A Magnetic-Free Radio-Wave Circulator on a Chip

We have recently created a radically smaller, more efficient, magnetic-free radio wave circulator that could be used in cellphones and other wireless devices. The new circulator has the potential to enable full-duplex functionality, meaning that devices can transmit and receive signals on the same frequency band at the same time. Since the advent of wireless technology 60 years ago, magnetic-based circulators have been in principle able to provide two-way communications on the same frequency channel, but they are not widely adopted because of the large size, weight and cost associated with using magnets and magnetic materials. Freed from a reliance on magnetic effects, the new circulator has a much smaller footprint while also using less expensive and more common materials. These cost and size efficiencies could lead to the integration of circulators within cellphones and other microelectronic systems, resulting in substantially faster downloads, fewer dropped calls and significantly clearer communications.

Our prototype circulator that is 2 centimeters in size — more than 75 times smaller than the wavelength of operation. The circulator may be further scaled down to as small as a few microns. The design is based on materials widely used in integrated circuits such as gold, copper and silicon, making it easier to integrate in the circuit boards of modern communication devices.

The device works by mimicking the way magnetic materials break the symmetry in wave transmission between two points in space, a critical function that allows magnetic circulators to selectively route radio waves in a non-reciprocal fashion. With the new circulator, we accomplish the same effect, but replacing the magnetic bias with a traveling wave spinning around the device.

Another unique feature is that the new circulator can be tuned in real time over a broad range of frequencies, a major advantage over conventional circulators. Additionally, because the design of the circulator is scalable and capable of circuit integration, it can potentially be placed in wireless devices.

The circulator also could benefit other industries that currently use magnetic-based circulators. For instance, circulators used in phased arrays and radar systems for aircraft, ships and satellites can be extremely heavy and large, so minimizing the size of these systems could provide significant savings.

We are also bringing this paradigm to other areas of science and technology. Our research team is working on using this concept to protect lasers and to create integrated nano-photonic circuits that route light signals instead of radio waves in preferred directions.

To learn more:

N. Estep*, D. Sounas*, J. Soric, and A. Alù, “Magnetic-Free Non-Reciprocity Based on Parametrically Modulated Coupled-Resonator Loops,” Nature Physics, in press. (web)

T. Simonite, “Simple Circuit Could Double Cell Phone Data Speeds,” MIT Technology Review, November 24, 2014.

S. Zaragoza, “Lighter, Cheaper Radio Wave Device Could Transform Telecommunications,” UT Austin Press Release, Phys.org, November 10, 2014

A. Sihvola, “Device physics: Power inequality,” Nature Physics, in press.