Friday, May 29, 2009

Cognitive Radio—the Basics

Cognitive Radio according to Wikipedia is the dynamic modification of the RF signal based on the spectrum, the user behavior, or the state of the network. It’s the logical next step after software defined radio in which the radio usage adjusts to the user and network’s needs. The idea here is that some parts of the spectrum are underutilized. By using cognitive radio techniques, unlicensed users can make use of licensed frequencies that have unused capacity—which is called Licensed Band Cognitive Radio.

There are variations of cognitive radio. The first is called Spectral Sensing Cognitive Radio in which only the radio frequency is monitored. Spectral sensing has been applied to TV channels in order to provide more bandwidth for high definition as well as emergency networks. The technique requires more than just detecting the energy in a channel. It requires a series of nodes to exchange information which is why research is moving towards Cognitive Networking.

The four main functions of Cognitive Radio are

1. Spectrum sensing –finding unused spectrum.
2. Spectrum management – finding the best available spectrum to use based on quality of service criteria.
3. Spectrum mobility –allowing for the shift from one frequency to another
4. Spectrum sharing – scheduling and sharing spectrum in a fair manner

Best regards,
Hall T.

Friday, May 22, 2009

Batteries Use Nanostructure Materials to Generate Power

As the need for portable power explodes due to the increasing number of mobile devices and the shift to alternative energies, battery technology receives substantial research funding and focus. In addition to improving safety, environmental impact, longevity, and power density, so battery makers seek ways to make the battery more malleable so they fit with portable devices and mobile applications.

Nanomaterials provide the structure for batteries. Using carbon nanotubes researchers are able to infuse paper with the ability to make a complete battery with the carbon acting as the electrodes. Medical device researchers are looking to sweat or blood as a potential electrolyte. Thus, by touching the paper, a person makes the paper a complete battery system. Medical researchers see applications in implantable devices in which the carbon nanotubes could be implanted just below the skin so the human body becomes the recharge mechanism for powering a defibrillator for example.

Another nano technique is to use copper nanorods as the active material and attach them to sheets of copper foil. This increases the energy capacity by increasing the surface area of the nanorods.

Application of these technologies can be done with fairly traditional machines. In this example the nanorods are treated like fibers that can be woven into the fabric of a soldier’s uniform and can recharge itself.

Another technology in the research phase is electrowetting which according to Wikipedia uses nanostructured materials to combine the electrolyte material into the electrode space. mPhase proposes to use the technology to power semiconductor based devices through the use of superhydrophobic techniques which combines a liquid electrolyte and active electrode material.

Best regards,
Hall T.

Friday, May 15, 2009

Higher Density Lithium-Ion Batteries for Hybrid Vehicle Use

Lithium ion batteries use cobalt for the positive electrode to achieve higher density. You can see a more detailed diagram here of a typical configuration along with a range of other materials used.

The key challenge is controlling thermal runaway when the separator material fails. That’s when the battery overheats. One solution is to add phosphate or other materials into the battery to help stabilize it.

For the hybrid vehicle application, Lithium-Ion is the current choice with research effort going into increasing the density of the battery so it lasts longer at a lower weight and size. Across the board, vendors are making higher density lithium-ion batteries including Hitachi, and Panasonic, to name a few.

There are other ways of improving Lithium-ion battery capability. In this paper, the authors use nanostructures to coat the cathode to increase the discharge factor of a battery. Another approach uses organic materials for the cathode instead of lithium metal oxides which makes the battery lighter and more environmentally friendly.

Best regards,
Hall T.

Thursday, May 07, 2009

Flexible Batteries That Never Need to Be Recharged

Another vector in the development of batteries is the combination of thin-film organic solar cell with a new type of polymer battery, which lets the battery charge itself with natural light. This works well on portable devices that one carries around as it can charge while it’s being used. Called flexible batteries the technology combines polymers and fullerenes into an ultra-thin, low-weight package. This ensures the device can recharge at even low-levels of light.

Flexible batteries based on polymer technology have been around for some time. Japanese researchers were showing off prototypes over two years ago.

Another technique uses nanocomposite materials carbon nanotubes which can be embedded into sheets of paper.

Best regards,
Hall T.