Electric Field Imaging Research Articles

Exposure Time Control Method for Higher Intermediate Frequency in Optical Heterodyne Imaging and Its Application to Electric-Field Imaging Based on Electro-Optic Effect.

We propose and demonstrate a method for equivalent time sampling using image sensors to selectively detect only the target frequency. Shortening the exposure time of the image sensor and using equivalent time sampling allows for the detection of frequency components that are higher than the frame rate. However, the imaging system in our previous work was also sensitive to the frequency component at 1/4 of the frame rate. In this study, we control the phase relationship between the exposure time and observed signal by inserting an additional interval once every four frames to detect the target frequency selectively. With this technique, we conducted electric field imaging based on the electro-optic effect under high noise conditions in the low-frequency band to which the conventional method is sensitive. The results demonstrated that the proposed method improved the signal-to-noise ratio.

Advanced Bionics HiRes Ultra and Ultra 3D Series Cochlear Implant Recall: Time Course of Anomalies.

To estimate median survival time until the appearance of anomalies indicating a potential implant failure associated with fluid ingress in implanted cochlear implant (CI) devices of the initial version of Advanced Bionics HiRes Ultra and HiRes Ultra 3D series. Retrospective review. Cochlear implantation was performed in a standard fashion. Implant integrity was tested at follow-up visits by measuring impedance and electrically evoked compound action potential (ECAP). Additional tests such as electrical field imaging (EFI) were conducted by the manufacturer. Based on these tests, the presence or absence of an anomaly was classified. Of the 349 devices implanted at this institution, 181 showed anomalies in accordance with the special failure mode and for this reason, 120 implants were already explanted. The median survival time without anomalies was 1062 days. So far, the suspicion of device failures has been confirmed in all cases in which a post-implantation analysis was already available. Regular tests at the follow-up visits are necessary to monitor the integrity of CIs. 3 Laryngoscope, 132:2484-2490, 2022.

Planar Near-Field Electric Field Sensor Array Applications Facilitated by Neural Networks

Electrical capacitance tomography is employed for various process tomography applications, typically with circular imaging regions (e.g., to estimate fluid levels in plastic pipes). Typical state-of-the-art implementations focus on circular or cylindrical sensor arrays. In contrast, this research explores using a planar 2D array of electric-field sensors to image volumes composed of various dielectric materials. The array is designed to be used with very-low-frequency electric fields, which are desirable due to their ability to differentiate between various non-conducting objects. D-dot sensors (i.e., charge induction sensors) are used as the electric-field sensing element. In this research, imaging regions of interest are modeled as a composition of (25 cm) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> voxels of dielectric material with randomized relative permittivities. Neural networks are utilized as the inversion algorithm to map measured E-field distortions to the voxels’ relative permittivities. Three applications are explored in a simulated environment: 1) predicting relative permittivities of the entire (pseudo-3D) imaging region from one measurement of electric-field distortions (modeled in free space), 2) imaging regions arbitrarily large (in two dimensions) using the planar array as an imaging kernel, and 3) repeating application (1) in a model of a practical, real-world imaging scenario both with and without interfering material. Application (3) is performed with a real-world experimental setup using a room-sized “E-field Cage” meant to generate a uniform electric field. This work showcases a new electric-field imaging modality using a planar 2D D-dot sensor array paired with a DNN-based inversion algorithm.

Nanoscale electric-field imaging based on a quantum sensor and its charge-state control under ambient condition

Nitrogen-vacancy (NV) centers in diamond can be used as quantum sensors to image the magnetic field with nanoscale resolution. However, nanoscale electric-field mapping has not been achieved so far because of the relatively weak coupling strength between NV and electric field. Here, using individual shallow NVs, we quantitatively image electric field contours from a sharp tip of a qPlus-based atomic force microscope (AFM), and achieve a spatial resolution of ~10 nm. Through such local electric fields, we demonstrated electric control of NV’s charge state with sub-5 nm precision. This work represents the first step towards nanoscale scanning electrometry based on a single quantum sensor and may open up the possibility of quantitatively mapping local charge, electric polarization, and dielectric response in a broad spectrum of functional materials at nanoscale.

Detection of Extracochlear Electrodes in Cochlear Implants with Electric Field Imaging/Transimpedance Measurements: A Human Cadaver Study.

Objectives:Extracochlear electrodes in cochlear implants (CI), defined as individual electrodes on the electrode array located outside of the cochlea, are not a rare phenomenon. The presence of extracochlear electrodes frequently goes unnoticed and could result in them being assigned stimulation frequencies that are either not delivered to, or stimulating neurons that overlap with intracochlear electrodes, potentially reducing performance. The current gold-standard for detection of extracochlear electrodes is computed tomography (CT), which is time-intensive, costly and involves radiation. It is hypothesized that a collection of Stimulation-Current-Induced Non-Stimulating Electrode Voltage recordings (SCINSEVs), commonly referred to as “transimpedance measurements (TIMs)” or electric field imaging (EFI), could be utilized to detect extracochlear electrodes even when contact impedances are low. An automated analysis tool is introduced for detection and quantification of extracochlear electrodes.Design:Eight fresh-frozen human cadaveric heads were implanted with the Advanced Bionics HiRes90K with a HiFocus 1J lateral-wall electrode. The cochlea was flushed with 1.0% saline through the lateral semicircular canal. Contact impedances and SCINSEVs were recorded for complete insertion and for 1 to 5 extracochlear electrodes. Measured conditions included: air in the middle ear (to simulate electrodes situated in the middle ear), 1.0% saline in the middle ear (to simulate intraoperative conditions with saline or blood in the middle ear), and soft tissue (temporal muscle) wrapped around the extracochlear electrodes (to simulate postoperative soft-tissue encapsulation of the electrodes). Intraoperative SCINSEVs from patients were collected, for clinical purposes during slow insertion of the electrode array, as well as from a patient postoperatively with known extracochlear electrodes.Results:Full insertion of the cochlear implant in the fresh-frozen human cadaveric heads with a flushed cochlea resulted in contact impedances in the range of 6.06 ± 2.99 kΩ (mean ± 2SD). Contact impedances were high when the extracochlear electrodes were located in air, but remained similar to intracochlear contact impedances when in saline or soft tissue. SCINSEVs showed a change in shape for the extracochlear electrodes in air, saline, and soft tissue. The automated analysis tool showed a specificity and sensitivity of 100% for detection of two or more extracochlear electrodes in saline and soft tissue. The quantification of two or more extracochlear electrodes was correct for 84% and 81% of the saline and soft tissue measurements, respectively.Conclusions:Our analysis of SCINSEVs (specifically the EFIs from this manufacturer) shows good potential as a detection tool for extracochlear electrodes, even when contact impedances remain similar to intracochlear values. SCINSEVs could potentially replace CT in the initial screening for extracochlear electrodes. Detecting migration of the electrode array during the final stages of surgery could potentially prevent re-insertion surgery for some CI users. The automated detection tool could assist in detection and quantification of two or more extracochlear electrodes.

Tip Fold-over in Cochlear Implantation: Case Series.

To describe the incidence, clinical presentation, and performance of cochlear implant (CI) recipients with tip fold-over. Retrospective case series. Tertiary referral center. CI recipients who underwent postoperative computed tomography (CT) scanning. Tip fold-over was identified tomographically using previously validated software that identifies the electrode array. Electrophysiologic testing including spread of excitation or electric field imaging (EFI) was measured on those with fold-over. Location of the fold-over; audiological performance pre and postselective deactivation of fold-over electrodes. Three hundred three ears of 235 CI recipients had postoperative CTs available for review. Six (1.98%) had tip fold-over with 5/6 right-sided ears. Tip fold-over occurred predominantly at 270 degrees and was associated with precurved electrodes (5/6). Patients did not report audiological complaints during initial activation. In one patient, the electrode array remained within the scala tympani with preserved residual hearing despite the fold-over. Spread of excitation supported tip fold-over, but the predictive value was not clear. EFI predicted location of the fold-over with clear predictive value in one patient. At an average follow-up of 11 months, three subjects underwent deactivation of the overlapping electrodes with two of them showing marked audiological improvement. In a large academic center with experienced surgeons, tip fold-over occurred at a rate of 1.98% but was not immediately identifiable clinically. CT imaging definitively showed tip fold-over. Deactivating involved electrodes may improve performance possibly avoiding revision surgery. EFI may be highly predictive of tip fold-over and can be run intraoperatively, potentially obviating the need for intraop fluoroscopy.

Symmetric Electrode Spanning Narrows the Excitation Patterns of Partial Tripolar Stimuli in Cochlear Implants

In cochlear implants (CIs), standard partial tripolar (pTP) mode reduces current spread by returning a fraction of the current to two adjacent flanking electrodes within the cochlea. Symmetric electrode spanning (i.e., separating both the apical and basal return electrodes from the main electrode by one electrode) has been shown to increase the pitch of pTP stimuli, when the ratio of intracochlear return current was fixed. To explain the pitch increase caused by symmetric spanning in pTP mode, this study measured the electrical potentials of both standard and symmetrically spanned pTP stimuli on a main electrode EL8 in five CI ears using electrical field imaging (EFI). In addition, the spatial profiles of evoked compound action potentials (ECAP) and the psychophysical forward masking (PFM) patterns were also measured for both stimuli. The EFI, ECAP, and PFM patterns of a given stimulus differed in shape details, reflecting the different levels of auditory processing and different ratios of intracochlear return current across the measurement methods. Compared to the standard pTP stimuli, the symmetrically spanned pTP stimuli significantly reduced the areas under the curves of the normalized EFI and PFM patterns, without shifting the pattern peaks and centroids (both around EL8). The more focused excitation patterns with symmetric spanning may have caused the previously reported pitch increase, due to an interaction between pitch and timbre perception. Being able to reduce the spread of excitation, pTP mode symmetric spanning is a promising stimulation strategy that may further increase spectral resolution and frequency selectivity with CIs.

Excitation Patterns of Standard and Steered Partial Tripolar Stimuli in Cochlear Implants.

Current steering in partial tripolar (pTP) mode has been shown to improve pitch perception and spectral resolution with cochlear implants (CIs). In this mode, a fraction (σ) of the main electrode current is returned within the cochlea and steered between the basal and apical flanking electrodes (with a proportion of α and 1 - α, respectively). Pitch generally decreases when α increases from 0 to 1, although the salience of pitch change varies across CI users. This study aimed to identify the mechanism of pitch changes with pTP-mode current steering and the factors contributing to the intersubject variability in pitch-ranking sensitivity. The electrical fields were measured for steered pTP stimuli on the same main electrode with α = 0, 0.5, and 1 in five implanted ears using electrical field imaging (EFI). The related excitation patterns were also measured physiologically using evoked compound action potential (ECAP) and psychophysically using psychophysical forward masking (PFM). Consistent with the pitch-ranking results in this study, the EFI, ECAP, and PFM centroids shifted apically with increasing α. An apical shift was also observed for the PFM peak but not for the EFI or ECAP peak. The pattern width was similar with different α values within a given measure (e.g., EFI, ECAP, or PFM), but the ECAP patterns were broader than the EFI and PFM patterns, possibly because ECAP was measured with smaller σ values than EFI and PFM. The amount of pattern shift with α depended on σ (i.e., the total amount of current used for steering) but was not correlated with the pitch-ranking sensitivity across subjects. The results revealed that the pitch changes elicited by pTP-mode current steering were not only driven by the shifts of excitation centroid.

Observation of Electric Potential Distribution in Model Capacitor Sample Using Electron Holography

The electrical potential distribution in a model capacitor specimen, made of single-crystalline BaTiO3 and thin Pt plates, has been revealed by electron holography. In order to represent the inherent potential distribution related to the capacitance, undesired phase information was eliminated by the analysis of electron holograms acquired in various conditions of applied voltage; the undesired information includes signals due to electrical charging, thickness variation, and modulation of the reference electron wave by a long-range electric field. The observation of electric potential showed reasonable agreement with simulation for the model specimen. (doi:10.2320/matertrans.MBW201108) depth electron holography studies on capacitor samples. These include unwanted phase information due to electrical charging which occurs during electron exposure to a non- conductive BaTiO3 region, significant change in the mean inner potential at the position of precipitates, thickness variation in the sample, Bragg reflections, and modulation of the reference electron wave caused by a long-range electric field. 5­8) These effects superpose artificial phase information on the observations. In order to reveal the inherent electric field distribution related to the capacitance, we need to reduce these undesired signals by using appropriate techniques. The purpose of this study was to obtain a method of precise electric-field imaging based on electron holography for electronic components, such as capacitors, containing stacked thin ferroelectric and metallic layers. In order to show the usefulness of electron holography for studies of capacitors, we employed a simple model specimen made of single-crystalline BaTiO3 layers and Pt electrodes, as shown in Fig. 1(a): this specimen reduces undesired phase informa- tion due to Bragg reflections in the BaTiO3 layers, which are particularly significant in polycrystalline materials. The model specimen did not include precipitates in the ferro- electric layer. We demonstrate that the inherent electric potential distribution in the capacitor can be obtained by suppressing the effects due to electric charging, modulation of the reference electron wave, thickness variations etc.

Two-dimensional junction identification in multicrystalline silicon solar cells by scanning Kelvin probe force microscopy

We report on a two-dimensional investigation of the p-n junction in multicrystalline silicon solar cells using scanning Kelvin probe force microscopy (SKPFM). The junction location and depth were identified by SKPFM potential measurement and subsequent data analysis, where a procedure taking bias-voltage-induced changes in the potential and electric field was developed to avoid the effects of surface Fermi level pinning. Device simulation supported the junction identification procedure and showed a possible deviation of ∼40 nm in the junction identification. The two-dimensional electric-field images show that the shape of the junction follows the surface topography of the device, or, in other words, the junction depth is identical over the device.

The facial nerve canal: an important cochlear conduction path revealed by Clarion electrical field imaging.

Electrical properties of the implanted scala tympani could be accurately modeled by means of a simple resistive ladder network model. The subject-specific model parameters can be obtained from electrical field imaging (EFI) recordings. It is a powerful tool for analysis of the cochlear current spread. In EFI mode, the telemetry systems of contemporary cochlear implants can measure the intracochlear potential distribution. At present, the clinical use of EFI is typically limited to checking the implant's proper functioning. Accurate EFI measurements and estimation algorithms have been developed to fit a small, yet physically relevant electrical model of the conductivity of the intracochlear structures. The model can attain up to 95% agreement with in vivo EFI data. A first discovery is that in a majority of the tested subjects, a substantial fraction of the monopolar current leaves the scala along the facial nerve canal. The role of the facial nerve canal has been confirmed by a temporal bone study and a high-resolution computed tomography (HRCT) scan in two of the implanted subjects. The clinical use of EFI is not limited to checking the implant's status. For the Clarion II implant, a purely resistive model is able to match in vivo EFI recordings. The model indicates that the facial nerve canal is an important conduction path to the reference electrode. EFI can provide clinically relevant information, especially in problematic cases of cochlear malformations, postoperative fibrosis/ossification, implanted otosclerotic cochleae, postoperative facial nerve stimulation, increased stimulation thresholds, and so on.

First results of the Clarion CII Bionic Ear System

The CII Bionic Ear System by Clarion (Advanced Bionics, Sylmar, California, USA) shows an improved stability of the device and a higher rate of stimulation in comparison to former generations of cochlear implants. The increased number of channels allows higher pulsatile rates and creates the possibility of measuring objective parameters such as electric field imaging (EFI) and neural response imaging (NRI).

Microwave electric-field imaging using a high-Tc scanning superconducting quantum interference device

We have used a 77 K thin-film YBa2Cu3O7 superconducting quantum interference device (SQUID) in a scanning SQUID microscope to image room-temperature sources of high-frequency electric field. We find that time-varying electric fields capacitively induce currents in the SQUID, which in turn are rectified by the nonlinearity of the SQUID current–voltage characteristics, leading to changes in the quasistatic voltage across the SQUID. By observing changes in the voltage modulation depth ΔV of the SQUID as a sample is scanned past the SQUID, we obtain electric-field images in the 1–15 GHz frequency range with a SQUID-to-sample separation of about 80 μm.

Comparative magnetic-field imaging, electric-field imaging, and scanning Auger microscopy study of metal–matrix composites

Abstract X-ray photoelectron emission microscopy (XPEEM) provides valuable chemical information at the micron or submicron level and has been successfully applied to a wide range of materials. We have initiated a study of metal–matrix composites (MMCs) using this technique, aimed at understanding the interfacial interactions that occur between the metal matrix and the ceramic reinforcement. The experiments have been performed on Ti/SiC (fiber) MMCs and SiC fibers. We have found that the method of preparing the sample plays a critical role in understanding the results of the measurements. Samples prepared by polishing and sputtering were examined using an electric-field imaging photoelectron microscope (EFIPM), and fractured samples were studied with a magnetic-field imaging photoelectron microscope (MFIPM). While the EFIPM exhibited exellent elemental contrast and resolution, the data were flawed by artifacts introduced by both the polishing and the sputtering. Although the spatial resolution of the MFIPM was lower than the EFIPM, the ability to study fractured samples greatly facilitated interpretation of the data, which revealed the intrinsic chemical states of the sample. These results will be interpreted in terms of the impact of sample preparation on the application of XPEEM to MMCs and other complex systems.