Circulator

Circulator is a term used in several disciplines to denote devices or roles that move something in a directed cycle. The common thread is directional flow, whether of signals, fluids, or care equipment.

In microwave and RF engineering, a circulator is a passive, non-reciprocal multi-port device that directs signals in a fixed sequence from one port to the next. Typically, a three-port circulator routes energy from port 1 to port 2, port 2 to port 3, and so on, while isolating the reverse paths. Circulators rely on ferrite materials and a static magnetic field to achieve non-reciprocity. They are used to separate transmission and reception paths, protect sources, and manage signal routing in systems such as radar, satellite links, and test equipment. Practical considerations include insertion loss, isolation, power handling, and the operating frequency band.

In fluid systems, a circulator pump (often simply called a circulator) moves heated or cooled water through a closed hydronic loop. It provides the flow that distributes thermal energy from boilers or chillers to radiators, coils, or heat exchangers. Circulator pumps are typically electric-driven centrifugal pumps, with many systems using variable-speed drives to improve efficiency and control. They must be compatible with the fluids circulating in the system and are chosen for flow rate, head, and reliability.

In medical settings, a circulating nurse, or circulator, is a member of the operating room team who works outside the sterile field to support the procedure. Responsibilities include preparing and passing instruments, supplying equipment, handling specimens, maintaining documentation, counting sponges and other items, and coordinating communication among staff. The circulator ensures patient safety and smooth workflow during surgery. See also: disambiguation of circulator.