The reciprocity principle in the theory of magnetic recording

The reciprocity principle that is used frequently in the theory of magnetic recording is generalized so as to be valid under rather general conditions, the most fundamental one of which requires the linearity of the materials with respect to their electric and magnetic properties. The general reciprocity principle is derived from Maxwell's equations and presented in two forms containing the open-circuit voltage and the short-circuit current, respectively, of the magnetic reproducing head. The familiar forms of the principle, which are currently used in the cases of impulse response and harmonic response of the reproducing head, are obtained as specializations of the general principle.