Abstract:
A passenger screening system including a first gradiometer, and a second gradiometer disposed adjacent the first gradiometer. The first and second gradiometers are each configured to operate at a first frequency and a second frequency to facilitate detecting the presence of an explosive material. A method of operating the passenger screening system is also described herein.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is entitled to the benefit of, and claims priority to, provisional U.S. Patent Application Ser. No. 60/781,057 filed on Mar. 10, 2006, and entitled “Integrated Verification and Screening Kiosk System”, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to personnel screening systems utilized at passenger terminals, and more particularly, to an integrated passenger screening system. 
     The Transportation Security Administration (TSA) has recently mandated more stringent inspection procedures be implemented by the travel industry to reduce the possibility of passengers boarding a carrier such as a plane, for example, carrying concealed weapons, explosives, or other contraband. To facilitate preventing passengers boarding a plane carrying concealed weapons, explosives, etc., the TSA requires that all passengers be screened prior to boarding the aircraft. 
     For example, passengers arriving at the airport terminal first submit to a manual verification process that generally includes presenting their boarding pass and a form of identification such as a driver&#39;s license or passport, for example, to security personnel. The security personnel then manually verify that the passenger has a valid boarding pass, the name on the identification corresponds to the name on the boarding pass, and that the picture on the license or passport corresponds to the passenger presenting the license and boarding pass to the security personnel. 
     After the manual verification process is completed, the passenger is requested to walk through a metal detector to ensure that the passenger is not carrying any concealed weapons. While the metal detector is reasonably effective at detecting specific quantities of metal, the metal detector is less effective at determining whether the shoes contain any explosive material. As such, security personnel frequently request that passengers remove their shoes and place their shoes into the baggage screening system such that security personnel can visually determine whether the shoes may conceal any explosive material or devices. As a result, the known metal detection system is time-consuming for the passengers, and does not effectively screen the shoes for explosive devices that may be hidden in the shoes or near the ankle/calf region of the passenger. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a passenger screening system is provided. The passenger screening system includes a first gradiometer, and a second gradiometer disposed adjacent the first gradiometer. The first and second gradiometers each configured to operate at a first frequency and a second frequency to facilitate detecting the presence of an explosive material. 
     In another aspect, a method for operating a passenger screening system is provided. The method includes operating a first gradiometer to detect the presence of an explosive material in a first shoe, and operating a second gradiometer to detect the presence of an explosive material in a second shoe, wherein the first and second gradiometers are each configured to operate at a first frequency and a second frequency to facilitate detecting the presence of the explosive material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an exemplary screening system; 
         FIG. 2  is a second perspective view of the screening system shown in  FIG. 1 ; 
         FIG. 3  is a side section view of the screening system shown in  FIG. 1 ; 
         FIG. 4  is a simplified block diagram of the screening system shown in  FIGS. 1-3 ; 
         FIG. 5  is a schematic illustration of an exemplary Quadrupole Resonance (QR) system that may be utilized with the screening shown in  FIGS. 1-4 ; 
         FIG. 6  is a perspective view of the screening system floor that has been modified to accept the screening system shown in  FIG. 5 ; and 
         FIG. 7  is a schematic illustration of an exemplary QR induction coil. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a perspective view of an exemplary passenger screening system  10 ,  FIG. 2  is a second perspective view of the passenger screening system shown in  FIG. 1 ,  FIG. 3  is a side section view of the passenger screening system  10  shown in  FIG. 1 , and  FIG. 4  is a simplified block diagram of the passenger screening system  10 . In the exemplary embodiment, system  10  includes at least one imaging modality  12 . Modality  12  is configured to detect the presence of explosive materials that may be concealed in a passengers shoes or proximate to the lower extremities of the passengers legs, for example. System  10  also includes at least one computer  18 , and a communications bus  20  that is coupled between modality  12  and computer  18  to enable operator commands to be sent to at least one of modality  12  and to allow outputs generated by modality  12  to be delivered to computer  18  and thus utilized by computer  18  for data analysis or utilized by an operator of computer  18 . In one embodiment, modality  12  is hardwired to computer  18 . In another embodiment, communications bus  20  is a local area network. Optionally, communications bus  20  includes an internet connection. 
     As shown in  FIG. 4 , modality  12  and computer  18  are integrated into a single screening system  10 . In the exemplary embodiment, modality  12 , and computer  18  are each housed within a screening system  10 . Optionally, computer  18  is housed remotely from screening system  10  and electrically coupled to modality  12  utilizing bus  20 . In the exemplary embodiment, screening system  10  includes a floor  30  that, in one exemplary embodiment, facilitates concealing at least a portion of modality  12  and provides a structural platform over the portion of modality  12  to facilitate scanning the passenger. Moreover, screening system  10  may include a pair of handrails to facilitate guiding the passenger through the screening process. Optionally, screening system  10  may include a pair of sidewalls (not shown) such that the passenger may enter screening system  10  through a first opening, traverse through screening system  10 , and exit screening system  10  through a second opening. 
     In the exemplary embodiment, shown in  FIGS. 1-3 , modality  12  may be implemented utilizing a quadrupole resonance (QR) detection system  60  that utilizes quadrupole resonance to detect explosives such as, but not limited to C4, Semtex, Detasheet, TNT, ANFO, and/or HMX since the quadrupole resonance signature of these explosives is unique and measurable in seconds. 
     Nuclear Quadrupole Resonance (NQR) is a branch of radio frequency spectroscopy that exploits the inherent electrical properties of atomic nuclei and may therefore be utilized to detect a wide variety of potentially explosive materials. For example, nuclei having non-spherical electric charge distributions possess electric quadrupole moments. Quadrupole resonance arises from the interaction of the nuclear quadrupole moment of the nucleus with the local applied electrical field gradients produced by the surrounding atomic environment. Any chemical element&#39;s nucleus which has a spin quantum number greater than one half can exhibit quadrupole resonance. Such quadrupolar nuclei include:  7 Li,  9 Be,  14 N,  17 O,  23 Na,  27 Al,  35 Cl,  39 Cl,  39 K,  55 Mn,  75 As,  79 Br,  81 Br,  127 I,  197 Au, and  209 Bi. Many substances containing such nuclei, approximately 10,000, have been identified that exhibit quadrupole resonance. 
     It so happens that some of these quadrupolar nuclei are present in explosive and narcotic materials, among them being  14 N,  17 O,  23 Na,  35 Cl,  37 Cl, and  39 K. The most studied quadrupolar nucleus for explosives and narcotics detection is nitrogen. In solid materials, electrons and atomic nuclei produce electric field gradients. These gradients modify the energy levels of any quadrupolar nuclei, and hence their characteristic transition frequencies. Measurements of these frequencies or relaxation time constants, or both, can indicate not only which nuclei are present but also their chemical environment, or, equivalently, the chemical substance of which they are part. 
     When an atomic quadrupolar nucleus is within an electric field gradient, variations in the local field associated with the field gradient affect different parts of the nucleus in different ways. The combined forces of these fields cause the quadrupole to experience a torque, which causes it to precess about the electric field gradient. Precessional motion generates an oscillating nuclear magnetic moment. An externally applied radio frequency (RF) magnetic field in phase with the quadrupole&#39;s precessional frequency can tip the orientation of the nucleus momentarily. The energy levels are briefly not in equilibrium, and immediately begin to return to equilibrium. As the nuclei return, they produce an RF signal, known as the free induction decay (FID). A pick-up coil detects the signal, which is subsequently amplified by a sensitive receiver to measure its characteristics. 
       FIG. 5  is a simplified schematic illustration of an exemplary quadrupole resonance system  60  that may be utilized to implement modality  12 . Quadrupole resonance system  60  may include a radio frequency source  62 , a pulse programmer and RF gate  64  and an RF power amplifier  66  that are configured to generate a plurality of radio frequency pulses having a predetermined frequency to be applied to a coil such as sensor  32 . A communications network  70  conveys the radio frequency pulses from radio frequency source  62 , pulse programmer and RF gate  64  and RF power amplifier  66  to sensor  32  that, in the exemplary embodiment, is positioned within screening system  10 . The communications network  70  also conducts the signal to a receiver/RF detector  72  from sensor  32  after the passenger is irradiated with the radio frequency pulses. 
       FIG. 6  is a perspective view of screening system  10  including QR system  60 . In the exemplary embodiment, system  60  includes an inductive sensor  32  that in the exemplary embodiment, is positioned beneath floor  30 . In accordance with this embodiment, inductive sensor  32  may be positioned within a recessed region  80  of floor  30 , between an entrance ramp  82  and an optional exit ramp. This recessed region  80  may also be referred to as the sensor housing. In  FIG. 6 , the inductive sensor  32  has been omitted to show sensor housing  80 , which is recessed within floor  30  of screening system  60 . 
     As shown in  FIG. 7 , and in the exemplary embodiment, inductive sensor  32  may be implemented using a first coil  90  and a second coil  92  which allow the QR imaging system  60  to scan a passenger at least two frequencies without switching capacitance into and out of coils  90 . Coil  90  is positioned to the left side of floor  30  and may be referred to as the left-side coil which is utilized to scan the passenger&#39;s left shoe and lower extremities, and coil  92  may be referred to as the right-side coil which is utilized to scan the passenger&#39;s right shoe and lower extremities. 
     In the exemplary embodiment, each of coils  90  and  92  are dual resonant gradiometer coils that may be utilized for either QR excitation and QR detection. More specifically, each of coils  90  and  92  include a first pair of capacitors  94  having a first capacitance and a second pair of capacitors  96  having a second capacitance that is different than the first capacitance. In the exemplary embodiment, each capacitor  94  has a predetermined capacitance that is sized such that during the first mode of operation, coils  90  and  92  generate a resonance frequency that is approximately equal to the quadrupole magnetic resonance frequency of the first material that is to be detected by system  10 . Moreover, ach capacitor  96  has a predetermined capacitance that is sized such that during the second mode of operation, coils  90  and  92  generate a resonance frequency that is approximately equal to the quadrupole magnetic resonance frequency of the second material that is to be detected by system  10 . 
     During operation, coils  90  and  92  are each operable at a plurality of frequencies. In the exemplary embodiment described herein, coils  90  and  92  are operable at a first frequency and a second frequency that is different than the first frequency. More specifically, during operation, the capacitance values of both first and second pairs  94  and  96 , respectively, are adjusted to create a double resonance indicated by the two sets of current paths wherein each current path pair represents the current for a given resonant mode of the circuit. For example, the first pair of capacitors  94  may be adjusted to generate a first pair of current paths  98  that are substantially parallel to each other. Moreover, the second pair of capacitors  96  may be adjusted to generate a second pair of current paths  100  that are each perpendicular to the first pair of current paths  96 . The current paths  98  and  100  may be placed in communication with an electrical source (not shown in this figure). During operation, current flow through the first pair of current paths  100  in a substantially anti-symmetric manner. That is the current flows through a first current path in a first direction and flows through a second current path in a second opposite direction. Moreover, the current flow through the second current path  100  in an anti-symmetric pattern. The term “anti-symmetric current flow” may be used to refer to the condition in which current flows through the current branches in substantially opposite directions. 
     Operation of QR screening system  60  in accordance with embodiments of the invention may proceed as follows. First, a person may be directed to enter screening system  10  at entrance ramp  82 . The person proceeds up entrance ramp  82  and stands with their left foot positioned of coil  90  and their right foot positioned over coil  92 . System  10  may include a visual or audio device to prompt the passenger to facilitate enabling their feet to be properly positioned. Optionally, labels are attached to the floor  30  to indicate where the passenger&#39;s feet should be placed. 
     The scan may be initiated automatically when the passenger stands on the sensor housing or may be initiated by security personnel. At this point, the lower extremities and specifically the shoes of the passenger are scanned using the inductive sensor  32  to determine the presence of a target substance such as, for example, an explosive, contraband, an illegal drug, a controlled substance, or a conductive object. In the case of QR detectable objects, this may be accomplished by a QR sensor providing RF excitation signals at a first frequency generally corresponding to a first predetermined, characteristic NQR frequency of a first target substance. Note that the excitation frequency need not be exactly the same as the target substance NQR frequency, but it is typically within about 500-1000 Hz. The resonant frequencies of the various target substances that may be detected using NQR are well known and need not be further described. 
     Moreover, the passenger may be scanned at a second frequency, generally corresponding to a second predetermined, characteristic NQR frequency of a second target substance. After the threat screening is completed, system  10  will direct the passenger to exit the screening system  10 . 
     Detection of QR explosives or anomalous metal content will result in an alarm that is conveyed to the security personnel. The QR alarm may be a simple pass/fail indicator or an indication of the explosive type and quantity. The anomalous metal alarm may be a simple pass/fail indicator, an indication of metal imbalance between shoes, or an image of the metal in the soles of the shoes. Moreover, because system  10  includes two coils  90  and  92  functioning as gradiometers, system  10  is configured to differentiate and identify which specific shoe may contain the suspect material. 
     Described herein is an exemplary passenger screening system. The screening system includes an explosives detection system that is configured to detect the presence of explosives that may be concealed in a passengers shoes or on their lower extremities. The explosive detection system facilitates reliable detection of explosives in shoes and the lower leg area which will allow for rapid screening of passengers entering secure areas (e.g. airport screening). 
     Specifically, electromagnetic induction methods can be used to detect the presence of metal in both shoes. As with a metal detector used for landmine detection, EMI detectors at both feet can measure attributes related to the rough size, geometry and type of metal (ferromagnetic or not) in each shoe. The characterization can be used to compare the metal signatures of the left and right shoes and will allow for discrimination between simple shoe shanks and potential weapons. 
     During operation, a passenger scanning process may be initiated automatically when the passenger stands on the sensor housing. Optionally, the passenger scanning process may be initiated manually by a security person, for example. If system  10  detects explosives and/or anomalous metal content within the passengers&#39; shoes, an alarm is conveyed to the security personnel. The alarm may be a simple pass/fail indicator or an indication of the explosive type and quantity. The anomalous metal alarm may be a simple pass/fail indicator, an indication of metal imbalance between shoes, or an image of the metal in the soles of the shoes (provided an MR sensor array is used). 
     Moreover, further reduction of RH can be achieved using adaptive noise cancellation. In adaptive noise cancellation, the background RH is detected using a set of reference antennas. The signal from the reference antennas is used to remove any RFI signals detected on the QR receiver. 
     Optionally, system  10  may include magnetoresistive sensors to measure magnetic field gradients created by the presence of metal in shoes. During operation, gradients in both the earth&#39;s magnetic field and induced magnetic fields (static or alternating) are measured to discriminate between ferromagnetic and non-ferromagnetic metals. The magnetic field gradients are then mapped to generate an image of metal objects in the shoe allowing an operator to discriminate between simple shoe shanks and potential weapons. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.