阅读说明：本技术 具有多重磁性矫顽力的磁性物理不可克隆函数 (Magnetic physical unclonable function with multiple magnetic coercivities ) 是由 加里·A·丹顿 詹姆斯·P·德拉蒙德 罗伯特·亨利·麦森肯斯 于 2020-03-20 设计创作，主要内容包括：描述了两种不同的磁性矫顽力材料的使用,以便在同一安全对象上具有永久性内容和非永久性内容两者。提供具有聚合物基质复合材料的安全装置,该聚合物基质复合材料含有均匀分布的低矫顽力磁性材料,例如但不限于磁铁矿。结合该均匀背景,随机分布的高矫顽力磁性材料例如但不限于钕、铁和硼的合金(NdFeB)可以混合在第一均匀背景材料内,以在低矫顽力均匀背景内形成持久的磁性签名。这可以例如通过在一次复合操作中将低矫顽力材料和高矫顽力材料与一种基质材料复合来实现。(The use of two different magnetic coercivity materials is described to have both permanent and non-permanent content on the same security object. Security devices are provided having a polymer matrix composite containing a uniformly distributed low coercivity magnetic material such as, but not limited to, magnetite. In conjunction with this uniform background, a randomly distributed high coercivity magnetic material such as, but not limited to, an alloy of neodymium, iron, and boron (NdFeB) may be mixed within the first uniform background material to form a persistent magnetic signature within the low coercivity uniform background. This can be achieved, for example, by compounding the low coercivity material and the high coercivity material with a matrix material in one compounding operation.)

1. A secure device having both persistent content and non-persistent content, comprising:

a polymer matrix composite material containing a uniformly distributed low coercivity magnetic material;

a high coercivity magnetic material randomly distributed within the polymer matrix, wherein the high coercivity magnetic material forms a persistent magnetic signature within a low coercivity uniform background.

2. The security device of claim 1, wherein the low coercivity material is magnetite.

3. The security device of claim 1, wherein the high coercivity material is an alloy of neodymium, iron and boron.

4. A method of manufacturing a secure device having both permanent content and non-permanent content, comprising:

compounding a low coercivity material with a first polymer matrix material in a first compounding operation to form pellets;

compounding the high coercivity particles with a second polymer matrix material in a second compounding operation to form pellets;

pre-magnetizing the pellets with the high coercivity particles;

the security device was molded using two sets of pellets, resulting in a uniform low coercivity background material with random individual magnetized particles in the matrix.

5. The method of claim 4, wherein the first polymer matrix material and the second polymer matrix material are the same.

6. The method of claim 5, wherein the low coercivity material is magnetite.

7. The method of claim 6, wherein the high coercivity material is an alloy of neodymium, iron, and boron.

8. A method of manufacturing a secure device having both permanent content and non-permanent content, comprising:

compounding a low coercivity material with a first polymer matrix material in a first compounding operation to form pellets;

compounding the high coercivity particles with a second polymer matrix material in a second compounding operation to form pellets;

pre-magnetizing the pellets with the high coercivity particles;

the low coercivity pellets and the high coercivity pellets are molded in a coinjection operation to produce a part having regions of low coercivity and regions of high coercivity particles within the same part.

9. The method of claim 8, wherein the first polymer matrix material and the second polymer matrix material are the same.

10. The method of claim 9, wherein the low coercivity material is magnetite.

11. The method of claim 10, wherein the high coercivity material is an alloy of neodymium, iron, and boron.

12. A method of manufacturing a magnetic physical unclonable object, comprising:

incorporating a magnetizable feedstock of fine powder having an average particle size of less than 100 microns into a resin having a higher melting temperature to delay the melting point in an injection molding machine until shortly before the resin matrix reaches the injection nozzle;

applying an alternating magnetic field to the molten feedstock shortly before it enters the molding cavity to magnetize the low coercivity particles; and

injection molding the molten raw material.

13. A method of manufacturing a magnetic physical unclonable object, comprising:

combining a blend of magnetisable raw materials to produce pellets, wherein a first raw material contains about 20 to 30% by weight particles of an alloy of neodymium, iron and boron, and a second raw material contains about 20 to 40% by weight particles of magnetite;

magnetizing particles in the pellets prior to placing the pellets in an injection molding machine; and

limiting heating of a feed screw of the injection molding machine such that the feed screw provides limited melting of mixed material to produce a non-homogeneous part.

Background

U.S. patent No. 9,553,582, entitled "Physical Unclonable Functions providing Magnetic and Non-Magnetic Particles," discloses a PUF (physically Unclonable function) that contains Magnetic Particles that generate a complex Magnetic field near the surface of a PUF component. The magnetic field may be measured along a path and data corresponding to the magnetic field component recorded for subsequent verification of the PUF component. U.S. patent No. 9,608,828, entitled "Elongated Physical operable Function," discloses the advantage of magnetizing a feedstock prior to an injection molding process to achieve random orientation of magnetization directions.

In these patents, small flakes of an alloy of neodymium, iron and boron (NdFeB) are cited as preferred magnetic particles. These flakes are typically about 35 microns thick with irregular shapes varying from 100 and 500 microns in width, but can be of a variety of sizes. The NdFeB alloy is not easily magnetized because it has an intrinsic coercivity (coercivity) of about 9,000 oersted. However, once magnetized, it has a residual induction (residual induction) of about 9,000 gauss, and the random position and magnetic orientation (magnetic orientation) of the flakes produces a spike in magnetic field strength of 10-30 gauss when measured at a distance of about 0.5mm from the surface of the PUF.

SUMMARY

The present invention proposes the use of two different magnetic coercivity materials in order to have both permanent and non-permanent content on the same security object.

Brief Description of Drawings

The above-mentioned and other features and advantages of the disclosed embodiments, and the manner of attaining them, will become more apparent and will be better understood by reference to the following description of the disclosed embodiments taken in conjunction with the accompanying drawings.

FIG. 1A shows a typical magnetic profile of one of the magnetic ink character recognition physical unclonable function gears.

Fig. 1B is a close-up of the central portion of fig. 1A.

FIG. 2 shows a magnetic profile generated by contacting a portion of a magnetic ink character recognition physically unclonable function gear to a striped magnetic rectangle having a surface field in excess of 400 Gauss.

Figure 3 shows a typical magnetic cross-section of a gear ring made at a specific radius from the gear center containing 10% NdFeB flakes and 25% MO4232 powder by weight.

Fig. 4 shows a cross-sectional view according to fig. 3 after the component has been pressed against a strip-like magnetic rectangle with a surface field exceeding 400 gauss.

FIG. 5 shows the results of applying an AC magnetic field (300 Gauss) locally to erase the effect of a bar magnet on FIG. 4.

Figure 6 is a gear with a PUF disc.

Detailed Description

It is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. As used herein, the terms "having," "containing," "including," "containing," and the like are open-ended terms that indicate the presence of the stated element or feature, but do not exclude additional elements or features. The articles "a", "an" and "the" are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

Terms such as "about" and the like have contextual meanings for describing various characteristics of an object, and these terms have their ordinary and customary meanings to those of ordinary skill in the relevant art. Terms such as "about" and the like are intended in a first context to be "approximately" to the extent understood by one of ordinary skill in the relevant art; and in a second context for describing various characteristics of the object, and in such second context means "within a small percentage" as understood by one of ordinary skill in the relevant art.

Unless limited otherwise, the terms "connected," "coupled," and "mounted," and variations thereof herein are used broadly and encompass direct connections, couplings, and mountings, as well as indirect connections, couplings, and mountings. Further, the terms "connected" and "coupled" and variations thereof are not restricted to physical or mechanical connections or couplings. For ease of description, spatially relative terms such as "top", "bottom", "front", "back", "rear", and "side", "under", "below", "lower", "over", "upper", and the like are used to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Terms such as "first," "second," and the like, are also used to describe various elements, regions, segments, etc., and are also not intended to be limiting. Like terms refer to like elements throughout the description.

The present invention proposes the use of two different magnetic coercivity materials in order to have both permanent and non-permanent content on the same security object. In one embodiment of the innovation, an identification/security tag is provided having a polymer matrix composite material comprising a uniformly distributed low coercivity magnetic material, such as, but not limited to, magnetite. In conjunction with this uniform background, a randomly distributed high coercivity magnetic material, such as but not limited to an alloy of neodymium, iron, and boron (NdFeB), may be mixed within the first uniform background material to form a persistent magnetic signature within the low coercivity uniform background. This can be achieved by compounding the low coercivity material and the high coercivity material with a matrix material in one compounding operation.

Alternatively, in another embodiment, the low coercivity material may be compounded in a separate compounding operation to produce uniform pellets (pellets) of low coercivity magnetic particles in a polymer matrix. In a second operation, the high coercivity particles may be compounded into the same type of polymer matrix material to form pellets of the matrix resin with the high coercivity magnetic particles. The second group of pellets may then be pre-magnetized. The two sets of pellets were used to mold labels therefrom, resulting in a uniform low coercivity background material with random individual magnetized particles in the matrix.

In use, such high coercivity material may continue to be used as a physically unclonable unique signature for the tag, but the industry using the tag may use a simple magnetic writing head to write additional data on the background of the low coercivity material without affecting the high coercivity material. In this way, a single magnetic reader can read both the permanent unique identifier and the temporary writable data (e.g., indexes, fiducials (fiducials), volume reduction, or other tracking information).

In another embodiment, both sets of the described pellets can be used in a "two shot" (co-injection) molding operation to produce a part having regions of low coercivity and regions of high coercivity particles within the same part, and thus writable and permanent regions in the part.

These devices may be used in a similar manner to that described above, using a single reader to read both permanent and temporary data. In variations of this embodiment, the separate regions may be joined by any of a number of joining operations, such as, but not limited to, laser welding or ultrasonic welding.

Injection molded magnets are typically fully dense magnetic powders blended with a variety of polymer matrix materials (base materials). Depending on the combination of magnetic material and polymer selected, a wide range of final material properties are possible. The magnetic powder may be ferrite, NdFeB or a composite of samarium and cobalt. Commonly used resins are nylon 6/12 (poly (hexamethylene dodecanamide)), nylon 12 (poly (dodecyl-12-lactam)), PPS (polyphenylene sulfide), and PMMA (polymethyl methacrylate).

Black MO4232 is a synthetic black magnetic iron oxide pigment (magnetite, triiron tetroxide) produced by the United states Thai Industries, Inc (Catay Industries USA, Inc). The pigment is used in magnetic ink character recognition ("MICR") toners. MICR toner is a specialized toner used by the banking industry for check processing. The black MO4232 is acicular in shape, has a low magnetic coercivity, and has a high curie temperature. Black MO4232 has long been in the magnetic ink and magnetic transfer ribbon (magnetic transfer ribbon) industry and is used for specialized high quality toners that require high remanent magnetization. Black MO4232 complies with the hazardous substances restriction regulation ("RoHS").

TABLE 1 magnetic and physical Properties of Black MO4232

Properties of	Value of	Unit of
			Hc, coercive force	310	(Oe,VSM)
Sigma M, specific magnetization	87	(emu/g)
			Sigma R, remanent magnetization	32	(emu/g)
Curie temperature	1085	°F
			Average length	0.45	μm
Length/width ratio	5:1

Referring to fig. 6, a sample disc 611 was injection molded in PMMA resin containing about 25% by weight MICR powder (black MO4232 from the american national tai industries). The MICR stock was pre-magnetized prior to use in the injection molding process. The molded disc was about 62mm in diameter and 1.2mm thick. The discs were machined to produce rings having an inner diameter of about 20mm and an outer diameter of 33 mm. The ring is mounted on the drive gear 621 and the magnetic profile is recorded on the tape about 1mm at a certain radius 631 from the center of the gear.

Figure 1A shows a typical magnetic profile view of one of the MICR PUF gears. FIG. 1B is a close-up of the central portion of the magnetic profile. The amplitude of the magnetic profile is typically less than 1 gauss at the time of molding. Random magnetic profile amplitudes in excess of 5 gauss predicted by finite element modeling (finite element modeling) are possible. The low magnetic field amplitudes observed are believed to be due to the thorough mixing (homogenization) of the magnetite compound in the injection molding machine.

Figure 2 shows a magnetic profile generated by exposing a portion of a MICR PUF gear to a strip-like magnetic rectangle with a surface field in excess of 400 gauss. Magnetic profile amplitudes in excess of 10 gauss indicate that this compound can be readily magnetized to produce a magnetic profile readable with a low cost three-dimensional ("3D") magnetometer integrated circuit chip.

PUF gear rings comprising 10% NdFeB flakes and 25% MO4232 powder by weight were also manufactured. Figure 3 shows a typical magnetic profile of one of these rings at a certain radius from the center of the gear. Fig. 4 shows a cross-section of the same track after the part has been pressed against the bar magnet used in fig. 2.

Fig. 5 shows the result of locally applying an AC magnetic field (-300 gauss) to erase the effect of a bar magnet.

The magnetic PUF object is injection molded using a blend of raw material pellets selected from table 1 below. Since the magnetite feed is a fine powder (average particle size less than about 100 microns), it may be advantageous to incorporate this material into a resin having a higher melting temperature to retard the melting point in the injection molding machine until shortly before the injection nozzle. Thus, a non-uniform distribution of magnetite particles will be achieved. An alternative method of achieving random orientation of the MICR compound would be to apply an alternating magnetic field of 500-1000 oersted to the molten feedstock shortly before it enters the molding cavity to magnetize the low coercivity particles.

TABLE 2 raw pellet blend

Type of raw material	Weight% of plastic	Plastic/melting temperature	Weight% NdFeB	Weight% magnetite
					1	50％	PA-6,12/190℃	20％	30％
2	70-80％	PA-6,12/190℃	20-30％	0％
					3	60-80％	PA-6,10/215℃	0％	20-40％
4	50％	PPS/280℃	0％	50％

Example 1. blend of feedstock No. 2 and feedstock No. 3 was used to mold PUF parts. The raw material pellets containing the magnetic material are magnetized before entering the injection molding machine. The feed screw and heating of the injection molding machine are designed or modified so that they provide limited mixing of the molten material and do not produce homogeneous parts. The molded part may have visible eddies or bands of the two materials, i.e., it will not appear homogeneous.

Within each band/domain of # 3 material, the magnetization direction may slowly vary with position in a random manner, producing a measurable contribution to the magnetic "fingerprint" of each PUF component, which is recorded and used for later verification.

If the PUF is attached to a printer toner cartridge, for example, when the toner cartridge is empty, an AC magnetic field may be applied to the PUF causing the low coercivity magnetic material to be erased or magnetized in a different pattern. Such a change in the magnetic fingerprint will cause future authentication failures of this toner cartridge and will prevent unauthorized refilling of the toner cartridge.

Alternatively, such PUF concepts may be used to authenticate a user-exchangeable article at the beginning of life, and the low coercivity pattern may be gradually erased at a radial angle (X% of a 360 ° radial path) or at an amplitude during the life of the article. Such an implementation may, for example, prevent the item from being reset to a new or "toner filled" state when the remaining life of the item is less than 30%.

If the item undergoes re-verification over a later lifetime, a verification algorithm may be written to accept lower correlation or verification test results depending on the amount of lifetime remaining for the item. This would allow authentic toner cartridges to be transferred between printers over a later life, but it would prevent a refilled cartridge after the cartridge has reached the end of life.

Example 2 PUF parts were moulded using raw material No. 1. Conventional mixing of molten raw materials during the injection molding process results in a homogeneous mixture of materials. To create regions in which the magnetite pigment particles are significantly magnetized, an alternating magnetic field may be applied to the molten material shortly before it enters the molding cavity. This will change the direction of the MICR particle magnetization without affecting the magnetization of the NdFeB platelets. Again, if so desired, the MICR component of the magnetic field may be erased at the end of the cartridge life.

Example 3 PUF parts were molded using raw material No. 1. Conventional mixing of molten raw materials during the injection molding process results in a homogeneous mixture of materials. The molded part will have random magnetic fingerprints generated from NdFeB flakes. By momentarily contacting the PUF object with a permanent magnet, the PUF object is subjected to a secondary magnetization step. The permanent magnet preferably has multiple north and south poles, which are used to magnetize low-coercivity magnetite particles in the PUF object. This creates a complex magnetic fingerprint that can be used for authentication. Again, if so desired, the MICR component of the magnetic field may be erased at the end of the cartridge life to prevent further use of the associated toner cartridge. During the manufacturing registration procedure, the disc fingerprint may be registered before and after the secondary permanent magnet magnetization step. This will allow the printer in the field to distinguish the cartridge as a genuine/authentic cartridge even after the cartridge is empty and has been magnetically erased.

Example 4.5 stock was extruded into a sheet or ribbon, i.e., less than about 0.5mm thick. This material was cut into flakes and the flakes were compounded with No. 2 feedstock to form pellets with both NdFeB and MICR flakes. These pellets are magnetized and used as a raw material for injection molding PUF objects. These PUF objects will have a mixture of high and low coercivity flakes that generate random magnetic fingerprints. And at the end of the cartridge life, the low coercivity flakes can be erased to alter the magnetic fingerprint and thereby prevent the cartridge from being authenticated.

Example 5 PUF parts are moulded in a double injection moulding process. On the first injection, feed No. 2 was used to mold the inner ring of the pre-magnetized high coercivity magnetic compound. At the second injection, raw material No. 3 was used to mold the outer ring of the low coercivity magnetic compound. The magnetic fingerprint of the inner ring is measured and processed to generate enrolment data.

Variable data (e.g., PUF serial number, geographic location, toner load, etc.) may be encrypted and written on the outer loop. If the data is written in a radial stripe about 0.5mm wide, then the 100-200 bits of data can be read by a second Hall effect sensor chip in the printer in a manner similar to reading a PUF profile. Such a double ring component may also be formed by molding each ring separately and then joining the rings in a secondary operation.

When the supply item has reached the end of its life, the information on the outer ring may be erased and unauthorized refilling/reuse of the supply item may be detected and prevented. Similar to example 1, the numerical information on the outer ring may be erased in stages to indicate the remaining life of the article.

Embodiment 6. in an alternative form, PUF features are moulded in the same way as in embodiment 5, however these features are not necessarily uniform rings of annular material. The initial injection of high coercivity material may be a partial disc with segments missing (in this example). A subsequent second shot (or portion) may fill the gap in the initial shot and produce a low coercivity (writable) segment within the same annular path. This may allow the same sensor travelling on a circular path to be used for reading signals from both the writable segment and the permanent segment of the PUF. The writeable segment may be used for serial numbers, toner levels, or other short-term information about manufacturing.

A desirable feature of this embodiment is that a single signal from one sensor path may be used as the unique PUF signal for verification, and a portion of that signal path may be written to include identification information as an integral part of the verification data. These data will be needed in the signal in order to create a cloned PUF. However, when the PUF reaches the end of life, this identification segment may be overwritten or erased, and then the PUF will not be able to pass the verification. However, since the PUF verification data still contains "unclonable" permanent data from the high coercivity segment of the code, even if a portion of the code is writable, the cloner is still unable to clone the PUF.

The foregoing description of embodiments has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the disclosure to the precise steps and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.