Mechanism of electromagnetic emission in plastically deformed ionic crystals

Abstract

Experiments on the plastic deformation of LiF ionic monocrystals under uniaxial compression are performed with simultaneous recording of acoustic ͑AE͒ and electromagnetic ͑EME͒ emissions. A strong correlation between AE and EME events has been found, which clearly demonstrates that the observed EME is caused by a dynamical interaction between moving dislocations and charged vacancies in the ionic lattice during work hardening. The mechanism proposed to explain EME is based on the assumption that gliding edge dislocations sweep up the vacancies of a preferable sign. As a result, when a dislocation pileup is formed, a certain nonequilibrium charge density is accumulated at its head, resulting in electric polarization of the deformed crystal. As the external loading increases, a locked dislocation pileup bursts through the stoppers and quickly loses its bounded charge. The relaxation of this charge produces an intrinsic polarization current generating an electric pulse. It is assumed that the relaxation current can be described as an athermic viscous motion of vacancies under the kinetic friction force ϳBv ͑B is the friction coefficient and v is the vacancy velocity͒ in a self-consistent electric field determined by the distribution of the total charge density. A nonlinear integrodifferential equation of motion for the nonequilibrium charge density is derived. For a special form of the initial charge density distribution, an automodel solution of this equation describing the polarization current has been built. The electrical signal generated by an acting slip system has been calculated. By comparing the calculated and experimentally measured electric signal patterns, the friction coefficient for the linear chain of vacancies ͑the analog of an edge dislocation extra plane͒ in LiF has been estimated to be B Ӎ 0.9 ϫ 10 −5 g cm −1 s −1 . This value is in accordance with the corresponding coefficient for dislocations in ionic lattices.

Unfolding the procedure of characterizing recorded ultra low frequency, kHZ and MHz electromagnetic anomalies prior to the L'Aquila earthquake as pre-seismic ones - Part 2

“…Hazards Earth Syst. Sci., 10, [275][276][277][278][279][280][281][282][283][284][285][286][287][288][289][290][291][292][293][294]2010 www.nat-hazards-earth-syst-sci.net/10/275/2010/ scale (Hayakawa and Fujinawa, 1994;Hayakawa, 1999;Hayakawa et al, 1999;Gershenzon and Bambakidis, 2001;Hayakawa and Molchanov, 2002;Bahat et al, 2005;Eftaxias et al, 2007a;Muto et al, 2007;Hadjicontis et al, 2007). Studies on the small (laboratory) scale reveal that the MHz EM radiation appears earlier than the kHz one, while the kHz EM emission is launched from 97% up to 100% of the corresponding failure strength (Eftaxias et al, 2002 and references therein).…”

Relationship between electromagnetic and acoustic emissions in deformed piezoelectric media: Microcracking signals

“…(Hadjicontis et al, 2007(Hadjicontis et al, , 2011. Granite samples sized of 1 Â 1 Â 3 cm were uniaxially compressed with hydraulic machine.…”

“…In our previous papers (Hadjicontis et al, 2007(Hadjicontis et al, , 2011 the mechanism of EME formation based on charge transport by mobile dislocations in ionic dielectrics (non-irradiated (Hadjicontis et al, 2007) and gamma-irradiated (Hadjicontis et al, 2011)) has been studied elaborately and the relationship between EME and AE in such type of crystals has been investigated. Here we study another EME mechanism which is based on direct acousto-electromagnetic transformation in isotropic piezoelectrics whose typical representatives are natural crusts.…”

“…Then electromagnetic irradiation of brittle dielectrics and concretes was in details studied both experimentally and theoretically (Miroshnichenko and Kuksenko, 1980;O'Keefe and Thiel, 1995;Rabinovich et al, 2001Rabinovich et al, , 2007Frid et al, 2003;Fukui et al, 2005;Lacidogna et al, 2011;Carpinteri et al, 2012) in view of its possibly applications to materials science, geophysics and industry. An appreciable progress in establishing the physical background of the corresponding phenomena was obtained when the correlation between AE and EME in ionic monocrystals and natural rocks with piezoelectricity was studied experimentally in (Hadjicontis et al, 2004) and interpreted in (Hadjicontis et al, 2007(Hadjicontis et al, , 2011 for ionic lattices. The goal of the present paper is to study both experimentally and theoretically the strong correlation between AE and EME in natural granites in an attempt to elucidate the physical background of corresponding phenomena.…”

Measurement and Study of Electromagnetic Emission Generated by Tensile Fracture of Polymers and Carbon Fibres

“…The term electromagnetic emission (EME) comprises a wide range of emission effects. This can be electromagnetic radiation directly emitted during and after local mechanical processes, such as fracture [1,2], plastic deformation [3,4] or friction [5,6] as well as the emission of charged particles (sometimes referred to as fracto-emission [7,8]). As sources for the electromagnetic fields, the separation, displacement or movement of bound or free charges are considered.…”