Adaptable Antenna
Injecting liquid metal into polymer molds produces efficient antennas that can twist and stretch

Source: “Reversibly Deformable and Mechanically Tunable Fluidic Antennas”
Michael D. Dickey et al.
Advanced Functional Materials 19: 3632-3637

Results: Engineers at North Carolina State University created a flexible yet efficient antenna using a liquid metal, a gallium-indium alloy. The antenna is as efficient as a standard copper antenna, transmitting over a broad frequency range at about 90 percent efficiency. It remains functional even when it is twisted, folded, or stretched to 40 percent beyond its normal length.

Why it matters: The antenna could make it easier to send and receive data from flexible electronics, such as sensors incorporated into clothing, electronic paper, or implantable biomedical devices. The radio frequencies it responds to change as it stretches, which means that it could be embedded in machinery or in a concrete structure such as a bridge to monitor it for strain over time.

Methods: The researchers poured liquid poly­dimethylsiloxane (PDMS) into a mold. Once cured, the PDMS formed a pliable structure with a hollow channel inside. They injected the gallium-indium mixture into the channel and sealed it, creating a simple dipole antenna (like the “rabbit ears” used for analog TV reception).

Next steps: The researchers are building and testing liquid-metal antennas in other shapes, such as the loops, ­helices, and patches more commonly used in devices like cell phones and GPS transceivers. They are also evaluating other polymers, since PDMS might interfere with the efficiency of these differently shaped antennas.

Securing Web Apps
Experimental system watches applications to make sure they’re not misbehaving on the user’s end

Source: “Ripley: Automatically Securing Web Applications Through Replicated Execution”
Krishnaprasad Vikram et al.
ACM Conference on Computer and Communications Security, November 9-13, 2009, Chicago, IL

Results: Researchers designed a system that secures Web applications by protecting against attacks on the portion of the application’s code that runs on users’ machines rather than on Web servers. They found that the system protected five sample applications, and also a test version of Hotmail, without straining the network, the user’s computer, or the server.

Why it matters: The user side of Web applications has been notoriously difficult to defend, because the code on the user’s computer can be compromised very easily–even by the user. As a result, some important functions must run on the server, a requirement that slows the system down. For example, an online shopping site could work faster if each user’s shopping-cart information and purchase totals were manipulated directly in the browser, but these functions are assigned to the server lest a user hack the system to add fraudulent discounts. The new system would make sure that no such unauthorized behavior occurred.

Methods: The system replicates the part of the application running within the user’s browser and runs that replica on the server. Values computed by the replica are compared with those from the real application to ensure that the code is running on the user’s machine as it’s supposed to; if they don’t match, the system disconnects the client, ending the transaction. To avoid overburdening the server’s memory and processors, the researchers pared down the cloned software so that it performs only essential actions.

Next steps: The researchers designed their system for applications written with .NET, a software framework that runs on Microsoft Windows. They now hope to see their techniques adapted for applications written using other common programming technologies, such as Silverlight and Flash.