Object detection method and apparatus
Method and apparatus for detecting objects. In one embodiment, a person entering a secured zone is illuminated with low-power polarized radio waves. Differently polarized waves which are reflected back from the person are collected. Concealed weapons are detected by measuring various parameters of the reflected signals and then calculating various selected differences between them. These differences create patterns when plotted as a function of time. Preferably a trained neural network pattern recognition program is then used to evaluate these patterns and autonomously render a decision on the presence of a weapon.
1. A method of determining a presence of an object associated with a target, the method comprising the steps of:
illuminating a target with polarized illuminating radiation;
collecting first radiation reflected from the target which has a same polarization as the illuminating radiation;
collecting second radiation reflected from the target which has an opposite polarization from the illuminating radiation; and
employing a weighted plurality of criteria of the first radiation and the second radiation converted to a time domain by a Chirp-Z Transform process to determine the presence of the object, the criteria selected from the group consisting of a first magnitude of the first radiation at zero time after conversion to the time domain by the Chirp-Z Transform process, a second magnitude of the second radiation at zero time after conversion to the time domain by the Chirp-Z Transform process, and a difference between the first magnitude and the second magnitude; and employing a time of arrival difference between the first radiation and the second radiation.
2. A method as recited in claim 1 , wherein the employing step comprises employing a magnitude spread of one or both of the first radiation and the second radiation at a plurality of times.
3. A method as recited in claim 1 , wherein the employing step comprises employing a measurement of the shape of a curve of one or both of the first radiation and the second radiation in the time domain or frequency domain.
4. A method as recited in claim 3 , wherein the measurement comprises a ratio of a peak value of the curve to a total area under the curve.
5. A method as recited in claim 1 wherein the method is repeated a plurality of times, and further comprising the step of combining results of each performance of the method.
6. A method as recited in claim 1 , further comprising the step of training a neural network on calibration data.
7. A method as recited in claim 6 wherein the employing step further comprises the step of using the neural network to autonomously determine presence of the object.
8. A method as recited in claim 1 , in which the target comprises a person.
9. A method as recited in claim 1 , in which the object comprises a concealed weapon.
10. A method as recited in claim 9 , in which the concealed weapon is selected from the group consisting of a knife, firearm, gun, bomb, explosive device, and suicide vest.
11. An apparatus for detecting an object associated with a target, said apparatus comprising:
a transmit antenna for illuminating the target with polarized illuminating radiation;
a first receive antenna for collecting first radiation reflected from the target which has a same polarization as the illuminating radiation;
a second receive antenna for collecting second radiation reflected from the target which has an opposite polarization from the illuminating radiation; and
a processor for employing a weighted plurality of criteria of the first radiation and the second radiation converted to a time domain by a Chirp-Z Transform process to determine a presence of the object, the criteria selected from the group consisting of a first magnitude of said first radiation at zero time after conversion to the time domain by the Chirp-Z Transform process, a second magnitude of said second radiation at zero time after conversion to the time domain by the Chirp-Z Transform process, and a difference between said first magnitude and said second magnitude; and said processor employs a time of arrival difference between said first radiation and said second radiation.
12. An apparatus as recited in claim 11 , wherein said processor employs a magnitude spread of one or both of said first radiation and said second radiation at a plurality of times.
13. An apparatus as recited in claim 11 wherein said processor employs a shape of a curve of one or both of said first radiation and said second radiation in the time domain or frequency domain.
14. An apparatus as recited in claim 11 , wherein said processor employs a variation in time of one or both of the first radiation and the second radiation.
15. An apparatus as recited in claim 11 , wherein a single dual-polarized antenna comprises said first receive antenna and said second receive antenna.
16. An apparatus as recited in claim 11 , wherein said processor combines results from a plurality of applications of the illuminating radiation to the target.
17. An apparatus as recited in claim 11 , in which the target is a person.
18. An apparatus as recited in claim 11 , in which the object is a concealed weapon.
19. An apparatus as recited in claim 18 , in which the concealed weapon is selected from the group consisting of a knife, firearm, gun, bomb, explosive device, and suicide vest.
20. An apparatus as recited in claim 11 wherein said processor employs a neural network to automatically detect the presence of the object.
21. An apparatus as recited in claim 20 wherein said processor assigns a value to each of said criteria and determines the presence of the object based on a combination of values of said criteria.