Development of all metal electrothermal actuator and its applications

The in-plane motion of microelectrothermal actuator ("heatuator") has been analyzed for Si-based and metallic devices. It was found that the lateral deflection of a heatuator made of a Ni metal is about ∼60% larger than that of a Si-based actuator under the same power consumption. Metals are much better for thermal actuators as they provide a relatively large deflection and large force, for a low operating temperature and power consumption. Electroplated Ni films were used to fabricate heatuators. The electrical and mechanical properties of electroplated Ni thin films have been investigated as a function of temperature and plating current density, and the process conditions have been optimized to obtain stress-free films suitable for microelectromechanical systems applications. Lateral thermal actuators have been successfully fabricated, and electrically tested. Microswitches and microtweezers utilizing the heatuator have also been fabricated and tested. © 2005 Society of Photo-Optical Instrumentation Engineers.

Microgripper using a diamond like carbon/metal bilayer

A novel normally closed microcage has been fabricated and characterized. This device was made from a highly compressively stressed diamond like carbon (DLC) and electroplated Ni bimorph structure. The large stress in the DLC causes the bimorph layer to curve once it is released from the substrate. The radius of curvature is in the range of 18 - 50μm, and can be controlled by varying the DLC and the Ni thicknesses. The devices can be operated in a pulsed mode current with low operation temperature, and can be opened by ∼60μm laterally with a power consumption of only ∼16mW. © 2004 IEEE.

Normally closed microgrippers based on diamond-like carbon/Ni bimorph and diamond-like carbon/metal/polymer trimorph structures

Multi-finger, normally-closed microgrippers made from a bilayer of a metal and diamond-like carbon (DLC) or a trilayer of a polymer, metal and DLC have been analysed, simulated and fabricated. Temperatures of ∼700 K are necessary to open Ni/DLC bimorph structures. Microgrippers made from an SU8/DLC bilayer or SU8/Al/DLC trilayer have also been fabricated, and fully closed microcages with diameters of ∑40 μm have been obtained. Using SU8 reduces the opening temperature of these devices to only ∼400 K.

Lateral field emitters fabricated using carbon nanotubes

We report on the fabrication of lateral emitters using carbon nanotubes (CNTs) grown via plasma enhanced chemical vapour deposition (PECVD). Carbon nanotubes are dispersed randomly onto a substrate, mapped, contacted with metal, and by etching the substrate, a suspended lateral emitter structure is formed. Field emission measurements from the lateral emitters show a turn-on voltage as low as 12 V. The emission characteristics showed good fits to the Fowler-Nordheim (FN) theory indicating that conventional field emission was indeed observed from these devices. © 2003 Elsevier Science B.V. All rights reserved.

Self-aligned split gate electrodes fabricated on suspended carbon nanotubes

We describe the fabrication of self-aligned split gate electrodes on suspended multiwalled carbon nanotube structures. A suspended multiwalled carbon nanotube structure was used as an evaporation mask for the deposition of metal electrodes resulting in the formation of discontinuous wire deposition. The metal deposits on the nanotubes are removed with lift-off due to the poor adhesion of metal to the nanotube surface. Using Al sacrificial layers, it was possible to fabricate self-aligned contact electrodes and control electrodes nanometers from the suspended carbon nanotubes with a single lithography step. It was also shown that the fabrication technique may also be used to form nano-gaped contact electrodes. The technique should prove useful for the fabrication of nano-electromechanical systems.

Study of multi-walled carbon nanotube structures fabricated by PMMA suspended dispersion

We report on the electrical characteristics of plasma enhanced chemical vapour deposition (PECVD)-grown, multi-walled carbon nanotube (MWCNT) devices made by a new fabrication method, PMMA suspended dispersion. This method makes it possible to suspend nanotubes between metal electrodes and to remove unwanted nanotubes from the substrate. The measurements show that the MWCNTs are metallic and able to maintain a current density ∼2×106 A/cm2 for more than 15 days with a maximum current density of ∼1.8×107 A/cm2. This high current density and reliability will make PECVD-grown MWCNTs applicable to field emission cathodes. © 2002 Elsevier Science B.V. All rights reserved.

Self-aligned split gate electrodes fabricated on suspended carbon nanotubes

We describe the fabrication of self-aligned split gate electrodes on suspended multiwalled carbon nanotube structures. A suspended multiwalled carbon nanotube structure was used as an evaporation mask for the deposition of metal electrodes resulting in the formation of discontinuous wire deposition. The metal deposits on the nanotubes are removed with lift-off due to the poor adhesion of metal to the nanotube surface. Using Al sacrificial layers, it was possible to fabricate self-aligned contact electrodes and control electrodes nanometers from the suspended carbon nanotubes with a single lithography step. It was also shown that the fabrication technique may also be used to form nano-gaped contact electrodes. The technique should prove useful for the fabrication of nano-electromechanical systems. © 2003 Materials Research Society.

The technical potential for reducing metal requirements through lightweight product design

Metal production consumes around 10% of all global energy, so is a significant driver of climate change and other concerns about sustainability. Demand for metal is rising and forecast to double by 2050 through a combination of growing total demand from developing countries, and ongoing replacement demand in developed economies. Metal production is already extremely efficient, so the major opportunities for emissions abatement in the sector are likely to arise from material efficiency - using less new metal to meet demand for services. Therefore this paper examines the opportunity to reduce requirements for steel and aluminium by lightweight design. A set of general principles for lightweight design are proposed by way of a simple analytical example, and are then applied to five case study products which cumulatively account for 30% of global steel product output. It is shown that exploiting lightweight design opportunities for these five products alone could reduce global steel requirements by 5%, and similar savings in aluminium products could reduce global aluminium requirements by 7%. If similar savings to those in the design case studies were possible in all steel and aluminium products, total material requirements could be reduced by 25-30%. However, many of these light-weighting measures are, at present, economically unattractive, and may take many years to implement. © 2011 Elsevier B.V. All rights reserved.

The practical feasibility of using RFID in a metal environment

Passive Radio Frequency Identification (RFID) has revolutionized the way in which products are identified. This paper considers the effect of metals on the performance of RFID at ultra high frequency (UHF). The paper establishes read patterns in space, highlighting the interference of RF waves due to three different metals, one ferrous and the other two non ferrous, when placed behind a transponder. The effect of thickness of the metal plate is also examined. Different metals have been found to have different interference effects although there are some similarities in their read patterns related to their material properties. Also experiments have been carried out to identify and establish various methods of improving this performance. Finally, differences between performance-measuring parameters, namely attenuating transmitted power and calculating read rate at a fixed attenuation are established and possible reasons of these observations are presented. © 2007 IEEE.

Fabrication of carbon nanotubes on inter-digitated metal electrode for switchable nanophotonic devices

This paper reports the modeling and characterization of interdigitated rows of carbon nanotube electrodes used to address a liquid crystal media. Finite Element Method modeling of the nanotube arrays was performed to analyze the static electric Fields produced to Find suitable electrode geometry. A device was fabricated based on the simulation results and electro optics characteristics of the device are presented. This Finding has applications in the development of micron and submicron pixels, precise beem steering and nanotube based active back planes.

Bulk forming of sheet metal

Ever increasing demands on functional integration of high strength light weight products leads to the development of a new class of manufacturing processes. The application of bulk forming processes to sheet or plate semi-finished products, sometimes in combination with conventional sheet forming processes creates new products with the requested properties. The paper defines this new class of sheet-bulk metal forming processes, gives an overview of the existing processes belonging to this class, highlights the tooling aspects as well as the resulting product properties and presents a short summary of the relevant work that has been done towards modeling and simulation. © 2012 CIRP.

Sintered metal foams for acoustic absorption

Metal foams fabricated via sintering offer novel mechanical and acoustic properties. Previously, polymer foams have been used as a means of absorbing acoustic energy. However, the structural applications of these foams are limited. The metal sintering approach offers a cost-effective means for the mass-production of open-cell metal foams. The static flow resistance of sintered metal foams was characterized for a range of practical pore sizes and porosities. The measured values for the flow resistance were subsequently used in a phenomenological acoustic model to predict the impedances and propagation constants of the foams. The predictions were then compared to acoustic measurements. At low frequencies (0-1000Hz), the phenomenological model captures the magnitude and frequency dependence of the absorption. At higher frequencies, as expected, the phenomenological model underpredicted the acoustic properties of the foams. However, an alternative microstructural model demonstrated good correlation to the measured results in this frequency range. The effects of foam type and arrangement on the absorption pattern were examined. General trends were identified for enhancing the low frequency performance of an acoustic absorber incorporating sintered foams.

Product life trade-offs: what if products fail early?

Increasing product life allows the embodied emissions in products to be spread across a longer period but can mean that opportunities to improve use-phase efficiency are foregone. In this paper, a model that evaluates this trade-off is presented and used to estimate the optimal product life for a range of metal-intensive products. Two strategies that have potential to save emissions are explored: (1) adding extra embodied emissions to make products more sturdy, increasing product life, and (2) increasing frequency of use, causing early product failure to take advantage of improvements in use-phase efficiency. These strategies are evaluated for two specific case studies (long-life washing machines and more frequent use of vehicles through car clubs) and for a range of embodied and use-phase intensive products under different use-phase improvement rate assumptions. Particular emphasis is placed on the fact that products often fail neither at their design life nor at their optimal life. Policy recommendations are then made regarding the targeting of these strategies according to product characteristics and the timing of typical product failure relative to optimal product life.