Identification and mapping of underground facilities
A system or method of creating a map of voids in the ground based on a scattered electromagnetic signal includes traversing a receiver/probe in a near field above a target area; generating a signal from a signal transmitter, the signal having a predetermined wavelength λ; receiving a scattered signal with the receiver/probe, the scattered signal including indications of subsurface variations via reflection of the generated signal; and detecting evanescent components of the scattered signal to provide a predetermined resolution. The method includes the use of an electrically small antenna for resolution of subwavelength features. The metamaterial-based antenna is on the order of meters and has an efficient transmit/receive capability. The ESA is 1/10 of the length of the equivalent dipole length, and may be scaled down to 1/10,000. Such an antenna may include phase sensitive current injection in the metamaterial resonant structures for loss-compensation.
1. A method of creating a map of voids in the ground based on reflected electromagnetic signal, comprising:
traversing a metamaterial electrically small antenna receiver/probe in a near field above a target area;
generating a signal from a signal transmitter located above the target area, the signal having a predetermined wavelength λ of between 10 kHz to 500 kHz;
receiving a reflected signal with the metamaterial electrically small antenna receiver/probe, the reflected signal including indications of subsurface variations via reflection of the generated signal; and
detecting components of the reflected signal to provide a predetermined resolution.
2. The method of claim 1 , wherein the predetermined wavelength is defined by a hypothetical underground facility, the underground facility having a dimension that is characterized by the following equation:
λ/ N ; wherein N is at least 10.
3. The method of claim 1 , wherein the step of traversing the metamaterial electrically small antenna receiver/probe in a near field above a target area includes traversing a path in a low altitude that follows a profile of the Earth's surface.
4. The method of claim 1 , wherein the altitude of the path is in the range of thirty meters to fifty meters.
5. The method of claim 1 , wherein the altitude of the path is in the range often meters to one kilometer.
6. The method of claim 1 , wherein the signal transmitter is disposed in a far field.
7. The method of claim 1 wherein the signal transmitter in the far field includes an antenna having a length between about ½ and ¼ of the predetermined wavelength λ.
8. The method of claim 7 , wherein an incident wave generated by the signal transmitter is substantially a plane wave.
9. The method of claim 1 , wherein the transmitter includes an electrically-small antenna.
10. The method of claim 9 , wherein the length of the electrically-small antenna being in the range of λ/10 to λ/10,000 of the predetermined wavelength λ.
11. The method of claim 9 , wherein the transmitted signal is a generally conical beam.
12. The method of claim 9 , wherein the capability of the metamaterial electrically small antenna receiver/probe to resolve objects compared to a wavelength of interrogation is a function of the fact that the transmitter transmits the signal in the near field of a source and an object.
13. The method of claim 1 , wherein the signal transmitter and the metamaterial electrically small antenna receiver/probe are deployed on an aircraft that traverses the flight path in a near field, the flight path approximately conforming to the profile of a surface above a region of interest.
14. The method of claim 1 , wherein the altitude of the flight path is approximately λ/N, wherein λ is the wavelength and N is an integer value greater than 1.
15. A method of creating a map of voids in the ground based on a reflected electromagnetic signal, comprising:
traversing in an aircraft having a metamaterial electrically small antenna receiver/probe and signal transmitter, in a near field above a target area;
generating a signal from a signal transmitter located above the target area, the signal having a predetermined wavelength λ of between 10 kHz to 500 kHz;
receiving a reflected signal with the metamaterial electrically small antenna receiver/probe, the reflected signal including indications of subsurface variations via reflection of the generated signal; and
detecting components of the reflected signal to provide a predetermined resolution.
16. The method of claim 15 , wherein the predetermined wavelength is defined by a hypothetical underground facility, the underground facility having a dimension that is characterized by the following equation:
λ/ N ; wherein N is at least 10.
17. The method of claim 15 , wherein the step of traversing includes traversing a path in a low altitude that follows a profile of the Earth's surface.
18. The method of claim 15 , wherein the metamaterial electrically small antenna receiver/probe be the altitude of the path is in the range of thirty meters to fifty meters.
19. The method of claim 15 , wherein the transmitter includes an electrically-small antenna.
20. The method of claim 19 , wherein the electrical length of the electrically-small antenna is in the range of λ/10 to λ/10,000 of the predetermined wavelength λ.
21. The method of claim 15 , wherein the flight path approximately conforms to a profile of a surface above a region of interest.
22. The method of claim 15 , wherein the altitude of the flight path is approximately between 10 meters and a kilometer.