Papers by Keyword: Impedance Measurement

Abstract: Transesterification is commonly used to produce biodiesel from methylester. In order to control the conversion process is useful to employ process monitoring, in particular monitoring of the mass transfer processes that limits the initial rates of transesterification. Monitoring of these initial stages of the reaction may allow for process optimization. Many methods have been identified to monitor reaction progress. This paper proposes a method to monitor the initial stages of the biodiesel production process using impedance measurement. The impedance measurements presented show the expected sigmoid curves that are associated with mass transfer (mixing) processes taking place during the early stages of the transesterification process.

Abstract: The impedance of the inertance tubes which include the mass flows, pressure amplitudes and phase shifts between them at the inlet of the inertance tubes were measured by correcting the mass flows at the surface of the compressor piston. The experimental results are compared with the theoretical values based on simplified turbulent-flow thermoacoustic model. The wide range of impedance measurements with different inertance tube geometries and operating parameters enable us to summarize the general rules of their effects on impedance respectively, also the differences between the experiments and calculations can be used to modify the theoretical model.

Abstract: The paper deals with a measurement method of the input impedance in the radiating section of a coplanar waveguide (CPW) Composite Right / Left-Handed (CRLH) antenna. In this respect were used the technical facilities offered by an on-wafer measurement equipment contacting the antenna feeding line. With appropriate formulas derived from the theory of the transmission lines, the resistive Rs and the reactive Xs parts of the CRLH radiating structure impedance Zs = Rs + jXs were found. The results for three antenna samples were: Zs1 (Ω) = 48.5326 - j×16.9639, Zs2 (Ω) = 48.6053 - j×16.8143 and Zs3 (Ω) = 48.1786 - j×16.3707. As it is normal, the reactive parts of the measured impedances are negative due to the CRLH line construction with series interdigital capacitors inducing left hand behavior.

Abstract: Electromechanical impedance technique which based on smart material is a new method for structural damage detection, and it could be widely applied in structural health monitoring field. However, a very expensive and bulky analyzer is being used to measure the impedance, which is not practical for on-line system. Therefore, this paper developed a device that can measure the electric impedance using small modular electric components and reasonable circuit. Experiments are carried out to test the aluminum beam crack. Results indicate that the device can measure the electric impedance and detect the damage effectively. The proposed method provides a solution to miniaturize the impedance-measuring equipment and reduce the cost of measurement.

Abstract: Deposition experiments in a Hull cell showed that high conductivity suspensions yield uniform deposits while low conductivity suspensions result in non-uniform deposits. This difference in deposition behavior is related to the resistance increase of the deposit during EPD. Impedance measurements during EPD showed that the ratio of the deposit resistance to the suspension resistance increases much more for high than for the low conductivity suspensions. They also showed that the total resistance of the EPD cell dropped almost to the suspension resistance after the electric field was turned off. This means that the deposit has no inherent resistance, but that its resistance during polarization is caused by the interaction of ions with the deposit and by the depletion of ions at the deposition electrode. The change in ion concentrations near the deposition electrode changes the acid/base properties of the particles in the deposit, as proven by adsorbed pH indicators on the particles. The change in acid/base behavior is quasi irreversible and results in a memory effect of the deposit resistance when the voltage is reapplied.

Abstract: Iron-Zinc oxide films were deposited by the well known ultrasonic spray pyrolysis method from an aqueous solution of iron nitrate and zinc acetate ([Zn]/[Fe] = 0.30). A Franklinite structure of these films turned out from XRD measurements. Additional basic characterization with UV-Vis and infrared spectroscopies and AFM was also performed. Electrical measurements under a small alternating current signal (15 mV RMS) were performed under dry air, humid air (53 % R:H.) and humid air plus propane. Frequency scans yielded sensitivities as high as 260% to humidity and  475% to propane at 30 °C. At 250 °C lower sensitivities were obtained, but in all cases the highest values came from the reactive response of the film. From dynamical response measurements, the response time was also assessed. The mechanisms of sensing are discussed as well.

Abstract: Although characterization of piezoceramics from resonance is a customary technique, the works dealing with the determination of the ten elastic, dielectric and piezoelectric coefficients that are needed in the full matrix characterization of such 6mm symmetry materials are rather scarce. Even more, if the complex characterization is foreseen, thus accounting with the three types of losses, few are the methods avaliable to obtain the material linear coefficients. This work deals with such complex characterization by the use of Alemany et al. automatic iterative method. This method has been applied to the four modes of resonance that are sufficient for the purpose: (1) the length extensional mode of long rods, length poled, (2) the thickness extensional mode and (3) the radial mode of a thin disk, thickness poled, and (4) the thickness shear mode of a thin plate. Recent work of the authors has shown the limits in characterizing materials that arise from the use of the Standard shear geometry and, therefore, and alternative geometry is used here. This work presents the matrix characterization of some piezoceramics and the Finite Element Analysis (FEA) simulation based on such characterization, of the samples used as a reliability criteria of the results obtained by comparison of the experimental and simulated values at resonance of the electrical parameters.