Dielectric elastomer actuators which consist of an electrode/dielectric elastomer/electrode sandwich structure show
greater than 100% electromechanical strain performance when high electrical field is applied. The strain in the dielectric
elastomer film occurs due to attraction of opposite charges across the dielectric film and repulsion of similar charges on
each compliant electrode. Structural defects present in these elastomers such as gel particles, uneven thickness, and stress
concentration may cause dielectric breakdown, leading to premature failure during continuous or repeated actuations.
Dielectric breakdown consequently reduces production yield and device lifetime. Carbon nanotubes (CNTs) have been
introduced as compliant electrodes for dielectric elastomers. Higher than 100% electromechanical strain was obtained
with ultrathin CNT electrodes due to the high aspect ratio and the high electrical conductivity of the nanotubes. These
ultrathin CNT electrodes also exhibit fault-tolerance in dielectric elastomers through the local degradation of CNTs
during dielectric breakdown. The degraded areas electrically isolate the defects, while keeping the rest of the elastomer
active. The "self-clearing" electrodes significantly increase the lifetime of the dielectric elastomers, making the dielectric
elasomer actuator much more reliable.
Dielectric elastomer actuators exert strain due to an applied electric field. With advantageous properties such as high efficiency and their light weight, these actuators are attractive for a variety of applications ranging from biomimetic robots, medical prosthetics to conventional pumps and valves. The performance and reliability however, are limited by dielectric breakdown which occurs primarily from localized defects inherently present in the polymer film during actuation. These defects lead to electric arcing, causing a short circuit that shuts down the entire actuator and can lead to actuator failure at fields significantly lower than the intrinsic strength of the material. This limitation is particularly a problem in actuators using large-area films. Our recent studies have shown that the gap between the strength of the intrinsic material and the strength of large-area actuators can be reduced by electrically isolating defects in the dielectric film. As a result, the performance and reliability of dielectric elastomers actuators can be substantially improved.
Electronic detection of biomolecules is gradually emerging as effective alternative of optical detection methods. We describe transistor devices with carbon nanotube conducting channels that have been used for biosensing and detection. Both single channel field effect transistors and devices with network conducting channels have been fabricated and their electronic characteristics examined. Device operation in (conducting) buffer and in a dry environment - after buffer removal - is also discussed. The devices readily respond to changes in the environment, such effects have been examined using gas molecules and coating layers with specific properties. Finally the interaction between devices and biomolecules will be summarized. The application of devices for detecting biological processes and bio-electronic integration is described in the paper 5593-07.
Nanoscale electronic devices offer bio-detection schemes that are complementary to optical detection methods. This paper reviews the utilization of field effect transistor devices with carbon nanotubes as conducting channels - the device architectures and detection schemes are reviewed in the paper 5592-34 presented at this meeting- for the detection and monitoring biological processes such as ligand-receptor interactions and enzymatic processes. A complex device with both biological and electronic functionality is also discussed.
We discuss two types of resonant techniques for measuring the electrodynamic properties of conductors in the millimeter and sub-millimeter wave spectral ranges. Using a series of backward wave oscillator sources, we can obtain essentially complete coverage of the frequency range 30 - 1000 GHz. At 100 GHz and below, cylindrical cavity resonators operating the in their TE011 mode are employed to measure both components of the complex surface impedance of bulk samples. Above approximately 100 GHz, a Fabry-Perot resonator, consisting of a sapphire plate with a conducting sample placed against one side, is used. Both thin film and bulk samples may be measured with this technique. We focus on measurement on thin film samples, where the complex conductivity can be obtained directly from the transmission spectra.
I will contrast the eleczodynarnics as explored by experiments in the millimeter wave spectre range, of conventional superconductors, such as Pb and Nb and high temperature superconductors. While in the low temperature superconductors the response is in full agreement with predictions based on the BCS ground state, significant differences between theory and experiments are observed for high temperature superconductors. The possible reason for this behavior will be digcussed,
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