Image: CNT emitter ray
Long range communications are a vital part of our lives for business, entertainment or just keeping in contact with friends and family. Much of this, especially to remote areas, is made possible through communications using satellite-based transmitters. There are typically 50 microwave amplifiers on board a satellite, each weighing about 1kg and measuring about 30cm in length.
Currently it costs about 10,000 pounds sterling to send a single kilogram of payload (data) into space. There is an advantage, both in terms of cost savings and extra payload which can be carried, if the weight and size of the microwave devices are reduced.
The microwave amplification devices used in space today are based on what's known as hot cathode technology. Ken and his team have demonstrated that a cold cathode source, based on carbon nanotube technology, can deliver electrons directly at microwave, that is gigahertz, frequencies and hence can be utilized in these microwave devices without delay, with potential weight and size savings of up to 50%. This will not only reduce the cost and increase the capability of conventional satellite systems, but will also enable the drive towards very low cost micro-satellites which weigh about 10kg.
Right: High frequency CNT cathode
Carbon nanotubes are graphite sheets of carbon which are rolled up to form tubes. These tubes have diameters which are in the nanometer range and lengths from the micron to millimeter range. Carbon nanotubes are extremely conductive and have great mechanical strength. Ken and his team use carbon nanotubes as very sharp, highly conductive needles. The nanotubes are laid out into an array, with every nanotube having roughly the same height and diameter. They look like a bed of needles, but at the nanoscale. When these carbon nanotube needles are subjected to an electric field, such as that from an electromagnetic wave, they release electrons from their tips. By injecting radio frequency waves at the nanotubes, they are able to cycle them on and off at the frequency of the injected wave and thus create an electron beam at high frequency. They have done this at 1.5GHz and recently at 32GHz as well. Frequencies of 30Ghz and above, where there are plentiful channels, are where the communication links of the future will reside.
The new cold cathode source is very different from conventional hot cathode amplifiers. These have 4 parts: the direct current hot cathode electron source at 1000 degrees centigrade which generates a constant stream of electrons; an input stage to impose the signal onto the electrons; an output stage to retrieve the amplified signal from the electrons; and finally a collector stage to catch any wasted electrons. They are bulky, heavy, inefficient and slow to heat up.
In summary the advantages of this new carbon nanotube source are as follows. No heating is required and the source can be turned on and off instantaneously. The source and input stages of the microwave amplifier are also combined, producing a size and weight reduction. Finally, the whole concept of operation is different. With the conventional hot cathode source, we have a stream of electrons in which the electrons are modulated by speed to create bunches, and it is these bunches which are extracted as useful output. With the new cold cathode carbon nanotube source, the electrons bunches are instantaneously created at the source.
For more information please go to
http://www-g.eng.cam.ac.uk/cnt
Source: University of Cambridge
Related stories:
Ocean Wind Power Maps Reveal Possible Wind Energy Sources
Efforts to harness the energy potential of Earth's ocean winds could soon gain an important new tool: global satellite maps from NASA. Scientists have been creating maps using nearly a decade of data from NASA's QuikSCAT satellite that reveal ocean areas where winds could produce wind energy.
Brightest X-ray Vision at the Nano-scale
Technology-development studies at Cornell University and Jefferson Laboratory are showing how to use the brightest X-ray light ever generated for the scientific examination of everything from human proteins to forged art.
Satellites illuminate pollution's influence on clouds
Clouds have typically posed a problem to scientists using satellites to observe the lowest part of the atmosphere, where humans live and breathe, because they block the satellite's ability to capture a clear, unobstructed view of Earth's surface. It turns out, however, that these "obstructions" are worth a closer look, as clouds and their characteristics actually serve a valuable role in Earth's climate. That closer look is now available by satellites comprising the Afternoon Constellation, or A-Train.
MIT professor will lead science team for NASA satellite to map Earth's water cycle
MIT Professor Dara Entekhabi will lead the science team designing a NASA satellite mission to make global soil moisture and freeze/thaw measurements, data essential to the accuracy of weather forecasts and predictions of global carbon cycle and climate. NASA announced recently that the Soil Moisture Active-Passive mission (SMAP) is scheduled to launch December 2012.
The future of computing -- carbon nanotubes and superconductors to replace the silicon chip
The future of computing is under the spotlight at the Institute of Physics’ Condensed Matter and Materials Physics conference at the Royal Holloway College of the University of London on 26-28 March.
Study confirms 1966 prediction: The most energetic particles in the universe are not from the neighborhood
Final results from the University of Utah’s High-Resolution Fly’s Eye cosmic ray observatory show that the most energetic particles in the universe rarely reach Earth at full strength because they come from great distances, so most of them collide with radiation left over from the birth of the universe.
Study: Dark matter in newborn universe doused earliest stars
“Dark star crashes, pouring its light into ashes” – The Grateful Dead, 1967. Perhaps the first stars in the newborn universe did not shine, but instead were invisible “dark stars” 400 to 200,000 times wider than the sun and powered by the annihilation of mysterious dark matter, a University of Utah study concludes.
NASA Goddard Space Flight Center's carbon nanotube manufacturing technology wins Nano 50 Award
NASA Goddard Space Flight Center in Greenbelt, Md. announced that its method for manufacturing high-quality carbon nanotubes (CNT) has been named a winner in the third annual Nanotech Briefs Nano 50 awards in the Technology category. This award will be celebrated at the Nano 50 awards dinner November 14 at the NASA Tech Briefs National Nano Engineering Conference (NNEC 2007) in Boston, Mass.
