Mid-frequency Region Research Articles

Development of Ultrasensitive Biomimetic Auditory Hair Cells Based on Piezoresistive Hydrogel Nanocomposites.

With an ageing population, hearing disorders are predicted to rise considerably in the following decades. Thus, developing a new class of artificial auditory system has been highlighted as one of the most exciting research topics for biomedical applications. Herein, a design of a biocompatible piezoresistive-based artificial hair cell sensor is presented consisting of a highly flexible and conductive polyvinyl alcohol (PVA) nanocomposite with vertical graphene nanosheets (VGNs). The bilayer hydrogel sensor demonstrates excellent performance to mimic biological hair cells, responding to acoustic stimuli in the audible range between 60 Hz to 20 kHz. The sensor output demonstrates stable mid-frequency regions (∼4-9 kHz), with the greatest sensitivity as high frequencies (∼13-20 kHz). This is somewhat akin to the mammalian auditory system, which has remarkable sensitivity and sharp tuning at high frequencies due to the "active process". This work validates the PVA/VGN sensor as a potential candidate to play a similar functional role to that of the cochlear hair cells, which also operate over a wide frequency domain in a viscous environment. Further characterizations of the sensor show that increasing the sound amplitude results in higher responses from the sensor while taking it to the depth drops the sensor outputs due to attenuation of sound in water. Meanwhile, the acoustic pressure distribution of sound waves is predicted through finite element analysis, whereby the numerical results are in perfect agreement with experimental data. This proof-of-concept work creates a platform for the future design of susceptible, flexible biomimetic sensors to closely mimic the biological cochlea.

Low- and mid-frequency wall-pressure sources in a turbulent boundary layer

Abstract

Vibroacoustic performance assessment of aircraft panels in low, mid and high frequency regimes

In the present work, vibroacoustic (VA) characteristics, namely sound transmission loss (STL), overall sound pressure levels (OASPLs) of aircraft panels made up of aluminum, composites and fiber metal laminates (FML) are studied. The investigation involves modeling of aircraft panels using finite element method (FEM) for low frequency, Boundary Element Method (BEM) for mid-frequency and statistical energy analysis (SEA) in high-frequency bands. To obtain the VA characteristics of the panels, twin chambers, namely source and receiver are numerically modeled, and the panels are placed in between them. The VA performances of the considered panels under low, mid and high-frequency sound environments are numerically simulated using an infinite duct model. The sound source in low, mid and high frequency is modeled in the source chamber as sound pressure, plane wave and diffusive acoustic field, respectively and the receiver chamber is idealized as an anechoic chamber at the ends. This numerical study helps in understanding the VA behavior of aircraft materials and also minimizes the cost and time involved in conducting experiments. The results are presented in the form of STL and OASPL. From this study, it was found that the aluminum and fiber metal laminates have good VA characteristics when compared to composites in all the three frequency regimes and composite panels behaving better in the mid-frequency region of 200 Hz to 300 Hz than aluminum and fiber metal laminates. An optimization approach for aircraft panels is also presented.

High temperature impedance spectroscopy study of KTaO3 (001) single crystal

Dielectric, impedance, electric modulus, and ac conductivity properties of KTaO3 (001) (KTO) single crystal have been investigated for temperature and frequency range of 573–973 K and 100 Hz - 1 MHz, respectively. Our results suggest two separate conduction processes attributed to bulk and the sample surface-electrode interface. The analysis of impedance and electrical modulus data shows a temperature-independent relaxation process dominated by delocalized charge carriers in bulk. For temperatures ≥ 773, Intriguing tailing behaviour at lower frequencies observed in Nyquist plots for impedance, and it has been attributed to the sample surface-electrode interface effect. The ac conductivity obeys Jonscher’s Power Law for temperatures<773 K. However, for temperatures ≥773, the ac conductivity exhibits an anomalous behaviour in the low-frequency region as ac conductivity decreases with an increase in frequency up to a critical point in the mid-frequency region. A conduction mechanism has been proposed to explain the electrical response related to bulk and sample surface-electrode interface. Thermally activated vacancies are responsible for bulk conduction. However, migration of K+ ions from bulk to surface at higher temperatures and consequent formation of KO islands is accountable for forming an additional conduction channel at the sample surface-electrode interface. Our topographical AFM images support the formation of KO islands at the KTO surface at higher temperatures. X-ray diffraction results confirm a single crystalline bulk phase of the sample even after high temperature annealing. Our study reveals that the cation (K+) role should be taken into account along with conventional anion vacancies hopping in bulk to gain an overall understanding of the high temperature impedance spectroscopy measurements of KTO.

Monitoring the Isothermal Dehydration of Crystalline Hydrates Using Low-Frequency Raman Spectroscopy.

Detection of the solid-state forms of pharmaceutical compounds is important from the drug performance point of view. Low-frequency Raman (LFR) spectroscopy has been demonstrated to be very sensitive in detecting the different solid-state forms of pharmaceutically relevant compounds. The potential of LFR spectroscopy to probe the in situ isothermal dehydration was studied using piroxicam monohydrate (PXM) and theophylline monohydrate (TPMH) as the model drugs. The dehydration of PXM and TPMH at four different temperatures (95, 100, 105, and 110 °C and 50, 60, 70, and 80 °C, respectively) was monitored in both the low- (20-300 cm-1) and mid-frequency (335-1800 cm-1) regions of the Raman spectra. Principal component analysis and multivariate curve resolution were applied for the analysis of the Raman data. Spectral differences observed in both regions highlighted the formation of specific anhydrous forms of piroxicam and theophylline from their respective monohydrates. The formation of the anhydrous forms was detected on different timescales (approx. 2 min) between the low and mid-frequency Raman regions. This finding highlights the differing nature of the vibrations being detected between these two spectral regions. Computational simulations performed were also in agreement with the experimental results, and allowed elucidating the origin of different spectral features.

Numerical investigation of the vibro-acoustic response of functionally graded lightweight square panel at low and mid-frequency regions

The focus of this paper is to investigate numerically the vibro-acoustic responses of functionally graded lightweight square panel (FGLSP) made from Al/Al2O3 with various boundary conditions (BCs). The approach of analysis is restricted to low and mid-frequency regions. First-order shear deformation theory and finite element method are employed to model the vibro-acoustic response of the FGLSP. Its properties vary along its thickness and are obtained by the Voigt’s rule of mixture as well as a simple power law distribution. Modal responses of pristine aluminium material (PAM) obtained analytically and experimentally are used to validate the numerical approximation of modal responses of PAM. These results are used to compare the numerical results of FGLSP and the first twelve mode shapes are obtained for all BCs. A comparison of the result shows that at low and mid-frequency regions, the sound transmission loss of FGLSP is higher than the conventional PAM. The study reveals that FGLSP can compete favourably with their pristine material counterparts. This material are particularly useful for noise reducing casings which surround noisy devices, household appliances or industrial machines, and limit noise transmission to the environment.

Robust image watermarking based on generative adversarial network

Digital watermark embeds information bits into digital cover such as images and videos to prove the creator's ownership of his work. In this paper, we propose a robust image watermark algorithm based on a generative adversarial network. This model includes two modules, generator and adversary. Generator is mainly used to generate images embedded with watermark, and decode the image damaged by noise to obtain the watermark. Adversary is used to discriminate whether the image is embedded with watermark and damage the image by noise. Based on the model Hidden (hiding data with deep networks), we add a high-pass filter in front of the discriminator, making the watermark tend to be embedded in the mid-frequency region of the image. Since the human visual system pays more attention to the central area of the image, we give a higher weight to the image center region, and a lower weight to the edge region when calculating the loss between cover and embedded image. The watermarked image obtained by this scheme has a better visual performance. Experimental results show that the proposed architecture is more robust against noise interference compared with the state-of-art schemes.

Extraction of winding parameters for 33/11 kV, 30 MVA transformer based on finite element method for frequency response modelling.

This paper proposes an alternative approach to extract transformer’s winding parameters of resistance (R), inductance (L), capacitance (C) and conductance (G) based on Finite Element Method (FEM). The capacitance and conductance were computed based on Fast Multiple Method (FMM) and Method of Moment (MoM) through quasi-electrostatics approach. The AC resistances and inductances were computed based on MoM through quasi-magnetostatics approach. Maxwell's equations were used to compute the DC resistances and inductances. Based on the FEM computed parameters, the frequency response of the winding was obtained through the Bode plot function. The simulated frequency response by FEM model was compared with the simulated frequency response based on the Multi-conductor Transmission Line (MTL) model and the measured frequency response of a 33/11 kV, 30 MVA transformer. The statistical indices such as Root Mean Square Error (RMSE) and Absolute Sum of Logarithmic Error (ASLE) were used to analyze the performance of the proposed FEM model. It is found that the simulated frequency response by FEM model is quite close to measured frequency response at low and mid frequency regions as compared to simulated frequency response by MTL model based on RMSE and ASLE analysis.

Dielectric, impedance, and modulus spectroscopic studies of lanthanum-doped nickel spinel ferrites NiLaxFe2-xO4 nanoparticles

A series of lanthanum (La)-doped nickel (Ni) ferrites NiLaxFe2-xO4 with doping concentrations (x = 0.0, 0.01, 0.02, 0.03, 0.04, and 0.05) is synthesized via a sol–gel auto-combustion method. Structural properties are determined with the help of X-ray diffraction (XRD). The effect of La doping on dielectric properties of Ni ferrites is discussed. XRD analysis confirms the existence of pure FCC spinel phase, and no impurity phase was detected. The lattice constant decreases initially due to strain produced by La3+ ions replacement. At higher doping concentrations, the lattice constant increases due to the large ionic radius of La3+ as compared to Fe3+. Tangent loss (tanδ), dielectric constant, and dielectric loss values are determined in the 1 MHz to 3 GHz frequency range, and explained by the Maxwell–Wagner model. A persistent behavior of dielectric loss and dielectric constant was found in the mid microwave frequency region. The most stable behavior of the dielectric constant (e′) and dielectric loss (e″) in the high-frequency region is found with (x = 0.04). Ac conductivity is also discussed in the 1 MHz to 3 GHz region, and is found to be impacted by grain and grain boundary resistive behavior at low and high frequencies. Cole–Cole plots of different samples, corresponding to different doping concentrations, are used to describe the conduction phenomena. The stable response of dielectric constant (e′) and dielectric loss (e″) in the mid microwave frequency region makes NiLaxFe2-xO4 nanoparticles a potential candidate for microwave devices.

Acoustic–structure modeling and analysis of an engineering machinery cab based on the hybrid method and experimental investigations

To study the mid-frequency acoustic–structure in the cab of construction machinery vehicle, a prediction model was established based on the FE–SEA hybrid method. Model parameters, such as the modal density, the internal loss factor and the coupling loss factor of each subsystem, were calculated by the theoretical methods. The sound pressure excitation and vibration excitation of the model obtained through the real vehicle experimental tests and the mid-frequency vibration characteristics of the cab in the frequency range of 100–800 Hz under composite excitation were studied. In order to verify the accuracy of the hybrid model, the full FE acoustic–structure coupling model of the cab was also established, and the modal calculation of the cab was carried out. In the end, the two methods were verified by the real sound pressure test in the cab. The results show that the hybrid model has a great deviation from the experimental results in the low-frequency region of 20–80 Hz, and the calculation accuracy is lower than that of the FE model. The prediction accuracy starts to rise when frequency is higher than 80 Hz; especially in the mid-frequency region of 100–800 Hz, the hybrid model accuracy reaches the highest with results basically consistent with the experiment. In addition, in the high-frequency range, higher than 800 Hz, the prediction results also agree well with the experimental ones. It should be pointed out that the hybrid model cannot accurately capture the peak value of the response in the noise prediction, but it can guarantee the accuracy, improve the calculation efficiency and improve the prediction accuracy in the mid-frequency region.

A novel hybrid deterministic-statistical approach for the mid-frequency vibro-acoustic problems

It is difficult to predict precisely the frequency response of a complex vibro-acoustic system in mid-frequency region. To overcome this deficiency, a novel hybrid stable node-based smoothed finite element method/statistical energy analysis model is proposed in this work. The whole vibro-acoustic system can be divided into a combination of a structural subsystem with statistical behavior and an acoustic subsystem with deterministic feature. The recently developed stable node-based smoothed finite element method is employed here to simulate the deterministic subsystem, and the statistical energy analysis is utilized to deal with the statistical subsystem. Based on the so-called diffuse field reciprocity relation, these two subsystems can be easily connected and coupled. Due to the introducing of gradient smoothing and compensation operation, our algorithm can significantly reduce the dispersion error compared with the traditional finite element method. Thus, it is expected that the present coupled model can provide ultra-accurate results. Numerical examples, including both benchmark and practical engineering cases, demonstrate that our algorithm works very well in mid-frequency vibro-acoustic analysis.

The research on amorphous coatings for future GW detectors

The high mechanical losses of the multilayer reflecting coating deposited on the mirror surface account for the main contribution to the thermal noise, limiting the sensitivity in the mid-frequency region of the detection band of the future gravitational waves detectors. Several European laboratories of the Virgo Collaboration have joined their efforts to improve the coating mechanical performances. The research lines of this collaboration are all focused on amorphous coatings, which represent a viable solution for the future GW detector generations. The main target is to find a way to reduce by a factor three the mechanical losses of the coating for the next generation of room temperature operating detectors. Some activities are also meant to be relevant for cryogenic operations. The status of this collaborative work will be described as well as the latest results of the different research lines.

Electrochemical impedance spectroscopy study of lithium-rich material 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 in the first two charge-discharge cycles

Lithium-rich material 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 is successfully prepared by a co-precipitation method. Electrochemical impedance spectroscopy (EIS) is measured under various charge/discharge voltages in the first and second cycles. A reasonable equivalent circuit model is designed for EIS analysis and the fitting curves are aligned well with the experimental curves, suggesting that the proposed equivalent circuit model is an ideal model for lithium battery. According to the analysis on the shape changes of the semicircle in high-frequency and mid-frequency regions during the charging and discharging process, it can be considered that the lithium-rich material is a composite structure of Li2MnO3 phase and LiNi1/3Co1/3Mn1/3O2 phase after its preparation, but it becomes a solid solution structure after the first charging process. The changes of Rct also support above conclusions. According to the changes of the straight line in the low-frequency region and the changes of RSEI during the charging and discharging process, it can be confirmed that the solid electrolyte interphase (SEI) film on the surface of the cathode is gradually formed during the first charging process, and it has been very stable and has stable Li+ migration ability after two cycles. The calculation results of Li+ solid-phase diffusion coefficient also supports above conclusions.

Double deletion of Panx1 and Panx3 affects skin and bone but not hearing.

Pannexins (Panxs), large-pore channel forming glycoproteins, are expressed in a wide variety of tissues including the skin, bone, and cochlea. To date, the use of single knock-out mouse models of both Panx1 and Panx3 have demonstrated their roles in skin development, bone formation, and auditory phenotypes. Due to sequence homology between Panx1 and Panx3, when one Panx is ablated from germline, the other may be upregulated in a compensatory mechanism to maintain tissue homeostasis and function. To evaluate the roles of Panx1 and Panx3 in the skin, bone, and cochlea, we created the first Panx1/Panx3 double knock-out mouse model (dKO). These mice had smaller litters and reduced body weight compared to wildtype controls. The dKO dorsal skin had decreased epidermal and dermal area as well as decreased hypodermal area in neonatal but not in older mice. In addition, mouse skull shape and size were altered, and long bone length was decreased in neonatal dKO mice. Finally, auditory tests revealed that dKO mice did not exhibit hearing loss and were even slightly protected against noise-induced hearing damage at mid-frequency regions. Taken together, our findings suggest that Panx1 and Panx3 are important at early stages of development in the skin and bone but may be redundant in the auditory system. KEY MESSAGES: Panx double KO mice had smaller litters and reduced body weight. dKO skin had decreased epidermal and dermal area in neonatal mice. Skull shape and size changed plus long bone length decreased in neonatal dKO mice. dKO had no hearing loss and were slightly protected against noise-induced damage.

Measurement of mid-frequency wavefront error for large optical components with ptychography.

In a high power laser system, the wavefront quality of large optical components in the mid spatial frequency band plays a critical role in system performance and safe operation. A simple and efficient method based on ptychography is used to measure mid-frequency wavefront error, which has the advantages of simple structure, strong anti-interference ability, flexible frequency-range selection, and low cost. It has excellent frequency response in the entire mid-frequency region. The transfer function is demonstrated to be greater than 0.7 at 1/2 Nyquist frequencies (8.33 mm-1) for 60mm field-of-view experimentally. The method has been successfully applied to the wedged focused lens (WFL) to achieve high-fidelity measurement. Without any auxiliary lens, the power spectrum of the WFL at the frequency of interest is obtained through large-aperture measurement. This technique is especially suitable for optical components difficult to be measured using interferometers and opens up a new perspective for measuring mid-frequency wavefronts.

Winding turn‐to‐turn short‐circuit diagnosis using FRA method: sensitivity of measurement configuration

Frequency response analysis (FRA) is increasingly being accepted as an effective technique to diagnose transformer faults. Transformer electric parameters are affected by such faults in a complex manner, and there is yet no standard approach for interpretation of FRA results. Most studies have focused on diagnosing winding and core deformations, but subtle defects in the winding insulation and turn-to-turn short circuits can develop into a more serious fault, and their early diagnosis is equally important. Furthermore, there are several test configurations which have different sensitivities to different faults. This study reports a study where the winding input impedance is measured to diagnose turn-to-turn short circuits using different measurement configurations. A comparison is made between the sensitivities of each measurement configuration to faults of increasing severity. It is found that this fault is detected in the low- and mid-frequency regions as significant reduction in impedance and a shift in resonance peaks towards high frequencies. The results, analysed using different statistical parameters, indicate differences in sensitivities with different levels of short circuits. Marginal variations were found between the sensitivities of statistical parameters in different frequency regions. The study provides useful contribution into interpretation of FRA signatures for turn-to-turn short-circuit diagnosis of transformers.

Energy harvesting and self-powered microphone application on multifunctional inorganic-organic hybrid nanogenerator

Piezoelectric nanogenerators are forthcoming alternative choices for scavenging different types of wasted mechanical energies. An inorganic-organic hybrid piezoelectric nanogenerator (HPNG) has been realized by incorporating zinc sulphide nanorods (ZnS-NRs) into electrospun poly(vinylidene fluoride) (PVDF) nanofibers for self-powered multifunctional sensing. As an acoustic energy harvester, the HPNG possesses a resonance frequency of 86 ± 3 Hz and an acoustic sensitivity of ∼3 V Pa−1. It can distinguish sound waves from low to mid frequency region that makes it suitable for noise detection. In addition, HPNG demonstrates the very high wind energy conversion efficiency of ∼58% that make it capable of detecting human exhalation. Apart from its noise detection and power generation capabilities, HPNG is possible to use as a self-powered microphone. This electromechanical coupling, integrated with their flexibility, makes it usable as a flexible electro-acoustic sensor for security purpose as well. These results establish the potential of hybrid piezoelectric structure, with their multi functionalities for several promising applications such as noise detection, wind energy harvesting, security monitoring and most promisingly to develop the self-powered system.

Investigating the Capacitive Inter-Winding Response of Power Transformer

This paper presents an investigation on the occurrence of oscillation in the frequency response of transformer due to aging process. The frequency response was obtained using frequency response analysis (FRA) test and capacitive inter-winding test configuration. It has been reported that, there is abnormal occurrence to the frequency response after some period of operating time. The response shows a small oscillation at the mid-frequency region. Although, this oscillation was not there at first measured response. Therefore, three case studies are presented to investigate this occurrence, the measurement, the transfer function mathematical equation and the developed circuit. The case studies of the transfer function and the developed circuit are simulated using MATLAB and being compared with the actual measured response. The parameters that control the mid–frequency oscillation are also studied. The oscillation occurred at mid-frequency region is related with the actual condition of the transformer experiencing aging process. The new finding provides an understanding on the factors that affecting transformer aging. It is believed that, thermal, moisture and oil degradation are the main contributors of transformer aging process. Therefore, the significance of this study is to present the relationship between occurrence of mid-frequency oscillation and transformer aging condition.

Constructing a quadratic-exponential FIR-filter with an extended frequency response midrange

This article is concerned with synthesizing filter with finite impulse response (FIR-filters) employed to correct radially symmetric distortions such as defocusing. We propose a new parametric class of finite impulse response filters (FIR-filters) based on a model of the one-dimensional radially symmetric frequency response. In the proposed method, the one-dimensional frequency response is composed of quadratic and exponential functions. The two-dimensional impulse response of the filter is constructed by sampling one-dimensional impulse responses for all directions. The development consists in introducing an extended mid-frequency region of the frequency response, thus increasing the contribution of the frequencies to image correction. Examples are given in order to illustrate the possibility of the high-quality distortion correction. In particular, it is shown that the proposed method provides the restoration quality higher than that obtained when using an optimal Wiener filter (taken from OpenCV).

Direct comparison of low- and mid-frequency Raman spectroscopy for quantitative solid-state pharmaceutical analysis

This study considers the potential of low-frequency (terahertz) Raman spectroscopy in the quantitative analysis of ternary mixtures of solid-state forms. Direct comparison between low-frequency and mid-frequency spectral regions for quantitative analysis of crystal form mixtures, without confounding sampling and instrumental variations, is reported for the first time. Piroxicam was used as a model drug, and the low-frequency spectra of piroxicam forms β, α2 and monohydrate are presented for the first time. These forms show clear spectral differences in both the low- and mid-frequency regions. Both spectral regions provided quantitative models suitable for predicting the mixture compositions using partial least squares regression (PLSR), but the low-frequency data gave better models, based on lower errors of prediction (2.7, 3.1 and 3.2% root-mean-square errors of prediction [RMSEP] values for the β, α2 and monohydrate forms, respectively) than the mid-frequency data (6.3, 5.4 and 4.8%, for the β, α2 and monohydrate forms, respectively). The better performance of low-frequency Raman analysis was attributed to larger spectral differences between the solid-state forms, combined with a higher signal-to-noise ratio.