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86 results on '"Nabavi, Seyedfakhreddin"'

1. Portable Devices for In-Vitro Characterization Based on Ultrasound

Author

Nabavi, Seyedfakhreddin

Subjects
Physics - Medical Physics
Abstract

We propose a portable cartridge based lab-on-a-chip platform. The main sensing mechanism uses high frequency acoustic waves. Feasibility of two different transducers has been investigated for biological measurements. We used zincoxide (ZnO) based piezoelectric transducers for blood coagulation time measurements. The method is based on the measurement of amplitude of acoustic reflections from a microfluidic channel which is filled with blood. The volume of the microfluidic channel could be as low as 1 micro-litre. A low cost disposable cartridge made of glass has been designed to perform the measurements. The cartridge is composed of two glass substrates and a double sided tape layer where the channel is defined. One of the glass substrates has a micromachined ZnO based transducer that operates at 400 MHz on the outer surface of the cartridge where electrical connections are also provided. The transducer is aligned with the channel to generate acoustic pulses in the fluid that is filling the channel. The reflections coming from the top of the channel propagate through the liquid therefore their amplitude and phase are affected by the fluid properties. In the experiments whole blood was used without any sample preparation. The viscosity of the blood changes during coagulation therefore by monitoring the amplitude of the reflection coming from the top of the channel one can measure the coagulation time. The method which requires only 1 micro-litre of blood has been tested with calcium and activated partial thromboplastin (aPTT) reagents. The proposed method has a potential to be used in a low cost portable coagulation time measurement system for patient self-testing. The second transducer was made of CMUTs (Capacitive Micromachined Ultrasonic Transducers). We introduce this technology for immersion in liquids as a biological sensor for viscosity measurements., Comment: Master Thesis, Ozyegin University, Istanbul, Turkey 2015

Published
2017

12. Anchor loss reduction in micro-electro mechanical systems flexural beam resonators using trench hole array reflectors

Author

Kazemi, Mohammad, Nabavi, Seyedfakhreddin, Gratuze, Mathieu, Nabki, Frederic, Kazemi, Mohammad, Nabavi, Seyedfakhreddin, Gratuze, Mathieu, and Nabki, Frederic

Abstract

The quality factor of microelectromechanical resonators is a crucial performance metric and has thus been the subject of numerous studies aimed at maximizing its value by minimizing the anchor loss. This work presents a study on the effect of elastic wave reflectors on the quality factor of MEMS clamped–clamped flexural beam resonators. The elastic wave reflectors are a series of holes created by trenches in the silicon substrate of the resonators. In this regard, four different shapes of arrayed holes are considered, i.e., two sizes of squares and two half circles with different directions are positioned in proximity to the anchors. The impact of these shapes on the quality factor is examined through both numerical simulations and experimental analysis. A 2D in-plane wave propagation model with a low-reflecting fixed boundary condition was used in the numerical simulation to predict the behavior, and the MEMS resonator prototypes were fabricated using a commercially available micro-fabrication process to validate the findings. Notably, the research identifies that half-circle-shaped holes with their curved sides facing the anchors yield the most promising results. With these reflectors, the quality factor of the resonator is increased by a factor of 1.70 X in air or 1.72 X in vacuum.

Published
2023

13. Multi Degrees-of-Freedom Hybrid Piezoelectric-Electrostatic MEMS Actuators Integrated With Displacement Sensors

Author

Rabih, Almur A. S., Nabavi, Seyedfakhreddin, Menard, Michael, and Nabki, Frederic

Abstract

This work presents novel multi degrees-of-freedom (DOF) actuators based on piezoelectric and electrostatic actuation to generate both in-plane and out-of-plane motions, intended to position a suspended optical waveguide for chip-to-chip alignment in photonic integrated circuits. In this context, the mechanical structures of the actuators with a suspended platform to carry the waveguide, are designed to house aluminum nitride (AlN) as the piezoelectric material for generating out-of-plane motion and a comb-drive, whose fixed and moveable fingers are positioned on the same layer for in-plane motion. Two distinct designs, i.e., a 2-DOF design with motions along the Z-and Y-axes and a 3-DOF design with motions along the Z-, Y-, and X-axes were fabricated and tested. Both designs include capacitive-based displacement sensors to track the motions in Z-and Y-axes. Experimental results at ±60 V indicate that 3 devices of each design give an average displacement of 3.16 ± $0.34~\mu \text{m}$ and 0.63 ± $0.04~\mu \text{m}$ in the Z-axis for the 2-DOF and 3-DOF designs, respectively. For the Y-axis at 120 V, the average results for the two designs respectively were found to be 3.06 ± $0.17~\mu \text{m}$ and 7.38 ± $0.29~\mu \text{m}$ , with the ability to extended the later to $10.69~\mu \text{m}$ at 140 V. In the X-axis, the 3-DOF design can produce total of 300 nm of displacement at ±100 V. The capacitance measurements were found to correlate well with the tracked displacement. Furthermore, simultaneous activation of more than one actuator could mitigate misalignment and align the platform with a fixed surface. [2023-0148]

Published
2024
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14. A 3 Degrees-of-Freedom Electrothermal Micro-Positioner for Optical Chip-to-Chip Alignment

Author

Rabih, Almur A. S., Nabavi, Seyedfakhreddin, Menard, Michael, and Nabki, Frederic

Abstract

This article proposes an electrothermal three-degrees-of-freedom (3-DOF) micro-positioner equipped with a waveguide path, which can potentially be used for chip-to-chip alignment in photonic integrated circuits. The micro-positioner provides translational displacements along the x-, y- and z- axes with manageable levels of cross-sensitivity between axes. A fabricated prototype provides displacements of $\pm 3.35~\mu \text{m}$ at 105 mW along the x-axis, and $+4.5~\mu \text{m}$ at 140 mW along the y-axis. Moreover, $+7~\mu \text{m}$ of out-of-plane displacement is achieved along the z-axis when 210 mW is applied to the x-axis actuators to buckle the structure. The AC response of the micro-positioner shows that the fundamental resonance mode occurs at 18.8 kHz. [2023-0208]

Published
2024
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29. A SOI Out-of-Plane Electrostatic MEMS Actuator Based on In-Plane Motion.

Author

Nabavi, Seyedfakhreddin, Menard, Michael, and Nabki, Frederic

Subjects
*ELECTROSTATIC actuators, *VERTICAL motion, *MICROELECTROMECHANICAL systems, *ACTUATORS, *MICROMACHINING, *MEMS resonators
Abstract

This work describes a novel micromechanical structure capable of producing out-of-plane motion from in-plane forces generated by electrostatic microelectromechanical system (MEMS) actuators. The MEMS actuator is fabricated in a commercial silicon-on-insulator (SOI) MEMS process and is anchored at two distinct locations through a pair of beams with a relatively low stiffness in the vertical direction. A comb-drive, whose fixed and moveable fingers are implemented in the same layer with a uniform thickness, is employed to create an attractive electrostatic force. This in-plane electrostatic force rotates the actuator along an axis defined by the anchors, which results in the vertical motion of a suspended platform. Due to the simple structure of the actuator, it can be readily manufactured with standard bulk micromachining processes. Experimental results demonstrate that the actuator can provide $1.02~\mu \text{m}$ of vertical displacement at a resonant frequency of 395 Hz when it is excited in air by a 10 V AC signal, while the displacement can be considerably increased in vacuum. It is further shown that the functionality of the actuator is not dependent on the type of excitation voltage; therefore, it can produce a $3.09~\mu \text{m}$ static out-of-plane motion when excited by a 40 V DC voltage. A comprehensive comparison to the published works in the literature indicates that the proposed actuator is the only SOI electrostatic MEMS actuator with a relatively thick structural layer, i.e., $10~\mu \text{m}$ , that can provide out-of-plane motion at low actuation voltage reported to date. [2022-0069] [ABSTRACT FROM AUTHOR]

Published
2022
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49. Portable devices for In-Vitro characterization based on ultrasound

Author

Nabavi, Seyedfakhreddin, Yaralıoğlu, Göksen Göksenin, and Elektrik-Elektronik Mühendisliği Anabilim Dalı

Subjects
Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
Abstract

Bu projede taşınabilir kartuş tabanlı lab-on-a-chip platformu öneriliyor. Ve bu platformun ana algılama mekanizması yüksek frekanslı akustik dalgalar ile çalışmaktadır. Biyolojik ölçümler için iki farklı transdüserin uygulanabilirliği incelenmiştir. Kan pıhtılaşma zamanı ölçümleri için ise çinkooksit (ZnO) tabanlı piezoelektrik transdüserler kullanılmıştır. Yöntem olarak kan ile dolu olan bir mikroakışkan kanaldan akustik yansımaların genliğinin ölçülmesi kullanımıştır. Mikroakışkan kanal hacmi 1 mikro-litre gibi düşük bir değer olabilir. Düşük maliyetli tek kullanımlık cam kartuş ise ölçümlerin yapılması için tasarlanmıştır. Kartuş iki cam alt tabakadan ve kanalın bulunduğu bir çift taraflı şerit tabakadan oluşur. Cam alt tabakalarından biri kartuşun dış yüzeyi üzerinde elektrik bağlantıları da sağlanmışbir şekilde 400 MHz'de çalışan bir mikroişlenmiş ZnO transdüsere sahiptir. Transdüser ise kanalı dolduran sıvı içinde akustik darbeleri üretmek için kanal ile hizalanmıştır. Kanalın üstünden gelen yansımalar sıvı içinden yayılmakta ve bu nedenle onların genlik ve fazları sıvının özelliklerinden dolayı etkilemektedir. Deneylerde tüm kan herhangi bir numune hazırlanmadan kullanılmıştır. Pıhtılaşma sırasında kan akışmazlığı değişir dolayısıyla kanalın üst kısmından gelen yansıma genliği izlenerek pıhtılaşma süresi ölçülebilir. Kanın sadece 1 mikro-litre gerektiren yöntem kalsiyum ile test edilmiş ve parsiyel tromboplastin (aPTT) reaktifler ile aktive edilmiştir. Önerilen yöntem, hastanın kendisini test etmek için kullanabileceği pıhtılaşma zamanını ölçen düşük maliyetli ve taşınabilir bir sistem için potansiyele sahiptir. İkinci transdüser CMUTs olarak yapılmıştır. Bu teknolojiyi akışmazlık ölçümleri için sıvıların içine batırılan bir biyolojik sensör olarak tanıtıyoruz. Membran tipi rezonatörler için sınır koşulları kalite faktörünü arttırmak amacıyla değiştirilmiştir. Bu değişim sensöre yüksek hassasiyet kazandırmıştır. Kalite faktöründeki iyileşme sonlu eleman analizi kullanarak gösterilmiştir. We propose a portable cartridge based lab-on-a-chip platform. The main sensing mechanism uses high frequency acoustic waves. Feasibility of two different transducers has been investigated for biological measurements. We used zincoxide (ZnO) based piezoelectric transducers for blood coagulation time measurements. The method is based on the measurement of amplitude of acoustic reflections from a microfluidic channel which is filled with blood. The volume of the microfluidic channel could be as low as 1 micro-litre. A low cost disposable cartridge made of glass has been designed to perform the measurements. The cartridge is composed of two glass substrates and a double sided tape layer where the channel is defined. One of the glass substrates has a micromachined ZnO based transducer that operates at 400 MHz on the outer surface of the cartridge where electrical connections are also provided. The transducer is aligned with the channel to generate acoustic pulses in the fluid that is filling the channel. The reflections coming from the top of the channel propagate through the liquid therefore their amplitude and phase are affected by the fluid properties. In the experiments whole blood was used without any sample preparation. The viscosity of the blood changes during coagulation therefore by monitoring the amplitude of the reflection coming from the top of the channel one can measure the coagulation time. The method which requires only 1 micro-litre of blood has been tested with calcium and activated partial thromboplastin (aPTT) reagents. The proposed method has a potential to be used in a low cost portable coagulation time measurement system for patient self-testing. The second transducer was made of CMUTs (Capacitive Micromachined Ultrasonic Transducers). We introduce this technology for immersion in liquids as a biological sensor for viscosity measurements. Boundary conditions for membrane type resonators have been modified in order to increase the quality factor. This enabled a sensor with high sensitivity. We demonstrate the quality factor improvement using FEM analysis. 74

Published
2015

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