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Dive into the research topics where Arvind Raman is active.

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Featured researches published by Arvind Raman.


Journal of Applied Physics | 2006

Hydrodynamic loading of microcantilevers vibrating in viscous fluids

Sudipta Basak; Arvind Raman; Suresh V. Garimella

The hydrodynamic loading of elastic microcantilevers vibrating in viscous fluids is analyzed computationally using a three-dimensional, finite element fluid-structure interaction model. The quality factors and added mass coefficients of several modes are computed accurately from the transient oscillations of the microcantilever in the fluid. The effects of microcantilever geometry, operation in higher bending modes, and orientation and proximity to a surface are analyzed in detail. The results indicate that in an infinite medium, microcantilever damping arises from localized fluid shear near the edges of the microcantilever. Closer to the surface, however, the damping arises due to a combination of squeeze film effects and viscous shear near the edges. The dependence of these mechanisms on microcantilever geometry and orientation in the proximity of a surface are discussed. The results provide a comprehensive understanding of the hydrodynamic loading of microcantilevers in viscous fluids and are expected to be of immediate interest in atomic force microscopy and microcantilever biosensors.


Applied Physics Letters | 2006

Ultrasensitive mass sensing using mode localization in coupled microcantilevers

Matthew Spletzer; Arvind Raman; Alexander Q. Wu; Xianfan Xu; R. Reifenberger

We use Anderson or vibration localization in coupled microcantilevers as an extremely sensitive method to detect the added mass of a target analyte. We focus on the resonance frequencies and eigenstates of two nearly identical coupled gold-foil microcantilevers. Theoretical and experimental results indicate that the relative changes in the eigenstates due to the added mass can be orders of magnitude greater than the relative changes in resonance frequencies. Moreover this sensing paradigm possesses intrinsic common mode rejection characteristics thus providing an alternate way to achieve ultrasensitive mass detection under ambient conditions.


Applied Mechanics Reviews | 2004

Microscale pumping technologies for microchannel cooling systems

Vishal Singhal; Suresh V. Garimella; Arvind Raman

A review of the state of the art in micropumping technologies for driving fluid through micro-channels is presented with a particular emphasis on small-scale cooling applications. An extensive variety of micropumping techniques developed over the past fifteen years in the literature is reviewed. The physical principles, engineering limitations, and advantages of approximately twenty different kinds of micropumps are reviewed. The available micropump-ing techniques are compared quantitatively, primarily in terms of the maximum achievable flow rate per unit cross-sectional area of the microchannel and the maximum achievable back pressure. A concise table is developed to facilitate the convenient comparison of the micro-pumps based on different criteria including their miniaturization potential, size ͑in-plane and out-of-plane͒, actuation voltage and power required per unit flow rate, ease and cost of fabrication , minimum and maximum frequency of operation, and suitability for electronics cooling. Some important performance characteristics of the micropumps, which are likely to be decisive for specific applications, are also discussed. The current state of the art in micropump design and fabrication is also comprehensively reviewed. There are 171 references cited in this review article.


Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences | 2003

Nonlinear dynamics of atomic-force-microscope probes driven in Lennard-Jones potentials

Sebastian Rützel; Soo Il Lee; Arvind Raman

The near‐resonant, nonlinear dynamic response of microcantilevers in atomic force microscopy is investigated through numerical continuation techniques and simulations of discretized models of the microcantilever interacting with a surface through a Lennard‐Jones potential. The tapping‐mode responses of two representative systems, namely a soft silicon probe‐silicon sample system and a stiff silicon probe‐polystyrene sample system, are studied. Van der Waals interactions are shown to lead to a softening nonlinearity of the periodic solution response, while the short‐range repulsive interactions lead to an overall hardening nonlinear response. Depending on the tip‐sample properties, the dynamics of the microcantilevers occur either in asymmetric single‐well potential regions or in asymmetric double‐well potential regions. In both cases, forced periodic motions of the probe tip destabilize through a sequence of period‐doubling bifurcations, while, in the latter, the tip can also escape the potential well to execute complex and unpredictable cross‐well dynamics. The results predict a broad range of nonlinear dynamic phenomena, many of which have been observed in the literature on experimental atomic force microscopy.


Nano Today | 2008

Cantilever dynamics in atomic force microscopy

Arvind Raman; John Melcher; Ryan Tung

Dynamic atomic force microscopy, in essence, consists of a vibrating microcantilever with a nanoscale tip that interacts with a sample surface via short- and long-range intermolecular forces. Microcantilevers possess several distinct eigenmodes and the tip-sample interaction forces are highly nonlinear. As a consequence, cantilevers vibrate in interesting, often unanticipated ways; some are detrimental to imaging stability, while others can be exploited to enhance performance. Understanding these phenomena can offer deep insight into the physics of dynamic atomic force microscopy and provide exciting possibilities for achieving improved material contrast with gentle imaging forces in the next generation of instruments. Here we summarize recent research developments on cantilever dynamics in the atomic force microscope.


Applied Physics Letters | 2008

Highly sensitive mass detection and identification using vibration localization in coupled microcantilever arrays

Matthew Spletzer; Arvind Raman; Hartono Sumali; John P. Sullivan

We study the use of vibration localization in large arrays of mechanically coupled, nearly identical microcantilevers for ultrasensitive mass detection and identification. We demonstrate that eigenmode changes in such an array can be two to three orders of magnitude greater than relative changes in resonance frequencies when an analyte mass is added. Moreover, the changes in eigenmodes are unique to the cantilever to which mass is added, thereby providing a characteristic “fingerprint” that identifies the particular cantilever where mass has been added. This opens the door to ultrasensitive detection and identification of multiple analytes with a single coupled array.


Applied Physics Letters | 2007

Dynamics of tapping mode atomic force microscopy in liquids : Theory and experiments

Sudipta Basak; Arvind Raman

A mathematical model is presented to predict the oscillating dynamics of atomic force microscope cantilevers with nanoscale tips tapping on elastic samples in liquid environments. Theoretical simulations and experiments performed in liquids using low stiffness probes on hard and soft samples reveal that, unlike in air, the second flexural mode of the probe is momentarily excited near times of tip-sample contact. The model also predicts closely the tip amplitude and phase of the tip at different set points.


Applied Physics Letters | 2004

Enhanced mass sensing using torsional and lateral resonances in microcantilevers

L. B. Sharos; Arvind Raman; S. Crittenden; R. Reifenberger

We present a method to detect, with enhanced sensitivity, a target mass particle attached eccentrically to a microcantilever by measuring multiple three-dimensional modes in the microcantilever vibration spectrum. Peaks in the spectrum reveal a complex coupling between the bending, torsional, and lateral motions and detailed finite element models assist in their interpretation. The mass sensitivities of the torsional and lateral mode frequencies are an order of magnitude greater, and their Q factors significantly higher, than that of the conventionally used fundamental bending mode. These modes offer significantly enhanced mass sensing capabilities within the realm of existing microcantilever technology.


Journal of Applied Physics | 2007

Comparative dynamics of magnetically, acoustically, and Brownian motion driven microcantilevers in liquids

Xin Xu; Arvind Raman

Magnetic, acoustic, and thermal (Brownian motion induced) excitations are commonly used for dynamic atomic force microscopy (AFM) in liquids, yet the fundamental differences in microcantilever vibration response for these different excitations remain poorly understood. In this work we discuss theoretically and experimentally several major differences between the amplitude and phase response of magnetically, acoustically, and thermally excited cantilevers in liquids and propose a way to estimate quantitatively the unsteady structure-borne and fluid-borne excitation forces acting on the acoustically excited AFM cantilever. The results have significant implications both for amplitude and frequency modulated AFM operation in liquids.


Applied Physics Letters | 2007

Equivalent point-mass models of continuous atomic force microscope probes

John Melcher; Shuiqing Hu; Arvind Raman

The theoretical foundations of dynamic atomic force microscopy (AFM) are based on point-mass models of continuous, micromechanical oscillators with nanoscale tips that probe local tip-sample interaction forces. In this letter, the authors present the conditions necessary for a continuous AFM probe to be faithfully represented as a point-mass model, and derive the equivalent point-mass model for a general eigenmode of arbitrarily shaped AFM probes based on the equivalence of kinetic, strain, and tip-sample interaction energies. They also demonstrate that common formulas in dynamic AFM change significantly when these models are used in place of the traditional ad hoc point-mass models.

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