Soft Contact Materials Research Articles

Ultra-durable and high-output triboelectric nanogenerator based on coupling of soft-soft contact and volume effect

Output performance and durability are two key issues for the practical application of triboelectric nanogenerators (TENGs). Although the soft contact structure design is a preferred strategy currently for improving the working life of TENGs, it is difficult to achieve a high output performance. Exploring physical and chemical properties of soft contact materials is a reliable way to achieve ultra-durable and high-output TENGs. Herein, an advanced structure for soft-soft contact is designed by combining ultra-soft PU foam and a spring steel sheet. The soft-soft contact triboelectric nanogenerator (SS-TENG) maintains 100 % of the initial output after 1000,000 operation cycles. More importantly, the high leakage characteristics of PU foam enable the triboelectric charge to migrate up and down inside the dielectric material, significantly improving the output performance of the SS-TENG (charge density and peak power are 144 μC/m−2 and 178 mW, respectively). This study provided an effective approach for promoting the output and durability of TENGs. Meanwhile, this work offers a reliable solution for the development of self-powered sensor networks for smart agriculture.

Development of Environmentally Friendly Cellulose Derivative-Based Hydrogels for Contact Lenses Using a Radiation Crosslinking Technique

Although they have potential environmental pollution issues, soft contact lenses are value-added biodevices for medical use. Thus, it is important to reconsider starting materials and production methods to achieve sustainable development. In this study, hydrogels composed of hydroxypropyl cellulose (HPC) as an environmentally friendly material were produced by radiation and investigated for use in disposable soft contact lenses. HPC-based hydrogels with good mechanical properties and transparency were prepared by irradiation of electron beams on highly concentrated aqueous solutions containing HPC, polyethylene glycol #1000 dimethacrylate (23G), and 2-hydroxyethyl methacrylate (HEMA). The addition of 23G to HPC aqueous solutions resulted in an increase in the gel fraction as well as improved mechanical properties, such as tensile strength and elongation at break. The tensile strength and the elongation at break of HPC/HEMA/23G hydrogel obtained by the further addition of HEMA with HPC/23G aqueous solutions exhibited 0.2 MPa and 124%, which were approximately 2.0 and 1.8 times larger than these of the pure HPC hydrogel, respectively. The evaluation of the properties of the HPC/HEMA/23G hydrogel demonstrated its potential as a soft contact material with improved mechanical properties.

Middle Palaeolithic Percussive Tools from the Last Interglacial Site Neumark-Nord 2/2 (Germany) and the Visibility of Such Tools in the Archaeological Record

Despite a strong increase in the research on hominin percussive tool use, the primary focus in the study of technological behaviour still lies on flaked stone artefacts, especially for the Middle Palaeolithic. This paper aims to contribute to a more thorough understanding of the full spectrum of homi;nin technological behaviour, by presenting a systematic analysis of ground stone tools from the Last Interglacial Middle Palaeolithic site Neumark-Nord 2/2 (NN2/2) (Germany). At NN2/2, coarse gravel- and cobble-sized pieces (n = 351) were sourced from local outcrops of glacial deposits, with a preferential selection for quartzite and sandstone. Low-power use wear analysis and the archaeological context of these finds provide evidence for the possible use of at least 58 pieces for active (hammerstones) and 5 for passive (anvils) percussive tasks, specifically lithic production and potentially bone processing. These grounds stone tools are larger and heavier than the manuports. The hammerstones were preferentially made of quartz and quartzite, while the anvils are mostly of limestone. The limited build-up of use wear on the tools is interpreted as expedient use. The presence of post-depositional surface modifications, their relatively expedient use and their potential application on soft contact materials (e.g. nuts) resulted in a relatively low discernibility of the wear. With expediency being a key factor in Middle Palaeolithic lithic technology, we can expect comparable patterns for other similar-aged ground stone assemblages. Moreover, external factors, like geological context and raw material availability, post-depositional conditions and research focus and intensity, further contribute to the invisibility of such finds in the Middle Palaeolithic record.

A Complementary Dual-Contact MEMS Switch Using a “Zipping” Technique

This paper presents a microelectromechanical systems contact switch having both hard and soft contact materials in a single cantilever-type switching device. It operates with a zipping mechanism within which both contact materials (Pt-to-Pt and Au-to-Au) make individual contact sequentially and then detach in a reverse sequence to take advantage of both contact materials: low contact resistance and high reliability in a hot switching condition. In addition, an extended gate electrode and double T-shape cantilever beam structures effectively facilitate the sequential actuation. The fabricated switch successfully demonstrated a “dual-contact concept”-it made two sequential contacts at 31 (Pt-to-Pt) and 56 V (Au-to-Au) and it was then detached at 49 (Au-to-Au) and 23 V (Pt-to-Pt) in a single switching operation. Also, it achieved a low contact resistance of 0.3-0.5 Ω (including beam and some portion of the signal line resistances) at gate voltage from 60 to 70 V owing to the Au-to-Au contact in the device. Simultaneously, negligible contact resistance variation was observed during 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> cycles at a voltage/current level of 10 V/10 mA under hot switching and unpackaged environments, representing >100-fold longer lifetime than that of a conventional Au-to-Au cantilever switch fabricated on the same wafer.

Complementary Dual-Contact Switch Using Soft and Hard Contact Materials for Achieving Low Contact Resistance and High Reliability Simultaneously

This paper reports a dual-contact microelectromechanical switch, which consists of two contacts in a single switch: one with a soft contact material and the other with a hard contact material to achieve low contact resistance and high reliability at the same time under hot switching conditions. In a single switching operation, the proposed dual-contact switch makes contact twice in sequence, where the first contact is made with a hard contact material (Pt-to-Pt) that can withstand an abrupt hot switching condition (high electric field or micro-arcing). The second contact is then accomplished with the soft contact material (Au-to-Au) that has low-contact resistance, through which most of the current flows. In contrast, when the switch releases contact, the Au-to-Au contact is initially detached, and this is followed by the release of the Pt-to-Pt contact. In this way, the dual-contact switch showed longer lifetime than that of a single Au-to-Au contact-only switch by up to fortyfold, and even better lifetime than that of a single Pt-to-Pt contact-only switch by more than two times in open laboratory environments (unpackaged). At the same time, contact resistance of the dual-contact switch was under 0.3 Ω at 50 V of the gate voltage, which is more than seven times smaller than that of the single Pt-to-Pt contact-only switch (2.2 Ω), due to the Au-to-Au contact sub-switch (the contact resistance of the single Au-to-Au contact-only switch was 2.2 Ω).

Análisis de microhuellas de uso mediante Microscopio Electrónico de Barrido (MEB) de artefactos óseos de un sitio Arcaico tardío del valle de Mauro (Región de Coquimbo, Chile): Aportes para una reconstrucción contextual

This paper presents the results of Scanning Electron Microscope (SEM) analysisperformed on seven bone tools from MAU085, a Late Archaic site in the semiarid northof Chile (31o 57` S-71o 01`O, IV Region). The main objective of this analysis was todetermine the function of a set of bone tools and their relation with the morphologicalvariability identified. Given prior hypothesis linking the functionality of these bonetools to flaking and resharpening of projectile points and cutting artifacts, we soughtcomplementary information in both artefactual and ecofactuals evidence, specificallythe lithic remains. Analysis by Scanning Electron Microscope shows that the bonetools studied were used in lithic as well as soft contact materials such as leather/skinand textile fibers, thus expanding the use of artefacts traditionally considered boneretouchers.

Design theory analysis of biface technology at the Botanie Lake Dam site (EcRj 15), south-central British Columbia

Editor’s note: This article appears as a reprint from Volume 18 due to printing errors. Nexus apologizes to the author for the delay in publishing the work in its entirety. A design analysis is applied to six bifacial tools recovered from the Botanie Lake Dam site (EcRj 15) on the Plateau of southern British Columbia. While these artifacts, selected from the lithic assemblage of this late pre-contact period mat lodge campsite, show some internal variation, they share important characteristics indicative of their use by Plateau peoples. Acute edge angles and less durable raw material suggests that these bifacial tools were used to cut relatively soft contact materials such as herbaceous plants. Their lengthy use lives and multifunctionality make them effective solutions for the requirements of plant and animal processing during a mobile seasonal round. This application of design theory to a small sample of lithic artifacts from a seasonal camp site with an hypothesized focus on root resource harvesting and processing adds to the growing number of studies employing this approach to lithic analysis.

Active Opening Force and Passive Contact Force Electrostatic Switches for Soft Metal Contact Materials

This paper reports on a mechanically bi-stable, electrostatically actuated switch mechanism with a large active opening force and a small passive closing force, designed to fit the contact and opening force requirements of soft contact materials such as gold. So far, most microelectromechanical systems (MEMS) switch designs have been optimized for a large contact force without paying too much attention to the opening force. In the "conventional," most commonly used electrostatic microswitch concept, the force of the actuator is used to close the switch contacts, and the switch is opened by the passive restoring force of the deflected cantilever or membrane. This concept results in a large contact force, but the opening force is typically too small to overcome the contact adhesion force of soft metals, which makes this concept less suitable for contact materials such as gold with its low contact resistance at low contact forces. The switch concept presented in this paper is based on two cantilevers laterally moving by curved electrode actuators. The tips of the cantilevers are endowed with hooks which can be mechanically interlocked. In the latched state, the spring forces of the deflected cantilevers also act as the passive contact force between the switch contacts. The opening force is actively created by the curved-electrode actuators, which are utilized close to their best electromechanical operating point resulting in a maximum contact separation force. The theoretical discussion of the new concept as compared to conventional switch designs is supported by simulation results, measurements on fabricated devices, and by an analysis of exemplary switches published in the literature

Design Theory Analysis of Biface Technology at the Botanie Lake Dam Site (EcRj 15), South-Central British Columbia

A design analysis is applied to six bifacial tools recovered from the Botanie Lake Dam site (EcRj 15) on the Plateau of southern British Columbia. While these artifacts, selected from the lithic assemblage of this late pre-contact period mat lodge campsite, show some internal variation, they share important characteristics indicative of their use by Plateau peoples. Acute edge angles and less durable raw material suggests that these bifacial tools were used to cut relatively soft contact materials such as herbaceous plants. Their lengthy use lives and multifunctionality make them effective solutions for the requirements of plant and animal processing during a mobile seasonal round. This application of design theory to a small sample of lithic artifacts from a seasonal camp site with an hypothesized focus on root resource harvesting and processing adds to the growing number of studies employing this approach to lithic analysis.

On the use of ceramic PVD coatings to replace metallic coatings in electrical contacts

In electrical contacts the combination of high normal pressures and soft contact materials results in large contact areas and low contact resistance, but also in massive plastic deformation and wear. This paper examines some of the potential advantages and disadvantages of replacing one of the soft metallic coatings in electrical power connectors with a hard ceramic coating. Three ceramic PVD coatings (Ti/TiN, Nb/NbN and CrN) all 2–3 μm thick, deposited on copper, were laboratory tested under fretting conditions against a silver coating and compared with the corresponding traditional contact between two silver surfaces. The model contact consisted of two crossed cylinders (Ø 10 mm) continuously powered with 10 a d.c. Five combinations of normal force (20–60 N) and vibration stroke (15–30 μm), all resulting in gross weld regime fretting for silver mated to silver [1,2], were tested. The fretting contacts were primarily studied with respect to contact resistance behaviour and silver surface damage. Despite the relatively high resistivity of the ceramic materials the contact resistance levels were quite low. This is primarily due to the extensive contact area growth during fretting out also due to the fretting aiding in removing thin oxide or corrosion films from the ceramic coating surface. Furthermore, the silver deformation was less severe in the silver-to-ceramic contact than in the corresponding silver-to-silver contact. For comparison, the influence of thin coatings of relatively high resistivity on the electrical potential and the temperature distributions was investigated using a single-spot contact finite element model.

高強度ステンレス鋼のフレッティング疲労特性

Fretting fatigue tests of high strength stainless steel 440C were carried out to investigate the basic properties of fretting fatigue and the effects of contact material and variable loading on fretting fatigue strength. The fatigue life and the fatigue limit of 440C steel decreased significantly under the fretting fatigue condition. A soft contact material was effective to improve the fretting fatigue strength. The difference in fatigue life among contact materials will be caused by the difference in the concentration of frictional force in the edge region of contact surface: The softer the contact material, the lower the concentration of frictional force. Therefore, the softer contact material induces the lower acceleration of crack growth rate, and gives the higher fatigue limit and the longer fatigue life. The modified Miner's rule seemed to hold in the case of fretting fatigue under a program loading simulating the actual load of bearing for airplane.