TRANSDUCER

A multistage flextensional transducer includes at least one inner elongate driver member within and mechanically coupled to an inner shell that is nested within an outer shell; the inner shell comprising a pair of contact portions abutting the driver member and a pair of transmission portions on opposite sides of the inner shell between the contact portions; the outer shell being arranged so that the transmission portions act as bridging driver members between the said inner and outer shells, flexure of the outer shell being driven, on actuation of the transducer, by movement of the bridging driver members. The transducer may act as a push or pull actuator or sensor, may magnify displacement and may employ smart materials as driver members. Also cylindrical modules containing thin flextensional actuators may provide axial displacement in a downhole environment and may move a device axially along a downhole pipe or close a valve opening or inch along the pipe.