Non-ideal Shape Research Articles

Measuring Conductivities of Highly Conductive Membranes

The theoretical and experimental aspects of an electrochemical approach for evaluating the conductivites of highly conductive membranes are described. The methods developed involve either a current or a potential step at a solid‐state electrochemical cell. It is assumed, and we prove, that only capacitive currents flow during these current or potential step experiments. The theory for these methods is derived from classical electrochemical theory for current and potential steps at RC circuits. We show that if the conductivity of the system under study is not too high (less than ca. 0.2 Ω−1 m−1), the classical theory provides accurate conductivity data. However, we also show that if the conductivity of the system is greater than ca. 0.2 Ω−1 m−1, conductivities obtained from the classical expressions are inaccurate. The modified theoretical analysis developed here, however, yields very accurate conductivity data for such highly conductive systems. The modifications of the classical theory entail accounting for the nonideal wave shape of real potential or current step waveforms.

Determination of state-of-discharge of zinc-silver oxide button cells. II. Impedance measurements

The prediction of the state-of-discharge of numerous types of Zn-Ag2O button cells from six international manufacturers has been investigated using the impedance technique over an extended frequency range. The frequency responses at various states-of-discharge are presented and it is shown that the changes in impedance which result from discharging provide several potential parameters for the state-ofdischarge prediction. The complex impedance plot of the undischarged cells usually shows a fairly welldefined semicircle at high frequencies and a straight line with a slope between 40 and 50° at low frequencies. As discharge proceeds, the diameter of the semicircle increases and the overlap between the semicircle and the low-frequency straight line increases. The most attractive method would be to determine a parameter such as a characteristic relaxation frequency in the complex impedance plot. Unfortunately, no unambiguous characteristic parameter can be extracted due to the non-ideal shape of the impedance response at high frequencies. The determination of the diameter of the high-frequency semicircle has been faced with the same difficulties. The most reliable test was found to be the determination of either the phase of the impedanceϕ, or a corrected phaseϕ− taken from the high-frequency intercept. The proposed prediction is a ‘go/no go’ indication on the basis of one- or two-frequency measurements forϕ or,ϕ− respectively. The selection is made at 20–40% state-of-discharge. The charge withdrawn is negligibly small and the time of the test is between 1 and 100 s depending on the type of cell. A calibration is necessary for each cell dimension and each manufacturer. Some 10–16% of the types of cells investigated could not be selected successfully, mainly because of too large a dispersion of the electrical characteristics of the cells, especially for small newly developed types, and of the similarity of the (ϕ and ϕ′ values in the low and high state-of-discharge in the appropriate frequency range. The latter difficulty arises from the difference of the frequency response between the undischarged and the partly discharged cells occurring at high frequencies.

Creation of a flux-free environment

For the proper operation of flux sensitive cryogenic devices such as those in Josephson computers a nearly zero field environment is essential. Since shieldings based on ferromagnetic mu-metal has been found to be not effective enough, superconducting shieldings are required. In this paper flux penetration into superconducting disks of ideal and non-ideal shape is investigated with respect to flux free regions in the disk. Based on the experimental results of the linear dimension of flux free belts in disk shaped type-I superconductors an arrangement is proposed to create flux free regions large enough for practical applications.

Design and demonstration of a klystron with 62 percent efficiency

Extensive design optimization studies on a prototype series of klystrons have been carried out using a digital computer simulation, Five parameters were investigated for their effect on efficiency: 1) penultimate cavity tuning; 2) pre-penultimate cavity tuning; 3) beam perveance; 4) pre-pre-penultimate cavity tuning; and 5) output gap transit angle, These studies indicate that the power conversion efficiency of a high-power narrow-band multicavity klystron of optimum design should lie in the 70-80 percent range. A tube of near-optimum design was built and its performance was carefully measured as a function of two parameters: 1) penultimate and pre-penultimate cavity tuning; and 2) beam voltage. The measured data were used as a guide to determine the choice of beamfilling factor and beam power interception for best correlation with computed results. The measured efficiency was 62±1.5 percent compared to the computed value of 64 percent. Careful attention was paid to the repeatability of the efficiency measurements and to the effect of nonideal pulse shape on calorimetric measurements. Beam interception at large-signal levels appears to be the phenomenon which limits efficiency in the present tube.