Abstract:
The present invention relates to a portable metal detector adapted for detection of dangerous metallic items carried by individuals, for example during access to a departure lounge in an airport, comprising a casing which houses a transmitter/receiver winding, the casing being extended by a gripping and handling handle, and a processor which feeds a loop of the winding to generate a magnetic field and which detects perturbations of the magnetic field caused by the environment, characterised in that the detector comprises a sensor for detecting orientation of the detector in a vertical position of the handle and which, when the detector is in a vertical position, activates a single dynamic detection mode of the winding whereas, when the detector is in another position, it activates a static operating mode of the winding.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation in part of U.S. patent application Ser. No. 14/451,799, filed on Aug. 5, 2014, which claims benefit to French Application No. 1357790, filed Aug. 5, 2013, the disclosures of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of portable metal detectors adapted for detection of dangerous metallic items carried by individuals, for example during access to a departure lounge in an airport, or any other similar place of controlled access. 
       STATE OF THE ART 
       [0003]    Many portable metal detectors have already been proposed adapted for detection of dangerous metallic items carried by individuals. 
         [0004]    The attached  FIG. 1  illustrates by way of non-limiting example the general structure of such known sensors. 
         [0005]    As is evident from the attached  FIGS. 1 and 2 , known sensors  10  generally comprise a casing  20  extended by a gripping and handling handle  30 . 
         [0006]    The casing  20  contains an electric winding  22  in the form of a loop centred about an axis  23  which extends perpendicularly to the longitudinal direction  32  of the handle  30 . The winding  22  is connected to a processor  40  and a power supply  42 . 
         [0007]    The processor  40  is adapted alternatively for a) feeding the winding  22 , forming a transmitter winding by electrical voltage producing a magnetic field and b) detecting, as the winding  22  forms a receiver winding, perturbations of the magnetic field resulting from metallic pieces placed in the environment of the detector. 
         [0008]    Known sensors can form the subject of many embodiments, especially as to the geometry of the winding, the nature of the electrical voltage applied to the winding (most often high-frequency alternative electrical voltage, and preferably successively frequency scanning), and the configuration of the winding  22  (a single winding can be provided, used alternatively and sequentially at the transmitter when supplied to generate a magnetic field and at the receiver when used to detect perturbations due to the environment or at least two separate windings respectively forming transmitter and receiver). As illustrated schematically in the attached  FIG. 3 , portable metal detectors  10  adapted for detection of dangerous metallic items carried by an individual are most often used by a security agent SA for body-scanning a suspect individual SI, for example in airports at the access to the departure lounge, after passing through a metal-detector gantry which has indicated the possible presence of a metal object on a suspect individual SI. 
       GENERAL AIM OF THE INVENTION 
       [0009]    Based on the observation that a conventional detector is highly sensitive to the environment, especially to concrete rebar forming the supporting floor, when it is used at foot level of a suspect individual to verify that this individual is not hiding a dangerous object, for example a knife, in his shoes or socks, as shown in  FIG. 4 , the aim of the present invention now is to propose means for eliminating drawback. 
         [0010]    This aim is attained according to the invention by a portable metal detector adapted for detection of dangerous metallic items carried by individuals, comprising a casing which houses a transmitter winding and a receiver winding, the casing including a gripping and handling handle and a processor which feeds a loop of the transmitter winding to generate a magnetic field and which is connected to the receiver winding to detect perturbations of the magnetic field caused by the environment on the basis of the electrical signal issued from the receiver winding, wherein the detector comprises a sensor which detects orientation of the detector in a vertical position of the handle and which, when the detector is in a vertical position, activates a first dynamic detection mode of the winding wherein the processor detects only the perturbations which are not constant over a defined time range and ignores the perturbations detected which remain constant over a defined time range, whereas when the detector is in another position than the vertical, it activates a second static operating mode of the winding wherein all constant perturbations and non-constant perturbations are detected. 
       DESCRIPTION OF FIGURES 
       [0011]    Other characteristics, aims and advantages of the present invention will emerge from the following detailed description in relation to the attached diagrams given by way of non-limiting examples and in which: 
         [0012]      FIGS. 1 to 4  mentioned previously schematically illustrate a known portable detector and its use, 
         [0013]      FIG. 5  schematically illustrates a non-limiting example of a portable detector according to the present invention, 
         [0014]      FIG. 6  schematically illustrates a variant embodiment of the winding according to the present invention, 
         [0015]      FIG. 7  schematically illustrates the electric and electronic means of a portable detector according to the present invention, 
         [0016]      FIG. 8  schematically illustrates the operation of the portable detector according to the present invention. 
     
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 5  schematically illustrates a sensor  100  according to the present invention comprising a casing  120  extended by a gripping and handling handle  130  which extends according to a longitudinal axis  132 . 
         [0018]    The casing  120  contains an electric winding  122 . 
         [0019]    The winding  122  is connected to a processor  140  and a power supply  142 . 
         [0020]    The processor  140  is adapted alternatively a) to feed the winding  122 , forming a transmitter winding, by electrical voltage producing a magnetic field and b) detect, as the winding  122  forms a receiver winding, perturbations of the magnetic field resulting from metal pieces placed in the environment of the detector. That is, the detections received by the winding due to perturbations of the magnetic field are passed to the processor  140 . 
         [0021]    The winding  122  is preferably located in the median plane of the casing  120  located in the extension of the axis  132  of the handle  130 , and centred about an axis  123  which extends perpendicularly to the longitudinal direction  132  of the handle  130 . 
         [0022]    As indicated previously according to the present invention, the detector also comprises a sensor  150 , such as for example a triple-axle accelerometer, for detecting orientation of the detector in a vertical position of the handle  130  and which, when the detector is in this vertical position, activates only a dynamic detection mode of the winding  122 , whereas when the detector is in another position it activates a static and operating mode dynamic of the winding  122 . 
         [0023]    &lt;&lt;Orientation of the detector in a vertical position of the handle  130 &gt;&gt; means at least substantially vertical orientation, for example 15° close to the longitudinal direction  132  of the handle  130 . 
         [0024]    When just the dynamic operation of the winding  122  is activated, the processor ignores the perturbations detected which remain constant over a defined time range, whether the detector is being held in a constant position or being moved. This arrangement according to the present invention ignores perturbations due to rebar in the support flooring, but does detect a metal object carried at floor level by an individual, for example a knife, when the detector is moved at foot level of an individual. 
         [0025]    However when dynamic and static operation of the winding  122  is activated, the processor  140  takes into account all perturbations detected, the detector being considered as being far from the floor. 
         [0026]    Typically when the dynamic operation of the winding  122  is activated the processor  140  ignores the perturbations detected which remain constant over a defined time range, whether the detector is being held in a constant position or being moved, by taking into account only the part of the electrical signal representative of perturbations which has a frequency above 2.5 Hz or equal to 2.5 Hz. 
         [0027]    Rejection of the perturbations which remain constant over a defined time range, such as perturbations having a frequency less than 2.5 Hz, for contrarily operating only the perturbations which are not constant, such as the perturbations having a frequency above or equal to 2.5 Hz, could be made by a high pass filter having a frequency threshold at 2.5 Hz. 
         [0028]    Such a high pass filter is illustrated on  FIG. 7  under reference  160 .  FIG. 7  more precisely illustrates the winding  122 , the processor  140 , the power supply  142 , the sensor  150  and the high pass filter  160 . 
         [0029]    When the sensor  150  detects that sensor  100  is in a vertical position, the processor  140  activates the first dynamic detection mode, so that the signal representative of the perturbations is passed through the high pass filter  160  and the processor  140  uses only the dynamic signal issued at the output of the high pass filter  160  and consequently the processor  140  detects only the perturbations which are not constant over a defined time range and ignores the perturbations detected which remain constant over a defined time range. 
         [0030]    Contrarily when the sensor  150  detects that sensor  100  is not in a vertical position, the processor  140  activates the second static operating mode of the winding, so that the signal representative of the perturbations does not pass through the high pass filter  160  and the processor  140  uses consequently all constant perturbations and non-constant perturbations. 
         [0031]    The processor  140  operates to feed the winding  122  and successively perform detection. The processor  140  may be any kind of digital processor, like a microprocessor, or an analog circuit device adapted to analyze the electrical signal issued by the receiver winding to detect any change in this electrical signal compared to the electrical signal issued by the receiver winding at rest when the detector is at distance of any metal object, corresponding to a perturbation of the magnetic field generated by the transmitter winding by a metal object. In the first dynamic detection mode, the processor  140  analyzes only the part of the perturbations signal having a frequency above a threshold, for example above 2.5 Hz. In the second static operating mode the processor  140  analyses all the components of the perturbations signal, i.e. the constant perturbations and the non-constant perturbations. 
         [0032]    The position sensors formed by a triple-axle accelerometer are known per se. They will therefore not be described in any more detail hereinbelow. 
         [0033]    Of course, the present invention is not limited to the embodiments which just been described, but extends to all variants in keeping with its central idea. 
         [0034]    In particular, the geometry of the winding  122  can form the object of many variant embodiments. 
         [0035]      FIG. 6  illustrates a variant embodiment according to which the winding  122  comprises a multipolar winding in  8 . 
         [0036]    This multipolar winding  122  comprises two elementary loops  124  and  126  placed electrically in series and wound in opposite directions such that identical perturbations caused simultaneously on each elementary coil are compensated and cancelled at the output of the winding  122 . The loops  124  and  126  are centred about respective axes  123 ,  125 . 
         [0037]    The number of turns of the two elementary loops  124  and  126  is preferably identical. Similarly, the surfaces of both elementary loops  124  and  126  are preferably identical. 
         [0038]    Preferably, as is evident from  FIG. 6 , the adjacent strands  124   a ,  126   a  of the two elementary loops  124  and  126  of the winding  122 , located in the median part of the winding in  8 , do not extend orthogonally to the longitudinal direction  132  of the handle  130 , but are inclined relative to this direction, so as not to create a neutral median zone on the magnetic plane at the level of which a metal object would not be detected. Because of the inclination of these strands  124   a  and  126   a , it is actually guaranteed that an object placed near the middle of the winding  122  cuts field lines of the elementary coils  124 ,  126  when the detector is moved by scanning in an alternative pivoting movement centred about an axis centred overall on the wrist of the user and orthogonal to the direction  132 . 
         [0039]    In an embodiment, the winding  122  or inductive transducer is formed by a simple winding constituting transmitter and receiver. 
         [0040]    In another embodiment, the transducer  122  is formed by two windings forming respectively transmitter and receiver, and is appropriate alternatively. 
         [0041]    In all cases, the windings preferably comprise several loops in series of inverse directions for neutralising the effects of external parasites. 
         [0042]    Also, the inductive transducer  122  can advantageously comprise windings offset to each other, both at the level of transmission and reception, to limit mutual inductance generated by the windings of the inductive transducer. 
         [0043]    Of course, the number of transmitter windings and the number of receiver windings is not limited to one or two. Also, the number of transmitter windings is not necessarily identical to the number of receiver windings. 
         [0044]      FIG. 8  explains how the signal generated by the concrete rebar in the floor is canceled with the present invention due to the switch of the detector in the dynamic mode using a high-pass filter  160  when the detector is displaced as illustrated on  FIG. 4 . 
         [0045]    Considering: 
         [0046]    Sy as the variation of the detection signal due to the variation of distance between the detector and the floor during displacement of the detector (when rebars are embedded in the concrete floor), 
         [0047]    Sx the variation of the detection signal due to metallic object M (for example a knife) to identify located in a shoe, 
         [0048]    the vertical displacement speed Vy is lower than the horizontal displacement speed Vx. 
         [0049]    Moreover the mass M is confined on a limited area, while the metal in the floor extends along a great area in the floor. As a consequence the oscillation period Ty due to the floor metal rebars is greater than the oscillation period Tx due to the metal object M and the corresponding frequency Fy is lower to the frequency Fx. 
         [0050]    In other words : Vy&lt;&lt;Vx, thus Ty&gt;&gt;Tx and fy&lt;&lt;fx. 
         [0051]    When the detector  100  is in the vertical position, the dynamic mode allows to cancel, with the high-pass filter  160 , the part of the signal having a low frequency Ty due to the floor metal rebars. This is illustrated on  FIG. 8  wherein the graph Sy illustrates the perturbation signal due to the floor metal rebars at the input of the high pass filter  160  while the graph S′y illustrates the corresponding signal at the output of the high pass filter  160 . 
         [0052]    But in the dynamic mode the perturbation signal due to a metal object M which is not constant is taken into account by the processor  140 . This is also illustrated on  FIG. 8  wherein the graph Sx illustrates the perturbation signal due to the metal object M at the input of the high pass filter  160  while the graph S′x illustrates the corresponding signal due to the metal object M at the output of the high pass filter  160 . 
         [0053]    When the detector  100  is not in the vertical position, the static mode allows contrarily to analyze all the components of the detected signal.