effect of electrospun pvdf fibers orientation for vibration sensing

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Carbon Nanotube Micropillars for Strain Sensing

A miniaturized strain sensor based on carbon nanotube (CNTs) micropillars is presented. The micropillars consist of square shaped forests of oriented CNTs sitting on Pt electrodes. The study focused on the analysis of the electron transport mechanisms and their correlation with the device geometry and deformation modes for increasing compression states (up to nearly 80% axial compression). The electrical resistance was found to be nonlinearly related to the device deformation in compression and decompression (full cycle). All tested devices were sensitive to deformations for an extremely wide range of strain values (significantly higher than conventional sensors), with a superior sensitivity for ultra-small deformations which makes them ideal for nanoscale sensing. Finally, it is believed that the CNTs micropillars have the potential to lead to strain sensing devices with a tuneable sensitivity and sensing range capability since the electron transport properties were found to be influenced by the device geometry

SELF-ACTUATED MORPHING COMPOSITE WITH TUNABLE FREQUENCY AND DAMPING

In this paper, an innovative approach is proposed to realize a morphing material with loadbearing capability that can self-activate with temperature. In particular the material can provide large-scale shape changes with fast response that can be induced with tuneable energy levels. The above properties are achieved with a simple and reliable multi-scale design of the material which leads to an effective morphing system

Auxetic Films with a Miniaturized Cellular Structure

Auxetic materials represent a relatively new class of materials that are characterized by a cellular structure and a negative Poisson coefficient. Auxetics are extremely useful for morphing applications thanks to their synclastic deformation capability. Most of these materials have been developed with macro-scaled cellular units. However there are some applications (e.g., micro-air vehicles or biomedical applications) for which polymeric morphing materials need to be applied in relatively small areas. In these cases, a material scale reduction that leads to lightweight auxetic films with a miniaturized cellular structure could be of great interest. With this in mind, an experimental study was conducted to analyze the response of films that are characterized by a miniaturized cellular structure. The unit cells in this study were made of an aggregation of microwires and micronodes that were strategically interconnected to form auxetic expansions and contractions. The reduction in scale of the cellular units has a significant impact on the material characterization and properties. The response of polymeric micro-scaled cells is in fact here demonstrated to be strongly influenced by surface forces and dramatic changes in gaseous or liquid environment. This represents the most critical aspect and key variation when comparing these films with standard macro-auxetics. The extremely challenging (at this length-scale) fabrication and testing processes were optimized. Single cells, were thus successfully tested in different environments with programmed and digital micro-stages while being monitored under a microscope with a video camera. Digital image correlation techniques were used to highlight the deformation. The expansion/contraction process was found to be fully reversible after several cycles and at different deformation speeds

A monolithic functional film of nanotubes/cellulose/ionic liquid for high performance supercapacitors

A novel monolithic, pre-fabricated, fully functional film made of a nanostructured free-standing layer is presented for a new and competitive class of easy-to-assemble flexible supercapacitors whose design is in-between the all solid state and the traditional liquid electrolyte. The film is made of two vertically aligned multi-walled carbon nanotube (VANT) electrodes that store ions, embedded-in, and monolithically interspaced by a solution of microcrystalline cellulose in a room temperature ionic liquid (RTIL) electrolyte (1-ethyl-3-methylimidazolium acetate-EMIM Ac). The fine tuning of VANTs length and electrolyte/cellulose amount leads, in a sole and continuous block, to ions storage and physical separation between the electrodes without the need of the additional separator layer that is typically used in supercapacitors. Thus, physical discontinuities that can induce disturbances to ions mobility, are fully eliminated significantly reducing the equivalent series resistance and increasing the knee frequency, hence outclassing the best supercapacitors based on VANTs and non-aqueous electrolytes. The excellent electrochemical response can also be addressed to the chosen electrolyte that, not only has the advantage of leading to a significantly simpler and more affordable fabrication procedure, but has higher ionic conductivity, lower viscosity and higher ions mobility than other electrolytes capable of dissolving cellulose

Shape-Changing Carbon Fiber Composite with Tunable Frequency and Damping

A shape-adaptable Carbon Fiber Reinforced Composite (CFRC) is proposed to derive a material with tunable mechanical properties in order to optimize its response to external excitations. The composite is bi-stable thanks to internal stresses arising in the manufacturing process and is characterized by a built-in heating system that can control the temperature of the material. This approach allows to gradually change the actual curvature of the material as well as tuning its natural frequencies and damping properties

Moving towards high-power, high-frequency and low-resistance CNT supercapacitors by tuning the CNT length, axial deformation and contact resistance

"In this paper it is shown that the electrochemical behaviour of vertically aligned multi-walled. carbon nanotube (VANT) supercapacitors is influenced by the VANTs’ length (electrode. thickness), by their axial compression and by their interface with the current collector. It is. found that the VANTs, which can be interpreted as a dense array of nanochannels, have an. active area available to ions that is strongly affected by the electrode’s thickness and. compressional state. Consequently, the tested thinner electrodes, compressed electrodes or a. combination of the two were found to be characterized by a significant improvement in terms. of power density (up to 1246%), knee frequency (58 822% working up to 10 kHz), equivalent. series resistance (ESR, up to 67%) and capacitance (up to 21%) when compared with thicker. and\/or uncompressed electrodes. These values are significantly higher than those reported in. the literature where long VANTs with no control on compression are typically used. It is also. shown that the ESR can be reduced not only by using shorter and compressed VANTs that. have a higher conductance or by improving the electrode\/collector electrical contact by. changing the contact morphology at the nanoscale through compression, but also by. depositing a thin platinum layer on the VANT tips in contact with the current collector (73%. ESR decrease)

Self-rechargeable Composite Structures with Carbon Nanoteubs Sueprcapacitors

Advances toward the development of light-weight fully electric aerospace structures leads to the need of replacing on-board batteries with lighter and more efficient energy storage devices and systems. Here a novel self-rechargeable multifunctional carbon fiber composite is presented. The composite has the capability to provide the required energy to the on-board equipment while keeping its structural integrity and strength, increasing its life-time and power capability and decreasing the global weight of the overall aerospace structure. The self-recharging capability is given by a series of miniaturized supercapacitor cells that are first prefabricated on a strategic support already integrated with the necessary circuitry and then are embedded in a cost-effective manner between the layers of the composite. Here it is also demonstrated that supercapacitor cells made with carbon nanotubes electrodes can become lighter and can provide superior performance by thinning its electrodes. For instance, going from 400m to 20m thick electrodes a 1246% power increase, a 21% specific capacitance increase and a 60% electrode resistance reduction were recorded. Moreover the ultra-thin supercapacitors were found to provide these high performance responses with a reaction speed about 30% superior than ever reported in the literature and over an extremely wide frequency range (up to 10KHz). This study is important because it shows for the first time the feasibility along with the great potential of realizing self-rechargeable light-weight structural composites that can work as great energy storage devices and can provide energy during critical flight conditions (e.g. during take-off) and recharge when less energy consumption is required