Heat generated by electronic devices must be dissipated in order to ensure reliability and prevent device failure. In order to design devices properly, it is important to have precise knowledge of materials' thermal properties at the nano and micro scales. Here we present a series of experimental studies of heat transport for two different types of material: a two dimensional (2D) material such as MoS2 and micron scale particles. We used frequency domain thermoreflectance (FDTR) to conduct all thermal property measurements. This technique can measure thin film thermal properties as well as characterize the interface between two materials. Molybdenum disulfide (MoS2), a transition metal dichalcogenide, is a 2D material that has potential applications as a transistor in nanoelectronics due to its semiconductor properties. We studied cross plane thermal transport across exfoliated monolayer and few layer MoS2 deposited on two distinct substrates: SiO2 and Muscovite mica. The cross plane direction is critical in layer structure devices since the largest thermal resistances are found along this way. The results show enhanced thermal transport across monolayer MoS2 on both substrates indicating that monolayer MoS2 has superior thermal properties for its use in electronic devices. On the other hand, thermally conductive micro particles are used as fillers in composite materials in order to improve the thermal conductivity of the host or matrix material. They can be embedded in polymers for die attach applications as well as in metals to create more efficient heat sinks. We developed new FDTR based thermal models that apply to isolated particles as well as particles surrounded by another material. We tested the models with isolated diamond and silicon micron size particles and with diamond particles embedded in tin. We were able to obtain the thermal conductivity of individual particles, an effective particle volume and the thermal interface conductance between a particle and its surrounding matrix. This technique could have important applications in industry since it could be used to measure in situ the thermal interface conductance between particles and their matrix, often the highest thermal resistance in composite materials.

No description available.

In the aspect of electric-ship grounding, the time-domain behavior of the ship hull is needed. The grounding scheme impacts the nature of voltage transients during switching events and faults, identifiability and locatability of ground faults, fault current levels, and power quality. Due to the large size of ships compared with the wavelengths of the desired signals, time-domain measurement or simulation is a time-consuming process. Therefore, it is preferred that the behavior be studied in the frequency-domain. In the frequency-domain one can break down the whole ship hull into small blocks and find the frequency behavior of each block (scattering parameters) in a short time and then connect these blocks and find the whole ship hull scattering parameters. Then these scattering pa- rameters should be transferred to the time-domain. The problem with this process is that the measured frequency-domain data (or the simulated data) is band-limited so, while calculating time-domain solutions, due to missing DC and low frequency content the time-domain response encounters causality, passivity and time-delay problems. Despite availability of several software and simulation packets that convert frequency-domain information to time-domain, all are known to suffer from the above mentioned problems. This dissertation provides a solution for computing the Time-Domain Impulse-Response for a system by using its measured or simulated scattering parameters. In this regard, a novel wavelet computational approach is introduced.

Active noise control (ANC) is a real-time process in which a system measures an external, unwanted sound source and produces a canceling waveform. The cancellation is due to destructive interference by a perfect copy of the received signal phase-shifted by 180 degrees. Existing active noise control systems process the incoming and outgoing audio on a sample-by-sample basis, requiring a high-speed digital signal processor (DSP) and analog-to-digital converters (ADCs) with strict timing requirements on the order of tens of microseconds. These timing requirements determine the maximum sample rate and bit size as well as the maximum attenuation that the system can achieve. In traditional noise cancellation systems, the general assumption is that all unwanted sound is indeterminate. However, there are many instances in which an unwanted sound source is predictable, such as in the case of a song. This thesis presents a method for active acoustic cancellation of a known audio signal using the frequency characteristics of the known audio signal compared to that of a sampled, filtered excerpt of the same known audio signal. In this procedure, we must first correctly locate the sample index for which a measured audio excerpt begins via the cross-correlation function. Next, we obtain the frequency characteristics of both the known source (WAVE file of the song) and the measured unwanted audio by taking the Fast Fourier Transform (FFT) of each signal, and calculate the effective environmental transfer function (degradation function) by taking the ratio of the two complex frequency-domain results. Finally, we attempt to recreate the environmental audio from the known data and produce an inverted, synchronized, and amplitude-matched signal to cancel the audio via destructive interference. Throughout the process, we employ many signal conditioning methods such as FIR filtering, median filtering, windowing, and deconvolution. We illustrate this frequency-domain method in Native Instruments’ LabVIEW running on the Windows operating system, and discuss its reliability, areas for improvement, and potential future applications in mobile technologies. We show that under ideal conditions (unwanted sound is a known white noise source, and microphone, loudspeaker, and environmental filter frequency responses are all perfectly flat), we can achieve a theoretical maximum attenuation of approximately 300 dB. If we replace the white noise source with an actual song and the environmental filter with a low-order linear filter, then we can achieve maximum attenuation in the range of 50-70 dB. However, in a real-world environment, with additional noise and imperfect microphones, speakers, synchronization, and amplitude-matching, we can expect to see attenuation values in the range of 10-20 dB.

A procedure is presented for using a primary resonance excitation in experimentally identifying the nonlinear parameters of a model approximating the response of a cantilevered beam by a single mode. The model accounts for cubic inertia and stiffness nonlinearities and quadratic damping. The method of multiple scales is used to determine the frequency-response function for the system. Experimental frequency- and amplitude-sweep data are compared with the prediction of the frequency-response function in a least-squares curve-fitting algorithm. The algorithm is improved by making use of experimentally known information about the location of the bifurcation points. The method is validated by using the parameters extracted to predict the force-response curves at other nearby frequencies. We then compare this technique with two other techniques that have been presented in the literature. In addition to the amplitude- and frequency-sweep technique presented, we apply a second frequency-domain technique and a time-domain technique to the second mode of a cantilevered beam. We apply the restoring-force surface method assuming no a priori knowledge of the system and use the shape of the surface to guide us in assuming a form for the equation of motion. This equation is used in applying the frequency-domain techniques: a backbone curve-fitting technique based on the describing-function method and the amplitude- and frequency-sweep technique based on the method of multiple scales. We derive the equation of motion from a Lagrangian and discover that the form assumed based on the restoring-force surface is incorrect. All of the methods are reapplied with the new form for the equation of motion. Differences in the parameter estimates are discussed. We conclude by discussing the limitations encountered for each technique. These include the inability to separate the nonlinear curvature and inertia effects and problems in estimating the coefficients of small terms with the time-domain technique. / Master of Science

Vehicle Suspension is an important sub-system in an automobile as it is directly related to the subjective qualities of ride comfort that the passengers perceive. A vehicle suspension works by insulating the driver and the passengers from the irregularities of the road. Moreover, a suspension is required to ensure the tires properly contact the surface for adequate traction. This study aims to analyze whether a damper that is made out of two individual dampers joined together can be used to provide better ride comfort and better road handling with appropriate control strategies and if this damper can work more effectively than a single semi-active damper / Master of Science / A car's suspension is crucial for a smooth ride and passenger comfort, as it absorbs bumps and keeps your tires in contact with the road. This research looks at a new type of shock absorber made of two connected parts to see if it improves ride comfort and handling compared to the traditional single shock absorber. We'll explore how this new design, along with smart control methods, might make driver and passenger comfort better.

No description available.

No description available.

No description available.

No description available.