Identification of potential threat materials using active electromagnetic waves

• US 8,390,504 B2
• Filed: 07/01/2009
• Issued: 03/05/2013
• Est. Priority Date: 07/01/2008
• Status: Active Grant

• Current Assignee: Smiths Detection Ireland Limited
• Original Assignee: Smiths Detection Ireland Limited
• Inventors: Abdillah, Mohammed Ben, Lyons, Brendan, Entchev, Emil
• Primary Examiner(s): Keith, Jack W
• Assistant Examiner(s): BYTHROW, PETER M
• Application Number:
  US13/000,876
• Publication Number:
  US 20110102235A1
• Time in Patent Office: 1,343 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: G01S 7/412 based on a comparison between measured values and known or stored values
• CPC Class Codes: G01V 8/005 operating with millimetre waves, e.g. measuring the black losey radiation

Abstract

Electrical properties of concealed dielectric objects, such as the dielectric permittivity, can be deduced from incident, reflected, and transmitted electromagnetic waves in an imaging system. In a confocal arrangement a horn illuminates a reflect array and the reflect array is configured to focus the radiation at an element in the scan volume. The reflections are in turn refocused by a reflect array at the horn aperture. The reflect array is electronically configured to scan the focal point throughout the scan volume in a systematic way. Knowledge of the horn pattern and the scan strategy allows the system to compute the geometry associated with each volume element. Amplitude and phase variations between the object and the surrounding volume and the computed geometry are used to estimate the relative permittivity and thus facilitate categorization of the object using a database of material relative permittivities.

Claims

1. An imaging system comprising

a transmitter for directing radiation at a scan volume in which there is a target;

a receiver for receiving scattered radiation from the volume; and

a reflect array for focusing incident beam radiation;

a processor for processing the scattered radiation to generate an image according to amplitude and phase of the received radiation;

a display coupled to the processor, for generating an image display;

wherein the transmitter is adapted to transmit the incident radiation with a substantially single frequency;

wherein the system is adapted to identify a concealed material;

wherein the processor is adapted to classify a concealed dielectric material according to permittivity relative to that of the human body, said relative permittivity being deduced from amplitude and phase information in the received radiation;

wherein the processor is adapted to measure phase and amplitude of scattered radiation both near the concealed material and at the concealed material, that near the concealed material providing a reference; and

wherein the system is adapted to detect radiation from two or more volume elements, a volume element providing reference data if it does not include the concealed material;

wherein the transmitter and the receiver comprise a horn in a confocal arrangement, in which the horn illuminates a reflect array and the reflect array is configured to focus the radiation at an element in the scan volume, and the reflections are in turn refocused by the reflect array at the horn aperture, and the processor is adapted to control the reflect array to scan the focal point throughout the scan volume in a systematic way, and to use horn pattern and the scan strategy to compute the geometry associated with each volume element in terms of individual rays, and in which amplitude and phase variations between the object and the surrounding volume and the computed geometry are used to estimate the relative permittivity; and

wherein for each transmitted ray data for two returned rays is processed by the processor, in which a first ray is reflected off the surface of the object and a second ray is transmitted through the object and reflected at an interface between the object and the body, and in which the processor is adapted to perform an estimation process which tracks both rays and identifies the following events;

neither ray is recovered by the horn and therefore plays no part in the estimation process, the first ray is recovered and is accounted for in the estimation process but the second ray is lost,

the second ray is recovered and is accounted for in the estimation process but the first ray is lost, and

both rays are recovered and both contribute to the estimation process.

2. The imaging system as claimed in claim 1, wherein said frequency is in the range of 1 GHz to 300 GHz.

3. The imaging system as claimed in claim 1, wherein said frequency is in the range of 1 GHz to 80 GHz.

4. The image processing system as claimed in claim 1, wherein the processor is adapted to automatically identify anomalies at edges in the recorded images, and to use said anomalies when deriving relative permittivity data.

5. The imaging system as claimed in claim 1, wherein the processor is adapted to classify materials based on a database of relative permittivities, and said database includes permittivity data or relative permittivity data for specified threat materials such as explosives or narcotics.

6. The imaging system as claimed in claim 1, wherein the processor is adapted to process amplitude and phase contrast from element to element in the scan volume to generate an image of the scan volume.

7. The imaging system as claimed in claim 1, wherein the processor is adapted to process amplitude and phase contrast from element to element in the scan volume to generate an image of the scan volume;

and wherein different amplitude and phase responses for the elements are used by the processor to detect the location and the orientation of a concealed material.

8. The imaging system as claimed in claim 1, wherein the processor is adapted to execute algorithms implementing Snell'"'"'s law coupled to the electromagnetic properties of fields in the vicinity of boundaries to compute amplitude as a level of attenuation, and phase, Tmodel and Φ

model, of received radiation.

9. The imaging system as claimed in claim 1, wherein the processor is adapted to execute algorithms reflecting the electromagnetic properties of wave impedance and reflection coefficient in the vicinity of boundaries to compute amplitude as a level of attenuation, and phase, Tmodel and Φ

model, of received radiation.

10. The imaging system as claimed in claim 1, wherein the processor is adapted to execute confocal image theory algorithms to compute amplitude as a level of attenuation and phase, model and Φ

model, of received radiation.

11. The imaging system as claimed in claim 1, further comprising a reflector for reflecting scattered radiation, and the receiver is mounted to receive radiation after being reflected.

12. The imaging system as claimed in claim 1, further comprising a reflector for reflecting scattered radiation, and the receiver is mounted to receive radiation after being reflected;

and wherein the reflector comprises a reflect array configured to focus the transmitted radiation at successive elements in the scan volume.

13. The imaging system as claimed in claim 1, wherein the transmitter and the receiver comprise a horn antenna, and the system comprises a reflect array arranged in tiles, each tile consisting of an array of patch antennas with switching transistors and an associated controller for controlling the transistors, and in which the controller is adapted to configure phases of the patch antennas to achieve a particular pattern in space when the array is illuminated by the horn antenna, in which the processor is adapted to:

calculate and sum distance from the horn antenna to a patch and distance from the patch to the focal point,

convert said distance into wavelengths at the operating frequency, and

convert a fractional portion of the distance into phase by multiplying by a number of degrees, and in which for each patch to constructively contribute to the focus the phases must be substantially identical.

14. The imaging system as claimed in claim 13, wherein a transistor is selected to add 0 or 180 degree phase shift depending on the calculated phase by turning it on and 0 degrees by turning it off, scanning being implemented over the volume by applying appropriate patterns of switching the transistors.