摘要:

Unoriented and biaxially oriented phase‐II poly(vinylidene fluoride) films were poled at very high fields up to 4.0×106V/cm at room temperature. Changes in molecular orientation and crystal structure induced by the high‐field poling were studied using x‐ray and DSC methods. The piezoelectric coefficientsd31ande31together with the dielectric response (&egr;′ and &egr;″) were determined using a Piezotron Model U (Toyo Seiki, Tokyo) for the poled films. The piezoelectric activity did not increase steadily with poling field, but showed four distinct regions depending on poling field. At low fields (Ep<106V/cm), when x‐ray and DSC data indicated that the films were predominantly in the phase‐II structure, the piezoelectric activity was small (e31<2×10−3C/m2). For poling fields between 1×106and 2×106V/cm the piezoelectric activity was observed to rise rapidly with poling field until a value ofe31∼14.5 C/m2was observed. In this region the x‐ray scans indicated that phase‐II crystallites were being transformed to a polar phase. At poling fields from 2 ×106to 3.2×106V/cm a plateau region was observed with very little change in the value of the piezoelectric coefficient. X‐ray and DSC data showed that very little change in the structure and molecular orientation occurred in this region. At the very highest poling field applied (4×106V/cm) the piezoelectric data indicated the commencement of a very rapid increase in piezoelectric activity (e31∼19.5×10−3C/m2). At this poling field the x‐ray and DSC data indicated that a crystal transformation to phase I had occurred. The piezoelectric coefficients of the unoriented films was not measured. X‐ray diffraction data indicated that, in addition to the structural and orientation changes occurring in the biaxially oriented film, an x‐ray reflection, which could not be indexed using phase I, II, or III unit cells, increased in intensity with poling field. The DSC data showed the appearance of a new endothermic peak which also increased with poling field. These data indicated that molecular chains oriented perpendicular to the plane of the films transformed to some new structure under the action of the high applied fields.

ISSN:0021-8979    

DOI:10.1063/1.325778

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Investigations of the dynamic piezoelectric response (d*31ande*31) of unoriented poled poly(vinylidene fluoride) films containing different volume fractions of phase‐I and phase‐II crystalline materials show a linear relationship between phase‐I content and piezoelectric response. Samples were poled under conditions (106V/cm at 23 °C) which produced no observable changes in x‐ray diffraction patterns taken before and after poling. The piezoelectric strain constant of the unoriented phase‐II film isd′31=0.48×10−12C/N, while that of the unoriented phase‐I sample isd′31=6.68×10−12C/N. The data supports a model in which the piezoelectric activity is primarily due to a bulk polarization of the PVF2by a 180° dipole switching mechanism in the polar phase‐I crystals.

ISSN:0021-8979    

DOI:10.1063/1.325779

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Infrared spectra representative of crystalline regions of cast films of phase‐III poly(vinylidene fluoride) (PVF2) have been obtained by absorbance subtraction techniques using a FT‐IR instrument. The spectra contain more bands than previously reported and are not consistent with current models for the crystal structure. Several possible models and their relationship to the corresponding crystalline spectra of phase II and phase I are discussed.

ISSN:0021-8979    

DOI:10.1063/1.325780

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A moving plasma with directed flow velocitiesvlarger than the ion acoustic speedcsis used as a source of high‐current ion beams in the 10–20‐keV range of energies. Current densities up to 3 A/cm2are obtained at the plasma boundary which is an order of magnitude larger than the limiting value of Bohm current in a stationary plasma. The observed current densities were proportional tov, unlike the Bohm current densities which are proportional to ion acoustic speed. Total ion currents up to ∼100 A were extracted from the plasma through a two electrode extraction system. Simple geometric shaping of the electrodes enabled an 8‐cm‐diam beam to be focused to ∼7 mm.

ISSN:0021-8979    

DOI:10.1063/1.325781

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A N2‐pumped tunable dye laser has been used to obtain the phosphorescence‐excitation spectra at 1.00 Torr and room temperature of the 000‐000, 010‐000, 020‐000, 100‐000, and 110‐000 vibrational bands of the3B1→1A1transition of sulfur dioxide. These spectra support earlier absorption studies regarding perturbations of the3B1state. The results of perturbations in the 110‐000 band fromK′=15 upwards are especially pronounced in the emission studies presented here.

ISSN:0021-8979    

DOI:10.1063/1.325782

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Momentum is exchanged between free electrons and light when the interaction length is limited. An analysis and a computer simulation determine the characteristics of this energy transfer. Possible experimental schemes at optical and infrared wavelengths are explored.

ISSN:0021-8979    

DOI:10.1063/1.325783

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A family of complex electron lenses, consisting of two coaxial double‐cylinder elements with unequal diameters, is investigated. It is concluded that the dominant contribution to the spherical aberration of such lenses arises in the accelerating component. Considerable reduction of the shperical aberration coefficient is possible in comparison with the unipotential and bipotential lenses customarily employed in cathode‐ray‐tube electron‐optical systems.

ISSN:0021-8979    

DOI:10.1063/1.325784

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Intense electron‐beam propagation in a dielectric guide, without external magnetic fields, has been studied for 30–100‐keV beams with &ngr;/&ggr;?1. The electron beam was injected into an evacuated cavity lined by dielectric materials with a thickness exceeding the electron range. The beam did not propagate until it was charge neutralized by ions removed from the dielectric following surface flashover caused by electron bombardment. The charge transported was a linear function of the cylindrical guide length, and the beam could be focused by a conical guide. Transport efficiency was reduced for dielectrics made of SiO2compared to various plastics.

ISSN:0021-8979    

DOI:10.1063/1.325785

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We report calculations for the impedance of a long solenoid which surrounds a cylinder of conducting material containing a radial surface crack of constant depth. The calculation is accomplished by solving for the longitudinal ac magnetic field in the interior of the ’’cracked’’ cylinder in terms of an infinite series of cylindrical Bessel functions. All the coefficients in the series are determined in principle by boundary‐condtion requirements and the most significant terms are obtained numerically by truncation of the series. The resulting impedance is calculated for a wide range of values of the ratios of crack depth to radius and radius to skin depth. The results are tabulated in a form useful for nondestructive testing purposes.

ISSN:0021-8979    

DOI:10.1063/1.325786

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The electron density distribution in electron beams produced in high‐current field‐emission diodes often shows striations in the form of periodic maxima and minima. The nature of the striations depends on the shape of the cathode. A theory of these striations applicable to cylindrical cathodes is given. The current is taken to be flowing through the cathode flare plasma formed in the diode during the course of beam emission and the stability of such a current‐carrying plasma is studied. For certain wavelengths of perturbation, the perturbation grows exponentially and leads to an instability which manifests itself as striations in the current distribution. The unstable wavelengths are related to the characteristic dimensions of the cathode.

ISSN:0021-8979    

DOI:10.1063/1.325787

出版商:AIP    

年代:1979

数据来源: AIP