Photoacoustic measurement apparatus and photoacoustic measurement method

Abstract

To provide a photoacoustic measurement apparatus that performs highly accurate measurement in accordance with an external environment.SOLUTION: A photoacoustic measurement apparatus includes a first acoustic cell that measures external noise sound, a second acoustic cell that measures a reference sample by irradiation with light of a first frequency, a third acoustic cell that measures an observation sample by irradiation with light of a second frequency, and a processor that analyzes acoustic wave data. The processor performs frequency analysis on the external noise sound, sets a frequency having a low noise sound level as the first frequency, causes the second acoustic cell to measure the reference sample at the first frequency, analyzes signal fluctuation and noise level fluctuation of the reference sample to calculate a component determination threshold for the observation sample, outputs a result of determining a component of the observation sample using the component determination threshold, causes the third acoustic cell to measure the observation sample using the second frequency in parallel with measurement of the reference sample, and changes the frequency from the second frequency to the first frequency and causes the third acoustic cell to measure the observation sample when a noise sound level at the second frequency is high.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a configuration of a photoacoustic measurement device and a method thereof, and in particular to a technique that is effective when applied to measurements in an environment where external noise is generated. [Background technology]

[0002] In recent years, there has been an increasing need for non-destructive testing of organic materials such as plastics in the recycling process. When impurities are mixed into plastics or when components have changed over time, this can lead to a deterioration in the quality of the resulting recycled product, so it is necessary to quickly analyze the components in plastics. Photoacoustic spectroscopy, which can be used to measure organic materials regardless of their state (solid, liquid, gas, or powder), is an effective method for non-destructive testing.

[0003] The principle of a physical property measurement device using photoacoustic spectroscopy is as follows: When a light source irradiates a measurement object with periodic intermittent light, the measurement object absorbs the light, generating heat, which is converted into kinetic energy that causes the surface to repeatedly expand and contract locally. As a result, sound waves (i.e., photoacoustic waves) are generated by the pressure in the space, which are detected by a microphone. Essentially, sound waves corresponding to the frequency of the intermittent light irradiated from the light source are measured, and by performing signal processing (physical property analysis) on these detection results, it is possible to evaluate substances and impurities.

[0004] However, manufacturing sites such as recycling plants are subject to a variety of external environmental sounds, and the photoacoustic waves generated by the photoacoustic effect are very weak. Therefore, in order to perform highly sensitive and accurate nondestructive testing, it is necessary to construct a measurement system that minimizes the influence of external noise as much as possible.

[0005] Background art in this technical field includes, for example, technology such as that described in Patent Document 1. Patent Document 1 discloses a technology that uses two photoacoustic cells, places a target gas for odor measurement in one cell and odorless ambient air in the other cell, measures external environmental noise, and performs noise cancellation by subtracting the latter measurement value from the former measurement value, thereby reducing ambient environmental noise. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-179332 Summary of the Invention [Problem to be solved by the invention]

[0007] In photoacoustic spectroscopy, it is preferable to perform frequency analysis of external noise and shift the frequency of the intermittent light irradiated onto the photoacoustic cell, i.e., the frequency to be measured of the photoacoustic wave, from a frequency at which the external noise is strong. If strong external noise is superimposed on the frequency to be measured and cannot be completely removed by noise canceling, a large error will occur in the measurement results, resulting in a problem of poor accuracy of the test results.

[0008] Furthermore, because ambient external noise is usually not constant but changes over time, it is effective to monitor the external noise and check whether strong noise is occurring at the same frequency as the intermittent light used in the photoacoustic cell. However, if the external noise becomes large during measurement and the frequency used for measurement is changed to another frequency where the intensity of the noise is relatively low, the sensitivity of the measurement before the change will change, making it necessary to recalibrate the sensitivity and reset the threshold for test judgment, which creates the problem that the unknown sample to be measured cannot be tested during this process.

[0009] When noise cancellation is performed using two cells using the technology of Patent Document 1, it may be difficult to completely cancel external noise due to differences in the two microphones that measure the photoacoustic waves of each cell, or because the positions of the two microphones are not exactly the same relative to the location where the noise is generated, and there is room for improvement.

[0010] Therefore, an object of the present invention is to provide a photoacoustic measurement device and a photoacoustic measurement method that are less susceptible to the influence of external noise and can continuously perform highly accurate measurements in accordance with a changing external environment. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, the present invention provides an acoustic wave measuring device comprising a first acoustic cell that measures external noise sound, a second acoustic cell that measures a reference sample by irradiating the reference sample with light of a first frequency modulated by a first frequency modulator, a third acoustic cell that measures an observation sample by irradiating the reference sample with light of a second frequency modulated by a second frequency modulator, and a processor that analyzes acoustic wave data measured by the first acoustic cell, the second acoustic cell, and the third acoustic cell, wherein the processor performs a frequency analysis of the external noise sound, defines a frequency with a low noise sound level from the result of the frequency analysis as the first frequency, and converts the first frequency by the first frequency modulator. the first frequency is modulated by the second frequency modulator, the reference sample is measured by the second acoustic cell, the reference sample is measured by the second acoustic cell, signal fluctuations and noise level fluctuations of the reference sample are analyzed to calculate a component determination threshold for the observation sample, a result of determining the components of the observation sample using the component determination threshold is output, the signal is modulated by the second frequency modulator using the second frequency different from the first frequency, the observation sample is measured by the third acoustic cell in parallel with the measurement of the reference sample, and if the noise sound level of the second frequency is high as a result of the frequency analysis, the frequency is changed from the second frequency to the first frequency and the observation sample is measured by the third acoustic cell.

[0012] The present invention also provides a method for measuring an external noise sound by using a first acoustic cell, a second acoustic cell different from the first acoustic cell, and a processor for analyzing acoustic wave data measured by the first acoustic cell and the second acoustic cell. The method measures an observation sample using the second acoustic cell at a second frequency, and the processor performs a frequency analysis of the external noise sound measured by the first acoustic cell, and sets a frequency with a low noise sound level as a first frequency from the results of the frequency analysis. If the noise sound level of the second frequency is high from the results of the frequency analysis, the frequency is changed from the second frequency to the first frequency and the observation sample is measured using the second acoustic cell.

[0013] The present invention is also characterized by including the steps of: (a) performing a frequency analysis of external noise; (b) defining a frequency with a low noise level from the results of the frequency analysis in step (a) as a first frequency, modulating the first frequency with a first frequency modulator, measuring a reference sample with a second acoustic cell, analyzing signal fluctuations and noise level fluctuations of the reference sample, calculating a component determination threshold for the observation sample, and outputting a result of determining the components of the observation sample using the component determination threshold; (c) modulating the second frequency with a second frequency modulator that is different from the first frequency, and measuring the observation sample with a third acoustic cell in parallel with the measurement of the reference sample; and (d) if the noise level of the second frequency from the results of the frequency analysis in step (a) is high, changing from the second frequency to the first frequency and measuring the observation sample with the third acoustic cell. [Effects of the Invention]

[0014] According to the present invention, it is possible to realize a photoacoustic measurement device and a photoacoustic measurement method that are less susceptible to the influence of external noise and that can continuously perform highly accurate measurements in accordance with a changing external environment.

[0015] This enables highly accurate non-destructive testing using the photoacoustic effect.

[0016] Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing a schematic configuration of an inspection device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing details of a photoacoustic cell. [Figure 3] FIG. 10 is a diagram showing an example of measuring external noise with the first photoacoustic cell. [Figure 4] FIG. 10 is a diagram showing an example in which a reference sample is measured using a second photoacoustic cell. [Figure 5] FIG. 10 is a diagram showing an example in which an observation sample is measured using a third photoacoustic cell. [Figure 6] FIG. 10 is a diagram showing an example in which a reference sample is measured using a second photoacoustic cell. [Figure 7] 1 is a flowchart showing a photoacoustic measurement method according to Example 1 of the present invention. [Figure 8] FIG. 10 is a diagram showing the relationship between the frequency of irradiated light in photoacoustic measurement and fluctuations in sensitivity and reference sample measurement peaks. [Figure 9] FIG. 10 is a diagram showing a schematic configuration of an inspection device according to a third embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing a schematic configuration of an inspection device according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same components are designated by the same reference numerals, and detailed description of overlapping parts will be omitted.

[0019] The inspection device of this embodiment measures external noise using a photoacoustic cell (hereinafter simply referred to as an "acoustic cell" or "cell") that does not contain a sample, places a sample that will serve as a reference for inspection, such as a known sample that does not contain impurities, in the reference sample measurement cell to measure the photoacoustic waves, and places the observation sample to be inspected in the unknown sample measurement cell to perform measurements.

[0020] In the cell that measures external noise, it is checked whether the intensity of external noise is increasing at the frequency used for the test. If the intensity of external noise increases, a candidate frequency for switching to another frequency, i.e., a frequency with a lower intensity of external noise, is selected and transmitted to the test device.

[0021] In the cell for measuring the reference sample, the sensitivity and noise level of the reference sample are measured using the frequency used for the test, and a decision threshold value to be used for analyzing the measurement results of the unknown sample measurement cell is determined and transmitted to the test device. Furthermore, the sensitivity and noise level of the reference sample are measured using another candidate frequency for switching obtained from the external noise sound measurement.

[0022] In the unknown sample measurement cell, the photoacoustic waves originating from the observation sample are measured, and the necessary inspection results are analyzed using the decision threshold received from the inspection device. [Example]

[0023] First Embodiment A photoacoustic measurement device and a photoacoustic measurement method according to a first embodiment of the present invention will be described with reference to FIGS.

[0024] FIG. 1 is a diagram showing a schematic configuration of an inspection device 1 of this embodiment.

[0025] As shown in FIG. 1, the inspection device 1 of this embodiment mainly comprises a computer 10 and a plurality of acoustic cells 20, 21, and 22 (three in FIG. 1).

[0026] Acoustic cell 20 is an acoustic cell for measuring external noise and corresponds to the "first acoustic cell." Acoustic cell 21 is an acoustic cell for measuring a reference sample and corresponds to the "second acoustic cell." Acoustic cell 22 is an acoustic cell for measuring an observation sample that the user wishes to inspect and corresponds to the "third acoustic cell." Microphones 23, 24, and 25, which measure sounds generated within acoustic cells 20, 21, and 22, are electrically connected to computer 10 via wires or wirelessly.

[0027] Acoustic cells 21 and 22 are provided with light sources 26 and 27 for irradiating light onto the samples inside, and optical path choppers or optical path shutters 28 and 29 for generating chopped light, and are connected to frequency modulators 30 and 31 for controlling the chopped light frequency. These frequency modulators 30 and 31 receive a frequency setting value from computer 10 and control the optical path choppers or optical path shutters 28 and 29 so as to irradiate chopped light of that frequency.

[0028] The computer 10 includes a processor 11 and a memory 12. The computer 10 may further include a communication circuit, an input / output circuit, a user interface device, and the like, all of which are not shown.

[0029] The memory 12 is a storage device including a main storage device and an auxiliary storage device. Any type of storage element can be used for the memory 12. The memory 12 is provided with a database 112 that has the function of storing data collected by the data collection unit 110.

[0030] The processor 11 is a circuit that performs arithmetic processing. The processor 11 is, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a combination of these. The processor 11 is not limited to a CPU or a GPU, and other semiconductor devices may be used as long as they are capable of executing predetermined processing.

[0031] The processor 11 is provided with a data collection unit 110, an FFT (Fast Fourier Transform) analysis unit 111, an analysis unit 113, a frequency change determination unit 114, a sample determination unit 115, and a GUI unit (user interface unit) 116. In other words, the processor 11 executes a predetermined computer program stored in the memory 12 to realize a process of collecting data (110), a process of performing FFT analysis of the data (111), a process of analyzing the data (113), a process of determining the sample from the analysis results (115), and a process of inputting and outputting data to and from a user interface device (116).

[0032] The data collection unit 110 has the function of collecting acoustic cell output values ​​(hereinafter simply referred to as "output values" or "measured values") from the acoustic cells 20, 21, and 22. The FFT analysis unit 111 has the function of performing frequency analysis on the output values ​​obtained from the acoustic cell 20. Note that the method used by the FFT analysis unit 111 to perform frequency analysis on the obtained acoustic data is not limited to FFT, and other methods such as sweeping the lock-in frequency of the board circuit may also be used. The data collection unit 110 also measures data such as the relationship between frequency and signal strength obtained so far by the acoustic cells 21 and 22, noise levels, and fluctuations in signal strength in reference sample measurements, and stores this data in the database 112. In other words, the database 112 stores the data obtained from the data collection unit 110 and the FFT analysis unit 111 as a database.

[0033] The analysis unit 113 analyzes the measurement results of the acoustic cell 21 and the acoustic cell 22 obtained by the data collection unit 110, obtains the relationship between the intermittent light frequency and the photoacoustic wave signal, acquires the noise level, and analyzes the signal intensity derived from the sample. The analysis unit 113 also sets the threshold value required by the sample determination unit 115. The frequency change determination unit 114 determines whether to change the intermittent light frequency based on the results of the FFT analysis unit 111 and the analysis unit 113, and selects a new frequency when changing.

[0034] The sample determination unit 115 performs a determination useful to the user based on the measurement results of the unknown sample from the analysis results obtained by the analysis unit 113. For example, when testing for the presence or absence of impurities, the sample determination unit 115 calculates the impurity concentration and ranks the samples.

[0035] The GUI unit (user interface unit) 116 includes an information providing device that provides information to the user and an information input device into which information is input by the user (neither is shown). The information providing device is, for example, a monitor display, a printer, a voice synthesizer, a lamp, etc. The information input device is, for example, a keyboard switch, a touch panel, a voice instruction device, etc.

[0036] FIG. 2 is a diagram showing the photoacoustic cell in detail.

[0037] The acoustic cells 20, 21, and 22 will be described with reference to Fig. 2. The acoustic cells 20, 21, and 22 are basically acoustic cells of the same dimensions and structure. As an example, the acoustic cell 22 will be described.

[0038] The acoustic cell consists of a space with a diameter of about several millimeters and a height of about several millimeters, and is provided at one end with a glass window 40 to allow light to pass into the cell. After a measurement sample 41, such as a piece of plastic, is placed in the cell, the cell space is sealed with a presser plate 42, such as a metal plate. The part 43 where light is irradiated is preferably made of a material such as metal that does not generate photoacoustic waves. When intermittent light is irradiated onto the measurement sample 41 through the glass window 40, photoacoustic waves are generated within the cell according to the sample components.

[0039] The frequency of the intermittent light will be described later, but as for the wavelength, light in the mid-far infrared region of about a few mm is usually used, and it is best to appropriately select a wavelength that provides high absorption of the measurement component and high sensitivity to the photoacoustic wave. In order to irradiate the sample with light of an appropriate wavelength, it is best to install an optical filter (not shown) downstream of the light source or to use a light source that irradiates a specific wavelength. In this case, the wavelength of light used in acoustic cell 21 and acoustic cell 22 is basically the same. A microphone 25 for measuring sound waves is connected to the space in the acoustic cell.

[0040] The acoustic cell 20 is an acoustic cell (blank cell) that measures external noise. Therefore, nothing is placed in the cell space, and noise within the sealed space is measured by the microphone 23. The measured noise is collected by the data collection unit 110, and the sound intensity distribution for each frequency is analyzed by the FFT analysis unit 111. Note that a method other than FFT may be used to perform frequency analysis.

[0041] The acoustic cell 21 is an acoustic cell (reference sample measurement cell) that measures a reference sample. For example, when the inspection device 1 measures the presence or absence of impurities in plastic, the reference sample is a pure plastic piece that does not contain impurities.

[0042] FIG. 4 is a diagram showing an example in which a reference sample is measured with the acoustic cell 21 (second photoacoustic cell).

[0043] Intermittent light of frequency f1, generated by the light source 26, frequency modulator 30, and optical path chopper 28, is irradiated onto a reference sample in the acoustic cell 21, and the photoacoustic wave is measured. When the resulting photoacoustic wave is subjected to frequency analysis in the same manner as the noise measurement of the acoustic cell 20, an intensity distribution with a peak S at frequency f1 is obtained, as shown in Figure 4. Furthermore, at frequencies other than f1, the level of measurement noise can be ascertained. By performing this measurement multiple times, the variation in peak S and the average measurement noise level can be obtained.

[0044] In the acoustic cell 22, similar to the acoustic cell 21, light emitted from the light source 27 is chopped by the frequency modulator 31 and the optical path chopper 29 to form light of frequency f1, which is then irradiated onto the observation sample in the acoustic cell 22. Photoacoustic waves corresponding to the molecular structure and concentration of the observation sample are generated and detected by the microphone 25. The measured values ​​from the microphone 25 are collected by the data collection unit 110 and then analyzed by the analysis unit 113, and the presence or absence of impurities, for example, is determined by the sample determination unit 115.

[0045] At this time, it is preferable to change the threshold value for determining the presence or absence of impurities, for example, according to the variation in the peak S obtained by the analysis of the acoustic cell 21 described above and the change in the measurement noise level.

[0046] FIG. 5 is a diagram showing an example in which an observation sample is measured using the acoustic cell 22 (third photoacoustic cell).

[0047] In an environment where there is a variety of external noise sounds and these noises change over time, or where temperature, humidity, and other factors affect detection sensitivity, the sensitivity of the target component in the observation sample measured by the acoustic cell 22 changes, and the threshold is therefore changed in response to these changes, as shown in Figure 5. For example, if the measurement noise intensity measured by the acoustic cell 21 increases or if the sensitivity increases, the judgment threshold for the acoustic cell 22 is also increased. Furthermore, if the variance in the peak S of the measurement noise intensity measured by the acoustic cell 21 increases, the judgment threshold is changed depending on whether the false positive or false negative rate is given more importance. Of course, in an environment where the sensitivity and measurement noise do not fluctuate greatly, the judgment threshold may be fixed and used for judgment.

[0048] The above is the flow of normal measurement. Below, we will explain the flow of changing from the frequency f1 used for measurement to another frequency when the surrounding external noise becomes louder.

[0049] FIG. 3 is a diagram showing an example in which external noise is measured by the acoustic cell 20 (first photoacoustic cell).

[0050] As shown in Figure 3, a threshold is set in advance to determine whether to change the frequency of the intermittent light used in the measurement for the obtained noise sound intensity distribution for each frequency. If threshold 2 is exceeded, the frequency is changed, but threshold 1, which is lower than threshold 2, is set, and preparations are made to switch to another frequency when threshold 1 is exceeded.

[0051] When the above-described preparations are started, first, candidate frequencies with low noise intensity are selected from the results of frequency analysis of the noise sound from the acoustic cell 20. For example, in FIG. 3, f2 and f3, which have low noise levels, are selected as candidate frequencies for the initially used frequency f1. In the following, an example in which two candidate frequencies are selected is described, but a single candidate frequency or three or more candidate frequencies may also be selected.

[0052] Using the selected candidate frequencies, the reference sample is measured in the acoustic cell 21 using intermittent light at frequencies f2 and f3. The signal strength of a photoacoustic wave generally increases at lower frequencies, but because the experimental environment also influences this, actual measurements are taken in the acoustic cell 21, and the peak intensity S and measurement noise level are determined by the analysis unit 113. At this time, if measurements of the observation sample in the acoustic cell 22 continue at frequency f1, the investigation of this frequency change and measurements of the unknown sample can be performed in parallel, eliminating measurement time loss. However, since measurements at frequency f1, which was normally performed in the acoustic cell 21, can no longer be performed, it is best to continue using the value before the investigation began as the judgment threshold for the acoustic cell 22.

[0053] FIG. 6 is a diagram showing an example in which a reference sample is measured with the acoustic cell 21 (second photoacoustic cell).

[0054] As shown in Figure 6, the frequency to be selected is determined based on the measurement results of the two frequencies f2 and f3 mentioned above, i.e., the survey results. Methods for doing so include choosing the frequency with the lowest measurement noise, the highest peak intensity S, or the lowest temporal variation of the peak intensity S. Alternatively, several combinations can be used, for example, by taking the ratio of the magnitude of the peak intensity S to the magnitude of the measurement noise N, and selecting the frequency with the highest S / N ratio.

[0055] A new decision threshold is calculated for the selected frequency, for example, f2, to be used in the acoustic cell 22. The investigation for the frequency change is now complete, and the value of the changed frequency f2 is sent to the frequency modulator 31 of the acoustic cell 22 to change the frequency of the intermittent light to f2. The decision threshold is then changed to the changed threshold described above.

[0056] The above measurement sequence is shown in Fig. 7. Fig. 7 is a flowchart showing the photoacoustic measurement method of this embodiment.

[0057] When the computer 10 starts the process, first, in step S1, a sample is placed in the photoacoustic cell to complete preparation for measurement.

[0058] Next, in step S2, the unknown sample is measured at frequency f1. In parallel with this, external noise is measured in a blank cell, and a reference sample is measured in a reference sample measurement cell.

[0059] Next, in step S3, it is determined whether or not the external noise sound exceeds the specified threshold value 1. If it is determined that the external noise sound exceeds the specified threshold value 1 (Yes), the process proceeds to step S4. On the other hand, if it is determined that the external noise sound does not exceed the specified threshold value 1 (No), the process returns to step S2.

[0060] Next, in step S4, an investigation for frequency change is carried out in the reference sample measurement cell.

[0061] Next, in step S5, it is determined whether or not the signal strength exceeds the specified threshold value 2. If it is determined that the signal strength exceeds the specified threshold value 2 (Yes), the process proceeds to step S6. On the other hand, if it is determined that the signal strength does not exceed the specified threshold value 2 (No), the process returns to step S2.

[0062] Next, in step S6, the frequency for measuring the unknown sample is changed from f1 to f2, and the process returns to step S2.

[0063] Finally, in step S7, the diagnosis result (positive) of the sample in step S2 is displayed to the user, and the process ends.

[0064] By using such an apparatus configuration and procedure, the following effects are obtained.

[0065] (1) Highly accurate measurements and judgments can be made according to the changing external environment, and (2) since measurements of unknown observation samples can continue even during investigations for frequency changes, there is no impact on measurement throughput, i.e., no time loss.

[0066] Although the configuration in Figure 1 uses three acoustic cells, it is also possible to use multiple cells rather than one acoustic cell for each function: external noise measurement, reference sample measurement, and unknown observation sample measurement. [Example]

[0067] Second Embodiment A photoacoustic measurement device and a photoacoustic measurement method according to a second embodiment of the present invention will be described with reference to FIG.

[0068] FIG. 8 is a diagram showing the relationship between the frequency of the irradiated light in photoacoustic measurement and the fluctuation of the sensitivity and the reference sample measurement peak.

[0069] In this embodiment, the results of measuring a reference sample with the acoustic cell 21 of the first embodiment are stored in the database 112 and used as a reference when changing the frequency. In other words, this is an example in which the database 112 is used as an additional function to the first embodiment.

[0070] As in the first embodiment, three acoustic cells 20, 21, and 22, an analysis unit 113, etc. are used. In the first embodiment, during normal measurements, a reference sample is measured in the acoustic cell 21 using the frequency f1 used in measuring an unknown observation sample in the acoustic cell 22, but the measurement results and the results of measurements at other frequencies, for example, f2 and f3, in an investigation for changing the frequency are stored in the database 112 and are used to select candidate frequencies when changing the frequency, which is a difference from the first embodiment.

[0071] The left diagram in Figure 8 shows the relationship between the intermittent frequency of the irradiated light and sensitivity (signal strength) in photoacoustic measurements. Generally, the lower the frequency, the higher the sensitivity. However, there are various noises at the measurement site that affect the measurement. For example, as shown in the right diagram in Figure 8, the intermittent frequency and fluctuations in the reference sample measurement peak S, or measurement noise, are saved as a database from the results of normal measurements and measurements in preparation for frequency changes.

[0072] In the first embodiment, in the candidate frequency selection process for preparing to change the frequency of the intermittent light when external noise increases, candidates are selected solely from the results of external noise measurement by the acoustic cell 20, i.e., frequencies with relatively low external noise are selected. In this embodiment, however, candidate frequencies with high sensitivity and low signal noise are also selected from a stored database. Similar to the first embodiment, a survey measurement is performed again with the selected frequency in the acoustic cell 21 to determine the threshold judgment value, or if the results are highly reproducible in the database, the frequency may be changed without remeasurement.

[0073] The advantage of using a database, as in this embodiment, is that it makes it easier to select a frequency that is highly sensitive and stable when conducting an investigation to change the frequency. This makes it possible to make highly accurate judgments when measuring an unknown observation sample with the acoustic cell 22 at the changed frequency. The data for each frequency stored in the database can be accumulated by investigating and accumulating the acoustic cell 21 by changing the frequency finely and widely, but since this takes time, it is also possible to sequentially add previously acquired data and interpolate any missing parts. [Example]

[0074] Third Embodiment A photoacoustic measurement device and a photoacoustic measurement method according to a third embodiment of the present invention will be described with reference to FIG.

[0075] FIG. 9 is a diagram showing a schematic configuration of the inspection device 1 of this embodiment.

[0076] While the first embodiment uses three acoustic cells, namely acoustic cells 20, 21, and 22, the present embodiment is an example of a configuration using two acoustic cells, namely acoustic cells 21A and 22A. In the following embodiments including this embodiment, differences from the first embodiment will be mainly described.

[0077] The acoustic cell 21A of this embodiment has two functions: the acoustic cell 20 and the acoustic cell 21 of the first embodiment. That is, the light irradiated onto the sample is switched on and off by sending a signal from the FFT analysis unit 111 to the light source 26 to control it. A reference sample is placed inside the acoustic cell 21A, and when the light source 26 is turned off, no photoacoustic waves are generated from the reference sample, and external noise sound is measured. On the other hand, when the light source 26 is turned on, intermittent light is irradiated onto the reference sample, generating photoacoustic waves. Note that when measuring external noise sound, the light source 26 may remain on, and the frequency of the frequency modulator 30 may be set to 0, so that the intermittent light is not irradiated onto the sample.

[0078] In the first embodiment, the external noise measurement and the reference sample measurement are performed in different acoustic cells, but in this embodiment, they are performed in the same acoustic cell 21 A. The function of the acoustic cell 22 A is the same as that of the acoustic cell 22 in the first embodiment, and it is used to measure an unknown observation sample and allow the user to make the necessary judgments.

[0079] The measurement flow in this embodiment is as follows.

[0080] First, the light source 26 of the acoustic cell 21A is turned off to measure external noise. Then, the light source 26 is turned on to measure the reference sample. The obtained results are used for analysis of the decision threshold, etc., as in the first embodiment.

[0081] The light source 26 of the acoustic cell 21A is turned on and off periodically to alternately measure external noise and the reference sample. The frequency and timing are determined appropriately depending on the environment in which the measurement is performed.

[0082] Alternatively, the measurement flow may be such that external noise is measured with the light source 27 of the acoustic cell 22A turned off, and measurement of the reference sample in the acoustic cell 21A is continued at all times. However, while external noise is being measured with the acoustic cell 22A, measurement of the unknown observation sample cannot be performed.

[0083] The use of the above-described instrument configuration and measurement flow has the advantage of simplifying the measurement by reducing the number of acoustic cells required, but has the disadvantage that simultaneous acoustic wave measurements of the reference sample or the sample under observation are not possible while the light source is turned off. [Example]

[0084] Fourth Embodiment A photoacoustic measurement device and a photoacoustic measurement method according to a fourth embodiment of the present invention will be described with reference to FIG.

[0085] FIG. 10 is a diagram showing a schematic configuration of the inspection device 1 of this embodiment.

[0086] In the first embodiment, three acoustic cells, 20, 21, and 22, are used, whereas this embodiment is an example of a configuration in which two acoustic cells, 20X and 22Y, are used.

[0087] The acoustic cell 20X has the function of the acoustic cell 20 of Example 1. That is, it measures external noise in the same way as Example 1. In this example, there is no cell for measuring the reference sample as in Example 1, so this example is effective when the measurement target does not have sensitivity fluctuations or baseline fluctuations.

[0088] The unknown sample measured by the acoustic cell 22Y changes depending on the frequency of the irradiated intermittent light, but the relationship between frequency and sensitivity as shown in Figure 8 is collected in advance or made available theoretically.

[0089] The measurement flow in this embodiment is as follows.

[0090] First, external noise is measured using the acoustic cell 20X, and an unknown sample is measured using the acoustic cell 22Y with a predetermined chopped light frequency f1.

[0091] If the measurement results of acoustic cell 20X indicate that the noise level of the currently used chopped light frequency is high, the frequency is switched to another frequency. Acoustic cell 22Y measures the unknown sample using the other chopped light frequency, but the threshold for the test judgment is changed based on the relationship between frequency and sensitivity that has been determined in advance.

[0092] The use of the above-described device configuration and measurement flow has the advantage of simplifying the measurement by reducing the number of acoustic cells required. However, it has the disadvantage of reducing measurement accuracy when sensitivity or baseline fluctuations occur due to changes in the measurement environment, since the reference sample is not measured.

[0093] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0094] Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be partially or entirely implemented in hardware, for example, by designing them as integrated circuits. The above-described configurations, functions, etc. may also be implemented in software, with a processor interpreting and executing a program that implements each function. Information such as the programs, tables, and files that implement each function can be stored in a memory, a recording device such as a hard disk or SSD (Solid State Drive), or a recording medium such as an IC card, SD card, or DVD.

[0095] <<Additional Notes>> The present invention also has the following features.

[0096] a first acoustic cell for measuring external noise; a second acoustic cell for measuring a reference sample by irradiating the reference sample with light of a first frequency modulated by a first frequency modulator; a third acoustic cell that measures the observation sample by irradiating it with light of the second frequency modulated by the second frequency modulator; a processor that analyzes acoustic wave data measured by the first acoustic cell, the second acoustic cell, and the third acoustic cell; The processor performs a frequency analysis on the external noise sound, Among the results of the frequency analysis, a frequency with a low noise sound level is set as the first frequency, and the frequency is modulated at the first frequency by the first frequency modulator. The reference sample is measured by the second acoustic cell, the signal fluctuations and noise level fluctuations of the reference sample are analyzed, a component determination threshold for the observed sample is calculated, and the results of determining the components of the observed sample using the component determination threshold are output. [Explanation of symbols]

[0097] 1: Inspection equipment 10: Computer 11: Processor 12: Memory 20, 20X: (1st) acoustic cell 21, 21A: (Second) Acoustic Cell 22, 22A, 22Y: (Third) Acoustic Cell 23, 24, 25: Microphone 26,27:Light source 28, 29: Optical path chopper (optical path shutter) 30, 31: Frequency modulator 40: Glass window 41: Measurement target sample 42: Retaining plate 43: Acoustic cell components 110: Data collection section 111:FFT analysis section 112: Database 113:Analysis Department 114: Frequency change determination unit 115: Sample determination unit 116: GUI section.

Claims

1. a first acoustic cell for measuring external noise; a second acoustic cell for measuring a reference sample by irradiating the reference sample with light of the first frequency modulated by the first frequency modulator; a third acoustic cell that measures the observation sample by irradiating it with light of the second frequency modulated by the second frequency modulator; a processor that analyzes acoustic wave data measured by the first acoustic cell, the second acoustic cell, and the third acoustic cell; The processor performs a frequency analysis on the external noise sound, a frequency with a low noise sound level among the results of the frequency analysis is set as the first frequency, the frequency is modulated at the first frequency by the first frequency modulator, the reference sample is measured by the second acoustic cell, signal fluctuations and noise level fluctuations of the reference sample are analyzed, a component determination threshold value for the observation sample is calculated, and a result of determining the components of the observation sample using the component determination threshold value is output; modulating the second frequency, which is different from the first frequency, by the second frequency modulator, and measuring the observation sample in the third acoustic cell in parallel with measuring the reference sample; If the noise sound level of the second frequency is high as a result of the frequency analysis, the frequency is changed from the second frequency to the first frequency and the observation sample is measured with the third acoustic cell.

2. The photoacoustic measurement device according to claim 1, A photoacoustic measurement device characterized in that the frequency to be changed from the second frequency when measuring the observation sample with the third acoustic cell is calculated from a database that stores the measurement results of the reference sample measured with the second acoustic cell.

3. The photoacoustic measurement device according to claim 1, A photoacoustic measurement device characterized in that the frequency to be changed from the second frequency when measuring the observation sample with the third acoustic cell is selected to be a frequency that has low measurement noise, high signal strength, and small variation when measuring the reference sample with the second acoustic cell.

4. The photoacoustic measurement device according to claim 1, A photoacoustic measuring device, characterized in that the wavelengths of the light irradiated onto the sample by the second acoustic cell and the third acoustic cell are the same and are changed depending on the sample.

5. a first acoustic cell for measuring external noise; a second acoustic cell different from the first acoustic cell; and a processor that analyzes acoustic wave data measured by the first acoustic cell and the second acoustic cell; measuring the observation sample with the second acoustic cell using a second frequency; The processor performs a frequency analysis on the external noise sound measured by the first acoustic cell, A frequency having a low noise level in the result of the frequency analysis is defined as a first frequency; a photoacoustic measurement device characterized in that, when the noise level of the second frequency is high as a result of the frequency analysis, the second frequency is changed to the first frequency and the observation sample is measured using the second acoustic cell.

6. The photoacoustic measurement device according to claim 5, a first acoustic cell for measuring a reference sample by irradiating the reference sample with light of the first frequency, and for measuring the external noise sound without irradiating the reference sample with light of the first frequency;

7. The photoacoustic measurement device according to claim 6, The photoacoustic measurement device is characterized in that the first frequency to which the second frequency is changed when measuring the observation sample with the second acoustic cell is selected to be a frequency that has low measurement noise, high signal strength, and small variation when measuring the reference sample with the first acoustic cell.

8. The photoacoustic measurement device according to claim 5, the first acoustic cell is a blank cell containing no sample; The photoacoustic measurement apparatus is characterized in that the second acoustic cell is an unknown sample measurement cell for measuring an observation sample.

9. A photoacoustic measurement method comprising the steps of: (a) performing a frequency analysis on an external noise sound; (b) a step of determining a frequency with a low noise sound level from the results of the frequency analysis in step (a) as a first frequency, modulating the first frequency with a first frequency modulator, measuring a reference sample with a second acoustic cell, analyzing the signal fluctuation and noise level fluctuation of the reference sample, calculating a component determination threshold for the observation sample, and outputting the result of determining the components of the observation sample using the component determination threshold; (c) modulating the sample with a second frequency different from the first frequency by a second frequency modulator and measuring the sample in parallel with the measurement of the reference sample in a third acoustic cell; (d) if the noise level of the second frequency is high as a result of the frequency analysis in step (a), changing from the second frequency to the first frequency and measuring the observation sample with the third acoustic cell.

Images