Photoacoustic property measurement equipment

Abstract

To provide a photoacoustic physical property measurement device that can respond relatively easily to the change of a resonance frequency due to an arrangement state of a measurement object and a state of a gap between a photoacoustic cell and the measurement object or the like, and that can measure physical properties of the object in a comparatively short time without deteriorating detection sensitivity.SOLUTION: A photoacoustic physical property measurement device includes: a light irradiation section for irradiating an object with modulated light; a photoacoustic cell for amplifying a photoacoustic wave to be generated in the object by radiating the modulated light from the light irradiation section; a sonic wave generation section for generating a sonic wave inside the photoacoustic cell; a microphone for detecting the photoacoustic wave amplified in the photoacoustic cell and the sonic wave generated inside the photoacoustic cell from the sonic wave generation section; and a physical property analysis section for analyzing the physical properties of the object based on the photoacoustic wave detected by the microphone.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a photoacoustic property measuring apparatus and a measuring method. [Background technology]

[0002] In recent years, there has been an increasing need for "non-destructive testing" that can perform product inspections without destroying the object. In particular, non-destructive testing of organic materials is performed multiple times, such as when raw materials for electrical and electronic equipment are received, during the manufacturing process, and immediately before shipping. Photoacoustic spectroscopy is effective for non-destructive testing of organic materials, as it can be used to measure regardless of the state of the object being measured (solid, liquid, gas, powder).

[0003] The principle of a physical property measurement device using photoacoustic spectroscopy is as follows: When the object to be measured is irradiated with intermittent light from a light source, the object absorbs the light, generating heat, which is converted into kinetic energy that causes the surface to expand and contract locally. As a result, fluctuations in pressure in the space (= photoacoustic waves) are generated, which are detected by a microphone. Signal processing of the detection results (physical property analysis) makes it possible to evaluate substances and impurities.

[0004] However, since the photoacoustic waves generated by the photoacoustic effect are weak, in order to realize a highly sensitive nondestructive inspection device, it is necessary to confine the generated acoustic waves in a photoacoustic cell and resonantly amplify them.

[0005] When the photoacoustic cell is made into a resonant structure, weak sound waves can be amplified, but if the resonant frequency at which the photoacoustic wave resonates in the photoacoustic cell does not match the measurement frequency, the measurement sensitivity changes or decreases. Furthermore, if a gap occurs between the photoacoustic cell and the measurement object, the effective size of the photoacoustic cell changes, and the resonant frequency of the photoacoustic wave changes.

[0006] Therefore, if measurements are performed without correcting for changes in the resonance frequency due to the placement of the measurement object, the state of the gap between the photoacoustic cell and the measurement object, etc., the effect of resonance amplification cannot be obtained and the detection sensitivity decreases. Therefore, it is important to have a measurement technique that searches for the resonance frequency of the photoacoustic cell before the actual measurement and then uses the search results to perform the actual measurement.

[0007] Regarding the setting of the resonant frequency of the photoacoustic cell, for example, a technology is reported in Patent Document 1. In the component concentration measuring device described in Patent Document 1, a plurality of laser light sources with different wavelengths are prepared, and the acoustic mode is estimated from the change in the light intensity of the laser light sources, and the length of the photoacoustic cell is adjusted, and then the actual measurement is performed, thereby compensating for the acoustic mode dependency of the concentration sensitivity for the component to be measured. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2018-171178 A Summary of the Invention [Problem to be solved by the invention]

[0009] In the method described in Patent Document 1, the physical length of the acoustic cell is changed, so there is a possibility that compensation cannot be made when the resonant frequency changes significantly in the above-mentioned problem. In addition, since the length of the photoacoustic cell is adjusted, it takes time to identify the resonant frequency, and there is a possibility that the throughput will be reduced when measuring multiple points sequentially.

[0010] The present invention solves the problems of the conventional technology described above and provides a photoacoustic property measuring device and measurement method that can relatively easily respond to changes in resonant frequency due to the placement of the object to be measured or the state of the gap between the photoacoustic cell and the object to be measured, and that enables the physical properties of the object to be measured in a relatively short time without reducing detection sensitivity. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, in the present invention, a photoacoustic property measuring device that detects a photoacoustic signal generated by irradiating light onto an object and measures the physical properties of the object is configured to include a light irradiating unit that irradiates modulated light onto the object, a photoacoustic cell that amplifies the photoacoustic wave generated in the object by irradiating modulated light from the light irradiating unit, a sound wave generating unit that generates sound waves inside the photoacoustic cell, a microphone that detects the photoacoustic waves amplified by the photoacoustic cell and the sound waves generated inside the photoacoustic cell from the sound wave generating unit, and a physical property analysis unit that analyzes the physical properties of the object based on the photoacoustic waves detected by the microphone.

[0012] In addition, in order to solve the above-mentioned problems, the present invention provides a photoacoustic property measurement method in which light modulated at a predetermined frequency emitted from a light irradiation unit is irradiated onto an object to be irradiated, a photoacoustic signal generated from the sample irradiated with the light modulated at a predetermined frequency and resonating inside a photoacoustic cell is detected by a microphone, and the physical properties of the sample are analyzed using the photoacoustic signal detected by the microphone.The predetermined frequency of light irradiated to the object from the light irradiation unit is set based on the peak frequency searched for by generating sound waves from a speaker inside the photoacoustic cell, receiving the sound generated inside the photoacoustic cell by this sound wave, searching for the peak frequency of the sound received by the microphone by a peak frequency search unit, and setting the frequency based on the peak frequency searched for by the peak frequency search unit.

[0013] Furthermore, in order to solve the above-mentioned problems, in the present invention, a photoacoustic property measurement method is provided in which light modulated at a predetermined frequency emitted from a light irradiation unit is irradiated onto an object to be irradiated, a photoacoustic signal generated from the sample irradiated with the light modulated at a predetermined frequency and resonating inside the photoacoustic cell is detected by a microphone, and the physical properties of the sample are analyzed using the photoacoustic signal detected by the microphone. A predetermined frequency of light is irradiated onto the object from the light irradiation unit, and light with a modulated frequency changed from the light irradiation unit is sequentially irradiated onto the sample, and the frequency characteristics of the photoacoustic signal are obtained and stored from the signal detected by the microphone that resonates inside the photoacoustic cell, a sound wave is generated inside the photoacoustic cell from a speaker, the photoacoustic signal generated inside the photoacoustic cell by this sound wave is received by the microphone, and a peak frequency is searched for from a signal obtained by subtracting the frequency characteristic component previously determined and stored from the photoacoustic signal received by the microphone in the peak frequency search unit, and the peak frequency is set based on the peak frequency searched for by the peak frequency search unit. Effect of the Invention

[0014] According to the present invention, it is possible to relatively easily respond to changes in resonant frequency due to the placement of the object to be measured or the state of the gap between the photoacoustic cell and the object to be measured, making it possible to measure the physical properties of the object to be measured in a relatively short time without reducing detection sensitivity. [Brief description of the drawings]

[0015] [Figure 1] 1 is a block diagram showing a schematic configuration of a photoacoustic property measuring apparatus according to a first embodiment of the present invention. [Diagram 2] 1 is a flowchart showing the steps of a photoacoustic property measuring method according to a first embodiment of the present invention. [Diagram 3] 3 is a graph showing the relationship between frequency and sound wave intensity, illustrating the principle of the photoacoustic property measuring method according to the first embodiment of the present invention. [Figure 4] 4 is a graph showing frequency characteristics of sound waves generated from the speaker according to the first embodiment of the present invention. [Diagram 5]FIG. 11 is a block diagram showing a schematic configuration of a photoacoustic property measuring apparatus according to a second embodiment of the present invention. [Figure 6] 10 is a flowchart showing the steps of a photoacoustic property measuring method according to a second embodiment of the present invention. [Figure 7] 10 is a graph showing frequency characteristics of sound waves generated from a speaker according to a second embodiment of the present invention. [Figure 8] FIG. 11 is a block diagram showing a schematic configuration of a photoacoustic property measuring apparatus according to a third embodiment of the present invention. [Figure 9] 11 is a graph showing an example of frequency characteristics of a photoacoustic signal detected by a frequency search unit. [Figure 10] 13 is a graph showing another example of the frequency characteristics of a photoacoustic signal detected by the frequency search unit. [Figure 11] FIG. 11 is a block diagram showing a schematic configuration of a photoacoustic property measuring apparatus according to a fourth embodiment of the present invention. [Figure 12] FIG. 13 is a block diagram showing a schematic configuration of a photoacoustic property measuring apparatus according to a fifth embodiment of the present invention. [Figure 13] FIG. 13 is a block diagram showing a schematic configuration of a photoacoustic property measuring apparatus according to a sixth embodiment of the present invention. [Figure 14] FIG. 13 is a block diagram showing a schematic configuration of a photoacoustic property measuring apparatus according to a seventh embodiment of the present invention. [Figure 15] 13 is a flowchart showing the steps of a photoacoustic property measuring method according to a seventh embodiment of the present invention. [Figure 16] FIG. 13 is a block diagram showing a schematic configuration of a photoacoustic property measuring apparatus according to an eighth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In this invention, before measurement, wideband sound waves are generated from a speaker placed in the photoacoustic cell, and the sound waves are detected by a microphone and signal-processed to search for the resonant frequency, thereby speeding up frequency calibration and achieving high sensitivity in measurements.

[0017] In addition, the present invention determines the resonant frequency between the photoacoustic cell and the object to be measured by attaching a sound source such as a speaker to the photoacoustic cell and detecting the frequency characteristics of the sound waves emitted from this sound source, thereby shortening the time required to determine the resonant frequency compared to conventional techniques and improving the throughput of physical property measurements using photoacoustics.

[0018] Furthermore, the resonant frequency is determined by detecting the frequency characteristics of the wideband sound waves generated from a sound source attached to the photoacoustic cell, making it possible to detect the peak frequency even when there is a large fluctuation in the resonant frequency, thereby enabling highly sensitive non-destructive measurement to be realized.

[0019] The present invention also provides a photoacoustic property measuring device that has a light source, a driving circuit, a photoacoustic cell, a microphone, a high-sensitivity amplifier circuit, a physical property analysis unit, and a measurement area for storing a sample, and is further configured to include a signal generating circuit, a speaker, and a peak frequency search unit, and prior to the actual measurement, wideband sound waves are generated from the signal generating circuit and the speaker, the peak frequency of the signal detected by the microphone is calculated by the peak frequency search unit, the light source is driven using the frequency calculated by the peak frequency search unit to irradiate light onto the sample, and the actual measurement is performed by the microphone, the high-sensitivity amplifier circuit, and the physical property analysis unit.

[0020] In addition, the present invention provides a photoacoustic property measurement device having a light source, a driving circuit, a photoacoustic cell, a microphone, a high-sensitivity amplifier circuit, a physical property analysis unit, a signal generating circuit, a speaker, and a peak frequency search unit, in which wideband sound waves are generated from the signal generating circuit and the speaker before the actual measurement, the peak frequency of the signal detected by the microphone is calculated by the peak frequency search unit, the light source is driven using this frequency to irradiate light onto the sample, and the actual measurement is performed by the microphone, the high-sensitivity amplifier circuit, and the physical property analysis unit to correct fluctuations in the resonant frequency, thereby preventing a decrease in measurement sensitivity due to fluctuations in the resonant frequency of the photoacoustic cell caused by the arrangement and shape of the sample, and enabling highly sensitive photoacoustic measurement to be realized.

[0021] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiment, the same reference numerals are used to denote the same functions, and the repeated description is omitted as a rule.

[0022] However, the present invention should not be construed as being limited to the description of the embodiments shown below. It will be easily understood by those skilled in the art that the specific configurations can be modified without departing from the concept or spirit of the present invention. EXAMPLES

[0023] A first embodiment of the present invention will be described with reference to FIGS. Fig. 1 shows the configuration of a photoacoustic property measurement apparatus 100-1 according to this embodiment. The photoacoustic property measurement apparatus 100-1 according to this embodiment includes a light source 1, a driving circuit 2, an optical chopper 3, a photoacoustic cell 4, a microphone 5, an amplifier circuit 6, a property analysis unit 7, a speaker 10, a signal generating circuit 11, and a peak frequency search unit 12. The example shown in Fig. 1 shows a state in which the photoacoustic cell 4 is brought close to a sample 8 stored in a measurement area 9, and the physical properties of the sample 8 are measured.

[0024] A laser or a white light source is used as the light source 1. Furthermore, a MEMS speaker or an electret speaker is used as the speaker 10.

[0025] As in the example shown in Fig. 1, the photoacoustic cell 4 and the sample 8 may not be in close contact and may be tilted, resulting in the formation of a gap 13 as indicated by the dotted line. When the photoacoustic cell 4 and the sample 8 are in the state shown in Fig. 1, the resonant frequency f2:32 between the photoacoustic cell 4 and the sample 8 deviates from the resonant frequency f1:31 in an ideal state in which the photoacoustic cell 4 and the sample 8 are in close contact, as shown in Fig. 3.

[0026] Therefore, in this embodiment, taking into account the shift in resonance frequency as shown in FIG. 3, a calibration measurement is performed to determine the resonance frequency using sound wave 41 having a frequency characteristic in a relatively wide frequency band as shown in FIG. 4, and then the main measurement is performed at this calibrated frequency.

[0027] A procedure for measuring the properties of a sample 8 using the photoacoustic property measurement apparatus 100-1 having the configuration shown in FIG. 1 will be described with reference to the flowchart of FIG.

[0028] First, with the photoacoustic cell 4 in contact with the sample 8, a wideband signal is generated from the signal generating circuit 11 and input to the speaker 10 (S1). The speaker 10 to which this wideband signal is input generates a wideband sound wave with a wide bandwidth, for example as shown in FIG. 4, toward the inside of the photoacoustic cell 4 (S2). The wideband sound wave generated from the speaker 10 toward the photoacoustic cell 4 is received by the microphone 5, and the signal received by the microphone 5 is processed by the peak frequency search unit 12 to search for the peak frequency f2 (S3). Steps S1 to S3 are calibration measurements.

[0029] Next, for the actual measurement, the drive circuit 2 operates the optical chopper 3 at a peak frequency f2 (S4), the light source 1 emits light, and the light modulated by the optical chopper 3 is irradiated onto the sample 8 through the photoacoustic cell 4 (S5).

[0030] Photoacoustic waves generated from the sample irradiated with this modulated light are detected by the microphone 5 and amplified by the amplifier circuit 6 (S6).

[0031] This amplified signal is input to the physical property analysis unit 7. The physical property analysis unit 7 searches for the frequency at which the signal strength is maximum using signal processing such as Fourier transform, and calculates the peak frequency f1. By comparing and analyzing the signal information at this found peak frequency f1 with data stored in a database, the physical properties of the sample 8 according to the purpose of measurement, such as the type, concentration, and film thickness, are analyzed (S7) and output.

[0032] According to this embodiment, the sound waves generated from the speaker 10 are detected by the microphone 5, the peak frequency is determined by the peak frequency search unit 12, and the driving frequency of the optical chopper 3 is corrected, thereby calibrating the fluctuation in the resonant frequency of the photoacoustic cell 4 caused by a misalignment of the positional relationship of the sample 8 relative to the photoacoustic cell 4, thereby enabling non-destructive measurement to be performed using highly sensitive photoacoustic spectroscopy. EXAMPLES

[0033] A second embodiment of the present invention will be described with reference to FIGS. 5 shows the configuration of a photoacoustic property measurement apparatus 100-2 according to this embodiment. The configuration of the photoacoustic property measurement apparatus 100-2 according to this embodiment differs from the configuration of the photoacoustic property measurement apparatus 100-1 described in FIG. 1 in the first embodiment in that a memory 14 and a frequency band switching unit 15 are added.

[0034] In this embodiment, as shown in Fig. 7, a sound wave having a frequency characteristic with a relatively narrow bandwidth compared to the case of Fig. 4 in embodiment 1 is generated from speaker 10. In this embodiment, the frequency band is divided by frequency band switching unit 15 to drive signal generating circuit 11, and sounds of frequency bands 71, 72, 73, 74, ... are generated from speaker 10 by sequentially switching between them.

[0035] A procedure for measuring the properties of the sample 8 using the photoacoustic property measurement apparatus 100-2 having the configuration shown in FIG. 5 will be described with reference to the flowchart of FIG.

[0036] First, the frequency band to be divided is determined by the frequency band switching unit 15 (S101). In the example of Fig. 6, the number of divisions is set to N. Next, i is set to 1 (S102), and a signal of the first frequency band is transmitted from the signal generating circuit 11 to the speaker 10 in response to a command from the frequency band switching unit 15 (S103). The speaker 10, which has received the signal from the signal generating circuit 11, generates sound waves of the first frequency band toward the inside of the photoacoustic cell 4 (S104).

[0037] Next, the sound waves generated by the speaker 10 are received by the microphone 5, and the received signal from the microphone 5 is received by the peak frequency search section 12-1 to search for a peak frequency (S105), which is then stored in the memory 14 (S106).

[0038] Next, i is incremented by 1 (S107), and the processes from S103 to S105 are repeated until i reaches the division number N set in S101 (S108).

[0039] When i becomes N (No in S108), the peak frequency search unit 12-1 searches for the frequency peak with the highest signal level from the peak frequency signals in each frequency band stored in the memory 14 (S109). Next, the drive circuit 2 controls the optical chopper 3 based on the searched peak frequency to modulate the light emitted from the light source 1 (S110), and the modulated light is irradiated onto the sample 8 (S111).

[0040] Photoacoustic waves generated from the sample irradiated with this modulated light are detected by the microphone 5 and amplified by the amplifier circuit 6 (S112).

[0041] This amplified signal is input to the physical property analysis unit 7. The physical property analysis unit 7 searches for the frequency at which the signal strength is maximum using signal processing such as Fourier transform, and calculates the peak frequency f1. By comparing and analyzing the signal information at this found peak frequency f1 with data stored in a database, the physical properties of the sample 8 according to the purpose of measurement, such as the type, concentration, and film thickness, are analyzed (S113) and output.

[0042] According to this embodiment, in addition to obtaining the same effect as in the first embodiment, by dividing the frequency band of the sound waves generated from the speaker 10, the total amount of signals input to the microphone 5 and the amplifier circuit 6 for each frequency band can be reduced, and deterioration of the accuracy of peak search due to insufficient dynamic range of the microphone 5 and the amplifier circuit 6 can be suppressed. EXAMPLES

[0043] Next, a third embodiment will be described with reference to FIGS.

[0044] 8 shows the configuration of a photoacoustic property measurement apparatus 100-3 according to this embodiment. The configuration of the photoacoustic property measurement apparatus 100-3 according to this embodiment differs from the configuration of the photoacoustic property measurement apparatus 100-1 described in FIG. 1 in the first embodiment in that a threshold determination unit 16, a result display unit 17, and a frequency input unit 19 are added.

[0045] In the first and second embodiments, a case has been described in which only one peak signal is detected by the peak frequency search unit 12 for each frequency band. However, as shown in FIG. 9, a signal waveform 90 having multiple peaks 91, 92 at levels higher than a preset threshold 93 may be detected, or as shown in FIG. 10, a signal waveform 110 in which the levels of peaks 111, 112 are lower than a preset threshold 113 may be detected.

[0046] In this embodiment, in order to cope with the case where multiple peaks are detected in this way, the peak frequency found by the peak frequency search unit 12 is compared with a preset threshold value by a threshold value judgment unit 16 to judge the result, and the result is displayed on a result display unit 17 to inform a user 18. Based on the displayed result, the user 18 inputs the frequency for driving the optical chopper 3 into a frequency input unit 19, or corrects the positional relationship between the photoacoustic cell 4 and the sample 8.

[0047] That is, when the levels of peaks 91 and 92 are higher than threshold 93 as shown in Fig. 9, the frequency for driving optical chopper 3 based on the displayed result is input to frequency input unit 19. In this case, drive circuit 2 drives optical chopper 3 based on the frequency input from frequency input unit 19, and analyzes the physical properties of sample 8 in the procedure described in embodiment 1 or 2.

[0048] On the other hand, if the relationship between the peak frequency displayed on the result display unit 17 and the threshold value is as shown in Figure 10, and both peaks 111 and 112 are lower than the threshold value 113, the user 18 temporarily suspends the measurement, corrects the positional relationship between the photoacoustic cell 4 and the sample 8, and then resumes the measurement.

[0049] According to this embodiment, by notifying the user of the peak frequency search result, even if multiple peaks exist in the detected waveform, if the peak value is higher than the threshold value, a frequency for controlling the optical chopper 3 is selected, thereby making it possible to stably perform highly sensitive measurement. On the other hand, if the peak value is lower than the threshold value, the positional relationship between the photoacoustic cell 4 and the sample 8 is corrected, thereby making it possible to reliably perform highly sensitive measurement. EXAMPLES

[0050] A fourth embodiment of the present invention will be described with reference to FIG. The configuration of the photoacoustic property measurement apparatus 100-4 according to this embodiment shown in FIG. 11 differs from the configuration of the photoacoustic property measurement apparatus 100-1 shown in FIG. 1 described in the first embodiment in that the configuration according to this embodiment shown in FIG. 11 does not include an optical chopper 3.

[0051] That is, in the photoacoustic property measurement apparatus 100-4 according to this embodiment, the light source 1A is directly controlled by the driving circuit 2 based on the peak frequency found by the peak frequency search section 12 from the sound wave signal detected by the microphone 5.

[0052] For this reason, in this embodiment, a light source whose modulation frequency can be controlled, such as a semiconductor laser, is used as the light source 1A.

[0053] The procedure for measuring the properties of sample 8 using photoacoustic property measurement apparatus 100-4 in this embodiment is basically the same as that described using the flowchart of FIG. 2 in embodiment 1, but S4 and S5 are integrated, and light is emitted from light source 1A at peak frequency f1 and irradiated onto sample 8.

[0054] Although this embodiment has been described in terms of the difference from the configuration of the photoacoustic property measurement apparatus 100-1 described in the first embodiment, the present embodiment can also be applied to the configurations of the second embodiment or the third embodiment by removing the optical chopper 3 in the configuration of the photoacoustic property measurement apparatus 100-2 described in the second embodiment or the photoacoustic property measurement apparatus 100-3 described in the third embodiment and replacing the light source 1 with the light source 1A.

[0055] According to this embodiment, in addition to the effects described in the first to third embodiments, the optical chopper 3 is not used, and therefore the device can be made smaller. EXAMPLES

[0056] A fifth embodiment of the present invention will be described with reference to FIG. The configuration of the photoacoustic property measurement apparatus 100-5 according to this embodiment shown in FIG. 12 differs from the configuration of the photoacoustic property measurement apparatus 100-1 shown in FIG. 1 described in the first embodiment in that the configuration according to this embodiment shown in FIG. 12 includes a synchronous detection unit 20 connected to the amplifier circuit 6 and the peak frequency search unit 12.

[0057] That is, in the photoacoustic property measuring apparatus 100-5 according to this embodiment, the sound wave signal detected by the microphone 5 is amplified by the amplifier circuit 6, and then the synchronization detection unit 20 detects a signal that is synchronized with the frequency of the peak signal detected by the peak frequency search unit 12, and sends this synchronously detected signal to the property analysis unit 7.

[0058] The procedure for measuring physical properties using the photoacoustic property measurement apparatus 100-5 of this embodiment is similar to the flowchart shown in FIG. 2 in the first embodiment, except that a step of detecting a signal synchronized with the peak frequency f2 from the signal amplified by the amplifier circuit 6 is added between steps S6 and S7.

[0059] The configuration described in this embodiment can also be applied to the configurations of Examples 2, 3, or 4 by adding a synchronization detection unit 20 to the configuration of the photoacoustic property measurement apparatus 100-2 described in Example 2, the photoacoustic property measurement apparatus 100-3 described in Example 3, or the photoacoustic property measurement apparatus 100-4 described in Example 4.

[0060] According to this embodiment, in addition to the effects described in the first to fourth embodiments, it is possible to realize high sensitivity detection. EXAMPLES

[0061] A sixth embodiment of the present invention will be described with reference to FIG. The configuration of a photoacoustic property measurement apparatus 100-6 according to this embodiment shown in Fig. 13 differs from the configuration of the photoacoustic property measurement apparatus 100-1 shown in Fig. 1 described in Example 1 in that the configuration according to this embodiment shown in Fig. 13 includes a camera 21 and a database 22. Data on the placement of the sample 8 (the positional relationship between the photoacoustic cell 4 and the sample 8) and the resonant frequency according to the material of the sample 8 are recorded in the database 22.

[0062] In the photoacoustic property measurement apparatus 100-6 according to this embodiment, the shape and arrangement of the sample 8 are measured by the camera 21, and the measurement results are compared with the database 22 to determine the frequency band of the signal to be generated from the signal generating circuit 11. This makes it possible to narrow the frequency band of the signal to be generated from the signal generating circuit 11 compared to the case where the camera 21 and the database 22 are not used as described in the first to fifth embodiments, and makes it possible to suppress deterioration of the accuracy of peak search due to insufficient dynamic range of the microphone 5 and the amplifier circuit 6.

[0063] The procedure for measuring physical properties using photoacoustic property measurement apparatus 100-6 of this embodiment is basically the same as the flowchart shown in FIG. 2 in Example 1, except that an additional step is added before S1 in which the shape and arrangement of sample 8 are measured by camera 21, and the measurement results are compared with database 22 to determine the signal frequency band to be generated from signal generating circuit 11, and in step S1, a signal of the frequency band determined by referring to database 22 is input from signal generating circuit 11 to speaker 10.

[0064] According to this embodiment, in addition to the effects described in the first to fifth embodiments, it is possible to suppress deterioration of the accuracy of peak search due to insufficient dynamic range of the microphone 5 and the amplifier circuit 6, thereby realizing high sensitivity detection. EXAMPLES

[0065] A seventh embodiment of the present invention will be described with reference to FIGS. When detecting acoustic waves with the photoacoustic cell 4, the acoustic waves are affected by surrounding vibrations and noise, which are added to the output signal of the photoacoustic cell 4 as noise components, causing a decrease in detection accuracy.

[0066] In this embodiment, the noise components added to the output signal of the photoacoustic cell 4 are measured and stored in advance, and the previously measured noise components are subtracted from the detection signal obtained by detecting the photoacoustic wave from the sample. This prevents the dynamic range of the microphone 5 and the amplifier circuit 6 from becoming insufficient due to the expansion of the frequency range searched by the peak frequency search unit 12.

[0067] The configuration of a photoacoustic property measurement apparatus 100-7 according to this embodiment is shown in Fig. 14. The photoacoustic property measurement apparatus 100-7 according to this embodiment differs from the photoacoustic property measurement apparatus 100-1 shown in Fig. 1 described in the first embodiment in that a frequency characteristic measurement unit 23 and a memory 14 are disposed between the microphone 5 and the peak frequency search unit 12.

[0068] In the configuration of the photoacoustic property measuring device 100-7, when broadband sound waves are not emitted from the speaker 10, an acoustic wave generated in the photoacoustic cell 4 by irradiating the sample 8 with intermittent light of frequency f0 from the light source 1 side becomes a noise component compared to the acoustic wave detected when broadband sound waves are emitted from the speaker 10.

[0069] Therefore, in the photoacoustic property measuring device 100-7 according to this embodiment, first, in a state where light is emitted from the light source 1, the optical chopper 3 is driven while changing the driving frequency by the driving circuit 2, and frequency-modulated light is irradiated onto the sample 8, generating a photoacoustic wave inside the photoacoustic cell 4, which is detected by the microphone 5, and the frequency characteristic measuring unit 23 measures the frequency characteristic of the output signal from the microphone 5 and stores it in the memory 14. Next, a signal waveform is created by subtracting the frequency characteristic signal component stored in the memory 14 from the output signal waveform from the microphone 5 that detects the acoustic wave generated by the photoacoustic cell 4 in a state where a wideband sound wave is emitted from the speaker 10, and the signal waveform is input to the peak frequency search unit 12 to search for a peak frequency.

[0070] A procedure for measuring the properties of the sample 8 using the photoacoustic property measurement apparatus 100-7 having the configuration shown in FIG. 14 will be described with reference to the flowchart of FIG.

[0071] First, with the photoacoustic cell 4 in contact with the sample 8, the optical chopper 3 is operated while changing the drive frequency with the drive circuit 2, and light emitted from the light source 1 and transmitted through the optical chopper 3 is irradiated onto the sample 8 via the photoacoustic cell 4. In this state, the acoustic wave generated in the photoacoustic cell 4 is detected by the microphone 5, and the output signal from the microphone 5 is input to the frequency characteristic measuring unit 23 to measure the frequency characteristic of the acoustic wave detected by the microphone 5 and input it to the memory 14 (S201).

[0072] Next, with the photoacoustic cell 4 in contact with the sample 8, a wideband signal is generated from the signal generating circuit 11 and input to the speaker 10 (S202). The speaker 10 to which this wideband signal has been input generates a wideband sound wave having a wide bandwidth, such as that described in Example 1 using FIG. 4, toward the inside of the photoacoustic cell 4 (S203). The wideband sound wave generated from the speaker 10 toward the photoacoustic cell 4 is received by the microphone 5, and the signal received by the microphone 5 is input to the frequency characteristic measuring unit 23 (S204).

[0073] In the frequency characteristic measuring unit 23, a process is performed to subtract the result received by the microphone 5 when wideband sound waves are generated from the speaker measured in step S204 and stored in memory 14 from the result received by the microphone 5 when wideband sound waves are generated from the speaker measured in step S204, thereby removing noise components from the result measured in S204 (S205).

[0074] Next, in the peak frequency search unit 12, a peak frequency f2 as described using Figure 3 in Example 1 is searched for from the signal from which the noise components have been removed in S205, and the light emitted from the light source 1 is modulated at the frequency f2 by operating the optical chopper 3 at the peak frequency f2 found through this search (S206), and the light is irradiated onto the sample 8 inside the measurement area 9 via the photoacoustic cell 4 (S207).

[0075] Next, the photoacoustic wave generated from the sample 8 irradiated with the light modulated at the frequency f2 is detected by the microphone 5 and amplified by the amplifier circuit 6 (S208).

[0076] This amplified signal is input to the physical property analysis unit 7, which searches for the frequency at which the signal strength is maximum using signal processing such as Fourier transform to calculate the peak frequency f1. By comparing and analyzing the signal information at this found peak frequency f1 with the data stored in the database, the physical properties of the sample 8 according to the purpose of measurement, such as the type, concentration, and film thickness, are analyzed (S209) and output.

[0077] According to this embodiment, the sound waves generated from the speaker 10 are detected by the microphone 5, the peak frequency is determined by the peak frequency search unit 12, and the driving frequency of the optical chopper 3 is corrected, so that the fluctuation in the resonant frequency of the photoacoustic cell 4 caused by a misalignment of the positional relationship of the sample 8 relative to the photoacoustic cell 4 can be calibrated using a signal from which the background signal has been removed.This makes it possible to prevent the dynamic range of the microphone 5 and the amplifier circuit 6 from becoming insufficient when measuring the physical properties of the sample 8, and enables non-destructive measurement using highly sensitive photoacoustic spectroscopy. EXAMPLES

[0078] An eighth embodiment of the present invention will be described with reference to FIG. 1 in Example 1, a movable mirror 25 is provided between the optical chopper 3 and the photoacoustic cell 4. In this example, this configuration makes it possible to displace the position at which light is irradiated onto the sample 8 via the photoacoustic cell 4 without moving the positions of the photoacoustic cell 4 and the sample 8 relatively. This makes it possible to measure the sample 8 on a surface by sequentially irradiating light onto a plurality of points on the sample 8 while keeping the position of the photoacoustic cell 4 fixed with respect to the measurement area 9 storing the sample 8.

[0079] The procedure for analyzing the physical properties of sample 8 in this embodiment is basically the same as the procedure described in embodiment 1 with reference to Fig. 2. In this embodiment, the difference is that after S6 in the flow in Fig. 2 is executed, movable mirror 25 is driven to move by one pitch to move the irradiation position of light on sample 8 by one pitch, and steps starting from S1 are repeated in sequence. According to this embodiment, by using a configuration in which the position at which light is irradiated onto the sample 8 is sequentially changed by the movable mirror 25, it is possible to measure the surface of the sample 8 with a relatively simple configuration without using a driving mechanism for moving the positions of the photoacoustic cell 4 and the sample 8 relative to one another.

[0080] The invention made by the present inventor has been specifically described above based on the embodiments, but it goes without saying that the present invention is not limited to the above embodiments and can be modified in various ways without departing from the gist of the invention. For example, the above embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the configurations described. In addition, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0081] 1, 1A...light source 2...driving circuit 3...optical chopper 4...photoacoustic cell 5...microphone 6...amplification circuit 7...physical property analysis section 8...sample 9...measurement area 10...speaker 11...signal generation circuit 12, 12-1...peak frequency search section 14, 24...memory 15...frequency band switching section 16...threshold judgment section 17...result display section 19...frequency input section 20...synchronous detection section 21...camera 22...database 23...frequency characteristics measurement section 25...movable mirror.

Claims

1. A photoacoustic property measuring apparatus for measuring physical properties of an object by detecting a photoacoustic signal generated by irradiating the object with light, comprising: A light irradiation unit that irradiates the object with modulated light; A photoacoustic cell that amplifies a photoacoustic wave generated in the object by irradiating modulated light from the light irradiation unit; A sound wave generating unit that generates sound waves inside the photoacoustic cell; A microphone that detects the photoacoustic wave amplified by the photoacoustic cell and the sound wave generated inside the photoacoustic cell from the sound wave generating unit; a physical property analysis unit that analyzes physical properties of the object based on the photoacoustic wave detected by the microphone; An imaging unit that images a positional relationship between the object and the photoacoustic cell; a database storing a positional relationship between the object imaged by the imaging unit and the photoacoustic cell and a resonance frequency of the photoacoustic cell; The sound wave generating unit includes a speaker that generates sound waves inside the photoacoustic cell, and a signal generating circuit unit that controls a frequency band of the sound waves emitted from the speaker, The signal generating circuit unit controls the frequency band of the sound waves generated from the speaker based on the relationship between the positional relationship between the object and the photoacoustic cell stored in the database and the resonant frequency of the photoacoustic cell.

2. 2. The photoacoustic property measuring apparatus according to claim 1, The photoacoustic property measuring device further comprises: a light source; an optical chopper; a peak frequency search unit that detects the peak frequency of the sound wave generated inside the photoacoustic cell from the sound wave generating unit detected by the microphone; and a drive circuit unit that drives the optical chopper based on the peak frequency of the sound wave generated inside the photoacoustic cell from the sound wave generating unit searched for by the peak frequency search unit.

3. 2. The photoacoustic property measuring apparatus according to claim 1, The photoacoustic property measuring device further comprises: a light source; an optical chopper; a peak frequency search unit that detects the peak frequency of the sound wave generated inside the photoacoustic cell from the sound wave generating unit detected by the microphone; a threshold determination unit that compares the peak frequency detected by the peak frequency search unit with a predetermined threshold; a display unit that displays the result determined by the threshold determination unit; a frequency input unit that inputs a frequency for driving the optical chopper; and a drive circuit unit that drives the optical chopper based on the frequency for driving the optical chopper input from the frequency input unit.

4. 2. The photoacoustic property measuring apparatus according to claim 1, The photoacoustic property measuring device is characterized in that the light irradiation unit further comprises a light source, a peak frequency search unit that detects the peak frequency of the sound wave generated inside the photoacoustic cell from the sound wave generating unit detected by the microphone, and a drive circuit unit that modulates and drives the light source based on the peak frequency of the sound wave generated inside the photoacoustic cell from the sound wave generating unit searched for by the peak frequency search unit.

5. 3. The photoacoustic property measuring apparatus according to claim 2, A photoacoustic property measuring device characterized in that it further comprises a synchronous detection unit that detects the photoacoustic wave detected by the microphone in synchronization with the peak frequency of the sound wave generated inside the photoacoustic cell from the sound wave generating unit detected by the peak frequency search unit, and sends the synchronously detected signal to the property analysis unit.

6. 3. The photoacoustic property measuring apparatus according to claim 2, The photoacoustic property measuring device further includes a frequency measuring unit that determines the frequency characteristics from the signal detected by the microphone of the photoacoustic wave generated by the photoacoustic cell by irradiating the modulated light from the light irradiation unit onto the object, and a memory unit that stores the frequency characteristics determined by the frequency measuring unit, wherein the peak frequency search unit determines the peak frequency of the sound wave generated inside the photoacoustic cell using the signal detected by the microphone of the sound wave generated inside the photoacoustic cell from the sound wave generating unit and the frequency characteristics stored in the memory unit, and controls the drive circuit unit based on the determined peak frequency.

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