Data sent by background static alone, in a Stanford lab

In a foam-lined chamber at Stanford, a transmitter and a receiver sit at room temperature, and data passes between them without the transmitter producing a single radio wave. Assistant professor Zerina Kapetanovic's team has shown that the background static of electronics can carry information. The result, published in the Proceedings of the National Academy of Sciences, describes a method the researchers call thermal noise communication.

Thermal noise is the faint static created by the vibration of electrons in electrical conductors. Radio and cellular systems normally struggle against it. Its strength depends on temperature, and sensitive instruments can pick it up: astronomers use the thermal noise emitted by distant planets and stars to study them. Kapetanovic's earlier research on agricultural sensing led her to wonder whether a device could work like the RFID window tags used for highway tolls, answering a query without an energy-intensive radio signal. A conventional radio transmitter can use up to 1,000 times as much energy to send information as a transmitter using only thermal noise, according to the study.

The mechanism is simple to describe. The transmitter, fitted with an antenna, alternates between two electrical states, an open circuit and a short circuit, which stand for the bits one and zero. In one state it absorbs the ambient noise, in the other it reflects it. The receiver amplifies the noise bouncing off the antenna and sees a pattern: the reflected noise looks hotter or colder. The amplifier, which the researchers compare to an electron refrigerator, slows the electrons down and makes the noise appear colder. Joseph Kahn compares the transmitter to a castaway signalling with a hand mirror: "It's just a reflector." It modulates the signal without cooling anything, which is what made the experiment puzzling at first.

To understand the link, the team derived a channel model, the equation that defines the fundamental variables of the system, a tool used in all forms of wireless communication. Adjusting the setup according to that model improved the data transfer rate by 100 times. The study does not give the resulting speed in absolute terms, and the experiments still take place inside the insulated box. The next steps are linking several transmitters into a network and making sure the signal is not lost in noisier environments.

What changes for the moment is a question of where low-power communication could go. The researchers see the approach as suited to situations where small amounts of data must move and power is scarce, such as environmental sensing, and to places sensitive to electromagnetic interference, like medical devices or astronomy observatories. "We're hoping that this unconventional communication system can unlock wireless communication where it hasn't been able to go before," said Geneva Ecola. The study gives no timeline for applications outside the laboratory, and the system has not been tested in the field.