Lauro P. Silva Neto

Soliton Generation Using Nonlinear Transmission Lines

In recent years, there has been great interest in the study of nonlinear transmission lines (NLTLs) for high-power radio frequency (RF) generation. The periodicity of the NLTL accounts for dispersion effects, whereas its nonlinear elements (inductors and/or capacitors) are responsible for the nonlinear processes. Both of these mechanisms acting simultaneously on a propagating pulse allow the generation of high-frequency oscillations at the output. The objective of this paper is to study the quantifiable characteristics of these lines for RF generation by means of SPICE circuit simulation and on basis of experiments. The RF generation at 40 MHz is demonstrated through measurement of the fast Fourier transform of the RF signal extracted at the load and by comparison with the corresponding simulated spectrum. It is expected that the technique presented here can be useful for the design of NLTLs to drive compact RF antennas for space applications and defense mobile platforms.

Characterization of Ceramic Dielectrics for Sub-GHz Applications in Nonlinear Transmission Lines

Low loss dielectric materials with high permittivity and nonlinear behavior are essential for use in capacitive nonlinear transmission lines (NLTLs) for RF generation. NLTLs have a great potential to generate soliton waves for high-power microwave applications in mobile defense platforms and satellite communications. In this paper, the dielectric properties of a piezoelectric capacitor based on lead-zirconate-titanate (PZT) was characterized in a broadband frequency range from 10 MHz to 1 GHz for use in NLTLs. Three commercial ceramic capacitors made of barium titanate (BaTiO3) were also assessed for comparison with the PZT capacitor. The characterization of materials consisted of measuring the relative dielectric constant (real and imaginary parts) as function of the applied voltage and frequency to calculate the loss tangent of the material. The results showed that PZT material has a better performance for use in NLTLs than barium titanate because of its lower losses. As discussed here, however, the use of PZT and barium titanate-based materials in NLTLs are compromised by the self-resonant frequency of the capacitors because of the inherent parasitic inductance associated with the capacitor at high frequencies.

State of the art of nonlinear transmission lines for applications in high power microwaves

Nonlinear transmission lines have been used with great success in pulse sharpening for obtaining output fast pulse rise times in nanosecond and picosecond ranges. Nowadays recent research on this field has shown a great prospect for RF generation using these devices in aerospace application such as in ultra-wide band radar for communications, remote sensing and surveillance due to less attenuation and electromagnetic interference. Also other important applications are envisioned in high power microwave sources for battlefield communication disruption and space vehicle systems as they can replace electronic tubes without the need of vacuum and heating. A nonlinear transmission line basically consists of a lumped LC line using a nonlinear element (variable inductance or capacitance) or a continuous transmission line using a nonlinear medium (ferroelectric or ferrimagnetic). In this paper the state of art for both configurations are discussed as well as their main characteristics and limitations.

Adherence Enhancement of Metallic Film on PZT-Type Ceramic Using Nitrogen Plasma Implantation

Lead zirconate titanate (PZT)-type ceramics used as piezoelectric sensors have electrodes made by metallic film deposition on the ceramic substrate, which has low adherence on substrate surface. During the welding process in electronic component manufacture, the metallic film releases from surface due to the electrode delamination caused by the large difference in thermal expansion gradients between the film and ceramic. Delamination is a serious problem found in the manufacture of ceramic capacitors since the metallic electrode is split into several layers, leading to a component failure as the electrode is not in contact with the ceramic surface anymore. Therefore, in order to increase the film adherence on the ceramic it is proposed in this paper to treat the PZT samples covered with silver metallic films by means of plasma immersion ion implantation (PIII) technique using a high voltage 100-kV/1-μs stacked Blumlein pulser. By using this technique, it is shown that the mechanical adherence of the electrode metallic silver film is increased, which allows the welding process of terminals for the piezoelectric device manufacture without film release failure. Thermal stress relief treatment known as annealing process was also used in this paper as an alternative to the PIII method for increasing the film anchoring on ceramic substrate.

High-Power RF Generation From Nonlinear Transmission Lines With Barium Titanate Ceramic Capacitors

In recent years, nonlinear transmission lines (NLTLs) have been investigated for high-power radio frequency generation. High-power waves produced using NLTLs can be applied in mobile defense platforms and satellite communications as they can reach tens of MW of peak power. Their principle of operations is based on the nonlinearity of inductive and/or capacitive lumped elements used in such lines. In this paper, an NLTL using commercial ceramic capacitors as nonlinear elements and linear inductors was simulated and built. Experimental and simulated results show good agreement, validating the model of ceramic capacitors. The frequency obtained from soliton generation at the output of the line was about 4 MHz with peak power of the order of 8 kW.

Study of the ceramic capacitor dielectric for pulsed power

Summary form only given. In this work it is shown that the dielectric constant or the capacitance of commercial capacitors are dependent on the following parameters: the voltage applied, the charge and discharge of pulse repetition rate, temperature, and frequency. The study of these parameters is essential for applications of ceramic capacitors in high-energy storage systems and in nonlinear transmission lines (NLTLs) used for RF generation. To accomplish that two basic circuits are described for measuring the capacitance or ε: 1) on static conditions (i.e. by varying the charging DC voltage across C for checking the dielectric nonlinearity) and 2) on dynamic conditions (under pulse repetition rate or temperature variation) to determine the respective C variation. Finally, the ESR (equivalent series resistance) of the dielectric and its dissipation factor are also measured using an Agilent LCR bridge/ 30 MHz to verify the ceramic capacitor losses, a key issue for NLTL applications as the line attenuation constant increases with frequency.

Influence of Input Pulse Shape on RF Generation in Nonlinear Transmission Lines

Nonlinear transmission lines (NLTLs) are nonlinear LC ladder networks that can act as a nonlinear and dispersive medium, thus allowing the generation of soliton bursts. Several papers have been published indicating that NLTLs offer a new option for pulse shaping and RF generation. In this paper, we investigated the response of an NLTL driven by three different pulse shapes: a rectangular, a half sine, and a triangular waveform. The performance of the NLTL was evaluated through time- and frequency-domain analysis of the RF signal sampled at the 29th section of a 30-section capacitive NLTL. The frequency of the generated RF signal is correlated with the shape of the input signal, whereby the output frequency can be adjusted by the amplitude-time characteristics of the pulse at the input of the capacitive NLTL. Higher frequency oscillations, around 30 MHz, were generated by the rectangular wave train due to its shorter rise time. The propagation of solitons along the NLTL is influenced by the input pulse rise time. Namely, the rectangular pulse showed smaller delay time as it had the shortest rise time (less than 10 ns). Maximum efficiency was obtained for the input pulsewidth of 150 ns under a duty cycle of 1/3 for the three pulse shapes (rectangular, half sine, and triangular), and this combination of parameters yielded the highest RF conversion efficiency of the NLTL. The capacitive NLTL showed a higher RF conversion efficiency (16.4%) when driven by the rectangular input signal.

Frequency Characterization of Ferrite Beads in the Microwave Range for Nonlinear Applications

Ferrite beads are ferromagnetic materials that exhibit a small inductance at low frequencies, becoming resistive at high frequencies. These devices are used as low pass filters for reducing electromagnetic interference (EMI) in communications and power electronics because the resistive losses attenuate the undesired frequencies. As ferrite beads have a nonlinear behavior with current and frequency they have been used in nonlinear transmission lines (NLTLs) for high power microwave generation in space and defense applications. In this work, high frequency ferrite beads are characterized in the frequency range up to 1 GHz by measuring S11 reflection parameter in order to calculate their complex permeability and losses, key parameters in the design of NLTLs. In addition, X-ray diffraction (XRD) is used to identify their chemical element composition. Finally, the motivation for this work is basically due to the limited information on ferrite materials provided by the manufacturers.

Systems Concurrent Engineering for the Conception of an Attitude and Orbit Control System

This paper presents a systems concurrent engineering approach for the conception of an Attitude and Orbit Control System for a Satellite (AOCS). Systems Engineering uses a multidisciplinary approach in order to better understand complex systems and its processes, its products and its organization. The main goal is to satisfy all stakeholders involved in the product and its processes. In this paper several concepts of Systems Engineering, as well as its methodology, were applied in the main processes of the life cycle of an AOCS of an artifitial satellite, in order to give a better understanding of the development of this kind of product, from requirements analysis to system operation.