CN205669992U - A kind of optical fibre bending sensor of band the air gap - Google Patents

Abstract

The utility model discloses the optical fibre bending sensor of a kind of band the air gap, use single mode step index fiber, including fibre core and covering, an one fixed width and the gap of the degree of depth is offered on the top of optical fiber, constitute the optical fibre bending sensor of band the air gap, the optical fibre bending sensor of band the air gap is pasted onto in measurement structure, opening is laterally, when optical fiber follow measurement structure bend time, change along with angle of bend, also changed by the light intensity of this air gap, by measuring the bending radius being obtained measurement structure by the light intensity attenuation of the air gap.This utility model can directly measure light intensity, it is not necessary to the equipment such as expensive spectroanalysis instrument, improves measurement sensitivity simultaneously.

Description

A kind of optical fibre bending sensor of band the air gap

Technical field

This utility model relates to the optical fibre bending sensor of a kind of band the air gap, belongs to stress-strain measurement technology neck Territory.

Background technology

The bending of structure, is a kind of important parameter.Traditional strain gauge utilizes the relation between strain and curvature Indirectly extrapolating structural curvature, but when structural thickness is relatively thin, strain may be the least, this makes the measurement of strain gauge become to compare Difficulty.

Fibre Optical Sensor, has high temperature resistant, highly sensitive, fast response time, electromagnetism interference, corrosion-resistant, electrical insulating property Energy is good, burn-proof and explosion prevention, volume are little, simple in construction, and is easy to form the advantages such as telemetry network with fibre-optic transmission system (FOTS).Optical fiber Bragg sensor is one of Fibre Optical Sensor study hotspot in recent years, of a relatively high, quite for the precision of structural bending detection In 10 microstrains, the bending radius flexural deformation at below 200m can be detected.When external environment (such as temperature) impact is bigger, additionally Also need to the equipment such as expensive spectroanalysis instrument.The optical fiber surface of intensity modulation type Fibre Optical Sensor is untreated, is only The principle utilizing the optical fiber intensity loss when deep camber macrobend to increase suddenly is made, and therefore, sensitivity is the lowest.

Utility model content

Technical problem to be solved in the utility model is the defect overcoming prior art, it is provided that a kind of band the air gap Optical fibre bending sensor and flexural measurement method, increase a air gap on optical fiber, as photo sensitive area, utilize light loss Consumption is with the diastrophic curvature about Characteristics Detection structure.

For solving above-mentioned technical problem, this utility model provides the optical fibre bending sensor of a kind of band the air gap, including Optical fiber, described optical fiber uses single mode step index fiber, and including fibre core and covering, the refractive index of described fibre core is n₁, radius is a, institute The refractive index stating covering is n₂, radius is R, offer on the top of optical fiber a width be d, the degree of depth be the gap of H, constitute band empty The optical fibre bending sensor in gas gap.

Meet between width d and bending radius W of measurement structure of aforesaid the air gap and limit as follows:

$d<W\&times;arccos\frac{R+W-a}{R+W+a}$

The beneficial effect that this utility model is reached:

The utility model proposes one the air gap of increase on optical fiber, as photo sensitive area, utilize its light loss same Diastrophic relevant characteristic, directly measures angle of bend or radius, can directly measure light intensity, it is not necessary to expensive spectrum The equipment such as analyser, improve measurement sensitivity simultaneously.

Accompanying drawing explanation

Fig. 1 is the optical fibre bending sensor structural representation of band the air gap of the present utility model, before Fig. 1 (a) is for bending Structure, Fig. 1 (b) is structure after bending；

Fig. 2 is the transmission schematic diagram of light in the air gap；

Light intensity attenuation verses figure when Fig. 3 is differently curved degree；

Fig. 4 is the hot spot coordinate on fiber end face；

Fig. 5 is fiber end face glazing strong component schematic diagram；

Fig. 6 is the simulation result in the case of d=1mm.

Detailed description of the invention

Below in conjunction with the accompanying drawings this utility model is further described.Following example are only used for this is clearly described The technical scheme of utility model, and protection domain of the present utility model can not be limited with this.

Shown in optical fibre bending sensor structure such as Fig. 1 (a) of band the air gap of the present utility model, use single mode step light Fibre, including fibre core and covering, the refractive index of fibre core is n₁, radius is a, and the refractive index of covering is n₂, radius is R, upper at optical fiber Portion offer a width be d, the degree of depth be the gap of H, constitute band the air gap optical fibre bending sensor.In figure, n₃For air Refractive index.

Measuring principle of the present utility model is as follows:

Being pasted onto in measurement structure by the optical fibre bending sensor of the band the air gap of above-mentioned design, opening is laterally. As shown in Fig. 1 (b), when optical fiber follow measurement structure bend time, along with the change of angle of bend, by this air gap Light intensity also change, by measuring the bending radius being obtained measurement structure by the light intensity attenuation of the air gap.Such as Fig. 3 institute Showing, during differently curved degree, light intensity attenuation situation is different, and the factor affecting light intensity attenuation mainly has following:

1., when light enters opening from optical fiber, the interface on the left of opening produces R₁Reflection, the light intensity that meter is corresponding is saturating The rate of penetrating is T₁,

According to Fresnel law, transmission coefficient is:

$t_s=\frac{2n_1}{n_1+n_3}---\left(1\right)$

Transmisivity is:

$T_1=\frac{n_3}{n_1}{t}_s^2=\frac{4n_1{n}_3}{{(n_1+n_3)}^2}---\left(2\right)$

2. entering the light of opening, have can enter opposite side optical fiber, and such as the RED sector in Fig. 2 gap, have can not Entering the optical fiber of opposite side, such as the green portion in Fig. 2 intermediate gap, meter can enter the transmisivity of the fibre core of opposite side optical fiber For T₂。

Owing to using single-mode fiber, injecting the light of the air gap from optical fiber, the direction of propagation is perpendicular to fiber openings End face.In triangle Δ OAB, as it is shown in figure 1, O represents the center of circle of bending circle, A represents that light is in side end face, the air gap one On eye point, B represents light incidence point on the opposite side end face of the air gap, it is known that:

R+W+y2=(R+W+y1)/cos θ (3)

Y2=(R+W+y1)/cos θ-R-W (4)

Wherein,

$\mathrm{\&theta;}=\frac{d}{W}$

X, y1 represent abscissa and the vertical coordinate of light eye point on side end face, the air gap one, and y2 represents that light exists The vertical coordinate of the incidence point on the opposite side end face of the air gap, abscissa is identical with eye point, shown in Figure 4, and W represents measurement The bending radius of structure, θ represents the angle of bend of measurement structure.

Hot spot coordinate on fiber end face as shown in Figure 4, when the light through the air gap falls on opposite side end face Coordinate meets:

During-a ＜ x ＜ a,

Light can pass through gap, continues to transmit in optical fiber.

In view of in single mode step index fiber, the distribution of relative light energy, meet following relation:

$\mathrm{\&delta;}={E_r}^2=J_0^2\left(U\frac{r}{a}\right)/J_0^2\left(U\right)---\left(5\right)$

Wherein, J₀() is zero Bessel function, and a is fiber core radius, and r is radial distance in optical fiber, value model Enclose for-a ＜ r ＜ a.U is a nondimensional amount, and its value is determined by following formula:

$\frac{{\mathrm{UJ}}_1\left(U\right)}{J_0\left(U\right)}=\frac{\sqrt{V^2-U^2}{K}_1\left(\sqrt{V^2-U^2}\right)}{K_0(V^2-U^2)}---\left(6\right)$

Wherein: J₀(·)、J₁() is respectively zeroth order, first-order bessel function, K₀(·)、K₁() be respectively zeroth order, one Rank Hankel function；V is the normalized frequency of optical fiber, and its value is:

$V=\frac{2\mathrm{\&pi;}a}{\mathrm{\&lambda;}}\sqrt{{n_1}^2-{n_2}^2}---\left(7\right)$

λ is operation wavelength.

Then:

$T_2=\frac{{\&Integral;}_{-a}^a{\&Integral;}_{-\sqrt{a^2-x^2}}^{\sqrt{a^2-x^2}}dy2dx}{{\&Integral;}_{-a}^a{\&Integral;}_{-\sqrt{a^2-x^2}}^{\sqrt{a^2-x^2}}dy1dx}=\frac{{\&Integral;}_{-a}^a{\&Integral;}_{-a}^{(R+W+\sqrt{a^2-x^2})\cos \left(\mathrm{\&theta;}\right)-(R+W)}{E_r}^{2}dy1dx}{{\&Integral;}_{-a}^a{\&Integral;}_{-\sqrt{a^2-x^2}}^{\sqrt{a^2-x^2}}{E_r}^{2}dy1dx}---\left(8\right)$

3., when light enters optical fiber from the air gap, the end face of opposite side optical fiber produces reflection R₃, cause light intensity loss, Counting this part transmisivity is T₃。

Light portion energy in optical fiber can pass through opening, continues to transmit in optical fiber.

The angle of incidence entering the light on opposite side fiber end face is α₁=θ, then according to the law of refraction, refraction angle is:

${\mathrm{\&alpha;}}_2=\arcsin \left(\frac{n_3}{n_1}{\mathrm{sin\&alpha;}}_1\right),---\left(9\right)$

As it is shown in figure 5, the photolysis inciding fiber end face isThe pattern of two direction of vibration.

Wherein,Parallel with fiber end face, according to Fresnel law, transmisivity is:

${T_3}^x=\frac{n_1}{n_3}|\frac{2n_3{\mathrm{cos\&alpha;}}_1}{n_3{\mathrm{cos\&alpha;}}_1+n_1{\mathrm{cos\&alpha;}}_2}{|}^2---\left(10\right)$

Resolve into the both direction being parallel to end face He being perpendicular to end face, be parallel to the transmisivity of fiber end face Identical with above formula, the transmisivity of vertical fiber end face is:

${T_3}^y=\frac{n_1}{n_3}|\frac{2n_3{\mathrm{cos\&alpha;}}_1}{n_3{\mathrm{cos\&alpha;}}_2+n_1{\mathrm{cos\&alpha;}}_1}{|}^2---\left(11\right)$

It is assumed thatEnergy is identical, and the most whole transmisivity is:

T₃=(1+cos²α₁)T₃ ^x+sin²α₁·T₃ ^y (12)

4., owing to being single-mode fiber, the only light along shaft axis of optic fibre transmission can be obtained by detector, transmission light intensity is divided Solving as along shaft axis of optic fibre part of propagation with along optical fiber radial transport part, the light intensity that finally can be obtained by detector is for along optical fiber Axis propagation part, the transmisivity of this part is T₄:

T₄=cos α₂ (13)

Whole light by the absorbance of the air gap is:

T=T₁T₂T₃T₄ (14)

Then light intensity attenuation is: p=10log₁₀(1-T)

Thus, the bending radius of measurement structure has been obtained and through the relation between the light intensity attenuation of the air gap.

When bending radius diminishes, the light good general being again introduced into fiber-optic transfer through the air gap dies down, until all of Light all cannot be again introduced into optical fiber.

Therefore, for needing to meet following restriction between the bending radius (W) of air gap width (d) and measurement structure:

$d<W\&times;arccos\frac{R+W-a}{R+W+a}---\left(15\right)$

As shown in Figure 6, in the case of air gap width d=1mm, angle of bend and the simulation curve of light intensity attenuation.

The above is only preferred implementation of the present utility model, it is noted that for the common skill of the art For art personnel, on the premise of without departing from this utility model know-why, it is also possible to make some improvement and deformation, these change Enter and deform and also should be regarded as protection domain of the present utility model.

Claims (2)

1. the optical fibre bending sensor of a band the air gap, it is characterised in that include optical fiber, described optical fiber uses single mode step Optical fiber, including fibre core and covering, the refractive index of described fibre core is n₁, radius is a, and the refractive index of described covering is n₂, radius is R, Offer on the top of optical fiber a width be d, the degree of depth be the gap of H, constitute band the air gap optical fibre bending sensor.

The optical fibre bending sensor of a kind of band the air gap, it is characterised in that described the air gap Width d and bending radius W of measurement structure between meet following restriction:

$d<W\&times;arccos\frac{R+W-a}{R+W+a}$