Week of September 12, 2005

Power walking

Someday in the not too distant future, as you carry an increasingly burdensome backpack down a seemingly endless trail, you might be able to take comfort in at least not having to carry extra batteries.

Researchers from the University of Pennsylvania have developed a backpack that generates electricity by letting its load slide up and down against the frame. The motion is captured by a pinion gear that is attached to an electrical generator. The process generates serious amounts of electricity -- nearly 3 watts for a 44 pound load at a brisk walking pace of 4 miles per hour and as much as 7.37 watts for an 84 pound load at the same speed. Handheld devices like cellphones typically require less than a watt and citizens band radios take 5 to 7 watts.

Generating electricity this way requires only a little more exertion from the backpack wearer than it would take to carry an ordinary backpack; the food needed to fuel the extra exertion weighs far less than the equivalent batteries, according to the researchers. The backpack wearer's walking mechanics change when carrying the sliding load compared to the fixed load, which probably accounts for the efficiency of the device.

The backpack could be used to charge batteries and power mobile devices, including cellphones, global positioning system receivers and night vision goggles, according to the researchers.

(Generating Electricity While Walking with Loads, Science, September 9, 2005)

Blinded by the light

The proliferation of camera phones and credit-card-sized digital cameras makes it difficult avoid having your picture taken. Help could be on the way, however, for the security and privacy conscious.

Researchers from the Georgia Institute of Technology have come up with a way of temporarily disabling digital cameras within certain spaces. The technique involves detecting the signal from a cameras chip and targeting bright light pulses at it to ruin the picture.

The key to the technique is that the charge-coupled devices (CCD) used in most consumer-level digital cameras are retroreflective, meaning light beams bounce off of them in the direction they came from rather than at an angle. The researchers attached infrared emitters to an infrared camera to detect CCD's, and configured a projector to shine bright light in the direction of detected devices.

(Preventing Camera Recording by Designing a Capture-Resistant Environment, Ubiquitous Computing 2005 (Ubicomp '05), Tokyo, Japan, September 11-14, 2005)

Projecting a well-compensated image

The challenge to using projectors to display computer-generated images has been finding suitable places -- preferably flat white surfaces -- to project the images on.

Researchers at Bauhaus University Weimar in Germany are aiming to get around the just-flat-white-surfaces problem with a projection method that combines several existing techniques for correcting images distorted by irregular and colored surfaces. The method involves tracking each pixel of projected images and compensating for distortions by adjusting the color and focus of each pixel, and by warping images when necessary.

The method makes it possible to project three-dimensional images on wallpaper and curved surfaces and to project architectural elements like stairs and posts in a room.

(Enabling View-Dependent Stereoscopic Projection in Real Environments, Special Interest Group Graphics (Siggraph) 2005, Los Angeles, July 31-August 4, 2005)

Indoor cellphone tracking

Services that track your position via your cellphone can locate the nearest post office or pizza parlor or indicate which of your friends are nearby, but they don't work indoors.

Researchers from Tartu University in Estonia, the University of Toronto and Intel Research Seattle are aiming to change that. They have developed an indoor localization system that picks up cellphone signals. The ability to track people room by room is a key requirement for ubiquitous computing, allowing, for example, co-workers to find each other easily and location-specific information to be delivered to a person's cellphone.

The system uses Global System for Mobile telecommunications (GSM) technology that transmits communications to cellphones using the six strongest signals from base station antennas. The system uses as many as 29 other signals from base station antennas that are too far away to be useful for communications but can be used to help identify the location of a cellphone.

The method is as accurate as using indoor wireless communications networks for localization -- about 5 meters -- and offers three advantages: it uses widely available signals, ubiquitous cellphones, and works in buildings with no power.

(Accurate GSM Indoor Localization, Ubiquitous Computing 2005 (Ubicomp '05), Tokyo, Japan, September 11-14, 2005)

Bits and pieces

Zinc oxide nanosprings could be key components of nanoelectricomechanical devices; a simulation shows that even small quantum computers can do somethings that ordinary computers can't; a study shows that nanotubes suspended in the air don't conduct electricity as well as nanotubes on surfaces.