WO2022056300A1

WO2022056300A1 - Authentication of dendritic structures

Info

Publication number: WO2022056300A1
Application number: PCT/US2021/049929
Authority: WO
Inventors: Michael N. Kozicki
Original assignee: Arizona State University ASU; Arizona State University Downtown Phoenix campus
Current assignee: Arizona State University ASU; Arizona State University Downtown Phoenix campus
Priority date: 2020-09-10
Filing date: 2021-09-10
Publication date: 2022-03-17
Anticipated expiration: 2023-03-10
Also published as: EP4211186A1; EP4211186A4; US20230394857A1; US12602944B2

Abstract

Assessing the authenticity of a dendrite on a substrate includes illuminating the dendrite and the substrate with radiation, obtaining a first image of the dendrite on the substrate at a first polarization angle, obtaining a second image of the dendrite on the substrate at a second polarization angle, and assessing a difference in intensity of a multiplicity of corresponding pixels of the candidate structure in the first image and the second image. If the difference in intensity of each pair of pixels of the multiplicity of corresponding pixels exceeds a preselected value, the dendrite is identified as authentic.

Description

AUTHENTICATION OF DENDRITIC STRUCTURES

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Application No. 63/076,708 filed on September 10, 2020, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] This invention relates to authentication of a dendritic structure based on the analysis of reflected light from a surface of the dendritic structure that is illuminated with polarized or unpolarized light.

BACKGROUND

[0003] A dendritic structure, or dendrite, is a structure that develops with a typical multi- branching, tree-like form. Dendritic patterns are common in nature and are seen in diverse phenomena such as snowflake formation and lightning. Dendritic crystallization forms a natural fractal pattern. A fractal is generally defined as a rough or fragmented geometric shape that can be subdivided into parts, each of which is (at least superficially) a reduced-size copy of the whole, a property called self-similarity. This self-similarity leads to a fine structure at arbitrarily small scales. Because they appear similar (but not identical) at all levels of magnification, fractals are often considered to be infinitely complex. In practice, however, the finest observable levels of structure are typically limited by physical and/or chemical constraints.

SUMMARY

[0004] This disclosure describes systems and methods for assessing the authenticity of dendrites or dendritic structures. The authentication is based on the analysis of reflected light from the surface of a dendrite or dendritic structure that is illuminated with polarized or unpolarized light. As used herein, a dendrite is “authentic” if variations in reflected light from a dendrite illuminated with polarized or unpolarized radiation at different polarization angles exceed a threshold value. Examples of authentic dendrites include dendrites that include facets (e.g., dendrites, such as metallic dendrites, formed by electrodeposition), dendrites that have compositional variations within a volume of material (e.g., particulate material, such as metal particles, within a binder), and dendrites that have phase separated regions. The dendrite can be formed on the substrate (e.g., a metallic dendrite formed by electrodeposition) or placed on the substrate after it is formed. The dendrite can be formed using multi-fluid systems and methods in which a first fluid is provided between a surface of a first substrate and a surface of a second substrate, and introducing a second fluid between the surface of the first substrate and the surface of the second substrate. In some cases, the first fluid includes particulate material, such as metallic particles (e.g., metal flakes).

[0005] These systems and methods are effective for dendrites with or without a protective layer transparent to the wavelength(s) of light used. A dendrite that is not authentic typically has a flat and featureless surface (e.g., a photographic image of a dendrite) or a three- dimensional structure without facets or compositional variation (e.g., a dendrite cast from a mold). For dendrites that are not authentic, the degree of linear polarization (DoLP) and the angle of linear polarization (AoLP) of the reflected light depend at least in part on material parameters, particularly refractive index and Brewster’s angle, and are typically uniform across the sample area. In the case of an authentic dendrite (e.g., an electrodeposited metallic dendrite, a dendrite with an appropriate compositional variation, a dendrite formed using multi-fluid systems and methods, or other materials and processes that form dendrites) extending from a surface of the substrate on which it is deposited, the morphology or composition of the surface typically causes slight changes in both DoLP and AoLP as a function of the location on the dendrite from which the light is reflected), so that a two- dimensional representation of these parameters provides a unique optically derived signature of the dendrite that cannot easily be reproduced by other means.

[0006] Although the disclosed inventive concepts include those defined in the attached claims, it should be understood that the inventive concepts can also be defined in accordance with the following embodiments.

[0007] In addition to the embodiments of the attached claims and the embodiments described above, the following numbered embodiments are also innovative.

[0008] Embodiment 1 is a method of assessing the authenticity of a dendrite on a substrate, the method comprising: illuminating the dendrite and the substrate with radiation; obtaining a first image of the dendrite on the substrate at a first polari zati on angle; obtaining a second image of the dendrite on the substrate at a second polarization angle; assessing a difference in intensity of a multiplicity of corresponding pixels of the candidate structure in the first image and the second image; and if the difference in intensity of each pair of pixels of the multiplicity of corresponding pixels exceeds a preselected value, identifying the dendrite as authentic.

[0009] Embodiment 2 is the method of embodiment 1 , wherein illuminating the dendrite with radiation comprises illuminating the dendrite with an illuminator or ambient light.

[0010] Embodiment 3 is the method of embodiments 1 or 2, wherein the radiation is in the visible range.

[0011] Embodiment 4 is the method of any one of embodiments 1-3, wherein obtaining the first image, the second image, or both comprises obtaining an image with a camera.

[0012] Embodiment 5 is the method of embodiment 4, wherein obtaining the first image, the second image, or both comprises operatively coupling the camera to two or more polarizers.

[0013] Embodiment 6 is the method of embodiment 4, wherein the camera is a polarization camera comprising polarizers.

[0014] Embodiment 7 is the method of any one of embodiments 1 -6, wherein a difference between the first polarization angle and the second polarization angle is at least 10°.

[0015] Embodiment 8 is the method of any one of embodiments 1-7, further comprising obtaining one or more additional images of the dendrite at one or more additional polarization angles.

[0016] Embodiment 9 is the method of embodiment 8, wherein the one or more additional polarization angles comprise a third polarization angle.

[0017] Embodiment 10 is the method of embodiment 9, where the first polarization angle is 0°, the second polarization angle is 90°, and the third polarization angle is 135°.

[0018] Embodiment 1 1 is the method of embodiment 8, wherein the one or more additional polarization angles comprise a third polarization angle and a fourth polarization angle.

[0019] Embodiment 12 is the method of embodiment 11, wherein the first polarization angle is 0°, the second polarization angle is 45°, the third polarization angle is 90°, and the fourth polarization angle is 135°.

[0020] Embodiment 13 is the method of any one of embodiments 1-12, further comprising obtaining an additional image of the dendrite with an unfiltered light component.

[0021] Embodiment 14 is the method of any one of embodiments 1-13, wherein the radiation is unpolarized.

[0022] Embodiment 15 is the method of any one of embodiments 1-13, wherein the radiation is polarized. [0023] Embodiment 16 is the method of any one of embodiments 1-15, wherein the preselected value is determined using a machine learning technique based on a multiplicity of images of authentic and non-authentic dendrites taken over a multiplicity of polarization angles.

[0024] Embodiment 17 is the method of embodiment 16, wherein the preselected value is based at least in part on one or more of a composition of the dendrite, a morphology of the dendrite, and a location of each pair of pixels with respect to the dendrite.

[0025] Embodiment 18 is the method of any one of embodiments 1-17, wherein the preselected value corresponds to, for each pair of pixels, a 5%, 10%, or 15% difference in intensity.

[0026] Embodiment 19 is the method of any one of embodiments 1-18, wherein the dendrite is a metallic dendrite or a multi -fluid dendrite.

[0027] Embodiment 20 is the method of embodiment 19, wherein the multi-fluid dendrite comprises metallic particles.

[0028] Embodiment 21 is a method of assessing the authenticity of a dendrite on a substrate, the method comprising: illuminating the dendrite and the substrate with radiation; obtaining a multiplicity of images of the dendrite on the substrate at a multiplicity of polarization angles; obtaining a degree of linear polarization image, an angle of linear polarization image, or both from the multiplicity of images; assessing a difference between an intensity of a pixel corresponding to the substrate and a pixel corresponding to the dendrite in the degree of linear polarization image, the angle of linear polarization image, or both; and if the difference exceeds a preselected value, identifying the dendrite as authentic.

In Embodiment 21, the multiplicity of polarization angles comprises two or more polarization angles.

[0029] Embodiment 22 is the method of embodiment 21, where the multiplicity of polarization angles comprise 0°, 90°, and 135°.

[0030] Embodiment 23 is the method of embodiment 21 or 22, wherein multiplicity of polarization angles comprise 0°, 45°, 90°, and 135°.

[0031] Embodiment 24 is the method of any one of embodiments 21-23, further comprising obtaining an additional image of the dendrite on the substrate with an unfiltered light component. [0032] Embodiment 25 is the method of any one of embodiments 21-24, wherein the multiplicity of images comprises a first image obtained at a first polarization angle and a second image obtained at a second polarization angle.

[0033] Embodiment 26 is the method of embodiment 25, wherein a difference between the first polarization angle and the second polarization angle is at least 10°.

[0034] Embodiment 27 is the method of any one of embodiments 21-26, wherein the dendrite comprises a coating transparent to the polarized or unpolarized radiation.

[0035] Embodiment 28 is the method of any one of embodiments 21-27, wherein the intensity of the pixels corresponding to the dendrite in the degree of linear polarization image, the angle of linear polarization image, or both is substantially uniform.

[0036] Embodiment 29 is the method of any one of embodiments 21-28, further comprising comparing the degree of linear polarization image, an angle of linear polarization image, or both with an unfiltered image of the dendrite and the substrate.

[0037] Embodiment 30 is the method of any one of embodiments 21-29, wherein the dendrite is a metallic dendrite or a multi-fluid dendrite.

[0038] Embodiment 31 is the method of embodiment 30, wherein the multi-fluid dendrite comprises metallic particles.

[0039] Embodiment 32 is the method of any one of embodiments 21-31, wherein the radiation is polarized.

[0040] Embodiment 33 is the method of any one of embodiments 21-31, wherein the radiation is unpolarized.

[0041] Embodiment 34 is the method of any one of embodiments 21-33, wherein the preselected value is determined using a machine learning technique based on a multiplicity of images of authentic and non-authentic dendrites taken over a multiplicity of polarization angles.

[0042] Embodiment 35 is the method of embodiment 34, wherein the preselected value is based at least in part on one or more of a composition of the dendrite, a morphology of the dendrite, and a location of each pair of pixels with respect to the dendrite.

[0043] Embodiment 66 is the method of any one of embodiments 21-35, wherein the preselected value corresponds to, for each pair of pixels, a 5%, 10%, or 15% difference in intensity.

[0044] The details of one or more embodiments of the subject matter of this disclosure are set forth in the accompanying drawings and the description. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

[0045] FIG 1 is an image of a silver dendrite grown on photographic paper. [0046] FIG. 2A is a degree of linear polarization (DoLP) image of the dendrite of FIG 1. FIG. 2B is an angle of linear polarization (AoLP) image of the dendrite of FIG; 1 .

DETAILED DESCRIPTION

[0047] This disclosure describes systems and methods for the authentication of a dendrite or dendritic structure. “Dendrite” and “dendritic structure” are used interchangeably herein. As described herein, each dendritic structure has a plurality of members extending away from a common point to form a stochastically branched arrangement of the members, wherein regions of the dendritic structure are stochastically self-similar to the entire dendritic structure. A maximum dimension of the dendrites is typically in a range of 5 mm to 5 cm. [0048] Metallic (i.e., metal or metal-containing) dendrites can be formed by electrodeposition in an ion conductor (i.e., an electrolyte) by generating an ion current in the ion conductor and using the flow of ions to build up the dendritic structure in or on the ion conductor via electrochemical processes. Metallic dendrites can include copper or silver.

The ion conductor can be liquid, gel, or solid, or a combination thereof. Additional details regarding metallic dendrites are found in U.S. Patent No. 10,074,000, which is incorporated herein by reference.

[0049] Multi-fluid dendrites can be formed by providing a first fluid between a surface of a first substrate and a surface of a second substrate and introducing a second fluid between the surface of the first substrate and the surface of the second substrate. The second fluid is in direct contact with the first fluid at a formation temperature, and a viscosity of the first fluid at the formation temperature exceeds a viscosity of the second fluid at the formation temperature. Formation of multi-fluid dendrites further includes separating the first substrate and the second substrate to yield a dendrite comprising the first fluid on the surface of the first substrate. The first fluid is hardened (e.g., by removing a solvent in the first fluid or polymerizing the first fluid) to solidify the dendrites. In one example, the first fluid includes (meth)acrylate monomers, (meth)acrylic resin, or both. The first fluid can also include particles that reflect light, such as metallic particles, glass particles, or the like. The second fluid can be a gas (e.g., air). In some examples, the resulting dendrites are acrylic or steel- reinforced acrylic.

[0050] As used herein, an “authentic dendrite” generally refers to a dendrite for which variations in reflected light from the dendrite illuminated with polarized or unpolarized radiation at different polarization angles exceed a threshold value. Additional details relating to polarized scanning of dendritic structures are found in U.S. Patent Publication No.

2020/0117882, which is incorporated herein by reference. The dendrite may be formed on a substrate (e.g., a metallic dendrite formed by electrodeposition, or a multi-fluid dendrite) or placed on the substrate after it is formed. The authentication is based on the analysis of reflected light from the surface of the dendrite.

[0051] The dendrite is illuminated with polarized or unpolarized light (e.g., from an illuminator or from ambient lighting), and the reflected light is analyzed using polarization optics. A polarization camera can be used as the imaging device. A unique optical signature is obtained for each authentic dendrite.

[0052] Systems and methods described herein are effective for dendrites with or without a protective layer transparent to the wavelength(s) of light used. For a flat and featureless surface, the degree of linear polarization (DoLP) and the angle of linear polarization (AoLP) of the refl ected light depend at least in part on material parameters, particularly refractive index and Brewster’s angle, and are typically uniform across the sample area. In the case of an authentic dendrite (e.g., an electrodeposited metallic dendrite, a dendrite with an appropriate compositional variation, a multi-fluid dendrite, or other materials and processes that form dendrites), the micro-roughness of the surface typically causes slight changes in both DoLP and AoLP as a function of location on the dendrite from which the light is reflected, so that a two-dimensional representation of these parameters provides a unique optically derived signature of the dendrite that cannot easily be reproduced by other means.

[0053] In polarization theory', the Stokes V ector elements are defined as:

where the flux measurements P through polarizing elements are: P_H horizontal linear polarizer (0°) P_v vertical linear polarizer (90°)

P₄₅ 45° linear polarizer

P₁₃₅ 135° linear polarizer

P_R right circular polarizer P_L left circular polarizer.

[0054] For linearly polarized light, the degree of linear polarization (DoLP) and the angle of linear polarization (AoLP) can be calculated by the following equations:

Both DoLP and AoLP are dependent on the material that is reflecting the light into the polarizing elements and can be influenced by the nature of the surface.

[0055] In one implementation, these measurements are performed with a camera and a number of polarizing elements that are sequentially placed between the object being analyzed (i.e., the dendrite) and the camera that is used to determine flux (via intensity). In one implementation, the polarizing elements are coupled to a wheel or a strip and mechanically swapped. In another implementation, these measurements are performed using a polarization camera (e.g., with polarizing elements built into the imaging sensor). An image of the dendrite is typically obtained at two or more polarization angles. One example includes two polarization angles greater than 10° apart. Another example includes three polarization angles (e.g., 0°, 90°, and 135°) and an unfiltered light component. Yet another example includes four polarization angles. Angles of 0°, 45°, 90°, and 135° can be used the Stokes Vector calculations; however, other combinations are possible.

[0056] The images are processed with software configured to assess a change in intensity for a multiplicity of corresponding pixels, where “corresponding pixels” refers to the set of pixels corresponding to the same location on the dendrite (or within, for example, a radius of one to three pixels), with each corresponding pixel associated with an image taken at a different polarization angle. In one example, the multiplicity of pixels is 1000 pixels and there are images at four different polarization angles, yielding 1000 sets of corresponding pixels, with four pixels in each set, all of which are associated with a specific location in the dendrite (i.e., a pixel in each image that corresponds to the same location on the dendrite). A difference in intensity for corresponding pixels refers to an intensity difference for each pair of pixels in each pixel set (e.g., six intensity differences for a set of four pixels).

[0057] If these intensity changes are within an expected range (or exceed a preselected value) and spatial distribution (e.g., a radius of one to three pixels) for the dendrite being imaged (e.g., electrodeposited metallic dendrites, dendrites with appropriate compositional variations, dendrites formed using multi-fluid systems and methods, or dendrites formed with other materials or processes), the dendrite can be confirmed as genuine (i.e., authentic). A preselected value of intensity change (e.g., a difference in intensity of each pair of pixels of corresponding pixels obtained in images at different polarization angles) can be determined using machine learning techniques trained using multiple images of genuine (authentic) and fake (not authentic) dendrites taken over a multiplicity of polarization angles. The preselected value is based at least in part, on a composition of the dendrite, a morphology of the dendrite, and a location of each pixel set with respect to the dendrite. In one example, the preselected value corresponds to, for each pair of pixels in each pixel set, at least a 10% difference in intensity, where the difference in intensity is calculated by the difference of two measured intensities at two polarization angles (e.g., (I1-I2)) and dividing this difference by the sum of these intensities (e.g., (I1-I2)/(I1+I2)).

[0058] If there is little or no change in intensity at each pixel on the pattern for the different polarization angles (i.e., if the change in intensity does not meet or exceed the preselected value for each pair of pixels in each pixel set), it is likely that the dendrite is not genuine (i.e., not authentic). A preselected value of intensity difference (e.g., a difference in intensity of each pair of pixels for each pixel set) can be determined using machine learning techniques trained using multiple images of genuine (authentic) and fake (not authentic) dendrites taken over a multiplicity of polarization angles. The preselected value is based at least in part on one or more of a composition of the dendrite, a morphology of the dendrite, and a location of the pixel in each pixel set with respect to the dendrite. Preselected values for the difference in intensity include, for example, 5%, 10%, or 15%, [0059] FIG. 1 is an image of a silver dendrite 100 grown on photographic paper 102. The silver dendrite 100 is formed on screen-printed silver electrode 104. FIGS. 2A and 2B are images showing the degree of linear polarization (DoLP) and the angle of linear polarization (AoLP), respectively, of dendrite 100. The colors in the scale bars correspond to the degree (from dark blue (0) to deep red (1)) and angle (from dark blue (0°) to deep red (180°)) of linear polarization. These images were obtained using a polarization camera. The relief of the electrodeposited structure is emphasized in the DoLP image 200 with the photographic paper background giving a uniform value around 0.1 and the edges of the dendritic pattern giving a value close to 0.5. The AoLP image 202 is even more distinctive with the background giving a fairly uniform value close to 60°and the edges of the pattern ranging from less than 50°to over 100°. Both of images 200, 202 are unique to this electrodeposited pattern and can be used to authenticate it and to differentiate it from, for example, a photographic copy, particularly when used in conjunction with the unfiltered image as shown in FIG. 1. Note that the use of 0°, 45°, 90°, and 135° polarizing filters can be needed for Stokes Vector calculations that lead to accepted values of DoLP and AoLP, as other polarization angles can be used to yield a unique polarization signature.

[0060] Although this disclosure contains many specific embodiment details, these should not be construed as limitations on the scope of the subject matter or on the scope of what may- be claimed, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this disclosure in the context of separate embodiments can also be implemented, in combination, in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments, separately, or in any suitable sub-combination. Moreover, although previously described features may be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[0061] Particular embodiments of the subject matter have been described. Other embodiments, alterations, and permutations of the described embodiments are within the scope of the following claims as will be apparent to those skilled in the art. While operations are depicted in the drawings or claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed (some operations may be considered optional), to achieve desirable results.

[0062] Accordingly, the previously described example embodiments do not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure.

Claims

WHAT IS CLAIMED IS:

1 . A method of assessing the authenticity of a dendrite on a substrate, the method comprising: illuminating the dendrite and the substrate with radiation; obtaining a first image of the dendrite on the substrate at a first polarization angle; obtaining a second image of the dendrite on the substrate at a second polarization angle; assessing a difference in intensity of a multiplicity of corresponding pixels of the candidate structure in the first image and the second image; and if the difference in intensity of each pair of pixels of the multiplicity of corresponding pixels exceeds a preselected value, identifying the dendrite as authentic,

2. The method of claim 1, wherein illuminating the dendrite with radiation comprises illuminating the dendrite with an illuminator or ambient light.

3. The method of claim 1, wherein the radiation is in the visible range.

4. The method of claim 1, wherein obtaining the first image, the second image, or both comprises obtaining an image with a camera.

5. The method of claim 4, wherein obtaining the first image, the second image, or both comprises operatively coupling the camera to two or more polarizers,

6. The method of claim 4, wherein the camera is a polarization camera comprising polarizers.

7. The method of claim 1, wherein a difference between the first polarization angle and the second polarization angle is at least 10°.

8. The method of claim 1, further comprising obtaining one or more additional images of the dendrite at one or more additional polarization angles,

9. The method of claim 8, wherein the one or more additional polarization angles comprise a third polarization angle.

10. The method of claim 9, where the first polarization angle is 0°, the second polarization angle is 90°, and the third polarization angle is 135°.

11. The method of claim 9, wherein the one or more additional polarization angles comprise a third polarization angle and a fourth polarization angle.

12. The method of claim 9, wherein the first polarization angle is 0°, the second polarization angle is 45°, the third polarization angle is 90°, and the fourth polarization angle is 135°.

13. The method of claim 1, further comprising obtaining an additional image of the dendrite with an unfiltered light component.

14. The method of claim 1, wherein the radiation is unpolarized.

15. The method of claim 1, wherein the radiation is polarized.

16. The method of claim 1, wherein the preselected value is determined using a machine learning technique based on a multiplicity of images of authentic and non-authentic dendrites taken over a multiplicity of polarization angles.

17. The method of claim 14, wherein the preselected value is based at least in part, on one or more of a composition of the dendrite, a morphology of the dendrite, and a location of each pair of pixels with respect to the dendrite.

18. The method of claim 1, wherein the preselected value corresponds to, for each pair of pixels, a 5%, 10%, or 15% difference in intensity.

19. The method of claim 1, wherein the dendrite is a metallic dendrite or a multi -fluid dendrite.

20. The method of claim 17, wherein the multi-fluid dendrite comprises metallic particles.

21. A method of assessing the authenticity of a dendrite on a substrate, the method comprising: illuminating the dendrite and the substrate with radiation; obtaining a multiplicity of images of the dendrite on the substrate at a multiplicity of polarization angles; obtaining a degree of linear polarization image, an angle of linear polarization image, or both from the multipli city of images; assessing a difference between an intensity of a pixel corresponding to the substrate and a pixel corresponding to the dendrite in the degree of linear polarization image, the angle of linear polarization image, or both; and if the difference exceeds a preselected value, identifying the dendrite as authentic.

22. The method of claim 21, where the multiplicity of polarization angles comprise 0°, 90°, and 135°.

23. The method of claim 21, wherein multiplicity of polarization angles comprise 0°, 45°, 90°, and 135°.

24. The method of claim 21, further comprising obtaining an additional image of the dendrite on the substrate with an unfiltered light component.

25. The method of claim 21, wherein the multiplicity of images comprises a first image obtained at a first polarization angle and a second image obtained at a second polarization angle.

26. The method of claim 25, wherein a difference between the first polarization angle and the second polarization angle is at least 10°.

27. The method of claim 21, wherein the dendrite comprises a coating transparent to the polarized or unpolarized radiation.

28. The method of claim 21 , wherein the intensity of the pixels corresponding to the dendrite in the degree of linear polarization image, the angle of linear polarization image, or both is substantially uniform.

29. The method of claim 21, further comprising comparing the degree of linear polarization image, an angle of linear polarization image, or both with an unfiltered image of the dendrite and the substrate.

30. The method of claim 21, wherein the dendrite is a metallic dendrite or a multi-fluid dendrite.

31. The method of claim 30, wherein the multi-fluid dendrite comprises metallic particles.

32. The method of claim 21, wherein the radiation is polarized.

33. The method of claim 21, wherein the radiation is unpolarized.

34. The method of claim 21, wherein the preselected value is determined using a machine learning technique based on a multiplicity of images of authentic and non-authentic dendrites taken over a multiplicity of polarization angles.

35. The method of claim 34, wherein the preselected value is based at least in part on one or more of a composition of the dendrite, a morphology of the dendrite, and a location of each pair of pixels with respect to the dendrite.

36. The method of claim 21 , wherein the preselected value corresponds to, for each pair of pixels, a 5%, 10%, or 15% difference in intensity.