Showing papers by "Rama B. Bhat published in 2011"

Interdigitated comb-like electrodes for continuous separation of malignant cells from blood using dielectrophoresis.

Abstract: In this paper, a method for continuous flow separation of circulating malignant cells from blood in a microfluidic device using dielectrophoresis is discussed. Separation of MDA231 breast cancer cells after mixing with normal blood cells was achieved with a level of accuracy that enabled precise counting of the malignant cells, separation and eventually, sub-culturing. MDA231 cells were separated from the blood to a daughter channel using two pairs of interdigitated activated comb-like electrode structures. All experiments are performed with conductivity adjusted medium samples. The electrode pairs were positioned divergent and convergent with respect to the flow. The AC signals used in the separation are 20 V peak-to-peak with frequencies of 10-50 kHz. The separation is based on balance of magnitude of the dielectrophoretic force and hydrodynamic force. The difference in response between circulating malignant cells and normal cells at a certain band of alternating current frequencies was used for rapid separation of cancer cells from blood. The significance of these experimental results is discussed in this paper, with detailed reporting on the suspension medium, preparation of cells, flow condition and the fabrication process of the microfluidic chip. The present technique could potentially be applied to identify incident cancer at a stage and size that is not yet detectable by standard diagnostic techniques (imaging and biochemical testing). Alternatively, it may also be used to detect cancer recurrences.

In-Plane free Vibration Analysis of an Annular Disk with Point Elastic Support

Abstract: In-plane freevibrations of an elasticand isotropic annular disk withelasticconstraints at theinner and outer boundaries, whichareappliedeither alongtheentireperipheryof thediskorat apoint areinvestigated. Theboundary characteristicorthogonal polynomials are employed in the Rayleigh-Ritz method to obtain the frequency parameters and the associated mode shapes. Boundary characteristic orthogonal polynomials are generated for the free boundary conditions of the disk while artificial springs are used to account for different boundary conditions. The frequency parameters for different boundary conditions of the outer edge are evaluated and compared with those available in the published studies and computed from a finite element model. The computed mode shapes are presented for a disk clamped at the inner edge and point supported at the outer edge to illustrate the free in-plane vibration behavior of the disk. Results show that addition of point clamped support causes some of the higher modes to split into two different frequencies with different mode shapes.

Clustered Natural Frequencies in Multi-Span Beams with Constrained Characteristic Functions

Abstract: A study of the natural frequencies and mode shapes of a multi-span beam is carried out by introducing constrained beam characteristic functions. The conventional method used for the dynamic analysis of such a beam is to consider span-wise characteristic function solution and then to solve it by using compatibility conditions such as the continuity in the a slope and bending moment at the intermediate supports and boundary conditions at the ends. In the method proposed here, the matrix size is reduced and, if the support conditions are symmetric about the midpoint, the symmetry and anti-symmetry conditions at the midpoint can be conveniently exploited for computational economy. The natural frequencies occur in clusters, each one containing the number of natural frequencies equal to the number of spans. The results are presented and discussed.

Trajectory tracking and vibration control of two planar rigid manipulators moving a flexible object

Abstract: This paper deals with the robust design of a control system for two planar rigid manipulators required to move the flexible object in the prescribed trajectory while suppressing the vibration of the flexible object. Without approximating or discretizing the beam, the complete system of dynamic equations are derived by combining the manipulator and beam dynamics. The resulting equations have rigid as well as flexible parameters which are coupled together. By using singular perturbation technique, the two subsystems, namely, slow and fast subsystems, are identified. For slow subsystem, a regressor based sliding mode control scheme is developed to track the desired rigid body motion of the object. For fast subsystem, a corresponding feedback control algorithm has been developed to suppress the vibration of the object. Exponential stability results for the closed-loop system with the developed control laws for both slow and fast subsystems are presented. Simulation results demonstrate the versatility of the proposed composite control scheme.

Simulation of PDMS microcantilever deflection using integrated optical fibers

Abstract: In this paper, a fully integrated flow sensor is designed and simulated. The sensor involves three PDMS layers, monolithic integration of microfluidic channels and detection unit. The middle thin layer includes the PDMS microcantilever and the microchannels network. The thin layer is sandwiched between the bottom and top PDMS layers to provide microfluidic environment and to release the cantilever for deflecting. The pressure difference on the cantilever causes the cantilever deflection. The optical fibers are embedded in the optical channels to send the light to the gold deposited cantilever tip and to detect the reflected light. Finite element analysis is done using COMSOL Multiphysics 3.5. Fluid structure interaction is done on the cantilever to find the cantilever defection in response to fluid flow in the microchannels. Optical power loss due to cantilever deflection is simulated by two integrated optical fibers. The numerical results confirm the feasibility of detecting the PDMS cantilever deflection in the range of regular microfluidic fluid flows.