Patent Application
20200264298
Known weapon detectors such as X-ray detectors, pulse induction metal detectors and backscatter radars are time consuming to operate and therefore create bottlenecks that can cause significant accumulation of individuals awaiting scan, which in turn can create significant numbers of vulnerable “soft targets” outside of protected areas. The 2017 Manchester bomb attack was an example where an attacker exploited the soft-target problem of the bottlenecked checkpoints.
Much of the bottlenecks problem at weapons scanner checkpoints arises because individuals to be scanned must empty their pockets, remove shoes and belts, and submit their hand baggage to time consuming secondary checks. False alarms triggering additional scans from hand-held metals detectors or chemical sensors further add to the time used to scan and clear each individual.
Thus a need exists to significantly speed up weapons checks so that soft target accumulation is greatly reduced. For example by allowing individuals to be scanned to keep metal objects in their pockets, hand baggage, and to wear their belts and shoes. A need also exists to improve on both the sensitivity and specificity of existing weapon detection systems.
In some embodiments, an apparatus includes a weapon detection system having a radar subsystem and a magnetometer. The radar subsystem is configured to detect a set of radio frequency (RF) response signals from an item under test (IUT). The magnetometer is configured to detect a set of magnetic response signals from the IUT. The weapon detection system is configured to calculate a composite multi-source detection signal based on the set of RF response signals and the set of magnetic response signals.
In some embodiments, multiple, quasi-independent signal evocation is used such that targets, such as firearms, knives and improvised explosive devices with fragmentation materials such as nails or ball bearings are detected and differentiated from clutter, i.e., signals from non-weapon metallic objects such as mobile devices, keys, belts, nail clippers, and steel shanks of shoes.
The majority of weapons of concern, contain high carbon steel or stainless steel having linear dimensions greater than two inches, and with metallurgy that offers opportunities for uniquely identifying the presence of such objects. Some embodiments described herein can exploit at least one of several unique properties of most weapons including (1) the total mass of carbon or stainless steel; (2) the linear dimensions and radar cross section of a range of weapons; (3) electromagnetic phenomena specific to high carbon and stainless steel; (4) the asymmetric aspect ratio of a handgun or rifle that produces a differential signal to plane polarization; and (5) the presence of explosives that outgas detectable molecules. In some embodiments, the electromagnetic phenomena include (1) relatively “hard” magnetic properties (remanence) which produce characteristic B field transients when the targets move through strong static magnetic fields; (2) hysteresis in the presence of alternating magnetic fields; and (3) ferromagnetic resonance upon illumination at specific RF frequencies, producing retroreflection curves specific to steel having high hysteresis (“hard” ferro-metal).
In some embodiments of a weapon detection system, both high sensitivity and specificity can be achieved by sensing multiple of the above phenomena, and combing signals in each modality into a composite signal that is acceptably reliable.
In some embodiments, a weapon detection system can include a body scanner and a baggage scanner separate from the body scanner. The body scanner is configured to scan a person and the baggage scanner is configured to scan an object such as a briefcase, suitcase, purse, personal belongs in a container, etc. In some embodiments, a weapon detection system can include a scanner, which can scan and detect weapon attached to a person or in an object.
In response to a signal from the CPU 110, after the IUT 104 is placed on the motor-driven shuttle 102, the motor-driven shuttle 102 moves the IUT 104 into a radar array (or a RF emitter array) in the radar subsystem 106 that emits radio frequency (RF) energy (or a set of RF excitation signals) at wavelengths for which a common range of weapon sizes can produce a strong retroreflective signal (or a set of RF response signals) based on the phenomenon of resonant absorption and re-radiation of energy for conductors at or near the half wavelength of the irradiating RF energy. A set of RF excitation signals with a single frequency, or a range of frequencies is emitted by the radar array. The range of frequencies of the set of RF excitation signals can be used to differentiate the range of dimensions (e.g., sizes, or shapes) of weapons of concern such as handguns and knives. In some implementations, as the set of RF excitations signals is emitted by the radar array, the radar transmit and receive antennas can be rotated substantially 360 degrees at a rate of 1-5 revolutions per second. In some implementations, the phase angle of the sinusoidal RF signal sent to an array of multiple transmit antennas (phased array of antennas) oriented at different polarization angles with respect to the IUT 104 is continuously changed such that the combined emission from the set of antennas rotates the polarization of the transmit signal continuously through substantially 360 degrees. Such rotation, whether produced by mechanical or phase steering, produces amplitude modulation of the retuned signal (or the set of RF response signals) that increases and decreases according to the orientation of the plane of polarization of the transmit and receive antennas to the IUT 104. For example, when the composite long axis of the IUT 104 is parallel to the plane of polarization of the transmit and receive antennas, the amplitudes of the returned signal (or the set of RF response signals) can be greater or at maximum. When the axis of orientation the composite long axis of the IUT 104 is perpendicular to the plane of polarization of the radar antennas, the amplitudes of the returned signal (or the set of RF response signals) can be lesser or at minimum. The transmit and receive antennas can be matched, and separated by a metal shield and RF absorbing material, such as carbon impregnated foam, that reduces cross talk between transmit and receive antennas. In some implementations, the plane of polarization of the transmit and receive antennas can be oriented at 90 degrees to each other to further decrease “cross talk”. The antennas are broadband devices, such as log periodic Yagi antennas with an approximately flat frequency response from 500 MHz to 3GHz. This broadband response allows use of a range of frequencies appropriate for targets of different dimensions (sizes or shapes), as well as assessment of ferromagnetic resonance, which is typically in the 2-5 GHz range for carbon and stainless steel.
Accordingly, the peak amplitude of radar return from a continuous wave (CW) emission will oscillate at twice the rotation frequency (due to the long axis of the IUT being parallel to the radar antenna plane of polarization twice per revolution) creating sidebands that can be easily detected on a spectrum analyzer, processing the Fourier Transform of the returned signals (or the set of RF response signals).
First order sidebands can appear on both side of the CW carrier in the spectrum analyzer output analyzed by the CPU 110 or 160, with higher order sidebands extending away from the carrier which are formed, for example, when the convolution of the antenna gain pattern and target re-radiation gain pattern produce periodic, consistent modulations of the return signal (each periodic intersection of gain pattern peaks and nulls). The presence of sidebands in the spectrum analyzer output indicates presence of a conductor at or near the dimensions of interest.
Similarly stated, at least one RF signature from the set of RF response signals includes sidebands that are generated when the at least one of the transmit antenna and the receive antenna is periodically rotated with respect to the IUT, when the at least one of the array of antennas is rotated via electrical phase steering and with respect to the IUT, or when the IUT is rotated with respect to the at least one of the transmit antenna, the receive antenna, or the array of antennas. The sidebands indicate the IUT is a metal object of a length typical of a weapon.
In some embodiments of the weapon detection system 100 or 150 shown in
The second scan (labeled “shuttle motor” 302) develops a signal Sp, that is proportional to the combined amplitudes of a set of magnetic signals. The set of magnetic signals are generated in response to a magnetic field by a set of magnetic field generators and detected by a set of magnetometers. A weighting coefficient “b” determines the contribution of the passive magnetic signal to the total signal Scot, and can, in some implementations, be based upon empirical evidence from multiple IUT configurations.
In a third scan (labeled “Radar motor” 303) with a stationary IUT a cyclically time-varying magnetic field from one set of magnetic antennas induces magnetization in ferro-metals in the IUT, generating a response that is sensed in another set of the magnetic antennas.
In “hard” ferro-magnetic materials such as high carbon steel and high strength stainless steel, an oscillating magnetic field causes an increase in magnetization up to the point where all of the magnetic domains within the material are oriented with the magnetic field, at which point saturation is reached and no further magnetization occurs. Thus, when the polarity of the magnetic field is reversed, there is delay or “hysteresis” in the polarity reversal in the IUT. The coercivity of a ferro-magnetic material can be a measure of the strength of the field applied to a material that has achieved domain saturation to reverse the polarization of magnetization, and the “remenance” is a measure of the residual magnetization that persists after the magnetization field has reversed polarity or ceased. The combined coercivity and remenance amplitudes constitute the “active” magnetic signal, Sa, which has a weighting coefficient “c” determined by empirical experience from multiple IUT configurations.
In other words, the weapon detection system includes a set of magnetic field generators configured to collectively generate an oscillating magnetic field. The magnetometer is configured to detect ferromagnetic hysteresis characteristics of the IUT in response to the oscillating magnetic field. The weapon detection system is configured to calculate the composite multi-source detection signal based on the ferromagnetic hysteresis characteristics.
Optionally, a chemical sensor near the radar (or located with at least one of the radar subsystem or the magnetometer) can detect air currents in and around the IUT to develop a chemical signal Sc which the CPU also stores. This sensor might comprise a “pulse-probe” laser spectrometer or passive optical spectrometer. The Sc terms, as other terms, receives a weighting coefficient “d” to determine its contribution to the composite Stot (combined Signal from all sources) detection signal (also referred to herein as “composite multi-source detection signal,” “composite detection signal” or “total detection signal”). The chemical sensor is configured to detect a chemical present with the IUT to improve hits and correct negative responses and to decrease misses and false alarms.
In another embodiment, after the radar completes multiple revolutions and side band signals are developed, it shifts frequency up to the ferromagnetic resonance range of high carbon and stainless steel used in weapons, and an Sfr signal is developed, indicating the presence of metal with resonant properties appropriate for metallurgy of weapons.
As the shuttle moves the IUT over the static magnetic fields, two consecutive measures are taken by the magnetometer assembly. The first measurement, Sp, registers passive magnetometer response of three magnetometers oriented in three different planes when the IUT passes through the peak of the static magnetic fields of permanent magnets under the shuttle.
The movement of ferromagnetic metal over permanent magnet induces temporary magnetization in the metal such that, while that metal continues to move it constitutes a moving magnetic “b field” in the presence of three, orthogonally oriented induction coils. According to Faraday's law, which stipulates that the voltage induced in a coil from a nearby changing magnetic field is given as E=−dB/dt, where B is the magnetic flux and E is the induced voltage. The magnetic flux exposed to a wire consulter in a coil will in turn, be proportional to the cosine of the angle between the direction of the lines of magnetic flux of that field and the wire in which a voltage is induced. Thus, with three magnetometer coils, each oriented in one of three orthogonal planes, an arbitrarily-oriented weapon will have an optimally oriented b field with respect to at least one of the coils, improving the ability of the ensemble of three magnetometer coils to detect moving ferromagnetic metal. The output of three magnetometer coils, each positioned on opposite sides and above of the shuttle is taken to develop the Sp signal.
Similarly stated, the weapon detection system can include a first magnetometer, a second magnetometer and a third magnetometer. The first magnetometer is oriented substantially within a first plane, the second magnetometer is oriented substantially within a second plane orthogonal to the first plane, and the third magnetometer oriented substantially within a third plane orthogonal the first plane and the second plane. The first magnetometer, the second magnetometer and the third magnetometer are collectively configured to substantially maximize detection sensitivity under a range of orientations and aspect ratios of the IUT.
In some embodiments, the weapon detection system can include a set of permanent magnets disposed under a motion path of the IUT to produce momentary magnetization of the IUT while moving with respect to the weapon detection system such that changes in magnetic fields are produced at the magnetometer. In such embodiments, the set of permanent magnets can be arrayed in one of a set of patterns including a line, a set of lines, and a matrix to differentiate sizes, shapes, or ferromagnetic metal content of a set of IUTs.
Owing to the relatively high remanence of high carbon steel and stainless steel, target passage over the static magnetic fields induces magnetization in the target which persists longer than for soft conductors such as iron, aluminum, copper and brass, thereby producing a prolonged secondary magnetic field whose change with motion is sensed in the magnetometer
The CPU then commands a relay to route an AC voltage from a signal generator , nominally at 400 HZ, but other frequencies are possible, to one of the magnetometer antennas, making that antenna radiate an alternating magnetic field when the shuttle stops just after passing the IUT over the static magnetic field generators. Due to hysteresis of the relatively “hard” carbon and stainless steel ferro-metals, the AC field produces in the receive magnetometer a signal with hysteria on a B-H plot as shown in
In some embodiments, the oriented magnetometers are copper wire wound in multiple layers over Mu metal cores, to achieve high sensitivity, but other sensors to sense changes in magnetic fields, such as hall-effect sensors, simple wire coils or quantum magnetometers are possible. To achieve fast time response to analyze hysteresis, simple air core multi-turn coils with relatively low inductance may also be employed either as stand-alone magnetometers or in conjunction with more sensitive Mu metal core antennas.
Taking hysteresis measurements to assess the presence of ferromagnetic metals with remenance while the IUT is close to permanent magnets, enhances the detection of hysteresis effects because the strong magnetic fields push the target metals closer to saturation (a state where all possible domains within the ferromagnetic material are oriented according to the imposed magnetic field), where hysteresis effects may be observed in an alternating polarity magnetic field.
Because high carbon steel and stainless steel used in firearms and knives have been found to exhibit higher remenance and coercivity than iron or other ferro-metals, the shape of hysteresis functions sensed helps differentiate metals of interest—i.e., typically those in firearms and cutting instruments.
Other means of diagnosing the magnetic properties of IUT from hysteresis are viable including analysis of responses to pulse induction stimuli.
With the pulse induction method, a series of discrete square wave pulses from a signal generator is passed through a transmit coil, and the induced magnetization is sensed by a receive magnetometer. In an alternate embodiment, periodic rotation of a strong permanent magnet near the IUT will induce an impulse response that may be evaluated for hysteresis.
Once hysteresis measurements are captured the CPU then commands the shuttle to move the IUT where it is then removed, and resets the relay to normally closed such that both magnetometers are set back to passive mode.
When all scans are completed, the CPU sums the different “S” terms, as shown in
If the composite signal, Stot, exceeds a threshold, the CPU activates an alarm notifying scanner operators that a weapon is likely present in the IUT.
The coefficients ultimately selected for developing the Stot will be determined through iteration, as in a simple model, or through a more complex a machine learning (ML) algorithm (or model), such as computational neural net (CNN) or gradient descent algorithm, that learns to distinguish samples where weapons are present from samples where weapons are absent, where large (>10,000) instances of different weapons-bearing and weapons-free samples are presented to the ML model. In the ML model, a function “” developed by the ML algorithm determines the coefficient weightings (e.g., coefficient weightings a, b, c, d and e) and overall transfer function of sensor inputs (e.g., Sr, Sp, Sa, Sc, and Sfr) to detect outputs (e.g., Stot).
S
tot
=f(aSr+bSp+cSa+dSc+eSfr)
In other words, the CPU of the weapon detection system is configured to execute a machine learning (ML) algorithm to produce a set of coefficient weights. Each coefficient weight from the set of coefficient weights is uniquely associated with one of the radar subsystem, the magnetometer and/or the chemical sensor. The CPU is configured to calculate a composite multi-source detection signal based on a sum of weighted contributions of the radar subsystem, the magnetometer and the chemical sensor. The detector system employs multiple techniques to improve the signal-to-noise, and signal to clutter ratios of both the RF stage and magnetometer stages of the system.
In the RF stage, a copper or silver, highly conductive two layer shield is placed between the transmit and receive antennas to reduce cross talk between the antennas. Ideally, this conducting shield comprises of two, non contacting sheets on opposite sides of a dielectric material.
In addition, a carbon impregnated foam sheet, such as those commonly employed in RF anechoic chambers is placed between the two antennas to further reduce cross talk. Crosstalk suppression improves sensor sensitivity by reducing automatic gain control used to keep RF signals inside the dynamic range of the RF receiver. Crosstalk suppression also increases the sideband-to-carrier ratio (also referred to herein as “total sideband-energy-to-carrier metric” or “total sideband-energy-to-carrier value”), which improves both sensitivity and selectivity of the detector.
RF absorbing foam is also placed around the transmit and receive antennas to restrict antenna side lobes and multi-path propagation that increase carrier cross crosstalk, and in the case of dynamic multiparty from moving objects, degradation of carrier spectral purity due to Doppler frequency shift effects. High spectral purity and low phase noise in the RF sensor improve both sideband modulation depth (also referred to herein as “total sideband-energy-to-noise-floor metric” or “total sideband-energy-to-noise-floor value”)and the sideband-to-carrier ratio.
An additional way to reduce RF cross talk between transmit and receive antennas is to orient the antennas such that their planes of polarization are perpendicular. Although doing this reduces the returned energy from targets, such a polarization scheme reduces crosstalk to a greater degree, again increasing sideband-to-carrier ratios. Similarly stated, the radar subsystem includes a transmit antenna having a polarization and a receive antenna having a polarization, the transmit antenna is disposed substantially with respect to a first plane, the receive antenna is disposed substantially with respect to a second plane substantially orthogonal to the first plane such that cross talk between the transmit antenna and the receive antenna is reduced.
For the magnetometer sections, which feature multiple layers of coil windings around a high magnetic permeability core, such as Mu metal, a slotted electrostatic shield, shunted to signal ground is employed to reduce electronic noise power lines from RF transmissions and nearby electrical devices.
In addition, the magnetometers are housed in a Mu metal shielded compartment that greatly reduces the changes in magnetic field at the coils from ambient sources.
As shown in
For example, in one embodiment, two end cap Mu metal sheets, bent into a U shape slide over the open ends of a cubical shielded compartment, and are mechanically clamped on the main body of the compartment to minimize magnetic field “leakage”. Alternatively, the end caps can be slidably disposed within the weapon detection system so that the end caps can be inserted and removed in synchrony with motion of the IUT to decrease ambient magnetic energy detected by the magnetometer
In another embodiment, hinged Mu metal flaps (also referred to herein as “doors”) open and close at both ends of the scan chamber (e.g., an entrance of the chamber and an exit of the chamber, such that the magnetic sensing environment is enclosed on all six sides while magnetic sensing, passive and/or active, is occurring. The Mu metal flaps can be, for example, hinged to the end/walls of the chamber or other moveably attached to the end/walls of the chamber. Similarly stated, the weapon detection system can include a first door disposed at an entrance of a portion of the weapon detection system having the magnetometer. The weapon detection system can include a second door disposed at an exit of the portion of the weapon detection system having the magnetometer. The first door and the second door being positioned relative to the magnetometer while the magnetometer detects the set of magnetic response signals from the IUT to reduce ambient changes in magnetic fields from being detected by the magnetometer.
Yet another method of increasing signal to noise in the magnetometer stage is to adjust the speed of shuttle transit to increase signal strength from target materials. According to the Faraday equation E=−dB/dt. the faster a target moved over magnets passed the magnetometers the greater will be the voltage generated in the magnetometer coils. Thus, if ambient changes in magnetic fields are sensed, even inside the Mu metal shielding, it will still be possible to develop target signals in excess of ambient noise because signal strengths from moving targets will increase, while ambient magnetic noise will not.
In some embodiments, the spatial gain profile of an IUT in motion, when irradiated by an RF field at a particular frequency, interacts with the spatial gain profile of the receive antenna to generate variations in receive signal amplitude as the IUT moves with respect to the receive antenna. Careful analysis of differences in such time-varying amplitude signals can indicate whether or not a conductor the size and shape of a weapon is in the IUT.
In this figure, gain profiles from irradiation of different objects are depicted at 2 different frequencies, 538 MHz (which elicits a strong response from a handgun) and double 538 MHz (1076 MHz). For 538 MHz the dimension of the handgun represents roughly one half wavelength, while for 1076 MHz the dimension of the handgun represents roughly 1 full wavelength,
IUT's containing only random RF reflecting clutter have a roughly isotropic gain pattern at frequencies representing both half and full wavelengths, but a handgun generates either a well defined two lobe pattern (at an irradiating frequency representing half wavelength) or sharp cloverleaf pattern (at an irradiating frequency representing one wavelength).
Thus, when an RF irradiated IUT with a handgun moves with respect to the receive antenna, the interaction of the handgun's radiation pattern with the receive antenna gain lobe will generate a distinctly different signal than will an isotropic—or approximately isotropic IUT radiator that does not have a handgun.
Although, as shown in
Such difference in time-varying amplitude of received signals as an IUT moves with respect to a receive antenna are shown in the
The purse could be moving on a conveyer belt past a receive antenna, or could be rotating in place under the receive antenna to move with respect to the receive antenna. In
As the roughly isotropic gain profile of the clutter-only IUT moves past the gain lobe of the receive antenna, a peak response develops corresponding to the maximum coupling of energy from the high gain regions of both the receive antenna and IUT occurs, followed by a sharp dip as the IUT moves into the null region of the receive antenna. But as the IUT moves past the second lobe of the receive antenna, a second peak develops as the isotropic profile of the IUT once again “stimulates” the relatively high gain of the receive antennas second lobe.
If a weapon is placed in an IUT, such as a purse containing random RF clutter, the radiation gain profile of the IUT can be more well-defined than that of an IUT containing only clutter, as shown in
Thus, one way to differentiate an IUT containing only clutter from an IUT that includes clutter plus a weapon, is to analyze the peak-to-peak amplitude of the receive signal, with a higher peak-to-peak amplitude indicating the presence of a weapon.
One way to greatly reduce the ambiguity of whether or not a time-varying amplitude signal represents the movement of a weapon past a receive antenna is to create a time-varying signal that is substantially different in both form and amplitude, depending upon the presence of a weapon in the IUT. As shown in
As shown in
As shown in
A solution to this problem is to irradiate the IUT at frequencies corresponding to both 0.5 and 1.0 wavelengths, then to subtract the characteristic two-peak pattern of a clutter-only IUT from the four-peak response, to develop a differential four-peak signal that has greater peak-to-peak amplitude, thereby improving the ability of the system to differentiate targets from clutter.
Frequency pairs other than 0.5 and 1.0 wavelengths are possible. Additions of more than two frequencies to enhance the signal-to-clutter ratio are also possible. In such instances, machine learning algorithms can be trained to differentiate waveforms where weapons are and are not present.
The two-frequency approach to improving target signal-to-clutter also can be applied to detecting concealed weapons on individuals who walk through a check point, without alerting those individuals that they are being scanned.
In some embodiments, the radar subsystem includes an array of receive antennas oriented in a linear pattern. A polarization plane of the array of receive antennas rotates as the person moves relative to the array of receive antennas. The radar subsystem is configured to detect the plurality of RF response signals via the array of receive antennas, such that the weapon detection system is configured to differentiate sizes and/or shapes of a plurality of IUTs that include the IUT based on the plurality of RF response signals and the plurality of magnetic response signals.
As shown in
The double disc cone antenna, with a long axis parallel to the ground, will have a gain profile similar to the gain profile shown in
In contrast, a human walking with a weapon will have a more distinct gain profile, producing a stronger two-peak response than without a weapon, as shown in
In some implementations, a two-frequency (or multiple frequencies) irradiation scheme, with differential analysis of 0.5 and 1.0 wavelength signals, can provide a strong four-peak response, indicating presence of a weapon.
It will be appreciated that both the transmit and receive antenna can be concealed such that a person walking through the transmit and receive antenna fields will not know that they are being scanned, which can enhance security by reducing countermeasures that a weapon carrying person might employ.
Different frequency pairs are feasible, as are more than two frequencies to irradiate the IUT/Human. As more frequencies are added, and results from the different waveforms they generate compared, greater precision can be achieved in discriminating the size and shape of weapon present.
In such instances, machine learning algorithms can be trained to differentiate waveforms where weapons are and are not present.
Although currently available hand-held weapon detectors rarely miss detecting weapons, owing to high sensitivity, such scanners have a very high false alarm rate and are not selective for ferrous typical of weapons and non-ferrous metals typical of “clutter.” Thus, manual checks for weapons can be time consuming and slow the scanning process.
A handheld weapon detector, using principles described for the bag checking magnetometer discussed earlier, with very high selectivity for ferrous vs. non-ferrous metals and low false alarm rate, is depicted in
A magnetometer coil having multiple layers of wires wound around a high permeability core (such as Mu metal) with an electrostatic shield to minimize electric field interference, sends voltage signals generated by the Faraday effect to a high resolution analog-to-digital converter (nominally 24 bits), which in turn sends digitized waveforms to a battery powered CPU controller driving a small display monitor and annunciator, such as a buzzer.
A permanent magnet attached to the end of the magnetometer coil produces a strong magnetic field, which, when moved over any conductor, will induce a changing magnetic field in that conductor that will, in turn, generate a voltage according to Faraday's law in the magnetometer coil. In some embodiments, users of the hand-held magnetometer will, in close, proximity to the person being tested, push and pull the magnetometer along the long axis of the magnetometer coil to minimize signals generated by sweeping the coil across lines of flux of the earth's magnetic field. Alternatively, the magnetometer can be translated up down or side to side, with minimal rotation about its long axis—or an axis perpendicular to the long axis—to minimize the contribution of the Earth's magnetic field. As shown in
The next signal, in the time series represents a stronger response when the magnetometer has a permanent magnet attached, because the permanent magnet induces a current and a changing magnetic field in the non-ferrous conductor, which are sensed by the magnetometer. The third waveform in the series represents the magnetometer response to a large ferrous weapon such as a handgun or knife. Note that, even without a permanent magnet attached to the moving magnetometer, a ferrous object will generate a significant signal in a close-by moving magnetometer, owing to changes in the earth's magnetic field near the ferrous object, which the magnetometer encounters and registers via the Faraday effect, as it moves past the ferrous object. Finally, in the presence of a moving permanent magnet, a much stronger signal is developed in the magnetometer because of both the induced current—and resulting magnetic field—in the ferrous object and the time-varying residual magnetization of the ferrous object which is sensed by the magnetometer.
As with the shuttle driven bag scanner described earlier, the presence of a weapon is indicated by both the amplitude and shape of the waveform. For example, a long knife or handgun will produce a longer lasting signal than a small ferrous object or non-ferrous conductor, as the changes in magnetic field while the magnetometer is scanned over a larger object will be of greater duration.
As with the shuttle bag checker described earlier, machine learning algorithms (e.g., supervised learning algorithms, unsupervised learning algorithms, reinforcement learning algorithms, and/or the like) are implemented to further enhance the high selectivity and low false alarm rate of the hand-held weapon detector by analyzing multiple parameters (e.g. amplitude, shape, pulse width) of the waveform.
A distinct advantage of the moving-magnetometer-with magnet hand-held scanner over existing scanners, is that the weapons can be detected at longer distances without physically touching the person being scanned. Also, due to greater detection range, the hand-scanning time can be reduced because, for example, a scan along the outside of a person's leg can simultaneously detect weapons on both sides of the leg and/or secreted in the crotch.
As shown in
While various embodiments have been described and illustrated herein, a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications are possible. More generally, all parameters, dimensions, materials, and configurations described herein are meant to be examples and the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the disclosure is used. It is to be understood that the foregoing embodiments are presented by way of example only and that other embodiments may be practiced otherwise than as specifically described and claimed. Embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.
Also, various concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.
The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”
The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.
This application is a non-provisional of and claims priority under 35 U.S.C. § 119 to U.S. provisional application Ser. No. 62/807,705, filed on Feb. 19, 2019, and entitled “Multi-Signal Weapon Detector,” the disclosure of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62807705 | Feb 2019 | US |
