Aperture structure and method for identifying plastics

Abstract

A beam with a frequency on the order of terahertz or gigahertz is reduced in diameter without being focused while maintaining its parallel light. [Solution] The aperture structure has a space inside through which a beam of electromagnetic waves, having a frequency on the order of terahertz or gigahertz and defined as parallel light, passes. The aperture structure includes an inlet opening that serves as the entrance for the beam to the space, an outer inclined surface tilted with respect to the direction of beam propagation, and an outer metal film covering the outer inclined surface. The diameter of the inlet opening is smaller than the diameter of the beam.

Description

[Technical Field]

[0001] The disclosed technology relates to an aperture structure and a plastic identification method. [Background Art]

[0002] The following techniques are known as technologies related to identification of plastics using terahertz waves. For example, Patent Document 1 describes a substance identification device including: an irradiation unit that irradiates an object with a plurality of sub-terahertz waves of different frequencies; a detection unit that detects the plurality of sub-terahertz waves reflected by the object; and an identification unit that identifies the type of substance constituting the object based on the reflectance of each of the plurality of sub-terahertz waves detected by the detection unit and the slope of the reflectance obtained from the reflectance with respect to frequency.

[0003] On the other hand, the following techniques are known as technologies related to members that limit beam diameter. For example, Patent Document 2 describes an aperture that narrows the beam diameter of laser light by passing the laser light through an opening. The aperture is made of a material that transmits laser light, both surfaces of an edge portion that limits excess laser light and narrows the beam diameter are formed as incident surfaces perpendicular to the laser light, and a notch having a reflective surface that totally reflects the laser light incident from the incident surface toward a predetermined interior is provided at the tip of the incident surface.

[0004] Patent Document 3 describes a spatial filter including a light shielding member that shields light and an opening hole provided in the shielding member, wherein the spatial filter limits the diameter of a passing light beam according to the aperture of the opening hole. In the opening hole, the aperture on the light incident side is smaller than the aperture on the light exit side. Further, at least a part of the inner wall of the opening hole is formed in a tapered shape. [Prior Art Documents] [Patent Documents]

[0005] [Patent Document 1] WO2023 / 033186 [Patent Document 2] Japanese Unexamined Patent Publication No. 2001-94180 [Patent Document 3] Japanese Patent Application Publication No. 10-333098 [Overview of the project] [Problems that the invention aims to solve]

[0006] In identifying plastics using gigahertz or terahertz waves, a beam with a frequency on the terahertz or gigahertz order is irradiated onto the plastic to be identified, and its transmittance is measured. There are two methods for irradiating the beam. The first method involves irradiating the plastic to be identified with a beam emitted from a light source, made into parallel light by a lens. This method is applied when the size of the plastic to be identified is sufficiently larger than the beam diameter.

[0007] The second method involves focusing a beam emitted from a light source and irradiating the plastic to be identified. This method is applicable when the size of the plastic to be identified is smaller than the beam diameter.

[0008] The first method, using a parallel beam, has the problem that it cannot be applied when the size of the plastic being identified is smaller than the beam diameter. The second method, using a focused beam, causes the beam to spread as it passes through the plastic being identified. Therefore, differences in the thickness and shape of the plastic can greatly affect the transmittance, making it difficult to obtain accurate information about the plastic. Furthermore, in the terahertz range, it is difficult to precisely control the focal length with lenses.

[0009] One method for reducing the beam diameter of a beam with frequencies on the terahertz or gigahertz order while keeping it parallel without focusing is to combine a convex lens and a concave lens. However, the Teflon® lenses currently used in experimental systems have a low refractive index in the terahertz region, making it difficult to effectively reduce the beam diameter in a confined space. Lenses made of materials with a high refractive index and low absorption in the terahertz region are still under development.

[0010] The disclosed technology was developed in view of the above points and aims to reduce the beam diameter of a beam having a frequency on the order of terahertz or gigahertz without focusing it as parallel light. [Means for solving the problem]

[0011] An aperture structure according to an embodiment of the disclosed technology has a space inside through which a beam of electromagnetic waves having a frequency on the order of terahertz or gigahertz and being parallel light passes. The aperture structure includes an outer inclined surface that is inclined with respect to the direction of propagation of the beam and surrounds an entrance opening that serves as the entrance for the beam to the space, and an outer metal film that covers the outer inclined surface. The diameter of the entrance opening is smaller than the diameter of the beam.

[0012] The space may include an inlet-side space having the inlet opening at one end, formed such that the area of ​​the cross-section perpendicular to the direction of beam propagation increases continuously along the direction of beam propagation.

[0013] The space may include an exit-side space that communicates with the inlet-side space and has an exit opening at one end which serves as the exit for the beam from the space. The aperture structure is provided inside the space and surrounds the inlet-side end of the exit-side space for the beam, and may further include an inner inclined surface inclined with respect to the direction of beam propagation and an inner metal film covering the inner inclined surface.

[0014] The diameter of the incident end of the beam in the exit-side space may be smaller than the diameter of the inlet opening.

[0015] The aperture structure has a front portion having the inlet-side space inside and a rear portion having the outlet-side space inside, and the front portion may be configured to be detachably attached to the rear portion.

[0016] The method for identifying plastics relating to the disclosed technology is an identification method using the aperture structure described above. The identification method includes irradiating the plastic with the beam that has passed through the space, deriving the transmittance of the plastic to the beam based on the intensity of the beam that has passed through the plastic, and deriving the identification result of the plastic using a classification model constructed by machine learning based on the derived transmittance.

[0017] Other aperture structures of the disclosed technology include a beam of parallel electromagnetic waves having a frequency on the order of terahertz or gigahertz, with a first beam and a second beam having different frequencies and directions of propagation, the first beam passing through a first space and the second beam passing through a second space. The aperture structure includes a first inlet opening that serves as the entrance for the first beam to the first space, a first outer inclined surface inclined with respect to the direction of propagation of the first beam, a first outer metal film covering the first outer inclined surface, a second inlet opening that serves as the entrance for the second beam to the second space, a second outer inclined surface inclined with respect to the direction of propagation of the second beam, and a second outer metal film covering the second outer inclined surface. The diameter of the first inlet opening is smaller than the diameter of the first beam, and the diameter of the second inlet opening is smaller than the diameter of the second beam.

[0018] The first space may have a first entrance side space having the first entrance opening at one end, and the area of ​​the cross-section perpendicular to the direction of travel of the first beam continuously increases along the direction of travel of the first beam. The second space may have a second entrance side space having the second entrance opening at one end, and the area of ​​the cross-section perpendicular to the direction of travel of the second beam continuously increases along the direction of travel of the second beam.

[0019] Optionally, the first space may include a first outlet-side space that communicates with the first inlet-side space and has, at one end thereof, an outlet opening that serves as an exit for the first beam from the first space. The second space may include a second outlet-side space that communicates with the second inlet-side space and has the outlet opening at one end thereof. The aperture structure may further comprise: a first inner inclined surface provided inside the first space, surrounding an end portion of the first outlet-side space on an incident side of the first beam, and inclined with respect to a traveling direction of the first beam; a first inner metal film covering the first inner inclined surface; a second inner inclined surface provided inside the second space, surrounding an end portion of the second outlet-side space on an incident side of the second beam, and inclined with respect to a traveling direction of the second beam; and a second inner metal film covering the second inner inclined surface.

[0020] Optionally, a diameter of the end portion of the first outlet-side space on the incident side of the first beam may be smaller than a diameter of the first inlet opening. A diameter of the end portion of the second outlet-side space on the incident side of the second beam may be smaller than a diameter of the second inlet opening.

[0021] Optionally, the aperture structure may comprise a first front portion having the first inlet-side space inside, a second front portion having the second inlet-side space inside, and a rear portion having the first outlet-side space and the second outlet-side space inside, wherein the first front portion and the second front portion are configured to be detachable from the rear portion.

[0022] Optionally, the aperture structure may be configured such that the first beam and the second beam intersect at the outlet opening.

[0023] Optionally, the aperture structure may have a plane including the outlet opening within the plane.

[0024] Another plastic identification method according to the disclosed technique is an identification method using the above aperture structure. The identification method comprises: irradiating the plastic with the first beam that has passed through the first space; irradiating the plastic with the second beam that has passed through the second space; deriving transmittances of the plastic for the first beam and the second beam based on respective intensities of the first beam and the second beam transmitted through the plastic; and deriving an identification result of the plastic using a classification model constructed by machine learning based on the derived transmittance for each beam. Effects of the Invention

[0025] According to the disclosed technique, it is possible to reduce the beam diameter of a beam having a frequency in the terahertz order or gigahertz order without condensing the beam while keeping it as parallel light. Brief Description of the Drawings

[0026] [Figure 1] It is a perspective view showing an example of the configuration of an aperture structure according to an embodiment of the disclosed technique. [Figure 2] It is a cross-sectional view along line 2-2 in FIG. 1. [Figure 3] It is a diagram showing an example of the configuration of an optical system for transmittance measurement using an aperture structure according to an embodiment of the disclosed technique. [Figure 4] It is a perspective view showing an example of the configuration of a first front portion according to an embodiment of the disclosed technique. [Figure 5] It is a cross-sectional view showing a cross-section parallel to the traveling direction of the first beam of the first front portion according to an embodiment of the disclosed technique. [Figure 6] It is a perspective view showing an example of the configuration of a rear portion according to an embodiment of the disclosed technique. [Figure 7] It is a cross-sectional view showing a cross-section parallel to the traveling direction of the first beam and the second beam of the rear portion according to an embodiment of the disclosed technique. [Figure 8]This is a cross-sectional view showing a section of an aperture structure according to an embodiment of the disclosed technology, parallel to the direction of propagation of the first and second beams. [Figure 9] This is a functional block diagram showing an example of the functional configuration of a computer used for identifying plastics. [Figure 10] This diagram shows an example of the processing flow that a computer performs when it executes a program. [Figure 11] This is a cross-sectional view showing an example of the configuration of an aperture structure related to a modified example. [Modes for carrying out the invention]

[0027] The embodiments of the disclosure will be described below with reference to the drawings. In each drawing, substantially identical or equivalent components or parts are given the same reference numerals.

[0028] Figure 1 is a perspective view showing an example of the configuration of an aperture structure 10 according to an embodiment of the disclosed technology. Figure 2 is a cross-sectional view along line 2-2 in Figure 1. Figure 3 is a diagram showing an example of the configuration of an optical system for transmittance measurement using the aperture structure 10.

[0029] First, an overview of plastic identification (classification) using the aperture structure 10 will be described. The aperture structure 10 is used for plastic identification using gigahertz waves or terahertz waves. Subterahertz waves can be suitably used for plastic identification. Subterahertz waves are electromagnetic waves in the frequency range between radio waves and light waves (e.g., 30 GHz to 180 GHz), and have properties intermediate between radio waves and light waves. That is, subterahertz waves have both the transparency of radio waves and the directivity of light waves. When subterahertz waves are irradiated onto a solid material, the increase or decrease in transmittance and / or reflectance due to the dispersion of dielectric constant is reflected in the spectrum. In particular, subterahertz waves generally have a low absorption coefficient due to moisture and oxygen in the atmosphere, and are less affected by the atmosphere when identifying plastics.

[0030] The aperture structure 10 has a space inside through which a beam of electromagnetic waves having a frequency on the order of terahertz or gigahertz and defined as parallel light passes. More specifically, the aperture structure 10 has a first space 11A through which the first beam 40A passes, and a second space 11B through which the second beam 40B, which has a different frequency and direction of propagation from the first beam, passes.

[0031] Light sources 30A and 30B are oscillators that emit a first beam 40A and a second beam 40B, respectively. The first beam 40A and the second beam 40B are emitted toward the aperture structure 10 from different directions. The first beam 40A and the second beam 40B are made into parallel light by passing through lenses 31A and 31B, respectively.

[0032] The first beam 40A, which is considered parallel light, enters the first space 11A through the first entrance opening 12A and exits the first space 11A through the exit opening 13. Similarly, the second beam 40B, which is also considered parallel light, enters the second space 11B through the second entrance opening 12B and exits the second space 11B through the exit opening 13.

[0033] The first beam 40A and the second beam 40B intersect at the exit opening 13. The aperture structure 10 has a plane 14 that includes the exit opening 13 in its plane. The plastic to be identified 50 is placed on the plane 14 so as to straddle the exit opening 13. That is, the plane 14 constitutes a sample stage. The first beam 40A and the second beam 40B are incident on the plastic to be identified 50 at an incident angle of 45°. The first beam 40A and the second beam 40B are irradiated onto the plastic 50 simultaneously or sequentially.

[0034] The first beam 40A, which has passed through the plastic 50 to be identified, is focused onto the detection surface of the detector 33A by the lens 32A. The detector 33A has a photoelectric conversion element such as a photodiode and detects the intensity of the first beam 40A that has passed through the plastic 50 to be identified. Similarly, the second beam 40B, which has passed through the plastic 50 to be identified, is focused onto the detection surface of the detector 33B by the lens 32B. The detector 33B has a photoelectric conversion element such as a photodiode and detects the intensity of the second beam 40B that has passed through the plastic 50 to be identified.

[0035] From the intensity of each beam that passes through the plastic 50, it is possible to derive the transmittance of the plastic 50 for each frequency. Furthermore, it is possible to identify (classify) the plastic 50 based on its transmittance for each frequency. Identification of the plastic 50 based on its transmittance for each frequency can be performed, for example, using an identification model such as a support vector machine constructed using machine learning with training data.

[0036] Next, the detailed structure of the aperture structure 10 will be described. The first space 11A through which the first beam 40A passes includes a first entrance-side space 15A having a first entrance opening 12A at one end. The first entrance-side space 15A is formed such that the area of ​​the cross-section perpendicular to the direction of travel of the first beam 40A increases continuously along the direction of travel of the first beam 40A. In other words, the cross-sectional shape of the first entrance-side space 15A parallel to the direction of travel of the first beam 40A is tapered, widening towards the end.

[0037] The first space 11A communicates with the first inlet space 15A and includes the first outlet space 16A having an outlet opening 13 at one end. The first space 11A includes the first central space 17A between the first inlet space 15A and the first outlet space 16A. The first central space 17A is formed such that the area of ​​the cross-section perpendicular to the direction of travel of the first beam 40A decreases continuously along the direction of travel of the first beam 40A. In other words, the cross-sectional shape of the first central space 17A parallel to the direction of travel of the first beam 40A is tapered in the opposite direction to that of the first inlet space 15A.

[0038] Similarly, the second space 11B through which the second beam 40B passes includes a second entrance-side space 15B having a second entrance opening 12B at one end. The second entrance-side space 15B is formed such that the area of ​​the cross-section perpendicular to the direction of travel of the second beam 40B increases continuously along the direction of travel of the second beam 40B. In other words, the cross-sectional shape of the second entrance-side space 15B parallel to the direction of travel of the second beam 40B is tapered and widens towards the end.

[0039] The second space 11B communicates with the second inlet space 15B and includes a second outlet space 16B having an outlet opening 13 at one end. The first outlet space 16A and the second outlet space 16B are connected to each other at a common outlet opening 13. The second space 11B includes a second central space 17B between the second inlet space 15B and the second outlet space 16B. The second central space 17B is formed such that the area of ​​the cross-section perpendicular to the direction of travel of the second beam 40B decreases continuously along the direction of travel of the second beam 40B. In other words, the cross-sectional shape of the second central space 17B parallel to the direction of travel of the second beam 40B is tapered in the opposite direction to that of the second inlet space 15B.

[0040] The aperture structure 10 has a first front section 18A having a first inlet-side space 15A inside, and a second front section 18B having a second inlet-side space 15B inside. The aperture structure 10 further has a rear section 19 having a first outlet-side space 16A and a second outlet-side space 16B inside. The first front section 18A and the second front section 18B are each detachable from the rear section 19. Suitable materials for the first front section 18A, the second front section 18B, and the rear section 19 include PLA resin (polylactic acid) or olefin resins such as PP (polypropylene) and PE (polyethylene) that exhibit high permeability to gigahertz waves or terahertz waves. The first front section 18A, the second front section 18B, and the rear section 19 can each be molded using a 3D printer.

[0041] Figure 4 is a perspective view showing an example of the configuration of the first front section 18A. Figure 5 is a cross-sectional view showing a section of the first front section 18A parallel to the direction of travel of the first beam 40A. Note that the configuration of the second front section 18B is the same as that of the first front section 18A, so it is not shown. The first front section 18A surrounds the first inlet opening 12A and has a cone-shaped first outer inclined surface 20A that is inclined with respect to the direction of travel of the first beam 40A. That is, the first inlet opening 12A is provided at the top of a frustoconical projection. The diameter φ1 of the first inlet opening 12A is set to be smaller than the diameter of the first beam 40A emitted from the light source 30A.

[0042] Similarly, the second front section 18B surrounds the second inlet opening 12B and has a cone-shaped second outer inclined surface 20B that is inclined with respect to the direction of travel of the second beam 40B. That is, the second inlet opening 12B is provided at the top of a frustoconical projection. The diameter φ1 of the second inlet opening 12B is smaller than the diameter of the second beam 40B emitted from the light source 30B.

[0043] The first outer inclined surface 20A and the second outer inclined surface 20B are covered with a first outer metal film 21A and a second outer metal film 21B, respectively, which reflect gigahertz waves or terahertz waves. For example, copper or aluminum films can be used as the first outer metal film 21A and the second outer metal film 21B. The first outer metal film 21A and the second outer metal film 21B can also be formed by vapor deposition.

[0044] Figure 6 is a perspective view showing an example of the configuration of the rear section 19. Figure 7 is a cross-sectional view showing a section of the first beam 40A and the second beam 40B of the rear section 19 parallel to the direction of travel. The rear section 19 has recesses 24A and 24B into which the first front section 18A and the second front section 18B are fitted, respectively.

[0045] The rear section 19 surrounds the incident end of the first beam 40A of the first exit side space 16A (hereinafter referred to as the incident end), and has a cone-shaped first inner inclined surface 22A that is inclined with respect to the direction of travel of the first beam 40A. The diameter φ2 of the incident end of the first exit side space 16A is smaller than the diameter φ1 of the first entrance opening 12A.

[0046] The rear section 19 surrounds the light-incident end of the second exit-side space 16B and has a cone-shaped second inner inclined surface 22B that is inclined with respect to the direction of travel of the second beam 40B. The diameter φ2 of the light-incident end of the second exit-side space 16B is smaller than the diameter φ1 of the second entrance opening 12B.

[0047] The first inner inclined surface 22A and the second inner inclined surface 22B are covered with a first inner metal film 23A and a second inner metal film 23B that reflect gigahertz waves or terahertz waves, respectively. For example, copper or aluminum films can be used as the first inner metal film 23A and the second inner metal film 23B. The first inner metal film 23A and the second inner metal film 23B can also be formed by vapor deposition.

[0048] The operation of the aperture structure 10 will be explained below with reference to Figure 8. The first beam 40A, which is composed of parallel light, enters the first space 11A through the first entrance opening 12A. The diameter φ1 of the first entrance opening 12A is smaller than the diameter of the first beam 40A emitted from the light source 30A. As a result, the portion of the first beam 40A outside the first entrance opening 12A is reflected by the first outer metal film 21A. In other words, the portion of the first beam 40A emitted from the light source 30A outside is removed as stray light.

[0049] Since the first outer metal film 21A is provided on a first outer inclined surface 20A that is inclined with respect to the direction of propagation of the first beam 40A, the light reflected by the first outer metal film 21A is guided in a direction away from the optical axis of the first beam 40A. This prevents interference caused by reflected light.

[0050] The first beam 40A, having passed through the first entrance opening 12A, travels through the first space 11A as parallel light. The first entrance-side space 15A is formed such that the area of ​​the cross-section perpendicular to the direction of travel of the first beam 40A increases continuously along the direction of travel of the first beam 40A. Therefore, reflection or propagation by the wall surface can be avoided while the first beam 40A is traveling through the first space 11A.

[0051] The diameter φ2 at the light-incident end of the first exit-side space 16A is smaller than the diameter φ1 of the first entrance opening 12A. As a result, the outer portion of the first beam 40A is reflected by the first inner metal film 23A. That is, the outer portion of the first beam 40A traveling through the first space 11A is removed as stray light. Since the first inner metal film 23A is provided on the first inner inclined surface 22A which is inclined with respect to the direction of travel of the first beam 40A, the light reflected by the first inner metal film 23A is guided in a direction away from the optical axis of the first beam 40A. This prevents interference caused by reflected light.

[0052] The first beam 40A has its outer portion removed by the first outer metal film 21A and the first inner metal film 23A, thereby reducing the beam diameter while maintaining parallel light. While the first beam 40A is traveling through the first space 11A, the beam diameter may expand due to diffraction. However, by removing stray light not only with the first outer metal film 21A but also with the first inner metal film 23A inside the first space 11A, the expansion of the beam diameter can be suppressed.

[0053] The first beam 40A, with its reduced beam diameter, exits the first space 11A through the exit opening 13 and irradiates the plastic 50 to be identified. The diameter φ1 of the first inlet opening 12A and the diameter φ2 of the light incident side end of the first exit side space 16A are determined according to the target value of the irradiation beam diameter for the plastic 50 to be identified. For example, by setting the diameter φ1 of the first inlet opening 12A to 17.5 mm and the diameter φ2 of the light incident side end of the first exit side space 16A to 15 mm, the diameter of the first beam 40A irradiating the plastic 50 to be identified can be set to 20 mm or less. The above explanation has referred to the first beam 40A, but the beam diameter of the second beam 40B is similarly reduced while maintaining parallel light.

[0054] The aperture structure 10 is configured such that the first and second front sections 18A and 18B are detachably attached to the rear section 19. Multiple types of first and second front sections 18A and 18B, each with a different diameter φ1 of the first and second inlet openings 12A and 12B, are prepared in advance, and by selectively using these, it is possible to match the diameter φ1 to the size of the plastic to be identified.

[0055] The first beam 40A, which has passed through the first space 11A, and the second beam 40B, which has passed through the second space 11B, intersect at the exit opening 13. The aperture structure 10 has a plane 14 that includes the exit opening 13 in its plane. The plastic 50 to be identified is placed on the plane 14 so as to block the exit opening 13. In other words, the plane 14 constitutes a sample stage. The first beam 40A and the second beam 40B are incident on the plastic 50 to be identified at an incident angle of 45°, respectively. The first beam 40A and the second beam 40B are irradiated onto the plastic 50 simultaneously or sequentially. Because the aperture structure 10 is equipped with a sample stage, it is possible to always irradiate the plastic 50 to be identified with the beams under the same conditions.

[0056] Below, we will describe an example of a method for identifying (classifying) plastics using an aperture structure 10.

[0057] The first beam 40A, which has passed through the plastic 50 to be identified, is focused onto the detection surface of the detector 33A by the lens 32A. The detector 33A detects the intensity of the first beam 40A that has passed through the plastic 50 to be identified. Similarly, the second beam 40B, which has passed through the plastic 50 to be identified, is focused onto the detection surface of the detector 33B by the lens 32B. The detector 33B detects the intensity of the second beam 40B that has passed through the plastic 50 to be identified.

[0058] Plastic identification is achieved by computer processing using the transmitted light intensity of the first beam 40A and the transmitted light intensity of the second beam 40B as input information. Figure 9 is a functional block diagram showing an example of the functional configuration of the computer 100 that performs plastic identification. The computer 100 is composed of hardware such as a CPU, RAM, non-volatile memory, and communication interface, which are not shown. The computer 100 functions as an acquisition unit 101, a transmittance derivation unit 102, and an identification unit 103 by executing a program (not shown) stored in the non-volatile memory.

[0059] Figure 10 shows an example of the processing flow performed by the computer 100 when it executes a program. In step S1, the acquisition unit 101 acquires the transmitted light intensity of the first beam 40A output from detector 33A and the transmitted light intensity of the second beam 40B output from detector 33B.

[0060] In step S2, the transmittance derivation unit 102 derives the transmittance of the plastic to be identified for each of the first beam 40A and the second beam 40B, based on the transmitted light intensity of the first beam 40A and the transmitted light intensity of the second beam 40B obtained in step S1.

[0061] The transmittance derivation unit 102 derives the transmittance T for each beam by performing the calculation shown in equation (1) below for each of the first beam 40A and the second beam 40B. In equation (1), I1 is the intensity of light incident on the plastic 50 to be identified (incident light intensity), and I2 is the intensity of light transmitted through the plastic 50 to be identified (transmitted light intensity). A value measured in advance may be used as I1. The transmitted light intensity obtained in step S1 is used as I2. T = I² / I¹ (1)

[0062] In step S3, the identification unit 103 derives the identification result of the plastic 50 to be identified based on the transmittance for each beam derived in step S2. The identification unit 103 identifies the plastic 50 to be identified using the identification model 104. The identification model 104 is a support vector machine constructed by machine learning using training data, and is a model that takes the transmittance for each frequency as input and outputs the identification result of the plastic.

[0063] [Examples] Aperture structure 10 was used to distinguish between PP (polypropylene) and PVC (polyvinyl chloride). Parallel beams of P-polarized and S-polarized light at 75 GHz, 95 GHz, and 100 GHz were irradiated onto the target plastic at an incident angle of 45°. As a comparative example, a focused beam formed using a horn antenna was irradiated onto the target plastic at an incident angle of 0°. Based on the transmittance measured for each frequency of each beam, a support vector machine constructed using machine learning was used to identify the plastic. Table 1 below shows the accuracy of the identification results.

[0064] The method of the embodiment (i.e., a method in which the beam diameter is reduced while maintaining parallel light and irradiates the plastic to be identified) was able to obtain a higher accuracy rate than the method of the comparative example (i.e., a method in which a focused beam is irradiated onto the plastic to be identified).

[0065] [Table 1]

[0066] As described above, according to the aperture structure 10 of the disclosed technology embodiment, it is possible to reduce the beam diameter without focusing a beam having a frequency on the order of terahertz or gigahertz while keeping it as parallel light.

[0067] Because gigahertz or terahertz waves have relatively long wavelengths and are less affected by the unevenness of the material, it is possible to fabricate the aperture structure 10 using inexpensive plastic that is easy to mold. The aperture structure 10 can be completed, for example, by fabricating the body part using a 3D printer and then attaching metal films as outer and inner metal films to each inclined surface.

[0068] Furthermore, according to the aperture structure 10 of this embodiment, since it has a first space 11A and a second space 11B through which the first beam 40A and the second beam 40B, which travel in different directions, respectively, it is possible to simultaneously irradiate the plastic to be identified with two beams that have different frequencies. This makes it possible to efficiently measure the transmittance of the plastic.

[0069] Figure 11 is a cross-sectional view showing an example of the configuration of a modified aperture structure 10A. The aperture structure 10A differs from the aperture structure 10 described above in that the space 11 through which the beam 40 passes is a single space. Therefore, in the aperture structure 10A, the inlet opening 12, inlet-side space 15, outlet-side space 16, outer inclined surface 20, outer metal film 21, inner inclined surface 22, and inner metal film 23 are all single-component structures. According to the modified aperture structure 10A, similar to the aperture structure 10 described above, it is possible to reduce the beam diameter without focusing a beam having a frequency on the order of terahertz or gigahertz while keeping it as parallel light.

[0070] The following additional information is disclosed regarding the embodiments described above. (Note 1) An aperture structure having a space inside through which a beam of electromagnetic waves having a frequency on the terahertz or gigahertz order and defined as parallel light passes, The entrance opening that serves as the entrance for the beam to the space is surrounded by an outer inclined surface that is inclined with respect to the direction of travel of the beam, An outer metal film covering the outer inclined surface, Includes, The diameter of the inlet opening is smaller than the diameter of the beam. Aperture structure.

[0071] (Note 2) The space includes an inlet-side space having the inlet opening at one end, and formed such that the area of ​​the cross-section perpendicular to the direction of beam propagation increases continuously along the direction of beam propagation. The aperture structure described in Appendix 1.

[0072] (Note 3) The aforementioned space is in communication with the inlet-side space and includes an outlet-side space having an outlet opening at one end which serves as the exit of the beam from the aforementioned space. Located inside the aforementioned space, surrounding the incident end of the beam in the exit-side space, and having an inclined inner surface that is inclined with respect to the direction of beam propagation, An inner metal film covering the inner inclined surface, An aperture structure as described in Appendix 2, further comprising the above.

[0073] (Note 4) The diameter of the incident end of the beam in the exit space is smaller than the diameter of the inlet opening. The aperture structure described in Appendix 3.

[0074] (Note 5) The front section having the aforementioned entrance-side space inside, The rear section having the aforementioned outlet-side space inside, It has, The front portion is configured to be detachably attached to the rear portion. The aperture structure described in Appendix 3 or Appendix 4.

[0075] (Note 6) A method for identifying plastics using an aperture structure described in any one of the appendices 1 to 5, The beam that has passed through the space is irradiated onto the plastic, Based on the intensity of the beam that has passed through the plastic, the transmittance of the plastic to the beam is derived. Based on the derived transmittance, the identification result of the plastic is derived using a classification model constructed by machine learning. Identification method.

[0076] (Note 7) An aperture structure having a first space through which the first beam passes and a second space through which the second beam passes, among a first beam and a second beam of electromagnetic waves having a frequency on the order of terahertz or gigahertz and being parallel light, wherein the first beam and the second beam have different frequencies and directions of propagation from each other, A first inlet opening, which serves as the entrance for the first beam to the first space, is surrounded by a first outer inclined surface that is inclined with respect to the direction of travel of the first beam, A first outer metal film covering the first outer inclined surface, A second inlet opening, which serves as the entrance for the second beam to the second space, is surrounded by a second outer inclined surface that is inclined with respect to the direction of travel of the second beam, A second outer metal film covering the second outer inclined surface, Includes, The diameter of the first inlet opening is smaller than the diameter of the first beam. The diameter of the second inlet opening is smaller than the diameter of the second beam. Aperture structure.

[0077] (Note 8) The first space has the first entrance opening at one end and is formed such that the area of ​​the cross-section perpendicular to the direction of travel of the first beam increases continuously along the direction of travel of the first beam. The second space has the second inlet opening at one end and is a second inlet-side space formed such that the area of ​​the cross-section perpendicular to the direction of travel of the second beam increases continuously along the direction of travel of the second beam. The aperture structure described in Appendix 7.

[0078] (Note 9) The first space is in communication with the first inlet space and includes a first outlet space having an outlet opening at one end which serves as the exit of the first beam from the first space. The second space is in communication with the second inlet space and includes a second outlet space having the outlet opening at one end. A first inclined surface is provided inside the first space, surrounding the incident end of the first beam in the first exit side space, and inclined with respect to the direction of propagation of the first beam, A first inner metal film covering the first inner inclined surface, A second inner inclined surface is provided inside the second space, surrounding the incident end of the second beam in the second exit side space, and inclined with respect to the direction of travel of the second beam, A second inner metal film covering the second inner inclined surface, An aperture structure as described in Appendix 8, further comprising the above.

[0079] (Note 10) The diameter of the incident end of the first beam in the first exit space is smaller than the diameter of the first inlet opening. The diameter of the incident end of the second beam in the second exit space is smaller than the diameter of the second inlet opening. The aperture structure described in Appendix 9.

[0080] (Note 11) The first front section having the first entrance-side space inside, The second front section having the second entrance-side space inside, A rear section having the first outlet side space and the second outlet side space inside, It has, The first front section and the second front section are configured to be detachably attached to the rear section. The aperture structure described in Appendix 9 or Appendix 10.

[0081] (Note 12) The first beam and the second beam intersect at the exit opening. The aperture structure described in Appendix 9.

[0082] (Note 13) Having a plane that includes the aforementioned outlet opening in its plane The aperture structure described in Appendix 12.

[0083] (Note 14) A method for identifying plastics using an aperture structure described in any one of the appendices 7 to 13, The first beam that has passed through the first space is irradiated onto the plastic, The second beam that has passed through the second space is irradiated onto the plastic, Based on the respective intensities of the first beam and the second beam that have passed through the plastic, the transmittance of the plastic to the first beam and the second beam is derived. Based on the derived transmittance for each beam, the identification result of the plastic is derived using a classification model constructed by machine learning. Identification method. [Explanation of symbols]

[0084] 10, 10A Aperture Structure 11 Space 11A 1st space 11B 2nd space 12 Inlet opening 12A 1st inlet opening 12B 2nd entrance opening 13 Outlet opening 14 plane 15 Entrance side space 15A 1st entrance side space 15B Second Entrance Side Space 16. Exit-side space 16A Exit 1 Side Space 16B Second Exit Side Space 17A Central Space 1 17B Central Space 2 18A 1st Floor 18B Part 2 Fronto 19 Riyabe 20 Outer inclined surface 20A First outer inclined surface 20B Second outer inclined surface 21 Outer metal film 21A First outer metal film 21B Second outer metal film 22 Inner inclined surface 22A First inner inclined surface 22B Second inner inclined surface 23 Inner metal film 23A First inner metal film 23B Second inner metal film 30A and 30B light sources 31A, 31B レンズ 32A, 32B レンズ 33A, 33B extractor 40 ビーム 40A No. 1 ビーム 40B No.2ビーム 50 プラスチック 100 コンピュータ 101 Obtained Department 102 Transmittance Derivation Section 103 Identification Department 104 Identifying モデル

Claims

1. An aperture structure having a space inside through which a beam of electromagnetic waves having a frequency on the terahertz or gigahertz order and defined as parallel light passes, The entrance opening that serves as the entrance for the beam to the space is surrounded by an outer inclined surface that is inclined with respect to the direction of travel of the beam, An outer metal film covering the outer inclined surface, Includes, The diameter of the inlet opening is smaller than the diameter of the beam. Aperture structure.

2. The space includes an inlet-side space having the inlet opening at one end, and formed such that the area of ​​the cross-section perpendicular to the direction of beam propagation increases continuously along the direction of beam propagation. The aperture structure according to claim 1.

3. The aforementioned space is in communication with the inlet-side space and includes an outlet-side space having an outlet opening at one end which serves as the exit of the beam from the aforementioned space. Located inside the aforementioned space, surrounding the incident end of the beam in the exit-side space, and having an inclined inner surface that is inclined with respect to the direction of beam propagation, An inner metal film covering the inner inclined surface, The aperture structure according to claim 2, further comprising the above.

4. The diameter of the incident end of the beam in the exit space is smaller than the diameter of the inlet opening. The aperture structure according to claim 3.

5. The front section having the aforementioned entrance-side space inside, The rear section having the aforementioned outlet-side space inside, It has, The front portion is configured to be detachably attached to the rear portion. The aperture structure according to claim 3.

6. A method for identifying plastics using an aperture structure according to any one of claims 1 to 5, The beam that has passed through the space is irradiated onto the plastic, Based on the intensity of the beam that has passed through the plastic, the transmittance of the plastic to the beam is derived. Based on the derived transmittance, the identification result of the plastic is derived using a classification model constructed by machine learning. Identification method.

7. An aperture structure comprising a first beam and a second beam, each having a frequency on the order of terahertz or gigahertz and composed of parallel light, wherein the first beam and the second beam have different frequencies and directions of propagation, and the first beam passes through a first space and the second beam passes through a second space within the structure, A first inlet opening, which serves as the entrance for the first beam to the first space, is surrounded by a first outer inclined surface that is inclined with respect to the direction of travel of the first beam, A first outer metal film covering the first outer inclined surface, A second inlet opening, which serves as the entrance for the second beam to the second space, is surrounded by a second outer inclined surface that is inclined with respect to the direction of travel of the second beam, A second outer metal film covering the second outer inclined surface, Includes, The diameter of the first inlet opening is smaller than the diameter of the first beam. The diameter of the second inlet opening is smaller than the diameter of the second beam. Aperture structure.

8. The first space has the first entrance opening at one end and is formed such that the area of ​​the cross-section perpendicular to the direction of travel of the first beam increases continuously along the direction of travel of the first beam. The second space has the second inlet opening at one end and is a second inlet-side space formed such that the area of ​​the cross-section perpendicular to the direction of travel of the second beam increases continuously along the direction of travel of the second beam. The aperture structure according to claim 7.

9. The first space is in communication with the first inlet space and includes a first outlet space having an outlet opening at one end which serves as the exit of the first beam from the first space. The second space is in communication with the second inlet space and includes a second outlet space having the outlet opening at one end. A first inclined surface is provided inside the first space, surrounding the incident end of the first beam in the first exit side space, and inclined with respect to the direction of travel of the first beam, A first inner metal film covering the first inner inclined surface, A second inner inclined surface is provided inside the second space, surrounding the incident end of the second beam in the second exit side space, and inclined with respect to the direction of travel of the second beam, A second inner metal film covering the second inner inclined surface, The aperture structure according to claim 8, further comprising the above.

10. The diameter of the incident end of the first beam in the first exit space is smaller than the diameter of the first inlet opening. The diameter of the incident end of the second beam in the second exit space is smaller than the diameter of the second inlet opening. The aperture structure according to claim 9.

11. The first front section having the first entrance-side space inside, The second front section having the second entrance-side space inside, A rear section having the first outlet side space and the second outlet side space inside, It has, The first front section and the second front section are configured to be detachably attached to the rear section. The aperture structure according to claim 9.

12. The first beam and the second beam intersect at the exit opening. The aperture structure according to claim 9.

13. Having a plane that includes the aforementioned outlet opening in its plane The aperture structure according to claim 12.

14. A method for identifying plastics using an aperture structure according to any one of claims 7 to 13, The first beam that has passed through the first space is irradiated onto the plastic, The second beam that has passed through the second space is irradiated onto the plastic, Based on the respective intensities of the first beam and the second beam that have passed through the plastic, the transmittance of the plastic to the first beam and the second beam is derived. Based on the derived transmittance for each beam, the identification result of the plastic is derived using a classification model constructed by machine learning. Identification method.

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