Application Cases

Experiment Name: Response Characteristics of Fiber Bragg Gratings under Multi-Source Excitation

Experiment Objective: To reveal the strain sensing characteristics of FBGs under multi-source excitation by analyzing the distributed strain signals measured by FBG.

Experimental Equipment: Signal generator, ATA-2041 high-voltage amplifier, tunable laser source, oscilloscope, photodetector

Experimental Content:
This study focuses on the influence of factors such as frequency, phase, amplitude, and position of two excitation sources on the response characteristics of FBGs, providing a parametric basis for subsequent damage localization.

Experimental Procedure:
This study primarily investigates the excitation parameter characteristics of an isotropic plate. The test object is a 6061 aluminum alloy thin plate with dimensions of 400 mm × 400 mm × 1 mm.

Construction of the Multi-Source Excitation Detection System:
The schematic diagram of the multi-source excitation-FBG sensing detection system based on the isotropic plate structure is shown in the figure. It mainly consists of an excitation part and an FBG demodulation part. The excitation part includes a signal generator and a high-voltage amplifier (ATA-2041). The FBG demodulation part mainly includes a broadband coupler, a tunable laser source, a photodetector, and an oscilloscope. Channel 1 signal of the signal generator is directly applied to a piezoelectric patch and amplified by the high-voltage amplifier. Channel 2 signal is amplified by a signal amplifier and then applied to the piezoelectric patch. Using the inverse piezoelectric effect, strain waves are generated in the plate structure, received by the FBG sensor, demodulated, converted into an electrical signal by the photodetector, and displayed on the oscilloscope.

Experimental Results:

(1) Excitation size parameters
Comparing the excitation effects of piezoelectric patches A (diameter 20 mm) and B (diameter 10 mm): When piezoelectric patches A and B acted alone, the response curves on #1 FBG were obtained, as shown in the figure. Within the range of 0–33 kHz, the output response under the action of piezoelectric patch A was much larger than that under piezoelectric patch B. Within the range of 33 kHz–100 kHz, except for individual frequency points that may have abrupt changes due to environmental factors, the overall variation trend remained basically unchanged. It can be concluded that with the same component thickness and excitation amplitude, a larger diameter results in a larger response amplitude. Therefore, to obtain a larger response amplitude, a suitably larger diameter can be chosen. However, if the diameter is too large, the influence of size in the analysis process cannot be ignored.

Figure: Excitation effect under different sizes

(2) Excitation angle parameters
Comparing the excitation effects of piezoelectric patches A (0° angle) and D (10° angle): When piezoelectric patches A and D acted alone, the response curves on #1 FBG were obtained, as shown in the figure. The response obtained when exciting in the axial direction (A) was generally better than that when exciting at a 10° angle (D), with the difference being large in some frequency bands and small in others. It is evident that the excitation angle has a certain influence on the FBG detection signal.

Figure: Response curve of #1 FBG under different excitation angles

Under the same excitation conditions, comparing the FBG sensing response effects at different positions, as shown in the figure, since excitation A was along the axis of #1 FBG, the black curve representing the response under excitation A in figure a shows a larger response. Similarly, since excitation C was along the axis of #2 FBG, the red curve representing the response under excitation C in figure b shows a larger response. It can be seen that regardless of #1 FBG or #2 FBG, the detection position directly facing the excitation element yields a better response effect.

Figure: FBG response curves at different positions

The relative position between the excitation source and the FBG has a certain impact on the detection results. When laying out the excitation elements, it is preferable to position them on the sensing axis of the FBG for better detection results. However, in distributed detection, it is impossible to simultaneously optimize the positions of multiple FBGs and excitation elements. Therefore, to reduce the influence of the angle factor, frequency bands with smaller angle factor deviations can be selected as the excitation frequency as much as possible.

Figure: Specifications of the ATA-2041 High-Voltage Amplifier