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Infrared technology and application|133 Article(s)
Low-power and high-precision SPAD array readout circuit based on built-in clock
Lixia Zheng, Yongqi Han, Chenggong Wan, Mouzhao Zhou... and Weifeng Sun|Show fewer author(s)
ObjectiveUsing the highly sensitive detection ability of avalanche photoelectricity to weak photon signals, the time of flight can be detected which is obtained after the active laser light source is reflected by the target object. The spatial distance distribution of the measured object, namely the depth of scene information, can be obtained, and the geometric contour image of the target object can be reproduced through relevant algorithms. This Laser Detection and Ranging system composed of APD and readout integrated circuit has the advantages of small size, fast detection rate, high sensitivity, strong anti-interference ability, and is widely used in laser radar, quantum communication, map construction, safe distance detection, unmanned navigation and other fields. With the continuous expansion of the scale of SPAD array and the complexity of application scenarios, higher requirements are put forward for the performance of ROIC. This design focuses on high-precision resolution under low-power constraints. Based on the detailed analysis of the mutual constraints of ROIC array precision, range, area and power consumption, the controllable built-in GRO high-frequency clock drive pixel architecture and event-driven operation mode are adopted to reduce the system power consumption and meet the application requirements of short-range and high-precision ranging imaging.MethodsThe readout integrated circuit for high-precision imaging is established. The ROIC array architecture selects the TDC fully built-in structure, which has unique advantages such as small nonlinearity and good clock phase-splitting uniformity, and eliminates many problems caused by the long-distance routing of polyphase high-frequency clock signals (Fig.1). At the same time, in order to reduce the power consumption, the quantization timing adopts the event-driven quantization method (Fig.3). In order to further pursue higher resolution at rated frequency, the TDC circuit adopts a two-stage structure (Fig.4). In order to ensure clock uniformity and low jitter clock, an external PLL driver with built-in GRO is used to provide the required clock signal (Fig.5).Results and DiscussionsThe packaging and related testing of the samples prepared by the MPW chip are completed using the test instrument provided by the laboratory. The PLL outside the array and the GRO inside the pixel meet the requirements, and the GRO function also meets the requirements (Fig.7). The quantization function and performance of the array are tested, the average resolution of TDC is 102 ps (Fig.8). After evaluating the linearity of pixel TDC, the test results show that the differential nonlinearity of TDC array is not greater than 0.8 LSB, and the integral nonlinearity is not greater than 1.3 LSB (Fig.9). The uniformity of TDC array pixels is tested, and the test results show that the total relative deviation is within ± 0.65%, which indicates that the clock frequency and phase generated by each pixel GRO are different (Fig.10). Compared with similar design schemes at home and abroad, the high-precision TDC array designed can obtain larger range with the same accuracy (Tab.1).ConclusionsIn this study, a readout integrated circuit based on built-in clock is designed. The performance of the readout circuit is tested using the test instrument provided by the laboratory. The resolution of the readout circuit is 102 ps, the differential nonlinearity of the pixel TDC is not more than 0.8 LSB, the integral nonlinearity is not more than 1.3 LSB, and the total relative deviation of the uniformity of the TDC array pixel is within ± 0.65%. By testing the performance of the readout circuit, for the sparse photon detection application environment, the circuit can meet the application requirements of short-range and high-precision, and provide stable imaging function for short-range detection. ObjectiveUsing the highly sensitive detection ability of avalanche photoelectricity to weak photon signals, the time of flight can be detected which is obtained after the active laser light source is reflected by the target object. The spatial distance distribution of the measured object, namely the depth of scene information, can be obtained, and the geometric contour image of the target object can be reproduced through relevant algorithms. This Laser Detection and Ranging system composed of APD and readout integrated circuit has the advantages of small size, fast detection rate, high sensitivity, strong anti-interference ability, and is widely used in laser radar, quantum communication, map construction, safe distance detection, unmanned navigation and other fields. With the continuous expansion of the scale of SPAD array and the complexity of application scenarios, higher requirements are put forward for the performance of ROIC. This design focuses on high-precision resolution under low-power constraints. Based on the detailed analysis of the mutual constraints of ROIC array precision, range, area and power consumption, the controllable built-in GRO high-frequency clock drive pixel architecture and event-driven operation mode are adopted to reduce the system power consumption and meet the application requirements of short-range and high-precision ranging imaging.MethodsThe readout integrated circuit for high-precision imaging is established. The ROIC array architecture selects the TDC fully built-in structure, which has unique advantages such as small nonlinearity and good clock phase-splitting uniformity, and eliminates many problems caused by the long-distance routing of polyphase high-frequency clock signals (Fig.1). At the same time, in order to reduce the power consumption, the quantization timing adopts the event-driven quantization method (Fig.3). In order to further pursue higher resolution at rated frequency, the TDC circuit adopts a two-stage structure (Fig.4). In order to ensure clock uniformity and low jitter clock, an external PLL driver with built-in GRO is used to provide the required clock signal (Fig.5).Results and DiscussionsThe packaging and related testing of the samples prepared by the MPW chip are completed using the test instrument provided by the laboratory. The PLL outside the array and the GRO inside the pixel meet the requirements, and the GRO function also meets the requirements (Fig.7). The quantization function and performance of the array are tested, the average resolution of TDC is 102 ps (Fig.8). After evaluating the linearity of pixel TDC, the test results show that the differential nonlinearity of TDC array is not greater than 0.8 LSB, and the integral nonlinearity is not greater than 1.3 LSB (Fig.9). The uniformity of TDC array pixels is tested, and the test results show that the total relative deviation is within ± 0.65%, which indicates that the clock frequency and phase generated by each pixel GRO are different (Fig.10). Compared with similar design schemes at home and abroad, the high-precision TDC array designed can obtain larger range with the same accuracy (Tab.1).ConclusionsIn this study, a readout integrated circuit based on built-in clock is designed. The performance of the readout circuit is tested using the test instrument provided by the laboratory. The resolution of the readout circuit is 102 ps, the differential nonlinearity of the pixel TDC is not more than 0.8 LSB, the integral nonlinearity is not more than 1.3 LSB, and the total relative deviation of the uniformity of the TDC array pixel is within ± 0.65%. By testing the performance of the readout circuit, for the sparse photon detection application environment, the circuit can meet the application requirements of short-range and high-precision, and provide stable imaging function for short-range detection.
Infrared and Laser Engineering
- Publication Date: Sep. 25, 2023
- Vol. 52, Issue 9, 20220896 (2023)
Linear APD hybrid time-of-flight ranging model and readout circuit design
Jiaqi Shao, Honglei Chen, and Ruijun Ding
ObjectiveCurrently, 3D image sensors based on time-of-flight ranging have been widely used in military and civil applications, such as astronomical detection, target identification, and unmanned vehicles. They are currently being developed in the direction of high sensitivity, high accuracy, and low power consumption in the future. Hybrid time-of-flight ranging, which can achieve high accuracy and high range of lidar ranging, is based on the principle of indirect time-of-flight ranging while incorporating the notion of direct time-of-flight ranging. It has become one of the development paths of time-of-flight ranging. For this purpose, a hybrid ranging model and a 5×5 array readout circuit with 50 µm center distance are designed based on an APD in linear mode as the detector.MethodsA two-segment, two-phase hybrid ranging model is built in this paper (Fig.4). Based on this model, the time-of-flight solution was implemented and the error of background light and counter clock frequency was simulated (Fig.6-7). In order to adapt to the model, the readout circuit selects Capacitor Feedback Transimpedance Amplifier (CTIA) as the input stage, outputs a voltage signal through a sample-and-hold circuit, and generates an 8-bit digital signal through a positive feedback comparator and True Single Phase Clock counter (Fig.3). The accuracy of intensity information is determined by calculating the linearity of the analog voltage output (Fig.9). The accuracy of distance measurement is analyzed by combining analog and digital signals, calculating the time of flight in the vicinity of 108.75 m, and comparing the result to the ideal value (Fig.10).Results and DiscussionsThe hybrid ranging readout circuit can be passively integrated over a range of 0.5 V to 2.5 V with high injection efficiency. CTIA output voltage has 99.83% linearity (Fig.9). In the hybrid ranging simulations over a range of 108.75 m, the K values were correctly determined for most subperiods. The maximum and average errors in the last subperiod are 11.355 cm and 4.415 cm respectively (Fig.10). This error can be greatly reduced by optimizing the data at the first and last ends. Performance of the readout circuit meets design requirements. The simulation results of the main parameters are compared with the advanced designs at home and abroad in various ranging modes (Tab.1). It can be seen that the small array readout circuit based on LM-APD in the paper achieves a much higher range than indirect ranging at a lower modulation frequency using a medium process. It also achieves a higher accuracy with a very low counter cost and good linearity compared with the direct ranging scheme. It provides a hybrid ranging scheme that can be applied to near-medium range.ConclusionsIn this study, a hybrid ranging model is established and systematically analyzed by combining the advantages of direct ranging and indirect ranging. Based on the model, the intensity of reflected background light and continuous pulse light can be found. By using LM-APD, a 5×5 array with 50-μm pixel center distance two-stage two-phase hybrid ranging readout circuit is designed. It consists of two sub-frames of phase in a single frame, with two steps of integration process in each sub-frame. Both a voltage analog output and an 8 bit counter digital output are available from the readout circuit, which employs CTIA as its input stage. Simulation results show that the analog output achieves 99.83% linearity at a modulation frequency of 20 MHz, and the readout circuit achieves a maximum error of 11.355 cm and an average error of 4.415 cm over a hybrid ranging range of 108.75 m. It extends the range to 29 times that of pure indirect ranging, and the readout circuit has great potential for key performance such as accuracy and range. The preliminary simulation results have shown the advantages of hybrid ranging and verified the feasibility of the hybrid ranging model, providing a theoretical and circuit reference for the design of a larger-scale infrared focal plane 3D imaging readout circuit. Further validation and improvement are pending after the flow of the chip. ObjectiveCurrently, 3D image sensors based on time-of-flight ranging have been widely used in military and civil applications, such as astronomical detection, target identification, and unmanned vehicles. They are currently being developed in the direction of high sensitivity, high accuracy, and low power consumption in the future. Hybrid time-of-flight ranging, which can achieve high accuracy and high range of lidar ranging, is based on the principle of indirect time-of-flight ranging while incorporating the notion of direct time-of-flight ranging. It has become one of the development paths of time-of-flight ranging. For this purpose, a hybrid ranging model and a 5×5 array readout circuit with 50 µm center distance are designed based on an APD in linear mode as the detector.MethodsA two-segment, two-phase hybrid ranging model is built in this paper (Fig.4). Based on this model, the time-of-flight solution was implemented and the error of background light and counter clock frequency was simulated (Fig.6-7). In order to adapt to the model, the readout circuit selects Capacitor Feedback Transimpedance Amplifier (CTIA) as the input stage, outputs a voltage signal through a sample-and-hold circuit, and generates an 8-bit digital signal through a positive feedback comparator and True Single Phase Clock counter (Fig.3). The accuracy of intensity information is determined by calculating the linearity of the analog voltage output (Fig.9). The accuracy of distance measurement is analyzed by combining analog and digital signals, calculating the time of flight in the vicinity of 108.75 m, and comparing the result to the ideal value (Fig.10).Results and DiscussionsThe hybrid ranging readout circuit can be passively integrated over a range of 0.5 V to 2.5 V with high injection efficiency. CTIA output voltage has 99.83% linearity (Fig.9). In the hybrid ranging simulations over a range of 108.75 m, the K values were correctly determined for most subperiods. The maximum and average errors in the last subperiod are 11.355 cm and 4.415 cm respectively (Fig.10). This error can be greatly reduced by optimizing the data at the first and last ends. Performance of the readout circuit meets design requirements. The simulation results of the main parameters are compared with the advanced designs at home and abroad in various ranging modes (Tab.1). It can be seen that the small array readout circuit based on LM-APD in the paper achieves a much higher range than indirect ranging at a lower modulation frequency using a medium process. It also achieves a higher accuracy with a very low counter cost and good linearity compared with the direct ranging scheme. It provides a hybrid ranging scheme that can be applied to near-medium range.ConclusionsIn this study, a hybrid ranging model is established and systematically analyzed by combining the advantages of direct ranging and indirect ranging. Based on the model, the intensity of reflected background light and continuous pulse light can be found. By using LM-APD, a 5×5 array with 50-μm pixel center distance two-stage two-phase hybrid ranging readout circuit is designed. It consists of two sub-frames of phase in a single frame, with two steps of integration process in each sub-frame. Both a voltage analog output and an 8 bit counter digital output are available from the readout circuit, which employs CTIA as its input stage. Simulation results show that the analog output achieves 99.83% linearity at a modulation frequency of 20 MHz, and the readout circuit achieves a maximum error of 11.355 cm and an average error of 4.415 cm over a hybrid ranging range of 108.75 m. It extends the range to 29 times that of pure indirect ranging, and the readout circuit has great potential for key performance such as accuracy and range. The preliminary simulation results have shown the advantages of hybrid ranging and verified the feasibility of the hybrid ranging model, providing a theoretical and circuit reference for the design of a larger-scale infrared focal plane 3D imaging readout circuit. Further validation and improvement are pending after the flow of the chip.
Infrared and Laser Engineering
- Publication Date: Sep. 25, 2023
- Vol. 52, Issue 9, 20220892 (2023)
Spectral responsivity of mosaic SWIR detectors
Qingjun Liao, Xiaoning Hu, Aibo Huang, Honglei Chen... and Ruijun Ding|Show fewer author(s)
ObjectiveHyperspectral imaging can not only get the two-dimensional geometric spatial information of the observed objects, but also obtain the continuous high-resolution spectral information which can reflect the physical and chemical characteristics of the target. It is a very important method for target detection and recognition based on hyperspectral remote sensing information. Spectral range of typical imaging spectrometer is 0.4-2.5 µm due to the ground objects' reflection of solar radiation. Mercury Cadmium Telluride (Hg1-xCdxTe) detectors cover a bandwidth of 0.8-30 µm as the alloy composition of Hg1-xCdxTe material is tuned in terms of cut-off wavelength. Hg1-xCdxTe detectors are the major part of the imaging spectrometer for detection in short waveband. As the swath width of the imaging spectrometer increased, larger scale infrared focal plane array (IRFPA) is needed. Mosaic ultra-large scale shortwave infrared (SWIR) detectors can meet the demand for wide field of view detection in space application. The detector modules for butting have their own spectral responsivity. Hyperspectral imaging demands that the mosaic IRFPA has high uniformity of the spectral response. Therefore, it is necessary to measure and analyse the spectral responsivity specification of the mosaic IRFPA accurately and quantitatively for the hyperspectral imaging application. For this purpose, a method for evaluating the absolute spectral responsivity of the mosaic SWIR detectors is proposed in this paper. MethodsThis paper presents a method for measuring the absolute spectral responsivity accurately and quantitative analysis of the spectral responsivity specification of the mosaic 2 000×256 SWIR detector for imaging spectrometer. The relative response spectrum is measured by a precisely calibrated grating monochromator system. Five optical filters with different center wavelength (CW) and full width at half maximum (FWHM) were chosen to analyze and measure the narrow band responsivity (Tab.1). The center wavelength of the filter is 1225 nm, 1670 nm, 2062 nm, 2420 nm and 2470 nm respectively. The bandwidth is 10 nm and 50 nm, and the cut-off depth is OD3 (optical density). Spectral responsivity is calculated by relative response and narrow-band responsivity.Results and DiscussionsThe cut-off wavelength of detector to be tested is 2.6 μm, and its pitch size is 30 μm×60 μm. The integration time of the read-out integrated circuit (ROIC) is 4.4 ms and integration capacity is 65 fF. F number of the Dewar is 0.9. The results of output signal analysis with filter of different CW at different black body temperature show that narrow-band responsivity is much lower than out-of-band response (Tab.2, Fig.3) with 1# filter and much higher (Tab.2, Fig.4) with 5# filter. The possibility of narrow-band signal's accurate measurement at 1200 nm is discussed if the bandwidth is widened to 200 nm and the cut-off depth is adapted to OD4 and OD5 (Tab.3). It shows that narrow band responsivity can be measured precisely only when cut-off depth is smaller than OD5 and FWHM is wider than 200 nm. Based on the result of the analysis, for HgCdTe SWIR detector the measurement error is smallest when the filter's center wavelength is 2470 nm, FWHM is 50 nm, and cut-off depth is OD3 at 80 ℃ black body temperature. The absolute spectral responsivity of four HgCdTe detectors is measured by the relative response curve and narrow-band responsivity (Fig.7). According to the spectral responsivity curve, the responsivity non-uniformity of four detectors can be calculated to be 6.23%, 6.06%, 4.07% at 1 μm, 1.9 μm and 2.5 μm respectively (Fig.8). ConclusionsIn this study, a quantitative method for measuring the spectral responsivity accurately and analyzing the spectral responsivity specification of the mosaic 2000×256 SWIR detector for imaging spectrometer is proposed. The results of this study demonstrated that spectral responsivity of Hg1-xCdxTe SWIR can be measured accurately when the filter's center wavelength is 2470 nm, FWHM is 50 nm, and cut-off depth is OD3 at 80 ℃ black body temperature. Narrow-band spectral response output signal is much larger than signal caused by out-of-band response. The spectral responsivity non-uniformity of the four detectors helps to evaluate the response uniformity of spectral dimension response of 2000×256 SWIR detector quantitatively. The results have demonstrated that the use of this measuring method promotes appropriate application of IRFPA detectors in hyperspectral imaging. ObjectiveHyperspectral imaging can not only get the two-dimensional geometric spatial information of the observed objects, but also obtain the continuous high-resolution spectral information which can reflect the physical and chemical characteristics of the target. It is a very important method for target detection and recognition based on hyperspectral remote sensing information. Spectral range of typical imaging spectrometer is 0.4-2.5 µm due to the ground objects' reflection of solar radiation. Mercury Cadmium Telluride (Hg1-xCdxTe) detectors cover a bandwidth of 0.8-30 µm as the alloy composition of Hg1-xCdxTe material is tuned in terms of cut-off wavelength. Hg1-xCdxTe detectors are the major part of the imaging spectrometer for detection in short waveband. As the swath width of the imaging spectrometer increased, larger scale infrared focal plane array (IRFPA) is needed. Mosaic ultra-large scale shortwave infrared (SWIR) detectors can meet the demand for wide field of view detection in space application. The detector modules for butting have their own spectral responsivity. Hyperspectral imaging demands that the mosaic IRFPA has high uniformity of the spectral response. Therefore, it is necessary to measure and analyse the spectral responsivity specification of the mosaic IRFPA accurately and quantitatively for the hyperspectral imaging application. For this purpose, a method for evaluating the absolute spectral responsivity of the mosaic SWIR detectors is proposed in this paper. MethodsThis paper presents a method for measuring the absolute spectral responsivity accurately and quantitative analysis of the spectral responsivity specification of the mosaic 2 000×256 SWIR detector for imaging spectrometer. The relative response spectrum is measured by a precisely calibrated grating monochromator system. Five optical filters with different center wavelength (CW) and full width at half maximum (FWHM) were chosen to analyze and measure the narrow band responsivity (Tab.1). The center wavelength of the filter is 1225 nm, 1670 nm, 2062 nm, 2420 nm and 2470 nm respectively. The bandwidth is 10 nm and 50 nm, and the cut-off depth is OD3 (optical density). Spectral responsivity is calculated by relative response and narrow-band responsivity.Results and DiscussionsThe cut-off wavelength of detector to be tested is 2.6 μm, and its pitch size is 30 μm×60 μm. The integration time of the read-out integrated circuit (ROIC) is 4.4 ms and integration capacity is 65 fF. F number of the Dewar is 0.9. The results of output signal analysis with filter of different CW at different black body temperature show that narrow-band responsivity is much lower than out-of-band response (Tab.2, Fig.3) with 1# filter and much higher (Tab.2, Fig.4) with 5# filter. The possibility of narrow-band signal's accurate measurement at 1200 nm is discussed if the bandwidth is widened to 200 nm and the cut-off depth is adapted to OD4 and OD5 (Tab.3). It shows that narrow band responsivity can be measured precisely only when cut-off depth is smaller than OD5 and FWHM is wider than 200 nm. Based on the result of the analysis, for HgCdTe SWIR detector the measurement error is smallest when the filter's center wavelength is 2470 nm, FWHM is 50 nm, and cut-off depth is OD3 at 80 ℃ black body temperature. The absolute spectral responsivity of four HgCdTe detectors is measured by the relative response curve and narrow-band responsivity (Fig.7). According to the spectral responsivity curve, the responsivity non-uniformity of four detectors can be calculated to be 6.23%, 6.06%, 4.07% at 1 μm, 1.9 μm and 2.5 μm respectively (Fig.8). ConclusionsIn this study, a quantitative method for measuring the spectral responsivity accurately and analyzing the spectral responsivity specification of the mosaic 2000×256 SWIR detector for imaging spectrometer is proposed. The results of this study demonstrated that spectral responsivity of Hg1-xCdxTe SWIR can be measured accurately when the filter's center wavelength is 2470 nm, FWHM is 50 nm, and cut-off depth is OD3 at 80 ℃ black body temperature. Narrow-band spectral response output signal is much larger than signal caused by out-of-band response. The spectral responsivity non-uniformity of the four detectors helps to evaluate the response uniformity of spectral dimension response of 2000×256 SWIR detector quantitatively. The results have demonstrated that the use of this measuring method promotes appropriate application of IRFPA detectors in hyperspectral imaging.
Infrared and Laser Engineering
- Publication Date: Sep. 25, 2023
- Vol. 52, Issue 9, 20220890 (2023)
Optimization of nBn dual-band mid-/long-wavelength detector based on InAs/GaSb superlattice
Wenjing Liu, Lianqing Zhu, Dongliang Zhang, Xiantong Zheng... and Ming Liu|Show fewer author(s)
ObjectiveInfrared photodetectors are useful for a variety of military and civil applications, such as space science, military equipment, industrial production and so on. Presently, infrared photodetectors are developing towards high performance and low cost to meet the technical requirements. Compared to single color detectors, dual-band infrared detectors covering different atmospheric windows allow for simultaneous acquisition of target information in both wavelengths which is the most obvious advantage. Therefore, the dual-band capability of the detector makes it possible to discriminate between different temperatures and objects, improving the accuracy of temperature measurement and target recognition. Complex infrared backgrounds can be suppressed and it is possible to reduce the false alarm rates significantly in early warning, searching and tracking systems. Mid-long wavelength dual-band infrared detectors based on type II superlattice have great advantages in terms of cost and performance, and have become a popular research topic in the field of new infrared detectors. However, infrared detectors need to reduce dark current density and crosstalk to achieve better performance. The nBn superlattice detector has a unique band gap engineering approach, which can work at a higher temperature and has better thermal stability compared to traditional single color detectors. This leads to better performance and longer operating life in harsh environments. Additionally, the nBn structure has a high absorption coefficient, resulting in a high detectivity and low noise. However, the development of nBn superlattice dual-band detectors faces several challenges, such as the difficulties in fabrication and the limitations in performance. The fabrication of the nBn structure requires precise control of the layer thickness and doping levels, which is a complex process. Besides, the performance of the nBn detector is limited by dark current and temperature. These issues need to be addressed through further research and development. To this end, the paper designs an InAs/GaSb superlattice mid/long dual-band infrared detector with nBn structure to reduce dark current density and crosstalk by simulation of silvaco.MethodsThe materials of the mid-band and the long-band absorber are selected by calculating the band gap of InAs/GaSb using the k.p model to meet the requirements of the design objectives. The mid/long dual-band infrared detectors model with nBn structure is eatablished by silvaco, and the responsivity and dark current density values of the mid/long waveband channels are compared by simulating some device structures at different bias voltages. The effects of the barrier layer thickness, absorber layer thickness, and doping in different regions are analyzed to obtain the best model parameters to reduce the dark current density and crosstalk.Results and DiscussionsBy modeling and simulating the nBn type II superlattice mid/long dual-band infrared detector structure, the thickness of the absorber and barrier layers and the doping concentration are optimized to reduce the dark current and the crosstalk in the mid-band and the long-band channel. At 77 K, the cutoff wavelengths of the dual-band detector are 4.8 µm （50%） at 0.3 V and 10.5 µm （50%） at -0.3 V (Tab.8) with the detectivies of 3.9×1011 cm·Hz1/2W-1 and 4.1×1011 cm·Hz1/2W-1 (Tab.9). The dark current density is 4×10-5 A·cm-2 and 1.3×10-4 A·cm-2 respectively (Tab.7). This provides a theoretical basis for subsequent material growth and device processes. ConclusionsThe advantages of the designed superlattice mid/long dual-band infrared detector are simple device structure, low dark current density, and similar detection rate compared with the foreign InAs/InAsSb infrared detectors based on nBn structure and domestic InAs/GaSb infrared detectors based on PπMN structure. The simulation performance will have some differences with the actual device performance, so the subsequent material growth and device process will be carried out to further feedback the simulation, and the device structure will be further improved. ObjectiveInfrared photodetectors are useful for a variety of military and civil applications, such as space science, military equipment, industrial production and so on. Presently, infrared photodetectors are developing towards high performance and low cost to meet the technical requirements. Compared to single color detectors, dual-band infrared detectors covering different atmospheric windows allow for simultaneous acquisition of target information in both wavelengths which is the most obvious advantage. Therefore, the dual-band capability of the detector makes it possible to discriminate between different temperatures and objects, improving the accuracy of temperature measurement and target recognition. Complex infrared backgrounds can be suppressed and it is possible to reduce the false alarm rates significantly in early warning, searching and tracking systems. Mid-long wavelength dual-band infrared detectors based on type II superlattice have great advantages in terms of cost and performance, and have become a popular research topic in the field of new infrared detectors. However, infrared detectors need to reduce dark current density and crosstalk to achieve better performance. The nBn superlattice detector has a unique band gap engineering approach, which can work at a higher temperature and has better thermal stability compared to traditional single color detectors. This leads to better performance and longer operating life in harsh environments. Additionally, the nBn structure has a high absorption coefficient, resulting in a high detectivity and low noise. However, the development of nBn superlattice dual-band detectors faces several challenges, such as the difficulties in fabrication and the limitations in performance. The fabrication of the nBn structure requires precise control of the layer thickness and doping levels, which is a complex process. Besides, the performance of the nBn detector is limited by dark current and temperature. These issues need to be addressed through further research and development. To this end, the paper designs an InAs/GaSb superlattice mid/long dual-band infrared detector with nBn structure to reduce dark current density and crosstalk by simulation of silvaco.MethodsThe materials of the mid-band and the long-band absorber are selected by calculating the band gap of InAs/GaSb using the k.p model to meet the requirements of the design objectives. The mid/long dual-band infrared detectors model with nBn structure is eatablished by silvaco, and the responsivity and dark current density values of the mid/long waveband channels are compared by simulating some device structures at different bias voltages. The effects of the barrier layer thickness, absorber layer thickness, and doping in different regions are analyzed to obtain the best model parameters to reduce the dark current density and crosstalk.Results and DiscussionsBy modeling and simulating the nBn type II superlattice mid/long dual-band infrared detector structure, the thickness of the absorber and barrier layers and the doping concentration are optimized to reduce the dark current and the crosstalk in the mid-band and the long-band channel. At 77 K, the cutoff wavelengths of the dual-band detector are 4.8 µm （50%） at 0.3 V and 10.5 µm （50%） at -0.3 V (Tab.8) with the detectivies of 3.9×1011 cm·Hz1/2W-1 and 4.1×1011 cm·Hz1/2W-1 (Tab.9). The dark current density is 4×10-5 A·cm-2 and 1.3×10-4 A·cm-2 respectively (Tab.7). This provides a theoretical basis for subsequent material growth and device processes. ConclusionsThe advantages of the designed superlattice mid/long dual-band infrared detector are simple device structure, low dark current density, and similar detection rate compared with the foreign InAs/InAsSb infrared detectors based on nBn structure and domestic InAs/GaSb infrared detectors based on PπMN structure. The simulation performance will have some differences with the actual device performance, so the subsequent material growth and device process will be carried out to further feedback the simulation, and the device structure will be further improved.
Infrared and Laser Engineering
- Publication Date: Sep. 25, 2023
- Vol. 52, Issue 9, 20220837 (2023)
Stray light analysis and suppression of long-wave infrared Dewar component for cold optics
Haiyong Zhu, Junlin Chen, Zhijiang Zeng, Xiaokun Wang... and Xue Li|Show fewer author(s)
ObjectiveAs the main detection spectrum of infrared earth optical payload, infrared spectrum (8-12.5 μm) plays an important role in earth remote sensing. With the development of space imaging optical technology, the requirements for the detection performance of imaging satellites are constantly improving, and the imaging satellites are developing towards high resolution, high spatial resolution and wide radiation. For example, Venezuela’s Remote Sensing Satellite (VRSS) infrared camera, NASA's Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) infrared camera, etc. The infrared imager achieves a spatial resolution of 30 m and a width of 300 km by whiskbroom, which ensures high resolution and improves the imaging width. The influence of stray light on it is particularly prominent when the infrared remote sensing instrument with high resolution and large field of view extracts the remote sensing information of weak targets. If the suppression of stray light is insufficient, the energy distribution on the image plane is uneven, which leads to the decrease of signal-to-noise ratio and modulation transfer function (MTF), and the nonuniformity becomes worse. In severe cases, the detection signal of the detector is annihilated by stray light of background radiation, which results in the failure of the detector. Therefore, the design of stray light suppression for infrared imager is the premise to ensure its on-orbit imaging quality. The long-wave infrared Dewar module is an important part of the imager. Because the optical structure of the Dewar module is close to the detector, the detector is more sensitive to the optical structure, so the design of stray light suppression of the Dewar module is particularly important.MethodsIn view of the above requirements, this research analyzed four key surfaces of spurious radiation in opto-mechanical system, including lens, lens barrel, Dewar window and window cap, among which lens barrel was the main source of spurious radiation (Fig.2). Cryogenic optical design was adopted to reduce stray radiation, including 195 K lens, 180 K lens barrel, 200 K Dewar window cap and window design (Tab.2). In order to realize the low-temperature Dewar design, flexible bellows were introduced into the Dewar package structure to increase the thermal resistance between the refrigerator coupling surface and the window cap, and realize the thermal isolation between the 200 K low-temperature window cap and the 240 K expander (Fig.1). The effects of window, window shell, cold screen structure and surface treatment technology of Dewar module on stray light in Dewar were studied (Fig.6, Fig.8, Fig.9).Results and DiscussionsBased on the analysis above, the innovative results are as follows. (1) The flexible bellows were introduced into the Dewar package structure to increase the thermal resistance between the coupling surface of the refrigerator and the window cap, and the design of 200 K low temperature window and window cap was realized, and the radiation suppression in the optical machine was at a good level (Tab.2). After the measurement, the temperature gradient of cold end and hot end of bellows reached 37-48 K (Tab.1). (2) The cold screen adopted three-stage baffle design, and the filter was integrated in three bands. Considering the assembly and machining accuracy, the cold screen and the filter bracket were separated. The radiation suppression in the optical-mechanical system was at a good level (Fig.10-12, Tab.3).ConclusionsThe main objective is to reduce the radiation stray light of infrared remote sensing instrument with high resolution and large field of view. Reasonable low temperature design is beneficial to restrain the stray radiation of the module, and the flexible bellows shell insulation structure with 0.1 mm wall thickness is an effective means to realize the design of 200 K low temperature window and window cap. As the main source of optical-mechanical stray internal radiation, the influence of lens barrel on it should be considered when considering the processing and design of cold screen and window. This research provides theoretical and technical reference for the design and processing of low-temperature Dewar. ObjectiveAs the main detection spectrum of infrared earth optical payload, infrared spectrum (8-12.5 μm) plays an important role in earth remote sensing. With the development of space imaging optical technology, the requirements for the detection performance of imaging satellites are constantly improving, and the imaging satellites are developing towards high resolution, high spatial resolution and wide radiation. For example, Venezuela’s Remote Sensing Satellite (VRSS) infrared camera, NASA's Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) infrared camera, etc. The infrared imager achieves a spatial resolution of 30 m and a width of 300 km by whiskbroom, which ensures high resolution and improves the imaging width. The influence of stray light on it is particularly prominent when the infrared remote sensing instrument with high resolution and large field of view extracts the remote sensing information of weak targets. If the suppression of stray light is insufficient, the energy distribution on the image plane is uneven, which leads to the decrease of signal-to-noise ratio and modulation transfer function (MTF), and the nonuniformity becomes worse. In severe cases, the detection signal of the detector is annihilated by stray light of background radiation, which results in the failure of the detector. Therefore, the design of stray light suppression for infrared imager is the premise to ensure its on-orbit imaging quality. The long-wave infrared Dewar module is an important part of the imager. Because the optical structure of the Dewar module is close to the detector, the detector is more sensitive to the optical structure, so the design of stray light suppression of the Dewar module is particularly important.MethodsIn view of the above requirements, this research analyzed four key surfaces of spurious radiation in opto-mechanical system, including lens, lens barrel, Dewar window and window cap, among which lens barrel was the main source of spurious radiation (Fig.2). Cryogenic optical design was adopted to reduce stray radiation, including 195 K lens, 180 K lens barrel, 200 K Dewar window cap and window design (Tab.2). In order to realize the low-temperature Dewar design, flexible bellows were introduced into the Dewar package structure to increase the thermal resistance between the refrigerator coupling surface and the window cap, and realize the thermal isolation between the 200 K low-temperature window cap and the 240 K expander (Fig.1). The effects of window, window shell, cold screen structure and surface treatment technology of Dewar module on stray light in Dewar were studied (Fig.6, Fig.8, Fig.9).Results and DiscussionsBased on the analysis above, the innovative results are as follows. (1) The flexible bellows were introduced into the Dewar package structure to increase the thermal resistance between the coupling surface of the refrigerator and the window cap, and the design of 200 K low temperature window and window cap was realized, and the radiation suppression in the optical machine was at a good level (Tab.2). After the measurement, the temperature gradient of cold end and hot end of bellows reached 37-48 K (Tab.1). (2) The cold screen adopted three-stage baffle design, and the filter was integrated in three bands. Considering the assembly and machining accuracy, the cold screen and the filter bracket were separated. The radiation suppression in the optical-mechanical system was at a good level (Fig.10-12, Tab.3).ConclusionsThe main objective is to reduce the radiation stray light of infrared remote sensing instrument with high resolution and large field of view. Reasonable low temperature design is beneficial to restrain the stray radiation of the module, and the flexible bellows shell insulation structure with 0.1 mm wall thickness is an effective means to realize the design of 200 K low temperature window and window cap. As the main source of optical-mechanical stray internal radiation, the influence of lens barrel on it should be considered when considering the processing and design of cold screen and window. This research provides theoretical and technical reference for the design and processing of low-temperature Dewar.
Infrared and Laser Engineering
- Publication Date: Jul. 25, 2023
- Vol. 52, Issue 7, 20220823 (2023)
Numerical simulation of infrared radiation characteristics of the B-2-like aircraft
Rong Lv, Qinglin Niu, and Shikui Dong
ObjectiveThe B-2-like aircraft is the only active strategic bomber with excellent stealth performance in the world, and its low detectability is attributed to its unique radar absorbing coating and small radar cross section. However, the high-temperature gas from the exhaust plume cannot be directly concealed and eliminated, becoming a potential main source of infrared radiation. For B-2-like aircraft, the infrared radiation may comes from the high-temperature components such as the engine's high-temperature plume, skin, and nozzle. The exhaust plume of an engine often contains components such as CO2, H2O, and CO, which can emit intense infrared radiation at specific wavelengths through vibrotational transitions at high temperatures. In addition, the skin subjected to aerodynamic heating will also emit a continuous spectrum that follows Planck's law. This paper numerically analyzes the infrared radiation characteristics of the B-2 like aircraft at different observation angles under a representative flight condition (12 km@0.8 Ma), including the spectrum, integrated radiances, and synthetic IR image. MethodsTaking the B-2-like aircraft as the research object (Fig.3), the flow and thermal characteristic parameters of the engine nozzle are calculated by using the segmental specific heat method in the ideal gas state. The Navier-Stokes equation is solved based on the FVM method to obtain the flow field. The skin temperature is calculated based on the radiation equilibrium wall condition. Based on the statistical narrow-band (SNB) model, the physical properties of radiating gases are calculated, and the radiation transport equation (RTE) is solved using the light-of-sight (LOS) method. The Cartesian coordinate system is used to describe the radiation distribution in observation angles in 2π space, and the observation angle is described by the zenith angle θ and the circumference φ (Fig.5). Results and DiscussionsThe high-temperature regions of the aircraft is mainly located near the handpiece, air intake, engine compartment lid, and nozzle, with the highest temperature approaching 250 K (Fig.7). A significant afterburning effect occurs within a certain range from the nozzle, resulting in an increase of the plume temperature to 540 K, and an increase of the mass fractions of H2O and CO2 to 0.045 and 0.025, respectively (Fig.8). The spectral intensity of the skin is the highest in the top view with a peak value of 596 W/(sr·μm). The peak spectral intensity in the bottom view is 78.2% of that in the top view. The peak spectral intensity in the side, front, and rear views is similar, which is 12.8% of that in the top view (Fig.9). In the top view, the total spectral radiation intensity of the target is nearly 3 orders of magnitude higher than that of the skin, and the spectral peak value is in bands of 2.7 μm, 4.3 μm and 5-8 μm (Fig.12). The integrated radiation intensities of skin in the MWIR and LWIR bands are 8.2 W/sr and 1.9×103 W/sr, respectively (Fig.10-11), and the total radiation intensity of the target is 1×103 W/sr and 2.01×103 W/sr (Fig.13-14). The maximum radiation intensity of the plume of the B-2-like aircraft in the MWIR band is approximately 2 times that of the LWIR band and four times that of the 4.3 μm band. In particular, the radiation intensity in the MWIR band is nearly three orders of magnitude higher than that in the 2.7 μm band (Fig.16). ConclusionsThe radiation intensity of the B-2-like aircraft strongly depends on the wave band and observation angle, and the radiation intensity of the target is the strongest in the top view. The main sources of target radiation intensity in the MWIR band and the LWIR band are the exhaust plume and the aircraft body, respectively. This work can provide a theoretical reference for target characteristic identification of the B-2-like aircraft. ObjectiveThe B-2-like aircraft is the only active strategic bomber with excellent stealth performance in the world, and its low detectability is attributed to its unique radar absorbing coating and small radar cross section. However, the high-temperature gas from the exhaust plume cannot be directly concealed and eliminated, becoming a potential main source of infrared radiation. For B-2-like aircraft, the infrared radiation may comes from the high-temperature components such as the engine's high-temperature plume, skin, and nozzle. The exhaust plume of an engine often contains components such as CO2, H2O, and CO, which can emit intense infrared radiation at specific wavelengths through vibrotational transitions at high temperatures. In addition, the skin subjected to aerodynamic heating will also emit a continuous spectrum that follows Planck's law. This paper numerically analyzes the infrared radiation characteristics of the B-2 like aircraft at different observation angles under a representative flight condition (12 km@0.8 Ma), including the spectrum, integrated radiances, and synthetic IR image. MethodsTaking the B-2-like aircraft as the research object (Fig.3), the flow and thermal characteristic parameters of the engine nozzle are calculated by using the segmental specific heat method in the ideal gas state. The Navier-Stokes equation is solved based on the FVM method to obtain the flow field. The skin temperature is calculated based on the radiation equilibrium wall condition. Based on the statistical narrow-band (SNB) model, the physical properties of radiating gases are calculated, and the radiation transport equation (RTE) is solved using the light-of-sight (LOS) method. The Cartesian coordinate system is used to describe the radiation distribution in observation angles in 2π space, and the observation angle is described by the zenith angle θ and the circumference φ (Fig.5). Results and DiscussionsThe high-temperature regions of the aircraft is mainly located near the handpiece, air intake, engine compartment lid, and nozzle, with the highest temperature approaching 250 K (Fig.7). A significant afterburning effect occurs within a certain range from the nozzle, resulting in an increase of the plume temperature to 540 K, and an increase of the mass fractions of H2O and CO2 to 0.045 and 0.025, respectively (Fig.8). The spectral intensity of the skin is the highest in the top view with a peak value of 596 W/(sr·μm). The peak spectral intensity in the bottom view is 78.2% of that in the top view. The peak spectral intensity in the side, front, and rear views is similar, which is 12.8% of that in the top view (Fig.9). In the top view, the total spectral radiation intensity of the target is nearly 3 orders of magnitude higher than that of the skin, and the spectral peak value is in bands of 2.7 μm, 4.3 μm and 5-8 μm (Fig.12). The integrated radiation intensities of skin in the MWIR and LWIR bands are 8.2 W/sr and 1.9×103 W/sr, respectively (Fig.10-11), and the total radiation intensity of the target is 1×103 W/sr and 2.01×103 W/sr (Fig.13-14). The maximum radiation intensity of the plume of the B-2-like aircraft in the MWIR band is approximately 2 times that of the LWIR band and four times that of the 4.3 μm band. In particular, the radiation intensity in the MWIR band is nearly three orders of magnitude higher than that in the 2.7 μm band (Fig.16). ConclusionsThe radiation intensity of the B-2-like aircraft strongly depends on the wave band and observation angle, and the radiation intensity of the target is the strongest in the top view. The main sources of target radiation intensity in the MWIR band and the LWIR band are the exhaust plume and the aircraft body, respectively. This work can provide a theoretical reference for target characteristic identification of the B-2-like aircraft.
Infrared and Laser Engineering
- Publication Date: Jul. 25, 2023
- Vol. 52, Issue 7, 20220810 (2023)
Research on long wave detection of low feature surface aircraft in sea environment
Minmin Song, Tao Lv, Xueyi Sang, Fenfen Xue, and Jianping Su
ObjectiveMost of the new generation of surface aircraft further use stealth, power control and other means to improve their penetration ability, and their infrared radiation energy has dropped significantly, bringing more and more challenges to shipborne air defense. The medium and long wave dual-band infrared detection method effectively utilizes the different characteristics of the target radiation in the two bands to enhance the detection ability of different radiation energy areas of the surface aircraft with low characteristics at the same time.MethodsThe infrared radiation model of an surface aircraft at different detection angles is established by using ray tracing and inverse Monte Carlo method, and the medium-long wave infrared radiation intensity of an surface aircraft at different detection angles is completed. Then, based on the calculation results of side-to-head radiation intensity, the differences of medium-long wave detection under special conditions such as rain and sea fog in the marine environment are compared and analyzed, and the medium-long wave detection data at different distances are obtained by means of the detection test of weak and small targets under the complex sea background in the actual outfield, and the equivalent temperature difference between the target and the sea background is statistically analyzed.Results and DiscussionsThe calculation results of medium and long wave infrared radiation intensity distribution of an surface aircraft at different detection angles are shown in Figure 5; The impact of sea haze, overcast rain and other weather on medium-long wave detection is shown in Figure 6 and Figure 7 respectively; The influence of sea clutter on medium and long wave detection is shown in Figure 8 and Table 2. Through the above work, the advantages and disadvantages of medium-wave and long-wave bands under different climate and sea background conditions are statistically analyzed, and the advantages of medium-wave and long-wave composite detection technology are fully verified.ConclusionsIn sunny weather and good visibility, long-wave detection has advantages in weak and small target recognition and anti-sea clutter interference. However, in case of sea fog, rainfall conditions and poor visibility, medium-wave detection is superior to long-wave detection. Therefore, it is necessary to use the medium-long wave composite detection method to learn from each other's strong points and compensate for the weak and small target recognition probability under various sea environment conditions. ObjectiveMost of the new generation of surface aircraft further use stealth, power control and other means to improve their penetration ability, and their infrared radiation energy has dropped significantly, bringing more and more challenges to shipborne air defense. The medium and long wave dual-band infrared detection method effectively utilizes the different characteristics of the target radiation in the two bands to enhance the detection ability of different radiation energy areas of the surface aircraft with low characteristics at the same time.MethodsThe infrared radiation model of an surface aircraft at different detection angles is established by using ray tracing and inverse Monte Carlo method, and the medium-long wave infrared radiation intensity of an surface aircraft at different detection angles is completed. Then, based on the calculation results of side-to-head radiation intensity, the differences of medium-long wave detection under special conditions such as rain and sea fog in the marine environment are compared and analyzed, and the medium-long wave detection data at different distances are obtained by means of the detection test of weak and small targets under the complex sea background in the actual outfield, and the equivalent temperature difference between the target and the sea background is statistically analyzed.Results and DiscussionsThe calculation results of medium and long wave infrared radiation intensity distribution of an surface aircraft at different detection angles are shown in Figure 5; The impact of sea haze, overcast rain and other weather on medium-long wave detection is shown in Figure 6 and Figure 7 respectively; The influence of sea clutter on medium and long wave detection is shown in Figure 8 and Table 2. Through the above work, the advantages and disadvantages of medium-wave and long-wave bands under different climate and sea background conditions are statistically analyzed, and the advantages of medium-wave and long-wave composite detection technology are fully verified.ConclusionsIn sunny weather and good visibility, long-wave detection has advantages in weak and small target recognition and anti-sea clutter interference. However, in case of sea fog, rainfall conditions and poor visibility, medium-wave detection is superior to long-wave detection. Therefore, it is necessary to use the medium-long wave composite detection method to learn from each other's strong points and compensate for the weak and small target recognition probability under various sea environment conditions.
Infrared and Laser Engineering
- Publication Date: Jul. 25, 2023
- Vol. 52, Issue 7, 20220807 (2023)
Analysis of airborne infrared detection performance of submarine thermal wake in stratified seawater
Yingchao Li, Ze Pan, Guanlin Li, Haodong Shi, and Qiang Fu
ObjectiveAt present, most of the calculation methods for thermal wake detection by MRTD analysis consider the water body as uniformly distributed seawater. The stratified nature of seawater temperature and density has great influence on the inversion accuracy of submarine thermal wake on the surface temperature distribution, rise time and wake rise distance. However, the research at home and abroad mainly focuses on the improvement of MRTD algorithm of infrared system or derivation of the detection ability of infrared detector based on other parameters of the system, as well as the influence of weather and other factors on wake detection, and has not analyzed the influence of seawater stratification on wake detection and inversion. Therefore, the research on infrared radiation detection of thermal wake under the conditions of stratified seawater temperature and density is of great significance to the infrared detection of submarines.MethodsFor the lack of infrared detection of submarine thermal wake under the condition of stratified sea water temperature and density, the calculation error of detection distance and inversion accuracy error of submarine are large. Based on the finite element analysis method, the research on submarine infrared radiation characteristics under the condition of seawater stratification is carried out in this paper. Firstly, the finite element analysis method is used to simulate the floating process of submarine thermal wake in stratified seawater by a full-size submarine model with propeller and bridge characteristics. Then, according to the sea surface infrared radiation model and atmospheric transmission model, the full-link mathematical and physical model of the wake from floating diffusion, atmospheric transmission atmospheric attenuation to sensor detection is built, and the detection distance of the infrared detector to the submarine thermal wake under the condition of layered seawater is calculated according to the specific infrared detector performance parameters.Results and DiscussionsThe comparison shows that the stratification condition of seawater has a great influence on the detection of wake. With 95% detection probability, the detection distance of the wake increases by 10.61%, the identification distance of the wake increases by 9.32%, and the recognition distance of the wake increases by 8.28% (Tab.2). In the case of stratified water, the wake is presented as a cold wake on the water surface. The temperature difference between the cold wake and the sea surface is 0.152 K larger than that between the hot wake and the sea surface in the case of non-stratified water. The submarine travels 340 m forward without stratified seawater and 101.8 m under stratified seawater temperature and density. Compared with seawater stratification, the inversion error of submarine without stratification reaches 238.2 m, and the wake temperature difference on the surface is not only 0.152 K, but also cold wake phenomenon. It can be seen that the seawater stratification condition has a great influence on the submarine's inversion accuracy, and even directly leads to incorrect results.ConclusionsThe mathematical and physical model of the wake from floating diffusion, atmospheric decay to full link of sensor detection under the condition of seawater temperature and density stratification is established. The influence of seawater temperature and density stratification on the wake floating speed, the detection distance of the infrared detection system to the wake and the inversion error of the wake are obtained by simulation calculation. That is, it takes 101.8 s for the wake to rise to the surface at 50 m under the condition of stratified seawater temperature and density. Under the same conditions, when the seawater is not stratified, the time taken for the wake to rise to the surface is 340 s, which is much longer than that for the stratified seawater. This is due to the lower underwater temperature of the stratified seawater and the large density difference conducive to the floating of the hot wake. The discovery distance of the delaminated water body wake is 6.451 km, the identification distance of the wake is 1.631 km, and the recognition distance of the wake is 0.824 km. The unclassified detection distance, identification distance and recognition distance are 5.832 km, 1.492 km and 0.761 km, respectively. Compared with seawater delamination, the inversion error of submarine wake is 238.2 m without delamination, the temperature difference of wake on water surface is 0.152 K, and the cold and hot wakes on sea surface are different. ObjectiveAt present, most of the calculation methods for thermal wake detection by MRTD analysis consider the water body as uniformly distributed seawater. The stratified nature of seawater temperature and density has great influence on the inversion accuracy of submarine thermal wake on the surface temperature distribution, rise time and wake rise distance. However, the research at home and abroad mainly focuses on the improvement of MRTD algorithm of infrared system or derivation of the detection ability of infrared detector based on other parameters of the system, as well as the influence of weather and other factors on wake detection, and has not analyzed the influence of seawater stratification on wake detection and inversion. Therefore, the research on infrared radiation detection of thermal wake under the conditions of stratified seawater temperature and density is of great significance to the infrared detection of submarines.MethodsFor the lack of infrared detection of submarine thermal wake under the condition of stratified sea water temperature and density, the calculation error of detection distance and inversion accuracy error of submarine are large. Based on the finite element analysis method, the research on submarine infrared radiation characteristics under the condition of seawater stratification is carried out in this paper. Firstly, the finite element analysis method is used to simulate the floating process of submarine thermal wake in stratified seawater by a full-size submarine model with propeller and bridge characteristics. Then, according to the sea surface infrared radiation model and atmospheric transmission model, the full-link mathematical and physical model of the wake from floating diffusion, atmospheric transmission atmospheric attenuation to sensor detection is built, and the detection distance of the infrared detector to the submarine thermal wake under the condition of layered seawater is calculated according to the specific infrared detector performance parameters.Results and DiscussionsThe comparison shows that the stratification condition of seawater has a great influence on the detection of wake. With 95% detection probability, the detection distance of the wake increases by 10.61%, the identification distance of the wake increases by 9.32%, and the recognition distance of the wake increases by 8.28% (Tab.2). In the case of stratified water, the wake is presented as a cold wake on the water surface. The temperature difference between the cold wake and the sea surface is 0.152 K larger than that between the hot wake and the sea surface in the case of non-stratified water. The submarine travels 340 m forward without stratified seawater and 101.8 m under stratified seawater temperature and density. Compared with seawater stratification, the inversion error of submarine without stratification reaches 238.2 m, and the wake temperature difference on the surface is not only 0.152 K, but also cold wake phenomenon. It can be seen that the seawater stratification condition has a great influence on the submarine's inversion accuracy, and even directly leads to incorrect results.ConclusionsThe mathematical and physical model of the wake from floating diffusion, atmospheric decay to full link of sensor detection under the condition of seawater temperature and density stratification is established. The influence of seawater temperature and density stratification on the wake floating speed, the detection distance of the infrared detection system to the wake and the inversion error of the wake are obtained by simulation calculation. That is, it takes 101.8 s for the wake to rise to the surface at 50 m under the condition of stratified seawater temperature and density. Under the same conditions, when the seawater is not stratified, the time taken for the wake to rise to the surface is 340 s, which is much longer than that for the stratified seawater. This is due to the lower underwater temperature of the stratified seawater and the large density difference conducive to the floating of the hot wake. The discovery distance of the delaminated water body wake is 6.451 km, the identification distance of the wake is 1.631 km, and the recognition distance of the wake is 0.824 km. The unclassified detection distance, identification distance and recognition distance are 5.832 km, 1.492 km and 0.761 km, respectively. Compared with seawater delamination, the inversion error of submarine wake is 238.2 m without delamination, the temperature difference of wake on water surface is 0.152 K, and the cold and hot wakes on sea surface are different.
Infrared and Laser Engineering
- Publication Date: May. 25, 2023
- Vol. 52, Issue 5, 20220741 (2023)
Research and prospect of intelligent technology of optoelectronic imaging terminal guidance
Junting Yu, Shaoyi Li, Ping Zhang, and Zhenyu Luo
SignificanceIn recent years, various military powers are actively applying AI technology to precision-guided weapons, and have made certain technological breakthroughs, such as the development of LRASM anti-ship missiles, "maritime destroyers", "SPICE-250" precision-guided bombs and other intelligent weapons and equipment to improve the operational effectiveness of complex battlefield environments. In the process of realizing the intelligence of precision-guided weapons, the significant improvement of the performance of imaging terminal guidance technologies such as autonomous perception of complex battlefield environment, automatic target acquisition (ATA), automatic target recognition (ATR), adaptive guidance and so on depends on the deep fusion application of artificial intelligence technology. Therefore, the research on the intelligent technology of imaging terminal guidance and its future development direction has important reference significance for following the development trend of guidance mode and realizing the revolutionary improvement of weapon operational performance.ProgressFirstly, the development status of typical photoelectric imaging terminal guidance equipment for sea-to-sea, ground-to-ground and air-to-air, the different complex interference environments and target characteristics faced by the terminal guidance process are analyzed. The typical terminal guidance intelligent information processing principles such as small target detection in the long-range target interception stage, identification, tracking and anti-interference in the medium-close target tracking stage, and identification of key parts at the end of the close range in three scenarios are analyzed. Secondly, the development status and intelligent equipment achievements of intelligent technology of terminal-guided weapons in the United States, Israel, Norway and other foreign countries are summarized, and the intelligent technology principles in automatic target recognition, track planning and other aspects are analyzed, as well as the combat requirements of intelligent weapons in the future complex combat mode, including the significant improvement of target survivability, the increasingly complex and changeable task environment, and the increasingly fierce confrontation environment. Finally, this paper proposes several key technologies for the intelligent requirements of future electro-optical imaging terminal guidance weapons: distributed/heterogeneous autonomous collaborative detection capabilities, multi-dimensional information intelligent fusion processing capabilities, battlefield environment awareness and situation understanding capabilities, detection and guidance integration and autonomous decision-making capabilities, self-learning self-evolution self-reasoning capabilities, collaborative identification and collaborative anti-interference capabilities. At the same time, it is proposed to divide the intelligence of imaging terminal guidance into three stages: functional intelligent technology, system-level single intelligent technology, and system-level group intelligent technology.Conclusion and ProspectsThis paper analyzes the challenges brought by future high-performance targets, complex confrontation environments, multi-task requirements, and new combat modes to the intelligence of imaging terminal guidance technology. Starting from artificial intelligence technology and future combat requirements, six capability feature requirements and three development stages for realizing intelligent imaging terminal guidance are proposed. Through the development analysis of foreign imaging terminal guidance intelligent technology, it provides reference for the development of intelligent technology of photoelectric imaging terminal guidance weapons in China. SignificanceIn recent years, various military powers are actively applying AI technology to precision-guided weapons, and have made certain technological breakthroughs, such as the development of LRASM anti-ship missiles, "maritime destroyers", "SPICE-250" precision-guided bombs and other intelligent weapons and equipment to improve the operational effectiveness of complex battlefield environments. In the process of realizing the intelligence of precision-guided weapons, the significant improvement of the performance of imaging terminal guidance technologies such as autonomous perception of complex battlefield environment, automatic target acquisition (ATA), automatic target recognition (ATR), adaptive guidance and so on depends on the deep fusion application of artificial intelligence technology. Therefore, the research on the intelligent technology of imaging terminal guidance and its future development direction has important reference significance for following the development trend of guidance mode and realizing the revolutionary improvement of weapon operational performance.ProgressFirstly, the development status of typical photoelectric imaging terminal guidance equipment for sea-to-sea, ground-to-ground and air-to-air, the different complex interference environments and target characteristics faced by the terminal guidance process are analyzed. The typical terminal guidance intelligent information processing principles such as small target detection in the long-range target interception stage, identification, tracking and anti-interference in the medium-close target tracking stage, and identification of key parts at the end of the close range in three scenarios are analyzed. Secondly, the development status and intelligent equipment achievements of intelligent technology of terminal-guided weapons in the United States, Israel, Norway and other foreign countries are summarized, and the intelligent technology principles in automatic target recognition, track planning and other aspects are analyzed, as well as the combat requirements of intelligent weapons in the future complex combat mode, including the significant improvement of target survivability, the increasingly complex and changeable task environment, and the increasingly fierce confrontation environment. Finally, this paper proposes several key technologies for the intelligent requirements of future electro-optical imaging terminal guidance weapons: distributed/heterogeneous autonomous collaborative detection capabilities, multi-dimensional information intelligent fusion processing capabilities, battlefield environment awareness and situation understanding capabilities, detection and guidance integration and autonomous decision-making capabilities, self-learning self-evolution self-reasoning capabilities, collaborative identification and collaborative anti-interference capabilities. At the same time, it is proposed to divide the intelligence of imaging terminal guidance into three stages: functional intelligent technology, system-level single intelligent technology, and system-level group intelligent technology.Conclusion and ProspectsThis paper analyzes the challenges brought by future high-performance targets, complex confrontation environments, multi-task requirements, and new combat modes to the intelligence of imaging terminal guidance technology. Starting from artificial intelligence technology and future combat requirements, six capability feature requirements and three development stages for realizing intelligent imaging terminal guidance are proposed. Through the development analysis of foreign imaging terminal guidance intelligent technology, it provides reference for the development of intelligent technology of photoelectric imaging terminal guidance weapons in China.
Infrared and Laser Engineering
- Publication Date: May. 25, 2023
- Vol. 52, Issue 5, 20220725 (2023)
Simulation of flow field infrared radiation over reentry vehicle with ablation of carbon-based thermal protection material
Tiesuo Gao, Tao Jiang, Mingsong Ding, Qingzong Liu... and Weizhong Dong|Show fewer author(s)
ObjectiveHypersonic vehicle travels at a very high speed in atmosphere. Due to the high flight velocity, hypersonic vehicle has to endure very high heating rates on surface, ablative material is widely used in the design of thermal protection system (TPS). During the ablation process, gaseous ablator species are injected into the flow field, these gaseous species can involve inflow air in the chemical reaction, which changes flow field species distribution and temperature distribution, thus changing the target infrared radiation characteristics of hypersonic vehicle. Infrared radiation characteristics are the foundation of aircraft detection, identification and interception. Therefore, it is necessary to study the effect of thermal protection material ablation on aircraft target infrared radiation characteristics. For this purpose, this paper focuses on strategic warhead blunt body configuration with carbon-based thermal protection material. Numerical simulation of flow field and its infrared radiation is conducted, ablation effects on infrared radiation of flow over reentry body are discussed.MethodsNumerical simulation of flow field is conducted by solving three-dimensional thermal-chemical non-equilibrium Navier-Stokes equations. To simulate the surface ablation effect, surface velocity boundary condition, surface mass balance condition and surface energy balance condition are introduced into the computation process of flow field simulation. Oxidation, catalytic reaction and sublimation reaction of surface ablation material are also taken into account. To simulate the chemical reactions in the flow field, chemical reactions model of high temperature air with gaseous ablator species is used. Based on spectral band radiation model and by solving high temperature gas radiation transport equation, numerical simulation of flow field infrared radiation is conducted, the radiation mechanism of NO, CO, CO2, CN, N2, O, N is considered. Results and discussionNumerical simulation results at typical condition agree well with experiments and numerical simulation results in literature (Fig.1-3), the computation model and method are validated. The main ablation product on surface is CO, infrared radiation in the waveband of 0.8-8 μm of flow field mainly comes from the radiation of high temperature CO, NO, CO2 and CN (Fig.4). Ablation effect can increase flow field infrared radiation intensity, this phenomenon is more significant in 3-8 μm waveband than 1-3 μm waveband (Fig.5). Radiation from 3-8 μm waveband mainly comes from CO and NO, mass fraction of these species and flow field temperature increases as flight altitude decreases and flight velocity increases. Due to this, the radiation of 3-8 μm waveband increases as the flight altitude decreases and flight velocity increases (Fig.7-8). Radiation from 1-3 μm waveband in flow field around vehicle body increases as flight velocity increases, the radiation from 1-3 μm waveband in wake flow shows nonmonotonic variation due to the change of flow structure (Fig.7-8). ConclusionsIn this paper, the ablation effects on infrared radiation of flow over reentry body covered with carbon-based thermal protection material is studied. By solving high temperature gas dynamics equations and radiation transfer equations, numerical simulation of thermal protection material ablation flow field and its infrared radiation is conducted. The distribution and changing rules of infrared radiation in different wavebands from ablation flow are analyzed. The study shows that ablation effect has significant influence on infrared radiation of reentry flow, which makes integral radiation intensity of wake flow increase more than one order of magnitude compared with non-ablation case in 3-8 μm waveband; The infrared radiation of ablation flow mainly comes from CO, NO and CO2, and the ablation effect has less effect on the radiation in 1-3 μm waveband; The infrared radiation intensity of ablation flow increases with the decrease of reentry height at the same flight velocity, which weakens with the decreasing reentry velocity at the same flight height in 3-8 μm waveband. ObjectiveHypersonic vehicle travels at a very high speed in atmosphere. Due to the high flight velocity, hypersonic vehicle has to endure very high heating rates on surface, ablative material is widely used in the design of thermal protection system (TPS). During the ablation process, gaseous ablator species are injected into the flow field, these gaseous species can involve inflow air in the chemical reaction, which changes flow field species distribution and temperature distribution, thus changing the target infrared radiation characteristics of hypersonic vehicle. Infrared radiation characteristics are the foundation of aircraft detection, identification and interception. Therefore, it is necessary to study the effect of thermal protection material ablation on aircraft target infrared radiation characteristics. For this purpose, this paper focuses on strategic warhead blunt body configuration with carbon-based thermal protection material. Numerical simulation of flow field and its infrared radiation is conducted, ablation effects on infrared radiation of flow over reentry body are discussed.MethodsNumerical simulation of flow field is conducted by solving three-dimensional thermal-chemical non-equilibrium Navier-Stokes equations. To simulate the surface ablation effect, surface velocity boundary condition, surface mass balance condition and surface energy balance condition are introduced into the computation process of flow field simulation. Oxidation, catalytic reaction and sublimation reaction of surface ablation material are also taken into account. To simulate the chemical reactions in the flow field, chemical reactions model of high temperature air with gaseous ablator species is used. Based on spectral band radiation model and by solving high temperature gas radiation transport equation, numerical simulation of flow field infrared radiation is conducted, the radiation mechanism of NO, CO, CO2, CN, N2, O, N is considered. Results and discussionNumerical simulation results at typical condition agree well with experiments and numerical simulation results in literature (Fig.1-3), the computation model and method are validated. The main ablation product on surface is CO, infrared radiation in the waveband of 0.8-8 μm of flow field mainly comes from the radiation of high temperature CO, NO, CO2 and CN (Fig.4). Ablation effect can increase flow field infrared radiation intensity, this phenomenon is more significant in 3-8 μm waveband than 1-3 μm waveband (Fig.5). Radiation from 3-8 μm waveband mainly comes from CO and NO, mass fraction of these species and flow field temperature increases as flight altitude decreases and flight velocity increases. Due to this, the radiation of 3-8 μm waveband increases as the flight altitude decreases and flight velocity increases (Fig.7-8). Radiation from 1-3 μm waveband in flow field around vehicle body increases as flight velocity increases, the radiation from 1-3 μm waveband in wake flow shows nonmonotonic variation due to the change of flow structure (Fig.7-8). ConclusionsIn this paper, the ablation effects on infrared radiation of flow over reentry body covered with carbon-based thermal protection material is studied. By solving high temperature gas dynamics equations and radiation transfer equations, numerical simulation of thermal protection material ablation flow field and its infrared radiation is conducted. The distribution and changing rules of infrared radiation in different wavebands from ablation flow are analyzed. The study shows that ablation effect has significant influence on infrared radiation of reentry flow, which makes integral radiation intensity of wake flow increase more than one order of magnitude compared with non-ablation case in 3-8 μm waveband; The infrared radiation of ablation flow mainly comes from CO, NO and CO2, and the ablation effect has less effect on the radiation in 1-3 μm waveband; The infrared radiation intensity of ablation flow increases with the decrease of reentry height at the same flight velocity, which weakens with the decreasing reentry velocity at the same flight height in 3-8 μm waveband.
Infrared and Laser Engineering
- Publication Date: May. 25, 2023
- Vol. 52, Issue 5, 20220606 (2023)
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