Acoustic Treatment Research Articles

On-demand liquid microlens arrays by non-contact relocation of inhomogeneous fluids in acoustic fields.

Microlens arrays (MLAs) are key micro-optical components that possess a high degree of parallelism and ease of integration. However, rapid and low-cost fabrication of MLAs with flexible focusing remains a challenge. Herein, liquid MLAs with dynamic tunability are presented using non-contact acoustic relocation of inhomogeneous fluids. By designing ring-shaped acoustic pressure node (PN) arrays, the denser fluid of miscible liquids is relocated to PNs, and liquid MLAs with ideal morphology are obtained. The experimental results demonstrate that the liquid MLAs possess a powerful reconfigurability with long-term stability and sharp imaging that can conveniently switch between the on and off state and can dynamically magnify by simply adjusting the acoustic amplitude. Moreover, the high biocompatibility inherited from liquids accompanied by the acoustic treatment allows cells to be within working distance of the MLAs without immersion, as would be required for a solid lens. This innovative liquid MLA is inexpensive to manufacture and possesses continuous focus, fast response, and satisfactory bioaffinity, and thus offers promising potential for microfluidic adaptive imaging and biomedical sensing, especially for live cell imaging.

Efficient realization of on-demand functional ultrasonic fields based on prolate spheroidal wave functions from sampling theorem.

The past decades have witnessed great efforts in the on-demand ultrasonic field design in which the time reversal technology was widely used in the whole-space acoustic hologram. In practice, the acoustic field of interest is usually bounded in a finite region with flexible distribution. Here, the use of prolate spheroidal wave functions to generate an arbitrary ultrasonic field in a finite region is proposed. The prolate spheroidal functions, which form a complete set of band limited functions and are orthogonal in the infinite and finite regions, can be efficiently reconstructed by the sampling theorem. To display the validation of the proposed method, two types of functional ultrasonic fields are numerically simulated. One type is the ultrasound standing wave field for which six nodes and two nodes are separately realized for two different types of standing waves in the limited range of (-2λ, 2λ). In addition, a composite standing wave field is stimulated with more complicated nodal distributions. The other type is the ultrasound focusing field, where three focal spots with the mainlobe sizes of λ, 0.5λ, and 0.35λ are demonstrated. It is worth noting that the nontrivial side lobes for super-oscillation focusing are designed to be about 3λ away from the central focal spot (the mainlobe size 0.35λ). This work has much significance in the applications of acoustic tweezing, ultrasonic imaging, and treatment.

Experimental evaluations of acoustic properties and long-term analysis of a novel indoor living wall

Indoor living walls are important decorative elements that can recreate a natural garden in enclosed spaces. Several aspects are addressed by the scientific literature such as, for instance, classification, the effects on air quality and indoor temperature, greater aesthetic and psychological impact, and improved acoustic treatment of indoor spaces. The main objective of this study is to analyse the acoustic performances of a novel indoor living wall (LW) where plants are rooted in felt layers and grown in hydroponics with no growing medium. The sound absorption of different LW solutions was measured in laboratory (reverberation room). One of them was installed in a Test Building, where sound absorption and sound insulation were measured. The LW has been installed for about two years in the Test Building under controlled conditions of temperature and relative humidity. This gave the unique opportunity to test the sound absorption of the same living wall in the same reverberation room after about two years. The results obtained indicate that the sound absorption performance of the LW is stable, as long as the plants remain in good health. Moreover, an estimation was performed with a calculation model of the reverberation time of the room containing the living wall. Evaluation in real working conditions confirms that indoor living walls can improve the acoustic comfort of indoor spaces by increasing both the sound insulation and the sound absorption area, allowing to reach the optimal reverberation time values provided for by Italian regulations.

Evaluation of the effects of sound exposure and low field electromagnetism on growth and antibiotics susceptibility of some microorganisms

BackgroundThe emergence of antibiotic-resistant microorganisms has been largely associated with drug misuse, drug abuse, and indiscriminate disposal of drugs; however, the interactions between some environmental factors and antibiotic resistance by microorganisms have been understudied. In this study, the effects of sound and electromagnetic field on the growth and antibiotic susceptibility of selected microorganisms to antibiotics were investigated.ResultsMicroorganisms used include Gluconobacter oxydans ATCC 19,357, Rhodobacter sphaeroides ATCC 17,023, Citrobacter freundii ATCC 33,128, Yersina pestis ATCC 11,953, Bacillus subtilis 6633, Acetobacter aceti ATCC 15,973, Escherichia coli ATCC 25,922, Pseudomonas aeuriginosa ATCC 9027, Streptococcus pyogenes ATCC 19,613, Klebsiella pneumonia ATCC 25,955, Staphylococcus aureus ATCC 25,923 and Serratia marcescens ATCC 14,766. The antibiotics used were: Ciprofloxacin 5 μg, Imipenem 10 μg, Ampicillin 10 μg, Ceftazidime 30 μg and Tetracycline 30 μg for Gram-negative bacteria while Pefloxacin 10 μg, Gentamycin 10 μg, Amplicillin + Cloxacillin 30 μg, Cefuroxime 20 μg, Amoxacillin 30 μg, Ceftriaxone 25 μg, Ciprofloxacin 10 μg, Streptomycin 30 μg, Co-trimoxazole 30 μg, and Erythromycin 10 μg for Gram-positive bacteria, respectively. Acoustic treatment had varying effects on the antibiotics susceptibility profile of all test bacterial culture. Before exposure, P. aeruginosa had the highest zone of inhibition of 34 ± 3.4 mm, while B. subtilis had least inhibition zone of 12 ± 2.8. After exposure to acoustic treatment at 5000 Hz/90 dB at 72 h, C. freundii had highest zone of inhibition of 32 ± 0.7 mm and the least zone of 11 ± 1.4 mm observed in P. aeruginosa. At 1125 Hz/80 dB after 72 h, R. sphaeroides had highest zone of 34 ± 0.7 mm while A. aceti had least zone of inhibition of 10 ± 0 mm. Effect of electromagnetic flux treatment of 15 min showed E. coli to be the most inhibited having a growth rate of 0.08 log cfu/mL, antibiotics testing showed G. oxydans to have the highest zone of inhibition of 28 ± 3.5 mm and least zone was observed in B. subtilis having a zone of 13 ± 2.8 mm.ConclusionThis study showed that environmental factor such as sound and electromagnetic flux (EMF) could interfere with the physiology of bacteria including resistance/susceptibility to antibiotics. However, further investigation will be needed to understand full mechanisms of action of sound and electromagnetic field on bacteria.

Subjective Experience of Speech Depending on the Acoustic Treatment in an Ordinary Room.

In environments such as classrooms and offices, complex tasks are performed. A satisfactory acoustic environment is critical for the performance of such tasks. To ensure a good acoustic environment, the right acoustic treatment must be used. The relation between different room acoustic treatments and how they affect speech perception in these types of rooms is not yet fully understood. In this study, speech perception was evaluated for three different configurations using absorbers and diffusers. Twenty-nine participants reported on their subjective experience of speech in respect of different configurations in different positions in a room. They judged sound quality and attributes related to speech perception. In addition, the jury members ranked the different acoustic environments. The subjective experience was related to the different room acoustic treatments and the room acoustic parameters of speech clarity, reverberation time and sound strength. It was found that people, on average, rated treatments with a high degree of absorption as best. This configuration had the highest speech clarity value and lowest values for reverberation time and sound strength. The perceived sound quality could be correlated to speech clarity, while attributes related to speech perception had the strongest association with reverberation time.

Carbon nanotubes-reinforced preparation of flat MoS2 nanomaterials: Co-enhancement of acoustic exfoliation efficiency and dye removal capacity

A novel and effective preparation technology was developed to prepare ultrathin molybdenum disulfide (MoS2) crystals with a high yield of the top-down exfoliation. Multidimensional carbon nanotubes (MWCNTs) were selected to be an assistant to enhance the effect of the traditional ultrasonic exfoliation efficiency. The rough and messy tubes strengthened the shear force in some parts during the acoustic treatment, which helped to weaken the van der Waals force between the MoS2 layers. Excitingly, this high-efficiency strategy can increase the dispersion concentration of nanosheets by 15 times compared to the traditional acoustic production, which represented the preparation yield was improved greatly. It is found that the addition of MWCNTs not only facilitated the exfoliation efficiency of bulk material but also indirectly improved the adsorption of malachite green (MG) in wastewater. With a maximum removal capacity of 87.80 mg g−1, the adsorption ability of the nanotubes-reinforced layered adsorbent was effectively strengthened. In addition, the performance of reproducibility, stability, functioning free radical types, and the adsorption models were systematically studied.

Binaural Speech Intelligibility in a Real Elementary Classroom

Since the fundamental phases of the learning process take place in elementary classrooms, it is necessary to guarantee a proper acoustic environment for the listening activity to children immersed in them. In this framework, speech intelligibility is especially important. In order to better understand and objectively quantify the effect of background noise and reverberation on speech intelligibility various models have been developed. Here, a binaural speech intelligibility model (BSIM) is investigated for speech intelligibility predictions in a real classroom considering the effect of talker-to-listener distance and binaural unmasking due to the spatial separation of noise and speech source. BSIM predictions are compared to the well-established room acoustic measures as reverberation time (T30), clarity or definition. Objective acoustical measurements were carried out in one Italian primary school classroom before (T30= 1.43s±0.03 s) and after (T30= 0.45±0.02 s) the acoustical treatment. Speech reception thresholds (SRTs) corresponding to signal-to-noise ratio yielding 80% of speech intelligibility will be obtained through the BSIM simulations using the measured binaural room impulse responses (BRIRs). A focus on the effect of different speech and noise source spatial positions on the SRT values will aim to show the importance of a model able to deal with the binaural aspects of the auditory system. In particular, it will be observed how the position of the noise source influences speech intelligibility when the target speech source lies always in the same position.

Farmed Salmon Show No Pathological Alterations When Exposed to Acoustic Treatment for Sea Lice Infestation

The use of bioacoustic methods to address sea lice infestation in salmonid farming is a promising innovative method but implies an exposure to sound that could affect the fish. An assessment of the effects of these techniques related to the salmon’s welfare is presented here. The fish were repeatedly exposed to 350 Hz and 500 Hz tones in three- to four-hour exposure sessions, reaching received sound pressure levels of 140 to 150 dB re 1 µPa2, with the goal of reaching total sound exposure levels above 190 dB re 1 µPa2 s. Gross pathology and histopathological analysis performed on exposed salmons’ organs did not reveal any lesions that could be associated to sound exposure. The analysis of their otoliths through electron microscopy imaging confirmed that the sound dose that was used to impair the lice had no effects on the fish auditory organs.

Innovative Acoustic Treatments of Nacelle Intakes Based on Optimised Metamaterials

Modern turbofans with high bypass ratios, low blade passage frequencies and short nacelles require continuous development of acoustic linings to achieve the noise reductions expected by the international aviation authorities. Metamaterials and metafluids have been recently proposed as promising technologies for designing innovative acoustic treatments dedicated to reducing aeronautic turbofan noise emissions. In this work, a phase-gradient metasurface treatment is investigated as a way to tackle the noise radiation from an axially symmetric nacelle. This paper aims to study the potential benefits of the mentioned technology, and is not an attempt to design a complete new liner or nacelle. The metasurface is modelled through an equivalent metafluid, and a simulation-based optimisation is used in defining the design parameters. The tonal contribution of the blade passage frequency is considered, and the numerical results with the metafluid optimised on one azimuthal mode at a time show a significant effect in terms of acoustic levels and directivity over an arc of virtual receivers.

Directional off-axis acoustic-vortex beams passing through a preassigned point

As a special kind of tweezers, the acoustic-vortex (AV) beam with a bent or inclined trajectory shows its great significance in contactless manipulations, especially for objects behind obstacles. By introducing additional phase delays to the traditional single-side ring-array of planar transducers, directional off-axis acoustic-vortex (OA-AV) beams passing through a preassigned point are constructed. Numerical simulations and experimental measurements of the axial and cross-sectional profiles for OA-AV beams of different orders with various radial offsets are conducted for transducers of various radiation patterns. An approximately linear trajectory of OA-AV beams with the slope determined by the preassigned point is demonstrated. The axial distribution of OA-AV beams formed by the main-lobes and side-lobes with corresponding zero-pressure nodes is decided by the directivity of the sources, while the vortex radius can be adjusted by the topological charge. By combining with the technologies of ultrasonic imaging, acoustic treatment, particle assembly, and targeted drug delivery, the precise positioning and flexible regulation of tilted OA-AV beams can be applied to accurately route acoustic packets along a predictable trajectory in three dimensions, suggesting more promising potentials of obstacle-avoidant object manipulation in biomedical applications.

Effect of voice support level and spectrum on conversational speech.

One's own voice (autophony) is transmitted to the ears as direct airborne sound, bone conduction, and indirect airborne sound from reflections characterized by overall gain and spectro-temporal features. This study investigates how the spectral profile and gain of simulated indirect airborne sound, quantified as voice support (STV), affect the speaking voice of talkers. Pairs of participants performed a conversation elicitation task in anechoic conditions. The indirect airborne sound was provided in real-time via open headphones that maintain the direct airborne transmission path. Experimental conditions included high-pass, low-pass, and all-pass versions of STV, each presented at three overall gains, and a Baseline condition with no electroacoustic contribution to STV. The results show an overall speech level reduction of 0.22 dB for every additional dB of speech-weighted STV, i.e., a -0.22 dB/dB slope. There was some effect of STV spectrum on speech: slope for the high-pass condition was steeper (statistically significant) and significantly different from the all-pass slope; spectral balance (2-4 kHz vs 0-2 kHz) of speech showed an interaction effect between gender and experimental conditions. This paper's findings may inform acoustic treatments in environments where overall sound reduction is of interest for favorable ergonomics and occupational health for voice professionals.

Frequency responses of headphones modulate alpha brain oscillations related to auditory processing

The perception of sound can differ significantly, regardless of its physical properties. The frequency content of a sound can provoke different psychoacoustic effects on humans, and simultaneously, it modulates differently brain oscillations. Audio devices such as headphones are variables that have not been taken into consideration in many studies concerning acoustic therapies, which strongly depend on the transmission means. Headphones become a fundamental key in acoustic treatments since they are responsible for transmitting auditory stimuli. It is known that the frequency response of audio devices can change the frequency content of a signal. However, it is still unknown if their limited (or even inappropriate) functioning could affect acoustic therapy effectiveness. Therefore, the present work aims to analyze alpha (resonance frequency at which neurons decode auditory information) brain oscillations in healthy individuals when listening to the same sound but through different frequency responses of headphones. For this purpose, the frequency responses of three headphone models were firstly obtained: Atvio® supra-aural headphones (ATVIO), Shure® SRH1840 circum-aural headphones (SHURE), and Apple® EarPods® intra-aural headphones (APPLE). The estimated frequency responses showed that ATVIO and APPLE headphones presented a major difference in comparison with an ideal frequency response (same gain at every frequency of the headphone bandwidth, i.e., a flat frequency response). Then, inverse filters on the difference of the responses were implemented. Finally, the alpha brain oscillations of 29 individuals were analyzed while they were listening to pink noise through the filters of the three models. The findings suggested that the three headphones modulated alpha brain oscillations accordingly their frequency response. Namely, mapping of alpha brain oscillations for ATVIO and APPLE headphones reflected lower neural activity associated with decoding of auditory information, possibly due to the loss of gain at different frequencies. In contrast, SHURE headphones, which presented a flatter frequency response, reflected higher neural activity related to decoding and interpretation of acoustic information since frequency response was much less affected.

Architectural acoustic design: Observation of use cases including audio-only and multimodal auralizations

Auralization technology has reached a satisfactory level of ecological validity, enabling its use in architectural acoustic design. Only recently have the actual uses of auralization in the consulting community been explored, resulting in the identification of a variety of uses, including (1) to present to clients, (2) to test design ideas, (3) as a verification tool, (4) as a verification tool, (5) as a marketing tool, and (6) to improve internal company discussions. Taking advantage of methodologies from ergonomics research, the present study investigates effective uses through the observation of a collaboration project between an acoustic research team and an acoustic consultant, as a case study. Two spaces have been auralized in the context of the conception of a new skyscraper during the design phase of the project. The two spaces faced different problematics: an Atrium for which three different acoustic treatment options were suggested and experienced through multi-modal auralizations and audio-only auralizations of an Auditorium where an intrusive noise was to be acoustically treated. The ergonomic observation and analysis of this project revealed key impediments to the integration of auralization in common acoustic design practices.

An Acoustic Treatment to Mitigate the Effects of the Apple Snail on Agriculture and Natural Ecosystems

Global change is the origin of increased occurrence of disturbance events in natural communities, with biological invasions constituting a major threat to ecosystem integrity and functioning. The apple snail (Pomacea maculata) is a freshwater gastropod mollusk from South America. Considered one of the 100 most harmful invasive species in the world, due to its voracity, resistance, and high reproductive rate, it has become a global problem for wetland crops. In Catalonia, it has affected the rice fields of the Ebre Delta since 2010 with significant negative impact on the local economy. As a gastropod mollusc it possesses statocysts consisting of a pair of sacs, one located on each side of the foot, that contain multiple calcium carbonate statoconia. This study shows the first ultrastructural images of pathological changes in the sensory epithelium of the statocyst of apple snail adults with an increase in the severity of the lesions over time after exposure to low frequency sounds. Sound-induced damage to the statocyst could likely result in an inhibition of its vital functions resulting in a potential reduction in the survival ability of the apple snail and lead to an effective mitigation method for reducing damage to rice fields.

High fidelity modeling tools for engine liner design and screening of advanced concepts

With aircraft engines trending toward ultra-high bypass ratios, resulting in lower fan pressure ratios, lower fan RPM, and therefore lower blade pass frequency, the aircraft engine liner design space has been dramatically altered. This result is also due to the associated reduction in both the available acoustic treatment area (axial extent) as well as thickness (liner depth). As a consequence, there is current need for novel acoustic liner technologies that are able to meet multiple physical constraints and simultaneously provide enhanced noise attenuation capabilities. In addition, recent advances in additive manufacturing have enabled the consideration of complex liner backing structures that would traditionally be limited to honeycomb cores. This paper provides an overview of engine liner modeling and a description of the key physical mechanisms, with some emphasis on the use of low to high-fidelity tools such as empirical models and commercially available software such as COMSOL, Actran, and PowerFLOW. It is shown that the higher fidelity tools are a critical enabler for the evaluation and construction of future complex liner structures. A systematic study is conducted to predict the acoustic performance of traditional single degree of freedom liners and comparisons are made to experimental data. The effects of grazing flow and bias flow are briefly addressed. Finally, a more advanced structure, a metamaterial, is modeled and the acoustic performance is discussed.

Food calls enhance visual discrimination learning in chimpanzees (Pan troglodytes verus).

Social learning is of universal importance to animal life, and communication is likely to foster it. How do animals recognize when others produce actions that lead to relevant new information? To address this, we exposed 4 chimpanzees to an arbitrary learning task, a 2-choice visual discrimination paradigm presented on a touch screen that led to food reward. In each trial, images were paired with 1 of 4 acoustic treatments: (a) relevant or (b) irrelevant chimpanzee calls ("rough grunts" to food; "pant grunts" to a dominant conspecific), (c) a mechanical noise (hammer knocking sounds) and (d) silence. As we were interested in the effect of food calls on learning speed as compared to control stimuli, each chimpanzee was tested with the food call treatment, and 1 of the 3 control stimuli (either the pant grunt, mechanical noise, or silence condition). We found that learning was significantly enhanced in the contextually correct "rough grunt" condition, suggesting that food calls may play a role in the cultural transmission of food preferences, by priming individuals about a learning opportunity. We discuss these findings and propose that, at least in chimpanzees, the enhancing effect of these vocalizations may be related to the way they affect receivers' motivational/emotional and/or attentional systems. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Optimization of 3D printed porous materials accounting for manufacturing defects

Open-cell materials are well-known for their low price, low weight, and broadband acoustic behavior. They form one of the most used class of acoustic treatments but suffer from a lack of versatility when made by conventional manufacturing processes. Recent advances in additive manufacturing allow to produce porous materials having a controlled microstructure. In this way, the design of treatments including porous materials is not limited to a catalog of existing media. The macroscopic behavior is governed by the micro-geometry of the porous medium, which can be estimated by numerical models. Then, acoustic treatments can be optimized numerically using predicting models and minimization algorithms. However, additive manufacturing induces defects often too complex to be accounted for numerically. In this presentation, a method allowing to obtain the parametric model of the intrinsic behavior of a 3D-printed porous material is presented. The corrected model is used in the optimization of several porous treatments; namely, graded porous materials, folded porous materials and metaporous surfaces. These treatments are versatile and display remarkable properties. They provide quasi-perfect absorption at several frequencies that can be out of reach of standard porous treatments in normal or oblique incidence. Experimental validations confirm the relevance of the proposed design processes.

The challenges and successes of passive acoustic treatments on the International Space Station

Habitable space environments pose unique challenges to the selection of passive acoustic treatments used to mitigate noise. On the International Space Station, strict regulations regarding flammability, particulate release, and off-gassing must be considered during material selection, resulting in the exclusion of many common acoustic treatments used in ground-based applications. The Johnson Space Center Acoustics Office has identified a small subset of acoustic absorption and barrier materials that meet these stringent requirements, and has developed numerous treatments for noise mitigation, including duct-wrapping and liners, acoustic absorption and barrier blankets, and mufflers. The Acoustics Office utilizes impedance and transmission loss tubes to optimize the layering of acoustic materials for these treatments while observing restrictive volume and mass limits. Future acoustic mitigation development will focus on moisture and microbial-resistant materials and treatments that can be utilized in enclosed spaces that require higher scrutiny in regards to cleanliness, such as waste management bays and surfaces surrounding exercise equipment or galleys.

Proposal of Acoustic Liners Combined with Fine-Perforated-Film

This paper deals with a resonant type liner panel with a special surface structure. A typical resonant type liner panel generally consists of a perforated face plate, cells, and a back rigid plate. One of the technical challenges of the acoustic liners applied to the future ultra-high bypass ratio engines is to increase the sound absorption efficiency under grazing conditions because the nacelle, covering of the engine, tends to reduce its length and the lined area. It is known that the sound absorption of the conventional liners tends to deteriorate as grazing flow increases. The authors introduced a special thin acoustically transparent film over the face plate of the acoustic liner. The film, a fine perforated film (FPF), is expected to prevent the interaction of the grazing flow with the opening of the liner face plate. An experimental result with a flow duct rig in JAXA confirmed that the proposed combination of the acoustic liner and the FPF improved the absorption in acoustic energy under grazing conditions, compared with the sole acoustic liner and simple treatment of the FPF.

SEA model for structural acoustic coupling by means of periodic finite element models of the structural subsystems

Statistical Energy Analysis (SEA) often relies on simplified analytical models to compute the parameters required to build the power balance equations of a coupled vibro-acoustic system. However, the vibro-acoustic of modern structural components, such as thick sandwich composites, ribbed panels, isogrids and metamaterials, is often too complex to be amenable to analytical developments without introducing further approximations. To overcome this limitation, a more general numerical approach is considered. It was shown in previous publications that, under the assumption that the structure is made of repetitions of a representative unit cell, a detailed Finite Element (FE) model of the unit cell can be used within a general and accurate numerical SEA framework. In this work, such framework is extended to account for structural-acoustic coupling. Resonant as well as non-resonant acoustic and structural paths are formulated. The effect of any acoustic treatment applied to coupling areas is considered by means of a Generalized Transfer Matrix (TM) approach. Moreover, the formulation employs a definition of pressure loads based on the wavenumber-frequency spectrum, hence allowing for general sources to be fully represented without simplifications. Validations cases are presented to show the effectiveness and generality of the approach.