Researchers have developed a tiny, electrically tuneable infrared filter that could help shrink bulky thermal sensing systems on to portable chips – technology that could lead to handheld pollution detectors, compact multispectral cameras and next-generation chemical sensing devices.
Developed by researchers from The University of Western Australia and The Australian National University through the Australian Research Council Centre of Excellence for Transformative Meta-Optical Systems, the technology works in the long-wave infrared region – the part of the spectrum associated with thermal radiation emitted by objects that are near room temperature.
Published in Advanced Materials Technologies, the study revealed the new device was designed to help infrared systems distinguish between different materials and gases based on their spectral ‘fingerprints’, unlike conventional thermal cameras that mainly measure heat intensity.
PhD candidate Oleg Bannik, lead author from UWA’s School of Engineering, suggested thinking of the technology as ‘colour vision’ for thermal imaging.
“Instead of seeing only hot and cold, a camera could compare several carefully selected infrared bands, similar to how the human eye combines red, green and blue wavelengths to perceive colour,” Mr Bannik said.
“That could allow systems to tell the difference between gases, chemicals or materials that look identical in ordinary thermal images.”
For decades, infrared spectroscopy was restricted to labs, military systems and expensive industrial equipment and was often too bulky and power-hungry to leave controlled environments.
The device is a microscopic ‘sandwich’ of suspended gold and silicon membranes perforated with nanoscale holes. By electrically changing the small gap between the layers, researchers could continuously tune which infrared wavelengths passed through the structure.
“The most counterintuitive part is changing a gap by only a few hundred nanometres can strongly tune infrared light with wavelengths around ten microns,” Mr Bannik said.
Environmental monitoring is one of the strongest potential applications for the device, particularly for detecting methane leaks and industrial emissions.
“The technology could also benefit industrial safety, thermal imaging, medical diagnostics and defence systems where identifying materials matters more than simply measuring temperature,” Mr Bannik said.
The paper points to the possibility of medical application, with spectrally selective thermal imaging systems capable of detecting subtle physiological changes invisible to conventional thermal cameras.
“The most realistic applications are non-contact diagnostics and advanced thermal imaging,” Mr Bannik said. “Different tissues emit infrared radiation differently, so spectrally selective thermal imaging could potentially help identify inflammation, monitor wounds or detect subtle physiological changes invisible to standard thermal cameras.”
The lightweight, low-power infrared sensors could also be useful in drones and portable field systems.
“Drones are probably the most realistic near-term platform because they benefit enormously from lightweight, low-power sensors,” he said.
