Army-funded research developed a microwave radiation sensor with 100,000 times higher sensitivity than currently available commercial sensors. Researchers said better detection of microwave radiation will enable improved thermal imaging, electronic warfare, radio communications, and radar.
The research team includes scientists from Harvard University, the Institute of Photonic Sciences, MIT, Pohang University of Science and Technology, and Raytheon BBN Technologies. The Army, in part, funded the work to fabricate this bolometer by exploiting the giant thermal response of graphene to microwave radiation.
“The microwave bolometer developed under this project is so sensitive that it is capable of detecting a single microwave photon, which is the smallest amount of energy in nature,” said Dr. Joe Qiu, program manager for solid-state electronics and electromagnetics in the Army Research Office, an element of the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory. “This technology will potentially enable new capabilities for applications such as quantum sensing and radar and ensure the U.S. Army maintains spectral dominance in the foreseeable future.”
The graphene bolometer sensor detects electromagnetic radiation by measuring the temperature rise as the photons are absorbed into the sensor. Graphene is a two-dimensional, one-atom-layer-thick material. The researchers achieved a high bolometer sensitivity by incorporating graphene in the microwave antenna.
A key innovation in this advancement involved a Josephson junction – a quantum mechanical device that is made of two superconducting electrodes separated by a barrier. The temperature rise was measured by superconducting the Josephson junction while maintaining a high microwave radiation coupling into the graphene through an antenna. Researchers said the coupling efficiency is essential in a high sensitivity detection because “every precious photon counts.”
In addition to being thin, the electrons in graphene are also in a very special band structure in which the valence and conduction bands meet at only one point.
“The density of states vanishes there so that when the electrons receive the photon energy, the temperature rise is high while the heat leakage is small,” said Dr. Kin Chung Fong of Raytheon BBN Technologies.
With increased sensitivity of bolometer detectors, this research has found a new pathway to improve the performance of systems detecting electromagnetic signal such as radar, night vision, LiDAR, and communication. It could also enable new applications such as quantum information science, thermal imaging, and the search for dark matter.