Detection system

Abstract

This system suppresses noise caused by ambient light, improving the accuracy of object detection. [Solution] In the scanning surface Sa, the range of angle β centered on the axis F detected by the detector 1 is the range in which electromagnetic waves traveling from outside the passage Pa toward axis F are shielded by the housing 10 of the detector 1, which is facing the detector 1 across the passage Pa. However, in the range of angle α, electromagnetic waves from outside the passage Pa are not shielded by the housing 10 of the detector 1 facing the passage Pa. Since the shielding object 2 is installed on the upper part of the housing 10 of the detector 1, it shields electromagnetic waves traveling from outside the passage Pa toward the opposing detector 1 and prevents them from reaching it.

Description

Technical Field

[0001] The present invention relates to the technology of a detection system that inspects items carried by a person using electromagnetic waves.

Background Art

[0002] As a method for carrying out personal item inspection, there is a method of inspecting for the presence or absence of dangerous objects hidden under clothes using electromagnetic waves. For example, Patent Document 1 discloses a technique for acquiring a thermal image of a shoe and determining the lower limit of the foot and the position of the shoe. This technique detects a target object hidden in a shoe.

[0003] In addition, Patent Document 2 discloses a passive imaging device that receives electromagnetic waves radiated from the human body of a subject, detects and sums the signal intensity for each frequency band and each scanning angle, thereby suppressing the offsetting of the reduction in reception level caused by electromagnetic waves being blocked by an article by the electromagnetic waves radiated from the article. This technique reduces oversight of carried items in personal item inspection.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problem to be Solved by the Invention

[0005] The passive body scanner described above uses a high-sensitivity sensor to capture relatively weak electromagnetic waves such as terahertz waves emitted by the human body itself. Sensors tend to be more likely to generate noise as their sensitivity increases.

[0006] On the other hand, body scanners are sometimes required to be installed and used outdoors for temporary events, etc. When portable body scanners are installed and used outdoors, electromagnetic waves emitted from sunlight, streetlights, etc., can enter the sensor and cause noise to appear in the detected image, reducing image contrast, and obscuring the shape of the human body and shadows cast by belongings. Similarly, even indoors, if there is lighting such as a halogen lamp, temporary body scanners installed under it are prone to similar noise. Noise caused by such ambient light interferes with the accurate detection of belongings.

[0007] One of the objectives of this invention is to improve the accuracy of detecting personal belongings by suppressing noise generated by ambient light. [Means for solving the problem]

[0008] The present invention provides, in a first embodiment, a detection system comprising: a detector that scans electromagnetic waves arriving from a passerby in a passage along a scanning plane intersecting the passage to detect the passerby's possessions; and a shielding object provided on the passage opposite the detector, with a shape along the scanning plane, to shield electromagnetic waves arriving from objects other than the passerby.

[0009] According to the first embodiment of the detection system, noise generated by ambient light can be suppressed, thereby improving the accuracy of detecting the person's belongings.

[0010] In the first embodiment of the detection system, a second embodiment may be adopted in which the detector is housed in each of a pair of housings facing each other across the passage, and the shielding is installed in each of the housings.

[0011] According to the detection system of the second embodiment, the shielding object can be configured integrally with the detector.

[0012] A third embodiment may be adopted in which, in the detection system of the second embodiment, the shielding object is a plate-shaped member installed on the upper part of the housing.

[0013] According to the detection system of the third embodiment, ambient light irradiated from the top of the housing that houses the detector toward a detector facing it across a passage can be shielded.

[0014] In the detection system of the third embodiment, a fourth embodiment may be adopted in which the plate-shaped member is provided with a material that absorbs, diffuses, or diffusely reflects electromagnetic waves of a predetermined frequency on the surface facing the detector.

[0015] According to the detection system of the fourth embodiment, ambient light reflected from the surface of the shield facing the detector can be suppressed from reaching the detector. [Brief explanation of the drawing]

[0016] [Figure 1] A plan view showing an example of a detection system 9 according to an embodiment of the present invention. [Figure 2] A diagram illustrating the scanning plane of detector 1. [Figure 3] A block diagram showing the configuration of detector 1. [Figure 4] A diagram showing an example of the functional configuration of detector 1. [Figure 5] A diagram illustrating Shielding Object 2. [Figure 6] A diagram illustrating the function of shielding object 2. [Modes for carrying out the invention]

[0017] <Embodiment> <Configuration of the detection system> Hereinafter, in the drawings, the space in which each component is arranged is expressed as an XYZ right-handed coordinate space or an xyz right-handed coordinate space. Among the coordinate symbols shown in the drawings, the symbol with a dot inside a circle represents an arrow pointing from the far side to the near side of the drawing sheet. A direction along the x-axis in the space is referred to as an x-axis direction. Further, in the x-axis direction, the direction in which the x-component increases is referred to as the +x direction, and the direction in which the x-component decreases is referred to as the -x direction. The y- and z-components, as well as the X, Y, and Z components, are defined in the same manner as the x-component.

[0018] FIG. 1 is a plan view showing an example of a detection system 9 according to an embodiment of the present invention. In FIG. 1, the -Z direction is downward, that is, the direction of gravity, the X-axis direction is the width direction of a passage Pa, and the Y-axis direction is the direction along the passage Pa. The detection system 9 is a system for inspecting belongings of a passerby Q walking in the +Y direction along the passage Pa. The detection system 9 comprises a detector 1 and a shield 2.

[0019] A total of four detectors 1 are arranged, two on each of the left and right sides facing the traveling direction (+Y direction) of the passage Pa. When the passerby Q and an item carried by the passerby Q (referred to as a belonging) are located near the center of the passage Pa in the Y-axis direction, these four detectors 1 each receive electromagnetic waves such as terahertz waves radiated to the surroundings.

[0020] The detector 1 on the front right side and the detector 1 on the rear left side as viewed from the passerby Q moving in the +Y direction along the passage Pa form a pair and are arranged opposite to each other. The detector 1 on the front right side and the detector 1 on the rear left side perform one-dimensional scanning on the passerby Q with a part of a plane including a straight line connecting the coordinates of their respective receiving points and a straight line parallel to the height direction (that is, the Z-axis direction) as a scanning surface Sa. The scanning surface Sa is set to cross a space through which the passerby Q traveling in the +Y direction along the passage Pa can pass.

[0021] The same applies to the relationship between the detector 1 on the front left side and the detector 1 on the rear right side as viewed from the passerby Q moving in the +Y direction along the passage Pa, and these detectors 1 perform one-dimensional scanning on the passerby Q by a scanning surface Sb shown in FIG. 1.

[0022] As a passerby Q passes over scanning surfaces Sa and Sb, where one-dimensional scanning is repeatedly performed, the four detectors 1 described above perform a two-dimensional scan of the passerby Q and their belongings.

[0023] The shielding object 2 is positioned to cross either the scanning plane Sa or the scanning plane Sb. For example, in the detection system 9 shown in Figure 1, the shielding object 2 is positioned to cross the aforementioned extended plane and is placed on top of the detector 1. As a result, the shielding object 2 shields electromagnetic waves that travel along either the scanning plane Sa or the scanning plane Sb to either detector 1.

[0024] <Detector configuration> Figure 2 is a diagram illustrating the scanning plane of detector 1. Figure 2 shows detector 1 located to the left rear of a moving pedestrian Q (upper left in Figure 1), viewed along the line II-II.

[0025] Here, the xyz right-handed coordinate system shown in Figure 1 is obtained by rotating the XYZ right-handed coordinate system around the Z axis and changing the names of X, Y, and Z to x, y, and z, respectively. Therefore, the z-axis direction of the xyz right-handed coordinate system is the same as the Z-axis direction of the XYZ right-handed coordinate system. And in Figure 2, the direction in which detector 1 is viewed is the -y direction in the xyz right-handed coordinate system.

[0026] The detector 1 shown in Figure 2 is housed in a housing 10. A radome 100 is provided on one side of the housing 10, on the side facing the passage Pa. The radome 100 is a plate-shaped member and is made of a resin material that is relatively permeable to electromagnetic waves, such as polyethylene, polypropylene, polytetrafluoroethylene, polymethylpentene, glass fiber reinforced plastic (GFRP), or polyimide film. The radome 100 allows electromagnetic waves arriving from outside the housing 10 of the detector 1 to pass through to the inside while protecting the inside from dust and other debris.

[0027] The motion sensor 18 is installed on the wall surface of the housing 10 facing the passage Pa, as shown in Figures 1 and 2. This motion sensor 18 is a sensor that detects the presence of a passerby Q walking through the passage Pa.

[0028] The motion sensors 18 are arranged in pairs, for example, with one facing the other across the passageway Pa. One motion sensor 18 emits infrared light towards the passageway Pa, and the other senses the infrared light arriving from the passageway Pa. In this way, the motion sensors 18 detect a passerby Q passing through the passageway Pa. As shown in Figure 1, pairs of motion sensors 18 are installed on the entrance side (lower side in Figure 1) and the exit side (upper side in Figure 1) of the passageway Pa, respectively.

[0029] Furthermore, the line scan camera 16 and the terahertz camera 17 are housed inside the housing 10, for example, as shown in Figure 2. Both the line scan camera 16 and the terahertz camera 17 are cameras that capture images of pedestrians Q passing through the passage Pa via the radome 100.

[0030] The line scan camera 16 is a digital still camera that receives visible light traveling along a scanning plane Sa or scanning plane Sb and converts it into pixel values ​​arranged in a straight line. By continuously capturing images of a pedestrian Q walking in the +Y direction, the line scan camera 16 generates a planar image showing the appearance of the pedestrian Q.

[0031] The terahertz camera 17 is a camera that receives terahertz waves traveling along a scanning plane Sa or scanning plane Sb and converts them into pixel values ​​arranged in a straight line. The terahertz camera 17 shown in Figure 2 has an optical system 171 and a sensor 172. The terahertz camera 17 is, for example, a rectangular parallelepiped unit with a width of 200 millimeters, a depth of 300 millimeters, and a height of 400 millimeters.

[0032] The optical system 171 includes, for example, a polygon mirror and a focusing mirror (not shown). The polygon mirror is a polygonal mirror that rotates around an axis F extending in the y-axis direction in Figure 2, and its shape is, for example, a square pyramid. Electromagnetic waves propagating along the scanning plane Sa pass through the radome 100, are reflected by the polygon mirror of the optical system 171, and are guided to the focusing mirror.

[0033] Due to rotation around axis F, the reflective surface of the polygon mirror changes angle, so the range of reception by the polygon mirror becomes a sector-shaped region Ra centered on axis F, as shown in Figure 2.

[0034] Region Ra is the region where electromagnetic waves can be detected by the terahertz camera 17. Region Ra, shown in Figure 2, is within the range of angle φ and radius r in the direction from +z to -z around axis F. The angle φ is, for example, 100 degrees. The radius r is, for example, 1 meter. The thickness of region Ra in the y-axis direction is several centimeters.

[0035] The terahertz camera 17 shown in Figure 2 is installed on the detector 1 on the left rear side (upper left in Figure 1) of a passerby Q moving in the +Y direction, and is paired with the terahertz camera on the detector 1 on the right front side (lower right in Figure 1). The terahertz camera 17 on the detector 1 on the right front side of the passerby Q moving in the +Y direction similarly has a fan-shaped region Ra and receives electromagnetic waves that arrive along this region.

[0036] The scanning plane Sa described above is a plane that integrates the regions Ra on which each of these pair of terahertz cameras 17 receives electromagnetic waves. The scanning plane Sa is parallel to the xz plane and is positioned so that a pedestrian Q traveling in the +Y direction along the passage Pa passes through it.

[0037] The focusing mirror in the optical system 171 is a mirror that reflects electromagnetic waves induced by scanning the region Ra with a polygon mirror and focuses them onto the sensor 172. The focusing mirror is, for example, a parabolic mirror.

[0038] The sensor 172 shown in Figure 2 detects electromagnetic waves such as terahertz waves emitted from the passerby Q shown in Figure 1 and collected by a focusing mirror, and measures their intensity. These terahertz waves are, for example, electromagnetic waves with a frequency of 100 GHz or more and less than 10 THz.

[0039] Figure 3 is a block diagram showing the configuration of detector 1. Detector 1, as shown in Figure 3, includes the line scan camera 16, terahertz camera 17, and human presence sensor 18. Detector 1 also includes a processor 11, memory 12, interface 13, operation unit 14, and display unit 15. These components are connected to each other via, for example, a bus, enabling communication between them.

[0040] Memory 12 includes RAM (Random Access Memory), ROM (Read Only Memory), a solid-state drive, a hard disk drive, etc., and stores computer programs (hereinafter simply referred to as "programs").

[0041] The processor 11 controls each part of the detector 1 by reading and executing a program from the memory 12. The processor 11 is, for example, a CPU (Central Processing Unit). Alternatively, the processor 11 may be, for example, an FPGA (Field Programmable Gate Array), or may include an FPGA. Furthermore, this processor may have an ASIC (Application Specific Integrated Circuit) or other programmable logic device, and control may be performed by these.

[0042] Interface 13 is a communication circuit that connects the detector 1 to other devices via wired or wireless means, enabling communication between them.

[0043] The control unit 14 is equipped with various control elements such as control buttons, a keyboard, a touch panel, and a mouse for issuing various instructions. It receives operations and sends signals corresponding to the operations to the processor 11. These operations include, for example, pressing keys on the keyboard or making gestures on the touch panel.

[0044] The display unit 15 has a display screen such as a liquid crystal display and displays an image under the control of the processor 11. A transparent touch panel of the operation unit 14 may be placed on top of the display screen. Note that the detector 1 does not necessarily have an operation unit 14 and a display unit 15. The detector 1 may be operated from an external device via the interface 13, or may present information to an external device.

[0045] For example, when a pair of motion sensors 18 directed towards the entrance of passageway Pa detects the passage of a passerby Q, the processor 11 of the detector 1 activates the line scan camera 16 and the terahertz camera 17 and starts imaging.

[0046] Then, when a pair of motion sensors 18 directed towards the exit of passageway Pa detects the passage of pedestrian Q, the processor 11 stops the line scan camera 16 and the terahertz camera 17 and ends the imaging.

[0047] As described above, if a passerby Q, who is emitting terahertz waves from their body, hides an object such as metal that is difficult for terahertz waves to penetrate inside their clothing, the terahertz waves emitted by the passerby Q will be blocked by that object. Therefore, when the terahertz camera 17 continuously scans the walking passerby Q, it generates an image in which there is a difference in the intensity of the received waves at the contour of the aforementioned object. The generated image is stored in the memory 12 under the control of the processor 11. The detector 1 uses this to identify the shape of the object that the passerby Q is carrying.

[0048] In this way, detector 1 detects objects (possessions) such as metal, explosives, ceramics, and flammable liquids that passerby Q has hidden inside their clothing. In other words, detector 1 is an example of a detector that scans electromagnetic waves arriving from passersby along a scanning surface that intersects the passageway to detect the possessions of those passersby.

[0049] Furthermore, due to the spatial resolution of sensor 172, the objects that detector 1 can inspect are, for example, those with a size of 10 centimeters square or larger and a thickness of 3 centimeters or larger. Also, due to the temporal resolution of sensor 172, the upper limit of the movement speed at which the object can be inspected even if it moves is 4 kilometers per hour. In addition, the time required for detector 1 to perform an inspection is, for example, 0.03 seconds.

[0050] <Functional configuration of the detector> Figure 4 shows an example of the functional configuration of the detector 1. The processor 11 of the detector 1 functions as the instruction unit 111, acquisition unit 112, and calculation unit 113 shown in Figure 4 by reading and executing a program stored in the memory 12.

[0051] The instruction unit 111 instructs the line scan camera 16 and the terahertz camera 17 to take images from the time the motion sensor 18 detects the entry of pedestrian Q until it detects their exit.

[0052] The acquisition unit 112 acquires images captured by the line scan camera 16 and the terahertz camera 17, respectively, using visible light and terahertz waves.

[0053] The calculation unit 113 performs predetermined calculations on the acquired image and displays the processed image on the display unit 15.

[0054] <Structure of the shielding> Figure 5 is a diagram illustrating the obstruction 2. Figure 5 shows an elevation view of the detection system 9 in the -Y direction. The two detectors 1 shown in Figure 5 are positioned on the left rear side and the right front side, respectively, as viewed from a pedestrian Q moving in the +Y direction. These two detectors 1 are housed in each of a pair of housings 10 facing each other across the passageway Pa, forming a scanning surface Sa. The pedestrian Q crosses this scanning surface Sa while passing through the passageway Pa. In other words, these detectors 1 are examples of detectors housed in each of a pair of housings facing each other across a passageway.

[0055] The shielding element 2 is installed on the upper part of the housing 10 of the detector 1. This shielding element 2 is, for example, a plate-shaped member made of resin, ceramic, or the like. The material of the shielding element 2 is selected to have a transmittance of electromagnetic waves, particularly terahertz waves, that is lower than a predetermined level. In other words, this shielding element 2 is an example of a shielding element that is a plate-shaped member installed on the upper part of the housing that houses the detector. Note that the shielding element 2 does not have to be installed on the upper part of the housing. For example, the shielding element 2 may be installed on a structure other than the housing, or it may be fixed to the side of the housing. By providing the shielding element 2 in contact with the housing 10 of the detector 1, the housing 10 of the detector 1 and the shielding element 2 can be manufactured as a single unit. Furthermore, the shielding element 2 may be formed to be detachably attached to a predetermined part of the housing 10.

[0056] Figure 6 is a diagram illustrating the function of the shielding 2. The axis F shown in Figure 6 is the rotation center of the polygon mirror of the optical system 171 of the detector 1, which is located on the left rear side as viewed from a passerby Q moving in the +Y direction. The fan-shaped region Ra (see Figure 2) formed around this axis F is the region in which the detector 1 can receive electromagnetic waves, and it integrates with the region Ra of the detector 1 opposite across the passage Pa to form a scanning surface Sa.

[0057] In the scanning plane Sa shown in Figure 6, the range of angle β centered on axis F is the area where electromagnetic waves traveling from outside the passage Pa toward axis F are shielded by the housing 10 of the detector 1, which is located across the passage Pa. However, the height of this housing 10 is lower than the scanning plane Sa. Therefore, the range of angle α centered on axis F shown in Figure 6 is the area where electromagnetic waves from outside the passage Pa are not shielded by the housing 10 of the detector 1, which is located across the passage Pa.

[0058] Shielding 2 is installed on the top of the housing 10 of detector 1 and is formed to extend, for example, in the +Z direction. Therefore, shielding 2 blocks electromagnetic waves from outside the passage Pa toward the opposing detector 1, preventing them from reaching it. In other words, electromagnetic waves from objects other than passersby Q traveling through passage Pa, that are located in the region Re above the housing 10, such as the sun and halogen lamps, are shielded by this shielding 2 and do not reach detector 1 which is positioned opposite to it across passage Pa.

[0059] The thickness of the shielding material 2 in the Y-axis direction should be sufficient to shield electromagnetic waves from objects other than passersby Q. The shielding material 2 may, for example, be provided with a constant thickness along the scanning surface Sa. In addition, although the shielding material 2 was a plate-like member extending in the Z-axis direction, it can be any shape that follows the scanning surface Sa. In other words, this shielding material 2 is an example of a shielding material provided in a location opposite the detector across a passageway, with a shape that follows the scanning surface, to shield electromagnetic waves from objects other than passersby.

[0060] With this configuration, the shield 2 can shield electromagnetic waves that travel along the scanning surface Sa from the outside of the passage Pa toward axis F. In other words, the detection system 9 shields electromagnetic waves emitted from objects other than passersby Q, such as ambient light from sunlight and halogen lamps, thus making it easier to prevent false detections due to noise.

[0061] The configurations, shapes, sizes, and arrangements described in the above embodiments are merely schematic representations to the extent that the present invention can be understood and implemented. Therefore, the present invention is not limited to the described embodiments and can be modified in various forms as long as it does not deviate from the scope of the technical idea set forth in the claims.

[0062] <Variation> The above describes the embodiment, but the contents of this embodiment can be modified as follows. Furthermore, the following modifications may be combined.

[0063] <1> In the embodiment described above, the material of the shielding 2 was selected to have an electromagnetic wave transmittance lower than a predetermined level, but other materials may be attached to the surface of the shielding 2 by means of adhesive or other means. For example, as shown in Figure 6, the surface Su of the wall of the shielding 2 facing the opposing detector 1 may be provided with a material that absorbs, diffuses, or diffusely reflects terahertz waves. In other words, this shielding 2 is an example of a plate-shaped member on which a material that absorbs, diffuses, or diffusely reflects electromagnetic waves of a predetermined frequency is provided on the surface facing the detector.

[0064] With this material in place, the shield 2 absorbs terahertz waves that reach this surface Su from the passage Pa side, so these terahertz waves are reflected by surface Su and are less likely to reach axis F. In other words, the detection system 9 can suppress the arrival of ambient light reflected from the surface of the shield 2 facing the detector 1 to the detector 1.

[0065] <2> In the embodiment described above, the floor surface of the passageway Pa may be provided with a slope that becomes higher as it moves away from the center. Having such slopes on both the left and right sides guides pedestrians Q to walk in the center of the passageway Pa, making it easier to pass through the scanning surface Sa. [Explanation of symbols]

[0066] 1...Detector, 10...Housing, 100...Radome, 11...Processor, 111...Instruction Unit, 112...Acquisition Unit, 113...Calculation Unit, 12...Memory, 13...Interface, 14...Operation Unit, 15...Display Unit, 16...Line Scan Camera, 17...Terahertz Camera, 171...Optical System, 172...Sensor, 18...Human Motion Sensor, 2...Obstruction, 9...Detection System

Claims

1. A detector that scans electromagnetic waves arriving from passersby in a passageway along a scanning surface that intersects the passageway to detect the passersby's belongings, A shielding object is provided across the passage from the detector, in a shape aligned with the scanning surface, to shield electromagnetic waves arriving from objects other than passersby. A detection system having the following features.

2. The detector is housed in each of a pair of housings that face each other across the passage, The shielding is installed on each of the housings. The detection system according to claim 1.

3. The shielding is a plate-shaped member installed on the upper part of the housing. The detection system according to claim 2.

4. The plate-shaped member is provided with a material on the surface facing the detector that absorbs, diffuses, or diffusely reflects electromagnetic waves of a predetermined frequency. The detection system according to claim 3.

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