Communications of the ACM
The Walls Have Ears: Princeton Researchers Develop Walls That Can Listen, and Talk
Electrical engineering graduate students (from left) Liechao Huang, Josue Sanz Robinson and Warren Rieutort-Louis demonstrate the flexibility of a radio built on a thin plastic sheet.
Credit: Frank Wojciechowski
The realization of new devices such as structural monitors for roads and bridges and concealed in-building communications systems could be helped by Princeton University researchers' successful incorporation of ultrathin radios on plastic sheets, which can be applied to walls and other structures.
The key to this technology is fabricating low-temperature circuits, which is accomplished using transistors that are based on amorphous silicon rather than crystalline silicon. The tradeoff is the lack of a highly ordered inner structure, and Princeton professor James Sturm concedes that "these transistors do not perform nearly as well as the ones that Intel would make on one of its chips." To overcome this problem, professor Naveen Verma and a team of graduate students tapped the concept of a super-regenerative circuit to boost the radio's frequency and circumvent the amorphous silicon transistors' relatively poor performance.
"Essentially, you take the electrons and you slosh them back and forth between the inductor and capacitor, and the rate of this sloshing does not depend on getting electrons through the transistor," Verma says.
Large, high-quality inductors and capacitors were used to avoid significant electron loss during this process, and the final device operated well at the large scale despite the transistors' performance issues.
From Princeton University
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