סמינר מחלקתי Enbar Shnaider and Avi Abadi

School of Mechanical Engineering Seminar
Wednesday, January 21, 2015 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Arrays of Parametrically Excited Micro Cantilevers

Interacting through Fringing Electrostatic Fields

Inbar Schneider

School of Mechanical Engineering, Faculty of Engineering

Tel Aviv University, Israel

Dynamics of large arrays of micro- and nanoelectromechanical (MEMS/NEMS) oscillators in most cases assembled from cantilever-type individual elements interacting through nonlinear elastic, electromagnetic, or dissipative forces have received a great deal of attention over recent years. Apart from their rich dynamic behavior, these devices can be potentially used in ultrasensitive chemical or biological sensors or for light processing. Among the architectures reported so far the arrays interacting trough mechanical coupling support traveling waves (has real eigenfequencies in the case of a bounded system) and exhibit many interesting phenomena but lack tunability. On the other hand, the arrays interacting through electrostatic forces provided by close-gap electrodes can be easily tuned by voltage but does not support traveling waves. In the present work, we introduce a design of an array incorporating mechanically and electrostatically coupled micro cantilevers interacting through fringing electrostatic fields. This simple robust device architecture supports traveling waves and is distinguished by an easily tunable coupling stiffness and an efficient parametric excitation using a time-dependent voltage.  Reduced order model of the cantilevers was built based on the Galerkin decomposition and was used for the investigation of the interplay between the elastic and electrostatic coupling forces and their influence on the array’s dynamics. The non-local mechanical coupling matrix was extracted using the full scale finite elements analysis of the structure combined with sub-structuring procedure. The electrostatic interaction forces were approximated by a fit based on the the-dimensional numerical analysis.  The resonant responses of the arrays consisting of 500 mm long and 5 mm thick single crystal Si cantilevers were visualized by time-averaged temporally aliased video imaging and measured by laser Doppler vibrometry. Collective behavior, synchronization and abrupt transitions between standing wave patterns in arrays of micromechanical oscillators were observed in the experiments. Our experimental and model results collectively demonstrate that under a slowly varying drive frequency the standing wave patterns remain unchanged in certain frequencies intervals, followed by an abrupt change in the pattern.

School of Mechanical Engineering Seminar
Wednesday, January 21, 2014 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Minimal invasive medical micro-robot for brain parenchyma burrowing

Abadi Avi

MSc Student of Dr. Kosa Gabor

Microsystem locomotion is a key component for minimally invasive neurosurgical procedures. A self-propelling micro-robot facilitates targeted drug delivery, biopsy and neuro-stimulator positioning in brain parenchyma. In high frequency small deformation burrowing conditions, the soft brain tissue behaves as a viscoelastic fluidic environment and therefore Stokes swimmer techniques can be applied to move in the tissue.

We use a piezoelectric vibrating bimorph bender in order to propel an electrode in the brain parenchyma. The vibrational motion of the beam is stimulated by a top piezoelectric layer, divided into three separately actuated segments. Flexural vibration is created by each segment by sinusoidal excitation. The frequency, amplitudes and phases combinations govern the total shape of the beam’s vibration.

In order to discard the need for actuation modeling, we utilize the bottom piezoelectric layer of the bimorph for sensing. Three separated sensing segments convert the bending strain of the beam to electrical displacements and measured as voltages. By this measurement we are able to identify the frequency response (FR) of the beam vibration. We investigate the FR of a fully clamped commercially available piezoelectric bimorph in silicon oil. The implementation of the sensing abilities obtains maximal flow of the silicon oil, which indicates maximal propulsion forces. The suggested open loop control enables the system’s identification of a swimming micro-robot in highly viscous fluids. Results were confirmed using particle image velocimetry (PIV) methods under a microscope camera.