Methods of making physical unclonable functions having magnetic and non-magnetic particles
View Patent ↗A method of making a physical unclonable function (PUF) having magnetic and non-magnetic particles is disclosed. Measuring both magnetic field and image view makes the PUF difficult to counterfeit. PUF may be incorporated into a user-replaceable supply item for an imaging device. A PUF reader may be incorporated into an imaging device to read the PUF. Other methods are disclosed.
1. A method of making a security device comprising:
mixing a substrate material, a plurality of magnetizable particles each having a diameter greater than 25 microns, and a plurality of non-magnetizable particles each having a diameter greater than 100 microns;
causing the substrate material, magnetizable particles, and non-magnetizable particles to become solid as aggregate pellets;
magnetizing the magnetizable particles in the aggregate pellets so that a magnetic field orientation of the magnetized particles will be random; and
forming the aggregate pellets into the security device,
wherein the magnetizable particles have an average diameter of between 50 and 500 microns inclusive and the non-magnetizable particles have an average diameter of between 200 and 2000 microns inclusive.
2. The method of claim 1 , wherein the magnetizable particles are flakes having an average thickness that is less than their average diameter.
3. The method of claim 1 , wherein the non-magnetizable particles are flakes having an average thickness that is less than their average diameter.
4. The method of claim 1 , wherein the average diameter of the non-magnetizable particles is at least twice as large as the average diameter of the magnetizable particles.
5. The method of claim 1 , wherein the non-magnetizable particles are reflective.
6. The method of claim 1 , wherein the magnetizable particles contain neodymium and iron and boron.
7. The method of claim 1 , wherein the magnetizable particles contain samarium and cobalt.
8. The method of claim 1 , wherein the non-magnetizable particles contain metal.
9. A method of making a security device comprising:
mixing a substrate material, a plurality of magnetizable particles, and a plurality of non-magnetizable particles;
causing the substrate material, magnetizable particles, and non-magnetizable particles to become solid as aggregate pellets;
magnetizing the magnetizable particles in the aggregate pellets so that a magnetic field orientation of the magnetized particles will be random; and
forming the aggregate pellets into the security device,
wherein a ratio of the number of non-magnetizable particles to the number of magnetizable particles is between 1/10 and 2/1 inclusive.
10. The method of claim 9 , wherein the magnetizable particles are flakes having an average thickness that is less than an average diameter of the flakes.
11. The method of claim 9 , wherein the magnetizable particles have an average diameter of between 50 and 500 microns inclusive.
12. The method of claim 9 , wherein the non-magnetizable particles have an average diameter of between 200 and 2000 microns inclusive.
13. The method of claim 9 , wherein the magnetizable particles have a first average diameter, the non-magnetizable particles have a second average diameter, and the second average diameter is at least twice as large as the first average diameter.
14. The method of claim 9 , wherein the non-magnetizable particles are reflective.
15. The method of claim 9 , wherein the magnetizable particles contain neodymium and iron and boron.
16. The method of claim 9 , wherein the magnetizable particles contain samarium and cobalt.