Imaging equipment

Abstract

This photography device (10b) comprises a light source (20a) including a radiation surface (22a) for radiating sub-terahertz waves onto an object under measurement and a detector (30c) including an image sensor (31) for receiving sub-terahertz waves that have been radiated from the radiation surface (22a) and reflected by the object under measurement. The light source (20a) comprises one or more point light sources (21a) for radiating sub-terahertz waves and a reflection plate (24a) for producing the sub-terahertz waves to be radiated from the radiation surface (22a) by diffusely reflecting the sub-terahertz waves radiated from the one or more point light sources (21a). A reflection surface of the reflection plate (24a) is a rough surface having an average roughness curve element length RSm of 0.3 mm or longer.

Description

[Technical field]

[0001] Regarding the imaging device. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there has been known an imaging device that images an object that is hidden under clothing or the like and cannot be directly seen (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 8,835,849 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, there is known an imaging device that includes a point light source that radiates electromagnetic waves that pass through clothing toward a person, and a detector that receives the reflected waves of the electromagnetic waves radiated from the point light source, and that captures an object hidden under the person's clothing. In the conventional imaging device, the electromagnetic waves that pass through the clothing are specularly reflected by the human body, metal, etc. For this reason, the conventional imaging device can only capture an image of an area of ​​the human body, metal, etc. that specularly reflects the electromagnetic waves radiated from the point light source at an angle at which the reflected waves are incident on the detector. Therefore, it is difficult for the conventional imaging device to capture with high accuracy the shapes of the human body, metal, etc. that are hidden under clothing and cannot be directly seen.

[0005] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide an imaging device capable of imaging the shape of an object that is hidden under clothing or the like and cannot be seen directly with the naked eye with greater accuracy than conventional devices. [Means for solving the problem]

[0006] An imaging device according to an embodiment of the present disclosure includes a surface light source including an emission surface that emits sub-terahertz waves toward a measurement object, and a detector including an image sensor that receives the sub-terahertz waves emitted from the emission surface and reflected by the measurement object, the surface light source includes one or more point light sources that emit sub-terahertz waves, and a reflector that diffusely reflects the sub-terahertz waves emitted from the one or more point light sources to generate sub-terahertz waves emitted from the emission surface, and the reflecting surface of the reflector is an uneven surface with an average length RSm of roughness curve elements of 0.3 mm or more. The term "sub-terahertz waves" refers to electromagnetic waves with a frequency of 0.08 THz or more and 1 THz or less. Effect of the Invention

[0007] According to an image capturing device according to an aspect of the present disclosure, the shape of an object that is hidden under clothing or the like and cannot be seen directly can be captured with greater accuracy than ever before. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing the relationship between the attenuation rate and frequency when an electromagnetic wave passes through a material. [Diagram 2] FIG. 2 is a diagram showing the relationship between the wavelength of an electromagnetic wave and the resolution. [Diagram 3] FIG. 3 is a block diagram showing a configuration of the imaging device according to the first embodiment. [Figure 4] FIG. 4 is a schematic diagram showing a configuration of a light source according to the first embodiment. [Diagram 5] FIG. 5 is a schematic cross-sectional view of the detector according to the first embodiment receiving a reflected wave. [Figure 6] FIG. 6 is a schematic diagram showing a cross section of a detector according to a first comparative example receiving a reflected wave. [Figure 7] FIG. 7 is a schematic diagram showing how the imaging device according to the first embodiment is installed. [Figure 8] FIG. 8 is a block diagram showing a configuration of an imaging device according to the second embodiment. [Figure 9]FIG. 9 is a schematic diagram showing a cross section of the third detector according to the second embodiment receiving a reflected wave. [Figure 10] FIG. 10 is a schematic diagram showing a cross section of a detector according to a second comparative example receiving a reflected wave. [Figure 11] FIG. 11 is a schematic diagram showing a cross section of an installation of an imaging device according to the second embodiment. [Figure 12] FIG. 12 is a flowchart of the image analysis process. [Figure 13] FIG. 13 is a block diagram showing a configuration of an imaging device according to the third embodiment. [Figure 14] FIG. 14 is a schematic diagram showing how the imaging device according to the third embodiment images an object to be measured. [Figure 15A] FIG. 15A is a schematic diagram showing how a reflecting surface of a reflector according to a comparative example reflects sub-terahertz waves. [Figure 15B] FIG. 15B is a schematic diagram showing an interference fringe occurring due to the sub-terahertz wave reflected by the reflecting surface of the reflector according to the comparative example. [Figure 15C] FIG. 15C is an enlarged cross-sectional view showing an example of the reflecting surface of the reflector according to embodiment 3. As shown in FIG. [Figure 16A] FIG. 16A is a plan view of each of a plurality of unit regions according to the third embodiment. [Figure 16B] FIG. 16B is a schematic diagram showing a state in which a plurality of unit regions are arranged on the reflecting surface of the reflector according to embodiment 3. In FIG. [Figure 17] FIG. 17 is a schematic diagram showing a cross section of an inclined portion of the unevenness on the reflecting surface according to the third embodiment. [Figure 18A] FIG. 18A is a schematic diagram showing the relationship between a subject and a real image in an optical system according to embodiment 3. FIG. [Figure 18B] FIG. 18B is a schematic diagram showing the relationship between a subject and a real image in the optical system according to the third embodiment. [Figure 18C]FIG. 18C is a schematic diagram showing how a point at the position of the imaged sub-terahertz wave radiation region according to the third embodiment forms an image on an image sensor. [Figure 18D] FIG. 18D is a schematic diagram showing how a point at the position of the imaged sub-terahertz wave radiation region according to the third embodiment forms an image on an image sensor. [Figure 19] FIG. 19 is a schematic diagram showing a part of the external appearance of an imaging device according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] (How one aspect of the present disclosure was achieved) The inventors have conducted extensive research into an imaging device capable of capturing images that enable the detection of dangerous objects (such as knives) concealed under clothing, in a bag, or the like.

[0010] The details of the investigations carried out by the inventors will be described below.

[0011] The inventors have studied the relationship between the attenuation rate and frequency when electromagnetic waves pass through materials that are used for clothing, bags, and the like.

[0012] FIG. 1 is a diagram showing the relationship between the attenuation rate and frequency when an electromagnetic wave passes through a material.

[0013] As shown in Figure 1, electromagnetic waves with frequencies below 1 THz can penetrate many of the materials used to make clothes, bags, and other items.

[0014] As a result of the above investigation, the inventors have come to the conclusion that in order to detect dangerous objects concealed under clothing, in a bag, etc., it is appropriate to use electromagnetic waves with a frequency of 1 THz or less.

[0015] The inventors also considered the frequency that would achieve a resolution that would allow the shape of a hazard to be photographed.

[0016] The relationship between the frequency (wavelength) of electromagnetic waves and resolution is expressed by what is known as Abbe's equation (Equation 1).

[0017]

number

[0018] In (Equation 1), δ is the resolution, λ is the wavelength of the electromagnetic wave, NA is the numerical aperture of the lens, n is the refractive index of the medium between the object and the lens, and θ is the maximum angle with respect to the optical axis of the light ray incident on the lens from the object. Here, the entrance pupil diameter of the imaging lens is D, and by approximating the distance from the entrance pupil position of the imaging lens to the object as d, where d>>D, we obtain (Equation 2).

[0019]

number

[0020] FIG. 2 is a graph of (Equation 2) assuming an air environment, where n=1, D=0.5 m, and d=2.5 m.

[0021] As shown in Figure 2, by using electromagnetic waves with a frequency of 80 MHz (0.08 THz) or higher, it is possible to capture images of the shapes of dangerous objects such as blades.

[0022] As a result of the above investigation, the inventors have found that in order to photograph the shape of a dangerous object such as a blade, it is appropriate to use electromagnetic waves with a frequency of 0.08 THz or higher.

[0023] In other words, through these considerations, the inventors have come to the knowledge that in order to take photographs that can detect dangerous objects concealed under clothing, in bags, etc., it is appropriate to use sub-terahertz waves, which are electromagnetic waves with frequencies between 0.08 THz and 1 THz.

[0024] In addition, it is known that sub-terahertz waves do not have adverse effects on the human body, so there is no problem from the standpoint of safety in using sub-terahertz waves as electromagnetic waves to be radiated toward the human body.

[0025] On the other hand, sub-terahertz waves are specularly reflected by the human body, metals, etc. For this reason, in conventional imaging using electromagnetic waves (here, sub-terahertz waves) emitted from a point light source, it is difficult to accurately image the shape of the human body or the shape of dangerous metallic objects such as knives. In order to solve this problem, the inventors have studied the shape of the light source emitting the sub-terahertz waves, etc. As a result, the inventors have found that if the light source emitting the sub-terahertz waves is a surface light source, it is possible to irradiate the sub-terahertz waves to the object to be imaged from various angles compared to when the light source is a point light source, and therefore it is possible to image the shapes of objects that specularly reflect the sub-terahertz waves, such as the human body and metals, with higher accuracy than conventional imaging.

[0026] Based on the above findings, the inventors have come up with the following imaging device.

[0027] An imaging device according to an embodiment of the present disclosure includes a surface light source including an emission surface that emits sub-terahertz waves toward a measurement object, and a detector including an image sensor that receives the sub-terahertz waves emitted from the emission surface and reflected by the measurement object, the surface light source includes one or more point light sources that emit sub-terahertz waves, and a reflector that generates sub-terahertz waves emitted from the emission surface by diffusively reflecting the sub-terahertz waves emitted from the one or more point light sources, and the reflecting surface of the reflector is an uneven surface having an average length RSm of roughness curve elements of 0.3 mm or more. Here, the diffuse reflection means that the sub-terahertz waves incident on the reflecting surface at one incidence angle from a macroscopic perspective are reflected at multiple reflection angles due to the structure of the uneven surface having multiple microscopic unevenness.

[0028] The imaging device performs imaging using sub-terahertz waves emitted from a surface light source. Therefore, the imaging device can image the shapes of objects such as human bodies and metals that are hidden under clothing and cannot be directly seen with the naked eye with greater accuracy than conventional imaging devices. Furthermore, the average length RSm of the roughness curve elements of the reflecting surface is equal to or greater than the wavelength of the sub-terahertz waves. Therefore, the imaging device can suppress the occurrence of interference fringes in the sub-terahertz waves emitted from the radiation surface, even if the sub-terahertz waves emitted from each point light source are coherent electromagnetic waves.

[0029] Furthermore, the detector may have an optical system that forms an image of the reflected wave on the image sensor, and when an entrance pupil diameter of the optical system is Φ, a distance between the radiation surface and the object to be measured is b, and a distance between the object to be measured and the optical system is c, the reflecting surface may have one or more unit areas consisting of an uneven surface containing two or more frequency components below (Φ×b / c) / λ in the spatial frequency domain, where λ is the wavelength of the sub-terahertz waves emitted from the one or more point light sources, and each of the one or more unit areas may have a width of Φ×b / c or more, and an average length RSm of the roughness curve elements may be less than 2×Φ×b / c.

[0030] Furthermore, the one or more unit areas may be a plurality of units including a first unit area and a second unit area, the first unit area and the second unit area being in contact with each other along a shared side, and the uneven shape in the first unit area and the uneven shape in the second unit area may be in an axisymmetric relationship with respect to the shared side.

[0031] Furthermore, the detector has an optical system that forms an image of the reflected wave on the image sensor. When the width of an imaging range of the measurement object is a and the distance between the measurement object and the optical system is c, the angle θ1 at which the half width at half maximum of the intensity of the sub-terahertz wave is diffusely reflected by the reflector is given by:

number

[0032] Furthermore, the detector has an optical system that forms an image of the reflected wave on the image sensor. When the width of the photographing range of the measurement object is a and the distance between the measurement object and the optical system is c, the angle θ2 at half width at half maximum of the inclination angle distribution of the unevenness of the reflection surface is expressed as follows:

number

[0033] Hereinafter, a specific example of an imaging device according to one aspect of the present disclosure will be described with reference to the drawings. Each embodiment shown here shows one specific example of the present disclosure. Therefore, the numerical values, shapes, components, arrangement and connection of the components, steps (processes) and the order of steps shown in the following embodiments are merely examples and do not limit the present disclosure. In addition, each figure is a schematic diagram and is not necessarily illustrated precisely. In the following, the term plane means not only a surface that is an exact plane but also a surface that is substantially a plane. In addition, in the following, the term spheroid means not only a surface that is an exact spheroid but also a surface that is substantially a spheroid.

[0034] In addition, a comprehensive or specific aspect of the present disclosure may be realized by a system, a method, an integrated circuit, a computer program, or a recording medium such as a computer-readable CD-ROM, or may be realized by any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0035] (Embodiment 1) Here, an imaging device is described that radiates sub-terahertz waves to a person and receives the waves reflected by the person, thereby imaging a dangerous object such as a knife that the person is hiding under clothing, etc.

[0036] FIG. 3 is a block diagram showing a configuration of the imaging device 10 according to the first embodiment.

[0037] As shown in FIG. 3, the imaging device 10 includes a light source 20, a detector 30, and an image processing unit 40.

[0038] The light source 20 radiates sub-terahertz waves to a measurement object (here, person 100).

[0039] FIG. 4 is a schematic diagram showing the configuration of the light source 20. As shown in FIG.

[0040] As shown in FIG. 4, the light source 20 includes a point light source 21 and an optical element .

[0041] The point light source 21 radiates sub-terahertz waves radially in all directions around the point light source 21 .

[0042] Optical element 23 has an emission surface 22, and generates sub-terahertz waves emitted from emission surface 22 from the sub-terahertz waves emitted from point light source 21. Here, emission surface 22 is a flat surface. Therefore, optical element 23 functions as a surface light source that emits sub-terahertz waves from emission surface 22, which is a flat surface. Here, for convenience of explanation, the emission surface of the sub-terahertz waves is a flat surface, but it may be the inner surface of a spheroid or the inner surface of a sphere, which will be described later, or may be any curved surface.

[0043] FIG. 5 is a schematic diagram showing a cross section of how light source 20 functions as a surface light source that emits sub-terahertz waves, and how detector 30, which will be described later, receives the waves reflected by a measurement object.

[0044] As shown in FIG. 5, the optical element 23 includes a diffusion plate 24, and the principal plane on the front side of the diffusion plate 24 serves as a radiation surface 22.

[0045] Diffusion plate 24 diffuses and transmits the sub-terahertz waves emitted from point light source 21, thereby generating sub-terahertz waves emitted from radiation surface 22. From a macroscopic perspective, diffusion plate 24 has a flat plate shape parallel to radiation surface 22. On the other hand, from a microscopic perspective, diffusion plate 24 has minute undulations formed all over its surface so as to diffuse the transmitted sub-terahertz waves.

[0046] 5, in light source 20, point light source 21 is disposed on the back side of optical element 23. The sub-terahertz waves emitted from point light source 21 penetrate into optical element 23 from the main surface on the back side of optical element 23 and reach diffuser plate 24. The sub-terahertz waves that reach diffuser plate 24 are diffused and transmitted through diffuser plate 24. The sub-terahertz waves that have been diffused and transmitted through diffuser plate 24 propagate to radiation surface 22 and are radiated from radiation surface 22 to the outside.

[0047] Returning to FIG. 3, the description of the imaging device 10 will continue.

[0048] The detector 30 includes an image sensor 31 .

[0049] The image sensor 31 converts an image of the sub-terahertz waves emitted from the subject into an electrical signal according to its intensity. Then, the image sensor 31 generates an image based on the converted electrical signal. Hereinafter, the generation of an image including an image of the subject by the image sensor 31 is also referred to as "capturing an image". As shown in Fig. 3, when the sub-terahertz waves emitted from the light source 20 are reflected by the measurement target (here, person 100) that is the subject, and the reflected waves reach the image sensor, the image sensor 31 receives the reflected waves.

[0050] As described above, sub-terahertz waves are specularly reflected by the human body, metal, etc. Therefore, the image sensor 31 receives reflected waves from an area of ​​the body of the person 100 and a knife concealed by the person 100 at an angle at which the specularly reflected reflected waves enter the image sensor 31.

[0051] As described above, the light source 20 functions as a surface light source that emits sub-terahertz waves from the emission surface 22. Therefore, the light source 20 can irradiate the person 100 with sub-terahertz waves from various angles. Therefore, the image sensor 31 can receive reflected waves from a relatively wide area 101 on the surface of the person 100, that is, on the body of the person 100 and on the surface of the knife concealed by the person 100, as shown in Fig. 5. Therefore, the image capturing device 10 can capture an image of a relatively wide area 101 on the body of the person 100 and on the surface of the knife concealed by the person 100.

[0052] FIG. 6 is a schematic diagram showing a cross section of a detector 30 receiving a reflected wave in an imaging device according to a first comparative example in which the optical element 23 is removed from the light source 20, that is, in an imaging device according to the first comparative example in which the sub-terahertz waves emitted by the point light source 21 are radiated directly to the outside.

[0053] 6, in the imaging device according to the first comparative example, the image sensor 31 can only receive reflected waves from an area 101a of the body of the person 100 and the surface of the knife concealed by the person 100, where the specular reflected waves are incident on the image sensor 31 at an angle. Therefore, the imaging device according to the first comparative example can only image a relatively narrow area 101a of the body of the person 100 and the surface of the knife concealed by the person 100.

[0054] In this way, the image capturing device 10 according to the first embodiment can capture an image of the body of the person 100 and the shape of a blade concealed by the person 100 with greater accuracy than the image capturing device according to the first comparative example.

[0055] 3, the description of the photographing device 10 will continue. The detector 30 outputs an image generated by the image sensor 31 to the image processing unit .

[0056] Upon receiving an image from the detector 30, the image processing unit 40 outputs the received image to the outside, and also performs image processing on the received image and outputs the result of the image processing to the outside.

[0057] The image processing performed by the image processing unit 40 may be, for example, a process of determining whether or not an object having a predetermined characteristic (e.g., an object having the characteristics of a blade) is included in the image output from the detector 30, and outputting a predetermined detection signal (e.g., an alarm indicating that an object having the characteristics of a blade has been photographed) when it is determined that an object having the predetermined characteristic is included. The image processing unit 40 may be realized by, for example, including a processor and a memory, and by the processor executing a program stored in the memory.

[0058] The photographing device 10 having the above configuration is installed, for example, in an airport passageway or near a ticket gate at a station.

[0059] FIG. 7 is a schematic diagram showing the state in which the image capturing device 10 is installed in an airport passage.

[0060] As shown in FIG. 7, the image capturing device 10 may be installed, for example, with the optical element 23 and the detector 30 embedded inside the wall of a crank-shaped passageway 200 in an airport.

[0061] 7, sub-terahertz waves radiated from radiation surface 22 inside the wall penetrate the wall and are irradiated onto person 100. The sub-terahertz waves reflected by person 100 penetrate the wall again and are incident on detector 30. In this way, image capture device 10 can capture an image of a dangerous object such as a knife that person 100 passing through passage 200 is carrying concealed under clothing or the like.

[0062] (Embodiment 2) Here, a description will be given of an imaging device according to embodiment 2, which is a part of the configuration of imaging device 10 according to embodiment 1. The following description will focus on the differences between the imaging device according to embodiment 2 and imaging device 10.

[0063] FIG. 8 is a block diagram showing a configuration of an image capturing device 10a according to the second embodiment.

[0064] As shown in FIG. 8, the photographing device 10a is configured by changing the light source 20 from the photographing device 10 of embodiment 1 to a first light source 20a and a second light source 20b, changing the detector 30 to a first detector 30a and a second detector 30b, and changing the image processing unit 40 to an image processing unit 40a.

[0065] The first light source 20a radiates sub-terahertz waves to a measurement object (here, person 100).

[0066] FIG. 9 is a schematic diagram showing a cross section of the configuration of the first light source 20a, how the first light source 20a functions as a surface light source, and how a first detector 30a (described later) receives a reflected wave.

[0067] As shown in FIG. 9, the first light source 20a includes a point light source 21a and an optical element 23a.

[0068] The point light source 21a radiates sub-terahertz waves radially in all directions around the point light source 21a.

[0069] The optical element 23a has a first radiation surface 22a, and generates a sub-terahertz wave radiated from the first radiation surface 22a from the sub-terahertz wave radiated from the point light source 21a. Here, the first radiation surface 22a is an inner surface of a spheroid. Therefore, the optical element 23a functions as a surface light source that radiates the sub-terahertz wave from the first radiation surface 22a, which is an inner surface of the spheroid.

[0070] As shown in FIG. 9, the optical element 23a includes a reflector 24a, the inner curved surface of which serves as a first radiation surface 22a.

[0071] The reflector 24a diffusely reflects the sub-terahertz waves emitted from the point light source 21a to generate the sub-terahertz waves emitted from the first radiation surface 22a. From a macroscopic perspective, the reflector 24a has a similar shape to the first radiation surface 22a, and is equal to or larger than the first radiation surface 22a, and the positions of its two focal points respectively coincide with the positions of the two focal points of the first radiation surface 22a. On the other hand, from a microscopic perspective, the reflector 24a has minute undulations formed on the entire reflecting surface so that the reflected sub-terahertz waves are diffused.

[0072] As shown in FIG. 9, in the first light source 20a, the point light source 21a is disposed at one focus 301a of the two focuses of the first radiation surface 22a. The sub-terahertz waves emitted from the point light source 21a penetrate into the inside of the optical element 23a from the first radiation surface 22a and reach the reflector 24a. The sub-terahertz waves that reach the reflector 24a are diffusely reflected by the reflector 24a. The sub-terahertz waves that are diffusely reflected by the reflector 24a propagate to the first radiation surface 22a and are radiated to the outside from the first radiation surface 22a. The sub-terahertz waves radiated to the outside are irradiated to, for example, a person 100 in the vicinity of the other focus 302a of the two focuses of the first radiation surface 22a.

[0073] In this embodiment, the first radiation surface 22a and the reflector 24a are described as being separate structures, but this is not necessarily limited to the example in which they are separate structures. For example, the first radiation surface 22a may be the reflecting surface of the reflector 24a.

[0074] 8 has the same function as the first light source 20a, and its shape is a mirror image of the first light source 20a. Therefore, the second light source 20b can be explained by replacing the point light source 21a with the point light source 21b, the optical element 23a with the optical element 23b, the reflector 24a with the reflector 24b, the one focal point 301a with the one focal point 301b, and the other focal point 302a with the other focal point 302b, based on the explanation of the first light source 20a, except that its shape is a mirror image of the first light source 20a.

[0075] Returning to FIG. 8, the description of the photographing device 10a will continue.

[0076] The first detector 30a includes a first image sensor 31a. The first detector 30a is similar to the detector 30 according to the first embodiment. That is, the first image sensor 31a is similar to the image sensor 31 according to the first embodiment.

[0077] The second detector 30b is similar to the first detector 30a, and therefore the second detector 30b will be described by substituting the first image sensor 31a for the second image sensor 31b in the description of the first detector 30a.

[0078] As described above, the first light source 20a functions as a surface light source that emits sub-terahertz waves from the first radiation surface 22a. Therefore, the first light source 20a can irradiate the person 100 near the other focal point 302a with sub-terahertz waves from various angles. Therefore, the first image sensor 31a can receive reflected waves from a relatively wide area 102 on the surface of the person 100, that is, the body of the person 100 and the surface of the knife concealed by the person 100, as shown in FIG. 9. Therefore, the image capturing device 10a can capture an image of a relatively wide area 102 on the body of the person 100 and the surface of the knife concealed by the person 100.

[0079] 10 is a schematic diagram showing a cross section of the first detector 30a receiving the reflected wave in an imaging device according to a second comparative example in which the reflector 24a is replaced by the reflector 24aa from the first light source 20a. Here, the reflector 24aa has the same shape as the reflector 24a when viewed from a macroscopic point of view, while the entire reflecting surface is formed smoothly so that the reflected sub-terahertz wave is mirror-reflected when viewed from a microscopic point of view. Therefore, the sub-terahertz wave emitted from one focal point 301a and reflected by the reflector 24aa all travels toward the other focal point 302a, regardless of where the sub-terahertz wave is reflected on the reflector 24aa. 10, in the imaging device according to the second comparative example, the first image sensor 31a can only receive reflected waves from the area 102a located at the other focal point 302a among the body of the person 100 near the other focal point 302a and the surface of the knife concealed by the person 100. Therefore, the imaging device according to the second comparative example can only image a relatively narrow area 102a among the body of the person 100 and the surface of the knife concealed by the person 100.

[0080] In this way, the image capturing device 10a according to the second embodiment can capture an image of the body of the person 100 and the shape of a blade concealed by the person 100 with greater accuracy than the image capturing device according to the second comparative example.

[0081] Returning to FIG. 8, the description of the photographing device 10a will continue.

[0082] The first detector 30a and the second detector 30b output the first image and the second image generated by the first image sensor 31a and the second image sensor 31b, respectively, to the image processing unit 40a.

[0083] When the image processing unit 40a receives the first image and the second image from the first detector 30a and the second detector 30b, respectively, it outputs the received first image and second image to the outside, and also performs image processing on the received first image and second image and outputs the results of the image processing to the outside.

[0084] The image processing performed by the image processing unit 40a may be, for example, a process of determining whether or not an object having a predetermined characteristic (e.g., an object having a characteristic of a blade) is included in the first image and the second image output from the first detector 30a and the second detector 30b, and outputting a predetermined detection signal (e.g., an alarm indicating that an object having a characteristic of a blade is photographed) when it is determined that an object having the predetermined characteristic is included in at least one of the first image and the second image. The image processing performed by the image processing unit 40a may further include a process of generating a composite image by relatively brightening the first image and the second image when it is not determined that an object having the predetermined characteristic is included in at least one of the first image and the second image, determining whether or not an object having the predetermined characteristic is included in the generated composite image, and outputting a predetermined detection signal when it is determined that an object having the predetermined characteristic is included in the composite image. The image processing unit 40a may be, for example, equipped with a processor and a memory, and may be realized by the processor executing a program stored in the memory.

[0085] The image capturing device 10a having the above configuration is installed, for example, in an airport passageway or near a ticket gate at a station.

[0086] FIG. 11 is a schematic diagram showing a cross section of the photographing device 10a installed in a passageway near a ticket gate at a station.

[0087] 11, the photographing device 10a may be installed such that, for example, the optical element 23a and the optical element 23b are embedded inside the wall of a passage 400 near a ticket gate of a station. More specifically, the photographing device 10a may be installed such that, for example, the optical element 23a is embedded inside a wall 401a which is one side wall of the passage 400, and the optical element 23b is embedded inside a wall 401b which is the other side wall of the passage 400. In this case, it is desirable to install the optical elements 23a and 23b such that the other focal point 302a of the optical element 23a and the other focal point 302b of the optical element 23b approximately coincide with each other on the center line of the passage 400. By arranging them in this way, the sub-terahertz waves emitted from the point light source 21a and the sub-terahertz waves emitted from the point light source 21b can be irradiated from various angles to the area (hereinafter also referred to as the "focal area") near the other focal point 302a and the other focal point 302b. Therefore, the first image sensor 31a and the second image sensor 31b included in the first detector 30a and the second detector 30b, respectively, can receive reflected waves from a relatively wide area 103 of the surface of the person 100 walking in the focal area, that is, the body of the person 100 and the surface of the knife concealed by the person 100, as shown in FIG. 11. Therefore, the image capture device 10a can capture an image of the relatively wide area 103 of the body of the person 100 and the surface of the knife concealed by the person 100. Furthermore, the first image sensor 31a and the second image sensor 31b included in the first detector 30a and the second detector 30b respectively receive reflected waves from the area 103 at different angles. Therefore, the image capturing device 10a can capture images of the body of the person 100 and the blade concealed by the person 100, which are the same subject, from different angles.

[0088] The operation of the photographing device 10a having the above configuration will be described below.

[0089] The photographing device 10a performs, as an example, image analysis processing, in which the photographing device 10a captures a first image and a second image, and outputs a detection signal that is a warning indicating that an object having the characteristics of a blade has been captured based on the captured first image and second image.

[0090] FIG. 12 is a flowchart of the image analysis process performed by the image capturing device 10a.

[0091] The image analysis process is initiated when a person enters the focal area.

[0092] When a person enters the focus area, the image capturing device 10a detects that the person has entered the focus area. The image capturing device 10a may detect that the person has entered the focus area by receiving a signal indicating that the person has entered the focus area from an external sensor that detects that the person has entered the focus area, for example.

[0093] When a person is detected to have entered the focal region, the first light source 20a and the second light source 20b radiate sub-terahertz waves at the same timing in synchronization with each other (step S100). The first detector 30a and the second detector 30b also radiate sub-terahertz waves in synchronization with each other to capture an image of the person who has entered the focal region at the timing when the first light source 20a and the second light source 20b radiate sub-terahertz waves in synchronization with each other (step S110). The first detector 30a and the second detector 30b then output the first image and the second image to the image processing unit 40a, respectively.

[0094] When the first image and the second image are output, the image processor 40a receives the output first image and the second image, and outputs the received first image and the second image to the outside (step S120).Then, the image processor 40a determines whether or not at least one of the first image and the second image includes an object having a predetermined characteristic, that is, a blade characteristic (step S130).

[0095] In the process of step S130, if it is not determined that at least one of the first image and the second image contains an object having the predetermined characteristic (step S130: No), the image processing unit 40a generates a composite image by relatively brightening the first image and the second image, and outputs the generated composite image to the outside (step S140).Then, the image processing unit 40a determines whether or not the generated composite image contains an object having the characteristic of a blade, which is the predetermined characteristic (step S150).

[0096] In the processing of step S130, if it is determined that at least one of the first image and the second image contains an object having predetermined characteristics (step S130: Yes), or in the processing of step S150, if it is determined that an object having predetermined characteristics is contained in the composite image (step S150: Yes), image processing unit 40a outputs a detection signal to the outside, which is an alarm indicating that an object having the characteristics of a blade has been photographed (step S160).

[0097] When the processing of step S160 is completed, or when the processing of step S150 does not determine that the composite image contains an object having a predetermined characteristic (step S150: No), the photographing device 10a ends its image analysis processing.

[0098] (Embodiment 3) Here, a description will be given of an imaging device according to embodiment 3, which is a part of the configuration of imaging device 10a according to embodiment 2. The following description will focus on the differences between the imaging device according to embodiment 3 and imaging device 10a.

[0099] FIG. 13 is a block diagram showing a configuration of an image capturing device 10b according to the third embodiment.

[0100] As shown in FIG. 13, the photographing device 10b is configured by deleting the second light source 20b and the second detector 30b from the photographing device 10a of embodiment 2, changing the first detector 30a to a detector 30c, and changing the image processing unit 40a to an image processing unit 40b.

[0101] The detector 30 c includes an image sensor 31 and an optical system 32 .

[0102] The optical system 32 forms an image of the sub-terahertz waves radiated from the first radiation surface 22a and reflected by a measurement target (here, person 100) on the image sensor 31. The optical system 32 includes at least one lens including the lens 33. The entrance pupil diameter of the optical system 32 is Φ.

[0103] The detector 30c outputs the image generated by the image sensor 31 to the image processor 40b.

[0104] When the image processing unit 40b receives an image from the detector 30c, the image processing unit 40b outputs the received image to the outside, performs image processing on the received image, and outputs the result of the image processing to the outside. The image processing performed by the image processing unit 40b is the same as the image processing performed by the image processing unit 40 according to the first embodiment.

[0105] As described in the second embodiment, when viewed from a microscopic point of view, the reflector 24a constituting the first light source 20a has minute undulations formed on the entire reflecting surface so as to diffusely reflect the sub-terahertz waves emitted from the point light source 21a. Here, the structure of the reflecting surface of the reflector 24a will be described in more detail.

[0106] In order to realize the above-mentioned diffuse reflection, the reflecting surface of the reflector 24a is an uneven surface with a mean length RSm of the roughness curve elements of 0.3 mm or more.

[0107] The wavelength of the sub-terahertz waves emitted from the point light source 21a is 0.3 mm or less. Therefore, when the sub-terahertz waves emitted from the point light source 21a are irradiated onto a reflective surface that is an uneven surface with an average length RSm of the roughness curve elements of 0.3 mm or more, the sub-terahertz waves are diffusely reflected. In this way, the reflective surface of the reflector 24a is an uneven surface with an average length RSm of the roughness curve elements of 0.3 mm or more, thereby realizing diffuse reflection of the sub-terahertz waves emitted from the point light source 21a.

[0108] FIG. 14 is a schematic diagram showing how the image capturing device 10b captures an image of a measurement object.

[0109] 14, the imaging range 110 is a region on the surface of the measurement target that is to be imaged by the imaging device 10b. As described in the second embodiment, the imaging range 110 is a region in the vicinity of the other of the two focal points 302a (see FIG. 9, etc.) of the first radiation surface 22a. Meanwhile, the point light source 21a is located at one of the two focal points 301a (see FIG. 9, etc.) of the first radiation surface 22a.

[0110] The imaging sub-terahertz wave radiation region 120 is a partial region of the first radiation surface 22a, and is a region that radiates sub-terahertz waves that are the source of the reflected light components that form an image on the image sensor 31 out of the light reflected by the object to be measured.

[0111] The distance b is the distance between the first radiation surface 22a and the object to be measured. More specifically, the distance b is the distance between the imaged sub-terahertz wave radiation region 120 and the imaging range 110.

[0112] The distance c is the distance between the measurement object and the optical system 32. More specifically, the distance c is the distance between the shooting range 110 and the optical system 32.

[0113] The width Φ' of the imaged sub-terahertz wave radiation region 120 is determined by the positional relationship between the first radiation surface 22a, the object to be measured, and the optical system 32, as shown below in (Equation 3).

number

[0114] When a periodic structure exists on the reflecting surface of the reflector 24 a in the imaged sub-terahertz wave radiation region 120 , there is a possibility that interference fringes will occur in the reflected light that forms an image on the image sensor 31 .

[0115] FIG. 15A is a schematic diagram showing how a reflecting surface of a reflector according to a comparative example reflects sub-terahertz waves.

[0116] As shown in FIG. 15A, the radiation surface according to the comparative example has a periodic structure with a pitch d.

[0117] In the case where the reflecting surface of the reflector according to the comparative example has a periodic structure having such a pitch d, when a coherent sub-terahertz wave is reflected by this reflecting surface, the reflected wave has an angle θ determined by the following (Equation 4): n At this position, a bright line is formed, resulting in interference fringes.

number

[0118] FIG. 15B is a schematic diagram showing an interference fringe occurring due to the sub-terahertz wave reflected by the reflecting surface of the reflector according to the comparative example.

[0119] In this way, if the reflecting surface of reflector 24a in imaging sub-terahertz wave radiation region 120 has a periodic structure in the spatial frequency domain consisting of only one frequency component, Φ' / d, then if the sub-terahertz waves emitted from point light source 21a are coherent sub-terahertz waves, the image formed on image sensor 31 will be relatively strongly affected by interference fringes.

[0120] For this reason, the reflecting surface of the actual reflector 24a is an uneven surface that contains two or more frequency components below Φ' / λ in the spatial frequency domain, where λ is the wavelength of the sub-terahertz wave emitted from the point light source 21a.

[0121] As a result, even if the sub-terahertz waves radiated from the point light source 21a are coherent sub-terahertz waves, the influence of interference fringes on the image of the object to be measured formed on the image sensor 31 is reduced.

[0122] FIG. 15C is an enlarged cross-sectional view showing an example of the reflecting surface of the actual reflector 24a.

[0123] As shown in FIG. 15C, the reflecting surface of the reflector 24a is an uneven surface that includes spatial frequencies 1 to 5 with equal intensity in the spatial frequency domain.

[0124] From the viewpoint of reducing the influence of interference fringes on the image of the object to be measured formed on the image sensor 31, it is more preferable that the reflecting surface of the reflector 24a is an uneven surface having a random shape.

[0125] A specific example of the structure of the reflecting surface of the reflector 24a will be described below.

[0126] The reflecting surface of the reflector 24a has a plurality of unit areas each having a width of Φ×b / c or more. Here, each unit area is described as an area having a shape that is approximately rectangular when viewed from a direction perpendicular to the tangent plane of the spheroid of revolution in a macroscopic viewpoint of the reflecting surface. The width of a unit area refers to the shorter distance between the opposing sides of the approximately rectangular shape. Here, the reflecting surface of the reflector 24a is described as having a plurality of unit areas, but this is not necessarily limited to an example in which there is a plurality of unit areas, and it is sufficient if there is at least one unit area.

[0127] Fig. 16A is a plan view of each of the unit areas 500 (i.e., unit areas 500a to 500d) of the reflecting surface of the reflector 24a, viewed from a direction perpendicular to the tangent plane of the spheroid from a macroscopic viewpoint of the reflecting surface. Here, the position of each tangent plane contacting the spheroid is the center position of the rectangle illustrated as unit areas 500a to 500d in Fig. 16A.

[0128] Here, each unit area 500 is made of an uneven surface that contains two or more frequency components below Φ' / λ in the spatial frequency domain, where λ is the wavelength of the sub-terahertz wave emitted from the point light source 21a.

[0129] FIG. 16B is a schematic diagram showing a state in which a plurality of unit areas 500 are arranged on the reflecting surface of the reflector 24a.

[0130] 16A and 16B, on the reflecting surface of reflector 24a, unit areas 500a and 500b share a side 501a in unit area 500a and a side 501b in unit area 500b as one side, and are arranged in contact with each other at the shared side. The uneven shape in unit area 500a and the uneven shape in unit area 500b are in a line symmetrical relationship with respect to the one side.

[0131] Furthermore, on the reflecting surface of reflector 24a, unit areas 500a and 500c share a side 502a in unit area 500a and a side 502c in unit area 500c as one side, and are arranged in contact with each other at the shared side. The uneven shape in unit area 500a and the uneven shape in unit area 500c are in a line-symmetric relationship with respect to the one side.

[0132] Furthermore, on the reflecting surface of reflector 24a, unit area 500b and unit area 500d share a side 502b in unit area 500b and a side 502d in unit area 500d as one side, and are arranged in contact with each other at the shared side. The uneven shape in unit area 500b and the uneven shape in unit area 500d are in a line symmetrical relationship with respect to the one side.

[0133] Furthermore, on the reflecting surface of reflector 24a, unit areas 500c and 500d share a side 501c in unit area 500c and a side 501d in unit area 500d as one side, and are arranged in contact with each other at the shared side. The uneven shape in unit area 500c and the uneven shape in unit area 500d are in a line symmetrical relationship with respect to the one side.

[0134] As shown in FIG. 16B, unit regions 500a to 500d are arranged without any gaps on the entire reflective surface of reflector 24a.

[0135] With the above configuration, the reflective surface of the reflector 24a realizes, for any area with a width of Φ', an uneven surface that contains two or more frequency components below Φ' / λ in the spatial frequency domain, where λ is the wavelength of the sub-terahertz wave emitted from the point light source 21a.

[0136] Returning to FIG. 14, the description of the imaging device 10b will continue.

[0137] In FIG. 14, angle θ1 indicates the angle at which the half-width at half maximum of the intensity of the sub-terahertz wave is obtained when the sub-terahertz wave is diffusely reflected by an arbitrary position on the reflector 24a.

[0138] 14, the shooting range 110 is located within a range that falls within the angle θ1. That is, the angle θ1 satisfies the following (Equation 5).

number

[0139] As a result, within the imaging range 110, the variation in intensity of the sub-terahertz waves irradiated by the reflector 24a is reduced to ½ or less.

[0140] The uneven structure on the reflecting surface of the reflector 24a that realizes formula (5) will be described below.

[0141] FIG. 17 is a schematic diagram showing a cross section of an inclined portion of the unevenness on the reflecting surface of the reflector 24a.

[0142] As shown in Figure 17, when a sub-terahertz wave is incident perpendicular to the tangent plane on a bumpy structure in which the reflecting surface has an inclination angle of θ2 with respect to the tangent plane of the ellipsoid of revolution from a macroscopic perspective, the angle of the reflected wave with respect to the incident wave is 2θ2.

[0143] Therefore, in order to realize (Equation 5), the angle θ2 which is the half width at half maximum of the tilt angle distribution in the uneven structure on the reflecting surface of the reflector 24a satisfies (Equation 6) shown below.

number

[0144] As a result, within the imaging range 110, the variation in intensity of the sub-terahertz waves irradiated by the reflector 24a is reduced to 1 / 2 or less.

[0145] The upper limit of the average length RSm of the roughness curve elements of the reflecting surface of the reflector 24a will be considered below.

[0146] 18A and 18B are schematic diagrams showing the relationship between a subject and a real image in optical system 32. FIG.

[0147] 18A and 18B, focal length f is the focal length of optical system 32, distance A is the distance from optical system 32 to the subject, height B is the height of the subject, distance A' is the distance from optical system 32 to the real image of the subject formed by optical system 32, and height B' is the height of the real image.

[0148] In FIG. 18A, the triangle indicated by the thick solid line and the triangle indicated by the thick dashed line are similar to each other, and therefore the following (Equation 7) holds true. A:A´=B:B´ (Formula 7)

[0149] Furthermore, since the triangle indicated by the thick solid line and the triangle indicated by the thick dashed line in FIG. 18B are similar to each other, the following (Equation 8) holds true. B:B´=f:A´-f (Formula 8)

[0150] From (Equation 7) and (Equation 8), A:A´=f:A´-f Therefore, the following equation (9) holds. A´=f×A / (Af) (Equation 9)

[0151] 18C and 18D are schematic diagrams showing how a point at the position of the imaged sub-terahertz wave radiation region 120 forms an image on the image sensor 31 by the optical system 32. FIG.

[0152] 18C and 18D, distance c is the distance between the imaging range 110 and the optical system 32, distance e is the distance between the imaging sub-terahertz wave radiation region 120 and the optical system 32, that is, the sum of distance b and distance c between the imaging sub-terahertz wave radiation region 120 and the imaging range 110, distance c' is the distance between the optical system 32 and the image sensor 31, distance e' is the distance between the position where the point at the imaging sub-terahertz wave radiation region 120 is imaged and the optical system 32, and width Φ'' is the width of the image of the point at the imaging sub-terahertz wave radiation region 120 formed on the image sensor 31, that is, the width indicating the spread of the out-of-focus image of the point at the imaging sub-terahertz wave radiation region 120 formed on the image sensor 31. Also, in FIG. 18D, length P is the average length RSm of the roughness curve element of the reflecting surface of reflector 24a, and height P″ is the height of the real image of the subject at height P at the position of first radiation surface 22a, i.e., the height of the subject whose height is the average length RSm of the roughness curve element of the reflecting surface of reflector 24a.

[0153] In FIG. 18C, the triangle indicated by the thick solid line and the triangle indicated by the thick dashed line are similar to each other. Φ:Φ´´=e´:c´-e´ Therefore, the following equation (10) holds true. Φ´´=Φ×(c´-e´) / e´ (Equation 10)

[0154] Furthermore, from (Equation 9), the following (Equation 11) and (Equation 12) hold. c´=f×c / (cf) (Equation 11) e´=f×e / (ef) (Eq. 12)

[0155] Due to the similarity relationship in Figure 18D, P:P´=e:c´ Therefore, the following equation (13) holds true. P´=c´×P / e (Equation 13)

[0156] When an object of height P, that is, an object whose height is the average length RSm of the roughness curve elements of the reflecting surface of the reflector 24a, is on the reflecting surface of the reflector 24a, that is, when it is in the imaging sub-terahertz wave radiation region 120, both ends and the central point of the object of height P will be out of focus and will form a circular image of width Φ'' on the image sensor 31, and if the blurs at both ends and the center overlap, the object will not be resolved. Therefore, in order for the object of height P to not be resolved, the following (Equation 14) holds. Φ´´ / 2+Φ´´+Φ´´ / 2>P (Equation 14) From (Equation 10) to (Equation 14), the following equation holds: P<2×Φ(ec) / c

[0157] Here, since the distance e is the sum of the distance b and the distance c, the following (Equation 15) holds. P<2×Φ×b / c (Formula 15)

[0158] From (Equation 15), it can be seen that in order to resolve the uneven surface structure of the reflecting surface of reflector 24a, it is desirable for the average length RSm of the roughness curve elements of the reflecting surface of reflector 24a to be less than 2×Φ×b / c.

[0159] (Other embodiments) The imaging device according to one aspect of the present disclosure has been described above based on the first and second embodiments. However, the present disclosure is not limited to these embodiments. As long as the modifications do not deviate from the spirit of the present disclosure, various modifications that would occur to those skilled in the art may be made to these embodiments, or a form constructed by combining components of different embodiments may also be included within the scope of one or more aspects of the present disclosure.

[0160] (1) In the second embodiment, the image capturing device 10a has been described as including a first light source 20a including an optical element 23a having a first radiation surface 22a that is an inner surface of an ellipsoid, and a second light source 20b including an optical element 23b having a second radiation surface 22b that is an inner surface of an ellipsoid. In contrast, an image capturing device according to a modification that is another example of one aspect of the present disclosure may be modified from the image capturing device 10a according to the second embodiment to include a first light source according to a modification in which the shape of the first radiation surface 22a that is an inner surface of an ellipsoid is changed to the inner surface of a sphere, instead of the optical element 23a, and a second light source according to a modification in which the shape of the second radiation surface 22b that is an inner surface of an ellipsoid is changed to the inner surface of a sphere, instead of the optical element 23b.

[0161] FIG. 19 is a schematic diagram showing a part of the external appearance of an imaging device according to a modified example.

[0162] As shown in Fig. 19, in the imaging device 10b according to the modification, the first light source 20c according to the modification includes a point light source 21a and an optical element 23c having a first radiation surface 22c which is an inner surface of a sphere. The point light source 21a is disposed near the center of the sphere. The second light source 20d according to the modification includes a point light source 21b and an optical element 23d having a second radiation surface 22d which is an inner surface of the sphere. The point light source 21b is disposed near the center of the sphere.

[0163] (2) In the first embodiment, the optical element 23 has been described as including the diffusion plate 24. However, as another example, the optical element 23 may be the diffusion plate 24 itself. In this case, the surface of the diffusion plate 24 becomes the radiation surface 22.

[0164] (3) In the second embodiment, the optical elements 23a and 23b are described as including the reflectors 24a and 24b, respectively. In contrast, as another example, the optical elements 23a and 23b may be the reflectors 24a and 24b, respectively. In this case, the reflecting surface of the reflector 24a and the reflecting surface of the reflector 24b become the first radiation surface 22a and the second radiation surface 22b, respectively.

[0165] (4) In the first embodiment, it has been described that light source 20 includes one point light source 21. However, the point light source included in light source 20 is not necessarily limited to one, and may include multiple point light sources. In this case, optical element 23 generates sub-terahertz waves to be radiated from radiation surface 22 from the sub-terahertz waves radiated from the multiple point light sources.

[0166] (5) In the second embodiment, the first light source 20a and the second light source 20b are described as including one point light source 21a and one point light source 21b, respectively. However, the number of point light sources included in the first light source 20a and the second light source 20b is not necessarily limited to one, and each may include multiple point light sources. In this case, the optical element 23a and the optical element 23b generate sub-terahertz waves radiated from the first radiation surface 22a and the second radiation surface 22b, respectively, from the sub-terahertz waves radiated from the multiple point light sources.

[0167] (6) In the second embodiment, the first radiation surface 22a and the second radiation surface 22b are described as being the inner surfaces of a spheroid. However, the first radiation surface 22a and the second radiation surface 22b are not necessarily limited to being the inner surfaces of an exact spheroid, and may be, for example, a polyhedron made up of a large number of minute polygons that are approximated to a spheroid.

[0168] (7) In the third embodiment, each of the at least one unit area 500 has been described as being an area that is approximately rectangular in shape when viewed from a direction perpendicular to the tangent plane of the spheroid of rotation in a macroscopic viewpoint of the reflecting surface of the reflector 24a. However, each of the at least one unit area 500 does not necessarily have to be approximately rectangular in shape as long as the at least one unit area 500 can cover the entire reflecting surface of the reflector 24a without gaps. For example, each of the at least one unit area 500 may be an area that is approximately regular hexagonal in shape when viewed from a direction perpendicular to the tangent plane of the spheroid of rotation in a macroscopic viewpoint of the reflecting surface of the reflector 24a. In this case, the width of the unit area is the distance between the opposing sides of the approximately regular hexagon.

[0169] (8) One aspect of the present disclosure may be not only the imaging device according to the first to third embodiments, but also an imaging method having steps corresponding to characteristic components included in the imaging device, and may also be a program for causing a computer to execute each of the characteristic steps included in the imaging method. Another aspect of the present disclosure may be a computer-readable non-transitory recording medium having such a program recorded thereon. [Industrial Applicability]

[0170] The present disclosure is widely applicable to imaging devices that capture images of objects. [Explanation of symbols]

[0171] 10, 10a, 10b Imaging device 20 light source 20a, 20c First light source 20b, 20d Second light source 21, 21a, 21b point light source 22 Radiating Surface 22a, 22c First emitting surface 22b, 22d Second emitting surface 23, 23a, 23b, 23c, 23d Optical elements 24 Diffuser 24a, 24aa, 24b reflector 30, 30c Detector 30a First detector 30b Second detector 31 Image Sensor 31a First image sensor 31b Second Image Sensor 32 Optical system 33 Lens 40, 40a, 40b Image processing unit 100 people 101, 101a, 102, 102a, 103 area 110 Shooting range 120 Imaging sub-THz radiation region 200, 400 aisles 301a One Focus 302a The other focus 401a, 401b Wall 500a, 500b, 500c, 500d unit area Areas 501a, 501b, 501c, 501d, 502a, 502b, 502c, and 502d

Claims

1. a surface light source including an emission surface that emits sub-terahertz waves toward a measurement object; an optical system that forms an image of a sub-terahertz wave radiated from the radiation surface and reflected by the object to be measured; and a detector that includes an image sensor that receives the imaged reflected wave, The surface light source is One or more point light sources that emit sub-terahertz waves having a wavelength λ; a reflector that diffusely reflects the sub-terahertz waves emitted from the one or more point light sources to generate sub-terahertz waves emitted from the emission surface, When the entrance pupil diameter of the optical system is Φ, the distance between the radiation surface and the measurement object is b, and the distance between the measurement object and the optical system is c, The reflecting surface of the reflector has an uneven surface including two or more frequency components below (Φ×b / c) / λ in the spatial frequency domain, and the average length RSm of the roughness curve element is 0.3 mm or more. Filming equipment.

2. The reflective surface has one or more unit areas consisting of the uneven surface, each of the one or more unit regions has a width equal to or greater than Φ×b / c; The average length RSm of the roughness profile elements is less than 2×Φ×b / c The imaging device according to claim 1 .

3. The one or more unit areas include a first unit area and a second unit area, the first unit area and the second unit area are in contact with each other along a shared side; The shape of the projections and recesses in the first unit area and the shape of the projections and recesses in the second unit area are in a line-symmetric relationship with respect to the one side. The imaging device according to claim 2 .

4. When the width of the photographing range of the measurement object is a, The angle θ1 at which the half width at half maximum of the intensity of the sub-terahertz wave is diffusely reflected by the reflector is [0010] That's all. The imaging device according to claim 1 .

5. When the width of the photographing range of the measurement object is a, The angle θ2 at half width at half maximum of the inclination angle distribution in the unevenness of the reflecting surface is [0025] That's all. The imaging device according to claim 1 .

Images