TECHNICAL FIELD

[0001] The present disclosure relates to a system for identifying an object. The present disclosure also relates to a method for manufacturing the system, and a method for fitting a reflector on the system.

BACKGROUND

[0002] Terahertz (THz) imaging has been employed as a means for non-destructive testing and quality control due to its non-ionizing nature and high transparency to non-polar substances and non-conductive materials. Real-time THz imaging in the transmission mode may be employed in Materials Recovery Facilities (MRFs) for the identification and segregation of recyclable or reusable objects, e.g. plastic waste material. These MRFs typically include a conveyor belt system to move the objects along the conveyor belt for identification and segregation.

[0003] One solution for object (plastic waste material) identification and segregation includes mounting a detector under the conveyor belt for large-area THz imaging to receive information on the object (plastic waste material). The THz wave thus has to penetrate both the target object (plastic waste material) and the belt material. Conventional belt materials in MRFs typically include a black rubber belt material which attenuates the THz wave due to the presence of carbon which absorbs the THz wave, and/or metal, e.g. wires or cables which is not transparent to the THz wave. Thus, implementing this solution requires extensive modifications to existing conveyor belt systems to mount the detector under the belt, and to replace such conventional conveyor belt materials. In addition, impurities, e.g. dirt and/or moisture, irregularities, and the wear and tear of the belt material, can lead to signal errors in the detected wave, resulting in inaccuracies in the identification of the object (plastic waste material).

[0004] Another solution includes mounting the detector across an air-gap near an end of the moving conveyor belt. This however, can restrict the real-time identification of the object (plastic waste material), particularly, when the computing time of a processor (in communication with the detector) is slower than the moving speed of the conveyor belt. Further, this solution is only applicable for positive or negative sorting, and may not be applicable for the identification of multiple objects (plastic waste materials) at the same time. [0005] Accordingly, there exists a need for an improved object identification system which addresses at least one of the aforementioned problems.

SUMMARY

[0006] This disclosure was conceptualized to minimise modifications made to existing THz- based conveyor belt identification systems in MRFs, and to improve the accuracy of the identification of the object (plastic waste material). This disclosure provides a simple and facile means, e.g. a reflector, that can be easily fitted and applied to existing THz-based conveyor belt identification systems. The use of the reflector in such systems is compatible with conventional black rubber belt materials and/or metal wire-reinforced belts, and avoids the need to mount the detector under the belt. In addition, the reflected wave received by the detector may not be affected by impurities, e.g. dirt or spilled liquids, on the belt material, which may reduce or minimize signal errors, and thus improves the accuracy of the identification of the object (plastic waste material). Further, multiple objects (plastic waste material) may be simultaneously identified and segregated. This disclosure may be easily implemented and applied to waste identification and segregation systems, particularly, for real-time object (plastic waste material) identification and segregation for high-speed conveyor belt systems.

[0007] According to the present disclosure, a system for identifying an object as claimed in claim 1 is provided. A method for manufacturing a system for identifying an object is defined in claim 15. A method of fitting a reflector on a system for identifying an object is defined in claims 14 and 16.

[0008] The dependent claims define some examples associated with the system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The disclosure will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which:

- FIG. 1 shows a side-view of an embodiment of a system 100 for identifying an object 110;

- FIG. 2A shows a top perspective view of an embodiment of the system 200A for identifying the object 110, and FIG. 2B shows a part of a side-view of an embodiment of the system 200B with particular emphasis on the positioning of the one or more airjetting hole arrays 124 on the reflector 120, and in relation to the platform 102, mounting frames 122a, 122b, and the object 110; - FIG. 3 shows a side-view of another embodiment of a system 300 for identifying an object 110;

- FIGS. 4A and 4B show side-views of the various configurations of the positioning of the reflector 120 on, e.g. above the platform 102 in systems 400A, 400B for identifying an object 110;

- FIGS. 5A to 5C show side-views of the various configurations of the positioning of the reflector 120, when the reflector 120 is positioned below the platform 102 in systems 500A, 500B, 500C for identifying an object 110;

- FIG. 6 shows a schematic illustration of a method for manufacturing a system 600 for identifying an object;

- FIG. 7 shows a schematic illustration of a method for fitting a reflector 700 on a system for identifying an object; and

- FIG. 8 shows an image of an exemplary use condition of the system 800, and insets (i.) shows the top-view; (ii.) shows the cross-sectional view of the rubber material used in system 800.

DETAILED DESCRIPTION

[0010] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure. Other embodiments may be utilized and structural, and logical changes may be made without departing from the scope of the disclosure. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0011] The disclosure illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms “comprising”, “including,” containing”, etc. shall be read expansively and without limitation. The word "comprise" or variations such as "comprises" or "comprising" will accordingly be understood to imply the inclusion of a stated integer or groups of integers but not the exclusion of any other integer or group of integers. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the disclosure. Thus, it should be understood that although the present disclosure has been specifically described in exemplary embodiments and optional features, modification and variation of the disclosure embodied herein may be resorted to by those skilled in the art.

[0012] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and/or combinations and/or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0013] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

[0014] Throughout the description, the term “system for identifying of an object” refers broadly to THz-based systems for identifying an object. THz radiation consists of electromagnetic waves within the frequency range of 0.1 to 10 THz. THz radiation may transmit through non-polar and non-conductive materials, particularly plastic objects and may be used to identify the object.

[0015] Throughout the description, the term “object” includes any object, particularly recyclable or reusable objects that may be identified according to type, e.g. material type. For example, objects may be identified according to whether they are metal, paperboard or plastic objects. As a further example, plastic objects may be identified according to whether they are High Density Poly Ethylene (HDPE) plastic objects or Polyethylene terephthalate (PET) plastic objects. In some embodiments, the plastic object may be a plastic waste material. Such objects may include bottles, jars, containers, plates, bowls etc. of various shapes, forms, and sizes.

[0016] Throughout the description, the term “optically aligned” refers to the positioning and alignment of the various components of the system so as to enable the system to operate as intended. For example, the electromagnetic radiation source and excitation assembly, the detector and detection assembly, the reflector and beam splitter may be optically aligned or synchronized, such that the detector receives the maximum signal of the reflected wave, and said signal is in focus with the sensing window of the detector.

[0017] FIG. 1 shows a side-view of an embodiment of a system 100 for identifying an object 110. FIG. 2A shows a top perspective view of an embodiment of the system 200A for identifying the object 110, and FIG. 2B shows a part of a side view of an embodiment of the system 200B with particular emphasis on the positioning of the one or more air-jetting hole arrays 124 on the reflector 120, and in relation to the platform 102, mounting frames 122a, 122b, and the object 110. It is appreciable that system 200A and system 200B may refer to the same system, showing different views. Referring to FIG. 1, the system 100 includes a platform 102 configured to support an object 110, and a reflector 120 positioned in relation to the platform 102. In some embodiments, the platform 102 may be a conveyor belt which acts as the carrying medium to support the object 110. The platform 102 may be supported by a conveyor belt system which includes a frame 104, and two or more pullies, such as a tail pulley 106, a head / drive pulley, and a plurality of carrying idlers (not shown in the FIGS). In other words, the platform 102 may be a moveable / rotatable platform 102 and the object 110 may move along the platform 102 to overlap the reflector 120.

[0018] The system 100 may include a motion controller 105 configured to control and move the platform 102 in a closed loop, e.g. in the direction as shown by arrow 107, such that the platform 102 rotates about tail pulley 106, the head / drive pulley and the plurality of carrying idlers. The motion controller 105 may be configured to move the platform 102 in a bi-directional manner, i.e. along or against the direction of travel as shown by arrow 107. In some embodiments, the platform 102 moves against the direction of travel as shown by arrow 107. The motion controller 105 may be configured to move the platform 102 in the direction 107 at a speed ranging from 0.4 m/s to 5 m/s. In some embodiments, the platform 102 moves at a speed of 0.75 m/s to 2.5 m/s, preferably at 1.0 m/s. In other words, the platform 102 moves the object 110 in the direction 107 along the platform 102 for identification and segregation. In an embodiment, the platform 102 may be a conveyor belt of a conveyor belt system in MRFs, particularly MRFs for identifying and segregating objects such as plastic waste material. It is contemplated that the platform 102 may be supported by various other conveyor systems.

[0019] As shown in FIGS. 2A and 2B, the reflector 120 may be positioned on, e.g. above the platform 102, and may be mounted to the sides 104a, 104b of the frame 104 via mounting frames 122a, 122b. In an embodiment, the reflector 120 may be positioned parallel to the platform 102. The reflector 120 may be spaced apart from the platform 102 and may or may not be in contact with the platform 102. In some embodiments, the reflector 120 may be spaced apart from the platform 102 by a distance ranging from 1 to 5 mm, preferably 1 to 2 mm, such that the reflector 120 remains stationary in relation to the moving platform 102 supporting the object 110 (which moves in the direction 107). In some embodiments, the reflector 120 may be in contact with platform 102, but may remain stationary (via mounting frames 122a, 122b) in relation to the moving platform 102. In other words, the reflector 120 is mounted to the mounting frames 122a, 122b, which are mounted onto the sides 104a, 104b of the frame. The spacing between the reflector 120 and the platform 102 may be minimized to facilitate smooth movement of the object 110 in the direction 107, when the platform 102 moves at a relatively high-speed, e.g. 2.5 m/s.

[0020] In some embodiments, the platform 102 may move in a direction 107 parallel to the reflector 120. Since the object 110 moves in the direction 107 along the platform 102, the object 110 may overlap the reflector 120 at a given point in time (as shown in FIG. 1). In other words, the object 110 may be in contact with the reflector 120 when the object 110 overlaps the reflector 120. In some embodiments, one or more air-jetting hole arrays 124 adapted to project an air stream may be placed on or at the sides the reflector 120 and may thus be positioned in line with the reflector 120. At least one of the holes formed on the one or more air-jetting hole arrays 124 may be an inclined open hole, e.g. angled hole array that is in line with the direction of movement 107 of the object 110. Accordingly, the air stream projected from the air-jetting hole arrays 124 may facilitate smooth movement, since the provided air stream gently pushes the object 110 in the direction of movement 107 along the platform 102. In some embodiments, all of the holes formed on the air-jetting hole arrays 124 may be inclined open holes.

[0021] In some embodiments, the reflector 120 may be any metallic device configured to reflect an electromagnetic wave or light beam, i.e. wave reflector, such as, but not limited to: metallic plates, flat or curved mirrors, retroreflectors. It is contemplated that the reflector 120 may include a plurality of reflectors mounted to the sides 104a, 104b of the frame 104 such that the plurality of reflectors is positioned on, e,g, above the platform 102. The width of the reflector 120 may be dependent on a sensing window of a detector 140, and may preferably be wider than the sensing window of the detector 140. In some embodiments, the width of the reflector 120 may be in range of 1 to 10 mm, preferably 5 mm. This allows the reflector 120 to receive a modified wave 136 and direct the modified wave 136 back into the object 110 to produce a reflected wave 142 received by the detector 140 (as will be explained below).

[0022] The system 100 includes an electromagnetic radiation source 130 configured to generate an excitation wave 132. The excitation wave 132 may be an electromagnetic radiation wave in the THz frequency range of 0.1 to 10 THz. In some embodiments, the electromagnetic radiation source 130 comprises a continuous wave THz source, in particular a continuous wave THz source operating in a transmission mode. The generated THz excitation wave 132 travels in a light of sight and transmits through non-conducting materials such as plastics, paper, wood, ceramics and cloth. The THz excitation wave 132 may not transmit through metal or liquids. The electromagnetic radiation source 130 may include any source configured to generate THz waves, such as but not limited to: Impact Ionization Transit Time sources (IMPATT diodes), Gallium Phosphide (GaP) non-linear optical crystal modules with fiber lasers, Gunn diodes, heterostructure barrier varactor (HBV) diodes, Schottky diodes multiplier-based sources, backward wave oscillators (BWO), and tunable photo-mixing sources. It is contemplated that the electromagnetic radiation source 130 may include a continuous wave THz source operating in a reflection mode, for example in the identification of non-plastic objects.

[0023] As shown in FIG. 1, the excitation wave 132 in the THz frequency range transmits and penetrates through the object 110, and the excitation wave 132 is modified by the object 110 to form a modified wave 136. For example, one or more spectral properties, such as the amplitude, frequency, wavelength, power intensity, electric field, of the excitation wave 132 may be modified to form the modified wave 132. As a further example, at a fixed continuous wave THz emitting frequency, the power intensity of the excitation wave 132 may be altered due to the medium’s, i.e. object 110 THz absorption, reflection and/or transmission properties, to form the modified wave 136. In general, non-polar plastics are observed to have relatively higher THz transmission properties, as compared to polar plastics and/or glass. Liquids and metal are observed to have relatively higher absorption, and reflective properties, respectively, and hence the excitation wave 132 is not transmitted through such objects 110. In some embodiments, the modified wave 132 may be in the THz frequency range.

[0024] The electromagnetic radiation source 130 is arranged in optical alignment with the reflector 120. As shown in FIG. 1, the object 110 is positioned in relation, e.g. on or above, the platform 102 such that the object 110 overlaps and is in contact with the reflector 120 when the excitation wave 132 is transmitted through the object 110, and onto the reflector 120 underlying the object 110. The reflector 120 receives the modified wave 136, and directs (reflects) the modified wave 136 back into the object 110 to produce a reflected wave 142. In some embodiments, the reflected wave 142 may be in the THz frequency range. In other words, there is dual transmission of the modified wave 136 - in that the modified wave 136 is first transmitted through the object 110, and is subsequently transmitted through the object 110 again, since the underlying reflector 120 reflects said modified wave 136 back into the object 110 to produce a reflected wave 142.

[0025] The system 100 includes a detector 140 in optical alignment with the electromagnetic radiation source 130 and the reflector 120, and is configured to receive the reflected wave 142. Specifically, the detector 140 may include a sensing window configured to receive the reflected wave 142. For example, the scanning window may be 3 mm for a 100 GHz detector 140; and may be 0.5 mm for a 300 GHz detector 140. In general, a narrower scanning window may be preferred as it provides high-speed scanning capabilities (5000 lines per second) and good spatial resolution (0.5 mm). In some embodiments, the width of the reflector 120 may be wider than the sensing window of the detector 140, such that the maximal signal from the modified wave 136 can be directed back into the object 110 to produce the reflected wave 142. In an embodiment, the width of the reflector 120 may be 1 mm (for a 300 GHz detector 140), or may be 3.5 mm (for a 100 GHz detector 140). This allows the detector 140 to be adapted for real-time object 110 identification in a high-speed moving platform 102, for example a platform 102 moving at a speed of 1.0 m/s.

[0026] The detector 140 may include any detector configured to receive THz waves, such as but not limited to: Gallium Arsenide (GaAs) plasmonic array detectors, GaAs Schottky diode array detectors, array detectors based on GaAs / Aluminum GaAs (AIGaAs) quantum well high-mobility heterostructures. It is contemplated that the detector 140 may be another detector suitable for receiving the reflected wave 142 in the THz frequency range.

[0027] FIG. 3 shows a side-view of another embodiment of a system 300 for identifying an object 110. The system 300 may be based on systems 100, 200A, 200B (motion controller 105 not shown) and repeated descriptions are omitted for brevity. System 300 further comprises an excitation assembly 302 optically aligned to the electromagnetic radiation source 130. The electromagnetic radiation source 130 may emit a divergent excitation wave 132 and the excitation assembly 302 may be any optical device, e.g. lens, mirror, configured to collimate and focus the excitation wave 132 into a narrow wave profile. The excitation assembly 302 may be a linear lens such as a polytetrafluoroethylene (PTFE) cylindrical lens, or may be a concave metallic mirror. It is contemplated that the excitation assembly 302 may be any optical device that collimates the excitation wave 132. In some embodiments, the electromagnetic radiation source 130 and the excitation assembly 302 may be positioned to be parallel to the excitation wave 132 (as shown in FIGS. 4A to 5C). Alternatively or in addition, the excitation assembly 302 may be positioned to alter the direction of the excitation wave 132. For example, the excitation assembly 302 may be rotated about a pivot (not shown) or tilted, i.e. inclined such that the direction of the excitation wave 132 may be altered (see rotating arrow in FIG. 3), and the excitation wave 132 may not be parallel to the electromagnetic radiation source 130.

[0028] The system 300 also comprises a detection assembly 308 in optical alignment to the reflector 120 and the detector 140, to focus and collimate the reflected wave 142 onto the sensing window of the detector 140. In some embodiments, the reflected wave 142 may have a scattered, e.g. divergent wave profile and the detection assembly 308 may be useful in reshaping, collimating and focusing the reflected wave 142, particularly, if the detector 140 is positioned at a distance from the platform 102 and target object 110. The detection assembly 308 may be any linear optical device for THz wave collimation, such as but not limited to, a double convex cylindrical lens, a negative meniscus lens, or a double-lens configuration with plano-convex cylindrical lenses. It is contemplated that other linear optical devices for the collimation of the reflected wave 142 may be used in system 300.

[0029] The system 300 comprises a processor 310 configured to receive spectral information on the reflected wave 142 from the detector 140. The processor 310 may be in signal communication with the detector 140, such that the spectral information on the reflected wave 142 may be transmitted to the processor 310 for further processing. In some embodiments, the spectral information on the reflected wave 142 may be transmitted via wireless means according to a pre-defined wireless communication protocol. Examples of the pre-defined wireless communication protocols include: global system for mobile communication (GSM), enhanced data GSM environment (EDGE), wideband code division multiple access (WCDMA), code division multiple access (CDMA), time division multiple access (TDMA), wireless fidelity (Wi-Fi), voice over Internet protocol (VoIP), worldwide interoperability for microwave access (Wi-MAX), Wi-Fi direct (WFD), an ultra-wideband (UWB), infrared data association (IrDA), Bluetooth, ZigBee, SigFox, LPWan, LoRaWan, GPRS, 3G, 4G, LTE, and 5G communication systems. Alternatively, the processor 310 and the detector 140 may be in signal communication via wired means. The detector 140 and/or the processor 310 may also include a memory to store the spectral information on the reflected wave 142.

[0030] The spectral information on the reflected wave 142 may include the amplitude, frequency, phase, wavelength, electric field, power intensity, refractive index of the object 110. The processor 310 may be further configured to generate an object image for object 110 identification, for example, via Fourier-transform spectroscopy and/or THz time-domain spectroscopy techniques as would be known to those skilled in the art. In an embodiment, the object image may be a THz heatmap image of the object 110, and may be the THz power intensity distribution of the object 110. Based on the object image, the object 110 may be identified. It is contemplated that the object 110 may also be identified based on the spectral information on the reflected wave 142. It is also contemplated that processor 310 may apply pre- or post- image processing techniques to minimize noise and improve the accuracy of the object image. In some embodiments, the generated object image may provide for the identification of the object 110 based on material type, particularly, for HDPE or PET plastic object 110 identification. The object 110 may be further segregated or sorted based on said identification. [0031] As shown in FIGS. 1 to 3, the reflector 120 may be positioned parallel to the platform 120, and due to the positioning of the electromagnetic radiation source 130 and the detector 140, the excitation wave 132 may be incident on the object 110 at an angle, i.e. in that the angle of incidence of the excitation wave 132 is not at 90 °. Accordingly, a beam splitter may not be required to direct the reflected wave 142 onto the sensing window of the detector 140. [0032] FIGS. 4A and 4B show side-views of the various configurations of the positioning of the reflector 120 on, e.g. above the platform 102 in systems 400A, 400B for identifying an object 110. Systems 400A, 400B may be based on the systems as discussed in relation to FIGS. 1 to 3 (motion controller 105 and processor 310 are not shown) and repeated descriptions are omitted. Referring to FIG. 4A, the reflector 120 may be positioned parallel to the platform 102, in the same arrangement as that explained with reference to FIGS. 1 to 3. However, the electromagnetic radiation source 130 may be positioned directly above the object 110 such that the incident angle of the excitation wave 132 is at 90 °, and the detector 140 may be positioned perpendicular to the electromagnetic radiation source 130 and the object 110. Accordingly, the distance between the electromagnetic radiation source 130 and the detector 140 may be smaller (relative to configurations where the incident angle of the excitation wave 132 is not at 90 °, e.g. FIGS. 3 and 5B). This may provide ease of mounting of the reflector 120 in small area, e.g. in MRFs which may have space constraints.

[0033] In this configuration, system 400A may further comprise a beam splitter 306 in optical alignment with the electromagnetic radiation source 130, the detector 140 and the reflector 120, and is configured to direct the reflected wave 142 onto the sensing window of the detector 140. Specifically, the beam splitter 306 separates the excitation wave 132 from the reflected wave 142, such that only the reflected wave 142 is received at the detector 140. The beam splitter 306 may be a THz silicon crystal beam splitter, or a split mirror (dichroic mirror). It is contemplated that the beam splitter 306 may be any beam splitter configured to separate the excitation wave 132 from the reflected wave 142 in the THz frequency range, as would be known to those skilled in the art.

[0034] Referring to FIG. 4B, the reflector 120 may be positioned at an angle to a longitudinal axis of the platform. This provides smooth movement of the objects 110 when said objects 110 are moving in the direction 107 on the platform 102. In this configuration, the incident angle of the excitation wave 132 may be at almost 90 ° since the electromagnetic radiation source 130 is positioned directly above the object 110 and the reflector 120 is positioned at an angle. However, the detector 140 may be placed above and at an angle to receive the reflected wave 142, and a beam splitter may not be required. It is contemplated that the reflector 120 may be inclined in the opposite direction to that shown in FIG. 4B, and the detector 140 may be positioned to receive the reflected wave 142. In other words, the reflector 120 (which may adopt various positions), the electromagnetic radiation source 130 and the detector 140 are optically aligned, such that the detector 140 receives the reflected wave 142.

[0035] FIGS. 5A to 5C show side-views of the various configurations of the positioning of the reflector 120, when the reflector 120 is positioned below the platform 102 in systems 500A, 500B, 500C for identifying an object 110. Systems 500A, 500B, 500C may be based on the systems as discussed in relation to FIGS. 1 to 4B (motion controller 105 and processor 310 are not shown) and repeated descriptions are omitted. Referring to FIGS. 5A to 5C, the reflector 120 may be positioned below the platform 102, and may be mounted on the underlying frame 104 supporting the platform 102. In FIGS. 5A and 5B, the reflector 120 may be positioned parallel to the platform 120. As shown in FIG. 5A, the electromagnetic radiation source 130 may be positioned directly above the object 110 such that the angle of incidence of the excitation wave 132 is at 90 °, and the detector 140 may be positioned perpendicular to the electromagnetic radiation source 130 and the object 110 to receive the reflected wave 142. Accordingly, the distance between the electromagnetic radiation source 130 and the detector 140 may be smaller (relative to configurations where the incident angle of the excitation wave 132 is not at 90 °). This may provide ease of mounting of the reflector 120 in small area, e.g. in MRFs which may have space constraints. Further, system 500A may comprise a beam splitter 306 in optical alignment with the electromagnetic radiation source 130, the detector 140 and the reflector 120, which is configured to direct the reflected wave 142 onto the sensing window of the detector 140. In another embodiment, the electromagnetic radiation source 130 and the detector 140 may be positioned above and at an angle to the reflector 120, such that the incident angle of the excitation wave 132 may not be at 90 ° and a beam splitter may not be required (as shown in FIG. 5B). Referring to FIG. 5C, system 500C may include a reflector 120 positioned at an angle to the longitudinal axis of the platform 102. The reflector 120 may be mounted to the underlying frame 104 by mounting frames 122. The electromagnetic radiation source 130 may be positioned directly above the object 110 such that the incident angle of the excitation wave 132 may be at 90 °, and the detector 140 may be positioned to receive the reflected wave 142. Thus, a beam splitter may not be required in this configuration. It is contemplated that the reflector 120 may be inclined in the opposite direction to that shown in FIG. 5C and the detector 140 may be positioned to receive the reflected wave 142.

[0036] As shown in FIGS. 5A to 5C, the excitation wave 132 transmits through the object 110 to form the modified wave 136, and is received and directed by the reflector 120 positioned below the platform 102. As such, the modified wave 136 has to transmit through the material of the platform 102. In some embodiments, the platform 102 is a conveyor belt, and the conveyor belt material may be a material transparent to allow THz waves, i.e. modified wave 136, to be transmitted to the reflector 120. Examples of conveyor belt materials with a high transparency to THz waves may be plastic materials such as but not limited to Teflon, polyurethane or polyvinyl chloride (PVC). In some embodiments, the platform 102 may not include metal components, e.g. metal wires, cables or foils, since THz waves may not transmit but reflect through metal. In other embodiments, the platform 102 may not include carbon, since carbon absorbs THz waves and may preclude the THz imaging process.

[0037] Although the width of the reflector 120 may be illustrated to have a pre-determined width in FIGS. 5A to 5C, it is contemplated that the reflector width 120 may not be limited to the pre-determined width range, when the reflector 120 is positioned beneath the platform 102.

[0038] In an aspect of the disclosure, the reflector 120 may be fitted on the systems 100 to 500C discussed with reference to FIGS. 1 to 5C. In some embodiments, the reflector 120 may be positioned on, e.g. above the platform 102 such that the modified wave 136 does not transmit through the platform 102 material, and may be positioned parallel or at an angle to the longitudinal axis of the platform 102 (as shown in FIGS. 1 to 4B). In some other embodiments, the reflector 120 may be positioned below the platform 102, and may be positioned parallel or at an angle to the longitudinal axis of the platform 102 (as shown in FIGS. 5A to 5C). Upon fitting the reflector 120 on the system 100 to 500C, the reflector 120 may be adjusted to be in optical alignment with the other optical components, e.g. electromagnetic radiation source 130, excitation assembly 302, detector 140, detection assembly 308, and beam splitter 306 (as shown in FIGS. 4A and 5A).

[0039] In the embodiments shown in FIGS. 3 to 5C, the positioning of the reflector 120 at a parallel position on or below the platform 102 may provide easy mounting of the reflector 120 on existing conveyor belt systems. Alternatively, the reflector may be positioned at an inclined position on or below the platform 102 such that the incident angle of the excitation wave 132 may be almost at 90 ° and the detector 140 positioned at an angle, thus obviating the need for a beam splitter (as shown in FIGS. 4B and 5C).

[0040] FIG. 6 shows a schematic illustration of a method for manufacturing a system 600 for identifying an object. Method 600 comprises steps of: (i.) providing a platform configured to support the object (step 602); (ii.) providing an electromagnetic radiation source configured to generate an excitation wave, wherein the excitation wave is transmitted through the object to form a modified wave modified by the object (step 606); and (iii.) providing a reflector optically aligned to the electromagnetic radiation source, wherein the reflector is configured to receive the modified wave and direct the modified wave back into the object to produce a reflected wave which is received by a detector optically aligned to the electromagnetic radiation source and the reflector (step 608).

[0041] The system may be the system 100 to 500C as described with reference to the embodiments shown in FIGS. 1 to 5C. In some embodiments, the system 100 to 500C may be in the form of a THz-based conveyor belt system for the identification of plastic objects.

[0042] FIG. 7 shows a schematic illustration of a method for fitting a reflector 700 on a system for identifying an object. Method 700 comprises the steps of: (i.) positioning a reflector on a platform configured to support the object (step 702); (ii.) positioning an electromagnetic radiation source configured to generate an excitation wave, the electromagnetic radiation source optically aligned to the reflector, wherein the excitation wave is transmitted through the object to form a modified wave modified by the object (step 706); and (iii.) positioning a detector configured to receive a reflected wave, the detector optically aligned to the electromagnetic radiation source and the reflector, wherein the reflector is configured to receive the modified wave and direct the modified wave back into the object to produce the reflected wave which is received by the detector (step 708).

[0043] The reflector may be positioned spaced apart to or in contact with the platform such that the reflector remains stationary when the platform is moving. In some embodiments, the reflector may be parallel to the platform. In some other embodiments, the reflector may be positioned at an angle to a longitudinal axis of the platform.

[0044] The system may be the system 100 to 400B described with reference to the embodiments shown in FIGS. 1 to 4B. In some embodiments, the system for identifying an object may be any existing THz-based conveyor belt system in MRFs, for the identification of plastic objects. In some embodiments, the platform (conveyor belt) material may include a rubber material, and may further include metal wires or cables. In some embodiments, it is contemplated that step 702 may include positioning the reflector below the platform (as shown in FIGS. 5A to 5C). In various configurations where the reflector is positioned below the platform, the rubber material may be removed or modified to enable the electromagnetic radiation to pass there-through.

[0045] FIG. 8 shows an image of an exemplary use condition of the system 800, and insets (i.) shows the top-view; (ii.) shows the cross-sectional view of the rubber material used in system 800. System 800 may be used in MRFs, particularly MRFs for plastic object 110 identification and segregation. System 800 may be based on systems 100 to 400B described with reference to FIGS. 1 to 4B. In FIG. 8, the platform 102 may be a conveyor belt supported by the conveyor belt system as discussed above, and may move at a high-speed of about 1.0 m/s to move the object 110 along the belt. The electromagnetic radiation source 130 and the detector 140 (not shown in FIG. 8) may be positioned above the conveyor belt to generate the excitation wave 132, and to receive the reflected wave 142, respectively. In some embodiments, the detector 140 may be selected based on the speed of the conveyor belt system to provide for high-speed scanning capabilities, and good spatial resolution.

[0046] The platform 102 material (conveyor belt material) may be a metal-reinforced rubber material, e.g. black rubber typically used in such MRFs, which may include EP 400 / 3-ply oil proof belts with a thickness of 9 mm (as shown in insets (i.) and (ii.)), which generally attenuates THz waves due to the presence of metal which blocks transmission of the THz wave, and carbon (in the rubber material) which absorbs the THz waves. A reflector 120 (not shown in FIG. 8) may be positioned on and spaced apart from or be in contact with the conveyor belt (denoted by position “A” in FIG. 8). In use, the reflector 120 may be positioned on, e.g. above the belt such that the object 110 overlaps the reflector 120, to receive the modified wave 136 and direct the modified wave 136 back into the object to produce the reflected wave 142 received by the detector 140. In some embodiments, the width of the reflector 120 may be selected based on the width of the sensing window of the detector 140. [0047] The disclosure provides a simple and facile means, via the reflector, that can be easily fitted and applied to existing THz-based conveyor belt (platform) identification system, thereby obviating the need to modify such systems in the MRFs. The reflector may be easily positioned, e.g. parallel or inclined to the platform, to accommodate the configurations of the other components in existing THz-based conveyor belt identification systems (e.g. electromagnetic radiation source 130 and/or detector 140). In addition, the reflector 120 which is positioned on, e.g. above the platform 102 may produce a reflected wave that is not affected by impurities on the platform, which in turn reduces signal error. Further, multiple objects may be identified simultaneously. As a result, the system, method for manufacturing said system, and method for fitting the reflector on existing THz-based identification systems may be used for real-time identification and segregation of plastic objects 110 in high-speed conveyor belt systems.

[0048] While the disclosure has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the disclosure as defined by the appended claims. The scope of the disclosure is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.