THREAT DETECTION AND DISCRIMINATION USING MULTIPLE FREQUENCY SPECTRA
A method includes receiving, from a plurality of magnetic field receivers including magnetic sensors, data characterizing samples obtained by the plurality of magnetic field receivers, the samples of a combination of a first magnetic field and a second magnetic field resulting from interaction of the first magnetic field and an object; determining, using the received data, a polarizability index of the object, the polarizability index characterizing a magnetic polarizability property of the object; classifying, using the determined polarizability index, the object as threat or non-threat; and providing the classification. Related apparatus, systems, techniques, and articles are also described.
1 . A method comprising:
receiving, from a plurality of magnetic field receivers including magnetic sensors, data characterizing samples obtained by the plurality of magnetic field receivers, the samples comprising a combination of a first magnetic field and a second magnetic field resulting from interaction of the first magnetic field and an object, the first magnetic field including at least:
a first frequency component, a second frequency component, and a third frequency component;
determining, using the received data, a polarizability index of the object, the polarizability index characterizing a magnetic polarizability property of the object, wherein the polarizability index includes:
a first polarizability index component determined based at least on the first frequency component,
a second polarizability index component determined based at least on the second frequency component, and
a third polarizability index component determined based at least on the third frequency component;
classifying, using the determined polarizability index, the object as threat or non-threat; and
providing the classification.
2 . The method of claim 1 , wherein the classifying includes determining at least one material property of the object based at least on the first polarizability index component associated with the first frequency component and determining a first property of the object based at least on the second polarizability index component associated with the second frequency component and/or the third polarizability index component associated with the third frequency component.
3 . The method of claim 1 , wherein the first frequency component is configured to characterize at least one of a ferrous material property and a non-ferrous material property of the object.
4 . The method of claim 1 , further comprising:
determining at least one of a location, a speed, and an orientation of the object based on the first frequency component.
5 . The method of claim 1 , wherein the first frequency component is less than 50 Hz.
6 . The method of claim 1 , wherein the second frequency component is between 100 Hz and 200 Hz.
7 . The method of claim 1 , wherein the third frequency component is between 200 Hz and 1000 Hz.
8 . The method of claim 1 , wherein the polarizability index of the object characterizes at least a shape, a permeability, and a conductivity of the object.
9 . The method of claim 1 , wherein determining the polarizability index comprises:
solving a set of trial solutions via a precomputed pseudo-inverse,
determining a residual for each of the trial solutions, and
selecting the trial solution resulting in a smallest residual.
10 . The method of claim 1 , wherein determining the polarizability index comprises:
defining a set of trial solutions, each trial solution including a location, a speed, and a time-shift;
calculating an associated polarizability index and an associated residual for each trial solution; and
selecting a final trial solution, the final trial solution including the trial solution of the set of trial solutions that is associated with the smallest residual.
11 . The method of claim 10 , further comprising:
determining a confidence measure associated with the final trial solution, wherein the confidence measure is determined based on applying a residual function generated by a predictive model, trained in a machine learning process, to receive a first data set of observed object properties and a second data set including a location, a speed, and a time-shift of the final trial solution as inputs and to output a distance between the first and second data sets, the distance characterizing the confidence measure.
12 . The method of claim 1 , further comprising:
localizing the object within a volume under inspection, the localization including determining an object speed, an object position, and an object time-offset relative to a predetermined plane.
13 . The method of claim 1 , further comprising:
generating one or more signals for driving a magnetic field transmitter at the first frequency component, the second frequency component, and the third frequency component.
14 . The method of claim 1 , wherein the polarizability index of the object includes a complex tensor including at least six elements characterizing directional polarizability components of the object at one or more frequencies employed by a transmitting system emitting the first magnetic field.
15 . The method of claim 1 , further comprising:
determining a first magnetic moment of the object based on a first complex tensor of the first polarizability index component, wherein the first magnetic moment is determined based on extrapolating the first frequency component to 0 Hz,
determining a second magnetic moment associated with an environmental magnetic field at a location of the plurality of magnetic field receivers, and
determining a third magnetic moment based on subtracting the second magnetic moment from the first magnetic moment, the third magnetic moment characterizing a manufacturing process of the object.
16 . A system comprising:
a magnetic field transmitter configured to generate a first magnetic field including a first frequency component, a second frequency component, and a third frequency component;
a plurality of magnetic field receivers including magnetic sensors, the plurality of magnetic field receivers configured to sample a combination of the first magnetic field and a second magnetic field resulting from interaction of the first magnetic field and an object; and
at least one data processor configured to at least:
receive data characterizing the samples obtained by the plurality of magnetic field receivers;
determine, using the received data, a polarizability index of the object, the polarizability index characterizing a magnetic polarizability property of the object, wherein the polarizability index includes:
a first polarizability index component determined based at least on the first frequency component,
a second polarizability index component determined based at least on the second frequency component, and
a third polarizability index component determined based at least on the third frequency component;
classify, using the determined polarizability index, the object as threat or non-threat; and
provide the classification.
17 . The system of claim 16 , wherein the classifying includes determining at least one material property of the object based at least on the first polarizability index component associated with the first frequency component and determining a first property of the object based at least on the second polarizability index component associated with the second frequency component and/or the third polarizability index component associated with the third frequency component.
18 . The system of claim 16 , wherein the first frequency component is configured to characterize at least one of a ferrous material property and a non-ferrous material property of the object.
19 . The system of claim 16 , wherein the at least one data processor is further configured to determine at least one of a location, a speed, and an orientation of the object based on the first frequency component.
20 . The system of claim 16 , wherein the first frequency component is less than 50 Hz.
21 . The system of claim 16 , wherein the second frequency component is between 100 Hz and 200 Hz.
22 . The system of claim 16 , wherein the third frequency component is between 200Hz and 1000 Hz.
23 . The system of claim 16 , wherein the polarizability index of the object characterizes at least a shape, a permeability, and a conductivity of the object.
24 . The system of claim 16 , wherein determining the polarizability index comprises:
solving a set of trial solutions via a precomputed pseudo-inverse, determining a residual for each of the trial solutions, and selecting the trial solution resulting in a smallest residual.
25 . The system of claim 16 , wherein determining the polarizability index comprises:
defining a set of trial solutions, each trial solution including a location, a speed, and a time-shift;
calculating an associated polarizability index and an associated residual for each trial solution; and
selecting a final trial solution, the final trial solution including the trial solution of the set of trial solutions that is associated with the smallest residual.
26 . The system of claim 25 , wherein the at least one data processor is further configured to:
determine a confidence measure associated with the final trial solution, wherein the confidence measure is determined based on applying a residual function generated by a predictive model, trained in a machine learning process, to receive a first data set of observed object properties and a second data set including a location, a speed, and a time-shift of the final trial solution as inputs and to output a distance between the first and second data sets, the distance characterizing the confidence measure.
27 . The system of claim 16 , wherein the at least one data processor is further configured to:
localize the object within a volume under inspection, the localization including determining an object speed, an object position, and an object time-offset relative to a predetermined plane.
28 . The system of claim 16 , wherein the at least one data processor is further configured to:
generate one or more signals for driving a magnetic field transmitter at the first frequency component, the second frequency component, and the third frequency component.
29 . The system of claim 16 , wherein the polarizability index of the object includes a complex tensor including at least six elements characterizing directional polarizability components of the object at one or more frequencies employed by a transmitting system emitting the first magnetic field.
30 . The system of claim 16 , wherein the at least one data processor is further configured to:
determine a first magnetic moment of the object based on a first complex tensor of the first polarizability index component, wherein the first magnetic moment is
determined based on extrapolating the first frequency component to 0 Hz, determine a second magnetic moment associated with an environmental magnetic field at a location of the plurality of magnetic field receivers, and
determine a third magnetic moment based on subtracting the second magnetic moment from the first magnetic moment, the third magnetic moment characterizing a manufacturing process of the object.