ELLIPTICAL POLARIZERS, TAGS AND IDENTIFICATION SYSTEMS USING FREQUENCY SELECTIVE SURFACES

• US 20090121014A1
• Filed: 05/28/2008
• Published: 05/14/2009
• Est. Priority Date: 11/08/2007
• Status: Active Grant

• Current Assignee: University of Central Florida Research Foundation Inc. (State University System of Florida)
• Original Assignee: University of Central Florida Research Foundation Inc. (State University System of Florida)
• Inventors: Tharp, Jeff, Boreman, Glenn, Mullally, Daniel E.
• Granted Patent: US 7,629,569 B2
• Time in Patent Office: Days
• US Class Current: 235/380
• CPC Class Codes: G02B 5/204 in which spectral selection is performed by means of a conductive grid or array, e.g. frequency selective surfaces for use with wavelengths longer than the infrared light H01Q15/0006
• CPC Class Codes: G02B 5/3058 comprising electrically conductive elements, e.g. wire grids, conductive particles
• CPC Class Codes: G06K 19/06009 with optically detectable marking G06K19/063, G06K19/08 take precedence

Abstract

An optical combination includes a substrate, a linear polarizer on the substrate, and a first frequency selective surface (FSS) based elliptical polarization filter on the linear polarizer. The first FSS comprises at least one periodic pattern of spaced apart electrically conductive lines having a sub-wavelength line-to-line spacing orientated along a first axis. The pattern is operable to impose a phase differential for one orthogonal linear polarization state relative to the other linear polarization state for electromagnetic radiation having a wavelength between 400 nm and 1 mm, such as 1 μm to 12 μm. An identification system and associated method for identifying objects includes at least one tag having encoded information attached to the surface of an object to be identified, wherein the tag includes a first FSS-based elliptical polarization filter which provides the encoding. A remotely located receiver including a second FSS-based elliptical polarization filter and a linear polarizer optically coupled to the second filter is operable for differentially attenuating the first and second orthogonal polarization states allowing a determination whether the intensity pattern corresponds to the encoded information.

Claims

1. An optical combination, comprising:

a substrate;

a linear polarizer on said substrate, and

a elliptical polarization filter comprising a first frequency selective surface (FSS) on said linear polarizer, said first FSS comprising least one periodic pattern of spaced apart electrically conductive lines having a sub-wavelength line-to-line spacing, said lines including at least one subwavelength geometrical feature, said pattern being operable to impose a phase differential for one orthogonal linear polarization state relative to the other linear polarization state for electromagnetic radiation having a wavelength from 400 nm to 1 mm.

2. The combination of claim 1, wherein said wavelength is from 1 μ

m to 12 μ

m.

3. The combination of claim 1, further comprising a linear polarizer in optical alignment with said first FSS.

4. The combination of claim 3, wherein said linear polarizer is stacked together with said first FSS.

5. The combination of claim 3, wherein said linear polarizer is spaced apart from said first FSS.

6. The combination of claim 1, wherein said linear polarizer is oriented at an angle of 43 to 47 degrees with respect to an axis said lines are aligned along.

7. The combination of claim 1, wherein substrate comprises a flexible substrate, wherein a thickness of said flexible substrate is <

20 μ

m.

8. The combination of claim 1, wherein an absolute value of said phase differential imposed by said polarization filter is from 86 to 94 degrees or 175 to 185 degrees.

9. The combination of claim 1, wherein said features comprise shapes selected from the group consisting of a square wave, sawtooth and sinusoid.

10. The combination of claim 1, wherein said at least one pattern comprises a plurality of first and a plurality of second sub-patterns, said lines associated with said first sub-pattern aligned along a first axis and said lines associated with said second sub-pattern being along a second axis rotated 70 to 90 degrees relative to said first axis.

11. The combination of claim 1, further comprising:

a first dielectric layer on said first FSS, and

a second FSS on said first dielectric layer, said second FSS comprising a second periodic pattern of spaced apart electrically conductive lines having a sub-wavelength line-to-line spacing, said lines including at least one subwavelength geometrical feature, said first pattern and said second pattern including at least one optically coupled portion.

12. The combination of claim 11, wherein said first and said second pattern are aligned within 10 degrees relative to one another.

13. The combination of claim 11, wherein said first and second pattern each comprise a first and second sub-pattern, said lines associated with said first sub-pattern aligned along a first axis and said lines associated with said second sub-pattern being along a second axis rotated 70 to 90 degrees relative to said first axis.

14. The combination of claim 11, wherein said linear polarizer is oriented at an angle of 43 to 47 degrees with respect to an axis said lines of said first FSS are aligned along.

15. The combination of claim 11, wherein a thickness of said first dielectric is within 15% of a quarter of an effective mean wavelength of radiation being processed by said combination.

16. The combination of claim 11, wherein an absolute value of said phase differential imposed by said combination is from 86 to 94 degrees or 175 to 185 degrees.

17. An identification systems comprising:

at least one tag having encoded information attached to the surface of an object to be identified, said tag comprising a first elliptical polarization filter, said first elliptical polarization filter comprising a first frequency selective surface (FSS) disposed on said surface, said first FSS comprising least a first periodic pattern of spaced apart electrically conductive lines having a sub-wavelength line-to-line spacing, said lines including at least one subwavelength geometrical feature, said pattern being operable to receive incident radiation having a wavelength between 400 nm and 1 mm and output radiation having a phase differential for one orthogonal linear polarization state relative to the other linear polarization state;

a receiver remotely located from said tag operable for differentially attenuating said first and said orthogonal polarization states comprising a second elliptical polarizing filter coupled to receive said output radiation, said second elliptical filter comprising a second FSS comprising least one periodic second pattern of spaced apart electrically conductive lines having a sub-wavelength line-to-line spacing, said lines including at least one subwavelength geometrical feature, and a first linear polarizer optically coupled to said second elliptical polarizing filter;

a photodetector optically coupled to said linear polarizer for generating an intensity pattern, and

a processor operable for determining whether said intensity pattern corresponds to said encoded information.

18. The system of claim 17, wherein said wavelength is from 1 μ

m to 12 μ

m.

19. The system of claim 17, wherein said first pattern comprises a plurality of first and a plurality of second sub-patterns, said lines associated with said first sub-pattern aligned along a first axis and said lines associated with said second sub-pattern being along a second axis rotated 70 to 90 degrees relative to said first axis.

20. The system of claim 19, wherein at least a portion of said second pattern is substantially aligned and has at least a pattern portion substantially matching said first sub-pattern or said second sub-pattern operable for passing said output radiation from said first or said second sub-pattern, wherein after processing by said linear polarizer and detection by said photodetector radiation transmitted by said pattern portion forms bright regions in said intensity pattern.

21. The system of claim 17, wherein substrate comprises a flexible substrate.

22. The system of claim 17, wherein an absolute value of said phase differential imposed by said first filter is from 86 to 94 degrees or 175 to 185 degrees.

23. The system of claim 17, wherein said tag further comprises a second linear polarizer sandwiched between said surface of said object and said first FSS, whereby said system is a passive system.

24. The system of claim 17, further comprising a light source for providing said incident radiation, wherein said incident radiation is linearly polarized.

25. The system of claim 24, wherein said tag further comprises a reflective layer interposed between said first FSS and said surface of said object.

26. A method for identifying objects using a remotely located receiver and at least one polarizing tag comprising a frequency selective surface (FSS) comprising a first and at least a second different elliptical polarization emitting portion disposed on a surface of an object to be identified, comprising:

responsive to radiation received at or emitted from said surface, said tag emitting encoded information by emitting a first elliptically polarized emission from said first portion and a second different elliptically polarized emission from said second portion, and

differentially attenuating one of said first and said second elliptically polarized emission to create a differential intensity pattern between said first and said second polarization emitting portion when viewing radiation emanating from said surface received at said remotely located receiver, and

determining whether said intensity pattern corresponds to said encoded information.

27. The method of claim 26, wherein said tag emits left and right hand circular polarization from said first and said second portions, respectively.

28. The method of claim 26, further comprising the step of adhering said tag along with a binder material to said surface, wherein said binder material comprises a substantially infrared transparent material.

29. The method of claim 28, wherein said at least one tag comprises a plurality of said tags in said binder.

30. The method of claim 26, wherein said radiation received at said surface consists essentially of thermal radiation emanating from said object.

31. The method of claim 26, wherein said radiation received at said surface comprises radiation provided by an external radiation source.