Yakov Botsev

Using Fiber Bragg Gratings to Measure Lamb Waves in an Anisotropic Composite Plate

The potential for using fiber Bragg grating rosettes for the location of ultrasound sources in anisotropic structures is discussed. Anisotropic propagation of Lamb waves in a carbon fiber composite plate has been investigated using two approaches. Firstly, a finite element model of the displacements/strains produced by the wave was developed and, secondly, in-plane ultrasonic strain mapping was carried out, utilizing the directional properties of FBG sensors. The possibility of designing FBG rosette configurations for use on anisotropic structures is discussed in light of these results.

Residual strain measurement in bonded composite repairs for aging aircraft by embedded fiber Bragg grating sensors

Embedded Fiber-Bragg-Grating sensors are used for tracking the initiation of structural bonding and measuring the residual strains, during the curing process, of bonded composite patches used for aging aircraft structural repairs. FBG reading are shown to have direct correlation with the residual strains that are important in assessing the long-term durability of the repaired structure under fatigue load spectrum.

Fiber Bragg grating sensing in smart composite patch repairs for aging aircraft

A Fiber-Bragg-Grating based, advanced co-cured smart composite patch for the repair of metallic structures is proposed and demonstrated. Advantages include real time cure monitoring and long-term in-service structural integrity evaluation.

Health and Usage Monitoring of Unmanned Aerial Vehicles Using Fiber-Optic Sensors

An airborne, high resolution, load tracking and structural health monitoring system for unmanned aerial vehicles composite structure is presented. The system is based on embedded optical fibre Bragg sensors, interrogated in real time during flight. The vibration signature during ground testing has been recorded and analyzed, making it possible to identify and trace the dynamic response of the airborne structure and engine during flight. Tracking the structural behaviour over time can be used for Condition Based Maintenance (CBM), reducing maintenance cost.

Load tracking and structural health monitoring of unmanned aerial vehicles using optical fiber sensors

An airborne, high resolution, load tracking and structural health monitoring system for unmanned aerial vehicles is presented. The system is based on embedded optical fiber Bragg sensors interrogated in real time during flight at 2.5 kHz. By analyzing the recorded vibration signature it is now possible to identify and trace the dynamic response of an airborne structure and track its loads.

Damage detection under a composite patch using an embedded PZT-FBG ultrasonic sensor array

An array of piezoelectric ultrasonic exciters/sensors and fiber Bragg grating sensors is embedded between an Aluminum plate and a composite patch. Using Lamb waves, the array is shown to be capable of detecting a developing damage in the aluminum plate, as well as locating it.

The use of fibre Bragg gratings to detect ultrasound in anisotropic materials

In previous work we have described the detection and location of damage in isotropic materials using fibre Bragg gratings rosettes to directionally detect Lamb waves. To extend this technique to composite materials it is necessary to understand the propagation characteristics of ultrasound in these materials as a function of their orientation with respect to the ply, and also the directional response of fibre Bragg gratings to them. Finite element modeling of Lamb wave propagation in a 0°, 90° carbon fibre plate is described, as are experiments to detect these waves for various orientations of the source and alignments of the FBG transducers. Results of the experiments are interpreted with respect to predictions from the FE modeling and are shown to give good qualitative agreement.

On the actual bandwidth of some dynamic fiber-optic strain/temperature interrogators

The measurement accuracy of dynamic fiber-optic sensing interrogators, which use frequency scanning to determine the value of the measurand, err as either the event bandwidth approaches half the instrument sampling frequency or when the event dynamic range comes close to the instrument designed value. One main source of error is the common practice of assigning sampling at a non-uniform grid to a uniform one. Harmonics higher than −20 dB are observed for signal frequencies exceeding 25% of the sampling rate and/or for signal amplitudes higher than 15% of the instrument dynamic range. These findings have applications to fiber-Bragg-grating and Brillouin interrogators.

Utilization of negative beat-frequencies for maximizing the update-rate of OFDR

In traditional OFDR systems, the backscattered profile of a sensing fiber is inefficiently duplicated to the negative band of spectrum. In this work, we present a new OFDR design and algorithm that remove this redundancy and make use of negative beat frequencies. In contrary to conventional OFDR designs, it facilitates efficient use of the available system bandwidth and enables distributed sensing with the maximum allowable interrogation update-rate for a given fiber length. To enable the reconstruction of negative beat frequencies an I/Q type receiver is used. In this receiver, both the in-phase (I) and quadrature (Q) components of the backscatter field are detected. Following detection, both components are digitally combined to produce a complex backscatter signal. Accordingly, due to its asymmetric nature, the produced spectrum will not be corrupted by the appearance of negative beat-frequencies. Here, via a comprehensive computer simulation, we show that in contrast to conventional OFDR systems, I/Q OFDR can be operated at maximum interrogation update-rate for a given fiber length. In addition, we experimentally demonstrate, for the first time, the ability of I/Q OFDR to utilize negative beat-frequencies for long-range distributed sensing.