1,720,965 research outputs found
Metal-Free Multilayer Hybrid PENG Based on Soft Electrospun/-Sprayed Membranes with Cardanol Additive for Harvesting Energy from Surgical Face Masks
No full textDisposable surgical face masks are usually used by medical/nurse staff but the current Covid-19 pandemic has caused their massive use by many people. Being worn closely attached to the people's face, they are continuously subjected to routine movements, i.e., facial expressions, breathing, and talking. These motional forces represent an unusual source of wasted mechanical energy that can be rather harvested by electromechanical transducers and exploited to power mask-integrated sensors. Typically, piezoelectric and triboelectric nanogenerators are exploited to this aim; however, most of the current devices are too thick or wide, not really conformable, and affected by humidity, which make them hardly embeddable in a mask, in contact with skin. Different from recent attempts to fabricate smart energy-harvesting cloth masks, in this work, a wearable energy harvester is rather enclosed in the mask and can be reused and not disposed. The device is a metal-free hybrid piezoelectric nanogenerator (hPENG) based on soft biocompatible materials. In particular, poly(vinylidene fluoride) (PVDF) membranes in the pure form and with a biobased plasticizer (cardanol oil, CA) are electrospun onto a laser-ablated polyimide flexible substrate attached on a skin-conformable elastomeric blend of poly(dimethylsiloxane) (PDMS) and Ecoflex. The multilayer structure of the device harnesses the piezoelectricity of the PVDF nanofibers and the friction triboelectric effects. The ultrasensitive mechanoelectrical transduction properties of the composite device are determined by the strong electrostatic behavior of the membranes and the plasticization effect of cardanol. In addition, encapsulation based on PVDF, PDMS, CA, and parylene C is used, allowing the hPENG to exhibit optimal reliability and resistance against the wet and warm atmosphere around the face mask. The proposed device reveals potential applications for the future development of smart masks with coupled energy-harvesting devices, allowing to use them not only for anti-infective protection but also to supply sensors or active antibacterial/viral devices
Multifunctional sub-100 μm thickness flexible piezo/triboelectric hybrid water energy harvester based on biocompatible AlN and soft parylene C-PDMS-EcoflexTM
No full textNanogenerators have emerged recently as a new technology for harvesting energy from renewable and clean energy sources. Water in nature carries high amounts of kinetic and electrostatic energy; it is ubiquitous and widely accessible in different forms: i.e. as droplets, flows or waves. Either piezoelectric or triboelectric nanogenerators (PENGs, TENGs) have been shown to be effective for harvesting energy from liquids and ocean but the integration of both transduction mechanisms in a single hybrid device allows to exploit several operating conditions and to optimize performances, overcoming the limits of single components. Current piezo-tribo hybrid devices are mostly based on scarcely durable polymers or thick lead-based ceramic materials. Additionally, they are often limited to a specific application or environment due to their architecture and employed materials. In this work, a multifunctional, flexible and conformal hybrid nanogenerator (HNG) has been developed with a sub-100 μm thickness and with a novel combination of biocompatible thin-film piezo-ceramic and soft polymeric materials, for harvesting energy of different water sources, i.e. impacts, raindrops and buoying waves. The PENG component is based on a double-sided metallized AlN thin film, sputtered on polyimide. The TENG component is made of a metallized porous patch made of a mixture of PDMS and platinum-catalyzed silicone (EcoflexTM), encapsulated by a friction film of Parylene C surface-treated with UV/ozone. As a result, the HNG exhibits non-algebraic enhanced performances: the resulting power densities under tapping are ~ 6.5 mW/m2 for PENG, 65 mW/m2 for TENG, ~ 230 mW/m2 for HNG. Multifunctionality is demonstrated by harvesting energy from different water-conveyed sources (i.e. impacts/breakwaters, raindrops, buoying waves). In particular, the device shows optimal and reliable energy harvesting performance under strong impulsive impacts (~ 0.8 W/m2) and raindrops impacts (~ 9 mW/m2). A custom buoyant device, called piezo-JellyFish (pJF), is proposed to exploit the HNGs for harvesting wave energy, based on a connection of three HNGs acting as oral arms: this system yields ~ 3.2 mW/m2, with 3 cm-amplitude standing waves. Finally, the HNG exhibits optimal adhesion on the skin and can be also used for monitoring human motions, revealing its multifunctionality also as a wearable conformal sensor
Conformal, Ultra-thin Skin-Contact-Actuated Hybrid Piezo/Triboelectric Wearable Sensor Based on AlN and Parylene-Encapsulated Elastomeric Blend
No full textFlexible electronics based on piezoelectric/triboelectric devices is an attractive technology for human sensing. Their hybridization overcomes the limitations of single components, resulting in compliant skin sensors with enhanced performances and applicability. Such hybrid devices are typically based on wide-area scarcely durable polymers or lead-containing piezoelectric materials; they are often not biocompatible and poorly skin-adaptable, lacking in multifunctionality. In this work, a novel compliant, conformal hybrid piezoelectric-triboelectric ultra-thin wearable sensor made of biocompatible materials is reported. The device is in contact with skin through an ultra-soft patch covered on both sides by a thin friction parylene film. Its working principle is unprecedently based on three simultaneous, complementary and mutually enhancing effects: piezoelectric, skin-contact-actuation, and piezo-tribo hybrid contact. The device can detect, with high sensitivity and wide measurement range, both the impulsiveness of sudden motions and the slower micro-friction phenomena due to skin deformations, ensuring a stable and repeatable identification of bio-signals typical of body movements. The device multifunctionality is shown for identifying gait walking, distinguishing hand gestures with a 5-sensor system on the hand back, and monitoring human joints motions (neck, wrist, elbow, knee, ankle). The assessed energy harvesting capabilities demonstrate the suitability for fabrication of more complex self-powered sensing systems
Novel flexible triboelectric nanogenerator based on metallized porous PDMS and Parylene C
No full textTriboelectric nanogenerators (TENGs) have recently become a powerful technology for energy harvesting and self-powered sensor networks. One of their main advantages is the possibility to employ a wide range of materials, especially for fabricating inexpensive and easy-to-use devices. This paper reports the fabrication and preliminary characterization of a novel flexible triboelectric nanogenerator which could be employed for driving future low power consumption wearable devices. The proposed TENG is a single-electrode device operating in contact-separation mode for applications in low-frequency energy harvesting from intermittent tapping loads involving the human body, such as finger or hand tapping. The novelty of the device lies in the choice of materials: It is based on a combination of a polysiloxane elastomer and a poly (para-xylylene). In particular, the TENG is composed, sequentially, of a poly (dimethylsiloxane) (PDMS) substrate which was made porous and rough with a steam-curing step; then, a metallization layer with titanium and gold, deposited on the PDMS surface with an optimal substrate-electrode adhesion. Finally, the metallized structure was coated with a thin film of parylene C serving as friction layer. This material provides excellent conformability and high charge-retaining capability, playing a crucial role in the triboelectric process; it also makes the device suitable for employment in harsh, wet environments owing to its inertness and barrier properties. Preliminary performance tests were conducted by measuring the open-circuit voltage and power density under finger tapping (∼2 N) at ∼5 Hz. The device exhibited a peak-to-peak voltage of 1.6 V and power density peak of 2.24 mW/m2 at ∼0.4 MW. The proposed TENG demonstrated ease of process, simplicity, cost-effectiveness, and flexibility
Nanogenerators for harvesting mechanical energy conveyed by liquids
No full textThe huge mechanical energy available in the environment, mostly in form of kinetic energy of fluids such as wind, ocean and river currents or waves, is currently harvested by cumbersome, low efficiency and high environmental impact technologies. New approaches are needed for producing more compact and distributed mechanical energy converters. Nanogenerators and related micro and nanotechnologies can help in developing new environmentally friendly and biocompatible technologies. To face this challenge, new conversion physical principle, device structures and system architectures are currently being studied and developed. This work reviews the most recent advances on nanogenerators for harvesting energy transported by liquids in the environment such as water motion in rivers and marine environments and kinetic energy in rain. It discusses the most common physical transduction mechanisms, with a focus on piezoelectric and triboelectric nanogenerators (PENG/TENG), the requirements for producing flexible devices for effective conversion and the system architectures for optimizing the fluid-device interaction for producing large and fast oscillations, such as flapping, fluttering or galloping, from quasi-static or quasi-laminar fluid motion. Additionally, the work encompasses challenges such as waterproofing and antibiofouling, important issues in sub-marine and underwater environment
Microstructure and Electrical Properties of Novel piezo-optrodes Based on Thin-Film Piezoelectric Aluminium Nitride for Sensing
No full textThin-film piezoelectric materials are currently employed in micro-and nanodevices for energy harvesting and mechanical sensing. The deposition of these functional layers, however, is quite challenging onto non-rigid/non-flat substrates, such as optical fibers (OFs). Besides the recent novel applications of OFs as probes for biosensing and bioactuation, the possibility to combine them with piezoelectric thin films and metallic electrodes can pave the way for the employment of novel opto-electro-mechanical sensors (e.g., waveguides, optical phase modulators, tunable filters, energy harvesters or biosensors). In this work the deposition of a thin-film piezoelectric wurtzite-phase Aluminium Nitride (AlN), sandwiched between molybdenum (Mo) electrodes, on the curved lateral surface of an optical fiber with polymeric cladding, is reported for the first time, without the need of an orientation-promoting interlayer. The material surface properties and morphology are characterized by microscopy techniques. High orientation is demonstrated by SEM, PFM and X-ray diffraction analysis on a flat polymeric control, with a resulting piezoelectric coefficient (d33) of ∼5.4 pm/V, while the surface roughness Rms measured by AFM is 9 ÷ 16 nm. The output mechanical sensing capability of the resulting AlN-based piezo-optrode is investigated through mechanical buckling tests: The peak-To-peak voltage for weakly impulsive loads increases with increasing relative displacements (up to 30%), in the range of 20 ÷ 35 mV. Impedance spectroscopy frequency sweeps (10 kHz-1 MHz, 1 V) demonstrate a sensor capacitance of ∼8 pF, with an electrical Q factor as high as 150. The electrical response in the long-Term period (two months) revealed good reliability and durability
Flexible saw microfluidic devices as wearable ph sensors based on zno nanoparticles
Full text linkIn this work, a new flexible and biocompatible microfluidic pH sensor based on surface acoustic waves (SAWs) is presented. The device consists of polyethylene naphthalate (PEN) as a flexible substrate on which aluminum nitride (AlN) has been deposited as a piezoelectric material. The fabrication of suitable interdigitated transducers (IDTs) generates Lamb waves (L-SAW) with a center frequency ≈500 MHz traveling in the active region. A SU-8 microfluidics employing ZnO nanoparticles (NPs) functionalization as a pH-sensitive layer is fabricated between the IDTs, causing a shift in the L-SAW resonance frequency as a function of the change in pH values. The obtained sensitivity of ≈30 kHz/pH from pH 7 to pH 2 demonstrates the high potential of flexible SAW devices to be used in the measurement of pH in fluids and biosensing
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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