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| 1 |
ID:
130767
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| Publication |
2013.
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| Summary/Abstract |
In this paper we report the design and development of an electro-optically Q-switched diode pumped Nd:YAG laser with intracavity optical parametric oscillator, generating ~ 5 ns laser pulses of ~8 mJ energy at eye safe wavelength of 1534 nm. A Z-shaped laser resonator has been designed with porro prism end reflector in Q-switch arm containing RTP Q-Switch and a suitably oriented waveplate. The gain arm consists of a Ø3 x 72 mm Nd: YAG laser rod, pumped from one side by 3 x 5 bar laser diode array stack emitting total optical peak power of 740 W at 804 nm at 38 °C. Thermoelectric coolers (TECs) have been employed to maintain the optimum temperature of laser diode arrays and the combined heat load from the pump chamber and TECs is distributed over the system base plate with embedded heat pipes. Such cooling mechanism has eliminated the requirement of fins and fans in the laser system. Eye safe radiation is out-coupled through intra cavity KTA OPO (5 x 5 x 20 mm3) placed in the gain arm. Laser was operated at 20 Hz for several duty cycles of 10 min on and 10 min off and output energy remained stable within ±0.5 mJ without any forced air/liquid cooling.
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| 2 |
ID:
130765
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| Publication |
2013.
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| Summary/Abstract |
In this paper authors present the design and simulation results achieved for pixel structure of amorphous Si (a-Si) based bolometer array. Most uncooled IR detectors in the world are based on VOx material. But this is not a standard material in IC technology and has many inherent disadvantages. The a-Si, an alternative material with high TCR is becoming as popular. However, large TCR values, in this material are achieved only in films of high resistivity. To achieve TCR value more than 2.5%/K, a-Si film resistivity is ~ 80 ohms-cm. This gives rise to very large pixel resistance of the order of 100 Mega ohms depending upon the design of the leg structure. This high pixel resistance causes very large noise and hence lower sensitivity. If leg width or membrane thickness is increased in order to reduce the pixel resistance, then this results in higher thermal conductance which also decreases sensitivity. To overcome this problem, pixel structure is so designed that within a pixel, only part of the electrical conduction is through a-Si and rest is through metal. Simulation using Coventorware software has been done to optimize pixel resistance as well as thermal conductance through legs so that maximum sensitivity could be obtained. Optimization is also carried out in order to reduce sensitivity of pixel resistance to variation in material resistivity.
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| 3 |
ID:
130764
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| Publication |
2013.
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| Summary/Abstract |
A reliable miniature cryocooler is one of the basic and foremost requirements for successful operation of high performance cooled infrared focal plane array (IRFPA) used for defence applications. Technological complexity and requirement of long duration fail-safe operation of the cryocooler demands robust design, fabrication and assembly with tolerances and, perfection of an array of sub-technologies. The paper presents the progress of the development activities in Stirling cryocooler technology at SSPL, which evolved through essential milestones like the development of single and dual piston linear motor driven split coolers to the state-of-the-art integral Brushless DC (BLDC) motor crank-driven type highly miniaturized coolers of capacities ranging from 0.25 to 0.5W at 80K. The theoretical investigations in the design of Stirling cycle cryocooler have been reported and the issues related to the design aspects are discussed in sufficient details. Experimental results of cryocooler performance tests are also presented. The paper also focuses on regenerator design optimization. The results of optimizations have been shown at the end considering a sample data.
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| 4 |
ID:
130769
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| Publication |
2013.
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| Summary/Abstract |
The proliferation of the missile threats in the existing threat scenario for airborne platform is a serious point of consideration for any mission planning. Missile warning system is an electronic warfare support system which gives warning to the pilot when a missile is detected in the scenario. The airborne platform has to be installed with missile warning sensors to give a spherical coverage, so that the sensors can detect the IR intensity variation in the ground scenario. This IR intensity variation has to be further analysed to differentiate the raising missile intensity from the varying background clutter. In order to differentiate the threat from the background clutter, the system should have sufficient background data set for online comparison thereby having less false alarm rate. The efficiency and performance of any missile warning system is validated with respect to its probability of declaration against the false alarm rate. Hence, to realize an efficient functioning of missile warning system, building IR background data base and missile signature database are the primary task. This paper details the methodology to be adapted for the building of tactical missile IR signatures and background data.
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| 5 |
ID:
130768
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| Publication |
2013.
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| Summary/Abstract |
This paper describes a large aperture tip-tilt mirror (TTM) assembly for correction of beam jitter in high power lasers. The design intricacies and trade-offs among various parameters of TTM to meet the desired goals are discussed. The TTM assembly uses a 180 mm diameter and 5 mm thick silicon mirror glued onto the movable ring of a solid flexure. Four stacked piezo-ceramic based actuators have been used to incorporate angular tilts of the mirror along two orthogonal directions. Simulation studies have been carried out to study the dynamics of the TTM. The performance of the TTM assembly in both static and dynamic condition is provided. An experimental set-up is described to test the TTM performance in closed loop conditions. A tilt correction of ±200 micro-radians along two orthogonal directions with a closed loop bandwidth of 20 Hz has been achieved.
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| 6 |
ID:
130761
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| Publication |
2013.
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| Summary/Abstract |
This short article describes the recent developments of cooled infrared products at Sofradir. These developments are driven by the future systems needs like the increase in resolution and detection range, the reduction of the detector size and consequently of the pixel pitch and the reduction of the power consumption. To answer to these needs, Sofradir develops in collaboration with the French infrared laboratory (CEA-LETI) new products based on Mercury Cadmium Telluride technology: Scorpio LW 640x512/15 µm pitch, sensitive in the long wavelength, Jupiter MW 1280 x 1024/15 µm pitch sensitive in mid wavelength, HOT detectors operating at 150 K and the 10 µm pitch detectors.
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| 7 |
ID:
130771
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| Publication |
2013.
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| Summary/Abstract |
This paper describes formulation of plastic bonded explosives (PBXs) compositions based on 2,4,6- triamino-1,3,5-trinitrobenzene (TATB), Octahydro l,3,5,7-tetranitro- 1,3,5,7-tetrazocine (HMX) by varying their relative amounts with Viton A as polymeric binder by slurry coating technique. These PBXs compositions are studied for mechanical and detonic properties. It has been observed that sensitivity and explosive performance of PBXs based on mixture of HMX and TATB were varied over a wide considerable range by varying relative amounts of TATB and HMX. The detonation study revealed there was increased in velocity of detonation (VOD) and detonation pressure with increasing amount of HMX from 10-80 % by weight. The sensitivity test results exhibited that insensitivity to impact for PBXs compositions was found to decrease with increasing HMX amount. Friction sensitivity study showed that no reactions were observed upto 36 kg load for PBXs compositions namely HT6030, HT5040, HT4050, HT3060, HT2070 and HT1080. The compressive strength of these PBXs compositions was found within the range of 9-11 MPa.
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| 8 |
ID:
130770
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| Publication |
2013.
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| Summary/Abstract |
The blast tube flowfield of a solid rocket motor is explored numerically by solving 3-D RANS equations with SST Turbulence model using a commercial computational fluid dynamics (CFD) software CFX-10. Parametric studies are carried out to find out the effect of the blast tube diameter on the total pressure loss in the rocket motor. It is observed that the total pressure loss in the rocket motor is less than 4 per cent and the blast tube is contributing less than 1 per cent. It is also found out that higher the blast tube diameter, the lesser the drop in the total pressure. Blast tube geometry is not found to contribute significantly in the overall thrust and specific impulse in the rocket motor.
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| 9 |
ID:
130772
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| Publication |
2013.
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| Summary/Abstract |
The objective of this work is to estimate the sparse angular power spectrum using a towed acoustic pressure sensor (APS) array. In a passive towed array sonar, any reduction in the analog sensor signal conditioning receiver hardware housed inside the array tube, significantly improves the signal integrity and hence the localization performance. In this paper, a novel sparse acoustic pressure sensor (SAPS) array architecture is proposed to estimate the direction of arrival (DOA) of multiple acoustic sources. Bearing localization is effectively achieved by customizing the Capons spatial filter algorithm to suit the SAPS array architecture. Apart from the Monte Carlo simulations, the acoustic performance of the SAPS array with compressively sensed minimum variance distortionless response (CS-MVDR) filter is demonstrated using a real passive towed array data. The proposed sparse towed array architecture promises a significant reduction in the analog signal acquisition receiver hardware, transmission data rate, number of snapshots and software complexity.
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| 10 |
ID:
130773
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| Publication |
2013.
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| Summary/Abstract |
Through-wall human target detection is highly desired in military applications. We have developed an impulse through-wall radar (TWR) to address this problem. In order to obtain a robust detection performance, firstly we adopt the exponential average background subtraction (EABS) method to mitigate clutters and improve the signal-to-clutter ratio (SCR). Then, different from the conventional constant false alarm rate (CFAR) methods that are applied along the fast-time dimension, we propose a new CFAR method along the slow-time dimension to resist the residual clutters in the clutter mitigation output because of timing jitters, based on the presence of a larger relative variation of human target moving in and out in comparison with that of residual clutters in the slow-time dimension. The proposed method effectively solves the false alarm issue caused by residual clutters in the conventional CFAR methods, and obtains robust detection performance. Finally, different through-wall experiments are provided to verify the proposed method.
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| 11 |
ID:
130766
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| Publication |
2013.
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| Summary/Abstract |
The advancement in infrared (IR) detector technologies from 1st to 3rd generation and beyond has resulted in the improvement of infrared imaging systems due to availability of IR detectors with large number of pixels, smaller pitch, higher sensitivity and large F-number. However, it also results in several problems and most serious of them is sensor non-uniformities, which are mainly attributed to the difference in the photo-response of each detector in the infrared focal plane array. These spatial and temporal non-uniformities result in a slowly varying pattern on the image usually called as fixed pattern noise and results in the degradation the temperature resolving capabilities of thermal imaging system considerably. This paper describes two types of non uniformity correction methodologies. First type of algorithms deals with correction of sensor non-uniformities based upon the calibration method. Second type of algorithm deals with correction of sensor non uniformities using scene information present in the acquired images. The proposed algorithms correct both additive and multiplicative non uniformities. These algorithms are evaluated using the simulated & actual infrared data and results of implementations are presented. Furthermore, proposed algorithms are implemented in field programmable gate array based embedded hardware.
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| 12 |
ID:
130762
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| Publication |
2013.
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| Summary/Abstract |
For the highest end mid-wave-infrared (MWIR) applications, SCD offers a family of cryogenically cooled detectors with background limited performance (BLIP). The matured InSb planar technology is implemented in a variety of focal plane arrays, from a 320 x 256 format with a 30 µm pitch to a 1280 x 1024 format with a 15 µm pitch, all of which are operated at 77K. A major challenge is to reduce the cooling requirements. Then substantial reductions in size, weight, and power (SWaP) can be achieved by using a smaller cooler and Dewar assembly. SCD's new epi-InSb detectors, grown by molecular beam epitaxy (MBE), have a BLIP temperature of ~100 K at F/3. This enhanced operating temperature reduces the required cooling power by ~20 % compared with the conventional 77 K operation. For a very high operating temperature, we have developed the new XBn-InAsSb detector with a 4.2 µm cut-off wavelength. This detector exhibits a BLIP temperature of ~160K at F/3 and a reduction in cooling power of ~60 %. These HOT detectors enable an improved range of solutions, including faster cool-down time and mission readiness, longer mission times, and higher cooler reliability. We can also exploit their reduced dark current to obtain an enhanced signal to noise ratio at lower operating temperatures. The well-established 25 µm pitch family of uncooled µ-Bolometer detector has two basic formats, 384 x 288 and 640 x 480, and several sensitivity grades. The very high sensitivity 25 µm pitch detector has been demonstrated at F/2.4 for mid-range systems. The wide-band detector is optimized for both the long-wave-infrared and mid-wave-infrared spectral bands. Recently we developed the new 17 µm pitch family of detectors. The 640x480 format is a leading candidate for applications such as thermal weapon sights, driver vision enhancers and other mid-range IR systems. The 17 µm family is currently being expanded with the high sensitivity grade and with the addition of two new formats: the compact 384 x 288 for low SWaP applications, and the large 1024 x 768 format for applications requiring high resolution and a wide field of view.
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| 13 |
ID:
130760
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| Publication |
2013.
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| Summary/Abstract |
The high level of accumulated expertise by ULIS and CEA/LETI on uncooled microbolometers made from amorphous silicon enables ULIS to develop uncooled IRFPA with 17 µm pixel-pitch to enable the development of small power, small weight and power (SWaP) and high performance IR systems. Key characteristics of amorphous silicon based uncooled IR detector is described to highlight the advantage of this technology for system operation. A full range of products from 160 x 120 to 1024 x 768 has been developed and we will focus the paper on the ¼ VGA with 17 µm pixel pitch. Readout integrated circuit (ROIC) architecture is described highlighting innovations that are widely on-chip implemented to enable an easier operation by the user. The detector configuration (integration time, windowing, gain, scanning direction), is driven by a standard I²C link. Like most of the visible arrays, the detector adopts the HSYNC/VSYNC free-run mode of operation driven with only one master clock (MC) supplied to the ROIC which feeds back pixel, line and frame synchronisation. On-chip PROM memory for customer operational condition storage is available for detector characteristics. Low power consumption has been taken into account and less than 60 mW is possible in analogue mode at 60 Hz. A wide electrical dynamic range (2.4V) is maintained despite the use of advanced CMOS node. The specific appeal of this unit lies in the high uniformity and easy operation it provides. The reduction of the pixel-pitch turns this TEC-less ¼ VGA array into a product well adapted for high resolution and compact systems. Noise equivalent temperature difference (NETD) of 35 mK and thermal time constant of 10 ms have been measured leading to 350 mK.ms figure of merit. We insist on NETD trade-off with wide thermal dynamic range, as well as the high characteristics uniformity and pixel operability, achieved thanks to the mastering of the amorphous silicon technology coupled with the ROIC design. This technology node associated with advanced packaging technique, paves the way to compact low power system.
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