Dynamic infrared scene generation is a key technology in semi-physical simulation and dynamic performance index testing of various infrared detection systems such as infrared imaging seekers, forward-looking infrared (FLIR) systems, infrared search and tracking systems (IRST), and infrared warning systems. . With the development of infrared detection systems in the direction of high frame rate, large dynamic range, and high resolution, higher requirements are imposed on the simulation of dynamic infrared scenes. Only dynamic infrared scenes that achieve higher resolution and higher frame rate Simulation can meet the needs of closed-loop semi-physical simulation and high-confidence dynamic index testing of various infrared detection systems.
Dynamic infrared scene generation technology is widely used in the research and development and testing of infrared weapon equipment. Internationally, a variety of dynamic infrared scene generation technologies have been applied to various guidance weapon equipment simulation systems. There are:
1. Infrared liquid crystal light valve: Use visible light to modulate the orientation of liquid crystal molecules, change the secondary refractive index of the liquid crystal, rotate the polarization vector of incident infrared light, realize the conversion of visible light to infrared light, and have excellent spatial resolution. However, there are limitations in frame rate, temperature, and dynamic range.
2. Infrared CRT: The working principle is similar to that of a TV. Using the luminous effect of a cathode ray tube, under the action of a driving circuit, an electron beam modulated by video information scans a target screen and excites the phosphor to generate a dynamic infrared image. Infrared CRT also needs improvement in terms of increasing frame rate and reducing flicker.
3. Laser diode array: It consists of linear lead-salt laser diodes, high-speed optical scanners and drive circuits. When the scene of the laser tube array sweeps through the sensor with the focal plane array, corresponding energy is generated on each detector To produce an infrared scene. It has the advantages of high frame rate, no dead pixels, high resolution, large format, etc., but the spatial uniformity and quality are not good, and it needs a large Dewar package.
4. Resistor array: Based on the blackbody radiation theory, the infrared radiation in different wave bands can be obtained by adjusting the current through the thermal resistance. The advantages are low power consumption, large temperature range, high frame rate, high resolution, high duty cycle, and no flicker However, the physical characteristics of the material limit the response time of the device, thus limiting the frame rate. Obtaining greater temperature radiation and higher frame rate while reducing power consumption is a problem to be solved in the development of resistor arrays.
5. Blackbody film: It is mainly a vacuum chamber with a film coated with gold and black on it. It absorbs the visible light radiation from the image on one side, causing the film to heat up, and outputs the corresponding infrared image from the other side. It has the advantages of simple structure and low price. The disadvantages are slow response speed, small temperature range, and low conversion efficiency.
6. Digital micromirror device (DMD): DMD dynamic infrared scene projection technology is a dynamic scene generation method developed by American Optical Science Corporation (OSC), called micromirror array projection system (MAPS), and its core device is Texas ( TI) Digital Micromirror Device (DMD) produced by the company. This technology is the infrared modulation of infrared radiation to obtain infrared scenes. In the visible and ultraviolet bands, this projection technology can also produce realistic dynamic scenes, with high spatial resolution, high frame rate, no dead pixels, Good uniformity, small size and low cost.
The basic working principle of dynamic infrared scene generation based on digital micromirror device (DMD) is mainly completed by DMD semiconductor chips. Its mirror surface is a rectangular array composed of millions of subtle reflection mirror surfaces, and each mirror surface corresponds to an optical pixel in the projected picture. The DMD pixel unit is mainly composed of a storage unit that stores image signals, a pillar supporting a micromirror, a rotating hinge, a frame, a mirror, and three electrodes. Above the bottom layer is the metal layer, which mainly includes the bias / reset electrode and the frame addressing electrode. The bias / reset electrode is connected to the micromirror and the frame, and the required voltage and waveform are directly provided by the off-chip driving circuit. The role is mainly to reduce the voltage required to drive the micromirror. The frame addressing electrode and the upper micromirror addressing electrode are respectively connected to the two complementary output terminals of the image signal storage unit, between the micromirror and the mirror addressing electrode and between the frame and the frame addressing electrode The electrostatic gravitation is synthesized to generate effective electrostatic torque. At this time, the torque generated by the hinge is opposite to the electrostatic torque, and the rotation of the micromirror is controlled by the action of these two torques. The upper layer is the mechanical part of DMD, which is composed of frame, hinge and micro-mirror addressing electrode. The rotating hinge fixed on the pillar can drive the frame to rotate. The uppermost layer is the reflective micromirror, which is fixed on the frame and can rotate with the frame. This structure that installs the micromirror on the frame and drives the micromirror to rotate together can greatly increase the area of ​​the micromirror, almost cover the entire unit, and occupy a space factor of more than 90%, thereby improving the use of incident light Efficiency, can form a seamless, high-contrast image. Each micro-mirror can reflect light from two directions. The actual reflection direction depends on the state of the bottom memory cell. When the memory cell is in the "ON" state, the reverse mirror will rotate to +12 degrees. If the memory cell is in the "OFF" state, the mirror will rotate to -12 degrees. As long as the DMD, appropriate light source and projection optical system are combined, the mirror will reflect the incident light into or out of the light transmission hole of the projection lens, making the "ON" state mirror look very bright and the "OFF" state mirror It looks very dark. The grayscale effect can be obtained by using two-bit pulse width modulation. If a fixed or rotating color filter is used, and one or three DMD chips are used, a color display effect can be obtained.
The DMD dynamic infrared scene generation system developed by Beijing Aerospace Measurement and Control Technology Development Company consists of three parts: one is the infrared thermal image projector, the other is the power and video control components, and the third is the control computer.
1. Infrared thermal image projector: including digital micromirror device, digital micromirror drive circuit, black body light source, black body light source controller, projector optical system, etc. Its working principle is: the infrared image data generated by the computer is input to the DMD device through the video processing circuit and the DMD drive circuit; the device is evenly irradiated with the black body radiation source, and the infrared thermal image is generated by using the DMD to reverse modulate the incident radiation. The generated infrared scene is projected to the entrance pupil of the measured object UUT through the optical collimation projection system, so that the infrared scene is consistent with the real target and background image spot size and the spatial distribution of radiation energy on the detector. The light source of the infrared thermal image projector is an infrared black body, and the optical system of the infrared projector is composed of a black body front condenser, a semi-transparent mirror, and a collimated projection system.
2. Power and video conversion component functions: (1) Provide various working power for infrared scene generation system, such as: provide working power for infrared projector electronic system, provide working power for black body light source, etc .; (2) control computer generated or external input The dynamic scene video signal is converted into a signal format that can be received by the DMD drive circuit, and the parameters of the video synchronization signal are changed programmatically according to the requirements of the infrared detection system under test.
3. Control computer: realize the setting of infrared projector's operating parameters, real-time infrared thermal image video signal generation, and real-time monitoring during system operation. The control computer is respectively configured with operation management and monitoring software, real-time thermal image generation software and corresponding video signal output interface boards.
The main key technologies of the aerospace measurement and control DMD dynamic infrared scene generation system are: realizing the synchronous driving of high frame rate infrared image output and realizing the generation of ultraviolet, visible, and infrared multi-band dynamic infrared scenes.
With the advancement of technology, semi-physical simulation and dynamic performance testing will gradually cover the full life cycle of the photoelectric detection system, and the simulation of dynamic scenarios will be the key to high-confidence semi-physical simulation. High frame rate, high resolution, same gray scale resolution, high apparent temperature and multi-band dynamic photoelectric scene physical generation will be widely used in the development, testing and evaluation of photoelectric weapon equipment.
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