Publications by authors named "S Devasia"

8 Publications

Bio-mimetic silicone cilia for microfluidic manipulation.

Lab Chip 2009 Jun 9;9(11):1561-6. Epub 2009 Mar 9.

Department of Mechanical Engineering, University of Washington, Seattle, WA 98195, USA.

This paper presents a bio-mimetic microfluidic device that mimics the high compliance and the beating frequency of biological cilia in order to achieve bio-compatible manipulation of microfluidics. Because the highly compliant cilia can easily collapse due to interaction energy and surface tension, the major challenge in developing a bio-mimetic device is the manufacturing of highly compliant cilia. An underwater fabrication method is developed to avoid the cilia collapse by lowering the surface energy of the cilia. Another challenge is to mimic the low beating frequency (10-100 Hz) of biological cilia. The proposed microfluidic device is excited by a piezo actuator to resonate the cilia in water. Due to the highly compliant nature of the silicone cilia, the resulting actuation frequency is in the beating frequency range of biological cilia. Simulations and experiments are presented to demonstrate microfluidic manipulation by resonance of the assembled cilia array.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/b817409aDOI Listing
June 2009

High-bandwidth control of a piezoelectric nanopositioning stage in the presence of plant uncertainties.

Nanotechnology 2008 Mar 20;19(12):125503. Epub 2008 Feb 20.

Australian Research Council's Center of Excellence for Complex Dynamic Systems and Control, The University of Newcastle, Callaghan, NSW, Australia.

Inversion-based feedforward techniques have been known to deliver accurate tracking performance in the absence of plant parameter uncertainties. Piezoelectric stack actuated nanopositioning platforms are prone to variations in their system parameters such as resonance frequencies, due to changes in operating conditions like ambient temperature, humidity and loading. They also suffer from nonlinear effects of hysteresis, an inherent property of a piezoelectric actuator; charge actuation is applied to reduce the effects of hysteresis. In this work, we propose and test a technique that integrates a suitable feedback controller to reduce the effects of parameter uncertainties with the inversion-based feedforward technique. It is shown experimentally that the combination of damping, feedforward and charge actuation increases the tracking bandwidth of the platform from 310 to 1320 Hz.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0957-4484/19/12/125503DOI Listing
March 2008

Iterative image-based modeling and control for higher scanning probe microscope performance.

Rev Sci Instrum 2007 Aug;78(8):083704

Department of Mechanical Engineering, University of Washington, Seattle, WA 98195, USA.

In this article, we develop an image-based approach to model and control the dynamics of scanning probe microscopes (SPMs) during high-speed operations. SPMs are key enabling tools in the experimental investigation and manipulation of nano- and subnanoscale phenomena; however, the speed at which the SPM probe can be positioned over the sample surface is limited due to adverse dynamic effects. It is noted that SPM speed can be increased using model-based control techniques. Modeling the SPM dynamics is, however, challenging because currently available sensing methods do not measure the SPM tip directly. Additionally, the resolution of currently available sensing methods is limited by noise at higher bandwidth. Our main contribution is an iterative image-based modeling method which overcomes these modeling difficulties (caused by sensing limitations). The method is applied to model an experimental scanning tunneling microscope (STM) system and to achieve high-speed imaging. Specifically, we model the STM up to a frequency of 2000 Hz (corresponds to approximately 23 of the resonance frequency of our system) and achieve approximately 1.2% error in 1 nm square images at that same frequency.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.2773534DOI Listing
August 2007

Control Issues in High-speed AFM for Biological Applications: Collagen Imaging Example.

Asian J Control 2004 Jun;6(2):164-178

This article considers the precision positioning problem associated with high-speed operation of the Atomic Force Microscope (AFM), and presents an inversion-based control approach to achieve precision positioning. Although AFMs have high (nanoscale) spatial resolution, a problem with current AFM systems is that they have low temporal resolution, i.e., AFM imaging is slow. In particular, current AFM imaging cannot be used to provide three-dimensional, time-lapse images of fast processes when imaging relatively-large, soft samples. For instance, current AFM imaging of living cells takes 1-2 minutes (per image frame) - such imaging speeds are too slow to study rapid biological processes that occur in seconds, e.g., to investigate the rapid movement of cells or the fast dehydration and denaturation of collagen. This inability, to rapidly image fast biological processes, motivates our current research to increase the operating speed of the AFM. We apply an inversion-based feedback/feedforward control approach to overcome positioning problems that limit the operating speed of current AFM systems. The efficacy of the method, to achieve high-speed AFM operation, is experimentally evaluated by applying it to image collagen samples.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1356882PMC
http://dx.doi.org/10.1111/j.1934-6093.2004.tb00195.xDOI Listing
June 2004

High-speed solution switching using piezo-based micropositioning stages.

IEEE Trans Biomed Eng 2001 Jul;48(7):806-14

Mechanical Engineering Department, University of Utah, Salt Lake City 84112, USA.

Motion-induced vibration is a critical limitation in high-speed micropositioning stages used to achieve solution switching. Controlled rapid solution switching is used to study the fast activation and deactivation kinetics of ligand-gated ion-channel populations isolated in excised membrane patches--such studies are needed to understand fundamental mechanisms that mediate synaptic excitation and inhibition in the central nervous system. However, as the solution-switching speed is increased, vibration induced in the piezo-based positioning stages can result in undesired, repeated, ligand application to the excised patch. The article describes a method to use knowledge of the piezo-stage's vibrational dynamics to compensate for and reduce these unwanted vibrations. The method was experimentally verified using an open-electrode technique, and fast solution switching (100 micros range) was achieved.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1109/10.930905DOI Listing
July 2001
-->