Electromagnetic window

1. A device configured to be substantially transparent to electromagnetic radiation of a certain frequency band defined by two frequencies F 1 and F 2 of the maximal transparency of the device, the device comprising at least one dielectric structure of a predetermined thickness loaded with inclusions forming a predetermined substantially periodic pattern inside said at least one dielectric structure, wherein a value of said predetermined thickness is defined by a central frequency between said frequencies F 1 and F 2 and is such that said at least one dielectric structure in its unloaded state has minimal transparency for said central frequency, and the inner pattern is formed by a two-dimensional array of spaced-apart substantially identical sub-resonant capacitive elements, which are disconnected from each other and are made of an electrically conducting material capable of scattering the electromagnetic radiation, said capacitive elements having a geometry and size and being spaced from one another in an array such that the device is tuned to be substantially transparent to said frequencies F 1 and F 2 .

2. The device according to claim 1 , wherein the periodicity of said inner pattern is such that average density of the elements is approximately the same all along a patterned area.

3. The device according to claim 1 , wherein dimensions of the radiation scattering elements and spaces between them are selected such that the scattering from said elements substantially compensates for reflection effects from dielectric discontinuities at and inside the device.

4. The device according to claim 1 , wherein the array of said elements is positioned in a plane located at the middle of the dielectric structure parallel to planes defined by upper and lower surfaces of the dielectric structure.

5. The device according to claim 1 , wherein the size of the electrically conductive element is such that the fundamental resonance frequency of the element is above said certain frequency band.

6. The device according to claim 1 , wherein the thickness of the dielectric structure is such that the dielectric structure without the inner pattern has first and second reflection minima in the frequency domain, the center of said certain frequency band of the device being approximately a mid point between said first and second reflection minima.

7. The device according to claim 1 , wherein the dielectric structure comprises a single dielectric layer formed with said inner pattern.

8. The device according to claim 7 , wherein the electrically conductive element has the size smaller than the half-wavelength of propagation of said electromagnetic radiation in said dielectric structure.

9. The device according to claim 7 , wherein the thickness of the dielectric layer is about 0.75, wherein is the wavelength of propagation of said radiation in the dielectric layer.

10. The device according to claim 1 , wherein said at least one structure is a substantially symmetrical structure formed by a stack of dielectric layers, wherein the central dielectric layer is formed with said inner pattern.

11. The device according to claim 10 , wherein the dielectric layers are made of different dielectric materials characterized by different wavelengths of propagation of said electromagnetic radiation.

12. The device according to claim 11 , wherein the electrically conductive element has the size smaller than the half of at least maximal wavelength of propagation of said electromagnetic radiation in said dielectric structure.

13. The device according to claim 11 , wherein the thickness of the device is in the range from three quarters of the shortest wavelength and three quarters of the longest wavelength of radiation propagation in the different dielectric layers at the central frequency of said frequency band.

14. The device according to claim 1 , wherein said elements are made of a metal-containing material.

15. The device according to claim 1 , wherein said elements are formed by coating conductive elements with one or more dielectric layers.

16. The device according to claim 1 , wherein said elements are formed by coating dielectric elements by at least one conducting layer.

17. The device according to claim 1 , wherein said elements are formed by selective coating of through-holes or honeycomb cores.

18. The device according to claim 1 , wherein said at least one dielectric structure has a constant thickness all along its length, thereby providing a constant thickness of the device all along the device.

19. The device according to claim 1 , wherein said at least one dielectric structure has a varying thickness all along its length, thereby providing a varying thickness of the device all along the device.

20. The device according to claim 1 , wherein said elements have circular or polygonal cross-section.

21. The device according to claim 1 , wherein said elements are voluminous.

22. The device according to claim 1 , and also comprising electrically conductive strips arranged in a spaced-apart parallel relationship on opposite surfaces of said at least one dielectric structure.

23. The device according to claim 1 , and also comprising at least two layers made of a ferroelectric material at opposite sides of said at least one dielectric structure.

24. The device according to claim 23 , wherein said ferroelectric layers are formed with electrically conductive strips arranged in a spaced-apart parallel relationship to be charged and grounded during an application of an electric field to the ferroelectric layers.

25. The device according to claim 1 , capable of transmitting the electromagnetic radiation impinging thereon at an angle of incidence up to 60 degrees.

26. The device according to claim 1 , and also comprising at least one additional dielectric structure with a predetermined substantially periodic inner pattern formed by a two-dimensional array of spaced-apart substantially identical sub-resonant capacitive elements made of an electrically conducting material and capable of scattering said electromagnetic radiation, and arranged in a disconnected from each other spaced-apart relationship, the at least two structures being located one above the other.

27. A device substantially transparent to electromagnetic radiation of a certain frequency band defined by two frequencies F 1 and F 2 of the maximal transparency of the device, the device comprising at least one dielectric structure of a thickness of about 0.75 λ, wherein λ is the wavelength of propagation of said radiation in the dielectric structure; said dielectric structure being loaded with inclusions forming a predetermined substantially periodic pattern inside said at least one dielectric structure, said thickness of said at least one dielectric structure causing said at least one dielectric structure, in its unloaded state, to have minimal transparency for a central frequency between said two frequencies F 1 and F 2 said periodic, pattern being formed by a two-dimensional array of spaced-apart substantially identical sub-resonant capacitive elements, which are disconnected from each other and are made of an electrically conducting material capable of scattering the electromagnetic radiation, said elements having a geometry and size and being space from one another in an array such that the device is tuned to be substantially transparent to said frequencies F 1 and F 2 .

28. A device substantially transparent to electromagnetic radiation of a certain frequency band defined by two frequencies F 1 and F 2 of the maximal transparency of the device, the device comprising a dielectric layer of a thickness of about 0.75 λ, wherein λ is the wavelength of propagation of said radiation in the dielectric layer, said dielectric layer being loaded with inclusions forming a predetermined substantially periodic pattern inside said dielectric layer, said thickness of the dielectric layer causing said dielectric layer, in its unloaded state, to have minimal transparency for a central frequency between said two frequencies F 1 and F 2 , said pattern inside said dielectric layer being formed by a two-dimensional array of spaced-apart substantially identical sub-resonant capacitive elements, which are disconnected from each other and are made of an electrically conducting material capable of scattering the electromagnetic radiation, each of the elements having a size smaller than λ/2, said elements having a geometry and being spaced from another in an array such that the device is tuned to be substantially transparent to said frequencies F 1 and F 2 .

29. A radiation source for generating electromagnetic radiation of a certain frequency band, the radiation source comprising the device constructed according to claim 1 , accommodated adjacent to an emitter of the electromagnetic radiation.

30. A frequency-selective multi-reflector device comprising a sub-reflector element substantially transparent for certain frequencies and totally reflective for other frequencies, wherein said sub-reflector is the device of claim 10 .

31. A radiation source for generating electromagnetic radiation of a certain frequency band, the radiation source comprising an emitter of the electromagnetic radiation, and a window device accommodated adjacent to said emitter and being substantially transparent with respect to said certain frequency band of the electromagnetic radiation, said band being defined by two frequencies F 1 and F 2 of the maximal transparency of the window device, the window device comprising at least one dielectric structure of a predetermined thickness, and loaded with inclusions forming a predetermined substantially periodic pattern inside said at least one dielectric structure, wherein a value of said predetermined thickness is defined by a central frequency between said two frequencies F 1 and F 2 and is such that said at least one dielectric structure in its unloaded state has minimal transparency for said central frequency between said two frequencies F 1 and F 2 , and said periodic pattern is formed by a two-dimensional array of spaced-apart substantially identical sub-resonant capacitive elements, which are disconnected from each other and are made of an electrically conducting material capable of scattering the electromagnetic radiation, said elements having a geometry and size and being spaced from one another in an array such that the window device is tuned to be substantially transparent to said frequencies F 1 and F 2 .

32. A controllable device for transmitting electromagnetic radiation of a certain frequency band defined by two frequencies F 1 and F 2 of the maximal transparency of the window device, the device comprising:

at least one dielectric structure of a predetermined thickness, which is defined by a central frequency between said two frequencies F 1 and F 2 and is such that said at least one dielectric structure in an unloaded state has minimal transparency for the central frequency between said two frequencies F 1 and F 2 ;

an inner pattern formed by inclusions inside said at least one dielectric structure, the pattern being in the form of a two-dimensional array of substantially identical electrically conductive sub-resonant capacitive elements capable of scattering said electromagnetic radiation, said elements being disconnected from each other in a spaced-apart relationship, and having a geometry and size to enable tuning of the window device to be substantially transparent to said frequencies F 1 and F 2 ; and

at least two ferroelectric layers located at opposite sides of said at least one dielectric structure, such that application of an electric field to said ferroelectric layer effects a change in a dielectric constant of said ferroelectric layer.

33. A method for constructing a device to be substantially transparent to electromagnetic radiation of a certain frequency band defined by two frequencies F 1 and F 2 of the maximal transparency of the window device, the method comprising: fabricating at least one dielectric structure made from at least one dielectric material of a predetermined dielectric constant and having a predetermined thickness, which is defined by a central frequency between said two frequencies F 1 and F 2 and is such that said at least one dielectric structure in an unloaded state has minimal transparency for the central frequency between said two frequencies F 1 and F 2 ; and loading said at least one dielectric structure with inclusions forming an inner pattern inside said at least one dielectric structure in the form of a two-dimensional array of substantially identical sub-resonant capacitive electrically conductive scattering elements arranged in a disconnected spaced-apart relationship, the geometry and size of the electrically conductive scattering elements being provided with a geometry and size and a spacing and between the elements to ensure that the scattering from said elements compensates for reflection effects from the dielectric discontinuities to thereby tune the device to be substantially transparent to said frequencies F 1 and F 2 .

34. The device according to claim 1 , wherein the thickness of the dielectric structure is such that said dielectric structure in its unloaded state, free of any inclusions, is maximally reflective to said central frequency and is maximally transparent for a certain non-zero frequency lower than said frequency band.

35. A device configured to be maximally transparent to electromagnetic radiation of two predetermined frequencies F 1 and F 2 , the device comprising:

at least one dielectric structure made of a certain dielectric material with a certain dielectric constant, said at least one dielectric structure having a thickness selected to define a central frequency between said frequencies F 1 and F 2 and is of about three quarters of a wavelength of propagation of the electromagnetic radiation in said dielectric structure at said central frequency;

a plurality of inclusions defining a substantially periodic pattern of electrically conductive elements inside the dielectric material, said inclusions consisting of an array of substantially identical sub-resonant capacitive elements disconnected from each other, and having a geometry and size with spaces between each other in the array such that the device is tuned to be substantially transparent to said frequencies F 1 and F 2 , said device being tuned by balancing the radiation reflected from dielectric discontinuities of the dielectric structure with the radiation scattered from the conducting inclusions.

36. A device configured to be maximally transparent to electromagnetic radiation of two predetermined frequencies F 1 and F 2 , the device comprising:

at least one dielectric structure having a thicknesses selected to define a central frequency between said frequencies F 1 and F 2 , such that the dielectric structure in an unloaded state, free of any inclusions, has minimal transparency for the central frequency between said frequencies F 1 and F 2 and is maximally transparent for a certain non-zero frequency lower than said frequencies F 1 and F 2 ;

a plurality of inclusions defining a substantially periodic pattern of electrically conductive elements inside said dielectric structure, said inclusions consisting of a plurality of substantially identical sub-resonant capacitive elements disconnected from each other, and having a geometry, size and spaces between one another such that the device is tuned to be maximally transparent to said frequencies F 1 and F 2 , said device being tuned by balancing the radiation reflected from dielectric discontinuities of the dielectric structure with the radiation scattered from the conducting inclusions.

37. A method for constructing a window device to be maximally transparent to electromagnetic radiation of predetermined frequencies F 1 and F 2 , the method comprising:

providing at least one dielectric structure made from at least one dielectric material of a predetermined dielectric constant and having a predetermined thickness selected to define a central frequency between said frequencies F 1 and F 2 , said thickness being such that said dielectric structure in an unloaded state, free of any inclusions, has minimal transparency for said central frequency between the frequencies F 1 and F 2 and is transparent for a certain non-zero frequency lower than said frequencies F 1 and F 2 ;

loading the dielectric structure with electrically conductive inclusions forming an inner pattern inside the dielectric structure, said inner pattern of the inclusions consisting of an array of substantially identical, sub-resonant, capacitive, electrically conductive, scattering elements arranged in a disconnected spaced-apart relationship, the geometry and size of the electrically conductive scattering elements and the spaces between the elements being selected so as to enable tuning of the window device to said frequencies F 1 and F 2 by balancing the radiation reflected from the dielectric discontinuities of the dielectric structure with the radiation scattered from said elements.