L. P. Silva Neto

Study of HV dielectric ceramics for applications in compact pulsed power

The scientific interest of this paper consists of the study of ceramic dielectrics for applications in compact pulsed power systems. The reason for this is that ceramic dielectrics with large dielectric constant and high breakdown strength have great potential for decreasing the volume required for pulsed power supplies in future envisioned pulsed power-driven systems on mobile platforms. In particular, the main idea here is to check the dielectric properties of PZT (Lead Zirconate Titanate) ceramics for use in storage systems because of their high dielectric constant (300–3000) and excellent performance in HV explosive-driven ferroelectric generators.

Characterization of dielectric properties of commercial ceramic capacitors for pulsed power applications

It is found currently a wide diversity of dielectrics used for the construction of capacitors, where barium and strontium titanate-based ceramics are the most used. This study concerns the dielectric characterization of commercial ceramics capacitors for use in high voltage capacitors of high-energy storage systems and soliton wave generation for RF production in space applications. To characterize the dielectric material two commercial ceramic capacitors were submitted to HV tests to determine the dielectric constant variation with the applied voltage and the dielectric strength voltage (breakdown -BD) under pulsed conditions. The results show that ceramic capacitors present BD strength of the order of 90–200 kV/cm and non linear behavior, i.e. the ceramic dielectric constant is greatly reduced with the voltage increase.

Prospects of building capacitive nonlinear lines using ceramic PZT for high-frequency operation

The objective of this paper is the study of ceramic dielectrics for nonlinear transmission line (NLTL) applications in high-voltage (HV) compact pulsed power systems at high frequencies. Barium and strontium titanate (BST) ceramics have been used with great success as excellent dielectrics in the construction of high voltage (HV) commercial ceramic capacitors with reduced dimensions because of their high dielectric constant. However, the attempts to reach frequencies above 500 MHz up to 1 GHz using BST ceramics in nonlinear lumped lines have been unsuccessful due to the loss in the dielectric material that limits the operating frequencies up to about 250 MHz. On the other hand, these results indicated that the use of a lower loss nonlinear dielectric of reduced permittivity could be the solution for achieving higher frequencies in nonlinear capacitive lines. Therefore, the main point of this work is to characterize another type of ceramic known as PZT (Lead Zirconate Titanate), which is promising for NLTL applications.

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 non linear transmission lines (NLTLs) for RF generation. NLTLs have a great potential to generate solitons waves for high power microwave applications in mobile defense platforms and satellite communications. In this work the dielectric properties of a piezoelectric capacitor based on lead-zirconate-titanate (PZT) was characterized in a broadband frequency from 10 MHz to 1 GHz for use in NLTLs. Also three commercial ceramic capacitors made of barium titanate (BaTiO3) were also assessed for comparison with the PZT capacitor. The characterization of materials consists 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 shown here, however, the use of PZT and barium titanate based materials in NLTLs are compromised by the self-resonant frequency of the capacitors due to the inherent parasitic inductance associated to the capacitor at high frequency.

High power RF generation in nonlinear lumped transmission lines using commercial ceramic capacitor as nonlinear elements

In recent years, nonlinear transmission lines (NLTLs) have been investigated for high-power radiofrequency (RF) 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 the lumped elements (Ls and/or Cs) used in these lines. In this work, a 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 1 kW.

Improvement on PMMA surface breakdown using plasma immersion ion implantation

Polymer dielectrics are used in several areas. Previous works have shown a great influence of hydrophobicity on the surface breakdown (BD) voltage of some dielectrics. The use of energetic particles to modify polymer surfaces is a method widely employed. In this work, the surface of a poly-methyl-methacrylate (PMMA) polymer sample has been modified by a treatment technique known as plasma immersion ion implantation (PIII) in order to test its surface BD. After treatment by PIII, it was shown that the polymer resistance to the surface flashover was improved, which is important for insulators in space applications with partial vacuum in lower orbit satellites. The treated samples were characterized by means of contact angle and surface BD measurements to verify respectively changes on surface hydrophobicity and surface resistance to flashover. Surface BD measurements were carried out by using a special breakdown testing pulser.

Key issues in design of NLTLs

Dielectric nonlinear element transmission lines (NLTLs) have demonstrated great potential in RF generation. Their main characteristic is that they do not require an electron beam to operate. However, there are some key points in their operation not clarified yet. For instance, they generate output oscillations with frequency near half the line Bragg frequency with unmatched load less than full characteristic impedance; however, for high resistive load this frequency appears to be near the Bragg frequency. In this paper, these points are checked experimentally by measuring the standard FFT of the signal along a varactor diode NLTL made with 30 sections, whose operation frequency is in the range of 25-40 MHz depending on the load.

Adherence enhancement of metallic film on PZT type ceramic using nitrogen plasma implantation

PZT (Lead zirconate titanate) 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 [1]. 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 work 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/1μs 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 work as an alternative to the PIII method for increasing the film anchoring on ceramic substrate.

Pulse sharpening and RF generation using nonlinear transmission lines

A nonlinear lumped element transmission line (NLETL) with linear inductors and using capacitors as nonlinear elements was built to operate as a high voltage pulse sharpener. NLETLS are suitable for use in fast sampling pulse generation circuits and in the formation of high-voltage solitons, among other applications. In this paper, a NLETL built with 30 sections was tested up to 500 V providing a pulse rise reduction of 700 ns for an input rise time of about 2.5 μs on a 70 ohms resistive load when using a 1.2 kV IGBT solid state switch. Comparison of experimental results with Spice simulation from equivalent NLTL circuit modeling has shown good agreement.

Operation of dielectric nonlinear transmission lines based on ceramic PZT slabs

De-poled PZTs (Lead-Zirconium-Titanate) were studied in the terms of nonlinearity properties, dielectric losses and breakdown. As shown in this paper de-poled PZTs have lower permittivity and dielectric losses compared to poled ones and BT (Barium Titanate) ceramic dielectrics. This was confirmed by measuring the permittivity, polarization curve and, tangent loss (δ) of this material. As discussed herein lower dielectric losses and permittivity may favor the replacement of BT tiles by PZTs in dielectric nonlinear transmission lines used for RF generation.