Advances in Solid-State Pulsed Power Applications

A quantitative X-ray Photoelectron Spectroscopy (XPS) study has been undertaken on different experimental data sets of ZrN thin films deposited using reactive Bipolar Pulsed Dual-Magnetron Sputtering (BPDMS) on silicon/stainless steel substates, to obtain dense, pure and homogeneous coatings, free from morphological defects. Zirconium nitride (ZrN) occupies a central role within the class of transition metal nitrides (TMN) for its excellent properties, such as high hardness, low resistivity and chemical/thermal stability when its stoichiometric ratio is 1:1. Many deposition techniques, reported in the literature, tried to obtain oxygen-free and defect-free structures, but they proved a hard task. In this paper it has been demonstrated, using quantitative XPS, that stoichiometric, pure and homogeneous ZrN films have been grown at certain deposition conditions, optimized also via optional accessories mounted on the deposition apparatus. Almost all the films considered for microanalytical characterization resulted as completely oxygen-free, pure (with a lowest-detection limit of 1%) and homogeneous. Apart from these features, a stoichiometric ratio (N/Zr) close to one was calculated for six samples of the ten investigated, with a precision of ± 0.01. In this frame XPS, widely known for being a highly surface-sensitive technique (average depth resolution of 20–30 Å), and powerful for characterizing the chemical composition of materials, has been extensively employed to extract information both in the surface regions and in depth. A cluster ion beam Ar+ ₂₅₀₀ facility on our main XPS chamber has not proved adequate for depth-profiling acquisitions. Therefore, Ar+ ion sputtering was performed instead. To the best of our best knowledge, the results achieved in the present paper possess a level of accuracy never reached before. Rigorous calibration procedures before and during experimental spectrum acquisitions and a careful and scrupulous data processing using software CasaXps v.2.3.24PR1 were carried out to ensure a low percentage error. Progress has also been made for shake-up satellite extraction and interpretation from Zr 3d high-resolution spectra with the help of the literature milestones reported in the text. The total absence of oxygen inside most of the films prevented the formation of zirconium oxide compounds during deposition, which are generally resonant with the binding energy of the shake-up satellite peaks and hide them. A little summary about the experimental shake-up satellite peaks revealed and extracted from the Zr 3d region, after Shirley background subtraction and data processing, will be presented in the last subparagraph of the “Results” section for the ZrN samples analyzed. Figures of Zr 3d deconvoluted spectra for in-depth area analysis have been reported. The quantitative satellite contribution to the Zr 3d total area would not be included in stoichiometric calculations. Full article

For the pulsed electric field treatment of plant material on an industrial scale, Marx-type pulse modulators are used as a pulse source. The combination of a conventional Marx generator design equipped with solid-state switches with the concept of resonant charging via current-compensated chokes enables the set-up of a Marx generator having only one active semiconductor switch per stage. Thereby, the pulse shape is defined by the passive components of the RLC-pulse circuit. In the course of the design of such a resonant charging circuit, common-mode current components through the current-compensated chokes need to be considered. Moreover, especially for a generator having its ground connection at its centre, induced voltages versus ground need to be addressed. Therefore, an investigation based on circuit simulations has been made. The simulations showed that the common-mode current components decay to zero just after the resonant charging process and cause a voltage transient at the terminal of the power supply, which needs to be floating versus ground. In order to reduce the amplitude of this transient, the effects of adding a damping resistor have been studied. However, adding this resistor may involve an increase in the common-mode current components. Moreover, the common-mode current components of different chokes are influenced by the on-time of the switches. In the paper, based on the simulation results, different operation modes with and without the damping resistor are discussed. Thereby, the on-time of the switches has been varied. Selected simulation results have been verified by means of measurements. Full article

Nonlinear transmission lines (NLTLs) offer compact, low-cost, all solid-state high-power microwave (HPM) generation. This article experimentally investigates the RF output power for composite-based 10, 25, and 50 Ω NLTLs used as a combined pulse forming line and HPM source. We manufactured coaxial NLTLs containing 10% barium strontium titanate and 15% nickel zinc ferrite encased in polydimethylsiloxane. The output voltage and power in the time and frequency domains, respectively, showed that the 10 Ω NLTL generated the greatest RF output. The 25 Ω NLTL generated greater output power from 500–1100 MHz than the 50 Ω NLTL. This occurs because reducing the NLTL impedance induces a larger transient current for a given charging voltage. This transient current corresponds to a stronger transient magnetic field, which facilitates magnetic moment alignment to allow for coherent magnetic moment rotation to occur. This setup eliminates the separate pulse forming network and magnetic field bias that typically occurs in other NLTL systems, which provides additional flexibility in tuning the NLTL impedance and reducing device footprint. Full article

The traditional Marx generators based on avalanche BJTs usually use a DC voltage source to charge the storage capacitors, and many theoretical studies have proved that the existence of DC voltage source leads to low energy efficiency. This paper proposes a novel nanosecond Marx generator based on avalanche BJTs, which is charged by a series-resonant power supply. This power supply charges all capacitors with a constant average current and all BJTs avalanche breakdown stage by stage without any triggering signals. When the resistors are replaced by inductors, the efficiency can be further improved. The pulse repetition frequency can be adjusted by controlling the resonant average current. The output voltage can be increased by connecting more avalanche BJTs in series or increasing the number of stages of the Marx generators. The control method and the structure of the circuit are simple. Experimental results show that negative pulses with an adjustable frequency of 10–60 kHz, a pulse width of 8.45 ns, and an amplitude of 4 kV were obtained on a resistive load. The energy efficiency of the Marx generator was increased to 94%. Full article

Eucalyptus extract-based pharmaceutical products are widely used because of their medicinal properties and their rich content of secondary metabolites, mainly phenolic compounds. This study aimed to maximise the extraction yield of these compounds and reduce the extraction duration by using a pulsed electric field (PEF) level of 6 kV/cm. The pulse width (T), number of pulses (n), and solvent concentration [C] were analysed. Several ethanolic extracts were obtained from the leaves of Eucalyptus globulus, and the content of total phenols, total flavonoids, and condensed tannins was measured through spectrophotometry. The results, obtained immediately after PEF treatment, revealed that for optimal values of the analysed factors, the total phenol content doubled and the flavonoid content increased significantly. However, PEF pre-treatment had no effect on the tannin yield. Moreover, optimisation was performed using the design of experiments methodology for identifying optimal values of the analysed factors. Full article

Essential oils, EOs, are concentrated liquids with complex mixtures of volatile organic compounds that can be extracted from different plant materials. EOs have been used by humans throughout history due to their natural properties: from pleasant fragrances, to anti-bacterial/fungal activities. This work presents the impact of pulsed electric fields, PEF, application as a pre-treatment for the extraction of EOs from eucalyptus, rosemary, and thyme leaves. The initial PEF pre-treatment was first applied to eucalyptus and rosemary leaves two weeks after harvesting, with a 2 kV/cm electric field and a specific energy of approximately 10 kJ/kg, followed by EO extraction by hydrodistillation, HD, with distillation times of 30 and 60 min. The best results were obtained for PEF pre-treated samples and 30 min HD, exhibiting an increasing trend in the average extraction yield of approximately 17% and 11% for eucalyptus and rosemary, respectively, in comparison with no PEF applied. The composition of the EOs extracted from eucalyptus was analyzed for their total phenolic content, TPC, where PEF pre-treated samples showed a higher polyphenol extraction, reaching 30% for 30 min HD. Finally, the optimization of the PEF pre-treatment was also studied, for maximizing the quantity of EO extracted from dry thyme leaves, while aiming for a minimization of energy consumption, for different distillation times. For this study it was observed that, for this plant material, an electric field of 1 kV/cm with 0.4 kJ/kg and an HD time of 30 min, after PEF application, was able to achieve an extraction yield up to 40% higher than the conventional method. Full article