Common Ground Electrode Research Articles

The association between electrode impedance and short-term outcomes in cochlear implant recipients of slim modiolar and slim straight electrode arrays

Objectives Electrode impedance measurements from cochlear implants (CI) reflect the status of the electrode array as well as the surrounding cochlear environment, and could provide a clinical index of functional changes with the CI. The goals of this study were to examine (1) the impact of electrode array type on electrode impedance, and (2) the relationship between electrode impedance and short-term hearing preservation and speech recognition outcomes. Methods Retrospective study of 115 adult hearing preservation CI recipients of a slim modiolar or slim straight array. Common ground electrode impedances, pre- and post-operative hearing thresholds and CNC word recognition scores were retrieved. Results Electrode impedances were significantly higher for recipients of the straight electrode array. Within individuals, electrode impedances were stable after the first week post-activation. However, increased standard deviation of electrode impedances was associated with greater loss of low frequency hearing at initial activation, and with poorer speech recognition at 6 months post-implantation. Conclusions Results demonstrate that electrode impedances depend on the type of implanted array. Findings also suggest that there may be a role for the variability in electrode impedance across electrodes as an indicator of changes in the intracochlear environment that contribute to outcomes with a CI.

Three-dimensional multilayer concentric bipolar electrodes restrict spatial activation in optic nerve stimulation

Objective. Intraneural nerve interfaces often operate in a monopolar configuration with a common and distant ground electrode. This configuration leads to a wide spreading of the electric field. Therefore, this approach is suboptimal for intraneural nerve interfaces when selective stimulation is required. Approach. We designed a multilayer electrode array embedding three-dimensional concentric bipolar (CB) electrodes. First, we validated the higher stimulation selectivity of this new electrode array compared to classical monopolar stimulation using simulations. Next, we compared them in-vivo by intraneural stimulation of the rabbit optic nerve and recording evoked potentials in the primary visual cortex. Main results. Simulations showed that three-dimensional CB electrodes provide a high localisation of the electric field in the tissue so that electrodes are electrically independent even for high electrode density. Experiments in-vivo highlighted that this configuration restricts spatial activation in the visual cortex due to the fewer fibres activated by the electric stimulus in the nerve. Significance. Highly focused electric stimulation is crucial to achieving high selectivity in fibre activation. The multilayer array embedding three-dimensional CB electrodes improves selectivity in optic nerve stimulation. This approach is suitable for other neural applications, including bioelectronic medicine.

Low-Noise Voltage Controlled Oscillator with Coupled Microstrip Lines of Different Lengths

Introduction. Coupled two- or three-wire microstrip lines are often used to reduce a phase noise of voltage-controlled oscillators (VCOs). Unfortunately, the phase noise was not optimized depending on the lengths of a three-wire coupled microstrip lines. Aim. For the three-wire coupled microstrip structure, the task of determining of the optimal lengths of its stabs was set. The stabs were corresponded to the reduced phase noise of the selected VCO. Materials and methods . In the oscillator example, the resonator model with three electromagnetically coupled microstrip lines was studied. Herein the second line from the first and the third from the second line differed by the same physical length. The widths of the first and of the third lines were the same, and their coupling clearances with the second line were the same too. On the one hand, in this three-wire microstrip line short-end modes with a common ground electrode were implemented. On the other, at the ends of the first and of the third lines open-end modes were implemented. The free end of the second line is line input. Results. For the considered oscillator, the basic formulas for calculating its frequency-setting elements and resonator model parameters were obtained. By these formulas the estimation of base contours impedances for two oscillators with three-coupled microstrip lines of the same and different lengths, and also for the oscillator using a two-coupled microstrip line was given. For comparison, the proposed VCO near the optimal difference in the three-wire line microstrips lengths had the base contour impedance phase steepness 2...4 times greater, as well as its modules graphs had the width 4...10 times less. Conclusion. In comparison with the known VCOs, the possibility of obtaining lower phase noise spectrum levels at 6...10 dB/Hz in the designed oscillator with the calculated lengths of the selected three-coupled line microstrips was experimentally confirmed.

Array of Freestanding Planar Lipid Bilayers for Parallel Optical and Electrical Recordings

Here we report on the design and validation of an array platform for parallel high-resolution electrophysiological and optical recordings. The recording chip is based on a SU-8 coated glass slide (ca. 200 μm thickness) containing 4 cavities with individual ring-shaped Ag/AgCl-microelectrodes as well as a common ground electrode. Four suspended lipid bilayers can be self-assembled on the chip surface over the cavities. The electrodes are connected to a multichannel amplifier capable of simultaneous electrical recording with high-bandwidth and low noise (<1pA [email protected]). The ring shape of the electrodes creates an optical window allowing access with a high-NA oil or water-immersion objective on an inverted microscope. This allows for e.g. single-molecule fluorescence measurements from one of the four bilayers using time-correlated-single-photon-counting (TCSPC). Fluorescently labeled alpha-hemolysin for optical and electrical measurements was expressed in-vitro and purified. BODIPY at position 131 was incorporated during the translation in a site-directed manner via stop or four-base codon suppression using pre-charged tRNAs. A series of characterization and validation experiments performed with the system include: (1)Studies of diffusion rates of fluorescently labelled Hemolysin and lipid molecules in the bilayer using fluorescence correlation spectroscopy (FCS); (2)Monitoring of alpha-hemolysin membrane insertion using fluorescence lifetime imaging (FLIM) and (3)Visualization of fusion of labeled proteoliposomes resulting in membrane channel insertion. In the two latter cases, changes in fluorescence intensity were monitored simultaneously with alterations in membrane conductance. This system allows for rapid membrane array formation and by providing ready combination of fluorescence microscopy with high-resolution electrophysiology, enables correlated optical and electrical characterization and monitoring of the interactions of channel forming proteins in artificial lipid bilayers on a single-molecule level. The technology can be further implemented for studies of membrane protein folding and mobility as well as of membrane transport.

A forming-free bipolar resistive switching behavior based on ITO/V2O5/ITO structure

Forming-free bipolar resistive switching behavior in an ITO/V2O5/ITO structure is observed. While the bottom ITO layer functions as a common ground electrode, the top ITO layer is an active element and used as an oxygen reservoir, with an additional metal electrode patterned on its top for making contact. In contrast to typical metal/transition metal oxide/metal based resistive memories, our device exhibits a low resistance state in its virgin state and is switched to a high resistance state when a forward bias of ∼+2.5 V is applied. The device can be reset to its original state at a reverse bias of ∼–1.5 V. A noticeable decrease in switching voltage with a reduced top contact area is observed, indicating a strong electric field enhanced switching mechanism. Different from the widely seen conductive filament mechanism in bipolar switching, we explain the switching behavior by the migration of oxygen ions at the top ITO/V2O5 interface. When oxygen ions are extracted to the ITO side, an interfacial layer with reduced oxidation states is formed and acts as a Schottky barrier that suppresses the current through the whole device. The results suggest future applications in low power, high speed integrated non-volatile memories.

Vanadium Oxide Based RRAM Device

ABSTRACTForming-free bipolar resistive switching characteristics in a Vanadium oxide based sandwich structure is observed for the first time. The bottom conducting layer is the common ground electrode for all devices. The top conducting layer acts as an active element with an additional Cr/Al/Cr electrode patterned on its top for making contact. Different from the typical metal/transition metal oxide/metal sandwich structure based resistive memories, our device exhibits a low resistance state (LRS) in its virgin state, and can be switched to a high resistance state (HRS) when a positive bias of +2.5V is applied to the top electrode. Following this, the device can be reset to a LRS when a negative bias of approximately 2.5V is applied. A significant decrease of switching voltages is observed when the diameter of the top contact decreases, indicating an electric field enhanced switching mechanism. Simulation using TCAD confirms that electric field beneath the top metal contact increases due to fringing. The results suggest future applications in low power integrated non-volatile memories.

Mutual interference of neighboring grounding systems and approximate formulation

The paper develops mathematical models for the analysis of the mutual interference of closely positioned ground electrodes in order to assess the safety risks that might appear in various circumstances often characteristic for urban areas. The potentially hazardous situation that might arise in open pit mines at the equipment grounded by connection with the common ground electrode is also investigated. In the scope of the analysis of possible dangerous circumstances the maximum touch – and step – voltages that appear at the sites protected by the grounding grids are calculated for various distances between the grids and in case of uniform and nonuniform two – layer soil. Approximate expressions for assessing some interference effects are also provided and successfully checked for various cases. Based upon the results of the conducted series of calculations, the safety risks are determined for all investigated cases. It was shown that the highest safety risks can appear in the case when the neighboring grids are unintentionally connected as well as in the case when the neighboring grid is connected with some grounded objects, which is characteristic for urban areas and for open pit mines with common ground electrodes.

Rapid Activity Screening of Ion Channels Expressed in Cell-Free Systems Using a Lipid Bilayer Array Pcb-Device

Cell-free expression is a rapidly developing tool for the efficient production of membrane proteins with enormous potential. Here we report on the design of a setup for parallel high-resolution electrophysiological recordings allowing for the screening of functional activity of ion channels synthesized in-vitro in various lipid environments.The developed recording chamber is based on a SU-8 coated printed circuit board containing 4 cavities (50µm) with individual microelectrodes (Micro-Electrode-Cavity-Array (MECA) as well as a common ground electrode. 4 suspended lipid bilayers can be self-assembled on the nonpolar chip surface from phospholipids in organic solvent. The MECA-PCB is connected to a multichannel amplifier capable of simultaneous recording of electrical activity from the ion channels functionally reconstituted into the bilayers with high-bandwidth and low noise (<1 pA rms ≅ 10 kHz).To test the capability of the MECA-PCB-chip, the tetrameric potassium channel KcsA was expressed in-vitro with co-translational insertion into supplied liposomes containing di-myristoyl-glycerophosphocholine or asolectin. The collected proteoliposomes were extruded through 100 nm polycarbonate filter and fused with preformed bilayers. Activity from the single channels inserted in different bilayers was recorded in parallel under identical conditions. We show thatKcsA expressed in-vitro displays the typical single-channel kinetic behavior and sensitivity to blockers (Ba2+) described for the protein isolated from cellular membrane preparations. Channel open times and open probability are shown to be dependent on lipid environment with negatively-charged phospholipids stabilizing the open channel conformation.The combination of the cell-free protein expression system and MECA-PCB-chip electrophysiology allows for functional characterization of the synthesized ion channel within several hours starting from the DNA template. The current PCB-chip design could be easily adapted for higher throughput and automated bilayer formation as recently reported1.1Del Rio Martinez et.al. Small 2014.

A piezoelectric active mirror suspension system embedded into low-temperature cofired ceramic

Low-temperature cofired ceramic (LTCC) has proven to be a cost-effective, flexible technology for producing complicated structures such as sensors, actuators, and microsystems. This paper presents a piezoelectric active mirror suspension system embedded into LTCC. In the structure, the LTCC was used as a package, for the passive layers of piezoelectric monomorphs, as support for the mirrors, and as a substrate for the conductors. The active mirror structure, 17 mm in diameter, was made by compiling 20 LTCC layers using common LTCC processing techniques. Each sample contained a laser-micromachined bulk lead zirconate titanate (PZT) structure which formed a monomorph with the LTCC during the firing process. A mirror substrate (diameter 4 mm) was mounted in the middle of the monomorph arms for evaluation of the positioning performance, where each of the three arms had independent signal electrodes and a common ground electrode. Electrical and electromechanical properties were investigated with an LCR meter, network analyzer, and laser vibrometer for the different arms and the mirror. The active mirror structure exhibited more than 1 μm dc displacement for mirror leveling and also allowed small changes in mirror angle up to 0.06°. The first bending resonance frequency of the structure with the mirror was detected at 11.31 kHz with 4.0 μm displacement; 13.02 kHz and 2.7 μm were obtained without the mirror. The structure exhibited characteristics feasible for further utilization in tunable Fabry-Perot filter applications, allowing the mounting of active mirrors on both sides with distance and angle control.

Delta-Shaped Piezoelectric Ultrasonic Motor for Two-Dimensional Positioning

By fabricating on from lambda-shaped motors, bimorph delta-shaped motors have been developed and tested. A delta motor consists of two piezoelectric layers (bimorph structure) with four input electrodes and one common ground electrode – separated by an inactive bar that aids dimensional control in the sintering process. Two driving sources with a 90° phase difference were used for the x-, z-, and diagonal-axis direction driving. The design of the motor was modified and optimized by changing the relative dimensions and angle of the motor with the aid of ATILA finite element method (FEM) software. The optimum design with a small bandwidth between resonance modes, which provides the largest elliptical displacement, was fabricated using thick films. The fabricated motor size was below 10 mm2 with several hundreds of nano meter motion at the tip. The speed of revolution, torque and efficiency in the two-dimensional space were measured.

Sensitivity and Specificity of Averaged Electrode Voltage Measures in Cochlear Implant Recipients

The primary purpose of this study was to evaluate the diagnostic accuracy of averaged electrode voltages (AEVs) for identifying malfunctioning electrodes in cochlear implant users. AEVs were measured using common ground (N = 33 ears) and monopolar stimulation modes (N = 40 ears) in adult subjects implanted with the Nucleus 24M or Nucleus 24R(CS) cochlear implant. AEV measures were then compared with common ground electrode impedance measures as well as to subjective judgments of electrode sound quality to determine the sensitivity and specificity of AEVs. Results showed excellent specificity for both modes of AEV testing: 97.9% for common ground and 99.8% for monopolar. Sensitivity for common ground AEV testing was 91.7%; however the sensitivity of monopolar AEVs was very poor, at 7.7%. Monopolar AEVs accurately identified open circuits but missed all short circuits. These results are consistent with the sensitivity of impedance measures made with each of the two stimulation modes. Common ground AEVs are more reliable than monopolar AEVs for identifying malfunctioning electrodes.

Innovative Electrode Designs for Electrohydrodynamic Conduction Pumping

In the absence of a direct charge injection, pumping of an isothermal liquid can be achieved through the charges associated with the heterocharge layers of finite thickness in the vicinity of the electrodes. These charges are based on the process of dissociation of a neutral electrolytic species and recombination of the generated ions. This type of pumping is referred to as electrohydrodynamic (EHD) conduction pumping. The EHD conduction pumping mechanism is experimentally investigated with four innovative electrode designs, with refrigerant R-123 as the working fluid in this paper. Specifically, two different types of perforated disks and two different types of porous disks are used as the high-voltage electrode while a ring is used as the common ground electrode for the four designs. Pressures up to approximately 1400 Pa (at 18.5-kV potential with 0.23 W of power consumption) are generated with one electrode pair. Such pressure generations make the EHD conduction pumping attractive to certain applications in the presence and absence of gravity, such as capillary pumped loops and heat pipes.

Threshold, comfortable level and impedance changes as a function of electrode-modiolar distance.

The study investigated the hypothesis that threshold and comfortable levels recorded from cochlear implant patients would reduce, and dynamic range increase, as distance of the electrode from the modiolar wall (radial distance) decreases. Two groups of cochlear implant patients participated; one group using the Nucleus' 24 Contour electrode array, and one group using the Nucleus standard straight (banded) array. The Nucleus 24 Contour array has been shown in temporal bone studies to lie closer to the modiolus than the banded array. The relationship of electrode impedance and radial distance is also investigated. The study, conducted at three centers, evaluated 21 patients using the Contour array, and 36 patients using the banded array. For each patient, threshold, comfortable levels and dynamic range were measured at four time points. Common ground electrode impedance was recorded clinically from each patient, at time intervals up to 12 wk. An estimate of the radial distance of the electrode from the modiolus was made by analysis of Cochlear view x-rays. Threshold and comfortable levels were significantly lower for the Nucleus 24 Contour array than for the banded array. However, dynamic range measurements did not show the predicted increase. In a majority of subjects, a significant correlation was found between the estimated radial distance of the electrode from the modiolus and the measured threshold and comfortable levels. This trend was not observed for dynamic range. The analysis indicates that other factors than radial distance are involved in the resultant psychophysical levels. Clinical impedance measures (common ground) were found to be significantly higher for the Contour array. However, the electrodes on the Contour array are half-rings, which are approximately only half the geometric size of the full rings as electrodes of the standard array. When the geometric electrode area in the two array designs are normalized, the trends in the electrode impedance behavior are similar. The results support the hypothesis that the relationship between the radial distance of the electrode and the psychophysical measures are influenced by patterns of fibrous tissue growth and individual patient differences, such as etiology and neural survival. Impedance measures for the Nucleus 24 Contour electrode array were higher than the banded electrode array, but this is primarily due to the reduction in electrode surface area. The different outcomes in impedance over time suggest differences in the relative contributions of the components of impedance with the two arrays.

A longitudinal study of electrode impedance, the electrically evoked compound action potential, and behavioral measures in nucleus 24 cochlear implant users.

The primary goal of this study was to examine changes that may occur in electrode impedance, electrically evoked compound action potential (EAP) threshold and slope of the EAP growth function, and behavioral measures of threshold T-level) and maximum comfort (C-level) over time in both adult and child cochlear implant users. Secondary goals were to determine whether changes in these measures are consistent between children and adults, and to determine whether behavioral measures (MAP T- and C-levels) and electrophysiologic measures (EAP thresholds) exhibit the same trends over time. Thirty-five children and 33 adults implanted with the Nucleus CI24M between November 1996 and August 1999 participated in this study. Subjects were included in this study if 1) they had used their implant for at least 1 yr after device connection, and 2) they had participated in the necessary data collection at a minimum number of the time intervals assessed in this study. EAP threshold, slope of the EAP growth function, and common ground electrode impedance measures were collected intraoperatively, at initial stimulation, and at several subsequent visits up to 2 yr post initial stimulation. MAP T- an d C-levels weremeasured at initial stimulation and at the same time intervals as described above. Changes in electrode impedance, EAP thresholds, and slope of the EAP growth function from measures made intraoperatively, at initial stimulation, and at 1 to 2 mo post initial stimulation were similar in both children and adults. Beyond the 1- to 2-mo visit, children exhibited significant increases in electrode impedance, EAP thresholds, slope, and MAP T-levels, whereas these samemeasures in adults remained relatively stable. EAP thresholds in children stabilized by the 3- to 8-mo visit, and electrode impedance stabilized by the 6- to 8-mo visit, while slope of the EAP growth function, MAP T-levels,and MAP C-levels werestable by 1 yr post initial stimulation. C-levels in adults increased up to 1 yr post initial stimulation; however, the amount of increase was much smaller than that seen in children. In both children and adults, longitudinal trends in EAP thresholds mirrored T-level more closely than C-level. The results of this study suggest that peripheral changes occur in many children that do not generally occur in adults within the first year of cochlear implant use. One implication of these results is that if EAP thresholds are to be used to assist in programming the speech processor for children, it is best to make those measures at the same time interval as device programming rather than using measures made intraoperatively or at the initial programming session to set MAP levels at later visits.