Power/Performance Bits: July 5

More storage with electromagnetic switch

Scientists at Hokkaido University designed a device that employs both magnetic and electronic signals, potentially doubling the storage capacity of conventional memory devices. In addition to the binary 0/1 method of storing information, this would add an A/B store for the information as well. To do this would require finding a material that can switch back and forth from a magnet to a non-magnet state.

The team investigated two forms of strontium cobalt oxide (SrCoOx): one is an insulating non-magnet while the other is a metal magnet. By changing the oxygen content in this compound, the team could cause it to switch between the two forms.

(Source: Takayoshi Katase, Yuki Suzuki and Hiromichi Ohta)

However, the two methods currently available to do this have big drawbacks. One method requires using a high temperature heat treatment. This would make it impossible to use in devices that work at room temperature, such as your mobile phone. The other method involves using a dangerous alkaline solution. This would require a device that is sealed so that the solution does not leak. This method is difficult to miniaturize and is thus not suitable for information storage devices.

To overcome the issues with both methods, the team developed a new way to use strontium cobalt oxide safely at room temperature in air. They applied a sodium tantalate thin film, which can be used at room temperature without leaking alkaline solution, over layers of strontium cobalt oxide.

When a three-volt current was applied (or about one-seventh of the voltage required in currently available USB flash drives), the insulating form of SrCoO2.5 reversibly switched to its metal magnet form, SrCoO3, in three seconds. By comparison, current devices can store information in 0.01 seconds.

Making the device smaller would shorten the time needed for the compound to switch between an insulator and a magnet, the researchers say.

Lightbulb network

Researchers at Disney Research and ETH Zurich demonstrated modified consumer-grade LED bulbs which could both illuminate a room and provide a communications link for devices in that room.

LEDs can both produce light and serve as light sensors. By having individual LEDs alternate between sending modulated light signals and serving as receivers of signals, it is possible to create a network of bulbs that can send messages to each other and connect to devices, while having no discernible effect on room lighting.

“Interconnecting appliances, sensors and a wide variety of devices into the Internet of Things has many potential benefits, but using radio links to do so threatens to make the radio spectrum an even scarcer resource,” said Markus Gross, vice president at Disney Research. “Visible light communication networks conserve the radio spectrum, while also making it difficult to eavesdrop for anyone out of line of sight of the network.”

Fully assembled light bulb containing the SoC running Linux, VLC controller, additional power supply, and four photodiodes. The base (seen on the left) and the diffusion dome (right) are from the commercial LED light bulb, the center section holds the additional electronics, with two photodiodes visible. (Source: Disney Research)

“We used commercially available, off-the-shelf LED light bulbs as our starting point,” said Stefan Schmid, a Ph.D. student at Disney Research and ETH Zurich. “They are readily available at low cost and can be used in any lamp with standard sockets. This leads to an easy-to-setup and flexible testbed that can be readily duplicated.” The bulbs were modified, however. An SoC running an embedded version of Linux was added to each bulb, as well as photodiodes to enhance sensing of incoming signals and an additional power supply for the added electronics.

The researchers deployed four such bulbs for their proof-of-concept system. They showed that their system architecture and protocols enabled the bulbs to create stable networks that could support the low bandwidth applications typical of most IoT devices. They also showed it was possible to use the system to estimate the position of devices in the room, an example of the additional applications that the system could support.