Impedance Phase Research Articles

Facile manufacturing of sub-mm thick CNT-based RC filters

CNT-Based RC networks are described with the purpose of showing empirical findings on the influence of the interdigitated electrodes (IDE) spacing, the dispersant compound and the number of deposited layers, on the impedance magnitude and phase of the CNTs. Additionally, we propose use-cases for these networks, applying them to the realization of filters of second order with easily tunable cut-off frequency, and with the inherent advantages of CNTs and printed technologies, rendering them a prime choice for applications where thin and flexible second order filters are necessary.

Studies of Radial and Thickness Acoustic Resonance Modes of a Piezoceramic with Mixed Polarization Geometry

In this study, the Pb(Zr0.65Ti0.35)O3 (PZT) structure was produced by the solid state reaction method, and a new polarization geometry was used to obtain the radial and thickness modes in cylindrical samples with more efficiency. The polarization procedure was investigated by varying the temperature from 30°C to 80°C. The experimental excitation of radial and thickness modes was observed, and a comparative study was performed with numerical simulations. The comparative analysis of the acoustic response of the cylindrical PZT samples under theoretical and experimental conditions was validated by COMSOL Multiphysics® software. The new polarization geometry technique was used to generate radial thickness and acoustic mixed modes with more efficiency. The results show that the resonance frequency and antiresonance, as well as the impedance mode and phase angle are well adjusted, showing the validation of the technique presented between the theoretical and experimental measurements.

Bioelectrical Impedance Phase Angle and Its Determinants in Patients with Classic Congenital Adrenal Hyperplasia

Background Patients with congenital adrenal hyperplasia due to 21-hydroxylase deficiency (CAH21OHD) have increased fat mass and metabolic alterations. The bioelectrical impedance phase angle (PhA) is an indicator of cellular integrity in several diseases. This study aimed to determine the influence of adiposity levels, sex, CAH21OHD, pubertal development, body composition, and treatment on the PhA of patients with CAH21OHD. Methods Forty girls and 30 boys with CAH21OHD aged 15.3 ± 5.8 years were evaluated. Sexual maturation was assessed by a pediatrician. The PhA was assessed using bioelectrical impedance, percentage of fat mass (% FM), and lean soft tissue (LST) with dual-energy X-ray absorptiometry. Adiposity levels were compared using % FM tertiles and body mass index (BMI). Glucocorticoid dosage was converted using hydrocortisone dose equivalent (HDE). Results No differences were found in the PhA values among the clinical form (p = 0.103), BMI (p = 0.498), and % FM (p = 0.654) groups. High PhA values were observed in boys (p = 0.011) and postpubertal (p < 0.001) patients. LST, HDE, and height in girls (r2 = 0.68, p < 0.001) and age, HDE, and FM in boys (r2 = 0.82, p < 0.001) determined the PhA variations. BMI explained 14% (p = 0.032) of the PhA variations, whereas LST, height, HDE, and FM (kg) explained 66% (p < 0.001) in the prepubertal, pubertal, and postpubertal groups, respectively. Conclusion LST determined the PhA variations in girls and the postpubertal group. Age and BMI were determinants in boys and the pre- and pubertal groups, respectively.

A Rapid Electrochemical Impedance Spectroscopy and Sensor-Based Method for Monitoring Freeze-Damage in Tangerines

This study focuses on the analysis and early detection of freeze-damage in tangerines using a specific double-needle sensor and Electrochemical Impedance Spectroscopy (EIS). Freeze damage may appear in citrus fruits both in the field and in postharvest processes resulting in quality loss and a difficult commercialization of the fruit. EIS has been used to test a set of homogeneous tangerine samples both fresh and later frozen to analyze electrochemical and biological differences. A double-needle electrode associated to a specifically designed electronic device and software has been designed and used to send an AC electric sinusoidal signal 1 V in amplitude and frequency range [100Hz to 1MHz] to the analyzed samples and then receive the electrochemical impedance response. EIS measurements lead to distinct values of both impedance module and phase of fresh and frozen samples over a wide frequency range. Statistical treatment of the received data set by Principal Components Analysis (PCA) and Partial Least Squares Discriminant Analysis (PLS-DA) shows a clear classification of the samples depending on the experienced freeze phenomenon, with high sensitivity (1.00), specificity (≥ 0.95) and confidence level (95%). Later Artificial Neural Networks (ANN) analysis based on 20-3-1 architecture has allowed to create a mathematical prediction model able to correctly classify 100% of the analyzed samples (CCR =100% for training, validation and test phases, and overall classification), being fast, easy, robust and reliable, and an interesting alternative method to the traditional laboratory analyses.

Effects of Ih and TASK-like shunting current on dendritic impedance in layer 5 pyramidal-tract neurons.

Pyramidal neurons in neocortex have complex input-output relationships that depend on their morphologies, ion channel distributions, and the nature of their inputs, but which cannot be replicated by simple integrate-and-fire models. The impedance properties of their dendritic arbors, such as resonance and phase shift, shape neuronal responses to synaptic inputs and provide intraneuronal functional maps reflecting their intrinsic dynamics and excitability. Experimental studies of dendritic impedance have shown that neocortical pyramidal tract neurons exhibit distance-dependent changes in resonance and impedance phase with respect to the soma. We, therefore, investigated how well several biophysically detailed multicompartment models of neocortical layer 5 pyramidal tract neurons reproduce the location-dependent impedance profiles observed experimentally. Each model tested here exhibited location-dependent impedance profiles, but most captured either the observed impedance amplitude or phase, not both. The only model that captured features from both incorporates hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and a shunting current, such as that produced by Twik-related acid-sensitive K+ (TASK) channels. TASK-like channel density in this model was proportional to local HCN channel density. We found that although this shunting current alone is insufficient to produce resonance or realistic phase response, it modulates all features of dendritic impedance, including resonance frequencies, resonance strength, synchronous frequencies, and total inductive phase. We also explored how the interaction of HCN channel current (Ih) and a TASK-like shunting current shape synaptic potentials and produce degeneracy in dendritic impedance profiles, wherein different combinations of Ih and shunting current can produce the same impedance profile.NEW & NOTEWORTHY We simulated chirp current stimulation in the apical dendrites of 5 biophysically detailed multicompartment models of neocortical pyramidal tract neurons and found that a combination of HCN channels and TASK-like channels produced the best fit to experimental measurements of dendritic impedance. We then explored how HCN and TASK-like channels can shape the dendritic impedance as well as the voltage response to synaptic currents.

The relevance of whole or segmental body bioelectrical impedance phase angle and physical performance in adolescent athletes

Objective. The physical condition of athletes can be assessed easily and quantitatively using objective indicators. Bioelectrical impedance measures the phase angle (PA), representing hydration and cell function, and is a potential clinical indicator of physical condition. This study aimed to investigate the association between PA and physical performance in adolescent athletes. Approach. Overall, 170 adolescent athletes underwent a sports medical check-up, including body composition measurements and physical performance tests. Whole-body and segmental PAs (arm and leg) were determined based on body composition values. Isometric grip power and knee isokinetic muscle strength were measured as parameters of muscle strength. Counter movement jump height and squat jump height were measured as jump parameters. Associations between PA and each muscle strength or jump parameters were analysed using Pearson product-moment correlation coefficient or Spearman’s rank correlation coefficient. Main results. Whole-body and upper limb PAs were highly correlated with grip power (r = 0.70–0.80). Whole-body and lower limb PAs were correlated with knee isokinetic muscle strength (r = 0.43–0.59). Whole and all segmental PAs were correlated with counter movement jump height (r = 0.46–0.57) and squat jump height (r = 0.42–0.52). Significance. PA can be used to monitor physical condition and sports performance in adolescent athletes. Segmental PAs can help assess the condition of the corresponding body part.

Low temperature performance evaluation of electrochemical energy storage technologies

• Low temperature performance of 9 commercial batteries and supercapacitors compared. • Performance loss mainly due to Ionic conductivity and interfacial charge transfer. • Reliable temperature estimation through single frequency phase angle demonstrated. • Optimal pre-heating temperature calculated to maximise cell net energy output. The performance of electrochemical energy storage technologies such as batteries and supercapacitors are strongly affected by operating temperature. At low temperatures (<0 °C), decrease in energy storage capacity and power can have a significant impact on applications such as electric vehicles, unmanned aircraft, spacecraft and stationary power storage. In this work, the discharge behaviour of nine different commercial electrochemical cells are evaluated, representing a variety of lithium-ion, nickel metal hydride, lead acid and supercapacitor technologies. Discharge capacity, energy, maximum power and impedance spectra with equivalent circuit analysis are compared at temperatures ranging from +20 °C to −70 °C. Results demonstrate that despite exhibiting the greatest loss in performance with temperature reduction, the lithium-ion batteries tested provide the highest energy and power densities down to −30 °C due to higher capacity and operating voltage. At lower temperatures, the lead-acid cell gives the highest energy density and supercapacitor the highest power density. A new simplified empirical method is introduced for lithium-ion cells to determine the optimum pre-heating temperature for maximum net energy output including heating efficiency. This new method can be used to assess the benefits of different cold-start thermal management strategies for electric vehicles. It is also demonstrated that the temperature of the lithium-ion cells tested can be accurately predicted from impedance phase change at low temperatures across a range of electrode materials.

Phase angle and standardized phase angle from bioelectrical impedance measurements as a prognostic factor for mortality at 90 days in patients with COVID-19: A longitudinal cohort study

Background & aimsSevere acute COVID-19 has taken on pandemic proportions with growing interest in identification of prognostic factors for mortality. Standardized bioelectrical impedance (BI) phase angle (SPhA), which is PhA adjusted by age and sex, has been related to mortality in patients with several diseases but never investigated in COVID-19. Inflammation, a consequence of COVID-19 infection, affects fluid status (hydration) and can be identified with PhA. The aim of this study was to determine the predictive role of PhA on 90 days survival of adults with COVID-19.MethodsWe studied 127 consecutive patients diagnosed with COVID-19. BI measurements determined with a 50 kHz phase-sensitive BI device, body composition parameters and laboratory markers were evaluated as predictors of mortality.ResultsNon-surviving COVID-19 patients had significantly lower PhA and SPhA values (p < 0.001) and increased hydration (p < 0.001) compared to surviving patients. Patients in the lowest SPhA quartile had increased (p < 0.001) mortality and hospital stay, hyperhydration (p < 0.001), increased inflammation biomarkers [CRP (p < 0.001)], decreased nutritional parameters: body mass cell index [BCMI (p < 0.001) albumin (p < 0.001)], and reduced other biomarkers [D-dimer (p = 0.002)].Multivariate analysis (Cox regression) revealed that PhA and hydration status, adjusted for age, sex, BMI, diabetes, hypertension, dyslipidaemia or heart disease, were associated (p < 0.001) with increased mortality. The hazard ratio was 2.48 (95% CI, 1.60–3.84, p < 0.001) for PhA and 1.12 (95% CI, 1.04–1.20, p = 0.003) for hydration percentage. PhA <3.95° was the cut-off for predicting mortality in acute COVID-19 with 93.8% sensitivity and 66.7% specificity. PhA offers greater sensitivity as a predictive prognostic test at admission, compared to the established analytical parameters of poor prognosis (CRP, lymphocytes, prealbumin).ConclusionsLow PhA (<3.95°), independent of age, sex, BMI, and comorbidities, is a significant predictor of mortality risk in COVID-19. These findings suggest that the evaluation of body composition with single-frequency phase-sensitive BI measurements should be included in the routine clinical assessment of COVID-19 patients at hospital admission to identify patients at increased mortality risk.

Thickness measurement of circular metallic film using single-frequency eddy current sensor

In many advanced industrial applications, the thickness is a critical index, especially for metallic coatings. However, the variance of lift-off spacing between sensors and test pieces affects the measured voltage or impedance, which leads to unreliable results from the sensor. Massive research works have been proposed to address the lift-off issue, but few of them applies to the thickness measurement of planar metallic films with finite-size circular (disk) geometry. Previously, a peak-frequency feature from the swept-frequency inductance was used to compensate the measurement error caused by lift-offs, which was based on the slow-changing rate of impedance phase term in the Dodd-Deeds formulas. However, the phase of measured impedance is nearly invariant merely on a limited range of sample thicknesses and working frequencies. Besides, the frequency sweeping is time-consuming, where a recalibration is needed for different sensor setups applied to the online real-time measurement. In this paper, a single-frequency algorithm has been proposed, which is embedded in the measurement instrument for the online real-time retrieval of thickness. Owing to the single-frequency measurement strategy, the proposed method does not need to recalibrate for different sensor setups. The thickness retrieval is based on a triple-coil sensor (with one transmitter and two receivers). The thickness of metallic disk foils is retrieved from the measured electrical resistance of two transmitter-receiver sensing pairs. Experiments on materials of different electrical conductivities (from direct current), thicknesses and planar sizes (radii) have been carried out to verify the proposed method. The error for the thickness retrieval of conductive disk foils is controlled within 5% for lift-offs up to 5 mm.

High-resolution impedance mapping using electrically activated quantitative phase imaging

Retrieving electrical impedance maps at the nanoscale rapidly via nondestructive inspection with a high signal-to-noise ratio is an unmet need, likely to impact various applications from biomedicine to energy conversion. In this study, we develop a multimodal functional imaging instrument that is characterized by the dual capability of impedance mapping and phase quantitation, high spatial resolution, and low temporal noise. To achieve this, we advance a quantitative phase imaging system, referred to as epi-magnified image spatial spectrum microscopy combined with electrical actuation, to provide complementary maps of the optical path and electrical impedance. We demonstrate our system with high-resolution maps of optical path differences and electrical impedance variations that can distinguish nanosized, semi-transparent, structured coatings involving two materials with relatively similar electrical properties. We map heterogeneous interfaces corresponding to an indium tin oxide layer exposed by holes with diameters as small as ~550 nm in a titanium (dioxide) over-layer deposited on a glass support. We show that electrical modulation during the phase imaging of a macro-electrode is decisive for retrieving electrical impedance distributions with submicron spatial resolution and beyond the limitations of electrode-based technologies (surface or scanning technologies). The findings, which are substantiated by a theoretical model that fits the experimental data very well enable achieving electro-optical maps with high spatial and temporal resolutions. The virtues and limitations of the novel optoelectrochemical method that provides grounds for a wider range of electrically modulated optical methods for measuring the electric field locally are critically discussed.

A Highly Efficient and Linear mm-Wave CMOS Power Amplifier Using a Compact Symmetrical Parallel–Parallel Power Combiner With IMD3 Cancellation for 5G Applications

This paper presents a fully integrated linear power amplifier (PA) in a 65-nm CMOS process for mm-wave 5G applications. The proposed linear PA employs a compact symmetrical 4-way parallel–parallel power combiner with a third-order intermodulation distortion (IMD3) cancellation method to achieve high linear output power with a high power-added efficiency (PAE). An on-chip 4-way parallel–parallel power combiner, which combines the output power from 8-unit PAs, is designed with a compact footprint ( $241\,\,\mu \text{m}\,\,\times 241\,\,\mu \text{m}$ ). Conventional series power-combining transformer based power combiners have poor symmetrical performance for the amplitude and phase of the input impedance among unit PAs owing to the parasitic effects of the power combiners. However, the proposed parallel–parallel power combiner, which is based on parallel power-combining transformer structures, shows good symmetrical performances among unit PAs. Moreover, an IMD3 cancellation method using a parallel–parallel power combiner is proposed in this work. The proposed IMD3 cancellation method can support high-order modulation signals without increasing the complexity and reduce the dependence for digital predistortion (DPD). Consequently, the proposed linearization method obtains a high linear POUT and PAE without DPD. The PA in 65-nm CMOS demonstrates a saturated output power (PSAT) of 23.2 dBm, a 15.9-dB power gain, a 1-dB compressed output power ( $\text{P}_{\mathrm {O,1dB}}$ ) of 22 dBm, and a peak power-added efficiency (PAE) of 33.5% at 28 GHz. The measured error vector magnitude with 100 Msym/s of 256/512-QAM is −31.2/−32.1 dB with average output power of 18.02/17.73 dBm, average PAE of 17.6/16.1%, and adjacent channel power ratio (ACPR) of −30/−33.1 dBc without DPD. To the best of the authors’ knowledge, the proposed PA demonstrates high output power with the highest PAE performance supporting 256/512-QAM compared to the recently published fully integrated mm-wave 5G CMOS PAs.

Fractional-Order Bio-Impedance Modeling for Interdisciplinary Applications: A Review

Bio-impedance circuit modeling is a popular and effective non-invasive technique used in medicine and biology to fit the measured spectral impedance data of living or non-living tissues. The variations in impedance magnitude and/or phase at different frequencies reflect implicit biophysical and biochemical changes. Bio-impedance is also used for sensing environmental changes and its use in the agriculture industry is rapidly increasing. In this paper, we review and compare among the fractional-order circuit models that best fit bio-impedance data and the different methods for identifying the parameters of these circuits. Four different vegetables species (Carrot, Tomato, Zucchini, Cucumber) in three different conditions (fresh, frozen, and heated) are used to demonstrate the differences among these models.

Design and Validation of a Portable AD5933–Based Impedance Analyzer for Smart Agriculture

This paper presents a portable impedance analyzer based on the AD5933 integrated circuit, specifically designed for fruit quality monitoring throughout its entire supply chain. The custom designed system allows to flexibly tune the parameters (i.e. excitation voltage, feedback resistor, settling time) for each AD5933 frequency range from 10Hz to 100kHz, leading to a precise system calibration and consequently, measurement. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FruitMeter</i> runs MicroPython on an STM32 microcontroller, allowing ease of development, advanced low-power mode, and both on-demand and scheduled measurements. The system employs Low-Energy Bluetooth and USB communication with a micro SD data storage which, together with its small size (7.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 4cm in volume) and the 300mAh rechargeable battery with USB recharge, increases the system portability and connectivity, critical for smart agriculture on-field applications. The developed portable system is validated by comparing its performance with a benchtop impedance analyzer with both passive components and fruit samples (apple, avocado, banana, mango and tomato). The comparison resulted in an average Root Mean Square Error (RMSE) of 1.0% and 4.3% for the passive components and of 1.36% and 6.8% for the fruit samples, for impedance magnitude and phase, respectively. We finally validated the system for a real use-case regarding the evaluation of banana aging evolution.

Fundamental Experiment on Invisible Crack Detection of Concrete Covered with Fiber Reinforced Polymer (FRP) through Electrical Impedance Variations and Phase Transition

Fundamental Experiment on Invisible Crack Detection of Concrete Covered with Fiber Reinforced Polymer (FRP) through Electrical Impedance Variations and Phase Transition

Application of Improved Droop Control Based on Grid Impedance in Photovoltaic Grid-Connected Power Generation system

When the power grid impedance mutates, the output power of the grid-connected photovoltaic power generation system controlled by drooping will become very unstable. To solve this problem, an improved droop control algorithm based on network impedance detection is proposed. Taking photovoltaic grid-connected power generation system as the research object, the influence of power grid impedance on traditional droop control is firstly expounded by introducing power grid impedance value into traditional droop control. Then the method of real-time network impedance extraction is introduced. Furthermore, according to the bandwidth and phase angle constraints of the equivalent output impedance phase frequency characteristics of the photovoltaic grid-connected inverter, the controller parameters are updated in real time to achieve the purpose of adaptive network impedance mutation. Finally, the proposed method is tested and verified by real-time simulation in the loop respectively. The results show that the proposed method is correct.

Label-Free Quantification of Cell Cycle Synchronicity of Human Neural Progenitor Cells Based on Electrophysiology Phenotypes.

The ability to coax human-induced pluripotent stem cells (hiPSCs) into human neural progenitor cells (hNPCs) can lead to novel drug discovery and transplant therapy platforms for neurological diseases. Since hNPCs can form organoids that mimic brain development, there is emerging interest in their label-free characterization for controlling cell composition to optimize organoid formation in three-dimensional (3D) cultures. However, this requires the ability to quantify hNPCs in heterogeneous samples with subpopulations of similar phenotype. Using high-throughput (>6000 cells per condition), single-cell impedance cytometry, we present the utilization of electrophysiology for quantification of hNPC subpopulations that are altered in cell cycle synchronicity by camptothecin (CPT) exposure. Electrophysiology phenotypes are determined from impedance magnitude and phase metrics for distinguishing each cell cycle phase, as validated by flow cytometry, for a wide range of subpopulation proportions. Using multishell dielectric models for each cell cycle phase, electrophysiology alterations with CPT dose could be predicted. This label-free detection strategy can prevent loss of cell viability to speed the optimization of cellular compositions for organoid development.

Implementation of output impedance in single‐phase inverters with repetitive control and droop control

A strategy for the implementation of the output impedance in single-phase inverters connected in parallel with droop control for uninterruptible power supply applications is proposed in this study. The proposal allows the load current to be distributed in proportion to the power capacity of the inverters connected in parallel, by establishing the magnitude and phase of the output impedance at the fundamental frequency and its harmonics, when the voltage control is performed through odd harmonic repetitive controllers. This is accomplished through the design of an output impedance profile based on the transfer function of a second-order high-pass filter and a virtual impedance loop. The proposal achieves a correct operation of the droop control strategy and the proper sharing of the harmonics of the non-linear load current between the inverters connected in parallel, obtaining reduced values of individual harmonic content and harmonic distortion in the output voltage with reduced processing requirements. The validity of the proposal is verified through a 2 kVA experimental prototype, considering the requirements of the international quality standards IEC62040-3 and IEC61000-2-2, in terms of output voltage regulation, individual harmonic content, and harmonic distortion for inverters operating both in islanded-mode and in parallel.

Impedance Spectroscopic Analysis of the Interidigitated Flexible Sensor for Bacteria Detection

In this paper we present economical interdigitated flexible sensor on the paper substrate for bacteria detection. The impedance measurement was performed in the frequency range of 12.6 kHz–100 kHz for the suspensions with cell density of $1.5\cdot 10^{8}$ CFU/mL, $1.5\cdot 10^{5}$ CFU/mL and $1.5\cdot 10^{2}$ CFU/mL of Pseudomonas aeruginosa and Staphylococcus aureus bacteria, as well as for a sterile saline. Using the measured impedance data, we observed that sensor impedance magnitude increases when bacteria concentration increases. Moreover, impedance spectroscopic analysis was carried out to identify an equivalent electrical circuit for the sensor modelling. Through statistical analysis it was found that all model parameters changes according to the bacteria type and concentration. Additionally, obtained results showed that all fittings results in root mean square errors lower than $0.072~\Omega $ for impedance magnitude, and 0.157° for impedance phase angle.

Refining Measurements of Power Absorbance in Newborns: Probe Fit and Intrasubject Variability.

Because unresolved debris in the ear canal or middle ear of newborns may produce high false positive rates on hearing screening tests, it has been suggested that an outer/middle ear measure can be included at the time of hearing screening. A potential measure is power absorbance (absorbance), which indicates the proportion of power in a broadband acoustic stimulus that is absorbed through the outer/middle ear. Although absorbance is sensitive to outer/middle dysfunction at birth, there is large variability that limits its accuracy. Acoustic leaks caused by poor probe fitting further exacerbate this issue. The objectives of this work were to: (1) develop criteria to indicate whether a change in absorbance occurs in association with probe fit; (2) describe the variability in absorbance due to poor fitting; and (3) evaluate test-retest variability with probe reinsertions, excluding poor fits. An observational cross-sectional design was used to evaluate changes in absorbance due to probe fit and probe reinsertion. Repeated measurements were recorded in 50 newborns (98 ears) who passed TEOAE screenings and were <48 hours of age. One absorbance measurement was chosen as the baseline that served as a best-fit reference in each ear. Changes in absorbance, called absorbance probe-fit Δ, were calculated relative to the baseline in each ear. Correlations were assessed between the absorbance probe-fit Δ and low-frequency absorbance, impedance magnitude, impedance phase, and equivalent volume, to determine which measures predicted poor fits. Criteria were derived from the strongest of these correlations and their performance was analyzed. Next, measurements with poor/leaky fits were identified, and the changes in absorbance that they introduced were analyzed. Excluding the poor fits, test-retest differences in absorbance, called reinsertion Δ, were determined. Variability was assessed using the SDs associated with absorbance, absorbance probe-fit Δ, and reinsertion Δ. Based on the analysis of 12 moderate-strong correlations, the following criteria were adopted to identify measurements with poor fits: (1) impedance phase-based criterion (500 to 1000 Hz) > -0.11 cycles and (2) absorbance-based criterion (250 to 1000 Hz) > 0.58. Poor-fit measurements introduced statistically significant increases in absorbance up to 0.1 for 1000 to 6000 Hz, and up to 0.4 for frequencies <1000 Hz. Reinsertion Δ were ≤0.02, and were significant for 500 to 5000 Hz. The SDs of absorbance probe-fit Δ were greatest and similar to overall absorbance SD in the low frequencies. Separately, the SDs of reinsertion Δ were also greatest and similar to low-frequency absorbance SD. Poor probe fits introduced the greatest inflation in absorbance for frequencies < 500 Hz, and a smaller but significant inflation for higher frequencies, consistent with controlled experiments on acoustic leaks in adults. Importantly, inflation of absorbance in diagnostically sensitive 1000 to 2000 Hz may impact its clinical performance. Test-retest with probe reinsertion contributed significantly to absorbance variability, especially in the low frequencies, consistent with reports in adults, even though changes were smaller than those associated with poor probe fit. The results indicate that variability in absorbance was reduced by minimizing acoustic leaks. Pending further validation, the probe-fit criteria developed in this work can be recommended to ensure proper probe fit.

A novel H-plane loaded on a double-staggered grating waveguide slow-wave structure for W-band traveling-wave tubes

A novel H-plane loaded on a double-staggered grating waveguide (DSGW) slow-wave structure (SWS) is proposed. The main advantage of this SWS is its high interaction impedance and low phase velocity, based on which higher output power can be expected. Electromagnetic characteristics and particle-in-cell simulations were performed using CST Microwave Studio software. The dispersion diagram of the SWS was optimized for a central frequency of 94 GHz which corresponds to a beam voltage of 13.2 kV in the second spatial harmonic (2 $$\pi$$ –3 $$\pi$$ ). A sheet electron beam with a current of 200 mA is used to interact with the longitudinal electric field. The reflection signal at the input port is below −15 dB for frequencies of 89–98 GHz and a small-signal gain of 35 dB is achieved at the output port for a tube length of 80 mm.