Fabrication and electrical integration of robust carbon nanotube micropillars by self-directed elastocapillary densification

Vertically-aligned carbon nanotube (CNT) "forest" microstructures fabricated by chemical vapor deposition (CVD) using patterned catalyst films typically have a low CNT density per unit area. As a result, CNT forests have poor bulk properties and are too fragile for integration with microfabrication processing. We introduce a new self-directed capillary densification method where a liquid is controllably condensed onto and evaporated from CNT forests. Compared to prior approaches, where the substrate with CNTs is immersed in a liquid, our condensation approach gives significantly more uniform structures and enables precise control of the CNT packing density and pillar cross-sectional shape. We present a set of design rules and parametric studies of CNT micropillar densification by this method, and show that self-directed capillary densification enhances the Young's modulus and electrical conductivity of CNT micropillars by more than three orders of magnitude. Owing to the outstanding properties of CNTs, this scalable process will be useful for the integration of CNTs as functional material in microfabricated devices for mechanical, electrical, thermal, and biomedical applications

Synergistic Degradation Mechanism in Single Crystal Ni-Rich NMC//Graphite Cells

Acknowledgments We acknowledge Diamond Light Source for time on beamline I09 under Proposals SI30201-1 and SI30201-2. This work is supported by the Faraday Institution under Grants FIRG044, FIRG024, and FIRG060.Peer reviewedPublisher PD

Programmable transformation of vertically aligned carbon nanotubes into 3D microstructures

Capillary forming of carbon nanotubes (CNTs) enables the fabrication of unique 3D microstructures over large areas. In this paper we focus on the simulation as well as on the integration of these structures in MEMS devices. We developed finite element models (FEM) that enables qualitative prediction of shape transformations caused by capillary forming; and show how capillary formed CNT structured can be integrated with conventional lithographic processing for patterning of polymers and metals in concert with CNTsstatus: publishe

Pneumatic and hydraulic microactuators : a new approach for achieving high force and power densities at microscale

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Pneumatic and hydraulic microactuators : a new approach for achieving high force and power densities at microscale

Gedurende afgelopen decennia heeft het onderzoek naar microsystemen zich voornamelijk toegespitst op de ontwikkeling van electrostatische en elektromagnetische microactuatoren. Recente ontwikkelingen hebben echter uitgewezen dat hydraulische en pneumatische aandrijvingen hogere kracht- en vermogendichtheden kunnen realiseren in systemen die maar een paar kubieke millimeters groot zijn. Tot hiertoe zijn deze actuatoren slechts zelden toegepast in microsystemen omwille van twee belangrijke technologische uitdagingen. Eerst en vooral dienen microafdichtingen ontwikkeld te worden die in staat zijn om hoge drukken lekvrij af te sluiten, zonder daarbij wrijving in de aandrijving te introduceren. Ten tweede moeten er specifieke productietechnieken onderzocht worden om nauwkeurige tolerantie op driedimensionale micro-onderdelen te kunnen realiseren, hetgeen moeilijk is met behulp van traditionele microproductietechnieken. Gedurende dit onderzoek zijn een aantal klassieke afdichtingen zoals hermetische- en lipafdichtingen voor het eerst toegepast op miniatuur pneumatische en hydraulische aandrijvingen. Hiernaast zijn een aantal nieuwe afdichtingen ontwikkeld specifiek voor microtoepassingen. In het bijzonder laten oppervlaktespanning- en ferrofluïdum-afdichtingen toe om microsystemen lekvrij en met weinig wrijving af te dichten. Actuatoren met een buitendiameter van 1.3 mm en een lengte van 13 mm zijn in staat om een aandrijfkracht van 1 N, een snelheid tot 1 m/s en een slag van 10 mm te realiseren bij een aandrijfdruk van 15 bar. De kracht- en vermogendichtheid van deze systemen is beduidend hoger dan dat van klassieke microactuatoren met gelijkaardige afmetingen. Gedurende dit onderzoek werd ook een inductieve positiesensor ontwikkeld die efficiënt in hydraulische en pneumatische microactuatoren kan worden ingebouwd. Met behulp van PI- en variabele structuurcontrole laat deze sensor toe om tot op 30 µm nauwkeurig te positioneren. Dit is een anzienlijke verbetering in vergelijking met gelijkaardige systemen die in de literatuur beschreven zijn. Daarom behoren de hier ontwikkelde actuatoren tot de krachtigste bestaande mechatronische microaandrijvingen.status: publishe

Pneumatic and hydraulic microactuators: a review

The development of MEMS actuators is rapidly evolving and continuously new progress in terms of efficiency, power and force output is reported. Pneumatic and hydraulic are an interesting class of microactuators that are easily overlooked. Despite the 20 years of research, and hundreds of publications on this topic, these actuators are only popular in microfluidic systems. In other MEMS applications, pneumatic and hydraulic actuators are rare in comparison with electrostatic, thermal or piezo-electric actuators. However, several studies have shown that hydraulic and pneumatic actuators deliver among the highest force and power densities at microscale. It is believed that this asset is particularly important in modern industrial and medical microsystems, and therefore, pneumatic and hydraulic actuators could start playing an increasingly important role. This paper shows an in-depth overview of the developments in this field ranging from the classic inflatable membrane actuators to more complex piston-cylinder and drag-based microdevices. © 2010 IOP Publishing Ltd.status: publishe

Design of a linear hydraulic microactuator

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A hybrid surface tension seal for pneumatic and hydraulic microactuators

Recent research revealed that microactuators driven by pressurized fluids are able to generate high power and force densities at microscale. One of the main technological barriers in the development of these actuators is the fabrication low friction seals. This paper presents a novel scalable seal technology, which resists the actuation pressure relying on a combination of a clearance seal and a surface tension seal. This approach allows to seal pressures of more than 800 kPa without leakage. The seal is tested on an actuator with a bore of 0.8 mm2 and a length of 13 mm, which was able to generate forces up to 0.32 N. © 2008 Springer-Verlag.status: publishe

Development of a hybrid ferrofluid seal technology for miniature pneumatic and hydraulic actuators

Future microrobotic applications require actuators that can generate a high actuation force and stroke in a limited volume. Up to now, little research has been performed on the development of pneumatic and hydraulic microactuators, although they offer great prospects in achieving high force densities. One of the main technological barriers in the development of these actuators is the fabrication of powerful seals with low leakage. This paper presents a seal technology for linear fluidic microactuators based on ferrofluids. A design and simulation method for these seals has been developed and validated by measurements on miniaturized actuator prototypes. These actuators have an outside diameter of 2 mm, a length of 13 mm and have been tested using both pressurized air and water. Our current actuator prototypes are able to operate at pressures up to 1.6 MPa without leakage. At these pressures, forces up to 0.65 N have been achieved. The stroke of the actuators is 10 mm. © 2009 Elsevier B.V. All rights reserved.status: publishe

A ferrofluid seal technology for fluidic microatuators

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