Encapsulated thermoacoustic projector based on freestanding carbon nanotube film

A suspended nanotube film (or films) producing sound by means of the thermoacoustic (TA) effect is encapsulated between two plates, at least one of which vibrates, to enhance sound generation efficiency and protect the film. To avoid the oxidation of carbon nanotubes at elevated temperatures and reduce the thermal inertia of surrounding medium the enclosure is filled with inert gas (preferably with high heat capacity ratio, γ=Cp/Cv, and low heat capacity, Cp). To generate sound directly as the first harmonic of applied audio signal without use of an energy consuming dc biasing, an audio signal modulated carrier frequency at much higher frequency is used to provide power input. Various other inventive means are described to provide enhanced projected sound intensity, increased projector efficiency, and lengthened projector life, like the use of infrared reflecting coatings and particles on the projector plates, non-parallel sheet alignment in sheet stacks, and cooling means on one projector side.Board of Regents, University of Texas Syste

Electrochemical artificial muscle yarns and textiles that harvest and store environmentally available energies

Mechanical energy harvesters are needed for such diverse applications as self-powered wireless sensors, structural and human health monitoring systems, and cheaply harvesting energy from ocean waves. The here reported nanofiber yarn harvesters can electrochemically convert tensile or torsional mechanical energy into electrical energy. Stretching coiled yarns generated 250 W/kg of peak electrical power when cycled up to 30 Hz, and up to 41.2 J/kg of electrical energy per mechanical cycle, when normalized to the weight of the harvester yarn. Unlike for other harvesters, torsional rotation produces both tensile and torsional energy harvesting and no bias voltage is required, even when electrochemically operating in salt water. Since homochiral and heterochiral coiled harvester yarns provide oppositely directed potential changes when stretched, both contribute to output power in a dual-electrode yarn. These energy harvesters were used in the ocean to harvest wave energy, combined with thermally-driven artificial muscles to convert temperature fluctuations to electrical energy, sewn into textiles for use as self-powered respiration sensors, and used to power a LED and to charge a storage capacitor. The development of “piezoelectrochemical spectroscopy” and insights into the hierarchical origins of capacitance increased fundamental understanding. When run in the reverse direction, these muscle types can provide powerful artificial muscles, and the same fibers used as harvesters and muscles can be used to store electrical energy. This work is collaborative with researchers at Hanyang University, University of Texas at Dallas, Lintec of America; Jiangnan Graphene Research Institute, Virginia Tech, and the Wright-Patterson Air Force Research Laboratory

Powerful artificial muscles for morphing composites and other applications

Three successive generations of twist-spun artificial muscles are described and used to make morphing composites and textiles that are electrically, thermally, or chemically powered.1 Our first generation of twist-spun muscles, which are electrochemically powered by volume changes induced by double-layer charge injection, provide torsional rotation speeds of 590 rpm, and torsional strokes of 250° per millimeter of actuator length, which is 1000 times that for earlier artificial muscles. Our second generation muscles, which require no electrolyte and are based on guest-infiltrated carbon nanotube yarns, can torsionally actuate at 11,500 rpm and deliver 85 times higher power density during contraction than natural muscles. Our third generation muscles, which are thermally, electrothermally, or chemically powered polymer fibers, can rotate a heavy rotor to above 70,000 rpm, contract by up to 49%, generate 5 times the gravimetric power of a car engine, lift 100 times heavier loads than the same length and weight human muscle, or actuate at 7.5 cycles/s for millions of cycles. These polymer muscles can be cheaply made from fishing line or sewing thread. Demonstrated applications using these muscles include peristaltic pumps based on polymer muscle composites; self-powered valves that automatically open and close depending on fluid temperature or composition; torsional and tensile electrical energy harvesters for converting low-grade thermal energy into electrical energy; environmentally powered windows that open and close depending upon temperature; and morphing textiles for comfort adjusting clothing. The combination of theory and experiment will be used to explain and optimize actuation for muscles that are highly twisted or so highly twisted that they coil

Carbon nanotube foils for electron stripping in tandem accelerators

Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 261 (2007): 44-48, doi:10.1016/j.nimb.2007.03.023.Carbon nanotube technology has rapidly advanced in recent years, making it possible to create meter-long, ~4 cm wide films of multi-walled tubes of less than 3 μg/cm2 areal density in a bench top open-air procedure [1]. The physical properties of individual carbon nanotubes have been well established, equaling or surpassing electrical and thermal conductivity and mechanical strength of most other materials, graphite in particular. The handling and transport of such nanotube films, dry-mounted self-supporting on metal frames with several cm2 of open area, is problem-free: the aerogel films having a volumetric density of about 1.5 mg/cm3 survived the trip by car and air from Dallas to Oak Ridge without blemish. In this paper we will present the results of first tests of these nanotube films as electron stripper media in a tandem accelerator. The tests were performed in the Model 25 URC tandem [2] of the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory. We will discuss the performance of nanotube films in comparison with chemical vapor deposition and laser-ablated carbon foils.This work was supported by a grant from the “Cecil H. and Ida M. Green Technology Innovation Awards” program of the Woods Hole Oceanographic Institution and in part by the U.S. National Science Foundation through Cooperative Agreement 82899613 and the Robert A. Welch Foundation grant AT-0029

Carbon nanotube electroactive polymer materials: opportunities and challenges

Carbon nanotubes (CNTs) with macroscopically ordered structures (e.g., aligned or patterned mats, fibers, and sheets) and associated large surface areas have proven promising as new CNT electroactive polymer materials (CNT-EAPs) for the development of advanced chemical and biological sensors. The functionalization of CNTs with many biological species to gain specific surface characteristics and to facilitate electron transfer to and from them for chemical- and bio-sensing applications is an area of intense research activity. Mechanical actuation generated by CNT-EAPs is another exciting electroactive function provided by these versatile materials. Controlled mechanical deformation for actuation has been demonstrated in CNT mats, fibers, sheets, and individual nanotubes. This article summarizes the current status and technological challenges for the development of electrochemical sensors and electromechanical actuators based on carbon nanotube electroactive materials

Multifunctional Characteristics of Carbon Nanotube (CNT) Yarn Composites

By forming composite structures with Carbon Nanotube (CNT) yarns we achieve materials capable of measuring strain and composite structures with increased mechanical strength. The CNT yarns used are of the 2-ply and 4-ply variety with the yarns having diameters of about 15-30 micrometers. The strain sensing characteristics of the yarns are investigated on test beams with the yarns arranged in a bridge configuration. Additionally, the strain sensing properties are also investigated on yarns embedded on the surface of a flexible membrane. Initial mechanical strength tests also show an increase in the modulus of elasticity of the composite materials while incurring a weight penalty of less than one-percent. Also presented are initial temperature characterizations of the yarns