MS, University of Cincinnati, 2024, Engineering and Applied Science: Biomedical Engineering

Burn injuries are devastating and leave patients without their first line of defense – the skin. Today's advanced therapeutics for major skin loss includes implementation of tissue engineered skin substitutes, but even these are lacking in a few areas including substrate mechanical strength, elasticity, durability, encouraging angiogenesis, and innervation. Here, we aim to address the lack of innervation and mechanical strength of tissue engineered skin substrates by utilizing piezoelectric polyvinylidene-trifluoroethylene (PVDF-TrFE) for its biocompatibility, mechanics, and mechano-electrical properties to promote Schwann cell elongation and sensory neuron extension. In this work, we characterized electrospun PVDF-TrFE scaffolds over a variety of electrospinning parameters, including 1, 2, and 3 h aligned and unaligned fibers, to determine ideal thickness, porosity, and tensile strength to mimic in vivo skin tissue. We then electrically activated PVDF-TrFE through mechanical deformation from low-intensity pulsed ultrasound waves as a non-invasive means to trigger the piezoelectric properties of the scaffold and deliver electric potential to cells. Using this therapeutic modality, neurite integration in these in vitro tissue-engineered skin substitutes was quantified including neurite alignment, elongation, and vertical perforation into PVDF-TrFE scaffolds. Results show that stimulation with LIPUS promoted cellular alignment on the aligned scaffolds. Further, LIPUS stimulation significantly increased Schwann cell elongation and sensory neuron extension separately and in coculture on aligned scaffolds but significantly decreased the elongation and extension on unaligned scaffolds. This was also seen in cell perforation depth analysis into scaffolds which indicated that LIPUS enhanced perforation of Schwann cells, sensory neurons, and cocultures on scaffolds. Taken together, this work demonstrates the immense potential for non-invasive electric stimulation of an in vi (open full item for complete abstract)

Committee: Greg Harris Ph.D. (Committee Chair); Stacey Schutte Ph.D. (Committee Member); Leyla Esfandiari Ph.D. (Committee Member) Subjects: Biomedical Engineering

Doctor of Philosophy, Case Western Reserve University, 2023, Macromolecular Science and Engineering

Polymer film capacitors are suitable for capacitive energy storage in the expanding market of electric vehicles and high-speed trains, as their advantages of high electric breakdown, long lifetime, and high ripple current tolerance. The state-of-the-art polymer capacitor material is biaxially oriented polypropylene (BOPP), due to its ultralow loss, long operating lifetime, and high breakdown strength. However, its temperature rating of ~85 °C limits its application in electric vehicles since the ambient temperature, where DC-link capacitors are installed, is around 140 °C. Multilayer technology has proved its potential to achieve high energy density, high breakdown strength, and high-temperature rating simultaneously. These multilayer films (MLFs) are composed of a high temperature/low loss polymer and a high dielectric constant polymer. Under extreme conditions (e.g., high electric fields and high temperatures), an important loss mechanism of AC electronic conduction occurs in MLF capacitors by homocharge injection at the metal electrode/polymer interfaces and subsequently charge recombination, leading to heat generation. In this dissertation, this mechanism was studied for high temperature polycarbonate (HTPC)/poly(vinylidene fluoride) (PVDF) MLFs with either HTPC (MLF@HTPC) or PVDF (MLF@PVDF) as the outer skin layers. Based on DC/AC breakdown strength, DC lifetime measurements, and electric displacement-electric field loop analysis on metal electrode/MLF/metal electrode capacitor devices, it is concluded that the charge injection can be largely minimized when aluminum is used as the metal electrode material and HTPC is used as skin layers. In addition, the Tg effect of three PC MLFs was also studied by dielectric breakdown, lifetime, and leakage current measurements. From the experimental results, we conclude that charge injection was largely reduced with HTPC MLFs, leading to significantly enhanced insulation properties with high breakdown strength and l (open full item for complete abstract)

Committee: Lei Zhu (Committee Chair); Geneviève Sauvé (Committee Member); Gary Wnek (Committee Member); Eric Baer (Committee Member) Subjects: Energy; Plastics

Master of Science, University of Toledo, 2022, Mechanical Engineering

In recent years, flexible and stretchable sensors have been a subject of intensive research to replace the traditional sensors made up of metal and semiconductors. This thesis has been conducted with the objective of exploring the possible applications of Graphene/PVDF nanocomposite in various kinds of flexible sensors as a potential sensing material. Initially, graphene/PVDF nanocomposite was synthesized by the solution-phase mixing method. A thin film of 20-22 μm was coated on a glass substrate to investigate the characteristics of the composite by using XRD and SEM techniques. This nanocomposite was best suited for piezoresistive-based sensors where the sensor senses the external stimuli and outputs the response in terms of change in electrical properties such as resistance, voltage, or current. The synthesized graphene/PVDF nanocomposite was coated on different kinds of substrates to make three different kinds of flexible sensors. They are airflow sensor, knittle pressure sensor, and accelerometer. The airflow sensor was designed and fabricated by applying a thin film of nanocomposite on the polyethylene (PE) substrate and placed inside a PVC pipe at an angle to the central axis of the pipe. The response of the sensor was tested by passing air at various speeds and recorded in terms of resistance change. The linearity and repeatability of the curves were observed. Temperature dependence on electrical conductivity was studied by heating and cooling the sample between room temperature and below the melting point of PVDF. Further, the sensing characteristics were simulated using COMSOL Multiphysics software, and the modeled data were compared with the experimental result. Another application of our in-house fabrication with the use of the nanocomposite is a knittle pressure sensor. The primary purpose of developing knittle pressure is to monitor health by either attaching to the skin or using it inside the health monitoring device. The use of fabric substrate a (open full item for complete abstract)

Committee: Ahalapitity Jayatissa (Advisor) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2022, Engineering and Applied Science: Electrical Engineering

Severe peripheral nerve injuries are currently limited in their available treatment approaches. Standard clinical therapies include the use of nerve grafts or nerve conduits to guide axons across the injury gap, however many of these approaches show variable outcomes in functional recovery, possibly due to a lack of cues directing the nerve regeneration. Polyvinylidene flouride triflouroethylene (PVDF-TrFE) is a piezoelectric polymer that generates electric charge in response to mechanical deformation, and can provide a suitable regenerative microenvironment by imparting electrical stimulation to direct peripheral nervous system cells and function. In this thesis, PVDF-TrFE nanofibrous scaffolds are fabricated through electrospinning and are extensively characterized for their material and electrical properties. Further, the PVDF-TrFE scaffolds are functionalized with decellularized extracellular matrix (dECM), presenting a promising outlook for a piezoelectric biomaterial for tissue engineering.

Committee: Leyla Esfandiari Ph.D. (Committee Member); Tao Li Ph.D. (Committee Member); Greg Harris Ph.D. (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2021, Mechanical Engineering

Flexible sensors can be seamlessly integrated into arbitrarily curved surfaces including artificial skins, automotive structures, and wind sensing systems. Polyvinylidene fluoride (PVDF) films are excellent candidates for development of flexible devices owing to their large mechanical compliance, piezoelectric, and dielectric properties. In spite of their favorable properties, their inability to measure static loads and their large voltage response to changes in temperature (pyroelectricity) have limited them to only measurement of dynamic events and energy harvesting applications. The broad objectives of this research are to provide PVDF sensor systems with the ability to measure static loads, develop understanding of piezoelectric behavior and pyroelectric responses, and devise strategies to compensate their pyroelectric responses under non-isothermal conditions. A concurrent investigation of design and manufacturing techniques to embed PVDF sensors into metal structures for non-destructive testing applications is also presented. In order to increase resolution in wind pressure sensing applications, a PVDF-based capacitive sensing technology is found to be superior to piezoelectric PVDF pressure sensors owing to its inherent ability to measure static events and its low sensitivity to temperature changes. The performance of the flexible capacitive sensor is evaluated by integrating it with an airfoil-shaped anemometer developed for measurement of wind speed and direction. Each objective is accompanied by analytical or finite element models to aid and supplement the characterization effort. Intellectual merit: A framework for near-static strain and pressure sensing methods under varying environmental conditions using flexible PVDF films is presented using compensated charge amplification and change in capacitance techniques, backed by analytical modeling tools and practical implementation. A novel rapid fabrication process of metal structures embedded with pie (open full item for complete abstract)

Committee: Marcelo Dapino (Advisor); Hanna Cho (Committee Member); Renee Zhao (Committee Member) Subjects: Mechanical Engineering

Master of Sciences, Case Western Reserve University, 2021, EMC - Mechanical Engineering

At high temperatures, polymer separators in conventional Li-ion Batteries are prone to melt, fail to separate the electrodes, and cause internal short circuits. A PVDF-based hybrid electrolyte with Li1.3Al0.3Ti1.7(PO4)3 (LATP) and Al2O3 filler, prepared with NMP/glycerol dual solvents by slurry coating is reported in this thesis. The effects of fillers and glycerol on the ionic conductivity of the hybrid electrolyte membrane are studied. It was found that the use of glycerol and Al2O3 nanoparticles can increase the hybrid electrolyte's ionic conductivity. The dual-solvent prepared sample with a specific composition of PVDF/LATP/Al2O3=3/6/1 shows the highest ionic conductivity of 1.39 mS/cm, which is 30% higher than the sample without Al2O3. The membrane also exhibits better thermal stability compared to a Celgard 2325 commercial polymer separator. Li//Li symmetrical cell assembled using the prepared membrane shows excellent stability. In NMC half-cell cycling tests, capacity retention of 92.8% and 92.1 % are achieved on 50 cycles at 0.5 C and 1 C, respectively.

Committee: Chris Yuan (Advisor); Bo Li (Committee Member); Burcu Gurkan (Committee Member) Subjects: Engineering

Master of Science, University of Toledo, 2020, Mechanical Engineering

Thin-film pressure sensors have received widespread attention in recent times due to its ease of manufacture, characterization, and fatigue strength. Commercial fabrication of these sensors is inexpensive and compatible with the current manufacturing technologies. It has been found that the sensitivity of the flexible pressure sensor depends on the sensing pressure, the microstructural dispersion of nanoparticles, and the compatibility of the binder and the nanoparticles. The binder/particle dispersion should be such that it facilitates the formation of a greater number of conduction paths with a slight change in sensing pressure. The objective of this thesis includes the fabrication and characterization of a thin-film pressure sensor using different novel materials. The first material to be investigated was ZnO. ZnO thin-film materials that have received a great deal of attention due to its unique properties of being a semiconductor with wide bandgap and piezoelectric effect. The sensor characteristic of ZnO was compared with barium-titanate (BaTiO3) Gallium arsenic (GaAs) and Polyvinylidene fluoride (PVDF). The second material to be investigated was aluminum-doped zinc oxide (AZO). AZO has attracted a great deal of attention in many applications because of its nontoxicity, abundancy, and lower cost than other materials such as indium tin oxide (ITO). The AZO films were deposited on polyethylene (PE) substrates by a radiofrequency (rf) magnetron sputtering method. The piezoresistive sensor was tested for different pressures in vacuum and gage pressure conditions. The response characteristics indicated that resistance increased with the bending of the AZO layer in both compressive and tensile operation modes. The sensor characteristics exhibited that the AZO piezoresistive sensor can be used to measure ambient pressure quantitatively. This investigation indicated that AZO can be used as an alternative material for the fabrication of pressure sensors. Lastly (open full item for complete abstract)

Committee: Ahalapitiya Jayatissa (Committee Chair); Anju Gupta (Committee Member); Adam Schroeder (Committee Member); Raghav Khanna (Committee Member) Subjects: Engineering; Mechanical Engineering

Master of Science, Miami University, 2020, Mechanical and Manufacturing Engineering

Polyvinylidene fluoride (PVDF), a thermoplastic polymer, has been attracting a lot of attention since it was shown to have piezoelectric potential. Processes such as drawing and solvent casting usually result in thin films, limiting the application of PVDF based piezoelectric materials to lithography or electronic subsystems. On the other hand, 3D printing processes have pushed the limits of traditional manufacturing processes, creating unique shapes that otherwise would not be feasible. In this study, a single screw extruder is used to compound PVDF–ZnO and PVDF-TiO2 polymer composites into 3D printer filaments. The mechanical and materials properties of these two polymer nanocomposites were characterized as a function of nanofiller fraction. Properties such as thermal stability and transitions, dynamic and static mechanical analysis, and the crystalline behavior and phases of PVDF-ZnO composites have been analyzed on the extruded filament and, 3D printed test specimens. Furthermore, an attempt was made to detect piezoelectricity in the 3D printed specimens. TGA proved the suitability of ZnO over TiO2 as a nanofiller. DSC results gave promising indications about the formation of the electroactive β-phase in the composite filament. Furthermore, FT-IR confirmed the transformation into β--phase as s α−β ratio was decreasing. Rheometry results indicated that the composites were suitable for melt extrusion. DMA experiment showed the stiffening effect of the ZnO nanofillers over a large temperature range. Tensile and Flexural tests further confirmed the stiffening effect as seen in the increasing trend of tensile and flexural modulus, especially for the HCR specimen. Tensile strengths remained fairly constant. These results show that the PVDF-ZnO composites are a viable option for 3D printing because of the transformation from α to β phase, the stiffening effect of ZnO nanofillers and their suitability for melt extrusion.

Committee: Giancarlo Corti (Advisor); Fazeel Khan (Committee Member); Kumar Singh (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2018, Mechanical Engineering

The wetting of the electrodes due to liquid electrolyte used in Li-ion batteries can significantly impact the mechanochemical properties of polymer binders. To observe and characterize this, we employed in-situ atomic force microscopy (AFM) based force spectroscopy. Two different polymer binders for Si anodes, sodium (Na) alginate and polyvinylidene fluoride (PVdF), are immersed in a solution of di-methyl carbonate (DMC) and analyzed using a micro-cantilever with a Si tip, to mimic the actual Si – binder interface in Si anodes. Na-alginate is found to have orders of magnitude higher adhesive forces than PVdF after immersion in liquid electrolyte, which can be attributed to a functional carboxyl group in Na-alginate, possibly leading to a formation of hydrogen bonds and/or ion-dipole interaction with Si. In comparison PVdF demonstrates considerably weaker adhesive forces owing to Van der Waals' interaction. It is also found that Na-alginate retains its mechanical strength better than PVdF in liquid electrolyte, by retaining more than 90% of its Youngs modulus, while the Young's modulus of PVdF decreases to lower than 80% after immersion in electrolyte for 4 hours. Our nano-scale AFM analysis data agrees well with literature that are mostly based on macro-scale characterization. Furthermore, this study demonstrates the benefits of using force spectroscopy, AM-FM, and in-situ AFM techniques to characterize the evolution of interfaces between electrode components at a nano-scale under battery operating conditions.

Committee: Hanna Cho (Advisor); Jung-Hyun Kim (Advisor) Subjects: Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2016, Chemistry

Polycarbonate (PC)/poly(vinylidene fluoride) (PVDF) multilayer films (MLFs) with normal PC and high temperature PC (HTPC) were studied with broadband dielectric spectroscopy (BDS), electric displacement-electric field (D-E) loop, leakage current, and breakdown measurements to determine their high temperature performance and loss mechanism. The MLF containing HTPC performed better, which is attributed to its higher glass transition temperature (Tg), better maintaining interfacial polarization and providing a “blocking electrode” preventing charge carrier injection from PVDF into PC. Twelve (12) new polyimides (PIs) with nitrile (CN) groups attached to the polymer main chains were studied with BDS and D-E loop measurements. A ratio of experimental and theoretical dipolar polarization was calculated to estimate how easily the CN dipoles could rotate in response to the external electric field. Experimental results show that adding polar groups to PIs increased the permittivity but dielectric loss increased too because the dipoles in the rigid PI structures were difficult to rotate. An online mass spectrometry probe was developed for the detection of volatile reaction products and intermediates of electrochemical reactions in an aqueous solution. A wall-jet configuration was used to produce a laminar flow of electrolyte on the surface of a solid Au electrode in the center of the probe. The mass spectrometric ion current correlated well with the hydrazine oxidation current.

Committee: Lei Zhu (Advisor); Clemens Burda (Committee Chair); Anna Samia (Committee Member); Geneviève Sauvé (Committee Member); Donald Schuele (Committee Member) Subjects: Aerospace Materials; Automotive Materials; Chemistry; Energy; Polymers

Master of Science in Engineering (MSEgr), Wright State University, 2013, Electrical Engineering

Hearing loss is a prevalent issue, affecting all ages in innumerable occupations. Cochlear implants are one solution to sensorineural hearing complications; and though they are commonly used, the electronic devices have limitations in power consumption and external equipment. Piezoelectric films emulate the relationship between the basilar membrane and inner hair cell structures of the human cochlear epithelium, inducing a potential difference in response to sound pressure. Through proper MEMS fabrication and material selection, an artificial cochlear can be developed utilizing piezoelectrics, which is self-sustainable and functions naturally with the mechanisms of the human ear. This research investigates the feasibility of piezoelectric films in achieving adequate voltage output and frequency selectivity to replace the human cochlea. Piezoelectric samples were manufactured for different resonant frequencies and subjected to air vibrations, after which the resulting voltage was recorded. Through both simulated and experimental data, the necessary 5-10mV to stimulate nerve bundles connected to the hearing centers of the brain was realized. The response spanned the human speech register of 500 to 8000 Hz.

Committee: Yan Zhuang Ph.D. (Advisor); Robert Goldenberg M.D. (Committee Member); Reiter Chad Ph.D. (Committee Member) Subjects: Biomedical Engineering; Electrical Engineering; Materials Science

MS, University of Cincinnati, 2006, Engineering : Materials Science

This thesis describes the efforts undertaken in the development of a highly sensitive piezoelectric device to eventually be used as a stand-alone cochlear implant. Through previous studies the most important device requirements were found to be highly sensitive with small dimensions, large voltage response in the audible frequency range (~20 Hz – 20,000 Hz), highly impedance matched with water, and be biocompatible. Previous studies by Mukherjee, Dwividi, Mitra, and Kant, respectively, have found the ‘toothbrush' design to be a highly effective candidate to meet the above requirements with the exception of size limitations. Thus a ‘ribbon' style device was devised and tested to give a more readily implantable device. Testing of the ribbon style prototypes showed very good correlation to the previous toothbrush tests. Maximum responses given by a single element ribbon device was in the order of 3.5V to 5V. Double element ribbon devices showed much large coupling of individual voltages (~50% increase in toothbrush designs and ~65% to 95% increase in ribbon designs). In addition to the large voltage responses to semi-quantitative testing, the ribbon devices have shown response to frequency in the audible range. Thus, the ribbon devices has shown to be as effective (and in the cases of multi-array systems more effective) as the toothbrush designs in achieving large voltage responses while dramatically reducing the size of the overall device to a point where implantation can be realized in upcoming studies.

Committee: Dr. Rodney Roseman (Advisor) Subjects: Engineering, Materials Science

MS, University of Cincinnati, 2003, Engineering : Materials Science

This research thesis describes the efforts undertaken towards the development of a successful polymer electrode based piezoelectric cochlear implant hearing aid device. A thorough review of the cochlear environment and processes resulted in the identification of the requirements of such a device, most critical of which are high sensitivity, small dimensions and flexibility, impedance matching and biocompatibility. Based on these requirements and initial experiments, proper electrode material was identified. Two biomimetic device designs, based on the cochlear basilar membrane (ribbon device) and the cochlear stereocilia (toothbrush device) have been taken into consideration. These devices are based on flexible polymer piezoelectric films, used in the bending/flexure mode of deformation. The material chosen was PVDF, as it is the most sensitive piezoelectric polymer and high quality commercial films are readily available. Polypyrrole was identified as the most appropriate electrode material in working towards developing an all-polymer system. The suitability of Polypyrrole (PPY) material for this application was investigated. It was shown that PPY has similar I-V characteristics as those of the Ni-Cu electrodes. For the cochlear implant application, the devices with PPY electrodes showed much higher voltage responses than those from metal electroded devices. Polypyrrole electrode films, developed, were characterized for adhesion, morphology and structure. Effect of substrate surface pretreatment, heat treatment on the performance of these electrodes was studied. To measure the piezoelectric sensitivity of these devices to acoustic waves, both in-air and underwater measurements were carried out. Devices measured display very high sensitivity in air (several volts for conversational sounds at close range). Dependence of in-air sensitivity on device dimensions and dielectric coating was investigated and seen that substantial amplification can be obtained by increasing t (open full item for complete abstract)

Committee: Dr. Rodney Roseman (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2012, Mechanical Engineering

Smart materials have significantly varied properties and their various types are used broadly in many different engineering applications. In order to grow the field and promote its long term viability, it is important to develop tools which enable researchers and practitioners to determine the best smart material for the application. Computerized material selection databases and systems have been recently developed by design and materials engineers to help users select the best materials for an application. However, documentation of smart materials is limited, especially for those aimed at the use of these materials in devices and applications. In this dissertation, system-level simulation models and collected material data are compiled in a GUI-based computer software called Polymers and Smart Materials Software (PSMS). This material selection tool encompasses material properties and material-level models as well as systems level smart material applications for a wide range of smart materials. This type of compiled data can expedite the material selection process when designing smart material based systems by allowing one to choose the most effective material for the application. The PSMS tool consists of the following three major sections: 1) Polymers (Polymer types and properties, Polymeric behaviors including dielectric and liquid crystal elastomers); 2) Smart Materials (Piezoelectric Ceramics/Polymers, Shape Memory Alloys/Polymers, Thermoelectrics, Electrorheological and Magnetorheological Fluids); 3) More information (External databases, Cost information, etc.). The software tool offers a wide variety of design and selection features. Material property and performance charts are provided to compare material properties and to choose the best material for optimal performance. The tool is also flexible in that it enables users to categorize material properties and create their own databases. In areas where existing models were inadequate for systems level integra (open full item for complete abstract)

Committee: Gregory Washington (Advisor); Marcelo Dapino (Advisor); Carlos Castro (Committee Member); Mark Walter (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2012, Biomedical Engineering

Researchers are predicting cancer will be the number one cause of deaths in the United States by 2030. Therefore, better methods of detecting and diagnosing cancer cells are required. Further research has shown that cancer cells act very differently than normal cells, and that these characteristics can be used to detect and diagnose certain cancers. One such characteristic is the force exerted by cells undergoing tumorigenesis. Polyvinylidene Fluoride (PVDF) has been of particular interest in recent years in bioMEMS devices because of its biocompatibility and piezoelectric properties. A device that takes advantage of PVDFs properties could measure these forces. Cellular force sensing can open new frontiers for diagnoses of diseases, better understanding of cellular mechanics, and a faster and less expensive than alternative methods of cellular force sensing. This thesis presents the development of a sensor based on a microstructured piezoelectric thin film on a CCD to measure these cell forces. First, a model was designed to show the feasibility of such a device. The model provided a theoretical range of forces that can be expected from the device. The model showed that each pillar would be capable of measuring forces from about 26fN/s to 100pN/s, which correlated with the forces measure by other cellular force sensors. Finally, a prototype device was created as a proof of concept. This device reacted to force stimuli and gave results that were expected.

Committee: Derek Hansford PhD (Advisor); Yi Zhao PhD (Committee Member) Subjects: Biomedical Engineering

Doctor of Philosophy, The Ohio State University, 2010, Mechanical Engineering

Piezoelectric materials have the ability to transfer energy between the electric and mechanical domains. Polyvinylidene fluoride (PVDF) exhibits higher piezoelectricity than other polymer materials such as nylon and polyvinyl chloride. PVDF is a superior material for sensors because its stress constant, the ability to convert stress into electrical energy, is more than 20 times higher than that of lead zirconate titanate. Nonetheless, there is significant interest in improving the effective stress constant of PVDF devices beyond the intrinsic sensitivity of the material. Significant research has focused on improvements in material properties, such as increasing β phase ratio or artificially introducing defects, and processing, such as optimizing stretch ratio and poling temperature or applying a high electric field. This research is focused on improving the stress constant, or sensor sensitivity, by means of design. The acoustic sensor presented in this dissertation exploits the key advantages of PVDF as a sensor material by means of two key design elements aimed at increasing the charge and decreasing the effective device capacitance. The first design element is a stress amplification mechanism through the area ratio between the overall surface exposed to acoustic waves and the area of an array of PVDF micro-pillars. Because PVDF responds to stress, this mechanism increases the amount of charge for a given pressure level. The second design element is top and bottom electrodes selectively patterned to form an overlapping active area determined by the micro-pillars. Excluding the capacitance of the other inactive area, the design with patterned electrodes reduces the capacitance of the sensor and hence increases the voltage generated by the sensor. The small size, high stiffness, and reduced mass of MEMS sensors are of great interest because such devices can significantly improve both the temporal and spatial measurement bandwidth. The sensor realization requires mic (open full item for complete abstract)

Committee: Marcelo Dapino (Advisor); Derek Hansford (Committee Member); Ahmet Selamet (Committee Member); Gregory Washington (Committee Member) Subjects: Acoustics; Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2008, Mechanical Engineering

Active structures flexible enough to be molded in desired shapes and coupled with the ability to be controlled have been pursued for many high precision applications. Membrane-thin but extremely large (>10 m) optical mirrors and reflectors for combined RF-Optical applications are one of the important high precision applications where shape and vibration control of a structure is highly desirable. In this application the precision demands of the optical surface mitigate the combined benefit of the large aperture.Polyvinylidene Fluoride or PVDF is a semi-crystalline piezoelectric polymer with strong orthotropic in-plane properties. This material is suitable for making large reflectors due to its availability in thin sheets and almost linear and nonhysteretic behavior at low to moderate operating voltages. Its low cost and ease of manufacture also make it suitable for shape and vibration control of large reflecting structures. This research focuses on a three-layer laminated actuator with two layers of PVDF film bonded with a layer of epoxy. The electrodes are applied externally on the top PVDF film in a given pattern such that the applied electric field will yield the desired shape of the laminate. The bottom layer of the bimorph is the reflecting surface and acts as the ground. The actuator itself acts as the RF and optical surface and therefore requires no secondary surface. Research has been performed by Sumali et. al. and Massad et. al. for quasi-static deflection of a PVDF bimorph with both simply supported and corner supported boundary conditions under an applied electric field. This methodology produced excellent results under ideal conditions with no disturbances. Due to lack of any kind of feedback, the methodology was an open loop technique lacking the ability to acclimatize under inclement real world conditions. This research takes a step further and removes this demerit by dynamic modeling of a three layer PVDF laminated plate with simply supported bounda (open full item for complete abstract)

Committee: Gregory Washington PhD (Advisor); Vadim Utkin PhD (Committee Member); Daniel Mendelsohn PhD (Committee Member); Rajendra Singh PhD (Committee Member) Subjects: Engineering; Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2012, Chemical Engineering

There is a need in electronic systems and pulsed power applications for capacitors with high energy density. Current state-of-the-art polymeric capacitors (BOPP, PET) only have a maximum energy density of 5-6 J/cc. From a material standpoint, the energy density improves with increasing dielectric constant and/or breakdown strength, and the loss is diminished by reducing dissipation factor and high field polarization hysteresis. Our approach to improve polymer film capacitors is to combine, through microlayer coextrusion, two polymers with complimentary properties: one with a high dielectric constant (polyvinylidene fluoride type polymers - PVDF) and one with a high breakdown strength (polycarbonate). Multilayered films with many alternating layers of polymers exhibited improved breakdown characteristics due to the development of a “treeing” type failure mechanism. In addition, a reduction of polarization hysteresis was observed due to layer confinement effects on charge migration in the PVDF based layers. This charge migration, either from surfactant or catalyst residue, was studied in detail using broadband dielectric spectroscopy, which revealed an ion concentration and diffusion coefficient of 2E21 ions/m3 and 2E-13 m2/s, respectively, for films with layer thicknesses of 430 to 50 nm. Using the understanding gained from these systems, films with energy densities as high as 16 J/cc while maintaining a dissipation factor of 0.009 and low hysteresis were obtained. Selection and optimization of future layered structures can be carried out to obtain even higher energy densities and lower dielectric losses. In particular, the morphological structure within the semi-crystalline polymeric layers may be used to further enhance the dielectric properties. Microlayering in combination with heat treatment were used to control the morphology of several layered systems (i.e. PC/PVDF, PSF/PVDF, and PC/P[VDF-TFE]). A range of crystal orientations were produced that included isotr (open full item for complete abstract)

Committee: Eric Baer (Committee Chair); Heidi Martin (Committee Member); Gary Wnek (Committee Member); Lei Zhu (Committee Member); Daniel Lacks (Committee Member); Donald Schuele (Committee Member) Subjects: Energy; Morphology; Polymers

Doctor of Philosophy, Case Western Reserve University, 2012, Chemical Engineering

There is a need in electronic systems and pulsed power applications for capacitors with high energy density. Current state-of-the-art polymeric capacitors (BOPP, PET) only have a maximum energy density of 5-6 J/cc. From a material standpoint, the energy density improves with increasing dielectric constant and/or breakdown strength, and the loss is diminished by reducing dissipation factor and high field polarization hysteresis. Our approach to improve polymer film capacitors is to combine, through microlayer coextrusion, two polymers with complimentary properties: one with a high dielectric constant (polyvinylidene fluoride type polymers - PVDF) and one with a high breakdown strength (polycarbonate). Multilayered films with many alternating layers of polymers exhibited improved breakdown characteristics due to the development of a “treeing” type failure mechanism. In addition, a reduction of polarization hysteresis was observed due to layer confinement effects on charge migration in the PVDF based layers. This charge migration, either from surfactant or catalyst residue, was studied in detail using broadband dielectric spectroscopy, which revealed an ion concentration and diffusion coefficient of 2E21 ions/m3 and 2E-13 m2/s, respectively, for films with layer thicknesses of 430 to 50 nm. Using the understanding gained from these systems, films with energy densities as high as 16 J/cc while maintaining a tan delta of 0.009 and low hysteresis were obtained. Selection and optimization of future layered structures can be carried out to obtain even higher energy densities and lower dielectric losses. In particular, the morphological structure within the semi-crystalline polymeric layers may be used to further enhance the dielectric properties. Microlayering in combination with heat treatment were used to control the morphology of several layered systems (i.e. PC/PVDF, PSF/PVDF, and PC/P[VDF-TFE]). A range of crystal orientations were produced that included isotropic, on (open full item for complete abstract)

Committee: Eric Baer (Committee Chair); Lei Zhu (Committee Member); Donald Schuele (Committee Member); Gary Wnek (Committee Member); Daniel Lacks (Committee Member); Heidi Martin (Committee Member) Subjects: Electrical Engineering; Energy

Master of Science, The Ohio State University, 2013, Mechanical Engineering

Polyvinylidene Fluoride (PVDF), a piezoelectric polymer, is an excellent stress sensor. The objective of this research is to investigate the application of the PVDF sensors for detection of in-plane stress waves in 31 and 32 modes. This was achieved by focusing on aspects of PVDF sensing related to determination of impact force, detection of stress wave propagation, and the stress averaging effect of PVDF sensors. An experimental method was developed for calculating a proportionality constant between a PVDF sensor's voltage and the impact force, on a solid bar and a hollow beam. This was used to demonstrate that impact force on a structure can be determined using PVDF sensors. Finite element models were also created using the software LS-DYNA to simulate the impact tests. The speed of sound for longitudinal wave propagation in a slender rod was determined experimentally, using two PVDF sensors. The results demonstrate that PVDF sensors can detect high speed stress wave propagation in a structure. Finally, the stress averaging effect of the PVDF sensor was analyzed to investigate its influence on the generated voltage during stress wave detection. Equations modeling the stress averaging effect were derived for periodic applied stress waves and impact-induced stress waves. Numerical simulations were conducted to study the influence of sensor length, applied wave frequency, and structure's material on the stress averaged PVDF response.

Committee: Marcelo Dapino PhD (Advisor); Daniel Mendelsohn PhD (Committee Member) Subjects: Mechanical Engineering