Browsing by Author "Çetin, Hakan"

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Coriolis Effect on elastic waves propagating in rods
(Elsevier, 2020-10-27) Çetin, Hakan; Yaralıoğlu, Göksen Göksenin; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin; Çetin, Hakan
Vibration analysis of rods that are subjected to rotation is presented. It is shown that flexural-flexural, longitudinal-flexural and torsional-flexural wave coupling occur due to the Coriolis Effect. First, we carried out our analysis for thin rods where the wavelength is much larger than the radius. It is shown that the wavenumbers change due to the Coriolis Effect. Then, we characterize the 3-D wave propagation in rotating rods by using the Finite Element Method (FEM) in order to determine the corresponding wavenumber shifts for each type of wave. We show that for different drive frequency (ω0) and rotation rate (Ω), wave couplings exhibit different characteristics. For flexural-flexural wave coupling, the wavenumber increases for the primary flexural wave whereas the wave number decreases for the coupled flexural wave where Ω < ω0. For the Coriolis coupling between flexural-longitudinal waves, the wavenumber increases for the flexural wave and decreases for the longitudinal wave where Ω < ω0. For the Coriolis coupling between flexural-torsional waves, the wavenumber increases for both flexural and torsional waves.
Open Access
Flexural wave-based soft attractor walls for trapping microparticles and cells
(Royal Society of Chemistry, 2021-02-07) Aghakhani, A.; Çetin, Hakan; Erkoc, P.; Tombak, G. I.; Sitti, M.; Çetin, Hakan
Acoustic manipulation of microparticles and cells, called acoustophoresis, inside microfluidic systems has significant potential in biomedical applications. In particular, using acoustic radiation force to push microscopic objects toward the wall surfaces has an important role in enhancing immunoassays, particle sensors, and recently microrobotics. In this paper, we report a flexural-wave based acoustofluidic system for trapping micron-sized particles and cells at the soft wall boundaries. By exciting a standard microscope glass slide (1 mm thick) at its resonance frequencies <200 kHz, we show the wall-trapping action in sub-millimeter-size rectangular and circular cross-sectional channels. For such low-frequency excitation, the acoustic wavelength can range from 10-150 times the microchannel width, enabling a wide design space for choosing the channel width and position on the substrate. Using the system-level acousto-structural simulations, we confirm the acoustophoretic motion of particles near the walls, which is governed by the competing acoustic radiation and streaming forces. Finally, we investigate the performance of the wall-trapping acoustofluidic setup in attracting the motile cells, such asChlamydomonas reinhardtiimicroalgae, toward the soft boundaries. Furthermore, the rotation of microalgae at the sidewalls and trap-escape events under pulsed ultrasound are demonstrated. The flexural-wave driven acoustofluidic system described here provides a biocompatible, versatile, and label-free approach to attract particles and cells toward the soft walls.
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Gyroscopes based on acoustic waveguides
(2016-08) Çetin, Hakan; Yaralıoğlu, Göksen Göksenin; Yaralıoğlu, Göksen Göksenin; Bozkurt, A.; Demiroğlu, Cenk; Department of Electrical and Electronics Engineering; Çetin, Hakan
We propose novel gyroscope architectures based on acoustic waves propagating in a waveguide. This thesis is composed of two parts. In the first part, the fundamentals of the proposed gyroscope are discussed. The new gyroscope will consist of a closed annular waveguide and a piezoelectric transducer, which excites the suitable acoustic modes of the waveguide. The piezoelectric transducer will generate two acoustic waves, which propagate in the opposite directions in the waveguide. When the waveguide is subjected to a rotational motion, due to the Coriolis forces, the acoustic waves that propagate in the opposite directions will gain different amounts of phases. The relative phase difference of these two waves will increase in proportional to the angular velocity of the waveguide. In other words, by measuring the phase difference between these two waves, one can monitor the rate of rotational motion. During our analysis of waveguides, we observed that the resonances of the waveguide structure shift. This is due to the upward and downward velocity shift of the counter-propagating waves in response to Coriolis force. Based on this observation, we performed in-depth analysis of vibrating gyroscope structures. This analysis constitutes the second part of the thesis. A typical vibrating gyroscope has two parts which are called drive and sense systems. Until now, the coupling between these two systems has been ignored and they have been analyzed separately. In the second part of this thesis, we demonstrate the analysis of the gyroscope including the coupling between drive and sense systems for the first time. Vibratory gyroscopes have attracted a lot of interest recently with the development of MEMS gyroscopes. These gyroscopes made their way through portable devices and smart phones. Novel gyroscope architectures have been proposed and analyzed in detail. However in most of these analyses, the coupling between the sense and drive systems were ignored. We analytically show that the drive and sense systems are coupled together via Coriolis force. As a result, resonances of the mechanical structure shift as the rotation rate increases for linear and torsional gyroscope systems. Starting from a simple gyroscope system, we calculated the sense and drive resonant frequency shifts in various configurations. Then, for more complex systems where analytical solution is difficult to obtain, we used commercially available FEM tools to determine the corresponding frequency shift. In general, we found that the shift is small and can be ignored for mode-matched linear vibratory gyroscopes, where Q of the sense system is less than 2500. But for higher Q systems, the frequency shift may affect the linearity of these gyroscopes. This sets a fundamental limit for the linearity of vibratory gyroscopes. Based on our calculations, the non-linearity is above 1% for linear 2-DOF mode-matched vibratory gyroscopes, where Q is above 3000 and for torsional 2-DOF mode-matched vibratory gyroscopes where Q is above 600. Multi-DOF and ring vibratory gyroscopes were also examined. We found that the effect is less pronounced for Multi-DOF gyroscopes.
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High shear rate propulsion of acoustic microrobots in complex biological fluids
(American Association for the Advancement of Science, 2022-03-11) Aghakhani, A.; Pena-Francesch, A.; Bozuyuk, U.; Çetin, Hakan; Wrede, P.; Sitti, M.; Çetin, Hakan
Untethered microrobots offer a great promise for localized targeted therapy in hard-to-access spaces in our body. Despite recent advancements, most microrobot propulsion capabilities have been limited to homogenous Newtonian fluids. However, the biological fluids present in our body are heterogeneous and have shear rate–dependent rheological properties, which limit the propulsion of microrobots using conventional designs and actuation methods. We propose an acoustically powered microrobotic system, consisting of a three-dimensionally printed 30-micrometer-diameter hollow body with an oscillatory microbubble, to generate high shear rate fluidic flow for propulsion in complex biofluids. The acoustically induced microstreaming flow leads to distinct surface-slipping and puller-type propulsion modes in Newtonian and non-Newtonian fluids, respectively. We demonstrate efficient propulsion of the microrobots in diverse biological fluids, including in vitro navigation through mucus layers on biologically relevant three-dimensional surfaces. The microrobot design and high shear rate propulsion mechanism discussed herein could open new possibilities to deploy microrobots in complex biofluids toward minimally invasive targeted therapy.
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Noise analysis of mode matched vibratory gyroscopes
(Springer, 2023-01) Çetin, Hakan; Yaralıoğlu, Göksen Göksenin; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin; Çetin, Hakan
MEMS (micro-electromechanical system) vibratory gyroscopes have attracted a lot of interest recently and these gyroscopes made their way through portable devices and smart phones. However, their performance is not enough to cope with the demanding requirements of applications such as dead reckoning. Mode-matched gyroscopes can be a solution for this problem. Various mode-matched gyroscope architectures have been proposed and their noise performances have been analyzed in detail. However, in most of these analyses zero-rate output was considered and the noise analysis for dynamic cases were ignored. In this paper, we demonstrate the noise analysis of mode-matched vibratory gyroscope using the power spectral density (PSD) and the Allan deviation methods while in rotation. We show that for mode-matched gyros the noise performance of a rotating gyro can be significantly different from that of a gyro that does not experience any rotation. We also show that this difference is due to the coupling between the drive and sense systems via Coriolis force. This sets a fundamental limit for the noise performance of mode-matched vibratory gyroscopes where ARW (angle random walk) increases proportionally with the rotation rate for the open loop and the force to rebalance operation modes.