Method for detecting a covered dielectric object

• US 8,760,175 B2
• Filed: 03/18/2010
• Issued: 06/24/2014
• Est. Priority Date: 05/05/2009
• Status: Active Grant

• Current Assignee: Nokia Corporation, Rohde & Schwarz GmbH & Company KG
• Original Assignee: Rohde & Schwarz GmbH & Company KG
• Inventors: Ostwald, Olaf, Ahmed, Sherif Sayed
• Primary Examiner(s): Hollington, Jermele M
• Assistant Examiner(s): HOQUE, FARHANA AKHTER
• Application Number:
  US13/319,294
• Publication Number:
  US 20120049863A1
• Time in Patent Office: 1,559 Days
• Field of Search: 324/642, 324/22, 342/22
• US Class Current: 324/642
• CPC Class Codes: G01F 23/0023 with a probe suspended by a wire or thread with floats G01F23/40
• CPC Class Codes: G01S 13/887 for detection of concealed objects, e.g. contraband or weapons
• CPC Class Codes: G01S 13/89 for mapping or imaging
• CPC Class Codes: G01S 7/411 Identification of targets based on measurements of radar reflectivity G01S7/415 takes precedence
• CPC Class Codes: G01V 8/005 operating with millimetre waves, e.g. measuring the black losey radiation

Abstract

The invention relates to a method for detecting a covered dielectric object, where a microwave signal that can be modified in frequency is generated at a particular bandwidth and transmitted in the direction of the covered dielectric object. The microwave signal reflected by the object is then obtained from the three-dimensional measurement result in a lateral, two-dimensional pattern, a highest signal amplitude and a second-highest signal amplitude within a particular time period before or after the received microwave signal is identified in a plurality of pattern points of the pattern. The object is detected if an accumulation of pattern points of the pattern is present, in which the difference in each case between the highest and the second highest signal amplitude of the received microwave signal is less than a defined threshold value.

Claims

1. A method for detecting a concealed dielectric object, said method comprising:

generation and transmission of a microwave signal in the direction towards the concealed object,

registration of the microwave signal reflected from the object in a spatial raster,

identification of a highest signal amplitude and a second highest signal amplitude preceding or following the highest signal amplitude within a given time interval over the time course of the registered microwave signal at several raster points of the raster,

formation of a difference between the highest and second-highest signal amplitude of the registered microwave signal determined at each raster point and comparison of the difference with an specified threshold value, and

detection of the object if an accumulation of raster points of the raster at which the difference between the highest and the second-highest signal amplitude of each registered microwave signal is smaller than the specified threshold value, is present.

2. The method according to claim 1, wherein the object is a substance with a permittivity different from the permittivity of the human body and of the air of the surrounding atmosphere.

3. The method according to claim 2, wherein the concealed object is disposed within or beneath an item of clothing which is worn on a human body.

4. The method according to claim 2, wherein the spectrum of the generated microwave signal is windowed by means of filtering, preferably by means of filtering according to Hamming, Hann, Gauss or Chebychev.

5. The method according to claim 2, wherein the identification of an accumulation of raster points comprises the following method steps:

specification of several adjacent groups each comprising a specified number of preferably an identical number of adjacent raster points for every raster point, which are each positioned in the proximity of the respective raster point, in an angular segment relative to the respective raster point,

counting of raster points with a difference between the highest and second-highest signal amplitude within each group of raster points disposed below the threshold value, and

identification of a raster point associated with the accumulation of raster points, if at least one specified number of raster points with a difference between the highest and the second-highest signal amplitude disposed below the threshold value are present respectively in each of its associated groups of raster points.

6. The method according to claim 2, wherein the identification of an accumulation of raster points comprises the following method steps:

successive addition of raster points in each case directly adjacent in two directions to a raster point with a difference between the highest and the second-highest signal amplitude disposed below the threshold value, to a group of coherent raster points, if a difference between the highest and the second-highest signal amplitude disposed below the threshold value has been determined within the raster points.

7. The method according to claim 2, wherein raster points positioned within the accumulation of raster points which each provide a difference between the highest and the second-highest signal amplitude disposed above the threshold value, are added to the accumulation of raster points.

8. The method according to claim 1, wherein the concealed object is disposed within or beneath an item of clothing which is worn on a human body.

9. The method according to claim 8, wherein the raster points not associated with the accumulation of raster points contains a rastered image of the human body.

10. The method according to claim 9, wherein the concealed dielectric object is detected repeatedly within a given time raster, and the detected values associated with different time rasters are correlated or averaged.

11. The method according to claim 8, wherein the raster points not associated with the accumulation of raster points contains an optical image of the human body.

12. The method according to claim 8, wherein the concealed dielectric object is detected repeatedly within a given time raster, and the detected values associated with different time rasters are correlated or averaged.

13. The method according to claim 1, wherein the spectrum of the generated microwave signal is windowed by means of filtering, preferably by means of filtering according to Hamming, Hann, Gauss or Chebychev.

14. The method according to claim 1, wherein the identification of an accumulation of raster points comprises the following method steps:

specification of several adjacent groups each comprising a specified number of preferably an identical number of adjacent raster points for every raster point, which are each positioned in the proximity of the respective raster point, in an angular segment relative to the respective raster point,

counting of raster points with a difference between the highest and second-highest signal amplitude within each group of raster points disposed below the threshold value, and

identification of a raster point associated with the accumulation of raster points, if at least one specified number of raster points with a difference between the highest and the second-highest signal amplitude disposed below the threshold value are present respectively in each of its associated groups of raster points.

15. The method according to claim 14, wherein the identified accumulation of raster points is supplemented by those raster points which are positioned within an edge region surrounding the accumulation of raster points, wherein the width of the edge region can be specified.

16. The method according to claim 1, wherein the identification of an accumulation of raster points comprises the following method steps:

successive addition of raster points in each case directly adjacent in two directions to a raster point with a difference between the highest and the second-highest signal amplitude disposed below the threshold value, to a group of coherent raster points, if a difference between the highest and the second-highest signal amplitude disposed below the threshold value has been determined within the raster points.

17. The method according to claim 16, wherein the identified accumulation of raster points is supplemented by those raster points which are positioned within an edge region surrounding the accumulation of raster points, wherein the width of the edge region can be specified.

18. The method according to claim 1, wherein raster points positioned within the accumulation of raster points which each provide a difference between the highest and the second-highest signal amplitude disposed above the threshold value, are added to the accumulation of raster points.

19. The method according to claim 1, wherein the raster points associated with the identified accumulation of raster points are displayed on a screen displaying the entire, lateral, two-dimensional raster with a first marking, especially in a first colour.

20. The method according to claim 1, wherein the raster points not associated with the accumulation of raster points are displayed on the screen with a second marking, especially in a second colour.