Adjacent Electrode Pairs Research Articles

Electrically evoked mismatch negativity responses to loudness and pitch cues in cochlear implant users

Objective measurements could improve cochlear implant (CI) fitting, especially for CI users who have difficulty assessing their hearing impressions. In this study, we investigated the electrically evoked mismatch negativity (eMMN) brain potential as a mainly preattentive response to pitch and loudness changes. In an electrophysiological exploratory study with 21 CI users, pitch and loudness cues were presented in controlled oddball paradigms that directly electrically stimulated the CI via software. Out of them 17 valid data sets were analyzed. A pitch cue was produced by changing the stimulating CI electrodes (pairs of adjacent electrodes). A loudness cue originated from changing the stimulation amplitude on one CI electrode. MMN responses were measured unsing clinical electroencephalography recording according to a standard recording protocol. At the group level, significant eMMN responses were elicited for loudness cues and for pitch cues at basal electrode pairs but not at apical electrode pairs. The effect of deviance direction was not significant and no stimulus artifacts were observed. Recording an electrically evoked MMN in response to loudness changes in CI users is generally feasible, and is, therefore, promising to support CI fitting procedures in the future. Detection of pitch cues would require a greater electrode distance between selected electrodes for standard and deviant stimuli, especially in apical regions. A routine clinical setup can be used to measure eMMN.

Localized strain profile in surface electrode array for programmable composite multiferroic devices

We investigate localized in-plane strains on the microscale, induced by arrays of biased surface electrodes patterned on piezoelectrics. Particular focus is given to the influence that adjacent electrode pairs have on one another to study the impact of densely packed electrode arrays. We present a series of X-ray microdiffraction studies to reveal the spatially resolved micrometer-scale strain distribution. The strain maps with micrometer-scale resolution highlight how the local strain profile in square regions up to 250 × 250 μm2 in size is affected by the surface electrodes that are patterned on ferroelectric single-crystal [Pb(Mg1/3Nb2/3)O3]x-[PbTiO3]1−x. The experimental measurements and simulation results show the influence of electrode pair distance, positioning of the electrode pair, including the angle of placement, and neighboring electrode pair arrangements on the strength and direction of the regional strain. Our findings are relevant to the development of microarchitected strain-mediated multiferroic devices. The electrode arrays could provide array-addressable localized strain control for applications including straintronic memory, probabilistic computing platforms, microwave devices, and magnetic-activated cell sorting platforms.

Temporal Pitch Perception in Cochlear-Implant Users: Channel Independence in Apical Cochlear Regions.

Two-electrode stimuli presented on adjacent mid-array contacts in cochlear-implant users elicit pitch percepts that are not consistent with a summation of the two temporal patterns. This indicates that low-rate temporal rate codes can be applied with considerable independence on adjacent mid-array electrodes. At issue in this study was whether a similar independence of temporal pitch cues can also be observed for more apical sites of stimulation, where temporal cues have been shown to be more reliable than place cues, in contrast to middle and basal sites. In cochlear-implant recipients with single-sided deafness implanted with long lateral-wall electrode arrays, pitch percepts were assessed by matching the pitch of dual-electrode stimuli with pure tones presented to the contralateral normal-hearing ear. The results were supported with an additional pitch-ranking experiment, in a different subject population with bilateral deafness. Unmodulated pulse trains with 100, 200, and 400 pulses per second were presented on three pairs of adjacent electrodes. Pulses were separated by the minimal interchannel delay (1.7 µs) in a short-delay configuration and by half the pulse period in a long-delay configuration. The hypothesis was that subjects would perceive a pitch corresponding to the doubled temporal pattern for the long-delay stimuli due to the summation of excitation patterns from adjacent apical electrodes, if those electrodes were to activate largely overlapping neural populations. However, we found that the mean matched acoustic pitch of the long-delay pulses was not significantly different from that of the short-delay pulses. These findings suggest that also in the apical region in long-array cochlear-implant recipients, temporal cues can be transmitted largely independently on adjacent electrodes.

Dielectrophoretic medium exchange around droplets for on-chip fabrication of layer-by-layer microcapsules.

Continuous medium exchange within a microchannel represents a highly sought-after technique in functionalizing micro-objects with coating layers, enabling a myriad of applications ranging from biomedical engineering to materials science. Herein, we introduce a unique medium exchange approach, namely, tilted-angle dielectrophoresis, to accomplish layer-by-layer (LbL) coating on droplets in a wide microchannel. Pairs of adjacent tilted parallel electrodes arranged in a zigzag fashion are exploited to consecutively and repeatedly guide particles/droplets travelling through three parallel laminar streams comprising two reagents and a washing buffer. The performance of medium exchange is demonstrated using PS microparticles and oil droplets. We show that multi-cycle medium exchange, droplet transfer accompanied with purification, and multi-mode medium exchange around different micro-objects are achieved by conveniently regulating the applied voltage and the inlet flow rate, indicating a flexible, versatile and label-free alternative for characterizing and handling colloidal particles. Furthermore, LbL coating on droplets utilizing the presented strategy is implemented in the parallel coating-chemical and washing streams to obtain multiple layers of microcapsules. The linearly increasing fluorescence intensity of the coated droplets with each subsequent fluorescent coating demonstrates the capability of the tilted-angle dielectrophoretic medium exchanger for on-chip generation of LbL microcapsules on demand. The presented medium exchange strategy, together with its unique features of simple geometric configuration, facile control and multifunctionality, can provide a refined alternative for further expanding the utility scope in functional particles and cells.

Conductance-Based Interface Detection for Multi-Phase Pipe Flow.

Sediment and flow depth monitoring in sewers is important for informing flow models and for predicting and mitigating against sewer blockage formation and surcharge. In this study, a novel sensor based on conductance measurement has been developed and tested under a laboratory environment and validated by a finite-element model. The relative conductance is measured between pairs of adjacent electrodes to provide a conductance profile along the sensor length. A piecewise linear relationship between conductance and electrode length was derived and the interface positions between sediment, water, and air can be determined from the profile. The results demonstrated that the root mean square error of the model and the measured interface level are within 1.4% and 2.6% of sensor’s measurement range. An error distribution of interface height shows that all anticipated errors are within the resolution of the electrode length increments. Furthermore, it was found that the conductivity of the measured medium is proportional to the gradient of the linear relationship of conductance and electrode length. It could therefore prove a valuable new tool for the accurate quantification of sediment and flow levels in sewer conduits, coastal environments, drainage systems for transport networks, and other industrial or academic applications.

Sweep-type triboelectric linear motion sensor with staggered electrode

For use in modern industrial automation, a sweep-type triboelectric linear motion sensor (ST-TLMS) is demonstrated that can monitor the position, displacement, velocity and direction of sliding objects. The ST-TLMS consists of a slider, a stator, and an acrylic groove box for housing them. They are configured allowing a flexible copolymer film to be fixed on the slider and moves with it and the stator to be coated with three pairs of copper electrode arrays arranged uniformly. The phases of adjacent pairs of electrodes are staggered by one third. Three periodic friction electrical signals are generated on the copper electrode by the back and forth sweeping of the stator and film. The experimental results show that the output amplitude after voltage amplification and signal processing remains basically unchanged at different sliding velocities, showing good stability. More importantly, the dominant frequency of the signal is consistent with the sliding velocity. Through real-time noise reduction and the signal transformation of the three output signals, the resolution and accuracy of the motion perception are effectively improved. Additionally, after 32 h of continuous operation, the output signal of the sensor had not decayed, which meets the requirements of durability in practical applications.

Source Consistency Electrical Impedance Tomography

In electrical impedance tomography (EIT), multiple electrodes are attached around an imaging domain such as the human thorax to inject currents and measure induced boundary voltages. Using the measured boundary voltage data, cross-sectional images of an internal conductivity distribution are reconstructed. Taking advantage of its fast temporal resolution, time-difference EIT can be used for image-based monitoring of physiological functions such as lung ventilation and cardiac blood flow. Among numerous data collection protocols, we assume current injections and voltage measurements between adjacent pairs of electrodes. The measured voltage difference between the $j$th electrode pair subject to the current injection between the $k$th electrode pair, for example, changes with time and its time-series is called a voltage channel in this paper. Investigating shapes of voltage channels, a new technique called source consistency EIT (scEIT) is proposed to extract voltage channel data originating from a physiological function or source of interest. The proposed scEIT technique suggests each voltage channel can be expressed up to a scale factor and offset value from a single shape-reference voltage channel when there exists only one time-varying source. When multiple physiological sources exist to concurrently produce correspondingly different conductivity changes, measured voltage channels are influenced by all of the sources. Using the scEIT method, each voltage channel can be expressed as a weighted sum of multiple shape-reference voltage channels of the sources. The proposed scEIT technique is verified through numerical simulations and animal experiments. Future experimental studies of applying the scEIT technique to in vivo human experiments are proposed.

Investigation and analysis of a fluidized bed dryer by process tomography sensor

In the pharmaceutical industry, fluidized beds are typically used for pellets drying, coating and granulation. The gas–solids flow characteristic in the process plays an important role to control the heat and mass transfer as well as the end-point product quality. Therefore, it is necessary to investigate the flow characteristics based on advanced measurement technologies. In this research, electrical capacitance tomography (ECT) sensor with eight electrodes was used to investigate the pharmaceutical fluidized bed drying process with different operation conditions. Key process parameters including solids concentration, particle moisture and capacitance signals in the process are given and analysed based on the ECT sensor. In addition, the fluidized bed process with Wurster tube is also investigated based on this ECT sensor. The effect of Wurster tube on the hydrodynamic behaviour and the dominant frequency spectrum distribution in the chamber were analysed based on fast Fourier transform. Test results reveal that process moisture change can be addressed from the raw capacitance of adjacent electrode pair combined with calibration model. Experimental result also indicates that ECT technology can provide useful information for process monitor in a fluidized bed dryer.

Deterministic multi-step rotation of magnetic single-domain state in Nickel nanodisks using multiferroic magnetoelastic coupling

We demonstrate deterministic multi-step rotation of a magnetic single-domain (SD) state in Nickel nanodisks using the multiferroic magnetoelastic effect. Ferromagnetic Nickel nanodisks are fabricated on a piezoelectric Lead Zirconate Titanate (PZT) substrate, surrounded by patterned electrodes. With the application of a voltage between opposing electrode pairs, we generate anisotropic in-plane strains that reshape the magnetic energy landscape of the Nickel disks, reorienting magnetization toward a new easy axis. By applying a series of voltages sequentially to adjacent electrode pairs, circulating in-plane anisotropic strains are applied to the Nickel disks, deterministically rotating a SD state in the Nickel disks by increments of 45°. The rotation of the SD state is numerically predicted by a fully-coupled micromagnetic/elastodynamic finite element analysis (FEA) model, and the predictions are experimentally verified with magnetic force microscopy (MFM). This experimental result will provide a new pathway to develop energy efficient magnetic manipulation techniques at the nanoscale.

Arts of electrical impedance tomographic sensing.

This paper reviews governing theorems in electrical impedance sensing for analysing the relationships of boundary voltages obtained from different sensing strategies. It reports that both the boundary voltage values and the associated sensitivity matrix of an alternative sensing strategy can be derived from a set of full independent measurements and sensitivity matrix obtained from other sensing strategy. A new sensing method for regional imaging with limited measurements is reported. It also proves that the sensitivity coefficient back-projection algorithm does not always work for all sensing strategies, unless the diagonal elements of the transformed matrix, ATA, have significant values and can be approximate to a diagonal matrix. Imaging capabilities of few sensing strategies were verified with static set-ups, which suggest the adjacent electrode pair sensing strategy displays better performance compared with the diametrically opposite protocol, with both the back-projection and multi-step image reconstruction methods. An application of electrical impedance tomography for sensing gas in water two-phase flows is demonstrated.This article is part of the themed issue ‘Supersensing through industrial process tomography’.

Parylene-Based Electrochemical-MEMS Force Sensor for Studies of Intracortical Probe Insertion Mechanics

To investigate the mechanical interactions between the implanted cortical multielectrode probes and brain tissue, a Parylene C-based electrochemical-microelectromechanical systems force sensor array was developed. The array consists of seven linearly distributed sensor units arranged along the length of a flexible Parylene C microchannel. The seven sensor units are formed by eight fluidically coupled and adjacent platinum electrode pairs enclosed within the microchannel. Deformation of the top surface of the mechanically compliant microchannel changes the volumetric conduction path between the pairs of sensing electrodes, and therefore, the measured electrochemical impedance, which is proportional to the magnitude of the contacting force. Each sensor unit demonstrated a linear response from 0 to 60 mN with a sensitivity of 0.13 ± 0.01 percentage change in impedance/ $\mu \text{N}$ (%/ $\mu \text{N}$ ; mean ± SE, ${ {n}} = 6$ ). The sensor arrays were mounted onto a ceramic intracortical probe and inserted into the tissue phantoms to verify in situ functionality and assess interfacial probe mechanics. Probe surface force distribution was measured under various insertion speeds and the results indicated that interfacial forces are distributed nonuniformly along the probe shaft length, concentrating within the first 1 mm of the advancing probe tip. Faster insertion speeds were also found to decrease the magnitude of the interfacial forces, suggesting that the tissue strain during cortical implantation may be minimized through appropriate selection of the insertion speed.[2014-0320]

Pitch Discrimination: An Independent Factor in Cochlear Implant Performance Outcomes.

Objective:To assess differences in pitch-ranking ability across a range of speech understanding performance levels and as a function of electrode position.Study Design:An observational study of a cross-section of cochlear implantees.Setting:Tertiary referral center for cochlear implantation.Patients:A total of 22 patients were recruited. All three manufacturers’ devices were included (MED-EL, Innsbruck, Austria, n = 10; Advanced Bionics, California, USA, n = 8; and Cochlear, Sydney, Australia, n = 4) and all patients were long-term users (more than 18 months). Twelve of these were poor performers (scores on BKB sentence lists <60%) and 10 were excellent performers (BKB >90%).Intervention:After measurement of threshold and comfort levels, and loudness balancing across the array, all patients underwent thorough pitch-ranking assessments at 80% of comfort levels.Main Outcome Measure:Ability to discriminate pitch across the electrode array, measured by consistency in discrimination of adjacent pairs of electrodes, as well as an assessment of the pitch order across the array using the midpoint comparison task.Results:Within the poor performing group there was wide variability in ability to pitch rank, from no errors, to a complete inability to reliably and consistently differentiate pitch change across the electrode array. Good performers were overall significantly more accurate at pitch ranking (p = 0.026). Consistent pitch ranking was found to be a significant independent predictor of BKB score, even after adjusting for age. Users of the MED-EL implant experienced significantly more pitch confusions at the apex than at more basal parts of the electrode array.Conclusions:Many cochlear implant users struggle to discriminate pitch effectively. Accurate pitch ranking appears to be an independent predictor of overall outcome. Future work will concentrate on manipulating maps based upon pitch discrimination findings in an attempt to improve speech understanding.

Effect of adenosine triphosphate on left atrial electrogram interval and dominant frequency in human atrial fibrillation

BackgroundComplex fractionated atrial electrograms (CFAEs) and high dominant frequency (DF) are targets for atrial fibrillation (AF) ablation. Although adenosine triphosphate (ATP) is known to promote AF by shortening the atrial refractory period, its role in the pathogenesis of CFAEs and DF during AF is not fully understood. MethodsWe recorded electrical activity from a 64-electrode basket catheter placed in the left atrium (LA) of patients with paroxysmal AF (PAF, n=18) or persistent AF (PerAF, n=19) before ablation. Atrial electrogram fractionation intervals (FIs) and DFs were measured from bipolar electrograms of each adjacent electrode pair. Offline mean atrial FIs and DFs were obtained before bolus injection of 30mg ATP. Peak effect was defined as an R–R interval >3s. ResultsWith ATP, the mean FI decreased (from 110.4±29.1ms to 90.5±24.7ms, P<0.0001) and DF increased (from 6.4±0.6Hz to 7.1±0.8Hz, P<0.0001) in all patients. There was no difference in the FI decrease between the two groups (−20.3±20.5ms vs. −19.6±14.5ms, P=0.6032), but the increase in DF was significantly greater in PAF patients (1.1±0.8Hz vs. 0.3±0.6Hz, P=0.0051). ConclusionsATP shortens atrial FIs and increases DFs in both PAF and PerAF patients. The significant increase in DF in PAF patients suggests that pathophysiologic characteristics related to the frequency of atrial fractionation change as atrial remodeling progresses.

Evoked effective connectivity of the human neocortex

The role of cortical connectivity in brain function and pathology is increasingly being recognized. While in vivo magnetic resonance imaging studies have provided important insights into anatomical and functional connectivity, these methodologies are limited in their ability to detect electrophysiological activity and the causal relationships that underlie effective connectivity. Here, we describe results of cortico-cortical evoked potential (CCEP) mapping using single pulse electrical stimulation in 25 patients undergoing seizure monitoring with subdural electrode arrays. Mapping was performed by stimulating adjacent electrode pairs and recording CCEPs from the remainder of the electrode array. CCEPs reliably revealed functional networks and showed an inverse relationship to distance between sites. Coregistration to Brodmann areas (BA) permitted group analysis. Connections were frequently directional with 43% of early responses and 50% of late responses of connections reflecting relative dominance of incoming or outgoing connections. The most consistent connections were seen as outgoing from motor cortex, BA6-BA9, somatosensory (SS) cortex, anterior cingulate cortex, and Broca's area. Network topology revealed motor, SS, and premotor cortices along with BA9 and BA10 and language areas to serve as hubs for cortical connections. BA20 and BA39 demonstrated the most consistent dominance of outdegree connections, while BA5, BA7, auditory cortex, and anterior cingulum demonstrated relatively greater indegree. This multicenter, large-scale, directional study of local and long-range cortical connectivity using direct recordings from awake, humans will aid the interpretation of noninvasive functional connectome studies.

An electrocorticographic electrode array for simultaneous recording from medial, lateral, and intrasulcal surface of the cortex in macaque monkeys.

Electrocorticography (ECoG) permits recording electrical field potentials with high spatiotemporal resolution over a large part of the cerebral cortex. Application of chronically implanted ECoG arrays in animal models provides an opportunity to investigate global spatiotemporal neural patterns and functional connectivity systematically under various experimental conditions. Although ECoG is conventionally used to cover the gyral cortical surface, recent studies have shown the feasibility of intrasulcal ECoG recordings in macaque monkeys. Here we developed a new ECoG array to record neural activity simultaneously from much of the medial and lateral cortical surface of a single hemisphere, together with the supratemporal plane (STP) of the lateral sulcus in macaque monkeys. The ECoG array consisted of 256 electrodes for bipolar recording at 128 sites. We successfully implanted the ECoG array in the left hemisphere of three rhesus monkeys. The electrodes in the auditory and visual cortex detected robust event related potentials to auditory and visual stimuli, respectively. Bipolar recording from adjacent electrode pairs effectively eliminated chewing artifacts evident in monopolar recording, demonstrating the advantage of using the ECoG array under conditions that generate significant movement artifacts. Compared with bipolar ECoG arrays previously developed for macaque monkeys, this array significantly expands the number of cortical target areas in gyral and intralsulcal cortex. This new ECoG array provides an opportunity to investigate global network interactions among gyral and intrasulcal cortical areas.

Simulation of Electric Field for Carbon Nanotube Assembly by Dielectrophoresis

In the process of carbon nanotube assembly by dielectrophoresis, the geometry and spacing of electrodes are significantly affecting the assembly precision. In the simulation process, we showed the geometrical shape of conical, round and rectangular electrode and compared the electric field distribution with these electrodes. Compared with single electrode pairs, comb electrodes can achieve high-yield manipulation. Simulation results show that when the distance between adjacent electrode pairs is larger than twice electrode width, it will avoid electric field superimposition. A method of using floating metal posts within the electrode gap can realize precise positioning of assembled carbon nanotubes.

Theoretical and numerical investigations of an electroosmotic flow micropump with interdigitated electrodes

In this work, an electroosmotic flow micropump is proposed and investigated using theoretical analysis and numerical simulations. The micropump comprises an array of interdigitated electrodes on the top and the bottom surfaces of a rectangular microchannel. Theoretical analysis and extensive numerical simulations are performed to predict the pressure-flow characteristics of the micropump. The results of the model and simulations are compared which show good agreement with each other. The effects of various geometrical parameters including spacing between a pair of electrodes, gap between adjacent pairs of electrodes, width and height of the electrodes, and width of the microchannel and operating parameter including applied voltage on the performance of the micropump in terms of flow and pressure capacity is investigated.

A microfabricated module for isolating cervical carcinoma cells from peripheral blood utilizing dielectrophoresis in stepping electric fields

The ability to isolate rare cells, such as circulating tumor cells (CTC), circulating fetal cells, and stem cells, is important for medical diagnostics and characterization. The present study develops a microfabricated module that can effectively isolate cervical carcinoma cells (HeLa) from a peripheral blood sample. Circular microelectrodes that generate a stepping electric field by switching the electric field between adjacent electrode pairs by relays are designed herein. Positive dielectrophoretic cells are guided by the movement of the high-electric-field region. The magnitude of the dielectrophoresis (DEP) force acting on HeLa cells is about sevenfold that on red blood cells (RBCs) under a given electric field distribution in a sucrose medium, making it possible to separate HeLa cells from normal blood cells. Both HeLa cells and RBCs are pushed to the outermost electrodes when an outward stepping electric field (16 V peak-to-peak; 1 MHz) is applied. When an inward stepping electric field (10 V peak-to-peak; 1 MHz) is applied, the movement of HeLa cells toward the center electrodes is faster than that of RBCs. As a result, HeLa cells are concentrated onto the central microelectrode and isolated from the blood sample. Experimental results demonstrate the feasibility of isolating HeLa cells from blood samples.

Time–frequency analysis of single pulse electrical stimulation to assist delineation of epileptogenic cortex

Epilepsy surgery depends on reliable pre-surgical markers of epileptogenic tissue. The current gold standard is the seizure onset zone in ictal, i.e. chronic, electrocorticography recordings. Single pulse electrical stimulation can evoke epileptic, spike-like responses in areas of seizure onset also recorded by electrocorticography. Recently, spontaneous pathological high-frequency oscillations (80-520 Hz) have been observed in the electrocorticogram that are related to epileptic spikes, but seem more specific for epileptogenic cortex. We wanted to see whether a quantitative electroencephalography analysis using time-frequency information including the higher frequency range could be applied to evoked responses by single pulse electrical stimulation, to enhance its specificity and clinical use. Electrocorticography data were recorded at a 2048-Hz sampling rate from 13 patients. Single pulse electrical stimulation (10 stimuli, 1 ms, 8 mA, 0.2 Hz) was performed stimulating pairs of adjacent electrodes. A time-frequency analysis based on Morlet wavelet transformation was performed in a [-1 s : 1 s] time interval around the stimulus and a frequency range of 10-520 Hz. Significant (P = 0.05) changes in power spectra averaged for 10 epochs were computed, resulting in event-related spectral perturbation images. In these images, time-frequency analysis of single pulse-evoked responses, in the range of 10-80 Hz for spikes, 80-250 Hz for ripples and 250-520 Hz for fast ripples, were scored by two observers independently. Sensitivity, specificity and predictive value of time-frequency single pulse-evoked responses in the three frequency ranges were compared with seizure onset zone and post-surgical outcome. In all patients, evoked responses included spikes, ripples and fast ripples. For the seizure onset zone, the median sensitivity of time-frequency single pulse-evoked responses decreased from 100% for spikes to 67% for fast ripples and the median specificity increased from 17% for spikes to 79% for fast ripples. A median positive predictive value for the evoked responses in the seizure onset zone of 17% was found for spikes, 26% for ripples and 37% for fast ripples. Five out of seven patients with <50% of fast ripples removed by resection had a poor outcome. A wavelet transform-based time-frequency analysis of single pulse electrical stimulation reveals evoked responses in the frequency range of spikes, ripples and fast ripples. We demonstrate that time-frequency analysis of single pulse electrical stimulation can assist in delineation of the epileptogenic cortex using time-frequency single pulse-evoked fast ripples as a potential new marker.

A handheld preconcentrator for the rapid collection of cancerous cells using dielectrophoresis generated by circular microelectrodes in stepping electric fields

The ability to concentrate biological cells, such as circulating tumor cells, circulating fetal cells, and stem cells, is an important issue in medical diagnostics and characterization. The present study develops a handheld device capable of effectively preconcentrating cancerous cells. Circular microelectrodes were designed to generate a stepping electric field by switching the electric field to an adjacent electrode pair by relays. Cancerous cells with a positive dielectrophoretic response are guided toward the center of the circular microelectrodes due to the region of high electric field between the adjacent electrodes being gradually decreased in the direction of the stepping electric field. Numerical simulations of the electric fields were performed to demonstrate the concept of the proposed design. The preconcentration of HeLa cells, which are a human cervical carcinoma cell line, was achieved in 160 s with an efficiency of around 76%, with an applied peak-to-peak voltage of 16 V at a frequency of 1 MHz.