Krishnan Balasubramaniam

Bio: Krishnan Balasubramaniam is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Ultrasonic sensor & Lamb waves. The author has an hindex of 40, co-authored 486 publications receiving 6266 citations. Previous affiliations of Krishnan Balasubramaniam include University of Colorado Boulder & Marshall Space Flight Center.

An Overview of Existing Algorithms for Resolving the 180° Ambiguity in Vector Magnetic Fields: Quantitative Tests with Synthetic Data

Abstract: We report here on the present state-of-the-art in algorithms used for resolving the 180° ambiguity in solar vector magnetic field measurements. With present observations and techniques, some assumption must be made about the solar magnetic field in order to resolve this ambiguity. Our focus is the application of numerous existing algorithms to test data for which the correct answer is known. In this context, we compare the algorithms quantitatively and seek to understand where each succeeds, where it fails, and why. We have considered five basic approaches: comparing the observed field to a reference field or direction, minimizing the vertical gradient of the magnetic pressure, minimizing the vertical current density, minimizing some approximation to the total current density, and minimizing some approximation to the field's divergence. Of the automated methods requiring no human intervention, those which minimize the square of the vertical current density in conjunction with an approximation for the vanishing divergence of the magnetic field show the most promise.

Functionalized graphene reinforced thermoplastic nanocomposites as strain sensors in structural health monitoring

Abstract: Functionalized graphene–polyvinylidene fluoride (f-G–PVDF) nanocomposite films were synthesized using a simple solvent casting technique. The investigation demonstrates the real time strain response of f-G–PVDF nanocomposites on the macro-scale under tensile loads and the use of this nanocomposite as strain sensor. This is ascribed to the variation of electrical properties of graphene–polymer upon mechanical deformation at the nanoscale.

Chirality of Chromospheric Filaments

Abstract: We use the chromospheric full-disk Hα observations to study the chirality of 2310 filaments from 2000-2001. For each filament, we identify the spine and its barbs and determine the filament chirality as fraction of dextral/sinistral barbs of the total number of barbs. We find that 80.2% (558 out of 696) of quiescent filaments in the northern hemisphere are dextral and 85.5% (633 out of 740) of filaments in southern hemisphere are sinistral, in agreement with the well-known hemispheric helicity rule. Our data also show that the active-region filaments follow the same rule, though the hemispheric dependence is weaker: 74.9% (338 out of 451) of active-region filaments in the northern hemisphere are dextral, and 76.7% (297 out of 387) of filaments in the southern hemisphere are sinistral. We show that quiescent filaments formed on leading and returning arms of the same switchback exhibit the same chirality. We also investigate a possible change in the hemispheric rule with polarity reversal of the polar field, and we find no such change.

Interaction of the primary anti-symmetric Lamb mode (Ao) with symmetric delaminations: numerical and experimental studies

Abstract: The interaction of an ultrasonic guided Lamb wave mode with delamination type defects in a quasi-isotropic laminated composite plate has been studied, using both simulations and experiments. In a laminated composite plate with a symmetric delamination, when the primary anti-symmetric mode, Ao, is incident at the entrance and exit of a delamination, it generates a new mode, So, that is confined only to sub-laminates and undergoes multiple reflections in the delaminated region. It was observed that only the incident and mode-converted Ao modes propagate in the main laminate. The two modes reverberate between the two ends of the delaminations while undergoing multiple mode conversions, leading to a trail of signals that is captured by the finite element model. The numerical observations were validated using experiments conducted using air coupled ultrasonic transducers.

One-pot synthesis of conducting graphene–polymer composites and their strain sensing application

Abstract: In situ reduction of graphite oxide in polymer powder has been implemented using focused solar electromagnetic radiation. The simultaneous reduction of graphite oxide, melting of the polymer and embedding of reduced graphite oxide nanoflakes in polymer offer a new way of synthesizing conducting graphene/polymer composites. An electromechanical application of the present reduced graphite oxide–PVDF nanocomposite has been proposed with a gauge factor of 12.1.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

The Helioseismic and Magnetic Imager (HMI) Investigation for the Solar Dynamics Observatory (SDO)

Abstract: The Helioseismic and Magnetic Imager (HMI) instrument and investigation as a part of the NASA Solar Dynamics Observatory (SDO) is designed to study convection-zone dynamics and the solar dynamo, the origin and evolution of sunspots, active regions, and complexes of activity, the sources and drivers of solar magnetic activity and disturbances, links between the internal processes and dynamics of the corona and heliosphere, and precursors of solar disturbances for space-weather forecasts. A brief overview of the instrument, investigation objectives, and standard data products is presented.

Highly Stretchable Piezoresistive Graphene–Nanocellulose Nanopaper for Strain Sensors

Abstract: Highly stretchable graphene-nanocellulose composite nanopaper is fabricated for strain-sensor applications. Three-dimensional macroporous nanopaper from crumpled graphene and nanocellulose is embedded in elastomer matrix to achieve stretchability up to 100%. The stretchable graphene nanopaper is demonstrated for efficient human-motion detection applications.

Wearable and Highly Sensitive Graphene Strain Sensors for Human Motion Monitoring

Abstract: Sensing strain of soft materials in small scale has attracted increasing attention. In this work, graphene woven fabrics (GWFs) are explored for highly sensitive sensing. A flexible and wearable strain sensor is assembled by adhering the GWFs on polymer and medical tape composite film. The sensor exhibits the following features: ultra-light, relatively good sensitivity, high reversibility, superior physical robustness, easy fabrication, ease to follow human skin deformation, and so on. Some weak human motions are chosen to test the notable resistance change, including hand clenching, phonation, expression change, blink, breath, and pulse. Because of the distinctive features of high sensitivity and reversible extensibility, the GWFs based piezoresistive sensors have wide potential applications in fields of the displays, robotics, fatigue detection, body monitoring, and so forth.