J. William Boley

Bifurcation-based mass sensing using piezoelectrically-actuated microcantilevers

In conventional implementations, resonant chemical and biological sensors exploit chemomechanically-induced frequency shifts, which occur in linear systems, for analyte detection. In this letter, an alternative sensing approach, based upon dynamic transitions across saddle-node bifurcations is investigated. This technique not only has the potential to render improved sensor metrics but also to eliminate frequency tracking components from final device implementations. The present work details proof-of-concept experiments on bifurcation-based sensing, which were conducted using selectively functionalized, piezoelectrically-actuated microcantilevers. Preliminary results reveal the proposed sensing technique to be a viable alternative to existing resonant sensing methods.

Label-Free Detection of Staphylococcus aureus Captured on Immutable Ligand Arrays

The rapid capture and label-free detection of Staphylococcus aureus , an opportunistic bacterium that can infect upon contact, can be performed using periodic microarrays of ligand-protein conjugates created by noncontact (inkjet) printing, darkfield imaging conditions, and a FFT-based readout method. Ink solutes were prepared using bovine serum albumin (BSA) conjugated to a glycan with high affinity for bacterial adhesins and printed as dot-matrix arrays with periodicities of 80-120 μm using a thermal injection method. Upon exposing the glycan-BSA microarrays to live strains of S. aureus , patterns emerge that can be detected under optical darkfield conditions. These patterns can be decoded by fast Fourier transform (FFT) analysis to generate fault-tolerant readout signals that correspond to the capture of S. aureus, with a limit of detection between 10(2) and 10(3) cfu/mL. Inkjet printing provides independent control over array periodicity, enabling FFT signals to be assigned to specific frequencies in reciprocal k-space.

Coalescence constraints for inkjet print mask optimization

A print mask is a unique way of controlling the firing sequence of nozzles in inkjet printing. It is desirable to design a print mask which maximizes throughput while maintaining desired image quality. This can be formulated as an optimization problem where the objective is to maximize throughput by minimizing printing time subject to image quality constraints under uncertainties and variations in the printing process. Coalescence is an important image quality artifact. This paper outlines the development of a coalescence model, which can be used as an image quality constraint in finding an optimal print mask. The proposed coalescence model computes the probability of coalescence as a function of time between two adjacent drops. Monte Carlo simulation is used based on experimentally obtained distributions of model parameters. Given an acceptable coalescence probability the minimum printing time between adjacent drops can be determined, which translates to a minimum distance between pixels in a print mask that can be printed on the same pass.

Hybrid Self-Assembly during Evaporation Enables Drop-on-Demand Thin Film Devices

We propose and demonstrate a hybrid self-assembly process as the mechanism for producing strikingly uniform deposits from evaporating drops composed of cosolvents. This assembly process leverages both particle-fluid interactions to carry the particles to the drop surface and particle-interface interactions to assemble the particles into a uniform film. We anchor our results in a cosolvent evaporation model that agrees with our experimental observations. We further employ the process to produce thin film devices such as flexible broadband neutral density filters and semitransparent mirrors. Our observations suggest that this assembly process is free of particle-substrate interactions, which indicates that the results should be transferable across a multitude of material/substrate systems.

Modeling, Analysis, and Experimental Validation of a Bifurcation-Based Microsensor

The potential to detect very small amounts of added mass has driven research in chemical and biological sensors based on resonant micro- and nanoelectromechanical systems over the past two decades. While traditional resonant mass sensors utilize chemomechanically induced shifts in linear natural frequency for mass detection, alternate sensing approaches which exploit near-resonant nonlinear behaviors have garnered interest from the research community due to their potential to yield improved sensor metrics and to simplify final device implementations. This paper investigates the development of an amplitude-based mass sensing approach which utilizes the dynamic transitions that occur near a cyclic-fold/saddle-node bifurcation in the nonlinear frequency response of a piezoelectrically actuated microcantilever. Specifically, the work details the modeling, analysis, and experimental validation of this mass sensing technique. The experimental results presented here not only prove the feasibility of the proposed sensing approach but also allow for the direct evaluation of pertinent sensor metrics.

Linear and Nonlinear Mass Sensing Using Piezoelectrically-Actuated Microcantilevers

Chemical and biological sensors based on resonant microcantilevers offer distinct utility due to their small size, low power consumption, high sensitivity, and, when bulk fabricated, comparatively-low cost. Modern resonant mass sensors typically utilize chemomechanically-induced frequency shifts in linear resonators for analyte detection. Recent results, however, have indicated that nonlinear sensors, which actively exploit dynamic transitions across sub-critical or saddlenode bifurcations in the device’s frequency response, have the potential to exhibit improved performance metrics and operate effectively at smaller scales. This relatively-novel sensing approach directly exploits chemomechanically-induced amplitude shifts, instead of frequency shifts, for detection. Accordingly, it has the potential to eliminate the need for numerous power-consuming signal processing components in final sensor implementations. The present work details the ongoing development of low-cost, linear and nonlinear, bifurcation-based mass sensors founded upon selectivelyfunctionalized, piezoelectrically-actuated microcantilevers. Specifically, the work describes the modeling, analysis, microinkjet functionalization, and experimental characterization of these devices.

Stochastic Modelling of Drop Coalescence on Non-Porous Substrates for Inkjet Applications

Coalescence between two drops on a substrate is one of the important factors that can affect print quality in inkjet applications. Two stochastic models (constant contant angle mode and constant contact area mode) that consider drop placement error, drop impact, and drop evaporation are proposed for determining the probability of coalescence between adjacently printed drops on nonporous substrates. Experiments are conducted to measure the probability of coalescence with respect to deposition time difference between adjacently printed drops and compared to the predictions of the models. The measured coalescence follows the constant contact angle mode evaporation model during the initial phase of the life of the first drop, which is followed by a mix between the constant contact angle mode and the constant contact area mode models for the remainder of the life of the first drop. This study shows that for probabilities of coalescence between 10 % and 80 % the constant contact angle mode model can be used to determine deposition time difference threshold values for adjacent drops in applications promoting drop coalescence while the constant contact area mode model can be used for applications avoiding drop coalescence. Further efforts are needed to capture the dynamics of the mixed-model evaporation and to more accurately predict larger (greater than 80 %) and smaller (less than 10 %) occurrences of coalescence.Copyright

Syringe Position Control for Back Pressure Modulated Drop Volume in Functional Inkjet Printing

Inkjet printing technologies have been common and well developed over the past few decades, and more recently have gained significant acceptance in functional printing and additive manufacturing applications. Control of dot gain in the deposition process is a desirable capability for a printing system from the perspective of process control and throughput, and preliminary data suggests dot gain and drop volume can be controlled in inkjet systems through manipulation of the reservoir back pressure. In order to help facilitate further exploration, the design of a back pressure control system is proposed, and the system modeled, with linear and nonlinear control designs proposed and compared in simulation for this nonlinear plant application, where the nonlinear control design, a sliding mode controller, outperforms the tested linear control design. NOMENCLATURE A Syringe surface area, m2 Vp Piping volume, m3 Vs Syringe volume, m3 Vt Total reservoir volume, m3 PR Reservoir (absolute) pressure, Pa PA Ambient pressure, Pa Pb Back pressure, Pa x Syringe deflection from initial position, m x0 Initial syringe position, m Vt,initial Total reservoir volume at x = 0, m3 PR,initial Initial reservoir pressure, Pa n Number of moles of gas (air), mol R Ideal gas constant, J/(K*mol) T Air temperature, K Kg Gas right-hand side constant, N*m Fs Syringe nonlinear spring force, N Ff Syringe friction force, N Fc Coulomb friction force, N Fe ”External force” for friction model, N Fv Voice coil actuator force, N Fk Voice coil spring return force, N c Syringe viscous damping coefficient, N/(m/s) Kc Voice coil return spring constant, N/m ms Syringe plunger mass, kg ma Voice coil armature mass, kg mt Total mass, kg Proceedings of the ASME 2014 Dynamic Systems and Control Conference DSCC2014 October 22-24, 2014, San Antonio, TX, USA