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Nonlinear transmission lines (NLTLs) provide a means to generate high-repetition-rate, high-power microwaves with fewer auxiliary systems than conventional sources. They are typically driven by pulse forming networks (PFNs) or Marx generators, and one would intuitively hypothesize that the microwave generation would not depend significantly on the method used to generate the input pulse to the NLTL. This study examines the implications on microwave output by using a Blumlein pulse generator with a 10-ns pulse duration and 1.5-ns rise and fall times to drive coaxial NLTLs produced using composites with nickel zinc ferrite and barium strontium titanate (BST) inclusions. Applying a 30-kV pulse to the composite NLTLs produced frequencies ranging from 1.1 to 1.3 GHz with output powers over 20 kW. The output frequencies increased with increasing volume fraction of BST. Measured results and simulations using LT SPICE showed that Blumlein modulators were insufficient to drive NLTLs to produce high-power oscillations; however, LT SPICE simulations showed that applying a standard PFN to the same NLTL produced the expected oscillations. This difference arises because the mechanism for Blumlein pulse formation cancels the shockwaves responsible for inducing microwave production by the NLTL.

Nonlinear transmission lines (NLTLs), which exhibit permittivity as a function of electric field and/or permeability as a function of magnetic field strength, are of increasing importance for sharpening pulses to less than 100 ps and serving as radio frequency (RF) sources; however, NLTLs often are not easily modified to achieve different output parameters. One method under investigation involves combining nonlinear dielectric [barium strontium titanate (BST)] and/or magnetic [nickel zinc ferrite (NZF)] inclusions to tune the NLTL properties by adjusting the inclusion loading fractions. This article focuses on measuring the nonlinear permeability and magnetic loss tangent of composites comprising various volume loadings of NZF or NZF and BST inclusions encapsulated in a silicon matrix. We measured the relative permeability from 1 to 4 GHz using a coaxial airline while biasing the samples in an external dc magnetic field from 0 to 171 kA/m. The permeability decreased from 1 to 4 GHz for each volume fraction but increased with increasing magnetic field strength at low-magnetic field strengths with sufficient NZF volume loading. The magnetic loss tangent of the composites increased with increasing frequency and/or NZF volume fraction but was suppressed by increasing the external magnetic field strength. Adding BST to NZF composites did not cause a significant change in permeability compared to NZF alone, based on an analysis of variance (ANOVA) and multiple comparison test. These results elucidate the frequency dependence of NZF volume loading at microwave frequency and provide initial information for simulating NLTLs and examining more comprehensive RF system behavior.

Nonlinear transmission lines (NLTLs) have been increasingly studied to produce high power microwaves (HPM) at higher repetition rates than conventional HPM devices without requiring the same auxiliary systems. The ability to array NLTLs to produce higher power and achieve beam steering provides an additional capability. This review summarizes the various NLTL topologies designed to achieve these design objectives. Specifically, we summarize modeling and experimental studies for three primary topologies: the lumped element NLTL, the split ring resonator, and the traditional transmission line geometry using nonlinear materials. The lumped element NLTL and the traditional transmission line constructed with nonlinear materials lend themselves to higher power applications, while the split ring resonator is better suited for applications involving antennas. We provide a detailed summary of past studies for these topologies and conclude by exploring ongoing work and future opportunities for technological development.

Nonlinear transmission lines (NLTLs) are typically driven by pulse forming lines (PFLs) or Marx generators to generate high repetition rate, high power microwaves (HPMs) with fewer auxiliary systems than conventional sources. This paper reports the development of an even more compact HPM system that utilizes a composite-based hybrid NLTL as the PFL and HPM generator in a single device. We designed the following three different combinations of nickel zinc ferrite (NZF) and barium strontium titanate (BST) inclusion volume loads in a polydimethylsiloxane host material to provide magnetic field dependent permeability and electric field dependent permittivity, respectively: 25% NZF, 10% BST/15% NZF, and 15% BST/10% NZF. By constructing the NLTL in a coaxial geometry, this device uses the capacitance and length of the NLTL to generate a fast rise-time high voltage pulse with microwave oscillations that occurred both during and after the pulse after exceeding a threshold charging voltage. The output frequency of the NLTLs ranged from 950 MHz to 2.2 GHz during the pulse for all volume loadings and was 1 GHz after the pulse for the 10% BST/15% NZF and 15% BST/10% NZF volume loadings. The oscillations generated after the pulse were much higher in amplitude and achieved 160 kW at a 15 kV charging voltage for the 15% BST/10% NZF composite-based NLTL.

Nonlinear transmission lines (NLTLs) provide high power RF production and solid state construction, which eliminates many auxiliary systems required by conventional HPM systems 1 . NLTLs use field dependent permittivity and/or permeability to achieve pulse sharpening and RF production. Hybrid NLTLs, which combine both nonlinear permittivity and permeability, have only been implemented previously as lumped element NLTLs 2 . We examine the feasibility of constructing hybrid distributed lines containing nonlinear magnetic and dielectric inclusions, which can tune both the linear permittivity and permeability 3 , 4 and the nonlinear permeability 5 .

Nonlinear transmission lines (NLTLs) offer a compact, solid state alternative to more traditional vacuum high power microwave (HPM) devices 1 . NLTLs have been realized in several topologies; however, these systems are typically limited by power handling capabilities, size, and/or the need for cumbersome auxiliary systems 1 . To mitigate these limitations, we have alternatively designed distributed NLTLs made of composites containing various loadings of ferroelectric and/or ferrimagnetic inclusions 2 , 3 .

Nonlinear transmission lines (NLTLs) can sharpen electric pulses to generate high power microwaves with high repetition rate 1 . This work uses COMSOL Multiphysics to model coaxial, NLTLs composed of ferroelectric and/or ferromagnetic composites to construct a hybrid, distributed NLTL. We have measured the linear electromagnetic properties 2 and nonlinear permeability 3 of such composites from 1-4 GHz to demonstrate the feasibility of adjusting inclusion selection and volume loading to tune electromagnetic properties to adjust NLTL performance. These results justify our use of hyperbolic tangent functions to model the nonlinear electromagnetic properties. Treating an NLTL containing a ferromagnetic composite as a homogeneous domain allows us to assume an effective gyromagnetic ratio and damping factor in the Landau-Lifshitz (LL) equation for specific ferromagnetic composites based on our NLTL experiments. We then solve the LL equation for the gyromagnetic rotation of the magnetization of the composite 4 exposed to an applied external magnetic bias. The NLTL simulation results are compared with our experimental results. Implications to NLTL system design, particularly integrating with an antenna for HPM propagation, will be discussed.

Nonlinear transmission lines (NLTLs) offer a robust, solid state solution for generating high power microwaves (HPM). NLTLs use nonlinear dielectric and/or magnetic materials whose permittivity and permeability, vary with voltage and current, respectively, to modulate a delivered pulse and generate RF. Materials such as barium strontium titanite (BST) and nickel zinc ferrites (NZF) are used for their nonlinear dielectric and magnetic properties, respectively. This study examines the development of composites containing various volume loads of BST, NZF, or combined loadings to tune dielectric and magnetic properties. It was found that by increasing the volume fraction of BST, one can effectively increase the permittivity of a bulk sample. Similarly, by increasing the volume loading of NZF, a samples permeability can also be increased. These results are promising for the development of tunable NLTLs.

We present computational and theoretical assessments on the effective dielectric properties of the nonlinear composites comprised of ferroelectric ceramic inclusions (barium strontium titanate (BST)) and/or ferromagnetic inclusions (nickel zinc ferrite (NZF)) in a linear host to serve as materials for nonlinear transmission lines (NLTLs). We compare classical effective medium theories (EMTs) and computational models using CST Microwave Studio (CST MWS) to predict the dielectric and magnetic properties of the composites in the linear region to measurements. The composite models in CST MWS agree well with measurements and the Lichtenecker rule for NZF composites, while classical EMTs generally fail to estimate effective properties for the cases with high volume loadings and strong dielectric contrast.

While numerous experiments have demonstrated the efficacy of high voltage cold atmospheric pressure plasmas (HVCAPs) in sealed packages for microbial inactivation, the influence of the package on the emitted species measured during HVCAP discharge is poorly understood. This study elucidates the impact of the package on plasma generation in sealed packages for four separate gases (ambient air, commercial grade compressed air, a helium/air mixture, and nitrogen) placed in commercially available transparent plastic containers and bags representative of the materials used in the food industry. The container and bag individually reduced emission signal intensity by an average of 63 and 45%, respectively, across the measured wavelengths of 200–1100 nm, demonstrating that they acted as broadband absorbers. Neither the container nor bag caused additional emission lines to appear, indicating no significant effect on the types of species generated. Considering the minimum applied voltage necessary to induce a discharge, the power dissipated by the nitrogen and ambient air plasma generated at 72 ± 3.7 kV RMS were comparable to the compressed dry air discharge generated at 80 ± 3.7 kV RMS. The helium discharge at 37 ± 3.7 kV RMS absorbed approximately 92% more power than these gases. Rotational temperatures ranged from 285 K for helium to 479 K for compressed air. These results indicate that the package impacts the intensity distribution but not the presence of the most dominant peaks, although further studies are required to elucidate the impact on less intense peaks.

The importance of nonlinear dielectric and magnetic materials for developing nonlinear transmission lines for high power microwave applications necessitates characterization of the behavior of composites containing these inclusions at microwave frequencies. Here, we apply commercial finite element software and various effective medium theories (EMTs) to predict the effective permittivity and permeability of composites containing inclusions with volume fractions of up to 25 % barium strontium titanate (Ba2/3Sr1/3TiO3, BST) and/or nickel zinc ferrite (Ni1/2Zn1/2 Fe2O4, NZF) in a silicon-based host from 1 to 4 GHz. The modelling results suggest that limited agglomerations of high dielectric contrast BST inclusions may create effective higher aspect ratio inclusions that may enhance the effective dielectric properties of BST composites. For the three-phase composites containing BST and NZF in polydimethylsiloxane (PDMS), we first treated the NZF and PDMS as an intermediate “host,” which we subsequently mixed with BST inclusions to construct an effective two-phase EMT. The modelling results agree with the measured permittivity and permeability of the two- and three-phase composites in the linear region and may be used as predictive tools to guide composite design.

Composites with barium strontium titanate (BST) or nickel zinc ferrite (NZF) spherical inclusions mixed in a silicone matrix were manufactured at volume fractions ranging from 5% to 25%. The dielectric and magnetic parameters were measured from 1 to 4 GHz using a coaxial airline. The relative permittivity increased from 2.74 ± 0.01 for the polydimethylsiloxane (PDMS) host material to 7.45 ± 0.33 after combining PDMS with a 25% volume fraction of BST inclusions. The relative permittivities of BST and NZF composites were relatively constant across all measured frequencies. The relative permeability of the composites increased from 1.001 ± 0.001 for PDMS to 1.43 ± 0.04 for a 25% NZF composite at 1 GHz. The relative permeability of the 25% NZF composite decreased from 1.43 ± 0.05 at 1 GHz to 1.17 ± 0.01 at 4 GHz. The NZF samples also exhibited low dielectric and magnetic loss tangents from 0.005 ± 0.01 to 0.091 ± 0.015 and 0.037 ± 0.001 to 0.20 ± 0.038, respectively, for all volume fractions, although the dielectric loss tangent did increase with volume fraction. For BST composites, all volume fraction changes of at least 5% yielded statistically significant changes in permittivity; no changes in BST volume fraction yielded statistically significant changes in permeability. For NZF composites, the change in permittivity was statistically significant when the volume fraction varied by more than 5% and the change in permeability was statistically significant for variations in volume fraction greater than 10%. The DC electrical breakdown strength of NZF composites decreased exponentially with increasing volume fraction of NZF, while BST composites exhibited no statistically significant variation with volume fraction.

The growing importance of nonlinear transmission lines for pulsed power and high power microwave devices in defense and industrial applications motivates material development for system optimization. This study investigates composites manufactured with various volume loadings of both nonlinear magnetic (nickel zinc ferrite) and dielectric (barium strontium titanate) inclusions in a silicone matrix. Increasing the volume fraction of barium strontium titanate (BST) and nickel zinc ferrite (NZF) increased the permittivity with a stronger dependence on BST volume fraction. Increasing NZF volume fraction increased the magnetic permeability, while changing BST volume fraction had no effect. The DC dielectric breakdown voltage decreased exponentially with increased NZF volume fraction. Adding as little as 5% BST to an NZF composite more than doubled the breakdown threshold compared to a composite containing NZF alone. For example, adding 10% BST to a 15% NZF composite increased the breakdown strength by over 800%. The combination of tunability of permittivity and permeability by managing BST and NZF volume fractions with the increased dielectric breakdown strength by introducing BST make this a promising approach for designing high power nonlinear transmission lines with input pulses of hundreds of kilovolts.

Conventionally, microsecond electric pulses have been used for electroporation (μsEP) and electrochemotherapy (ECT). Recently, various studies have used nanosecond electric pulses (nsEP), which have different membrane effects. In addition to the differences in membrane effects, nanosecond pulses can directly manipulate intracellular organelles. Thus, it is of practical interest to study these two phenomena. In this study, changes in MDA-MB-231 human breast cancer cell viability were explored under both μsEP and nsEP, using 100 μs, 240 μs, and 60 ns, with electric field strengths of 1.2, 0.5, and 35 kV/cm, respectively. With curcumin, eight, 0.5 kV/cm, 240 μs pulses the viability was 42%, compared to 75% at eight 0.5 kV/cm, 240μs pulses alone. These had an energy equivalent of 480J/cm3. In comparison, at 580 J/cm3, the nsEP, with curcumin and eight 35 kV/cm, 60 ns, the viability was 70%, and it was only 71% at eight 35 kV/cm, 60 ns pulses alone. This indicates that for the same energy, μs pulses reduce the viability more with curcumin, than with pulses only. In nsEP, without curcumin, the viability was inversely proportional to pulse energy, as viability reduced 2.5× with 2.5× increase in pulse number from 8 to 20 at 35 kV/cm, 60 ns. These results might be helpful in selecting more appropriate parameters for μsEP and nsEP for clinical applications.

High-intensity electric pulses (EPs) alter the mechanical structure of mammalian cells by creating small pores in the plasma membrane 1. One can correlate these EP induced structural changes to changes in electrical properties 2, 3. One electrical characterization technique is time domain dielectric spectroscopy (TDDS), in which one applies low intensity EP to a cell suspension and measures the reflected signal. From this, one can extract the conductivity and permittivity of the plasma membrane, cytoplasm, nuclear envelope, and nucleoplasm in cells by using a two-shell model 2, 3. However, TDDS uses sensitive equipment that prohibits measuring the changes of these properties during a high-intensity EP. In this study, we measure the changes in cell suspension conductivity in real time to elucidate ion transport during EPs. We fix EP application at three different energy densities for three cell media of different conductivity and ion concentration and pulse durations of 60 ns and 300 ns. The conductivity increased during the pulse, indicating ion motion from the cell to the extracellular medium. While similar to the increased conductivity observed by TDDS [2], those measurements occurred greater than one minute after exposure, meaning that diffusion could contribute while the measurements during the EP would only consider electrophoresis. We use a mathematical model 4 coupling the asymptotic Smoluchowski representation of EP induced pore formation with the Nernst-Planck model for ion motion to predict ion motion for the EP parameters studied here to elucidate the contributions of electrophoresis and diffusion. The implications for the mechanisms involved in EP-induced electropermeabilization and ion transport will be discussed.

High voltage cold atmospheric plasmas (HVCAPs) are a novel, inexpensive method for treating produce to enhance shelf-life and eradicate microorganisms that may cause illness 1. Previous work has elucidated the effects of container material during plasma generation 2. Despite numerous studies on jet and dielectric barrier discharge (DBD) discharges, few studies have addressed higher voltages above tens of kilovolts 1, 3. This work explores the effects of higher voltage on plasma generation in the DBD. Applying 36.4, 44.8, 58.1, and 71.0 kV to generate a helium air discharge sealed inside of a container using the B4170 seal bags. We collected the light from the plasma using a fiber optic cable that was provided with the SP2500 spectrometer. We simultaneously measured electrical and OES data and processed it using custom MATLAB scripts to plot the current and voltage, the N 2 Second Positive system, and intensity spectra ranging from 250 to 500 nm to observe species generation. From this, we generated text files that were fed into SEPCAIR to calculate temperatures. Optical emission spectroscopy (OES) measurements show that higher voltages generate higher concentrations of radical species while not directly correlating to an increase in intensity. We also did not observe any change in speciation in the wavelength range studied, suggesting that voltage level primarily changes species concentration and not container material or generation of new reactions. Future studies for HVCAPs must address species generation at higher voltages for different wavelength ranges, fill gases and containers to fully characterize high voltage impact of plasma species generation.

Gas breakdown is typically driven by Townsend avalanche and predicted mathematically by Paschen’s law (PL). Gas breakdown deviates from PL at microscale due to field emission, which depends critically on electrode condition; however, understanding of the impact of initial electrode surface roughness and multiple breakdown events on breakdown voltage is incomplete. This paper assesses the variation of breakdown voltage for a pin-to-plate electrode setup in air at atmospheric pressure for gap distances of 1 ± 0.5 μm, 5 ± 0.5 μm, and 10 ± 0.5 μm with different surface roughnesses. Breakdown voltage generally increases with increasing gap distance and decreasing surface roughness for a single breakdown event; however, the breakdown voltage after ten breakdown events does not depend on initial gap distance. Atomic force microscopy and optical microscopy show that multiple discharges create circular craters on the flat cathode up to 40 μm deep, with more pronounced craters created at smaller gap sizes and greater cathode surface roughness. The resulting effective gap distances (deff, the sum of cathode placement distance and crater depth) for subsequent breakdown events are similar to those of the initially larger gap distances. Moreover, deff becomes sufficiently large to exceed the Meek criterion for streamer formation, indicating a potential for breakdown mechanisms to change from field emission to Townsend avalanche to streamer formation for a single electrode separation distance. The resulting impact of this change in the breakdown mechanism could have significant implications for ensuring consistent microdevice operation.Gas breakdown is typically driven by Townsend avalanche and predicted mathematically by Paschen’s law (PL). Gas breakdown deviates from PL at microscale due to field emission, which depends critically on electrode condition; however, understanding of the impact of initial electrode surface roughness and multiple breakdown events on breakdown voltage is incomplete. This paper assesses the variation of breakdown voltage for a pin-to-plate electrode setup in air at atmospheric pressure for gap distances of 1 ± 0.5 μm, 5 ± 0.5 μm, and 10 ± 0.5 μm with different surface roughnesses. Breakdown voltage generally increases with increasing gap distance and decreasing surface roughness for a single breakdown event; however, the breakdown voltage after ten breakdown events does not depend on initial gap distance. Atomic force microscopy and optical microscopy show that multiple discharges create circular craters on the flat cathode up to 40 μm deep, with more pronounced craters created at smaller gap sizes and great...

Room temperature atmospheric plasma offers an efficient, inexpensive method for treating produce to enhance shelf-life and eradicate microorganisms that may cause illness1. One approach for produce treatment involves creating plasmas within a package2 and varying the fill gas within the container to optimize microorganism deactivation3. While optimization may be possible, the impact of the package material on the plasma remains poorly understood. We performed optical emission spectroscopy (OES) to assess the impact of the package material on the plasma generated within the package for applied voltages from 45kV to 88kV. Replacing the standard packaging with a sealed low-density polyethylene bag reduced the intensity of the OES measurement, but did not significantly impact species generation in the packaging. Similar behavior arose for other fill gases. We observed molecular OH species from 200 to 300 nm and molecular N2 species from 315 to 379 nm for both package types using air as a fill gas while a Ha peak from 647 to 682 nm could not be fully resolved due to limited instrument resolution. Voltage and current measurements enabled quantification of the power delivered to the target, which provides a benchmark for standardizing plasma treatments across samples. The impact of packaging, fill gas, and power on species generation, as well as the potential impact of these results on treatment efficacy and system optimization, will be discussed.

Electric pulses (EPs) can permeabilize cell membranes and intracellular organelles for ion and molecule transport. One can modulate these biophysical effects by changing the pulse shape and duration. Electrically, EPs change the permittivity and conductivity of the cell membrane and intracellular structures; however, measuring these parameters during the EPs is challenging. We assess the impact of EPs on extracellular conductivity to assess membrane permeabilization and ion transport into or out of the cells. For low conductivity buffer solutions, the extracellular conductivity increases from ∼0.15 S/m to 1.1 S/m during 300 ns EPs, indicating membrane pore formation and ion motion out of the cell. For buffer conductivity on the order of the intracellular conductivity, extracellular conductivity changes from ∼1.8 S/m without cells to ∼1.6 S/m, suggesting much less ion flow. The implications of these results are discussed.

Pulsed electric fields (PEFs) may interact with the cell and/or intracellular membranes depending upon the pulse duration and rise time. The resulting modifications in cell structure and function may be observed through changes in the electrical properties of the cell suspension or of the individual components of the cell, such as the cell membrane, cytoplasm, nuclear envelope, and nucleoplasm. Some past experiments have used time domain dielectric spectroscopy (TDDS) to measure the changes induced by PEFs; however, TDDS cannot be used to measure real time changes since the PEF's high voltage would damage the sensitive measurement electronics. Thus, we extend previous cell suspension conductivity measurements by measuring the voltage and current across a cuvette during single or multiple pulses and calculating the resulting cell suspension conductivity. Additionally, this approach will enable the use of standard electroporation buffers (e.g. Hank's Balanced Salt Solution) that have higher conductivities than can be used in TDDS due to electrode polarization. Implications of membrane permeabilization, buffer conductivity, and pulse parameters on PEF induced cell suspension conductivity changes will be discussed.

WHEN still unversed in the science of aero‐dynamics, and seeking to learn all that was possible about the subject, I happened upon the foundation of what later developed into an aeroplane performance prediction chart which it is the purpose of this article to describe.