JP2021012214A - Foreign matter detection device and method - Google Patents

Abstract

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 matter detecting device and method for detecting a foreign matter contained in an object by using a terahertz wave.

In recent years, research and development of terahertz wave imaging has become active, and there are high expectations for its application to, for example, non-destructive inspection. As an example of non-destructive inspection, it is obtained by placing an object in a container consisting of a first part that transmits terahertz waves and a second part that reflects terahertz waves, and analyzing the reflected waves of the terahertz waves from the container. A technique for inspecting whether or not a foreign substance is contained in an object from a tomographic image or the like has been proposed (see Patent Document 1).

JP-A-2014-2024

In the measurement method using the terahertz wave reflected by the object as in the technique described in Patent Document 1, when the object contains a foreign substance, the terahertz wave detected by the foreign substance becomes weak. It ends up. Therefore, there is a technical problem that the detection accuracy of the foreign matter inspection is lowered. Even when a container that reflects terahertz waves is used as in the technique described in Patent Document 1, if the focal point of the irradiated terahertz waves is not appropriate, the reflected terahertz waves are efficiently detected. Is difficult. Therefore, even if a container that reflects terahertz waves is used, it is difficult to improve the detection accuracy of foreign matter inspection.

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

In order to solve the above problems, the foreign matter detecting device of the present invention has an irradiation means for irradiating a terahertz wave toward an object, a reflecting means for reflecting the terahertz wave transmitted through the object, the object and the object. The receiving means for receiving the terahertz wave reflected by the reflecting means and the specific means for specifying the time waveform related to the terahertz wave reflected by the reflecting means as a detection target signal from the output of the received signal are specified. A detection means for detecting a foreign substance contained in the object is provided based on the detection target signal, and the focus of the terahertz wave irradiated by the irradiation means is set on the reflection means.

In order to solve the above problems, the foreign matter detecting method of the present invention comprises an irradiation means for irradiating a terahertz wave toward an object, a reflecting means for reflecting the terahertz wave transmitted through the object, the object and the object. A method for detecting a foreign matter in a foreign matter detecting device including a receiving means for receiving the terahertz wave reflected by the reflecting means, wherein a time waveform related to the terahertz wave reflected by the reflecting means is obtained from the output of the received signal. The focus of the terahertz wave irradiated by the irradiation means is provided with a specific step of specifying as a detection target signal and a detection step of detecting a foreign substance contained in the object based on the specified detection target signal. Is set in the reflection means.

The actions and other gains of the present invention will be apparent from the embodiments described below.

It is a figure which shows the main part of the foreign matter detection apparatus which concerns on 1st Example. It is a schematic block diagram which shows the structure of the foreign matter detection apparatus which concerns on 1st Example. This is an example of the time waveform of the 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 matter detection processing 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 / 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 the reflection part which concerns 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 the reflection part which concerns 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 the reflection part which concerns on 4th Example. It is a conceptual diagram which shows the concept of the trimming range which concerns on 4th Example.

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

The foreign matter detecting device according to the embodiment is configured to include an irradiation means, a reflection means, a receiving means, a specific means, and a detection means.

The irradiation means irradiates the object 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 by using a member having a relatively high reflectance for 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 research of the inventor of the present application, the following matters have been found. That is, when the object is irradiated with a terahertz wave and the reflected wave from the foreign matter contained in the object is detected, the reflected wave from the foreign matter is weak and the SN ratio is lowered depending on the reflectance of the foreign matter. Therefore, the accuracy of foreign matter detection may decrease.

Therefore, in the present embodiment, 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 by the specifying means. Here, in particular, in the present embodiment, the focal point of the irradiated terahertz wave is set to the reflecting means. Therefore, the signal intensity (that is, the amplitude) of the time waveform related to the terahertz wave reflected by the reflecting means becomes relatively high.

The detecting means detects a foreign substance contained in the object based on the detection target signal specified by the specific means. Here, when a foreign substance is contained in the object, a part of the terahertz wave is reflected by the foreign substance, so that the signal intensity of the time waveform related to the terahertz wave reflected by the reflecting means is lowered. 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, for example, whether or not the target object contains a foreign substance depending on the strength of the signal strength. it can.

As a result of the above, according to the foreign matter detecting device according to the embodiment, the foreign matter contained in the object can be efficiently detected by using the terahertz wave.

In one aspect of the foreign matter detecting device according to the embodiment, the specific means first acquires a time waveform related to the terahertz wave in advance from the output of the receiving means when the object containing no foreign matter is irradiated with the terahertz wave. Here, the time waveform related to the terahertz acquired in advance includes the time waveform related to the terahertz wave reflected by the object and the time waveform related to the terahertz wave reflected by the reflecting means.

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

From the output of the receiving means, for example, a time signal relating to a terahertz wave reflected by an object, particularly a terahertz wave reflected by a foreign substance can also be obtained. When a terahertz wave is applied to an object containing no foreign matter, the time waveform related to the terahertz wave reflected by the reflecting means appears prominently 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 object containing no foreign matter is irradiated with the terahertz wave is acquired in advance, the time waveform related to the terahertz wave reflected by the reflecting means, such as the appearance timing and the waveform, can be obtained. Can be identified. Therefore, the time waveform related to the terahertz wave reflected by the reflecting means from the output of the receiving means this time can be specified as the detection target signal.

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

With this configuration, the time waveform related to the terahertz wave reflected by the reflecting means can be relatively easily specified as the detection target signal.

The period during which the time waveform related to the terahertz wave reflected by the reflecting means appears varies slightly depending on, for example, the thickness of the object. Therefore, in the "predetermined period", even if the appearance timing of the time waveform related to the terahertz wave reflected by the reflecting means is slightly deviated, the margin in which the time waveform can be detected is set to, for example, before and after the specified period. It may be set by having it.

In the embodiment in which the time waveform appearing within the predetermined period is specified as the detection target signal, the foreign matter detection device further includes a distance acquisition means for acquiring the distance between the object and the reflection means, and the specific means is At least one of the start and end of a predetermined period may be changed based on the distance acquired by the distance acquisition means.

The "distance between the object and the reflecting means" may be specified by some sensor such as a distance sensor and may be acquired by acquiring an output signal from the sensor, or the foreign matter detecting device of the foreign matter detecting device. It may be acquired by inputting by the user.

Alternatively, in the embodiment in which the time waveform appearing within the predetermined period is specified as the detection target signal, the foreign matter detecting device sets the positional relationship between the irradiating means and the receiving means and the reflecting means along the reflecting surface of the reflecting means. Further provided with a relative position changing means that changes relative to the direction, the specific means is reflected by the reflecting means when the total distance between the distance between the irradiation means and the reflecting means and the distance between the receiving means and the reflecting means is maximized. At least one of the start and end of a predetermined period can be specified 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 minimized can be specified. You may change it.

Alternatively, in the embodiment in which the waveform appearing within the predetermined period is specified as the detection target signal, the foreign matter detecting device further includes a thickness information acquisition means for acquiring the thickness information of the object, and the specific means has been acquired. Based on the thickness information, the time waveform related to the terahertz wave reflected by the reflecting means after passing through the thickest part of the object, and the time waveform related to the terahertz wave reflected by the reflecting means after passing through the thinnest part of the object. At least one of the start and end of a predetermined period may be changed so that the time waveform related to the terahertz wave and the time waveform can be identified.

In another aspect of the foreign matter detecting apparatus according to the embodiment, the detecting means is specified by the specific means when the terahertz wave transmitted through the object containing no foreign matter and reflected by the reflecting means is received by the receiving means. Based on the amplitude of the detection target signal, it is determined that the object this time contains a foreign substance on condition that the amplitude of the detection target signal identified this time by the specific means is equal to or less than a predetermined ratio.

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

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

The foreign matter detecting method according to the embodiment receives an irradiation means for irradiating a terahertz wave toward an object, a reflecting means for reflecting the terahertz wave transmitted through the object, and a terahertz wave reflected by the object and the reflecting means. It is a foreign matter detecting method in a foreign matter detecting apparatus provided with a receiving means.

The foreign matter detection method includes a specific step and a detection step. In the specific 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, foreign matter contained in the object is detected based on the identified detection target signal. Here, the focus of the terahertz wave irradiated by the irradiation means is set to the reflection means.

According to the foreign matter detecting method according to the embodiment, the foreign matter contained in the object can be efficiently detected by using the terahertz wave, similarly to the foreign matter detecting device according to the above-described embodiment. In the foreign matter detecting method according to the embodiment, various aspects similar to those of the foreign matter detecting device according to the above-described embodiment can be adopted.

Examples of the foreign matter detecting device and the foreign matter detecting method of the present invention will be described with reference to the drawings.

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

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

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

The terahertz wave transmission / reception unit 10 irradiates 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 reflection unit 20. Hereinafter, the "reflected terahertz wave" is appropriately referred to as "reflected light".

In this embodiment, in particular, the focus of the terahertz wave emitted from the terahertz wave transmission / reception unit 10 is set on the reflection unit 20. Further, the reflective portion 20 is made of a member having a relatively high reflectance, such as an aluminum plate.

When the sample 50 to be measured does not contain the foreign matter 51, the signal intensity (amplitude) caused by the reflected light from the reflecting unit 20 remarkably appears in the received signal caused by the reflected light received by the terahertz wave transmitting / receiving unit 10. .. On the other hand, when the sample 50 to be measured contains the foreign matter 51, the terahertz wave is reflected by the foreign matter 51, so that the terahertz wave reaching the reflecting portion 20 is reduced, which is caused by the reflected light from the reflecting portion 20. The signal strength is also reduced.

Therefore, when the signal intensity caused by the reflected light from the reflecting portion 20 is compared with the signal intensity caused by the reflected light from the reflecting portion 20 when the sample 50 to be measured does not contain the foreign matter 51, the presence or absence of the foreign matter 51 is compared. Can be detected.

By the way, the received signal includes, for example, a signal caused by the reflected light from the sample 50 to be measured, in addition to the signal caused by the reflected light from the reflecting unit 20. Therefore, if the signal caused by the reflected light from the reflecting unit 20 is not specified, foreign matter detection may not be performed correctly.

Therefore, in this embodiment, the trimming unit 301 cuts out the received signal corresponding to the period during which the signal waveform caused by the reflected light from the reflecting unit 20 appears among the received signals. The foreign matter detecting unit 302 determines whether or not the foreign matter 51 is contained in the sample to be measured 50 based on the intensity of the signal output from the trimming unit 301 (that is, the cut-out received signal).

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

The pulse width of the terahertz wave is on the order of subpicoseconds. Therefore, it is difficult to directly detect the time waveform of the terahertz wave. Therefore, the foreign matter detecting device 1 indirectly detects the time waveform of the terahertz wave by 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 ultrashort pulse laser light of subpicosecond order or less. The pulsed laser light emitted from the laser unit 111 during the operation of the foreign matter detecting device 1 is divided into pump light and probe light by the beam splitter 113.

The pump light is applied to the terahertz wave transmitting unit 101 of the terahertz transmitting / receiving 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. Since various known modes can be applied to the optical delay unit 112, a detailed description thereof will be omitted.

The terahertz transmission / reception unit 10 includes a terahertz wave transmission 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 reception unit 108.

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

A gap portion is formed in the central portion of the photoconducting antenna, and when a pump light is irradiated to the gap portion while a bias voltage is applied to the gap portion, carriers are generated in the semiconductor by photoexcitation. , Subpicosecond order 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 embodiment is a photoconductive antenna (PCA).

The terahertz wave generated by the terahertz wave generating element of the terahertz wave transmitting unit 101 is applied to the sample 50 to be measured via the silicon lens 102, the collimating lens 103, the beam splitter 104, and the objective lens 105. Here, in particular, the focus of the terahertz wave emitted from the terahertz wave transmitting unit 101 is set on the reflecting unit 20.

The reflected light from the sample to be measured 50 or the reflecting unit 20 enters the terahertz wave receiving unit 108 via 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 detection element is also a photoconductive antenna.

When probe light is incident on the terahertz wave detection element via the optical delay portion 112, 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 is generated at the moment when the carrier 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 received signal output from the terahertz wave receiving unit 108 is amplified by the signal amplification unit 303, and the lock-in detection unit 305 performs known lock-in detection. 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 outputs a bias voltage modulated based on the reference signal to the terahertz wave transmission unit 101. It is applied to the terahertz wave generating element.

As a result of the lock-in detection, the time waveforms of the reflected light from the sample 50 to be measured, the reflected light from the reflecting portion 20, and the reflected light from the foreign matter 51 when the foreign matter 51 is contained in the sample 50 to be measured. Is obtained.

The acquisition of the time waveform of the reflected light (that is, the terahertz wave) is executed together with the driving of the terahertz wave transmission / reception unit 10 by the scanning mechanism 12. The operation of the scanning mechanism 12 is controlled by the scanner driving unit 307. The scanner drive 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 in a plane 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. The scanning mechanism 12 may drive the reflecting unit 20 instead of the terahertz wave transmitting / receiving unit 10.

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

The terahertz wave generating element and the terahertz wave detecting element are not limited to the above-mentioned photoconductive antenna, and for example, a resonance tunnel diode (Resonant Tunneling Diode: RTD) or the like can be applied. When a resonance tunnel diode is used, it is not necessary to provide the laser oscillation unit 11, so that the foreign matter detection device can be miniaturized.

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

Prior to the detection of foreign matter in the sample 50 to be measured, a reference sample known in advance to be free of foreign matter is arranged between the terahertz wave transmission / reception unit 10 and the reflection unit 20. Next, the reference sample is irradiated with the terahertz wave from the terahertz wave transmission / reception unit 10, 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, for example, as shown in FIG. 3A, the time waveform related to the terahertz wave reflected by the reflecting unit 20 appears remarkably. This is because the reflecting unit 20 is composed of a member having a relatively high reflectance such as an aluminum plate, and the focus 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 reflecting unit 20 by adjusting the position of the objective lens 105 or the like so that the amplitude of the time waveform related to the terahertz wave reflected by the reflecting unit 20 is maximized. ..

The trimming unit 301 detects the peak of the time waveform of the acquired reflected light, and assumes that the detected peak is the 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 at which the detected peak appears as the trimming range. The trimming unit 301 stores the set trimming range.

It should be noted that the optimum value of how much time t1 is set before time t0 and how much time t2 is set after time t0 is obtained by, for example, an experiment or the like. The value may be stored in advance in the memory of the trimming unit 301 or the like, and when the time t0 is specified, the value may be determined with reference to the stored value.

The foreign matter detecting unit 302 stores the peak amplitude of the time waveform of the terahertz wave reflected by the reflecting unit 20 detected by the trimming unit 301 as a reference amplitude.

When the foreign matter of the sample to be measured 50 is detected, the sample to be measured 50 is arranged at the position where the reference sample is arranged. Here, in particular, in the present embodiment, since the focus of the terahertz wave emitted from the terahertz wave transmission / reception unit 10 is set on the reflection unit 20, the terahertz wave emitted every time the sample to be measured 50 is replaced. Since it is not necessary to adjust the focal position, it is possible to start detecting foreign matter in the sample 50 to be measured relatively quickly.

Next, the terahertz wave is irradiated from the terahertz wave transmission / reception unit 10 to the sample 50 to be measured, and the time waveform of the 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 the reflected light. The foreign matter detection unit 302 acquires the amplitude of the time waveform cut out by the trimming unit 301, compares the acquired amplitude with the reference amplitude, and determines whether or not the foreign matter 51 is contained in the sample 50 to be measured. judge.

Here, when the sample 50 to be measured contains the foreign matter 51, the time waveform of the reflected light acquired by the lock-in detection unit 305 is reflected by the foreign matter 51, for example, as shown in FIG. 3B. The peak of the time waveform related to the terahertz wave 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, it is necessary to perform a process of identifying the peak of the time waveform related to the terahertz wave reflected by the reflecting unit 20 from the time waveform of the reflected light acquired by the lock-in detection unit 305. Must be. Then, the process of identifying the peak must be performed for each scanning point, and the processing load related to the detection of foreign matter becomes relatively 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, so the above peak is specified. There is no need to carry out processing. Further, since the image processing unit 306 and the foreign matter detecting unit 302 need only process the time waveform cut out by the trimming unit 301, the amount of data to be processed can be reduced. As a result, according to the foreign matter detecting device 1 according to the present embodiment, the processing load related to the foreign matter detection can be reduced.

Further, when the terahertz wave is focused on the sample 50 to be measured instead of the reflection unit 20 and the time waveform of the reflected light is acquired, for example, as shown in FIG. 3C, the sample 50 to be measured contains the foreign matter 51. Even if it is, since the terahertz wave cannot be focused on the foreign matter 51, the signal strength of the time waveform related to the terahertz wave reflected by the foreign matter 51 is relatively weak. That is, the SN ratio of the time waveform is relatively low, and the reliability of foreign matter detection may decrease.

On the other hand, in this embodiment, as described above, the foreign matter detection unit 302 compares the amplitude of the time waveform cut out by the trimming unit 301 with the reference amplitude, so that the foreign matter 51 is included in the sample 50 to be measured. It is determined whether or not it is. The smaller the amplitude of the cut out time waveform, the larger the difference from the reference amplitude. That is, when the terahertz wave is reflected by the foreign matter 51, the amplitude of the time waveform related to the terahertz wave reflected by the reflecting unit 20 becomes relatively small, but the difference from the reference amplitude becomes large, and as a result, the foreign matter 51 becomes Whether or not it is included can be determined relatively easily. Further, 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 the error in obtaining the difference from the reference amplitude becomes small. Therefore, also in this case, it is relatively easy to determine whether or not the foreign matter 51 is contained.

Next, the foreign matter detection process executed by the foreign matter 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 transmission / reception unit 10 irradiates the reference sample with the terahertz wave (step S101). Subsequently, the terahertz wave transmission / reception unit 10 receives the terahertz wave reflected by the reference sample or the reflection unit 20 and outputs the received 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. From the acquired time waveform, the trimming unit 301 identifies the time when the peak of the time waveform related to the terahertz wave reflected by the reflection unit 20 appears (step S102).

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

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

The terahertz wave transmission / reception 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 a time waveform within the trimming range from the acquired time waveform of the reflected light. The foreign matter detecting unit 302 acquires the amplitude of the time waveform cut out by the trimming unit 301 (step S203).

The foreign matter detection unit 302 compares the acquired amplitude with the reference amplitude (step S204). Subsequently, the foreign matter detection unit 302 determines whether or not the ratio of the acquired amplitude to, for example, the reference amplitude 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 a predetermined value (step S205: Yes), the foreign matter detection unit 302 determines that the foreign matter 51 is contained in the sample 50 to be measured (step S206), and determines the determination result. 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 larger than the predetermined value (step S205: No), the foreign matter detecting unit 302 determines that the sample 50 to be measured does not contain the foreign matter 51 (step S207), and determines the determination result. Store (step S208).

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

The "predetermined value" according to this embodiment is a value for determining whether or not the sample 50 to be measured contains the foreign matter 51, and is set in advance as a fixed value or a variable value according to some physical quantity or parameter. Has been done. Such a predetermined value is set by the reflecting unit 20 experimentally, empirically, or by simulation when, for example, foreign matter of various materials and various thicknesses is contained in an object imitating the sample to be measured. It may be obtained based on the amplitude of the peak of the time waveform related to the reflected terahertz wave and the comparison result with the reference signal.

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

<Modification example of terahertz wave transmitter / receiver>
The terahertz wave transmitter / receiver 10 may have an optical system as shown in FIG. 6, for example. In FIG. 6, the terahertz wave generated by the terahertz wave transmitting unit 101 irradiates the sample 50 to be measured via the silicon lens 102, the collimating lens 103, and the objective lens 151. The reflected light from the sample to be measured 50 or the reflecting unit 20 enters the terahertz wave receiving unit 108 via the objective lens 152, the collimating lens 106, and the silicon lens 107. In the optical system shown in FIG. 6, the focus of the terahertz wave emitted from the terahertz wave transmitting unit 101 is set on the reflecting unit 20.

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

<Modification example 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 the bias signal generation unit 354 and the lock-in detection unit 305 (see FIG. 2) with a band limiting filter. A unit 355 is provided.

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

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

<Second Example>
A second embodiment according to the foreign matter detecting device and the foreign matter detecting method of the present invention will be described with reference to FIGS. 8 and 9. The second embodiment is the same as the first embodiment described above, except that the trimming range setting method is partially different. Therefore, with respect to the second embodiment, the description overlapping with the first embodiment is omitted, the common parts on the drawings are indicated by the same reference numerals, and FIGS. 8 and 9 are shown only for the fundamentally different points. It will be explained with reference to.

In the second embodiment, as shown in FIG. 8, the distance between the terahertz wave transmission / reception unit 10 of the foreign matter detection device 1 and the reflector 20 changes depending on the scanning position. Note that FIG. 8 exaggerates the inclination of the reflecting portion 20 so that it can be recognized that the reflecting portion 20 is tilted.

For example, when the distance between the terahertz wave transmitter / receiver 10 and the reflector 20 changes by 0.15 mm, the time for the terahertz wave reflected by the reflector 20 to reach the terahertz wave transmitter / receiver 10 is one picosecond earlier or later. Become.

Therefore, when the trimming range is set, if the trimming range is determined from the time waveform related to the terahertz wave reflected at one point on the reflecting unit 20, it is reflected by the terahertz wave transmitting / receiving unit 10 along with scanning. When the distance to the unit 20 changes, the reliability of the foreign matter detection result may decrease.

Therefore, in this 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 scanning start position and the scanning end position. The time waveform is acquired. The trimming unit 301 identifies the peak of the time waveform related to the terahertz wave reflected by the reflection unit 20 for each of the acquired plurality of time waveforms, and specifies the time when the peak appears.

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

When determining the earliest time and the latest time when the peak of the time waveform related to the terahertz wave reflected by the reflecting unit 20 appears, for example, a known mathematical means such as extrapolation method or interpolation method is used. May be good.

In the foreign matter detecting device 1 according to the present embodiment, since the trimming range is set as described above, it is possible to prevent the reliability of the foreign matter detecting result from being lowered.

The distance between the terahertz wave transmission / reception unit 10 of the foreign matter detection device 1 and the reflection plate 20 changes depending on the scanning position, so that the focal position of the terahertz wave deviates from the reflection unit 20 to detect foreign matter. In order to prevent the accuracy from being lowered, 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, at at least two points such as the scanning start position and the scanning end position, the position of the objective lens 105 that maximizes the amplitude of the time waveform related to the terahertz wave reflected on the reflecting unit 20 is investigated, and this is determined. Remember. Next, the position of the objective lens 105 at an intermediate position between these points is calculated based on the positions of the objective lens 105 at at least two points. Then, based on the calculation result, the position of the objective lens 105 may be changed according to the scanning position of the terahertz wave transmission / reception unit 10.

By such a method, it is possible to prevent the reliability of the foreign matter detection result from being lowered due to the distance between the terahertz wave transmission / reception unit 10 of the foreign matter detection device 1 and the reflector 20 changing depending on the scanning position.

<Third Example>
A third embodiment according to the foreign matter detecting device and the foreign matter detecting method of the present invention will be described with reference to FIGS. 10 and 11. The third embodiment is the same as the first embodiment described above, except that the trimming range setting method is partially different. Therefore, with respect to the third embodiment, the description overlapping with the first embodiment is omitted, the common parts on the drawings are indicated by the same reference numerals, and FIGS. 10 and 11 are shown only for the fundamentally different points. It will be explained with reference to.

In the third embodiment, as shown in FIG. 9, the thickness of the sample to be measured 50 changes depending on the scanning position. Note that FIG. 10 exaggerates the change in thickness so that it can be recognized that the thickness of the sample 50 to be measured has changed.

The refractive index of the air layer and the sample to be measured are different from each other. When the thickness of the sample to be measured 50 changes, the distance of the air layer to which the terahertz wave irradiated from the terahertz wave transmission / reception unit 10 propagates and the distance of the sample to be measured change. As a result, the time when the terahertz wave reflected by the reflecting unit 20 reaches the terahertz wave transmitting / receiving unit 10 fluctuates.

Therefore, 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 reflecting unit 20, the reliability of the foreign matter detection result may decrease. There is sex.

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

The trimming unit 301 obtains the 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 the time when 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 of the set trimming range forward by the obtained change amount (corresponding to the time t9 in FIG. 11), and adjusts the end of the set trimming range to the obtained change. It is corrected after 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 reflected by the reflecting portion 20 appears through the thinnest portion p2 (see FIG. 10) of the sample 50 to be measured is also measured. The time t8 (see FIG. 11) at which the peak of the time waveform related to the terahertz wave reflected by the reflecting portion 20 appears through the thickest portion p3 (see FIG. 10) of the sample 50 is also included in the corrected trimming range. Will be.

In the foreign matter detecting device 1 according to the present embodiment, since the trimming range is set as described above, it is possible to prevent the reliability of the foreign matter detecting result from being lowered.

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

<Fourth Example>
A fourth embodiment according to the foreign matter detecting device and the foreign matter detecting method of the present invention will be described with reference to FIGS. 12 and 13. The fourth embodiment is the same as the first embodiment described above, except that the trimming range setting method is partially different. Therefore, with respect to the fourth embodiment, the description overlapping with the first embodiment is omitted, the common parts on the drawings are indicated by the same reference numerals, and FIGS. 12 and 13 are shown only for the fundamentally different points. It will be explained with reference to.

In the fourth embodiment, the sample 50 to be measured is an object whose thickness can be arbitrarily changed, such as a powder material. The sample 50 to be measured is sandwiched between, for example, a belt or the like so that the thickness is constant. Foreign matter detection of the sample to be measured 50 is executed by, for example, moving the sample to be measured 50 from the left to the right in the drawing.

In this embodiment, as shown in FIG. 12, since the sample 50 to be measured and the reflecting portion 20 are arranged at intervals, the time t12 at which the peak of the time waveform related to the terahertz wave reflected at the position h1 appears. The interval between (see FIG. 13) and the 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 sample to be measured 50 and the reflection 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 inputting by the user of the foreign matter 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 (time in FIG. 13). (Corresponding to t13) is specified.

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

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

<Fifth Example>
A fifth embodiment according to the foreign matter detecting device and the foreign matter detecting method of the present invention will be described. The fifth embodiment is the same as the first embodiment described above, except that the acquisition method of the time waveform of the terahertz wave is partially different. Therefore, the description of the fifth embodiment that overlaps with that of the first embodiment will be omitted, and only the points that are basically different 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), a predetermined trimming range is obtained from the acquired time waveform by the trimming unit 301. The time waveform of is cut out.

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

Specifically, in the pump-probe method used in the foreign matter detection device 1, the time axis is the amount of optical delay applied to the probe light by the optical delay unit 112 (see FIG. 2) and the time waveform of the reflected light. It is closely related to the time when plotted above. Therefore, the control / signal processing unit 30 acquires the received signal output from the terahertz wave receiving unit 108 only when the amount of optical delay applied to the probe light by the optical delay unit 112 corresponds to the set trimming range. To do.

The method for setting the trimming range is not limited to the method described in the first embodiment, and any method from the second embodiment to the fourth embodiment can be applied.

The present invention is not limited to the above-described embodiment, and can be appropriately modified within the scope of claims and within a range not contrary to the gist or idea of the invention that can be read from the entire specification, and a foreign matter detection device accompanied by such a modification. And methods are also within the technical scope of the invention.

1 ... Foreign matter detection device, 10 ... Terahertz wave transmitter / receiver, 11 ... Laser oscillator, 12 ... Scanning mechanism, 20 ... Reflector, 30 ... Control / signal processing unit

Claims (8)

Irradiation means that irradiates the terahertz wave toward the object,
A reflective means that reflects terahertz waves that have passed through the object,
A receiving means for receiving the terahertz wave reflected by the object and the reflecting means, and
A specific means for specifying the time waveform related to the terahertz wave reflected by the reflection means as a detection target signal from the output of the receiving means, and
A detection means for detecting a foreign substance contained in the object based on the identified detection target signal, and
With
A foreign matter detection device characterized in that the focus of the terahertz wave irradiated by the irradiation means is set on the reflection means. The specific means acquires in advance a time waveform related to the terahertz wave from the output of the receiving means when the object containing no foreign matter is irradiated with the terahertz wave, and obtains the time waveform in advance from the output of the receiving means this time. The foreign matter detection device according to claim 1, wherein the time waveform related to the terahertz wave reflected by the reflection means is specified as the detection target signal based on the time waveform. Based on the time waveform acquired in advance, the specific means specifies a period in which the time waveform related to the terahertz wave reflected by the reflection means appears, and is specified from the output of the receiving means this time. The foreign matter 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. Further provided with a distance acquisition means for acquiring the distance between the object and the reflection means.
The foreign matter detection device according to claim 3, wherein the specific means changes at least one of the start and end of the predetermined period based on the acquired distance. Further, a relative position changing means for changing the positional relationship between the irradiation means, the receiving means, and the reflecting means relative to the direction along the reflecting surface of the reflecting means is provided.
The specific means includes a time waveform related to a terahertz wave reflected by the reflection means when the total distance between the irradiation means and the reflection means and the distance between the reception means and the reflection means is maximized. It is characterized in that at least one of the start and end of the predetermined period is changed so that the time waveform related to the terahertz wave reflected by the reflection means when the total distance is minimized can be specified. The foreign matter detecting means according to claim 3. Further provided with a thickness information acquisition means for acquiring the thickness information of the object,
Based on the acquired thickness information, the specific means has a time waveform related to a terahertz wave reflected by the reflecting means after passing through a portion of the object having the maximum thickness, and a thickness of the object. The claim is characterized in that at least one of the start and end 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 detecting means according to 3. When the terahertz wave transmitted by the object containing no foreign matter and reflected by the reflecting means is received by the receiving means, the detecting means uses the amplitude of the detection target signal specified by the specific means as a reference. Any one of claims 1 to 6, wherein it is determined that the object of this time contains a foreign substance on condition that the amplitude of the signal to be detected that is identified this time by the specific means is equal to or less than a predetermined ratio. The foreign matter detection device described in the section. An irradiation means for irradiating a terahertz wave toward an object, a reflecting means for reflecting the terahertz wave transmitted through the object, and a receiving means for receiving the terahertz wave reflected by the object and the reflecting means. It is a foreign matter detection method in the foreign matter detection device provided.
A specific step of specifying the time waveform related to the terahertz wave reflected by the reflecting means from the output of the received signal as a detection target signal, and
A detection step of detecting a foreign substance contained in the object based on the identified detection target signal, and
With
A method for detecting a foreign substance, wherein the focus of the terahertz wave irradiated by the irradiation means is set on the reflection means.

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