1,720,961 research outputs found
Semi-classical modeling of nano-mechanical transistors
No full textThe introduction of vibration-based Nano Electro-Mechanical Transistors (NEMT) opens a new horizon for mechanics in computer science. NEMT working principle is based on an electrical charge shuttle between two electrodes operated by a vibrating conductor body. Advantages of these novel devices would be very low power dissipation, limited influence of external electromagnetic disturbances, and improved thermal resistance. The paper introduces an analytical model for such a device, in which the matching of a mechanical resonator and an electric circuit is studied: the coupling is provided by capacitance effects, electrostatic force and the quantum tunneling. The approach is quasi-classical, describing the quantum phenomena through a non-linear conductance and using a continuous variable for the charges. Through suitably introduced simplifications, the model is reduced to a set of two differential equations in terms of pillar position and charge. These equations represent the simplest model still preserving the basic phenomenology of the investigated system. Numerical simulations show different possible motion regimes, both in the single- and multiple-module configurations, the latter able to reproduce the conventional transistor functionality. This opens the way to mechanical voltage-driven switches or amplifiers
Modelling of MEMS/NEMS Resonators and Functional Design of a Mechanical Transistor
No full textThe most basic example of charge transport is represented by the collective motion of free charge carriers in a conductive medium. In the context of electromechanical devices, more complex forms of charge transport, labeled with the umbrella term electron shuttle, exist.
The simplest system exhibiting a shuttle mechanism comprises a set of three conductors: two fixed electrodes and a vibrating element between them. Under certain boundary conditions a limit-cycle is established, and the oscillator alternatively takes and releases a finite amount of electrons while approaching the electrodes. Since this form of charge transport relies on the presence of mechanical vibrations, the described phenomenon constitutes the archetype of a “mechanical charge carrier”.
Although the first concept of electron shuttle is over two centuries old, only in recent times [Gorelik and Isacsson, 1998] it found reinvigorated interest in the field of nanotechnology, producing a novel branch of both theoretical and experimental research. In fact, the introduction of quantum effects in shuttle devices produces interesting motion regimes peculiar of nanoscale. Refer to such systems as Quantum Shuttle Modules (QSMs).
Many original architectures have been conceptualized and realized in the last decade. A promising application is contained in a patent [Blick and Marsland, 2008] which proposes a switching element based on electron shuttle and capable of reproducing the main functionalities of a conventional transistor, depicted as composed by an array of mechanically coupled QSM subsystems, whose vibrating elements are nanocantilevers. Refer to this invention as the NanoMechanical Transistor (NMT). At the present day, the NMT is an unexplored concept: no experimental setup has been realized nor theoretical model has been proposed yet.
The research work contained in this thesis is intended to provide a first theoretical description and an early design stage for such NMT device. Notice that, since the NMT is composed by a set of QSMs, a preliminary study of these systems is needed. This work is consequently divided in two Parts: the first one focuses on the QSMs with an exquisitely theoretical approach, while the second one is intended to assess the feasibility of a real application, the NMT.
A brief description of the thesis contents is presented ahead.
Part One begins by introducing the fundamental concepts of quantum tunneling and Coulomb blockade. Then, the general scheme of a QSM is presented. As usual in literature, a concentrated parameters model is used, and the state of the system is reduced to a couple of lagrangian descriptors: the oscillator position and charge. Conductive and dynamical properties are investigated with both analytical and numerical approaches. Then, a systematic study of QSMs is attempted by considering two basic shuttle mechanisms: in the first case, the oscillator is self-excited by a shuttle current between electrodes at different voltages; in the second case, the oscillator vibrates under parametric resonance and a shuttle current is established between two electrodes at the same voltage. The portrayed phenomenologies are complementary, meaning each QSM presents a combination of these two fundamental forms of electron shuttle.
Part Two opens with an overview of the conventional transistors and an analysis of the NMT patent. Follows the choice of the characteristic scales of the device and the typology of QSM to be the best candidate as NMT subsystem. Under suitable approximations, closed-form formulae for capacitances, quantum tunneling and electrostatic force are produced. A flexible set of equations is obtained, allowing to perform a large number of numerical experiments. First, a single QSM subsystem is considered: a predictive model is proposed in which a QSM is related to a Turing machine whose admitted states are represented by the feasible motion regimes. Then, more QSM subsystems are arranged to realize the NMT: each module is electrostatically independent but mechanically coupled with its nearest neighbors. A functional analysis of the whole system is presented, in which peculiar motion regimes are investigated, and a set of design and control strategies aimed to correctly reproduce switching and amplification functionalities is proposed. Last, the black-box electrical characterization of the device is outlined.
In conclusion, the main original contributions of this research work are: i) the theoretical study of a novel device – the NMT – which has led to synthetize a series of design requirements and control strategies; II) the conceptualization of a parametric resonant QSM, which – differently from the self-excited one – constitutes a new archetype of electron shuttle
Investigation on a nanomechanical transistor
No full textIn this paper, we propose the mathematical model of a novel device, the nanomechanical transistor, able to control a current through a small drive voltage. The novelty of the device relies in its mechanical working principle where nanopillars vibrate between electrodes under a self-excitation regime which provides a continuative electric charge transportation. The dynamics of the investigated system involves electromechanical phenomena with the addition of quantum effects due to the electron tunneling of charges from pillars to electrodes. The theory here presented is an attempt to build a general model for those multiphysics phenomena (electrical-mechanical with presence of quantum effects) frequently met in nanotechnology that do not fit yet into a systematic frame
Self-excitation of electro-mechanical resonators: nanomechanical transistor
No full textIn recent times MEMS and NEMS technologies open new perspectives in modelling mechanical phenomena. In particular, interaction between electrical and mechanical forces determines new scenarios in the field of self-excitation, chaotic dynamics and stability. This paper describes a physical and mathematical model of a novel conceived computer component: the nanomechanical transistor. It is able to work through a DC pilot voltage. Its mechanical working principle involves coupled nanopillars vibrating between electrodes, providing a mechanical shuttling mechanism for electric charge transport. These vibrations are controlled by elastic and electrostatic forces in a way intriguing dynamic regimes are detected. The theory here presented has a general character and is an attempt to build a model that keeps for those multiphysics phenomena (electro-mechanical with presence of quantum effects) so frequently met in nanotechnology and not yet fitted into a systematic frame
Vibration-based Nano-Mechanical Transistor: Theoretical Modelling and Numerical Simulations
No full textThe introduction of vibration-based Nano Electro-Mechanical Transistors (NEMT) opens a new horizon for mechanics in computer science. NEMT working principle is based on an electrical charge shuttle between two electrodes operated by a vibrating conductor body. The paper introduces a quasi-classical analytical model for such a device describing the quantum phenomena through a non-linear conductance and using a continuous variable for the charges. Through suitably introduced simplifications, the model is reduced to a set of two differential equations in terms of pillar position and charge. These equations represent the simplest model still preserving the basic phenomenology of the system. Numerical simulations show different possible motion regimes of the device
SEALAB: Aero-hydro mechanics of a three-wings jumping vehicle
No full textIn a recent project, named SEALAB, a novel marine vehicle has been developed. Its main characteristic is
the presence of special skid surfaces surfing over rough water. A suspension system controls the vertical
motion of the skid, softening the sequential impacts and vibrations induced by the water, similarly to a
wheeled vehicle in off-road trials. The hull-skid-suspension set is modeled by prototypical equations. The
system undergoes special regimes when the vessel speed at sea is varied. In particular, for some
combinations of the forward speed and sea-state, the skid still maintains the contact with the water. In
other navigation conditions the skid indeed jumps out the water with a complete different average
transmitted force and vibration characteristics of the hull. This paper presents a theory that outlines these
phenomena identifying conditions that lead to the jumping skid condition
Stability analysis of a three-wings high-speed craft
No full textA recent project for development of an innovative high-speed marine vehicle, SEALAB, poses a new problem in the dynamic stability of marine crafts. In fact, SEALAB is a three-wings concept ship that navigates at high speed in sea waves. The three-wings system consists of aero-hydro-foils and of a set of skids connected to a sophisticated suspension link. The ability of the vehicle to keep its stability and the desired trim at sea, depends on the lift and drag characteristics of the wings together with the link elastic and geometric properties. A mathematical model of the navigation mechanics at constant forward speed is developed enlightening its stability characteristics. This prototype model discloses interesting new phenomena in the field of aero-hydro-elasticity and it provides a useful guide for a safe concept design of the craft stability. The linearized model offers a closed form tool based on a Lyapunov analysis. However, the effectiveness of this approach is tested in the frame of a global nonlinear navigation simulator of the craft comparing the numerically observed instabilities with the ones predicted on the basis of the linearized model
SEALAB: Aero-hydro mechanics of an extreme-speed marine vehicle
No full textThe paper presents an overview on the SEALAB project, a technology platform to develop new concepts in design of high-speed marine vehicles. In particular in this paper the aerohydro-mechanics of the new vessel is discussed, with the aim of developing analytical and numerical models to describe its response and to optimize the navigation performances
Modelling and simulations of a nano-mechanical transistor
No full textThis paper describes a physical and mathematical model of a new device called nanomechanical transistor able to control a current through a small pilot voltage. The novelty of the device relies in its mechanical working principle where nanopillars vibrate between electrodes providing a mechanical shuttling mechanism for electric charge transportation. The dynamics of the investigated system involves electromechanical phenomena with the addition of quantum effects due to the charge tunnelling appearing in contactless charge transfer from pillars to electrodes. The theory here presented has a general character and is an attempt to build a general model for those multiphysics phenomena (electrical-mechanical with presence of quantum effects) frequently met in nanotechnology that do not yet fit into a systematic frame
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