First progress report on a multi-channel magnetic drum inner ...

III-3
commonly is assembled from two semicircles into a ring closed everywhere
except for an exceedingly narrow gap, on the order of oOOl inch. (See
sketch C52020) A current through the coil produces magnetic flux, some
of which goes directly across the gap while the remainder "fringes"
out to the side and constitutes the useful magnetic field effecting the
recording process. In sound-recording practice the heads are aligned
with this gap transverse to the direction of relative motion of the
magnetic medium, (see sketch C52019) with which they are usually
maintained in rubbing contact, A brisf current pulse applied to this
system produces on the surface of the medium a magnetized spot in the
form of a small dipole, coplanar with the surfac* and with sixis parallel
to the direction of relative motion. In applying such sound-recording
heads to the present purpose the technique would be to use the same
orientation but to operate at a narrow clearance rather than in rubbing
contact with the magnetizeable surface of the drum. Under these conditions
of separation, the fringing flux is even less effective and a smaller
percentage of the total, and therefore most i>f the flux produced by the
signal current serves no more useful purpose than to raise the inductance
of the device to an excessive value.
4) The category of ills just described are all symptomatic of
the same disease, namely poor coupling between the conductor system
("•winding") and the medium to be magnetically inscribed. For convenient
reference these and their essentially synonomous diagnoses are listed: