Patent Publication Number: US-2023156327-A1

Title: System and method for system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation U.S. Application No. 17/317338, filed May 11, 2021, which claims priority from Japanese Patent Application No. 2020-085565, filed May 15, 2020, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     The aspect of the embodiments relates to a terahertz wave camera system. 
     Description of the Related Art 
     Japanese Patent Application Laid-Open No. 2018-087725 discusses a camera system to which a terahertz wave is applied. Specifically, Japanese Patent Application Laid-Open No. 2018-087725 discusses an active terahertz wave camera system having a configuration in which a terahertz wave is generated from a plurality of terahertz wave light sources, an object is irradiated with the terahertz wave, and then the terahertz wave reflected by the object is detected. 
     SUMMARY OF THE DISCLOSURE 
     According to an aspect of the embodiments, a system includes a transmission unit configured to generate an electromagnetic wave, a first reception unit configured to detect the electromagnetic wave, and a processing unit configured to determine whether an output of the electromagnetic wave from the transmission unit is more than or equal to a threshold based on first image information obtained by capturing an image of the transmission unit in a state where the transmission unit is irradiating the electromagnetic wave. 
     According to another aspect of the embodiments, a method for a system includes acquiring first image information obtained by capturing an image of a transmission unit in a state where the transmission unit is irradiating an electromagnetic wave, and determining whether an output of the electromagnetic wave from the transmission unit is more than or equal to a threshold based on the first image information. 
     Further features of the disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram illustrating a configuration of a camera system according to a first exemplary embodiment. 
         FIGS.  2 A and  2 B  are schematic diagrams each illustrating an image captured by the camera system according to the first exemplary embodiment, and  FIG.  2 C  is a schematic graph illustrating a method for processing therefor. 
         FIGS.  3 A and  3 B  are flowcharts each illustrating an operation to be executed by the camera system according to the first exemplary embodiment. 
         FIG.  4 A  is a schematic diagram illustrating a configuration of a camera system according to a second exemplary embodiment, and  FIG.  4 B  is a schematic diagram illustrating an image captured by the camera system according to the second exemplary embodiment. 
         FIG.  5 A  is a schematic diagram illustrating a configuration of a camera system according to a third exemplary embodiment, and  FIGS.  5 B and  5 C  are schematic diagrams each illustrating an image captured by the camera system according to the third exemplary embodiment. 
         FIG.  6    is a schematic diagram illustrating a configuration of a camera system according to a fourth exemplary embodiment. 
         FIG.  7    is a schematic diagram illustrating a configuration of a camera system according to a fifth exemplary embodiment. 
         FIGS.  8 A,  8 B,  8 C and  8 D  are schematic diagrams each illustrating an image captured by the camera system according to the fifth exemplary embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     A terahertz wave is an electromagnetic wave in an invisible wavelength band and thus is not visible to human eyes. Accordingly, it is difficult for a human to visually check whether a terahertz wave at a desired frequency is generated from a light source. 
     Thus, if a malfunction occurs in a light source or a system and a desired terahertz wave is not generated from the light source, it is difficult to normally capture an image of an object. Additionally, a terahertz wave at an unintended frequency may be generated by an oscillation due to a parasitic capacitance in a circuit of the light source. In this case, an amount of current that is substantially equal to an amount of current to flow during a normal operation flows to the circuit of the light source. For this reason, the abnormality cannot be detected even by monitoring the current flowing to the light source. Thus, some measures to check the operation of a light source of the terahertz wave are to be provided. 
     A terahertz wave will be described. A terahertz wave is a radio wave typically having a frequency band from 0.1 THz to 30 THz. A terahertz wave has a longer wavelength than visible light and infrared light, and thus is less affected by scattering of light from an object and has high permeability to many substances. The wavelength of a terahertz wave is shorter than that of a millimeter wave, so that a high spatial resolution can be obtained. By taking advantage of these characteristics, applications to a safe imaging technique using terahertz waves in place of X-rays are expected. Specific examples of the expected applications to the imaging technique include a security check and a surveillance camera in a public place. 
     Exemplary embodiments will be described in detail below with reference to the accompanying drawings. The following exemplary embodiments illustrate an example where a terahertz wave camera system is used as a camera system. Each of the terahertz wave camera systems according to the exemplary embodiments can be applied to a security check and a surveillance camera, which are examples of the expected applications. The following exemplary embodiments are not intended to limit the disclosure. Multiple features are described in the exemplary embodiments. However, not all of these features are essential to the disclosure, and multiple such features can be combined as appropriate. In the accompanying drawings, the same or like components are denoted by the same reference numerals, and redundant descriptions are omitted. 
     A camera system  1001  according to a first exemplary embodiment will be described with reference to  FIGS.  1  to  3 B . 
       FIG.  1    is a schematic diagram illustrating a configuration example of the camera system  1001 . The camera system  1001  includes a reception unit  100 , a transmission unit  103 , a transmission unit  104 , a transmission unit  105 , a display unit  111 , and a processing unit  110 . In the camera system  1001  according to the present exemplary embodiment, the transmission units  103  to  105  are disposed at positions within a field angle where terahertz waves from the transmission units  103  to  105  can be received by the reception unit  100 . 
     The transmission units  103  to  105  each irradiate an object  109  with a terahertz wave. The term “irradiation” used herein can also be referred to as radiation. The camera system  1001  includes a plurality of transmission units. However, the number of transmission units is not limited to three and the camera system  1001  can include any number of transmission units. For example, the number of transmission units included in the camera system  1001  can be one, two, or 16 or more. The frequency of a terahertz wave irradiated from each of the transmission units  103  to  105  includes any frequency components or a single frequency in a range from 0.1 THz to 30 THz. In a case where a human body is included as the object  109 , many clothes have high permeability up to 1 THz. Accordingly, for example, in a case where the camera system  1001  is used for a concealed-object inspection, a terahertz wave in a frequency band from 0.3 THz to 1 THz can be used. Assume that, in the present exemplary embodiment, a frequency band including 0.45 THz is used. Also assume that the object  109  is moving along a movement direction  112 . 
     In the transmission unit  103 , a plurality of transmitters  106 , each of which emits a terahertz wave, is disposed. For example, in the transmission unit  103 , the transmitters  106  are disposed in an array of 2 × 2. In the transmission unit  104 , a plurality of transmitters  107 , each of which emits a terahertz wave, is disposed. For example, in the transmission unit  104 , the transmitters  107  are disposed in an array of 2 × 2. In the transmission unit  105 , a plurality of transmitters  108 , each of which emits a terahertz wave, is disposed. For example, in the transmission unit  105 , the transmitters  108  are disposed in an array of 2 × 2. The layout method and the number of the transmitters  106 ,  107 , and  108  can be appropriately selected depending on the intensity and a directivity of terahertz waves. 
     The transmitters  106 ,  107 , and  108  are each composed of one or more transmission elements, and are each mounted on a casing as a single chip. The casing is also referred to as a package or a mount member. Examples of the transmission elements can include a terahertz wave transmission element of a semiconductor element such as a resonant tunneling diode, and a photoexcitation terahertz wave transmission element. In one embodiment, each of the transmission elements includes an antenna structure so that impedance matching with atmosphere and terahertz wave generation efficiency can be improved. The size of the antenna structure is designed to be substantially equal to a wavelength to be used. 
     The reception unit  100  is an element that can detect a terahertz wave. The reception unit  100  can also be referred to as a terahertz wave camera. The reception unit  100  includes a receiver  102  and an optical system  101 . The receiver  102  is a sensor that is partitioned by a plurality of pixels. The optical system  101  focuses a terahertz wave on a reception surface of the receiver  102 . Further, the optical system  101  can image the terahertz wave on the reception surface of the receiver  102 . The reception unit  100  has a configuration similar to a camera in which the receiver  102  and the optical system  101  are integrally mounted. However, the reception unit  100  can have a configuration in which the receiver  102  and the optical system  101  are stored in separate casings, respectively, and are installed in combination. 
     The receiver  102  is composed of one or more reception elements, and is mounted on a casing as a single chip. The casing is also referred to as a package or a mount member. Examples of the reception element can include a thermal detection element such as a bolometer, and a semiconductor detection element such as a Schottky barrier diode. Since the reception unit  100  functions as a camera to detect an image, the number of reception elements can also be referred to as the number of pixels, and the size of each reception element can also be referred to as a pixel size. For example, in a case where the camera system  1001  is used for a concealed-object inspection, 10,000 or more pixels are to be used. In other words, the receiver  102  can also be referred to as an area sensor having 100 pixels × 100 pixels. Since the wavelength of a terahertz wave is several hundred µm, the size of a single reception element is determined based on this value. In view of the above, the size of the receiver  102  is typically 10 mm or more × 10 mm or more. In view of the resolution and size, the number of pixels to be used is 20,000 pixels or more, and the size of the receiver  102  is several tens of mm or more on each side. The number of pixels to be used can be 100,000 pixels or more, and the size of the receiver  102  can be 500 mm or more on each side. Further, in order to improve the impedance matching with atmosphere and detection efficiency of the terahertz wave, in one embodiment, each reception element includes an antenna structure. The size of the antenna structure is designed to be substantially equal to a wavelength to be used. 
     The optical system  101  images the terahertz wave on the reception surface of the receiver  102 . The optical system  101  can be an optical element such as a lens or a mirror. In a case where a lens is used as the optical system  101 , it is to use, as a lens material, a material with a small loss against a terahertz wave to be used. Examples of the lens material can include Teflon® and high density polyethylene. The optical system  101  is an imaging optical system, and can be designed by a visible light method. A dashed-dotted line illustrated in  FIG.  1    represents an optical axis of the optical system  101 . In one embodiment, the optical axis matches the center of mass of the reception surface of the receiver  102 . An aperture diaphragm can be provided in the optical system  101 . A depth of focus of an object can be increased by stopping down the aperture diaphragm, i.e., by increasing an F-value. In other words, an object image in a wide range can be obtained. However, if the F-value is increased, the intensity of the terahertz wave that has been transmitted through the optical system  101  may be decreased. In one embodiment, the aperture is adjusted in view of the intensity of the terahertz wave from each of the transmission units  103  to  105 . 
     The processing unit  110  is a processing apparatus such as a computer including a central processing unit (CPU), a memory, and a storage device. Image information acquired by the reception unit  100  is sent to the processing unit  110 , and the processing unit  110  performs signal processing on the image information. The functions of the processing unit  110  can be provided in the reception unit  100 . The processing unit  110  can perform determination processing to be described below and signal processing, and can control overall operations of the camera system  1001 . In other words, the processing unit  110  can include a determination unit, a signal processing unit that processes signals, and a control unit. The processing unit  110  needs not necessarily be a processing apparatus such as a computer, but instead at least a part of processing can be performed in a cloud system. Further, a part of processing can be performed by an artificial intelligence (AI). The present exemplary embodiment illustrates a configuration in which the processing unit  110  includes the determination unit, the signal processing unit, and the control unit. However, the determination unit, the signal processing unit, and the control unit can be separately provided. 
     The display unit  111  can be a monitor of the computer of the processing unit  110 , or can be prepared to display an image. The display unit  111  displays an image based on the image information formed by the processing unit  110 . 
     To facilitate explanation of the present exemplary embodiment, assume that the following transmitters are provided in the configuration illustrated in  FIG.  1   . Assume that a terahertz wave is not generated from a transmitter  107   a  of the transmission unit  104 , or an electromagnetic wave at a frequency different from a desired frequency is generated due to a parasitic oscillation or the like. Also assume that a transmitter  108   a  of the transmission unit  105  generates a terahertz wave at a desired frequency, but the intensity of the terahertz wave is decreased. The transmitters  107   a  and  108   a  are illustrated for descriptive purposes assuming a case where a malfunction occurs in the transmitters. 
       FIGS.  2 A and  2 B  are schematic diagrams each illustrating an image captured by the camera system  1001  illustrated in  FIG.  1   , and  FIG.  2 C  is a schematic graph illustrating a method for processing the image in  FIG.  2 B .  FIG.  2 A  illustrates an image obtained by capturing an image of the object  109 . This image capturing operation is performed in a main image capturing operation. For example, a concealed object is detected from the captured image. The main image capturing operation indicates an operation of capturing an image of an object. In the present exemplary embodiment, the captured image indicates an image obtained by capturing an image in a direction perpendicular to the movement direction  112  of the object  109 , that is, an image obtained by capturing an image of a side surface of the object  109 . An image capturing direction can be changed depending on the intended use. The image capturing direction can be identified based on a direction of the optical axis of the optical system  101 . While the present exemplary embodiment assumes a case where the reception unit  100  detects a terahertz wave reflected by the object  109 , the reception unit  100  can also detect a terahertz wave that has been transmitted through the object  109 . Accordingly, positional relationships other than the positional relationship between the reception unit  100  and the transmission units  103  to  105 , such as the positional relationship between the reception unit  100  and the object  109  and the positional relationship between the object  109  and the transmission units  103  to  105 , can be changed as appropriate. 
       FIG.  2 B  illustrates a captured image of the transmission units  103  to  105 . This image is captured in a state where the object  109  is not present, or in a state where the object  109  is located outside of a range of the field angle of the reception unit  100 . The image illustrated in  FIG.  2 B  indicates a two-dimensional distribution of light and dark images depending on the intensity of the terahertz wave generated from each of the transmission units  103  to  105 . As the intensity increases, a lighter image can be obtained. In the image illustrated in  FIG.  2 B , the portions respectively corresponding to the transmission units  103  to  105  and the transmitters  106  to  108  illustrated in  FIG.  1    are denoted by the same reference numerals. In this case, the contrast of the images respectively corresponding to the transmitters  107   a  and  108   a  is different from that of the images respectively corresponding to the transmitters  106  to  108 .  FIG.  2 C  is a schematic graph illustrating an output of a terahertz wave at a location indicated by a broken line  212  illustrated in  FIG.  2 B . A vertical axis represents an output. This output can also be referred to as an intensity. 
     A portion corresponding to the transmitter  107   a  illustrated in  FIG.  2 B  is dark, and no signal is present in a desired terahertz wave band. The output corresponding to the transmitter  107   a  illustrated in  FIG.  2 C  is “0”. Accordingly, it is obvious that the transmitter  107   a  does not generate a terahertz wave at a desired frequency. A portion corresponding to the transmitter  108   a  illustrated in  FIG.  2 B  is lighter than the portion corresponding to the transmitter  107   a , but is darker than the other portions. The output corresponding to the transmitter  108   a  illustrated in  FIG.  2 C  is lower than the other outputs. Therefore, it is obvious that the transmitter  108  generates a terahertz wave at a desired frequency, but the intensity of the terahertz wave is decreased. 
     Examples of a method for detecting a decrease in the intensity include a method in which an allowable lower-limit threshold  213  is preliminarily determined as illustrated in  FIG.  2 C  and a determination is made based on whether the intensity is lower than the threshold. The output can be obtained based on an output intensity in a one-dimensional direction indicated by the broken line  212  in  FIG.  2 B , or can be set based on an output in each area identified from the image illustrated in  FIG.  2 B . As the output in each area, any value, such as a combined value of outputs from pixels in each area, or an average value of outputs from pixels in each area, can be set. Further, the output in each area can be obtained based on an output from one pixel in each area. This determination processing is performed by the processing unit  110  illustrated in  FIG.  1   , but instead a determination circuit can be provided in a readout circuit of the receiver  102 . In the manner as described above, a transmission unit inspection operation can be performed. 
       FIG.  3 A  is a flowchart illustrating the transmission unit inspection operation. First, in step S 300 , an operating state of each transmission unit is checked. In this step, it is checked whether each transmission unit irradiates a terahertz wave. Depending on the operating state, a sub-flow for switching an operation of the transmission unit can be performed. Further, an operation flow for skipping the subsequent step S 301  depending on the operating state can be added. In step S 301 , the irradiation of terahertz waves is started. The transmission units  103  to  105  operate to irradiate terahertz waves. In a case where the transmission units  103  to  105  are already in an irradiation state, the irradiation state is maintained. The irradiation state is also referred to as a light state. In step S 302 , images of the transmission units  103  to  105  are captured. The reception unit  100  detects the terahertz waves irradiated from the transmission units  103  to  105 . The image acquired in the irradiation state is also referred to as a light image. In step S 303 , it is determined whether the output of each of the transmission units  103  to  105  is more than or equal to a threshold based on a detected signal or an image based on the signal. In a case where the output is more than or equal to the threshold (Yes in step S 303 ), the inspection is completed. In a case where the output is less than the threshold (No in step S 303 ), the processing proceeds to step S 304 . In step S 304 , for example, the processing unit  110  issues an instruction and displays a warning on the display unit  111 . In addition, in a case where the output is less than the threshold (N in step S 303 ), for example, the processing unit  110  can perform an operation to issue an alert sound. This operation enables checking of the operation of each of the transmission units  103  to  105  that cannot be visually recognized. 
     In some cases, spatial noise or shading may be superimposed on the image illustrated in  FIG.  2 B  due to the circuit of the receiver  102 . In this case, the following operation is to be performed.  FIG.  3 B  is a flowchart illustrating another operation to be executed in the transmission unit inspection operation. In  FIG.  3 B , the descriptions of operations similar to those illustrated in  FIG.  3 A  are omitted. In step S 311 , the irradiation of terahertz waves is stopped. For example, the operation of each of the transmission units  103  to  105  is stopped to thereby stop the irradiation of terahertz waves. Alternatively, the transmission units  103  to  105  operate to stop the irradiation of terahertz waves. More alternatively, a member for blocking terahertz waves is disposed in front of the transmission units  103  to  105 . In a case where the transmission units  103  to  105  are already in a non-irradiation state, the non-irradiation state is maintained. The non-irradiation state is also referred to as a dark state. In step S 312 , images of the transmission units  103  to  105  are captured in the non-irradiation state. Each of the images captured in the non-irradiation state is also referred to as a dark image. Then, the operations in steps S 301  and S 302  are performed. In step S 313 , signal processing is performed. In the signal processing, processing for removing information about the dark image from information about the light image is performed. The dark image is referred to as a reference signal. In other words, in the signal processing, the reference signal is removed from the light image. In step S 303 , the determination is made in a state where the signal processing has been performed, and then the processing is completed, or step S 304  is executed. This processing leads to a reduction in noise and an improvement in the accuracy of the determination in step S 303 . The improvement in determination accuracy leads to an improvement in the accuracy of detecting a malfunction in the transmission units  103  to  105 . 
     If noise randomly occurs during a predetermined period of time, the following operation can be performed. In the operation flow illustrated in  FIG.  3 A , step S 302  can be performed a plurality of times and a plurality of light images can be averaged. Step S 302  can be performed based on the averaged image. In the operation flow illustrated in  FIG.  3 B , if noise randomly occurs during a predetermined period of time, step S 312  can be performed a plurality of times and a plurality of dark images can be averaged. In step S 313 , information about the averaged dark image can be removed from the light image. Further, in the operation flow illustrated in  FIG.  3 B , if noise randomly occurs during a predetermined period of time, each of steps S 302  and S 312  can be performed a plurality of times, and then a plurality of light images can be averaged and a plurality of dark images can be averaged. In step S 313 , information about the averaged dark image can be removed from the averaged light image. This processing makes it possible to reduce noise that randomly occurs during a predetermined period of time. Consequently, it is possible to improve the accuracy of detecting a malfunction in the transmission units  103  to  105 . 
     In steps S 301  and S 302 , the following operation can be performed. For example, in step S 301 , all the transmission units  103  to  105  can be brought into the irradiation state, and then step S 302  can be performed. Alternatively, the transmission units  103  to  105  can be brought into the irradiation state from the non-irradiation state by rotation, and an image capturing operation can be performed every time any of the transmission units  103  to  105  is brought into the irradiation state. In other words, steps S 301  and S 302  are performed a plurality of times by changing the operating state of each of the transmission units  103  to  105 . First, in step S 301 , the transmission unit  103  is brought into the irradiation state, and the transmission unit  104  and the transmission unit  105  are brought into the non-irradiation state. Then, step S 302  is performed. Step S 301  is performed again, and the transmission unit  103  and the transmission unit  105  are brought into the non-irradiation state and the transmission unit  104  is brought into the irradiation state. Then, step S 302  is performed. Step S 301  is performed again, and the transmission unit  103  and the transmission unit  104  are brought into the non-irradiation state and the transmission unit  105  is brought into the irradiation state. Then, step S 302  is performed. Not only the transmission units  103  to  105 , but also the transmitters  106  to  108  can be sequentially turned on and the image capturing operation can be performed every time this turning-on operation is performed. Alternatively, the image capturing operation can be performed by turning on a specific transmission unit or transmitter as an inspection target. 
     The image capturing operation in respective steps S 302  and S 312  can be an operation of capturing one frame (still image), a plurality of discontinuous frames, or temporally continuous frames (moving image). In the case of capturing a moving image, data corresponding to one frame can be extracted from the image and the extracted data can be processed. 
     Information about the number of transmission units and transmitters and an arrangement relationship between the transmission units and transmitters can be preliminarily held in the processing unit  110 . Examples of the information include information indicating that the three transmission units  103  to  105  each including four transmitters disposed in an array of 2 × 2 are aligned. Based on this information, each transmission unit and each transmitter can be extracted from the captured images of the transmission units and transmitters. Each transmission unit and each transmitter can also be extracted from the images using the AI. The AI can be provided in the processing unit  110 , a cloud system, or the like. This processing enables the display unit  111  to display the state of each of the transmission units  103  to  105 . Therefore, at least one of an improvement in the efficiency of the transmission unit inspection operation and an improvement in the convenience of the transmission unit inspection operation can be achieved. 
     The camera system  1001  can include an extra transmission unit (not illustrated). After step S 304 , the extra transmission unit can be switched to be operated. After step S 304 , the output of each of the transmission units  103  to  105  can also be increased. 
     The flow of the transmission unit inspection operation illustrated in  FIGS.  3 A and  3 B  can be carried out, when the camera system  1001  is installed in a place for operation, when maintenance work is periodically performed, or when the operation of the camera system  1001  is started. Such flow can be carried out every time the main image capturing operation is performed. In other words, after step S 304 , the processing can transition to the main image capturing operation. 
     The dark image acquired in step S 312  can also be acquired by bringing the transmission units  103  to  105  into a transmission state. In this case, a method for preventing the reception unit  100  from being directed toward the transmission units  103  to  105  is to be provided, or the reception unit  100  or the transmission units  103  to  105  are to be provided with a blocking unit for blocking terahertz waves, and when the dark image is acquired, the blocking unit are moved to a space between the reception unit  100  and the transmission units  103  to  105 . This operation makes it possible to acquire the dark image in a state where terahertz waves are not incident on the reception unit  100 . This method can be carried out in a case where the operation of the transmission units  103  to  105  or the other portion is unstable due to the operation of switching the state of each of the transmission units  103  to  105 . 
     A camera system  1002  according to a second exemplary embodiment will be described with reference to  FIGS.  4 A and  4 B . 
       FIG.  4 A  is a schematic diagram illustrating a configuration example of the camera system  1002 . A configuration of an optical system in the camera system  1002  is different from that of the camera system  1001  according to the first exemplary embodiment. An optical system  401  has a configuration in which an adjustment mechanism  402  for adjusting a focus is added to the optical system  101  illustrated in  FIG.  1   . Components of the second exemplary embodiment that are the same as those of the first exemplary embodiment are denoted by the same reference numerals and detailed descriptions thereof are omitted. 
     The adjustment mechanism  402  can focus the object  109  when an image of the object  109  is captured, and can focus the transmission units  103  to  105  when the transmission unit inspection operation is performed. 
       FIG.  4 B  illustrates an image captured by the camera system  1002  illustrated in  FIG.  4 A . Reference numerals used in  FIG.  4 B  are the same as those used in  FIG.  2 B . The adjustment mechanism  402  can perform the image capturing operation by focusing an electromagnetic wave on each of the transmission units  103  to  105 . Accordingly, a clearer image i.e., an output with higher precision than that of the first exemplary embodiment can be obtained. 
     With this configuration, the transmission unit inspection operation can be performed with high accuracy even in a layout in which a distance from the reception unit  100  to the transmission units  103  to  105  is different from a distance from the reception unit  100  to the object  109 . Further, the degree of freedom of installation of the transmission units  103  to  105  can be improved. 
     A camera system  1003  according to a third exemplary embodiment will be described with reference to  FIGS.  5 A to  5 C . 
       FIG.  5 A  is a schematic diagram illustrating a configuration example of the camera system  1003 . The camera system  1003  has a configuration in which a movable unit  500  that changes an orientation of the reception unit  100  is added to the camera system  1001  according to the first exemplary embodiment. Further, the camera system  1003  differs from the camera system  1001  in regard to the number of transmission units and the layout of the transmission units. Components of the third exemplary embodiment that are the same as those of the first exemplary embodiment are denoted by the same reference numerals and detailed descriptions thereof are omitted. 
     The camera system  1003  includes transmission units  501  to  506 . The transmission units  501  to  503  are grouped as a set of transmission units, and the transmission units  504  to  506  are grouped as another set of transmission units. The object  109  is located between the set of the transmission units  501  to  503  and the set of the transmission units  504  to  506 . The reception unit  100  is located between the set of the transmission units  501  to  503  and the set of the transmission units  504  to  506 . The movable unit  500  is a member that changes the image capturing direction of the reception unit  100  and also supports the reception unit  100 . In the case of performing the transmission unit inspection operation on the transmission units  501  to  503 , the movable unit  500  is rotated in a direction A. In the case of performing the transmission unit inspection operation on the transmission units  504  to  506 , the movable unit  500  is rotated in a direction B. The movable unit  500  receives a signal from the processing unit  110  and operates in response to the signal. The movable unit  500  can communicate with the processing unit  110 . In the configuration illustrated in  FIG.  5 A , the movable unit  500  communicates with the processing unit  110  through the reception unit  100 , but instead can directly communicate with the processing unit  110 . 
       FIGS.  5 B and  5 C  illustrate images captured with the configuration illustrated in  FIG.  5 A .  FIG.  5 B  illustrates images captured when the movable unit  500  is rotated in the direction A.  FIG.  5 C  illustrates images acquired when the movable unit  500  is rotated in the direction B.  FIG.  5 B  illustrates the images corresponding to the transmission units  501  to  503 , respectively.  FIG.  5 C  illustrates the images corresponding to the transmission units  504  to  506 , respectively. Each white area corresponds to a transmitter in each transmission unit. The provision of the movable unit  500  having a configuration as described above makes it possible to inspect a plurality of transmission units located in multiple directions by using one reception unit  100 . As illustrated in the layout of  FIG.  5 A , in a case where an irradiation surface of each of the transmission units  501  to  506  and a reception surface of the reception unit  100  do not face each other, the output of each of the transmission units  501  to  506 , which is detected by the reception unit  100 , may be decreased due to a directivity of each of the transmission units  501  to  506  and the cosine law. In this case, signal processing to correct the output before the output is determined is performed. Alternatively, the threshold value is to be changed. During the image capturing operation, images can be continuously captured while the movable unit  500  is moved in the direction A or in the direction B. Like in the second exemplary embodiment, the optical system  101  can be provided with the adjustment mechanism  402 , or a wide angle lens can be used. In this case, a plurality of transmission units can be captured in one image, but the resolution of each transmission unit is decreased. Accordingly, it is desirable to carry out the image capturing operation by taking into consideration the number of pixels. 
     During the transmission unit inspection operation, a reflecting member can be provided at a position corresponding to the object  109 . The reflecting member makes terahertz waves, which are irradiated from the transmission units  501  to  506 , be reflected, and the reflected waves can be detected by the reception unit  100 . It is also possible to inspect the light source in a state where an image of a front surface of each transmission unit is captured by adjusting the position or angle of the reflecting member. 
     The movable unit  500  according to the present exemplary embodiment can perform a rotational operation in the direction A or in the direction B, i.e., can move in a horizontal direction, but instead can move in any direction including a vertical direction. The structure of the movable unit  500  can also be applied to a general structure. 
     As described above in the present exemplary embodiment, the provision of the movable unit  500  that changes the image capturing direction makes it possible to effectively inspect a plurality of transmission units located in multiple directions. 
     A camera system  1004  according to a fourth exemplary embodiment will be described with reference to  FIG.  6   . 
       FIG.  6    is a schematic diagram illustrating a configuration example of the camera system  1004 . The camera system  1004  has a configuration in which another reception unit  600  is added to the camera system  1001  according to the first exemplary embodiment. Components of the fourth exemplary embodiment that are the same as those of the first exemplary embodiment are denoted by the same reference numerals and detailed descriptions thereof are omitted. In  FIG.  6   , the processing unit  110  and the display unit  111  are not illustrated. 
     Like the reception unit  100 , the reception unit  600  includes an optical system  601  and a receiver  602 . A component  650  that is reflected by the object  109  and is included in the terahertz waves generated from the transmission units  103  to  105  is imaged on the receiver  602 , and the receiver  602  detects a signal. In the present exemplary embodiment, the reflected wave from the object  109  is detected. Accordingly, the transmission units  103  to  105 , the object  109 , and the reception unit  600  are located in a V-shape as illustrated in  FIG.  6   . In other words, a direction connecting the transmission units  103  to  105  and the object  109  intersects with a direction connecting the object  109  and the reception unit  600 . The reception unit  100  is provided to inspect the transmission units  103  to  105 . The transmission unit inspection operation can be performed at a timing when the object  109  is not present. 
     With this configuration, the reception unit  600  that captures an image of the object  109  and the reception unit  100  that performs the transmission unit inspection operations are separately provided. Accordingly, each configuration can be simplified, for example, by fixing the focus or image capturing direction, and the transmission unit inspection operation and the image capturing operation can be effectively performed. 
     A camera system  1005  according to a fifth exemplary embodiment will be described with reference to  FIG.  7    to 8D. 
       FIG.  7    is a schematic diagram illustrating a configuration example of the camera system  1005 . The camera system  1005  has a configuration in which a reception unit  700  and transmission units  703  to  705  are added to the camera system  1001  according to the first exemplary embodiment. The reception unit  100  captures an image of a back surface of the object  109 , and the reception unit  700  captures an image of a front surface of the object  109 . Components of the fifth exemplary embodiment that are the same as those of the first exemplary embodiment are denoted by the same reference numerals and detailed descriptions thereof are omitted. In  FIG.  7   , the processing unit  110  and the display unit  111  are not illustrated.  FIGS.  8 A to  8 D  illustrate images captured with the configuration illustrated in  FIG.  7   . The components illustrated in  FIG.  8 A  that correspond to those illustrated in  FIG.  2 B  are denoted by the same reference numerals. 
     In the camera system  1005 , the units are disposed as follows. The reception unit  100  is disposed to face the transmission units  103  to  105 , and the reception unit  700  is disposed to face the transmission units  703  to  705 . A direction connecting the reception unit  100  and the transmission units  103  to  105  intersects with a direction connecting the reception unit  700  and the transmission units  703  to  705 . 
     Like the reception unit  100 , the reception unit  700  includes an optical system  701  and a receiver  702 . A component  750  that is reflected by the object  109  from the terahertz waves generated from the transmission units  103  to  105  is imaged on the receiver  702 , and the receiver  702  detects the signal. 
     The operation of the camera system  1005  will be described below with reference to  FIG.  3 A . In steps S 301  and S 302 , the reception unit  100  captures images of the transmission units  103  to  105 , and the reception unit  700  captures images of the transmission units  703  to  705 . Based on the captured images, the transmission units  103  to  105  and the transmission units  703  to  705  are inspected. Steps S 301  and S 302  may be executed on the transmission units  103  to  105 , may be executed on the transmission units  703  to  705 , or may be executed on the transmission units  103  to  105  and the transmission units  703  to  705 . In any case, the reception unit  100  or the reception unit  700  is used depending on the case.  FIG.  8 A  illustrates images obtained when the reception unit  100  captures images of the transmission units  103  to  105 .  FIG.  8 B  illustrates images obtained when the reception unit  700  captures images of the transmission units  703  to  705 . 
     In the main image capturing operation, the following operation is performed. Terahertz waves irradiated from the transmission units  103  to  105  are reflected on the front surface of the object  109 , and the reflected component  750  is received by the reception unit  700 . Thus, an image of the front surface of the object  109  can be acquired. Terahertz waves irradiated from the transmission units  703  to  705  are reflected on the back surface of the object  109 , and a reflected component  751  is received by the reception unit  100 . Thus, an image of the back surface of the object  109  can be acquired.  FIG.  8 C  illustrates the image obtained when the reception unit  700  captures an image of the object  109 .  FIG.  8 D  illustrates the image obtained when the reception unit  100  captures an image of the object  109 . 
     In the camera system  1005  capable of capturing images of the front surface and the back surface of the object  109 , the image of the object  109  can be captured and the transmission unit inspection operation can be performed. This configuration leads to simplification of the entire system of the camera system  1005 , and makes it possible to effectively perform the light source inspection operation. 
     Some exemplary embodiments of the disclosure have been described above. However, the disclosure is not limited to the above-described exemplary embodiments and can be modified or altered in various ways within the scope of the disclosure. The components of the camera systems according to the above-described exemplary embodiments can be combined and used. 
     Further, in each exemplary embodiment, operations to be performed by the reception units, the transmission units, and the movable unit can be converted into a system to be automatically controlled. Specific examples of the operations include turning on/off operations of the transmission units, an operation of changing the image capturing direction by rotating the movable unit, focus adjustment and image capturing operations of the reception units, and a periodical transmission unit inspection operation. These operations can be arbitrarily combined and automated, which leads to a reduction in human workload. 
     While the disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.