Absolute Value Of Impedance Research Articles

Control of the Corrosion of Magnesium for Implant Application by Hydrothermally Deposited Biodegradable Calcium Phosphate Coating

The corrosion protection of hydrothermally deposited calcium phosphate coatings on AZ31 magnesium alloy was studied in simulated body fluid (SBF) solution for their potential use as biodegradable implants. The coating mainly consisted of bioresorbable monetite phases. Potentiodynamic and electrochemical impedance spectroscopy (EIS) confirmed that the coatings provided varying levels of corrosion protection depending on the coating deposition temperature. By increasing the deposition temperature and corresponding growth in coating thickness the corrosion current density of the coated magnesium was 10,000 fold lower compared to the bare metal; indicating significantly enhanced corrosion performance of Mg substrate, reaching the corrosion protection requirement for magnesium implant. The barrier effect of Ca-P layers was further supported by the observed magnitude of anodic and cathodic Tafel slopes. Coated samples displayed much larger slopes than bare Mg substrate.EIS results showed that the size of capacitance loops and the absolute impedance value (|Z|) increases. By increasing the deposition time the corrosion mechanism was changed as a result of partial delamination of top surface of coating. In agreement with the electrochemical experiments, immersion tests in SBF also indicated large improvement in corrosion protection as the mass loss was reduced almost three times when coating was applied as compared to the bare metal. The uncoated Mg substrate undergoes severe and non-uniform corrosion after 28 days immersion in SBF solution; while, the coated samples displayed intact coating and no obvious pits were observed on the coating surface.The described biocompatible and biodegradable coatings significantly improved corrosion resistance of Mg substrate and can be promising candidate for biomedical application.

Ultrasonic characteristic of phase shift of layered structure and the determination of layer thickness

For the ultrasonic normally-incident reflected method, the phase shift of the mid-layer in a multi-layered structure has been theoretically derived and expressed as a sum form of the measured phase shift and the crossing phase shift. Using the sum form, the characteristics of phase shifts of a linear-viscoelastic layer on the two different elastic substrates of half-space of the infinite extent are first analyzed. By the replacement of phase shift of the upper elastic substrate with the corresponding measured phase shift, the substitution function of the input acoustical impedance of a next inaccessible layer has been developed. It is concluded that the corresponding relation of the layer phase shift with the minima/maxima of the absolute value of the input acoustical impedance of the inaccessible layer is repeated by those of the substitution function. Without giving the substrate thickness and considering the introduced misalignment and distortion problems, based on the corresponding relation, the thickness of the inaccessible layer can be determined by searching the frequencies of the minima/ maxima of the absolute value of the substitution function.

Evaluation of algorithms for calculating bioimpedance phase angle values from measured whole-body impedance modulus

This paper addresses the problem of calculating the bioimpedance phase angle from measurements of impedance modulus. A complete impedance measurement was performed on altogether 20 healthy persons using a Solatron 1260/1294 system. The obtained impedance modulus (absolute impedance value) values were used to calculate the Cole parameters and from them the phase angles. In addition, the phase angles were also calculated using a Kramers–Kronig approach. A correlation analysis for all subjects at each frequency (5, 50, 100 and 200 kHz) for both methods gave R2 values ranging from 0.7 to 0.96 for the Cole approach and from 0.83 to 0.96 for the Kramers–Kronig approach; thus, both methods gave good results compared with the complete measurement results. From further statistical significance testing of the absolute value of the difference between measured and calculated phase angles, it was found that the Cole equation method gave significantly better agreement for the 50 and 100 kHz frequencies. In addition, the Cole equation method gives the four Cole parameters (R0, R∞, τz and α) using measurements at frequencies up to 200 kHz while the Kramers–Kronig method used frequencies up to 500 kHz to reduce the effect of truncation on the calculated results. Both methods gave results that can be used for further bioimpedance calculations, thus improving the application potential of bioimpedance measurement results obtained using relatively inexpensive and portable measurement equipment.

M2055 Multiple Intraluminal Impedance (MII) Can Detect Flow Across the Esophago Gastric Junction (EGJ): Validation in Normal Subjects

Background: MII technique has been used to detect gastroesophageal reflux and transit of bolus in the esophagus. It is not clear if MII can also be used to study flow across the EGJ. Aims: Define impedance criteria for esophageal emptying. Methods: Studies were conducted in healthy subjects using a 4 mm combined high resolution manometery (HRM) and multi intraluminal impedance (MII) catheter probe equipped with 36 pressure sensors (1 cm apart) and 18 impedance electrodes (2 cm apart) (Sierra Scientific Instruments). Ten swallows of 5ml saline were performed in each subject. The pressure and impedance data were displayed as superimposed color plots using the Sierra Scientific program. Impedance data were exported to determine absolute impedance values from the pair of electrodes just above and below the EGJ. We hypothesized that in order for the flow across the EGJ to take place the 2 impedance values should drop below 2kΩ and be equal to each other. Pressure gradients between the esophagus and EGJwere determined before, during and after impedance detected flow across the EGJ. Results: HRM and impedance color plots show development of a pink color bridge (as a marker of flow, not clear in black and white photos) across the EGJ (Left and right panels). However, the width of the bridge is strongly influenced by the low and high filters setting of impedance thus making it a subjective marker of flow across the EGJ. Absolute impedance value graphs show that all of the 60 swallows met our criteria of flow across the EGJ. The duration of flow across the EGJ was 1.3±0.2 (mean±SE) seconds. Esophageal and EGJ pressure gradient during flow across the EGJ was significantly smaller compared to the periods when no flow was detected by impedance. 57 swallows were associated with flow across the EGJ. Flow stopped with inspiration related diaphragmatic/ EGJ contractions during 3 swallows. Conclusion: Impedance color plots can't determine flow across the EGJ in an objective fashion. We propose strict impedance criteria, based on the absolute impedance values recorded by electrodes above and below the EGJ to determine flow across the EGJ.

Higher order mode impedances and cut-off frequencies of overmoded coaxial waveguides

Using both theoretical and experimental methods the critical geometrical ratios for effective higher order mode superposition in coaxial waveguides are identified for SDMA beam forming antenna applications. Higher order mode impedances are also important in the design of such antennas and a closed form expression for the power-voltage definition of impedance is derived together with estimates for the voltage-current and power-current forms. An industry standard finite element solver is used to confirm the accuracy of these formulations for a 60 mm radius overmoded coaxial waveguide. In the second part of the paper, the mode chart is used to design a coaxially fed, overmoded air-spaced coaxial waveguide “T” junction supporting the TEM, TE 11 and TE 21 modes. A Green's function based model of the input impedance of this junction establishes that the power-voltage characteristic impedance occurs naturally in calculations requiring absolute impedance values. Finally, this input impedance model, which includes higher order and evanescent mode propagation, is demonstrated to agree well with experimental data for this junction.

Construction of High-Resolution Acoustic Impedance Data for Reservoir Modeling

The 3-D models of absolute acoustic impedance values were built integrating well, seismic and geologic data utilizing deterministic and stochastic inversion techniques to bet utilized as soft data in reservoir property models to aid the development of the Rotliegend Gas Field, northwestern Germany.

Evaluation of the Performance of Photoelastic Modulator by Admittance Parameter Measurements

An automatic system for admittance measurements has been built to evaluate the performance of a photoelastic modulator (PEM). It consists of an LCR meter, a frequency synthesizer, and a personal computer. With this system, the resonance frequency, the frequency dependence of an absolute value of impedance |Z|, and the phase angle θ of the PEM are measured automatically with a 0.1 Hz step. The value of |Z| at θ=0 is the resistance R of the equivalent electric circuit of the PEM. The quality factor Q is evaluated from the frequency dependence of admittance parameters. A PEM with a small value of R and high value of Q is found to be efficient and have a small residual birefringence in optical measurements. It is known that the residual birefringence of the PEM brings about errors and artifacts in polarization modulation instruments such as the modern circular dichroism spectrometer. Thus, it is worthwhile to estimate the performance of the PEM from admittance parameter measurements without installing the PEM into a spectrometer.

三次元地震探査データのポアソン比と音響インピーダンスによるガス砂岩分布の予測

The purpose of this study is to verify the applicability of the 3D seismic inversiondata for the hydrocarbon determination. The 3D seismic data consisting of two angle stack data (0-22 .5 degree and 22.5-45 degree), were inverted into acoustic impedance and Poisson's ratio data. The target interval is the Upper Cretaceous, Coniacian sand and we tried to discriminate between the gas sand and the water sand by them.The two sets of angle stack data were inverted for angle impedance. Angle impedance is a physical quantity which depends on acoustic impedance, shear impedance and the angle of reflection wave.The match between the angle impedance results from the 3D seismic data and the angle impedance logs is rated from good to very good with respect to both reflector placement and absolute angle impedance value. The near angle stack data results in the better solution than the far angle stack data.Poisson's ratio and acoustic impedance volumes were calculated from the angle impedance inversion results. Comparison of the calculated AVO attributes with the well log data shows that the acoustic impedance volume is of very good quality and tha Poisson's ratio volume is of good to poor quality.A lithology cube was produced on the basis of lithology probability calculated from the cross-plotting of Poisson's ratio versus acoustic impedance. Although an amplitude anomaly of full stack data yields only a sand distribution, a gas sand distribution was interpreted by using this cube.

High-frequency behavior of magnetically soft wires

In addition to opening the possibility of interesting applications, the study of the behavior of soft wires up to GHz frequencies permits a comparison between theory and experiment, which is more difficult at low frequencies, at which domain wall motion is possible. Obviously, the importance of this comparison depends upon the sophistication both of the experiments and of the models. Agreement between experimental measurements of the form of impedance as a function of frequency and of field and theoretical models is excellent, especially at high frequencies. For samples with low enough magnetization to permit the observation of both ferromagnetic resonance and ferromagnetic antiresonance in impedance, it is possible to deduce a number of fundamental properties of the material. However, the observed amplitudes of the maxima and minima of impedance or of permeability are in disagreement with the predictions of the simplest models. In order to understand the cause, or causes, of this disagreement, it is desirable to improve both the experimental and theoretical situations. We discuss the present state of experiment and of theory, and consider the comparison between theoretical predictions and experimental results. While there are some successes in modelling, there remain discrepancies. To explain these, the possible effects of surface anisotropy, damping mechanism, and anisotropy dispersion on the absolute value of impedance, as a function of field and frequency are investigated. The role of the last of these is particularly subtle.

An analogue instrument for the measurement of respiratory impedanceusing the forced oscillation technique

The successful development of non-invasive assisted ventilation via anasal mask has led to the requirement for improved methods of monitoring therespiratory system. Measurements of respiratory impedance during assistedventilation using acoustic methods are showing considerable promise inproviding this clinical data.The method involves imposing very low amplitude acoustic oscillations onto thespontaneous or assisted respiratory airflow. The subsequent interaction withthe respiratory system modifies the pressure and flow relationship of theforced oscillations. The ratio of pressure to flow can be used to measure inreal time the absolute value of respiratory input impedance. As a result aversatile, non-invasive and repeatable profile of respiratory mechanics isobtained. Using a 5 Hz conventional forced oscillation frequency, data highlysensitive to airflow obstruction and capable of tracking mechanical events andresponses become available to the clinician. Recent studies with ventilatedand sleeping subjects confirm future potential for the forced oscillationtechnique in vivo.We describe an instrument named the respiratory impedance monitor (5 Hz), whichutilizes the forced oscillation technique (FOT). This fully developed deviceis designed in accordance with agreed international clinical guidelines.Comparative clinical data from normal subjects and patients with chronicobstructive pulmonary disease is presented.

Comparison of hand‐to‐leg and leg‐to‐leg bioelectric impedance devices in the assessment of body adiposity in prepubertal children. The STRIP study

The body composition of 40 seven-year-old children and of 50 of their parents was measured using two bioelectric impedance devices, the Model 101, RJL Systems, USA (conventional hand-to-leg device) and TANITA body fat analyser, TBF 105, Tanita Co, Tokio, Japan (newer leg-to-leg device). There were strong correlations between impedances obtained by these two devices [r= 0.95, r = 0.93, r= 0.82, r = 0.81 for girls (n = 22), boys (n = 18), mothers (n = 27) and fathers (n = 23), respectively (p < 0.0001 for all)]. However, there was a clear difference in the absolute impedance values due to the fact that the devices measure different segments of the body. Fat percentages based on built-in equations of the two devices correlated in girls, mothers and fathers (r = 0.71, r = 0.94, r = 0.80, respectively; p < 0.001) but not in boys (r = 0.21, p = 0.41). Using the Bland-Altman comparison method, a large intraindividual difference was observed in the fat percentages by the two devices, independent of adiposity level. Both devices detected significant gender differences in fat percentages in 7-y-old girls and boys with similar BMIs. When using the Tanita 105 leg-to-leg bioelectric impedance device to assess adiposity in children there is an obvious need for revised equations. For this, comparative studies using more validated methods, i.e. densitometry or DEXA, as part of a multi-compartment model are needed.

Utilization of Impedance Measurements in Pallidotomy Using a Monopolar Electrode

Object: This study was performed to evaluate the reliability and utility of using monopolar impedance monitoring for estimation of the location of the thermocouple electrode during a pallidotomy procedure. Methods: In 26 patients, impedance profiles were measured at 2-mm intervals and anatomical boundaries were marked on postoperative MRI studies in 19 patients. The pattern of change in impedance as the electrode was towards the target coordinates in the globus pallidus was studied empirically in relation to MRI-defined anatomy and by electrical stimulations. The pattern of impedance change was of greater reliability than absolute impedance values. A drop in impedance was noted in 10 cases where the electrode entered the putamen or globus pallidus upon exiting the internal capsule, and in 9 of these this drop was measured before or at the distal boundary of the internal capsule. A variable pattern in the region of the base of the globus pallidus was observed, with 10 of 19 cases demonstrating a decrease and 8 cases an increase, consistent with the proximity of a CSF cistern in the former and the ansa lenticularis and optic tract in the latter. Simulations showed that the monopolar electrode was more sensitive to the approach of a boundary than the bipolar electrode. Conclusion: Our measurements and simulations suggest that a monopolar electrode could predict a nearby region of high or low impedance before penetrating it and a trend of decreasing impedance as the distal edge of the globus pallidus is approached.

Frequency-dependent properties of cerebral blood transport—An experimental study in anaesthetized rabbits

Carotid arterial blood pressure and blood flow velocity in the basilar artery were studied in nine New Zealand rabbits under general anaesthesia. The cerebrovascular impedances for mean and maximal flow velocity were defined as the ratios of the respiratory and pulse waveforms of arterial blood pressure and blood flow velocities. The absolute values of these impedances were expressed and analysed as functions of frequency. Both functions decreased as frequency increased, demonstrating that a pulsatile blood movement need a lower energy expenditure than a continuous one. A minimum absolute value of impedance for flow velocity mean was found near 2.5–4 Hz in each rabbit. The impedance for mean flow velocity could be modelled by a second-order circuit, whereas the distribution of impedance for the maximal velocity had a more uniform character and could be approximated by a first-order model. A method of assessment of changes in cerebrovascular resistance using frequency properties of calculated impedance was proposed.

The use of the impedance method of non-destructive testing on honeycomb structures

The operation of the impedance method of non-destructive inspection on honeycomb structures with carbon fibre reinforced plastic (CFRP) skins has been investigated. The mechanical impedance at positions of skin-core disbonds of different sizes has been compared with that in good areas of panels with 0·5 mm and 1 mm thick skins. It has been shown that when the honeycomb thickness is over 10 mm, the method will detect defects 10 mm in diameter under 0·5 mm thick skins, but that defects 20 mm in diameter are close to the margin of detectability under 1 mm thick skins. However, when the honeycomb thickness is reduced below 10 mm, the reliability of the test is greatly reduced. The tests reported here were carried out with an impedance head, and it has been shown that this transducer is an attractive alternative to the vibrating rod transducer used in commercially available testing instruments, since an absolute value of impedance can readily be obtained, whereas the output of the vibrating rod transducer is a highly non-linear function of impedance so only comparative measurements are produced.

多孔質アルミニウム・アノード酸化皮膜と熱水との反応 ＩＩＩ インピーダンス測定による水和皮膜の酸溶解特性の解析

Porous anodic oxide films formed in an oxalic acid solution were hydrated to various extents by allowing them to react with hot water at 99.5°C. The films were then dissolved in a chromic acidphosphoric acid solution and the dissolution was followed by impedance measurements in a neutral borate solution. The results were analyzed by plotting the log of the absolute value of impedance against the log of the frequency. The equivalent circuit of the hydrated film was found to consist of the capacitance of the barrier oxide layer (Cb) combined in series with a parallel combination of the capacitance and resistance components of the hydrous oxide formed in the pores (Ch and Rh). The values of Cb-1, Rh and Ch-1 and the their variation with the dissolution time (td) were determined. It was found for the films filled up with the hydrous oxide that the film-dissolution proceeds uniformly from the outside at a rate controlled by the dissolution of hydrous oxide, the dissolution rate decreases with the time of the reaction with hot water (th). The outermost part of the hydrous oxide formed at th>30min was very resistant to acid-dissolution. It was recognized that the decrease in dissolution rate is always accompanied by an increase in the specific resistance of the hydrous oxide. The barrier oxide layer next to the metal begins to dissolve at the time when the outer part of the film containing the hydrous oxide in the pores is completely dissolved. The dissolution characteristics of the barrier layer itself is little affected by the hot water treatment. These findings agree quite well with the results of a previous investigation conducted by gravimetry.

A comparison between the transthoracic electrical impedance method and the direct Fick and the dye dilution methods for cardiac output measurements in man

In fourteen patients referred for preoperative evaluation of heart disease we compared the transthoracic electrical impedance method to the direct Fick (four patients) and dye dilution methods (ten patients) for estimation of cardiac output. On statistical analysis of paired differences we found no reliable agreement between the absolute impedance values and the reference methods. The reproducibility was, however, acceptable, and the coefficient of variation for impedance cardiac output was 7.8%, and for impedance stroke volume 7.6%. Our conclusion is that in patients with advanced heart disease cardiac output cannot be determined with accuracy with the impedance cardiographic method. In clinical practice this must be considered so important, that we hesitate to use the method for monitoring cardiac output in critically ill patients even if the reproducibility for individual changes is acceptable.

Continuous monitoring of circulating blood hematocrit.

The relationship between the hematocrit value and the absolute value of impedance of whole blood was analyzed. The results indicated that the hematocrit value was linearly proportional to the logarithm of the impedance of whole blood over the range of hematocrit values of 10 to 60% with a correlation coefficient of 0.995. The circuit used for detection of the impedance of whole blood was described. It required no adjustments during measurements and had a wide linear range. The sources of error during continuous measurements were the rate of blood flow through the sensor cell, the temperature of the blood, and the concentrations of plasma proteins and ions. Accordingly, the flow and temperature of blood were kept constant during measurements. Changes in the concentrations of plasma proteins and ions within physiological ranges caused errors of +/- 2.0%. Typical results of continuous measurements were presented, showing that the hematocrit values obtained by this method agreed well with those obtained by the conventional methods from the packed cell volume. An advantage of this method over the conventional methods was that it could follow rapid and transient changes in the hematocrit.

A STUDY ON RHEOGRAPHY OF HEART AND AORTA

In order to record the mechanical movements of heart and aorta, an apparatus for rheography was originated for trial by our research group. Having examined this apparatus and method. we made studies on the rheograms of the healthy and of the arrhythmic patients followed by considerations of its clinical significances. 1) On rheography the A.C. bridge has been used as a transducer, i.e. one electrode is placed on the anterior chest wall and another on the back, positioning so that the heart or aorta to become in between them, connecting both to one arm of A.C. bridge, and 40 KC more or less frequency A.C. was transmitted. This apparatus is possible to record the mechanical movements of heart or aorta by the fluctuation of unbalanced current of A.C. bridge caused through the changes of impedance between the both electrodes. 2) An impedance equivalent to that of human body has been measured and have noticed that the values of phase angles of human body impedance are constantly negative and its absolute values decrease in accordance with the frequency increase. Hence, it became known that this A.C. bridge requires relatively simple composition : i.e. the arm of fixed impedance value is necessary for resistance only, and the other arm for adjustment may be joined in series both resistance and capacitance. 3) Having studied the characteristics of the A.C. bridge as a transducer, we have also noticed that the fluctuation of unbalanced current of the A.C. bridge is in proportion to the human body, in case the arm impedance fluctuation joined to body compared to the electrodes impedance, is negligibly small. Theoretically and from the results of our experimental researches, the bridge with equal absolute value of impedance on every arm was found to be most sensitive and advantageous for this experiment, from the viewpoint of this apparatus structure. On the other hand, through the outcome of our examination on the convergent loci of the A.C. bridge, the A.C. bridge as a transducer has been also recognized as most sensitive in case used in the slightly unbalanced state. Whereas, when recording the rheograms of heart or aorta, we have arrived at the conclusion that it is most advantageous to be recorded in the unbalanced state of slightly increased resistance and capacitance (from the balanced state). 4) We have devised a calibrating method to calibrate the fluctuation of impedance between the 2 electrodes as a vector; That is, the determination of vector value induced from the deviated curve which is caused by changing resistance and capacitance of the arm for adjustment respectively in the course of recording. 5) The A.C. distribution in a piece of fish-flesh was examined. Also we further studied the wave forms of rheograms by placing electrodes on several parts of human body. From these experiments in case a small electrode is uesd, we have recognized that the current density of the place adjacent to the electrode was greatest.

Impedance change of the skin during the galvanic skin reflex.

As an approach to understanding of the peripheral effector mechanisms of the galvanic skin reflex (GSR), impedance changes were measured at the palm and dorsum of hand on 17 healthy male adults with special reference to COLE'S circuit. The measurement was conducted with sinusoidal current of nine different frequencies ranging from 30 to 10, 000c/s and with low frequency square pulses.1. At each frequency of sinusoidal currents, resting impedance of the skin was measured with the result that impedance locus for each frequency was found to occur fairly well on a circular arc as was expected from the assumption that COLE'S circuit is suitable as equivalent to impedance of the skin.2. By means of Lissajous' figures, changes in resistance, in reactance and in absolute value of impedance were measured at each frequency of the sinusoidal currents. It was found that resistance of the skin decreased at lower frequencies and increased at higher frequencies, whereas reactance always decreased irrespective of frequency. In spite of this variation in resistance change, the absolute value of impedance always decreased, although to a progressively lesser extent with increase in frequency.3. On the basis of these experimental results and of the results obtained by analyzing the traces of the impedance loci during the GSR, it was suggested that impedance change of the skin during the GSR may be only due to decrease of the leakage resistance R2 of COLE'S circuit.4. In the experiment with square pulses, initial resistance, initial capacitance and residual resistance were measured from the polarization curves during the GSR. Residual resistance decreased markedly without any appreciable change either in initial resistance or in initial capacitance. These results are in agreement with those obtained by the use of sinusoidal currents.