JP2003130863A - Optical fiber humidity sensor, and humidity detecting system and respiration detecting system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber humidity sensor of high sensitivity capable of largely changing the intensity of transmitted light in accordance with the change of humidity. SOLUTION: A humidity sensitive clad is formed by mixing an acrylic acid water-soluble polymer including a copolymer, and a deliquescent substance, on a core of a plastic optical fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber humidity sensor using an optical fiber and a humidity detecting system and a respiratory detecting system using the same.

[0002]

2. Description of the Related Art Heretofore, a humidity sensor using a plastic optical fiber has been proposed which uses a moisture sensitive layer containing polyvinyl alcohol as a main component and potassium acetate (or magnesium chloride or sodium hydrogen sulfate) as a cladding. (Japanese Patent Laid-Open No. 5-60689).

[0003]

However, the one using polyvinyl alcohol has a weak hygroscopic property, and the surface of the moisture-sensitive layer or the interface between the moisture-sensitive layer and the core is roughened, or the fiber is bent into a semicircular shape. Therefore, it was necessary to devise to promote the change of transmitted light intensity. Therefore, an object of the present invention is to provide a high-sensitivity optical fiber humidity sensor with a large change in transmitted light intensity according to a change in humidity, and a humidity detection system and a respiration detection system using the same.

[0004]

In order to achieve the above object, in the present invention, a core of a plastic optical fiber is mixed with a water-soluble acrylic acid-based polymer containing a copolymer and a deliquescent substance to obtain a moisture-sensitive material. The optical fiber humidity sensor has a clad. This makes it possible to obtain a highly sensitive optical fiber humidity sensor.

Further, even if the acrylic acid type water-soluble polymer is any of polymethacrylic acid, polyacrylic acid or hydroxyacrylic acid, a highly sensitive optical fiber humidity sensor can be obtained.

Further, even if the deliquescent substance is any one of sodium acetate, potassium acetate, magnesium chloride, calcium chloride, sodium hydrogensulfate, sodium carbonate, potassium carbonate, sodium nitrate, or potassium nitrate, it is highly sensitive. An optical fiber humidity sensor can be obtained.

Further, if the humidity detecting system is formed by using the optical fiber humidity sensor as described above, the humidity detecting system can be made highly sensitive.

If a respiratory detection system is formed by using the optical fiber humidity sensor as described above, a highly sensitive respiratory detection system can be obtained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partial view of an optical fiber humidity sensor 10 according to an embodiment of the present invention, in which the claddings 2 and 4 are sectioned.

A commercially available plastic optical fiber 1 is cut into a predetermined length, and the clad 2 is removed by using an organic solvent (dioxane or the like) to obtain only a polymethylmethacrylate (PMMA) core 3. 100 g of polymethacrylic acid (PMA) and 10 g of sodium acetate in 2000 g of water
The core 3 is dipped in a solution in which 0 g is dissolved and then dried to form the humidity detecting clad 4 on the surface of the core. Both end surfaces of the fiber 1 are polished to be mirror surfaces. In this way, the optical fiber humidity sensor 10 is completed.

The optical fiber humidity sensor 10 thus obtained
Was placed between a light source such as a light emitting diode (LED) and a photodiode (PD) as a light receiving element, and the transmitted light intensity was measured while changing the humidity. A correlation diagram between the humidity and the intensity of transmitted light is shown in FIG. At low humidity, the refractive index of the clad 4 of the optical fiber humidity sensor 10 is higher than that of the core 3, and since the core 3 does not function as a waveguide, most of the light entering the sensor from one end leaks. Sensor 1
It does not reach the other side of 0. However, as the humidity increases, the clad 4 absorbs water and swells, and the density decreases, so that the refractive index decreases. When the refractive index of the clad 4 becomes smaller than that of the core 3, the core functions as a waveguide, and the light incident from one end reaches the other side so that it can be detected by a PD or the like. become. Since the degree of swelling of the clad 4 has a correlation with humidity, the humidity can be monitored by measuring the intensity of transmitted light that has passed through the optical fiber humidity sensor 10. Measured humidity 3
A nearly linear relationship is obtained in the range of 0% to 95%,
It can be seen that the humidity sensor has excellent characteristics. Further, the intensity of transmitted light at a humidity of 95% exceeds 200% with respect to the intensity of transmitted light at a humidity of 30%, which indicates that the intensity is sufficient for a humidity sensor.

Next, a structural example of the humidity detecting system 19 using the optical fiber humidity sensor 10 will be described with reference to FIG.

LD (laser diode) or LED
A light emitting section circuit 11 incorporating a (light emitting diode);
Photodetector circuit 14 incorporating D (photodiode)
And the above-mentioned optical fiber humidity sensor 10 arranged between them, a voltage value / humidity value conversion circuit 15 for converting the output voltage of the light receiving unit circuit 14 into a humidity value determined by an experiment in advance, and this humidity The display circuit 16 is provided for displaying the value on the display 17 in association with the passage of time. The display circuit 16 may be a circuit that causes the display 17 to display only the humidity value from the voltage value / humidity value conversion circuit 15 at that time.

The optical fiber humidity sensor 10 is placed in a certain humidity state for measurement, and the signal light from the light emitting unit circuit 11 passes through the optical fiber humidity sensor 10 and changes in light intensity to enter the light receiving unit circuit 14. . The light receiving unit circuit 14 converts the light intensity into a voltage value and outputs it to the voltage value / humidity value conversion circuit 15. The voltage value / humidity value conversion circuit 15 converts the voltage value into a humidity value, and the display circuit 16 displays the humidity value on the display 17 in association with the passage of time.

FIG. 4 shows the optical fiber humidity sensor 1 described above.
An example of the configuration of the respiratory detection system 29 according to the present invention using 0 is shown.

LD (laser diode) or LED
Light emitting unit circuit 2 for transmitting signal light transmitted by incorporating
The signal light output at 1 is incident on the optical fiber 22.
The signal light incident on the optical fiber 22 is placed under the nostril of the nose 8 and passes through the optical fiber humidity sensor 10 having a cover having a large number of holes, and the optical fiber 23 receives light incorporating a PD (photodiode). The light is received by the partial circuit 24. The light receiving section circuit 24 detects an output voltage corresponding to the intensity of the received transmitted signal light as the transmitted light intensity. Since the signal detected by the light receiving unit circuit 24 is an analog signal, it is converted into a digital signal by the A / D converter 25 to capture the respiratory data, and the waveform of the transmitted light intensity change due to the respiratory is displayed on the display 26. Display it. FIG. 5 shows a detected output voltage waveform displayed on the display 26 of the respiratory detection system 29.

Although polymethacrylic acid is used in the above example, the same effect can be obtained by using a water-soluble polymer such as polyacrylic acid or hydroxyacrylic acid. Although sodium acetate was used as the deliquescent substance in the above example, a deliquescent substance such as potassium acetate, magnesium chloride, calcium chloride, sodium hydrogen sulfate, sodium carbonate, potassium carbonate, sodium nitrate, potassium nitrate was used. However, the same effect can be obtained.

According to the above-mentioned embodiment, the acrylic acid water-soluble polymer containing the copolymer and the deliquescent substance are mixed and used as the clad of the optical fiber humidity sensor. It is possible to obtain a high-sensitivity humidity sensor with a simple structure, without the need to roughen the interface of the fiber, nor to bend the fiber in a semicircular shape, and it is possible to fabricate a humidity detection system and a respiratory detection system using it is there.

[0020]

As described above, in the present invention, an optical fiber in which a moisture-sensitive clad is formed by mixing a water-soluble acrylic acid-based polymer containing a copolymer and a deliquescent substance in the core of a plastic optical fiber. The humidity sensor was used. This makes it possible to obtain a highly sensitive optical fiber humidity sensor.

[Brief description of drawings]

FIG. 1 is a partial view of an optical fiber humidity sensor according to an embodiment of the present invention, in which a clad has a cross section.

FIG. 2 is a correlation diagram of humidity and transmitted light intensity in the optical fiber humidity sensor of FIG.

3 is a configuration diagram of a humidity detection system using the optical fiber humidity sensor of FIG.

4 is a configuration diagram of a respiratory detection system using the optical fiber humidity sensor of FIG.

5 is a waveform diagram showing a voltage waveform displayed on a display of the respiratory detection system shown in FIG.

[Explanation of symbols]

1, 22, 23 optical fiber, 2 clad, 3 core, 4 clad, 10 optical fiber humidity sensor, 11,
21 light emitting part circuit, 14, 24 light receiving part circuit, 15 voltage value / humidity value converting circuit, 16 display circuit, 17, 26
Display, 19 Humidity detection system, 25 A /
D converter, 29 Respiratory detection system.

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[Procedure amendment]

[Submission date] October 23, 2001 (2001.10.
23)

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02B 6/00 G02B 6/00 B 2H050 391 391 391 4C038 F term (reference) 2G042 AA01 BB01 CA01 CA10 CB01 DA10 FA19 FB06 HA02 HA07 2G045 CB22 DB22 FA13 GC10 HA09 JA01 JA07 2G054 AA01 AA06 AA10 AB10 CA11 CE01 EA04 FA07 FA16 FA27 FB02 FB03 GA05 JA01 JA04 2G059 AA01 BB01 CC10 DD03 EE01 GG01 GG02 KK01 PP04 2H038 AA02 2H050 ABA13 AB43 AB01 AB43 AB01 AB04

Claims (5)

[Claims] 1. An optical fiber humidity sensor characterized in that a moisture-sensitive clad is formed by mixing a water-soluble acrylic acid-based polymer containing a copolymer and a deliquescent substance in a core of a plastic optical fiber. 2. The acrylic acid-based water-soluble polymer is any one of polymethacrylic acid, polyacrylic acid, and hydroxyacrylic acid.
The optical fiber humidity sensor described. 3. The deliquescent substance is any one of sodium acetate, potassium acetate, magnesium chloride, calcium chloride, sodium hydrogensulfate, sodium carbonate, potassium carbonate, sodium nitrate, or potassium nitrate. Item 1. The optical fiber humidity sensor according to item 1. 4. A humidity detection system using the optical fiber humidity sensor according to claim 1. 5. A respiratory detection system using the optical fiber humidity sensor according to any one of claims 1, 2 and 3.