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: Reference heads for use in flexible data storage cards are disclosed. In one embodiment, a reference head includes a planar card surface for attachment to an interior housing surface of a flexible data storage card, and a non-planar reference surface opposite the planar card surface. In one embodiment, a non-symmetric reference head for use in a flexible data storage card housing a rotatable media disc includes a body defining a first planar surface opposite an optically smooth second planar surface, and a location feature formed in the body. In this regard, the location feature is configured to reproducibly orient the optically smooth second planar surface toward the rotatable media disc.

Abstract: A method of manufacturing media reference surfaces for use in a flexible data storage card is described that includes providing a metal sheet and processing the metal sheet into a plurality of media reference surfaces. The metal sheet has a first side and a second side, where at least one side has an optically smooth surface characterized by an average surface roughness not greater than 8 micro-inch. Each media reference surface is characterized by having at least one curved edge adjacent the optically smooth surface. The processing is characterized by an absence of hand polishing.