Abstract: The invention is directed to a magnetic field sensing device (FSD) capable of visually indicating exposure to a magnetic field with a strength that exceeds a threshold value. The magnetic FSD comprises a magnetic layer magnetized in a pattern and a material positioned adjacent the magnetic layer to render the pattern visible. When the FSD is exposed to a magnetic field with a strength that exceeds the threshold, the pattern visibly alters. The threshold value is approximately equal to a coercivity of the magnetic layer of the FSD, which is at least approximately 3000 Oersteds.

Abstract: The invention is directed to a magnetic field sensing device (FSD) capable of visually indicating exposure to a magnetic field with a strength that exceeds a threshold value. The magnetic FSD comprises a magnetic layer magnetized to define a pattern. The threshold value is approximately equal to a coercivity of the magnetic layer of the FSD, which is at least approximately 3000 Oersteds. The pattern becomes visible when a finely divided magnetic material is applied over the magnetic layer. Then, when the FSD is exposed to a magnetic field with a strength that exceeds the threshold, the pattern visibly alters (e.g., typically disappears altogether). Accordingly, upon re-application of the finely divided magnetic material, the alteration of the pattern is evidence of successful degaussing.

Abstract: A magnetic field strength detector includes a magnetic field sensing element that outputs voltage as a function of magnetic field strength. In some embodiments, the magnetic field sensing element comprises a coil, and voltage is induced across the coil as a function of the magnetic field strength. A magnetic field strength detector also includes an indicator that alters as a function of the voltage output by the magnetic field sensing element when the magnetic field strength exceeds a threshold. The alteration is substantially irreversible and, in some embodiments, visible. The detector may be used to, for example, measure the strength of a magnetic field generated by a degaussing device, or to confirm that a particular medium was exposed to a magnetic field with a strength adequate to degauss the medium.

Abstract: The invention is directed to a servo writing apparatus having accurate alignment of write gaps of servo write heads. In particular, the write gaps substantially align in a servo channel corresponding to a servo band of a magnetic data storage tape. The servo band is fully magnetized (a.k.a. DC erased) in one direction by a direct current (DC) magnetic field across the write gap of one of the servo write heads. Time-based servo markings magnetized in a second direction are recorded on the fully magnetized servo band by a pulsed magnetic field across the write gaps of the other servo write head. The servo write heads may be mounted in a mounting structure within the servo writing apparatus. Maintaining a large mounting structure width to servo write head separation distance ratio improves write gap alignment accuracy, which assures full servo signal strength across the servo band without magnetizing adjacent data bands.