Defence Science Journal
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RF Sputtered MoO3 Thin Film on Si (100) for Gas Sensing Applications
Get PDFMolybdenum Trioxide (MoO3) films are grown on Si(100) substrates by reactive RF magnetron sputtering in plasma containing a mixture of Argon and Oxygen, using a pure Molybdenum target. In this paper, we report the deposition of (MoO3) films on Si(100) substrates under varying gas flow (O2 + Ar gas) (20 sccm to 30 sccm with the duration of deposition~ 1hr) by RF reactive magnetron sputtering at room temperature. To get crystalline MoO3 films annealing in O2 environment at 500 °C for 4 h is done. Phase formation and orientation of the film is characterized by Glancing incidence X-ray diffraction (GIXRD). The identification of the orthorhombic MoO3 phase is investigated by XRD and Raman spectroscopy. Raman lines at 819 cm-1 and 995 cm-1 are due to the (A1g, B1g) symmetric stretching (Mo-O–Mo) bond and asymmetric stretching band (Mo=O) respectively. Surface morphology and cross-sectional image of the deposited thin films were investigated by FE-SEM image. UV-Visible reflectance and cross-sectional FE-SEM image confirm the thickness of the MoO3 films with oxygen-rich and oxygen deficient phase formation occur. Reverse leakage current density of 20 sccm 1hr sample is low (1×10-6 mA/cm2) as compared to 30 sccm 1hr sample (1×10-3 mA/cm2). The higher leakage is due to crack formation during the ex-situ annealing of MoO3 films. This MoO3 films can be used in Gas sensing and switching devices
Field Programmable Gate Array based Readout for Surface Acoustic Wave Portable Gas Detector
Get PDFSurface acoustic wave (SAW) is one of the most promising technology in the field of gas sensing at low concentrations. Field deployable portable SAW detectors are, however, prone to noise, there by limiting the detection at low concentrations. To meet the current requirements of gas detection at low concentrations, the readout methodology needs to be based on minimal hardware and better noise management. In this paper we describe a readout scheme for portable SAW gas detectors incorporating a field programmable gate array (FPGA). The developed readout system includes a modified reciprocal frequency counter for differential SAW sensor, median noise filtering and moving averages smoothing for noise management, peak detection and interfacing with external display, all implemented in FPGA. The developed readout was tested against VOCs using a lab developed vapour generator and the results have been presented in the paper. The readout system is compact, low power consuming and expandable through software thus ideal for portable handheld applications
Self heating Effects in GaN High Electron Mobility Transistor for Different Passivation Material
Get PDFIn this paper effect of self-heating has been studied of AlGaN/GaN high electron mobility transistor (HEMT) for different passivation layers which is promising device for high power at high frequencies. The different passivation layers used are aluminium oxide (Al2O3), silicon nitride (SiN) and silicon dioxide (SiO2). The device GaN HEMT has been simulated and characterised for its thermal behaviour by the distribution of lattice temperature inside the device using device simulation tool ATLAS from SILVACO. The transfer and output characteristics with and without self-heating has been studied for electrical characterisation. The channel temperature for different passivation observed is 448 K, 456 K and 471 K forAl2O3, SiN and SiO2 respectively. The observed different temperatures are due to difference in their thermal conductivity. This channel temperature information is critical to study the reliability of the device at high power levels
Shooting Control Application from a Quadruped Robot with a Weapon System via Sliding mode Control Method
Get PDFWith the developing technological process, it is expected that the usage of robots will increase in defense systems as in every field. One of the main objectives of the robotic studies for the defense industry is to capture the targeted success under all kinds of disruptive effects with robotic systems and to present this technology to the service of the army. A weapon system with a single degree of freedom was placed on a quadruped robot. System’s dynamic behavior, which has 12 degrees of freedom and planar movements, is modeled mathematically. Simulations of the shots made to the fixed targets were carried out during the walking of the quadruped robot. The gun barrel stabilization was realized to achieve accurate shots under disruptive effects. The sliding-mode control method was used to perform the barrel stabilisation. In this study, it is shown that a quadruped robot with a weapon system can perform successful shots against fixed targets. MATLAB is used for simulations and the results are shown with figures, graphics, and tables
A Case based Online Trajectory Planning Method of Autonomous Unmanned Combat Aerial Vehicles with Weapon Release Constraints
Get PDFAs a challenging and highly complex problem, the trajectory planning for unmanned combat aerial vehicle (UCAV) focuses on optimising flight trajectory under such constraints as kinematics and complicated battlefield environment. An online case-based trajectory planning strategy is proposed in this study to achieve rapid control variables solution of UCAV flight trajectory for the of delivery airborne guided bombs. Firstly, with an analysis of the ballistic model of airborne guided bombs, the trajectory planning model of UCAVs is established with launch acceptable region (LAR) as a terminal constraint. Secondly, a case-based planning strategy is presented, which involves four cases depending on the situation of UCAVs at the current moment. Finally, the feasibility and efficiency of the proposed planning strategy is validated by numerical simulations, and the results show that the presented strategy is suitable for UCAV performing airborne guided delivery missions in dynamic environments
Indirect Rotational Energy Harvesting System to Enhance the Power Supply of the Quadcopter
Get PDFThis paper presents a simple energy harvesting system using unpowered freewheeling propellers mounted on the quadcopter without changing its actual design. Different layout configurations have been analysed and its thrust variation also tested to place the harvesting system in a suitable place in the quadcopter. The same and different size freewheeling propellers running coordination and its speed ratio are examined at various speed. To know the flow performance the freewheeling propellers Reynolds number is calculated. The freewheeling propellers rotational energy which creates an electrical power by means of micro BLDC generator. The harvested energy from the BLDC generator is maximized using three-phase MOSFET enabled controlled rectifier with hysteresis comparator. To meet the requirement of powering the quadcopter the output voltage from the generator is boosted and regulated using single DC-DC SEPIC boost converter with high voltage and current range. This energy can be directly charge secondary battery or power the other electronic payloads. The freewheeling propeller energy harvesting system has been implemented and tested in the laboratory at static condition which gives 51 per cent of harvested current
Heavy Military Land Vehicle Mass Properties Estimation Using Hoisting and Pendulum Motion Method
Get PDFMass properties such as the centre of gravity location, moments of inertia, and total mass are of great importance for vehicle stability studies and deployment. Certain parameters are required when these vehicles need to be arranged inside an aircraft for the carrier to achieve proper mass balance and stability during a flight. These parameters are also important for the design and modelling process of vehicle rollover crash studies. In this study, the mass properties of a military armoured vehicle were estimated using hoisting and pendulum method. The gross total weight, longitudinal and vertical measurements were recorded by lifting the vehicle using a mobile crane and the data were used to estimate the centre of gravity. The frequency of vehicle oscillation was measured by applying swing motion with a small angle of the vehicle as it is suspended on air. The centre of gravity and mass moment of inertia were calculated using the vector mechanics approach. The outcomes and limitations of the approach as discussed in details
Effect of Helical Winding Angle on External Pressure based Buckling of Partially Filled Thin Composite Cylindrical Shells
Get PDFEffect of helical winding angle on buckling load of thin composite tubes is investigated in this work. Experiments are conducted on both empty and partially filled S2 glass tubes to estimate contribution of strength to the tubes by the filler material. Chosen filler material mechanically simulates behavior of typical solid propellant used in aerospace application. FE analysis with non-linear effect correlates well with the experimental data. Three series of experiments are conducted to quantify effect of helical winding angle and increase in volumetric loading fraction(VLF). Results confirm appreciable improvement in strength of filled tubes for higher VLF. For the chosen pattern of winding, lower winding angle provides more strength to the tubes against external pressure buckling.
 
Anti submarine Warfare Oceanography
Get PDFAnti-submarine warfare (ASW) Oceanography has become an important and independent discipline, especially after World War II as the threat perceptions from hostile underwater platforms has been on a continuously rising trajectory worldwide. There is no doubt that till date, acoustic energy remains the only viable and most effective means to detect underwater objects. However, sound waves are highly susceptible to refraction, reflection, scattering, reverberation and absorption in the ocean medium. Among these, refraction is controlled by the 3D sound speed structure in the specific ocean region and reflection loss by the sea state and ocean bottom characteristics. Water quality parameters such as sediment concentration and suspended biological masses influence attenuation, scattering, reverberation and absorption. Oceanographic variability emerges from diurnal heating, seasonal changes, river discharges, etc. and are the most important environmental factors deciding the 3D sound speed structure in any given area in the ocean
Warmest Sea Surface Temperature Event in the South Eastern Arabian Sea over the Decade using Satellite and INS Sagardhwani Observations
Get PDFSouth Eastern Arabian Sea is well known for its prolonged and warmer sea surface temperature (>30 °C) events generally known as Arabian Sea mini warm pool occurring during the pre-monsoon periods (March-May). To study the intensity and spatial extent of the warm pool, ten years (2007-2016) of satellite-derived weekly averaged SST and in-situ data measured from INS Sagardhwani are used. The analysis is done based on the precondition ‘sea surface temperature > 30 °C’ and lasts more than a week. These analysis demonstrate the existence of a strong inter-annual variability. It is also identified that the sea surface temperature in the year 2016 is the hottest over the decade with maximum spatial coverage and prolonged period of occurrence. These anomalous events are also explained in terms of variabilities of the atmospheric water vapour and wind at the sea surface