Electro-mechanical transducer

Claim 2

A moving coil transducer comprising a bobbin of magnetically soft ferro-magnetic material having a cylindrical portion wound with an actuating windiNg between end cheeks, each of the end cheeks being disposed in the gap between a pair of axially spaced magnetically linked pole pieces at each end comprising parallel plates having apertures shaped to admit the end cheeks and spaced apart at a distance approximately equal to the thickness of the end cheeks.

Claim 3

A moving coil transducer according to claim 1 in which the innermost pair of pole pieces are connected by soft iron yokes, and the outermost pair are connected by soft iron yokes, and permanent magnets are arranged between the yokes of the inner pair and the yokes of the outer pair to magnetically link the pole pieces and maintain the pole pieces with the required polarities.

Claim 4

A moving coil transducer comprising a bobbin of magnetically soft ferro-magnetic material having a cylindrical portion wound with an actuating winding between end cheeks, each of the end cheeks being disposed in the gap between a pair of pole pieces comprising parallel plates having apertures shaped to admit the end cheeks and spaced apart at a distance approximately equal to the thickness of the end cheeks, said bobbin being supported with its end cheeks in the pole piece gaps by a pair of flexible diaphragms, the spring stiffness of the diaphragms providing a restoring force to maintain the end cheeks centralised in the gaps when no current is flowing through the actuating winding.

Claim 5

A moving coil transducer comprising a bobbin of magnetically soft ferro-magnetic material having a cylindrical portion wound with an actuating winding between end cheeks, each of the end cheeks being disposed in the gap between a pair of pole pieces comprising parallel plates having apertures shaped to admit the end cheeks and spaced apart at a distance approximately equal to the thickness of the end cheeks, said bobbin being supported with its end cheeks in the pole piece gaps by a pair of flexible diaphragms, the spring stiffness of the diaphragms providing a restoring force to maintain the end cheeks centralised in the gaps when no current is flowing through the actuating winding.

Claim 6

A moving coil transducer according to claim 3 having an axial rod of non-magnetic material passing centrally through the bobbin and screwed at its ends to take clamping nuts by means of which the bobbin is clamped to the diaphragms.

Claim 7

A moving coil transducer comprising a bobbin of magnetically soft ferro-magnetic material having a cylindrical portion wound with an actuating winding between end cheeks, each of the end cheeks being disposed in the gap between a pair of pole pieces comprising parallel plates having apertures shaped to admit the end cheeks and spaced apart at a distance approximately equal to the thickness of the end cheeks, the innermost pole piece at each end being coupled to the outermost pole piece at the other end by one or more soft magnetic cores carrying magnetising windings.

Claim 8

A moving coil transducer comprising a bobbin of magnetically soft ferro-magnetic material having a cylindrical portion wound with an actuating winding between end cheeks, each of the end cheeks being disposed in the gap between a pair of pole pieces comprising parallel plates having apertures shaped to admit the end cheeks and spaced apart at a distance approximately equal to the thickness of the end cheeks, the innermost pole piece at each end being coupled to the outermost pole piece at the other end by one or more soft magnetic cores carrying magnetising windings.

Claim 9

A moving coil transducer according to claim 5 in which the actuating winding is connected in series with the magnetising windings so that in operation the force acting on the bobbin is proportional to the square of the current passing through the transducer.

Claim 10

A moving coil transducer according to claim 5 in combination with two sources of direct current connected one to the actuating winding and the other to the magnetising winding so that in operation the force on the bobbin is proportional to the product of the two currents.

Claim 11

A moving coil transducer according to claim 5 in combination with a source of two alternating currents of the same frequency applied one to the actuating winding, and the other to the magnetising windings, so that the force acting on the bobbin is a measure of the phase difference between the currents in the two coils.