Infrared secrets: How thermal radiation can hide messages

Researchers in Australia have developed a new communication method that can transmit sets of information while remaining effectively invisible to outside observers by disguising the signal as ordinary thermal radiation.

The technology relies on a phenomenon known as “negative light”, which allows data to be hidden within natural background infrared emissions. Using this approach, scientists successfully transmitted data at a speed of 100 kilobits per second without producing any detectable signal that information was being sent, according to a report highlighted by Live Science.

Most existing methods of secure communication conceal information by embedding it within other data streams or encrypting it so that it cannot be understood without a decryption key. In contrast, the new system makes detection itself extremely difficult because observers have no indication that any signal is present.

The researchers noted that the method can still be combined with traditional encryption techniques to add another layer of security. Their findings were published on March 5 in the journal Light: Science & Applications.

The hidden transmission method relies on infrared radiation, the portion of the electromagnetic spectrum just beyond visible red light. Although invisible to the human eye, infrared radiation can be detected with thermal cameras and is commonly experienced as heat emitted by warm objects. All objects naturally release faint infrared radiation as part of their thermal signature.

Michael Nielsen, a professor of engineering at the University of New South Wales, Sydney and lead author of the study, compared the concept to an unusual type of flashlight.

He explained that it works like a device that could “project darkness” rather than light against a bright background.

To achieve this effect, the team used specialised components known as thermoradiative diodes. These devices generate patterns of slightly brighter or darker infrared emissions that blend into the natural “noise” of background radiation. While the variations appear indistinguishable from normal environmental signals, a specially designed receiver can interpret them as digital information.

Technology adapted from previous research

The thermoradiative diodes used in the experiment were originally developed for another project exploring “night-time solar” energy generation. In that earlier work, the research team demonstrated that it is possible to produce electricity after sunset by capturing infrared radiation that the Earth releases as it cools during the night.

By harnessing this outgoing heat energy, the diodes were able to generate a small amount of electrical power.

Potential for faster hidden communication

Although the current system achieved data transfer speeds of around 100 kbps, the researchers say significantly faster rates should be possible.

According to Nielsen, the main limitation during the experiment was the availability of advanced electronic components required for the setup. With existing technology, the system could theoretically reach tens of megabits per second, while further improvements in device design and detectors could eventually push speeds into the gigabits-per-second range, the team said.

By Nazrin Sadigova