CN203772683U - Liquid surface tension coefficient measuring device based on optical fiber FP (Fluorescence Polarization) cavity - Google Patents

Abstract

The liquid surface tension coefficient measuring device based on an optical fiber FP cavity disclosed by the utility model adopts a wide spectrum with a center wavelength of 1550 nm as a light source for measurement, and uses a single-mode hollow-core optical fiber as an FP cavity, and the liquid to be measured enters the hollow core under capillary action The optical fiber changes the length of the air cavity of the hollow-core fiber, that is, the FP cavity, resulting in a change in the interference fringes of the output light. By monitoring this change, the surface tension coefficient of the measured liquid can be obtained. The utility model has the advantages of: the surface tension coefficient of the liquid can be accurately measured by using the interference fringe changes of light, the measurement accuracy is high, the structure is simple, and the use is convenient, which avoids the low accuracy and controllability caused by the difference in individual operation in the traditional measurement method. Poor sex and other shortcomings. The method is suitable for scientific research, medicine and other occasions where the surface tension coefficient of liquid needs to be measured quickly and accurately.

Description

Liquid Surface Tension Coefficient Measuring Device Based on Optical Fiber FP Cavity

technical field

The utility model belongs to the field of liquid surface parameter measurement, in particular to a measuring device capable of measuring the surface tension coefficient of liquid.

technical background

Liquid surface tension determines the flow ability and characteristics of liquid substances, and is the source of power for liquid substances in microscopic capillaries to invade solid substances. It has long been highly concerned by researchers in the field of fluid materials at home and abroad. The traditional methods for measuring the surface tension coefficient of liquids include pull-off method, hanging ring method, drop weight method, capillary rise method, etc. These methods, due to the poor controllability of the measurement intermediate parameters and the differences in individual operations with manual participation, lead to slow measurement speed. , low precision, unable to meet the needs of the application field. In recent years, with the rapid development of optical fiber sensing technology, the application of optical fiber technology in the measurement of liquid surface tension has also received attention. Using optical fiber sensing technology to achieve non-contact measurement of liquid surface tension coefficient has real-time, fast, high-precision Etc. Some researchers have used the capillary waves on the surface of the liquid to be measured combined with the principle of free space light interference to measure the surface tension coefficient of the liquid. However, this method has a large amount of calculation, and is affected by the measurement environment and other aspects. The accuracy of the measurement results is not high and the reliability is low. .

The utility model adopts optical fiber Bragg grating and hollow-core optical fiber as the sensor head for measuring liquid surface tension coefficient, and adopts a wide-spectrum light source with a center wavelength of 1550nm as the light source for measurement. When the liquid to be measured enters the hollow-core optical fiber under capillary action, changes The length of the air cavity of the hollow-core fiber, that is, the FP cavity, causes the spacing of the output light interference fringes to change, and the surface tension coefficient of the measured liquid can be obtained by monitoring the change. The measurement method can obtain the measurand only by detecting the change of the interference fringes of light, avoiding the disadvantage of poor controllability of intermediate variables in traditional measurement, and has the advantages of high measurement accuracy, simple structure, and convenient measurement.

Contents of the invention

The purpose of the utility model is to propose a device for measuring the surface tension coefficient of optical fiber liquid with simple structure and high measurement accuracy.

The technical solution of the present utility model is as follows:

The liquid surface tension coefficient measuring device based on the optical fiber FP cavity is characterized in that it includes a wide-spectrum light source, an optical circulator, a liquid surface tension measuring sensor head composed of an optical fiber Bragg grating and a hollow-core optical fiber, and a spectrum analyzer. The optical circulator has three ports, in which the input port is connected to the wide-spectrum light source, the output port is connected to any end of the fiber Bragg grating, the reflection port is connected to the spectrum analyzer, and the other port of the fiber Bragg grating is connected to any end of the hollow-core fiber .

In the utility model, the operating wavelength of the mentioned broadband light source is 1530nm-1570nm; the mentioned liquid surface tension measurement sensing head is composed of a fiber Bragg grating and a hollow-core optical fiber, wherein the length of the hollow-core optical fiber is 1mm-1570nm. 10mm.

The beneficial effects of the utility model are:

The liquid surface tension coefficient measuring device based on the optical fiber FP cavity of the utility model is suitable for measuring the surface tension coefficient of the liquid, and the liquid surface tension coefficient can be accurately obtained only by the change of the interference fringes of the light, and the measurement accuracy is high, the structure is simple, and the use It is convenient and avoids the shortcomings of low precision and poor controllability caused by differences in individual operations in traditional measurement methods.

Description of drawings

Fig. 1 is a schematic structural diagram of a liquid surface tension coefficient measurement device based on an optical fiber FP cavity.

Detailed ways

Below in conjunction with accompanying drawing, the utility model is further described.

Referring to Fig. 1, the optical fiber FP cavity liquid surface tension coefficient measurement device includes a wide-spectrum light source 1, an optical circulator 2, a liquid surface tension measurement sensor head composed of a fiber Bragg grating 3 and a hollow fiber 4, and a spectrum analyzer 5 . The optical circulator 2 has three ports, wherein the input port is connected to the wide-spectrum light source 1, the output port is connected to any end of the fiber Bragg grating 3, the reflection port is connected to the spectrum analyzer 5, and the other port of the fiber Bragg grating 3 is connected to the air. Any end of the core fiber 4 is connected.

The working wavelength of the above-mentioned broadband light source is 1530nm-1570nm; the liquid surface tension measurement sensor head is composed of a fiber Bragg grating 3 and a hollow-core fiber 4, wherein the length of the hollow-core fiber 4 is 1mm-10mm.

The utility model is based on the following principles:

Drop the liquid to be tested on the glass slide placed on the movable platform, adjust the movable platform so that the liquid surface touches the sensor head placed vertically, the capillary action makes the liquid surface enter the air hole of the hollow-core optical fiber, and the degree of entry is the same as the measured The coefficient of surface tension of the liquid. The surface tension coefficient γ of the liquid can be expressed as:

$\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; mg</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, F is the surface tension of the liquid, s is the perimeter of the rising liquid surface, m is the mass of the liquid entering the hollow-core fiber, g is the acceleration of gravity, and F _p is the pressure of the air in the FP cavity on the liquid surface. Theoretical research shows that F _p >> mg, so the formula (1) can be simplified as

$\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula, P ₀ is the external atmospheric pressure, L and L ₀ are the length of the air cavity (FP cavity) and the length of the hollow-core fiber, respectively, and r is the core radius of the hollow-core fiber.

After the measurement light passes through the FP cavity, the relationship between the distance Δλ of its interference fringes and the length L of the air cavity can be expressed as:

$\mathrm{<span\; class="notranslate">\; \&Delta;\&lambda;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; nL</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula, λ is the central wavelength of the measurement light, n is the refractive index of the gas in the hollow-core fiber, and the cavity is air here, so n=1.

Combining formula (2) and formula (3), the relationship between the liquid surface tension coefficient and the interference fringe spacing can be expressed as follows:

$\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&lambda;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

In the formula, L ₀ , P ₀ , λ, and r are all known quantities, and they do not change with the change of the measured liquid. When measuring, observe the interference fringes in the spectrum analyzer caused by the contact of the sensor head with different measured liquids The change of the liquid surface tension coefficient γ can be measured.

Claims (3)

1. A liquid surface tension coefficient measuring device based on an optical fiber FP cavity, characterized in that it includes a wide-spectrum light source (1), an optical circulator (2), a liquid surface composed of a fiber Bragg grating (3) and a hollow-core optical fiber (4) Tension coefficient measurement sensor head, spectrum analyzer (5), and optical circulator (2) have three ports, wherein the input port is connected to the wide-spectrum light source (1), and the output port is connected to any end of the fiber Bragg grating (3) , the reflection port is connected to the spectrum analyzer (5), and the other port of the fiber Bragg grating (3) is connected to any end of the hollow-core fiber (4). the 2. The liquid surface tension coefficient measuring device based on an optical fiber FP cavity according to claim 1, characterized in that the operating wavelength of the broadband light source (1) is 1530nm-1570nm. the 3. according to the liquid surface tension measuring device based on optical fiber FP cavity according to claim 1, it is characterized in that the liquid surface tension measuring sensing head is made up of fiber Bragg grating (3) and hollow-core optical fiber (4), wherein The length of the hollow-core optical fiber (4) is 1mm-10mm. the