Custom copper “headphones” increase the reception of nuclear radio by 100 times

Scientists from the National Institute of Standards and Technology (NIST) have increased the sensitivity of their nuclear radio a hundredfold by placing a small glass cylinder with cesium atoms inside what looks like non-standard copper “headphones”.

The structure – the square top loop that connects the two square panels – amplifies the input radio signal or electric field that is applied to the gaseous atoms in the bulb (known as the vapor cell) between the panels. This improvement allows the radio to detect much weaker signals than before. The demonstration is described in a new article that was published in the journal Letters on Applied Physics.

The structure of the headphones is technically a bifurcated ring resonator that acts as a metamaterial – a material created with new structures to achieve unusual properties. “We can call it a structure inspired by metamaterials,” said NIST project manager Chris Holloway.

Researchers from NIST have previously demonstrated atom-based radio. Among other possible benefits, an atomic sensor can be physically smaller and work better in noisy conditions than conventional radios.

The length of the steam chamber is about 14 millimeters (0.55 inches) with a diameter of 10 mm (0.39 inches), about the size of a nail or computer chip, but thicker. The upper loop of the resonator is about 16 mm (0.63 inches) on the side, and the ear pads – about 12 mm (0.47 inches) on the side.

The NIST radio relies on the special state of atoms. Researchers are using two different color lasers to prepare the atoms contained in the steam cell in a high-energy state (“Rydberg”), which have new properties such as extreme sensitivity to electromagnetic fields. The frequency and strength of the applied electric field affect the color of the light absorbed by the atoms, and this results in the conversion of the signal strength into an optical frequency that can be accurately measured.

The radio signal applied to the new resonator creates a current in the upper circuit that creates a magnetic flux or voltage. The dimensions of the copper structure are less than the wavelength of the radio signal. As a result, this small physical gap between the metal plates stores energy around the atoms and amplifies the radio signal. This increases performance efficiency or sensitivity.

“The loop captures the incoming magnetic field, creating tension in the gaps,” Holloway said. “Because the gap is small, a large electromagnetic field is formed through the gap.”

The dimensions of the loop and the gap determine the natural, or resonant, frequency of the copper structure. In NIST experiments, the gap was just over 10 mm, limited by the outer diameter of the available steam cell. The researchers used a commercial mathematical simulator to determine the loop size needed to create a resonant frequency of about 1,312 GHz, where Rydberg atoms switch between energy levels.

Several external staff members helped model the resonator design. The simulation suggests that the signal can be made 130 times stronger, whereas the measurement result was about a hundred times, probably due to energy loss and structural imperfections. A smaller gap will result in more gain. Researchers plan to investigate other resonator designs, smaller steam cells and different frequencies.

With further development,[{” attribute=””>atom-based receivers may offer many benefits over conventional radio technologies. For example, the atoms act as the antenna, and there is no need for traditional electronics that convert signals to different frequencies for delivery because the atoms do the job automatically. The atom receivers can be physically smaller, with micrometer-scale dimensions. In addition, atom-based systems may be less susceptible to some types of interference and noise.

Reference: “Rydberg atom-based field sensing enhancement using a split-ring resonator” by Christopher L. Holloway, Nikunjkumar Prajapati, Alexandra B. Artusio-Glimpse, Samuel Berweger, Matthew T. Simons, Yoshiaki Kasahara, Andrea Alù and Richard W. Ziolkowsk, 5 May 2022, Applied Physics Letters.
DOI: 10.1063/5.0088532

The research is funded in part by the Defense Advanced Research Projects Agency and the NIST on a Chip program. Modeling assistance was provided by collaborators from the University of Texas, Austin; City University of New York, N.Y.; and University of Technology Sydney, Australia.