Detection of concealed object by standing waves

• US 7,804,441 B1
• Filed: 07/13/2007
• Issued: 09/28/2010
• Est. Priority Date: 07/13/2007
• Status: Expired due to Fees

• Current Assignee: United States Secretary of the Navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: DeChiaro, Louis F. Jr.
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Barker; Matthew M
• Application Number:
  US11/890,098
• Time in Patent Office: 1,173 Days
• Field of Search: 342/22
• US Class Current: 342/22
• CPC Class Codes: G01S 13/887 for detection of concealed objects, e.g. contraband or weapons
• CPC Class Codes: G01V 8/005 operating with millimetre waves, e.g. measuring the black losey radiation

Abstract

A process is provided to detect an object within a defined region using standing longitudinal cavity mode waves. The process includes disposing first and second electromagnetic reflectors within the region at opposite ends of the axis; transmitting an electromagnetic signal into the region in proximity to the first reflector, measuring a received signal in proximity to the second reflector, extracting an appropriate parameter from the received signal to obtain a received characteristic, comparing the received characteristic to an established characteristic that lacks the object to obtain a characteristic differential, and analyzing the characteristic differential to obtain a position of the object between the reflectors. The analyzing can be performed by Fourier transform across wave modes. In an alternate embodiment, the process involves first and second conductive lines disposed substantially parallel to the axis for a specified length and separated from each other by a specified width, the length and width bounding the defined region. The alternative process further includes transmitting an electromagnetic signal through the first line at a set frequency, returning the transmitted signal through the second line, measuring power from a reflected signal through the first line, adjusting the set frequency based on the measured power, extracting an appropriate parameter from the reflected signal to obtain a reflected characteristic, comparing the reflected characteristic to an established characteristic that lacks the object to obtain a characteristic differential, and analyzing the characteristic differential to obtain a position of the object along the length.

Claims

1. A method for detecting an object within a defined region having a longitudinal axis, the method comprising:

disposing first and second wave reflectors within the region at opposite ends of the axis, the wave reflectors separated by a cavity length;

transmitting a band-width plurality of electromagnetic microwave signals over a predetermined bandwidth into the region in proximity to the first reflector to produce a standing wave pattern;

measuring a received signal in proximity to the second reflector;

extracting an appropriate parameter from the received signal to obtain a received characteristic, the parameter dependent on a longitudinal mode of the length;

comparing the received characteristic town established characteristic that lacks the object to obtain a characteristic differential; and

analyzing the characteristic differential to obtain a position of the object between the reflectors.

2. The method according to claim 1, wherein the appropriate parameter for obtaining the received and established characteristics is at least one of frequency, power, quality and finesse.

3. The method according to claim 1, wherein the analyzing operation further includes Fourier transforming the characteristic differential.

4. The method according to claim 1, wherein the analyzing operation further includes transforming the characteristic differential by Discrete Fourier-transform.

5. The method according to claim 1, wherein the comparing operation further comprises:

comparing a first amplitude at a received mode to a second amplitude at an established mode to determine a difference between the first and second amplitudes.

6. The method according to claim 5, wherein the analyzing operation further comprises:

Fourier transforming the characteristic difference over a plurality of wave modes to obtain the position for the object.

7. The method according to claim 1, wherein the appropriate parameter is frequency, and comparing operation further includes determining an offset between a first frequency for the received signal and a second frequency for the established signal.

8. The method according to claim 1, wherein the parameter is photon density S_m and the characteristic is mode loss α

_m, being each associated with associated with the m^th longitudinal mode, the mode loss being related by;

9. A system for detecting an object within a defined region having a longitudinal axis, the system comprising:

first and second electromagnetic reflectors disposed within the region at opposite ends of the axis, the wave reflectors separated by a cavity length;

an electromagnetic signal transmitter for transmitting a plurality of electromagnetic microwave signals over a predetermined bandwidth into the region in proximity to the first reflector to produce a standing wave pattern;

an electromagnetic signal receiver for measuring a received signal in proximity to the second reflector;

an extracter for extracting an appropriate parameter from the received signal to obtain a received characteristic, the parameter dependent on a longitudinal mode of the length;

a comparator for comparing the received characteristic to an established characteristic that lacks the object to obtain a characteristic differential; and

an analyzer for analyzing the characteristic differential to obtain a position of the object between the reflectors.

10. The system according to claim 9, wherein the appropriate parameter to obtain the received and established characteristics is at least one of frequency, power, quality and finesse.

11. The system according to claim 9, wherein the analyzer performs Fourier transform on the characteristic differential.

12. The system according to claim 11, wherein the analyzer Fourier transforms the characteristic difference over a plurality of wave modes to obtain the position for the object.

13. The system according to claim 9, wherein the analyzer transforms the characteristic differential by Discrete Fourier-transform.

14. The system according to claim 9, wherein the comparer compares a first amplitude at a received mode to a second amplitude at an established mode to determine a difference between the first and second amplitudes.

15. The system according to claim 9, wherein the parameter is photon density S_m and the characteristic is mode loss α

_m, being each associated with associated with the m^th longitudinal mode, the mode loss being related by;