JP7475145B2 - Electromagnetic wave detector and scanner - Google Patents

Description

The present invention relates to an electromagnetic wave detection device that detects electromagnetic waves, and a scanner that uses the same to detect electromagnetic waves and inspect, for example, the internal condition of an object to be inspected.

For example, one known technology for detecting objects is one that uses a rectangular polygon mirror and multiple light receiving units (see Patent Document 1). Another known technology is one that uses terahertz waves to perform body scans (see Patent Document 2).

However, in a configuration that uses a polygon mirror to detect objects as exemplified in Patent Document 1, it may not be possible to maintain uniform light reception over a wide range (angle). For example, even if an attempt is made to use the technology described in Patent Document 1 to perform a body scan using terahertz waves as in the technology described in Patent Document 2, proper detection may not be possible.

JP 2014-115182 A JP 2019-190951 A

The present invention has been made in consideration of the above points, and aims to provide an electromagnetic wave detection device that can maintain uniform electromagnetic wave detection even when the angle is widened, and a scanner using the same.

To achieve the above objective, the electromagnetic wave detection device includes a rotating mirror having a reflective surface that is inclined at a predetermined angle relative to the rotation axis and reflects electromagnetic waves, a focusing optical system that focuses the components of the electromagnetic waves that pass through the rotating mirror and are incident from a specific direction relative to the reflective surface, and a light receiving element that receives the electromagnetic waves focused by the focusing optical system.

The electromagnetic wave detection device described above can maintain the state in which the electromagnetic waves to be detected while the reflecting surface of the rotating mirror rotates are components that are incident on the reflecting surface from a specific direction. This makes it possible to maintain uniform electromagnetic wave detection, i.e., light reception, even if the rotation angle of the rotating mirror is increased, i.e., widened.

In a specific aspect of the present invention, the reflecting surface of the rotating mirror is a plane inclined at a predetermined angle of 45° with respect to the axis of rotation, and reflects components of electromagnetic waves incident from a specific direction in a direction parallel to the axis of rotation. In this case, it is possible to more reliably extract and focus components incident from a specific direction.

In another aspect of the present invention, the focusing optical system is a parabolic mirror, and the light receiving element is provided at the focal position of the parabolic mirror. In this case, the parabolic mirror enables highly efficient light reception.

In yet another aspect of the present invention, the focusing optical system is a focusing lens, and the light receiving element is provided at the focal position of the focusing lens. In this case, the focusing lens enables highly efficient light reception.

A scanner for achieving the above objective includes any of the above electromagnetic wave detection devices and an object detection unit that detects an object based on the light reception results of the light receiving element.

The above scanner is capable of maintaining uniform electromagnetic wave detection, i.e., light reception, even when the electromagnetic wave detection device has a wide angle, and this can be used to perform accurate object detection.

1 is a block diagram showing a configuration example of an electromagnetic wave detection device according to a first embodiment. 1A and 1B are perspective views showing an example of the operation of an electromagnetic wave detection device. 1 is a conceptual cross-sectional view showing how light is received in an electromagnetic wave detection device. FIG. 2 is a conceptual plan view showing how light is received in an electromagnetic wave detection device. 1A is a conceptual plan view showing an example of a scanner equipped with an electromagnetic wave detection device, and FIG. FIG. 13 is a conceptual plan view showing a modified example of the scanner. FIG. 1A is a conceptual plan view illustrating an example of the light receiving range of an electromagnetic wave detection device, and FIG. 1B is a diagram illustrating the intensity of electromagnetic waves emitted from the surface of a detection object. 13A and 13B are conceptual diagrams for explaining the relationship between the light receiving range and the characteristics of the electromagnetic waves generated from the object to be inspected. FIG. 11 is a conceptual cross-sectional view showing a configuration example of an electromagnetic wave detection device according to a second embodiment. 13A to 13C are diagrams showing modified examples of the rotating mirror. FIG. 11 is a perspective view showing another configuration example of an electromagnetic wave detection device.

First Embodiment
An example of an electromagnetic wave detection device according to the first embodiment will be described below with reference to Fig. 1 etc. Fig. 1 is a block diagram showing an example of the configuration of an electromagnetic wave detection device 100 according to this embodiment, showing each component. Meanwhile, Fig. 2(A) and Fig. 2(B) are perspective views showing an example of the shape and operation of each optical member for guiding and focusing a specific electromagnetic wave inside the device, among the components of the electromagnetic wave detection device 100.

The electromagnetic wave detection device 100 illustrated in FIG. 1 is a device for collecting and detecting electromagnetic waves. Here, as an example, the electromagnetic wave detection device 100 is a device that detects the electromagnetic waves to be detected as terahertz waves naturally emitted from an object. The electromagnetic wave detection device 100 includes a rotating optical system 10, a parabolic mirror 20 that is a collecting optical system, a light receiving unit 30, a radome (radar dome) 40, and a main control unit 50. The electromagnetic wave detection device 100 is a device that can be mounted on, for example, a scanner (body scanner) described below.

Hereinafter, as shown in Fig. 2(A) and Fig. 2(B), in an XYZ Cartesian coordinate system, the axial direction of the rotation axis AX in the rotating optical system 10 is defined as the Z direction, and the in-plane directions perpendicular to this are defined as the X direction and the Y direction. In the illustrated example, the arrangement direction of the parabolic mirror 20 and the light receiving unit 30 fixedly installed in the electromagnetic wave detection device 100 is defined as the Y direction, and the direction perpendicular to the Z direction and the Y direction is defined as the X direction. The rotating rotating optical system 10 is further defined in an xyz Cartesian coordinate system, which will be described later.

Returning to FIG. 1, the rotating optical system 10 of the electromagnetic wave detection device 100 is a reflective member that rotates and bends the optical path of the terahertz wave incident from the outside through the radome 40, and includes a rotating mirror 11 having a reflecting surface RS1 for bending the optical path, a motor 12 that rotates the rotating mirror 11 around the rotation axis AX, and a drive control unit 13 that is a driver that controls the rotation drive of the motor 12. As illustrated in the perspective views of FIG. 2(A) and FIG. 2(B), the rotating mirror 11 has a quadrangular pyramid shape, and is a regular quadrangular pyramid with the bottom surface B located on the upper side (+Z side). Of these, the perpendicular line drawn from the apex A to the bottom surface B coincides with the rotation axis AX. In addition, a reflecting surface RS1 is formed on the side of the regular quadrangular pyramid, and here, in particular, the reflecting surface RS1 is a plane inclined at 45° with respect to the rotation axis AX. That is, as shown in FIG. 1, the predetermined angle α between the reflecting surface RS1 and the rotation axis AX is α=45°. In the above case, in the rotating optical system 10, the rotating mirror 11 rotates with the rotation axis AX as the central axis, and the reflecting surface RS1 as the rotating surface rotates while maintaining the above-mentioned predetermined angle α. Regarding the rotation drive, the drive control unit 13 outputs various electrical signals such as a drive signal to the motor 12 according to instructions from the main control unit 50, and the rotating mirror 11 is rotated by the motor 12.

As shown in Fig. 2(A) and Fig. 2(B), the direction of the rotating mirror 11, which changes direction by rotating around the rotation axis AX, is defined as the z direction in an xyz Cartesian coordinate system, and the in-plane directions perpendicular to the axial direction of the rotation axis AX, i.e., the z direction, are defined as the z direction, and the in-plane directions perpendicular to the z direction are defined as the x direction and the y direction. In the example shown in the figure, the direction parallel to one side of the square base B is the x direction, and the direction parallel to the other side perpendicular to the x direction is the y direction. For example, the state shown in Fig. 2(A) shows a state in which the above-mentioned XYZ directions and the xyz directions are aligned, but when this is rotated around the rotation axis AX to the state shown in Fig. 2(B), for example, the x direction and the y direction will change.

Next, in the electromagnetic wave detection device 100, the parabolic mirror 20 has a curved surface (also called a paraboloid of revolution or simply a paraboloid) shape that is generated when a parabola is rotated around its axis, as illustrated in the perspective views of Figures 2(A) and 2(B), and is a focusing optical system having a reflecting surface RS2 inside the curved surface shape. As described above, the rotating mirror 11 is rotatable inside the electromagnetic wave detection device 100, whereas the parabolic mirror 20 is fixedly installed. The parabolic mirror 20 functions as a focusing optical system by focusing the component RL of the terahertz wave that has passed through the rotating mirror 11 and is incident from a specific direction relative to the reflecting surface RS1 at the focal position of the curved surface by reflection from the reflecting surface RS2. Details of the optical path of the terahertz wave will be described later with reference to Figure 3, etc.

Returning to FIG. 1, the light receiving unit 30 of the electromagnetic wave detection device 100 includes a light receiving element 31 and a light receiving signal processing unit 32, and detects electromagnetic waves, i.e., terahertz waves, in a fixed installation state. The light receiving element 31 of the light receiving unit 30 is composed of, for example, a photodiode, and receives the terahertz wave components collected by the parabolic mirror 20 as a light collecting optical system. The light receiving signal processing unit 32 is composed of, for example, various circuits, and performs various processes related to the light reception by the light receiving element 31, and outputs the light reception result as a signal to the main control unit 50. Here, the light receiving position RP of the light receiving element 31 is set at the focal position of the parabolic mirror 20, so that the components collected by the parabolic mirror 20 are captured. Also, here, the light receiving position RP is aligned so as to be on the rotation axis AX. In other words, the central axis of the parabolic mirror 20, which is a paraboloid of revolution, is aligned with the axis of rotation AX, and the focal position of the parabolic mirror 20 is aligned with the position of the axis of rotation AX of the rotating mirror 11, and further, the light receiving position RP of the light receiving element 31 is aligned with the focal position of the parabolic mirror 20.

The radome 40 is provided on the front side of the optical path of the rotating mirror 11, and serves as an entrance window through which terahertz waves from the outside enter the inside of the electromagnetic wave detection device 100. The radome 40 is a flat member made of a resin material, such as polyethylene or Teflon (registered trademark), that absorbs and generates little terahertz waves.

The main control unit 50 is composed of various electronic circuits, for example, and is connected to each part of the electromagnetic wave detection device 100, such as the drive control unit 13 and the light receiving signal processing unit 32, to provide overall control over the operation of each part and enable various signal processing. In particular, the drive control unit 13 controls the rotational operation of the rotating mirror 11, i.e., controls the attitude of the reflecting surface RS1, and receives a signal related to the light receiving result from the light receiving signal processing unit 32, making it possible to detect the received light intensity of terahertz waves from a specific direction relative to the reflecting surface RS1. The main control unit 50 is capable of outputting the results related to the detected light receiving intensity to an external device (for example, a scanner control device).

The light reception in the electromagnetic wave detection device 100 will be described below with reference to the cross-sectional view in Figure 3 and the plan view in Figure 4. Figure 3 conceptually shows a cross-sectional view of the rotating mirror 11 taken parallel to the zy plane at a position passing through the rotation axis AX, and Figure 4 conceptually shows the appearance of each part as viewed from the direction indicated by C-C in Figure 3.

First, referring to FIG. 3, if we consider tracing the optical path of the terahertz wave backwards in the electromagnetic wave detection device 100 configured as above, the component RL that is focused at the light receiving position RP, i.e., received, is a component that is parallel to the central axis, i.e., the rotation axis AX, of the parabolic mirror 20 just before reflection at the parabolic mirror 20. Furthermore, since the reflecting surface RS1 is a plane inclined at 45° with respect to the rotation axis AX, the component RL that is parallel to the rotation axis AX is a component that is bent by 90° at the reflecting surface RS1. From the above, the component RL that is focused at the light receiving position RP out of the terahertz wave that enters the electromagnetic wave detection device 100 via the radome 40 comes from a specific direction indicated by the arrow DD1 in the figure. Note that the specific direction indicated by the arrow DD1 is the -y direction for the rotating mirror 11.

Regarding the above optical path, when we look at the reflecting surface RS1 of the rotating mirror 11, the reflecting surface RS1 is a plane inclined at a predetermined angle α of 45° with respect to the rotation axis AX, and reflects the component RL of the terahertz wave, which is an electromagnetic wave, that is incident from a specific direction (-y direction) indicated by the arrow DD1 in a direction parallel to the rotation axis AX.

On the other hand, terahertz wave components coming from directions other than the specific direction indicated by arrow DD1 are not focused at the light receiving position RP. For example, the terahertz wave component RLx indicated by the dashed line in the figure is a component that is incident from a direction different from the direction of arrow DD1, and such terahertz wave component RLx does not head toward the light receiving position RP even if it is reflected by reflecting surfaces RS1 and RS2. In other words, the electromagnetic wave detection device 100 focuses only the component RL that is incident from a specific direction (the direction indicated by arrow DD1) relative to reflecting surface RS1.

The relationship between the light receiving position RP and the specific direction of the received component RL is always maintained while the rotating mirror 11 rotates, as shown in FIG. 4. Specifically, for example, when the rotating mirror 11 is in a position shown as rotating mirror 11A facing slightly toward the -X side from the Y direction, the component RLa from the specific direction shown by the arrow DD1a is the light receiving target at the light receiving position RP. Similarly, when the rotating mirror 11 is in a position shown as rotating mirror 11B, the component RLb from the specific direction shown by the arrow DD1b is the light receiving target at the light receiving position RP, and when the rotating mirror 11 is in a position shown as rotating mirror 11C, the component RLc from the specific direction shown by the arrow DD1c is the light receiving target at the light receiving position RP. In other words, in all of these cases, the positional relationship shown in FIG. 3 is maintained. In other words, the electromagnetic wave detection device 100 is configured to receive only the component from the specific direction depending on the posture of the rotating mirror 11.

As described above, in this embodiment, by reflecting the component RL parallel to the plane on which the rotating mirror 11 rotates, i.e., the xy plane, in the direction of the rotation axis, it is possible to always obtain a constant amount of received light regardless of the rotation angle of the rotating mirror 11.

For example, when the electromagnetic wave detection device 100 is used as a scanner (body scanner) that detects whether a person being inspected is carrying a dangerous object such as a bladed weapon, it is important that a constant light receiving state is maintained in any state, independent of the angle of the mirror when taking in light. This is because a body scan based on electromagnetic wave detection identifies whether the object being inspected is a person or a bladed weapon based on the difference (change) in the amount of received light. Also, for practical purposes when performing detection, it is desirable for the light receiving range, i.e., the angle range (rotation range), to be as wide as possible.

In contrast, as described above, this embodiment is configured to collect only the components incident from a specific direction, so that the light receiving state can be kept constant so that it does not change depending on the detection range (detection direction). Furthermore, in this embodiment, the light receiving range can be made wider by adjusting the rotation range of the rotating mirror 11 and the shape of the parabolic mirror 20 accordingly. In other words, the electromagnetic wave detection device 100 can maintain uniform electromagnetic wave detection even when the angle is widened.

An example of the scanner according to this embodiment will be described below with reference to FIG. 5. The scanner 500 equipped with the electromagnetic wave detection device 100 illustrated in FIG. 5(A) and FIG. 5(B) functions as a body scanner that scans a person HU to be inspected by combining multiple electromagnetic wave detection devices 100 and linking them in a control device MP. The control device MP is composed of, for example, a PC equipped with a CPU, a storage device, etc., and controls various operations. The control device MP functions as an object detection unit OD that detects an object based on the light reception result of the light receiving element 31 (see FIG. 1, etc.) built into each electromagnetic wave detection device 100. Note that FIG. 5(A) is a conceptual plan view showing an example of the scanner 500, showing a state where the person HU is viewed from above. Meanwhile, FIG. 5(B) is a conceptual front view showing a state where the person HU is viewed from the front.

Here, as an example, as shown in FIG. 5(A), the scanner 500 is a person HU who is a pedestrian passing through a specific passage such as a ticket gate at a station, and the person HU moves (proceeds) in the direction of the arrow AR1, and the electromagnetic wave detection devices 100 are arranged along the direction of the arrow AR1. In this example, the electromagnetic wave detection devices 100 are arranged in a set of two, arranged in the vertical direction for the person HU, as shown in FIG. 5(B), and as shown in FIG. 5(A), a first scanner 500F is arranged in two sets, one on each side of the back side in the traveling direction, and a second scanner 500B is arranged in two sets, one on each side of the front side. That is, in this case, the scanner 500 is composed of a total of eight electromagnetic wave detection devices 100. For example, in the first scanner 500F, as shown in FIG. 5B, one set on the right side of the person HU is composed of the upper electromagnetic wave detection device 100A and the lower electromagnetic wave detection device 100C, and one set on the left side is composed of the upper electromagnetic wave detection device 100B and the lower electromagnetic wave detection device 100D. Furthermore, as shown in FIG. 5A, the Z direction, which is the rotation axis direction of each electromagnetic wave detection device 100, is a horizontal in-plane direction for the person HU. As a result, each electromagnetic wave detection device 100 scans the person HU in the up-down direction. While each electromagnetic wave detection device 100 continues to scan the person HU in the up-down direction, the person HU moves in the direction of the arrow AR1, and each part of the person HU is scanned sequentially. With regard to scanning in the up-down direction, the electromagnetic wave detection devices 100A and 100B arranged on the upper side mainly scan the upper body of the person HU, and the electromagnetic wave detection devices 100C and 100D arranged on the lower side mainly scan the lower body of the person HU.

As shown in the figure, the Z directions of the electromagnetic wave detection devices 100 are different from each other in the horizontal in-plane direction (for example, directions that differ by 90°). This allows different positions of the person HU to be scanned. Specifically, the first scanner 500F scans the front side of the person HU, and the second scanner 500B scans the rear side of the person HU.

In the case of FIG. 5(A), the first scanner 500F and the second scanner 500B are installed at a certain distance in the direction of the arrow AR1, so that when the person HU is sandwiched between the first scanner 500F and the second scanner 500B, scanning is performed simultaneously from the left and right sides of the front and the left and right sides of the rear.

In contrast to this, as shown in a modified example in FIG. 6, which corresponds to FIG. 5A, the first scanner 500F and the second scanner 500B may not be spaced apart very far from each other, and the first scanner 500F may be placed at the front in the direction of travel, while the second scanner 500B may be placed at the back. In this case, the first scanner 500F first scans the front side of the person HU, and after the person HU passes the first scanner 500F, the second scanner 500B scans the rear side of the person HU.

As described above, the electromagnetic wave detection device 100 according to this embodiment includes a rotating mirror 11 having a reflecting surface RS1 that is inclined at a predetermined angle α with respect to the rotation axis AX and reflects terahertz waves as electromagnetic waves, a parabolic mirror 20 that is a focusing optical system that focuses the component RL of the terahertz waves that have passed through the rotating mirror 11 and are incident from a specific direction (arrow DD1) relative to the reflecting surface RS1, and a light receiving element 31 that receives the terahertz waves focused by the parabolic mirror 20. In this case, the electromagnetic wave detection device 100 can maintain a state in which the terahertz waves to be detected while the reflecting surface RS1 of the rotating mirror 11 rotates are the components that are incident from the specific direction DD1 relative to the reflecting surface RS1. This allows uniform electromagnetic wave detection, i.e., light reception, to be maintained even if the rotation angle of the rotating mirror 11 is increased, i.e., widened. In addition, in this embodiment, a refractive system is not used as the optical system for changing the optical path of the terahertz waves, and instead, it is configured with only a reflective system (mirror system), which means that no chromatic aberration occurs and it is possible to detect terahertz waves with a wide wavelength band.

In addition, the scanner 500 according to this embodiment can maintain uniform electromagnetic wave detection, i.e., light reception, even when the electromagnetic wave detection device 100 is mounted at a wide angle, allowing accurate object detection.

Below, we will consider the relationship between the light receiving range of the electromagnetic wave detection device 100 and the radiation characteristics of terahertz waves from the detection target with reference to Figures 7 and 8.

First, as shown in FIG. 7, the radome 40 serving as the entrance window is assumed to be a flat member parallel to the XZ plane. Also, the length of the entrance width H1 of the terahertz wave component RL to be received by the rotating mirror 11 is assumed to be 1.

In this case, if the xyz directions of the rotating mirror 11 are aligned with the XYZ directions, the incidence width H2 of the component RL in the X direction at the radome 40 is also 1. Note that the rotation angle of the rotating mirror 11 around the rotation axis AX in this state is 0°.

In contrast, when the rotating mirror 11 rotates and the rotation angle is θ, the length of the incident width H1 at the rotating mirror 11 remains 1, but the corresponding incident width H2 at the radome 40 becomes 1/cosθ. In other words, the incident width H2 becomes 1/cosθ times the incident width H1.

On the other hand, as shown in FIG. 7B, when the surface SF of the object to be detected is completely dissipative, the intensity LI of the light (terahertz wave) emitted from any one point SP on the surface SF is proportional to the cosine of the angle between the normal to the surface SF and the observation direction. In other words, as shown in the figure, if the intensity of the component LIc directed toward the front (intensity at an angle of 0° relative to the front) is set to 1, it is known that the intensity of the component LIp emitted in the direction of angle θ is relatively multiplied by cos θ (Lambert's cosine law).

Therefore, first, as shown in FIG. 8(A), when the component LIc of the detection target that is directed toward the front is incident on the electromagnetic wave detection device 100 (i.e., when θ = 0°), its relative intensity is 1. On the other hand, the width of the incidence width H2 of the component RL in the X direction in the radome 40, which serves as the incidence window that receives it, is relatively 1. In other words, the overall light amount is 1 x 1 = 1.

Next, as shown in FIG. 8(B), when component LIp emitted in a direction of angle θ (≠0°) from the detection target enters the electromagnetic wave detection device 100, its relative intensity is cosθ. On the other hand, the width of the incidence width H2 of component RL in the X direction in the radome 40, which serves as an incidence window that receives this, is relatively 1/cosθ. In other words, the total amount of light is cosθ×1/cosθ=1.

From the above, it is believed that uniform electromagnetic wave detection, i.e., light reception, is maintained even if the rotation angle of the rotating mirror 11 changes.

Second Embodiment
An example of an electromagnetic wave detection device according to the second embodiment will be described below with reference to Fig. 9. The electromagnetic wave detection device of this embodiment is similar to the electromagnetic wave detection device 100 shown as an example in the first embodiment, except for the configuration of the light collecting optical system, so that common components in the overall configuration are given the same reference numerals, and detailed description of parts other than the light collecting optical system will be omitted.

Figure 9 is a conceptual cross-sectional view of an example configuration of the electromagnetic wave detection device 200 according to this embodiment, and corresponds to Figure 3.

As shown in the figure, the electromagnetic wave detection device 200 of this embodiment differs from the electromagnetic wave detection device 100 illustrated in Figures 1 and 3, etc. in that it has a focusing lens 220 instead of a parabolic mirror 20 (see Figure 3, etc.) as the focusing optical system.

The focusing lens 220 as the focusing optical system is, for example, a spherical convex lens or a part thereof, and the lens optical axis coincides with the rotation axis AX. Furthermore, the light receiving position RP of the light receiving element 31 is aligned with the focal position of the focusing lens 220. In other words, the light receiving element 31 is provided at the focal position of the focusing lens 220.

As in the first embodiment, in the electromagnetic wave detection device 200, the rotating mirror 11 is rotatable within the electromagnetic wave detection device 100, whereas the light receiving unit 30 including the focusing lens 220 and the light receiving element 31 is fixedly installed. In the above configuration, the reflecting surface RS1 of the rotating mirror 11 is a plane inclined at a predetermined angle α of 45° with respect to the rotation axis AX, and reflects the component RL of the terahertz wave, which is an electromagnetic wave, incident from a specific direction indicated by the arrow DD1 in a direction parallel to the rotation axis AX. In contrast, the focusing lens 220 focuses the component RL parallel to the rotation axis AX, which is a parallel light beam with respect to the optical axis, at the focal position, i.e., the light receiving position RP.

The focusing lens 220 is not limited to a single spherical convex lens, but may be composed of various lenses or multiple lenses whose focal position can be used as the light receiving position RP. For example, by using an achromatic lens, it may be possible to accommodate a wide wavelength band of terahertz waves.

By adopting the above-mentioned configuration, even in this embodiment, uniform electromagnetic wave detection, i.e., light reception, can be maintained even if the rotation angle of the rotating mirror 11 is increased, i.e., widened. In particular, in the case of this embodiment, the focusing lens 220 enables highly efficient light reception.

〔others〕
The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit and scope of the present invention.

First, in the above, the shape of the rotating mirror 11 constituting the rotating optical system 10 is a regular square pyramid, but this is not limited to this, and various shapes having a reflective surface RS1 that can rotate while maintaining a predetermined angle α with respect to the rotation axis AX can be adopted. For example, embodiments shown in three-sided views in Figures 10(A) to 10(C) are possible. First, as shown in Figure 10(A), the cylindrical end may be cut diagonally to have one reflective surface RS1. Alternatively, as shown in Figure 10(B), the cylindrical end may be cut from two directions. Furthermore, as shown in Figure 10(C), the rotating mirror 11 may be a triangular pyramid (tetrahedron).

Furthermore, various modifications are possible with respect to the configuration of the reflecting surface RS1 of the rotating mirror 11 and the reflecting surface RS2 of the parabolic mirror 20, so long as the desired light guidance that can achieve the above-mentioned objective can be maintained. For example, as in another configuration example shown in FIG. 11, in the rotating mirror 311 that constitutes the rotating optical system 310, it is possible to limit the focused spot by making only a part of the inclined surface (side surface) the reflecting surface (mirror) RS1. For example, the focused spot may be made circular by making the reflecting surface RS1 an ellipse. Furthermore, the shape of the parabolic mirror 320 may be changed to match the shape of the reflecting surface RS1, as shown in the figure.

In the above, the predetermined angle α is set to 45°, but it is also possible to set it to another angle if the desired focusing is possible. In addition, the focusing position, i.e., the focal position of the focusing optical system, may also be set to a position other than the above.

In addition, although terahertz waves are given as an example of electromagnetic waves in the above, electromagnetic waves in wavelength bands other than terahertz waves (infrared light, visible light, ultraviolet light, etc.) may also be detected.

In addition, the above embodiment is a so-called passive type configuration in which the electromagnetic waves (terahertz waves) naturally emitted from an object are detected, but each of the above embodiments may be adopted in a so-called active type configuration in which the reflected components of the electromagnetic waves (terahertz waves) emitted by the object are detected. In this case, for example, by installing a light emitting source near the light receiving position or at a position optically equivalent to the light receiving position, it becomes possible to detect an object using the above embodiment.

10...rotating optical system, 11, 11A, 11B, 11C...rotating mirror, 12...motor, 13...drive control unit, 20...parabolic mirror (light-collecting optical system), 30...light-receiving unit, 31...light-receiving element, 32...light-receiving signal processing unit, 40...radome (radar dome), 50...main control unit, 100, 100A, 100B, 100C, 100D, 200...electromagnetic wave detection device, 220...light-collecting lens (light-collecting optical system), 310...rotating optical system, 311...rotating mirror, 3 20...parabolic mirror, 500, 500F, 500B...scanner, A...vertex, AR1...arrow, AX...rotation axis, B...bottom, DD1, DD1a, DD1b, DD1c...arrow, H1, H2...incident width, HU...person, LI...intensity, LIc, LIp...components, MP...control device, OD...object detection unit, RL, RLa, RLb, RLc, RLx...components, RP...light receiving position, RS1, RS2...reflecting surface, SF...surface, SP...point, α...angle, θ...angle

Claims (4)

a rotating mirror having a reflective surface that is inclined at a predetermined angle with respect to a rotation axis and that reflects, in a direction parallel to the rotation axis, a component of electromagnetic waves that are terahertz waves naturally emitted from an object and that are incident from a specific direction;
a parabolic mirror having the rotation axis as a central axis and configured to reflect and collect a component of the electromagnetic wave that has passed through the rotating mirror and is reflected by the reflecting surface in a direction parallel to the rotation axis;
a light receiving element that receives the electromagnetic waves collected by the parabolic mirror , and scans in one direction,
An electromagnetic wave detection device , wherein the rotation axis direction of the rotating mirror is different from the rotation axis direction of a rotating mirror of another electromagnetic wave detection device that scans in the one direction . The electromagnetic wave detection device according to claim 1, wherein the reflecting surface of the rotating mirror is a plane inclined at 45° with respect to the axis of rotation as the predetermined angle. The electromagnetic wave detection device according to claim 1 or 2, wherein the light receiving element is provided at the focal position of the parabolic mirror. An electromagnetic wave detection device according to any one of claims 1 to 3,
and an object detection unit that detects an object based on the light reception result at the light receiving element.

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