It is a ring form of a solenoid.

In these miniature circuit breakers, the current is run through a solenoid, and, in the event of excess current flow, the magnetic pull of the solenoid is sufficient to force open the circuit breaker's contacts (often indirectly through a tripping mechanism).

We also have been working with some scientists and engineers from UPenn to come up with a chemically actuated version of this amoeba robot.

To determine basic categories of fuzes and adopt Best Practices on fuze mechanisms so as to increase the discriminatory capacity of MOTAPM to the greatest extent and to prevent them from being actuated by the presence, proximity or contact of a person.