Control Strategies for Piezoelectrically Actuated Fast Mechanical Disconnect Switches for Hybrid Circuit Breakers

Piezoelectrically-actuated fast mechanical switches provide a low-loss conduction path in hybrid circuit breakers for medium-voltage, direct-current system protection. With the desired actuation performance being pushed towards the driving limit of the piezoelectric actuator, excessive vibration starts to dominate the underdamped travel curves of contact movements, which will lead to insulation failures and delayed operations in the fast mechanical switch. To improve underdamped responses into critically damped actuations, several switching motion control strategies have been proposed with active damping filters such as notch, lead and lag compensators in the closed-loop system. The switching motion controllers are built upon a vibrational dynamics model of a prestressed piezoelectric stack actuator with experimentally identified parameters. The controller tuning principles are derived to achieve optimized step responses with a minimized rising time down to 250 μs, a reduced undershoot around 10%, and a closed-loop control bandwidth up to 1760 Hz. The closed-loop simulation is performed to verify the performance of proposed switching motion controllers on both low-frequency external disturbance elimination and high-frequency internal vibration attenuation. According to the hardware implementation tests, the proposed control strategies have optimized the switching motions of a heavily loaded piezoelectric actuator with a 60% reduction in undershoot and a 45% reduction in settling time. At the same time, the sub-millisecond switching time has been preserved in the actively damped travel curves of this piezoelectric actuator. With optimized switching operations of the piezoelectric actuator, the overall fast mechanical switch can better serve the advanced hybrid circuit breakers to achieve reduced fault current and fault clearance time during circuit interruptions. Consequently, the overall medium-voltage direct-current systems can get better protected by the piezoelectrically-actuated fast mechanical switch.Ph.D

Nanocarbon/elastomer composites : characterization and applications in photo-mechanical actuation.

Materials that change shape or dimensions in response to external stimuli are widely used in actuation devices. While plenty of systems respond to heat, light, electricity, and magnetism, there is an emerging class of light-driven actuators based on carbon nanostructure/elastomer composites. The addition of nanomaterials to elastomeric polymers results not only in significant material property improvements such as mechanical strength, but also assists in creating entirely new composite functionalities as with photo-mechanical actuation. Efficient photon absorption by nanocarbons and subsequent energy transduction to the polymeric chains can be used to controllably produce significant amounts of pre-strain dependent motion. Photo-mechanical actuation offers a variety of advantages over traditional devices, including wireless actuation, electro-mechanical decoupling (and therefore low noise), electrical circuit elimination at point of use, massive parallel actuation of device arrays from single light source, and complementary metal–oxide–semiconductor / micro-electro-mechanical (CMOS/MEMS) compatible processing. Applications of photo-responsive materials encompass robotics, plastic motors, photonic switches, micro-grippers, and adaptive micro-mirrors. The magnitude and direction of photo-mechanical actuation responses generated in carbon nanostructure/elastomer composites depend on applied pre-strains. At low levels of pre-strains (3–9%), actuators show reversible photo-induced expansion while at high levels (15–40%), actuators exhibit reversible contraction. Large, light-induced reversible and elastic responses of graphene nanoplatelet (GNP) polymer composites were demonstrated for the first time, with an extraordinary optical-to-mechanical energy conversion factor (?M) of 7–9 MPa/W. Following this demonstration, similar elastomeric composite were fabricated with a variety of carbon nanostructures. Investigation into photo-actuation properties of these composites revealed both layer-dependent, as well as dimensionally-dependent responses. For a given carbon concentration, both steady-state photo-mechanical stress response and energy conversion efficiency were found to be directly related to dimensional state of carbon nanostructure additive, with one-dimensional (1D) carbon nanotubes demonstrating the highest responses (~60 kPa stress and ~5 × 10-3% efficiency at just 1 wt% loading) and three-dimensional (3D) highly ordered pyrolytic graphite demonstrating the lowest responses. Furthermore, development of an advanced dispersion technique (evaporative mixing) resulted in the ability to fabricate conductive composites. Actuation and relaxation kinetics responses were investigated and found to be related not to dimensionality, but rather the percolation threshold of carbon nanostructure additive in the polymer. Establishing a connective network of carbon nanostructure additive allowed for energy transduction responsible for photo-mechanical effect to activate carbon beyond the infrared (IR) illumination point, resulting in enhanced actuation. Additionally, in the conductive samples photoconductivity as a function of applied pre-strain was also measured. Photo-conductive response was found to be inversely proportional to applied pre-strain, demonstrating mechanical coupling. Following investigation into photo-mechanical actuation responses between the various carbon forms, use of these composite actuators to achieve both macroscopic as well as microscopic movement in practical applications was evaluated. Using dual GNP/elastomer actuators, a two-axis sub-micron translation stage was developed, and allowed for two-axis photo-thermal positioning (~100 µm per axis) with 120 nm resolution (limitation of the feedback sensor) and ~5 µm/s actuation speeds. A proportional-integral-derivative control loop automatically stabilizes the stage against thermal drift, as well as random thermal-induced position fluctuations (up to the bandwidth of the feedback and position sensor). Nanopositioner performance characteristics were found to be on par with other commercial systems, with resolution limited only by the feedback system used. A mathematical model was developed to describe the elastomeric composite actuators as a series of n springs, with each spring element having its own independent IR-tunable spring constant. Effects of illumination intensity, position, and amount of the composite actuator illuminated are discussed. This model provided several additional insights, such as demonstrating the ability to place not just one, but multiple stages on a single polymer composite strip and position them independently from one another, a benefit not seen in any other type of positioning system. Further investigation yielded interesting and novel photo-mechanical properties with actuation visible on macroscopic scales. Addition of a third component (thermally expanding microspheres), produced a new class of stimuli-responsive expanding polymer composites with ability to unidirectionally transform physical dimensions, elastic modulus, density, and electrical resistance. Carbon nanotubes and core-shell acrylic microspheres were dispersed in polydimethylsiloxane, resulting in composites that exhibit a binary set of material properties. Upon thermal or IR stimuli, liquid cores encapsulated within the microspheres vaporize, expanding the surrounding shells and stretching the matrix. Microsphere expansion results in visible dimensional changes, regions of reduced polymeric chain mobility, nanotube tensioning, and overall elastic to plastic-like transformation of the composite. Transformations include macroscopic volume expansion (\u3e500%), density reduction (\u3e80%), and elastic modulus increase (\u3e675%). Additionally, conductive nanotubes allow for remote expansion monitoring and exhibit distinct loading-dependent electrical responses. Compared to well-established actuation technologies, research into photo-mechanical properties of carbon-based polymer composites is still in its infancy. Results in this dissertation demonstrate some of the enormous potential of light-driven carbon-based composites for actuation and energy scavenging applications. Furthermore, mechanical response dependence to carbon nanostructure dimensional state could have significance in developing new types of carbon-based mixed-dimensional composites for sensor and actuator systems. As the fabrication processes used here are compatible with CMOS and MEMS processing, carbon-based polymer composites allow for not only scaling actuation systems, but also ability to pattern regions of tailorable expansion, strength, and electrical resistance into a single polymer skin, making these composites ideal for structural and electrical building blocks in smart systems. Continued development of carbon-based polymer composites will extend the promising potential of light-driven actuation technologies and will serve as a catalyst to inspire continued research into energy conversion devices and systems

Rapid dry exfoliation method for tuneable production of molybdenum disulphide quantum dots or large micron-dimension sheets

Two-dimensional (2D) materials offer outstanding mechanical, electronic and optical properties that enabled considerable developments in a variety of applications. As such, the synthesis methods for 2D materials have gained much research interest. The preparation and synthesis of 2D materials play a significant role in its quality, hence its properties and suitability for any application. Furthermore, the cost-effective, fast, large-scale industrial production has been always a top priority and a pivotal key to the success of any application employing 2D materials. The move towards rapid large production, however, often presents trade-offs to the quality of the final product. As such, a need arises to address the problem without compromising either quality or quantity at each other's expense. A class of 2D materials, known as transitional metal dichalcogenides, has taken the focus of research in 2D materials in the last ten years and even more recently; due to their natural abundance and interesting properties offered, when thinned down to 2D crystals. Molybdenum disulphide (MoS_2), in particular, has been extensively researched; due to its bulk form stability at room conditions, and the well-studied stability of its thinned form, allowing better control over its use, while having promising electronic and optical applications due to a suitable a bandgap, in addition to its catalytic properties, thus was found to be of use in biosensing and energy applications as well. Many techniques have been developed for producing 2D MoS_2, whether through bottom-up synthesis or top-down exfoliation from bulk. Through the review of synthesis techniques of 2D MoS_2, none of the present approaches gave a solution that does not compromise one aspect; dictating the use of one method over the other for each application, which are often performed on small lab scale with little potential for scaling-up. The synthesis of large micron-dimension single-layer sheets of these materials remains a challenge, especially if an alternative to the slow, expensive and complex bottom-up approaches such as chemical vapor deposition or molecular beam epitaxy is desired. The top-down conventional mechanical exfoliation tape method, which was first used by Geim and Novoselov in 2004 for isolating 2D graphene from graphite and ignited a spark for the 2D materials field, remains a golden standard for pristine quality 2D materials sheets synthesis. A simple but low yield multistep method that required a lot of skill with little potential for scaling-up, however, it is still considered the standard for high quality large sheets production; due to being one of the least invasive techniques. Other mechanical exfoliation methods have been devised to address the shortcoming of the very low yield, but they usually lacked scale-up potential and introduced the use of additives for the transfer and post processing. Another approach researched in parallel was the use of liquid solvents for exfoliation that has progressed through the years starting from the harsh chemically aided exfoliation to the less invasive ultrasonication assisted exfoliation, with a promising potential for scaling-up. The liquid exfoliation techniques had a limited success in obtaining large sheets, although not comparable to the very large sheets obtained from complex bottom-up approaches but could reach the size ranges from mechanical exfoliation tape methods but with compromises made to quality in exchange for scalability. Liquid exfoliation techniques excelled in the production of smaller quantum dots, though. They offered larger yields and better processing time with relatively less complex equipment used and less skill employed. On the other hand, the use of solvents or any additives, even after extensive post processing, still affected the quality of the produced 2D material, hence dictating the suitability for a specific application over the other. The objective of this work is mainly to review the current synthesis techniques for 2D materials and specifically MoS_2 as the most in use example of transitional metal dichalcogenides class of 2D materials. Then to evaluate each method advantages and highlight its drawbacks to ultimately choose a synthesis route and design a platform that addresses most of the shortcomings with little or no compromise to any aspect of the produced 2D material. A novel and a unique method to rapidly exfoliate MoS_2 is presented. Tuneability is offered to produce small nanometer-dimension quantum dots of a desired size range. Moreover, the platform flexibility allowed to produce large micron-dimension as well. Both products were predominantly monolayers to few layers and the exfoliation process was conducted in dry conditions with no use of liquids or additives. The platform employs nanometer-amplitude MHz-order surface vibrations in the form of surface acoustic waves. To produce quantum dots, the bulk material is subjected to massive surface acceleration -on the order of 10^8 m/s^2- to be repeatedly impacted, ejected and collide with miniature enclosure inner walls, in order to laterally break reducing its dimensions as well as thinned down to single or few layers. On the other hand, sheets are produced by suppressing the iterative impacts cycles through reducing the enclosure height to almost zero through the use adhesive tape in place of the miniature enclosure, which serves to fix upper layers of the bulk material while the lowermost one is subjected to a shearing force from the travelling surface acoustic wave, thus progressively thinning the material into sheets while preserving their lateral dimension. A dry stable exfoliated powder product with limited restacking problems is obtained that can stored as a stock and readily used. Depending on the intended application, further suspending it before use in an easily removable solvent such as water-ethanol binary mixture can be performed for finer size separation. The platform is applicable to larger particle size bulk material feed instead of the used commercially available 6 µm powder for demonstration, especially if optimization towards the production of sheets rather than quantum dots is intended. Furthermore, quantum dots are produced in a fast millisecond scale process in a miniaturized platform with potential for scaling-up through massive parallelization. In conclusion, a fast, additive-free and dry exfoliation platform is presented that potentially presents a simple yet scalable micromechanical exfoliation method towards viable commercial production of 2D transition metal dichalcogenides

MICROELECTROMECHANICAL SYSTEMS ENABLED TUNABLE TERAHERTZ METAMATERIALS

Ph.DDOCTOR OF PHILOSOPH

Thin-Film PZT Scanning Micro-actuators for Vertical Cross-sectional Imaging in Endomicroscopy

The advancement of optics and the development of microelectromechanical systems (MEMS) based scanners has enabled powerful optical imaging techniques that can perform optical sectioning with high resolution and contrast, large field of view, and long working distance to be realized in endoscope-compatible form factors. Optical endomicroscopes based on these imaging techniques can be used to obtain in vivo vertical cross-sectional images of dysplastic tissues in the hollow organs before they progress to mucosal diseases such as colorectal cancer. However, existing endomicroscopic systems that use imaging modalities compatible with the use of fluorescent biomarkers are not capable of deep vertical sectioning in real time. This work proposes a unique MEMS-based scanning mechanism to be incorporated into endoscopic microscopes for real-time in vivo deep into-tissue scanning for early cancer detection. For this task, a class of novel multi-axis micro-scanners based on thin-film lead-zirconate-titanate (PZT) has been developed. Leveraging the large piezoelectric strain coefficient of PZT, the prototypes have demonstrated more than 400 μm of out-of-plane displacement with bandwidths on the order of 100-200 Hz in only a 3.2 mm-by-3.2 mm footprint, which meets the requirements for this application. The scanners have a central rectangular-shaped reflector, whose corners are supported by four symmetric PZT bending legs that generate vertical translation. This design gives the reflector a three-axis motion. The challenges to fabricate high performance piezoelectric actuators are discussed with device failure mechanisms observed during the fabrication of the 1st generation scanners. Improved fabrication steps are presented that solve the issues with the 1st generation devices and enhance the robustness of the scanners for instrument integration. Remaining non-ideal fabrication outcomes cause MEMS devices to produce unwanted motions, which can degrade imaging quality. To overcome this problem, a method to drive MEMS actuators having multiple vibration modes with close frequencies to produce a desired motion pattern with a single input is presented, and was used to generate a pure vertical motion for imaging. Two-photon based vertical cross-sectional images of mouse colon was obtained in real time for the first time using a thin-film piezoelectric microscanner. To understand the effects of fabrication non-idealities on the device behavior and produce more robust scanner performance, analytical models that describes large vertical and rotational motions including multi-axis coupling were developed. A static model that was initially developed for design optimization was calibrated, along with a transient model, using experimental data to incorporate the effects of dimensional variations and residual stress. This models can be used with future integrated sensors and feedback controllers for more precise and robust motion of the scanner. This calibration technique can be useful in developing analytic models for MEMS devices subject to fabrication uncertainty. In addition, nonlinear dynamic behavior due to large vertical stroke in the presence of fabrication non-idealities is captured by linearizing an expanded dynamic model about different static positions obtained by numerically solving the expanded nonlinear model.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/137124/1/jongs_1.pd

Microfluidic systems based on electroactive polymers technology

Dielectric elastomer actuators (DEAs) have been widely investigated for more than 30 years. Lately, several fabrication methods have successfully allowed the creation of very thin elastomer and electrode layers. The development of attractive applications, in which DEAs offer advantages over conventional technologies, is thus necessary for the advance of the technology. In this work, new biocompatible microfluidic devices based on DEAs are developed. In the first part of this thesis, several prototypes of peristaltic pumps of single layer dielectric elastomer actuators are designed, manufactured and characterized. Although these prototypes were not able to produce fluid flow, novel insights into the capabilities of Electroactive Polymer technology were gained. In the second part of this work, a pumping micromixer as a novel application of dielectric elastomer stacked actuators is manufactured. The pumping micromixer is based on peristaltic movements, which gently act as a mixer and a pump for microfluidics. Experimental data show a maximal flow rate of 21.5 µL/min at 10 Hz. Image analysis at the outlet proves a 50/50 mixing when all actuators are functioning at the same pace and voltage. The performance of the pumping micromixer is further studied with the Finite Element Method, using the COMSOL Multiphysics® software. Simulations demonstrate the versatility of the pumping characteristics of such a microdevice, from very few µL/min to mL/min, and from a very low pressure in the range of Pa to hundreds of kPa, by only changing the duty cycle, phase shift and actuation frequency

Shaping surface acoustic waves for cardiac tissue engineering

The heart is a non-regenerating organ that gradually suffers a loss of cardiac cells and functionality. Given the scarcity of organ donors and complications in existing medical implantation solutions, it is desired to engineer a three-dimensional architecture to successfully control the cardiac cells in vitro and yield true myocardial structures similar to native heart. This thesis investigates the synthesis of a biocompatible gelatin methacrylate hydrogel to promote growth of cardiac cells using biotechnology methodology: surface acoustic waves, to create cell sheets. Firstly, the synthesis of a photo-crosslinkable gelatin methacrylate (GelMA) hydrogel was investigated with different degree of methacrylation concentration. The porous matrix of the hydrogel should be biocompatible, allow cell-cell interaction and promote cell adhesion for growth through the porous network of matrix. The rheological properties, such as polymer concentration, ultraviolet exposure time, viscosity, elasticity and swelling characteristics of the hydrogel were investigated. In tissue engineering hydrogels have been used for embedding cells to mimic native microenvironments while controlling the mechanical properties. Gelatin methacrylate hydrogels have the advantage of allowing such control of mechanical properties in addition to easy compatibility with Lab-on-a-chip methodologies. Secondly in this thesis, standing surface acoustic waves were used to control the degree of movement of cells in the hydrogel and produce three-dimensional engineered scaffolds to investigate in-vitro studies of cardiac muscle electrophysiology and cardiac tissue engineering therapies for myocardial infarction. The acoustic waves were characterized on a piezoelectric substrate, lithium niobate that was micro-fabricated with slanted-finger interdigitated transducers for to generate waves at multiple wavelengths. This characterization successfully created three-dimensional micro-patterning of cells in the constructs through means of one- and two-dimensional non-invasive forces. The micro-patterning was controlled by tuning different input frequencies that allowed manipulation of the cells spatially without any pre- treatment of cells, hydrogel or substrate. This resulted in a synchronous heartbeat being produced in the hydrogel construct. To complement these mechanical forces, work in dielectrophoresis was conducted centred on a method to pattern micro-particles. Although manipulation of particles were shown, difficulties were encountered concerning the close proximity of particles and hydrogel to the microfabricated electrode arrays, dependence on conductivity of hydrogel and difficult manoeuvrability of scaffold from the surface of electrodes precluded measurements on cardiac cells. In addition, COMSOL Multiphysics software was used to investigate the mechanical and electrical forces theoretically acting on the cells. Thirdly, in this thesis the cardiac electrophysiology was investigated using immunostaining techniques to visualize the growth of sarcomeres and gap junctions that promote cell-cell interaction and excitation-contraction of heart muscles. The physiological response of beating of co-cultured cardiomyocytes and cardiac fibroblasts was observed in a synchronous and simultaneous manner closely mimicking the native cardiac impulses. Further investigations were carried out by mechanically stimulating the cells in the three-dimensional hydrogel using standing surface acoustic waves and comparing with traditional two-dimensional flat surface coated with fibronectin. The electrophysiological responses of the cells under the effect of the mechanical stimulations yielded a higher magnitude of contractility, action potential and calcium transient

The 2019 surface acoustic waves roadmap

Today, surface acoustic waves (SAWs) and bulk acoustic waves are already two of the very few phononic technologies of industrial relevance and can been found in a myriad of devices employing these nanoscale earthquakes on a chip. Acoustic radio frequency filters, for instance, are integral parts of wireless devices. SAWs in particular find applications in life sciences and microfluidics for sensing and mixing of tiny amounts of liquids. In addition to this continuously growing number of applications, SAWs are ideally suited to probe and control elementary excitations in condensed matter at the limit of single quantum excitations. Even collective excitations, classical or quantum are nowadays coherently interfaced by SAWs. This wide, highly diverse, interdisciplinary and continuously expanding spectrum literally unites advanced sensing and manipulation applications. Remarkably, SAW technology is inherently multiscale and spans from single atomic or nanoscopic units up even to the millimeter scale. The aim of this Roadmap is to present a snapshot of the present state of surface acoustic wave science and technology in 2019 and provide an opinion on the challenges and opportunities that the future holds from a group of renown experts, covering the interdisciplinary key areas, ranging from fundamental quantum effects to practical applications of acoustic devices in life science

Microelectromechanical Systems and Devices

The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators