Electrode Displacements Research Articles

The influence of electrode location errors on EEG dipole source localization with a realistic head model

Objectives: Inaccurate information about the electrode locations on the scalp will introduce errors in electroencephalogram dipole source localization results. The present study uses computer simulations to evaluate such errors in a realistic head model and in the context of noise. Methods: A realistic head model was constructed from magnetic resonance imaging scans and 29 electrodes placed on the head according to the 10–20 International System. Twenty sets of electrode displacements, with a mean value of 5 mm, were generated and 200 single dipoles evenly located in the brain were used as test sources. The boundary element method was employed for the froward calculation and dipole fitting was carried out at different noise levels. Results: For a noise-free signal, the source localization error due to electrode misplacement is about 5 mm, whereas it is about 2 mm for normal noisy signals. Conclusions: For realistic head models, dipole estimation error due to electrode misplacement is negligible compared with errors caused by noise.

Experimental Investigation of Resistance Spot Welding for Sheet Metals Used in Automotive Industry.

Resistance spot welding (RSW) is used for the fabrication of sheet metal assemblies. The major advantages of spot welding are high speed and adaptability for automation in high-volume and/or high-rate production. Despite these advantages, resistance spot welding suffers from a major problem of inconsistent quality from weld to weld. This problem results from both the complexity of the basic process as well as from numerous sources of variability, noise, and errors. Any or all of these complicate automation, reduce weld quality, demand over welding and drive up production costs. For this reason, ensuring weld quality has been and remains a major challenge and goal. The objective of this research is to explore the phenomenon of how changes in a controllable parameter of % heat input affect a measurable output signal indicative of strength and weld quality for various sheet steels used in the automotive industry. The approach of this research is to create a relationship between a key process input variable and the key process output of a quality weld. The input parameter chosen is % heat input, as this directly effects the size and strength of the resulting weld. The output chosen is electrode displacement, as this has been shown to accurately reflect the formation and growth of a weld nugget. A series of experiments was conducted to explore how changes of % heat input and process variations affect the electrode displacement curve for various sheet steels used in the automotive industry. Experimental results show that the electrode displacement increased when higher % heat input was applied. Weld nugget starts to grow when electrode velocity cube changes from positive to negative. Characteristic electrode displacement curves were developed for process variations. A poor part fit-up condition shifted the electrode displacement curve to the right as a result of a smaller weld nugget being formed. Worn electrode lowers the electrode displacement curve. For bare steel, electrode displacement is higher than electrogalvanized and hot-dip galvanized steel. The higher strength steels have higher electrode displacements than for plain carbon steel.

Strain-imaging observation of the polarization freezing of the domains under the electrode of a Pb(Zr, Ti)O3 film

Strain imaging is used to measure and image piezoelectric properties by detecting electric-field-induced strains using a scanning probe microscope. In this letter, we present ferroelectric domain imaging under an electrode in a lead-zirconate-titanate (PZT) film. The imaging has been achieved by detecting the surface force modulation caused by the electrode displacements. Observation through the electrode suppresses the effect of space charges and enables us to investigate the PZT film in the same situation in devices. We observed the freezing of polarization of a PZT film deoxidized by atomic hydrogen produced by catalysis of platinum upper electrodes due to hydrogen annealing.

Stability of automated ECG classification for chest electrode displacements

Stability of automated ECG classification for chest electrode displacements

Use of the standard 12-lead ECG to simulate electrode displacements

Placement of the precordial electrodes for recording a 12-lead electrocardiogram (ECG) is subject to variation. Previous research has shown that displacements, especially in the longitudinal direction, can lead to changes in diagnosis. In practice, both the displacement and the effects of displacement on an individual ECG are unknown. To assess this effect for a given ECG, the authors developed a method to simulate ECGs at different displacements using only the recorded ECG. The material consisted of 746 body surface potential maps (BSPMs) containing 232 cases without abnormalities, 277 with myocardial infarction (MI), and 237 with left ventricular hypertrophy. By interpolating BSPMs, ECGs from closely spaced electrode positions could be derived. Taking electrode positioning errors that may be encountered in practice, 40 ECGs at different electrode displacements (displaced ECGs) for each BSPM were derived. Using half of the BSPMs, for each displacement, a transformation matrix that transforms the ECG at the standard 12-lead electrode positions (standard ECG) to the displaced ECG was determined. Using the other half of the BSPMs, each displaced ECG was compared with the ECG yielded by the corresponding transformation matrix (transformed ECG). For each comparison, the differences were assessed between the two sets of ECG signals and between the diagnostic computer classifications of the two sets. Signal differences were expressed as mean absolute amplitude differences over the QRS. Computer interpretation of MI and left ventricular hypertrophy was graded in five levels of certainty (no, consider, possible, probable, definite). For instance, for the largest longitudinal displacement studied of about one intercostal space, the 96th percentile mean absolute amplitude difference over the test set was 204 μV. The percentage of cases showing a change in MI classification of more than two certainty levels was 2.7% for this displacement. When comparing the standard ECG with the displaced ECG, these figures were 434 μV and 8.3%, respectively. It is concluded that ECGs from displaced electrodes can be well simulated by transforming the standard ECG, both for the ECG signal and diagnostic classifications.

Improved beat-to-beat timing measurements of His-bundle signal.

A simplified bioelectric model of the atrioventricular (AV) junction is proposed to better understand the underlying biophysical generation of intracardiac His-bundle signal and to analyze the effects of electrocatheter displacements on waveform morphology and estimation of AV node conduction time (AVCT). Based on this model, an inverse problem approach has been developed to estimate electrode displacements occurring in real recordings. A measurement correction method is proposed to improve estimation of AVCT. Results illustrate autonomic influences on AVCT, a phenomenon hardly measured with common techniques.

Volt balance realization of the volt at ETF in Zagreb

A volt balance having plate electrodes operating in a temperature-controlled atmosphere of dry nitrogen is described. The voltage is measured by a special procedure of substitution of a weight for the electrostatic force, with automatic control of the balance equilibrium. This, together with the application of very sensitive capacitive transducers for measuring the balance equilibrium and electrode displacements enables a weighing reproducibility of less than 0.1 ppm to be achieved. The earthed electrodes are suspended over the beam arms by means of two thin strips separated one from the other in such a way that optimal sensitivity to the existence of horizontal electrostatic forces is achieved. Through the remote adjustment of the horizontal position of the high-voltage (H-V) electrodes, and by measuring the displacement of the suspended and H-V electrodes, it is possible to eliminate horizontal electrostatic forces. The displacement of the H-V electrodes by 51 mm (corresponding to a capacitance change of 100 pF) enables highly precise capacitance and length measurements to be made. The third improved version of the Zagreb Faculty of Electrical Engineering (ETF) volt balances is now being completed. The mean result of six measurements obtained with two earlier balances indicates that the difference between the International System (SI) volt determined by the ETF volt balances and volt BI-76 is +7.1 ppm with a random one-standard-deviation (1σ) uncertainty of 0.4 ppm and a systematic 1σ uncertainty of 1.6 ppm.

Motor unit firing rate during static contraction indicated by the surface EMG power spectrum.

In this study, power spectral density functions (PSDF's) were computed of interference EMG of various facial and jaw-elevator muscles during nonfatiguing submaximal static contractions, recorded with surface electrodes. A distinct peak was found in the PSDF's in the frequency region below 40 Hz. It was shown that the peak was due to genuine EMG activity and that it could not be considered as an artifact, which was caused by electrode displacements during contraction. An increase of contraction strength resulted in a shift of the peak to higher frequencies and a decrease of peak amplitude relative to the power spectral estimates above 40 Hz, which were shown to be determined by the shape of the motor unit (MU) action potentials. In accordance with mathematical models of the EMG PSDF, it was demonstrated that the peak indicates the dominant firing rate of the sampled MU's. Our results suggest that this can be defined as the firing rate of the first recruited low-threshold MU's, which may be expected to dominate the interference EMG signal because of their preponderance in number. The data further suggest that the peak can be more readily observed in PSDF's of facial and jaw-elevator muscles than in PSDF's of limb muscles. This might be related to differences in MU firing statistics.

Hypertension induced by electrical stimulation of the subfornical organ (SFO)

In urethane anaesthetized rats, electrical, low intensity stimulations using bipolar concentric electrodes or monopolar glass pipettes were applied to SFO and to surrounding structure's populations. Blood pressure, recorded from the femoral artery, was systematically and rapidly increased when the electrical, as well as the mechanical (electrode displacements) stimulations were located within the SFO populations. Remote from the SFO, stimulations either were ineffective or produced non reliable responses. SFO cells seen to be involved in the defense against all hydroionic deficiencies, including those of blood pressure.

Chronic Dorsal Column Stimulation via Percutaneously Inserted Epidural Electrodes

31 patients suffering from intractable pain associated with chronic low back syndrome, terminal cancer, and other disorders have been studied after an average 6 months’ treatment by electrical stimulation of the spinal cord applied via electrodes inserted through a Tuohy needle into the epidural space. As judged by three different subjective rating methods, epidural stimulation successfully relieved otherwise intractable chronic pain in from 23 to 26 of the 31 patients. Reported improvements in the ability to perform various everyday activities, and elimination of drug usage by many patients, corroborate this finding. The side effects of stimulation, both as reported subjectively and as measured objectively by sensory testing, were not clinically significant. Spontaneous electrode displacements, leading to loss of analgesia and requiring minor surgery for repositioning, were encountered frequently, as were lead wire failures necessitating replacement. The partially implanted, externally powered stimulation system presently in use also suffers from problems of reliability and convenience to the patient.

Pacemaker wires and electrodes. A follow-up study.

In 362 patients on permanent pacing, a follow up with regard to pacemaker electrode function time and connection to pulse-generators has been carried out. In 12 patients Elema epicardial electrode were used with an average function time of 3.8 years. 232 Elema EMT 588 endocardial electrodes were used in 216 patients. Average observation time for the electrodes was 3.3 years. Sixty-eight electrodes have been followed for more than 5 years. Early electrode complications comprise 10 per cent of displacements before implantation of the pulse-generator and another 6 per cent of electrode displacements within the first 3 months after implantation. Eleven per cent of the electrodes had to be corrected due to high threshold value before implantation and another 6 per cent during the first 3 months after implanattion of pulse-generator. On hundred and fifty-five unipolar electrodes of the types Cordis, Medtronic, Elema EMT 282, and Stanium were implanted in 149 patients. Average observation time for the electrodes were 1.2 years. During the first 3 months after pacemaker implant 7 per cent of the electrodes were dislocated, 5 per cent failed due to high threshold value. Three perforations of the right ventricle occurred, without serious complications. Late complications i.e. after 3 months, for EMT 588 electrode included 4 per cent electrode dislocations, 4.5 per cent failure due to high threshold, 3 cases of wire break and 4 defects in the insulation. Many of the late electrode complications were probably caused by replacement operations for pulse-generators. The most frequent late complications for the conventional unipolar electrode was wire break which occurred in 5 cases.

Analysis of the operation of electret transducers subject to large electrode displacements

An analytical study of the operation of electret transducers subject to relative displacements of the electrodes comparable to the thickness of the air gap (or air gaps) between electret and electrodes is presented. In particular, the relations between generated voltage and time history of the transducer capacitance are derived for transducers terminated by a combination of resistive and capacitive components. Following this analysis, graphical and numerical results for the shape and peak amplitude of the voltage response due to displacements with trapezoidal time dependence are presented.