TECHNICAL FIELD

The subject matter described herein relates to a personnel inspection system, which in some example implementations, can be capable of performing threat detection and discrimination without personal item divestment.

BACKGROUND

Airport security attempts to prevent any threats or potentially dangerous situations from arising or entering the country. Some existing radio frequency (RF) imaging systems (such as those utilized by airport security for passenger screening) are large, expensive, and require individuals to remain stationary while an antenna rotates around the stationary individual to capture an image. In addition, these existing RF imaging systems can require divestment of personal items such as cell phones, keys, wallets, and the like, by the individual under inspection. Such divestment requirement can reduce throughput and usability of the imaging systems.

Some existing inspection systems, such as walkthrough metal detectors, can include coils to generate and measure changes in a magnetic field caused by magnetic or conductive materials (e.g., metallic) passing through the magnetic field. These existing inspection systems can be capable of measuring for metallic objects passing through a threshold but can lack any ability to distinguish personal items such as a cell phone, laptop, keys, belt buckle, and the like from threats, such as fire arms or improvised explosive devices. Accordingly, these example existing inspection systems require divestment of personal items thereby limiting their throughput and usability.

SUMMARY

In an aspect, 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.

One or more of the following features can be included in any feasible combination. For example, the polarizability index of the object can characterize at least a shape, a permeability, and a conductivity of the object. The polarizability index of the object can include a complex tensor including at least six elements characterizing directional polarizability components of the object at one or more frequencies employed by the transmitting system. Determining the polarizability index can include 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. Determining the polarizability index can include 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. The method can further include localizing the object within a volume under inspection, the localization including determining an object speed, an object position, and an object time-offset to a predetermined plane. The method can further include generating one or more signals for driving a magnetic field transmitter at a frequency that is less than 1,000 Hertz (Hz).

The plurality of magnetic field receivers can include flux gate sensors that measure a magnitude and phase of the combination of the first magnetic field and the second magnetic field in at least three axis at locations of the plurality of magnetic field receivers. The samples obtained by the plurality of magnetic field receivers can characterize a magnitude and a phase. Classifying, using the polarizability index, the object as threat or non-threat can include comparing the magnitude, the phase, and the polarizability index to a library of predetermined threat signatures. The first magnetic field can be generated by at least a first magnetic field transmitter and a second magnetic field transmitter. The first magnetic field transmitter and the second magnetic field transmitter can be oriented in a first direction. The first magnetic field transmitter and the second magnetic field transmitter can be spatially offset transverse to a predefined direction of motion and transverse to the first direction.

In another aspect, a system can include a magnetic field transmitter configured to generate a first magnetic field; 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; classify, using the polarizability index, the object as threat or non-threat; and provide the classification.

One or more of the following features can be included. For example, a transmit driver can be coupled to the magnetic field transmitter and configured to generate one or more signals for driving the magnetic field transmitter at a frequency that is less than 1,000 Hertz (Hz). The transmit driver can be configured to generate one or more signals for driving the magnetic field transmitter at a first frequency and a second frequency. The magnetic field transmitter can be driven at the first frequency and the second frequency. The first frequency can be between 5 Hz and 40 Hz and the second frequency can be between 100 Hz and 1000 Hz. A second magnetic field transmitter can be included. The transmit driver can include: first drive electronics to drive the magnetic field transmitter; and second drive electronics to drive the second magnetic field transmitter. The samples can be obtained by the plurality of magnetic field receivers and can characterize a magnitude and a phase. Classifying, using the polarizability index, the object as threat or non-threat can include comparing the magnitude, the phase, and the polarizability index to a library of predetermined threat signatures.

The plurality of magnetic field receivers can include flux gate sensors that measure a magnitude and phase of the combination of the first magnetic field and the second magnetic field in at least three axis at locations of the plurality of magnetic field receivers. A data acquisition base station can be included, coupled to the plurality of magnetic field receivers, and configured to filter, demodulate, and digitize the samples obtained by the plurality of magnetic field receivers. The data acquisition base station can be further configured to determine in-phase and quadrature data characterizing the second magnetic field. Determining the polarizability index can include determining a polarizability tensor. Determining the polarizability index can include 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.

The at least one data processor can be 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 to a predetermined plane. Determining the polarizability index can include: 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. The at least one data processor can be further configured to determine a measure of distortion of the second magnetic field based on an amount of metal present at a location where the system is deployed.

The system can further include a base plate configured to couple a first post and a second post. The magnetic field transmitter can be coupled to the first post and the plurality of magnetic field receivers can be coupled to the second post. The base plate can include a modular mounting system configured to couple the base plate to a surface upon which the base plate is positioned. The modular mounting system can include at least one of a plurality of suction cups, a plurality of gripping mechanisms, a plurality of piercing mechanisms, and a plurality of auger mechanisms. The base plate can include a base plate frame hidden within the base plate. The base plate frame can be configured to permanently install the base plate in a location where the system is deployed. A proximal end of the first post and a proximal end of the second post can be coupled to the base plate. A distal end of the first post and a distal end of the second post are not connected to an archway coupling the distal end of the first post to the distal end of the second post. At least one of an accelerometer or an inclinometer can be coupled to the first post and/or the second post.

The system can further include at least one camera coupled to the first post or the second post. The at least one camera can be configured to capture image and/or video data of the object. The camera can be selected from a group including a depth camera, a rear-facing camera, a fish-eye camera, an infrared camera, a thermal camera, a surface map camera, an electro-optical camera, and a stereo camera. The system can include a first camera coupled to the first post and a second camera coupled to the second post. The first camera can be configured to capture image at a first viewing angle and the second camera can be configured to capture image data a second viewing angle. The second viewing angle different than the first viewing angle. The image data captured by the first camera and the second camera is registered within a coordinate system of the system. Responsive to classifying the object as a threat, the processor can be further configured to generate a graphical indication identifying a location of the object and to overlay the graphical indication atop the image data in a display.

The details of one or more variations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features and advantages of the subject matter described herein will be apparent from the description and drawings, and from the claims.

