The study of the application of optical fibers with incorporated Bragg’s lattices as strain gauges integrated into the structure of compositional materials during their manufacturing is proposed....

Experimental method of temperature and strain discrimination with fiber Bragg gratings (FBGs) sensors embedded in carbon fiber-reinforced plastic is proposed. The method is based on two-fiber technique, when two FBGs inscribed in different fibers with different sensitivities to strain and/or temperature are placed close to each other and act as a single sensing element. The nonlinear polynomial approximation of Bragg wavelength shift as a function of temperature and strain is presented for this method. The FBGs were inscribed with femtosecond laser by point-by-point inscription technique through polymer cladding of the fiber. The comparison of linear and nonlinear approximation accuracies for array of embedded sensors is performed. It is shown that the use of nonlinear approximation gives 1.52 times better accuracy. The obtained accuracies of temperature and strain measurements are 2.63.8°C and 5083με in temperature and strain range of 30120°C and 0400με, respectively. Experimental method of temperature and strain discrimination with fiber Bragg gratings (FBGs) sensors embedded in carbon fiber-reinforced plastic is proposed. The method is based on two-fiber technique, when two FBGs inscribed in different fibers with different sensitivities to strain and/or temperature are placed close to each other and act as a single sensing element. The nonlinear polynomial approximation of Bragg wavelength shift as a function of temperature and strain is presented for this method. The FBGs were inscribed with femtosecond laser by point-by-point inscription technique through polymer cladding of the fiber. The comparison of linear and nonlinear approximation accuracies for array of embedded sensors is performed. It is shown that the use of nonlinear approximation gives 1.52 times better accuracy. The obtained accuracies of temperature and strain measurements are 2.63.8°C and 5083με in temperature and strain range of 30120°C and 0400με, respectively.

The paper considers the advantages and disadvantages of existing methods for temperature compensation of data from fiber-optic sensors based on fiber Bragg gratings as part of an embedded system for simultaneous testing of deformation and temperature of polymer composite materials. It is shown that when external temperature testing is impossible, it is most expedient to implement the method of two optical fibers with different sensitivity to at least one of these parameters due to different dopants. Technological issues related to the formation of a spatial topology and the provision of an effective survey of the embedded optical system for monitoring polymer composite materials by the two-fiber method are considered. The results of theoretical research of a linear model of temperature compensation, a model that takes into account the influence of cross sensitivity, as well as a quadratic model of temperature compensation of optical testing data are presented. It has been established that the linear model is the simplest, however, when using it, one should take into account the error associated with the inaccuracy of the approximation of optical inspection data by a linear function. At the same time, it is shown that in order to improve the quality and reliability of the results of optical testing, it is advisable to use a quadratic model of temperature compensation, which provides an error level comparable to the error of the fiber-optic sensor survey device. The results obtained can be used to develop methods for the simultaneous testing of samples, as well as monolithic and three-layer structures from structural layered polymer composite materials with limiting molding conditions (temperature less than 180°C, specific pressure lower than 0.7 MPa), as in the process of bench and other tests, and, in the future, in real operating conditions.

The paper presents a novel pH-sensor architecture based on an addressed fiber Bragg structure (AFBS) with fully-etched segment, designed for reliable operation in thermally unstable industrial environments. The sensor employs a fiber Bragg grating with dual π phase shifts, where one of the segments is fully etched to the core to enhance evanescent field interaction with the environment. This geometric modification significantly increases sensitivity to refractive index variations, which correlate with local pH changes. Numerical simulations confirm a near-linear dependence of the address frequency on pH levels ranging from 11.0 to 13.7, with thermal invariance maintained from −100 °C to +100 °C. The sensor’s dual-resonance spectral profile enables high-resolution microwave photonic interrogation and supports wavelength-division multiplexing for distributed measurements. A simulated multisensor configuration demonstrates clear spectral separation and addressability. Beyond refractive index sensitivity, the design provides electromagnetic immunity, real-time response, and compatibility with remote optical interrogation. These features make the etched AFBS (EAFBS) sensor highly suitable for deployment in industrial environments. Future work will focus on integrating EAFBS into multi-parameter fiber-optic platforms capable of simultaneous monitoring of pH, temperature, and flow rate.

This article describes the relevance of improving existing and creating new effective methods of non-destructive testing and technical diagnostics of highly loaded aircraft structures made of polymer composite materials to ensure safe operation. Approaches to the creation of efficient systems for the simultaneous embedded testing of deformations and temperature of structures made of polymer composite materials by an optical method using embedded fiber-optic sensors based on fiber Bragg gratings are considered. The world experience in creating such systems, the methodology of non-destructive testing are analyzed, taking into account the creation of a spatial topology of fiber-optic sensors in a real product. It is shown that to solve this problem, it is most expedient to use the method of two optical fibers with different sensitivity to deformation and temperature, or to one of these parameters. The results of experimental studies on the simultaneous control by the proposed method of deformation and temperature of a structurally similar sample from a carbon composite processed by a vacuum method from a prepreg are presented. It has been established that the use of a quadratic model for optical control of structurally similar samples of carbon composite makes it possible to increase the accuracy of deformation and temperature measurements in comparison with the linear control model. It is confirmed that the proposed experimental technique allows for simultaneous control of deformation and temperature of structurally similar samples from carbon composites, while it can be adjusted and adapted to the actual operating conditions of a particular structure.