An RF circulator for cell phones?
An RF circulator has multiple input/output ports, but signals entering one port get transmitted only to the next one. The setup usually involves a magnetized material that plays a role in canceling waves propagating in two different nearby paths. The use of magnetized material makes the whole thing bulky and too big to be practical for cell phones or other mobile gear. That could change soon thanks to the development of a solid-state circulator able to work at RF frequencies. The work was described in a recent issue of Nature Physics Letters and the lead author, Nicholas Estep, was at the IMS poster area with a working circuit.
The circuit implements a loop of resonators that include variable capacitors having values modulated by a signal. The resonators are 120 electrical degrees apart. They are modulated by external signals having the same 120° phase difference, imparting what Estep calls an effective electronic angular momentum to the system.
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