Spacing loss factor for the read back from a perpendicular medium with a soft underlayer

The read back signal from a perpendicular medium can be expressed as the medium magnetic charge multiplied by the spacing loss factor and the head characteristic matrix. The spacing loss factor for a perpendicular recording medium with a soft underlayer is given a simple analytical expression. The dependence of the spacing loss on the flying height and the recording wave number for a perpendicular medium is significantly different from that for a longitudinal medium. The spacing loss factor can be interpreted as the factor to be applied on the medium charge sheet in order to keep the field at the head constant when the sheet position is shifted.