Showing papers on "Electrical impedance published in 1978"

Reactively controlled directive arrays

Abstract: The radiation characteristics of an N -port antenna system can be controlled by impedance loading the ports and feeding only one or several of the ports. Reactive loads can be used to resonate a real port current to give a radiation pattern of high directivity. The theory of resonance is extended to include complex port currents and impedance loads. The initial design of an array is obtained by resonating a desired port current vector, which is then improved by an optimum seeking univariate search method. The direction of maximum gain can be controlled by varying the load reactances. Several numerical examples are given for a circular array of seven dipole elements.

Analysis of the alternating current properties of ionic conductors

Abstract: A method of analysis of inclined semicircular complex impedance (Z) diagrams for ionic conductors has been developed on the basis of the concept of “non-Debye” behaviour of solid dielectrics. This approach replaces the rather arbitrary distribution of relaxation times by the physically much simpler concept of a frequency-independent ratio of energy lost per cycle to energy stored. This criterion of dielectric behaviour leads directly to complex admittance (Y) plots in the form of straight lines inclined to the vertical which then transform to inclined semicircles in Z. The use of Y diagrams gives better accuracy of representation and it is shown how this can be further enhanced by plotting log Yi − log Yr instead of the usual linear representation. Different parts of the graphs are assigned to “bulk” and “barrier” regions on the basis of the value of the dielectric permittivity and it is shown that a hitherto unrecognized physical process can manifest itself as a strong dispersion at frequencies intermediate between the high-frequency bulk response and the low-frequency barrier-dominated behaviour.

Electrical properties of platinum electrodes: impedance measurements and time-domain analysis.

Abstract: The impedance of small platinum electrodes has been measured as a function of frequency. In the range of 0·1 Hz to 10 kHz, this impedance Z can be described accurately as K/(i2πf)m. The value of K is about 2·5 Mω for a surface are of 0·05 mm2. The values for m are in the order of 0·75. Various step responses are computed based on this expression and are compared to recorded wave forms. All step responses are shown to result directly and consistently from the same expression. The consequences of these results for various models and equivalent circuits of the electrode-medium interface are discussed.

A relatively short cylindrical broadband antenna with tapered resistive loading for picosecond pulse measurements

Abstract: A relatively short cylindrical antenna with continuously tapered resistive loading has been studied for the purpose of picosecond pulse measurements. The antenna considered is a nonconducting cylinder with continuously deposited varying-conductivity resistive loading. The current distributions on the antenna were numerically calculated using the method of moments. Using these current distributions, other quantities such as input admittance, near-field and farfield radiation patterns, and radiation efficiency, were also numerically calculated and compared with the results using the Wu-King's approximate current distribution. Agreement is relatively good except at high frequencies kh > \pi/2 where the method of moments appears to give better results. To verify the theoretical results, several resistively loaded antennas were fabricated, and their picosecond pulse receiving characteristics were analyzed for the frequency range between 5 kHz and 5 GHz. The experimental results indicate excellent linear amplitude and phase response over the frequency range. This provides the unique capability of this antenna to measure fast time-varying electromagnetic fields with minimal pulse-shape distortion due to nonlinear amplitude or phase characteristics.

Low-noise amplification of voltage and current fluctuations arising in epithelia.

Abstract: Two low‐noise differential input amplifiers designed for voltage and current fluctuation measurements in epithelia are described. The first one uses a matched pair of low‐noise transistors and is particularly suited for low‐frequency current and voltage noise measurements in frog skin and other preparations with impedances below 1 kΩ. The second one is designed around a matched pair of JFETs and can also be used for higher source impedance. Performance is demonstrated with Na+ current power density spectra obtained from frog skin with the transistor‐input stage.

Exact circuit analysis of spherical waves

Abstract: A circuit representation for the impedance of spherical waves radiating from a spherical boundary was derived using a partial fraction expansion by Chu in order to establish gain bandwidth limitations for antennas. These circuits are derived directly from the recurrence relations for spherical Bessel functions. They provide an exact analog of the field solution both inside and outside of a spherical surface for any values of permittivity ( \epsilon ) and permeability ( \mu ). Since the circuits have the form of high-pass filters, they provide significant physical insight into scattering and radiation problems, suggest suitable asymptotic or approximate forms and allow circuit concepts and theorems to be brought to bear in order to solve specific configurations or to set general performance bounds. As an example of their application, compact computer programs for the radar cross section of conducting and dielectric spheres, the minimum Q 's for antennas, the Q 's and resonant frequencies of dielectric spheres and the induced current at the specular and shadow points of a conducting sphere are given. Other illustrative results are the short pulse responses of a solid dielectric and a dielectric-coated sphere computed using the circuit surge impedance and multiple reflection terms; and the response of a hypothetical scatterer in which the TE and TM modes are coupled.

Conversion Loss and Noise of Microwave and Millimeterwave Mixers: Part 2--Experiment

Abstract: The theory of noise and conversion loss in millimeter-wave mixers, developed in a companion paper, is applied to an 80-120-GHz mixer. Good agreement is obtained between theoretical and experimental results, and the source of the recently reported "anomalous noise" is explained. Experimental methods are described for measuring the embedding impedance and diode equivalent circuit, needed for the computer analysis.

Analysis of the complex impedance data for ?-PbF2

Abstract: Previously published complex impedance plots for the ionic conductor β-PbF2 show the familiar depressed circular arcs with an angle 07 π/2 and an activation energy for the volume conductivity Wv=045 eV A detailed analysis of this behaviour in terms of the recently developed “non-Debye” model shows the real part of the relative dielectric permittivity to have a frequency dependence ω07−1, with a high frequency limit of 50 Hz and with only weak dependence on temperature The low-frequency “spurs” on the impedance plots are shown to indicate an interfacial barrier at each electrode having a similar “non-Debye” frequency characteristic to the bulk but showing a strong temperature dependence with an activation energy equal to Wv/2 This suggests the presence of low Debye-screened barriers of about k T height, resulting from depletion and accumulation of ionic carriers at incompletely transmitting electrodes There is no visible effect of inter-grain boundaries on the flow of direct current

Built-in passive fault detection circuitry for an aircraft's electrical/electronic systems

Abstract: Built-in test equipment (BITE) of the electrical/electronic systems of an aircraft is provided in-part by passive fault detection circuitry that is integrated into the electrical/electronic systems for continuous, in flight monitoring of line replaceable units (LRUs), such as temperature and pressure sensors. Both steady and intermittent failures of the LRU components are detected, and the type and location of each failure are identified and stored in a memory for continuous display or for subsequent recall by ground maintenance crews. The primary feature of the disclosed circuitry is its ability to detect and distinguish between an open impedance fault of a critical LRU component and an open wiring fault in the interconnect wiring that is associated with each component and is needed to electrically communicate signals developed at remotely mounted sensor components with a centralized controller, usually located in the avionics bay. To enable such differentiation between these two most frequent kinds of faults, each system component that is to be monitored is provided with one or more shunts having predetermined impedance relationships with the associated component so that an open component failure, when detected through the interconnect wiring, appears as a measurably different electrical condition than an open failure of the interconnected wiring which leads to that component. The capability of distinguishing between open component and open wiring faults minimizes the frequency at which LRUs incorporating critical components are simply replaced, without remedying the malfunction.

Intense electron‐beam pinch formation and propagation in rod pinch diodes

Abstract: Intense electron‐beam pinches are formed and propagated at relatively high impedance (5–25 Ω) using rod pinch diodes Pinch propagation of up to 20 cm with 45% efficiency and ion‐generation efficiency ≳15% has been observed

A technique for the measurement of tissue impedance from 1 to 100 MHz using a vector impedance meter

Abstract: A simple and quick technique for measuring the resistivity and relative permittivity of biological tissue over the frequency range 1-100 MHz is described. The technique utilises a commercially available, variable-frequency vector impedance meter to obtain results to within about 5% accuracy. Some typical results are presented.

Method of and apparatus for detecting ground faults in isolated power supply systems

Abstract: A line isolation monitor for detecting ground faults in isolated power systems by determining the potential personnel hazard current due to the complex ground fault impedances and a method for accomplishing the same. The total hazard current is determined by dividing the peak line voltage of the isolated power supply by the total impedance between ground and a common mode point, such as the center tap of the primary winding of the line isolation monitor transformer connected to the isolated power supply. This impedance is determined at line frequency by impressing a minute, phase-modulated, power line frequency test signal into the isolated power system and using an extremely selective, coherent filter to remove the signals in phase with the power line signal. The magnitude of the phase modulated test signal passed through the filter is related to the amount of fault impedance. Comparison of this test signal magnitude to the line voltage provides an indication of the total hazard current. The circuitry for accomplishing this procedure includes a closed loop system which adjusts the current level of the test signal until the voltage of the filtered test signal reaches a predetermined level related to the line voltage of the isolated system. The current level of the test signal is then related to the total hazard current.

Acoustic impedance variations at burn–nonburn interfaces in porcine skin

Abstract: The success of the ultrasonic pulse‐echo technique for measurement of the depth of burn necrosis in porcine skin [Med. Phys. 4, 259–263 (1977)] has led to the present investigation of the specific acoustic impedance difference between the necrotic (burn) tissue and the underlying viable (nonburn) tissue. Experimental results show that the ultrasonic group velocities and mass densities are approximately the same in these tissues yielding average values of (1.72±0.12) ×105 cm/s for group velocity and (1.093×0.009) g/cm3 for the density. The characteristic impedance (density times velocity) differs by at most 3% between necrotic and viable tissues. Measurements of acoustic attenuation show a difference of approximately 70% between these tissues. porcine skin is due primarily to the difference in acoustic attenuation.

Complex Radiation Impedance of Microstrip-Excited Magnetostatic-Interface Waves

Abstract: A technique is described for computing the radiation reactance of microstrip-excited MSSW's from a Hilbert transform of a previously derived expression of the radiation resistance. The series combination of the radiation reactance, radiation resistance, and an inductive reactance corresponding to a shorted section of microstrip line forms an equivalent circuit characterizing the excitation process. Supporting impedance measurements are presented and limitations of the model are discussed.

Coaxial wire measurements of the longitudinal coupling impedance

Abstract: The measurement of the longitudinal coupling impedance of an accelerator component by coaxial wire methods is discussed. Potential errors intrinsic to this method are pointed out and analyzed. It is concluded that measurements using the transmission rather than the reflection coefficient are preferable and are expected to give adequate results in the limit of thin center conductors.

Estimation of Higher Frequency Network Equivalent Impedances by Harmonic Analysis Natural Waveforms

Abstract: A digital method of analysing harmonics in a power system has been developed which permits the equivalent network impedance to be estimated by means of the switching of capacitor banks. The method records voltage and current digitally and by data processing computes the amplitude and phase of the harmonics. By comparing results before and after the switching of a capacitor bank on one phase, the equivalent network impedance is estimated at the odd harmonics. Precision of results is acceptable in amplitude but less accurate in phase.

Self‐magnetic insulation in vacuum for coaxial geometry

Abstract: Magnetic insulation obtained by employing the magnetic field of the line current in coaxial vacuum‐transmission lines is studied in experiments on two different relativistic electron‐beam accelerators, spanning the voltage range 0.4–10 MV. Effective magnetic insulation at fields up to 1.3 MV/cm is demonstrated. The self‐limiting impedance is measured and compared to a number of theories for magnetic insulation and it is found that none of the ’’standard’’ theories successfully describes the data. However, computer simulations using a self‐consistent two‐dimensional particle code give good agreement with the experimental data, as does a proposed modification of the parapotential flow model.

Model experiments on surface waves

Abstract: Experiments are described in which exponential attenuation factors for surface waves both in the direction of propagation along a complex impedance surface and perpendicular to the surface are measured. The surface impedance calculated from these attenuations is then compared to that measured in an impedance tube.

Extremely low current load device for integrated circuit

Abstract: A MOSFET random access memory having an extremely low current load memory cell is disclosed. The memory cell comprises a cross-coupled binary stage in which one or more paths to ground can be selectively switched on or off through true and complement data nodes. Impedance means connect a power supply node to the data nodes for charging the data nodes to predetermined voltage levels. The impedance means comprise an intrinsic-extrinsic junction of a substantially pure, intrinsic semiconductor material and a diffusion of extrinsic conductivity impurities disposed within a region of the intrinsic semiconductor material. The impedance means is formed by an isoplanar silicon gate process as an integral portion of a polycrystalline silicon strip which interconnects the power supply node to a data node. A portion of the polycrystalline silicon strip is extended from the data node to form the gate of the transistor to which it is cross-coupled.

Method and apparatus for identifying conductive objects by monitoring the true resistive component of impedance change in a coil system caused by the object

Abstract: The type of conductor, its property, and if a metal, its type and cross-sectional area can be obtained from measurements made at different frequencies for the amount of unbalance created in a previously balanced stable coil detection system. The true resistive component is accurately measured and thus reflects only the voltage loss attributable to eddy currents caused by introduction of the test sample to the coil system. This voltage divided by corresponding applied frequency gives a curve which peaks at a frequency dependent upon type of conductor. For a metal this peak frequency is proportional to the samples resistivity divided by its cross-sectional area.

Fluxgate magnetometer circuit with earth's field elimination

Abstract: A flux gate magnetometer system utilizes three independent flux gates for measuring the three mutually orthogonal components of the earth's magnetic field. A sensor for each flux gate includes a ring core with a toroidal winding as the drive winding and a differential winding for sensing the difference in saturation due to the earth's flux linkages in the core. The operation of the flux gate magnetometer system is stabilized by a second harmonic servo type null circuit. The output of the differential sense winding is beat with a signal twice the frequency of the drive signal and in phase with the sensor output. This demodulated signal is the error signal for an integration stage. The integration stage drives a high impedance current source which sums into the flux gate sense winding and eliminates the effect of the earth's field in the sensor. An error signal is generated only when the high impedance current source does not null the earth's flux linkages in the core. The flux gate magnetometer system provides a means for determining the components of the earth's magnetic field for use in a digital mineral logging system.

Apparatus for measuring microwave electromagnetic fields

Abstract: A microwave signal is transmitted from a transmitting antenna through a transfer medium to an electrically modulated and mechanically spun microwave scatterer. The scatterer may include an electric field responsive antenna, such as a dipole, for measurement of the electric field, or a magnetic field responsive antenna, such as a loop, for measurement of the magnetic field. An impedance within the scatterer is electrically modulated at an audio frequency, and the scatterer is mechanically spun at an angular frequency substantially below that at which it is electrically modulated. The scatterer thereby re-radiates to a receiving antenna a signal at the mocrowave source frequency which is modulated at both the frequency of electrical modulation and the mechanical spinning frequency of the scatterer. Signals from the microwave source and from the receiving antenna are combined to yield an output signal having a magnitude which is a function of the magnitude of the field received by the scatterer and which is phase shifted proportional to the phase shift of the microwave signal from the transmitting antenna to the scatterer and thence to the receiving antenna. The output signal may be compared with a signal coherent with the frequency of rotation of the scatterer to determine the tilt angle of the electric or magnetic field received by the scatterer.

Analysis and synthesis of an impedance-loaded loop antenna using the singularity expansion method

Abstract: The singularity expansion method (SEM) is used to represent the current on a loaded loop antenna. The shift in the poles of the loop due to impedance loading can be analyzed using contour plots in the complex frequency plane of the Fourier modal impedance transfer functions. The same plot may also be used to determine a loading function which will yield a specified pole pattern leading to frequency or time domain synthesis. A simple example of time-domain synthesis is presented.

Digital measurement of impedance ratios

Abstract: A circuit arrangement for measuring the ratio of first and second capacitances of a capacitance displacement transducer. An alternating signal is developed the amplitude of which is proportional to the values of the first and second capacitances during respective first and second timing periods, the alternating signal being synchronously demodulated in one phase in the first period and in the opposite phase in the second period. The demodulated signal is integrated so that the integrator is charged and discharged during the first and second periods respectively, and the ratio of the discharge time to the charge time is equal to the ratio of the two capacitances. A digitized output is provided by means of a clock pulse generator and counter.

Experimental determination of series resistance of p-n junction diodes and solar cells

Abstract: Various methods for determining the series resistance of p-n junction diodes and solar cells are described and compared. New methods involving the measurement of the ac admittance are shown to have certain advantages over methods proposed earlier.

Input overload protection circuit

Abstract: An input overload protection circuit particularly suited for use with a high impedance differential amplifier having two inputs is provided. The protection circuit prevents the flow of substantially all leakage currents for input signals within the linear operating range of the amplifier, and includes a first and second serial plurality of diode-action clamping means, such as diodes, connected respectively between the first and second input conductors to the amplifier input and a third conductor connected to a reference potential. Driven guard means operate to apply the voltage appearing on the respective first and second input conductors at their junction with the respective first and second clamping means to the respective first and second plurality of clamping means intermediate the respective ends thereof, thereby to substantially prevent leakage current from flowing through the clamping means from the pair of conductors.