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Flexible em Wave Absorber with High Angular Stability and Low Cross Polarization Reflection Level.
No full textIn this work, a flexible radar absorber structure is
presented which offers high absorbance within X band.
The proposed structure is designed by integrating two
different resonators which provides high angular-stability
properties. The theoretical and experimental results
indicate that the proposed absorber is polarization
insensitive and angular stable up to 600 in both the TE and
TM polarization cases. Apart from conventional
absorptivity analysis, the cross-polarization reflection of
the proposed absorber is also calculated. The simulated
results indicate that the proposed FSS configuration
behaves as proper absorber and not a polarization
convertor. The Radar Cross Section (RCS) of the proposed absorber is also calculated and compared with the RCS of a reflective sheet to analyze its suitability for practical applications at 10.95 GHz frequency in X band. The fabricated absorber is also tested for different angle
of bend to test the effects of its flexibility on absorption. The simulation and measurement results indicate that the proposed absorber is highly suitable for absorption
application within X-band
Facilitating Cryptojacking Through Internet Middle Boxes
No full textThe usage of anonymous proxies and virtual private network has increased due to the privacy and Internet censorship issues. The traffic passing through proxies (Middle boxes) can be easily intercepted and modified by the controller to perform man-in-the-middle attacks like data injection, data tampering, and data deletion. A stealthy attack called cryptojacking started infecting the popular Web sites to mine cryptocurrency without the Web site visitor’s consent. This paper proposes an effective and stealthy approach to perform cryptojacking attack by injecting cryptomining script on anonymous proxy’s Web site traffic. To increase the efficiency of the attack on larger scale, a testbed environment for private The onion router (Tor) network is deployed to implement the same attack on tor exit node. Our study shows that covertness of the attack can be improvised by varying the central processing unit usage of the victim during mining to avoid detection. The existing defensive mechanism to prevent this attack is also reviewed
3D Finite Element Rotor Dynamic Analysis of Turbine Test Rig Rotor-Shaft Systems
No full textDesign of a 385 kW turbine (T385 turbine) to drive the compressor of 1 kN small gas turbine engine is carried out in Propulsion Division, CSIR-NAL. Aero-thermodynamic performance evaluation of designed turbine stage was planned through experimental testing in VTTR, Propulsion Division, CSIR-NAL. The turbine speed is 50,500 rpm at the engine design point, and the equivalent design speed in test rig conditions is 30,000 rpm. Since performance evaluation at higher speeds consists of high-speed rotating components constituting a complex dynamic system, it is of prime importance to consider rotor dynamic characteristics to operate the turbine safely. Test section is designed for the T385 turbine rotor BLISK considering rotor-shaft system with bearings. The dynamic behavior of test rig rotor systems was evaluated for vibration reliability. This paper presents the 3D FE rotor dynamic analysis of T385 turbine rotor-shaft system. The stiffness of bearing supporting structure is evaluated along the direction of stress field using FEA. T385 turbine rig rotor system is modeled in FEA using lumped mass method. All the masses of rotor shaft sytem with inertias are considered in the analysis. The Campbell and response plots are plotted using frequencies and mode shapes to predict the critical speeds and unbalance response, respectively. The critical speeds from Campbell diagram indicates that rotor system is safe to operate in the test rig. The maximum amplitude due to unbalance is within the limits of clearance at the operating conditions. The predicted natural frequencies of T385 rotor system from modal analysis are compared with impact hammer test and frequencies are matching well with analysis
Stationary and Rotating Frame Instrumentation for Large Scale Rotating Rig
No full textThe Large Scale Rotating Rig at NAL is designed to carry out detailed experimental investigations of the flow through compressor and turbine stages. Instrumentation and data acquisition system (DAS) for stationary and rotating frame measurements, pressure distribution measurements across the vane and the blade surface and the flow measurement was developed in-house. This enabled making pressure measurements on the vane surfaces, blade surfaces, platforms and at the vane/blade exit wake flows. There were added challenges in terms of unsteady pressure measurements, transferring of data from rotating frame and condition monitoring of the rig. The DAS is developed using state-of-the-art instruments and is coupled with a GUI data acquisition software developed using LabVIEW to tackle all these challenges. This paper presents elaborated details of the multichannel instrumentation and the DAS
Synthesis, structural, magnetic and NO2 gas sensing property of CuO nanoparticles
No full textCupric oxide (CuO) nanoparticles are synthesized by the oxidation of Cu/Cu2O, which is obtained by the chemical reduction of Cu2+ ions with ascorbic acid. XRD pattern confirmed the formation of CuO, and FE-SEM image shows the clusters consisting of 25–30 nm sized particles. The band gap energy (3.7 eV) from optical absorption spectra is blue shifted to that of bulk values. The Néel temperature, TN ≈ 230 K for paramagnetic to antiferromagnetic transition was clearly seen. The magnetic hysteresis loops at 5 K showed weak ferromagnetic behavior. Based on the dc electrical conductivity (300–500 K), the apparent activation energy was 0.36 eV. The NO2 gas sensing property of CuO was reasonably good in the temperature range of 200–300 °C, and the sensitivity increased with an increase in gas concentration but the effect of temperature is marginal
Novel approach for pressure sensor calibration in 1.2m wind tunnel
No full textA new improved NI based pressure sensor calibration module is developed at CSIR-NAL 1.2m Wind Tunnel for calibrating and health monitoring of the pressure transducers. The Mach number and non-dimensional coefficients are computed using the pressure sensor data along with the balance data measured during the wind tunnel testing. The pressure transducers used for wind tunnel tests include static pressure transducers, total pressure transducers and base pressure transducers. These transducers are calibrated every six months to adhere to the ISO standards followed by NAL. The introduction of user friendly features and technology upgradation into the new system has enhanced the efficiency of calibration. This paper presents the approach for the new calibration scheme, software architecture, hardware features and typical results. The developed system has been tested and is currently used extensively at 1.2m wind tunne
Synergistic catalytic activity of palladium–silver alloy nanoparticle for anodic oxidation of ethanol in alkali
No full textPalladium and palladium-silver alloy nano catalysts were synthesized from aqueous precursor at room temperature via a single vessel chemical reduction and co-reduction methods in absence of capping agent. XPS analysis confirms the presence of Pd and Ag in the catalyst matrix. Microscopic analyses reveal spherical morphology of the catalyst in the nanoscale dimension. The electro-analytical investigation of the catalyst loaded on carbon electrode shows that the Pd4Ag nano alloy catalyst demonstrates marked improvement in electro-catalytic efficiency among all prepared catalysts for ethanol oxidation in alkali. The Pd4Ag/C catalyst shows the mass normalized peak current density of 522 mA mg−1Pd in cyclic voltammetric (CV) study, which is 1.97 times greater than that of similarly synthesized Pd/C (264.2 mA mg−1Pd) catalyst. Chronoamperometric and impedance analyses further establish the superiority of Pd4Ag/C catalyst. To discover the plausible mechanism, the CV study is typically extended to the intermediates like sodium acetate which reveals that though Pd is better for catalytic oxidation of intermediate than the best catalyst but the optimal OH− adsorption on the surface of the metal, favours catalytic oxidation of ethanol more on Pd4Ag catalyst. The mechanistic path of the reaction is anticipated by evaluating the ex-situ FTIR and chromatographic studies which explain the promotion of the formation of carboxylate in comparison to carbonate by Ag
A review on metal-oxide based p-n and n-n heterostructured nano-materials for gas sensing applications
No full textGas sensor is a device that converts the information of an analyte species into electrical signals using various detection principles. Electrical conductivity is one of the crucial properties of sensing materials. This basic property is modified with the formation of p-n and n-n heterostructures or by the inclusion of dopants. Surface morphology of a sensing material plays a vital role in the adsorption of analyte species for effective gas sensing behavior, further this can be improved with proper surface treatment viz., surface reactions by decorating with nanoparticles composed of various noble metals. The sensing mechanism differs owing to various morphologies with sensing materials. Sensing materials can either be polymers, metal oxides, nanoparticles or pertinent combination of these constituents. The sensor properties like selectivity, sensitivity, stability, response time and detection limits are influenced by morphology, material exposed to target gas and operating conditions. This review focusses on sensing mechanism and monitoring of nanostructures (nanorods, nanosheets, nanobelts, nanoribbons, nanowires, nanoflowers, spinel etc.) by appropriate combination of materials and dopants. The performance of numerous metal oxide-based gas sensing devices and their market trends are reviewed
Measurements of droplet velocity fields in sprays from liquid jets injected in high-speed crossflows using piv
No full textThe present work reports the measurement of planar droplet velocity field of a plain liquid jet injected into a high-speed crossflowing airstream. PIV was employed to measure the instantaneous and average droplet velocity field in the far-field region of the spray. Water was injected from a 1-mm orifice and crossflow air velocities up to 110 m/s were investigated. The approach using PIV was validated using experimental PDPA data reported in literature. The increase of droplet velocity with axial distance was clearly observed. In the region considered for analysis, the droplet velocity showed a peak in the central region suggesting contributions primarily from surface breakup
Superstrate-based patch antenna array with reduced in-band radar cross section
No full textTo design a low radar cross section (RCS) antenna, the major concern is not only to reduce scattering, but also to maintain its radiation parameters, viz. gain, voltage standing wave ratio (VSWR), etc. This paper presents a simple configuration of low RCS microstrip patch array with a periodic structure-based superstrate. The ground of the array is designed as reduced ground plane with high impedance surface elements, viz. rectangular patch and Jerusalem cross. The configuration of superstrate consists of multilayered, viz., two-layered and three-layered structures having partially absorbing and reflecting surfaces. In both the proposed configurations, the array gain of 12.5 dB is maintained with reduced structural RCS over the entire in-band frequency range. The reflection coefficient (~ −20 dB) and VSWR (~ 1.1) of the array are maintained. It is shown that the proposed superstrate-based patch array design has significantly reduced in-band RCS (−18 dBsm) at its resonant frequency