Ferroelectric Generators Research Articles

Completely explosive ultracompact high-voltage nanosecond pulse-generating system

A conventional pulsed power technology has been combined with an explosive pulsed power technology to produce an autonomous high-voltage power supply. The power supply contained an explosive-driven high-voltage primary power source and a power-conditioning stage. The ultracompact explosive-driven primary power source was based on the physical effect of shock-wave depolarization of high-energy Pb(Zr52Ti48)O3 ferroelectric material. The volume of the energy-carrying ferroelectric elements in the shock-wave ferroelectric generators (SWFEGs) varied from 1.2 to 2.6cm3. The power-conditioning stage was based on the spiral vector inversion generator (VIG). The SWFEG-VIG system demonstrated successful operation and good performance. The amplitude of the output voltage pulse of the SWFEG-VIG system exceeded 90kV, with a rise time of 5.2ns.

Probing helix formation in chains of vertex-linked octahedra

The rational design of crystal structures based on the chemical nature of molecular components, a longstanding and exciting research topic in organic solid state chemistry, is an emerging theme of crystal engineering in inorganic solid state chemistry. In particular, noncentrosymmetric structures, or those lacking inversion symmetry, are important for future technologies that are based on piezoelectricity, pyroelectricity, ferroelectricity and second harmonic generation (SHG). Materials that exhibit these properties provide a large and new class of solids for studies in basic science associated with the noncentrosymmetric (chiral, polar, or chiral–polar) space groups. Structures comprised of vertex-linked octahedra are common in inorganic solids. The subject of our Highlight is the rational synthesis of linear, zigzag or helical chains when two vertices of an octahedron, which are either adjacent (cis) or opposite (trans), are linked.

Theoretical treatment of explosive-driven ferroelectric generators

As a part of the New World Vistas Program, a series of ultra-compact explosive-driven ferroelectric generators (EDFEGs) has been designed, constructed, and tested by Texas Tech University providing well-documented EDFEG output parameters that were used to benchmark a theoretical model of the EDFEG developed at the Institute of Electromagnetic Research. A description of the model for the EDFEG is presented along with a brief description of the EDFEG, the experimental setup, and test procedures that were used. A comparison of the experimental and calculated results shows them to be in good agreement.

Two-dimensional ferroelectricity and second harmonic generation in PVDF Langmuir–Blodgett films

Two-dimensional (2D) ferroelectricity and 2D ferroelectric–paraelectric phase transitions are experimentally studied, for the first time, by means of optical second harmonic generation (SHG) in ultrathin Langmuir–Blodgett (LB) films of vinylidene fluoride with trifluoroethylene. The temperature dependence of the SHG intensity confirms the existence of two types of 2D ferroelectric–paraelectric phase transition: the first one in the topmost layer of LB films and the other, almost thickness independent, in the bulk of ferroelectric LB films.

First Type of Ferroelectricity Generated by Undulated-Prototypic to Ferroic Transition. II.f=2

This paper is concerned with the subject of transitions from artificially incommensurately undulated prototypic phases to ferroic phases. It is possible that such a transition generates ferroelectricity. Ferroelectricity of this category is referred to as U-ferroelectricity, when it needs to be distinguished from conventional ferroelectricity. The most important feature of U-ferroelectricity is that it vanishes when the prototypic phase becomes homogeneous. Several different types of U-ferroelectricity are possible. Only the first and simplest one of those types is dealt with in the present paper. By case study the details are clarified. For example, what term within the free energy function is responsible for the generation of ferroelectricity and in what forms spontaneous polarization and dielectric susceptibility depend on the prototype undulation are clarified.

First Type of Ferroelectricity Generated by Undulated-Prototypic to Ferroic Transition

This paper is concerned with the subject of transitions from artificially incommensurately undulated prototypic phases to ferroic phases. It is possible that such a transition generates ferroelectricity. Ferroelectricity of this category is referred to as U-ferroelectricity, when it needs to be distinguished from conventional ferroelectricity. The most important feature of U-ferroelectricity is that it vanishes when the prototypic phase becomes homogeneous. Several different types of U-ferroelectricity are possible. Only the first and simplest one of those types is dealt with in the present paper. By case study the details are clarified. For example, what term within the free energy function is responsible for the generation of ferroelectricity and in what forms spontaneous polarization and dielectric susceptibility depend on the prototype undulation are clarified.

Ferroelectricity and coherent phonon generation in piezoelectric composition-modulated structures

In this paper we suggest an approach to making new metastable ferroelectric materials and piezoelectric transducers which should be efficient in generating coherent phonons with wavelengths approaching interatomic distances. This involves the fabrication of composition-modulated (layered) structures consisting of piezoelectric components. The coherency strain accompanying short wavelength composition modulation leads to ferroelectricity; the periodic modulation of the piezoelectric parameters leads to an anomalously strong coupling to far infrared light when the composition wavelength is an odd half-multiple of the wavelength of a phonon at the driving frequency. Such transducers can open a new dimension in the study of phonons in dielectrics at low temperatures.

Traveling-Wave Harmonic Generation Along Nonlinear Transmission Lines

A perturbation solution is developed for determining the steady-state response of nonlinear TEM transmission lines and nonlinear cylindrical waveguides of arbitrary cross section. The nonlinear medium which is considered in this analysis is comprised of both nonlinear reactance and nonlinear resistance; and can be physically realized in the ferroelectric ceramic material composed of 73% BaTiO3 and 27% SrTiO3. From the results of the perturbation analysis and the known large signal microwave characteristics of this material, the properties of traveling-wave harmonic generation in ferroelectric ceramics are investigated. To assess the characteristics of ferroelectric traveling-wave harmonic generators, an example is worked out for an S-band rectangular waveguide completely filled with the above mentioned ceramic and excited in the TE10 mode at the fundamental frequency of 3 kMc. The predicted behavior of this device is then compared with the experimental characteristics of a cavity-type ferroelectric harmonic generator in order to determine the advantages and disadvantages of each type of device. The comparison brings out the superiority of the resonant system and indicates ways of improving the distributed system. Finally, based upon the treatment of the waveguide problem, the processes of frequency and mode conversion in nonlinear waveguides are discussed, both in general and with regard to the example of the rectangular guide.

Ferroelectric Harmonic Generator and the Large-Signal Microwave Characteristics of a Ferroelectric Ceramic

At microwave frequencies, ferroelectric ceramics behave as nonlinear dielectrics and exhibit large signal scalar nonlinear characteristics in both the dielectric constant and the rf conductivity. The nonlinear behavior of a ceramic of 73% BaTiO3-27% SrTiO3 has been used to construct a harmonic generator operating from 3 kMc to 9 kMc. An efficiency of 8.5% for a peak input power of 2200 w was attained. In addition, a new measurement technique has been developed for measuring the large signal properties of this ceramic as well as for other nonlinear materials. This technique makes explicit use of the anharmonic response of a resonant system that contains a nonlinear element. The analysis of both the harmonic generator and the nonlinear resonant system takes into account nonlinear reactance as well as nonlinear resistance. For temperatures about 30°C above the Curie temperature (the Curie temperature for the ceramic composed of 73% BaTiO3-27% SrTiO3 is approximately 20°C) the large signal dielectric constant and rf conductivity were found to be given by the expressions ε′(|E|)=ε0[2200−7.5×10−11|E |2] farad/m, and σ(|E|) =ωε0[160+29×10−12|E|2] mhos/m, where |E| is in volts per meter. These results were obtained at 3 kMc and are valid up to field strengths of 20 kv/cm.