Electrical impedance

About: Electrical impedance is a research topic. Over the lifetime, 36015 publications have been published within this topic receiving 371891 citations. The topic is also known as: electrical impedance & complex impedance.

P-N-P-N Transistor Switches

Abstract: The design, fabrication, and electrical characteristics of silicon p-n-p-n transistors with ?>1 for use as switches is discussed. The increase of alpha with injection level can be used to construct two terminal p-n-p-n switches. The high impedance characteristic has an impedance determined chiefly by the capacitance of the junctions. This capacity is of the order of tens of micromicrofarads. The low impedance portion of the switching characteristics has a slope resistance of a few ohms and a total voltage drop of approximately one volt. Methods of fabrication include suitable combinations of solid diffusion and alloying. Possible applications of p-n-p-n switches include function generators, photorelay, and talking path switches.

Electric impedance of nitella during activity.

Abstract: The changes in the alternating current impedance which occur during activity of cells of the fresh water plant Nitella have been measured with the current flow normal to the cell axis, at eight frequencies from 0.05 to 20 kilocycles per second, and with simultaneous records of the action potential under the impedance electrodes. At each frequency the resting cell was balanced in a Wheatstone bridge with a cathode ray oscillograph, and after electrical stimulation at one end of the cell, the changes in the complex impedance were determined from the bridge unbalance recorded by motion pictures of the oscillograph figure. An extension of the previous technique of interpretation of the transverse impedance shows that the normal membrane capacity of 0.9 µf./cm.2 decreases about 15 per cent without change of phase angle, while the membrane resistance decreases from 105 ohm cm.2 to about 500 ohm cm.2 during the passage of the excitation wave. This membrane change occurs during the latter part of the rising phase of the action potential, and it is shown that the membrane electromotive force remains unchanged until nearly the same time. The part of the action potential preceding these membrane changes is probably a passive fall of potential ahead of a partial short circuit.

Stacked dual dipole MMDS feed

Abstract: A multichannel, multipoint distribution services (MMDS) dipole antenna for receiving multiple channels in the S-band frequency range of 2000 and 3000 MHz is formed from a printed circuit board which is directly connected to a coaxial cable. On the printed circuit board are etched two stacked dipoles. Each of the dipoles has a first one-half element etched on the first side of the printed circuit board and the second one-half element etched on the second side of the printed circuit board. The first and second dipoles are oriented to be in phase with each other and are separated from each other at a wavelength spacing between 0.25 lambda and 0.40 lambda. The antenna of the present invention further uses a phase combining circuit and an impedance matching circuit etched on the printed circuit board for combining in phase the polarized signals, for canceling the non-polarized signals at 0° and 180°, from the two stacked dipoles and for matching the impedance from the two dipoles to the impedance of the coaxial cable.

A numerical solution for the near and far fields of an annular ring of magnetic current

Abstract: A simple method for calculating the near and far zone fields from an annular ring of circumferentially directed magnetic current which may be used to represent coaxial apertures is presented. Near-field contours are given for two ring sizes. The utility of the method has been illustrated by its application in several practical antenna problems where the magnetic ring current serves as the primary source. Among these are the analysis of dipole antennas mounted on a conducting sphere or cylinder, the impedance of a coaxially fed Yagi-Uda antenna, a coaxially driven wire loop, and the radiation from a coaxial aperture at the base of a cone.

A device for measurement of electrical impedance of organic and biological materials

Abstract: A device and method for noninvasive depth-selective detection and characterization of surface phenomena in organic and biological material such as tissues by surface measurement of the electrical impedance of the material. The device includes a probe with a plurality of measuring electrodes separated by a control electrode. Measuring equipment measures impedance in a desired frequency range. An adjustable amplifier maintains a chosen control signal derived from the potential of one of the measuring electrodes at the control electrode without loading the measuring electrode. Depth selectivity is achieved by controlling the extension of the electric field in the vicinity of the measuring electrodes by the control electrode actively driven with the same frequency as the measuring electrodes.