阅读说明：本技术 一种基于散斑相关性提高传感器灵敏度的方法 (Method for improving sensitivity of sensor based on speckle correlation ) 是由 杨玉峰 韩香 于 2021-07-02 设计创作，主要内容包括：本发明公开的一种基于散斑相关性提高传感器灵敏度的方法,通过数字散斑相关性测量系统的图像采集模块来获得变形前后的数字图像。典型的数字散斑相关性分析技术的图像采集系统中主要部件包括光源、光学元件、相机以及计算机。将相机放置在被测试样的正前方,保证相机的光轴垂直于被测物体表面,从而获取清晰完整的图像。通过相机拍摄,对从被测物体表面反射形成的散斑图样进行连续采集取样。采用点测式传感器避免探测多模光纤处受到的环境变化,减弱了多模光纤本身不稳定带来的影响。本发明高阶模式会在单模光纤和多模光纤的耦合处被激发,产生多模干涉散斑,用于传感探测,本发明提出的测点式光纤传感器比传统的光纤传感器灵敏度更高。(The invention discloses a method for improving the sensitivity of a sensor based on speckle correlation. The image acquisition system of a typical digital speckle correlation analysis technique has major components including a light source, optical elements, a camera, and a computer. The camera is placed right in front of the tested sample, and the optical axis of the camera is perpendicular to the surface of the tested object, so that a clear and complete image is obtained. And shooting by a camera, and continuously collecting and sampling speckle patterns formed by reflecting from the surface of the measured object. The point measurement type sensor is adopted to avoid detecting the environmental change suffered by the multimode fiber, and the influence caused by the instability of the multimode fiber is weakened. The high-order mode of the invention can be excited at the coupling position of the single-mode fiber and the multimode fiber to generate multimode interference speckles for sensing detection.)

1. A method for improving sensor sensitivity based on speckle correlation is characterized by comprising the following steps:

step 1: the digital images before and after deformation are obtained through an image acquisition module of a digital speckle correlation measurement system, the main components of the image acquisition system of a typical digital speckle correlation analysis technology comprise a light source, an optical element, a camera and a computer, the speckle image before environmental condition change is called a reference image, the speckle image after sample deformation or condition change is called a target image, after a plurality of groups of data are acquired, a set digital speckle correlation analysis program is used for calculation, and change information in the object surface or transmission conditions is reversely deduced through serial calibration work;

step 2: the speckle correlation is analyzed by using a normalized covariance function, in the speckle correlation analysis method, different correlation functions may correspond to different calculation precision and convergence speed, which may affect the calculation speed and accuracy of the sensor response, and what is described by using the normalized covariance correlation function is the matching degree between the reference image and the sample image:

wherein, I_R(k,l,t₀) Is the parameter speckle and target speckle collected at pixel point (k, l) at t₀Light intensity at time, I₀(k, l, t) is the intensity of the parameter speckle and the target speckle collected at the pixel point (k, l) at time t, t₀Is the initial time, t is the target speckle acquisition time after the condition change,andrespectively, the average light intensity values of the speckle patterns; m is the number of horizontal pixel grids, and N is the number of horizontal and vertical pixel grids; k is a first pixel grid in the transverse direction, and l is a first pixel grid in the longitudinal direction; the correlation function C is a common statistical scale, which is used to measure the correlation and the independence of a series of variables, and explains the statistical relationship between a plurality of groups of values, the normalized covariance correlation function can be used to measure the linear relationship between two groups of variables, and when two images have the same characteristics, C is 1; if the two images are completely inconsistent, C is 0;

and step 3: by using the change of speckles, recording speckle patterns at different moments, comparing and analyzing the speckle patterns at different moments with the original patterns to obtain a correlation coefficient C, summarizing the change rule of C, and reversely deducing the state of an environment variable;

and 4, step 4: a high-order mode is coupled and excited to be led into the multimode fiber between the single-mode fiber and the multimode fiber by using a dislocation fusion method, a connecting point between the single-mode fiber and the multimode fiber is a sensing point to obtain a randomly distributed speckle pattern, and a point measurement type sensor is adopted to avoid detecting environmental changes suffered by the multimode fiber and weaken the influence caused by instability of the multimode fiber.

2. The method for improving the sensitivity of the sensor based on the speckle correlation as claimed in claim 1, wherein the image acquisition system method in step 1 is to place the camera right in front of the sample to be tested, ensure that the optical axis of the camera is perpendicular to the surface of the object to be tested, so as to obtain a clear and complete image, and during the process, the camera is used for shooting, and continuously acquiring and sampling the speckle pattern formed by reflection from the surface of the object to be tested.

3. The method according to claim 1, wherein in step 2, if there is a linear correlation change between the gray scale of the reference image and the gray scale of the target image, the correlation function can better evaluate the similarity between the reference image and the target image according to the invariance principle of the normalized covariance correlation function on the linear transformation of the gray scale, so that when the external environmental conditions change, the speckle also changes, and the correlation function value between the target speckle and the reference speckle is smaller than 1 and becomes smaller as the difference increases, and the change factor of the sensing scene can be quantitatively measured through the relationship.

Technical Field

The invention belongs to the technical field of optical fiber sensing, and relates to a method for improving the sensitivity of a sensor based on speckle correlation.

Background

Fiber optic sensors have found wide application in many fields. Fiber bragg grating sensors (FBS) and the like, which are excellent in the field of sensing and detection, mainly need to work in cooperation with the measurement of a spectrometer, and the performance of the sensors depends on the wavelength shift detection of an output spectrum, but have the disadvantage that a large and expensive spectrometer needs to be equipped.

Disclosure of Invention

The invention aims to provide a method for improving the sensitivity of a sensor based on speckle correlation, which solves the problem of insufficient sensitivity of the sensor based on spectrometer measurement in the prior art.

In order to achieve the purpose, the invention adopts the following technical scheme: a method for improving sensor sensitivity based on speckle correlation comprises the following steps:

step 1: the digital images before and after deformation are obtained through an image acquisition module of a digital speckle correlation measurement system, the main components of the image acquisition system of a typical digital speckle correlation analysis technology comprise a light source, an optical element, a camera and a computer, the speckle image before environmental condition change is called a reference image, the speckle image after sample deformation or condition change is called a target image, after a plurality of groups of data are acquired, a set digital speckle correlation analysis program is used for calculation, and change information in the object surface or transmission conditions is reversely deduced through serial calibration work;

step 2: the speckle correlation is analyzed by using a normalized covariance function, in the speckle correlation analysis method, different correlation functions may correspond to different calculation precision and convergence speed, which may affect the calculation speed and accuracy of the sensor response, and what is described by using the normalized covariance correlation function is the matching degree between the reference image and the sample image:

wherein, I_R(k,l,t₀) Is the parameter speckle and target speckle collected at pixel point (k, l) at t₀Light intensity at time, I₀(k, l, t) is the intensity of the parameter speckle and the target speckle collected at the pixel point (k, l) at time t, t₀Is the initial time, t is the target speckle acquisition time after the condition change,andrespectively, the average light intensity values of the speckle patterns; m isThe number of horizontal pixel grids, and N is the number of horizontal and vertical pixel grids; k is a first pixel grid in the transverse direction, and l is a first pixel grid in the longitudinal direction; the correlation function C is a common statistical scale, which is used to measure the correlation and the independence of a series of variables, and explains the statistical relationship between a plurality of groups of values, the normalized covariance correlation function can be used to measure the linear relationship between two groups of variables, and when two images have the same characteristics, C is 1; if the two images are completely inconsistent, C is 0;

and step 3: by using the change of speckles, recording speckle patterns at different moments, comparing and analyzing the speckle patterns at different moments with the original patterns to obtain a correlation coefficient C, summarizing the change rule of C, and reversely deducing the state of an environment variable;

and 4, step 4: according to the method, a high-order mode is coupled and excited to be led into the multimode fiber by using a dislocation fusion method between the single-mode fiber and the multimode fiber, a connecting point between the single-mode fiber and the multimode fiber is a sensing point to obtain a randomly distributed speckle pattern, a point measurement type sensor is adopted to avoid detecting environmental changes suffered by the multimode fiber, and the influence caused by instability of the multimode fiber is weakened.

Preferably, the image acquisition system method in step 1 is to place the camera right in front of the sample to be tested, and ensure that the optical axis of the camera is perpendicular to the surface of the object to be tested, so as to obtain a clear and complete image.

Preferably, if there is a linear correlation change between the gray scale of the reference image and the gray scale of the target image in step 2, the correlation function can still better evaluate the similarity degree between the reference image and the target image according to the invariance principle of the normalized covariance correlation function on the linear gray scale transformation, so that when the external environmental condition changes, the speckle also changes, the correlation function value between the target speckle and the reference speckle is smaller than 1 and becomes smaller as the difference increases, and the change factor of the sensing scene can be quantitatively measured through the relationship.

By adopting the technical scheme of the invention, the invention has the beneficial effects that: compared with the prior art, the high-order mode of the invention can be excited at the coupling position of the single-mode fiber and the multimode fiber to generate multimode interference speckles for sensing detection. The optical fiber speckle sensor has obvious advantages relatively, a spectrometer is not needed to be matched, a small and light camera can complete sensing and detecting tasks, the single-mode-multimode optical fiber coupling model is adopted in the measuring point type sensor, the measuring point type sensor is more stable than other models utilizing light action, the environment change suffered by detecting multimode optical fibers can be avoided, the influence caused by instability of the multimode optical fibers is weakened, and the sensitivity of the sensor is improved.

Detailed Description

Preferred embodiments of the present invention are described. A method for improving sensor sensitivity based on speckle correlation comprises the following steps:

step 1: and acquiring digital images before and after deformation through an image acquisition module of the digital speckle correlation measurement system. The image acquisition system of typical digital speckle correlation analysis technology mainly comprises a light source, an optical element, a camera, a computer and the like, wherein the camera is placed in front of a sample to be tested, and the optical axis of the camera is ensured to be vertical to the surface of the object to be tested, so that clear and complete images are acquired;

step 2: the speckle correlation is analyzed using a normalized covariance function. In the speckle correlation analysis method, different correlation functions may correspond to different calculation precision and convergence speed, which may affect the calculation speed and accuracy of the sensor response to some extent, and the normalized covariance correlation function describes the matching degree between the reference image and the sample image:

wherein, I_R(k,l,t₀) And I₀(k, l, t) are the parameter speckle and target speckle collected at pixel point (k, l) at t, respectively₀And the light intensity at time t (t)₀Is the initial time, t is the target speckle acquisition time after the condition change),andthe correlation function C is a common statistical scale and is used for measuring the correlation and the independence of a series of variables, the statistical relationship among a plurality of groups of values is explained, the normalized covariance correlation function can be used for measuring the linear relationship between two groups of variables, and when two images have the same characteristics, C is 1; if the two images are completely inconsistent, C is 0, if linear correlation change exists between the gray scale of the reference image and the gray scale of the target image, the correlation function can still better evaluate the similarity degree between the reference image and the target image according to the invariance principle of the normalized covariance correlation function on the linear transformation of the gray scale, so when the external environment condition changes, the speckle also changes, the correlation function value of the target speckle and the reference speckle is smaller than 1 and becomes smaller along with the increase of the difference, and the change factor of the sensing scene can be quantitatively measured through the relation;

and step 3: by using the change of speckles, recording speckle patterns at different moments, comparing and analyzing the speckle patterns at different moments with the original patterns to obtain a correlation coefficient C, summarizing the change rule of C, and reversely deducing the state of an environment variable;

and 4, step 4: according to the method, a high-order mode is coupled and excited to be led into the multimode fiber by using a dislocation fusion method between the single-mode fiber and the multimode fiber, a connecting point between the single-mode fiber and the multimode fiber is a sensing point to obtain a randomly distributed speckle pattern, the point measurement type sensor can avoid detecting environmental changes suffered by the multimode fiber, and the influence caused by instability of the multimode fiber is weakened. In design, higher-order modes are excited at the coupling of the single-mode fiber and the multimode fiber, and multimode interference speckles are generated for sensing detection.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present invention or directly or indirectly applied to other related technical fields are included in the scope of the present invention.