Suppression of interference in threat detection

1. A method comprising:

receiving, by a data processor of an inspection system configured to detect a target object undergoing inspection, data characterizing a signal obtained by a plurality of magnetic field receivers of the inspection system, the signal formed of a combination of a first magnetic field, a second magnetic field resulting from interaction of the first magnetic field and the target object passing through the plurality of magnetic field receivers, and a third magnetic field resulting from motion of receivers within the first magnetic field and/or an external magnetic field other than the first magnetic field, the external magnetic field generated by an external source;

determining, by the data processor, a component of the signal characterizing a contribution of the second magnetic field to the signal, wherein determining the component includes canceling contributions of the third magnetic field to the signal by at least mapping the contributions of the third magnetic field to the signal, the determining further comprising:

transforming the received data characterizing the signal from a first basis to a second basis,

modifying the transformed data to generate modified data by at least cancelling portions of the transformed data corresponding to projections of the transformed data on a predetermined basis vector indicative of the external magnetic field generated by the external source,

transforming the modified data from the second basis to the first basis,

calculating a first matrix indicative of magnetic field measurements associated with magnetic fields generated by the external source in the absence of the first magnetic field, and

performing singular value decomposition on the first matrix to generate a second matrix comprising a plurality of left singular vectors of the first matrix and a third matrix including singular values associated with the first matrix in the diagonal of the third matrix; and

controlling, by the data processor, at least one magnetic field transmitter of the inspection system to dynamically generate a modified first magnetic field corresponding to the target object based on the determined component of the signal characterizing the contribution of the second magnetic field to the signal, wherein the controlling includes adjusting at least one of an amplitude and a frequency of the modified first magnetic field with respect to the first magnetic field.

2. The method of claim 1 , wherein transforming the received data from the first basis to the second basis includes multiplying the received data by the second matrix.

3. The method of claim 2 , further comprising generating a fourth matrix by at least setting a first singular value in the diagonal of the third matrix that is equal to or greater than a predetermined value to a zero, and by setting a second singular value in the diagonal of the third matrix that is less than the predetermined value to a one,

wherein a first left singular vector of the plurality of left singular vectors is associated with the first singular value, and

wherein the predetermined basis vector indicative of magnetic field generated by the external source includes the first left singular vector.

4. The method of claim 3 , wherein modifying the transformed data includes multiplying the result of the multiplication between the received data and the second matrix with the fourth matrix.

5. The method of claim 4 , wherein transforming the modified data from the second basis to the first basis includes multiplying the modified data with the transpose of the second matrix.

6. The method of claim 1 , further comprising calculating a polarizability index of the target object from the determined component of the signal characterizing the contribution of the second field to the signal, the polarizability index characterizing a magnetic polarizability property of the target object.

7. The method of claim 1 , further comprising:

calculating a fifth matrix indicative of magnetic field measurements resulting from rotation of one or more of the plurality of magnetic field receivers about a predetermined axis,

wherein a matrix element of the fifth matrix associated with a first magnetic field receiver is calculated by at least multiplying an angular displacement of the first magnetic field receiver with a predetermined expansion of a mode of the first magnetic field receiver associated with the angular displacement.

8. The method of claim 1 , wherein the external source is a stationary interference object.

9. A system comprising:

a plurality of magnetic field receivers;

at least one magnetic field transmitter;

at least one data processor communicatively coupled to the plurality of magnetic field receivers and the at least one magnetic field transmitter and configured to detect a target object undergoing inspection, and;

a memory coupled to the at least one data processor, the memory storing instructions to cause the at least one data processor to perform operations comprising:

receiving data characterizing a signal obtained by a plurality of magnetic field receivers, the signal formed of a combination of a first magnetic field, a second magnetic field resulting from interaction of the first magnetic field and the target object passing through the plurality of magnetic field receivers, and a third magnetic field resulting from motion of receivers within the first magnetic field and/or an external magnetic field other than the first magnetic field, the external magnetic field generated by an external source;

determining a component of the signal characterizing a contribution of the second magnetic field to the signal, wherein determining the component includes canceling contributions of the third magnetic field to the signal by at least mapping the contributions of the third magnetic field to the signal, the determining further comprising:

transforming the received data characterizing the signal from a first basis to a second basis,

modifying the transformed data to generate modified data by at least cancelling portions of the transformed data corresponding to projections of the transformed data on a predetermined basis vector indicative of the external magnetic field generated by the external source,

transforming the modified data from the second basis to the first basis,

calculating a first matrix indicative of magnetic field measurements associated with magnetic fields generated by the external source in the absence of the first magnetic field, and

performing singular value decomposition on the first matrix to generate a second matrix comprising a plurality of left singular vectors of the first matrix and a third matrix including singular values associated with the first matrix in the diagonal of the third matrix; and

controlling the at least one magnetic field transmitter to dynamically generate a modified first magnetic field corresponding to the target object based on the determined component of the signal characterizing the contribution of the second magnetic field to the signal, wherein the controlling includes adjusting at least one of an amplitude and a frequency of the modified first magnetic field with respect to the first magnetic field.

10. The system of claim 9 , wherein transforming the received data from the first basis to the second basis includes multiplying the received data by the second matrix.

11. The system of claim 10 , wherein the operations further comprising generating a fourth matrix by at least setting a first singular value in the diagonal of the third matrix that is equal to or greater than a predetermined value to a zero, and by setting a second singular value in the diagonal of the third matrix that is less than the predetermined value to a one,

wherein a first left singular vector of the plurality of left singular vectors is associated with the first singular value, and

wherein the predetermined basis vector indicative of magnetic field generated by the external source includes the first left singular vector.

12. The system of claim 11 , wherein modifying the transformed data includes multiplying the result of the multiplication between the received data and the second matrix with the fourth matrix.

13. The system of claim 12 , wherein transforming the modified data from the second basis to the first basis includes multiplying the modified data with the transpose of the second matrix.

14. The system of claim 9 , wherein the operations further comprising calculating a polarizability index of the target object from the determined component of the signal characterizing the contribution of the second field to the signal, the polarizability index characterizing a magnetic polarizability property of the target object.

15. The system of claim 9 , wherein the operations further comprising:

calculating a fifth matrix indicative of magnetic field measurements resulting from rotation of one or more of the plurality of magnetic field receivers about a predetermined axis,

wherein a matrix element of the fifth matrix associated with a first magnetic field receiver is calculated by at least multiplying an angular displacement of the first magnetic field receiver with a predetermined expansion of a mode of the first magnetic field receiver associated with the angular displacement.

16. A non-transitory computer readable medium comprising non-transitory machine-readable instructions that, when executed by at least one programmable processor that comprises at least one physical core and a plurality of logical cores, cause the at least one programmable processor to perform operations comprising:

receiving data characterizing a signal obtained by a plurality of magnetic field receivers of an inspection system configured to detect a target object undergoing inspection, the signal formed of a combination of a first magnetic field, a second magnetic field resulting from interaction of the first magnetic field and the target object, and a third magnetic field resulting from motion of receivers within the first magnetic field and/or an external magnetic field other than the first magnetic field, the external magnetic field generated by an external source;

determining a component of the signal characterizing a contribution of the second magnetic field to the signal, wherein determining the component includes cancelling contributions of the third magnetic field to the signal by at least mapping the contributions of the third magnetic field to the signal, the determining further comprising:

transforming the received data characterizing the signal from a first basis to a second basis,

modifying the transformed data to generate modified data by at least cancelling portions of the transformed data corresponding to projections of the transformed data on a predetermined basis vector indicative of the external magnetic field generated by the external source,

transforming the modified data from the second basis to the first basis,

calculating a first matrix indicative of magnetic field measurements associated with magnetic fields generated by the external source in the absence of the first magnetic field, and

performing singular value decomposition on the first matrix to generate a second matrix comprising a plurality of left singular vectors of the first matrix and a third matrix including singular values associated with the first matrix in the diagonal of the third matrix; and

controlling at least one magnetic field transmitter of the inspection system to dynamically generate a modified first magnetic field corresponding to the target object based on the determined component of the signal characterizing the contribution of the second magnetic field to the signal, wherein the controlling includes adjusting at least one of an amplitude and a frequency of the modified first magnetic field with respect to the first magnetic field.