Imaging system

Abstract

To provide an imaging system that enables photographing of a wide range of an object in the height direction, regardless of an arrangement position of a terahertz camera in an active terahertz system.SOLUTION: An imaging system comprises: a direct irradiation part for directly irradiating an object with a first terahertz wave; an indirect irradiation part for irradiating the object with a second terahertz wave after reflecting it at a point other than the object; and an imaging part, which is placed at a position capable of detecting a reflected wave reflected from the object irradiated with the first terahertz wave and / or the second terahertz wave, for performing imaging by detecting the reflected wave. The imaging part images a point of the object which can be detected by the reflected wave of either the first terahertz wave or the second terahertz wave by detecting at least the reflected wave of the first terahertz wave.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an imaging system, and more particularly to an active terahertz system having an illumination unit and an imaging unit. [Background technology]

[0002] Recently, preventing crimes involving concealed dangerous goods has become an issue at places like airports, and there is a demand for technology to detect dangerous goods in possession. One such inspection technology is the active terahertz system, which uses terahertz waves. In an active terahertz system, terahertz waves are irradiated onto an object under test, and the terahertz waves reflected from the object are detected by a terahertz camera to perform imaging and inspection. Terahertz waves (also called terahertz light) can be defined as electromagnetic waves with a frequency between 30 GHz and 30 THz.

[0003] Patent Document 1 discloses an active terahertz system. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-153974 Summary of the Invention [Problem to be solved by the invention]

[0005] Even with a terahertz camera, there are some people who find it morally offensive to install an imaging device at a low position and take images at a low angle. Furthermore, terahertz waves are characterized by little diffusion upon reflection and a strong specular reflection component. Therefore, in the conventional technology disclosed in Patent Document 1, the position where the terahertz camera should be placed is somewhat limited depending on the position of the terahertz illumination and the area to be detected. In other words, the terahertz camera must be placed in a position where it can detect the specular reflection component of the terahertz waves reflected by the subject. Therefore, depending on the location of the subject to be examined, if the imaging unit is not placed at a low position, the specular reflection component cannot be detected, and the examination may not be possible.

[0006] Therefore, an object of the present invention is to provide an imaging system in an active terahertz system that is capable of capturing an image of a wide range of a subject in the height direction regardless of the position where the terahertz camera is placed. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides an imaging device comprising: a direct irradiation unit that irradiates a first terahertz wave that is directly irradiated onto an object to be examined; an indirect irradiation unit that irradiates a second terahertz wave that is reflected by a location other than the object to be examined and then irradiated onto the object; and an imaging unit that is arranged at a position where it can detect reflected waves reflected from the object to which the first terahertz wave and / or the second terahertz wave has been irradiated, and that detects and images the reflected waves; the direct irradiation unit and the indirect irradiation unit are arranged to irradiate a predetermined location of the subject with the first terahertz wave or the second terahertz wave from different angular directions; The imaging unit is characterized in that it detects at least the reflected wave of the first terahertz wave and images a portion of the subject that can be detected by either the first terahertz wave or the reflected wave of the second terahertz wave. [Effects of the Invention]

[0008] According to the present invention, in an active terahertz system, a wide range of the subject can be imaged in the height direction regardless of the placement position of the terahertz camera. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing a configuration of an imaging system according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating a configuration example of a gate system in which an imaging system according to a first embodiment is disposed. [Figure 3] 3 is a schematic diagram illustrating an example of an optical path of a terahertz wave irradiated from an indirect illumination unit according to the first embodiment. FIG. [Figure 4] 3 is a schematic diagram illustrating an example of optical paths of terahertz waves emitted from a direct illumination unit and an indirect illumination unit according to the first embodiment. FIG. [Figure 5] FIG. 3 is a flowchart showing a processing procedure of the imaging system according to the first embodiment. [Figure 6] 10 is a schematic diagram showing an example of the optical path of the terahertz wave when the surface direction of the dangerous object is not perpendicular to the floor surface. FIG. [Figure 7] 10 is a schematic diagram illustrating an example of an illumination area of ​​a direct illumination unit and an indirect illumination unit according to Example 2. FIG. [Figure 8] 3A and 3B are schematic diagrams showing an example of illumination areas of a direct lighting unit and an indirect lighting unit, and an angle of view of an imaging unit. [Figure 9] 10 is a schematic diagram illustrating an example of an illumination area of ​​a direct illumination unit and an indirect illumination unit, and an angle of view of an imaging unit according to Example 3. FIG. [Figure 10] 10 is a schematic diagram showing an example of an optical path of a terahertz wave when the terahertz wave is irradiated only from a direct illumination unit. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments do not limit the scope of the invention. While the embodiments include multiple features, not all of these features are necessarily essential to the invention, and multiple features may be combined in any desired manner. In the accompanying drawings, the same reference numerals are used to designate identical or similar components, and redundant descriptions will be omitted.

[0011] Electromagnetic waves in the terahertz band, which can be roughly defined as frequencies between 30 GHz and 30 THz, have properties that differ from visible light depending on their wavelength. Due to their unique characteristic of combining the linearity of light waves with the transparency of radio waves, various applications are being explored, and in the imaging field in particular, applications to high-resolution, non-destructive, non-contact inspections on the order of millimeters are expected. The embodiments in this specification are intended to be inspection systems that perform non-destructive, non-contact imaging of the surface or interior of an object.

[0012] <Embodiment> 1 is a block diagram showing the configuration of an imaging system 100 according to an embodiment of the present invention. The imaging system 100 includes an illumination unit 110 (irradiation unit), an imaging unit 120, and a control unit 130. The imaging system 100 is a so-called active terahertz system that illuminates (irradiates) an object with terahertz waves, detects the terahertz waves reflected by the object, and captures an image based on the intensity of the detected waves. To achieve this, the imaging system 100 includes the illumination unit 110 and the imaging unit 120.

[0013] The illumination unit 110 has one or more direct illumination units (direct illumination units) 111 and one or more indirect illumination units (indirect illumination units) 112, and the direct illumination unit 111 and the indirect illumination unit 112 are oscillators that generate terahertz waves. The direct illumination unit 111 is arranged to directly irradiate the generated terahertz waves (hereinafter referred to as first terahertz waves) onto the subject. The indirect illumination unit 112 is arranged to irradiate the generated terahertz waves (hereinafter referred to as second terahertz waves) onto the subject after being reflected from a location other than the subject, in other words, a location other than the subject. The direct illumination unit 111 and the indirect illumination unit 112 have light distributions (which may also be referred to as illumination areas or illumination ranges) in both the horizontal and vertical directions.

[0014] The imaging unit 120 includes an imaging sensor having high sensitivity to terahertz waves and is disposed at a position where it can detect the first terahertz wave and / or the second terahertz wave reflected by the subject. The imaging unit 120 detects the first terahertz wave and / or the second terahertz wave and captures an image. The imaging unit 120 also includes a lens (not shown) and has an imaging angle of view in both the horizontal and vertical directions.

[0015] The control unit 130 processes signals output from the imaging unit 120 to generate images, controls the illumination of the illumination unit 110, and controls shooting by the imaging unit 120. The control unit 130 may be built into the same housing as the illumination unit 110 and the imaging unit 120, or may be provided in a separate device connected to these units via a signal path. The control unit 130 has a built-in CPU as a computer, and controls the operation of each unit of the entire device based on a computer program stored in a memory as a storage medium.

[0016] Example 1 An imaging system according to a first embodiment will be described below with reference to Fig. 2. The imaging system 100 according to this embodiment is installed in a gate system 200. The gate system 200 is, for example, a gate system installed in an X-ray gate at a security station in an airport or an entrance / exit control gate in a building.

[0017] FIG. 2 is a schematic diagram illustrating a configuration example of a gate system 200 in which an imaging system 100 according to the first embodiment is disposed, with FIG. 2(A) being a front view and FIG. 2(B) being a top view. The gate system 200 includes a gate 210. The gate 210 includes a pair of side walls 211a and 211b forming a passage 220. The imaging system 100 is disposed to acquire an image of an object 230 passing through the passage 220 between the gates 210. The object 230 is typically a human but may also be a non-human animal or a robot. It may also be, for example, luggage placed on a conveyor belt or a moving object. Because terahertz waves have the property of penetrating fabric, the imaging system 100 can detect, for example, concealed dangerous objects. Here, the illumination unit 110 of the imaging system 100 is, for example, installed on the side wall 211a of the gate 210, and the imaging unit 120 is disposed above the gate 210 via a pole 240 or the like. That is, in this embodiment, the imaging unit 120 is disposed at a position above a predetermined height. Note that there may be one or more illumination units 110 and one or more imaging units 120, and the number and detailed arrangement positions thereof are not limited to those shown in FIG. 2 and may be changed depending on the system. Furthermore, the imaging unit 120 may be disposed on the upper part of a side wall on a side different from that of the illumination unit 110, but in this embodiment, it is disposed on the side wall 211a on the same side. In this way, the imaging system 100 of this embodiment is configured to avoid low-angle photography from a low position by disposing the imaging unit 120 at a position above a predetermined height, such as above a gate.

[0018] It should be noted, however, that imaging with an active terahertz system differs from imaging with general visible light. As mentioned above, terahertz waves are electromagnetic waves in the frequency band of approximately 30 GHz to 30 THz, with wavelengths of approximately 10 μm to 1 mm, which are longer than visible light. Generally, electromagnetic waves are not diffused by irregularities smaller than their wavelength. Therefore, terahertz waves with long wavelengths are hardly diffused when reflected, and the specular reflection component is the main component. Therefore, in an active terahertz system, the area that can be imaged is limited by the arrangement of the illumination unit and imaging unit and the surface direction (reflection angle) of reflecting objects (hazardous objects, etc.) on the subject.

[0019] Therefore, when the imaging unit 120 is disposed above the gate as described above, the imageable area of ​​the subject 230 is determined by the arrangement of the illumination unit 110 and the surface direction of the reflecting object on the subject.

[0020] FIG. 10 is a schematic diagram showing an example of the optical path of terahertz waves when terahertz waves are irradiated only from the direct illumination unit 111. This figure shows the optical path of terahertz waves irradiated from the direct illumination unit 111 in a conventional gate system in which the direct illumination unit 111 is arranged at the bottom of the gate 210. The active terahertz system is a system that performs imaging and inspection by irradiating the object 230 with terahertz waves 113 and detecting the terahertz waves reflected by the object 230. Conventionally, direct illumination has been used for illumination only. However, assuming that the surface direction of the reflecting object on the object 230 is perpendicular to the floor (this assumption is also made in the following examples), when the imaging unit 120 is located above the gate, only a region above a predetermined height can be imaged. Specifically, as shown in FIG. 10, when the imaging unit 120 is located above the gate, even if the direct illumination unit 111 is arranged at the bottom of the gate 210, only a region above a predetermined height of the object 230 can be imaged. 10, that is, an area below the midpoint between the direct illumination unit 111 and the imaging unit 120, cannot be imaged. Therefore, when the imaging unit 120 is disposed above the gate 210, the imageable area is limited by the height of the gate 210, and the accuracy of detecting concealed dangerous objects and the like decreases. This is a physical constraint in an active terahertz system when the imaging unit 120 is disposed above the gate 210 and the illumination unit 110 is disposed inside the gate 210, and can become a blind spot in the inspection system.

[0021] FIG. 3 is a schematic diagram showing an example of the optical path of the terahertz wave irradiated from the indirect illumination unit 112 according to the first embodiment. This diagram shows a configuration example in which the indirect illumination unit 112 and the image capturing unit 120 are arranged so that the terahertz wave irradiated from the indirect illumination unit 112 is reflected by the floor surface, then reflected by the subject 230, and then detected, and the optical path of the terahertz wave. FIG. 3(A) is a diagram showing an example of the optical path when the region 250 is irradiated with the terahertz wave 114 from the indirect illumination unit 112. As shown in FIG. 3(A), the indirect illumination unit 112 is used to irradiate the terahertz wave via a location other than the subject 230, such as the floor surface, or in other words, to reflect the terahertz wave on the subject 230. This configuration makes it possible to capture an image of the region 250 even when the image capturing unit 120 is arranged above the gate 210.

[0022] In this way, the gate system 200 uses the indirect illumination unit 112 that reflects the terahertz waves off a place other than the subject 230, such as the floor, and then irradiates the subject 230. This makes it possible to image, for example, a lower region within the gate 210, such as region 250, using the terahertz waves, even if there is a restriction that the imaging unit 120 can only be placed at a position equal to or higher than a predetermined height.

[0023] By using terahertz waves irradiated through the floor by the indirect illumination unit 112, even if the height of the imaging unit 120 is limited by the location above the gate, theoretically, almost all areas of the subject 230 can be imaged, not just the area 250, as shown in FIG. 3(B). FIG. 3(B) illustrates an example of the optical path when terahertz waves 114 from the indirect illumination unit 112 are irradiated to an area above the area 250. However, as described above, in an active terahertz system, due to the characteristics of terahertz waves, it is necessary to detect the specular reflection component. Therefore, as shown in FIG. 3(B), in order to image a high position of the subject 230 using the light irradiated by the indirect illumination unit 112, it may be necessary to position the imaging unit 120 at a very high position, even above the gate. Furthermore, terahertz waves are attenuated by various factors, such as absorption or transmission when irradiated (reflected) by a material, absorption by moisture in the atmosphere, and light spreading over the optical path length. When the oscillation intensity of the terahertz wave oscillator is weak, the S / N ratio becomes even worse and the attenuation of the terahertz wave can become significant. Therefore, when imaging the object 230 using only the indirect illumination unit 112, it is effective for the object 230 that is relatively short, such as baggage, but may be disadvantageous for the object 230 that is relatively tall, such as a person. Specifically, as shown in FIG. 3(B), when the object 230 is a person, attempting to image a location other than the region 250 on the object 230 by illuminating it with the indirect illumination unit 112 may result in inaccurate imaging.

[0024] 4 is a schematic diagram showing an example of the optical paths of terahertz waves irradiated from the direct illumination unit 111 and the indirect illumination unit 112 according to the first embodiment. This diagram shows an example configuration of the gate system 200 shown in FIG. 2 in which the imaging system 100 is arranged so that the imaging unit 120 detects the terahertz waves irradiated from the direct illumination unit 111 and the indirect illumination unit 112, respectively, and the optical paths of the terahertz waves. As described above, one or more imaging units 120 may be provided. While FIG. 4 illustrates the terahertz waves from the direct illumination unit 111 and the terahertz waves from the indirect illumination unit 112 being detected by separate imaging units 120, this is not a limitation. For example, an imaging unit with a wider angle of view may be used, and the single imaging unit 120 may be arranged to detect both the terahertz waves irradiated from the direct illumination unit 111 and the indirect illumination unit 112.

[0025] As shown in FIG. 4 , terahertz waves 113 are directly irradiated onto the object 230 from a direct illumination unit 111 for areas other than a region 250, and terahertz waves 114 are indirectly irradiated onto the region 250 from an indirect illumination unit 112 via a floor or the like. The terahertz waves 113 and 114 reflected from the object 230 are detected by the imaging unit 120, thereby inspecting the object 230. In this manner, areas that can be imaged (detected) by the direct illumination unit 111 and the imaging unit 120 disposed above the gate 210 are imaged using the terahertz waves 113 from the direct illumination unit 111. Areas that cannot be imaged by the terahertz waves 113 from the direct illumination unit 111 are imaged using the indirect illumination unit 112, which indirectly irradiates the terahertz waves 114. With this configuration, even if there is a restriction that the imaging unit 120 can only be disposed at a position equal to or higher than a predetermined height, it is possible to image a wide range of the object in the height direction, thereby further improving the inspection accuracy.

[0026] FIG. 5 is a flowchart showing a processing procedure of the imaging system 100 according to the first embodiment. Each operation (step) shown in this flowchart can be performed by each computer in the control unit 130 executing a computer program stored in memory and controlling each unit. As shown in FIG. 5, in a gate system 200 in which the imaging system 100 is disposed, first, in step S601, terahertz waves are irradiated from the illumination unit 110 (direct illumination unit 111 and indirect illumination unit 112). At this time, direct irradiation by terahertz waves 113 from the direct illumination unit 111 is prioritized, but depending on the height position at which the imaging unit 120 is disposed, terahertz waves 114 are indirectly irradiated using the indirect illumination unit 112 only to areas that cannot be physically detected by direct illumination. The installation position of the indirect illumination unit 112 used for imaging or the position at which the indirect illumination unit 112 is installed may be determined in advance depending on the height position at which the imaging unit 120 is disposed. Next, in S602, the passage of the subject 230 is detected by, for example, a sensor (not shown). That is, the imaging system 100 may include a sensor (not shown) that detects the approach of the subject 230. Then, when the subject 230 passes through the passage 220, in S603, the terahertz waves reflected by the subject 230 are detected by the imaging unit 120 and an image is taken.

[0027] In the above flow, an example has been described in which the indirect illumination unit 112 to be used for imaging is determined in advance. However, for example, first, imaging of the subject 230 is performed by irradiating only the terahertz wave 113 from the direct illumination unit 111. Then, if a portion that cannot be detected (a portion that cannot be imaged) occurs, imaging may be performed by further using the indirect illumination unit 112 that can irradiate the corresponding portion with the terahertz wave 113.

[0028] As described above, imaging by active terahertz detection is performed preferentially by direct illumination unit 111 and imaging unit 120 arranged above gate 210. Then, for areas that cannot be physically imaged by illumination from direct illumination unit 111 alone, imaging is performed using indirect illumination from indirect illumination unit 112. This makes it possible to image a wide range of the subject in the height direction even in an active terahertz system in which a terahertz camera is arranged at a high position, improving the detection accuracy of dangerous objects, etc.

[0029] Here, we have described an example in which the terahertz waves 114 irradiated from the indirect lighting unit 112 are reflected on the floor surface of the passageway 220, but the terahertz waves 114 may also be reflected by the side wall of the gate or by a member placed on the gate for reflecting the terahertz waves 114.

[0030] Example 2 An imaging system according to a second embodiment will be described below with reference to FIG. 6. In the first embodiment, it is assumed that the surface direction of the hazardous object 260 held by the subject 230 is perpendicular to the floor surface. Under this assumption, as described in the first embodiment, an area that cannot be imaged by a direct illumination configuration using the direct illumination unit 111 and the imaging unit 120 is physically determined as the area 250. Therefore, in the first embodiment, the area to be imaged by direct illumination and the area that can only be imaged by indirect illumination are determined by the arrangement position of the imaging unit 120, which is determined by the height of the gate 210, and the arrangement position of the direct illumination unit 111 disposed within the gate 210. However, in reality, the surface direction of the hazardous object 260 held by the subject 230 is not necessarily perpendicular to the floor surface, and there are cases where the area to be imaged by direct illumination and the area that can only be imaged by indirect illumination cannot be physically determined.

[0031] FIG. 6 is a schematic diagram showing an example of the optical path of terahertz waves when the surface direction of a hazardous object 260 is not perpendicular to the floor surface. This diagram shows the configuration of the imaging system 100 in the gate system 200 shown in FIG. 2 and an example of the optical path of each terahertz wave when the surface direction of the hazardous object 260, etc. held by the subject 230, is not perpendicular to the floor surface. FIG. 6(A) is a schematic diagram showing an example of the optical path of terahertz waves 113 reflected by a hazardous object 260 whose surface direction is not perpendicular to the floor surface. As shown in FIG. 6(A), the direction of specular reflection of terahertz waves irradiated from the illumination unit 110 onto the subject 230 varies depending on the surface direction of the hazardous object 260. Therefore, as shown in FIG. 6(B), depending on the surface direction of the hazardous object 260, etc., an image of an area 250 may be captured using terahertz waves 113 from a direct illumination unit 111. In addition, an installation that allows for easy imaging of areas other than the area 250 using terahertz waves 114 from an indirect illumination unit 112 may be realized. As described above, in reality, the surface orientation of the dangerous object 260 etc. carried by the subject 230 varies, and as described in Example 1, it may be difficult to physically determine the area 250 that cannot be imaged by irradiating the terahertz wave 113 from the direct illumination unit 111.

[0032] FIG. 7 is a schematic diagram showing an example of the irradiation areas of the direct illumination unit 111 and the indirect illumination unit 112 according to the second embodiment. This diagram shows an example configuration of the imaging system 100 in the gate system 200 shown in FIG. 2, in which the illumination unit 110 has a wider light distribution characteristic (irradiation angle) than in the first embodiment and the imaging unit 120 has a wider angle of view than in the first embodiment, and the irradiation areas of each terahertz wave. FIG. 7(A) shows the irradiation area 115 of the terahertz wave 113 from the direct illumination unit 111, and FIG. 7(B) shows the irradiation area 116 of the terahertz wave 114 from the indirect illumination unit 112. The direct illumination unit 111 and the indirect illumination unit 112 may be irradiated simultaneously or at different times. In addition, in FIG. 7, the angle of view 121 of the imaging unit 120 is indicated by a dashed line. As shown in FIG. 7 , by irradiating not only area 250 but also all areas of object 230 with terahertz waves from both direct illumination unit 111 and indirect illumination unit 112, imaging corresponding to multiple surface directions can be performed. Specifically, terahertz waves are irradiated from multiple directions onto the same predetermined location on object 230. With this configuration, the reflection direction varies depending on the incident direction, and therefore, depending on the surface direction of a hazardous object 260, etc., one of the reflected waves may enter the angle of view of image capture unit 120, allowing detection and imaging. Note that, although the example shown in FIG. 7 has one direct illumination unit 111 and one indirect illumination unit 112 and two image capture units 120, this is not limiting. Having multiple illumination units 110 is advantageous because it allows terahertz waves to be irradiated onto the same location on object 230 from more angular directions, making it possible to detect reflective objects (hazardous objects, etc.) in all surface directions.

[0033] As described above, by irradiating and detecting terahertz waves from multiple angles to the same location on the object 230, active detection of reflecting objects in any surface direction becomes possible, improving the detection accuracy of dangerous objects and the like.

[0034] Example 3 An imaging system according to Example 3 will be described below with reference to Fig. 8. In Examples 1 and 2, it was assumed that the imaging unit 120 was arranged on an upper part of a side wall on the same left and right side as the illumination unit 110 with respect to the subject 230. Also, an example was described in which the imaging system 100 was arranged on only one side wall of the gate 210. In this Example, a case will be described in which the illumination unit 110 and the imaging unit 120 are arranged on upper parts of different gates (side wall parts 211a and 211b) with respect to the subject, and a case in which the imaging system 100 is arranged on both sides (side wall parts 211a and 211b) of the gate 210.

[0035] 8 is a schematic diagram showing an example of the illumination areas of the direct illumination unit 111 and the indirect illumination unit 112, and the angle of view of the imaging unit 120. This diagram shows the illumination areas and the angle of view when the illumination unit 110 and the imaging unit 120 are arranged above different gates on the left and right sides with respect to the subject 230, or when the imaging system 100 is arranged on both sides of the gate 210. FIG. 8 also shows an example of the illumination area 117 (light distribution) of the direct illumination unit 111 and the angle of view 121 of the imaging unit 120. As shown in FIG. 8, when the imaging unit 120 is located on the opposite side of the illumination unit 110 with respect to the subject 230, the illumination area 117 of the illumination unit 110 and the angle of view 121 of the imaging unit 120 may face each other and overlap. When the illumination area 117 of the illumination unit 110 and the angle of view 121 of the imaging unit 120 overlap in this manner, high-intensity terahertz waves that are not reflected by the subject 230 may directly enter the imaging sensor of the imaging unit 120, which may lead to overexposure in the captured image, resulting in a decrease in detection accuracy.

[0036] FIG. 9 is a schematic diagram illustrating an example of the illumination areas of the direct illumination unit 111 and the indirect illumination unit 112 and the angle of view of the image capture unit 120 according to the third embodiment. This diagram illustrates a configuration example in which, in a gate system 200, the illumination unit 110 and the image capture unit 120 are disposed on opposite sides of the subject 230, respectively, and the image capture system 100 is disposed so that the light distribution of the illumination unit 110 and the angle of view of the image capture unit 120 face each other and do not overlap. As shown in FIG. 9 , by utilizing the depth of the gate system 200 and performing active terahertz detection from an oblique front side of the subject 230 rather than from directly to the side, it is possible to prevent the illumination area 117 of the illumination unit 110 and the angle of view 121 of the image capture unit 120 from overlapping. In other words, the illumination unit 110 and the image capture unit 120 are disposed at an angle on a horizontal plane.

[0037] Note that the method for avoiding overlap between the illumination area 117 of the illumination unit 110 and the angle of view 121 of the imaging unit 120 is not limited to this. For example, a method of performing active detection from diagonally behind the subject 230 may be used. Alternatively, a method of simply arranging the illumination unit 110 and the imaging unit 120 so that their illumination areas and angles of view face each other and do not overlap, and then performing active detection from directly to the side of the subject may be used. In other words, the illumination unit 110 and the imaging unit 120 are arranged so that the terahertz waves from the illumination unit 110 do not directly enter the imaging sensor of the imaging unit 120.

[0038] As described above, by positioning the imaging system 100 so that the light distribution of the illumination unit 110 does not overlap with the angle of view of the imaging unit 120, which is positioned on the left and right opposite side of the illumination unit 110 with respect to the subject 230, direct incidence of terahertz waves from the illumination unit to the imaging unit can be prevented, thereby improving detection accuracy.

[0039] Note that when irradiation area 117 of terahertz waves irradiated from illumination unit 110 faces and overlaps with angle of view 121 of image capturing unit 120, control may be performed to differentiate the timing of imaging and irradiation. Specifically, control is performed by control unit 130 so that the imaging timing of image capturing unit 120 and the irradiation timing of illumination unit 110 where angle of view 121 of image capturing unit 120 and irradiation area 117 overlap are differentiated. This configuration also makes it possible to prevent terahertz waves from being directly incident on image capturing unit 120 from illumination unit 110.

[0040] (Other embodiments) Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention.

[0041] In the above embodiment, the intensity of the terahertz waves irradiated from the illumination unit 110 is not defined. However, for example, the intensity of the second terahertz waves 114 irradiated from the indirect illumination unit 112 may be greater than the intensity of the first terahertz waves 113 irradiated from the direct illumination unit 111. By increasing the intensity of the second terahertz waves 114 in this way, it is possible to compensate for the relative attenuation of the second terahertz waves due to reflection at locations other than the subject and the difference in optical path length with the first terahertz waves 113, thereby improving detection accuracy and visibility.

[0042] Furthermore, the means for suppressing the attenuation of the second terahertz wave 114 is not limited to this, and for example, a member having high reflectivity for terahertz waves may be disposed in a location other than the subject that reflects the second terahertz wave 114. Disposing a member having high reflectivity for terahertz waves in this manner not only suppresses the reflection attenuation of the terahertz wave but also enables reflection at locations that do not normally reflect terahertz waves, thereby enabling indirect irradiation of the terahertz wave from more angles. This suppresses the attenuation of the terahertz wave and enables active detection of reflecting objects in any surface direction, as described above, thereby improving the detection accuracy of dangerous objects, etc. [Explanation of symbols]

[0043] 100 Imaging System 110 Lighting Department 111 Direct lighting section 112 Indirect lighting section 113,114 Terahertz waves 115,116,117 Irradiation area 120 Imaging unit 121 angle of view 130 Control Unit 200 Gate System 230 Subjects

Claims

1. a direct irradiation unit that irradiates a first terahertz wave that is directly irradiated onto the subject; an indirect irradiation unit that irradiates a second terahertz wave that is reflected by a location other than the subject and then irradiated onto the subject; an imaging unit that is disposed at a position where it can detect a reflected wave reflected from the subject irradiated with the first terahertz wave and / or the second terahertz wave, and that detects and images the reflected wave, the direct irradiation unit and the indirect irradiation unit are arranged to irradiate a predetermined location of the subject with the first terahertz wave or the second terahertz wave from different angular directions; an imaging system characterized in that the imaging unit detects at least the reflected wave of the first terahertz wave and images a portion of the subject that can be detected by either the first terahertz wave or the reflected wave of the second terahertz wave.

2. The imaging system according to claim 1, wherein the direct irradiation unit and the imaging unit are arranged so that a portion of the subject that can be detected by both the first terahertz wave and the reflected wave of the second terahertz wave can be detected by at least the reflected wave of the first terahertz wave.

3. 3. The imaging system according to claim 1, wherein the direct illumination unit, the indirect illumination unit, and the imaging unit are arranged at an inclination on a horizontal plane.

4. The imaging system according to claim 1 , wherein the indirect irradiation unit irradiates the second terahertz wave having an intensity greater than an intensity of the first terahertz wave.

5. 5. The imaging system according to claim 1, wherein a member having high reflectivity to terahertz waves is disposed at a location other than the subject that reflects the second terahertz waves.

6. 6. The imaging system according to claim 1, wherein the imaging unit is disposed at a position equal to or higher than a predetermined height.

7. the direct irradiation unit and the indirect irradiation unit are disposed on a pair of side walls that form a passage through which the subject passes, The imaging system according to claim 1 , wherein the imaging unit is disposed on an upper portion of the side wall.

8. a direct irradiation unit that irradiates a first terahertz wave that is directly irradiated onto the subject; an indirect irradiation unit that irradiates a second terahertz wave that is reflected by a location other than the subject and then irradiated onto the subject; an imaging unit that is disposed at a position where it can detect a reflected wave reflected from the subject irradiated with the first terahertz wave and / or the second terahertz wave, and that detects and images the reflected wave, the direct irradiation unit, the indirect irradiation unit, and the imaging unit are arranged such that an irradiation area of ​​the first terahertz wave irradiated from the direct irradiation unit and an irradiation area of ​​the second terahertz wave irradiated from the indirect irradiation unit face an angle of view of the imaging unit and do not overlap with each other; an imaging system characterized in that the imaging unit detects at least the reflected wave of the first terahertz wave and images a portion of the subject that can be detected by either the first terahertz wave or the reflected wave of the second terahertz wave.

9. a direct irradiation unit that irradiates a first terahertz wave that is directly irradiated onto the subject; an indirect irradiation unit that irradiates a second terahertz wave that is reflected by a location other than the subject and then irradiated onto the subject; an imaging unit that is disposed at a position where it can detect a reflected wave reflected from the subject irradiated with the first terahertz wave and / or the second terahertz wave, and that detects and captures the reflected wave; a control unit that controls the direct irradiation unit, the indirect irradiation unit, and the imaging unit; Equipped with when an irradiation region of the first terahertz wave irradiated from the direct irradiation unit or the second terahertz wave irradiated from the indirect irradiation unit faces and overlaps with an angle of view of the imaging unit, the control unit makes an imaging timing of the imaging unit different from an irradiation timing of the direct irradiation unit or the indirect irradiation unit at which the angle of view of the imaging unit and the irradiation region overlap, an imaging system characterized in that the imaging unit detects at least the reflected wave of the first terahertz wave and images a portion of the subject that can be detected by either the first terahertz wave or the reflected wave of the second terahertz wave.

Images