Unidirectional near-field focusing using near-field plates
View Patent ↗A near-field plate is a non-periodically patterned surface that can overcome the diffraction limit and confine electromagnetic fields to subwavelength dimensions. By controlling the interference of the electromagnetic fields radiated by the near-field plate with that of a source, the near-field plate can form a subwavelength near-field pattern in a forward direction, while suppressing fields in other directions, such as those reflected. The resulting unidirectional near-field plate may find utility in many applications such as high resolution imaging and probing, high density data storage, biomedical targeting devices, and wireless power transfer.
1. A method for unidirectional subwavelength focusing and near-field manipulation using near-field plates, the method comprising:
generating a source field pattern from an excitation source at a focal plane;
generating a subwavelength field pattern from a near-field plate when the near-field plate is excited by the excitation source, the near-field plate being at a distance, d, from the excitation source;
forming a desired field pattern at the focal plane from the subwavelength field pattern and the source field pattern, the focal plane being at a distance, L, from the excitation source; and
configuring the desired field pattern to be a unidirectional subwavelength field pattern in a desired direction by increasing the amplitude of the desired field pattern in the desired direction.
2. The method of claim 1 , wherein increasing the amplitude of the desired field pattern includes varying an amplification factor that affects the field strength.
3. The method of claim 1 , wherein increasing the amplitude of the desired field pattern at the focal plane is based on combining the subwavelength field pattern and the source field pattern such that the subwavelength field pattern interferes constructively with the source field pattern in the desired direction while destructively in other undesired directions.
4. The method of claim 1 , further comprising forming the near-field plate as a plurality of non-periodically modulated surface impedance elements.
5. The method of claim 4 , wherein the plurality of non-periodically modulated surface impedance elements is formed using subwavelength metallic or dielectric patterning.
6. The method of claim 1 , wherein d is less than L.
7. The method of claim 1 , wherein the excitation source is an elementary electromagnetic source.
8. The method of claim 7 , wherein the excitation source induces currents on the near-field plate.
9. The method of claim 8 , wherein configuring the desired field pattern to form the unidirectional subwavelength field pattern in the desired direction includes matching the magnitude of the sum of the currents induced on the near-field plate to be close to the magnitude of the current source, and to have nearly opposite phase.
10. The method of claim 1 , wherein the excitation source is a probe in an imaging system, and the method further comprising:
disturbing the unidirectional subwavelength field pattern by placing one or more objects at the focal plane; and
measuring changes in the unidirectional subwavelength field pattern by examining the input impedance of the probe to detect the presence of the one or more objects.
11. The method of claim 1 , wherein the excitation source is a transmitting loop in a wireless power transfer system, and the method further comprising forming the unidirectional subwavelength field pattern in the desired direction for power transmission from the transmitting loop to a receiving loop, wherein a device is placed near the receiving loop to receive power transmitted by the transmitting loop.
12. The method of claim 11 , wherein the transmitting loop and near-field plate form a unidirectional field that illuminates the receiving loop.
13. The method of claim 12 , wherein the near-field plate comprises an arrangement of loops with loading impedances to form the unidirectional subwavelength field pattern, wherein the axes of the loops in the arrangement of loops are arranged perpendicularly or in-plane with respect to the surface of the near-field plate.
14. The method of claim 11 , wherein the device includes one or more of a computer, a smartphone, a biometric sensor device, a chargeable battery, or an automobile using a chargeable battery.
15. An apparatus for unidirectional subwavelength near-field focusing, the apparatus comprising:
an excitation source generating a source field pattern; and
a near-field plate generating a subwavelength field pattern when excited by the excitation source;
wherein after traversing a near-field distance, L, the source field pattern and the subwavelength field pattern form a desired field pattern at a focal plane, wherein the desired field pattern is a unidirectional subwavelength field pattern when the amplitude of the subwavelength field pattern is increased.
16. The apparatus of claim 15 , wherein the apparatus is configured to have an amplification factor that produces the unidirectional subwavelength field pattern.
17. The apparatus of claim 15 , wherein the excitation source and the near-field plate are configured to combine the subwavelength field pattern and the source field pattern such that the subwavelength field pattern interferes constructively with the source field pattern in the desired direction, while destructively in other undesired directions.
18. The apparatus of claim 15 , wherein the near-field plate comprises a plurality of non-periodically modulated surface impedance elements.
19. The apparatus of claim 18 , wherein the plurality of non-periodically modulated surface impedance elements have a subwavelength metallic patterning or subwavelength dielectric patterning.
20. The apparatus of claim 15 , wherein the excitation source is an elementary electromagnetic source.
21. The apparatus of claim 15 , wherein the excitation source induces currents on the near-field plate.
22. The apparatus of claim 21 , wherein the excitation source and the near-field plate are configured to form the unidirectional subwavelength field pattern in the desired direction is by matching the magnitude of the sum of the currents induced on the near-field plate to be close to the magnitude of the current source, and having an opposite phase.
23. The apparatus of claim 15 , wherein the excitation source is a transmitting loop in a wireless power transfer system, and wherein the unidirectional subwavelength field pattern in the desired direction is formed for power transmission from the transmitting loop to a receiving loop, wherein a device is placed near the receiving loop to receive power transmitted by the transmitting loop.
24. The apparatus of claim 23 , wherein the transmitting loop and near-field plate are configured to form a unidirectional field for the receiving loop.
25. The apparatus of claim 24 , wherein the near-field plate comprises an arrangement of loops with loading impedances to form the unidirectional subwavelength field pattern, wherein the axes of the loops in the arrangement of loops are arranged perpendicularly or in-plane with respect to the surface of the near-field plate.
26. The apparatus of claim 23 , wherein the device includes one or more of a computer, a smartphone, a biometric sensor device, a chargeable battery, or an automobile using a chargeable battery.