Electrical impedance

About: Electrical impedance is a research topic. Over the lifetime, 36015 publications have been published within this topic receiving 371891 citations. The topic is also known as: electrical impedance & complex impedance.

Simultaneous reconstruction of electrode contact impedances and internal electrical properties: I. Theory

Abstract: In electrical impedance tomography (EIT) currents are applied through the electrodes attached on the surface of the object and the resulting voltages are measured using the same or additional electrodes. The internal admittivity distribution is estimated based on the current and voltage data. When the voltages are measured on the current carrying electrodes the contact impedance that exists in the electrode–surface interface causes a voltage drop. In some cases this effect of the electrodes is known. However, this is not always the case and the contact impedance has to be taken into account in the image reconstruction. In this paper we propose an approach for estimating the contact impedance of the electrodes simultaneously with the estimation of the admittivity of the object. The complete electrode model (CEM) is used in the estimation procedure. We compare the proposed approach to a simple method which is based on the well known definition of the sample resistivity. The proposed approach is tested with real measurements by estimating the admittivity of isotonic saline solution in a cylindrical test cell and with simulations in a three-dimensional cylindrical domain. The CEM-based approach is shown to produce results that are similar to the results obtained with the simple approach in the test cell case. The advantage of the CEM-based approach over the simple approach is that the complete electrode model does not have any geometrical constraints, which makes it possible to utilize it in EIT studies. The results show that the CEM-based approach works well and can be used in practical contact impedance estimation with real measurements. This will be further studied in part II of this paper.

Noise Resistance Applied to Corrosion Measurements II. Experimental Tests

Abstract: Electrochemical noise (EN) measurements have been carried out on several corroding systems, utilizing the technique of simultaneous recording of current and voltage fluctuations, and calculating the frequency dependent spectral noise impedance R{sub sn}(f) as the square root of the ratio of the power spectral densities (PSD) of the voltage to current noise. The results are compared with the theoretical predictions stemming from an analysis of the technique, which is presented in the preceding paper. It is shown that, over a quite large range of conditions, R{sub sn}, coincides with the impedance modulus of the electrodes under study. From the relationship between R{sub sn} and the noise resistance R{sub n}, which is usually obtained calculating the ratio of the standard deviations of the voltage and current fluctuations, it is shown that the latter quantity can be equal to the zero frequency limit of the impedance only if certain conditions are satisfied.

Broadband parametric amplification with impedance engineering: Beyond the gain-bandwidth product

Abstract: We present an impedance engineered Josephson parametric amplifier capable of providing bandwidth beyond the traditional gain-bandwidth product. We achieve this by introducing a positive linear slope in the imaginary component of the input impedance seen by the Josephson oscillator using a λ/2 transformer. Our theoretical model predicts an extremely flat gain profile with a bandwidth enhancement proportional to the square root of amplitude gain. We experimentally demonstrate a nearly flat 20 dB gain over a 640 MHz band, along with a mean 1-dB compression point of −110 dBm and near quantum-limited noise. The results are in a good agreement with our theoretical model.