Showing papers on "Electrical impedance published in 1996"

Effect of skin impedance on image quality and variability in electrical impedance tomography: a model study

Abstract: A computer simulation is used to investigate the relationship between skin impedance and image artefacts in electrical impedance tomography. Sets of electrode impedance are generated with a pseudo-random distribution and used to introduce errors in boundary voltage measurements. To simplify the analysis, the non-idealities in the current injection circuit are replaced by a fixed common-mode error term. The boundary voltages are reconstructed into images and inspected. Where the simulated skin impedance remains constant between measurements, large impedances (> 2k omega) do not cause significant degradation of the image. Where the skin impedances 'drift' between measurements, a drift of 5% from a starting impedance of 100 omega is sufficient to cause significant image distortion. If the skin impedances vary randomly between measurements, they have to be less than 10 omega to allow satisfactory images. Skin impedances are typically 100-200 omega at 50 kHz on unprepared skin. These values are sufficient to cause image distortion if they drift over time. It is concluded that the patient's skin should be abraded to reduce impedance, and measurements should be avoided in the first 10 min after electrode placement.

Electric surgical device,electric surgical method,electric surgical processing method of tissue and electric surgical impedance feedback controller

Abstract: PROBLEM TO BE SOLVED: To judge the end point of coagulation of tissues by monitoring the electrical impedance of tissues between query electrode which are bipolar each other and arranged on the surfaces that touch a terminal effector of an electrot surgical instrument. SOLUTION: A jaw-shaped part 32 of a terminal effector 15 of an equipment 10 for cutting and stapling is fixed to a jaw-shaped part 34 as it can mobile, then electric poles 51 and 52 are set to the jaw-shaped parts 32 and 34. In order to begin to detect the completion of congelation by means of the inquiry electric poles 51 and 52, electric current of minimum is supplied to therapeutic electric poles, that is the anvil 18 and the U-shaped therapeutic electric pole 39. ITRMS of the output 86 of an RMS converter 84 is inputted to the comparator, and the output of the cooperator enables a peak detector inside the coagulation completion circuit. The coagulation completion circuit begins to operate by supplying electric current of which amount is larger than the minimum to the therapeutic electric pole 18. An impedance sensor judges whether the congelation has completed or not by ITRMS, VTRMS and the measured impedance Z(a).

A control system for neurosurgical electrosurgical unit

Abstract: A control system (10) and method for the operation of neurosurgical bipolar electrodes (11) provides a source of high frequency energy (13') connected to bipolar electrodes (11). Contacting surfaces are on the bipolar electrodes (11) of highly electrically conductive material. A current transducer attached to the source of high frequency energy (13') measures (20) the RMS current applied between the contact surfaces (25). A current transducer attached to the source of high frequency energy (13') provides a signal (26) correlated to the instantaneous values of the RMS voltage between the contacts. A control connects to the source of high frequency energy (13') for initially regulating the RMS current applied by the contacting surfaces in response to the impedance until the signal (19) divided by the measure (20) which is representative of the instantaneous impedance of the load reaches a predetermined value. The control regulates the RMS power applied by the contacting surfaces in accord with the impedance until the signal (19) divided by the measure (20) reaches a predefined value. The control responds to the measure (20) and the signal (19) so that the RMS voltage applied to the load being treated between the contacting surfaces regulated while its impedance is monitored until a prescribed value is reached. The control regulates the RMS voltage applied in accord with the impedance by changing the RMS voltage to a percentage of that applied until the prescribed value is obtained so that the tissues stay moist and are coagulated without drying and carbonizing or turning to eschar.

Plasma monitoring and control method and system

Abstract: A plasma monitoring and control method and system monitor and control plasma in an electronic device fabrication reactor by sensing the voltage of the radio frequency power that is directed into the plasma producing gas at the input to the plasma producing environment of the electronic device fabrication reactor. The method and system further senses the current and phase angle of the radio frequency power directed to the plasma producing gas at the input to the plasma producing environment. Full load impedance is measured and used in determining characteristics of the plasma environment, including not only discharge and sheath impedances, but also chuck and wafer impedances, primary ground path impedance, and a secondary ground path impedance associated with the plasma environment. This permits end point detection of both deposition and etch processes, as well as advanced process control for electronic device fabrication. The invention also provides automatic gain control features for applying necessary signal gain control functions during the end point and advanced process control operations.

An improved impedance-boundary algorithm for Fourier split-step solutions of the parabolic wave equation

Abstract: A new implementation of the previously published mixed Fourier transform (MFT) method for including impedance boundaries in split-step parabolic equation solutions is described and demonstrated. The new algorithm is formulated entirely in the discrete domain which results in extended applicability and increased computation speed. A brief review of the original MFT solution is followed by a detailed description of the discrete formulation. The performance of the new algorithm is then demonstrated with a few examples which rely heavily on the accuracy of the impedance boundary. These examples include 10 MHz surface wave propagation over smooth and rough sea surfaces and 10 GHz calculations utilizing an effective rough surface impedance.

Discrete-time current control of voltage-fed three-phase PWM inverters

Abstract: The discrete-time current control of three-phase voltage-fed pulsewidth modulation (PWM) inverters is discussed, with emphasis on important practical aspects. The inverter feeds a balanced three-phase load of R-L impedances in series with back-EMFs. The inverter-load system is modeled by using space vectors. The practical difficulties of the predictive control method are pointed out. In particular, effects of the delayed application of the manipulated voltage caused by controller computing time are investigated. A modified control law that eliminates the undesirable effects of the computing delay is introduced. Also, prediction of current reference is utilized, which would enable operation with any reference function. An estimation and prediction procedure for the back EMF is also introduced. Steady-state errors in the load current due to these predictions are calculated for sinusoidal operation. Simulation results for the predictive control and the modified control laws are presented and discussed.

Impedance spectra of tumour tissue in comparison with normal tissue; a possible clinical application for electrical impedance tomography

Abstract: Electrical characteristics of living tissues have been investigated for a long time in the search for further methods to complement the traditional investigations of pathology and physiology. Tumour tissue has been shown to exhibit a larger permittivity and conductivity than normal tissues. This might be associated with the fact that tumour cells have a higher water content and sodium concentration than normal cells, as well as different electrochemical properties of their cell membranes. To our knowledge only a few contributions on this subject have been published. This study describes an additional application on measurements of the complex impedance of tumour and normal tissues, in order to compare the impedance features of the two tissue types. The tissue sample is placed in a measuring cell in which the temperature is controlled. The measuring cell is connected to an impedance meter able to measure the complex impedance in terms of real and imaginary part curves for frequencies from 1.5 kHz to 700 kHz. The four-electrode principle is used with the current injected by the outer electrodes and the voltage difference measured between the inner electrodes. The current can be altered up to 1 mA. The instrument can be calibrated with known resistance and capacitance networks connected to the input of the instrument in order to minimize the measurement errors. The calibration routine uses a polynomial adaptation and can be applied interactively. Measurements performed by the instrument show promising results. Preliminary results show that this method can be extended to a new application for detection of tumour tissue by electrical impedance tomography (EIT).

Magneto‐impedance effect in NiFe plated wire

Abstract: The voltage V(t) induced by a sinusoidal drive current traversing a 125‐μm‐diameter BeCu wire plated with 1 μm NiFe is observed to be a very strong function of axial dc magnetic field. The basic physics of this phenomenon is explained classically in terms of Faraday’s law of induction and Stoner–Wohlfarth magnetization reversal, which yield theoretical predictions that are in good agreement with experiment. For drive current amplitudes of the order of 100 mA, and frequencies of the order of 5 MHz, the field sensitivity dV/dH can be as large as 1 V/Oe (per cm of wire), which offers the potential for application in relatively simple, very high sensitivity magnetic field sensors.

An Impedance-Based System Modeling Approach for Induced Strain Actuator-Driven Structures

Abstract: This paper presents the theoretical development and experimental verification of a system model of piezoelectric (PZT) patch actuators for induced strain actuation of two-dimensional active structures. The model includes the dynamic interaction between PZT actuators and their host structures. Analytical solutions of the output behavior of the PZT actuators have been developed based upon the actuator input impedance and the mechanical impedance of the host structures. The impedancebased model was then applied to thin plates and thin shells, and to beams. The case studies demonstrate the generality and utility of the impedance modeling approach. A simply-supported thin plate with surface-bonded PZT patches was built and tested so that the ability of the impedance model to accurately predict the dynamic performance of the actuator and the host structure has been verified. When compared with conventional static models, the impedance modeling method offers insight into the dynamic coupling of the integrated PZT/substrate systems.

Iontophoretic drug delivery device having high-efficiency dc-to-dc energy conversion circuit

Abstract: An iontophoresis system includes a transdermal patch (23) for placement against the skin of a patient and a controller (24, 26) electrically connected to the patch (23). The patch (23) includes an anode and cathode electrode, and holds an electrolyte and a medication. The controller includes a DC-DC converter circuit (24) which generates output voltage that is provided to the anode electrode. The controller also includes an adjustable current regulator circuit (26). The current regulator circuit (26) is coupled to the cathode electrode and is adjustable to provide a desired current flow through the electrodes and the skin of the patient. The DC-DC converter circuit (24) is responsive to the voltage drop across the electrodes and adjusts its ouptut voltage in response to this voltage drop and changes in the impedance of the patient's skin.

A review of electrical impedance techniques for the measurement of multiphase flows

Abstract: Various developments in the use of electrical impedance methods in multiphase flow are reviewed. Because the components of a multiphase flow often exhibit different electrical properties, a variety of probes have been developed to study such flows by measuring impedance in the region of interest. Nonintrusive devices are used to measure spatially averaged flow properties, such as void fraction. Local probes have been developed to measure a variety of pointwise flow quantities, including film thickness in annular flow, local void fraction in dispersed flows, bubble and particle sizes, and flow velocities. Such impedance probes are usually easy to build and use, and can have a high frequency response. However, the spatial resolution of the probes may be limited, calibration may be difficult, and the accuracy of some probes may be limited to specific phase distributions. Researchers are now using electric fields to reconstruct the impedance distribution within a measurement volume via Electrical Impedance Tomography (EIT). EIT systems employ voltage and current measurements on the boundary of a domain to create a representation of the impedance distribution within the domain. EIT inversion algorithms are discussed, and the application of EIT to multiphase flows is reviewed. The benefits and limitations of EITmore » systems are also discussed.« less

Programmable impedance output driver

Abstract: An output driver circuit is disclosed that generates an accurate and predictable output impedance driver value corresponding to a programmable external impedance. The output driver circuit includes an external resistance device, voltage comparator device, control logic, an evaluate circuit and off-chip driver (OCD) circuit. Voltage from the external resistance device (VZQ) is compared with voltage created from the evaluate circuit (VEVAL) by the voltage comparator device, which indicates to the control logic whether VEVAL is greater than or less than VZQ. The control logic will adjust the evaluate circuit accordingly with a count until the two voltages are basically equal (i.e., the count is alternating between two adjacent binary count values). At which time the control logic operates the OCD with the lower of the two adjacent count values to produce a proper and predictable driving impedance.

Current approaches to analogue instrumentation design in electrical impedance tomography

Abstract: Electrical impedance tomography (EIT) is a novel medical imaging method, which allows reconstructed tomographic images of the internal impedance of a subject to be made with the use of a ring of electrodes. High precision impedance measurements are needed, because the image reconstruction process is ill-conditioned and small errors in measurement can lead to large errors in the final image. In practice, there are formidable instrumentation problems, due to the interaction of finite current drive output impedance, recording amplifier common mode rejection, and unequal skin - electrode impedances. A number of different EIT systems have been constructed or are under development. These employ differing strategies, such as additional electrodes, multiple electrode current injection, or recording at multiple frequencies, to improve image accuracy. This paper reviews the nature of the instrumentation problems and the designs employed by differing groups in attempting to overcome them.

Radio-frequency accelerating system and ring type accelerator provided with the same

Abstract: In a radio-frequency accelerating system, a loop antenna is coupled with at least one of a plurality of magnetic core groups each including a plurality of magnetic cores or with at least one of the plurality of magnetic cores, and an impedance adjusting means is connected to the loop antenna. A relatively low voltage is applied to the impedance adjusting means. Therefore, the impedance adjusting means may be a circuit element having a low withstand voltage and hence the radio-frequency accelerating system can be formed to have a small construction.

Contact stability issues in position based impedance control: theory and experiments

Abstract: The contact stability has been considered based on simplified linearized models of robot and environment. It is shown that the most crucial parameter for contact stability is the target damping ratio. When a high compliance is required the stability boundary conditions require significantly overdamped impedance behavior to ensure a stable contact with a stiff environment. These conditions for a SISO system are defined in the analytic form. Obtained minimal damping ratio values are significantly lower than those previously proposed in the literature.

Sheath impedance effects in very high frequency plasma experiments

Abstract: The frequency dependence (13.56–70 MHz) of the ion energy distribution at the ground electrode was measured by mass spectrometry in a symmetrical capacitive argon discharge. Reduced sheath impedance at very high frequency allows high levels of plasma power and substrate ion flux while maintaining low levels of ion energy and electrode voltage. The lower limit of ion bombardment energy is fixed by the sheath floating potential at high frequency, in contrast to low frequencies where only the radio frequency voltage amplitude is a determinant. The capacitive sheaths are thinner at high frequencies which accentuates the high frequency reduction in sheath impedance. It is argued that the frequency dependence of sheath impedance is responsible for the principal characteristics of very high frequency plasmas. The measurements are summarized by simple physical descriptions and compared with a particle‐in‐cell simulation.

Meter for measuring battery charge delivered in an implantable device

Abstract: An improved apparatus and method are described for providing a measurement of the charge depleted from a battery used in an implantable device such as a cardiac pacemaker. The measurement is provided not by measuring the voltage level or impedance of the battery, but rather by continuously measuring the electrical current drawn from the battery and integrating that measured current over an integration time period. A precision current-sensing resistor provides a sense signal having a voltage that varies according to the magnitude of current being drawn, and this sense signal is integrated using a voltage-controlled oscillator circuit and counter, which are implemented using CMOS circuitry arranged in a switched-capacitor topology.

Low power programmable ring oscillator

Abstract: A novel ring oscillator integrated circuit whose frequency of oscillation is independent of supply voltage, temperature and process technology is described. In addition, the ring oscillator circuit consumes low power and its frequency of oscillation is programmable. The ring oscillator comprises one or more inverter sections cascaded together in series. The output of the final inverter stage is coupled to the input of the first inverter stage. Inserted in the feedback loop is feedback control circuitry which functions to control the start/stop operation of the oscillator. Each inverter section includes a p-channel transistor coupled to a parallel combination of impedance and capacitance, which gives the inverter section asymmetric operating characteristics. This asymmetry helps to achieve a frequency of oscillation independent of supply voltage. A plurality of transistors having predetermined impedance's are coupled in series with the p-channel transistor to form the current limiting impedance. An output buffer provides large drive capability and achieves low power consumption by eliminating normally present crowbar current during switching. Pull-down control circuitry provides individual gate control of each of the transistors making up the current limiter in each inverter section. Process independence is achieved by trimming the plurality of pull-down current limiting transistor so as to attain a particular frequency of oscillation.

Electrical conductivity in high‐frequency plasmas

Abstract: The electrical conductivity is an important parameter in understanding the mechanism by which power is coupled to a radio‐frequency (rf) discharge plasma, as well as in determining the external electrical characteristics of the discharge. We present the results of computations of the resistive and reactive components of the collisional impedance of an argon plasma at 13.56 MHz. The plasma conductivity is computed from the two‐term solution to the Boltzmann equation, and includes the velocity dependence of the electron collision frequency, as well as non‐Maxwellian electron energy distribution functions. We compare these results with those obtained from the widely used classical expression for plasma impedance, in which the electron collision frequency is computed either in the dc or high frequency limit. Our results show that neither of the classical limiting expressions are adequate for discharge pressures in the range of few mTorr to a few Torr, which includes the region of operation for many rf discharges used in many applications of plasma technology. Further, the classical formula assumes that in the high‐frequency limit the plasma reactance is due entirely to electron inertia. We demonstrate that the plasma reactance may be strongly influenced, and in some cases dominated, by electron collisions. Results are presented in graphical form, which are useful in evaluating the importance of these effects on the interpretation of experimental results and the modeling of rf discharges.

Pulse-based impedance measurement instrument

Abstract: In accordance with the present invention, a pulse-based impedance measurement instrument is provided. A pulse generator repetitively generates a stimulus pulse to a device under test (DUT). A digitizer circuit, consisting of a sample-and-hold circuit, an analog to digital converter, and acquisition memory, repetitively samples the response voltage across the DUT to create a time record of the voltage as a function of time during a pulse response measurement. Each time record is operated on by a Fast Fourier Transform (FFT) which converts the voltage versus time information into voltage versus frequency information in a manner well known in the art. By measuring a set of calibration resistors with known resistance values to generate a set of complex calibration constants, the impedance measurement instrument provides measurements of complex impedance and return loss versus frequency of a DUT.

A method to measure the complex permeability of thin films at ultra-high frequencies

Abstract: A swept frequency method for measuring the magnetic permeability of thin films for frequencies up to 2 GHz with a resolution at 1 GHz of /spl sim/0.1 /spl mu/m in permeance is described. It is based on the measurement of impedance of a strip loop loaded with the sample under test. The method employs a commercial impedance or network analyzer, is simple, and suitable for permeability measurements of thin magnetic films which are used in recording heads and microwave components.

Thermal impedance extraction for bipolar transistors

Abstract: This paper describes a method for extracting the thermal impedance of bipolar transistors. The measurement is a two-step process: first the fractional temperature coefficients are calibrated at dc and then a transient step response is measured to extract the thermal spreading impedance. Measurement configurations and an example measurement cycle are shown. The measurement results can be fitted to multiple-pole models for use in compact circuit modeling in SPICE.

Short vertical 160 meter band antenna

Abstract: A physically short broad-bandwidth multiband vertical antenna with 50 ohm input impedance and 25 foot square footprint for 160, 80, 40 and 17 meter radio bands Low ohmic resistance due to the small physical size combined with system impedance transformation and capacitive input coupling provide radiation resistance corresponding to an efficiency of about 85 percent The 2:1 SWR bandwidth is 50 kHz on 160 meters and 87 kHz on 80 meters A 30 foot mast, top hat capacitive load, and a plurality of parallel vertical skirt wires depending from the top hat around the mast are electrically connected together at the top of the mast An impedance transforming multi-tap coil is connected between mast and ground Skirt wires are in two sets separately fed at their lower ends by separate coaxial cable coupling capacitors for operation on different bands A 50 ohm feed line, skirt wires, coupling capacitors and impedance transforming coil all have terminal connections on a mast-base insulator End-pruning of coaxial cable capacitors combined with coil tap selection tunes the antenna for desired portions of the 160 and 80 meter bands for input impedance matching without additional matching devices Skirt wire sets, downwardly tensioned and spaced from the mast, are connected to input capacitors by separated crossed metal spreaders at the mast-base insulator Additional reactance-reducing components facilitate improved operation at 40 meters More independent center frequency tuning for both 160 and 40 meter bands is obtained by connecting the impedance transformation coil from ground to a higher point on the mast via an additional skirt system