INFERRING MECHANICAL RESONANCES IN MICRO - AND NANOCANTILEVERS USING THE HARMONIC DETECTION OF RESONANCE (HDR) METHOD TO DEVELOP A NOVEL SENSING PLATFORM

During the past two decades, advances in microelectromechanical systems (MEMS) have spurred efforts worldwide to develop sensing platforms based on smart microcantilevers. A microcantilever beam is one of the simplest MEMS structures which forms the basis for portable, fast and highly sensitive schemes that are capable of measuring small deflections in static or dynamic response due to changes in external parameters such as mass, pressure, charge, etc. In this dissertation, I mainly focus on MEMS sensors with transducers in the form of microcantilevers. Variations in the microcantilever\u27s response such as resonant frequency, amplitude, phase and quality factor when exposed to external stimuli are measured. Recently, we have developed a fully electrical sensing platform called the harmonic detection of resonance (HDR) method by which a silicon microcantilever (or a multiwalled carbon nanotube) can be electrically actuated and its resonance parameters electrically detected [4, 5] through capacitance changes. It is well known that a large interfering signal coming from the inherent parasitic capacitance in the circuit at the driving frequency , is present in the platforms which use the capacitive readout method. However, we found that by driving the cantilever at and detecting its response at higher harmonics of , the parasitic capacitance can be avoided, facilitating the measurement of dynamic capacitance with high sensitivity in micro and nano-cantilevers [1, 2]. A significant part of this dissertation is devoted to the study of the nonlinear dynamics of microcantilevers under varying gas environments and pressures using HDR [3]. I also discuss the characteristics of an electrostatically driven microcantilever which exhibits Duffing-like behavior using HDR. The first experimental demonstration of its potential use as a highly sensitive sensing platform is discussed. [4]. We also discuss the behavior of an unfunctionalized microcantilever sensor which can be used for active sensing of gaseous species under ambient conditions. Our sensing platform measures the changes in the mechanical response (in amplitude and/or phase) of the vibrating microcantilever in air at its resonant frequency when exposed to several vapors and gases [5]. Finally I present the preliminary results on sensing toxic gases using functionalized microcantilevers. In the final chapter, I present evidence for the fact that HDR method is scaleable and can be adapted for nanoscale cantilevers. In particular, I introduce the reader to bending modulus measurements of multiwalled carbon nanotubes performed in Prof. Rao\u27s group. One of the key factors in these measurements is an accurate knowledge of density of carbon nanotubes. I provide in-depth discussion of the gradient sedimentation technique which enables one to measure the density of both single- and multi-walled carbon nanotubes

COMPOSITES 4.0: ENABLING THE MODERNIZATION OF LEGACY MANUFACTURING ASSETS IN SOUTH CAROLINA

Composites 4.0 is the implementation of Industry 4.0 concepts to plastics and composites manufacturing with the goal to overcome the complexities associated with these materials. Due to very complex process-structure-property relationships associated with plastics and composites, a wide range of process parameters need to be tracked and monitored. Furthermore, these parameters are often affected by the tool and machinery, human intervention and variability and should thus, be monitored by integrating intelligence and connectivity in manufacturing systems. Retrofitting legacy manufacturing systems with modern sensing and control systems is emerging as one of the more cost-effective approaches as it circumvents the substantial investments needed to replace legacy equipment with modern systems to enhance productivity. The goal of the following study is to contribute to these retrofitting efforts by identifying the current state-of-the-art and implementation level of Composites 4.0 capabilities in the plastics and composites manufacturing industry. The study was conducted in two phases, first, a detailed review of the current state-of-the-art for Industry 4.0 in the manufacturing domain was conducted to understand the level of integration possible. It also helped gain insights into formulating the right questions for the composites manufacturing industry in South Carolina. Second, a survey of the plastics and composites manufacturing industries was performed based on these questions, which helps identify the needs of the industry and the gap in the implementation of Composites 4.0. The study focuses on the three leading composite manufacturing industries: injection molding, extrusion, and 3D printing of thermoset and thermoplastic materials. Through the survey, it was possible to identify focus areas and desired functionalities being targeted by the industries surveyed and concentrate research efforts to develop targeted solutions. After analyzing the survey responses, it was found that updating old protocols using manufacturer support and customized integration of cost-effective solutions like retrofit kits, edge gateways, and smart sensors were identified as best-suited solutions to modernize the equipment. Composites 4.0 is already being implemented for Preventive Maintenance (PM), Manufacturing Execution System (MES), and Enterprise Resource Planning (ERP) to some extent, and the focus is on process optimization and equipment downtime reduction. The inferences drawn from this study are being used to develop highly targeted, supplier-agnostic solutions to modernize legacy manufacturing assets

Effect of endometrial scratch injury on pregnancy rate after previously failed intrauterine insemination

Background: Endometrial receptivity plays an important role in implantation and successful pregnancy. In literature, various attempts have been made to improve endometrial receptivity. Endometrial scratch injury (ESI) is one such intervention widely offered to improve endometrial receptivity in women with a history of in-vitro-fertilization (IVF) failure. In our present study, this procedure of ESI was performed in cases with previously failed intrauterine insemination (IUI) and its effect on pregnancy rate was assessed. Methods: A prospective, randomised, controlled study was conducted at Fertility Clinic, Bhabha Atomic Research Centre Hospital, Mumbai. Total 200 women requiring IUI with previously failed one IUI were included in the study. They were randomly divided into 2 groups of 100 each. Both the groups underwent controlled ovarian stimulation with clomiphene citrate and gonadotropins followed by IUI. Study group underwent “endometrial scratching” in mid-proliferative phase of the same cycle preceding IUI. Control group underwent IUI alone. Pregnancy rates (clinical and ongoing) were compared in both the groups. Results: Endometrial scratching group had significantly higher (<0.0002) (8.4±2.3 mm versus 7.3±1.9 mm) endometrial thickness at the time of ovulation trigger. Clinical pregnancy rate was significantly higher (p<0.0001) (42% versus 16%) in endometrial scratching group with no significant difference in ectopic pregnancy, miscarriage and multiple pregnancy rates in both the groups. Conclusions: Due to its role in improving pregnancy rates in women with previously failed IUI,  clinicians should offer ESI in mid-proliferative phase of the same cycle preceding IUI, before offering advanced IVF treatment

Non-linear electrical actuation and detection

A method and system is disclosed to detect and analyze an electric signal based on movement between an element and a counter electrode influenced by a nonlinear electric field produced by an electrical signal impressed between the element and counter electrode. Through detection of changes in the distance between the element and the counter electrode characteristics of the element and/or the environment of the element may be ascertained. Changes in the distance between the element and the counter electrode may be monitored based on changes in the value of capacitance between the element and counter electrode. The disclosed devices and methods may be employed to detect, for instance, presence of chemical/biological species in a sample or measure physical parameters of a sample such as pressure/acceleration, density, viscosity, magnetic force, temperature, and/or extremely small masses

Process for preparing carbon nanostructures with tailored properties and products utilizing same

The present invention discloses a relatively simple CVD method for forming specifically tailored carbon-based nanostructures. In general, the method is a chemical vapor deposition method in which at least a portion of the precursor materials are provided as a liquid at atmospheric conditions. The precursor materials include at least one carbon source and at least one catalyst source. Optionally, the precursor materials can also include one or more dopant sources. The carbon source and the optional dopant source can be injected as liquids into the system, and the liquid catalyst source can be either injected into the system or located on a substrate in the reactor prior to the process. Very high yield of nanostructures exhibiting particular characteristics can be attained by the process. Control of electrical characteristics as well as structural characteristics of the products are possible via control of process parameters including the particular precursors used as well as the relative amounts of the precursors used

Determination of carbon nanotube density by gradient sedimentation

Density gradient centrifugation is a high-resolution technique for the separation and characterization of large molecules and stable complexes. We have analyzed various nanotube structures by preparative centrifugation in sodium metatungstate-water solutions. Bundled, isolated and acid-treated single-walled nanotubes (SWNTs) and multiwall nanotubes (MWNTs) formed sharp bands at well-defined densities. The structure of the material in each band was confirmed by transmission electron microscopy and Raman spectroscopy. Our data suggest respective densities of 1.87, 2.13, 1.74, and 2.1 g/cm(3) for bundled, isolated, and acid-treated SWNTs and MWNTs. These measured results compare well with their calculated densities

Synthesis and Raman Spectroscopy of Multiphasic Nanostructured Bi–Te Networks with Tailored Composition

Development of synthetic routes to control the morphology and composition of nanostructured thermoelectric materials and to leverage their unique performance enhancements presents challenges in the realization of practical thermoelectric systems. We report here the fabrication of intricate networks of nanostructured tellurium, bismuth telluride, and bismuth-rich compounds with diverse morphologies. The nanostructured networks synthesized via solution-phase techniques consist of nanocrystalline Bi₂Te₃ with a grain size of about 15–20 nm, 3–5 nm thick rolled-up nanosheets of Te forming tubular structures, nanotubes of Bi₂Te₃ about 300–400 nm in diameter, Te and Bi₄Te₃ nanowires ranging from 50 to 200 nm diameter, and microspheres of 3–7 μm diameter composed of self-assembled BiOCl nanorods. The formation and crystallinity of Bi-rich and Te-rich compounds were investigated using powder X-ray and electron back-scattered diffraction. We present the first detailed analysis of micro-Raman scattering of Bi_<i>x</i>Te_<i>y</i> nanostructures of above morphologies using six different laser wavelengths. The Bi_<i>x</i>Te_<i>y</i> nanostructures exhibit the most intense infrared (IR) active A_1u mode at 120 cm^–1 in the Raman spectra, which disperses with a change in the chemical composition and laser power. In addition, we observe new internal strain-induced peaks in the Raman spectra of Bi_<i>x</i>Te_<i>y</i> nanostructures. The rich morphologies and compositions present within the nanostructured Bi–Te compounds are expected to result in novel thermoelectric materials