Mid-frequency Range Research Articles

Mid-frequency propagation path analysis on vehicle body using structural intensity

With the penetration of electric vehicles, reduction of structure-borne road noise gets important issue to realize comfortable vehicles for customers.Sound generation mechanism of structure-borne road noise on vehicle body is analyzed basically by modal analysis in low-frequency range. On the other hand, as frequency increases, modal analysis cannot clarify vibration mechanism because vibration wavelength gets shorter, mode density gets high and mode shape gets complicated. Therefore, it is difficult to identify efficient countermeasure parts and inefficient damping materials are added to response panels in mid-frequency range. So alternative analytical methods in mid-frequency range are under research to understand vibration mechanism. In this paper, Structural intensity (SI) analysis is introduced to clarify sound propagation mechanism. This analysis method makes it possible to clarify the main energy propagation path from input point to vibrating panels on vehicle body. The results show that SI analysis unveils the main energy propagation path and gives the opportunity to reduce the panel vibration efficiently by controlling the energy propagation path in body frame structure without damping materials.

Exploring the frequency response of mobile phones applications for sound monitoring in urban green spaces

Citizen science engages non-professional scientists globally in scientific endeavors, fostering commitment to environmental conservation initiatives. This research explores the frequency response of mobile phones for sound monitoring, particularly in the context of urban green spaces. The method involves Laboratory tests at the Brazilian National Metrology Institute, Standardization, and Industrial Quality (Inmetro), evaluating two Android and one iOS devices using the NoiseCapture and Openoise apps. Laboratory tests conform to the frequency response standards outlined in IEC 61672-1, covering the 63Hz to 16kHz range. Following this, the devices captured audio scenes encompassing human, natural, and machine sounds at the University of São Paulo campus. Findings revealed that the frequency response of iPhones functioned as Class 2 sound level meters except for low-frequency bands. Android consistently performed similarly across both applications tested and exhibited acceptable performance in mid-range frequencies. Therefore, when considering citizen science projects, emphasis should be placed on app selection, prioritizing additional features like sound mapping. Field results showed minimal errors from human and transportation sounds but challenges with high-frequency components from birds, insects, and machines. The study concludes the necessity for alternative measurement systems identifying animal sound sources, along with involving non-professional scientists in scientific research.

Study on the effect of thickness on sound absorption performance of foam aluminum

Abstract This paper investigates the effects of different thicknesses on the sound absorption performance of foam aluminum with different pore sizes through a combination of experiments and theoretical research. The results show that the average sound absorption coefficient of small-pore foam aluminum increases with increasing material thickness. As the thickness increases, there is a trend of the peak sound absorption performance shifting towards lower frequencies. In the mid-frequency range, although the sound absorption coefficient increases with the thickness of foam aluminum, the growth rate decreases. The average sound absorption coefficient of large-pore foam aluminum significantly increases with the material thickness and is reflected across various frequency ranges. With the increase in thickness, the sound absorption efficiency also improves, but the rate of improvement gradually slows down after reaching a certain thickness. Samples with the same thickness exhibit different performances in sound absorption coefficient, especially in frequencies above 2000Hz, where these differences are more pronounced. In the high-frequency range, the sound absorption coefficient of 100mm-thick large-pore foam aluminum material approaches 1, approximately 0.95.

Analysis of Bacterial Characteristics Using the Electrical Impedance Spectroscopy Method

Microorganisms have various shapes, structures, and characteristics. This study uses the method of electrical impedance spectroscopy aimed at identifying and comparing the characteristics of Escherichia Coli, Salmonella Typhi, and Staphylococcus Aureus. Measurements from 1 Hz to 100,000 Hz show that Salmonella Typhi has the highest impedance value at low frequencies. In contrast, Escherichia Coli impedance decreases consistently, and Staphylococcus Aureus decreases sharply after 10 Hz. Significant changes are observed in the mid-frequency range of 100 Hz to 1000 Hz, with Salmonella Typhi showing the highest impedance values at 100 Hz compared to Staphylococcus Aureus and Escherichia Coli. At 100 Hz, Salmonella Typhi has the highest impedance value with a mass of 0,06 grams at approximately 39.000 Ohms, 0,08 grams at 35.000 Ohm, and 10 grams at 34.000 Ohm. This is followed by Staphylococcus Aureus, with a mass 0f 0,06 grams having an impedance value of 23.000 Ohms, 0,08 grams having a high impedance value of 31.000 Ohm, and 0,10 grams having an impedance value of 15.000 Ohm. Escherichia Coli, with a mass of 0.06 grams, has an impedance value of 9.000 Ohms, 0,08 grams with an impedance value of 5.000 Ohms, and 0,10 grams has an impedance value of 5.000 Ohms. Electrical Impedance Spectroscopy is effective for identifying and comparing Escherichia coli, Staphylococcus aureu, and Salmonella typhi as the intrinsic characteristics of bacterial cells more influence impedance than bacterial mass.

Design and experimental validation of a finite-size labyrinthine metamaterial for vibro-acoustics: enabling upscaling towards large-scale structures.

In this article, we present the design and experimental validation of a labyrinthine metamaterial for vibro-acoustic applications. Based on a two-dimensional unit cell, different designs of finite-size metamaterial specimens in a sandwich configuration including two plates are proposed. The design phase includes an optimization based on Bloch-Floquet analysis with the aims of maximizing the band gap and extruding the specimens in the third dimension while keeping the absorption properties almost unaffected. By manufacturing and experimentally testing finite-sized specimens, we assess their capacity to mitigate vibrations in vibro-impact tests. The experiments confirm a band gap in the low- to mid-frequency range. Numerical models are employed to validate the experiments and to examine additional vibro-acoustic load cases. The metamaterial's performances are compared with benchmark solutions, usually employed for noise and vibration mitigation, showing a comparable efficacy in the band gap region. To eventually improve the metamaterial's performance, we optimize its interaction with the air and test different types of connections between the metamaterial and the homogeneous plates. This finally leads to metamaterial samples largely exceeding the benchmark performances in the band gap region and reveals the potential of interfaces for performance optimization of composed structures.This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1)'.

Wideband circularly polarized reconfigurable metasurface antenna for 5G applications

Abstract A framework of a metasurface (MTS) – based wideband circularly polarized (CP) reconfigurable antenna for fifth generation (5G) wireless systems operating in the sub-6 GHz mid-frequency range is presented in this article. The proposed structure contains a simple patch antenna, which serves as the primary source, a shorting pin, two ring slots, and a metasurface superstrate. The shorting pin and two ring slots produce perturbation resulting in circular polarization with a narrow axial ratio (AR) bandwidth. A metasurface (MTS) superstrate composed of 4 × 4 rectangular patches stacked over the primary source antenna generates additional resonances that significantly improve the −10 dB impedance and 3 dB axial ratio (AR) bandwidth. Two PIN diodes are employed to alter the circular polarization between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). The prototype is made using an FR-4 epoxy substrate and has an overall size of 50 mm × 35 mm × 4.2 mm. The antenna has a −10 dB bandwidth of 44 % (4.0–6.2) and a 3 dB axial ratio bandwidth of 28 % (4.2–5.6). It also has a 3 dB beam width of 74° and 85° in the E and H planes, a gain of 7.1 dBi, cross-polar isolation of more than 15 dB, and a unidirectional radiation pattern. The simulated and measured results confirm that the implemented antenna is promising for sub-6 GHz 5G communication systems, particularly cognitive radio, wireless body area networks (WBAN), and satellite communication systems.

Data-driven hybrid modelling of waves at mid-frequencies range: Application to forward and inverse Helmholtz problems

In this paper, we introduce a novel hybrid approach that leverages both data and numerical simulations to address the challenges of solving forward and inverse wave problems, particularly in the mid-frequency range. Our method is tailored for efficiency and accuracy, considering the computationally intensive nature of these problems, which arise from the need for refined mesh grids and a high number of degrees of freedom. Our approach unfolds in multiple stages, each targeting a specific frequency range. Initially, we decompose the wave field into a grid of finely resolved points, designed to capture the intricate details at various wavenumbers within the frequency range of interest. Importantly, the distribution of these grid points remains consistent across different wavenumbers. Subsequently, we generate a substantial dataset comprising 1,000 maps covering the entire frequency range. Creating such a dataset, especially at higher frequencies, can pose a significant computational challenge. To tackle this, we employ a highly efficient enrichment-based finite element method, ensuring the dataset’s creation is computationally manageable. The dataset which encompasses 1000 different values of the wavenumbers with their corresponding wave simulation will be the basis to train a fully connected neural network. In the forward problem the neural network is trained such that a wave pattern is predicted for each value of the wavenumber. To address the inverse problem while upholding stability, we introduce latent variables to reduce the number of physical parameters. Our trained deep network undergoes rigorous testing for both forward and inverse problems, enabling a direct comparison between predicted solutions and their original counterparts. Once the network is trained, it becomes a powerful tool for accurately solving wave problems in a fraction of the CPU time required by alternative methods. Notably, our approach is supervised, as it relies on a dataset generated through the enriched finite element method, and hyperparameter tuning is carried out for both the forward and inverse networks.

Analysis of a film-forming amine response in impedance spectra

In this study, a detailed analysis of the dielectric response of a film-forming amine (1,3 N-oleyl propanediamine (OLDA)) in impedance spectra is presented, addressing both “bulk” OLDA and adsorbed OLDA layer on a carbon steel surface. The dielectric response of the “bulk” OLDA in the absence of electrolyte over an extensive temperature range (-150 °C to 50 °C) was explored by broadband dielectric spectroscopy (BDS). Subsequently, the response of the OLDA adsorbed layer on the steel surface was analysed by electrochemical impedance spectroscopy (EIS), for various immersion times (2 min to100 min) and temperatures (25 °C to 75 °C) in an aqueous NaCl solution.Impedance spectra (BDS and EIS), interpreted through the complex conductivity formalism, showed a resistive behaviour in the mid-frequency range and a capacitive behaviour at higher frequencies. The high frequency capacitive response in EIS spectra was shown to contain contributions from the OLDA layer and from the electrochemical double layer, as well. The temperature dependency of the OLDA conductivity was found to be similar to the temperature dependency of the electrolyte resistance, suggesting that the electrolyte (water and ions) crossed the OLDA layer to reach the steel surface. The presence of gauche defects in the OLDA alkyl chain, revealed by polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) analyses, may be a contributing factor to the disorder in the adsorbed layer, facilitating electrolyte infiltration.

Word frequency and cognitive effort in turns-at-talk: turn structure affects processing load in natural conversation.

Frequency distributions are known to widely affect psycholinguistic processes. The effects of word frequency in turns-at-talk, the nucleus of social action in conversation, have, by contrast, been largely neglected. This study probes into this gap by applying corpus-linguistic methods on the conversational component of the British National Corpus (BNC) and the Freiburg Multimodal Interaction Corpus (FreMIC). The latter includes continuous pupil size measures of participants of the recorded conversations, allowing for a systematic investigation of patterns in the contained speech and language on the one hand and their relation to concurrent processing costs they may incur in speakers and recipients on the other hand. We test a first hypothesis in this vein, analyzing whether word frequency distributions within turns-at-talk are correlated with interlocutors' processing effort during the production and reception of these turns. Turns are found to generally show a regular distribution pattern of word frequency, with highly frequent words in turn-initial positions, mid-range frequency words in turn-medial positions, and low-frequency words in turn-final positions. Speakers' pupil size is found to tend to increase during the course of a turn at talk, reaching a climax toward the turn end. Notably, the observed decrease in word frequency within turns is inversely correlated with the observed increase in pupil size in speakers, but not in recipients, with steeper decreases in word frequency going along with steeper increases in pupil size in speakers. We discuss the implications of these findings for theories of speech processing, turn structure, and information packaging. Crucially, we propose that the intensification of processing effort in speakers during a turn at talk is owed to an informational climax, which entails a progression from high-frequency, low-information words through intermediate levels to low-frequency, high-information words. At least in English conversation, interlocutors seem to make use of this pattern as one way to achieve efficiency in conversational interaction, creating a regularly recurring distribution of processing load across speaking turns, which aids smooth turn transitions, content prediction, and effective information transfer.

The acoustic-vibration characteristics of cylindrical roller bearings with raceway failures: Simulation and experiment

This paper presents a mathematical model for cylindrical roller bearings, the precision noise test and simulation investigation are employed, the discussion focuses on the systematic investigation of the vibration characteristics, noise properties, and noise transmission attributes of defective bearings. The findings indicate that severe displacement oscillations of rollers and oil film oscillations can be observed due to the raceway fault, the average slip rate of rollers is seriously affected, resulting in a reduction in the operational stability of the cage. The noise shock is also introduced, which is primarily reflected in the mid-frequency range (670–8000 Hz) of the spectrum, leading to a deviation from the normal distribution of noise data points. This characteristic makes it challenging to detect noticeable shock signals when testing bearing noise at a distance. This research holds the promise of deepening comprehension of faulty bearing dynamics, thereby furnishing richer means for precise fault diagnosis.

Fidelity of Finite Element–Based Virtual Tire Assembly Models Used for Vehicle Noise, Vibration, and Harshness Structural-Borne Noise Performance Considering Vibrational Modal and Steady-State Dynamic Simulation

ABSTRACT The increasing presence of battery electric vehicles brings about new challenges to the noise, vibration, and harshness performance of tires. One of the new challenges involves the expansion of frequency range for structural-borne noise virtual predictions. Current standard virtual tire simplifies the tire geometry as an axisymmetric body, neglecting the effect of complex tread pattern. It is perceived that this simplification can lead to prediction error for a tire’s structural-borne noise performance at mid-frequency range (250∼500 Hz). This study investigates how different tread pattern representation affects the structural-borne noise prediction. This study uses linear, steady-state dynamics finite element simulations of a modified SAE J2710 test and traveling sinusoid test. The resulting frequency responses of the virtual tires and the computational time to obtain each frequency response are compared. The comparison shows that while including the 3D tread pattern does show some differences under certain conditions, it is not necessary to use this technique for every case, especially during the early evaluation stage.

Aerodynamic noise analysis of tilting rotor in edgewise flow conditions

This paper presents a comprehensive experimental analysis of the noise characteristics of an isolated tilt-rotor system under edgewise flight conditions. The investigation explores the effect of rotor tilt on noise and aerodynamics using flow velocity, thrust, and far-field noise measurements. Flow field results show that as the tilting angles vary, there is a change in speed over the rotor blade surface, which influences vortex formation and wake attributes. The far-field noise spectra revealed a significant decrease in sound pressure level with increasing tilt angle, predominantly evident in both the high-amplitude tonal peaks and the broadband signal within the low-to-mid frequency range. The directivity patterns of the overall sound pressure level also demonstrated a reduction in magnitude with the tilting of the rotor. This reduction was observed consistently across all top-plane observation points, with a monopole directivity trend. Meanwhile, in the side plane array, the decrease was primarily evident above the plane of rotation with a dipole directivity pattern. The radiation direction at which the minimum sound pressure level occurs was identified near the rotation plane, irrespective of the tilt angle. Furthermore, the time-dependent noise analyses revealed dominant and persistent signal characteristics at the blade passing frequency, whereas the mid-frequency range exhibited more intermittent behaviour, and the high-frequency range indicated transient characteristics.

PowerScout: Security-Oriented Power Delivery Network Modeling for Side-Channel Vulnerability Analysis

The growing complexity of modern electronic systems leads to the design of more sophisticated power delivery networks (PDNs). Similar to other system-level shared hardware resources, the on-board PDN unintentionally introduces side channels across design layers and voltage domains which are not explicitly specified in the functional specification. Recent works have demonstrated that the exploitation of the side channel can compromise the system security such as information leakage and fault injection. In this work, we systematically investigate the PDN-based side channel as well as potential countermeasures. To facilitate this goal, we develop PowerScout, a security-oriented PDN simulation framework that unifies the modeling of different PDN-based side-channel attacks. PowerScout performs a fast nodal analysis of complex PDNs at the system level to quantitatively evaluate the severity of side-channel vulnerabilities. With the support of PowerScout, for the first time, we validate PDN side-channel attacks in the literature via simulation. Furthermore, we are able to quantitatively measure the security impact of PDN parameters and configurations. For example, towards information leakage, removing near-chip capacitors can increase intra-chip information leakage by a maximum of 23.23 dB at mid-frequency range and inter-chip leakage by an average of 31.68 dB at mid- and high-frequency range. Similarly, the optimal toggling frequency and duty cycle are derived to achieve fault injection attacks with higher success rate and more precise control. In addition, the vulnerabilities are evaluated when hiding-based countermeasures are implemented. Based on the evaluation, we can understand the optimal defense configuration and explore the trade-off between information leakage mitigation and power supply stability.

Analysis of wavy leading-edge noise reduction and source mechanism in rod-airfoil interactions

Inspired by the wings of owls and the tubercles present on humpback whales' flippers, leading-edge serrations have demonstrated the potential to mitigate airfoil–turbulence interaction noise. To deepen our understanding of the underlying mechanisms driving this noise reduction, we conducted compressible large-eddy simulations on a rod-airfoil configuration equipped with wavy leading edges (WLEs) of varying amplitudes. All tested serrations exhibited some degree of noise reduction, with the amplitude of the WLE exerting a significant influence on the overall noise reduction effect. Notably, the wavy airfoil with the largest amplitude demonstrated the most substantial noise reduction in the mid-frequency range, achieving a remarkable decrease in up to 2.2 dB in noise levels. Applying multi-process acoustic theory, we delved into sound production on surfaces and near-field structures responsible for generating noise sources. Our findings underscore a crucial mechanism contributing to noise reduction—the source cutoff effects manifested through the significant weakening of noise sources at hill regions along the serrations' surface. Stronger source cutoff effects were observed with larger WLE amplitudes. Furthermore, our study reveals that destructive relationships among sources also play a pivotal role in reducing flow noise. The reduction in mid-frequency noise results from a synergy of the source cutoff effect and destructive source relationships induced by WLEs, while the decrease in low-frequency noise primarily emanates from the source cutoff effect.

Vibroacoustic metamaterial for enhanced Sound Transmission Loss with variable frequency range designed for serial production

Recently, vibroacoustic metamaterials have been broadly investigated, especially for noise and vibration mitigation. By creating a band gap effect in flexural wave propagation in a base element, metamaterials improve its vibroacoustic parameters in low and mid frequency range while preserving low mass and structure dimensions. While the foundational assumptions and lab validations highlight the advantages of these metamaterials, the practical application of these structures in real-world scenarios remains a challenge. The main aspect that is widely investigated is achieving maximum effectiveness while maintaining the simplicity of geometry to optimize mass production costs. This work presents a vibroacoustic metamaterial design with geometry adapted to serial production using injection molding. The proposed geometry allows for adjusting the effective frequency range of the structure after the production process. Due to the distinctive configuration of the elements and the grouping of unit cells, the design facilitates the generation of broadband and multi-band structures as well. Numerical simulations were employed to assess the impact of the proposed metamaterial on Sound Transmission Loss and other vibroacoustic parameters. Experimental validation of prototype effectiveness was conducted through Sound Reduction Index measurements in a diffuse field.

Numerical investigation of seismic amplification characteristics in loess ridge region of Xiji, northwest China.

The seismic effects on sloped terrain, which are of paramount importance for engineering design and earthquake risk mitigation, have always been a central focus of earthquake engineering research. In this study, generalized geometric models of loess ridges at varying heights were created, and a three-dimensional nonlinear numerical model was established using FLAC3D. Seismic ground motion time histories at different frequencies and actual earthquake ground motion records were input into the model to analyze the peak acceleration amplification effects experienced by the surface of loess ridges when subjected to SV waves. The study's outcomes reveal that seismic amplification on the slopes of loess ridges is characterized by non-linearity with respect to slope height. Instead, it exhibits rhythmic variations, with the rate of change in these rhythms increasing in correspondence with the frequency of seismic motion and the height of the slope. Under low-intensity seismic motion, a linear increase in acceleration amplification is observed at the ridge's crest concerning the height of the loess ridge. However, under high-intensity seismic motion, the relationship between amplification and slope height becomes less significant. Typically, the peak acceleration at the ridge's crest is reported to be 1.5 to 2.5 times that observed at the slope's base. The amplification effect at the ridge's crest is more pronounced in the low-frequency and high-frequency segments when compared to the mid-frequency range. Conversely, significant amplification is observed in the high-frequency range in the lower sections of the slope near the base. It is further noted that the amplification effect at the ridge's crest displays distinct behavior at different frequencies, characterized by narrow frequency bands of maximum amplification, with peak amplification factors exceeding 10 in some cases. These research findings have practical significance and provide valuable references for engineering construction and seismic risk mitigation planning in loess regions.

Perception of voice cues in school-age children with hearing aids.

The just-noticeable differences (JNDs) of the voice cues of voice pitch (F0) and vocal-tract length (VTL) were measured in school-aged children with bilateral hearing aids and children and adults with normal hearing. The JNDs were larger for hearing-aided than normal-hearing children up to the age of 12 for F0 and into adulthood for all ages for VTL. Age was a significant factor for both groups for F0 JNDs, but only for the hearing-aided group for VTL JNDs. Age of maturation was later for F0 than VTL. Individual JNDs of the two groups largely overlapped for F0, but little for VTL. Hearing thresholds (unaided or aided, 500-400 Hz, overlapping with mid-range speech frequencies) did not correlate with the JNDs. However, extended low-frequency hearing thresholds (unaided, 125-250 Hz, overlapping with voice F0 ranges) correlated with the F0 JNDs. Hence, age and hearing status differentially interact with F0 and VTL perception, and VTL perception seems challenging for hearing-aided children. On the other hand, even children with profound hearing loss could do the task, indicating a hearing aid benefit for voice perception. Given the significant age effect and that for F0 the hearing-aided children seem to be catching up with age-typical development, voice cue perception may continue developing in hearing-aided children.

Development of sound-absorbing materials from rice straw

This paper primarily studies the potential of using agricultural waste, specifically rice straw, as a sustainable material for sound absorption in interior spaces. The acoustic properties of rice straw were characterized and compared to traditional sound-absorbing materials. Rice straw was found to have a high sound absorption coefficient in the mid-frequency range. The material was also environmentally friendly, as it is an agricultural waste product and can be easily replenished. This study does not need to use chemicals. Thus, the recycled paper was used as the binder. The results of this study indicate that rice straw mixed with recycled paper can be a cost-effective and sustainable alternative to traditional sound-absorbing materials.

A basic study on sound absorption characteristics of disordered hyperuniform periodic structures

Disordered hyperuniform systems are exotic states of matter that cover the intermediate regime between random and periodic structures. Despite appearing disordered and isotropic, they possess a hidden long-range order. Our study aims to develop disordered hyperuniform microperiodic structures that combine short-scale randomness and long-scale periodicity, making them versatile and useful for sound-absorbing materials, such as wall panels. To construct these structures, we generate a large number of three-dimensionally random waves within a specific frequency range, while applying periodic boundary conditions. Using the finite element method, we analyze the sound absorption of the hyperuniform structures. Compared to simple Gaussian random fluctuations, we observe an increase in surface area, resulting in higher airflow resistivity, and a rise in the sound absorption coefficient within the low to mid frequency range.

Research and sound quality analysis of little theaters in Guangdong universities

Little theaters have become a new type of theater form with their low investment costs, diverse space designs, and rich performance genres. In this paper the building acoustic design is focused on as a key point to research the audience hall space, the spatial shape, stage form and audience hall seating capacity in little theaters, and it is explored that the applicability of such new audience hall spaces to domestic theater design guidelines. One of the typical little theaters is studied by ODEON simulation. The simulation results show that the mid-frequency value of reverberation time (T30) is higher, which is not meet with the mid-frequency range of the domestic theater design guidelines for reverberation time.