Unexpected irreversible damage appeared in samples while investigating pulsed S-N switching in YBaCuO thin films. Examination of a scanning electron microscope image of a damaged film containing a defect revealed a step-like motion of the N-zone. Restoration of crack movement dynamics points to the formation of coherent jets. This would mean that cumulative convergence of unknown incompressible media took place. The known model of an edge barrier, when the S-N border, characterized by width λ _eff , bounds a semi elliptical N-zone at the film edges, was applied for clarification of the cumulative convergence. In that model, counteracting forces cause a wave-like unstable form of the barrier S-N border, and further current growth increases the amplitude of wave-like distortions of the border. Then, current reconnection separates bulges from the N-zone and induces the appearance of the circular currents with a trapped magnetic flux. Heat release at the places with trapped flux cause an expansion in these locations and coherent jets originate from touch points due to cumulative convergence. We substantiate that specific properties of the S-N border at λ _eff , such as high tensile strength, very high flexibility and also incompressibility, are responsible for the appearance of the cumulative effect. Thus, the N-zone propagation into S state begins by motion of the wave-like border. The non-damaging step-like N-zone propagation into the films without defects is clarified. It is concluded that both the critical current and the damage current are determined by the same barrier with the unstable S-N border, and, therefore, the irreversible damage of the films comes quickly after the current reaches the critical value.

It was experimentally registered pulsed electromagnetic (EM) radiation in frequency range higher than television one using wideband horns with coaxial and waveguide outputs. The EM radiation was received during shock loading of lead zirconate titanate (PZT) ceramics cylinders in conventional piezoelectric ignition mechanisms. Digital oscilloscope allows registering whole series of EM pulses and each pulse from the series transmitted from horn antenna of (1 – 18) GHz operating band frequencies. There is (1 – 4) ms delay between the shock and the first pulse of the series. Duration of the series is about (3 – 4) ms. The PZT cylinders were cleaved along their axes and the surfaces formed in the process were investigated by scanning electron microscope. It was concluded that from electrical point of view PZT ceramics contain interacting subsystems. It was found that EM radiation spectrum of pulse detected by waveguide detector heads has harmonics reaching 80 GHz. Presence of harmonics higher than 20 GHz indicates on radiation due to deceleration of electrons emitted during the switching. The EM pulses in the series appear randomly and have different amplitudes which partly confirmed thesis on independent switching dynamics of small volumes governed by a local electric field.DOI: http://dx.doi.org/10.5755/j01.ms.19.4.3137

The Barkhausen method is proposed to clarify the cause of radiation of electromagnetic (EM) pulses during high voltage pulse generation by piezoelectric igniters (PIs). Wide bandwidth of the experimental setup was narrowed for a simultaneous registration of electric and detected EM pulses by a two-channel oscilloscope. The PI was loaded on a high ohmic resistance and high voltage pulses of 8 – 17 kV amplitude and up to 150 ms in total duration were registered. These pulses contained a series of short pulses called Barkhausen type pulses. Duration of these pulses having the relatively high amplitude was 30 – 40 ns. The registration revealed that the radiating EM pulse series corresponded to Barkhausen type pulse series. Short non-radiating negative pulses appearing during the saturated voltage growth were also observed and they had relaxation tails. The analysis showed that the EM pulses are caused as a result of domain switching with high voltage spikes at the PZT cylinders bases, where high electric fields are created. The activity of these switchings weakens when the “age” of PIs increases. The non-radiated pulses resulted from fast internal screening processes in the volume of the cylinders, accompanied by the impact ionization. The increase of the saturation and PI’s “age” causes lengthening of the relaxation tails. The results of practical importance for PIs in monitoring systems are placed. It is concluded that the Barkhausen method in wideband configuration is a convenient experimental arrangement for investigation of powerful processes in ferro-piezoelectric ceramics.

Recent experimental study of electron transport in ZnO/ZnMgO and BeZnMgO/ZnO heterostructures containing two-dimensional electron gas (2DEG) channels of two polarities is reported where electrons are accelerated and become hot by a pulsed electric field. The measurements with electrical pulses ranging from 2 ns to 10 ns in duration ensure the control of self-heating effect. Electron transport in the ZnO 2DEG channels located in ZnO layers at the ZnMgO or BeZnMgO barrier or in ZnO 3DEG channels is treated mainly in terms of drift velocity. The highest values of 1.3 × 10⁷ cm/s at 360 kV/cm, 2.0 × 10⁷ cm/s at 270 kV/cm, and 2.5 × 10⁷ cm/s and 320 kV/cm, respectively, are attained and explained by emphasizing the effect of hot phonons.

The process of normal (N) zone propagation in three superconducting YBaCuO thin films with different Pearl length values was theoretically studied. The point appearance of the N zone was found to result from powerful energy release caused by micro-sized magnetic cumulation. Solutions of the heat equation for hot electrons, diffusing to ~15 nm depth into the edge of the Pearl length, were obtained for the two length cases. The hot electron thermalization induced a transition to N state at the aforementioned depth due to fast exceeding of T_c, followed by flash high temperature growth. In the third case, we considered a process of crack branching when the superconducting current concentrated at the tips, followed by the transition to N state caused by exceeding j_c. The superfast reaction of the superconductor allowed it to restore the energy loss at the Pearl length in all cases. This explains the step propagation process of the N zone with velocities up to 2.7 × 10³ and 1.1 × 10³ m/s in the first and second cases. In the third, the propagation can reach the detonation wave velocity of about 1 × 10⁴ m/s. It is concluded that the process of the N zone propagation has the character of a combustion wave.