Options
Harishankar Ramachandran
Loading...
Preferred name
Harishankar Ramachandran
Official Name
Harishankar Ramachandran
Alternative Name
Ramachandran, H.
Ramachandran, Harishankar
Ramachandran, H. S.
Main Affiliation
Email
ORCID
Scopus Author ID
Google Scholar ID
33 results
Now showing 1 - 10 of 33
- PublicationDistributed high temperature sensing using fiber bragg gratings(01-01-2008)
;Kuncha, Syam Prasad; ; In this paper we present a novel, practical approach for carrying out distributed high temperature sensing in boilers. We have demonstrated distributed high temperature sensing using fiber Bragg gratings encapsulated inside a rugged mechanical structure. The encapsulation is designed to not only protect the optical fiber from the harsh environment of the boiler, but also to scale the temperature down to a range over which the gratings are relatively stable. A key aspect of our work is the use of a Bayesian inference technique to retrieve the temperature outside the encapsulation within < 1°C accuracy based on the temperature measured by the fiber Bragg grating (FBG). - PublicationDesign of command and Data Management System for IITMSAT(29-09-2015)
;Suresh, Susurla V.S. ;Dommeti, Ch Saiteja ;Rosh, K. S.Green ;Kumar, K. C.Gopa ;Chaitanya, V. Viswa ;Gulati, Akshay K.; ; In this paper we describe the design and development of the Command and Data Management System (CDMS) of the nano-satellite of IIT Madras, named IITMSAT. The CDMS module uses a 32-bit ARM microcontroller from Freescale - KL46Z256VLL4. This module is responsible for decoding the telecommands sent from the ground station, and transmits the time-stamped payload data back as telemetry packets. The SD card on the CDMS board stores the satellite's health and science data as and when it is acquired in the orbit. The data is transmitted to the ground station (GS) during the satellite's visibility period. The interface board (I/F) links the Flight Computer module and CDMS board along with other electronics onboard. Throughout the design phase, the cost was kept as low as possible, without compromising on performance of the system. Custom-designed protocol and data frame format for communication between the satellite and ground station was completely developed from scratch, based on CCSDS cubesat standards. - PublicationEffect of polarization on the link dynamics of a spinning low-earth orbits satellite aligned with geomagnetic field(01-09-2021)
;Talashila, RajavardhanThis paper discusses the dynamic communication link aspects of IIT Madras student Satellite (IITMSAT). It is a Low-Earth Orbits satellite which has limited Attitude Determination and Control System (ADCS) ability to align one of its body axes with the geomagnetic field in orbit. The ADCS of IITMSAT has no control over its spin with respect to the axis along the geomagnetic field. This has a destructive influence on the link aspects between the satellite and the ground station. As the satellite spins over its axis, given the two-axis attitude control, the gain of the downlink antennas in the direction of the ground station vary all through the pass of the satellite over the ground station, which will, in turn, affect the signal received at the ground station. Similarly, the uplink is also affected. A rigorous analysis of the variation of the link strengths for uplink and downlink along typical passes of the satellite above a ground station located in Chennai, India, is presented, taking into account the geomagnetic field at the altitude of the orbit. This analysis helps in choosing the polarization (LHCP or RHCP) for uplink and stresses the need for polarization diversity at the ground station for downlink. This will ensure the link with the ground station remains robust through the pass of the satellite and hence achieving higher amounts of data transfer with the satellite. Further, this work helps design the satellite onboard antennas for better link performance, taking into account the ground station location and assisting in taking system-level decisions for small satellite missions. - PublicationDesign of Electrical Power Subsystem for IITMSAT(29-09-2015)
;Gopakumar, Sooraj ;Eega, Saisree ;Suresh, Susurla V.S. ;Reddy, Madadi Sai Sriram ;Antony, Anand; This paper describes the design, development and test results of the Electrical Power Subsystem (EPS) of IITMSAT - the nano-satellite project of Indian Institute of Technology Madras (IITM). IITMSAT's payload comprises of an indigenously designed and developed Space based Proton Electron Energy Detector (SPEED). It is designed to measure the high energy particle precipitations just below the Van Allen Belts. Apart from SPEED, the satellite electronics include the health monitoring sensors, attitude sensors, three 32-bit ARM microcontrollers to process the data, communication module, Beacon, Command and Data Management System (CDMS) and electromagnetic actuators (Torque Rods) to align the satellite along the Earth's local magnetic field in the Low Earth Orbit (LEO). This indigenous EPS was designed and developed using low-cost, high-performance commercial off-the-shelf (COTS) components of industrial grade, to power loads of about 6 Watts. This paper describes the satellite power requirements, EPS hardware design, simulation results followed by practical results obtained from the prototype hardware. - PublicationEikonal Analysis of the Boundaryless Beam Propagation Method(15-10-2015)
;Mukherjee, SwagatoThe boundaryless beam propagation method has been reported to suffer from reflections due to frequency aliasing. We propose an alternate explanation of reflection in the method, based on eikonal analysis of the wave equation in the mapped space, and show that reflection starts much before aliasing happens. We theoretically predict the reflection coefficient profile in a simulation and introduce an internal absorbing boundary condition (ABC), where reflection becomes appreciable. The a priori knowledge of the window size of the ABC does away with the arbitrariness in the design of such boundaries. Finally, we use the boundaryless scheme with the ABC to successfully model a dielectric bend. - PublicationDesign of flight computer module for IITMSAT(29-09-2015)
;Suresh, Susurla V.S. ;Rosh, K. S.Green ;Kumar, K. C.Gopa ;Penumatsa, Shruti ;Mridul, Kumar ;Chavan, Shubham ;Koilpillai, Nathanael ;Gulati, Akshay K. ;Gopakumar, Sooraj; ; In this paper, we describe the design and development of Flight Computer module of the nano-satellite of IIT Madras, named IITMSAT. The flight computer module uses a 32 bit ARM microcontroller from Freescale-KL46Z256VLL4 and handles the attitude control, beacon transmission and electrical power management functions. The data from the attitude sensors is used by the control algorithm to calculate the magnetic moment, and in turn the torque required to orient the satellite along the direction of the magnetic field of the Earth. Beacon signal is used to detect the visibility of the satellite by the ground station (GS) and to transmit some important health data of the satellite. Onboard power management is done by turning off the loads carefully to save power, whenever needed. Throughout the design phase, the cost was kept as low as possible, without compromising on the performance of the system. - PublicationSecrecy analysis of a free-space laser communication system with a coherent main channel(01-06-2023)
;Kalaimani, Manuel PrasannaPhysical layer security of a free-space optical (FSO) communication link is investigated for certain eavesdropping scenarios in which the eavesdropper exploits the divergence of the transmitted laser beam, which is subject to atmospheric turbulence, to compromise the security of the transmission link. A solution for physical layer security in which the legitimate receiver is positioned to receive only the coherent component of the transmitted laser beam is proposed. The irradiance fluctuations are modeled with separate distributions for the coherent and non-coherent components of the transmitted beam, corresponding to the main channel and the eavesdropper's channel, respectively. Complete secrecy analysis of this setup is presented, and closed form expressions of the probability of strictly positive secrecy capacity, average secrecy capacity, and secrecy outage probability are derived. The analytical results are verified by Monte-Carlo simulations. Secrecy performance for worst-case scenarios corresponding to an adversary with powerful resources to capture all of the leaked information is explored. Results are analyzed for different turbulence regimes, and it was found that secure communication is possible even in the region of strong turbulence. - PublicationAnalytic, nonlinearly exact solutions for an rf confined plasma(09-07-2008)
;Shah, KushalRF confined electron plasmas are of importance in Paul traps [W. Paul, Rev. Mod. Phys. 62, 531 (1990)]. The stability of such plasmas is unclear and statistical heating arguments have been advanced to explain the observed heating in such plasmas [I. Siemers, Phys. Rev. A 38, 5121 (1988)]. This study investigates the nature of a one-dimensional collisionless electron plasma that is confined by an rf field of the form [-B+A cos (ωt)] x, where x is the space coordinate and ω is the rf frequency. Nonlinearly exact solutions are obtained. The distribution function and the plasma density are obtained in closed form and have constant shapes with time varying oscillations. These oscillations are at the rf frequency and its harmonics, modulated by a low frequency related to the electron bounce time. The linear limit of weak fields is recovered. Analytic expressions are obtained for the required external field to make it consistent with prescribed distribution functions. These solutions remain valid even in the presence of collisions. Solutions involving multiple species are also obtained, though only for collisionless traps. It is found that the ponderomotive force response needs to be corrected to account for the temperature fluctuations. No stochastic heating is observed in this field configuration. © 2008 American Institute of Physics. - PublicationComparison of semiclassical and quantum descriptions of saturated Erbium Doped Fibre Amplifiers (EDFA)(15-05-2012)
;Karthikeyan, A. R.The Bit Error Rate (BER) performance of Erbium Doped fiber amplifiers (EDFA) is analysed in this paper. An analysis of the BER from quantum statistics is compared to the BER obtained from semiclassical approaches. In earlier work [1], the authors showed how the predictions of the two treatments approached each other in the case of ideal amplifiers for large gain. In this paper, the analysis is carried out for non-ideal, i.e., saturated EDFA and it is found that convergence of the two treatments occurs at a lower gain for saturated amplifiers than for ideal amplifiers. © 2012 IEEE. - PublicationElectron plasmas: Confinement and mode structure in a small aspect ratio toroidal experiment(09-10-2006)
;Pahari, S.; John, P. I.Toroidal electron plasmas have remained less explored due to their poor confinement properties. Their equilibrium, stability, and confinement properties are therefore not entirely understood and continue to remain a topic of intense ongoing research. Large aspect-ratio theory suggests poor confinement in toroidal devices can be overcome by the application of a radial electric field; this has been verified successfully in some of the recent experiments. In the present paper, we report the longest confinement time without these external forces. Increasing the toroidicity has helped us to generate these forces intrinsically. To this end, a trap to confine electron plasmas has been created in a small aspect-ratio (≈ 1.6) torus. Electrons after being injected from a thermionic source are seen to remain confined with a purely toroidal magnetic field. The confinement time is far more than known single particle drift time scales. Importantly, it is in the absence of any external electric field, additional rotational transform, and/or magnetic fields, which, although not required, in principle, may appear essential particularly due to their role in improving confinement in some of the recent large aspect-ratio traps. The successful confinement in the small aspect-ratio limit has also led to several interesting observations: the evolution of the confined plasma is marked by an interesting nonlinear (large amplitude), electrostatic wave activity. Coherent, periodic, double peak oscillations result from a low-frequency E × B motion of a toroidal vortex in a plasma that closely leans against the inner wall. As many as 16 highly phase-coherent harmonics with dominant power in m=2 suggest that the mode is not merely a center-of-charge motion. Rather, a strong coupling of modes leads to a novel nonlinear state. The predominant energy is present in the shaping of the electron cloud (m=2) and not in the displacement of the center of charge (m= 1) seen in large aspect-ratio traps. The absence of any power-law tail suggests absence of any turbulence, at least on time scales longer than the wall-probe resolution (40 ns). The frequency, (around 100 kHz at 200 G) shows an unusual shear in time: it reduces as the mode evolves, but later increases as the mode dies. © 2006 American Institute of Physics.