Friday, June 19, 2009

The Saser is like a laser, but for sound

It was an idea born out of curiosity in the physics lab, but now a new type of ‘laser’ for generating ultra-high frequency sound waves instead of light has taken a major step towards becoming a unique and highly useful 21st century technology.

Scientists at The Univ. of Nottingham, in collaboration with colleagues in the Ukraine, have produced a new type of acoustic laser device called a Saser. It’s a sonic equivalent to the laser and produces an intense beam of uniform sound waves on a nano scale. The new device could have significant and useful applications in the worlds of computing, imaging, and even anti-terrorist security screening.

Where a “laser” (light amplification by the stimulated emission of radiation), uses packets of electromagnetic vibrations called “photons”, the “Saser” uses sound waves composed of sonic vibrations called “phonons”. In a laser, the photon beam is produced by stimulating electrons with an external power source so they release energy when they collide with other photons in a highly reflective optical cavity. This produces a coherent and controllable shining beam of laser light in which all the photons have the same frequency and rate of oscillation. From supermarket scanners to DVD players, surgery, manufacturing, and the defense industry, the application of laser technology is widespread.

The Saser mimics this technology but using sound, to produce a sonic beam of “phonons”’ which travels, not through an optical cavity like a laser, but through a tiny manmade structure called a “superlattice”. This is made out of around 50 super-thin sheets of two alternating semiconductor materials, gallium arsenide and aluminium arsenide, each layer just a few atoms thick. When stimulated by a power source (a light beam), the phonons multiply, bouncing back and forth between the layers of the lattice, until they escape out of the structure in the form of an ultra-high frequency phonon beam.

A key factor in this new science is that the Saser is the first device to emit sound waves in the terahertz frequency range…the beam of coherent acoustic waves it produces has nanometer wavelengths (billionths of a meter). Crucially the ‘superlattice’ device can be used to generate, manipulate and detect these soundwaves making the Saser capable of widespread scientific and technological applications. One example of its potential is as a sonogram, to look for defects in nanometer scale objects like micro-electric circuits. Another idea is to convert the Saser beam to THz electromagnetic waves, which may be used for medical imaging and security screening. High intensity sound waves can also change the electronic properties of nanostructures so a Saser could be used as a high-speed terahertz clock to make the computers of the future a thousand times faster.

Professor Anthony Kent from the University’s School of Physics and Astronomy, says “While our work on sasers is driven mostly by pure scientific curiosity, we feel that the technology has the potential to transform the area of acoustics, much as the laser has transformed optics in the 50 years since its invention.”

The research team at Nottingham, with help from Borys Glavin of the Lashkarev Institute of Semiconductor Physics in the Ukraine, has won the immediate accolade of the publication of their paper on the Saser experiments in this month’s Physical Review. The team has also won a grant of £636,000 from the Engineering and Physical Sciences Research Council to develop Saser technology over the next four years.

SOURCE: Univ. of Nottingham

Light sensor breakthrough could enhance digital cameras

New research by a team of Univ. of Toronto scientists could lead to substantial advancements in the performance of a variety of electronic devices including digital cameras.

Researchers created a light sensor—like a pixel in a digital camera—that benefits from a phenomenon known as multi-exciton generation (MEG). Until now, no group had collected an electrical current from a device that takes advantage of MEG.

"Digital cameras are now universal, but they suffer from a major limitation: they take poor pictures under dim light. One reason for this is that the image sensor chips inside cameras collect, at most, one electron's worth of current for every photon (particle of light) that strikes the pixel," says Ted Sargent, professor in U of T's Department of Electrical and Computer Engineering. "Instead generating multiple excitons per photon could ultimately lead to better low-light pictures."

In solar cells and digital cameras, particles of light—known as photons—are absorbed in a semiconductor, such a silicon, and generate excited electrons, known as excitons. The semiconductor chip then measures a current that flows as a result. Normally, each photon is converted into at most one exciton. This lowers the efficiency of solar cells and it limits the sensitivity of digital cameras. When a scene is dimly lit, small portable cameras like those in laptops suffer from noise and grainy images as a result of the small number excitons.

"Multi-exciton generation breaks the conventional rules that bind traditional semiconductor devices," says Sargent. "This finding shows that it's more than a fascinating concept: the tangible benefits of multiple excitons can be seen in a light sensor's measured current."

SOURCE: Univ. of Toronto

Saturday, June 6, 2009

TrendNet Wifi on Beagleboard running Angstrom Linux

By default after every boot-up, Angstrom runs wpa_supplicant daemon which tries to use WPA instead of WEP regardless of configuration in /etc/network/interfaces, hence prevent us to use WEP as wifi encryption. We need to kill this daemon by executing:

root@beagleboard:~# start-stop-daemon -K -n wpa_supplicant
root@beagleboard:~# ps -ef | /bin/grep wpa*

Then reconfigure the wlan:

iwconfig wlan0
iwconfig wlan0 key

Try to see if the USB Wifi adapter gets our AP's MAC address:

root@beagleboard:~# ps -ef | /bin/grep wpa*


ifdown wlan0
ifup wlan0

It should get the IP (assuming our AP router is running DHCP service as well):

root@beagleboard:~# route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface * U 0 0 0 wlan0 * U 0 0 0 usb0
default UG 0 0 0 wlan0
default UG 0 0 0 usb0

(Note: the system used above was running Linux kernel 2.6.29:

root@beagleboard:~# uname -a
Linux beagleboard 2.6.29-omap1 #1 Wed Jun 3 18:10:47 PDT 2009 armv7l unknown


Monday, June 1, 2009

What is the best mobile Operating system?

Duh....smartphone environment is getting more crowded with more and more new operating systems. From Microsoft Windows Mobile, Blackberry O/S, Symbian, iPhone's OS, Google's Android and now Palm's WebOS.

Which one is the best from the following criterias?
  1. UI experiences (reponsiveness, easy to use, intuitiveness, beauty look)
  2. Features (view rotation, touch responses, supports to various wireless tech)
  3. Multi-tasking
  4. Development environment and toolkits (including rich sets of libraries)
  5. Portability
  6. Openness (open-system, open source, proprietary)
  7. Price
  8. Hardware supports
  9. Availability to developers to play (at least comes with a simulator)