A Study on the Braided Fabrication of Fiber Bragg Grating sensor

This study's objective was to propose the use of textile braiding manufacturing methods, thus facilitating the application of the high precision and accurate measurability of optical fiber Bragg grating sensors to various structures. The purpose of this study was to Combine 3d braid processing with the optical Bragg grating sensor's accurate metrology. Out of limits of the sensor's epoxy attachment methods, the textile braiding method can make applicable scope diversify. The braiding processing is capable of designing a 3D fabric module processing, multiple objective mechanical fiber arrangement, and material characteristics. Optical stress-strain response conditions were explored through the optimization of design elements between the Bragg grating sensor and braiding. For this study, Bragg grating sensors were located 75% apart from the fiber center. The sensor core structure is helical of 1.54 pitch. A polyurethane synthetic yarn was braided together with the sensor on the Weaving machine core part in a braiding. Prototyping results, a negative Poisson's ratio makes curled the braided Bragg grating sensor. The number of polyurethane string yarns has been conducted the role of wrap angle in braiding. The 12 strands condition showed an increase in double stress-strain response rate at a Poisson ratio of 1.3%, and 16 strands condition was found to affect the sensor with noise at a Poisson ratio of 1.5%. This study can suggest applying braid processing of the Bragg grating sensor, which is expected to create and develop a new monitoring sensor.

refractive index changes when a portion of an optical fiber core to which germanium or boron is added is exposed to an ultraviolet laser. The optical fiber grating element can induce periodic refractive index changes in the optical fiber core portion based on light sensitivity, thereby causing changes in light reflection or transmittance [1].
Where is the effective refractive index of the optical fiber grating, which means At this time, the wavelength variation induced by the change in the spacing of the optical fiber Bragg grating, which is measured by the complex factors of the displacement, curvature along the axis, and the elastic point that can be explained by the laws of physics and the imposed load. A detection method capable of quantitative analysis has a characteristic in which an external force changes the center frequency.

Braiding mechanical structure
While braiding, a bundle of three or more fibers is connected continuously without cutting. All threads are gathered upwards in the center of the track .and then stretched in the vertical direction to form a braid. There are two or more tracks, each with a group of spindles moving in different directions. The angled braid is characterized in that the continuous threads have a structured design element and become a columnar structure. 3d weaving of complicated purpose fabrics is possible and has been applied to various industries. [5] Braiding, one of the methods for weaving composite fibers, can be fabricated in the desired direction depending on the strength and stiffness of the desired structure.
The braid enables the continuous orientation of the fibers, allowing the mechanical prop-

Design of the braided Sensor
The core of the sensor used for this study was designed to optimize the blade. This The Bragg grating engraved sensor was attached to the plastic optical fiber with epoxy. When weaving tubular blading, it was fabricated by inserting it together into the bladder core yarn with irradiation of elastic pieces. The outer yarn was made of polypropylene fiber, and the blade angle was woven with a uniform distribution of 45 degrees.
The elastic knitting was investigated so that the number of strings for the same yarn of 12string and 16string could be uniformly distributed to the braided core yarn. The elastic piece irradiation was spirally wound around the tubular bladder core yarn, and an initial angle value of 45 degrees of blading was designated at four uniformly distributed points.
All threads were assembled upwards in the center of the orbit and bladed vertically. Three orbits were used, and a blade machine with eight spindle groups moving in different directions was used.
The below figure 1 is an explanatory diagram of the prototype to be used in this experiment. The braiding was composed of polyester nylon. Polyurethane yarn was used in between the braiding yarn and the flexible sensor rod To maintain the uniform internal tension. In other words, the anxiety decreases for the direction of a move of the load and increases the vertical direction and has a positive Poisson's ratio. In Figure 2 below, the principle of Poisson's ratio was explained by connecting the angle and pitch of the wrap angle with tubular braiding. In this experiment, two braided angles and wrap angles are applied to explore the structural principle that negatively affects Poisson's ratio. It is a common phenomenon that the material tends to become thinner when stretched. Rarely, some materials contract or stretch when stretched horizontally, indicating a negative value of the Poisson's ratio (PR). PR is called' auxetics. The negative Poisson's ratio enables the stiffness and resistance to be actively increased to respond to external stress action loads [6].

Subject
The sensor unit length (1 cm) and angle (1 degree) were measured before and after the blading. And the maximum and minimum values of the stress-strain response were investigated.

Experimental device and tools
For the protocol, the sensor strain measurement behavior was controlled using a device having an angle, and length adjustment range used for stage setup was used. It can be adjusted manually and has a 1mm and 1-degree adjustment resolution. The metronome controlled the speed of the experiment. 10 kHz measurable interrogator figure 3 ((a)c) was used to enable real-time monitoring measurements. Figure. 3. this shows the measurement equipment used in the experiment. Figure 3 B is a fanout that can accurately connect the laser and Bragg wavelength shift to the interrogator with a Bragg grating core. figure 3 A, (c)) is a passive optical machine with a 1 mm resolution. Figure 3 C is the 10 kHz interrogator, and Figure 3 (b) is the experimental picture.

Protocol
The stress-strain response was carried out through repeated experiments of increasing and decreasing the unit length and angle. Also, the maximum and minimum val-

prototype
The prototype was produced with three types, 12 strands braided sensor, 16 strands braided sensor, and flexible load sensor before braid. As a result of prototyping, 12 strands braided sensor induced cyclic curling with a diameter of 6 cm, and 16 strands braided sensor were produced with cyclic curling with a diameter of 3 cm.    The decrease in stress-strain response of angle and length displacement can be interpreted to be acted Pressure to free movement. However, in the internal polyurethane 12 strands condition, the sensor reactivity increased twofold due to internal helical auxetic stress.  Figure 9((a),(b)) shows the fast rate of responsiveness to stress-strain. Figure 9((c)(d))

Preprints
shows the stress-strain response minimum (0%) before and after braid on the optical waveguide axis. Before and after the stress-strain response, maximums (100%) were compared in figure 9((c), (e)).
This was due to the wrap yarn role of polyurethane, which resulted in positive interaction and fast stress-strain response from the helical auxetic stress in the Bragg sensor core. It is presented in Figure 9. The range of the helical auxetic stress was calculated using the conditions for 12 and 16 strands sensor. The impact range of the helical auxetic distortion rate in the sensors was analyzed in connection to the fiber optic sensor's cores pitch cycles in figure9.