Transformation of Acoustic Pulses into Electromagnetic Signals in Defective Structures

In this study, the physical foundations of the combined acoustic-electric method are examined for testing layered materials, as well as materials with defects in the form of solid inclusions. The numerical simulation results of the electromagnetic signals excited in a test material via pulsed acoustic impact are presented. The effect of sample layering on the electromagnetic response parameters under a determined acoustic impact is shown. Possible changes in the electromagnetic signals parameters with different charge states of dielectric defect structures, as well as changes in the parameters of electromagnetic signals at different amplitudes of acoustic exposure to a defective structure with a constant charge, are revealed. It is shown that the amplitude-frequency parameters of the emitted electromagnetic signals are directly related to the characteristics of the determined acoustic impact and the charge state of layered and defective structures. It was found that the change in the amplitude of electromagnetic signals linearly depends on the magnitude of the defect plates charge, as well as on the magnitude of the exciting acoustic pulse at a constant charge state of the defect. A research set-up and the model samples with solid-state inclusions in the form of layers and volume defects are described. The duration of the exciting acoustic pulse at the base was 50 μs, and its energy was varied within (8–15) mJ. The sensitivity at the input of the electromagnetic receiver was 0.5 mV, and the output gain was 10 or 100 selectively. The operating frequency range was 1–100 kHz. As a result of experimental studies, the correspondence of the amplitudes of electromagnetic responses to the distribution calculated in time and space of mechanical stresses arising in a layered or defective system during the propagation of an acoustic pulse was established. It is shown that the electromagnetic signals parameters, as well as the distribution of the acoustic pulse, are significantly affected by the difference between the sample and inclusion acoustic impedances.