Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Meindl, James D.; Committee Member: Bakir, Muhannad S.; Committee Member: Davis, Jeffrey A.; Committee Member: Gaylord, Thomas K.; Committee Member: Kohl, Paul A.; Committee Member: Naeemi, Azad. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.S.)--University of Wisconsin--Madison, 1981. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 33-34).

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaf 41). Also available on the World Wide Web.

With the advance in nanotechnology, we are more interested in the "smaller worlds". One of the practical applications of this is to measure a very small displacement or the mass of a nano-mechanical object. To measure such properties, one needs a very sensitive detector. A quantum point contact (QPC) is one of the most sensitive detectors. In a QPC, electrons tunnel one by one through a tunnel junction (a "hole"). The tunnel junction in a QPC consists of a narrow constriction (nm-wide) between two conductors. To measure the properties of a nano-mechanical object (which acts as a harmonic oscillator), we couple it to a QPC. This coupling effects the electrons tunneling through the QPC junction. By measuring the transport properties of the tunneling electrons, we can infer the properties of the oscillator (i.e. the nano-mechanical object). However, this coupling introduces noise, which reduces the measurement precision. Thus, it is very important to understand this source of noise and to study how it effects the measurement process. We theoretically study the transport properties of electrons through a QPC junction, weakly coupled to a vibration mode of a nano-mechanical oscillator via both the position and the momentum of the oscillator. %We study both the position and momentum based coupling. The transport properties that we study consist of the average flow of current through the junction, given by the one-time correlation of the electron tunneling event, and the current noise given by the two-time correlation of the average current, i.e, the variance. The first comprehensive experimental study of the noise spectrum of a detector coupled to a QPC was performed by the group of Stettenheim et al. Their observed spectral features had two pronounced peaks which depict the noise produced due to the coupling of the QPC with the oscillator and in turn provide evidence of the induced feedback loop (back-action). Benatov and Blencowe theoretically studied these spectral features using the Born approximation and the Markovian approximation. In this case the Born approximation refers to second order perturbation of the interaction Hamiltonian. In this approximation, the electrons tunnel independently, i.e., one by one only, and co-tunneling is disregarded. The Markovian approximation does not take into account the past behavior of the system under time evolution. These two approximations also enable one to study the system analytically, and the noise is calculated using the MacDonald formula. Our main aim for this thesis is to find a suitable theoretical model that would replicate the experimental plots from the work of Stettenheim et al. Our work does not use the Markovian approximation. However, we do use the Born approximation. This is justified as long as the coupling between the oscillator and QPC is weak. We first obtain the non-Markovian unconditional master equation for the reduced density matrix of the system. Non-Markovian dynamics enables us to study, in principle, the full memory effects of the system. From the master equation, we then derive analytical results for the current and the current noise. Due to the non-Markovian nature of our system, the electron tunneling parameters are time-dependent. Therefore, we cannot study the system analytically. We thus numerically solve the current noise expression to obtain the noise spectrum. We then compare our noise spectrum with the experimental noise spectrum. We show that our spectral noise results agree better with the experimental evidence compared to the results obtained using the Markovian approximation. We thus conclude that one needs non-Markovian dynamics to understand the experimental noise spectrum of a QPC coupled to a nano-mechanical oscillator. / Physics

The objective of this research is to develop a bearing fault detection scheme for electric machines via stator current. A new method, called the stator current noise cancellation method, is proposed to separate bearing fault-related components in the stator current. This method is based on the concept of viewing all bearing-unrelated components as noise and defining the bearing detection problem as a low signal-to-noise ratio (SNR) problem. In this method, a noise cancellation algorithm based on Wiener filtering is employed to solve the problem. Furthermore, a statistical method is proposed to process the data of noise-cancelled stator current, which enables bearing conditions to be evaluated solely based on stator current measurements. A detailed theoretical analysis of the proposed methods is presented. Several online tests are also performed in this research to validate the proposed methods. It is shown in this work that a bearing fault can be detected by measuring the variation of the RMS of noise-cancelled stator current by using statistical methods such as the Statistical Process Control. In contrast to most existing current monitoring techniques, the detection methods proposed in this research are designed to detect generalized-roughness bearing faults. In addition, the information about machine parameters and bearing dimensions are not required in the implementation.

The objective of this dissertation is to derive a set of compact physical models addressing power integrity issues in high performance gigascale integration (GSI) systems and three-dimensional (3-D) systems. The aggressive scaling of CMOS integrated circuits makes the design of power distribution networks a serious challenge. This is because the supply current and clock frequency are increasing, which increases the power supply noise. The scaling of the supply voltage slowed down in recent years, but the logic on the integrated circuit (IC) still becomes more sensitive to any supply voltage change because of the decreasing clock cycle and therefore noise margin. Excessive power supply noise can lead to severe degradation of chip performance and even logic failure. Therefore, power supply noise modeling and power integrity validation are of great significance in GSI systems and 3-D systems. Compact physical models enable quick recognition of the power supply noise without doing dedicated simulations. In this dissertation, accurate and compact physical models for the power supply noise are derived for power hungry blocks, hot spots, 3-D chip stacks, and chip/package co-design. The impacts of noise on transmission line performance are also investigated using compact physical modeling schemes. The models can help designers gain sufficient physical insights into the complicated power delivery system and tradeoff various important chip and package design parameters during the early stages of design. The models are compared with commercial tools and display high accuracy.

La détection des déplacements nano-mécaniques par les techniques de transport électronique a atteint un haut niveau de sensibilité et de polyvalence. Afin de détecter l'amplitude d'oscillation d'un oscillateur nano-mécanique, une technique largement utilisée consiste à coupler ce mouvement de façon capacitive à un transistor à un seul électron ou, plus généralement, à un dispositif de transport, et à détecter la modulation haute fréquence du courant à travers le mélange non linéaire avec un signal électrique à une fréquence légèrement désaccordée. Cette méthode, connue sous le nom de technique de mélange des courants, est utilisée notamment pour la détection de nanotubes de carbone suspendus et s'est avérée particulièrement efficace, ce qui a permis d'obtenir des records de sensibilité dans la détection de masse et de force. Dans cette thèse nous étudions théoriquement les conditions qui limitent la sensibilité de cette méthode dans différents types de dispositifs de transport. La sensibilité est un compromis entre le bruit, le bruit de rétroaction et la fonction de réponse. Cette dernière est proportionnel au couplage électromécanique. Pour ces raisons dans la thèse, nous étudions la fonction de réponse, l'effet des fluctuations de courant et de déplacement (back-action) dans les dispositifs de détection suivants: (i) le transistor métallique à électron unique, (ii) le transistor à un seul niveau électronique et (iii) le point quantique cohérent. La sensibilité optimale est obtenue, comme d'habitude, lorsque la rétroaction du dispositif de détection est égale au bruit du signal intrinsèque, ce qui, dans notre cas, est le bruit en courant. Nous avons constaté que les valeurs optimales typiques du couplage sont obtenues dans la limite de couplage fort, où une forte renormalisation de la fréquence de résonance est observée et une bistabilité de l'oscillateur mécanique est présente [comme discuté dans G. Micchi, R. Avriller, F. Pistolesi, Phys. Rev. Lett. 115, 206802 (2015)]. Nous trouvons donc des limites supérieures à la sensibilité de la technique de détection de mélange des courants. Nous considérons également comment la technique du mélange des courants est modifiée dans la limite où le taux de transmission tunnel devient comparable à la fréquence de résonance de l'oscillateur mécanique / Detection of nanomechanical displacement by electronic transport techniques has reached a high level of sensitivity and versatility. In order to detect the amplitude of oscillation of a nanomechanical oscillator, a widely used technique consists of coupling this motion capacitively to a single-electron transistor or, more generally, to a transport device, and to detect the high-frequency modulation of the current through the nonlinear mixing with an electric signal at a slightly detuned frequency. This method, known as mixing-current technique, is employed in particular for the detection of suspended carbon nanotubes and has proven to be particularly successful leading to record sensitivities of mass and force detection. In this thesis we study theoretically the limiting conditions on the sensitivity of this method in different kind of transport devices. The sensitivity is a compromise between the noise, the back-action noise, and the response function. The latter is proportional to the electromechanical coupling. For these reasons in the thesis we study the response function, the effect of current and displacement (back-action) fluctuations for the following detection devices: (i) the metallic single electron transistor, (ii) the single-electronic level single electron transistor, and (iii) the coherent transport quantum dot. The optimal sensitivity is obtained, as usual, when the back-action of the detection device equals the intrinsic signal noise that, in our case, is the current noise. We found that the typical optimal values of the coupling are obtained in the strong coupling limit, where a strong renormalization of the resonating frequency is observed and a bistability of the mechanical oscillator is present [as discussed in G. Micchi, R. Avriller, F. Pistolesi, Phys. Rev. Lett. 115, 206802 (2015)]. We thus find upper bounds to the sensitivity of the mixing-current detection technique. We also consider how the mixing-current technique is modified in the limit where the tunneling rate becomes comparable to the resonating frequency of the mechanical oscillator.