Acoustic Test Research Articles

Determining the effects of timber strength and wood species on the mechanical properties of CLT using non-destructive and destructive methods

ABSTRACT This study aimed to determine the effects of production parameters such as wood species and timber strength classes on some mechanical properties of CLT panels using both non-destructive and destructive methods. Additionally, the study compared the strength values obtained from non-destructive and destructive testing methods on CLT panels and elucidated the relationship between them through regression analyses. CLT panels were produced using spruce and alder timbers, as well as hybrid panels formed from combinations of these two wood species. According to the TS EN 338 standard, the C and D strength classes of the timbers were determined non-destructively using an acoustic testing device. Among the timbers whose strength classes were determined, a total of 6 different strength classes were selected for spruce and alder. The bending strength, modulus of elasticity, and screw withdrawal force tests were performed on the CLT panel groups both non-destructive and destructive. As a result of the regression analyzes, the determination coefficient (R2) between non-destructive screw withdrawal force and destructive bending strength values varied between 0.6135–0,9997. Moreover, the R2 value calculated between non-destructive and destructive modulus of elasticity values for CLT panels was found to be between 0.7076–0.9997.

Determining the Extent of damage in Snapped Southern Yellow Pine Trees with Acoustic Testing

Abstract Salvage of downed timber following a windstorm allows recovery of management options for landowners and wood products for industry. Because wood volumes are large and logging, transportation, mill storage, and processing capacities are limited, avoiding the selection of logs with damage can conserve those resources. Visual damage indicators are typically used to select and differentiate products, but damaged logs are still delivered to mills. Following experimental tree winching in 2021 and a tornado in 2023, we assessed lengths of broken trees with a Fakopp microsecond timer. Using a recognized defect limit (10% deviation from the maximum acoustic velocity) about 80 percent of volume in broken tops could be recovered. Standard rules of thumb applied from the end of visible damage resulted in the recovery of about 50 percent of the volume with a relatively low defect rate (<10%). Applying bucking rules developed from acoustic measurements based on distance from snap might be easier to apply and increase recovery rates to over 70 percent of broken top volume.

Evaluating the association between developmental language disorder and depressive symptoms in preschool children

This study aims to investigate the association between developmental language disorder (DLD) and depressive symptoms in preschool-aged children, building upon previous research that has demonstrated emotional difficulties in children with DLD. Forty-one children with DLD or children at risk for DLD (DLD group) and 41 children with typical language development (TLD) were included in this study. Language development was evaluated using the TEDIL test which is a Turkish adaptation of the Test of Early Language Development-3. Auto acoustic Emissions Testing and Immittance-Metric Assessment were used to exclude children with hearing impairment. Developmental delays were excluded by Denver Developmental Screening Test II. Mothers filled out the Sociodemographic Data Form and the Child Depressive Symptoms Assessment Scale. The results demonstrate that children in DLD group scored significantly higher on the Child Depressive Symptoms Assessment Scale, manifesting increased levels of aggression, separation anxiety, impulsivity, hyperactivity, and encountering greater social adaptation difficulties and deterioration in cognitive processes than TLD. Multivariate regression analysis suggests that increased impulsivity and hyperactivity, alongside social and cognitive challenges, are predictors of DLD. The study concludes that depressive symptoms are more prevalent in children in DLD group than in their typically developing counterparts. These findings underscore the necessity for targeted psychiatric and pedagogical interventions, as well as individualized educational programs that cater to the socio-emotional and cognitive needs of children with DLD.

Experimental investigation on aerodynamic noise of a small-scale multi-blade centrifugal fan

In this study, the aerodynamic noise of a small-scale centrifugal fan was experimentally investigated using acoustic testing techniques and time-resolved stereoscopic particle image velocimetry (SPIV). During the acoustic experiments, both far-field noise and near-field pressure fluctuations of the test fan were measured. The overall far-field noise towards the fan inlet side was found to be higher than that of the back side. The pressure fluctuations on the fan upper casing exceeded those on the side wall due to the uncontracted volute tongue, indicating pronounced flow-to-wall interactions. Moreover, based on a simultaneous measurement, the coherence between the near-field pressure fluctuations and far-field noise highlighted the significant contributions of impeller rotation to noise radiation. SPIV measurements uncovered the time-averaged and transient flow fields at the fan's inlet and outlet. The time-averaged results demonstrated the concentrated inlet flow and outlet flow separation, leading to high flow unsteadiness. Transient flow fields displayed an asymmetric jet-wake region characterized by both quasi-steady flow and rotational flow behaviours. The instantaneous flow results were analyzed using the dynamic mode decomposition (DMD) method, which clearly recognized the jet-wake patterns with frequencies corresponding to the rotational frequency. The observed consistency in frequency characteristics among noise, pressure fluctuations, and unsteady flow affirms that flow dynamics are crucial to the primary noise mechanisms.

The Auditory Steady-State Response and the Relationship between Electrophysiological and Behavioural Thresholds.

This study examined the relationship between behavioural thresholds as measured by pure tone audiometry and electrophysiological thresholds measured by the Auditory Steady-State Response (ASSR) in children with normal hearing and sensorineural hearing loss. After being assessed, 45 children of both sexes, ranging in age from 5 to 15, were split into four groups: 10 with moderate to moderately severe sensorineural hearing loss (G2M); 10 with steeply sloping sensorineural hearing loss (G2D); 10 with profound and severe sensorineural hearing loss (G2S); and 15 with normal hearing (G1). ASSR, tympanometry, acoustic reflex testing, pure tone audiometry, and speech audiometry (SRT and SDT) were performed. The electrophysiological maximum in the group with normal hearing thresholds varied from 19 to 27 dB NA. The correlation in the group with moderate to moderately severe hearing loss was 0.42-0.74. The correlation in the steeply sloping hearing loss group was 0.68-0.94. The correlation in the group of people with profound and severe hearing loss was 0.59-0.86. The normal hearing group's mean differences in ASSR threshold and audiometric threshold ranged from -0.3 to 12 dB, in the moderate and moderately severe hearing loss group from -9 to 2 dB, in the steeply sloping hearing loss group from 1.4 to 7.5 dB, and in the severe and profound hearing loss group from -0.40 to 8.5 dB. As expected, there was no strong relationship between behavioural and electrophysiological thresholds in the group with normal hearing. But in children with hearing loss, there was a strong correlation between electrophysiological and behavioural thresholds; this relationship was especially evident in children with severe and profound hearing loss and those with steeply sloping hearing loss.

Combined preparation and application of geopolymer pavement materials from coal slurry-slag powder-fly ash mining solid waste: A case study

The solid waste treatment problem generated in the process of coal mining has always been an important factor restricting safe and environmentally friendly production, and the coal slurry from the coal mine road surface is a new type of mine solid waste, so it is of great significance to treat and efficiently utilize the coal slurry. Currently, a common method of solid waste utilization is to add modifying reagents to prepare functional materials. Select coal slurry, slag powder and fly ash as raw materials, and sodium sulfate and sodium hydroxide were used as alkali exciters to prepare coal slurry based geopolymer pavement material (CSGPM). Response surface methodology was used to establish regression equations between the design optimization objectives (coagulation time, compressive strength) and the variables (mass fraction, mass ratio of slag powder to fly ash, mass ratio of sodium sulfate to sodium hydroxide). The effects of two-by-two interactions of the factors on the optimization objective were explored, and the use of different raw materials was obtained. Under the optimal proportioning parameters, the coagulation time of CSGPM was 33 min and the compressive strength of 24 h of curing was 11.20 MPa. In addition, the generation mechanism of AFt and C-S-H gel substances inside the specimen was explained with the help of microscopic scanning. CSGPM showed good mechanical properties in both load-bearing numerical simulations and acoustic emission tests. Numerical simulation was used to establish the relationship between the design objective of the roadbed (maximum subsidence of the roadbed after bearing) and the design variable (thickness of CSGPM paving). Comparative analyses yielded an optimal subgrade surface layer design thickness of 5 cm, with a maximum subsidence of 0.0033 m after bearing vehicles. Synchronization of roadbed material and concrete damage in combined specimen acoustic emission tests with uniform load transfer. The final coal mine pavement was successfully paved and the total cost of CSGPMD is 63.2 per cent of C30 concrete. Those results are important for the preparation of new pavement functional materials.

Biologically inspired piezoresistive MEMS acoustic vector sensor for underwater applications

Underwater acoustics has assumed a pivotal role in the detection, navigation, communication, and target identification of ships and submarines. In recent years, advancements in noise reduction from marine vessels have underscored the significance of underwater acoustic vector sensors. This paper presents a novel approach to the design, fabrication, and characterization of a two-dimensional Micro-Electro Mechanical Systems (MEMS) vector acoustic sensor tailored for underwater environments. Traditional underwater acoustic vector sensors often employ doped polysilicon or silicon/germanium sensing films on rigid silicon substrates. The inflexible nature of silicon substrates necessitates labor-intensive and costly chemical-mechanical polishing processes to achieve submicron thickness, often requiring extended clean-room usage. In contrast, this work proposes a simplified, cost-effective, and scalable alternative. The sensor design utilizes reduced graphene oxide (rGO) as the sensing material and Kapton as the substrate, chosen for their unique properties. rGO exhibits high carrier mobility and low intrinsic noise, ensuring clear signals with minimal external interference, thereby improving measurement accuracy in challenging environments. Kapton provides excellent thermal stability, mechanical strength, and chemical resistance, along with superior insulating properties that reduce electrical noise, enhancing the signal-to-noise ratio. The designed vector sensor leverages the piezoresistive transduction principle, incorporating a thin piezoresistive film of rGO on a flexible Kapton substrate via a straightforward drop-casting method. Inspired by the sensory mechanisms of aquatic life, the two-dimensional vector sensor not only detects pressure associated with acoustic signals but also discerns the direction from which these low and ultralow frequency signals originate. The device's performance characteristics, sensitivity, and directivity are comprehensively evaluated through static, dynamic, and acoustic tests conducted in both air and water mediums. Static tests reveal the piezoresistive behavior of rGO under applied displacement, yielding displacement sensitivities of 0.0279 V/mm and 0.0276 V/mm for axial and radial displacements, respectively. Dynamic and acoustic tests demonstrate the sensor's capability to detect low-frequency signals spanning from 0.25 Hz to 200 Hz, exhibiting a smooth and favorable frequency response. In air, the sensor exhibits receiving sensitivities ranging from −15.18 dB to −19.75 dB (X-channel) and −13.67 dB to −16.67 dB (Y-channel). In the underwater environment, these values range from −134.40 dB to −138.93 dB (X-channel) and −131.83 dB to −136.93 dB (Y-channel). Notably, the variation in receiving sensitivity across channels in both air and water is limited to within 6 dB. Furthermore, the device showcases a symmetrical directivity pattern resembling the shape of an "8," with an approximate sensitivity of −136.66 dB, a significant improvement compared to the −165 dB sensitivity of conventional polysilicon underwater vector sensors. These experimental findings affirm the feasibility of the proposed underwater vector sensor, based on the piezoresistive effect and MEMS technology, highlighting its two-dimensional directivity capabilities.

Acoustic characterization of the NASA Langley 14- by 22-Foot Subsonic Tunnel using single-microphone analysis techniques

An experimental campaign was carried out to assess recent acoustic modifications to the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel. This effort was undertaken in preparation for future rotorcraft, Advanced Air Mobility, and airframe noise acoustic tests. The tunnel is a closed circuit and typically operates in an open-jet configuration for acoustic studies. A vertical linear array of microphones and a phased array were placed on traverses outside of the core flow. Pole-mounted acoustic sources with known waveforms were used to identify sources of reflection under static conditions. A similar process was replicated with more compact sources in an aerodynamic fairing for flow speeds up to Mach 0.16. This allowed for acoustic characterizations of the test section core flow and bounding shear layer. Periodic averaging was investigated as a method for isolating acoustic sources and was shown to be capable of isolating periodic acoustic signals even for poor signal-to-noise ratio conditions. Benefits and limitations of single-microphone processing methods are identified. A companion paper utilizes a phased array in an effort to address the identified limitations to more traditional single-microphone data collection.

Thinking inside the box: a cost-effective approach to fan array noise reduction

Noise from fan arrays can contribute high sound pressure levels both to buildings and communities. Noise that travels from these units through ducts and into the spaces within buildings can be attenuated with silencers or duct lining. However, sound radiated from the unit through building structures or into communities can be more difficult to attenuate and often adds significant cost. While it is possible to attenuate sound from the unit using enclosures or sound walls, exploring the operation of the fan arrays themselves could be a more cost-effective noise reduction method. One particular noise reduction method for an existing fan array was proposed for a customer: review sound levels of each fan within the array to determine how they are contributing to the radiated sound power level of the unit. The assumption that sound levels between individual fans within fan arrays are consistent is not always correct. A series of acoustical tests were completed; results indicated that sound caused by turbulent airflow within the tested fan array was able to be lowered by reducing the fan speeds of individual fans. By reducing the fan speeds of problematic fans and increasing speeds for the quieter ones within the same fan array, the same level of cooling can be provided with lower overall radiated sound levels at no additional cost.

Advanced acoustic simulation of aircraft test environments: integration of the direct field acoustic testing methodology

In aeroacoustic engineering, replicating real-world environments in a controlled setting presents significant opportunities for reduced flight testing but also comes with challenges when precisely simulating the flight environment. This paper introduces an innovative acoustic simulation model that leverages the Boundary Element Method (BEM) and a Direct Field Acoustic Testing (DFAT) simulation module. The primary objective is to virtually reproduce test sound fields that closely mimic the full fluctuating pressure environments aircraft encounter during flight using only loudspeaker arrays. This approach involves virtually reproducing a sophisticated test setup, typically comprising hundreds of drivers actively managed to generate a specific sound field. This setup is designed to virtually replicate various complex pressure environments, such as those produced by a Turbulent Boundary Layer, the complex pressure fields generated by aircraft propellers or jet engines. The use of active noise generation simulation helps determine the feasibility of a given pressure field and the capability of a test facility to simulate it accurately. The virtually reproduced sound fields simulated by this model show remarkable potential in approximating real-world pressure loadings. This capability is particularly useful in establishing pre-test predictions for fuselage testing such as sidewall build-ups: including insulation, and damping treatments, TVAs and TMDs.

Multifractal Characterization of Coal Deterioration Induced by Cyclic Hydraulic Pressure Based on the Acoustic Emission Test and X-ray Microscopy

Multifractal Characterization of Coal Deterioration Induced by Cyclic Hydraulic Pressure Based on the Acoustic Emission Test and X-ray Microscopy

Influence of tectonic stress field on oil and gas migration in the Tahe Oilfield carbonate reservoir: Identification of areas favorable for reservoir formation

An understanding of the tectonic stress field distribution in the carbonate reservoirs of the Tahe Oilfield is essential for oil and gas migration and reservoir reconstruction. This study adopts a geological genesis perspective and integrates the unique attributes of the carbonate reservoirs in the Tahe Oilfield to simulate three-dimensional stress fields using the finite element method and Petrel software. The simulation, which takes pore pressure and boundary constraints into consideration, aligns with the findings of acoustic emission tests conducted by previous researchers and validates the model by corroborating the maximum horizontal principal stress direction with imaging logging interpretations. With subsequent utilization of the generalized Coulomb-Mohr shear failure criterion and the Griffith generalized maximum tensile stress criterion, the simulated stress enables the prediction of the total fracture intensity. To complement this analysis, we integrate seismic data and fault formation mechanisms to characterize variations in fracture intensity within distinct regions of the study area. Three key findings emerge from this investigation. First, due to the Hercynian thermal event, X-shaped conjugate faults display a disproportionately high degree of development compared to other primary fractures. Analyzing the mechanisms of formation and development of these X-shaped strike-slip faults reveals discernible differences in deformation characteristics between NW-trending and NE-trending faults, with the former exhibiting a greater propensity for fracture rupture and efficient oil-gas migration. Second, fault intersections are critical and efficient conduits for fluid accumulation and thereby contribute to reservoir formation. Lastly, exclusive of X-shaped conjugate faults, NE-trending faults exhibit the greatest propensity for oil and gas accumulation and migration. Collectively, these findings facilitate the identification of areas favorable for oil and gas migration and provide a crucial mechanical analysis that can inform the exploration and development of the Tahe Oilfield.

Incorporation of Silicone Mold Residues Influence on Acoustic Properties of Subfloor Mortars

The determination of minimum performance criteria for residential buildings has encouraged the development of new technologies by companies linked to the construction industry. In this context, the acoustic performance of floor systems is of great importance. One of the solutions to improve the performance of these systems is the incorporation of lightweight aggregates to replace natural fine aggregates in the subfloor mortars, with the aim of attenuating the noise caused by impact, thus improving acoustic performance. Therefore, the objective of this study was to analyze the properties of a subfloor mortar in a 1:4 ratio (cement:sand), with the incorporation of silicone mold residue, replacing natural fine aggregate, in proportions of 10%, 20%, and 30%. %, and a water/cement ratio (w/c) of 0.93. Tests were performed in the fresh and hardened state, such as incorporated air content, mass density, consistency index, flexural tensile strength, compressive strength, water absorption by capillarity, in addition to a specific test to determine the difference in sound pressure level between specimens. The results indicated that the mortar consistency was influenced by the incorporation of waste, increasing with its incorporation. The increase in consistency positively influenced the mechanical resistance of the mortars, which showed an increase with higher residue content, due to the reduction in the amount of voids. Consequently, densities also increased with high waste content. The acoustic test showed satisfactory results, with good attenuation of 10%, indicating an 8 dB improvement in the sound pressure level. The results presented show that the residue has great potential for acoustic attenuation.

A comparative study of acoustic and ultrasonic nondestructive testing for evaluating melon quality

Abstract Melon (Cucumis melo L.) is a high-value agricultural commodity known worldwide for its sweet taste and crisp flesh texture, which are important factors for quality and consumer acceptance. Unfortunately, quality testing and determining the optimal harvest time for achieving desired melon characteristics are traditionally performed through destructive methods. The aim of this study was to explore the potential of acoustic and ultrasonic tests for predicting the physicochemical properties of Honey Globe melons (Cucumis melo L. var. inodorus). A total of 100 melon samples were used in this study. For the nondestructive ultrasonic testing, attenuation values served as its variable, whereas in acoustic testing, variables included frequency, magnitude, short-term energy, and zero-moment. Fruit’s flesh firmness and total soluble solids (TSS) as physicochemical quality properties were determined using destructive tests. The calibration phase involved 80 melon samples, employing a K-Fold Cross Validation approach with ten folds, done on Partial Least Square Regression (PLS) modeling. Another 20 melon samples were used for blind testing. Reliability evaluation was done on key metrics, consisting of R2 values, RMSEC (Root Mean Square Error of Calibration), RMSECV (Root Mean Square Error of Cross-Validation), RMSEP (Root Mean Square Error of Prediction), and RPD (Ratio of Performance to Deviation). Analysis results on these metrics collectively support the conclusion that both ultrasonic and acoustic methods exhibit their potential to predict the firmness properties of melon fruits. The best evaluation result that has been conducted for the ultrasonic test uses attenuation, age, and density as predictors to predict fruit firmness, with R2 = 0.763 and RPD = 2.945, while the acoustic test achieved the best result with magnitude used as a predictor to predict fruit firmness with R2 = 0.718 and RPD = 2.230. However, evaluation metrics on the prediction of total soluble solids for both nondestructive tests were still not good enough for application with low R2 and RPD value.

Acoustic Emission Detection in Noisy Environments using Linear Prediction

In non-destructive testing, acoustic emission testing is an established technique with numerous applications in academia and the industry. In nearly all applications, the detection of relevant acoustic emission signals in continuous structure-borne sound recordings is a crucial step that forms the basis for subsequent analyses and should therefore neither miss any relevant acoustic emissions nor detect too many irrelevant events. That is because, in its most prevalent form, acoustic emission testing utilizes ultrasound signals that require large amount of storage, which might be an economically limiting factor especially for structural health monitoring of large civil infrastructures. In these monitoring applications, the signal-to-noise ratio is also expected to be worse compared to more controlled laboratory conditions, as they can be often found, for example, in materials research. We therefore propose the use of linear prediction, a time series forecasting technique, to extract relevant acoustic emissions from continuous recordings. The proposed methodology utilizes the residual between the signal predicted from a linear combination of previous time steps and the actual measurement to detect any anomalous events. Since the linear predictor can be initialized using the environmental noise only, no specific knowledge of the acoustic emission signals of interest is required beforehand and hence can automatically adapt to each measurement environment. We compare our approach with a simple amplitude-based detection as it is commonly implemented in commercially available acoustic emission systems. Especially for low signal-to-noise ratios, an increase in the area under the receiver operating characteristic curve of up to 0.7 compared to the amplitude-based detection is found.

Detecting wire breaks in post-tensioned tendons of wind turbines: A signal energy spectrum analysis approach

In the wind industry, recent advancements have led to the research and development of wind turbines featuring hybrid towers, a novel combination of steel tube and precast concrete segments. These concrete modules, which absorb the high stresses caused at the intersection between the tower and its foundation, are commonly joined with post-tensioned tendons. This study focuses on the identification of wire breaks in post-tensioned tendons through the application of acoustic emission testing. Measurements involve the evaluation of wire breaks under controlled laboratory conditions and the analysis of the dynamic operational environment of a functioning wind turbine. The investigation encompasses the development and assessment of a methodology based on principles of discrete Fourier transformation and Parseval’s theorem for analyzing the frequency-dependent energy distribution of acoustic signals. This analytical approach extends to the examination of wire breaks generated under varying stress levels as well as the operational noise within the actual wind turbine. The findings demonstrate a notable concentration of energy within the frequency range of 5-20 kHz in the wire break signals. In contrast, the operational noise signals show a distinct pattern, presenting an extreme value distribution within the 0-2 kHz range. The developed methodology exhibits robustness, even in the presence of high background noise levels, establishing itself as a valuable tool for wire break detection. Additionally, its potential for integration with machine learning algorithms offers the prospect of automated wire break detection, enabling further advancements in structural health monitoring for wind turbines.

Damage detection in wind turbine blades using embedded radar networks

To ensure the availability and operational safety of wind turbine blades, regular inspections are required according to specified maintenance intervals. As with all periodic inspections, damage that develops between two inspection dates remains undetected until the next inspection. In recent years, monitoring systems have therefore been developed that enable independent structural health monitoring (SHM) with permanently installed sensors. The most important representatives here include vibration analysis, acoustic emission testing and ultrasonic methods. In addition, it is necessary for an SHM system to distinguish between signal changes resulting from damage or changing environmental and operating conditions. The present work presents a new approach for the in-situ assessment of wind turbine blades via embedding radar networks in the frequency band from 58 to 63.5 GHz. Therefore, 40 FMCW (frequency-modulated continuous wave) radar sensors have been embedded into a wind turbine blade during manufacturing. This contribution provides additional information related to the hardware design of the sensor nodes, its preliminary testing and the specific implementation of the radar network during a fullscale fatigue test of a 31m long wind turbine blade [1]. Damage indicators can be formulated relative to baseline conditions to see the development of fatigue damage over time. Reference: [1] Simon, J.; Kurin, T.; Moll, J.; Bagemiel, O.; Wedel, R.; Krause, S.; Lurz, F.; Nuber, A.; Issakov, V. & Krozer, V., Embedded Radar Networks for Damage Detection in Wind Turbine Blades: Validation in a Full-scale Fatigue Test, Structural Health Monitoring, 2023, https://doi.org/10.1177/14759217231152815

A retrospective study on hearing outcomes of infants of COVID-19 mothers pre-vaccination era

Background: A COVID-19 infection can result in a variety of symptoms. Findings must be carefully reviewed because there is still a dispute over the potential involvement of the audiovestibular system. Moreover, there is debate over the intrauterine transfer of COVID-19 infection from mother to fetus in pregnant people. There are not many investigations on the audiovestibular symptomatology of infants exposed to COVID-19 during pregnancy. Aims and Objectives: This study looks at any potential links between the COVID-19 gestational infection and the start of hearing impairment in babies. The verification of hearing’s engagement in COVID-19 allows for the planning of the time and methods for children’s audiological evaluations. Materials and Methods: Newborns had audiological examination and screening for hearing loss. The automatic transient evoked otoacoustic emissions (OAEs) test is used to evaluate newborns for hearing impairments before they are released from the hospital. By employing the COVID-19 case history, otoscopy, acoustic immittance test, transient evoked OAEs test, and mother, pregnancy, and perinatal case histories, an audiological examination is conducted on children under 3 months of age, with 2 weeks, 1 month and 3 months of age follow-up. Results: The research comprised 100 children. Of these infants, 90% were part of the neonatal hearing screening initiative. Due to isolation protocols, the remaining 10 neonates did not undergo hearing screening; instead, a direct audiological examination was performed on them. Out of the 90 newborns that were tested, only 11 had a bilateral REFER test result, but the audiological examination revealed a normal hearing threshold. Conclusion: There is no data in this study that a mother’s COVID-19 infection results in hearing loss in newborn.

Earmuff performance in the presence of high-level impulse from a recoilless weapon firing in a confined space.

A noise attenuation performance test was conducted on earmuffs using a recoilless weapon launch platform in a confined space, along with two acoustic test fixtures (ATFs). The overpressure at the ATF's effective tympanic membrane comprised direct sound at 185 dB sound pressure level (SPL) and reflected sound at 179 dB SPL. Wearing earmuffs reduced these peaks to 162 dB SPL and 169 dB SPL, respectively. The reflected sound from walls was defined as delayed sound. An analytical model for earmuff noise attenuation simulated their effectiveness. The simulation revealed that when the earmuffs attenuated delayed sound, the acoustic impedance of acoustic leakage and the acoustic impedance of the earmuff material decreased by 96% and 50%, respectively. The negative overpressure zone between direct and delayed sound decreased the earmuffs' fit against the ATF. Additionally, the enclosed volume between the earmuff and the ear canal decreased by 12%. After the installation of bandages on the earmuffs, the overpressure peak of delayed sound was reduced by 5 dB. Furthermore, the acoustic impedance of the earmuff's sound leakage path and the acoustic impedance of the earmuff material deformation path increased by 100% and 809%, respectively.

A simple method improving acoustic mode identification capability based on genetic algorithms

This letter develops a simple approach of duct mode identification and reconstruction based on genetic algorithms, which can extend the azimuthal mode order range compared to the conventional method based on the (spatial) discrete Fourier transform. The underlying principle is reconstructing the dominant mode from the modal identification forward model through optimization by exploiting the sparsity of the mode amplitude vector. The performance is experimentally demonstrated for detections of one and two azimuthal modes under noisy conditions with nondominant modes. Overall, the proposed genetic-algorithm-based framework for solving acoustic inverse problems is beneficial to duct acoustic testing, particularly design evaluations of fan blades and acoustic liners for aeroengines.