Gyromagnetic Nonlinear Transmission Lines Research Articles

Finite element analysis of pulse sharpening effect of gyromagnetic nonlinear transmission line based on Landau–Lifshitz–Gilbert equation

Ferrite-loaded gyromagnetic nonlinear transmission line (GNLTL) provides a possible option to compress an input pulse to a narrower width for its remarkable sharpening effect. However, it is difficult to accurately predict the output of the GNLTL due to the complex interaction between the magnetic moment of ferrite and the bias magnetic field. In this paper, a finite element model of the GNLTL is established based on the Landau–Lifshitz–Gilbert equation to investigate the performance of the GNLTL. To validate this model, a prototype is used for experimental comparison. The result demonstrates good agreement between experiment and simulation. This paper further explores the influence of the bias magnetic field and the length of the GNLTL on the output pulse. Moreover, a method to sharpen the falling edge is proposed based on the reflection and superposition of the GNLTL output. Simulation and experimental results show its effectiveness and feasibility.

Test and Analysis on the Gyromagnetic Nonlinear Transmission Lines With Different Magnetic Cores

Test and Analysis on the Gyromagnetic Nonlinear Transmission Lines With Different Magnetic Cores

Verification of spinwave excitation in coaxial gyromagnetic nonlinear transmission lines.

The knowledge of physical mechanism of microwave generation in coaxial gyromagnetic nonlinear transmission lines (GNLTLs) is not complete up until now, especially the action of spinwave excitation during this process. In this paper, control experiments on different groups of GNLTLs with a single variable of NiZn ferrite material spinwave linewidth ΔHk are proposed as an indirect way to demonstrate this microscopic process. Comparative analyses of different groups of GNLTL experimental results are conducted to clarify the existence and effect of spinwave excitation. Theoretical treatment of conditions of spinwave excitation in GNLTLs is derived to explain the experimental results. It is illustrated that spinwave can be excited when the synchronism condition between the working frequency of GNLTL and the spinwave frequency spectrum is satisfied. The unstable spinwave excitation will consume the RF energy of GNLTLs heavily and cause a rapid decrease in RF oscillation.

Numerical Simulation Method of Gyromagnetic Nonlinear Transmission Lines Based on Coupled Solution of Maxwell and LLG Equations

Numerical Simulation Method of Gyromagnetic Nonlinear Transmission Lines Based on Coupled Solution of Maxwell and LLG Equations

The Gyromagnetic Nonlinear Transmission Lines Based on Microwave Ferrites

Nonlinear gyromagnetic coaxial lines with saturated ferrite rings of different types have been tested. The test results showed that microwave (mw) ferrites, with low losses at high frequencies, can improve the parameters of output mw oscillations. The line with the assembly of mw ferrite rings with a spinel structure provided a maximum increase in the leading peak amplitude by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 1.3 times to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 205 kV, with a modulation depth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 90%, and more oscillation periods with an effective frequency of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 2.2 GHz. It is also shown that mw ferrite rings with a rectangular hysteresis loop (RHL) are promising for the gyromagnetic lines with a permanent magnet bias system.

Theory and practice of pulse compression in hybrid and gyromagnetic non-linear transmission lines

This paper presents a comprehensive analysis of pulse compression capability in hybrid and gyromagnetic non-linear transmission lines (NLTLs). The corresponding theoretical analysis in the hybrid NLTLs is derived and discussed in detail with the generation and sharpening aspects of leading and trailing pulse edges. The parameters responsible for pulse sharpening are examined and their corresponding pulse compression capability is modelled by providing the output waveform while varying these parameters. A holistic overview and mathematical development of gyromagnetic NLTLs are also conducted, which are modeled and validated through an equivalent lumped element model. Important parameters such as saturation magnetization, gyromagnetic NLTL sections, and damping parameter are elaborated and their influences on pulse sharpening and compression capability are studied. Validation of the theoretical and parametric analysis is performed by an experimental demonstration. The results achieved from hybrid and gyromagnetic NLTLs are briefly summarized, and their corresponding advantages and disadvantages are highlighted. This research is set to provide a fresh and successful debut for investigating gyromagnetic and hybrid NLTLs and their inherent effects on pulse compression for future ultrafast electronic systems and interconnects.

A wideband high-power microwave radiation source based on gyromagnetic nonlinear transmission line and Vlasov antenna.

The gyromagnetic nonlinear transmission line (GNLTL) is a special kind of coaxial transmission line partially loaded with the ferrite material. A GNLTL system can modulate the input high-power pulses into wideband high-power microwaves without relying on the electron beam and confining magnetic field. The unique working mechanism gives the GNLTL system the potential to be a small portable wideband high-power microwave radiation source. In this study, a wideband high-power microwave radiation source based on a GNLTL system is designed and constructed. In order to effectively radiate the wideband microwaves into the air, a high-power wideband Vlasov antenna and a special absorption high-pass filter are developed. The designs of key subsystems and high-power radiation experiments have been introduced and discussed in detail. In the test experiments, a radiated pulse with a peak electric field strength of 23 kV/m was measured at 20m away from the transmitting antenna and the effective potential of radiation is 460 kV/m. The pulse width of the radiation pulse is about 4ns, the center frequency is about 2.25GHz, and the highest repetition rate can reach 25Hz.

100-MW-Level Experiments of a Gyromagnetic Nonlinear Transmission Line System

The wideband high-power microwave systems have the advantages of wide energy spectrum, electron beam independence, compactness, and low cost. The gyromagnetic nonlinear transmission line (GNLTL) has drawn much attention for its potential as a novel solid-state, frequency-agile, and compact wideband source. The working mechanism of GNLTL is different from that of the traditional electric vacuum tubes, and the strong dispersion and nonlinear characteristics make it difficult to be accurately theoretically calculated and simulated. In this article, a 100-MW-level GNLTL system based on a Tesla-type driver was designed and constructed. A series of test experiments were then carried out to investigate the effects of different configurations, including delay line length, ferrite cores’ assembly orientation, transmission line length, bias magnetic field magnitude, and excitation voltage. The changing laws of the key parameters of the output microwaves including the peak power, modulation depth, center frequency, and percentage band are summarized and the underlying physical mechanisms are analyzed. The results may be instructive for the predesign of GNLTLs, especially for the devices operating at high power. In addition, a multiple center frequency points’ phenomenon was discovered in the output signal, which may bring new application possibilities for GNLTL.

High-Voltage Microwave Systems Based on Ferrite Gyromagnetic Nonlinear Transmission Lines

Test results of high-voltage stationary four-channel generators based on the coaxial gyromagnetic ferrite-filled nonlinear transmission lines (NLTLs) with external magnetic bias and modulation frequency of the rapidly damping oscillations of ~ 8.7 GHz are presented. The peak amplitude of the output oscillations of −350 kV in the channel had a maximum modulation depth more than 80%. The single-channel stationary microwave system increased the peak amplitude to record value −695 kV in the frequency range ~ 10 (11.5) GHz. The compact two-channel gyromagnetic ferrite line system was also tested. The peak amplitude of output oscillations reached −170 kV when the modulation frequency is of ~ 6.5 GHz. Electrical strength of oil-isolated ferrite line was tested in the compact one-channel system at a repetition rate of 25 pps when an electrical field in the line reached ~ 185 kV/mm.

Analysis of the sharpening effect in gyromagnetic nonlinear transmission lines using the unidimensional form of the Landau-Lifshitz-Gilbert equation.

Continuous nonlinear transmission lines (NLTLs), also known as gyromagnetic lines, consist of ferrite-based magnetic cores biased by an external magnetic field. Over the past years, many analytical and experimental studies have predicted the rise time reduction of the input pulse to the range of a few nanoseconds or even hundreds of ps experimentally observed in such gyromagnetic lines. This effect, known as pulse sharpening, is investigated in this paper built on a model based on a periodic structure of inductive-capacitive cells in series with magnetization-driven voltage sources expressed by the one-dimensional form (1D) of the Landau-Lifshitz-Gilbert (LLG) gyromagnetic equation. We explore the model through parametric study under various input-pulse parameters to understand the physics behind the ferrimagnetic material responses. Moreover, the numerical results obtained from computational simulations using Mathematica (v. 12.1) show how the line parameters (input voltage, damping constant, saturation magnetization, and length) affect the sharpening effect, which is quantified by the switching time. Our results on ferrite-loaded coaxial lines have confirmed many results found in the literature. We validated with a good agreement the proposed model with the result obtained by Dolan in 1993 using the same 1D form of the LLG equation, thus showing that the model proposed here is suitable to quantify the sharpening effect produced by a gyromagnetic NLTL.

RF Pulse Generation in a Gyromagnetic Nonlinear Transmission Line With Periodically Placed Ferrites and Permanent Magnets

This article presents a work on development of a high-power radio pulse generator, which is a gyromagnetic nonlinear transmission line (GNLTL) in which periodically placed NiZn ferrites are saturated by an axial magnetic field produced by permanent magnets periodically placed inside the transmission line. Structurally, the line is a corrugated coaxial waveguide with permanent NdFeB magnets placed inside the inner conductor of the line. The transmission line geometry was optimized using numerical simulation by finite-difference time domain (FDTD) method. The excitation of high-frequency oscillations in the developed transmission line at central frequency of 1 GHz and above is shown experimentally using ferrite rings with 45 and 28 mm outer and inner diameters. The maximum peak power of microwave oscillations obtained in the experiments is 110 MW at the central frequency 1.3 GHz. The obtained RF power is comparable to that of more common GNLTL with continuous filling by ferrite rings having the same transverse size.

Numerical Analysis on the RF Characteristics of the Gyromagnetic Nonlinear Transmission Lines

The gyromagnetic nonlinear transmission line (GNLTL) is a special transmission line loaded with ferrite cores, which can be used as a kind of wideband high-power microwave (HPM) source due to the pulse modulation mechanism. This article carried out a series of simulations and analyses focused on the RF characteristics of GNLTL. Based on the classic transmission line model (TLM) method, a numerical model linking the transmission line equations and the microscopic magnetization dynamics equations was established. The simulations systematically studied the effects of key parameters on the output characteristics especially the RF characteristics, including the effects of transmission line geometry, excitation pulse, magnetic material, and the biasing magnetic field. The simulation results and analyses revealed that almost each parameter has effects on the output, and the effects of different parameters are different. The research introduced in this article preliminarily reveals how the output microwave varies with the parameters and provides a method to find the appropriate parameter values of a GNLTL.

RF generation using a compact bench gyromagnetic line

The search for new technologies aiming to reach radiofrequency (RF) generation in different manners for diverse ends is a constant demand for several applications. The goal is to develop cost-effective and simpler systems compared to those that already exist. Our motivation is to reach an alternative way of generating RF in pulsed transmission systems employing a gyromagnetic nonlinear transmission line (GNLTL). The GNLTL consists of a ferrite-loaded-coaxial transmission line and can produce a large frequency spectrum with RF conversion efficiency above 10% from about 200MHz up to the frequency of 2-4GHz (S-band) for potential space-based applications. In a GNLTL, the signal amplitude is related to its propagation velocity since the peak voltage travels faster than its portion of lower amplitudes since the ferrite permeability decreases with the current amplitude. As the pulse crest travels faster than its valley, a time reduction happens in the output rise time, called pulse sharpening. Besides, the magnetic moments of ferrite dipoles initially aligned with the axial magnetic bias are displaced from their original position by the azimuthal field generated around the inner conductor by the current pulse, resulting in a damped precession movement. This movement happens along the line length as the current pulse propagates, inducing high-frequency oscillations. In short, the paper's goal is to present the experimental results using a 60-cm gyromagnetic line to provide RF in the GHz range using a solenoid for magnetic bias on a testing bench. Finally, the paper discusses the influence of the azimuthal and the axial magnetic fields on the output signal with the ferrite rings operating in a saturation state during the current pulse propagation.

Nonlinear gyromagnetic transmission line design optimization for increasing radiopulse generation efficiency

Using numerical simulation an optimization of gyromagnetic nonlinear transmission line design was carried out. The goal of simulation was to increase efficiency of video pulse into radiofrequency pulse transformation. Several factors significantly influencing the efficiency of generators were found. Experimental validation of some obtained results is also discussed.

Material Selection for Axial Magnetization of a Gyromagnetic NLTL for Space Applications

Nonlinear Transmission Lines (NLTLs) are a new technique for radio frequency (RF) generation. A loaded ferrite NLTL, known as a gyromagnetic line, uses a solenoid to provide an external magnetic bias. In space applications, specifically in satellites, the replacement of these solenoids by permanent magnets is desirable, eliminating the need for a DC current source, and reducing the weight and the effective cost of the launch. This work investigated and selected permanent magnets for this application, and then computationally modeled the magnet assembly to analyze the resulting magnetic field generated and obtained a uniform field region to meet the NLTL operating specifications. For this, we employed selection charts for the proper choice of material to use in an arrangement of magnets simulated by the electromagnetic software CST Microwave Studio . Magnetic fields with uniformity variations of less than 6% and 23% in regions extended over 18.5 cm and 58.8 cm, corresponding to line lengths of 26.6 cm and 68.0 cm, respectively, were achieved in simulations.

Low-impedance high-power pulsed generator based on forming line with built-in Tesla transformer.

In order to meet the application needs of gyromagnetic nonlinear transmission lines, a pulsed power generator is required to output short duration pulses with a fast rising edge in high repetitive-rate mode. In this paper, a low-impedance high-power pulsed generator based on the forming line with a built-in Tesla transformer is explored and developed. The generator includes a 14 Ω coaxial forming line, a SF6/N2 gas switch, and a resistive dummy load, which can steadily operate in 100Hz mode and suits the needs above. The pulsed forming line adopts transformer oil as the insulation medium and has a large shell radius and short length to reduce impedance. It has been verified by CST simulation that a relatively high coupling coefficient (0.93) can be achieved when the length-radius ratio is 3.2. The maximum forming line charging voltage is -600 kV in single-shot mode, while the charging voltage is -520 kV in repetitive-rate mode. The output pulse duration is 13ns with a 4ns rising edge, and its amplitude for a 10 Ω load is -220 kV at a repetition rate of 100Hz. The experimental results showed the feasibility of the low-impedance nanosecond periodically pulsed generator based on an oil forming line charged from the high-coupling Tesla transformer. These efforts expand the technical route of the pulse forming line with a built-in Tesla transformer and set a good foundation for its application in the future.

Nonlinear transmission line-driven apparatus for short-pulse microwave exposure of aerosolized pathogens.

A system capable of exposing a flowing aerosol stream to short duration (2-4ns), high-power RF waveforms is described. The system utilizes a C-band gyromagnetic nonlinear transmission line source having peak power outputs ranging as high as 80 kW at a center frequency of 4.2GHz. RF electric field magnitudes of up to 280 kV/m ± 17% are achieved within the aerosol flow region of the RF exposure apparatus.

Operation analysis of the wideband high-power microwave sources based on the gyromagnetic nonlinear transmission lines.

The wideband High-Power Microwave (HPM) sources, which combine the advantages of narrowband and ultrawideband sources, have drawn much attention. As a kind of wideband source, the gyromagnetic nonlinear transmission lines (GNLTLs) can directly modulate the incident pulses into radio frequency pulses without relying on the interaction between e-beam and microwaves. Due to the special working mechanism of gyromagnetic precession, the center frequency of the GNLTL can also be adjusted in a certain range. Based on classical magnetism and a simplified model of the GNLTL, this paper semi-quantitatively and theoretically analyzed the generation mechanism of HPM and illustrated the influences of the variations of parameters on the output microwaves. Then, a simple simulation based on 1-dimensional transmission line modeling method was carried out to study the performance of the GNLTL quantitatively, with the coupling of 1D telegraphist equations and the 3D Landau-Lifshitz-Gilbert equation. Simulation results preliminarily verified the conclusions derived from the theoretical analysis, and some working characteristics of the GNLTL were also obtained. This paper may help to understand the special working mechanism of the GNLTL and provide certain guidance for related simulations and experiments.

Field-Line Coupling Method for the Simulation of Gyromagnetic Nonlinear Transmission Line Based on the Maxwell-LLG System

The gyromagnetic nonlinear transmission line (GNLTL) is a compact and solid-state high-power microwave source, which can be treated as a special coaxial transmission line partially filled with the ferrite material. Due to the complex interaction process of the electromagnetic fields with the dynamic damped precessional motion of the magnetization vector in the ferrite, it is of great challenge to theoretically predict the output of the GNLTL. Here, we present a novel field-line coupling simulation method to predict the output waveform of the GNLTL by simultaneously solving the coupled system of the Landau-Lifshitz-Gilbert equation and Maxwell's equations in the 2-D cylindrical coordinate system. In particular, the simulation model is validated by comparing the computation results with the experimental results obtained by Bragg et al. in the HPM experiment. The influences of the GNLTL length and bias magnetic field are analyzed. The proposed computation method can provide a solution for improving the performance of the GNLTL.

Gyromagnetic source of high power wideband pulses

In this paper we present the results on simulation and experimental research of RF oscillations excitement in gyromagnetic nonlinear transmission line. The oscillations were observed in the frequency range 1.5-1.7 GHz. The choice of the appropriate ferrite type and irradiating helix antenna was followed by the development of high power RF source. The irradiated RF pulses were characterized by 80 kV effective potential and close to circular polarization. The gyromagnetic RF source has shown stable operation at 400 Hz repetition rate.