Admittance Magnitude Research Articles

Reflection function, reflectance, and area function measurements in ears of children and adults.

The main experiment concerned time-domain measurements of the acoustical reflection function (RF) of the human ear in adults and children (aged 5 to 8 years) using a probe inserted into the ear canal. This RF was used to calculate the area function of the ear canal versus distance along its centerline. Acoustical reflectance was calculated in the frequency domain from the RF, as was the difference in sound pressure level near the tympanic membrane relative to the probe tip. Group responses in area function, total ear-canal length, absorbance and group delay, and admittance magnitude and phase were analyzed based on sex, ear, and age. Responses were compared between children/adults and younger/older adults relative to age 50 years. Ear and sex were never significant. Significant differences were observed in children compared to adults in the area function, absorbance and group delay, and admittance magnitude and phase (0.25-4 kHz). Group delay differed between younger and older adults. A second experiment assessed level dependence of responses to better understand limitations in probe performance observed in the main experiment. These results show the utility of time-domain measurements of the area function and derived reflectance to understand sound-transmission differences across age at frequencies important to middle-ear function.

A novel estimation methodology for multi-resonance equivalent inductance of transformer winding for inter-turn short-circuit fault detection

A novel, indirect measurement technique for estimating equivalent inductance associated with multi-resonance behavior of an isolated transformer winding is reported for both healthy and inter-turn short-circuit fault-condition. For healthy winding, the authors proposed measuring two unique admittance magnitude responses of the winding followed by utilizing their natural frequencies for estimating the said inductance. Here, the one response is for line-end excitation with neutral-end grounded and the other one is for two equal and opposite polarity excitations from two ends of the winding. For inter-turn shorting, driving-point admittance magnitude response with neutral-end open is also utilized. This inductance seems to be one important parameter for verifying the design constraint mainly for impulse behavior as well as for identifying inter-turn shorting of the winding. The proposed method was also verified by experimental measurements on two actual transformer windings; one of which incorporated an iron core within it. All pertinent analytical derivations and the associated results are also included in the paper.

Wideband acoustic immittance in superior semicircular canal dehiscence

ObjectiveThe apparent effect of superior semicircular canal dehiscence (SSCD) on middle ear- and cochlear impedance has led researchers to investigate the use of wideband acoustic immittance as a screening tool when SSCD is suspected. The purpose of the study was to describe the absorbance characteristics and tympanometric values of ears with confirmed SSCD measured at tympanometric peak pressure (TPP) and at ambient pressure. MethodsWideband Acoustic Immittance was performed at ambient pressure and at TPP on ten participants (12 ears) with confirmed SSCD, as well as on an age- and gender matched control group (12 ears). Inferential statistics were used to determine whether statistical differences existed for the absorbance values at each of the averaged frequencies, the resonance frequency (RF) and tympanometric data between the SSCD and control groups. ResultsThe mean absorbance of the SSCD group reached a maximum at 890.9 Hz and a minimum at 6349.6 Hz. When testing absorbance at TPP, a statistically significant increase/peak in the absorbance values of the SSCD group (compared to those of the control group) was found from 630 to 890.9 Hz and a decrease from 4489.8 to 6349.6 Hz. Similar patterns were observed for absorbance at ambient pressure. A lower mean RF for ears with SSCD as well as an increased mean admittance magnitude (AM) value at RF was found compared to those of the control group. ConclusionThe use of SSCD as a screening tool when SSCD is suspected was strengthened by results similar to those of previous studies. As a result of the significant difference in RF of SSCD ears compared to the RF of the control group, the potential value of measuring the RF of the middle ear to differentiate between mass-and stiffness dominated pathologies, was also illustrated.

Structural Damage Detection through EMI and Wave Propagation Techniques Using Embedded PZT Smart Sensing Units.

Lead Zirconate Titanate (PZT) sensors have become popular in structural health monitoring (SHM) using the electromechanical impedance (EMI) technique for damage identification. The vibrations generated during the casting process in concrete structures substantially impact the conductance signature’s (real part of admittance) magnitude and sensitivity. The concept of smart sensing units (SSU) is presented, composed of a PZT patch, an adhesive layer, and a steel plate. It is embedded in the concrete structure to study the impact of damage since it has high sensitivity to detect any structural changes, resulting in a high electrical conductance signature. The conductance signatures are obtained from the EMI technique at the damage state in the 10–500 kHz high-frequency range. The wave propagation technique proposes implementing the novel embedded SSUs to detect damage in the host structure. The numerical simulation is carried out with COMSOL multiphysics, and the received voltage signal is compared between the damaged and undamaged concrete beam with the applied actuation signal. A five-cycle sine burst modulated by a Hanning window is employed as the transient excitation signal. For numerical investigation, six cases are explored to better understand how the wave travels when a structural discontinuity is accounted for. The changes in the received signal during actuator–receiver mode in the damage state of the host structure are quantified using time of flight (TOF). Furthermore, the numerical studies are carried out by combining the EMI-WP technique, which implies synchronous activation of EMI-based measurements and wave stimulation. The fundamental idea is to implement EMI-WP to improve the effectiveness of SSU patches in detecting both near-field and far-field damage in structures. One SSU is used as an EMI admittance sensor for local damage identification. Meanwhile, the same EMI admittance sensor is used to acquire elastic waves generated by another SSU to monitor damages outside the EMI admittance sensor’s sensing area. Finally, the experimental validation is carried out to verify the proposed methodology. The results show that combining both techniques is an effective SHM method for detecting damage in concrete structures.

Theory for influence of ohmic resistance and electrode roughness on admittance voltammetry of reversible E and EE reactions

• Admittance voltammetric response for E and EE processes is influenced by roughness. • Random roughness is modeled through power spectrum of roughness. • Diffusion and uncompensated solution resistance are non-linearly coupled phenomena. • Characteristic peaks in admittance voltammetric response depend on finite fractal roughness. • Work emphasize on the enhanced sensitivity of this technique for E and EE processes. The theory is developed for the admittance voltammetry of reversible EE process under the influence of uncompensated solution resistance at random and fractally rough electrode. The theory accounts for the influence of random roughness through the power spectrum of roughness. The finite fractal model, with its three response controlling statistical parameters, viz. fractal dimension ( D H ), topothesy length ( ℓ τ ) or width of the interface and lower cut-off length ( ℓ ), is used to analyze the admittance voltammogram. DC biased admittance response of a rough electrode is determined by an interplay of morphological and phenomenological length scales. The characteristic phenomenological length scales of processes involved are diffusion length ( D / ω ) and DC bias dependent diffusion-ohmic coupling length ( L Ω ). These characteristic lengths significantly influence the potential dependent magnitude of admittance at a given temporal frequency or scan rate. The characteristic electron transfer admittance voltammetric peaks are significantly influenced by roughness in intermediate and high-frequency scans, i.e., ω > D/( L Ω 2 + ℓ τ 2 ). Similarly, at sufficiently low frequency, ω < D/( L Ω 2 + ℓ τ 2 ), the influence of roughness diminishes around the admittance peaks. The uncompensated solution resistance suppresses the height of admittance peaks and also alters the value of peak width at half peak height of both the electron transfer steps in moderately and strongly supported systems.

Wind events in a subtropical coastal upwelling region as detected by admittance analysis

Wind dominates the ocean surface circulation in the subtropical coastal upwelling regions. Although the wind events in these regions are mostly favorable for upwelling, other types of wind events are occasionally dominant. The typical patterns and statistics of wind events over the waters off northern Baja California are described. The identification of wind events was carried out using a systematic technique based on both the admittance magnitude and phase. This technique proved useful and has some of the crucial characteristics expected from a classification standpoint. This technique is applied to 29 years (1990–2018) of cross-calibrated multiplatform (CCMP) 10-m wind data. Equatorward along the coast (upwelling-favorable), offshore (Santa Ana), onshore, poleward along the coast (downwelling-favorable), and relaxation events are identified. The wind stress and wind stress curl mean fields and the statistics of occurrence are described on a year-to-year and month-to-month basis for each wind type. The upwelling-favorable and relaxation events are the most frequent and occur throughout the year; the typical duration is 4 and 1.5 days, respectively. The offshore (Santa Ana), onshore, and poleward wind events are sporadic and occur only during autumn-winter. The year-to-year variation of the frequency of occurrence of the equatorward wind events shows no trend during the study period.

Optimized Design of OTA-Based Gyrator Realizing Fractional-Order Inductance Simulator: A Comprehensive Analysis

A detailed analysis of an operational transconductance amplifier based gyrator implementing a fractional-order inductance simulator is presented. The influence of active element non-ideal properties on the gyrator operation is investigated and demonstrated by admittance characteristics and formulas for important values and cut-off frequencies in these characteristics. Recommendations to optimize the performance of the gyrator in terms of operation bandwidth, the range of obtainable admittance magnitude, and signal dynamic range are proposed. The theoretical observations are verified by PSpice simulations of the gyrator with LT1228 integrated circuit.

Theory for admittance voltammetry of reversible two step electron transfer process with DC bias at rough and fractal electrodes

We developed a phenomenological theory for DC-bias dependent electrochemical impedance response and admittance voltammetry of reversible two-step electron transfer (EE) process at randomly rough and fractal electrodes. The power spectrum of roughness is used to incorporate the statistical information of surface randomness. For the finite fractal model, statistical morphological parameters of roughness, viz., fractal dimension (DH), topothesy length (ℓτ) and lower cut-off length (ℓ), significantly influence the admittance response. The magnitude of admittance increases with an increase in the roughness of fractal electrode (e.g. increase in the value of DH or ℓτ or decrease in ℓ) for both the electron transfer steps. The magnitude of admittance with the variation of DC potential at fixed temporal frequency unravels the multi-electron transfer process. The two step electron transfer process has two characteristic peaks in their plot. The enhanced roughness of electrode increases the height of the admittance peaks and the regions around it (obtained at different fixed frequencies). Our theory is validated with experimental data for the ethyl viologen system at a moderately rough Pt electrode. Finally, our current methodology for admittance voltammetry has the dual advantage of impedance as well as of voltammetry.

Reverse Design of Ultrasonic Absorptive Coating for the Stabilization of Mack Modes

The effects of ultrasonic absorptive coating (UAC) admittance on the first and second modes in a high-speed boundary layer are analyzed using linear stability theory. It is shown that the growth rate of the first mode is increased as UAC admittance phase varies from to , whereas the second mode is amplified when tends to and damped if . The frequency range of the first mode is broadened when is in the vicinity of , and the second mode shifts to low frequencies when . Moreover, the stabilization or destabilization effects on Mack modes, frequency band broadening, and frequency shifting are promoted by large UAC admittance magnitudes. Based on the requirements of the admittance phase and magnitude for the stabilization of Mack modes, a design strategy for UAC is proposed to stabilize the second mode in a wide frequency range with the first mode little amplified.

Normative Wideband Acoustic Immittance Measurements in Caucasian and Aboriginal Children.

Purpose The aims of this study were to develop normative data for wideband acoustic immittance (WAI) measures in Caucasian and Australian Aboriginal children and compare absorbance measured at 0 daPa (WBA0) and tympanometric peak pressure (TPP; WBATPP) between the 2 groups of children. Additional WAI measures included resonance frequency, equivalent ear canal volume, TPP, admittance magnitude (YM), and phase angle (YA). Method A total of 171 ears from 171 Caucasian children and 87 ears from 87 Aboriginal children who passed a test battery consisting of 226-Hz tympanometry, transient evoked otoacoustic emissions, and pure tone audiometry were included in the study. WAI measures were obtained under pressurized conditions using wideband tympanometry. Data for WBA0, WBATPP, YM, and YA were averaged in one-third octave frequencies from 0.25 to 8 kHz. Results There was no significant ear effect on all of the 7 measures for both groups of children. Similarly, there was no significant gender effect on all measures except for WBATPP in Aboriginal children. Aboriginal boys had significantly higher WBATPP than girls at 1.5 and 2 kHz. A significant effect of ethnicity was also noted for WBATPP at 3, 4, and 8 kHz, with Caucasian children demonstrating higher WBATPP than Aboriginal children. However, the effect size and observed power of the analyses were small for both effects. Conclusion This study developed normative data for 7 WAI measures, namely, WBA0, WBATPP, TPP, Veq, RF, YM, and YA, for Caucasian and Aboriginal children. In view of the high similarity of the normative data between Caucasian and Aboriginal children, it was concluded that separate ethnic-specific norms are not required for diagnostic purposes.

Admittance Model for Three-phase AC Micro-grid with Unbalanced Load Compensated by the Multi-functional Grid-connected Inverter

The admittance model for the three-phase AC micro-grid is proposed in the paper considering the imbalance of the local load and active compensation of the multi-functional grid-connected inverter (MFGCI). By adopting complex variables, the model unified the positive-sequence and negative-sequence admittances for both the grid-connected inverter and the load. Moreover, the dq transformation based imbalance compensation algorithm is integrated into the model according to the harmonic linearization principle. The theoretical analysis and simulation verify the accuracy of the proposed admittance model. The analysis also indicates that while the adoption of the active compensation can decrease the imbalance of the system, the magnitude and phase characteristics of the equivalent admittance of the compensated load are significantly changed. The admittance model proposed in this paper can be the foundation work for the system stability study for the AC micro-grid.

Development of a Diagnostic Prediction Model for Conductive Conditions in Neonates Using Wideband Acoustic Immittance.

Wideband acoustic immittance (WAI) is an emerging test of middle-ear function with potential applications for neonates in screening and diagnostic settings. Previous large-scale diagnostic accuracy studies have assessed the performance of WAI against evoked otoacoustic emissions, but further research is needed using a more stringent reference standard. Research into suitable quantitative techniques to analyze the large volume of data produced by WAI is still in its infancy. Prediction models are an attractive method for analysis of multivariate data because they provide individualized probabilities that a subject has the condition. A clinically useful prediction model must accurately discriminate between normal and abnormal cases and be well calibrated (i.e., give accurate predictions). The present study aimed to develop a diagnostic prediction model for detecting conductive conditions in neonates using WAI. A stringent reference standard was created by combining results of high-frequency tympanometry and distortion product otoacoustic emissions. High-frequency tympanometry and distortion product otoacoustic emissions were performed on both ears of 629 healthy neonates to assess outer- and middle-ear function. Wideband absorbance and complex admittance (magnitude and phase) were measured at frequencies ranging from 226 to 8000 Hz in each neonate at ambient pressure using a click stimulus. Results from one ear of each neonate were used to develop the prediction model. WAI results were used as logistic regression predictors to model the probability that an ear had outer/middle-ear dysfunction. WAI variables were modeled both linearly and nonlinearly, to test whether allowing nonlinearity improved model fit and thus calibration. The best-fitting model was validated using the opposite ears and with bootstrap resampling. The best-fitting model used absorbance at 1000 and 2000 Hz, admittance magnitude at 1000 and 2000 Hz, and admittance phase at 1000 and 4000 Hz modeled as nonlinear variables. The model accurately discriminated between normal and abnormal ears, with an area under the receiver-operating characteristic curve (AUC) of 0.88. It effectively generalized to the opposite ears (AUC = 0.90) and with bootstrap resampling (AUC = 0.85). The model was well calibrated, with predicted probabilities aligning closely to observed results. The developed prediction model accurately discriminated between normal and dysfunctional ears and was well calibrated. The model has potential applications in screening or diagnostic contexts. In a screening context, probabilities could be used to set a referral threshold that is intuitive, easy to apply, and sensitive to the costs associated with true- and false-positive referrals. In a clinical setting, using predicted probabilities in conjunction with graphical displays of WAI could be used for individualized diagnoses. Future research investigating the use of the model in diagnostic or screening settings is warranted.

Robust Admittance Shaping Approach to Grid Current Harmonic Attenuation and Resonance Damping

This paper presents a novel grid current control of a grid-connected voltage source converter with an LCL filter. The proposed control method uses an $\mathcal {H}_\infty$ synthesis method to shape the input admittance of the converter, to track a given current reference, and/or to limit the controller actuation at different frequency ranges. The converter admittance is shaped, both in magnitude and phase, following a model reference defined by the designer in the frequency domain. By specifying a low admittance magnitude reference, the optimization algorithm will obtain a controller that actively damp the filter resonance and attenuate/reject the grid voltage oscillations, either in a wide frequency range or concentrated at the main harmonic frequencies. Additionally, the proposed controller design methodology takes advantage of its admittance phase shaping capability to improve the system robustness in front of grid uncertainties and minimizing converter impact over grid stability due to its positive-real nature. The synthesized controller only measures the grid current and voltage to achieve the aforementioned results, reducing the number of sensors (and their associated cost) required for its implementation. Experimental results illustrate the correct behavior of the closed-loop system with the designed controller in time and frequency domain.

A microfluidic device for motility and osmolality analysis of zebrafish sperm.

A microfluidic chip is described that facilitates research and quality control analysis of zebrafish spermwhich, due to its miniscule (i.e., 2-5 μl) sample volume and short duration of motility (i.e., <1min), present a challenge for traditional manual assessment methods. A micromixer molded in polydimethylsiloxane (PDMS) bonded to a glass substrate was used to activate sperm samples by mixing with water, initiated by the user depressing a transfer pipette connected to the chip. Sample flow in the microfluidic viewing chamber was able to be halted within 1s, allowing for rapid analysis of the sample using established computer-assisted sperm analysis (CASA) methods. Zebrafish sperm cell activation was consistent with manual hand mixing and yielded higher values of motility at earlier time points, as well as more subtle time-dependent trends in motility, than those processed by hand. Sperm activation curves, which indicate sample quality by evaluating percentage and duration of motility at various solution osmolalities, were generated with on-chip microfabricated gold floor electrodes interrogated by impedance spectroscopy. The magnitude of admittance was linearly proportional to osmolality and was not affected by the presence of sperm cells in the vicinity of the electrodes. This device represents a pivotal step in streamlining methods for consistent, rapid assessment of sperm quality for aquatic species. The capability to rapidly activate sperm and consistently measure motility with CASA using the microfluidic device described herein will help improve the reproducibility of studies on sperm and assist development of germplasm repositories.

Phase‐reshaping strategy for enhancing grid‐connected inverter robustness to grid impedance

As the grid inductor increases the phase difference between the inverter admittance and the grid admittance increases at their intersection frequency showing that the harmonic amplification coefficient is enhanced. When the phase difference exceeds 180° the admittance ratio cannot satisfy Nyquist criterion and the system becomes unstable. To address this problem a phase-reshaping strategy aiming to revise the phase of the inverter admittance in a wide frequency region without using any real-time information referring to the grid impedance or the resonant frequency is proposed. The strategy is realised by the combination of the feedforward of the voltage at the point of common coupling (PCC) and the harmonic compensators. In the feedforward, a phase lag network is employed to modify the admittance phase in a wide frequency region. The harmonic compensator in parallel to the current controller is used to offset the magnitude rise brought in by the PCC voltage feedforward. After adopting the proposed strategy, the upper limit of the phase difference is constrained at 150° and the magnitude of the inverter admittance is lower than that of the original one at low-order odd-harmonic frequency. The validity of the proposed strategy is verified by the experimental results.

Normative Study of Wideband Acoustic Immittance Measures in Newborn Infants.

The purpose of this study was to describe normative aspects of wideband acoustic immittance (WAI) measures obtained from healthy White neonates. In this cross-sectional study, wideband absorbance (WBA), admittance magnitude, and admittance phase were measured under ambient pressure condition in 326 ears from 203 neonates (M age = 45.9 hr) who passed a battery of tests, including automated auditory brainstem response, high-frequency tympanometry, and distortion product otoacoustic emissions. Normative WBA data were in agreement with most previous studies. Normative data for both WBA and admittance magnitude revealed double-peaked patterns with the 1st peak at 1.25-2 kHz and the 2nd peak at 5-8 kHz, while normative admittance phase data showed 2 peaks at 0.8 and 4 kHz. There were no significant differences between ears or gender for the 3 WAI measures. Standard deviations for all 3 measures were highest at frequencies above 4 kHz. The 3 WAI measures between 1 kHz and 4 kHz may provide the most stable response of the outer and middle ear. WAI measures at frequencies above 4 kHz were more variable. The normative data established in the present study may serve as a reference for evaluating outer and middle ear function in neonates.

Electrochemical Impedance Spectroscopy of Tethered Bilayer Membranes: An Effect of Heterogeneous Distribution of Defects in Membranes

The study focuses of the electrochemical impedance spectroscopy (EIS) response of tethered bilayer membranes (tBLMs) populated with heterogeneously distributed defects (pores). Such defects are common and may form spontaneously, or they may be produced by pore-forming agents, proteins, protein toxins, and peptides. To model heterogeneity in the populations of defects we assumed a log- normal distribution probability function. We found that the presence of heterogeneity results in specific transformations of EIS spectra compared to the spectra observed in homogeneous systems. These transformations may serve as a qualitative diagnostic criteria for the identification of heterogeneous distribution of defects in the tBLMs. We describe two simple algorithms that allows a quantitative estimation of the parameters determining heterogeneity, the standard deviation of distribution σ and the defect density Ndefo exhibiting the highest probability of occurrence. The first algorithm can be applied for systems populated with small radial defects with the radius smaller than approximately 5nm. In this case the position of the phase minimum in the frequency domain of EIS (admittance) Bode plots is a measure of Ndefo, while the phase value at the minimum is a measure of σ. In the case of large defects such as pore-forming toxins e.g., the cholesterol dependent cytolysins, which exhibit radii larger than approximately 5nm a more complex analysis is required. However, we demonstrate that if the assumption of linearity of the position of the admittance minimum and Ndefo and σ is applicable, then a simple algorithm allows assessing both Ndefo and σ. Finally, we critically assess the widely used term “membrane conductance” (“membrane resistance”), which is typically evaluated by measuring the magnitude of the electrochemical admittance (resistance). We demonstrate that in heterogeneous tBLM systems such a term is ill-defined, because the same number of the same defects (per area) depending on their mode of distribution results in different electrochemical impedance (admittance) magnitude values.

Finite-Element Modelling of the Acoustic Input Admittance of the Newborn Ear Canal and Middle Ear.

Admittance measurement is a promising tool for evaluating the status of the middle ear in newborns. However, the newborn ear is anatomically very different from the adult one, and the acoustic input admittance is different than in adults. To aid in understanding the differences, a finite-element model of the newborn ear canal and middle ear was developed and its behaviour was studied for frequencies up to 2000Hz. Material properties were taken from previous measurements and estimates. The simulation results were within the range of clinical admittance measurements made in newborns. Sensitivity analyses of the material properties show that in the canal model, the maximum admittance and the frequency at which that maximum admittance occurs are affected mainly by the stiffness parameter; in the middle-ear model, the damping is as important as the stiffness in influencing the maximum admittance magnitude but its effect on the corresponding frequency is negligible. Scaling up the geometries increases the admittance magnitude and shifts the resonances to lower frequencies. The results suggest that admittance measurements can provide more information about the condition of the middle ear when made at multiple frequencies around its resonance.

Identifying conductive conditions in neonates using wideband acoustic immittance

Wideband acoustic immittance (WAI) is an innovative method of middle ear assessment with significant advantages over currently available clinical tests. Previous large-scale studies in neonates have assessed accuracy against evoked otoacoustic emissions but further research is needed using a more stringent gold standard. The aim of this study was to evaluate the test performance of WAI in neonates against a composite reference standard consisting of distortion-product otoacoustic emissions (DPOAEs) and high-frequency tympanometry (HFT). Five hundred and five neonates were recruited from the maternity ward of the Townsville Hospital to participate in the study. DPOAEs and HFT were performed on each neonate to assess outer and middle ear function. Wideband absorbance and complex admittance (magnitude and phase) were measured from 226 to 8000 Hz in each neonate at ambient pressure using a click stimulus. Best separation between groups that passed and failed the reference standard occurred at frequencies from...

Nonreciprocal Dyakonov-wave propagation supported by topological insulators

The propagation of Dyakonov waves guided by the planar interface of a columnar thin film and a topological insulator was investigated by numerically solving the associated canonical boundary-value problem. The topological insulator was modeled as an isotropic dielectric material endowed with a nonzero surface admittance. The propagation directions for the Dyakonov waves, as well as the decay constants and phase speeds of the waves, were significantly modulated by varying the magnitude of the surface admittance. Most significantly, a Dyakonov wave propagating along the direction of a vector u_ has a different phase speed and different decay constants as compared with the Dyakonov wave which propagates along the direction of −u_. This nonreciprocity, with respect to interchanging the direction of Dyakonov-wave propagation, is not exhibited when the topological insulator is replaced by an isotropic dielectric material of the same refractive index but with a nonzero surface conductivity instead of a surface admittance.