Estimation of small effective gap length beyond recording resolution in magnetic data recording systems

A new method is described whereby extremely short effective gap lengths of ring type reproducing heads used in high resolution magnetic recording instruments can be determined. The method is based on comparison of the frequency or wavelength response of the short gap head with that of a second head of longer gap length which can be conveniently measured by the first null-point method reported previously. Experimental results for the measurement of a head gap of the order of 20 × 10⁻⁶ in are given as an illustration.