Magnetic keys having a plurality of magnet layers with holes
View Patent ↗Magnetic keys having a plurality of magnetic layers having holes are disclosed. The location and orientation of the holes are controlled to generate magnetic fields that are of sufficient strength to be reliably read and sufficient complexity to be difficult to counterfeit. The magnetic keys are located on imaging-device supply items along with non-volatile memory devices containing measurements of the magnetic fields that are digitally signed. These supply items are difficult to counterfeit. Other devices are disclosed.
1. A supply item for an imaging device comprising:
a body;
a magnetic key located on the body having a first magnet layer stacked above a second magnet layer, the first magnet layer has a first plurality of holes extending through the first magnet layer, the second magnet layer has a second plurality of holes extending through the second magnet layer, the first magnet layer and the second magnet layer generate a magnetic field having an intensity that varies along a top surface of the magnetic key; and
a non-volatile memory located on the body containing an array of numbers corresponding to the intensity of the magnetic field at a first plurality of locations above the top surface of the magnetic key and also containing a digital signature generated from the array of numbers,
wherein the first magnet layer surrounds the first plurality of holes and the second magnet layer surrounds the second plurality of holes.
2. The supply item of claim 1 , wherein the first magnet layer has a top surface with a north pole on its top surface and the second magnet layer has a top surface with a south pole on its top surface.
3. The supply item of claim 1 , further comprising a third magnet layer stacked below the second magnet layer, the third magnet layer has a third plurality of holes extending through the third magnet layer.
4. The supply item of claim 1 , wherein some holes in the first plurality of holes do not overlap with any holes in the second plurality of holes.
5. The supply item of claim 1 , wherein some holes in the first plurality of holes partially overlap with some holes in the second plurality of holes.
6. The supply item of claim 1 , wherein the first magnet layer has a top surface with both a north pole and a south pole.
7. The supply item of claim 1 , wherein the first plurality of holes has an average hole area that is less than one square mm.
8. The supply item of claim 7 , wherein the first magnet layer has a thickness that is between 0.1 and 0.5 mm inclusive.
9. The supply item of claim 8 , wherein the first magnet layer has a top surface, the second magnet layer has a bottom surface, and the distance between the first magnet layer top surface and the second magnet layer bottom surface is less than 1.5 mm.
10. The supply item of claim 1 , wherein the first plurality of holes has a first average hole area, the second plurality of holes has a second average hole area, and the second average hole area is greater than the first average hole area.
11. The supply item of claim 1 , wherein the first magnet layer contains a neodymium-iron-boron compound having a density greater than three g/cm 3 .
12. The supply item of claim 1 , wherein the first plurality of holes was formed by laser ablation.
13. The supply item of claim 1 , wherein the magnetic key has a bottom surface opposite the top surface of the magnetic key and the array of numbers contains numbers corresponding to the intensity of the magnetic field at a second plurality of locations below the bottom surface of the magnetic key.
14. A supply item for an imaging device comprising:
a body;
a magnetic key located on the body having a magnet layer having a first hole and a second hole with a strip of the magnet layer separating the first hole and the second hole, the magnet layer generates a magnetic field above a top surface of the magnetic key having an intensity that varies along the top surface; and
a non-volatile memory located on the body containing an array of numbers corresponding to the intensity of the magnetic field at a plurality of locations above the top surface and also containing a digital signature generated from the array of numbers,
wherein the magnet layer surrounds the first hole and the second hole, and the first hole and the second hole are relatively larger than the strip of the magnet layer separating the first hole and the second hole.
15. The supply item of claim 14 , wherein the strip of the magnet layer separating the first hole and the second hole is rectangular.
16. The supply item of claim 14 , wherein the strip of the magnet layer separating the first hole and the second hole is less than one mm at its narrowest width.
17. The supply item of claim 14 , wherein the magnet layer contains a neodymium-iron-boron compound having a density greater than three g/cm 3 .
18. The supply item of claim 14 , wherein the first hole and the second hole were formed by laser ablation.
19. A supply item for an imaging device comprising:
a body;
a magnetic key located on the body having a first magnet layer stacked above a second magnet layer, the first magnet layer has a first hole extending through the first magnet layer, the second magnet layer has a second hole extending through the second magnet layer, the first magnet layer and the second magnet layer generate a magnetic field above a top surface of the magnetic key having an intensity that varies along the top surface; and
a non-volatile memory located on the body containing an array of numbers corresponding to the intensity of the magnetic field at a plurality of locations above the top surface and also containing a digital signature generated from the array of numbers,
wherein the first hole is positioned directly above the second hole and the second hole is larger than the first hole.
20. The supply item of claim 19 , wherein the first hole was formed by laser ablation.