Paul R. Chiarot

A single vibration mode tubular piezoelectric ultrasonic motor

A novel tubular ultrasonic motor is presented that uses only a single vibration bending mode of a piezoelectric tube to generate rotation. When the piezoelectric tube bends, the diagonal motion of points on selected areas at the ends of the tube generates forces with tangential components along the same circumferential direction, driving the rotors to rotate. Bi-directional motion is achieved by simply switching the direction of bending. Because only one vibration mode is used, the motor requires only one driving signal and no vibration mode coupling is needed, simplifying the design, fabrication, assembly, and operation of the device. Two prototypes [one with cut-in lead zirconate titanate (PZT) teeth and one with added metal teeth] were built and tested using PZT tubes available to the authors. The tubes have an outside diameter of 6.6 mm, inner diameter of 5.0 mm, and length of 25.4 mm. The working frequencies of the two motors are 27.6 and 23.5 kHz. The motors achieved a maximum no-load speed of 400 rpm and a stall torque of 300 μN·m.

An Overview of Electrospray Applications in MEMS and Microfluidic Systems

Integrating electrospray into microelectromechanical systems (MEMS) and microfluidic systems supports applications in diverse fields from biotechnology to aerospace. Electrospray also functions as a production tool, allowing for novel methods of MEMS fabrication. This review covers the three most significant applications of electrospray in MEMS and microfluidic systems technology: 1) as an integral part of a microfluidic device, most notably electrospray emitters for coupling a microfluidic chip to a mass spectrometer; 2) as a method for fabricating and manufacturing MEMS; and 3) for micropropulsion in aerospace applications using MEMS-based emitters. Perspectives on future research directions and opportunities are provided.

On the Pulsed and Transitional Behavior of an Electrified Fluid Interface

Transient modes of an electrified fluid interface are investigated, specifically, (a) intermittent or pulsed cone-jet mode and (b) smooth and abrupt transitions of the interface in response to a step voltage. These modes were studied experimentally by capturing the motion of the interface and measuring the emitted ion current (via electrospray) as they occur. The observed phenomena are described using an analytical model for the equilibrium of an electrified fluid interface, and the effect of operational parameters on the transient modes is discussed. Pressure, which is related to the supplied flow rate, significantly influences the behavior of the transient modes. It is useful to understand transient modes so they can be avoided in applications that require a stable electrospray. However, with improved knowledge, the modes studied here can assist in the development of specialized applications.

Plane model of fluid interface rupture in an electric field

Modeling of an air-fluid interface in an electric field is presented. Specifically, equilibrium of the interface under the dominant forces—electric stress, surface tension, and pressure—is investigated. Since interface shape and equilibrium are related, the shape of an electrified interface is also addressed. To determine the electric stress, an analytical expression for the electric field in the vicinity of the interface is determined. The operating point of the interface is shown to exist in a three-dimensional parameter space that is divided by a critical surface into equilibrium, quasiequilibrium, and nonequilibrium subdomains. The three parameters are applied voltage, electrode separation, and pressure difference. Interface size, counterelectrode size, and fluid properties are also considered. The subdomain in which the operating point resides defines the important characteristics of the interface. The operating point moves within, and transfers between, equilibrium subdomains, and points on the crit...

Pulsations with reflected boundary waves: a hydrodynamic reverse transport mechanism for perivascular drainage in the brain.

Beta-amyloid accumulation within arterial walls in cerebral amyloid angiopathy is associated with the onset of Alzheimer’s disease. However, the mechanism of beta-amyloid clearance along peri-arterial pathways in the brain is not well understood. In this study, we investigate a transport mechanism in the arterial basement membrane consisting of forward-propagating waves and their reflections. The arterial basement membrane is modeled as a periodically deforming annulus filled with an incompressible single-phase Newtonian fluid. A reverse flow, which has been suggested in literature as a beta-amyloid clearance pathway, can be induced by the motion of reflected boundary waves along the annular walls. The wave amplitude and the volume of the annular region govern the flow magnitude and may have important implications for an aging brain. Magnitudes of transport obtained from control volume analysis and numerical solutions of the Navier–Stokes equations are presented.

Dielectrophoretic deflection of ink jets

In continuous ink jet systems, streams of ~10 pL liquid droplets (diameter ~30 ?m) are ejected from an orifice at rates of up to 350?000 per second with velocities in excess of 20 m s?1. Applications as diverse as printing, MEMS fabrication and microarraying benefit from this technology; however, reliable manipulation of the jet, including basic on/off control and steering of the liquid droplets, remains difficult to achieve. We report a novel scheme to manipulate the trajectories of droplets that rebound at shallow angles from a solid substrate using the dielectrophoretic force exerted by patterned electrodes. Varying the voltage applied to the electrodes provides precise control of the rebounding trajectories, mainly by shifting the location of the droplet impact. This technique can also be used to implement on/off control of the droplet stream. A simple dynamic model successfully predicts the modified trajectories of the droplets.

Application of an Equilibrium Model for an Electrified Fluid Interface—Electrospray Using a PDMS Microfluidic Device

An experimental investigation of an electrified fluid interface is presented. The experimental findings are related to a previously developed analytical model of Gubarenko , which is used to determine when a fluidic interface under electrical stress is in equilibrium, and to observations reported in the literature. The effect of key parameters on causing the interface to rupture, form, and maintain an electrospray is investigated. The experimental results reveal the dependence of interface shape on operational parameters, the impact of the interface apex angle on equilibrium, the conditions that cause either dripping mode or cone-jet mode, and the structure of operational domains. This paper confirms predictions made using the analytical model, including the range of parameters that cause the onset and steadiness of a quasi-equilibrium (electrospray) state of the interface. Testing is performed using an electrospray emitter chip fabricated from two layers of Polydimethylsiloxane and one layer of glass. The model and experimental results assist in design decisions for electrospray emitters. Applications of electrified interfaces (electrosprays) are found in mass spectrometry, microfluidics, material deposition, and colloidal thrusters for propulsion.

Membrane mechanical properties of synthetic asymmetric phospholipid vesicles

Synthetic lipid vesicles have served as important model systems to study cellular membrane biology. Research has shown that the mechanical properties of bilayer membranes significantly affects their biological behavior. The properties of a lipid bilayer are governed by lipid acyl chain length, headgroup type, and the presence of membrane proteins. However, few studies have explored how membrane architecture, in particular trans-bilayer lipid asymmetry, influences membrane mechanical properties. In this study, we investigated the effects of lipid bilayer architecture (i.e. asymmetry) on the mechanical properties of biological membranes. This was achieved using a customized micropipette aspiration system and a novel microfluidic technique previously developed by our team for building asymmetric phospholipid vesicles with tailored bilayer architecture. We found that the bending modulus and area expansion modulus of the synthetic asymmetric bilayers were up to 50% larger than the values acquired for symmetric bilayers. This was caused by the dissimilar lipid distribution in each leaflet of the bilayer for the asymmetric membrane. To the best of our knowledge, this is the first report on the impact of trans-bilayer asymmetry on the area expansion modulus of synthetic bilayer membranes. Since the mechanical properties of bilayer membranes play an important role in numerous cellular processes, these results have significant implications for membrane biology studies.

A Study of Passive Microfluidic Mixers

Three designs of passive microfluidic mixers (fabricated using Micralyne Protolyne technology on a glass substrate) are studied and compared to a basic straight channel diffusion mixer. The designs are analyzed under continuous and pulsating flow conditions using numerical and experimental tools; specifically finite element analysis and particle image velocimetry. Testing and analysis are performed at pressures that can be generated using reciprocating membrane micropumps integrated into a Micro Total Analysis System. It is determined that one of the proposed mixer concepts outperforms all of the other designs considered and enhanced mixing is achieved under pulsating flow. Performance is judged based on criteria that describes the amount of mixing performed, the concentration uniformity at the outlet of the mixer, and the net flow rate. Recommendations are made on how to improve the overall performance of the passive micromixers.

Evolution of Nanoparticle Deposits Printed Using Electrospray

In an electrospray, large electric potentials are used to generate a spray of highly charged droplets. Colloidal dispersions, consisting of nanoparticles in a volatile solvent, can be atomized using electrospray. Printing occurs by directing the emitted droplets toward a target substrate (TS). The solvent evaporation is rapid and dry nanoparticles are produced before reaching the surface. In this study, we investigate the structure of nanoparticle deposits printed using electrospray. Using dark field microscopy, four regimes are identified that mark the evolution of the deposit structure at early times. Electrospray imparts an excess electric charge onto the emitted particles. It is shown that the mutual Coulombic interaction between the particles governs their transport and ultimately the microstructure of the printed deposits. Electrospray offers enhanced control over the microstructure of printed nanomaterial deposits compared to traditional printing techniques. This has significant implications for the manufacturing of flexible electronic and photonic devices.