Modeling of eccentric nanoneedle in trolling-mode atomic force microscope

, Article Microscopy Research and Technique ; 2020 Chahari, M ; Sajjadi, M ; Sharif University of Technology

Wiley-Liss Inc 2020

Abstract

Limitations on installation of a standard TR-AFM nanoneedle can have unpredictable effects on dynamics of system. Therefore, it is crucial to pay close attention to the position and geometry of mounted nanoneedle when deriving the mathematical model. During TR-AFM fabrication process, the nanoneedle may not always deposit precisely at the middle of AFM tip, which would result in coupled bending-torsion modes in the dynamical operation of system. In this paper, we investigate the effect of eccentric nanoneedle in dynamic response of TR-AFM. To address this issue, a continuous mathematical model is developed. This model accounts for eccentric nanoneedle which can address the couplings in...

Modeling of eccentric nanoneedle in trolling-mode atomic force microscope

, Article Microscopy Research and Technique ; Volume 84, Issue 4 , 2021 , Pages 639-655 ; 1059910X (ISSN) Chahari, M ; Sajjadi, M ; Sharif University of Technology

John Wiley and Sons Inc 2021

Abstract

Limitations on installation of a standard TR-AFM nanoneedle can have unpredictable effects on dynamics of system. Therefore, it is crucial to pay close attention to the position and geometry of mounted nanoneedle when deriving the mathematical model. During TR-AFM fabrication process, the nanoneedle may not always deposit precisely at the middle of AFM tip, which would result in coupled bending-torsion modes in the dynamical operation of system. In this paper, we investigate the effect of eccentric nanoneedle in dynamic response of TR-AFM. To address this issue, a continuous mathematical model is developed. This model accounts for eccentric nanoneedle which can address the couplings in...

Nonlinear dynamic analysis of electrostatically actuated dual-axis micromirrors

, Article Journal of the Brazilian Society of Mechanical Sciences and Engineering ; Volume 45, Issue 3 , 2023 ; 16785878 (ISSN) Chahari, M ; Ahmadian, M. T ; Firoozbakhsh, K ; Sharif University of Technology

Springer Science and Business Media Deutschland GmbH 2023

Abstract

Dual-axis micromirrors are considered as the crucial components used for light deflection and control, which can be employed for arbitrary-direction optical beam steering with a low operating voltage. In order to achieve large scanning angles with a low driving voltage and presenting high resolution and scanning speeds, micromirrors are excited at their corresponding resonance frequencies. In addition, a bias DC voltage is also provided in order to scan around a desired nonzero tilt angle. Therefore, a comprehensive understanding of the mirror’s response to a DC-shifted primary resonance excitations is crucial. In this study, various design conditions including the primary resonances and the...

Chaos prediction in trolling mode atomic force microscopy: analytical approach

, Article Microsystem Technologies ; Volume 29, Issue 1 , 2023 , Pages 127-140 ; 09467076 (ISSN) Mohaqeqi, R ; Sajjadi, M ; Nejat Pishkenari, H ; Chahari, M ; Sharif University of Technology

Springer Science and Business Media Deutschland GmbH 2023

Abstract

Recently a novel mode of AFM called Trolling-mode AFM (TR-AFM) was developed with the ability to operate in liquid environments with an intrinsically high-quality factor. The presence of chaos in conventional tapping mode AFM severely limits the scanning speed, according to experimental and numerical observations. However, to enhance the scanning speed and imaging resolution, investigating the nonlinear dynamics of TR-AFM is imperative. The chaotic behavior is caused by highly nonlinear interaction between the tip and sample. The purpose of this research is to investigate the possibility of chaos phenomena and provide a safe range of parameters to prevent it in TR-AFM resonator. In this...

Nonlinear Vibration and Pull-in Analysis in Electrostatically Actuated Dual Axis Micromirrors

, M.Sc. Thesis Sharif University of Technology Chahari, Mahmood (Author) ; Ahmadian, Mohammad Taghi (Supervisor) ; Firoozbakhsh, Keykhosro (Supervisor)

Abstract

In recent decades, the important role of MEMS devices in optical systems has initiated the development of a new class of MEMS called Micro-Opto-Electro-Mechanical Systems (MOEMS), which torsional micromirror is one of these systems. Among variety kinds of micromirrors the dual axis micromirror has hopefully application such as high quality projection display, free-space fiber optical (FSO) communications and endoscopic optical coherence topography. Dual axis micromirror could play a key role in FSO applications such as satellite-to-satellite separated by hundreds of kilometers, as where. In medical applications, micromirror must could be able to rotates θ_x and θ_y.about two axis x and...

Controlling Local Scour Due to Hydraulic Jump Using Oblique Buried Plates

, M.Sc. Thesis Sharif University of Technology Borhani, Sanaz (Author) ; Borghei, Mahmood (Supervisor)

Abstract

Local scouring at the downstream of sluice gates in the erosive beds is one of the main concerns of hydraulic engineers because of the significant damage that it can cause to the hydraulic structures. It is important to control the local scour depth at downstream of hydraulic structures to ensure safety operation of these systems. Many researchers have conducted various studies to predict the maximum depth and diameter of scour hole and develop new methods in order to control this phenomenon. One way to overcome this problem is the use of apron, or non-erosive bed. In order to shorten the apron length or decrease the effect of the...

Experimental Study of Pressure Fluctuation in Two Phase Slug Flow In a Tunnel with Rectangular Cross Section with an Expansion Transition and Horizontal Slope

, M.Sc. Thesis Sharif University of Technology Jalilvand, Ehsan (Author) ; Borghie, Mahmood (Supervisor)

Abstract

Air enterance in to flowing water is something that is commonly seen in the water conveyance systems. The mixture of Air and water that flow together create a kind of flow that is called two phase flow. This kind of flow is often seen in culverts and water conveyance systems. There are different flow patterns in two phase flow. Considering pressure fluctuation, pressure drop and pressure recovery, slug flow pattern is the most complicated pattern among all.
Sometimes a singularity is used in a tunnel; one of the singularities that are frequently used in water conveyance system is expansion transition. In this study an experimental setup is used to model two phase slug flow, which passes...

Performance Analysis and Optimization of Optically Steered Arrayed Antennas with Gratings

, Ph.D. Dissertation Sharif University of Technology Shabani, Mostafa (Author) ; Akbari, Mahmood (Supervisor)

Abstract

It is well known that arrays of antennas make it possible to steer the radiation pattern without steering a physical structure. For the past few decades this has been considered for many civil and military communication systems. Recently, ultra-short pulses are considered for high resolution radars and ultra-wideband communication systems. Systems with short pulses and large antenna arrays may benefit from high resolution in both temporal and spatial domains. But the implementation of the ultra-wideband feeding circuits for such antenna arrays is a hard job even with state of the art electronics. Optical technology has been applied, successfully, to a number of radio applications such as...

Laboratory Investigation For Unsymmetric Rectangular Weir

, M.Sc. Thesis Sharif University of Technology Aghazadeh, Pooya (Author) ; Borghei, Mahmood (Supervisor)

Abstract

Sharp crested weirs are one of the main and oldest means of measuring discharge in water conveyance systems. Many studies have been done on sharp rectangular weirs and have provided many relationships regarding the effect of geometric parameters and various factors on discharge coefficient of the weirs.In some places, due to existence of obstacles or barriers in the channel, it is impossible to create a symmetrical continuous weir some other cases,multiple or asymmetric weirs should be used, which is the main concept of this project.Since it seems unlikely that a purely mathematical model can review the impact of the multiplicity and asymmetry of these weirs without using empirical...

Optimization of Maximum Frequency and Power, Extraction of Parameter Data and Final Publication Design of High Power Microwave Pulse Generation Using nonlinear Transmission Line with the Periodic Structure of the Gas Switch

, M.Sc. Thesis Sharif University of Technology Komeylian, Saeed (Author) ; Akbari, Mahmood (Supervisor)

Abstract

High-power (108 – 109 W) RF pulses with a carrier frequency of C band and a duration of several oscillation periods can be produced through direct energy conversion of a travelling high-voltage pulse with the use of nonlinear elements.
Nonlinear transmission lines consist either of lumped nonlinear elements and provide spatial dispersion of excited oscillations or of elements uniformly distributed on a certain line segment. The first type of NLTL’s can be referred to NLTL’s with spatial dispersion. The second type of NLTL’s is ensemble of nonlinear oscillators with a characteristic natural frequency and temporal dispersion. In the first case, the duration of electromagnetic pulses is...

An Estimation Model for Computation and Control of Trajectory Coverage Error in Additive Manufacturing

, M.Sc. Thesis Sharif University of Technology Zargar, Farinaz (Author) ; Houshmand, Mahmood (Supervisor)

Abstract

During 1980s Additive Manufacturing technologies for the purpose of prototyping with fast and less expensive, under the name of Rapid Prototyping was invented. But nowadays under the vast progress made in this field, it possesses a notable place in different industries such as automobile manufacturing, aerospace, architecture, medicine and so on for part manufacturing. In all AM machines, the CAD model design part is manufactured by adding layered to each other. In this research, at first by explaining manufacturing process and current different technologies, the place of this manufacturing process in today and future industry, is analyzed. For discussing replacement of this method instead...

Analysis and Simulation of Micrometre-scale Silicon Electro-optic Modulators Based on Ring Resonators

, M.Sc. Thesis Sharif University of Technology Jafari, Omid (Author) ; Akbari, Mahmood (Supervisor)

Improving Efficiency of Labyrinth Side Weirs Using Asymmetric Geometry

, M.Sc. Thesis Sharif University of Technology Parvaneh, Ali (Author) ; Borghei, Mahmood (Supervisor)

Abstract

One of the most important methods of controlling discharge in water industry which is widely used in irrigation, water distribution, waste-water engineering, drainage, flood control and other water related projects, is side weir. The hydraulic behavior of flow over side weir is spatially varied flow with decreasing discharge. Various investigators have related the weir discharge coefficient as a function of main channel upstream Froude number and the fraction of weir height to upstream depth . Performance of sharp crested side weirs with extended length (as labyrinth side weir with asymmetric geometry) has been studied in this thesis. The variables for this study are height of weir ,...

Analysis and Design of Nanoantenna Arrays

, M.Sc. Thesis Sharif University of Technology Dehmollaian, Ayyoub (Author) ; Akbari, Mahmood (Supervisor)

Abstract

If the size of the conventional telecommunication antennas -that are widely used in transmitting broadcasted radio and TV messages- is reduced by a nanometer size these antennas can be used at optical frequencies. Dimensions of these optical nanoantennas -that made of nanoparticles with highly permittivity- can be smaller than half of the wavelength. Based on this capability, optical nanoantennas have some important applications such as optical communication, photovoltaic devices, non-classical light, and optical sensing. After studying on optical nanoantennas and their features, in this project, we present distinctions between optical NAs and MW antennas and then investigate about different...

Optimized Design of Switch Circuit and Receiver Antenna in the Field of Fifth Generation Telecommunications to Reduce the Fading Effect

, M.Sc. Thesis Sharif University of Technology Bakhshi, Mehran (Author) ; Akbari, Mahmood (Supervisor)

Abstract

The Deep Fading Effect is a destructive factor in communication systems, one of the solutions to eliminate it is the use of Diversity, and there are two types of indicators of Diversity, Spatial Diversity and Polarization Diversity. Spatial Diversity is a common method to reduce the Fading Effect while increasing the cost and increasing the volume of the communication station, which to optimize the cost and reduce the volume of the communication station, the Polarization Diversity Structure is added to the telecommunication system. To apply Spatial Diversity, several Antennas with different Polarizations are used, which The most common method in mobile telecommunication station systems is...

Designing a New System for Proposing a Suitable Computer System for Customers Using Cloud Computing and Service Composition

, M.Sc. Thesis Sharif University of Technology Mousavi, Danial (Author) ; Hushmand, Mahmood (Supervisor)

Abstract

Cloud computing has brought about many changes in the new business arena. These changes do not only include technological changes, but have penetrated the business models of many companies. For example, in recent years, many companies have migrated from their former systems to cloud computing for reasons such as easy and low-cost access to high-performance hardware and software systems, and to avoid maintenance and repair costs and security costs.Due to the economic conditions in recent years and the high cost of electronic items, the criterion of purchase price has become much more important than in the past among people when buying such goods. Now in the Iranian electronics market,...

Design and Improvement of Meta-Surface Based MIMO Antennas for 5G Millimeter Wave

, M.Sc. Thesis Sharif University of Technology Molavi, Mehran (Author) ; Akbari, Mahmood (Supervisor)

Abstract

Wireless communication systems play a pivotal role in the daily lives of individuals. Given the escalating demand for higher data rates and enhanced reliability, there is an imperative need for cutting-edge communication technologies. Rigorous research is being conducted in these systems to refine and optimize antenna structures, aiming at augmenting performance, escalating data transmission rates, and mitigating interference. Microstrip antenna structures have garnered considerable attention due to their diminutive dimensions, adaptability to planar and non-planar surfaces, simplistic design, cost-effectiveness, and mechanical resilience. These antennas, featuring diverse patch shapes,...

Design and Implementation of an Audio Steganography System on FPGA

, M.Sc. Thesis Sharif University of Technology Ebrahimabadi, Mohammad (Author) ; Tabandeh, Mahmood (Supervisor)

Abstract

In recent years, along with development of technology and decrease in size of digital devices, copying and editing of digital multimedia products has become easier. Also, broadband technology caused simpler distribution of data. Considering above mentioned problems, we can use watermarking. Nowadays, watermarking has many applications such as secure transmission of data, owner identification, proof of ownership, authentication, broadcast monitoring etc. Watermarking is the process of hiding information in a secure host, in a way that it does not change the quality of signal. Watermarking is the science and art of hiding secret information in which neither the sender nor the receiver would...

Analysis of Wave Propagation Eigenproblem in Periodic Structures

, Ph.D. Dissertation Sharif University of Technology Faghihifar, Ehsan (Author) ; Akbari, Mahmood (Supervisor)

Abstract

The Fourier modal method is one of the most important methods in the analysis of flat periodic structures (gratings). Using this method, the problem of wave propagation in the periodic medium leads to an eigenproblem, in which eigenvalues represent the propagation constants and eigenvector or eigenfunctions determine the filed distribution of the modes. On the other side, considering all the generalizations and modifications reported so far, the Fourier modal method still faces two fundamental problems. First, for problems involving large dielectric constants or high contrasts, the matrix form of the eigenproblem (the modal matrix) can be large, dense, and require a high computational cost....

Simulation and plant wide Control of Combined Pervaporation/Distillation Process for MTBE Production

, M.Sc. Thesis Sharif University of Technology mozegar, Mostafa (Author) ; Pishvaei, Mahmood Reza (Supervisor)

Abstract

In this thesis we are about to simulate and control an MTBE production unit which use membrane instead of azeotropic distillation tower. At first an MTBE Production Unit with two distillation towers in separation part is simulated whit traditional method. One of these distillation towers is azeotropic. Then azeotropic distillation tower is replaced with membrane.After simulation the unit with best process indicators is selected. The goal is minimization of fixed and operating costs.In the next stage the best control loops in each unit is selected. The unit with best control indicators is determined. Control indicators are load rejection and set point tracking. All units have been simulated...