Variation Of Electrical Impedance Research Articles

Electrical Impedance Variations in Banana Ripening: An Analytical Study with Electrical Impedance Spectroscopy

AbstractFruit ripening is a very crucial event in food engineering as the fruits are very important and essential food materials for human health. Under‐ripening and over‐ripening both are not desirable to have all the essential and important nutrients in the fruits which are only available at their optimum‐ripening state. Hence, studying the ripening process of fruits is very much essential which will not only help the people to have the best fruit quality but also will help the researcher and scientist to analyze the food quality. Chemical and biochemical analyses conducted to analyze the fruit ripening are time‐consuming and destructive in nature; hence, these methods, generally, are not found suitable for routine, fast and repetitive inspections. A fast and nondestructive fruit ripening characterization method is found essential to study the ripening state and fruit nutrients levels. In this direction, the EIS studies have been conducted as a nondestructive evaluation method to study the electrical impedance variations during banana ripening. The electrical impedance of banana samples is measured by Agilent 4294A impedance analyzer at different states of ripening and the ripening states are correlated with their corresponding impedances. All the impedance parameters, Z, phase angle, real part of Z and imaginary part of Z are studied to analyze the ripening phenomena in terms of banana impedance. The results demonstrate that the complex impedance, real part and imaginary part of the impedance all increase with the progresses in the ripening process. Equivalent circuit modeling shows that the ripened banana contains constant phase elements. Statistical analysis conducted on the samples from a same bunch also shows that the electrical impedance spectroscopy technique can be applied for noninvasive characterization of banana ripening.Practical ApplicationsEIS conducted on banana ripening characterizes the banana ripening process in terms of its impedance variation and develops the equivalent circuit. EIS studies establish the correlation between the bioimpedance variation and ripening states which can be potentially utilized to study the banana ripening noninvasively. Statistical analysis shows that the standard deviation of all the impedance parameters of different banana samples obtained from a same bunch is very low compared to the corresponding mean values. It is observed that the EIS study conducted on one banana sample can represent the ripening state of the other bananas and hence the EIS studies conducted on limited number of samples can be utilized to characterize the ripening of the entire banana stacks. Thus EIS studies on banana ripening not only help us to find the optimum ripening state but also it will help the researchers to analyze its physiological changes, taste, and nutrient levels.

Variations in electrical impedance and phase angle among seedlings of Pinus densata and parental species in Pinus tabuliformis habitat environment

Electrical impedance (EI) and phase angle (PHI) parameters in AC impedance spectroscopy are important electrical parameters in the study of medical pathology. However, little is known about their application in variation and genetic relationship studies of forest trees. In order to test whether impedance parameters could be used in genetic relationship analysis among conifer species, EI and PHI were measured in a seedling experiment test composed of Pinus tabuliformis, Pinus yunnanensis, and Pinus densata in a habitat of Pinus tabuliformis. The results showed that variations in both EI and PHI among species were significant in different electric frequencies, and the EI and PHI values measured in the two populations of P. densata were between the two parental species, P. yunnanensis and P. tabuliformis. These results show that these two impedance parameters could reflect the genetic relationship among pine species. This was the first time using the two AC impedance spectroscopy parameters to test the genetic relationship analysis between tree species, and would be a hopeful novel reference methodology for future studies in evolution and genetic variation of tree species.

Real-time electrical impedance variations in women with and without breast cancer.

The chaotic vascular network surrounding malignant tumors leads to pulsatile blood flow patterns that differ from those in benign regions of the breast. This study aimed to determine if high-speed electrical impedance tomography (EIT) is able to detect conductivity changes associated with cyclic blood-volume changes and to gauge the potential of using these signatures to differentiate malignant from benign regions within the breast. EIT imaging of pulsating latex membranes submerged in saline baths provided initial validation of its use for tracking temporally varying conductivities. Nineteen women (10 with cancer, nine without) were imaged with EIT over the course of several heartbeats in synchrony with pulse-oximetry acquisition. Eight parameters ( rs, ϕ(rt,max), rt,max, Plow:full, Phigh:full, Plow:high) relating the conductivity images and pulse-oximeter signatures were extracted and used as a means of comparing malignant and benign regions of the breast. Significant differences between malignant and benign regions of interest were noted in seven of the eight parameters. The maximum correlation between conductivity and pulse-oximeter signals, rt,max , was observed to be the optimal discriminating parameter with a receiver operating characteristic area under the curve of 0.8 and a specificity of 81% at a sensitivity of 77%. Assessing the dynamic conductivity of breast may provide additional clinical utility to that of standard imaging modalities, but further investigation is necessary to better understand the biophysical mechanisms leading to the observed conductivity changes.

Electrical impedance as signal to monitor healthy state of eardrum-like membranes

Eardrum perforation is viewed as one kind of structural damage occurring in human being, which will cause loss of hearing when the damage becomes serious. This paper describes a preliminary concept to detect damage of eardrum-like membranes through measuring electrical impedance of a dynamic microphone. The dynamic microphone is inserted in one end of an ear canal-like tube and the eardrum-like membrane is attached at the other end of tube. Holes with different size are drilled in the membranes to represent the different damage levels. The electrical impedance of dynamic microphone is directly related to the mechanical impedance of the membrane, and any change in the electrical impedance signal can be considered an indication of change in the membrane integrity. For the different damage levels of membrane, variation of electrical impedance from the dynamic microphone is observed in experiment. Features are extracted from the curves of electrical impedance and used to train an artificial neural network. Through the trained neural network, damage in membrane can be monitored even in its incipient stage, and the damage levels can be easily estimated, which indicates electrical impedance is a good signal for non-destructive evaluation of structural health.

Resonance tracking and vibration stablilization for high power ultrasonic transducers

Resonant frequency shift and electrical impedance variation are common phenomena in the application of high power ultrasonic transducers, e.g. in focused ultrasound surgery and in cutting. They result in low power efficiency and unstable vibration amplitude. To solve this problem, a driving and measurement system has been developed to track the resonance of high power transducers and to stabilise their vibration velocity. This has the ability to monitor the operating and performance parameters of the ultrasonic transducers in real time. The configuration of the system, with its control algorithm implemented in LabVIEW (National Instruments, Newbury, UK), ensures flexibility to suit different transducers and load conditions. In addition, with different programs, it can be utilised as a high power impedance analyser or an instantaneous electrical power measurement system for frequencies in the MHz range. The effectiveness of this system has been demonstrated in detailed studies. With it, high transducer performance at high power can be achieved and monitored in real time.

Electrical impedance to detect accidental nerve puncture during ultrasound-guided peripheral nerve blocks

The objective of this study was to assess if an increase in electrical impedance was associated with intraneural (sub-epineural) needle tip placement. Two electrical impedance measurements were carried out in each of 140 peripheral nerve blocks. The first measurement was performed at a distance of 0.5-1cm from the nerve trunk (reference value), and the second measurement was performed close to the nerve, either immediately before local anesthetic injection if no nerve puncture was suspected, or immediately before repositioning the needle if nerve puncture was suspected. Nerve puncture was suspected if any one of the following indications was present: pain or paresthesia; motor responses with a minimal stimulating current<0.4mA; needle tip observed inside the nerve using ultrasound; nerve swelling after injection of local anesthetic. Electrical impedance variations were compared between the no puncture and the suspected puncture groups. Nerve puncture was suspected in 21 cases. The median variation [quartiles] of electrical impedance was +6.6% [-20; 36%] in the suspected puncture group (n=21) and -10.0% [-28; 0%] in the no puncture group (n=119) (P=0.02). Absolute values of electrical impedance close to the nerve were greater in the suspected puncture group (15.5kΩ [12.0; 18.0kΩ]) vs the no puncture group (12.0kΩ [8.9; 15.1% kΩ]) (P=0.013). A receiver operating characteristic (ROC) curve was constructed, and the optimal cut-off for impedance was +4.3%. A>4.3% increase in electrical impedance may indicate accidental nerve puncture during peripheral nerve block.

Biological sensor based on a lateral electric field-excited resonator

This paper describes a biological sensor based on a lateral electric field-excited resonator using an X-cut lithium niobate plate. Its potential was shown through the example of biological interaction between bacterial cells and specific bacteriophages. The detection was based on the analysis of the measured real and imaginary parts of electrical impedance for a resonator loaded by the biological suspension under study. It has been shown that the sensor is sensitive to specific interactions between bacterial cells and specific bacteriophages in a pure state as well as in the presence of extraneous microflora. The degree of electrical impedance variation resulting from the biological interaction depends on the numbers of phage particles and bacteria cells. The sensor may be used not only for the qualitative analysis of bacteria but also for their quantitative detection.

Non-destructive assessment of internal decay in three hardwood species of northeastern North America using sonic and electrical impedance tomography

Summary Sonic tomography and electrical impedance tomography ( EIT ) were used to detect and quantify internal decay in living trees. Twenty-two cross-sectional images, representing variations in sonic velocity and electrical impedance, were captured from nine trees (four Acer rubrum L., three Betula lenta L., and two Fagus grandifolia Ehrh.) in two forests in Connecticut. Following acquisition of tomographic data, 8 trees were felled, from which 19 stem disks were cut for comparison to the tomographic results. For one black birch, with extensive trunk rot and an internal cavity, sonic tomography (SoT) and EIT were very accurate in depicting both the area of the cavity as well as the area of fungal colonization and incipient decay. The use of both SoT and EIT to estimate area of decay resulted in a level of accuracy that far exceeded that produced from either method alone. Specifi c gravity values obtained from clear and decayed wood from three trees corroborated tomographic assessments, and permitted an estimation of the amount of carbon lost through decay. The implications of internal decay on carbon sequestration rates in temperate forests are also addressed.

0.18 µm CMOS integrated circuit design for impedance-based structural health monitoring

Piezoelectric materials constitute a class of intelligent materials that are helpful for monitoring the structural integrity. The principle of the piezoelectric impedance-based structural health monitoring technique is to measure the electrical impedance of a piezoelectric patch attached to a structure in a certain frequency range. Electrical impedance variations indicate physical changes in the structure due to the coupling between the electrical impedance and the mechanical impedance. Traditional methods use an impedance analyser that increases the inspection cost. The objective of this work is to introduce an electronic circuit for the piezoelectric impedance-based structural health monitoring. The circuit can monitor the electrical impedance variations of a piezoelectric patch attached to a structure. The frequency range is from 7.47 to 277.29 kHz. This frequency range covers the sensitive range of the piezoelectric structural integrity. The power consumption of the circuit is 18.15 mW. The chip area is 1.03 mm x 2.30 mm. The cost of the final design will be much lower than that of an impedance analyser. Using a wireless communication circuit, a sensor network might be established in the future.

Fourier analysis of electrical impedance variations in urinary bladder during changes of intravesical pressure

Original hardware and software system was used to record and analyze the variations of electrical impedance of the urinary bladder in narcotized rats (n=7) at rest, during instillation of physiological saline into the bladder resulted in elevation of intravesical pressure, and during subsequent urination accompanied by intravesical pressure release. Fourier analysis of impedance variations revealed three periodic components with the frequencies of heartbeat, respiration, and the Mayer wave (~0.1 Hz). In resting bladder, the amplitude of Mayer and respiratory spectrum peaks were high, and they increased to a different extent during physiological elevation of intravesical pressure, while a small cardiac peak did not changed significantly and tended to decrease at high intravesical pressure. Urination released intravesical pressure and restored all the peaks to the resting level. It is hypothesized that Mayer and respiratory bioimpedance oscillations of urinary bladder are neural in origin, while the cardiac peak is mainly determined by hydrodynamic arterial pulsations. The novel method can assess vesical circulation and its neural control at various phases of bladder activity.

Vibration analysis and measurement for piezoceramic rectangular plates in resonance

In this paper the transverse vibration characteristics of piezoceramic rectangular plates, with completely free and completely clamped boundary conditions, are investigated by theoretical analysis, experimental measurement, and numerical calculation. Using Ritz's method together with the equivalent material constants carries out the theoretical evaluations for resonant frequencies. Two optical techniques, amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) and laser Doppler vibrometer (LDV), based on the displacement measurement are employed to determine the transverse vibration modes. In addition, the impedance analyzer is also used to measure the electrical impedance variation. From the experimental results, it is found that the transverse vibration modes cannot be obtained by impedance analysis for the completely free piezoceramic plate; however, certain modes can be unexpectedly measured for the completely clamped piezoceramic plate owing to the imperfect boundary simulation in experiments. Numerical calculations using the finite element method (FEM) are performed and good agreement is obtained when comparing the theoretical analysis and experimental measurements. According to the theoretical analysis, frequency parameter versus equivalent Poisson's ratios ranging from 0.25 to 0.6 with different aspect ratios and material types are also presented for the first three transverse modes.

Assessment of Changes in Distribution of Lung Perfusion by Electrical Impedance Tomography

Background: Electrical impedance tomography (EIT) is able to detect variations in regional lung electrical impedance associated with changes in both air and blood content and potentially capable of assessing regional ventilation-perfusion relationships. However, regional lung perfusion is difficult to determine because the impedance changes synchronous with the heart rate are of very small amplitude. Objectives: The aim of our study was to determine the redistribution of lung perfusion elicited by one-lung ventilation using EIT with a novel region-of-interest analysis. Methods: Ten patients (65 ± 9 years, mean age ± SD) scheduled for elective chest surgery were studied after intubation with a double-lumen endotracheal tube during bilateral and unilateral ventilation of the right and left lungs. EIT data were acquired at a rate of 25 scans/s. Relative impedance changes synchronous with the heart rate were evaluated in the right and left lung regions. Results: During bilateral ventilation, the mean right-to-left lung ratio of the sum of heart rate-related impedance changes was 1.12 ± 0.20, but the ratio significantly changed (0.81 ± 0.16 and 1.48 ± 0.37) during unilateral left- and right-lung ventilation with reduced perfusion of the non-ventilated lung. Increased perfusion most likely occurred in the ventilated lung because the impedance values summed over both regions did not change (0.62 ± 0.23 vs. 0.58 ± 0.22) compared with bilateral ventilation. Conclusions: Our results indicate that redistribution of regional lung perfusion can be assessed by EIT during one-lung ventilation. The performance of EIT in detecting changes in lung perfusion in even smaller lung regions remains to be established.

High- and low-frequency noise in Cs and in liquid metal ion sources

Fundamental Physics space missions set rigid thrust noise limits for liquid metal ion thrusters used as actuators on drag-free platforms aboard the spacecraft. We have measured current-, voltage- and thrust noise of Cs and In LMIS, foreseen as prime candidates in these missions. In the high-frequency range, quasiperiodic oscillations around ∼10 5 Hz can be observed for both types of emitters with frequency depending on emission current. In the low-frequency range (1–10 −3 Hz), which is particularly important for drag-free control, different types of noise events are observed, which in some instances show definite signs of deterministic chaos (period doubling, self-similarity). High-frequency current oscillations are generally ascribed to electro-hydrodynamic oscillations of the TAYLOR cone and the jet at its apex, with concomitant emission of charged nanodroplets. Comparison of theory and experiment shows unsatisfactory agreement in predicted vs. measured current oscillation frequencies and large disagreement in droplet emission frequencies. No theory is presently available for describing low-frequency noise events. In terms of a linearized Mair theory it is, however, shown that these noise events can be efficiently described by spontaneous variations in electrical emitter impedance. In spite of this impedance noise, the mission requirements for thrust noise (<0.1 μN/Hz 1/2) can be met by a thrust-stabilized In emitter.

A novel technique for studying diffusion of contaminants in fine-grained soils

Diffusion is one of the predominant contaminant transport mechanisms in fine-grained soils. Usually, conventional methods such as half-cell and column tests are adopted for establishing diffusion characteristics of such soils. However, these techniques are destructive in nature, quite time-consuming, and require cumbersome chemical analysis of the soil and its pore-solution. Hence, development of a technique that would overcome these limitations and would yield precise results, in extremely short duration, becomes essential. With this in view, a modified Perspex diffusion cell with provision for inserting a series of stainless steel electrodes has been fabricated to monitor the diffusive contaminant transport, indirectly, based on the variation of electrical impedance of the soil. An LCR meter is employed to measure the electrical impedance of the soil across each electrode over a period. Further, the electrical impedance variation is indirectly correlated to the diffusion of contaminants that occurs in the soil. Details of the study and the test setup developed for this purpose are presented in this paper. It has been demonstrated that the technique based on electrical impedance measurement is quite useful and efficient for establishing diffusion characteristics of the fine-grained soil.

A Circuit Design for Impedance-based Structural Health Monitoring

Systems and structures monitoring their own structural integrity have become an active field. One method uses the piezoelectric impedance-based structural health monitoring technique (SHM), which utilizes a piezoelectric patch attached to a structure and measures its impedance within a certain frequency range. The frequency is maintained in the kiloHertz range for optimum sensitivity and coverage in damage detection. Owing to the coupling between electrical impedance and mechanical impedance, electrical impedance variations can indicate physical changes in the host structure. Based on the idea of a bridge circuit, a new electronic circuit to realize electrical impedance monitoring is presented (US patent pending). The proposed circuit generates a frequency sweep from 53 to 164kHz and measures the relative value of the electrical impedance modulus of a piezoelectric patch. The circuit can be integrated into a chip combined with a piezoelectric patch attached to a structure. With the help of a communication circuit, a remote SHM system can be set up in the future.

Heart Rate Detection From Plantar Bioimpedance Measurements

In this paper, a novel technique for heart rate measurement on a standing subject is proposed that relies on electrical impedance variations detected by a plantar interface with booth feet, such as those in some bathroom weighting scales for body composition analysis. Heart-related impedance variations in the legs come from arterial blood circulation and are below 500 mOmega. To detect them, we have implemented a system with a gain in excess of 600, and whose fully differential AC input amplifier has a gain of 4.5 and a common-mode rejection ratio (CMRR) higher than 90 dB at 10 kHz. Differential coherent demodulation based on synchronous sampling yields a signal-to-noise ratio (SNR) of about 54 dB . The system sensitivity is 610 mV/Omega. The technique has been demonstrated on 18 volunteers, whose bioimpedance signal and ECG were simultaneously recorded. A Bland-Altman plot shows a mean bias of -0.2 ms between the RR time intervals obtained from these two signals, which is negligible. The technique is simple and user friendly and does not require any additional sensors or electrodes attached to the body, hence no conductive gel or skin preparation.

An electro-acoustics impedance error criterion and its application to active noise control

Characteristics of radiation impedance and its inducing variation of electrical impedance for a controllable source have been investigated. An impedance-based error criterion has been proposed and its application to active noise control is demonstrated through a coil driven loudspeaker. A general formula of radiation impedance is derived for two control strategies, according to the criterion of total acoustic power output. The radiation impedances of some commonly used sound sources are calculated. We discuss in detail the relation between variation of the input electrical impedance and radiation impedance for the two control strategies. An AC-bridge circuit is designed to measure the weak variation of electrical impedance resulted from radiation impedance. The input electrical impedance of a loudspeaker was measured and the experimental result is consistent with that of theoretical analysis. An impedance-based error criterion is proposed since the AC-bridge relative output is unique for a certain control strategy. The implementation of this criterion applied to an active control system is analyzed by simulations. An analogue control system is set up and experiments are carried out in a semi-anechoic chamber to verify the new control approach.

Realization of a hard disk drive head servo-positioning system with a voltage-driven voice-coil motor

In this paper we describe a head servo-positioning system for hard disk drives (HDDs), in which the usual current command for the voice coil motor has been replaced by a simpler voltage command. Current command of the voice coil motor (VCM) has been preferred so far, due to its good performance in terms of robustness. With this solution, in fact, the characteristics of the system to be controlled by the servo-controller are rather independent from all possible variations of electrical impedance of the VCM and power supply voltage. However, this solution has some drawbacks. In fact, in order to realize the current command, a current loop uses a shunt resistor as a current sensor and a linear high power operational amplifier with some phase-shaping network as a current driver. Both shunt resistor and linear amplifier are major sources of power dissipation. Moreover, linear amplifiers need a large area on the silicon chip, increasing the cost of the power device. On the other hand, a fully digital current loop would require a costly A/D converter, and this is one of the reasons why the current controller is still implemented in analog way, thus impeding the implementation of smart control strategies at this level. All the above considerations have led to the realization of a servo system with a voltage-driven VCM. We developed a solution in which current measurement is no longer needed in order to guarantee the correct behavior of the servo controller. The solution is based on a digital, multi-rate pre-filter, driving a voltage amplifier. The filter is designed in such a way that the transfer function between input signal and VCM current is close to that of a standard current loop, so providing a one-to-one replacement to standard current drivers. With the proposed solution, no measurement on the VCM current or voltage is required. It can be shown that with a proper tuning of the pre-filter, the proposed solution exhibits a good robustness against variations of VCM parameters. Since the proposed solution is fully digital, digitally driven switching power stages can be used. Experimental results, including those related to robustness issues, show that the HDD servo-positioning performance obtained with the new voltage-driven system matches that obtained with a standard current loop, in both seek and track following operations. Finally, in order to adapt the pre-filter to operating conditions, an on-line parameter estimation procedure, capable of determining VCM windings resistance, is presented.

Strong correlation between high-temperature electronic and low-temperature magnetic ordering inLa1−xCaxMnO3continuous phase diagram

Optical and microwave impedance and magnetic mapping of continuous phase diagram of thin film ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ was achieved on a single chip. The optical and microwave impedance images obtained by charge-coupled device camera and scanned evanescent microwave probe showed abrupt variations in visible wavelength reflectance and microwave impedance as functions of composition at room temperature. The low-temperature magnetic order probed by scanning superconducting quantum interference device microscope is directly correlated with the room-temperature electrical impedance variation. Most of these variations may arise from remnant electronic orbital ordering persisting to room temperature in these compounds. We also observed a narrow singular stripe in composition with dramatically increased conductivity.

Two-dimensional finite element model for a long rectangular eddy current surface coil

An eddy current model for predicting the electrical impedance variation of a long rectangular surface coil due to a surface breaking defect in layered conductors is reported. The method is based on transforming a three-dimensional eddy current problem into the spatial frequency domain and solving the transformed diffusion problem for a limited number of the spatial spectrum components. The transformed problem has been assumed to be quasitwo dimensional (2D) for a long rectangular surface coil and formulated in terms of a two-component transformed vector magnetic potential Ā and scalar electric potential φ̄. The 2D problems have been solved with the finite element method using triangle elements. The system of algebraic equations was obtained using the Galerkin weak formulation and solved with the Gaussian elimination method. A high accuracy solution with ten spatial frequency components takes around 4 min on a Pentium 200 MHz PC. The accuracy of the solution has been tested experimentally at 200 kHz on coated stainless steel samples using a rectangular surface coil with the length-to-width ratio around 6. Agreement between theory and experiment is excellent. Discrepancies between the theory and experiment are within 15% and typically less. The method is useful for eddy current nondestructive evaluation and modeling, and can be also applied for the case of buried defects and for general multilayer coatings’ problem.