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.

Layer stripping: a direct numerical method for impedance imaging

Abstract: An impedance imaging problem is to find the electrical conductivity and permittivity distributions inside a body from measurements made on the boundary. The following experiment is considered: a set of electric currents are applied to the surface of the body and the resulting voltages are measured on that surface. The authors describe the performance of a direct numerical method for approximating the conductivity in the interior. The algorithm proceeds via two steps: first the conductivity is found near the bounding surface of the body from the data having the highest available spatial frequency; next the boundary data on an interior surface are synthesized using a nonlinear differential equation of Riccati type. The process is then repeated, and an estimate of the conductivity is found, layer by layer. They establish the theoretical basis for the algorithm and report on numerical tests.

Wide band dipole radiating element with a slot line feed having a Klopfenstein impedance taper

Abstract: A wideband radiating element including an input mechanism for receiving electromagnetic energy from a source and a balanced feeding mechanism extending from the input mechanism for transmitting the electromagnetic energy and for providing impedance matching over a range of frequencies. Finally, a dipole mechanism extending from the balanced feeding mechanism is provided for radiating the electromagnetic energy where the dipole mechanism has a shape to provide wide bandwidth impedance matching. In a preferred embodiment, an input mounting block is connected to the two opposing sides of a planar dielectric substrate. A balanced narrow conductor slot line extends from the input mounting block on both sides of the dielectric substrate to transmit the electromagnetic energy and to provide impedance matching over a frequency range of (0.5 to 18) GHz. The narrow conductor slot line is tapered to match the radiation resistance of a dipole element utilized to radiate the electromagnetic energy. The dipole element extends from the balanced narrow conductor slot line on both sides of the dielectric substrate with each wing having an expanded width for accommodating surface current of various distributions over the frequency range. The dipole element also includes an inner taper for radiating energy over the frequency range with the position of the dipole element relative to a ground plane being optimized to minimize radiation reflection.

Modeling of a Cantilever-Based Near-Field Scanning Microwave Microscope

Abstract: We present a detailed modeling and characterization of our scalable microwave nanoprobe, which is a micro-fabricated cantilever-based scanning microwave probe with separated excitation and sensing electrodes. Using finite-element analysis, the tip-sample interaction is modeled as small impedance changes between the tip electrode and the ground at our working frequencies near 1GHz. The equivalent lumped elements of the cantilever can be determined by transmission line simulation of the matching network, which routes the cantilever signals to 50 Ohm feed lines. In the microwave electronics, the background common-mode signal is cancelled before the amplifier stage so that high sensitivity (below 1 atto-Farad capacitance changes) is obtained. Experimental characterization of the microwave probes was performed on ion-implanted Si wafers and patterned semiconductor samples. Pure electrical or topographical signals can be realized using different reflection modes of the probe.

Electrode surface treatment and electrochemical impedance spectroscopy study on carbon/carbon supercapacitors

Abstract: Power improvement in supercapacitors is mainly related to lowering the internal impedance The real part of the impedance at a given frequency is called ESR (equivalent series resistance) Several contributions are included in the ESR: the electrolyte resistance (including the separator), the active material resistance (with both ionic and electronic parts) and the active material/current collector interface resistance The first two contributions have been intensively described and studied by many authors The first part of this paper is focused on the use of surface treatments as a way to decrease the active material/current collector impedance Al current collector foils have been treated following a two-step procedure: electrochemical etching and sol-gel coating by a highly-covering, conducting carbonaceous material It aims to increase the Al foil/active material surface contact leading to lower resistance In a second part, carbon-carbon supercapacitor impedance is discussed in term of complex capacitance and complex power from electrochemical impedance spectroscopy data This representation permits extraction of a relaxation time constant that provides important information on supercapacitor behaviour The influence of carbon nanotubes addition on electrochemical performance of carbon/carbon supercapacitors has also been studied by electrochemical impedance spectroscopy

Novel Modified UWB Planar Monopole Antenna With Variable Frequency Band-Notch Function

Abstract: A novel modified microstrip-fed ultrawideband (UWB) planar monopole antenna with variable frequency band-notch characteristic is presented. By inserting two slots in the both sides of microstrip feedline on the ground plane, much wider impedance bandwidth can be produced. A modified H-shaped conductor-backed plane with variable dimensions is used in order to generate the frequency band-stop performance and control its characteristics such as band-notch frequency and its bandwidth. The designed antenna has a small size of 22 x 22 mm2 and operates over the frequency band between 3.1 and 14 GHz for VSWR < 2 while showing the band rejection performance in the frequency band of 5.1 to 5.9 GHz.