JP2017020837A - Foreign matter detection device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently detect foreign matters contained in an object using a terahertz wave.SOLUTION: A foreign matter detection device (1) comprises: irradiation means (101) that irradiates a terahertz wave toward an object; reflection means (20) that reflects the terahertz wave transmitting the object; reception means (108) that receives the terahertz wave reflected upon the object and by the reflection means; determination means (301) that determines a time waveform pertaining to the terahertz wave reflected by the reflection means from an output of the reception means as a detection object signal; and detection means (302) that detects a foreign matter contained in the object on the basis of the detection object signal determined. A focus of the terahertz wave to be irradiated by the irradiation means has been set in the reflection means.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a technical field of a foreign object detection apparatus and method for detecting a foreign object contained in an object using terahertz waves.

  In recent years, research and development of terahertz wave imaging has been activated, and for example, it is expected to be applied to nondestructive inspection and the like. As an example of non-destructive inspection, an object is placed in a container composed of a first part that transmits a terahertz wave and a second part that reflects the terahertz wave, and is obtained by analyzing the reflected wave of the terahertz wave from the container A technique for inspecting whether or not a foreign object is included in an object from a tomographic image or the like has been proposed (see Patent Document 1).

JP 2014-2024 A

  In the measurement method using the terahertz wave reflected by the object as in the technique described in Patent Document 1, when the object includes a foreign object, the detected terahertz wave becomes weak due to the foreign object. End up. For this reason, there is a technical problem that the detection accuracy of the foreign substance inspection is lowered. Even when a container that reflects terahertz waves is used as in the technique described in Patent Document 1, if the focus of the irradiated terahertz waves is not appropriate, the reflected terahertz waves are efficiently detected. Is difficult. For this reason, even if a container that reflects terahertz waves is used, it is difficult to increase the detection accuracy of the foreign substance inspection.

  The present invention has been made in view of the above problems, for example, and provides a foreign substance inspection apparatus and method capable of efficiently detecting a foreign substance contained in an object using a terahertz wave. Let it be an issue.

  In order to solve the above-described problem, the foreign object detection apparatus of the present invention irradiates a terahertz wave toward an object, a reflecting means that reflects the terahertz wave transmitted through the object, the object, and the object Receiving means for receiving the terahertz wave reflected by the reflecting means; specifying means for specifying a time waveform related to the terahertz wave reflected by the reflecting means from the output of the received signal as a detection target signal; Detection means for detecting a foreign substance contained in the object based on the detection target signal, and the focal point of the terahertz wave irradiated by the irradiation means is set in the reflection means.

  In order to solve the above-described problem, the foreign object detection method of the present invention irradiates a terahertz wave toward an object, a reflecting means that reflects the terahertz wave transmitted through the object, the object, and the object Receiving means for receiving terahertz waves reflected by the reflecting means, and a foreign object detection method in a foreign object detection device comprising: a time waveform related to the terahertz waves reflected by the reflecting means from the output of the received signal; A focus step of the terahertz wave irradiated by the irradiating means, comprising: a specifying step of specifying as a detection target signal; and a detection step of detecting a foreign substance contained in the target based on the specified detection target signal Is set in the reflecting means.

  The effect | action and other gain of this invention are clarified from the form for implementing demonstrated below.

It is a figure which shows the principal part of the foreign material detection apparatus which concerns on 1st Example. It is a schematic block diagram which shows the structure of the foreign material detection apparatus which concerns on 1st Example. It is an example of the time waveform of reflected light. It is a flowchart which shows the trimming range determination process which concerns on 1st Example. It is a flowchart which shows the foreign material detection process which concerns on 1st Example. It is a figure which shows the optical system of the terahertz transmission / reception part which concerns on the modification of 1st Example. It is a block diagram which shows the structure of the control and signal processing part which concerns on the modification of 1st Example. It is a figure which shows the relationship between the terahertz transmission / reception part and reflection part which concern on 2nd Example. It is a conceptual diagram which shows the concept of the trimming range which concerns on 2nd Example. It is a figure which shows the relationship between the terahertz transmission / reception part and reflection part which concern on 3rd Example. It is a conceptual diagram which shows the concept of the trimming range which concerns on 3rd Example. It is a figure which shows the relationship between the terahertz transmission / reception part and reflection part which concern on 4th Example. It is a conceptual diagram which shows the concept of the trimming range which concerns on 4th Example.

(Foreign matter detector)
An embodiment according to the foreign matter detection apparatus of the present invention will be described.

  The foreign object detection device according to the embodiment includes an irradiating unit, a reflecting unit, a receiving unit, a specifying unit, and a detecting unit.

The irradiation means irradiates the target with a terahertz wave. Here, the terahertz wave is an electromagnetic wave belonging to a frequency region (that is, a terahertz region) around 1 terahertz (1 THz = 10 ¹² Hz). A part of the irradiated terahertz wave is reflected by the object, and the other part passes through the object and reaches the reflecting means.

  The reflecting means is configured using a member having a relatively high reflectivity with respect to terahertz waves such as an aluminum plate. The terahertz wave that has reached the reflecting means is reflected by the reflecting means.

  The receiving means receives the terahertz wave reflected by the object and the terahertz wave reflected by the reflecting means. The receiving means outputs a received signal corresponding to the received terahertz wave.

  Here, according to the inventor's research, the following matters have been found. That is, when a terahertz wave is irradiated on an object and a reflected wave from a foreign object included in the object is detected, the reflected wave from the foreign object is weak and the SN ratio is lowered depending on the reflectance of the foreign object. For this reason, there is a possibility that the accuracy of foreign object detection is lowered.

  Therefore, in the present embodiment, the specifying unit specifies the time waveform related to the terahertz wave reflected by the reflecting unit from the output of the receiving unit as the detection target signal. Here, in particular, in the present embodiment, the focal point of the terahertz wave to be irradiated is set to the reflecting means. For this reason, the signal intensity (that is, amplitude) of the time waveform related to the terahertz wave reflected by the reflecting means is relatively high.

  The detecting means detects a foreign substance contained in the target object based on the detection target signal specified by the specifying means. Here, when a foreign object is included in the object, a part of the terahertz wave is reflected by the foreign object, so that the signal intensity of the time waveform related to the terahertz wave reflected by the reflecting means is reduced. Therefore, as described above, if the time waveform related to the terahertz wave reflected by the reflecting means is specified as the detection target signal, it is possible to determine whether or not the target object contains foreign matters based on the strength of the signal intensity, for example. it can.

  As a result, according to the foreign object detection device according to the embodiment, it is possible to efficiently detect the foreign object contained in the object using the terahertz wave.

  In one aspect of the foreign object detection apparatus according to the embodiment, the specifying unit first acquires in advance a time waveform related to the terahertz wave from the output of the receiving unit when the terahertz wave is irradiated to an object that does not include the foreign object. Here, the time waveform relating to the terahertz wave acquired in advance includes the time waveform relating to the terahertz wave reflected by the object and the time waveform relating to the terahertz wave reflected by the reflecting means.

  Then, the specifying unit specifies the time waveform related to the terahertz wave reflected by the reflecting unit as the detection target signal based on the time waveform acquired in advance from the output of the receiving unit this time.

  From the output of the receiving means, for example, a time signal related to a terahertz wave reflected by an object, particularly a terahertz wave reflected by a foreign object is also obtained. When a terahertz wave is irradiated to an object that does not contain a foreign object, the time waveform related to the terahertz wave reflected by the reflecting means appears significantly in the time waveform related to the terahertz wave obtained from the output of the receiving means.

  If the time waveform related to the terahertz wave when the terahertz wave is irradiated to an object that does not include a foreign object is acquired in advance, the appearance timing, waveform, etc. of the time waveform related to the terahertz wave reflected by the reflecting means are obtained. Can be identified. For this reason, the time waveform concerning the terahertz wave reflected by the reflecting means from the output of the receiving means at this time can be specified as the detection target signal.

  In this aspect, the specifying unit specifies a period in which the time waveform related to the terahertz wave reflected by the reflecting unit appears based on the previously acquired time waveform, and is specified from the output of the receiving unit this time. A time waveform that appears within a predetermined period including the predetermined period may be specified as the detection target signal.

  If comprised in this way, the time waveform which concerns on the terahertz wave reflected by the reflection means can be specified comparatively easily as a detection target signal.

  The period in which the time waveform related to the terahertz wave reflected by the reflecting means appears varies somewhat depending on the thickness of the object, for example. For this reason, the “predetermined period” means that even if the appearance timing of the time waveform related to the terahertz wave reflected by the reflecting means is slightly shifted, the margin for detecting the time waveform is set, for example, before and after the specified period. What is necessary is just to set by giving.

  In an aspect in which the time waveform that appears within the predetermined period is specified as a detection target signal, the foreign object detection device further includes a distance acquisition unit that acquires a distance between the target and the reflection unit, and the specification unit includes: Based on the distance acquired by the distance acquisition means, at least one of the start period and the end period of the predetermined period may be changed.

  The “distance between the object and the reflecting means” is specified by some sensor such as a distance sensor, for example, and may be acquired by acquiring an output signal from the sensor, It may be acquired by a user input.

  Or in the aspect which specifies the time waveform which appears in this predetermined period as a detection target signal, the said foreign material detection apparatus follows the reflective surface of a reflection means about the positional relationship of an irradiation means, a receiving means, and a reflection means. A relative position changing unit that changes relative to the direction, and the specifying unit reflects the reflection unit when the total distance between the distance between the irradiation unit and the reflection unit and the distance between the reception unit and the reflection unit is maximum. At least one of a start period and an end period of a predetermined period so that the time waveform related to the terahertz wave and the time waveform related to the terahertz wave reflected by the reflecting means when the total distance is minimum can be specified You may change it.

  Or in the aspect which specifies the waveform which appears in this predetermined period as a detection target signal, the said foreign material detection apparatus is further equipped with the thickness information acquisition means which acquires the thickness information of a target object, and the identification means was acquired. Based on the thickness information, the time waveform related to the terahertz wave reflected by the reflecting means after passing through the maximum thickness portion of the object and the reflection by the reflecting means after passing through the minimum thickness portion of the object At least one of the start period and the end period of the predetermined period may be changed so that the time waveform related to the terahertz wave can be specified.

  In another aspect of the foreign object detection device according to the embodiment, the detection unit is specified by the specifying unit when the terahertz wave that has passed through the object that does not include the foreign object and is reflected by the reflection unit is received by the reception unit. Using the amplitude of the detection target signal as a reference, it is determined that the current target object contains a foreign object on the condition that the amplitude of the detection target signal specified this time by the specifying unit is equal to or less than a predetermined ratio.

  According to this aspect, it can be determined relatively easily whether or not a foreign object is contained in the object, which is very advantageous in practice.

(Foreign matter detection method)
An embodiment according to the foreign matter detection method of the present invention will be described.

  The foreign object detection method according to the embodiment receives an irradiation unit that irradiates a terahertz wave toward an object, a reflection unit that reflects the terahertz wave that has passed through the object, and a terahertz wave that is reflected by the object and the reflection unit A foreign matter detection method in the foreign matter detection device.

  The foreign object detection method includes a specifying step and a detection step. In the specifying step, the time waveform related to the terahertz wave reflected by the reflecting means is specified as the detection target signal from the output of the receiving means. In the detection step, a foreign substance contained in the target object is detected based on the specified detection target signal. Here, the focal point of the terahertz wave irradiated by the irradiation unit is set to the reflection unit.

  According to the foreign object detection method according to the embodiment, the foreign object included in the target object can be efficiently detected using the terahertz wave, similarly to the foreign object detection device according to the above-described embodiment. In the foreign object detection method according to the embodiment, various aspects similar to the various aspects of the foreign object detection apparatus according to the embodiment described above can be employed.

  Embodiments according to the foreign matter detection apparatus and foreign matter detection method of the present invention will be described with reference to the drawings.

<First embodiment>
(Configuration of foreign object detection device)
The configuration of the foreign object detection device according to the embodiment will be described with reference to FIGS. FIG. 1 is a diagram illustrating a main part of the foreign object detection device according to the first embodiment. FIG. 2 is a schematic configuration diagram illustrating the configuration of the foreign object detection device according to the first embodiment.

  The foreign object detection device according to the present embodiment is a so-called reflective terahertz wave foreign object detection device. In FIG. 1, the foreign object detection device 1 includes a terahertz wave transmission / reception unit 10, a reflection unit 20, a trimming unit 301, and a foreign object detection unit 302.

  The sample 50 to be measured is disposed between the terahertz wave transmitting / receiving unit 10 and the reflecting unit 20. In FIG. 1, the sample to be measured 50 is disposed so as to be in contact with the reflecting portion 20, but the sample to be measured 50 may be disposed at a distance from the reflecting portion 20.

  The terahertz wave transmitting / receiving unit 10 emits the terahertz wave toward the sample 50 to be measured, and receives the terahertz wave reflected by the sample 50 to be measured and the terahertz wave reflected by the reflecting unit 20. Hereinafter, the “reflected terahertz wave” is appropriately referred to as “reflected light”.

  Particularly in the present embodiment, the focal point of the terahertz wave emitted from the terahertz wave transmitting / receiving unit 10 is set on the reflecting unit 20. Moreover, the reflection part 20 is comprised by the member with comparatively high reflectance, such as an aluminum plate, for example.

  When the foreign object 51 is not included in the sample 50 to be measured, the signal intensity (amplitude) resulting from the reflected light from the reflecting unit 20 appears significantly in the received signal caused by the reflected light received by the terahertz wave transmitting / receiving unit 10. . On the other hand, when the foreign object 51 is included in the sample 50 to be measured, the terahertz wave is reflected by the foreign object 51, so that the terahertz wave reaching the reflection unit 20 is reduced and is caused by the reflected light from the reflection unit 20. Signal strength also decreases.

  Therefore, if the signal intensity resulting from the reflected light from the reflecting part 20 is compared with the signal intensity resulting from the reflected light from the reflecting part 20 when the sample 50 to be measured does not contain the foreign object 51, the presence or absence of the foreign object 51 Can be detected.

  By the way, the received signal includes, for example, a signal caused by reflected light from the sample 50 to be measured, in addition to a signal caused by reflected light from the reflecting unit 20. For this reason, if the signal resulting from the reflected light from the reflecting unit 20 is not specified, there is a possibility that foreign object detection will not be performed correctly.

  Therefore, in the present embodiment, the trimming unit 301 cuts out a reception signal corresponding to a period in which a signal waveform caused by the reflected light from the reflection unit 20 appears from the reception signal. The foreign object detection unit 302 determines whether or not the foreign object 51 is included in the measured sample 50 based on the intensity of the signal output from the trimming unit 301 (that is, the cut out reception signal).

  Next, the configuration of the foreign object detection device 1 will be described with reference to FIG.

  The pulse width of the terahertz wave is on the order of subpicoseconds. For this reason, it is difficult to directly detect the time waveform of the terahertz wave. Therefore, the foreign object detection apparatus 1 indirectly detects the time waveform of the terahertz wave using a known pump / probe method.

  In FIG. 2, the laser oscillation unit 11 includes a laser unit 111, an optical delay unit 112, and a beam splitter 113.

  The laser unit 111 can repeatedly output an ultrashort pulse laser beam of sub-picosecond order or less. During the operation of the foreign object detection device 1, the pulsed laser light emitted from the laser unit 111 is divided into pump light and probe light by the beam splitter 113.

  The pump light is applied to the terahertz wave transmission unit 101 of the terahertz transmission / reception unit 10. On the other hand, the probe light is applied to the terahertz wave receiving unit 108 of the terahertz transmitting / receiving unit 10 via the optical delay unit 112. Note that various known modes can be applied to the optical delay unit 112, and therefore, detailed description thereof is omitted.

  The terahertz transmitting / receiving unit 10 includes a terahertz wave transmitting unit 101, a silicon lens 102, a collimating lens 103, a beam splitter 104, an objective lens 105, a collimating lens 106, a silicon lens 107, and a terahertz wave receiving unit 108.

  The terahertz wave transmitting unit 101 includes a terahertz wave generating element (not shown) including a photoconductive antenna having a dipole antenna or the like on a semiconductor substrate formed of, for example, GaAs (Gallium Arsenide).

  A gap is formed at the center of the photoconductive antenna. When a bias voltage is applied to the gap and the gap is irradiated with pump light, carriers are generated in the semiconductor by photoexcitation. Sub-picosecond current is generated. As a result, a pulsed terahertz wave having an amplitude proportional to the time derivative of the generated current is emitted. That is, the terahertz wave generating element according to the present example is a photoconductive antenna (PCA).

  The terahertz wave generated by the terahertz wave generating element of the terahertz wave transmitting unit 101 is irradiated to the sample 50 to be measured through the silicon lens 102, the collimating lens 103, the beam splitter 104, and the objective lens 105. Here, in particular, the focal point of the terahertz wave emitted from the terahertz wave transmission unit 101 is set on the reflection unit 20.

  Reflected light from the sample 50 to be measured or the reflecting unit 20 enters the terahertz wave receiving unit 108 through the objective lens 105, the beam splitter 104, the collimating lens 106, and the silicon lens 107.

  The terahertz wave receiving unit 108 includes a terahertz wave detecting element (not shown) having the same configuration as the terahertz wave generating element. That is, the terahertz wave detecting element is also a photoconductive antenna.

  When the probe light via the optical delay unit 112 is incident on the terahertz wave detection element, carriers are generated in the semiconductor of the terahertz wave detection element. As a result, a current proportional to the amplitude of the reflected light incident on the terahertz wave detection element at the moment when the carrier is generated is generated. The terahertz wave receiving unit 108 converts the generated current into current and voltage by, for example, an IV conversion unit (not shown), and outputs it as a reception signal.

  The control / signal processing unit 30 includes a trimming unit 301, a foreign matter detection unit 302, a signal amplification unit 303, a modulation signal generation unit 304, a lock-in detection unit 305, an image processing unit 306, and a scanner drive unit 307. .

  The reception signal output from the terahertz wave reception unit 108 is amplified by the signal amplification unit 303, and known lock-in detection is performed by the lock-in detection unit 305. The modulation signal generation unit 304 generates a reference signal used for lock-in detection, outputs the reference signal to the lock-in detection unit 305, and supplies a bias voltage modulated based on the reference signal to the terahertz wave transmission unit 101. Applied to the terahertz wave generating element.

  As a result of the lock-in detection, the reflected light from the sample to be measured 50 and the reflected light from the reflecting part 20, and further, when the foreign object 51 is included in the sample to be measured 50, the time waveform of each reflected light from the foreign object 51 Is acquired.

  Acquisition of the time waveform of the reflected light (that is, the terahertz wave) is executed together with the driving of the terahertz wave transmitting / receiving unit 10 by the scanning mechanism 12. The operation of the scanning mechanism 12 is controlled by the scanner driving unit 307. The scanner driving unit 307 further outputs information indicating the scanning position to the image processing unit 306.

  The scanning mechanism 12 drives the terahertz wave transmission / reception unit 10 planarly along the reflection surface of the reflection unit 20. Since various known modes can be applied to the scanning mechanism 12, a detailed description thereof will be omitted. Note that the scanning mechanism 12 may drive the reflection unit 20 instead of the terahertz wave transmission / reception unit 10.

  The image processing unit 306 temporarily stores the time waveform extracted by the trimming unit 301 among the time waveform of the reflected light acquired by the lock-in detection unit 305 in a storage device or the like (not shown). Perform data processing. Then, the image processing unit 306 generates an imaging image of the sample 50 to be measured using the results of various data processing.

  Note that the terahertz wave generating element and the terahertz wave detecting element are not limited to the above-described photoconductive antenna, and, for example, a resonant tunneling diode (RTD) or the like is also applicable. When the resonant tunneling diode is used, it is not necessary to provide the laser oscillating unit 11, so that the foreign object detection device can be downsized.

(Foreign matter detection method)
Next, a foreign object detection method in the foreign object detection apparatus 1 configured as described above will be described.

  Prior to detection of foreign matter in the sample 50 to be measured, a reference sample that is known in advance to contain no foreign matter is disposed between the terahertz wave transmitting / receiving unit 10 and the reflecting unit 20. Next, the terahertz wave is irradiated from the terahertz wave transmitting / receiving unit 10 to the reference sample, and the time waveform of the reflected light is acquired by the lock-in detection unit 305.

  Here, as the time waveform of the reflected light when the reference sample is irradiated with the terahertz wave, the time waveform related to the terahertz wave reflected by the reflecting unit 20 appears remarkably as shown in FIG. This is because the reflecting unit 20 is made of a relatively high reflectance member such as an aluminum plate, and the focal point of the terahertz wave emitted from the terahertz wave transmitting / receiving unit 10 is set on the reflecting unit 20. It is due to that.

  The focal position of the terahertz wave is set on the reflection unit 20 by adjusting the position of the objective lens 105 and the like so that the amplitude of the time waveform related to the terahertz wave reflected by the reflection unit 20 is maximized. .

  The trimming unit 301 detects a peak of the time waveform of the acquired reflected light, and the detected peak is a peak of the time waveform of the terahertz wave reflected by the reflection unit 20. Then, the trimming unit 301 sets a predetermined period (here, time t1 to time t2) including the time t0 when the detected peak appears as a trimming range. The trimming unit 301 stores the set trimming range.

  It should be noted that how far the time t1 is set from the time t0 and how much the time t2 is set after the time t0 are obtained by, for example, obtaining an optimum value through experiments or the like. A value is stored in advance in a memory or the like of the trimming unit 301, and when the time t0 is specified, the value may be determined with reference to the stored value.

  The foreign object detection unit 302 stores the amplitude of the peak of the time waveform of the terahertz wave reflected by the reflection unit 20 detected by the trimming unit 301 as a reference amplitude.

  When foreign matter detection is performed on the sample 50 to be measured, the sample 50 to be measured is placed at the position where the reference sample has been placed. Here, in particular, in the present embodiment, the focal point of the terahertz wave emitted from the terahertz wave transmitting / receiving unit 10 is set on the reflection unit 20, so that the terahertz wave emitted every time the sample to be measured 50 is replaced. Since there is no need to adjust the focal position, foreign object detection of the sample 50 to be measured can be started relatively quickly.

  Next, a terahertz wave is irradiated from the terahertz wave transmitting / receiving unit 10 to the sample 50 to be measured, and a time waveform of reflected light is acquired by the lock-in detection unit 305.

  The trimming unit 301 cuts out a time waveform within the trimming range from the acquired time waveform of reflected light. The foreign object detection unit 302 acquires the amplitude of the time waveform cut out by the trimming unit 301, compares the acquired amplitude with a reference amplitude, and determines whether or not the foreign object 51 is included in the measured sample 50. judge.

  Here, in the case where the foreign object 51 is included in the sample 50 to be measured, the time waveform of the reflected light acquired by the lock-in detection unit 305 is reflected by the foreign object 51, for example, as shown in FIG. The peak of the time waveform related to the terahertz wave thus generated and the peak of the time waveform related to the terahertz wave reflected by the reflecting unit 20 appear.

  At this time, if no measures are taken, a process of identifying the peak of the time waveform related to the terahertz wave reflected by the reflection unit 20 from the time waveform of the reflected light acquired by the lock-in detection unit 305 must be performed. I must. And the process which specifies this peak must be implemented for every scanning point, and the processing load concerning a foreign material detection becomes comparatively heavy.

  On the other hand, in the present embodiment, the time waveform cut out by the trimming unit 301 includes the peak of the time waveform related to the terahertz wave reflected by the reflection unit 20, and thus the above peak is specified. There is no need to perform processing. In addition, the image processing unit 306 and the foreign object detection unit 302 need only process the time waveform cut out by the trimming unit 301, so that the amount of data to be processed can be reduced. As a result, according to the foreign object detection device 1 according to the present embodiment, it is possible to reduce the processing load related to foreign object detection.

  Further, when the terahertz wave is focused on the sample to be measured 50 instead of the reflection unit 20 and the time waveform of the reflected light is obtained, the sample to be measured 50 includes a foreign object 51 as shown in FIG. 3C, for example. Even so, since the terahertz wave cannot be focused on the foreign object 51, the signal intensity of the time waveform related to the terahertz wave reflected by the foreign object 51 is relatively weak. That is, the SN ratio of the time waveform is relatively low, and the reliability of foreign object detection may be reduced.

  On the other hand, in the present embodiment, as described above, the foreign object 51 is included in the sample to be measured 50 by comparing the amplitude of the time waveform cut out by the trimming unit 301 with the reference amplitude by the foreign object detection unit 302. It is determined whether or not. The smaller the amplitude of the extracted time waveform, the greater the difference from the reference amplitude. That is, when the terahertz wave is reflected by the foreign object 51, the amplitude of the time waveform related to the terahertz wave reflected by the reflecting unit 20 is relatively small, but the difference from the reference amplitude is large, and as a result, the foreign object 51 is Whether it is included or not can be determined relatively easily. In addition, when the amplitude of the time waveform related to the terahertz wave reflected by the reflection unit 20 is relatively large, the SN ratio of the time waveform is relatively large, so that an error in obtaining a difference from the reference amplitude is small. Accordingly, in this case as well, it can be relatively easily determined whether or not the foreign matter 51 is included.

  Next, foreign object detection processing executed by the foreign object detection device 1 according to the present embodiment will be described with reference to the flowcharts of FIGS. 4 and 5.

  In FIG. 4, after the reference sample is arranged, the terahertz wave transmitting / receiving unit 10 irradiates the reference sample with the terahertz wave (step S101). Subsequently, the terahertz wave transmitting / receiving unit 10 receives the terahertz wave reflected by the reference sample or the reflection unit 20 and outputs a reception signal.

  The lock-in detection unit 305 of the control / signal processing unit 30 acquires the time waveform of the reflected light based on the received signal. The trimming unit 301 specifies the time at which the peak of the time waveform related to the terahertz wave reflected by the reflection unit 20 appears from the acquired time waveform (step S102).

  Next, the trimming unit 301 sets a predetermined period including the specified time as a trimming range (step S103). Subsequently, the trimming unit 301 stores the set trimming range, and the foreign matter detection unit 302 calculates the amplitude of the peak of the time waveform of the terahertz wave reflected by the reflection unit 20 detected by the trimming unit 301 as the reference amplitude. (Step S104).

  In FIG. 5, after the sample to be measured 50 is arranged, the terahertz wave transmitting / receiving unit 10 irradiates the sample to be measured 50 with a terahertz wave (step S201). The scanner driving unit 307 of the control / signal processing unit 30 controls the scanning mechanism 12 to move the terahertz wave transmitting / receiving unit 10 to a predetermined scanning point (step S202).

  The terahertz wave transmitting / receiving unit 10 receives the terahertz wave reflected by the sample to be measured 50 or the reflection unit 20 and outputs a reception signal. The lock-in detection unit 305 of the control / signal processing unit 30 acquires the time waveform of the reflected light based on the received signal. The trimming unit 301 cuts out the time waveform within the trimming range from the acquired time waveform of the reflected light. The foreign object detection unit 302 acquires the amplitude of the time waveform cut out by the trimming unit 301 (step S203).

  The foreign object detection unit 302 compares the acquired amplitude with the reference amplitude (step S204). Subsequently, the foreign object detection unit 302 determines whether or not the ratio of the acquired amplitude with respect to the reference amplitude, for example, as a comparison result is equal to or less than a predetermined value (step S205).

  When it is determined that the comparison result is equal to or less than the predetermined value (step S205: Yes), the foreign object detection unit 302 determines that the foreign object 51 is included in the sample 50 to be measured (step S206), and the determination result is For example, it is stored in a memory or the like (step S208). On the other hand, when it is determined that the comparison result is greater than the predetermined value (step S205: No), the foreign object detection unit 302 determines that the foreign object 51 is not included in the measured sample 50 (step S207), and the determination result is obtained. Store (step S208).

  Next, the control / signal processing unit 30 determines whether or not all the predetermined scanning areas have been scanned (step S209). When it is determined that the entire region has been scanned (step S209: Yes), the foreign object detection device 1 ends the process. On the other hand, when it is determined that the entire region has not been scanned (step S209: No), the process of step S202 described above is performed.

  The “predetermined value” according to the present embodiment is a value that determines whether or not the sample 51 to be measured includes the foreign object 51, and is set in advance as a fixed value or a variable value according to some physical quantity or parameter. Has been. Such a predetermined value is determined by the reflecting unit 20 when, for example, foreign materials having various materials and various thicknesses are included in an object simulating a sample to be measured, experimentally, empirically, or by simulation. What is necessary is just to obtain | require based on the comparison result with the amplitude of the peak of the time waveform which concerns on the reflected terahertz wave, and a reference signal.

  The “reflecting unit 20”, the “terahertz wave transmitting unit 101”, the “terahertz wave receiving unit 108”, the “trimming unit 301”, and the “foreign substance detecting unit 302” according to the present embodiment are respectively “reflecting means” according to the present invention. ”,“ Irradiation means ”,“ reception means ”,“ specification means ”, and“ detection means ”. The “scanner driving unit 307” and the “scanning mechanism 12” according to the present embodiment are examples of the “relative position changing unit” according to the present invention. The “sample to be measured 50” and the “reference sample” according to the present embodiment are examples of the “object” according to the present invention.

<Modification of terahertz wave transceiver>
The terahertz wave transmitting / receiving unit 10 may have an optical system as shown in FIG. 6, for example. In FIG. 6, the terahertz wave generated by the terahertz wave transmission unit 101 is irradiated to the sample 50 to be measured through the silicon lens 102, the collimator lens 103, and the objective lens 151. Reflected light from the sample 50 to be measured or the reflecting unit 20 enters the terahertz wave receiving unit 108 through the objective lens 152, the collimating lens 106, and the silicon lens 107. In the optical system shown in FIG. 6, the focal point of the terahertz wave emitted from the terahertz wave transmission unit 101 is set on the reflection unit 20.

  With such a configuration, the number of optical members increases as compared with the optical system shown in FIG. 2, but it is not necessary to arrange a beam splitter, so that the power loss of the irradiated terahertz wave can be reduced.

<Modification of control / signal processing unit>
The control / signal processing unit 30 may be configured as shown in FIG. In FIG. 7, the control / signal processing unit 30 replaces the modulation signal generation unit 304 (see FIG. 2) with a bias signal generation unit 354, replaces the lock-in detection unit 305 (see FIG. 2) with a band limiting filter. A portion 355 is provided.

  The bias signal generation unit 354 applies a predetermined bias voltage to the terahertz wave generating element of the terahertz wave transmission unit 101 (see FIG. 2). The reception signal output from the terahertz wave receiving unit 108 (see FIG. 2) is amplified by the signal amplifying unit 303 and band-limited by the band-limiting filter 355.

  With this configuration, it is possible to transmit and receive a terahertz wave without using lock-in detection. As a result, the circuit can be simplified and the power consumption can be reduced.

<Second embodiment>
A second embodiment of the foreign matter detection apparatus and foreign matter detection method of the present invention will be described with reference to FIGS. The second embodiment is the same as the first embodiment described above except that the trimming range setting method is partially different. Therefore, in the second embodiment, the description overlapping with that of the first embodiment is omitted, and common portions in the drawing are denoted by the same reference numerals, and only FIGS. 8 and 9 are basically different only. The description will be given with reference.

  In the second embodiment, as shown in FIG. 8, the distance between the terahertz wave transmission / reception unit 10 of the foreign object detection device 1 and the reflection plate 20 varies depending on the scanning position. In FIG. 8, the inclination of the reflecting portion 20 is exaggerated so that it can be recognized that the reflecting portion 20 is inclined.

  For example, when the distance between the terahertz wave transmission / reception unit 10 and the reflection plate 20 changes by 0.15 mm, the time for the terahertz wave reflected by the reflection unit 20 to reach the terahertz wave transmission / reception unit 10 is 1 picosecond earlier or later. Become.

  For this reason, when the trimming range is determined from the time waveform related to the terahertz wave reflected at one point on the reflection unit 20 when the trimming range is set, the terahertz wave transmitting / receiving unit 10 and the reflection are reflected along with scanning. When the distance to the unit 20 changes, the reliability of the foreign object detection result may be reduced.

  Therefore, in the present embodiment, when the trimming unit 301 sets the trimming range using the reference sample, it relates to the terahertz wave reflected on the reflecting unit 20 at at least two points such as the scan start position and the scan end position. A time waveform is acquired. The trimming unit 301 identifies the peak of the time waveform related to the terahertz wave reflected by the reflecting unit 20 for each of the acquired plurality of time waveforms, and identifies the time at which the peak appears.

  The trimming unit 301 sets the trimming range from the earliest time (corresponding to the time t3 in FIG. 9) at the time when the specified peak appears, for example, a time previous by a value stored in advance in a memory or the like. (Corresponding to time t5 in FIG. 9) is set as the start of the trimming range. Further, the trimming unit 301 sets a trimming range from the latest time (corresponding to time t4 in FIG. 9) among the times when the specified peak appears, for example, by a value stored in advance in a memory or the like. (Corresponding to time t6 in FIG. 9) is set as the end of the trimming range.

  When obtaining the earliest and latest time at which the peak of the time waveform related to the terahertz wave reflected by the reflecting unit 20 appears, mathematical means such as a known extrapolation method or interpolation method is used. Also good.

  In the foreign object detection apparatus 1 according to the present embodiment, since the trimming range is set as described above, it is possible to prevent a decrease in the reliability of the foreign object detection result.

  In addition, due to the distance between the terahertz wave transmission / reception unit 10 of the foreign object detection device 1 and the reflection plate 20 changing depending on the scanning position, the focal position of the terahertz wave is shifted from the reflection unit 20 to detect foreign objects. In order to prevent the accuracy from decreasing, the focal position of the terahertz wave may be adjusted according to the scanning position of the terahertz wave transmitting / receiving unit 10 so that the focal position is always on the reflecting unit 20.

  Specifically, for example, the position of the objective lens 105 at which the amplitude of the time waveform related to the terahertz wave reflected on the reflection unit 20 is maximized at at least two points such as the scan start position and the scan end position is determined. Remember. Next, based on the position of the objective lens 105 at the at least two points, the position of the objective lens 105 at an intermediate position between these points is calculated. Based on the calculation result, the position of the objective lens 105 may be changed according to the scanning position of the terahertz wave transmitting / receiving unit 10.

  With such a method, it is possible to prevent a decrease in the reliability of the foreign object detection result due to the distance between the terahertz wave transmitting / receiving unit 10 of the foreign object detection device 1 and the reflection plate 20 changing depending on the scanning position.

<Third embodiment>
A third embodiment of the foreign matter detection apparatus and foreign matter detection method of the present invention will be described with reference to FIGS. The third embodiment is the same as the first embodiment described above except that the trimming range setting method is partially different. Accordingly, the description of the third embodiment that is the same as that of the first embodiment is omitted, and common portions in the drawing are denoted by the same reference numerals, and only FIGS. 10 and 11 are basically different only. The description will be given with reference.

  In the third embodiment, as shown in FIG. 9, the thickness of the sample 50 to be measured varies depending on the scanning position. In FIG. 10, the change in thickness is exaggerated so that the thickness of the sample 50 to be measured can be recognized.

  The refractive index is different between the air layer and the sample to be measured. When the thickness of the sample 50 to be measured changes, the distance of the air layer through which the terahertz wave irradiated from the terahertz wave transmitting / receiving unit 10 propagates and the distance of the sample to be measured change. As a result, fluctuation occurs in the time when the terahertz wave reflected by the reflecting unit 20 reaches the terahertz wave transmitting / receiving unit 10.

  For this reason, when the trimming range is set, if the trimming range is determined only from the time waveform related to the terahertz wave reflected at one point on the reflection unit 20, the reliability of the foreign object detection result may be reduced. There is sex.

  Therefore, in this embodiment, after the trimming range is set using the reference sample, the control / signal processing unit 30 displays the thickness information of the sample 50 to be measured before the foreign object detection processing of the sample 50 to be measured is started. get. The thickness information may be a measurement result of a known measurement method such as a measurement method using a laser, or may be thickness information of the sample 50 to be measured input by the user of the foreign object detection device 1. Good.

  The trimming unit 301 obtains a difference between the maximum thickness and the minimum thickness of the sample 50 to be measured based on the acquired thickness information. The trimming unit 301 obtains the amount of change in time at which the peak of the time waveform related to the terahertz wave reflected by the reflecting unit 20 appears due to the obtained difference. The trimming unit 301 corrects the start time of the set trimming range by the determined change amount (corresponding to the time t9 in FIG. 11), and sets the end time of the set trimming range to the determined change. The amount is corrected later by the amount (corresponding to time t10 in FIG. 11).

  As a result, the time t7 (see FIG. 11) at which the peak of the time waveform related to the terahertz wave transmitted through the thinnest portion p2 (see FIG. 10) of the sample 50 to be measured and reflected by the reflecting unit 20 appears is also measured. The time t8 (see FIG. 11) at which the peak of the time waveform related to the terahertz wave that has passed through the thickest part p3 (see FIG. 10) of the sample 50 and reflected by the reflecting unit 20 appears is also included in the corrected trimming range. Will be.

  In the foreign object detection apparatus 1 according to the present embodiment, since the trimming range is set as described above, it is possible to prevent a decrease in the reliability of the foreign object detection result.

  The “control / signal processing unit 30” according to the present embodiment is an example of the “thickness information acquisition unit” according to the present invention.

<Fourth embodiment>
A fourth embodiment of the foreign matter detection apparatus and foreign matter detection method of the present invention will be described with reference to FIGS. The fourth embodiment is the same as the first embodiment described above except that the trimming range setting method is partially different. Accordingly, the description of the fourth embodiment that is the same as that of the first embodiment is omitted, and common portions in the drawing are denoted by the same reference numerals, and only the points that are basically different are shown in FIGS. The description will be given with reference.

  In the fourth embodiment, the sample 50 to be measured is an object whose thickness can be arbitrarily changed, for example, a powdered material. The sample to be measured 50 is sandwiched between, for example, belts or the like so as to have a constant thickness. For example, when the sample 50 to be measured moves from the left to the right in the figure, foreign object detection of the sample 50 to be measured is executed.

  In the present embodiment, as shown in FIG. 12, since the sample 50 to be measured and the reflecting portion 20 are spaced apart, time t12 when the peak of the time waveform related to the terahertz wave reflected at the position h1 appears. The interval between (see FIG. 13) and time t13 (see FIG. 13) at which the peak of the time waveform related to the terahertz wave reflected on the reflecting portion 20 (position h2) appears is relatively long.

  The waveform appearing at time t11 in FIG. 13 is a time waveform related to the terahertz wave reflected at the position h0 in FIG.

  Therefore, the control / signal processing unit 30 acquires the distance d between the measured sample 50 and the reflecting unit 20. The distance d may be acquired by a known measurement method such as a measurement method using a laser, or may be acquired by input by the user of the foreign object detection device 1.

  When setting the trimming range using the reference sample, the trimming unit 301 first identifies the peak of the time waveform related to the terahertz wave reflected by the reflecting unit 20, and the time when the peak appears (the time in FIG. 13). (corresponding to t13).

  The trimming unit 301 sets, for example, a memory or the like in order to set a trimming range from the time when the terahertz wave propagates the distance d from the time when the specified peak appears and the time when the specified peak appears. The start of the trimming range is set between the previous time and the value stored in advance. Note that the trimming unit 301 trims a time (corresponding to a time t15 in FIG. 13) after a value stored in advance in a memory or the like to set a trimming range from the time when the specified peak appears. Set as end of range.

  The “control / signal processing unit 30” according to the present embodiment is an example of the “distance acquisition unit” according to the present invention.

<Fifth embodiment>
A fifth embodiment according to the foreign matter detection apparatus and foreign matter detection method of the present invention will be described. The fifth embodiment is the same as the first embodiment described above except that the method for acquiring the terahertz wave time waveform is partially different. Therefore, in the fifth embodiment, description overlapping with that in the first embodiment is omitted, and only fundamentally different points will be described.

  In the first to fourth embodiments described above, after the time waveform of the reflected light is acquired by the lock-in detection unit 305 (see FIG. 2), the trimming unit 301 acquires a predetermined trimming range from the acquired time waveform. The time waveform is cut out.

  In the fifth embodiment, the control / signal processing unit 30 acquires a reception signal output from the terahertz wave receiving unit 108 (see FIG. 2) of the terahertz wave transmitting / receiving unit 10 only in a preset trimming range (that is, sampling). )

  Specifically, in the pump-probe method used in the foreign object detection apparatus 1, the optical delay amount imparted to the probe light by the optical delay unit 112 (see FIG. 2) and the time waveform of the reflected light are represented on the time axis. The time plotted above is closely related. Therefore, the control / signal processing unit 30 acquires the reception signal output from the terahertz wave receiving unit 108 only when the optical delay amount applied to the probe light by the optical delay unit 112 falls within the set trimming range. To do.

  Note that the trimming range setting method is not limited to the method described in the first embodiment, and any of the methods in the second to fourth embodiments can be applied.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification. And methods are also within the scope of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Foreign object detection apparatus, 10 ... Terahertz wave transmission / reception part, 11 ... Laser oscillation part, 12 ... Scanning mechanism, 20 ... Reflection part, 30 ... Control and signal processing part

Claims (8)

Irradiation means for irradiating the target with terahertz waves;
Reflecting means for reflecting terahertz waves transmitted through the object;
Receiving means for receiving terahertz waves reflected by the object and the reflecting means;
A specifying means for specifying, as a detection target signal, a time waveform related to the terahertz wave reflected by the reflecting means from the output of the receiving means;
Detection means for detecting foreign matter contained in the object based on the specified detection target signal;
With
The focus of the terahertz wave irradiated by the irradiation unit is set to the reflection unit.   The specifying unit obtains in advance a time waveform related to the terahertz wave from the output of the receiving unit when a terahertz wave is irradiated to an object that does not contain a foreign object, and the pre-obtained from the output of the receiving unit this time The foreign object detection device according to claim 1, wherein a time waveform related to the terahertz wave reflected by the reflecting means is specified as the detection target signal based on the time waveform that has been generated.   The specifying unit specifies a period in which a time waveform related to the terahertz wave reflected by the reflecting unit appears based on the time waveform acquired in advance, and is determined from the current output of the receiving unit. The foreign object detection device according to claim 2, wherein a time waveform that appears within a predetermined period including a period is specified as the detection target signal. A distance acquisition means for acquiring a distance between the object and the reflection means;
The foreign object detection device according to claim 3, wherein the specifying unit changes at least one of a start period and an end period of the predetermined period based on the acquired distance. A relative position changing unit that relatively changes a positional relationship between the irradiating unit, the receiving unit, and the reflecting unit in a direction along a reflecting surface of the reflecting unit;
The specifying means includes a time waveform related to the terahertz wave reflected by the reflecting means when the total distance between the distance between the irradiating means and the reflecting means and the distance between the receiving means and the reflecting means is maximum. And changing at least one of the start period and the end period of the predetermined period so as to be able to identify the time waveform related to the terahertz wave reflected by the reflecting means when the total distance is minimum. The foreign matter detection means according to claim 3. Further comprising thickness information acquisition means for acquiring thickness information of the object;
Based on the acquired thickness information, the specifying means transmits a time waveform related to the terahertz wave reflected by the reflecting means after passing through a portion having the maximum thickness among the objects, and the thickness among the objects. The at least one of the start period and the end period of the predetermined period is changed so that the time waveform related to the terahertz wave reflected by the reflection means after passing through the minimum portion can be specified. The foreign matter detection means according to 3.   When the terahertz wave that has passed through an object that does not include foreign matter and is reflected by the reflecting means is received by the receiving means, the detecting means is based on the amplitude of the detection target signal specified by the specifying means, 7. The method according to claim 1, further comprising: determining that a foreign object is included in the current object on the condition that an amplitude of the detection target signal currently specified by the specifying unit is equal to or less than a predetermined ratio. The foreign object detection device according to item. Irradiation means for irradiating the target with terahertz waves; reflection means for reflecting terahertz waves transmitted through the object; and receiving means for receiving terahertz waves reflected by the object and the reflection means; A foreign matter detection method in a foreign matter detection device comprising:
From the output of the received signal, a specifying step for specifying a time waveform related to the terahertz wave reflected by the reflecting means as a detection target signal;
A detection step of detecting a foreign substance contained in the object based on the identified detection target signal;
With
The focus of the terahertz wave irradiated by the irradiation unit is set to the reflection unit.

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