Speaker: Yonatn Koral

M.Sc. student under the supervision of Prof. Miriam Furst-Yust and Prof. Shlomo Weiss

Wednesday, December 5^th, 2018 at 15:30

Room 011, Kitot Bldg., Faculty of Engineering

An Efficient Simulation Tool For the Auditory System By Parallel Processing
 

Abstract

            This work presents an auditory-emulation program that simulates the auditory neural response and determines hearing level based on a parallel time-domain nonlinear solution of the cochlea. Previous such simulations used a parallel calculation of the basilar membrane velocity and then calculated the serial neural response in the temporal and longitudinal dimensions. However, this approach suffers from limited efficiency because it requires copying large arrays and performing serial computation. In contrast, the proposed approach uses the graphics processing unit to do massively parallel computing, which accelerates threshold derivation based on the neural response calculation by a factor of 80 to 400. This is valuable both to calculate the hearing level for single-pitch signals and spoken words (with various types of noise or in silence) and to determine the benefit of different hearing aids to the hearing impaired.

(The talk will be given in English)

Speakers:   ALEXANDER OVSEEVICH AND ALEKSEY FEDOROV

                   Russian Academy of Sciences for Machine Learning at ETH Zurich

SUNDAY, November 18^th, 2018
15:00 - 16:00

Room 011, Kitot Bldg., Faculty of Engineering

STRING DAMPING: AN EXAMPLE IN ASYMPTOTIC CONTROL THEORY

Abstract

We study the problem of the minimum-time damping of a closed string under a bounded load, applied at a single _xed point. A constructive feedback control law is designed, which allows to bring the system to a bounded neighbourhood of the terminal manifold. The law has the form of the dry friction at the point, where the load is applied. The motion under the control is governed by a nonlinear wave equation. The existence and uniqueness of solution of the Cauchy problem for this equation are proved. The main result is the asymptotic optimality of the suggested control law.

Keywords maximum principle, reachable sets, linear system MSC 2010: 93B03, 93B07, 93B52.

Bio
AO born in Moscow, Russia in 1951, graduated From the mathematical department of the Moscow State University in 1973, and in 1976 defended PhD dissertation on number theory in the Mathematical Institute of the academy of sciences.

He obtained the next degree (Dr. of phys.-math. sc.) in 1997 from the Institute for Problems in mechanics, RAS for work in control theory. Worked in many areas of mathematics, from number theory to mathematical physics.

At present affiliated with the Institute for Problems in mechanics, RAS. Institute for Problems in Mechanics, Russian Academy of Sciences, 119526, Vernadsky av., 101/1, Moscow, Russia, ovseev@ipmnet.ru Russian Quantum Center, aleksey.fedorov@lptms.u-psud.fr

School of Mechanical Engineering Seminar
Monday, December 24, 2018 at 14.00
Wolfson Building of Mechanical Engineering, Room 206

Frequency Based Micro Sensors

Naftaly Krakover

 Ph.D. student of Prof. Slava Krylov

Micro- and nanoelectromechanical systems (MEMS/NEMS)-based sensors are indispensable components in a large variety of products as diverse as consumer electronics, industrial, automotive and defense systems. Simplicity, manufacturability and integrability all contribute to an increasingly widespread use of these small-size low-cost devices. In the realm of high-end sensors, one of the promising and intensively researched approaches for performance improvement is based on the monitoring of the spectral characteristics of the devices. Resonant frequencies of the vibrating structure are extremely sensitive to the external stimuli such as acceleration or pressure and can be measured with high accuracy.

In this work, two different frequency-based sensing approaches ae introduced and their feasibility is demonstrated theoretically and experimentally. The first is a resonant displacement/acceleration sensor, which exploits electrostatic frequency tuning. The device incorporates a vibrating beam located in a close proximity to a quasi-statically deflecting body and interacting with it through the electrostatic field.  Perturbations of the field induced by the body’s deflection affect the effective stiffness of the beam and its natural frequency.  Sensitivity is enhanced by tailoring the nonlinear coupling force using fringing electrostatic fields. The feasibility of the suggested sensing scenario was demonstrated using the deflection measurement of a single crystal silicon micro scale pressurized membrane. The sensitivity of ≈ 30 Hz/kPa, which is equivalent to the displacement sensitivity of ≈ 4 Hz/nm, was registered in the experiments.

The second approach is related to the vibration-based structural health monitoring, especially in the low frequency range. One of the main challenges encountered by the MEMS vibration sensors developers is a large mismatch between typical frequencies of macro and micro scale structures.  Our approach is based on a purely mechanical realization of the superheterodyne principle, which allows conversion of low frequency input signals into high frequency response. The device benefits from the inertial coupling between the translational and tilting vibrational modes of a proof mass attached to an oscillating substrate. The translational vibration creates a time-harmonic offset between the mass and the tilting axis. The frequency mixing moment emerges as a product between the inertial force and the translational displacement. The structure is distinguished by its ability to combine both sensing and signal processing functions by the same device. Our model and experimental results collectively support the feasibility of the suggested concept. Extremely low power consumption of the device makes it especially suitable for autonomous distributed sensors networks valuable for future Internet of Things (IoT) applications.

School of Mechanical Engineering Seminar
Monday, November 12, 2018 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Heat transfer During Phase Separation of Partially Miscible Liquid-Liquid Systems in Mini-Channels

by

Idan Shem Tov

This research was carried out in the School of Mechanical Engineering under the supervision of Prof. Amos Ullmann

and Prof. Neima Brauner

The increasing power density of miniaturized equipment requires advanced cooling technologies to maintain allowable temperatures and ensure safe operation. An experimental study has been conducted to explore the possibility of enhancing the convective heat transfer in mini-channels by temperature-induced phase separation of partially miscible liquid-liquid mixtures. The convective heat transfer of three different mixtures: triethylamine-water, propylene glycol propyl ether-water and lutidine-water was tested under conditions of constant wall heat fluxes. The phase separation of the mixtures showed up to 120% cooling enhancement compared to single-phase flow, up to 25% enhancement compared to water and up to 150% enhancement compared to the standard coolant of ethylene glycol-water mixture. The best results were achieved with triethylamine-water mixture under low Re number and high heating power. The creation and migration of droplets when phase-separation takes place and the resulting local fluid mixing in the heated wall vicinity, was found to be the main mechanism leading to the HTC enhancement. The local mixing can be represented as higher effective fluid thermal conductivity (k). The effective k values, circulated via CFD simulations, are up to 2.1 larger than those of the corresponding single-phase flow values. In parallel to this research, USA group, in collaboration with our research group, showed that the effect of HTC enchantment is preserved upon downscaling to micro-channel.