CN110006845B - A liquid refractive index measuring instrument based on electrowetting lens - Google Patents

Abstract

The invention proposes a liquid refractive index measuring instrument based on an electrowetting lens, which consists of a hard cavity, a light source, a collimating lens, a liquid measuring cavity, a water inlet, a water outlet, an electrowetting lens and an image sensor . In the initial state, there is no liquid in the liquid measurement cavity, the light source forms a parallel beam after passing through the collimating lens, and the external driving voltage of the electrowetting lens is adjusted, and the light spot is focused on the image sensor plane. After adding the liquid to be tested, the optical path changes, and the light spot cannot be focused on the original image sensor plane. Adjust the external driving voltage of the electrowetting lens again to make the light spot focus on the image sensor plane again. The refractive index of the liquid to be measured can be calculated according to the position of each element and the geometrical optics formula.

Description

A liquid refractive index measuring instrument based on electrowetting lens

1. Technical field

The present invention relates to a liquid refractive index measuring instrument, more particularly, the present invention relates to a liquid refractive index measuring instrument based on electrowetting lenses.

2. Background technology

The refractive index is an important optical parameter of liquid materials, and the accurate measurement of the refractive index of liquids is of great significance in chemical, pharmaceutical, food, petrochemical and other industrial fields. The measurement methods of liquid refraction can be roughly divided into two types: geometrical optics measurement and wave optics measurement. The geometrical optics measurement method is to measure the refractive index according to the law of refraction or the law of reflection by using the phenomenon of refraction or reflection produced by light passing through the liquid surface. This measurement method is relatively simple. The most common measurement instrument based on the geometrical optics method is the Abbe refractometer, which requires a very small amount of liquid to measure, is simple to operate, and has high precision, and the value of the refractive index can be read directly from the dial. However, Abbe refractometers measure according to the principle of total reflection, and the refractive index of the prism used limits the range that can be measured. The wave measurement method is to use the wave nature of light to interfere or diffract the measuring liquid to measure its refractive index. The measurement instruments based on the wave measurement method are generally more complicated and the operation is relatively cumbersome, and the usage of the measurement liquid is more demanding, and it is not suitable for the measurement of the refractive index of rare gold and precious liquids. It is not easy to realize online detection, and the practical engineering application is limited. Therefore, it is urgent to develop a liquid refractive index measuring instrument with low cost, simple operation, accurate measurement and wide measurement range.

3. Content of the Invention

The invention provides a liquid refractive index measuring instrument based on an electrowetting lens.

As shown in FIG. 1 , the liquid refractive index measuring instrument consists of a hard cavity, a light source, a collimating lens, a liquid measuring cavity, a water inlet, a water outlet, an electrowetting lens and an image sensor. Among them, the liquid measurement cavity is composed of two optical lens packages. The water inlet and outlet are symmetrically distributed on the liquid measuring cavity, and the diameter of the water inlet and the water outlet are the same. The geometric centers of the collimating lens, the liquid measuring cavity and the electrowetting lens are on the same line.

和电润湿透镜光焦度

分别为：The measurement principle of the liquid refractive index measuring instrument based on the electrowetting lens is shown in Figures 1 and 2. In the initial state, there is no liquid in the liquid measurement cavity, and the light source forms a parallel beam after passing through the collimating lens, passing through the liquid. Measure the cavity, and then adjust the external driving voltage of the electrowetting lens to focus the light spot on the image sensor plane. After adding the liquid to be tested, the optical path will change. At this time, the light spot cannot be focused on the original image sensor plane. At this time, it is necessary to adjust the external driving voltage of the electrowetting lens to make the light spot focus on the image sensor plane again, as shown in Figure 2. . In the present invention, the distance between the two optical lenses constituting the liquid measuring cavity is t, the refractive indices are n ₁ and n ₂ respectively, and the curvature radii are C ₁ and C ₂ respectively; are n ₃ and n ₄ respectively, the radius of curvature of the liquid-liquid contact surface is C ₃ ; the distance between the center of the liquid measuring cavity and the center of the electrowetting lens is d, and the back focal length of the entire measuring system is B. The optical power of the liquid measurement cavity can be derived from geometric optics

and electrowetting lens power

They are:

The back focal length of the entire measurement system is B can be expressed as:

From the above formulas, it can be known that the refractive index n _x of the liquid to be measured is a function of t, d, B, n ₁ , n ₂ , n ₃ and n ₄ , namely:

n _x = f(t,d,B,n ₁ ,n ₂ ,n ₃ ,n ₄ ,C ₁ ,C ₂ ,C ₃ ) (4)

Among them, C ₁ , C ₂ , n ₁ , n ₂ , n ₃ and n ₄ are known quantities; t, d, and B can be measured directly; C ₃ can be measured according to the curvature of the electrowetting lens and the driving voltage. Through the above formula, the refractive index of the liquid to be measured can be calculated.

The liquid measurement chamber shown in FIG. 1 is composed of two plano-convex lenses. It should be noted that this figure is only schematic, and can be composed of plano-concave lenses or parallel plates according to design requirements, and this content still belongs to the present invention. protected range.

Preferably, the two optical lenses composing the liquid measuring cavity have the same radius of curvature and the same material.

Preferably, when there is no liquid to be measured, the liquid measuring cavity is filled with air, and the refractive index n ₀ =1.000.

Preferably, the diameter R ₁ of the water inlet and the water outlet is smaller than the distance t between the two optical lenses of the liquid measuring cavity.

Preferably, the optical centers of the light source, the collimating lens, the liquid measuring cavity, the electrowetting lens and the image sensor are all located on the same straight line.

4. Description of drawings

FIG. 1 is a side view of the electrowetting lens-based liquid refractometer without measuring liquid.

FIG. 2 is a side view of the electrowetting lens-based liquid refractometer after filling with measuring liquid.

FIG. 3 is an optical simulation simulation diagram of an embodiment of a liquid refractive index measuring instrument based on an electrowetting lens.

FIG. 4 is a schematic diagram illustrating the variation of the driving voltage and the focal length of the electrowetting lens in an embodiment of the liquid refractive index measuring instrument based on the electrowetting lens.

The symbols in the above figures are:

1 hard cavity, 2 light source, 3 collimating lens, 4 liquid measuring cavity, 5 water inlet, 6 water outlet, 7 electrowetting lens, 8 image sensor.

It should be understood that the above drawings are schematic only and are not drawn to scale.

Five, the specific implementation

The following describes an embodiment of a liquid refractive index measuring instrument based on an electrowetting lens proposed by the present invention in detail, and further describes the present invention. It is necessary to point out that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art make some non-essential improvements and The adjustment still belongs to the protection scope of the present invention.

The liquid refractive index measuring instrument based on electrowetting lens is composed of a hard cavity, a light source, a collimating lens, a liquid measuring cavity, a water inlet, a water outlet, an electrowetting lens and an image sensor. Among them, the liquid measurement cavity is composed of two optical lens packages. The water inlet and outlet are symmetrically distributed on the liquid measuring cavity, and the diameter of the water inlet and the water outlet are the same. An embodiment of the present invention is: the hard cavity of the liquid refractive index measuring instrument is made of polymethyl methacrylate (PMMA) material, the outer diameter is 18mm, the length is 72mm, and the inner diameter of the cavity is 1mm; the collimating lens It is made of BK7 optical glass with a radius of curvature of 50mm; the two convex lenses forming the liquid measuring cavity are made of K9 optical glass with a radius of curvature of 150mm. The optical simulation diagram of this embodiment is shown in Figure 3. The model of the electrowetting lens in this embodiment is Arctic 39N0 produced by Varioptic Company, and a schematic diagram of the variation of the driving voltage and the focal length is shown in FIG. 4 . In the initial test state, no liquid is added to the liquid measuring cavity of the liquid refractive index measuring instrument, the light passes through the collimating lens and the liquid measuring cavity, and the external applied voltage of the electrowetting lens is adjusted, so that the light spot received by the image sensor reaches The minimum, at this time, the voltage applied outside the electrowetting lens is 48V. When NaCl solution with a concentration of 2% was added, the voltage applied outside the electro-wetting lens was adjusted to minimize the light spot received by the image sensor again. At this time, the voltage applied outside the electrowetting lens was 53V. The corresponding focal length was obtained by measuring the voltage and focal length of the electrowetting lens, and the refractive index of the NaCl solution was calculated according to the ynu ray tracing method to be 1.348.

Claims (2)

1. An electrowetting lens based liquid refractive index measurement instrument, comprising: the device comprises a hard cavity, a light source, a collimating lens, a liquid measuring cavity, a water inlet, a water outlet, an electrowetting lens and an image sensor; the device comprises a light source, a collimating lens, a liquid measuring cavity, an electrowetting lens and an image sensor, wherein the light source, the collimating lens, the liquid measuring cavity, the electrowetting lens and the image sensor are sequentially arranged at each part in the direction from the light source to the image sensor, and the optical centers of the parts are all positioned on the same straight line; in an initial state, no liquid exists in the liquid measuring cavity, and the external driving voltage of the electrowetting lens is adjusted to focus light spots on the plane of the image sensor; after liquid to be measured is added, adjusting the external driving voltage of the electrowetting lens to enable the light spot to be focused on the plane of the image sensor again; the distance between two optical lenses forming the liquid measuring cavity is t, and the refractive indexes are n respectively₁And n₂The radius of curvature is respectively C₁And C₂(ii) a The refractive indexes of two filling liquids of the electrowetting lens are n respectively₃And n₄The radius of curvature of the liquid-liquid contact surface is C₃(ii) a The distance between the center of the liquid measurement cavity and the center of the electrowetting lens is d, the back focal length of the whole measurement system is B, and then the focal power of the liquid measurement cavity is

And electrowetting lens power

Respectively, are as follows,

the back focal length of the whole measuring system is B,

the refractive index n of the liquid to be measured can be calculated by combining the above formulas_xIn order to realize the purpose,

n_x＝f(t,d,B,n₁,n₂,n₃,n₄,C₁,C₂,C₃)。

2. the liquid refractometer based on the electrowetting lens as claimed in claim 1, wherein the two optical lenses constituting the liquid measuring cavity have the same radius of curvature and material; when no liquid to be measured exists, the filling medium of the liquid measuring cavity is air, and the refractive index n₀＝1.000。

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