fig1 of the drawings illustrates for the sake of completeness the electrical circuit of one form of magnetic stimulator suitable for use in the present invention . the particular example is one of several different stimulators which are the subject of , and are more fully described in , u . s . pat . no . 5 , 766 , 124 to polson , commonly assigned herewith . this particular example has a high - voltage power supply 1 which charges a reservoir capacitor 2 . charge is transferred from the reservoir capacitor , substantially independently of the charging rate of the reservoir capacitor , via a transfer capacitor 5 to a ‘ discharge ’ capacitor 9 , which at appropriate intervals is discharged into a stimulating coil 11 . the transfer capacitor 5 is part of a charge pump which includes a unidirectional switch 3 , a series inductor 4 , the transfer capacitor 5 , a reverse diode 6 in parallel with the capacitor 5 , a series inductor 7 and a switching system 8 , which comprises controlled rectifiers 8 a , 8 b , 8 c and 8 d . the discharge of the capacitor 9 is . controlled by the switching system 10 comprising controlled rectifiers 10 a , 10 b , 10 c and 10 d . the discharge current may be in either direction through the coil 11 , which has an earth connection . discharge pulses , of magnitude and frequency which are controllable by the switching systems 8 and 10 , flow through the coil 11 . typically the instantaneous current may be of the order of 5 ka , i . e . considerably in excess of 1 ka ; the rms value of a typical pulse train may be hundreds of amps , such as 400 a . fig2 illustrates some of the physical components of the system . they are the coil 11 , which will be more fully described later , a flexible insulating conduit 12 , a heat exchanger connection box 14 and a conduit 15 . the ends of the coil inside their cooling tubes ( to be described ) pass through the conduit 12 to the box 14 and the coil ends pass through the conduit 15 to the rest of the stimulator as described with reference to fig1 . as will be described later , in this example the coil is disposed inside a flexible tube which conveys a fluid coolant . fig3 illustrates the connections between the coil , the heat exchanger and the stimulator . the stimulator 16 is for example as described with reference to fig1 . the conductor 11 a constituting the electrical element of the coil 11 is connected as shown in fig1 to the remainder of the stimulator . the conductor is preferably self - supporting but flexible . it may ( for example ) be copper wire having a diameter in the range 2 . 5 to 3 mm . the conductor 11 a , which has an insulating cover , forms the turns 18 of the coil of the coil 11 . over most of its length the conductor 11 a , which has an insulating cover ( not shown ) is enclosed in a flexible tube 17 which is connected to allow a pump 19 to pump fluid coolant through the tube 17 and a heat exchanger 20 . in this embodiment there are two segments and to the tube , the conductor at its middle part 11 b coming out of one end of one tube segment and entering the other tube segment . respective ends of the tube segments are connected to the pump and the heat exchanger . thus in this example there are two parallel paths for coolant to flow adjacent the coil , one flow cooling the inner turns of the coil and the other flow cooling the outer turns of the coil . coolant from the heat exchanger 20 flows to a reservoir 21 connected to the pump 19 and is recirculated through the tube 17 during the operation of the stimulator . fig4 - 6 are different views of the flexible cooled coil &# 39 ; s general construction . the conductor 11 a in its tube extends along and within the flexible elongate conduit 15 which comprises two end connectors 12 a and 12 b and an intermediate part comprising a ribbed plastics tube 12 c . the end connector 12 a is adapted in any convenient manner for connection to the connection box . the other end 12 b is connected to a generally disc - shaped sheath 22 within which the turns of the coil are located in the same plane . fig4 illustrates the ‘ rear ’ of the coil , i . e . that which faces away from the patient in use . fig5 illustrates a side view , showing the flat character of the sheath 22 in its original unflexed state . fig6 illustrates the coil head form the front , i . e . that which is adjacent the patient in use . embedded in the sheath 22 and close to its front surface are temperature sensors 23 with electrical connections 24 that extend back along the conduit to the stimulator . shown schematically is a safety switch 25 ( fig3 ) which in any convenient manner can disable the stimulator , to prevent current flow through the coil , if the sensed temperature is too high . there may be flow detectors within the coolant circuit comprising the pump , heat exchanger , reservoir and the connecting conduits . accordingly if the coolant flow reduces to below some pre - set value the application of current to the stimulating coil would be prevented . this is another safety feature to ensure that a thermally hazardous condition is avoided . by way of example a flow detector 26 within the coolant circuit is shown diagrammatically at 26 and is coupled to the safety switch 25 . fig7 illustrates the coil in section , the section being taken on the line x - x in fig4 . the coil , comprising the conductor 11 a and its surrounding tube 17 is encapsulated in the flexible , silicone rubber moulded disc - shaped sheath 22 . the tube 17 may be a silicone plastic material . the sheath 22 has on its rear side a bulge 26 which accommodates the lead - in and lead - out parts of the conductor in its tube 17 . the coolant can flow along the space 27 between the insulated conductor 11 a and the surrounding tube 17 . other forms of cooling system may be employed . in the particular example , the outer tube is a conduit through which coolant is driven to cool the coil . however , the coil may be disposed adjacent or within a jacket through which coolant may be driven . the coil could be hollow and itself define a conduit through which coolant may be driven . fig8 illustrates the flexing of the sheath 22 and thereby the coil 11 from a flat condition 11 - 1 thorough a moderately flexed condition to a fully flexed condition 11 - 3 . the flexing of the head may be plastic , in that it will remain in the particular flexed state and not elastically revert to the flat un - flexed state . the amount of flexure may be chosen by an administrator to suit the contour or shape of the body part against which the coil is located . it may be necessary to employ straps , or other holding means to locate the coil securely on the patient . alternatively the flexure may be elastic ; in this event the use of straps or other holding means is desirable to ensure that the coil is maintained in its flexed configuration and in position on the patient . a variety of materials would be suitable for the sheath 22 . a silicone rubber compound may be used . the degree of hardness of the rubber may be chosen according to the desired elasticity of the flexure ; a hard silicone rubber would be appropriate for an elastic sheath and a softer silicone rubber if the sheath is intended to flex plastically , the shape being maintained by the flexible copper wire inside the sheath .
a stimulating coil for use in the magnetic stimulation of neuro - muscular tissue comprises a self - supporting but flexible conductor in a flexible insulating sheath which can be adjusted by hand to conform the coil to the contours of a selected part of the human body . the coil is provided with a cooling system which includes a conduit disposed adjacent or within the coil and a pump for driving coolant through the conduit .