at the center of the back of the blackbody radiation panel 2, and the distribution of the other polyimide heating films is symmetrical about the center of the back of the blackbody radiation panel. By controlling the heating power of the polyimide heating films, the operating temperature of the blackbody radiation panel can be maintained at a high temperature range greater than 360K.

[0056] More specifically, a high-purity indium sheet is bonded between the polyimide heating film and the heat spreader plate using thermal grease to ensure good contact and heat conduction.

[0057] It should be noted that the temperature distribution plate 4, as an important transitional link in the blackbody radiation source, can uniformly distribute the temperature during liquid nitrogen cooling, which is beneficial to improving the temperature stability of the vacuum low-temperature surface source blackbody and shortening the temperature stabilization time. In this embodiment, the temperature distribution plate is made of aluminum.

[0058] In this embodiment, to meet the performance requirements for low-temperature operation of the blackbody, liquid nitrogen cooling is used to reduce the temperature of the blackbody radiation panel to 120K. To enhance heat exchange between the liquid nitrogen pipeline and the heat spreader 4, a pipeline back fixing mechanism 11 and a thermal bridge 9 are used to tightly fit the liquid nitrogen pipeline, and heat exchange between the liquid nitrogen pipeline and the heat spreader is achieved through the thermal bridge 9.

[0059] Furthermore, in this embodiment, as Figure 6-8As shown, the heat-conducting bridge 9 is I-shaped, with one end having an arc surface to wrap around the liquid nitrogen pipeline, and the other end having a flat structure to connect with the heat spreader 4. This structure ensures a large contact area between the heat-conducting bridge, the liquid nitrogen pipeline, and the heat spreader, thereby better transferring cold energy to the heat spreader 4.

[0060] In this embodiment, the liquid nitrogen pipeline 10 includes a liquid nitrogen inlet pipe 16, a liquid nitrogen outlet pipe 17, and several liquid nitrogen flow pipes; the top end of each liquid nitrogen flow pipe is connected to the liquid nitrogen inlet pipe, and the bottom end of each flow pipe is connected to the liquid nitrogen outlet pipe. In this embodiment, the liquid nitrogen inlet pipe 16, the liquid nitrogen outlet pipe 17, and the several liquid nitrogen flow pipes are all made of stainless steel.

[0061] It should be noted that, in order to provide a constant temperature cold source, the liquid nitrogen pipeline must be kept full of liquid nitrogen.

[0062] It should be noted that the heat-conducting bridge 9 is made of 304 stainless steel, and the inner diameter of the liquid nitrogen flow pipe is φ = 35mm. In this embodiment, a total of six liquid nitrogen flow pipes are provided.

[0063] In this embodiment, the heat spreader 4 is a key component used to connect the liquid nitrogen pipeline 10 and the blackbody radiation panel 2, achieving a relatively uniform distribution of cooling energy, ensuring contact, and further homogenizing the temperature field. To ensure good contact, such as... Figure 5 As shown, in this embodiment, the heat spreader and the thermal bridge are connected by a denser screw connection.

[0064] It should be noted that the heat insulation pads, heat insulation blocks, and heat insulation sheets are designed to reduce heat exchange between connected components. To better achieve the system's heat insulation function, all heat insulation pads, heat insulation blocks, and heat insulation sheets are made of polytetrafluoroethylene (PTFE). Furthermore, the surface of the heat insulation block that contacts the blackbody radiation panel is provided with grooves, which reduces the contact area between the heat insulation block and the blackbody radiation panel without affecting structural strength, thereby reducing the heat flow between them. Simultaneously, to reduce the overall weight of the surface-source blackbody, the heat insulation blocks are distributed at equal intervals along the four sides of the blackbody radiation panel.

[0065] In this embodiment, as Figure 10As shown, the vacuum cryogenic surface source blackbody also includes a control cabinet 101, a power supply system 102, a temperature control system 103, and a self-pressurizing liquid nitrogen tank 104; the temperature control system 103 is connected to the control cabinet 101; the blackbody radiation source 100 is located inside the vacuum chamber; the control cabinet 101, the temperature control system 103, and the power supply system 102 are all located outside the vacuum chamber, and the control cabinet 101 and the temperature control system 103 are powered by the power supply system; the leads of the temperature sensor 8 are soldered to a multi-core aviation connector, which is connected to the temperature control system 103 outside the vacuum chamber through an electrical flange; the liquid nitrogen pipeline 10 is connected to the self-pressurizing liquid nitrogen tank 104 through a control valve 105; the control valve 105, the heating mechanism 3, and the temperature control system 103 are all connected to the control cabinet 101.

[0066] Each temperature sensor 8 transmits the operating temperature of the blackbody radiation panel in its area to the temperature control system. The temperature control system compares the temperature data measured by the temperature sensors with the target operating temperature and transmits the calculation result to the control cabinet. The control cabinet then controls the heating power of the heating mechanism 3 and the opening and closing of the control valve 105 accordingly.

[0067] In this embodiment, the control cabinet 101 communicates with the remote control system in real time via a serial port and transmits the blackbody temperature data to the remote control system for storage and analysis.

[0068] It should be noted that the effective aperture of the blackbody is mainly determined by the external dimensions of the blackbody radiating plate. In this embodiment, the blackbody radiating plate has dimensions of 550mm × 550mm, with a 25mm heat insulation layer on one side, which meets the technical requirements for the effective aperture.

[0069] Example 2

[0070] This embodiment aims to further illustrate the vacuum low-temperature surface source blackbody described in Example 1 by using the COMSOL Multiphysics thermal module to simulate and analyze the blackbody based on its actual structure and thermal conditions. The simulation analysis includes heat flux and blackbody temperature field analysis, as well as the temperature uniformity of the radiating surface.

[0071] (I) Boundary conditions for thermal homogeneity analysis

[0072] The heat transfer processes considered in the model are: (1) radiation heat transfer; (2) internal heat conduction of the structure; (3) heating by the heating mechanism; and (4) liquid nitrogen cooling.

[0073] Geometric description: The structure includes a blackbody radiation panel, heating mechanism, heat spreader, liquid nitrogen pipeline, thermal bridge, outer shell, and insulation block.

[0074] Material description: (1) The blackbody radiation panel and the heat spreader are made of aluminum; (2) The heat insulation material is polytetrafluoroethylene; (3) The heating mechanism is made of polyimide film; (4) The outer shell and the cooling device are made of stainless steel. The relevant parameters are exported from the COMSOL material library.

[0075] Physical field description:

[0076] (1) Radiative heat transfer: Radiative heat transfer occurs on all external surfaces. The ambient temperature is 100K, and the emissivity of the blackbody radiating surface is 0.985. Considering the heat-insulating effect of the insulation cotton, the emissivity of the side of the blackbody radiating plate is set to 0.05, and the emissivity of other surfaces is set to 0.1.

[0077] (2) Heating mechanism heating: There is a boundary heat source with power of P2, which is used to simulate the power of the heating mechanism of 78K heating.

[0078] (3) Liquid nitrogen refrigeration: Liquid nitrogen pipeline is set at 78K.

[0079] Mesh description:

[0080] Using a standard cell mesh generation method, the complete mesh contains 740 vertex cells, 15108 edge cells, 96169 boundary cells, and 186286 cells. For example... Figure 11 As shown.

[0081] (II) Analysis of Heat Flow and Blackbody Temperature Field

[0082] Based on the actual operating conditions of the large-area blackbody device, the research will be divided into three stages:

[0083] (1) 120K≤T≤160K, with liquid nitrogen refrigeration as the main method and heating mechanism as the auxiliary method for temperature control.

[0084] (2) 160K≤T≤240K, the blackbody temperature is controlled by liquid nitrogen cooling and heating mechanism.

[0085] (3) 240K<T≤360K, heating mechanism is the main heating method.

[0086] 1. The influence of the location and quantity of liquid nitrogen flowing through the pipeline

[0087] In liquid nitrogen piping systems, the number of pipes through which liquid nitrogen flows has a significant impact on its cooling capacity. Based on the size of the heat spreader, simulation experiments were conducted to investigate the effect of different numbers of liquid nitrogen pipes on the temperature uniformity of the radiant surface. Two scenarios were selected: 78K with no heating and 78K with P = 2000W. The simulation results for a liquid nitrogen flow through 5 pipes are as follows: Figure 12 As shown, the specific simulation results are as follows: Figure 12 As shown, the simulation results when there are 6 liquid nitrogen pipelines are as follows: Figure 13 As shown.

[0088] When there are 5 liquid nitrogen pipelines, simulation analysis shows that the cooling capacity of liquid nitrogen at 72K reaches the radiating surface through the isothermal body, and the uniformity after stabilization is 0.0045K; when the temperature rises, the uniformity of the radiating surface reaches 1.5K when the power is 2000W.

[0089] When there are 6 liquid nitrogen pipelines, simulation analysis shows that the cooling capacity of liquid nitrogen at 72K reaches the radiating surface through the isothermal body, and the uniformity after stabilization is 0.004K; when the temperature rises, the uniformity of the radiating surface reaches 0.9K when the power is 2000W.

[0090] The location and number of liquid nitrogen pipes have little impact on the overall temperature uniformity of the radiant surface at extremely low temperatures, but a greater impact at high temperatures. When the number of liquid nitrogen pipes is small, there is a temperature gradient in the radiant surface. Increasing the number of pipes makes the cold source distribution more uniform, the temperature gradient of the radiant surface smoother, and the uniformity better.

[0091] 2. The impact of liquid nitrogen pipeline materials

[0092] Figure 14 The simulation results show the temperature field distribution of the copper liquid nitrogen pipeline. The simulation analysis shows that the temperature uniformity of the copper liquid nitrogen pipeline is 0.0045K at 78K. When the temperature starts to rise, the uniformity of the radiating surface reaches 0.9K when the power is 2000W.

[0093] Figure 15 The simulation results show the temperature field distribution of the stainless steel liquid nitrogen pipeline. The simulation analysis shows that the temperature uniformity of the stainless steel liquid nitrogen pipeline is 0.0045K at 78K. When the temperature starts to rise, the temperature rises slightly compared to the copper liquid nitrogen pipeline when the power is 2000W, and the uniformity of the radiation surface reaches 0.9K.

[0094] Research has shown that the material of liquid nitrogen pipelines does not significantly affect the uniformity of the radiant surface temperature, so stainless steel was chosen as the material for liquid nitrogen pipelines. Figure 16 The diagram shows the overall temperature distribution and the temperature distribution of the liquid nitrogen pipeline when the heating power is 2000W.

[0095] 3. Multi-temperature zone optimization strategy and temperature equalization strategy

[0096] The results show that the temperature difference on the radiating surface is mainly reflected in the center and four corners of the surface source, such as... Figure 17 As shown, the blackbody temperature is lower than the ambient temperature. During external heat exchange (radiation and conduction with the outer shell), the heat absorption rate at the edge of the blackbody will be higher than that at the center. Therefore, the temperature at the edge of the blackbody will also be higher than that at the center.

[0097] Based on the simulation results, this embodiment further confirms that a centrally symmetric multi-temperature zone optimization strategy is adopted to obtain better temperature field uniformity.

[0098] Based on the study of temperature uniformity of the blackbody radiating surface, individual temperature control is implemented at the four corners of the radiating surface, and auxiliary heating is used to compensate for heat leakage areas. The entire back of the radiating surface is divided into nine heating zones, each controlled by an individual PID temperature controller. This achieves good temperature uniformity while avoiding mutual interference issues associated with multi-zone control. Figure 18 The centrally symmetrical heating zone distribution diagram shown is used for further simulation analysis.

[0099] like Figure 19 As shown, before the heating conditions were optimized, the temperature uniformity of the blackbody radiating surface at 243K was 1K, and the temperature uniformity of the blackbody radiating surface at 400K was 0.25K.

[0100] like Figure 20 As shown, after optimizing the heating conditions, using a multi-temperature zone optimization strategy and a uniform temperature strategy, the temperature uniformity of the blackbody radiating surface at 243K is 0.18K, and the temperature uniformity of the blackbody radiating surface at 400K is 0.045K, which meets the design requirements.

[0101] 4. Experimental Verification of Vacuum Low-Temperature Surface Source Blackbody Radiation Source

[0102] The following section will conduct performance tests on the vacuum blackbody radiation source. Experiments will be performed on the source's spectral emissivity, brightness temperature, temperature stability, and uniformity. This will verify whether the technical specifications of the vacuum blackbody radiation source meet the required standards.

[0103] 4.1 Measurement of emissivity

[0104] 4.1.1 Band Emissivity Measurement

[0105] Emissivity measurement is performed on an emissivity measurement device based on controlled ambient radiation. The entire device includes a high-temperature radiation plate, a room-temperature radiation plate, a water-cooled aperture, a sample holder, a thermostat, a horizontal moving stage, a heating and temperature control device, a computer, a radiation thermometer (TRT), and a Fourier transform infrared spectrometer (FTIR). The sample is mounted on the sample holder, and two high-emissivity radiation plates are mounted on the horizontal moving stage, one at room temperature and the other at a high temperature. The water-cooled aperture is installed between the radiation plates and the infrared radiation thermometer to reduce stray radiation. Alternating the hot and cold baffles to the front of the blackbody alters the background radiation signal reflected by the blackbody source. The data acquisition system then acquires the temperature of the blackbody source (set to 1), including the center of the blackbody's bottom, the hot and cold baffles, the surrounding environment, and the blackbody source temperature measured by the infrared radiometer. Finally, an algorithm based on controlled background emissivity measurement is used to obtain the emissivity of the vacuum surface source blackbody in the 8-14 μm infrared band.

[0106] The emissivity of the vacuum surface-source blackbody radiation surface was calculated using the STEEP3 emissivity simulation software, yielding a result of 0.9927. Ten sets of normal emissivity measurements were performed on the vacuum surface-source blackbody radiation source using the aforementioned controlled background emissivity measurement platform. Each set included measurements of the blackbody source temperature, radiometer temperature, hot and cold baffle temperature, and room temperature under the hot and cold baffles. The ten sets of raw data recorded during the blackbody normal emissivity measurement process are as follows: Figure 21 As shown. From Figure 21 It can be seen that the average emissivity of 10 consecutive measurements is 0.9924, with a standard deviation of 0.03%. The measurement results are consistent with the simulation results, with a difference of less than 0.0003.

[0107] When infrared remote sensing equipment is calibrated using a surface-source blackbody, external factors can easily cause a difference in the azimuth angle between the equipment and the calibration blackbody, which can affect the calibration accuracy. Therefore, the directional emissivity was measured. The measurement tilt angle range was selected from 0-30°, with measurement points spaced at 5° intervals. The measurement results are as follows: Figure 21 As shown, the emissivity gradually decreases with increasing blackbody tilt angle. The standard deviation at each measurement point is less than 0.042%. The average emissivity is 0.9919, and the overall emissivity variation is better than 0.04%.

[0108] 4.1.2 Spectral Emissivity Measurement

[0109] The spectral emissivity measurement of the vacuum surface source blackbody was conducted using the Vacuum Low Background Infrared Hyperspectral Brightness Temperature Metrological Standard Device (VRTSF) developed by the National Institute of Metrology, China. This device was used as the measurement system.

[0110] To simulate an infrared remote sensing payload, a vacuum surface source blackbody is placed inside the vacuum sample chamber of the VRTSF (Vibration Reduction Test Forming Unit). A support beneath the blackbody rests on a PTFE (Polytetrafluoroethylene) heat insulation plate to minimize contact with the sample chamber and reduce the impact of heat conduction. The blackbody's own heating and temperature control system, along with an external liquid nitrogen cooling device, provides a stable background environment. The temperature is controlled by the temperature control system to reach and maintain a stable temperature. An MCT infrared detector is used. The basic process for vacuum low-background infrared brightness temperature calibration is as follows:

[0111] (1) Fix the vacuum surface source blackbody to the designated position in the vacuum chamber using tooling. Connect the temperature sensor lines, heating element lines, and liquid circulation pipelines through flanges, and check the equipment's operating status. Close the vacuum chamber door and evacuate the vacuum to below 10⁻² Pa;

[0112] (2) Set the temperature of the vacuum surface source blackbody and the standard variable temperature blackbody to the same temperature. Fill the liquid nitrogen zero point blackbody and the hexahedron with liquid nitrogen. When the vacuum surface source blackbody, the standard variable temperature blackbody, the liquid nitrogen blackbody and the optical path system are all in a stable state, start the experimental test using a spectrometer.

[0113] (3) Use a Fourier transform infrared spectrometer to measure the blackbody radiation signal. The basic measurement sequence is: standard variable temperature blackbody -> liquid nitrogen zero point blackbody -> blackbody to be calibrated. Record the contact temperature of the standard variable temperature blackbody and the vacuum surface source blackbody, as well as the laboratory ambient temperature, sample chamber temperature, and other data. Repeat the measurement 10 times in this order and observe the repeatability of the spectral response curve.

[0114] (4) Check the signals of 10 measurements. If there are no abnormalities, calculate the blackbody brightness temperature using the formula and calculate the blackbody spectral emissivity using the formula. Take the average of the 10 results as the final result.

[0115] (5) Change the temperature of the blackbody and measure the next temperature.

[0116] Following the experimental procedures outlined above, experiments were conducted to investigate the spectral emissivity of a vacuum surface source blackbody in the 8-14 μm range. Six temperature points were set up for the experiment: 280 K, 300 K, 310 K, 320 K, 330 K, and 340 K. The experimental results are as follows: Figure 22 As shown in (a)-(f).

[0117] Depend on Figure 22(a) As can be seen, at 280K, the spectral emissivity of the blackbody in the 8-14 μm range is between 0.987 and 0.993, with an overall average emissivity of 0.991. The emissivity uniformity is better than 0.11%, with a minimum at 8.8 μm and a maximum at 8 μm. Significant fluctuations are observed in the 8-9 μm range, exhibiting a distinct trough. The overall trend of spectral emissivity in the 9-14 μm range is relatively flat, with a standard deviation better than 0.07%. An in-depth investigation was conducted into the large fluctuations in spectral emissivity in the 8-9 μm range. The study revealed that even the high-rate coating of the vacuum surface-source blackbody exhibits a trough in this band. Even with the construction of an array pyramid structure on the radiating surface to increase light capture capability, the emissivity uniformity in this band could not be optimized.

[0118] Next, the vacuum surface source blackbody was heated, and the spectral emissivity of the 8-14 μm region under high-temperature conditions was measured. Figure 22 As shown in (b)-(f), the overall trend of spectral emissivity remains consistent. With increasing temperature, the change in spectral emissivity is minimal, with differences less than 0.3%. In summary, the vacuum surface source blackbody exhibits high emissivity and high emissivity uniformity in the 8-14 μm spectral range, which meets the practical requirements for calibration.

[0119] 4.2 Temperature Uniformity and Stability Test

[0120] The temperature uniformity and stability of the vacuum surface source blackbody are also important performance indicators. Temperature non-uniformity should be better than 0.5K below 160K and better than 0.2K above 160K, while temperature stability should be better than 0.05K / 30min. For temperature control accuracy testing, the automatic temperature control software is turned on, and the operating temperature is set. After the radiation source reaches the set temperature value, it is allowed to stabilize for a period of time. Then, the changes in the temperature values ​​measured by each resistor are recorded. The temperature uniformity and stability are verified through the measurement data.

[0121] 4.2.1 Temperature Uniformity and Stability Test under Atmospheric Environment

[0122] Vacuum surface source blackbodies can meet the calibration requirements under low-temperature vacuum conditions, and can also perform radiation calibration under high-temperature atmospheric conditions. In an atmospheric environment, the overall heat transfer process of a blackbody mainly includes radiative heat transfer between the radiating surface and the environment, internal structural heat conduction, convective heat transfer, and heating by the heating mechanism. Before the experiment, the indoor ambient temperature was kept stable to reduce the impact of indoor convection on the temperature non-uniformity and stability of the blackbody. Seven temperature points were set up for the experiment: 300K, 310K, 320K, 330K, 340K, 350K, and 360K to measure temperature stability and non-uniformity. Data were recorded for 30 minutes after the temperature was raised to the target temperature and held constant. The measurement results are shown in Table 1. Figure 23 (a)-(f) show the temperature change trend of each test point over 30 minutes.

[0123] Figure 23 (a) shows the temperature variation trend of the blackbody at room temperature under atmospheric conditions. It can be seen that the overall temperature uniformity is less than 0.02K and the stability is better than 0.01K / 30min, ensuring a relatively stable environment and that the overall operating state of the blackbody and the internal thermometer remain normal. Among the absolute values ​​of the temperature difference between all temperature measurement points and the average temperature, the maximum value is taken as the non-uniformity of the blackbody temperature.

[0124] As shown in Table 1, the blackbody temperature nonuniformity at 300K, 310K, 320K, 330K, 340K, 350K, and 360K is 0.036K, 0.038K, 0.052K, 0.074K, 0.088K, 0.061K, and 0.077K, respectively, which is generally better than 0.1K. The standard deviation of all temperature measurements within 30 minutes represents the temperature stability. The blackbody temperature stability is 0.021, 0.019, 0.021, 0.037, 0.031, 0.023, and 0.034, respectively, and the stability at all temperature points is better than 0.05 mK / 30 min. Figure 23 The temperature variation trends at each temperature point over 30 minutes are shown in detail. Furthermore, as the operating temperature increases, the temperature uniformity and stability also improve. This is because heat loss around the blackbody increases with increasing blackbody temperature.

[0125] Table 1 Results of blackbody temperature non-uniformity and stability

[0126]

[0127] 4.2.2 Temperature Uniformity and Stability Test under Vacuum Environment

[0128] The measurement of the temperature uniformity and stability of a blackbody under vacuum was also conducted using a VRTSF. The experimental conditions were as follows: Figure 24 As shown. Figure 25(a)-(f) show the temperature change trends over 30 minutes from 100 to 150 K. Figure 26 (a)-(l) represent the temperature change trends over 30 minutes from 160 to 360 K. The stable operation of a blackbody at 100 K is also one of its performance indicators, and a cooling experiment was conducted to assess this. The blackbody was cooled using liquid nitrogen; liquid nitrogen was connected to the vacuum chamber to ensure a low-temperature experimental environment; liquid nitrogen was also introduced into the heat shield inside the chamber to reduce heat exchange between the heat shield and the blackbody. The cooling experiment results are as follows: Figure 24 As shown, the temperature drops rapidly at the liquid nitrogen inflow point, taking a total of 16 hours to decrease from 293K to 90K.

[0129] In a vacuum environment, the overall heat transfer process of a blackbody mainly includes radiative heat transfer between the radiating surface and the environment, heat transfer between the solid within the structure, cooling by external liquid nitrogen, and heating by the heating mechanism. Data was recorded for 30 minutes after the temperature was raised to the target temperature and held constant.

[0130] 4.3 Measurement of Radiance Temperature

[0131] For vacuum low-temperature surface source blackbodies, the radiance temperature range of 2.5μm-16μm was measured. Figure 27 The brightness temperatures were measured at 310K, 320K, 330K, and 340K under vacuum conditions. Both INSB and MCT detectors were used for the measurements.

[0132] 4.4 Conclusion

[0133] The performance of the vacuum low-temperature surface source blackbody radiation source is shown in Table 2. The blackbody emissivity of 0.992 is better than the target requirement of 0.985; the temperature stability of ≤0.047K / 30min is better than the target requirement of 0.05K / 30min; and the temperature uniformity of 120K-160K≤0.28 and 160K-360K≤0.18 are better than the target requirements of 120K-160K≤0.5 and 160K-360K≤0.2.

[0134] Table 2 Test Indicator Completion Status

[0135]

[0136] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A vacuum low-temperature surface source blackbody, characterized in that, The system includes a blackbody radiation source, comprising a radiation-shielding shell, a fixed base, and a blackbody radiation panel, a heating mechanism, a heat spreader, a heat insulation pad, a temperature sensor, a thermal bridge, a liquid nitrogen pipeline, and a pipeline back-mounting mechanism fixed within the radiation-shielding shell. One side of the heating mechanism is located on the back of the blackbody radiation panel, and its other side is connected to one side of the thermal bridge via the heat spreader. The other side of the thermal bridge is connected to the pipeline back-mounting mechanism. The liquid nitrogen pipeline is located between the thermal bridge and the pipeline back-mounting mechanism and is in contact with both. A heat insulation pad is provided between the thermal bridge and the radiation-shielding shell. The temperature sensor is fixed to the blackbody radiation panel for measuring its temperature. The bottom of the radiation-shielding shell is fixed to the fixed base. The back of the blackbody radiation panel has multiple temperature measuring holes of the same depth arranged in an array. One temperature measuring hole is located at the center of the back of the blackbody radiation panel, and the other temperature measuring holes are symmetrical about the center of the back of the blackbody radiation panel. Each temperature sensor is embedded in the corresponding temperature measuring hole through a countersunk hole and is close to the front of the blackbody radiation panel. The thermal bridge is I-shaped, with one end having an arc surface to wrap the liquid nitrogen pipeline, and the other end having a flat structure to connect with the heat spreader.

2. The vacuum low-temperature surface source blackbody according to claim 1, characterized in that, The blackbody radiation source also includes a protective shell. The blackbody radiation panel, heating mechanism and heat spreader are all located inside the protective shell. A heat insulation block is provided between the outer wall of the blackbody radiation panel and the inner wall of the protective shell. A heat insulation gasket is provided between the outer wall of the protective shell and the inner wall of the radiation shielding shell.

3. The vacuum low-temperature surface source blackbody according to claim 1, characterized in that, The front of the blackbody radiation panel is formed by an array of multiple polygonal pyramids, and its surface is coated with high emissivity black paint.

4. The vacuum low-temperature surface source blackbody according to claim 3, characterized in that, The high emissivity black paint used is Nextel Velvet Black 811-21 black paint.

5. The vacuum low-temperature surface source blackbody according to claim 1, characterized in that, The heating mechanism includes multiple polyimide heating films; each polyimide heating film is attached to the corresponding heating area on the back of the blackbody radiation panel using thermal grease according to the distribution of the temperature sensors; wherein, one polyimide heating film is located in the central area of ​​the back of the blackbody radiation panel, and the distribution of the other polyimide heating films is symmetrical about the center of the back of the blackbody radiation panel.

6. The vacuum low-temperature surface source blackbody according to claim 5, characterized in that, A high-purity indium sheet is bonded between the polyimide heating film and the heat spreader plate using thermal grease to ensure good contact and heat conduction.

7. The vacuum low-temperature surface source blackbody according to claim 1, characterized in that, The liquid nitrogen pipeline includes a liquid nitrogen inlet pipe, a liquid nitrogen outlet pipe, and several liquid nitrogen flow pipes; the top end of each liquid nitrogen flow pipe is connected to the liquid nitrogen inlet pipe, and the bottom end is connected to the liquid nitrogen outlet pipe.

8. The vacuum low-temperature surface source blackbody according to claim 1, characterized in that, It also includes a control cabinet, a power supply system, a temperature control system, and a self-pressurizing liquid nitrogen tank; the temperature control system is connected to the control cabinet; the blackbody radiation source is located inside the vacuum chamber; the control cabinet, temperature control system, and power supply system are all located outside the vacuum chamber, and the control cabinet and temperature control system are powered by the power supply system; the leads of the temperature sensor are soldered to a multi-core aviation connector, which is connected to the temperature control system outside the vacuum chamber through an electrical flange; the liquid nitrogen pipeline is connected to the self-pressurizing liquid nitrogen tank through a control valve; the control valve, heating mechanism, and temperature control system are all connected to the control cabinet.

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