News Feature | December 20, 2016

Harvard Scientists Build World's Smallest Radio Receiver

Jof Enriquez

By Jof Enriquez
Follow me on Twitter @jofenriq

Harvard Scientists Build World's Smallest Radio Receiver

Researchers at Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have built the world's smallest radio receiver from a diamond crystal with atomic-scale imperfections. Due to the inherent strength and biocompatibility of diamonds, the radio could find applications in extremely harsh environments and in medical implants.

Diamond crystals can contain tiny impurities, including a nitrogen atom substituting for a carbon atom, and an empty space next to it, where another carbon atom should be. This nitrogen-vacancy (NV) combination, or center, essentially replaces two adjacent carbon atoms in a diamond's lattice of otherwise orderly structured carbon atoms, and is what gives the diamond special optical, electromagnetic, and quantum properties.

In Harvard's radio, electrons in the diamond's NV centers are powered by a green laser, which excites the electrons to pick up frequency-modulated (FM) radio waves that are then converted into red light. A photodiode then converts that light into an electrical current, which is turned into sound through a speaker. An electromagnet surrounding the diamond is used to change the frequency.

As detailed in Physical Review Applied, “The carrier frequency of the frequency-modulated signal is in the 2.8-GHz range, determined by the zero-field splitting in the NV electronic ground state. The radio can be tuned over 300 MHz by applying an external dc magnetic field. We show the transmission of high-fidelity audio signals over a bandwidth of 91 kHz using the diamond radio. We demonstrate operating temperature of the radio as high as 350 °C [660 °F].”

That temperature is just 200 degrees shy of the average temperature on Venus, but nearly 500 degrees higher than the average consumer radio, noted Motherboard.

“Diamonds have these unique properties,” said Marko Loncar, the Tiantsai Lin Professor of Electrical Engineering at SEAS, in a news release. “This radio would be able to operate in space, in harsh environments and even the human body, as diamonds are biocompatible.”

Besides NV defects, other scientists are experimenting with silicon-vacancy (SiV) and germanium-vacancy (GeV) defects in diamond to open up new possibilities. For example, GeV centers have been shown as a reliable source of single photons for quantum cryptography and as bright luminescent markers in living cells.

These diamonds are also being paired with complementary nanoparticles, such as silver or gold nanoparticles, to enhance their properties. In the future, these hybrid nanoparticles could make possible room-temperature qubits for quantum computers, brighter dyes for biomedical imaging, and highly sensitive magnetic and temperature sensors.

Image credit: Eliza Grinnell/Harvard SEAS