Army researchers have developed a new microwave radiation sensor that’s said to have 100,000 times higher sensitivity than currently-available commercial sensors.

The new microwave radiation sensor, which is a microwave bolometer, is claimed to lead to “significant improvements” in thermal imaging, radio communications, and electronic warfare say the Army researchers who published their work in the journal Nature.

“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 of the Army Research Office.


A bolometer is a device that measures the power of electromagnetic radiation through the heating of materials, which exhibit a temperature-electric resistance dependence. To date, they’re one of the most sensitive detectors used in infrared radiation detection and are integral tools for applications in advanced thermal imaging, night vision, and infrared technologies, among others. 

Diagram of the concept behind bolometers

Diagram of the concept behind bolometers. Image used courtesy of Berkeley University

Although bolometers have been proven as excellent sensors for the infrared range of radiation, they are not highly sensitive, fast responding, and, in some devices, apt at light absorption.

Many studies have looked at obtaining higher-sensitivity bolometers by seeking to reduce the size of the detector and thus increase the thermal response. In doing so, previous studies have found that graphene appears to be an excellent material for this.

A Graphene Bolometer Sensor

In this study, which is the latest in graphene bolometer research, the U.S. Army team presents a graphene microwave bolometer that is so sensitive that it is capable of detecting a single microwave photon, the smallest amount of energy in nature, explains Qiu. 

The graphene microwave bolometer

The graphene microwave bolometer developed by Army researchers under this project. It’s capable of detecting a single microwave photon, the smallest amount of energy in nature. Image used courtesy of the Army Research Office, U.S. Army Combat Capabilities Development Command

It detects electromagnetic radiation by measuring the temperature rise as photons are absorbed into the sensor. A key innovation in this research is to measure the temperature increase by superconducting Josephson junction—a quantum mechanical device made from two separated superconducting electrodes—while maintaining a high microwave radiation coupling into the graphene through an antenna.

The coupling efficiency is important in high-sensitivity detection because every photon counts. 

Special Band Structure

In addition to being thin, the graphene’s electrons are in a special band structure where the valence and conduction bands meet at a single Dirac 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.

Higher-sensitivity bolometer detectors could see new pathways being explored for improving the performance of systems that detect electromagnetic signals. “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,” Qiu concluded.

Source: All About Circuits