Microsized piston-cylinder pneumatic and hydraulic actuators fabricated by lithography

Future microrobotic applications require actuators that can generate a high actuation force in a limited volume. Up to now, little research has been performed on the development of pneumatic or hydraulic microactuators, although they offer great prospects in achieving high force densities. In addition, large actuation strokes and high actuation speeds can be achieved by these actuators. This paper describes a fabrication process for piston-cylinder pneumatic and hydraulic actuators based on etching techniques, UV-definable polymers, and low-temperature bonding. Prototype actuators with a piston area of 0.15 mm2 have been fabricated in order to validate the production process. These actuators achieve actuation forces of more than 0.1 N and strokes of 750 μm using pressurized air or water as driving fluid. © 2009 IEEE.

Design and characteristion of a hydraulic microactuator fabricated by lithography

To improve the force output of microactuators, this work focuses on actuators driven by pressurized gasses or liquids. Despite their well known ability to generate high actuation forces, hydraulic actuators remain uncommon in microsystems. This is both due to the difficulty of fabricating these microactuators with the existing micromachining processes and to the lack of adequate microseals. This paper describes how to overcome these limitations with a combination of anisotropic micromachining, UV definable polymers and low temperature bonding. The functionality of these actuators is proven by extensive measurements which showed that actuation forces of 0.1 N can be achieved for actuators with an active cross-section of 0.15 mm2. This is an order of magnitude higher than what is reported for classic MEMS actuators of similar size.

High performance nanocomposite thin film transistors with bilayer carbon nanotube-polythiophene active channel by ink-jet printing

Nanocomposite thin film transistors (TFTs) based on nonpercolating networks of single-walled carbon nanotubes (CNTs) and polythiophene semiconductor [poly [5, 5′ -bis(3-dodecyl-2-thienyl)- 2, 2′ -bithiophene] (PQT-12)] thin film hosts are demonstrated by ink-jet printing. A systematic study on the effect of CNT loading on the transistor performance and channel morphology is conducted. With an appropriate loading of CNTs into the active channel, ink-jet printed composite transistors show an effective hole mobility of 0.23 cm 2 V-1 s-1, which is an enhancement of more than a factor of 7 over ink-jet printed pristine PQT-12 TFTs. In addition, these devices display reasonable on/off current ratio of 105-10 6, low off currents of the order of 10 pA, and a sharp subthreshold slope (<0.8 V dec-1). The work presented here furthers our understanding of the interaction between polythiophene polymers and nonpercolating CNTs, where the CNT density in the bilayer structure substantially influences the morphology and transistor performance of polythiophene. Therefore, optimized loading of ink-jet printed CNTs is crucial to achieve device performance enhancement. High performance ink-jet printed nanocomposite TFTs can present a promising alternative to organic TFTs in printed electronic applications, including displays, sensors, radio-frequency identification (RFID) tags, and disposable electronics. © 2009 American Institute of Physics.

Analytical techniques for indentation of viscoelastic materials

Indentation of linearly viscoelastic materials is explored using elastic-viscoelastic correspondence analysis for both conical-pyramidal and spherical indentation. Boltzmann hereditary integrals are used to generate displacement-time solutions for loading at constant rate and creep following ramp loading. Experimental data for triangle- and trapezoidal-loading are examined for commercially-available polymers and compared with analytical solutions. Emphasis is given to the use of multiple experiments to test the fidelity and predictive capability of the obtained material creep function. Plastic deformation occurs in sharp indentation of glassy polymers and is found to complicate the viscoelastic analysis. A new method is proposed for estimating a material time-constant from peak displacement or hardness data obtained in pyramidal indentation tests performed at different loading rates.

Diverse 3D microarchitectures made by capillary forming of carbon nanotubes.

A new technology called capillary forming enables transformation of vertically aligned nanoscale filaments into complex three-dimensional microarchitectures. We demonstrate capillary forming of carbon nanotubes into diverse forms having intricate bends, twists, and multidirectional textures. In addition to their novel geometries, these structures have mechanical stiffness exceeding that of microfabrication polymers, and can be used as masters for replica molding

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 CNTs. © 2011 IEEE.