Imaging device

Abstract

An imaging device (10) uses sub-terahertz waves to image a person (100) who passes through an imaging space (102). The imaging device (10) comprises: an emission unit (20) that emits sub-terahertz waves with toward the person (100); and a detector (30). The detector (30) has: an optical system (32) that forms an image from reflected waves, which are the sub-terahertz waves emitted from the emission unit (20) and reflected by the person (100); and an image sensor (31) that includes a plurality of pixels which are in a planar arrangement and which receive the reflected waves formed into an image by the optical system (32), and that generates an image on the basis of a cumulative intensity, which is obtained by cumulating, for a prescribed time, the intensity of the reflected waves received by each of the plurality of pixels, and the planar arrangement of the plurality of pixels. The prescribed time is not less than λ / 1778 seconds, where λ is the wavelength, in mm, of the sub-terahertz waves.

Description

Imaging device

[0001] The present disclosure relates to an imaging device.

[0002] BACKGROUND ART Conventionally, imaging devices that capture images of an object using terahertz waves and sub-terahertz waves have been known. For example, Patent Document 1 discloses an imaging device that captures an image of an object using sub-terahertz waves.

[0003] International Publication No. 2021 / 255964

[0004] In an imaging device that captures an image of a subject using sub-terahertz waves, it is desirable to suppress uneven brightness in the image, which occurs regardless of the reflection characteristics of the sub-terahertz waves from the subject, in order to improve image quality, etc. For example, by utilizing the difference in the reflection characteristics of sub-terahertz waves between a human body and a dangerous object, images captured using sub-terahertz waves are used to detect whether a person is carrying a dangerous object. In this case, if uneven brightness occurs in the image, which occurs regardless of the reflection characteristics of the sub-terahertz waves from the subject, the accuracy of detecting the dangerous object decreases.

[0005] Therefore, the present disclosure provides an imaging device that can suppress uneven brightness in an image that occurs regardless of the reflection characteristics of sub-terahertz waves from an object to be imaged.

[0006] An imaging device according to one aspect of the present disclosure is an imaging device that uses sub-terahertz waves to capture an image of an object passing through a predetermined area, the imaging device comprising: a radiation unit that radiates the sub-terahertz waves toward the object; (i) an optical system that forms an image of the sub-terahertz waves radiated from the radiation unit reflected by the object; and (ii) a detector having an image sensor that is arranged in a plane and includes a plurality of pixels that receive the reflected waves imaged by the optical system, and that generates an image based on a cumulative intensity obtained by accumulating the intensity of the reflected waves received by each of the plurality of pixels over a predetermined time period and on the planar arrangement of the plurality of pixels, wherein the predetermined time period is λ / 1778 seconds or longer when the wavelength of the sub-terahertz waves is λ mm.

[0007] An imaging device according to one aspect of the present disclosure is an imaging device that uses sub-terahertz waves to capture an image of an object passing through a predetermined area, and includes: an emitter that emits the sub-terahertz waves toward the object; (i) an optical system that forms an image of the sub-terahertz waves emitted from the emitter, reflected by the object; and (ii) a detector that includes an image sensor that is arranged in a plane and includes a plurality of pixels that receive the reflected waves formed by the optical system, and that generates an image based on a cumulative intensity obtained by accumulating the intensity of the reflected waves received by each of the plurality of pixels over a predetermined time period and the planar arrangement of the plurality of pixels; a detector that detects the movement state of the object as it passes through the predetermined area; and a control unit that controls the operation of the imaging device based on the movement state, wherein the control unit determines the predetermined time period based on the movement state and causes the image sensor to generate the image based on the cumulative intensity accumulated over the determined predetermined time period.

[0008] According to an imaging device according to an aspect of the present disclosure, it is possible to suppress uneven brightness in an image that occurs regardless of the reflection characteristics of sub-terahertz waves from an object to be imaged.

[0009] FIG. 1 is a diagram for explaining the occurrence of uneven brightness in imaging using sub-terahertz waves. FIG. 2 is a schematic diagram showing the appearance of an imaging device according to an embodiment. FIG. 3 is a block diagram showing the configuration of the imaging device according to an embodiment. FIG. 4 is a schematic diagram of the imaging device according to an embodiment when viewed from above. FIG. 5 is a diagram showing an example of a circuit configuration of an image sensor according to an embodiment. FIG. 6 is a timing chart for explaining the operation of the image sensor shown in FIG. 5. FIG. 7 is a diagram showing another example of the circuit configuration of the image sensor according to an embodiment. FIG. 8 is a timing chart for explaining the operation of the image sensor shown in FIG. 7. FIG. 9 is a plan view showing an example of a retardation plate according to an embodiment. FIG. 10 is a cross-sectional view showing an example of an retardation plate according to an embodiment. FIG. 11 is a schematic diagram for explaining an example of movement of an example of a retardation plate according to an embodiment. FIG. 12 is a plan view showing another example of a retardation plate according to an embodiment. FIG. 13 is a schematic diagram for explaining an example of movement of another example of a retardation plate according to an embodiment. FIG. 14 is a plan view showing yet another example of a retardation plate according to an embodiment. FIG. 15 is a schematic diagram illustrating an example of movement of yet another example of a retarder according to an embodiment. FIG. 16 is a diagram illustrating an example of an image output by a detection unit according to an embodiment. FIG. 17 is a side view illustrating another example of the arrangement of the detection unit according to an embodiment. FIG. 18 is a top view illustrating yet another example of the arrangement of the detection unit according to an embodiment. FIG. 19 is a diagram illustrating an example of an image output by the detection unit shown in FIG. 17. FIG. 20 is a diagram illustrating an example of an image output by the detection unit shown in FIG. 18. FIG. 21 is a side view illustrating an example of a detection unit according to an embodiment, where the detection unit is configured with a pressure sensor. FIG. 22 is a top view illustrating an example of a detection unit according to an embodiment, where the detection unit is configured with a distance sensor. FIG. 23 is a side view illustrating an example of a detection unit according to an embodiment, where the detection unit is configured with a human presence sensor. FIG. 24 is a top view illustrating an example of a detection unit according to an embodiment, where the detection unit is configured with a speed sensor. FIG. 25 is a schematic diagram of an imaging device according to a first modification of an embodiment, as viewed from above. FIG. 26 is a schematic diagram illustrating an example of movement of an example of a retarder according to a first modification of an embodiment.FIG. 27 is a schematic diagram illustrating an example of movement of another example of a retarder according to Modification 1 of the embodiment. FIG. 28 is a schematic diagram illustrating an example of movement of yet another example of a retarder according to Modification 1 of the embodiment. FIG. 29 is a schematic diagram illustrating an image capture device according to Modification 2 of the embodiment when viewed from above. FIG. 30 is a schematic diagram illustrating an image capture device according to Modification 3 of the embodiment when viewed from above. FIG. 31 is a schematic diagram illustrating an example of movement of a light source according to Modification 3 of the embodiment. FIG. 32 is a schematic diagram illustrating another example of movement of a light source according to Modification 3 of the embodiment. FIG. 33 is a schematic diagram illustrating an image capture device according to Modification 4 of the embodiment when viewed from above. FIG. 34 is a diagram illustrating a change in the optical path length of a sub-terahertz wave due to movement of a person. FIG. 35A is a schematic diagram illustrating an example of an arrangement of pixels in a pixel array of an image sensor according to the embodiment. FIG. 35B is a schematic diagram illustrating an example of an imaging distance of a detector. FIG. 36 is a flowchart of operation example 1 of the image capture device according to the embodiment and each modification. Fig. 37 is a flowchart of operation example 2 of the imaging device according to the embodiment and each modification. Fig. 38 is a flowchart of operation example 3 of the imaging device according to the embodiment and each modification. Fig. 39 is a flowchart of operation example 4 of the imaging device according to the embodiment and each modification. Fig. 40 is a flowchart of operation example 5 of the imaging device according to the embodiment and each modification. Fig. 41 is a flowchart of operation example 6 of the imaging device according to the embodiment and each modification.

[0010] (How one aspect of the present disclosure was achieved) As described above, there is a need to suppress uneven brightness that occurs regardless of the reflection characteristics of sub-terahertz waves in an object to be photographed. The inventors have found that the following problems arise when photographing an object to be photographed using sub-terahertz waves.

[0011] When imaging using sub-terahertz waves, the sub-terahertz waves have a longer wavelength than visible light, and are therefore specularly reflected by an object to be imaged, such as a human body, making it difficult for an image sensor to efficiently receive the waves reflected by the object. Therefore, to facilitate reception of the waves reflected by the object by an image sensor, for example, the sub-terahertz waves are diffusely reflected by a reflector and then irradiated onto the object, thereby emitting the sub-terahertz waves toward the object from various angles. When such a method is used, sub-terahertz waves with different optical path lengths from the light source emitting the sub-terahertz waves to the object are incident on the object. As a result, the sub-terahertz waves incident on the object contain components with various phases.

[0012] FIG. 1 is a diagram illustrating the occurrence of uneven brightness in imaging using sub-terahertz waves. FIG. 1 illustrates an example of imaging a plate-shaped object B that uniformly reflects sub-terahertz waves. FIG. 1 (a) schematically illustrates an example of imaging a reflected wave reflected at a certain position P1 on the object B. FIG. 1 (b) schematically illustrates an example of imaging a reflected wave reflected at a position P2 different from position P1 on the object B. In FIG. 1, the reflected waves are indicated by arrows, and the reflected waves are imaged on an image sensor S. In FIG. 1, waveforms W1a, W1b, W2a, and W2b of the reflected waves are schematically illustrated on the arrows indicating the reflected waves.

[0013] As described above, the sub-terahertz waves incident on the object B contain components of various phases, and therefore the phase distribution of the reflected waves from the object B with respect to the reflection angle may vary depending on the reflection position. For example, as shown in FIG. 1A, the two components of the reflected waves reflected at position P1 have the same phase as shown by waveforms W1a and W1b. Therefore, the in-phase components interfere with each other when they are imaged on the image sensor S, resulting in a bright image. On the other hand, as shown in FIG. 1B, the two components of the reflected waves reflected at position P2 have different phases (e.g., a half-wavelength difference) as shown by waveforms W2a and W2b. Therefore, the out-of-phase components interfere with each other when they are imaged on the image sensor S, resulting in a dark image. Thus, even though the object B has uniform reflection characteristics, the resulting image may have uneven brightness.

[0014] As described above, the inventors have found that when imaging using sub-terahertz waves, the distribution of the phase of the reflected wave with respect to the reflection angle varies depending on the reflection position on the object being imaged, and therefore uneven brightness may occur in the resulting image. Note that in this specification, the "distribution of the phase of the reflected wave with respect to the reflection angle" may also be simply referred to as the "angular distribution of the phase of the reflected wave."

[0015] In view of the above, the present disclosure provides an imaging device that can suppress uneven brightness in an image that occurs regardless of the reflection characteristics of sub-terahertz waves from an object to be imaged.

[0016] As an overview of the present disclosure, an example of an imaging device according to the present disclosure is shown below.

[0017] An imaging device according to a first aspect of the present disclosure is an imaging device that uses sub-terahertz waves to capture an image of an object passing through a predetermined area, the imaging device comprising: a radiation unit that radiates the sub-terahertz waves toward the object; (i) an optical system that forms an image of the sub-terahertz waves radiated from the radiation unit reflected by the object; and (ii) a detector having an image sensor that is arranged in a plane and includes a plurality of pixels that receive the reflected waves imaged by the optical system, and that generates an image based on a cumulative intensity obtained by accumulating the intensity of the reflected waves received by each of the plurality of pixels over a predetermined time period and on the planar arrangement of the plurality of pixels, wherein the predetermined time period is λ / 1778 seconds or longer when the wavelength of the sub-terahertz waves is λ mm.

[0018] As a result, when the moving speed of the object to be photographed is 3.2 km / h (= 889 mm / s), which is the typical human movement speed, the object to be photographed moves over a given time period equal to or greater than half the wavelength of the sub-terahertz waves. As a result, the optical path length of the sub-terahertz waves emitted from the radiation unit, reflected by the object to be photographed, and incident on the image sensor changes by at least the wavelength of the sub-terahertz waves before and after the object moves over a given time period. Therefore, the image sensor can accumulate the intensity between the phase angular distribution patterns of two reflected waves that are shifted by the wavelength of the sub-terahertz waves over a given time period. As a result, the image sensor effectively accumulates the intensity of reflected waves with different phase angular distributions, thereby leveling out the brightness and darkness caused by the interference described above. Therefore, the imaging device according to this aspect can suppress the brightness and darkness unevenness in an image that occurs regardless of the reflection characteristics of the sub-terahertz waves from the object to be photographed, as described above.

[0019] Also, for example, an imaging device according to a second aspect of the present disclosure is an imaging device according to the first aspect, and includes a detection unit that detects the movement state of the object to be photographed as it passes through the specified area, and a control unit that controls the operation of the imaging device when the movement state is stationary.

[0020] As a result, when the optical path length of the sub-terahertz waves emitted from the radiation unit until they are reflected by the object and incident on the image sensor is unlikely to change within a predetermined time because the object is stationary, the operation of the image capturing device is controlled by the control unit. Therefore, even when the object is stationary, by appropriately controlling the operation of the image capturing device, uneven brightness in the image that occurs regardless of the reflection characteristics of the sub-terahertz waves from the object can be suppressed.

[0021] Also, for example, a photographing device according to a third aspect of the present disclosure is a photographing device according to the second aspect, in which the control unit determines the specified time based on the moving state, and causes the image sensor to generate the image based on the cumulative intensity accumulated over the determined specified time.

[0022] Furthermore, an imaging device according to a fourth aspect of the present disclosure is an imaging device that uses sub-terahertz waves to capture an image of an object passing through a predetermined area, and includes: an emitter that emits the sub-terahertz waves toward the object; (i) an optical system that forms an image of the sub-terahertz waves emitted from the emitter, reflected by the object; and (ii) a detector that includes an image sensor that is arranged in a plane and includes a plurality of pixels that receive the reflected waves formed by the optical system, and that generates an image based on a cumulative intensity obtained by accumulating the intensity of the reflected waves received by each of the plurality of pixels over a predetermined time period and the planar arrangement of the plurality of pixels; a detector that detects a movement state of the object as it passes through the predetermined area; and a control unit that controls the operation of the imaging device based on the movement state, wherein the control unit determines the predetermined time period based on the movement state, and causes the image sensor to generate the image based on the cumulative intensity accumulated over the determined predetermined time period.

[0023] As the object moves, the optical path length of the sub-terahertz waves emitted from the radiation unit, reflected by the object, and incident on the image sensor changes. The amount of change in the optical path length over a given time period during which the image sensor accumulates the intensity of the reflected waves is determined by the object's movement, such as its speed. Furthermore, the change in the optical path length also changes the angular distribution of the phases of the reflected waves received by the image sensor, so the angular distribution of the phases of the reflected waves received by the image sensor over a given time period is affected by the object's movement. The more easily the angular distribution of the phases of the reflected waves received by the image sensor over a given time period changes, the more the image sensor can accumulate the intensity of reflected waves with different phase angular distributions, thereby reducing image unevenness. Therefore, the likelihood of unevenness in the image generated by the image sensor is affected by the movement of the object. Therefore, by having the control unit determine the given time period based on the movement of the object, the amount of change in the optical path length over a given time period, which affects image unevenness, can be appropriately controlled. Therefore, it is possible to suppress uneven brightness in an image that occurs regardless of the reflection characteristics of the sub-terahertz wave from the object to be photographed.

[0024] Also, for example, an imaging device according to a fifth aspect of the present disclosure is an imaging device according to any one of the second to fourth aspects, wherein the detection unit detects the movement speed of the object to be photographed as it passes through the specified area as the movement state, and the control unit determines that the movement state of the object to be photographed is stationary when the movement speed is less than a specified speed.

[0025] This makes it possible to determine the movement state based on the movement speed of the object to be photographed, which is particularly susceptible to the optical path length from when the sub-terahertz waves are emitted from the radiation unit until they are reflected by the object and incident on the image sensor.

[0026] Also, for example, an imaging device according to a sixth aspect of the present disclosure is an imaging device according to any one of the second to fifth aspects, wherein the control unit causes the detector to stop generating the image when the moving state is stationary.

[0027] This prevents the generation of images that have large variations in brightness regardless of the reflection characteristics of the sub-terahertz waves from the object being photographed. Therefore, for example, when detecting a dangerous object using an image, an image that reduces the detection accuracy of the dangerous object is not output, and false detections can be suppressed.

[0028] Also, for example, an imaging device according to a seventh aspect of the present disclosure is an imaging device according to any one of the second to fifth aspects, and is provided with a display unit that displays the image, and when the moving state is stationary, the control unit stops the display of the image on the display unit or superimposes another image on the image.

[0029] This prevents the image generated by the detector from being displayed as is in cases where there is significant unevenness in the image that occurs regardless of the reflection characteristics of the sub-terahertz waves from the object being photographed, thereby preventing erroneous recognition when the user checks the image generated by the detector 30, for example.

[0030] Also, for example, an imaging device according to an eighth aspect of the present disclosure is an imaging device according to any one of the second to seventh aspects, and is equipped with an alarm that issues a warning, and the control unit causes the alarm to issue the warning when the moving state is stationary.

[0031] This means that even if the object being photographed is stationary and there is little or no change in the optical path length at a specified time, a warning can be issued to the object being photographed, prompting the object to change its moving state, such as by increasing its moving speed.

[0032] Furthermore, for example, an imaging device according to a ninth aspect of the present disclosure is an imaging device according to any one of the second to fifth aspects, and includes a phase modulation unit that changes the angular distribution of the phase of the reflected wave received by the image sensor during an exposure period when the image sensor generates the image, and the control unit causes the phase modulation unit to change the angular distribution of the phase when the moving state is stationary.

[0033] As a result, even if the change in the optical path length that affects the unevenness of the image is small or nonexistent over a given period of time because the object is stationary, the phase modulation unit can change the angular distribution of the phase of the reflected wave received by the image sensor, thereby suppressing unevenness of the image that occurs regardless of the reflection characteristics of the sub-terahertz wave at the object.

[0034] Furthermore, for example, an imaging device according to a tenth aspect of the present disclosure is the imaging device according to the ninth aspect, wherein the radiation unit includes a light source that emits the sub-terahertz waves and a reflector that diffusely reflects the sub-terahertz waves emitted from the light source, thereby radiating the sub-terahertz waves toward the imaging object, and the phase modulation unit is disposed between the light source and the reflector and includes a retardation plate that changes the phase of the transmitted sub-terahertz waves, and a retardation plate driving unit that moves the retardation plate under predetermined conditions.

[0035] This changes the phase of the sub-terahertz waves irradiated onto the object to be photographed, thereby effectively changing the angular distribution of the phase of the reflected waves received by the image sensor in a given time period.

[0036] In this specification, "diffuse reflection" means that sub-terahertz waves incident on a reflector at a single angle of incidence from a macroscopic perspective are reflected at multiple reflection angles by the uneven surface structure having multiple microscopic irregularities.

[0037] Furthermore, for example, an imaging device according to an eleventh aspect of the present disclosure is the imaging device according to the ninth aspect, wherein the phase modulation unit includes a retardation plate that is arranged on the optical path of the reflected wave between the predetermined area and the image sensor and that changes the phase of the transmitted reflected wave, and a retardation plate driving unit that moves the retardation plate under predetermined conditions.

[0038] This changes the phase of the reflected wave incident on the image sensor by the object being photographed, thereby effectively changing the angular distribution of the phase of the sub-terahertz wave received by the image sensor in a given period of time.

[0039] Furthermore, for example, an imaging device according to a twelfth aspect of the present disclosure is the imaging device according to the ninth aspect, wherein the phase modulation unit is at least a part of the optical system, and the optical system has, as the phase modulation unit, a mirror system that forms an image on the image sensor by reflecting the reflected wave, and the mirror system includes a plurality of mirrors, each of which changes the phase of the reflected wave reflected during an exposure period of the image sensor.

[0040] This makes it possible to integrate the phase modulation section and the detector, thereby changing the angular distribution of the phase of the reflected wave received by the image sensor.

[0041] Furthermore, for example, an imaging device according to a thirteenth aspect of the present disclosure is the imaging device according to the ninth aspect, wherein the radiation unit has a light source that emits the sub-terahertz waves and a reflector that diffusely reflects the sub-terahertz waves emitted from the light source, thereby radiating the sub-terahertz waves toward the imaging object, and the phase modulation unit includes a light source driving unit that moves the light source under predetermined conditions to change the angular distribution of the phase.

[0042] As a result, the optical path length changes when the light source moves, and therefore it is possible to effectively change the angular distribution of the phase of the reflected waves received by the image sensor in a given time period.

[0043] Furthermore, for example, an imaging device according to a fourteenth aspect of the present disclosure is the imaging device according to the ninth aspect, wherein the radiation unit has a light source that emits the sub-terahertz waves and a reflector that diffusely reflects the sub-terahertz waves emitted from the light source, thereby radiating the sub-terahertz waves toward the imaging object, and the phase modulation unit includes a reflector driving unit that moves the reflector under predetermined conditions to change the angular distribution of the phase.

[0044] As a result, the optical path length changes as the reflector moves, and it is therefore possible to effectively change the angular distribution of the phase of the reflected waves received by the image sensor in a given time period.

[0045] Furthermore, for example, an imaging device according to a fifteenth aspect of the present disclosure is an imaging device according to any one of the ninth to fourteenth aspects, wherein the phase modulation unit has a transport unit that moves the object to be imaged within the specified area by more than half the wavelength of the sub-terahertz wave during an exposure period of the image sensor, thereby changing the angular distribution of the phase.

[0046] This increases the amount of movement of the object being photographed during the exposure period, resulting in a larger change in the optical path length, which effectively changes the angular distribution of the phase of the reflected waves received by the image sensor during the exposure period.

[0047] Furthermore, for example, an imaging device according to a sixteenth aspect of the present disclosure is the imaging device according to any one of the first to fifteenth aspects, wherein the predetermined time is L / 27800 seconds or less when the shortest imaging distance of the detector is L mm.

[0048] This makes it easier for the positional shift of the pixel onto which the reflected wave from the object to be photographed is incident due to the movement of the object to be photographed over a given period of time to be less than half a pixel length, thereby suppressing blurring in the generated image.

[0049] Also, for example, an imaging device according to a seventeenth aspect of the present disclosure is an imaging device according to any one of the first to sixteenth aspects, wherein the specified time is the length of the exposure period in one frame of the image sensor.

[0050] This allows the image sensor to generate an image in one frame exposure period, thereby shortening the time required to generate one image.

[0051] Also, for example, an imaging device according to an eighteenth aspect of the present disclosure is the imaging device according to any one of the first to seventeenth aspects, wherein the predetermined time is λ / 254 seconds or longer.

[0052] This causes the optical path length to change more significantly before and after the movement of the object over a given time period, thereby further reducing uneven brightness in the image that occurs regardless of the reflection characteristics of the sub-terahertz waves from the object.

[0053] Furthermore, for example, an imaging device according to a 19th aspect of the present disclosure is an imaging device according to any one of the 1st to 18th aspects, wherein the frequency of the sub-terahertz waves is not less than 0.05 THz and not more than 2 THz, and the wavelength of the sub-terahertz waves is not less than 0.15 mm and not more than 6 mm.

[0054] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0055] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection configurations, steps, and step sequences shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components not recited in independent claims are described as optional components. Furthermore, the drawings are not necessarily strict illustrations. Therefore, for example, the scales and the like do not necessarily match between the drawings. Furthermore, in the drawings, substantially identical components are designated by the same reference numerals, and redundant descriptions may be omitted or simplified.

[0056] Furthermore, in this specification, terms indicating the relationship between elements, such as "parallel," terms indicating the shape of an element, such as "flat plate," terms indicating time, such as "immediately after," and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0057] (Embodiment) [Configuration] First, the configuration of an image capturing device according to the embodiment will be described.

[0058] 2 is a schematic diagram showing the appearance of the image capturing device 10 according to this embodiment, in which components other than the reflector 22 are omitted.

[0059] As shown in FIG. 2 , the image capturing device 10 is an image capturing device that, for example, irradiates sub-terahertz waves onto a person 100 as the person 100 passes through a capture space 102 on a passage 101 sandwiched between reflectors 22, and captures an image based on the reflected waves of the irradiated sub-terahertz waves by the person 100. That is, the image capturing device 10 uses sub-terahertz waves to capture an image of the person 100 passing through the capture space 102. The capture space 102 is, for example, a space on the passage 101 sandwiched between reflectors 22. The image capturing device 10 also captures an image of a dangerous object, such as a knife, that the person 100 is hiding under clothing, for example. The person 100 and the dangerous object, such as a knife, that the person 100 is hiding under clothing, are each an example of an object to be captured. The capture space 102 is also an example of a predetermined space. The imaging space 102 is not particularly limited as long as it is a space that can be irradiated with sub-terahertz waves and can capture an image of an object to be imaged in the imaging space 102 using the sub-terahertz waves.

[0060] In this specification, the term "sub-terahertz waves" refers to electromagnetic waves having a frequency of 0.05 THz to 2 THz and a wavelength of 0.15 mm to 6 mm. Sub-terahertz waves in this specification may also refer to electromagnetic waves having a frequency of 0.08 THz to 1 THz and a wavelength of 0.3 mm to 3.75 mm.

[0061] The following describes the details of each component of the imaging device 10. Fig. 3 is a block diagram showing the configuration of the imaging device 10 according to this embodiment. Fig. 4 is a schematic diagram of the imaging device 10 according to this embodiment as seen from above. Fig. 4 shows a person 100 passing through an imaging space 102. Fig. 4 also shows an example of the path of the sub-terahertz waves emitted from the light source 21, indicated by arrows.

[0062] The imaging device 10 includes an emitter 20 , a detector 30 , a controller 40 , a phase modulator 50 , a detector 60 , an alarm 70 , a transporter 80 , an image processor 90 , and a display 95 .

[0063] [Emitting Unit] The emitting unit 20 emits sub-terahertz waves toward the person 100. The emitting unit 20 has, for example, a light source 21 that emits sub-terahertz waves and a reflector 22 that diffusely reflects the sub-terahertz waves emitted from the light source 21. In this embodiment, the emitting unit 20 has two light sources 21 and two reflectors 22.

[0064] The light source 21 is a light source that emits sub-terahertz waves toward the reflector 22. Specifically, the light source 21 emits sub-terahertz waves toward the surface 22a of the reflector 22. As shown in Fig. 4 , the light source 21 emits sub-terahertz waves toward the reflector 22 so that at least a portion of the sub-terahertz waves emitted by the light source 21 is diffusely reflected by the reflector 22 one or more times. A portion of the sub-terahertz waves emitted by the light source 21 may be directly incident on the person 100. The light source 21 emits sub-terahertz waves of, for example, a substantially single wavelength. The light source 21 is a light source that emits coherent sub-terahertz waves, for example.

[0065] For example, one of the two light sources 21 emits sub-terahertz waves toward one of the two reflectors 22. The other of the two light sources 21 emits sub-terahertz waves toward the other of the two reflectors 22. One of the light sources 21 is located, for example, on the surface 22 a side of one of the reflectors 22 and on the first direction side of the one of the reflectors 22. The first direction is the direction in which the passage 101 extends and the person 100 moves in the imaging device 10. The first direction is, for example, parallel to the direction in which the reflector 22 extends when viewed from above (in other words, perpendicular to the thickness direction of the reflector 22). The other light source 21 is located, for example, on the surface 22 a side of the other reflector 22 and on the first direction side of the other reflector 22. The light source 21 and the reflector 22 are spaced apart, for example. Furthermore, the light source 21 is disposed, for example, at a position closer to the reflector 22 than the detector 30. The number of light sources 21 included in the emission unit 20 is not limited to two, and may be one, or three or more.

[0066] The light source 21 is, for example, a point light source that radiates sub-terahertz waves around the light source 21. Alternatively, the light source 21 may be a line light source that extends along the edge of the reflector 22 in the first direction and radiates sub-terahertz waves. The light source 21 is realized by, for example, a light source including a known sub-terahertz wave generating element.

[0067] The reflecting plates 22 cover the space above the passage 101 through which the person 100 passes, specifically the photographing space 102, from at least one of both sides of the passage 101. Specifically, covering at least one of both sides of the passage 101 means covering the space from both sides when the passage 101 is viewed from above, that is, from at least one of two directions perpendicular to the direction in which the passage 101 extends. In this embodiment, the reflecting plates 22 sandwich the photographing space 102 above the passage 101 through which the person 100 passes, from both sides of the passage 101. In other words, the reflecting plates 22 cover the photographing space 102 from both sides of the passage 101. The photographing space 102 is, for example, the space above the passage 101 that is sandwiched between the inner surfaces 22a of the two reflecting plates 22.

[0068] In this embodiment, two reflectors 22 are erected on the floor surface on both sides of the passage 101 and face each other. That is, the two reflectors 22 are arranged so as to sandwich the passage 101 when viewed from above. In the illustrated example, the two reflectors 22 are arranged so as to be parallel to each other. In the illustrated example, the two reflectors 22 are erected perpendicular to the floor surface on which the passage 101 is provided. Note that the imaging device 10 is only required to include at least one reflector 22, and may include, for example, only one of the two reflectors 22. For example, the imaging device 10 may further include a reflector other than the two illustrated reflectors 22, for example, a reflector located above the two reflectors 22. The reflector 22 may also be a tunnel-shaped reflector erected on the floor surface.

[0069] The two reflectors 22 are each plate-shaped. Each of the two reflectors 22 has a surface 22a, which is the front surface when viewed from the thickness direction of the reflector 22. The two reflectors 22 are arranged such that one surface 22a of each of the two reflectors 22 faces the other surface 22a of each of the two reflectors 22. In other words, the surface 22a is the surface of each of the reflectors 22 facing the imaging space 102. The shape of the reflectors 22 in a plan view is not particularly limited, but may be, for example, rectangular.

[0070] The reflector 22 diffusely reflects the sub-terahertz waves emitted from the light source 21. Specifically, the reflector 22 diffusely reflects the sub-terahertz waves incident from the imaging space 102 side at the surface 22a. Therefore, the surface 22a is a radiation surface for the sub-terahertz waves, and the reflector 22 functions as a surface light source.

[0071] The surface 22a of the reflector 22 is an uneven surface that diffusely reflects sub-terahertz waves. On the surface 22a, for example, the average length RSm of the roughness curve elements is equal to or greater than the wavelength of the sub-terahertz waves emitted from the light source 21. On the surface 22a, for example, the average length RSm of the roughness curve elements is equal to or greater than 0.15 mm, and may be equal to or greater than 0.3 mm. This allows the sub-terahertz waves to be efficiently diffusely reflected by the surface 22a.

[0072] The reflector 22 is made of, for example, a conductive material such as a metal or a conductive oxide at least in a portion including the surface 22 a. Note that the reflector 22 may have a protective member covering the surface 22 a. The protective member is made of, for example, a material such as a resin that transmits sub-terahertz waves.

[0073] 4, the sub-terahertz waves emitted from the light source 21 are diffusely reflected one or more times by at least one of the two reflectors 22 and then irradiated onto the person 100. In this way, by sandwiching the imaging space 102 between the reflectors 22 that diffusely reflect the sub-terahertz waves, the sub-terahertz waves that have entered the imaging space 102 tend to remain, and the sub-terahertz waves are irradiated onto the person 100 from various angles.

[0074] Furthermore, because the sub-terahertz waves emitted from light source 21 are diffusely reflected one or more times by reflector 22 before being emitted toward person 100, a distribution occurs in the optical path length of the sub-terahertz waves emitted from light source 21 until they are irradiated onto person 100. As a result, the phase of the sub-terahertz waves incident on person 100 is distributed due to the distribution of optical path length, and therefore an angular distribution of phases also occurs in the waves reflected by person 100. Therefore, when such a radiation unit 20 is used, as described with reference to FIG. 1 , brightness unevenness is likely to occur in an image captured from the reflected waves. With imaging device 10 according to this embodiment, such brightness unevenness in the image can be suppressed.

[0075] [Detector] The detector 30 generates an image based on the sub-terahertz waves emitted from the emitter 20 and reflected by the person 100. Generating an image is also referred to as "taking an image." In other words, the detector 30 of the imaging device 10 takes an image of the person 100 present in the imaging space 102. The detector 30 outputs the generated image to the image processing unit 90. The detector 30 has an image sensor 31 and an optical system 32. The detector 30 is placed in a position where it can receive the waves reflected by the person 100. The detector 30 is located, for example, on the first direction side of the reflector 22.

[0076] The image sensor 31 receives sub-terahertz waves reflected by the person 100 after being emitted from the light source 21 and diffusely reflected by the reflector 22. The image sensor 31 detects the intensity of the received reflected waves and generates an image based on the detected intensity. Specifically, the image sensor 31 includes a plurality of planarly arranged pixels that receive the reflected waves imaged by the optical system 32. The image sensor 31 generates an image based on a signal corresponding to a cumulative intensity obtained by accumulating the intensity of the reflected waves received by each of the plurality of pixels over a predetermined time period and the planar arrangement of the plurality of pixels. The predetermined time period is, for example, the length of an exposure period for one frame, but may also be the sum of the lengths of the exposure periods for multiple frames. The image sensor 31 converts, for example, an image of the reflected waves emitted from the person 100 into an electrical signal corresponding to the cumulative intensity. The image sensor 31 then generates an image based on the converted electrical signal. The image generated by the image sensor 31 is output to the image processing unit 90. The image sensor 31 also includes a control circuit 31a that controls each circuit of the image sensor 31. The detailed configuration of the image sensor 31 will be described later.

[0077] The optical system 32 forms an image of the sub-terahertz waves emitted from the emitting unit 20 and reflected by the person 100 on the image sensor 31. The optical system 32 includes, for example, at least one lens or mirror.

[0078] In the present embodiment, the image sensor 31 can be set to have a longer predetermined time for accumulating the intensity of the received reflected waves than conventional image sensors that generate images using sub-terahertz waves. For example, the predetermined time may be λ / 1778 seconds or longer, or λ / 254 seconds or longer, assuming that the wavelength of the sub-terahertz waves emitted by the radiation unit 20 is λ mm. This causes the angular distribution of the phases of the reflected waves received by the image sensor 31 to change by more than a predetermined amount during the predetermined time due to the movement of the person 100 within the imaging space 102, thereby reducing unevenness in brightness of the resulting image. Furthermore, from the viewpoint of reducing image blur, the predetermined time may be λ / 10 seconds or shorter, or λ / 30 seconds or shorter.

[0079] Here, a configuration of the image sensor 31 that can set a long predetermined time for accumulating the intensity of the received reflected waves will be described.

[0080] 5 is a diagram showing an example of the circuit configuration of the image sensor 31 according to the present embodiment. As shown in FIG. 5, the image sensor 31 includes a pixel array 910, an integration circuit 920, a multiplexer 930, an analog-to-digital converter 940, and a synthesis circuit 950.

[0081] The pixel array 910 includes a plurality of pixels 911 arranged in a plane. The pixel array 910 forms a wave receiving surface on which reflected waves are imaged. In the example shown in Fig. 5 , the plurality of pixels 911 are arranged in an array of 8 rows and 4 columns. In Fig. 5 , four pixels 911 are shown as representatives of the 32 pixels 911. Below, an example will be described in which the pixel array 910 includes 32 pixels 911, but the number of the plurality of pixels 911 is not particularly limited.

[0082] Each of the plurality of pixels 911 includes a conversion element such as a diode that converts the received sub-terahertz waves into an electric charge. Each of the plurality of pixels 911 generates an amount of electric charge according to the intensity of the received sub-terahertz waves (specifically, waves reflected by person 100). Note that the configuration of the plurality of pixels 911 is not limited to a configuration including a diode, and is not particularly limited as long as it includes a conversion element that can convert the received sub-terahertz waves into an electric signal.

[0083] The integration circuit 920 is a circuit that integrates inputs from the pixels 911 during an exposure period. The integration circuit 920 is connected to each of the multiple pixels 911 via a multiplexer 930. The integration circuit 920 receives input of charges (voltages) generated in the pixels 911.

[0084] The integration circuit 920 includes an operational amplifier 921 , a capacitance element 922 , and a switch 923 .

[0085] The inverting input terminal of the operational amplifier 921 is connected to the plurality of pixels 911 via the multiplexer 930. The non-inverting input terminal of the operational amplifier 921 is connected to a reference voltage Vref. The output of the operational amplifier 921 is connected to an analog-to-digital converter 940.

[0086] One end of the capacitance element 922 is connected between the inverting input terminal of the operational amplifier 921 and the multiplexer 930. The other end of the capacitance element 922 is connected between the output of the operational amplifier 921 and the analog-to-digital converter 940.

[0087] One end of the switch 923 is connected between the inverting input terminal of the operational amplifier 921 and the multiplexer 930. The other end of the switch 923 is connected between the output of the operational amplifier 921 and the analog-to-digital converter 940 via a resistor. The switch 923 is also connected in parallel with the capacitive element 922.

[0088] In the integration circuit 920, charges from the pixels 911 are accumulated in the capacitance element 922 (i.e., the voltage is integrated) while the switch 923 is off, and a voltage corresponding to the accumulated charges is output by the operational amplifier 921. Furthermore, when the switch 923 is turned on, the charges accumulated in the capacitance element 922 are discharged.

[0089] The multiplexer 930 selects the output of one pixel 911 from the outputs of the plurality of pixels 911 based on the selection signal, and outputs the selected output to the integration circuit 920 .

[0090] The analog-to-digital converter 940 converts the output from the integration circuit 920 into an analog-to-digital (AD) signal and outputs the converted signal to a subsequent circuit. The analog-to-digital converter 940 also outputs a signal that synchronizes the on / off operation of the switch 923 with the selection of the pixel 911 to be read.

[0091] The combining circuit 950 combines signals from each pixel 911 obtained over multiple frames. For example, the combining circuit 950 receives digital signals (pixel values) AD-converted by the analog-to-digital converter 940, stores them in a memory or the like, and integrates or averages the signals from each pixel 911 over multiple frames. Note that in the example shown in FIG. 5 , the combining circuit 950 is provided after the analog-to-digital converter 940, but it may also be provided before the analog-to-digital converter 940. For example, the combining circuit 950 may be a circuit that includes a multiplexer, a capacitive element, etc., and that holds and accumulates analog signals (voltages) from each pixel 911 over multiple frames before AD conversion. The analog signals accumulated by the combining circuit 950 may then be AD-converted.

[0092] 5, the operation of at least one of the pixel array 910, the integration circuit 920, the multiplexer 930, the analog-to-digital converter 940, and the synthesis circuit 950 is controlled by, for example, the above-mentioned control circuit 31a. The control circuit 31a may also have a function of modulating a clock that determines the exposure period (frame length) of the multiple pixels 911.

[0093] Next, an example of the operation of the image sensor 31 shown in Fig. 5 will be described. Fig. 6 is a timing chart for explaining the operation of the image sensor 31 shown in Fig. 5. In Fig. 6, the operation timing of signal readout of four pixels 911 out of the multiple pixels 911 is shown by rows indicated as pixel 1 to pixel 4.

[0094] 6 , first, a reset operation is performed during a reset period before integrating the signal of pixel 1. Specifically, the switch 923 is turned on to discharge the charge of the capacitance element 922, and the input of pixel 1 is selected by the multiplexer 930, thereby performing the reset operation.

[0095] Next, the switch 923 is turned off, starting the exposure period of pixel 1. During the period in which the switch 923 is off, charge from pixel 1 is accumulated in the capacitance element 922, and the input (voltage) of pixel 1 is integrated. In other words, the intensity of the reflected wave from person 100 is accumulated.

[0096] Next, during a readout period after the end of the exposure period of pixel 1, the integrated voltage is read out from the integration circuit 920. Specifically, the integrated voltage is input to an analog-to-digital converter 940, AD converted, and output to a subsequent circuit. As a result, a digital signal (pixel value) corresponding to the intensity of the reflected wave received by pixel 1, which has been integrated during the exposure period of pixel 1, is output.

[0097] After the readout period for pixel 1 ends, the reset period for pixel 2 begins, and pixel 2 also performs the same operations from reset to signal readout as pixel 1. Such operations are sequentially performed for pixel 3, pixel 4, and further for the other multiple pixels 911, whereby one frame period Tf ends and the pixel values ​​of the multiple pixels 911 are output.

[0098] In the image sensor 31 shown in FIG. 5 , one integration circuit 920 is connected to 32 pixels 911. Therefore, as can be seen from FIG. 6 , during the exposure period of one pixel 911, the exposure period of another pixel 911 cannot be set. As a result, the exposure period of one pixel 911 is Tf / 32 or less. Therefore, if the image sensor 31 does not include the combining circuit 950, an image is generated based on a signal corresponding to the accumulated intensity, where the intensity of the reflected wave has been accumulated for only a very short time. In contrast, if the image sensor 31 includes the combining circuit 950, an image can be generated by combining signals from the exposure periods of multiple frames, thereby lengthening the predetermined time for accumulating the intensity. In other words, the predetermined time for accumulating the intensity is the length of the exposure period multiplied by the number of frames for which signals are to be combined.

[0099] Next, a description will be given of another circuit configuration of the image sensor 31. Fig. 7 is a diagram showing another example of the circuit configuration of the image sensor 31 according to the present embodiment. In the following description, the description of the same components as those in Fig. 5 may be omitted or simplified.

[0100] As shown in FIG. 7, the image sensor 31 includes a pixel array 910, an integration circuit group 920A, an analog-to-digital converter 940, a multiplexer 960, and a multiplexer 970.

[0101] The integrating circuit group 920A includes a plurality of integrating circuits 920. In Fig. 7, the integrating circuit group 920A is shown with the plurality of integrating circuits 920 arranged vertically, but there are no particular limitations on the arrangement of the plurality of integrating circuits 920. The plurality of integrating circuits 920 do not have to be arranged in a row, and may be arranged discretely.

[0102] In the integration circuit group 920A, the multiple integration circuits 920 are connected to the multiple pixels 911 in a one-to-one relationship. That is, one integration circuit 920 is connected to one pixel 911. Therefore, in this example, there is no need for a multiplexer 930 between the pixel 911 and the integration circuit 920 as in the example shown in Fig. 5. Note that the multiple integration circuits 920 do not have to be connected to the multiple pixels 911 in a one-to-one relationship, and one integration circuit 920 may be connected to two or more pixels 911 via a multiplexer.

[0103] The multiplexer 960 is connected to the control lines of the switches 923 of the multiple integration circuits 920. The multiplexer 960 selects one integration circuit 920 from the multiple integration circuits 920 based on a selection signal, and outputs a signal to control the on / off of the switch 923.

[0104] The multiplexer 970 is connected to the outputs (output terminals of the operational amplifiers 921) of the plurality of integrating circuits 920. The multiplexer 970 selects the output of one of the plurality of integrating circuits 920 based on a selection signal, and outputs the selected output to the analog-to-digital converter 940.

[0105] 7, the operation of at least one of the pixel array 910, the integration circuit group 920A, the analog-to-digital converter 940, the multiplexer 960, and the multiplexer 970 is controlled by, for example, the above-described control circuit 31a. The control circuit 31a may also have a function of modulating a clock that determines the exposure period (frame length) of the multiple pixels 911.

[0106] Next, an example of the operation of the image sensor 31 shown in Fig. 7 will be described. Fig. 8 is a timing chart for explaining the operation of the image sensor 31 shown in Fig. 7. In Fig. 8, the operation timing of signal readout of four representative pixels 911 out of the plurality of pixels 911 is shown in rows indicated as pixel 1 to pixel 4.

[0107] 8, first, a reset operation before integrating the signal of pixel 1 is performed during a reset period. Here, the multiplexer 960 selects and turns on the switch 923 of the integration circuit 920 corresponding to pixel 1.

[0108] Next, the switch 923 of the integration circuit 920 corresponding to pixel 1 is turned off, and the exposure period of pixel 1 begins.

[0109] Next, during the exposure period of pixel 1, the reset operation of pixel 2 is performed during the reset period, and then the exposure period of pixel 2 begins. At this time, the switch 923 of the integration circuit 920 corresponding to pixel 2 is controlled by the selection of the multiplexer 960. In this way, the exposure period of pixel 1 and the reset and exposure periods of pixel 2 overlap.

[0110] Next, similarly to pixel 2, pixel 3, pixel 4, and other pixels 911 are reset during the exposure period of pixel 1, and the exposure periods thereof begin.

[0111] After the exposure periods of all the pixels 911 have started, the exposure period of pixel 1 ends, and during the readout period, the integration circuit 920 corresponding to pixel 1 is selected by the multiplexer 970, and the integrated voltage is read out from the integration circuit 920 corresponding to pixel 1. Specifically, the integrated voltage is input to the analog-to-digital converter 940, AD converted, and output to a subsequent circuit. As a result, a digital signal (pixel value) corresponding to the intensity of the reflected wave received by pixel 1, which has been integrated during the exposure period of pixel 1, is output. Here, the readout period of pixel 1 overlaps with the exposure periods of the pixels 911 other than pixel 1.

[0112] After the readout period for pixel 1 ends, a readout operation similar to that for pixel 1 is sequentially performed on the plurality of pixels 911 other than pixel 1. As a result, pixel values ​​for each of the plurality of pixels 911 are obtained, and an image is generated based on a signal corresponding to the accumulated intensity obtained by accumulating the intensity of the reflected waves received by each of the plurality of pixels 911 for a predetermined time period, and the planar arrangement of the plurality of pixels 911.

[0113] As shown in FIG. 8 , in this example, the image sensor 31 includes multiple integration circuits 920, allowing the exposure periods of the multiple pixels 911 to overlap. Therefore, the proportion of the exposure period in the frame period Tf can be increased for the multiple pixels 911. In this example, the predetermined time for the image sensor 31 to accumulate the intensity of the reflected wave is the length of the exposure period in one frame. Compared to the image sensor 31 shown in FIG. 5 , the image sensor 31 shown in FIG. 7 can ensure a longer exposure period, thereby lengthening the predetermined time for accumulating the intensity in one frame period Tf. This shortens the time required to generate an image. Furthermore, because the intensity of the reflected wave is accumulated over a continuous period, blurring of the resulting image can be reduced.

[0114] The image sensor 31 shown in FIG. 7 may further include the synthesis circuit 950 shown in FIG.

[0115] 3 and 4 , the control unit 40 is a control device that controls the operation of the image capturing device 10. For example, the control unit 40 controls the operation of at least one of the emitter 20, the detector 30, the phase modulator 50, the detector 60, the alarm 70, the carrier 80, and the display 95, as the control of the operation of the image capturing device 10. Furthermore, the control unit 40 controls the operation of the image capturing device 10, for example, based on the movement state of the person 100 detected by the detector 60 when passing through the image capturing space 102. Details of the control of the operation by the control unit 40 will be described later.

[0116] The control unit 40 includes, for example, a processor and a memory, and is realized by the processor executing a program stored in the memory.

[0117] [Phase Modulation Unit] The phase modulation unit 50 changes the angular distribution of the phase of the reflected wave received by the image sensor 31 during an exposure period when the image sensor 31 generates an image. In the present embodiment, the phase modulation unit 50 changes the phase of at least a portion of the component of the reflected wave after the sub-terahertz wave radiated from the radiation unit 20 is reflected by the person 100 before the reflected wave is incident on the image sensor 31, thereby changing the angular distribution of the phase of the reflected wave received by the image sensor 31. Note that the phase modulation unit 50 may change the phase of the sub-terahertz wave radiated to the person 100, thereby changing the angular distribution of the phase of the reflected wave received by the image sensor 31. An example in which the phase modulation unit 50 changes the phase of the sub-terahertz wave radiated to the person 100 will be described later.

[0118] The phase modulation section 50 operates, for example, under the control of the control section 40, but may operate constantly while the imaging device 10 is capturing an image.

[0119] The phase modulation section 50 includes a retardation plate 51 and a driving section 52. The driving section 52 is an example of a retardation plate driving section.

[0120] The phase difference plate 51 is a plate-like member that is transparent to sub-terahertz waves and changes the phase of the sub-terahertz waves that pass through it. In the phase difference plate 51, for example, the amount of change in the phase of the transmitted sub-terahertz waves varies depending on the position at which the waves pass through the phase difference plate 51. In this embodiment, the sub-terahertz waves that pass through the phase difference plate 51 are sub-terahertz waves that are radiated from the radiation unit 20 and reflected by the person 100. As the phase difference plate 51 is moved by the drive unit 52, the amount of change in the phase of the sub-terahertz waves that pass through the phase difference plate 51 changes depending on the position and time.

[0121] The retardation plate 51 transmits, for example, 50% or more of the sub-terahertz waves incident from the thickness direction of the retardation plate 51. The retardation plate 51 may transmit 80% or more, or 90% or more of the sub-terahertz waves incident from the thickness direction of the retardation plate 51.

[0122] The retardation plate 51 is disposed between the imaging space 102 and the image sensor 31 on the optical path of the reflected wave from the person 100 that enters the image sensor 31. In the example shown in FIG. 4 , the retardation plate 51 is disposed between the imaging space 102 and the optical system 32, but it may also be disposed between the optical system 32 and the image sensor 31.

[0123] A dielectric material such as a resin material that is transmissive to sub-terahertz waves is used as the material of the retardation plate 51. Examples of the resin material include polycarbonate resin, acrylic resin, epoxy resin, silicone resin, polystyrene resin, polyethylene resin, polypropylene resin, and fluorine resin.

[0124] The driver 52 is a driver that moves the retardation plate 51 under predetermined conditions to change the angular distribution of the phase of the reflected wave received by the image sensor 31. For example, the driver 52 moves the retardation plate 51 so as to change the amount of change in the phase of the sub-terahertz wave that passes through the retardation plate 51 during the exposure period of the image sensor 31. The driver 52 is composed of, for example, a driver such as a motor or an actuator, and power transmission members such as a belt, gears, pulleys, and connecting shafts for transmitting power to the retardation plate 51.

[0125] Here, the phase difference plate 51 will be described in detail with a specific example.

[0126] FIG. 9 is a plan view showing an example of a retardation plate 51 according to the present embodiment. FIG. 10 is a cross-sectional view showing an example of a retardation plate 51 according to the present embodiment. FIG. 10 shows a cross section taken along line X-X in FIG. 9. FIG. 11 is a schematic diagram for explaining an example of the movement of an example of a retardation plate 51 according to the present embodiment. In FIGS. 9 and 10, different patterns are applied to the first region 51a and the second region 51b in order to distinguish them from each other. This also applies to FIGS. 12 and 14, which will be described later.

[0127] 9 and 10 , the retardation plate 51 includes a first region 51a and a second region 51b. The first region 51a and the second region 51b each have transparency to sub-terahertz waves. The first region 51a and the second region 51b have different phase changes when the sub-terahertz waves pass through them. Specifically, the first region 51a and the second region 51b have different thicknesses, which results in different phase changes when the sub-terahertz waves pass through them. In this embodiment, the sub-terahertz waves passing through the first region 51a and the second region 51b are reflected waves from the person 100. In the illustrated example, the thickness of the first region 51a is smaller than the thickness of the second region 51b, but it may be larger.

[0128] For example, the amount of phase change of the sub-terahertz wave can be set to a desired amount by setting the thicknesses of the first region 51 a and the second region 51 b according to the refractive index of the material used in the retardation plate 51. Note that the amount of phase change of the sub-terahertz wave when the sub-terahertz wave passes through the first region 51 a may be different from that of the second region 51 b by changing the refractive index of the material used in the first region 51 a and the second region 51 b. In this case, the thicknesses of the first region 51 a and the second region 51 b may be the same.

[0129] The difference in the amount of change in the phase of the sub-terahertz waves when the sub-terahertz waves pass through the first region 51a and the second region 51b is, for example, between one-quarter and three-quarters of the wavelength of the sub-terahertz waves used in the imaging device 10 (i.e., between 90° and 270°), or may be one-half of the wavelength of the sub-terahertz waves used in the imaging device 10 (i.e., 180°). This effectively changes the angular distribution of the phase of the reflected waves received by the image sensor 31, thereby suppressing uneven brightness due to interference. Note that the retardation plate 51 may further include another region in which the amount of change in the phase of the sub-terahertz waves when the sub-terahertz waves pass through is different from that of the first region 51a and the second region 51b.

[0130] As shown in FIG. 11 , the retarder 51 is rotated by, for example, the driver 52 around a rotation axis R1 that passes through the center 32c of the optical system 32 and has an inclination angle of −10° to 10° with respect to a direction parallel to the incident direction D1 of the reflected wave into the optical system 32. Here, the rotation axis R1 is an imaginary axis and does not necessarily mean that a substantial axis exists. The same applies to the rotation axes described below. The incident direction D1 of the reflected wave into the optical system 32 is, for example, a direction connecting the focal point of the optical system 32 and the center 32c of the optical system 32 (in other words, the optical axis direction of the optical system 32). For example, the retarder 51 is moved by using a motor with a pulley as the driver 52 and connecting the pulley and the retarder 51 with a belt. The retarder 51 rotates, for example, one or more revolutions during the exposure period of the image sensor 31. The rotation speed of the retarder 51 is not particularly limited as long as it can be rotated by the driver 52. 9 and 11 , the rotation axis R1 is, for example, parallel to the thickness direction of the retarder 51 and passes through the center 51c of the retarder 51 in a planar view. By arranging the retarder 51 so that it rotates around the rotation axis R1 that passes through the center 32c of the optical system 32, the retarder 51 to be driven can be arranged compactly. The rotation axis R1 does not have to pass through the center 51c of the retarder 51. The rotation axis R1 may also pass through a position other than the center 32c of the optical system 32. The rotation axis R1 does not have to be parallel to the thickness direction of the retarder 51, and may be inclined with respect to the thickness direction (for example, at an angle of −10° or more and 10° or less).

[0131] As shown in FIG. 9 , the retarder 51 is, for example, circular in plan view, but the planar shape of the retarder 51 is not particularly limited. In this specification, "planar view" refers to the case where the retarder 51 is viewed along the thickness direction of the retarder 51. The first region 51a and the second region 51b are arranged to be aligned along the rotation direction of the retarder 51 in plan view. In this example, the first region 51a and the second region 51b are each, for example, fan-shaped with the center 51c of the retarder 51 as an apex, and the first region 51a and the second region 51b are aligned along the arc direction. Note that in the example shown in FIG. 9 , the retarder 51 includes one first region 51a and one second region 51b, but may include multiple first regions 51a and multiple second regions 51b. In this case, the first regions 51a and the second regions 51b are alternately aligned along the rotation direction of the retarder 51, for example.

[0132] In addition, in a plan view, the area of ​​the first region 51 a is larger than the area of ​​the second region 51 b. When there are multiple first regions 51 a and multiple second regions 51 b, the areas of the first region 51 a and the second region 51 b are each the total areas of the multiple regions.

[0133] The first region 51a includes, in a plan view, a symmetric region 51a1, where the first region 51a exists at a point-symmetric position across the rotation axis R1, and an asymmetric region 51a2, where the second region 51b exists at a point-symmetric position across the rotation axis R1. As a result, components of a reflected wave passing through two points that are point-symmetric with respect to the rotation axis R1 both pass through the symmetric region 51a1 at a given time, and the phases of the components of the reflected wave passing through the two points change in the same way. On the other hand, components of a reflected wave passing through the two points pass through the asymmetric region 51a2 and the second region 51b at a different time due to the rotation of the retarder 51, resulting in different amounts of phase change of the components of the reflected wave passing through the two points. Therefore, by rotating the retarder 51, the angular distribution of the phase of the reflected wave received by the image sensor 31 effectively changes during the exposure period of the image sensor 31, making it easier to suppress uneven brightness in the image.

[0134] In a plan view, the area of ​​the asymmetric region 51a2 is, for example, 1 / 8 to 3 / 8, inclusive, and may be 1 / 4, of the area of ​​the retardation plate 51. In addition, in a plan view, the area of ​​the symmetric region 51a1 is, for example, 3 / 8 to 5 / 8, inclusive, and may be 1 / 2, of the area of ​​the retardation plate 51. This reduces the difference between the time when the amount of change in phase of the components of the reflected wave passing through the above two points is the same and the time when they are different, and makes it possible to more effectively change the angular distribution of the phase of the reflected wave received by the image sensor 31.

[0135] The phase difference plate 51 is not particularly limited as long as it is a member that can change the phase of the transmitted sub-terahertz wave. Another example of the phase difference plate 51 will now be described. Fig. 12 is a plan view showing another example of the phase difference plate 51 according to the present embodiment. Fig. 13 is a schematic diagram for explaining an example of the movement of another example of the phase difference plate 51 according to the present embodiment.

[0136] 12, in another example, the retardation film 51 includes a plurality of first regions 51a and a plurality of second regions 51b. Note that in this example, the retardation film 51 may include only one first region 51a and one second region 51b.

[0137] As shown in FIG. 13 , the retarder 51 is rotated by, for example, a drive unit 52 around a rotation axis R2 that does not pass through the optical system 32 and has an inclination angle of −10° to 10° with respect to a direction parallel to the incident direction D1 of the reflected wave to the optical system 32. The retarder 51 rotates, for example, one or more revolutions during the exposure period of the image sensor 31. The rotation speed of the retarder 51 is not particularly limited as long as it is a speed at which the retarder 51 can be rotated by the drive unit 52. Also, as shown in FIGS. 12 and 13 , the rotation axis R2 is, for example, parallel to the thickness direction of the retarder 51 and passes through the center 51c of the retarder 51 in a planar view. By arranging the retarder 51 so that it rotates around the rotation axis R2 that does not pass through the optical system 32, the retarder 51 can be rotated simply by attaching a shaft to the retarder 51, thereby simplifying the structure. The rotation axis R2 does not have to pass through the center 51c of the retarder 51. Furthermore, the rotation axis R2 does not have to be parallel to the thickness direction of the retardation film 51, and may be inclined with respect to the thickness direction (for example, at an angle of −10° or more and 10° or less).

[0138] As shown in FIG. 12 , in this example, the retarder 51 is, for example, circular in plan view, but the planar shape of the retarder 51 is not particularly limited. As shown in FIG. 12 , in plan view, the first regions 51a and the second regions 51b are alternately arranged along the rotation direction of the retarder 51. In this example, the multiple first regions 51a and the multiple second regions 51b are, for example, sector-shaped with the center 51c of the retarder 51 as the apex, and the first regions 51a and the second regions 51b are alternately arranged along the arc direction. In plan view, the areas of the multiple first regions 51a and the multiple second regions 51b are, for example, equal to each other. Note that, in plan view, at least one of the areas of the multiple first regions 51a and the multiple second regions 51b may be different.

[0139] Next, a description will be given of yet another example of the retarder 51. Fig. 14 is a plan view showing yet another example of the retarder 51 according to the present embodiment. Fig. 15 is a schematic diagram for explaining an example of the movement of yet another example of the retarder 51 according to the present embodiment.

[0140] 14 , in yet another example, the retardation film 51 includes a plurality of first regions 51 a and a plurality of second regions 51 b. The first regions 51 a and the second regions 51 b are arranged to be aligned in a predetermined direction. Note that in this example, the number of at least one of the first regions 51 a and the second regions 51 b included in the retardation film 51 may be one.

[0141] 15 , the retardation plate 51 is moved by, for example, a driver 52 in a direction orthogonal to the incident direction D1 of the reflected wave to the optical system 32 and in a direction orthogonal to the thickness direction of the retardation plate 51. The retardation plate 51 is moved back and forth at a predetermined frequency along the moving direction of the retardation plate 51. The predetermined frequency is, for example, a frequency whose period is equal to or shorter than the exposure period of the image sensor 31. Furthermore, there is no particular upper limit to the predetermined frequency as long as the frequency allows for back and forth movement by the driver 52.

[0142] As shown in FIG. 14 , in this example, the retarder 51 has, for example, an oval shape having a major axis and a minor axis in a planar view; however, the planar view shape of the retarder 51 is not particularly limited. The planar view shape of the retarder 51 may be an ellipse or a rectangle having a major axis and a minor axis. The planar view shape of the retarder 51 may also be a circle, a square, a polygon, or the like. As shown in FIG. 14 , in a planar view, the first regions 51 a and the second regions 51 b are alternately arranged along the movement direction of the retarder 51. Therefore, in this example, the plurality of first regions 51 a and the plurality of second regions 51 b are each striped. The movement direction is, for example, parallel to the major axis direction of the retarder 51. The retarder 51 is moved along the movement direction so that the first regions 51 a and the second regions 51 b are interchanged at least at a predetermined position.

[0143] As described above, in this embodiment, the amount of change in the phase of the reflected wave passing through the phase difference plate 51 can be changed simply by rotating or reciprocating the phase difference plate 51 described with reference to Figures 9 to 15.

[0144] 3 and 4 again, the detection unit 60 is a sensor for detecting the movement state and the like of the person 100 in the imaging space 102. The detection unit 60 detects, for example, the movement state of the person 100, such as the movement speed of the person 100 when passing through the imaging space 102. The detection unit 60 may detect at least one of the presence, position, and posture of the person 100 in the imaging space 102. The detection unit 60 outputs the detection result to the control unit 40, for example. In the example shown in FIG. 4 , the detection unit 60 is arranged on the first direction side of the imaging space 102, but may be arranged anywhere as long as the movement state of the person 100 in the imaging space 102 can be detected.

[0145] The detection unit 60 is, for example, a visible light camera that captures moving images. The detection unit 60 may also have a distance measurement function. For example, the detection unit 60 detects at least one of the movement speed, presence, position, and posture of the person 100 in the imaging space 102 by capturing moving images. The detection unit 60 outputs information about the movement state as a detection result. The detection unit 60 may output the moving images to the control unit 40 as the detection result, or may determine at least one of the movement speed, presence, position, and posture of the person 100 from the moving images and output the determined result to the control unit 40 as the detection result. The detection unit 60 may also be another sensor, such as a human presence sensor or a speed sensor. Although the image capture device 10 includes one detection unit 60 in the example shown in FIG. 4 , the image capture device 10 may also include multiple detection units 60.

[0146] It should be noted that the image capturing device 10 does not necessarily have to include the detection unit 60. The control unit 40 may acquire detection results relating to the movement state of the person 100 from an external device such as a surveillance camera.

[0147] Here, the details of detection of the movement state by the detection unit 60 will be described. In the image capture device 10, the control unit 40 determines whether the movement state of the person 100 is stationary, for example, based on the movement state of the person 100 detected by the detection unit 60. In this specification, "stationary" refers not only to a state in which the person 100 is completely stationary, but also to a state in which the amount of movement of the person 100 per unit time is small, such as when the movement speed of the person 100 is less than a predetermined value (for example, less than the movement speed of an average person). In other words, in this specification, "stationary" refers to a state in which the amount of movement of the person 100 in a predetermined time is less than a predetermined amount.

[0148] First, a case will be described in which the detection unit 60 is a visible light camera placed at the position shown in Fig. 4. Fig. 16 is a diagram showing an example of an image output by the detection unit 60. Fig. 16 shows an example of an Nth frame image and an N+Mth frame image captured by the detection unit 60, which is a visible light camera. The number M is, for example, 1, but may be a natural number of 2 or greater. Note that in Fig. 16, the person 100 in the Nth frame image is shown with a dashed line, but in the actual image, only the person 100 shown with a solid line is captured. The same applies to Figs. 19 and 20, which will be described later.

[0149] As shown in FIG. 16 , the detection unit 60 outputs an image as information indicating the detected movement state. The control unit 40 determines, for example, whether the movement state is stationary based on the movement state detected by the detection unit 60. In the example shown in FIG. 16 , the control unit 40 determines whether the movement state of the person 100 is stationary based on a change in the size of the person 100 in the image. The control unit 40 compares the size of the person 100 in the Nth frame image with the size of the person 100 in the N+Mth frame image. The control unit 40 determines that the movement state is stationary if the change in size of the person 100 is less than a predetermined value, and determines that the movement state is moving rather than stationary if the change in size is equal to or greater than the predetermined value. The size of the person 100 is, for example, the height of the person 100 from the optical axis of the optical system 32, but may also be other indicators such as the overall height or width of the person 100. As an example of a specific criterion for determining the moving state, if the frame rate of the detection unit 60 is 20 fps, the shooting position (distance from the detection unit 60 to the person 100) is 4000 mm, the height of the person 100 from the optical axis is 400 mm, and the value M = 1, the control unit 40 will determine that the moving state is stationary if the change in size of the person 100 between the Nth frame image and the N+Mth frame image is less than 1.1%.

[0150] Next, a case will be described in which the detection unit 60, which is a visible light camera, captures an image of the person 100 from a direction perpendicular to the first direction. Fig. 17 is a side view illustrating another example of the arrangement of the detection unit 60. Fig. 18 is a top view illustrating yet another example of the arrangement of the detection unit 60. Note that Figs. 17 and 18 omit illustration of the configuration of the imaging device 10 other than the reflector 22 and the detection unit 60.

[0151] In the example shown in Fig. 17 , the detection unit 60 is disposed above the reflector 22. In the example shown in Fig. 18 , the detection unit 60 is disposed to the side of the reflector 22. In the example shown in Fig. 18 , the reflector 22 is formed using a material such as a transparent conductive oxide that transmits visible light while reflecting sub-terahertz waves. By disposing the detection unit 60 at a position as shown in Fig. 17 or 18 , the detection unit 60 can capture an image of the person 100 from a direction perpendicular to the first direction.

[0152] Fig. 19 is a diagram showing an example of an image output by the detection unit 60 shown in Fig. 17. Fig. 20 is a diagram showing an example of an image output by the detection unit 60 shown in Fig. 18. Figs. 19 and 20 show examples of an Nth frame image and an N+Mth frame image captured by the detection unit 60, which is a visible light camera. Fig. 19 shows an image of the person 100 captured by the detection unit 60 at the position shown in Fig. 17. Fig. 20 shows an image of the person 100 captured by the detection unit 60 at the position shown in Fig. 18.

[0153] In the examples shown in FIGS. 19 and 20 , the control unit 40 determines whether the movement state of the person 100 is stationary based on a change in the position of the person 100 in the images. The control unit 40 compares the position of the person 100 in the Nth frame image with the position of the person 100 in the (N+M)th frame image. The control unit 40 determines that the movement state is stationary if the change in the position of the person 100 is less than a predetermined value, and determines that the movement state is moving rather than stationary if the change is equal to or greater than the predetermined value. As a specific example of criteria for determining the movement state, when the frame rate of the detection unit 60 is 20 fps and the value M=1, the control unit 40 determines that the movement state is stationary if the change in the position of the person 100 between the Nth frame image and the (N+M)th frame image is less than 44 mm.

[0154] In the above description, the control unit 40 determines the movement state of a person from two frames of images output by the detection unit 60, but the movement state may be determined from three or more frames of images.

[0155] Next, a case where the detection unit 60 is not a visible light camera but is configured with other sensors will be described.

[0156] First, a case where the detection unit is configured as a pressure sensor will be described. Fig. 21 is a side view showing an example where the detection unit 60a according to this embodiment is configured as a pressure sensor. Note that Fig. 21 omits the illustration of the components of the imaging device 10 other than the reflector 22 and the detection unit 60a.

[0157] The imaging device 10 may include a detection unit 60a instead of the detection unit 60. As shown in FIG. 21 , the detection unit 60a is composed of multiple pressure sensors using piezoelectric elements or the like. The multiple pressure sensors are installed, for example, on the floor of the passageway 101 and lined up along the first direction. The detection unit 60a outputs the detection results of each of the multiple pressure sensors at a predetermined measurement interval. Furthermore, in the detection unit 60a, a high pressure is detected by the pressure sensor where the center of gravity of the person 100 is located, and the position of the person 100 is determined based on the position of the pressure sensor that detected the high pressure. Therefore, the detection unit 60a can detect the movement state of the person 100 by each of the multiple pressure sensors detecting pressure at a predetermined measurement interval. Note that the detection unit 60a may be installed in the transport unit 80.

[0158] The control unit 40 determines whether the movement state of the person 100 is stationary, for example, based on the change in position of the person 100 in the detection results of the detection unit 60a. The control unit 40 compares the detection results of the Nth measurement by the detection unit 60a with the detection results of the N+Mth measurement by the detection unit 60a. The number M is, for example, 1, but may be a natural number equal to or greater than 2. The control unit 40 determines that the movement state is stationary if the change in position of the person 100 is less than a predetermined value, and determines that the movement state is moving rather than stationary if the change is equal to or greater than the predetermined value. As a specific example of criteria for determining the movement state, when the measurement interval of the detection unit 60a is 0.1 seconds and the number M = 1, the control unit 40 determines that the movement state is stationary if the change in position of the person 100 between the Nth measurement and the N+Mth measurement is less than 8.9 mm.

[0159] Next, a case where the detection unit is configured as a distance sensor (distance measuring device) will be described. Fig. 22 is a top view showing an example where the detection unit 60b according to this embodiment is configured as a distance sensor. Note that Fig. 22 omits the illustration of the components of the imaging device 10 other than the reflector 22 and the detection unit 60b.

[0160] The imaging device 10 may include a detection unit 60b instead of the detection unit 60. As shown in FIG. 22 , the detection unit 60b is configured with a distance sensor that measures the distance between the detection unit 60b and the person 100. The detection unit 60b is provided, for example, on the first direction side of the reflector 22 (i.e., the first direction side of the imaging space 102). The detection unit 60b outputs the detection result of the distance sensor at a predetermined measurement interval. Furthermore, the detection unit 60b determines the position of the person 100 based on the distance between the detection unit 60b and the person 100. Therefore, the detection unit 60b can detect the movement state of the person 100 by having the distance sensor detect the distance between the detection unit 60b and the person 100 at a predetermined measurement interval.

[0161] The control unit 40 determines whether the movement state of the person 100 is stationary based on the change in position of the person 100 in the detection results of the detection unit 60b. The control unit 40 compares the detection results of the Nth measurement by the detection unit 60b with the detection results of the (N+M)th measurement by the detection unit 60b. The value M is, for example, 1, but may be a natural number equal to or greater than 2. The control unit 40 determines that the movement state is stationary if the change in position of the person 100 is less than a predetermined value, and determines that the movement state is moving rather than stationary if the change is equal to or greater than the predetermined value. As a specific example of criteria for determining the movement state, when the measurement interval of the detection unit 60b is 0.1 seconds and the value M = 1, the control unit 40 determines that the movement state is stationary if the change in position of the person 100 between the detection results of the Nth measurement and the (N+M)th measurement is less than 8.9 mm.

[0162] Next, a case where the detection unit is configured as a human presence sensor will be described. Fig. 23 is a side view showing an example where the detection unit 60c according to this embodiment is configured as a human presence sensor. Note that Fig. 23 does not show the components of the imaging device 10 other than the reflector 22 and the detection unit 60c.

[0163] The imaging device 10 may include a detection unit 60c instead of the detection unit 60. As shown in FIG. 23 , the detection unit 60c is composed of multiple motion sensors that use infrared rays or the like to detect the presence or absence of a person 100. The multiple motion sensors are, for example, lined up along a first direction above the reflector 22 (i.e., above the imaging space 102). Each of the multiple motion sensors detects the presence or absence of a person 100 within a predetermined range below the sensor. The detection unit 60c outputs the detection results of each of the multiple motion sensors at predetermined measurement intervals. Furthermore, the detection unit 60c determines the position of the person 100 based on the position of the motion sensor that detected the presence of the person 100. Therefore, the detection unit 60c can detect the movement state of the person 100 by each of the multiple motion sensors detecting the presence or absence of the person 100 at predetermined measurement intervals.

[0164] The control unit 40 determines whether the movement state of the person 100 is stationary based on the change in position of the person 100 in the detection results of the detection unit 60c. The control unit 40 compares the detection results of the Nth measurement by the detection unit 60c with the detection results of the N+Mth measurement by the detection unit 60c. The value M is, for example, 1, but may be a natural number equal to or greater than 2. The control unit 40 determines that the movement state is stationary if the change in position of the person 100 is less than a predetermined value, and determines that the movement state is moving rather than stationary if the change is equal to or greater than the predetermined value. As a specific example of criteria for determining the movement state, when the measurement interval of the detection unit 60c is 0.1 seconds and the value M = 1, the control unit 40 determines that the movement state is stationary if the change in position of the person 100 between the detection results of the Nth measurement and the N+Mth measurement is less than 8.9 mm.

[0165] In the above, the control unit 40 determines the movement state of a person from two detection results output by any of the detection units 60a to 60c, but the movement state may also be determined from three or more detection results.

[0166] Next, a case where the detection unit is configured as a speed sensor (speed measurement device) will be described. Fig. 24 is a top view showing an example where the detection unit 60d according to this embodiment is configured as a speed sensor. Note that Fig. 24 omits the illustration of the components of the imaging device 10 other than the reflector 22 and the detection unit 60d.

[0167] The image capturing device 10 may include a detection unit 60d instead of the detection unit 60. As shown in FIG. 24 , the detection unit 60d is configured with a speed sensor that measures the movement speed of the person 100. The detection unit 60d is provided, for example, on the first direction side of the reflector 22 (i.e., the first direction side of the image capturing space 102). The detection unit 60d outputs a detection result of the movement speed of the person 100 moving in the image capturing space 102. In the detection unit 60d, the speed sensor detects the movement speed of the person 100 moving in the image capturing space 102, thereby detecting the movement state of the person 100.

[0168] The control unit 40 determines whether the movement state of the person 100 is stationary or not based on the movement speed of the person 100 detected by the detection unit 60d. The control unit 40 determines that the movement state of the person 100 is stationary if the movement speed of the person 100 is less than a predetermined value, and determines that the movement state is moving rather than stationary if the movement speed is equal to or greater than the predetermined value. As a specific example of criteria for determining the movement state, the control unit 40 determines that the movement state of the person 100 is stationary if the movement speed of the person 100 is less than 889 mm per second. Furthermore, even when any of the detection units 60 to 60c is used, the control unit 40 may calculate the movement speed of the person 100 from the detection results of the detection units 60 to 60c, and determine whether the movement state of the person 100 is stationary or not based on the calculated movement speed of the person 100.

[0169] The specific example of the criteria for determining the moving state described above is a criterion based on the detection result when the person 100 is moving at less than 3.2 km / h (=889 mm / s), which is the typical moving speed of a person. This determination criterion is merely an example and is not limited to this. The moving speed of the person 100 that serves as the determination criterion is, for example, (B×λ / 2) / T mm / s, where λ mm is the wavelength of the sub-terahertz waves emitted by the emitter 20 and T seconds is the length of the exposure period of the image sensor 31. The constant B is, for example, a value between 1 and 15, or between 7 and 15, and is set depending on the specifications of the emitter 20 and the detector 30.

[0170] Furthermore, when the control unit 40 determines that the moving state is moving based on the moving state detected by any of the detection units 60 to 60d, it may further determine the degree of movement. For example, a predetermined threshold value different from the criterion for determining whether or not the vehicle is stationary is set, and the control unit 40 determines whether the amount of movement during movement is small or large depending on whether the value based on the moving state is equal to or smaller than the predetermined threshold value. Note that the classification of the degree of movement during movement is not limited to two levels, and may be classified into three or more levels of movement.

[0171] [Other Configurations] With reference again to FIGS. 3 and 4, other components of the image capturing device 10 will be described.

[0172] The alarm 70 issues a warning to the person 100. The warning is issued, for example, to notify the person 100 that the person 100 is stopped, such as moving slowly or stationary. The alarm 70 has, for example, at least one of a light source, a speaker, and a display, and issues the warning using at least one of light, sound, and an image. The alarm 70 may issue the warning simply by emitting light or sound, or may issue the warning by displaying information indicating that the person 100 is stopped, or information urging the person 100 to change their movement state, such as by increasing their movement speed. Note that the image capture device 10 does not necessarily have to be equipped with the alarm 70.

[0173] The transport unit 80 is a transport device that moves the person 100 within the imaging space 102 under predetermined conditions. The transport unit 80 may operate constantly, or may be controlled to operate as needed. The phase modulation unit 50 may have the transport unit 80 in addition to or instead of the retardation plate 51 and the drive unit 52. Note that the imaging device 10 does not necessarily have to have the transport unit 80.

[0174] For example, the transport unit 80 moves by at least half the wavelength of the sub-terahertz waves emitted by the light source 21 during the exposure period of the image sensor 31, thereby changing the angular distribution of the phase of the sub-terahertz waves received by the image sensor 31. For example, when the wavelength of the sub-terahertz waves emitted by the light source 21 is λ mm and the exposure period of the image sensor 31 is T seconds, the speed at which the transport unit 80 moves the person 100 is, for example, (λ / 2) / T mm per second or more, and may also be (7×λ / 2) / T mm per second or more. Furthermore, from the viewpoint of safety, the speed at which the transport unit 80 moves the person 100 may be (30×λ / 2) / T mm per second or less.

[0175] When the image processing unit 90 receives an image from the detector 30, it 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, for example.

[0176] The image processing performed by the image processing unit 90 may be, for example, a process of determining whether an object having predetermined characteristics (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) if it is determined that an object having the predetermined characteristics is included. The image processing unit 90 includes, for example, a processor and a memory, and is realized by the processor executing a program stored in the memory. The control unit 40 and the image processing unit 90 may share the processor and memory.

[0177] The imaging device 10 does not necessarily have to include the image processing unit 90, and the detector 30 may output the image to an external image processing device. Also, the function of the image processing unit 90 may be provided in the detector 30.

[0178] The display unit 95 displays an image under the control of the control unit 40. For example, it displays an image generated by the detector 30. This allows the user to check the image. The display unit 95 may also display an image other than the image generated by the detector 30, such as an image showing the result of image processing by the image processing unit 90. The display unit 95 is realized by a display panel such as a liquid crystal panel or an organic EL panel.

[0179] [Modification 1] Next, a description will be given of Modification 1 of the embodiment. In the following description, differences from the embodiment will be mainly described, and descriptions of commonalities will be omitted or simplified.

[0180] 25 is a schematic diagram of an imaging device 110 according to this modification, viewed from above. As shown in FIG. 25 , the imaging device 110 differs from the imaging device 10 according to the embodiment in that the retardation plate 51 is disposed between the light source 21 and the reflector 22, rather than being disposed on the optical path of the reflected wave incident on the optical system 32. In this modification, the retardation plate 51 transmits the sub-terahertz waves emitted from the light source 21 and changes the phase of the transmitted sub-terahertz waves. In other words, in this modification, the phase modulation unit 50 changes the phase of at least a portion of the components of the sub-terahertz waves radiated to the person 100, thereby changing the angular distribution of the phase of the reflected wave received by the image sensor 31.

[0181] The retardation plate 51 can have, for example, the various shapes described above using FIGS. 9, 12, and 14. Here, the movement of the retardation plate 51 will be described. FIG. 26 is a schematic diagram for explaining an example of the movement of one example of the retardation plate 51 according to this modification. FIG. 27 is a schematic diagram for explaining an example of the movement of another example of the retardation plate 51 according to this modification. FIG. 28 is a schematic diagram for explaining an example of the movement of yet another example of the retardation plate 51 according to this modification.

[0182] For example, when the example of the retarder 51 shown in FIGS. 9 and 10 is used, the retarder 51 is moved as shown in FIG. 26 . Specifically, the retarder 51 is rotated by, for example, the driver 52 around a rotation axis R3 that passes through the light emission center 21c of the light source 21 and has an inclination angle of −10° to 10° with respect to a direction parallel to the emission direction D2 of the sub-terahertz waves from the light source 21. The retarder 51 rotates, for example, one or more revolutions during the exposure period of the image sensor 31. The rotation speed of the retarder 51 is not particularly limited as long as it can be rotated by the driver 52. The emission direction D2 of the sub-terahertz waves from the light source 21 is, for example, the direction of the optical axis of the light source 21, i.e., the direction that is the center of the range in which the light source 21 emits the sub-terahertz waves. Furthermore, the rotation axis R3 is, for example, parallel to the thickness direction of the retarder 51 and passes through the center 51c of the retarder 51 in a planar view. The rotation axis R3 does not have to pass through the center 51c of the retarder 51. The rotation axis R3 may pass through a position other than the light emission center 21c of the light source 21. The rotation axis R3 does not have to be parallel to the thickness direction of the retarder 51, and may be inclined with respect to the thickness direction (for example, inclined at an angle of −10° or more and 10° or less).

[0183] Furthermore, for example, when another example of the retarder 51 shown in FIG. 12 is used, the retarder 51 is moved as shown in FIG. 27 . Specifically, the retarder 51 is rotated by, for example, the driver 52 around a rotation axis R4 having an inclination angle of −10° to 10° with respect to a direction parallel to the emission direction D2 of the sub-terahertz waves from the light source 21, without passing through the light source 21. The retarder 51 rotates, for example, one or more revolutions during the exposure period of the image sensor 31. The rotation speed of the retarder 51 is not particularly limited as long as it is a speed at which the retarder 51 can be rotated by the driver 52. Furthermore, the rotation axis R4 is, for example, parallel to the thickness direction of the retarder 51 and passes through the center 51c of the retarder 51 in a planar view. Note that the rotation axis R4 does not have to pass through the center 51c of the retarder 51. Furthermore, the rotation axis R4 does not have to be parallel to the thickness direction of the retardation plate 51, and may be inclined with respect to the thickness direction (for example, inclined at an angle of −10° or more and 10° or less).

[0184] 14 described above, the retarder 51 is moved as shown in FIG. 28 . Specifically, the retarder 51 is moved, for example, by the driver 52 in a direction perpendicular to the emission direction D2 of the sub-terahertz waves from the light source 21 and in a direction perpendicular to the thickness direction of the retarder 51. The retarder 51 is moved back and forth at a predetermined frequency along the moving direction, for example. The predetermined frequency is, for example, a frequency whose period is equal to or shorter than the exposure period of the image sensor 31. There is no particular upper limit to the predetermined frequency as long as the frequency allows for reciprocating movement by the driver 52.

[0185] 26 to 28 , by moving the retardation plate 51, the first region 51 a and the second region 51 b are switched at the position where the sub-terahertz waves emitted from the light source 21 pass. This makes it possible to change the phase of the sub-terahertz waves radiated to the person 100, and changes the angular distribution of the phase of the reflected waves received by the image sensor 31 during the exposure period of the image sensor 31.

[0186] [Modification 2] Next, a description will be given of Modification 2 of the embodiment. In the following description, differences from the embodiment will be mainly described, and descriptions of commonalities will be omitted or simplified.

[0187] Fig. 29 is a schematic diagram of an imaging device 210 according to this modification when viewed from above. As shown in Fig. 29, the imaging device 210 differs from the imaging device 10 according to the embodiment in that it includes a detector 230 and a phase modulation unit 250 instead of the detector 30 and the phase modulation unit 50.

[0188] The detector 230 differs from the detector 30 in that a mirror system 251 constituting the phase modulation unit 250 functions as an optical system instead of the optical system 32. In other words, the phase modulation unit 250 is at least a part of the optical system of the detector 230, and the optical system of the detector 230 has the mirror system 251 as the phase modulation unit 250.

[0189] In this modified example, the phase modulation unit 250 changes the phase of some components of the reflected wave after the sub-terahertz wave emitted from the emission unit 20 is reflected by the person 100, thereby changing the angular distribution of the phase of the reflected wave received by the image sensor 31.

[0190] The mirror system 251 forms an image of the sub-terahertz waves emitted from the radiation unit 20 and reflected by the person 100 on the image sensor 31. The mirror system 251 includes, for example, a plurality of mirrors arranged in a curved shape. Each of the plurality of mirrors in the mirror system 251 changes the phase of the reflected wave from the person 100 that is incident on the mirror during the exposure period of the image sensor 31. For example, in the mirror system 251, each of the plurality of mirrors changes the phase change characteristic when reflected by the mirror during the exposure period of the image sensor 31. Furthermore, in the mirror system 251, the amount of phase change of the reflected wave from the person 100 reflected by each mirror may differ. For example, the plurality of mirrors in the mirror system 251 may include, at a certain point in time, mirrors that reflect the reflected wave from the person 100 without changing the phase and mirrors that reflect the reflected wave from the person 100 by changing the phase, and the characteristics of these mirrors change over time. By using such a mirror system 251, it is possible to change the angular distribution of the phase of the reflected wave received by the image sensor 31. The phase-changing mirror reflects the wave by changing the phase by, for example, 180°. The mirror system 251 is configured, for example, with a reflective spatial light phase modulation element including a circuit for controlling the phase change.

[0191] In this way, by integrating the detector 30 and the phase modulation section 250, the structure of the imaging device 210 can be simplified.

[0192] [Modification 3] Next, a description will be given of Modification 3 of the embodiment. In the following description, differences from the embodiment will be mainly described, and descriptions of commonalities will be omitted or simplified.

[0193] 30 is a schematic diagram of an image capturing device 310 according to this modification when viewed from above. As shown in FIG. 30, the image capturing device 310 differs from the image capturing device 10 according to the embodiment in that it includes a phase modulation unit 350 instead of the phase modulation unit 50.

[0194] The phase modulation section 350 changes the phase of the sub-terahertz waves radiated to the person 100 , thereby changing the angular distribution of the phase of the reflected waves received by the image sensor 31 .

[0195] The phase modulation unit 350 has a drive unit 352. The drive unit 352 is an example of a light source drive unit. The drive unit 352 is a drive device that changes the angular distribution of the phase of the reflected wave received by the image sensor 31 by moving the light source 21 under predetermined conditions. Therefore, in the imaging device 310, the light source 21 is not fixed but is installed movably.

[0196] For example, during the exposure period of the image sensor 31, the driver 352 moves the light source 21 so as to change the phase of the sub-terahertz waves irradiated onto the person 100, thereby changing the angular distribution of the phase of the waves reflected by the person 100 and received by the image sensor 31. Specifically, as the light source 21 moves, the optical path length of the sub-terahertz waves emitted from the light source 21 until they are incident on the person 100 changes, and therefore the phase of the sub-terahertz waves changes at each position on the person 100 where the sub-terahertz waves are incident. As a result, the angular distribution of the phase of the waves reflected by the person 100 and received by the image sensor 31 changes.

[0197] The drive unit 352 is composed of, for example, a drive machine such as a motor and an actuator, and power transmission members such as a belt, gears, pulleys, and connecting shafts for transmitting power to the light source 21 .

[0198] Here, the movement of the light source 21 in this modified example will be described. Fig. 31 is a schematic diagram for explaining an example of the movement of the light source 21 in this modified example. Fig. 32 is a schematic diagram for explaining another example of the movement of the light source 21 in this modified example.

[0199] As shown in FIG. 31 , the light source 21 is reciprocated at a predetermined frequency by, for example, the driver 352 along a movement direction 1 perpendicular to the emission direction D2 of the sub-terahertz waves from the light source 21 or a movement direction 2 parallel to the emission direction D2. The predetermined frequency is, for example, a frequency whose period is equal to or shorter than the exposure period of the image sensor 31. Furthermore, as long as the frequency allows reciprocal movement by the driver 352, there is no particular upper limit to the predetermined frequency. Furthermore, the vibration range at this time is, for example, equal to or longer than the wavelength of the sub-terahertz waves emitted by the light source 21. Therefore, the light source 21 is moved so that the movement range during the exposure period of the image sensor 31 is equal to or longer than the wavelength of the sub-terahertz waves emitted by the light source 21. As a result, the optical path length of the sub-terahertz waves emitted from the light source 21 until they enter the person 100 changes by equal to or longer than the wavelength of the sub-terahertz waves. This effectively changes the angular distribution of the phase of the reflected waves from the person 100 received by the image sensor 31. The vibration range at this time is set, for example, within a range in which the sub-terahertz waves emitted by the light source 21 are irradiated onto the reflector 22 at any position during the reciprocating movement. The light source 21 may be reciprocated in a direction between the movement direction 1 and the movement direction 2 (i.e., in the direction of the combined vector).

[0200] 32 , the light source 21 is rotated by, for example, the driving unit 352 around a rotation axis R5 parallel to the emission direction D2 of the sub-terahertz waves from the light source 21, without passing through the light emission center 21c of the light source 21. That is, the light source 21 is moved so that the light emission center 21c describes a circular orbit. In the example shown in FIG. 32 , the rotation axis R5 does not pass through any position of the light source 21. By having the light source 21 describe a circular orbit in this way, the light source 21 can continue to move without stopping, thereby effectively changing the optical path length of the sub-terahertz waves emitted by the light source 21 until they enter the image sensor 31. The length of the orbit in this case is, for example, equal to or greater than the wavelength of the sub-terahertz waves emitted by the light source 21. Furthermore, the diameter of the orbit in this case may be equal to or greater than the wavelength of the sub-terahertz waves emitted by the light source 21. The length of the trajectory in this case is set, for example, within a range in which the sub-terahertz waves emitted by the light source 21 are irradiated onto the reflector 22 at any position on the trajectory. Note that the rotation axis R5 may intersect with the emission direction D2 or may be perpendicular to the emission direction D2 as long as it does not pass through the light emission center 21c.

[0201] [Modification 4] Next, a description will be given of Modification 4 of the embodiment. In the following description, differences from the embodiment will be mainly described, and descriptions of commonalities will be omitted or simplified.

[0202] 33 is a schematic diagram of an image capturing device 410 according to this modification when viewed from above. As shown in FIG. 33, the image capturing device 410 differs from the image capturing device 10 according to the embodiment in that it includes a phase modulation unit 450 instead of the phase modulation unit 50.

[0203] The phase modulation section 450 changes the phase of the sub-terahertz waves radiated to the person 100 , thereby changing the angular distribution of the phase of the reflected waves received by the image sensor 31 .

[0204] The phase modulation unit 450 has a drive unit 452. The drive unit 452 is an example of a reflector drive unit. The drive unit 452 is a drive device that moves the reflector 22 under predetermined conditions to change the angular distribution of the phase of the reflected wave received by the image sensor 31. Therefore, in the imaging device 410, the reflector 22 is not fixed but is installed movably.

[0205] For example, during the exposure period of the image sensor 31, the driver 452 moves the reflector 22 so as to change the phase of the sub-terahertz waves irradiated onto the person 100, thereby changing the angular distribution of the phase of the waves reflected by the person 100 and received by the image sensor 31. Specifically, the movement of the reflector 22 changes the optical path length of the sub-terahertz waves emitted from the light source 21 until they are incident on the person 100, and therefore the phase of the sub-terahertz waves changes at each position on the person 100 where the sub-terahertz waves are incident. As a result, the angular distribution of the phase of the waves reflected by the person 100 and received by the image sensor 31 changes.

[0206] The driving unit 452 is composed of, for example, a driving machine such as a motor and an actuator, and power transmission members such as a belt, gears, pulleys, and connecting shafts for transmitting power to the reflecting plate 22 .

[0207] Here, the movement of the reflector 22 according to this modification will be described. As shown in FIG. 33 , the reflector 22 is reciprocated by, for example, a driver 452 along a movement direction 3 parallel to the thickness direction of the reflector 22 at a predetermined frequency. The predetermined frequency is, for example, a frequency whose period is equal to or shorter than the exposure period of the image sensor 31. Furthermore, as long as the frequency allows reciprocation by the driver 452, there is no particular upper limit to the predetermined frequency. Furthermore, the vibration range at this time is, for example, equal to or greater than half the wavelength of the sub-terahertz waves emitted by the light source 21. Therefore, the reflector 22 is moved so that, for example, during the exposure period of the image sensor 31, the movement range of the reflector 22 in the thickness direction is equal to or greater than half the wavelength of the sub-terahertz waves emitted by the light source 21. By moving the position of reflector 22 in the thickness direction of reflector 22 by at least half the wavelength of the sub-terahertz waves, the optical path length from when the sub-terahertz waves emitted from light source 21 are reflected by reflector 22 to when they enter person 100 changes by at least the wavelength of the sub-terahertz waves. This makes it possible to effectively change the angular distribution of the phase of the waves reflected by person 100 and received by image sensor 31. The vibration range in this case is set so that imaging space 102 through which person 100 passes can be secured and so that the sub-terahertz waves emitted from surface 22 a can be irradiated onto person 100 passing through imaging space 102.

[0208] Furthermore, the reflector 22 may be reciprocated by the driver 452 along the movement direction 4 perpendicular to the thickness direction of the reflector 22 at a predetermined frequency. The predetermined frequency is, for example, a frequency whose period is equal to or shorter than the exposure period of the image sensor 31. Furthermore, as long as the frequency allows the driver 452 to reciprocate, there is no particular upper limit to the predetermined frequency. The vibration range at this time is, for example, equal to or longer than the wavelength of the sub-terahertz waves emitted by the light source 21. Therefore, for example, during the exposure period of the image sensor 31, the reflector 22 is moved so that the movement range in the direction perpendicular to the thickness direction of the reflector 22 is equal to or longer than the wavelength of the sub-terahertz waves emitted by the light source 21. By moving the position of the reflector 22 in the direction perpendicular to the thickness direction of the reflector 22 by more than the wavelength of the sub-terahertz waves, the position of the uneven shape of the surface 22 a, which is set according to the wavelength of the sub-terahertz waves to diffusely reflect the sub-terahertz waves, is shifted, thereby effectively changing the direction of diffuse reflection by the reflector 22. Therefore, the angular distribution of the phase of the waves reflected by the person 100 and received by the image sensor 31 can be changed effectively.

[0209] The reflector 22 may be moved back and forth in a direction between the movement direction 3 and the movement direction 4 (that is, in the direction of the combined vector) so as to fall within the movement range of the reflector 22 described above.

[0210] [Effect of changing the optical path length of sub-terahertz waves] Next, we will explain the effect of changing the optical path length of the sub-terahertz waves emitted from the light source 21, reflected by the person 100, and incident on the image sensor 31 when photographing using the photographing device of the embodiment and each modified example.

[0211] FIG. 34 is a diagram illustrating a change in the optical path length of sub-terahertz waves due to the movement of person 100. FIG. 34 shows a state in which person 100 is moving at a speed v within imaging space 102 along a first direction. In FIG. 34, solid lines indicate (i) person 100, (ii) an example of sub-terahertz waves incident on person 100, and (iii) an example of waves reflected by person 100 before the movement. Also, in FIG. 34, dashed lines indicate (i) person 100, (ii) an example of sub-terahertz waves incident on person 100, and (iii) an example of waves reflected by person 100 after the length of one frame of the exposure period of image sensor 31 has elapsed from the state before the movement. Note that FIG. 34 exaggerates the amount of movement of person 100 for ease of viewing.

[0212] 34 , the sub-terahertz waves emitted toward person 100 are reflected by person 100 and travel toward image sensor 31. Therefore, when person 100 moves along the first direction, the optical path length of the sub-terahertz waves emitted from light source 21, reflected by person 100, and incident on image sensor 31 changes by approximately twice the amount of movement of person 100.

[0213] To effectively change the angular distribution pattern of the phase of the reflected wave on the image sensor 31 to suppress uneven brightness in the image, for example, the optical path length is changed by at least the wavelength of the sub-terahertz waves. As a result, the angular distribution pattern of the phase of the reflected wave received by the image sensor 31 is shifted by the wavelength of the sub-terahertz waves. The amount of movement of the person 100 required to change the optical path length by at least the wavelength of the sub-terahertz waves is half the wavelength of the sub-terahertz waves. Therefore, if the exposure period of the image sensor 31 is set to a time during which the person 100 moves half the wavelength of the sub-terahertz waves, the image sensor 31 can accumulate the intensity between two angular distribution patterns of phases that are shifted by the wavelength of the sub-terahertz waves during the exposure period. As a result, the intensities of the reflected waves with different angular phase distributions are accumulated, and brightness due to interference is leveled out. For example, as explained using Figure 1, the angular distribution of the phase of the reflected wave at position P1 shown in Figure 1(a) and the angular distribution of the phase of the reflected wave at position P2 shown in Figure 1(b) occur during the exposure period in the reflected wave at the same reflection position of person 100, rather than at different reflection positions, and therefore the brightness and darkness of the signal corresponding to the intensity of the reflected wave accumulated during the exposure period are leveled out.

[0214] Specifically, if the moving speed of person 100 is v mm per second and the wavelength of the sub-terahertz waves emitted by radiation unit 20 is λ mm, then if the length of the exposure period is (λ / 2) / v seconds or longer, person 100 will move at least half the wavelength of the sub-terahertz waves during the exposure period. Therefore, if the moving speed of person 100 is 3.2 km / h (=889 mm / s), which is the moving speed of a typical person, setting the length of the exposure period to λ / 1778 seconds or longer can effectively suppress uneven brightness in the image, regardless of the reflection characteristics of the sub-terahertz waves from person 100. If the length of the exposure period of image sensor 31 is within this range, for example, imaging device 10 can suppress uneven brightness in the image even without phase modulation unit 50.

[0215] Furthermore, the greater the movement of person 100 during the exposure period of image sensor 31, the greater the effect of leveling out the brightness. When sub-terahertz waves are irradiated onto a photographic target with uniform reflectivity as shown and described in FIG. 1 , the inventors conducted a simulation study and found that integrating the intensities of eight angular distribution patterns with phases shifted by the wavelength of the sub-terahertz waves results in a pixel value ratio of the darkest area to the brightest area of ​​0.25 or less. Therefore, by setting the exposure period so that the optical path length changes by at least seven wavelengths of the sub-terahertz waves during the exposure period, i.e., by setting the exposure period to at least (7 × λ / 2) / v seconds, brightness unevenness can be further effectively suppressed. For example, as described above, if the moving speed of person 100 is 889 mm per second, brightness unevenness can be further effectively suppressed by setting the exposure period to at least λ / 254 seconds.

[0216] Furthermore, by using a similar principle, even when the optical path length of the sub-terahertz waves emitted from the light source 21 to the person 100 is changed by the phase modulation unit 350 or the phase modulation unit 450, as in the above-mentioned variants 3 and 4, the optical path length changes by more than the wavelength of the sub-terahertz waves during the exposure period, thereby effectively suppressing uneven brightness in the image that occurs regardless of the reflection characteristics of the sub-terahertz waves at the person 100.

[0217] In the above explanation, an example was given in which the intensity of the reflected wave is accumulated during the exposure period of one frame of the image sensor 31, but the same effect can be obtained even when the intensity of the reflected wave is accumulated during the exposure periods of multiple frames.

[0218] Furthermore, even if the length of the exposure period is less than λ / 1778 seconds, the phase modulation unit 50, 250, 350, 450 can change the angular distribution of the phases of the reflected waves received by the image sensor 31 during the exposure period of the image sensor 31, allowing the image sensor 31 to accumulate the intensities of reflected waves with different phase angular distributions and level out the brightness and darkness caused by interference. Therefore, it is possible to effectively suppress uneven brightness and darkness in the image that occurs regardless of the reflection characteristics of the sub-terahertz waves from the person 100. Furthermore, for example, when the phase modulation unit 50, 250, 350, 450 changes the angular distribution of the phases of the reflected waves received by the image sensor 31 during the exposure period of the image sensor 31, the length of the exposure period may be λ / 2000 seconds or less.

[0219] Furthermore, from the viewpoint of suppressing blurring during the exposure period by receiving reflected waves from the same location on person 100 mainly at the same pixel 911, the length of the exposure period may be set to a predetermined time or less based on the shooting distance of detector 30 and the arrangement of pixels 911 in pixel array 910 of image sensor 31. Here, the exposure period for suppressing blurring will be described with reference to Figures 35A and 35B.

[0220] Fig. 35A is a schematic diagram showing an example of the arrangement of pixels 911 in a pixel array 910 of the image sensor 31. Fig. 35B is a schematic diagram showing an example of the shooting distance L of the detector 30. Note that Fig. 35B schematically shows only the pixel array 910 and the optical system 32 of the detector 30. Also, in Fig. 35B, the person 100 to be photographed is indicated by a solid arrow, and the person 100 photographed at a position shifted by one pixel from the person 100 indicated by the solid arrow is indicated by a dashed arrow.

[0221] As shown in Fig. 35A , the length of one side of the pixel array 910 is T mm, and the number of pixels 911 on that side is N. Furthermore, the distance from the center of the pixel array 910 to the pixel 911 in the row at the end of the pixel array 910 is T1, and the distance from the center of the pixel array 910 to the pixel 911 in the row second from the end of the pixel array 910 is T2. In this case, the distances T1 and T2 are as shown in Fig. 35A .

[0222] As shown in FIG. 35B , assume that the shooting distance from the optical system 32 of the detector 30 to the person 100, who is the object to be photographed, is L mm, the distance between the pixel array 910 and the optical system 32 is b mm, the focal length of the optical system 32 is f mm, and the movement distance of the person 100 when photographed with a one-pixel shift is D mm. Furthermore, assume that when the person 100 is photographed with a one-pixel shift, reflected light from the person 100 also enters pixel 911 in an end row of the pixel array 910. In this case, as shown in FIG. 35B , D=L(1−T2 / T1). Therefore, if the person 100 moves at a speed of 889 mm per second, and the length of the exposure period is L(1−T2 / T1) / 889 seconds, the reflected light from the person 100 will enter the pixel array 910 with a one-pixel shift. From the viewpoint of suppressing blurring, the length of the exposure period is, for example, L(1-T2 / T1) / 1778 seconds or less, which can reduce the deviation of reflected light from person 100 incident on pixel array 910 to less than half a pixel. Furthermore, when the number of pixels 911 on one side of pixel array 910, N, is 32, and the length of one side of pixel array 910, T, is 100, the distances T1 and T2 are calculated from the conditions shown in FIG. 35A as L(1-T2 / T1) / 1778=L / 27800. In other words, the length of the exposure period may be L / 27800 or less. In this case, the shooting distance L is, for example, the shortest shooting distance at detector 30 when person 100 is photographed. Specifically, the shortest shooting distance L at detector 30 is, for example, the shortest distance between shooting space 102 and optical system 32.

[0223] [Operation Example] Next, an operation example of the image capture device according to the embodiment and each modification will be described. The following mainly describes the operation of the image capture device 10 according to the embodiment, but similar operations can also be performed by the image capture device according to each modification. Furthermore, the operation example described below is an example in which the control unit 40 controls the operation of the image capture device 10 based on the movement state of the person 100 when passing through the image capture space 102.

[0224] The image capturing device according to the embodiment and each modification may perform one of the following operation examples, or may perform a combination of two or more of them. The image capturing device according to the embodiment and each modification may also be an image capturing device that does not perform the following operations. In the following operation examples, the detection unit 60 detects the movement state of the person 100, but instead of the detection unit 60, any of the detection units 60a to 60d may detect the movement state of the person 100.

[0225] (1) Operation Example 1 First, an operation example 1 of the image capturing device according to the embodiment and each modification will be described. Fig. 36 is a flowchart of operation example 1 of the image capturing device according to the embodiment and each modification.

[0226] 36 , in the image capturing device 10, when a person 100 enters the image capturing space 102, the detection unit 60 detects the movement state of the person 100 (step S11). The detection unit 60 detects the movement state of the person 100, for example, by acquiring a moving image of the person 100 moving.

[0227] Next, the control unit 40 determines a predetermined time for accumulating the intensity of the reflected waves received by the image sensor 31 based on the movement state of the person 100 detected by the detection unit 60 in step S11 (step S12). For example, the control unit 40 determines whether the movement state of the person 100 is stationary using the method described above in [Detection Unit], and if the movement state of the person 100 is stationary, determines the predetermined time to be longer than if the movement state of the person 100 is not stationary. Furthermore, if the movement state of the person 100 is not stationary, the control unit 40 may further determine the degree of movement of the person 100 and determine the predetermined time based on the degree of movement. Furthermore, for example, the control unit 40 calculates the movement speed of the person 100 from the detection result of the detection unit 60, and determines the predetermined time to be (A×λ / 2) / v seconds, assuming that the movement speed of the person 100 is v mm per second and the wavelength of the sub-terahertz waves emitted by the emission unit 20 is λ mm. The constant A is, for example, a numerical value between 1 and 15, or between 7 and 15, and is set according to the specifications of the emitting unit 20 and the detector 30, etc.

[0228] Next, the control unit 40 causes the image sensor 31 to generate an image based on a signal corresponding to the cumulative intensity accumulated for the predetermined time period determined in step S12 (step S13). As a result, an image showing the person 100 is captured.

[0229] As described above, the optical path length of the sub-terahertz waves emitted from the light source 21 until they enter the image sensor 31 changes depending on the movement of the person 100. Furthermore, the amount of change in the optical path length within a predetermined time period during which the intensity of the reflected waves received by the image sensor 31 is accumulated is determined by the movement state of the person 100 (e.g., the movement speed of the person 100). Furthermore, the phase distribution of the reflected waves received by the image sensor 31 relative to the reflection angle also changes depending on the change in the optical path length. Therefore, the movement state of the person 100 affects the phase distribution of the reflected waves received by the image sensor 31 relative to the reflection angle at a predetermined time period. The more easily the angular distribution of the phase of the reflected waves received by the image sensor 31 changes within a predetermined time period, the more easily the image sensor 31 can accumulate the intensity of reflected waves with angular distributions of different phases, thereby suppressing unevenness in the image. Therefore, the likelihood of unevenness in the image generated by the image sensor 31 occurring is affected by the movement state of the person 100. In this operation example, in step S12, the control unit 40 determines the predetermined time based on the movement state of the person 100, thereby making it possible to appropriately control the amount of change in the optical path length over the predetermined time. For example, the control unit 40 can determine the predetermined time so that the optical path length can be changed by an amount equal to or greater than the wavelength of the sub-terahertz wave, as described above. Therefore, the image sensor 31 can accumulate the intensities of reflected waves with different phase angular distributions over an appropriate predetermined time, thereby generating an image with reduced unevenness in brightness.

[0230] (2) Operation Example 2 Next, an operation example 2 of the image capturing device according to the embodiment and each modification will be described. Fig. 37 is a flowchart of operation example 2 of the image capturing device according to the embodiment and each modification.

[0231] 37 , in the second operation example, first, in the image capturing device 10, when a person 100 enters the image capturing space 102, the detection unit 60 detects the movement state of the person 100 (step S21). Step S21 is the same as step S11 described above.

[0232] Next, the control unit 40 determines whether the movement state of the person 100 detected by the detection unit 60 in step S21 is stationary (step S22). The control unit 40 determines whether the movement state of the person 100 is stationary, for example, based on the detection result output from the detection unit 60, using the method described above in [Detection unit].

[0233] Next, if the control unit 40 determines that the person 100 is stationary (Yes in step S22), it causes the phase modulation unit 50 to change the angular distribution of the phase of the reflected wave received by the image sensor 31 (step S23). In step S23, the control unit 40 may determine conditions, such as the drive speed of the drive unit 52, for changing the angular distribution of the phase of the reflected wave based on the moving state, such as the moving speed, of the person 100, and cause the phase modulation unit 50 to change the angular distribution of the phase of the reflected wave received by the image sensor 31 based on the determined conditions. Note that in the operation of the imaging device according to each modification, the control unit 40 causes the phase modulation unit included in the imaging device according to each modification, instead of the phase modulation unit 50, to change the angular distribution of the phase of the reflected wave received by the image sensor 31.

[0234] Then, while operating the phase modulation unit 50, the control unit 40 causes the image sensor 31 to generate an image based on the received reflected wave (step S24). At this time, the image sensor 31 may generate an image based on a signal corresponding to the accumulated intensity accumulated for a period of λ / 1778 seconds or more.

[0235] On the other hand, if the control unit 40 determines that the person 100 is not stationary (No in step S22), it generates an image based on the reflected waves received by the image sensor 31 without operating the phase modulation unit 50 (step S24).

[0236] In operation example 2, when the person 100 is stationary, the control unit 40 causes the phase modulation unit 50 to change the angular distribution of the phase of the sub-terahertz waves received by the image sensor 31. Therefore, even when the person 100 is stationary due to a slow movement speed or being still, resulting in a small change in the angular distribution of the phase of the reflected waves received by the image sensor 31, the phase modulation unit 50 changes the angular distribution of the phase of the reflected waves received by the image sensor 31, thereby making it possible to suppress uneven brightness in the obtained image.

[0237] In the second operational example, the control unit 40 may determine whether the person 100 is present in a predetermined space based on the detection result of the detection unit 60, instead of determining whether the person 100 is stationary. For example, when the control unit 40 determines that the person 100 is present in the predetermined space, the control unit 40 causes the phase modulation unit 50 to change the angular distribution of the phase of the reflected waves received by the image sensor 31, regardless of the movement state of the person 100, and generates an image based on the reflected waves received by the image sensor 31. This makes it possible to more reliably suppress uneven brightness in the resulting image.

[0238] (3) Operation Example 3 Next, an operation example 3 of the image capturing device according to the embodiment and each modification will be described. Fig. 38 is a flowchart of operation example 3 of the image capturing device according to the embodiment and each modification.

[0239] 38, in the operation example 3, first, in the image capturing device 10, when a person 100 enters the image capturing space 102, the detection unit 60 detects the movement state of the person 100 (step S31). Step S31 is the same as step S11 described above.

[0240] Next, the control unit 40 determines whether the movement state of the person 100 detected by the detection unit 60 in step S31 is stationary (step S32). Step S32 is the same as step S22 described above.

[0241] Next, if the control unit 40 determines that the person 100 is stationary (Yes in step S32), it causes the alarm 70 to issue a warning (step S33). Then, the control unit 40 causes the image sensor 31 to generate an image based on the received reflected waves (step S34). For example, the control unit 40 causes the image sensor 31 to generate an image based on the received reflected waves after a certain time has elapsed since the control unit 40 caused the alarm 70 to issue a warning in step S33. The certain time is, for example, 0.5 to 5.0 seconds.

[0242] On the other hand, if the control unit 40 determines that the person 100 is not stationary (No in step S32), it generates an image based on the reflected waves received by the image sensor 31 without operating the alarm 70 (step S34).

[0243] In operation example 3, when the person 100 is stationary, the control unit 40 causes the alarm 70 to issue a warning. This can prompt the person 100 to change their movement state, such as by increasing their movement speed. When the person 100 increases their movement speed, the change in the angular distribution of the phase of the reflected waves received by the image sensor 31 increases, making it possible to suppress uneven brightness in the resulting image.

[0244] (4) Operation Example 4 Next, an operation example 4 of the image capturing device according to the embodiment and each modification will be described. Fig. 39 is a flowchart of operation example 4 of the image capturing device according to the embodiment and each modification.

[0245] 39, in the fourth operational example, first, in the image capturing device 10, when a person 100 enters the image capturing space 102, the detection unit 60 detects the movement state of the person 100 (step S41). Step S41 is the same as step S11 described above.

[0246] Next, the control unit 40 determines a predetermined time for accumulating the intensity of the reflected waves received by the image sensor 31 based on the movement state of the person 100 detected by the detection unit 60 in step S41 (step S42). Step S42 is the same as step S12 described above.

[0247] Next, the control unit 40 determines whether the movement state of the person 100 detected by the detection unit 60 in step S41 is stationary (step S43). Step S43 is the same as step S22 described above.

[0248] Next, when the control unit 40 determines that the person 100 is stationary (Yes in step S43), it causes the phase modulation unit 50 to change the angular distribution of the phase of the reflected wave received by the image sensor 31 (step S44). Step S44 is the same as step S23 described above.

[0249] Then, the control unit 40 causes the image sensor 31 to generate an image based on a signal corresponding to the cumulative intensity accumulated for the predetermined time period determined in step S42 (step S45), thereby capturing an image showing the person 100.

[0250] On the other hand, if the control unit 40 determines that the person 100 is not stationary (No in step S43), it generates an image based on the reflected waves received by the image sensor 31 without operating the phase modulation unit 50 (step S45).

[0251] In Operation Example 4, when the person 100 is stationary, the control unit 40 causes the phase modulation unit 50 to change the angular distribution of the phase of the reflected wave received by the image sensor 31. Furthermore, in step S42, the control unit 40 determines a predetermined time based on the movement state of the person 100. Therefore, even when the person 100 is stationary, both of the effects of suppressing unevenness in brightness of the obtained image described in Operation Example 1 and Operation Example 2 above are achieved.

[0252] As described above, in Operation Examples 1 to 4, the control unit 40 controls the operation of the image capturing device 10 based on the movement state of the person 100, which affects uneven brightness in the image, and therefore the image capturing conditions can be changed appropriately. For example, in Operation Examples 2 to 4, the control unit 40 controls the operation of the image capturing device 10 so that the operation of the image capturing device 10 differs from normal when the movement state of the person 100 detected by the detection unit 60 is stationary. This makes it possible to suppress uneven brightness in the image that occurs regardless of the reflection characteristics of the sub-terahertz waves from the person 100.

[0253] (5) Operation Example 5 Next, an operation example 5 of the image capturing device according to the embodiment and each modification will be described. Fig. 40 is a flowchart of operation example 5 of the image capturing device according to the embodiment and each modification.

[0254] 40, in the fifth operational example, first, in the image capturing device 10, when a person 100 enters the image capturing space 102, the detection unit 60 detects the movement state of the person 100 (step S51). Step S51 is the same as step S11 described above.

[0255] Next, the control unit 40 determines whether the movement state of the person 100 detected by the detection unit 60 in step S51 is stationary (step S52). Step S52 is the same as step S22 described above.

[0256] Next, when the control unit 40 determines that the person 100 is stationary (Yes in step S52), it causes the detector 30 to stop generating images (step S53). As a result, the image capturing device 10 no longer outputs images of the person 100.

[0257] On the other hand, if the control unit 40 determines that the person 100 is not stationary (No in step S52), it causes the image sensor 31 to generate an image based on the received reflected waves (step S54). The image sensor 31 generates an image based on a signal corresponding to the cumulative intensity accumulated for a period of time equal to or longer than λ / 1778 seconds, for example. Alternatively, the image sensor 31 may generate an image based on a signal corresponding to the cumulative intensity accumulated for a predetermined period of time determined based on the movement state of the person 100.

[0258] In operation example 5, when the movement state of person 100 is stationary, control unit 40 does not cause detector 30 to generate an image. Therefore, when the movement state of person 100 is stationary and the obtained image has large unevenness in brightness, no image is output from imaging device 10. Therefore, for example, when detecting a dangerous object using an image, an image that reduces the detection accuracy of the dangerous object is not output, and false detection can be suppressed.

[0259] (6) Operation Example 6 Next, an operation example 6 of the image capturing device according to the embodiment and each modification will be described. Fig. 41 is a flowchart of operation example 6 of the image capturing device according to the embodiment and each modification.

[0260] 41 , in the sixth operational example, first, in the image capturing device 10, when a person 100 enters the image capturing space 102, the detection unit 60 detects the movement state of the person 100 (step S61). Step S61 is the same as step S11 described above.

[0261] Next, the control unit 40 causes the image sensor 31 to generate an image based on the received reflected waves (step S62). The image sensor 31 generates the image based on a signal corresponding to the cumulative intensity accumulated for a period of time equal to or longer than λ / 1778 seconds, for example. Alternatively, the image sensor 31 may generate the image based on a signal corresponding to the cumulative intensity accumulated for a predetermined period of time determined based on the movement state of the person 100.

[0262] Next, the control unit 40 determines whether the movement state of the person 100 detected by the detection unit 60 in step S61 is stationary (step S63). Step S63 is the same as step S22 described above.

[0263] Next, when the control unit 40 determines that the moving state of the person 100 is stationary (Yes in step S63), the control unit 40 changes the display mode of the image displayed on the display unit 95 (step S64). For example, the control unit 40 stops displaying the image generated in step S62 on the display unit 95, or superimposes another image on the image generated in step S62. The other image is, for example, an image that indicates that the image generated in step S62 has large unevenness in brightness.

[0264] On the other hand, if the control unit 40 determines that the person 100 is not stationary (No in step S63), it causes the display unit 95 to display the image generated in step S62 in the normal display mode (step S65).

[0265] In Operation Example 6, when the person 100 is stationary, the control unit 40 changes the display mode of the image displayed on the display unit 95. Therefore, when the person 100 is stationary and the resulting image has large variations in brightness, the image generated by the detector 30 is not displayed as is. This prevents, for example, a user from misrecognizing the image generated by the detector 30.

[0266] (Other Embodiments) While the imaging device according to the present disclosure has been described above based on the embodiments and various modifications, the present disclosure is not limited to these embodiments and various modifications. As long as they do not deviate from the spirit of the present disclosure, various modifications that a person skilled in the art could conceive of to these embodiments and configurations constructed by combining components of different embodiments and various modifications are also included within the scope of one or more aspects of the present disclosure.

[0267] In the above-described embodiment and each modification, the light source 21 and the detector 30 are arranged only on the first direction side of the reflector 22, but this is not limiting. The light source 21 and the detector 30 may also be arranged on the opposite side of the reflector 22 from the first direction side. This makes it possible to capture images of both the front and back of the person 100.

[0268] In the above-described embodiment and each modification, the object to be photographed is a person 100, but this is not limiting. The object to be photographed may be luggage, etc. For example, the photographing device 10 may photograph luggage such as a suitcase, or a foreign object in a product.

[0269] Furthermore, in the above-described embodiment and each modified example, the retardation plate 51 includes both the first region 51 a and the second region 51 b, but this is not limiting. For example, the retardation plate 51 may be configured with only the first region 51 a or the second region 51 b. In this case, the retardation plate 51 is moved, for example, by the drive unit 52, so as to alternate between a position through which at least a portion of the sub-terahertz waves emitted from the light source 21 or at least a portion of the reflected waves incident on the optical system 32 pass and a position through which they do not pass.

[0270] Furthermore, in the above-described embodiment and each modified example, the radiation unit 20 includes the light source 21 and the reflector 22, but this is not limiting. For example, the radiation unit 20 may be configured with a plurality of light sources arranged so as to be able to radiate sub-terahertz waves from various angles relative to the person 100. Furthermore, for example, the radiation unit 20 may be a surface light source in which a plurality of sub-terahertz wave generating elements are arranged along a surface.

[0271] In the above-described embodiment and each modification, each component such as the control unit 40 and the image processing unit 90 may be configured with dedicated hardware or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or a processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0272] Each component may be a circuit (or integrated circuit). These circuits may form a single circuit as a whole, or each may be a separate circuit. Each of these circuits may be a general-purpose circuit or a dedicated circuit.

[0273] Furthermore, a comprehensive or specific aspect of the present disclosure may be realized as a system, an apparatus, a method, an integrated circuit, a computer program, or a non-transitory recording medium such as a computer-readable CD-ROM. Alternatively, the present disclosure may be realized as any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a non-transitory recording medium. For example, the present disclosure may be realized as a program for causing a computer to execute control performed by a control unit or the like provided in each component of an imaging device.

[0274] The order of the processes in the operation of the imaging device described in the above embodiment and each modification is merely an example. The order of the processes may be changed, or the processes may be performed in parallel.

[0275] Furthermore, the above-described embodiments and modifications can be subject to various changes, substitutions, additions, omissions, etc. within the scope of the claims or their equivalents.

[0276] The present disclosure is widely applicable to imaging devices that capture images of objects.

[0277] 10, 110, 210, 310, 410 Imaging device 20 Radiation unit 21 Light source 21c Light emission center 22 Reflector 22a Surface 30, 230 Detector 31 Image sensor 31a Control circuit 32 Optical system 32c, 51c Center 40 Control unit 50, 250, 350, 450 Phase modulation unit 51 Retardation plate 51a First region 51a1 Symmetric region 51a2 Asymmetric region 51b Second region 52, 352, 452 Driving unit 60, 60a, 60b, 60c, 60d Detection unit 70 Alarm 80 Transport unit 90 Image processing unit 95 Display unit 100 Person 101 Passage 102 Imaging space 251 Mirror system 910 Pixel array 911 Pixel 920 Integration circuit 920A Integration circuit group 921 Operational amplifier 922 Capacitor element 923 Switch 930, 960, 970 Multiplexer 940 Analog-to-digital converter 950 Combining circuit D1 Incident direction D2 Emitting direction R1, R2, R3, R4, R5 Rotation axis

Claims

1. An imaging device that uses sub-terahertz waves to capture an image of an object passing through a predetermined area, a radiation unit that radiates the sub-terahertz wave toward the object to be photographed; (i) an optical system that forms an image of the sub-terahertz waves radiated from the radiator, reflected by the object to be photographed; and (ii) a plurality of pixels that are arranged in a plane and receive the reflected waves imaged by the optical system. A detector that generates an image based on an accumulated intensity obtained by accumulating the intensity of the reflected waves received by each of the plurality of pixels for a predetermined time period and the planar arrangement of the plurality of pixels, The predetermined time is λ / 1778 seconds or more, where λ mm is the wavelength of the sub-terahertz wave. Filming equipment.

2. A detection unit that detects a moving state of the object to be photographed when the object passes through the predetermined area; and a control unit that controls an operation of the photographing device when the moving state is stationary. The imaging device according to claim 1 .

3. The control unit determines the predetermined time based on the moving state, and causes the detector to generate the image based on the accumulated intensity accumulated for the determined predetermined time. The imaging device according to claim 2 .

4. An imaging device that uses sub-terahertz waves to capture an image of an object passing through a predetermined area, a radiation unit that emits the sub-terahertz wave toward the object to be photographed; (i) an optical system that forms an image of the sub-terahertz waves radiated from the radiator, the reflected waves being reflected by the object to be photographed; and (ii) a plurality of pixels that are arranged in a plane and receive the reflected waves imaged by the optical system, the detector generating an image based on an accumulated intensity obtained by accumulating the intensity of the reflected waves received by each of the plurality of pixels for a predetermined time period and on the planar arrangement of the plurality of pixels. A detection unit that detects a moving state of the object to be photographed when the object passes through the predetermined area; and a control unit that determines the predetermined time based on the moving state, and causes the detector to generate the image based on the accumulated intensity accumulated for the determined predetermined time. Filming equipment.

5. The detection unit detects, as the moving state, a moving speed of the object when the object passes through the predetermined area, The control unit determines that the movement state of the object to be photographed is stationary when the movement speed is less than a predetermined speed. The imaging device according to claim 2 .

6. The control unit causes the detector to stop generating the image when the moving state is stationary. The imaging device according to claim 2 .

7. a display unit for displaying the image, When the moving state is a stop, the control unit stops displaying the image on the display unit or superimposes another image on the image. The imaging device according to claim 2 .

8. Equipped with an alarm that issues a warning, The control unit causes the alarm device to issue the warning when the moving state is a stationary state. The imaging device according to claim 2 .

9. a phase modulation unit that changes an angular distribution of phases of the reflected waves received by the plurality of pixels of the detector during an exposure period when the detector generates the image, The control unit changes the angular distribution of the phase to the phase modulation unit when the moving state is stationary. The imaging device according to claim 2 .

10. The radiation portion is a light source that emits the sub-terahertz wave; a reflector that diffusely reflects the sub-terahertz waves emitted from the light source and thereby radiates the sub-terahertz waves toward the object to be photographed, The phase modulation unit is a phase difference plate disposed between the light source and the reflector and configured to change a phase of the sub-terahertz wave passing through the phase difference plate; A retardation plate driving unit that moves the retardation plate under predetermined conditions. The imaging device according to claim 9.

11. The phase modulation unit is a phase difference plate that is disposed on an optical path of the reflected wave between the predetermined region and the plurality of pixels of the detector and changes a phase of the reflected wave that passes through the phase difference plate; A retardation plate driving unit that moves the retardation plate under predetermined conditions. The imaging device according to claim 9.

12. the phase modulation unit is at least a part of the optical system, the optical system includes, as the phase modulation unit, a mirror system that reflects the reflected wave to form an image on the plurality of pixels of the detector, The mirror system includes a plurality of mirrors; each of the plurality of mirrors changes a phase of the reflected wave reflected during an exposure period of the detector; The imaging device according to claim 9.

13. The radiation portion is a light source that emits the sub-terahertz wave; a reflector that diffusely reflects the sub-terahertz waves emitted from the light source and thereby radiates the sub-terahertz waves toward the object to be photographed, The phase modulation unit includes a light source driving unit that drives the light source under a predetermined condition to change the angular distribution of the phase. The imaging device according to claim 9.

14. The radiation portion is a light source that emits the sub-terahertz wave; a reflector that diffusely reflects the sub-terahertz waves emitted from the light source and thereby radiates the sub-terahertz waves toward the object to be photographed, The phase modulation unit includes a reflector driving unit that moves the reflector under a predetermined condition to change the angular distribution of the phase. The imaging device according to claim 9.

15. the phase modulation unit has a conveying unit that moves the object to be photographed within the predetermined region by half or more of the wavelength of the sub-terahertz wave during an exposure period of the detector to change the angular distribution of the phase; The imaging device according to claim 9.

16. The predetermined time is equal to or shorter than L / 27800 seconds, where L mm is the shortest shooting distance in the detector. The imaging device according to claim 1 .

17. the predetermined time is the length of an exposure period for one frame of the detector; The imaging device according to claim 1 .

18. The predetermined time is λ / 254 seconds or more. The imaging device according to claim 1 .

19. The frequency of the sub-terahertz wave is 0.05 THz or more and 2 THz or less, and the wavelength of the sub-terahertz wave is 0.15 mm or more and 6 mm or less. The imaging device according to claim 1 .

20. The method of claim 1, wherein the predetermined time is a length of an exposure period for a plurality of frames of the detector. The detector has a synthesis unit that synthesizes signals of the plurality of pixels obtained in the plurality of frames and generates the image based on the accumulated intensity accumulated for the predetermined time, or that accumulates signals of the reflected waves received by the plurality of pixels in the plurality of frames for the predetermined time and generates the image based on the accumulated intensity accumulated for the predetermined time. The imaging device according to claim 1 .