JPH06123700A - Method and device for measuring infrared-ray absorption - Google Patents

Abstract

PURPOSE:To quantitatively determine a light-absorption substance non- destructively. CONSTITUTION:An object to be measured is illuminated with infrared rays with two types of wavelengths, sufficiently large absorbance difference by a substance in the object to be measured, and a sufficiently small difference in the degree of scattering. The quantity of reflection light from the object to be measured is detected for each wavelength. Then, one of the quantity of the reflection light detected for each wavelength is calculated by the other for offsetting the contribution of scattered light and the absorbance of the infrared rays by the substance in the object to be measured is measured. Substances to be measured are water, alcohol, heavy water, benzene, n- hexylamine, etc. However, these molecules have H-O-H, R-O-H, O-D, C-H, and N-H bondings, respectively, the harmonics and combination tone of stretching vibration and deformation vibration show characteristic absorption spectra in a near infrared region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring infrared absorption of a substance in an object to be measured or measuring its distribution.

[0002]

2. Description of the Related Art In the near-infrared light region, OH, C--H, N--H (H is D ( Deuterium) is also acceptable). It is possible to measure 0-dimensional to 2-dimensional information of these absorption spectra, but at the same time, the scattering component is also taken in, and it is hard to say that the true absorption component is measured as it is.

[0003]

For this reason, it has been difficult to quantify the substance to be measured in the prior art. Here, the absorption spectrum of the substance largely changes depending on the wavelength in the near-infrared region, while the intensities of scattered light relatively change when the wavelengths are close to each other.

The present invention has been completed based on this finding, and the infrared absorption is measured by removing the contribution of scattered light from the observed light quantity, thereby enabling the concentration of the light-absorbing substance to be quantified. Methods and apparatus are provided.

[0005]

The measuring method according to the present invention is an infrared light having at least two kinds of wavelengths, and the difference in absorbance between the substances in the object to be measured is sufficiently large and the difference in scattering degree is sufficient. The first step of illuminating the object to be measured with infrared light having a small wavelength in the vicinity, and detecting (or imaging) the light amount of the reflected light from the object to be measured for at least two types of wavelengths, and detecting for each wavelength. (Or image) One of the reflected light quantity is calculated by the other, and the contribution of scattered light is virtually eliminated (all or most of it is eliminated), and the infrared light is absorbed by the substance in the DUT. A second step of measuring the degree (or its distribution). The concentration of the light-absorbing substance may be quantified based on the infrared absorption measured in the second step and the absorption of the substance in the object to be measured, which is obtained in advance.

Further, the measuring apparatus according to the present invention is an infrared ray having at least two kinds of wavelengths, and the difference in absorbance between substances in the object to be measured is sufficiently large and the difference in scattering degree is sufficiently small. An illumination unit that illuminates an object to be measured with infrared light having a wavelength, an image capturing unit that captures an image of reflected light from the object to be measured for at least two types of wavelengths, and an image of the reflected light captured for each wavelength. And a calculation means for calculating an image of one of the intensities by the other. Here, based on the image calculation data obtained by the calculating means and the distribution of the light absorption for each wavelength of the substance in the DUT obtained in advance, the quantitative determination of the distribution of the concentration of the light absorbing substance in the DUT. It may be configured to further include means.

[0007]

The substance to be measured by the present invention is a substance having a sufficiently large difference in absorption spectrum (that is, light absorptivity) with respect to infrared light of two different wavelengths in the vicinity. Examples of the substance include water, alcohol, heavy water, benzene, triethylamine and the like. These molecules are respectively H--O--H, R--O--H, O--D, C--
It has H, N-H bonds, and stretching vibration, bending vibration overtone, and coupling sound show characteristic absorption spectra in the near infrared region, respectively.

This is specifically shown in FIGS. 1 and 2. The present inventor has found that the wavelength of 1100 nm to 2300
In the range of nm, the wavelength dependence of the absorption was investigated for water, heavy water, ethanol, benzene, petroleum ether, and triethylamine. As shown in the figure, in the infrared region having a wavelength longer than that of red, a characteristic spectrum in which the light absorption property is rapidly changed by a slight wavelength change was confirmed. A cell with an optical path length of 200 μm was used for the measurement, and the scale on the vertical axis was 5 times, except for water and heavy water.

By the way, in the vicinity of the wavelength, the scattering intensity by the scattering substance on the surface or inside of the object to be measured does not become large, and it is almost equal according to Mie's scattering theory. Therefore, in the absorption spectrum curve of each bond, the absorption information at any two points that are monotonically continuous in the wavelength region with the largest differential coefficient before and after the maximum wavelength [λ ₀ ] is measured,
By performing appropriate arithmetic processing, it becomes possible to correct the scattering component of the substance to be measured (substantially eliminate the scattering component information) and measure the absorption component information more accurately.

[0010]

EXAMPLES Prior to the description of specific examples, the principle of the present invention will be described in more detail.

The object to be measured contains an absorbing substance, and its surface and inside have scattering properties (for example, the object to be measured is formed by impregnating plant fiber as a scatterer with water as a light absorbing substance). It is assumed that the infrared light of two wavelengths (λ ₁ , λ ₂ ) that are close to each other is irradiated.

Here, it is assumed that the scattering degrees of the infrared light λ ₁ and λ ₂ are S ₁ and S ₂ , and the absorption degrees are A ₁ and A ₂ . By irradiating this wavelength λ ₁ and λ ₂ light, the wavelength λ
The scattered reflected light of ₁ and λ ₂ is detected, and the energies of the detected lights are I ₁ and I ₂ . The irradiation light energy is I ₀ ,
When the reflected light energy is I and the scattering degree is represented by S and the absorption degree is represented by A, I = I ₀ · e ^{− (A + S)} (1), so that ln (I ₁ / I ₀ ) = - a _{(a 2 + S 2) ...} (3) - (a 1 + S 1) ... (2) ln (I 2 / I 0) =. When the difference between the expressions (2) and (3) is obtained, ln (I ₁ / I ₀ ) −ln (I ₂ / I ₀ ) = − (A ₁ + S ₁ ) + (A ₂ + S ₂ ) ... (4) ).

Here, if the scattering degrees S ₁ and S ₂ are equal because the wavelengths λ ₁ and λ ₂ are similar, then S ₁ = S ₂ can be obtained, and the equation (4) can be obtained. ln (I ₁ / I ₂₎ is = - a _{(a 1 + a 2) ...} (5). This means that the difference is only in the absorbance, and the absorption information in which the scattering information is substantially eliminated can be obtained by the calculation of the equation (5).

The above principle should not be illustrated with reference to FIGS. 3 and 4.
I will explain. First, as shown in FIG. 3, a light source (not shown)
Energy from₀Illuminates DUT 2 with
Then, the reflected light (energy is I) is detected by the photodetector 3.
To detect. Here, the light source has a wavelength λ ₁, Λ₂Including infrared light
And the filter 4 has a wavelength λ.₁, Λ₂Choose the light of
Then, it is designed to pass through alternatively.

The light having the relative energy I ₀ applied to a certain area of the object to be measured 2 is scattered according to the scattering degrees S ₁ and S ₂ of the object to be measured ₂ and also according to the absorbances A ₁ and A ₂ . The reflected light of the energies I ₁ and I ₂ is incident on the photodetector 3 via the filter 4. The photodetector 3 converts the energy difference between I ₁ and I ₂ into an electric signal and outputs it to the analyzer 5. The analyzer 5 A / D converts the output of the photodetector 3 and sends it to the output device 6, or sends the calculation result of the above equation (5) to the output device 6, and the output device 6 converts these data into a visible image. Display or output.

Here, as shown in FIG.
Assuming that the absorption A has a peak value at the wavelength λ ₀ and a bottom value at the wavelength λ ₃ , the absorption curve has a large differential coefficient at the wavelengths λ ₁ and λ ₂ . On the other hand, as shown in FIG. 4B, the scattering degree S changes gently over the wavelength λ ₀ → λ ₁ → λ ₂ → λ ₃ and is approximately equal at the approximated wavelengths λ ₁ and λ ₂ . . Therefore, by subtracting the contribution of the scattering degree S, only the contribution of the absorbance A can be obtained. The measurement data corresponding to the absorbance A corresponds to the concentration of the substance (light absorbing substance) contained in the DUT 2, and therefore the concentration can be quantified.

Next, the outline of the measuring apparatus and the measuring method according to the present invention will be described.

FIG. 5 is a schematic diagram showing the structure of the apparatus. The measured object 2, which is a sample placed in a container, has a scattering property and an absorptivity. This is illuminated by a tungsten lamp (300 W) which is the light source 1, and this light source 1 outputs light containing infrared light of at least two wavelengths (λ ₁ , λ ₂ ). The two wavelengths are approximate two wavelengths in which there is a large difference in the absorption of the substance to be measured and a large difference in the scattering.
The image of the object 1 to be measured is set by the optical lens system 7 and the filter holder 40.
The image is picked up by the infrared vidicon camera 31 via 2.

Here, the wavelength selection filters 41 and 42 are adapted to transmit only one of the infrared light having the two wavelengths λ ₁ and λ ₂ , respectively, and can be switched alternately by the filter holder 40. When the light source 2 can select and output only the infrared light of λ ₁ and λ ₂ , the wavelength selection filters 41 and 42 described above are not necessary.

The image data of the object 2 to be measured, which has been picked up by the infrared vidicon camera 5, is sent to the image processing device 8, converted into digital data, and then subjected to predetermined processing. That is, the image processing device 8 has at least the image storage unit 81 and the image calculation unit 82, and the image data of the wavelengths λ ₁ and λ ₂ are stored in the image storage unit 81, respectively. Then, the image calculation unit 82 performs a calculation corresponding to FIGS. 4 and (5), that is, a process of eliminating all or most of the contribution of scattering.

The image data obtained by performing the above calculation on the picked-up image data is displayed on the video monitor 91 as necessary or printed by the video printer 92. Thereby, the infrared absorption information of the measured object 2 can be two-dimensionally displayed and grasped.

Specific examples will be described in detail below.

Example 1 As a sample, a silica gel powder of 70 to 250 mesh contained in a container was used. In all the examples, unless otherwise specified, a 300 W × 4 tungsten lamp was used as a light source, an infrared vidicon camera was used as a detector, and an image analysis processing device was used for arithmetic processing. Also, as the wavelength selection optical filter, 1.94 μm
Filters having transmission characteristics of 1.8 μm and 1.68 μm were used.

A portion of the sample was moistened with water, and the image of that portion was taken into the image storage section through the above three types of filters. Next, in the image calculation unit that is the analyzer (1.94μ
m image) / (1.8 μm image) and (1.94 μm image) / (1.68 μm image).

The results are shown in the photographs of FIGS. 7 and 8. Comparing these two figures, it can be seen that the surface roughness of the silica gel looks smaller in FIG. 7 than in FIG. It should be noted that this is clear when looking at the brightness profile of the analyzer. The reason why the graininess in FIG. 7 appears smaller is that the contribution of scattered information is made smaller by the method of the present invention.

Example 2 A small piece of wood partially impregnated with water was used as a sample. 11, 12, 13, and 14 show the results obtained by taking in information in the memory, performing arithmetic processing in the same manner as in Example 1, and outputting the information to the video printer. 11,
12 shows the luminance profile in the horizontal direction, and FIGS. 13 and 14 show the luminance profile in the vertical direction. It can be seen that the method of the present invention reduces the surface scattering component and shows more accurate absorption information. .

Example 3 In Examples 1 and 2, reduction of the underlying surface scattering component in the image of absorption of water (absorption of O—H) was observed, but in this Example 3, together with O—H, C-by polystyrene was used. The absorption images of H absorption (C—H of benzene ring) are simultaneously compared. FIG. 6 shows the infrared absorbance of this water and polystyrene.

As the sample, silica gel powder was used as in Example 1, and polystyrene pieces and water were placed thereon. Then wavelengths of 1.94 μm, 1.8 μm and 1.6
FIGS. 9 and 10 show three images captured by an 8 μm filter into an image memory and subjected to the same calculation as in Example 1.
Shown in. According to the method of the present invention, scattering components are reduced (that is, more accurate quantification of absorption components), and C-H
The absorption and the OH absorption can be simultaneously measured as an inverted image of the luminance signal. This allows so-called qualitative determination of the substance to be measured.

Of course, the method of the present invention can be applied without using a filter even if the wavelength is selected by the light source, and can be applied to other substances having the above-mentioned coupling. Further, if the photodetector is replaced with a one-pixel sensor or a one-dimensional linear sensor, 0-dimensional or one-dimensional measurement can be performed.

[0030]

As described above, the substances to be measured by the present invention are H-O-H, R-O-H, O-D, C-H and N.
Although it has a bond such as -H, the stretching vibration, the overtone of the bending vibration, and the combined sound each have a characteristic absorption spectrum in the near infrared region. Absorbance changes rapidly.

On the other hand, at such wavelengths in the vicinity, the scattering intensities do not greatly vary depending on the scattering substance on the surface or inside of the object to be measured, and are substantially equal. Therefore, in the absorption spectrum curve of each bond, the absorption information at any two points that are monotonically continuous in the wavelength region with a large differential coefficient before and after the maximum wavelength is measured, and appropriate calculation processing is performed to determine the It becomes possible to correct the scattered component in a substantial sense and measure the absorbed component information more accurately.

Therefore, the amount of absorption can be quantified more accurately as compared with a conventional absorption amount measuring type quantification device. If it is used in the two-dimensional mode, more accurate absorption distribution can be known. Moreover, the influence of the shape of the sample is reduced.
Here, in the two-dimensional mode, a general glass optical lens can be used as an input lens to use the near-infrared region, and cooling of the detector is not required, so that the entire apparatus becomes inexpensive. Further, there is also an advantage that it is possible to easily identify objects that have been difficult to identify nondestructively until now.

[Brief description of drawings]

FIG. 1 is a diagram showing the wavelength dependence of infrared absorption.

FIG. 2 is a diagram showing wavelength dependency of infrared absorption.

FIG. 3 is an explanatory view of the principle of the present invention.

FIG. 4 is a diagram showing a relationship between infrared absorption and scattering.

FIG. 5 is an explanatory diagram of an apparatus according to an embodiment of the present invention.

FIG. 6 is a diagram showing the absorbance of water and polystyrene.

FIG. 7 is a photograph showing the measurement results.

FIG. 8 is a photograph showing the measurement results.

FIG. 9 is a photograph showing the measurement results.

FIG. 10 is a photograph showing the measurement results.

FIG. 11 is a photograph showing the measurement results.

FIG. 12 is a photograph showing the measurement results.

FIG. 13 is a photograph showing the measurement results.

FIG. 14 is a photograph showing the measurement results.

[Explanation of symbols]

1 ... DUT, 2 ... Light source, 3 ... Photodetector, 31 ... Infrared vidicon camera, 4, 41, 42 ... Wavelength selection filter,
5 ... Analyzer, 6 ... Output device, 7 ... Optical lens system, 8
Image processing device 81 Image storage unit 82 Image calculation unit 91 Video monitor 92 Video printer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Hiramatsu 1126-1126 Nomachi, Hamamatsu City, Shizuoka Prefecture Hamamatsu Photonics Co., Ltd.

Claims (10)

[Claims] 1. Infrared light having at least two kinds of wavelengths, wherein the difference in absorbance due to substances in the object to be measured is sufficiently large,
And a first step of illuminating the DUT with infrared light having a wavelength in the vicinity of which the scattering degree difference is sufficiently small, and detecting the amount of light reflected from the DUT for each of the at least two types of wavelengths, A second method in which one of the amounts of the reflected light detected for each wavelength is calculated by the other to substantially eliminate the contribution of scattered light, and the degree of absorption of infrared light by the substance in the measured object is measured. A method for measuring infrared light absorbance, comprising: 2. The substance in the object to be measured is OH, C-
The method for measuring infrared light absorption according to claim 1, which is a molecule containing any of H, N-H, and O-D bonds. 3. The infrared light according to claim 1, wherein the concentration of the substance is quantified based on the absorbance of the infrared ray measured in the second step and the absorbance of the substance in the measured object which is obtained in advance. Absorption measurement method. 4. Infrared light of at least two types of wavelengths, wherein the difference in absorbance due to the substances in the object to be measured is sufficiently large,
And a first step of illuminating the DUT with infrared light having a wavelength in the vicinity of which the scattering degree difference is sufficiently small, and capturing an image of reflected light from the DUT for each of the at least two types of wavelengths, One of the reflected light images picked up for each wavelength is image-operated by the other to substantially eliminate the contribution of scattered light, and the distribution of the absorption of infrared light by the substance in the measured object is measured. And a second step of performing the infrared light absorption measurement method. 5. The distribution of the concentration of the substance is quantified based on the distribution of the absorption of infrared light measured in the second step and the distribution of the absorption of the substance in the measured object which is obtained in advance. 4. The method for measuring infrared light absorption according to 4. 6. The substance in the object to be measured is OH, C--
The method for measuring infrared light absorption according to claim 4, which is a molecule containing any of H, N-H, and O-D bonds. 7. Infrared light of at least two types of wavelengths, wherein the difference in absorbance due to the substances in the object to be measured is sufficiently large,
And an illuminating means for illuminating the object to be measured with infrared light having a wavelength in the vicinity of which the difference in scattering degree is sufficiently small; An apparatus for measuring an infrared light absorption rate, comprising: a calculating unit that calculates an image of one of the intensities of the reflected light imaged for each wavelength by the other. 8. The illuminating means comprises OH, CH, N-
For molecules containing either H or OD bonds,
The infrared ray having a plurality of wavelengths having sufficient difference in light absorption and having substantially the same scattering ability is emitted, and the imaging unit captures an image of the reflected light for each of the plurality of wavelengths. Item 7. A measuring device for infrared light absorption according to item 7. 9. The light-absorbing substance concentration in the object to be measured based on the image calculation data obtained by the calculating means and the distribution of the light absorption for each wavelength of the substance in the object to be measured, which is obtained in advance. The infrared light absorption measuring apparatus according to claim 7, further comprising a quantifying means for quantifying the distribution of the. 10. The apparatus for measuring infrared light absorption according to claim 7, further comprising display means for displaying the image calculation data obtained by said calculation means.