JP2016080571A - Particle amount measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particle amount measurement device capable of measuring amount of particles caught on a mesh at a low cost without using any conventional spectrometer or array type optical detector.SOLUTION: A mesh 43 which has a periodic structure is irradiated with a beam of collimated monochromatic light L. Only the light D0, D1, etc., which is diffracted by the periodic structure, is blocked from propagation by a mask 56. Particles caught by the mesh 43 scatters the collimated monochromatic light L in various directions. An optical detector 58 selectively detects the scattered light S only.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an apparatus for measuring the amount of particles such as suspended fine particles such as PM2.5 and suspended particles in droplets.

  As one of methods for measuring the amount of suspended fine particles in air or suspended particles in droplets, there is a method using electromagnetic wave resonance in a mesh as described in Patent Document 1. The outline of this method is as follows. First, as shown in FIG. 1A, a periodic structure (mesh) 101 in which openings 102 corresponding to the size of fine particles to be measured are periodically arranged is prepared, and a predetermined wavelength is directed toward the mesh 101. The transmittance spectrum of the electromagnetic wave that radiates a range of electromagnetic waves and passes through the mesh 101 is measured. In this transmittance spectrum (solid line in FIG. 2), a trough of transmittance due to electromagnetic resonance occurs at a frequency (wavelength) corresponding to the period of the opening 102. Next, the fine particles 103 in the air or droplets are captured by the mesh 101, and the same electromagnetic wave is applied to the mesh 101 (FIG. 1 (b)) on which the fine particles 103 are placed to transmit a transmittance spectrum (in FIG. 2). Measure the broken line. The position (frequency) of the transmittance valley in the transmittance spectrum is shifted (Δf) from the case of the mesh 101 on which the fine particles 103 are not placed. Moreover, the depth of the valley also changes (FIG. 2). By measuring the relationship between the loading amount and shift (and change in depth) of various known fine particles in advance, and preparing a calibration curve as shown in FIG. Can be determined.

WO2012 / 132111 Publication

  In the conventional method, a spectroscope or an array type detector is required to obtain a spectrum of electromagnetic waves that have passed through the mesh. Further, the frequency of the valleys appearing in the transmittance spectrum is determined by the period of the mesh, but when it is necessary to allow fluid to pass through the mesh, the period of the mesh is about several μm in order to give mechanical strength. Corresponding electromagnetic waves are in the mid-infrared to far-infrared region, but a light source having sufficient intensity in such a band and a detector having sufficient sensitivity are generally expensive.

  The problem to be solved by the present invention is to provide an apparatus having a simpler structure and capable of measuring the amount of particles placed on a mesh at a low cost.

The thing of the 1st aspect of the particle amount measuring apparatus based on this invention made in order to solve the said subject is as follows.
a) a light source emitting parallel monochromatic light;
b) a periodic structure in which a periodic structure is formed by a transmitting portion that transmits the monochromatic light and a non-transmitting portion that does not transmit, in a plane arranged to face the light source;
and c) a photodetector provided on the opposite side of the light source with the periodic structure interposed therebetween and in a position behind the diffracted light by the periodic structure.

  FIG. 4 shows a schematic configuration of the particle amount measurement apparatus according to the first aspect of the present invention. The light detector 13 is located on the opposite side of the light source 11 with respect to the periodic structure 12 and deviated from the optical paths D0 and D1 where the parallel monochromatic light L from the light source 11 is diffracted by the periodic structure of the periodic structure 12 (" It is provided at a position behind the diffracted light. In FIG. 4, the periodic structure 12 (the surface on which the periodic structure is formed) is disposed perpendicular to the parallel monochromatic light L from the light source 11, but this may be oblique.

  When the parallel monochromatic light L from the light source 11 is irradiated onto the periodic structure 12, the monochromatic light L is diffracted by the periodic structure in addition to the 0th-order diffracted light D0 passing through the periodic structure as it is. Next diffracted light,... (All solid lines) and light traveling at a predetermined angle. Since the photodetector 13 is provided at a position that is not the optical path of these diffracted lights D0, D1,... ("The position behind the diffracted light"), no light enters the light detector 13 in a normal state.

  On the other hand, when the particles P are present on the periodic structure 12 as shown in FIG. 1B, the parallel monochromatic light L from the light source 11 is scattered by the particles P. Since the scattered light S (broken line) travels in various directions separately from the diffracted light D0, D1,... As described above, it can be detected by the photodetector 13 at the position. In this case, since the amount of light detected by the photodetector 13 corresponds to the amount of particles P existing on the periodic structure 12, the amount of particles P is measured by preparing a calibration curve in advance. can do. In FIG. 4, two photodetectors 13 are provided. Of course, one photodetector may be provided, or more photodetectors 13 may be provided to increase sensitivity.

The thing of the 2nd aspect of the particle amount measuring apparatus based on this invention made in order to solve the said subject is as follows.
a) a monochromatic light source emitting parallel monochromatic light;
b) a periodic structure in which a periodic structure is formed by a transmitting portion that transmits the monochromatic light and a non-transmitting portion that does not transmit, in a plane arranged to face the single-color light source;
c) a mask having a light-shielding portion at the position of the optical path of the diffracted light by the periodic structure, disposed on the opposite side of the light source with the periodic structure interposed therebetween;
d) a condensing lens provided behind the mask;
e) The condensing lens includes a photodetector provided at a position for condensing light from the periodic structure.

  FIG. 5 shows a schematic configuration of the particle amount measuring apparatus according to the second aspect of the present invention. The mask 23 is provided on the opposite side of the light source 21 with respect to the periodic structure 22, and the parallel monochromatic light L from the light source 21 is diffracted by the periodic structure of the periodic structure 22 along the optical paths D0, D1,. A light shielding part 23a is provided at the position. Light in other places is transmitted. 4, the periodic structure 22 (surface on which the periodic structure is formed) is arranged perpendicular to the parallel monochromatic light L from the light source 21 in FIG. 5, but this may be oblique. Absent. Further, the mask 23 may be inclined with respect to the periodic structure 22 as long as the diffracted light D0, D1,. The condensing lens 24 is provided behind the mask 23, that is, on the side opposite to the periodic structure 22 with respect to the mask 23, and the photodetector 25 is disposed further rearward of the condensing lens 24.

  When the parallel monochromatic light L from the light source 21 is applied to the periodic structure 22, the monochromatic light L is diffracted by the periodic structure in addition to the 0th-order diffracted light D0 that passes through the periodic structure as it is. Next diffracted light,..., And light traveling at a predetermined angle. Since the mask 23 has a light shielding portion 23a at the position of the optical path of these diffracted lights D0, D1,..., These diffracted lights D0, D1,.

  On the other hand, when the particles P are present on the periodic structure 22 as shown in FIG. 1B, the parallel monochromatic light L from the light source 21 is scattered by the particles P. Since the scattered light S (broken line) travels in various directions apart from the diffracted light D0, D1,... As described above, it passes through the portion other than the light shielding portion 23a of the mask 23 and travels toward the condenser lens 24. The scattered light S is collected by the condensing lens 24 and enters the photodetector 25. Therefore, the photodetector 25 can detect only the light S scattered by the particles P on the periodic structure 22. Since the amount of light corresponds to the amount of particles P existing on the periodic structure 22, the amount of particles P can be measured by preparing a calibration curve in advance.

The thing of the 3rd aspect of the particle amount measuring device based on this invention made in order to solve the said subject is as follows.
a) a monochromatic light source emitting parallel monochromatic light;
b) a periodic structure in which a periodic structure is formed by a transmitting portion that transmits the monochromatic light and a non-transmitting portion that does not transmit, in a plane arranged to face the single-color light source;
c) a first lens that is disposed on the opposite side of the light source with the periodic structure interposed therebetween and that focuses on the periodic structure;
d) a mask disposed behind the first lens and having a light-shielding portion at the position of the focal point of the diffracted light by the periodic structure;
e) a second lens provided behind the mask;
and f) a photodetector provided at the focal position of the second lens.

  FIG. 6 shows a schematic configuration of the particle amount measuring apparatus according to the third aspect of the present invention. In this aspect, the first lens 33 is first provided behind the periodic structure 32, and then the mask 34, the second lens 35, and the photodetector 36 are disposed. The distance between the periodic structure 32 and the first lens 33 is the focal length f of the first lens 33, and the distance between the first lens 33 and the mask 34 is also the same distance f. The inclination of the first lens 33, the mask 34, and the second lens 35 is allowed as in the above two aspects.

  When the parallel monochromatic light L from the light source 31 is irradiated on the periodic structure 32, the monochromatic light L is diffracted by the periodic structure in addition to the 0th-order diffracted light D0 passing through the periodic structure as it is. Next diffracted light, ... (solid line), and light traveling at a predetermined angle. Since these diffracted lights D0, D1,... Travel in parallel in the respective directions, the first lens 33 condenses these diffracted lights D0, D1,. Therefore, all of the diffracted light D0, D1,...

  On the other hand, when the particles P are present on the periodic structure 32 as shown in FIG. 1B, the parallel monochromatic light L from the light source 31 is scattered by the particles P. The scattered light S (broken line) travels in various directions apart from the diffracted light D0, D1,... As described above, but is made parallel light by the first lens 33 since it starts from the periodic structure 32. Then, the light passes through a portion of the mask 34 other than the light shielding portion 34 a and travels toward the second lens 35. The scattered light from these particles P is collected by the second lens 35 onto the photodetector 36. Since the amount of light measured by the photodetector 36 corresponds to the amount of particles P existing on the periodic structure 32, the amount of particles P can be measured by preparing a calibration curve in advance. it can.

  The particle amount measuring apparatus according to the present invention does not require a conventional spectroscope or array type detector in any aspect, and can measure the particle amount at low cost.

The top view (a) of an example of the periodic structure (mesh) used with a particle amount measuring apparatus, and the top view (b) of the state which the particle | grains adhered. Explanatory drawing which shows the state of the shift of the electromagnetic wave transmission spectrum by particle | grain adhesion on a periodic structure. The figure of an example of the analytical curve which shows the relationship between the frequency shift of an electromagnetic wave transmission spectrum, and the quantity of adhesion particle | grains. BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram of the 1st aspect of the particle amount measuring apparatus which concerns on this invention. The schematic block diagram of the 2nd aspect of the particle amount measuring apparatus which concerns on this invention. The schematic block diagram of the 3rd aspect of the particle quantity measuring apparatus which concerns on this invention. BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram of the particle amount measuring apparatus which is one Example of this invention.

An embodiment of the particle amount measuring apparatus according to the present invention will be described with reference to FIG. This particle amount measuring apparatus is an example according to the third aspect of the present invention.
The particle amount measuring apparatus 40 of the present embodiment is roughly composed of a light source unit 41 and a measuring unit 42, and a mesh mounting unit 45 for mounting a periodic structure (mesh) 43 is provided on the upper part of the measuring unit 42. It has been. The mesh 43 used in the particle amount measuring apparatus 40 of the present embodiment may be a metal net, or may be a net of other materials such as plastic as long as light is diffracted. By placing the mesh 43 in the fluid flow path, particles floating in the fluid can be captured. The amount of particles trapped on the mesh 43 in this way is considered to have a correlation with the amount of suspended particles in the air or fluid.

  The light source unit 41 includes a laser light source 51 and an optical system 52 for widening the light beam from the laser light source 51 in accordance with the size of the mesh 43. When the mesh 43 is small, this widening optical system 52 is not necessary.

  The measurement unit 42 is provided with a first lens 55, a mask 56, a second lens 57, and a photodetector 58 in order from the top, and these are housed in a cylindrical housing 59 whose inner surface is a light absorption surface. ing. The first lens 55 is provided below the surface of the mesh 43 placed on the mesh placement unit 45 (the surface on which the periodic structure is formed) by the focal length f of the first lens 55, and the mask 56 is The first lens 55 is provided below the same distance f. The photodetector 58 is provided at a focal position below the second lens 57.

The operation of the particle amount measuring apparatus 40 of the present embodiment is as described for the third aspect of the present invention (FIG. 6), and here, calculations relating to the diffracted light of this optical system are performed. Assuming that the wavelength of light (monochromatic light) L emitted from the laser light source 51 is λ and the interval (pitch) of the openings of the mesh 43 is d, when the monochromatic light L is incident on the mesh surface at an incident angle α, mth order ( The diffraction angle β of the diffracted light at m = 0, ± 1, ± 2,…) is
d ・ (sinα ± sinβ) ＝ m ・ λ… (1)
It can be calculated from the following formula.

For example, if a mesh 43 of d = 3 μm is used as a mesh for measuring PM2.5, and a laser light source 51 having a wavelength of λ = 0.78 μm is used (this light source is mass-produced for CD, low Can be obtained at a cost.) When the incident angle α = 0, the diffraction angle β is
m = 0 (0th order diffracted light): β = 0 °
m = ± 1 (first-order diffracted light): β = 15.1 °
m = ± 2 (2nd order diffracted light): β = 31.3 °
m = ± 3 (3rd order diffracted light): β = 51.3 °
It becomes. Therefore, if the 0th-order diffracted light and the 1st-order diffracted light are shielded by the light-shielding part 56a of the mask 56 and the second-order or higher-order diffracted light is absorbed by the side wall of the housing 59, The main body can be manufactured with a relatively compact housing.

DESCRIPTION OF SYMBOLS 101 ... Mesh 102 ... Opening 103 ... Fine particle 11, 21, 31, 51 ... Light source 12, 22, 32, 43 ... Periodic structure 13, 25, 36, 58 ... Photodetector 23, 34, 56 ... Mask 23a, 34a , 56a, the light shielding unit 24, the condensing lenses 33, 55, the first lens 35, 57, the second lens 40, the particle amount measuring device 41, the light source unit 42, the measuring unit 45, the mesh placing unit 52, and the widening optical system 59. ... Case

Claims (4)

a) a light source emitting parallel monochromatic light;
b) a periodic structure in which a periodic structure is formed by a transmitting portion that transmits the monochromatic light and a non-transmitting portion that does not transmit, in a plane arranged to face the light source;
and c) a photo detector provided on the opposite side of the light source across the periodic structure and at a position behind the diffracted light by the periodic structure. a) a monochromatic light source emitting parallel monochromatic light;
b) a periodic structure in which a periodic structure is formed by a transmitting portion that transmits the monochromatic light and a non-transmitting portion that does not transmit, in a plane arranged to face the single-color light source;
c) a mask having a light-shielding portion at the position of the optical path of the diffracted light by the periodic structure, disposed on the opposite side of the light source with the periodic structure interposed therebetween;
d) a condensing lens provided behind the mask;
e) a light amount detector provided at a position where the condensing lens condenses light from the periodic structure. a) a monochromatic light source emitting parallel monochromatic light;
b) a periodic structure in which a periodic structure is formed by a transmitting portion that transmits the monochromatic light and a non-transmitting portion that does not transmit, in a plane arranged to face the single-color light source;
c) a first lens that is disposed on the opposite side of the light source with the periodic structure interposed therebetween and that focuses on the periodic structure;
d) a mask disposed behind the lens and having a light shielding portion at the position of the focal point of the diffracted light by the periodic structure;
e) a second lens provided behind the mask;
and f) a photo detector provided at a focal position of the second lens.   4. The particle amount measuring apparatus according to claim 3, wherein the periodic structure, the first lens, the mask, the second lens, and the photodetector are surrounded by a light-absorbing cylinder.

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