Object detection method and apparatus employing polarized radiation

• US 6,342,696 B1
• Filed: 05/25/1999
• Issued: 01/29/2002
• Est. Priority Date: 05/25/1999
• Status: Expired due to Term

• Current Assignee: Peacock Myers PC
• Original Assignee: The MacAleese Companies, Inc.
• Inventors: Chadwick, George G.
• Primary Examiner(s): Allen, Stephone B.
• Assistant Examiner(s): PYO, KEVIN K
• Application Number:
  US09/318,196
• Time in Patent Office: 980 Days
• Field of Search: 250/225, 250/216, 250/559.09, 250/221, 250/222.1, 250/214.R, 342/22, 342/27, 342/28, 342/188, 109/6, 109/9
• US Class Current: 250/225
• CPC Class Codes: G01S 13/887 for detection of concealed objects, e.g. contraband or weapons
• CPC Class Codes: G01S 7/025 involving the transmission of linearly polarised waves
• CPC Class Codes: G01S 7/2883 using FFT processing
• CPC Class Codes: G01S 7/412 based on a comparison between measured values and known or stored values
• CPC Class Codes: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005

Abstract

Methods and apparatus for detecting objects are disclosed. In one embodiment of the invention, a person entering a secured or “Safe Zone™” is illuminated with low-power polarized radio waves. Differently polarized waves which are reflected back from the person are collected and measured. Persons carrying a concealed weapon such as a handgun are detected by calculating the difference of a pair of differences between levels of different polarized reflected energy. Alternative embodiments of the invention may be used to detect a wide variety of objects other than concealed firearms. The invention may be used for inventory control or to thwart shoplifting.

Claims

1. A method of detecting an object comprising the steps of:

illuminating a target with polarized radiation;

collecting first radiation reflected from said target which has a polarization which is the same as the radiation used to illuminate said target;

collecting second radiation reflected from said target which is oppositely polarized to that of said radiation which is used to illuminate said target; and

comparing a difference between amplitudes of said first and second radiation with a predetermined value representative of an expected difference when the object were not present.

2. A method as recited in claim 1, in which said polarized radiation that is used to illuminate said target is horizontally polarized.

3. A method as recited in claim 1, in which said reflected radiation that is used to illuminate said target is vertically polarized.

4. A method as recited in claim 1, in which said target is a person.

5. A method as recited in claim 4, in which said object is a concealed weapon.

6. A method as recited in claim 5, in which said concealed weapon is a firearm.

7. A method as recited in claim 1, in which said target is illuminated with radio waves.

8. A method as recited in claim 1, further comprising the step of:

using a Fast Fourier Transform to substantially discount the moving components of said target to improve the detection of unchanging components of said target.

9. A method of detecting an object comprising the steps of:

solving the equation ((α

-β

)−

(γ

-δ

))=X;

where

α

is the maximum amplitude of a waveform representing the expected horizontally polarized radiation that would be reflected back from a person who is not carrying a firearm;

β

is the maximum amplitude of a waveform representing the expected vertically polarized radiation that would be reflected from a person not carrying a firearm;

γ

is the maximum amplitude of a waveform representing the horizontally polarized radiation reflected back from a person carrying a firearm; and

δ

is the maximum amplitude of a waveform representing the vertically polarized radiation reflected back from a person carrying a firearm; and

determining that a firearm is present if X exceeds a predetermined constant.