Fracture induced electromagnetic radiation

Abstract

In our laboratory, we combine accurate electromagnetic radiation (EMR) measurements during fracture of rocks (carbonate and igneous) and transparent materials (glass, PMMA and glass ceramics) with careful fractographic methods. A critical analysis of experimental observations, accumulated here during the last decade together with supporting material from the works of other authors are used in this study to demonstrate the failure of all current models to explain the properties of EMR arising from fracture. The basic elements of a new model are proposed. These are (a) the EMR amplitude increases as long as the crack continues to grow, since new atomic bonds are severed and their contribution is added to the EMR. As a result, the atoms on both sides of the bonds are moved to 'non-equilibrium' positions relative to their steady state ones and begin to oscillate collectively in a manner similar to Debye model bulk oscillations-'surface vibrational optical waves'; (b) when the crack halts, the waves and the EMR pulse amplitude decay by relaxation. These basic elements are already enough to describe the characteristics of the experimentally obtained isolated individual EMR pulses. These characteristics include the shape of the EMR pulse envelope, and the frequency, time duration and rise-fall time of the pulse.

Studying electromagnetic signal of rock effected by acoustic impact under uniaxial compression

“…There are healed and unhealed cracks of different orientations and sizes. As a result, the heterogeneity of the composition, mineral spots, and structure imperfection leads to an increase in the number and length of the electric double layers, which leads to an increase in the number of dipoles, emitting electromagnetic pulses [6]. This fact contributes to the active transition of mechanical energy into electromagnetic energy at acoustic impacts of rock samples.…”

“…The Israeli scientists conducted in their works studying of EMS of rock and model samples under loading [6]. Studying of transparent model samples allowed for to figure out sequence of cracks origin, their growth and interactions.…”

Using the Oscillating Dipoles Model to Study the Electromagnetic Radiation Induced by Fracture of Rocks

“…Rabinovitch et al [5,23] proposed that the value of the v crack equal to the Rayleigh wave velocity in the same media. In our model, from Figure 1, we can find that L crack and W crack can be expressed by the parameters of the ellipse:…”

“…The charges on each of the dipoles, Q, is based on the Enomoto's rock notch experiments [11] and adjusted by the fitting result with the experiment results of Rabinovitch et al We use the least square method to fit the experiment results for the value of the damped factor of the vibration, α. Based on the Rabinovitch's compression experiments on the granites and chalks [5,6], the rock samples are all standard cylinders of 100 mm in length and 53 mm in diameter. The loop antenna was placed 20 mm away from the center of the samples with its normal pointing perpendicular to the cylinder axis.…”

“…Some representative measurements can be found, for example, in the paper by Cress et al and Frid et al [4,5], who carried out a series of compression experiments on granite and chalk samples. Rabinovitch et al proposed some numerical fitted formulations [5,6] for their observed EMR pulses induced by rock fractures. However, the origins of the EMR phenomenon are still not well understood.…”