Equivalent Circuit of the Concentration Transport in a Fluidic Channel

A new equivalent circuit is presented, which describes the transport of a chemical solution with a certain concentration in a fluidic channel. Channels are basic parts of a microfluidic systems and the concentration of the chemical solution can control the opening and closing of valves based on smart hydrogels. This type of microfluidic systems facilitates the autonomous control of fluid flow, e.g. in chemo-fluidic oscillators. Through this channel, the solution is transported at a velocity determined by the flow rate through the channel and its cross section. While the volumetric flow is not delayed in an ideal channel, the channel acts as delay line for the particles and thus for a certain concentration transport through the channel. In this setting, the transport of the dissolved chemical by water traveling along the delay channel can be described by the one-dimensional transport equation. In order to derive the equivalent circuit, the transport equation is numerically approximated based on the well-known Method of Lines. This method consists in approximating the original PDE via a large system of ODEs. The ODEs are obtained by discretizing the PDE in space, in such a way that each component of the resulting system of ODEs approximates the solution of the PDE at some grid point along the spatial interval. Once the system of ODEs has been constructed, a flow and a difference quantity can be defined and the ODEs interpreted as finite network elements. Since the equations are isomorphic to electrical ODEs of electrical network elements, the fluidic channel can be expressed by an equivalent circuit. Thus the transient behavior of the transport mechanism can be calculated using a circuit simulator as part of a design automation. Simulation results are presented.

Model Development for PZT Bimorph Actuation Employed for Micro-Air Vehicles

In the paper, we discuss the development of a model for PZT bimorph actuators used to power micro-air vehicles including Robobee. Due to highly dynamic drive regimes required for the actuators, models must quantify the nonlinear, hysteretic, and rate-dependent behavior inherent to PZT in these regimes. We employ the homogenized energy model (HEM) framework to model the actuator dynamics and numerically we illustrate the capability of the model to characterize the inherent hysteresis. This provides a comprehensive model, which can be inverted and implemented for certain control regimes.

Investigation of Ion Transport in Polypyrrole Modified Ultra-Microelectrodes During Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) is an electrochemical technique used to measure faradaic current changes local to the surface of a sample. The incorporation of shear force (SF) feedback in SECM enables the concurrent acquisition of topographical data of substrates along with electrochemical measurements. Contemporary SECM measurements require a redox mediator such as ferrocene methanol (FcMeOH) for electrochemical measurements; however, this could prove detrimental in the imaging of biological cells. In this article, nanoscale polypyrrole membranes doped with dodecylbenzene sulfonate (PPy(DBS)) are deposited at the tip of an ultra-microelectrode (UME) to demonstrate a novel modification of the contemporary SECM-SF imaging technique that operates in the absence of a redox mediator. The effect of distance from an insulating substrate and bulk electrolyte concentration on sensor response are examined to validate this technique as a tool for correlated topographical imaging and cation flux mapping. Varying the distance of the PPy(DBS) tipped probe from the substrate in a solution containing NaCl causes a localized change in cation concentration within the vicinity of the membrane due to hindered diffusion of ions from the bulk solution to the diffusion field. The cation transport into the membrane in close proximity to the substrate is low as compared to that in the electrolyte bulk and asymptotically approaches the bulk value at the sense length. At a constant height from the base, changing the bulk NaCl concentration from 5 mM to 10 mM increases the filling efficiency from 35% to 70%. Further, the sense length of this modified electrode in NaCl is about 440 nm which is significantly lower as compared to that of a bare electrode in ferrocene methanol (5–20 μm). It is postulated that this novel technique will be capable of producing high resolution maps of surface cation concentrations, thus having a significant impact in the field of biological imaging.

Novel Chiral Structure With Tailored Mechanical Response Exploiting Elastic Instabilities

This paper presents a structural concept that exploits elastic instabilities in novel periodic lattice structures for shape adaptation purposes. The nonlinear behaviour resulting from the occurrence of local buckling is utilised to achieve significant variations in the global structural response of the lattice. For the proposed structural concept, a unit cell is identified and utilised to investigate the mechanical characteristics for the load cases of uniaxial compression, shear, and rotation, conducting nonlinear finite element simulations. The results of the unit cell characterization are compared to the mechanical response of lattice structures under equivalent loading and convergence is achieved for all considered load cases. This paper therefore introduces a novel design concept to achieve selective compliance, especially beneficial for shape adaptation of wing structures.

Origami Metastructures for Tunable Wave Propagation

Wave propagation inside a host media with periodically distributed inclusions can exhibit bandgaps. While controlling acoustic wave propagation has large impact on many engineering applications, studies on broadband acoustic bandgap (ABG) adaptation is still outstanding. One of the important properties of periodic structure in ABG design is the lattice-type. It is possible that by reconfiguring the periodic architectures between different lattice-types with fundamentally distinct dispersion relations, we may achieve broadband wave propagation tuning. In this spirit, this research pioneers a new class of reconfigurable periodic structures called origami metastructures (OM) that can achieve ABG adaption via topology reconfiguration by rigid-folding. It is found that origami folding, which can enable significant and precise topology reconfigurations between distinct Bravais lattice-types in underlying periodic architecture, can bring about drastic changes in wave propagation behavior. Such versatile wave transmission control is demonstrated via numerical studies that couple wave propagation theory with origami folding kinematics. Further, we also exploit the novel ABG adaptation feature of OM to design structures that can exhibit unique tunable non-reciprocal behavior. Overall the broadband adaptable wave characteristics of the OM coupled with scale independent rigid-folding mechanism can bring on-demand wave tailoring to a new level.

Demonstration of a Novel Smart Structural System for Pointing Control of Trusses

We designed and developed a novel smart structural system for pointing control of large-scale support structures, such as trusses. The system consists of a pointing control mechanism, an internal displacement-sensor, and a controller. Remarkable points of our system are (1) artificial thermal expansion of truss members is utilized as linear actuators, (2) elastic hinges are applied instead of boll joints, and (3) the internal displacement-sensor which does not need external jigs and has high measuring accuracy is applied. In this paper, we conducted the feasibility study and the experimental demonstration. As a result of the feasibility study, the proposed pointing control mechanism can produce several hundred arcseconds of the rotational displacements within three minutes, therefore it has potential for using in practical operations. As a result of the experimental demonstration, we confirmed that the hysteresis of the pointing control mechanism can be kept sufficiently small due to the absence of the sliding parts, and has high control accuracy and followability (the error RMS value for a circle of the radius of 500 μm is 3.6 %).

Study on the Snap-Through Behavior of Bistable Plates

This paper aims to analyze snap-through behavior of two-layer cross-ply bistable composite laminate square plates. The analyses consider the factors of laminate thickness, temperature and external applied force. In this study, the model was performed on the basis of the classical thin plate theory, the Von Kármán large deformation theory and Principle of Virtual Work. Afterwards the statics equilibrium equation was available. Subsequently the analysis was presented by adjusting the laminate thickness for these prior factors. Through the numerical simulations with Matlab® software, the curvatures in x-direction and y-direction were calculated to investigate the snap-through behavior. Two stable cylindrical configurations and an unstable saddle shape were given with different curvatures to show the equilibrium positions. Then the figures prove the external applied distributed force plays a vital role to the snap-through behavior. The results show that under macroscopic view, the ratio of side-length to thickness is three hundred or less, as the plates are thinner, the snap-through will appear more frequently, and the external forces will be less needed.

Semi-Active Control of Sound Radiated From an Elastic Circular Plate Integrated With Adaptive Tuned Vibration Absorbers

While adaptive tuning of vibration absorbers (ATVA) have been widely studied for vibration control applications, limited studies have been done to explore their potential for noise control applications. This study aims to utilize magnetorheological elastomer (MRE)-based ATVA to control the radiated sound from an elastic plate excited by a plane wave especially at low frequencies. Radiated sound from a clamped circular plate integrated with MRE-based ATVA is analytically studied using classical plate theory. Rayleigh integral approach is, then, used to express the transmitted sound pressure in terms of the plate’s displacement modal amplitude. A MRE-based ATVA under shear mode is investigated. The semi-active Skyhook controller is proposed to attenuate the transverse displacement of the plate and subsequently reduce the radiated sound. The controller determines the current input to the electromagnet and tunes the MRE-based ATVA with the desired stiffness.

Pore-Spanning PPy(DBS) as a Voltage-Gated Synthetic Membrane Ion Channel

The transport of monovalent cations across a suspended PPy(DBS) polymer membrane in an aqueous solution as a function of its redox state is investigated. Maximum ion transport is found to occur when PPy(DBS) is in the reduced state, and minimum transport in the oxidized state. No deviation in the dynamics of ion transport based on the direction of the applied electrical field is observed. Additionally, it is found that ion transport rates linearly increased proportional to the state of reduction until a steady state is reached when the polymer is fully reduced. Therefore controlled, bidirectional ion transport is for the first time demonstrated. The effect of aqueous Li+ concentration on ion transport in the fully reduced state of the polymer is studied. It is found that ion transport concentration dependence follows Michaelis-Menten kinetics (which models protein reaction rates, such as those forming ion channels in a cell membrane) with an r2 value of 0.99. For the given PPy(DBS) polymer charge density and applied potential across the membrane, the maximum possible ion transport rate per channel is found to be 738 ions per second and the Michaelis constant, representing the concentration at which half the maximum ion transport rate occurs, is 619.5mM.