Energy Harvesting From Droplet Interface Bilayers

Biologically inspired droplet interface bilayers have found applications in the development of hair cell sensors and other mechanotransduction applications. In this research, the flexoelectric capability of the droplet bilayers under external excitation is explored for energy harvesting. Traditionally, membrane capacitance models are being used for inferring the magnitude of the membrane deflection which do not account for the relation between the applied force or deflection and the deflection of the interfacial membrane and time dependent variations. In this work, the dynamic behavior of the droplets under external excitation has been modeled using nonlinear finite element analysis. A flexoelectric model including mechanical, electrical, and chemical sensitivities has been developed and coupled with the calculated bilayer deformations to predict the mechanotransductive response of the droplets under excitation. Using the developed framework, the possibilities of energy harvesting for different droplet configurations have been investigated and reported.

The Contribution of LARES to Global Climate Change Studies With Geodetic Satellites

Satellite Laser Ranging (SLR) makes an important contribution to Earth science providing the most accurate measurement of the long-wavelength components of Earth’s gravity field, including their temporal variations. Furthermore, SLR data along with those from the other three geometric space techniques, Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS) and DORIS, generate and maintain the International Terrestrial Reference Frame (ITRF) that is used as a reference by all Earth Observing systems and beyond. As a result we obtain accurate station positions and linear velocities, a manifestation of tectonic plate movements important in earthquake studies and in geophysics in general. The “geodetic” satellites used in SLR are passive spheres characterized by very high density, with little else than gravity perturbing their orbits. As a result they define a very stable reference frame, defining primarily and uniquely the origin of the ITRF, and in equal shares, its scale. The ITRF is indeed used as “the” standard to which we can compare regional, GNSS-derived and alternate frames. The melting of global icecaps, ocean and atmospheric circulation, sea-level change, hydrological and internal Earth-mass redistribution are nowadays monitored using satellites. The observations and products of these missions are geolocated and referenced using the ITRF. This allows scientists to splice together records from various missions sometimes several years apart, to generate useful records for monitoring geophysical processes over several decades. The exchange of angular momentum between the atmosphere and solid Earth for example is measured and can be exploited for monitoring global change. LARES, an Italian Space Agency (ASI) satellite, is the latest geodetic satellite placed in orbit. Its main contribution is in the area of geodesy and the definition of the ITRF in particular and this presentation will discuss the improvements it will make in the aforementioned areas.

Reliability-Based Design Optimization for Nonlinear Energy Harvesters

This paper presents reliability-based design optimization (RBDO) and experimental validation of the purely mechanical nonlinear vibration energy harvester we recently proposed. A bi-stable characteristic was embodied with a pre-stressed curved cantilever substrate on which piezoelectric patches were laminated. The curved cantilever can be simply manufactured by clamping multiple beams with different lengths or by connecting two ends of the cantilever using a coil spring. When vibrating, the inertia of the tip mass activates the curved cantilever to cause snap-through buckling and makes the nature of vibration switch between two equilibrium positions. The reliability-based design optimization study for maximization of power density and broadband energy harvesting performance is performed. The benefit of the proposed design in terms of excellent reliability, design compactness, and ease of implementation is discussed. The prototype is fabricated based on the optimal design result and energy harvesting performance between the linear and nonlinear energy harvesters is compared. The excellent broadband characteristic of the purely mechanical harvester will be validated.

Further Insight on the Power Harvesting Capabilities of Magnetic Shape Memory Alloys

Magnetic shape memory alloys are a relatively new class of materials that are suitable for actuation, sensing, and power harvesting. The power harvesting capability comes from the change in magnetization that the material exhibits when internal martensitic variants change orientation. In typical power harvesting tests, the material is loaded with axial compression in the presence of a bias magnetic field applied normal to the compressive loading direction. However, previous results suggest that having a component of the bias magnetic field applied axially, parallel to the compressive stress, can increase the power output of MSMAs. Furthermore, most of the MSMAs power harvesting results reported to date focused on the open circuit voltage that the material can generate during cyclic loading. However, this information is not indicative of the true power harvesting capability of the material and one has to focus on the power output of the material instead. This paper presents voltage trends and power output data for a MSMA sample exposed simultaneously to a cyclic compressive stress and bi-axial magnetic field.

Developing a Generalized Harmonic Balance Method for Accurate Identification of Crack Depth in a Continuous Shaft-Disc System

In this work, the effect of a crack on the vibrational properties of a shaft-disc system has been studied applying a generalized harmonic balance method. In the reviewed literature, the reported methods to find the unbalance response of a continuous shaft-disc system provide only the first harmonic component of the response; whereas, the presented method gives the super-harmonic components as well. The shaft-disk system consists of a flexible shaft with a single rigid disc mounted on rigid short bearing supports. The shaft contains a transverse breathing crack (fatigue crack). The main concept for crack detection in vibration-based methods is basically the investigation of crack-induced changes in the selected vibrational properties. Shaft critical speeds and harmonic and super-harmonic components of the unbalance lateral response have been used as typical vibrational properties for crack detection in a rotating shaft system. A generalized harmonic balance method has been developed to efficiently investigate changes in vibrational properties due to the effect of crack properties, depth and location. The results of the developed analytical model have been compared with those obtained from the finite element model and close agreement has been observed.

A C-Battery Scale Energy Harvester: Part B — Transducer Optimization and Modeling

A two Degree-of-Freedom (2DoF) nonlinear electromagnetic energy harvester, which employs velocity amplification, with a volume of 26.7cm 3 and 25.6 cm3 (25.5mm diameter and 52.4mm height) is investigated in this work. These dimensions are very close to those of a C-battery (26.2mm diameter and 50mm length, for a volume of 27.8cm3), making the harvester suitable to be integrated in electronic devices. The harvester consists of a Halbach array of magnets oscillating inside a set of seven coils. The use of magnetic springs and the impacts between the two masses, leads to nonlinear harvester behaviour, broadening the harvester’s spectral response. Moreover, the impacts exploit velocity amplification on the secondary (smaller) mass, improving the electromagnetic conversion. The aim of this work is to optimize the performance of the electromagnetic transducer through analytical and numerical methods and to experimentally verify the optimization methods. This paper discusses the magnetic configuration that maximizes the variation of flux density and an analytical model is presented that predicts the optimal number of turns and wire diameter for the coils. A finite element simulation takes the output from the initial optimization calculations and predicts the output voltage of the harvester. Experimental results are then presented where various coil designs are tested and comparisons are made to the numerical results to validate the models. The experimental results also show a high volumetric Figure of Merit (FoMV), which highlights the benefits of the optimisation methods used. Finally, in order to give the reader an understanding of the system performance under real-world vibrations, the system was tested under excitation generated by human motion.

Incorporating Stimuli-Responsive Bacteria in Microfluidic Droplets

Model cellular membranes respond to chemical and electrical stimuli, regulating transport and exchange between two neighboring aqueous droplets. This regulated exchange may prove useful for controlling aqueous micro-environments for studying stimuli-responsive encapsulated bacteria. This concept is explored in this work, focusing on characterizing the bacterial response within a synthetic cellular environment. In the droplet interface bilayer (DIB) approach, aqueous micro-droplets deposited in an oil reservoir with dissolved lipids are coated with lipid monolayers and arranged into artificial cellular networks. This approach has been explored for potential use as a biologically-inspired smart material, but new material transduction pathways are necessary. This may be accomplished by combining this bottom-up approach to synthetic biology with living organisms such as stimuli-responsive bacteria. Bacteria encapsulation within the microfluidic droplets begins with a strain of Escherichia coli (E. coli), XL1-Blue. These flagellated bacteria naturally respond and move towards chemoattractants such as casamino acids, and their motion may be tracked through differential interference contrast (DIC) and fluorescent microscopy. Chemotaxis of XL1-Blue was assessed through low-flow perfusion of the chemoattractant (casamino acids) into a buffer solution containing the bacteria through a tailored capillary tube. Next, the response of bacteria within asymmetric DIB networks separating the bacteria and the chemoattractant were studied.

Non-Contact Tension Sensing Using Fe-Ga Alloy Strip

This paper describes a proof-of-concept non-contact strain sensor, using a magnetostrictive Fe-Ga alloy (Galfenol). Magnetostrictive materials demonstrate dimensional changes in response to a magnetic field. In contrast with typical piezoceramic materials, Galfenol is the most ductile of the current transduction materials and appears to have an excellent ability to withstand mechanical shock and tension. Galfenol also exhibits the inverse (Villari) effect: both the magnetization and permeability change in response to an applied stress. Galfenol has low hysteresis loses, less than ∼10% of its transduction potential over a range of −20 to +80 °C. The magnetization’s response to stress depends strongly on both magnetic field bias and alloy composition. Galfenol’s Villari effect can be used in various sensor configurations together with either a giant magnetoresistance (GMR) sensor, Hall Effect sensor or pickup coil to sense the magnetization / permeability changes in Galfenol when stressed. The sensor described in this paper utilizes the permeability change, which is not time dependent and can measure static loads. The design reported here targets low force, low frequency applications, such as inclination measurements and stress monitoring. The sensor was able to measure both static and dynamic stress. The static sensitivity was +3.64 Oe/kN for the Hall sensor close to the bias magnet and −1.49 Oe/kN for the Hall sensor at the other end of the Galfenol strip. We conclude that a Galfenol strain sensor is a viable candidate for bolt stress monitoring in critical applications.

Development Smart/Nervous Material With Novel Sensor Embedding Techniques: A Review

The paper discusses recent attempts to support the development of nervous materials based on structural health monitoring, augmented with corrective actions using actuators against any external effect or impending failure within the structure. This configuration features embedded sensors inside materials of structural importance e.g. metal and composites that could include comprehensive monitoring in terms of coverage area of the structure, variety of parameters to be measured, types of signals received and with fast information processing capabilities. Fast processing of information would allow the smart material to respond quickly and effectively to any external stimuli e.g. force, pressure or temperature. A review is provided to establish grounds to work on novel methods to embed off-the-shelf sensors for the development of smart material/structures. Actuation options have not been considered in this current review. Existing embedding technologies are reviewed for the sake of refining direction of research and possibilities on improvement of plausible methods. It is envisaged throughout this review to establish a clear understanding of the existing methods and develop improved and alternatives for performance improvement when developing smart and nervous materials.

Design and Analysis of a Magnetorheological Fluid Mount Featuring Uni-Directional Squeeze Mode

A magnetorheological fluid (MRF) mount featuring unidirectional squeeze mode for vehicle engine mounting system is proposed and designed to attenuate the engine vibration with characteristics of broadband and small amplitude. The MRF mount is comprised of upper and lower bases for installation, a main rubber for static load, a bobbin for electromagnetic coil winding and a squeeze plate. The bottom surface of the bobbin and the top surface of the squeeze plate form the polar plates, between which the MRF is squeezed during the rebound of the MRF mount. Combining dynamic stiffness property of passive hydraulic mounts without fluid and adjustable damping force of MRF at squeeze mode, the MRF mount could provide a unique variable dynamic stiffness and damping properties, by adjusting the exciting current. To evaluate the performance of the MRF mount, a mathematical model considering the behavior of MRF at squeeze mode is derived to theoretically analyze and numerically simulate the dynamic stiffness and equivalent damping properties of the MRF mount. Further, the MRF mount based quarter vehicle mounting system model considering suspension system is constructed to analyze the force transmissibility of engine mounting system in frequency domain and simulate the relative displacement response in time domain.