UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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Item Explorations of Carbon-Nanotube-Graphene-Oxide Inks: Printability, Radio-Frequency and Sensor Applications, and Reliability(2022) Zhao, Beihan; Das, Siddhartha SD; Dasgupta, Abhijit AD; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbon-Nanotube (CNT) is a novel functional material with outstanding electrical and mechanical properties, with excellent potential for various kinds of industrial applications. Additive manufacturing or 3D printing of CNT-based materials or inks has been studied extensively, and it is vital to have a thorough understanding of the fluid mechanics and colloidal science of CNT-based inks for ensuring optimum printability and the desired functionality of such CNT-based materials.In this dissertation, a custom-developed syringe-printable CNT-GO ink (GO: Graphene Oxide) is introduced and the fluid mechanics and colloidal science of this ink as well as the different devices (e.g., temperature sensor, humidity sensor, and RF antenna) fabricated with this ink are studied. The following topics are discussed in this dissertation: (1) the application and printability (in terms of the appropriate fluid mechanics and colloidal science) of CNT-based inks; (2) development of temperature sensors with CNT-GO inks; (3) development of humidity sensors with CNT-GO inks; (4) development of RF patch antenna with CNT-GO inks; and (5) evaporation-driven size-dependent nano-microparticulate three-dimensional deposits (CNTs serve as one type of nanoparticle examined in this part of the study). In Chapter 1 of this dissertation, a literature review is conducted on the application of CNT-based inks and the fluid mechanics and colloidal science issues dictating the printability and performance of such CNT-based inks. The problem statement and overall research plan are also introduced in this chapter. In Chapter 2, the development of our custom CNT-GO ink is introduced. Detailed material selection and the mechanism of shape-dependent arrest of coffee-stain effect, which ensured that the printable ink led to uniform deposition, are discussed in this chapter. Temperature sensor prototypes printed with the CNT-GO inks are also presented in Chapter 2. From Chapter 3 to Chapter 5, the performances of our CNT-GO based flexible temperature sensor, humidity sensor, and patch antenna prototypes are discussed. The ink printability on flexible thin PET films is studied, and a straightforward ‘peel-and-stick’ approach to use the CNT-trace (or patch)-bearing PET films on surfaces of widely varying wettabilities and curvatures as different prototypes is introduced. Excellent temperature and humidity sensitivity of our CNT-GO based sensors are presented in Chapter 3 and Chapter 4, and the potential of this CNT-GO material for fabrication of ultra-wideband (UWB) patch antennas is discussed in Chapter 5. Furthermore, the stability and reliability of these printed CNT-GO-based prototypes are also explored. In previous Chapters, the printed CNT-GO patterns were cured by evaporation-mediated deposition on flat substrates (i.e., 2D deposition spanning in x and y directions). This motivated the extension of the physics to the 3rd dimension and probing of particle deposition on a 3D substrate and particle deposition in all x, y, and z directions. Therefore, in Chapter 6, we perform an experiment to demonstrate this kind of possibility using three kinds of micro-nanoparticle-laden water-based droplets (i.e. coffee particles, silver nanoparticles, and CNTs). These droplets were first deposited at the bottom of an un-cured PDMS film; these droplets were lighter than the PDMS and hence, they rose to the top of the PDMS where they could have either attained a Neuman like state or simply remained as an undeformed spherical drop with the top of the drop breaching the air-liquid-PDMS interface. The calculations based on air-water, water-PDMS, and air-PDMS surface tension values confirmed that the Neuman like state was not possible, and the droplets were likely to retain their undeformed shapes as they breached the air-PDMS interface. The timescale differences between the fast PDMS curing and the slower droplet evaporation, led to the formation of spherical shape cavities inside the PDMS after completion of the curing, and allowed evaporation-driven deposition to occur in all x, y, and z directions inside the cavity, with the exact nature of the deposition being dictated by the sizes of the particles (as confirmed by the experiments conducted with coffee particles, silver nanoparticles, and CNTs). Finally, in Chapter 7, the major contributions of this dissertation and proposed future studies related to this dissertation work are listed.Item Electrical Properties of a Tube-in-a-Tube Semiconductor(2016) Ng, Allen Lee; Wang, YuHuang; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tube-in-a-tube (Tube^2) nanostructures were synthesized through the outer-wall selective covalent functionalization of double-walled carbon nanotubes (DWCNTs) at high functional densities. Upon functionalization, the properties of individual walls within the structure decouple resulting in an electrically insulating functional outer tube while the inner tube retains exceptional CNT properties. The exceptional electrical properties of Tube^2 semiconductor structures were demonstrated for applications that include molecular and biological sensors and patterning of CNTbased structures with electronic type specificity. Tube^2 thin film transistor (TFT) sensors exhibited simultaneous ultrahigh sensitivity and selectivity towards chemical and biological targets. Carboxylic acid terminated Tube^2 sensors displayed an NH3 sensitivity of 60 nM, which is comparable with small molecule aqueous solution detection using state-of-the-art TFT sensors while simultaneously attaining 6,000 times higher chemical selectivity towards a variety of amine containing analyte molecules over carboxylic acids. Similarly, 23-base ii oligonucleotide terminated Tube^2 sensors demonstrated concomitant sensitivity down to 5 nM towards their complementary sequence without amplification techniques and single mismatch selectivity without the use of a gate electrode. Unique sensor architectures can be designed with the requirement of a gate electrode, such as the creation of millimeter-scale point sensors. The optical features and unique structural features of Tube^2 thin films were also exploited to address the challenge of patterning CNT nanostructures with electronic type specificity. Patterned dot arrays and conductive pathways were created on an initially insulating Tube^2 thin film by tuning the resonance of the direct-writing laser with the electronic type of the inner tube (i.e., metallic or semiconducting). The successful patterning of Tube^2 thin films was unambiguously confirmed with in situ Raman spectral imaging and electrical characterization. Furthermore, a hybrid 2-D carbon nanostructure comprised of a functionalized graphene that covers a semiconducting (6,5) SWCNT network (fG/sSWCNT) was developed. The hybrid fG/sSWCNT nanostructure exhibits similar structural and electrical properties as a semiconducting Tube^2 thin film, but possesses a transconductance that is an order of magnitude larger than Tube^2 and ON/OFF ratios as high as 5400 without the useful of further processing steps such as electrical breakdown.Item ENERGY HARVESTING MICROGENERATORS FOR BODY SENSOR NETWORKS(2014) Dadfarnia, Mehdi; Baras, John S; Systems Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Body sensor networks have the potential to become an asset for personalizing healthcare delivery to patients in need. A key limitation for a successful implementation of body sensor networks comes from the lack of a continuous, reliable power source for the body-mounted sensors. The aim of this thesis is to model and optimize a micro-energy harvesting generator that prolongs the operational lifetime of body sensors and make them more appealing, especially for personalized healthcare purposes. It explores a model that is suitable for harvesting mechanical power generated from human body motions. Adaptive optimization algorithms are used to maximize the amount of power harvested from this model. Practicality considerations discuss the feasibility of optimization and overall effectiveness of implementing the energy harvester model with respect to body sensor power requirements and its operational lifetime.Item SENSING SMALL CHANGES IN A WAVE CHAOTIC SCATTERING SYSTEM AND ENHANCING WAVE FOCUSING USING TIME REVERSAL MIRRORS(2012) Taddese, Biniyam Tesfaye; Anlage, Steven M; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wave-based motion sensors, such as radar and sonar, are designed to detect objects within a direct line-of-sight of the sensor. As a result, surveillance of a cavity with multiple internal partitions generally demands use of a network of sensors. In the first part of the dissertation, we propose and test a new paradigm of sensing that can work in such cavities using a single sensor. The sensor utilizes the time reversal invariance and spatial reciprocity properties of the wave equation, and the ray chaotic nature of most real world cavities. Specifically, classical analogs of the quantum fidelity and the Loschmidt echo are developed. The sensor was used to detect perturbations to local boundary conditions of an acoustic cavity, and the medium of wave propagation. This result opens up various real world sensing applications in which a false negative cannot be tolerated. The sensor is also shown to quantitatively measure perturbations that change the volume of a wave chaotic cavity while leaving its shape intact. Volume changes that are as small as 54 parts in a million were measured using microwaves with 5cm wavelength inside a one cubic meter wave chaotic cavity. These results open up interesting applications such as monitoring the spatial uniformity of the temperature of a homogeneous cavity during heating up / cooling down procedures, etc. The second part of the dissertation is dedicated to improving the performance of time reversal (TR) mirrors, which suffer from dissipation. TR mirrors can, under ideal circumstances, precisely reconstruct a wave disturbance which happened at an earlier time, at any given later time. TR mirrors have found applications in imaging, communication, targeted energy focusing, sensing, etc. Two techniques are proposed and tested to overcome the effects of dissipation on TR mirrors. First, a tunable iterative technique is used to improve the temporal focusing of a TR mirror. Second, the technique of exponential amplification is proposed to overcome the effect of dissipation on TR mirrors. The applicability of these techniques is tested experimentally using an electromagnetic TR mirror, and numerically using a model of the star graph.Item A Hybrid Testing Platform for Realistic Characterization of Infrastructure Sensor Technology(2011) Mercado, Michael William; Zhang, Yunfeng; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In America's transportation infrastructure, maintaining safe and serviceable bridges is of paramount importance to America's transportation officials. In order to meet the increasing demands for information-based maintenance and repair of civil infrastructures such as highway bridges, an increasing number of structural health monitoring sensors and other non-destructive evaluation (NDE) devices have begun to be implemented on these structures. Before these health monitoring sensors can be implemented on a large scale, they must first be validated and characterized in a controlled environment. This thesis proposes and demonstrates the use of a hybrid testing platform to create a more realistic testbed to evaluate these structural health monitoring sensors for steel bridges. The details of this hybrid testing platform are discussed including the effects of ramp time, stress level, complexity of the virtual model, fatigue, and high temperature testing. The accuracy and practical implementation of this hybrid testing platform are also addressed.Item Implementation of Prognostics and Health Management for Electronic Systems(2007-06-06) Tuchband, Brian Adam; Pecht, Michael G; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An assessment has been undertaken to identify the state-of-practice for prognostics and health management of electronics. Based on a review of the prognostic approaches, case studies, publications, and the extent of intellectual property of numerous organizations, I identified the companies, universities, and government branches that are currently researching, developing, and/or implementing prognostics for their products and systems. Next, I developed a sensor selection process such that an optimal sensor system can be chosen prior to in-situ life cycle monitoring of electronic products and systems. I developed a questionnaire that can be used to understand the monitoring requirements of a particular PHM application, and identified criteria that one needs to consider in the sensor selection process in order to make the relevant tradeoffs. Finally, I provided guidelines on sensor selection to help a user validate their final selection. The process was demonstrated for two circuit card assemblies inside an avionics unit.