Sound Energy Research Articles

Optimal extraction, phytochemical and electrochemical potential assessment of pigments from Persicaria Lapathifolia for dye-sensitized solar cell application

In this study, we concentrated on optimal extraction, phytochemical, and electrochemical assessment of natural pigments from the roots and flowers of Persicaria lapathifolia as new sensitizers in dye-sensitized solar cells. The extraction technique required optimizing the use of acidified ethanol with acetic acid and hydrochloric acid as flower and root extractants, respectively. Photo-electrochemical tests revealed that these pigments could improve the efficiency of DSSCS. The optical characterization revealed maximal absorbance peaks at 462 and 654 nm for root dye and 535, 606 and 666 nm for blossom dye. Phytochemical examination revealed the presence of anthocyanins flavonoids glycoside linkage and betacyanin in both extracts. The Cyclic voltammetry tests revealed oxidation potential peaks in root and floral dyes the HOMO and LUMO potentials were calculated for both dyes, revealing values that could help improve DSSC performance. The DSSCS sensitized with flower extract had an open circuit voltage of 0.649 V a brief current pulse of 3.8 mA and an efficiency of 1.6335%. On the other hand root, pigment-based DSSCS performed slightly inferior with a Voc of 0.55 V an Isc of 3.7 mA, and an efficiency of 1.33%. These findings point to the potential of Persicaria lapathifolia pigments to boost DSSC efficiency emphasizing the relevance of sustainable energy sources. More research and optimization are required to realize the potential of these natural pigments for DSSC applications. This study adds to the investigation of green energy options, notably rooftop photovoltaic systems, in response to an increasing desire for ecologically sound energy solutions.

Numerical and experimental study on the aerodynamic noise characteristics of 600-km/h high-speed maglev trains

Abstract High-speed maglev trains represent a new mode of transportation; however, their 600-km/h traveling speed causes serious aerodynamic noise problems, with very little research on the aerodynamic noise of such trains. To clarify the aerodynamic noise source and radiation characteristics of high-speed maglev trains, both large eddy simulations and wind tunnel experiments with a 1:8 scale three-train model were conducted to obtain the aerodynamic noise source spectrum and spatial distribution characteristics of the maglev train at different speeds; the contribution of the dipole noise source was also analyzed. The results revealed that the train shape has a significant impact on the frequency distribution of the far-field aerodynamic noise below 1 kHz, with the highest sound power concentrated on the train head, especially in the areas around the track joint and streamlined sections. The surface dipole sound source energy increases linearly with speed and is mainly distributed at the bottom of the train head and tail train body. A short-streamlined train exhibited the highest ratio, especially in the trailing edge area, up to 1.42×1011 dB. The far-field sound pressure level of the short-streamlined maglev train is significantly higher, with a maximum difference of about 10 dB(A). The distribution pattern of far-field sound pressure level is influenced by the train type, reflected in the tail train and wake area. Different frequency intervals have different relationships between the acoustic pressure level and frequency; long-streamlined models may enhance broadband features in the sound field distribution of high-speed maglev trains. These findings could be used to guide the aero-acoustic design of maglev trains with a designed speed of 600 km/h.

Synthesis and characterization of antibacterial and low‐temperature resistant slow rebound polyurethane foams

AbstractSlow rebound polyurethane foam (SPUF) has been widely used due to its advantages such as sound insulation, energy absorption, and good tactile sensation. However, SPUF is prone to harden at low temperature, and its application in medical equipment and households requires significant antibacterial properties. In this paper, self‐made silicone modified polyethylene glycol (Si‐APEG) and graphene oxide supported allicin (Alc@GO) were prepared and used as low‐temperature resistant agent and antibacterial agent, respectively. Low‐temperature resistant polyurethane foam (LSPUF) and antibacterial LSPUF (ALSPUF) were prepared respectively with water as foaming agent. The morphology of ALSPUF was observed by scanning electron microscope. Properties studied include apparent core density and porosity, mechanical properties including tensile strength, 40% compressive hardness, and rebound resilience, as well as low‐temperature resistance. Effects of Si‐APEG content on the structures and properties were analyzed and the LSPUF with an Si‐APEG content of 10 wt.% showed the best comprehensive performance. Therefore, ALSPUFs with Si‐APEG content of 10 wt.% and Alc@GO content of 0–3 wt.% were prepared. The addition of Alc@GO increased the antibacterial ratio significantly without obvious effect on the structure and mechanical properties of LSPUF. The antibacterial ratio of ALSPUF reached 99.07% at a Alc@GO content of 2.5 wt.% and testing time of 60 min. This work provides an effective and feasible method for the preparation of ALSPUF which can be widely used in medical devices and households.Highlights Silicone modified polyether is a suitable low‐temperature resistant agent for PU foam. Allicin supported on GO provides good antibacterial property for PU foam. ALSPUF has better mechanical properties than SPU.

Long-Term Outcome of Surgery for Grade 4 Gynecomastia: A Single-Center Experience

Abstract Background Gynecomastia results in a feminine appearance of the male chest, leading to social embarrassment and loss of self-esteem in the afflicted males. Grade 4 gynecomastia is expected to have less than perfect results with liposuction and gland excision alone. This study was done to assess the long-term outcome of this surgery for grade 4 gynecomastia. Materials and Methods From January 2021 to December 2022, 81 patients with grade 4 gynecomastia were treated by us. All the patients underwent vibration amplification of sound energy at resonance (VASER) and suction-assisted liposuction of the chest and side rolls with excision of the gland with crescentic lift in the cases with ptosis. A retrospective study was done to analyze the long-term surgical outcomes in these patients by review of clinical records. Results Symmetry was achieved in 37/39 patients with grade 4a gynecomastia but only in 33/42 patients with grade 4b gynecomastia. The inframammary fold disappeared in 35/39 patients with grade 4a gynecomastia but only in 25/42 of grade 4b gynecomastia patients. Ptosis was corrected in 35/42 grade 4b gynecomastia patients. The mean follow-up was 15 months (range: 12–24 months). Only seven patients desired a second stage to correct the remaining deformity. Conclusion Liposuction with gland removal alone in grade 4a gynecomastia and with liposuction with crescentic nipple–areola complex (NAC) lift in patients of grade 4b gynecomastia give satisfactory results in patients with massively enlarged breasts. While grade 4a gynecomastia has overall better results and lesser complications as compared with grade 4b gynecomastia, the latter also has acceptable outcomes. Realistic prognosis needs to be explained to the patient preoperatively.

Turning up the heat: Effects of temperature on agonistic acoustic communication in the two-spotted goby (Pomatoschistus flavescens)

Acoustic communication is linked to fitness traits in many animals, but under the current scenario of global warming, sound signals can be affected by rising temperatures, particularly in ectothermic organisms such as fishes. This study examines the effect of water temperature in acoustic communication in the two-spotted goby, Pomatoschistus flavescens. To address this, we looked at the effect of different temperatures on the acoustic features of drums produced by males during territorial defence and related it with their auditory sensitivity. We also analysed the differences in acoustic features between male agonistic drums and previously reported male courtship sounds, to better understand how acoustic communication may be affected by different temperature conditions. We recorded two-spotted goby males during territorial intrusions for 10 min at 16 °C, 19 °C, and 21 °C in the laboratory. We found that agonistic drums were shorter, had fewer pulses and shorter pulse periods at higher temperature, in contrast with the peak frequency that remained unaffected. Male agonistic and mating drums (recorded in a previous study) at 16 °C only differed in pulse period, which was higher in mating drums. Hearing thresholds obtained with Auditory Evoked Potentials at 16 °C, revealed higher sensitivity below 400 Hz, matching the main energy of agonistic and mating sounds. Our findings suggest that increasing temperature could potentially affect acoustic communication in this species by reducing the duration of agonistic drums, which might hinder effective communication. Nevertheless, the impact may not be significant as there was a good match between the best hearing sensitivity and the peak frequency range of their calls, which was not influenced by temperature. As fish and other organisms are increasingly threatened by multiple anthropogenic stressors, including warming, future research should address how changes in water temperature impact acoustic communication within a more realistic multi-stressor scenario.

Numerical approach for the simulation of flow-induced noise around a structure with complex geometry: High-speed train bogie in a cavity

The bogie region is a significant source of aerodynamic noise on high-speed trains. Owing to its complex geometry and flow field, numerical simulations using computational fluid dynamics are especially challenging. The main challenge is to achieve a grid with adequate resolution, especially in the boundary layer, while ensuring computational affordability. This challenge is addressed here by employing a hybrid grid, integrating a structured hexahedral mesh near solid surfaces with an unstructured polyhedral mesh in the remaining volume. To limit the number of cells in the boundary layer region, the delayed detached eddy simulation method is adopted. Additionally, to achieve a further reduction in the cell count, the Reynolds number of the model is decreased by scaling down the model size and lowering the inflow speed. The hybrid grid generation and numerical settings are guided by validated simulations of flow over cylinders. A grid sensitivity study, conducted with a simplified half-width bogie model, reveals the meshing requirements for the full-width model. Aerodynamic results highlight the rear section of the cavity and bogie as primary noise sources, emphasizing the critical role of the detached shear layer from upstream components. Time-resolved surface pressure data are input into the Ffowcs Williams–Hawkings equation for far-field noise calculation. The results indicate that the sound energy is concentrated below 200 Hz in the full-scale model, with the cavity contributing more than the bogie. This study provides a practical numerical approach for simulating a structure with complex geometry, offering insights for realistic model simulations.

Spectral noise reduction of double-layer porous asphalt: From laboratory to field

The double-layer porous asphalt (DLPA) pavement is a practical way to mitigate traffic noise from the source. However, there hasn't been much research done on the spectral noise characteristics of the car/truck on this type of pavement with different surface conditions yet. The objective of this paper was to reveal these noise characteristics and the behaviors of the DLPA pavement by laboratory tests and field measurements. First, measurements were made of the road performance of different porous asphalt (PA) mixtures and DLPA structures. Then, a vector impedance measurement system was utilized to evaluate the effects of porosity, aggregate size, and thickness on the sound absorption coefficient (SAC) of the DLPA slabs. Third, a sound meter was used to record the noise levels outside/inside the car/truck on the roads with three surface conditions for the DLPA (PA-10+PA-20) and stone matrix asphalt (SMA) test section, which were paved on an elevated urban road. Finally, an analysis was done on the overall and spectral noise characteristics. The results demonstrated good road performance of these PA mixtures and DLPA structures. Relatively fine and coarse aggregates in the upper and lower layers, respectively, enhanced the sound absorption. But an increase in porosity beyond 20 % and a slight variation in thickness did not considerably improve the sound absorption. Compared to SMA pavement, the overall noises levels of the DLPA pavement were 4–8 dBA lower on the “dry” surface and 6 dBA lower on the “wet” surface. The DLPA pavement exhibited a noise reduction at the full frequency band, which attributed to the pore structure and the relatively fine aggregate used. The interior sound energy always concentrated on the low-frequency band. However, the exterior sound energy on the “dry” and “wet” road surfaces tended to the low-frequency and high-frequency bands, respectively. These findings would shed light on the spectral noise characteristics of the DLPA pavement and provide a new knowledge about the behaviors of the lower layer and upper layer in relation to noise reduction and road performance.

Superhydrophobic cement with hierarchically tunable pore structure by additive manufacturing towards super sound absorption

Noise pollution as a form of environmental problem can have significant negative impacts on human health and the economy. To address this issue, a variety of noise-reduction construction materials have been developed. However, most present noise reduction materials suffer from a narrow absorbing band due to the simple pore structure which restricts their ability to absorb sound energy across a wide frequency range. Here, we demonstrate a hydrogel templating method and create hierarchically structured cement-based materials with tunable pore sizes by means of additive manufacturing. The introduction of this hierarchically tunable structure with micro-nano pores generated by cement hydration contributes to the formation of multi-scale pores (micro-, meso- and macropores), which achieves a sound absorption coefficient of 0.89 at 1000 Hz and ensures broadband acoustic absorption performance (noise reduction coefficient of 0.54, around 50 % improvement compared to traditional construction sound absorption materials). Meantime, this lightweight material has good compressive strength (1.31 MPa) and superhydrophobicity (water contact angle of 152.5°), together with thermal conductivity (0.088 W m−1 K−1) and excellent fire resistance. This study provides a new approach for designing cement-based materials with super sound absorption.

Study on sporty exhaust sound of economical vehicle under acceleration

Exhaust sound quality is an important part of vehicle performance. In this paper, the sporty exhaust sound quality of an economical vehicle equipped with a 4-cylinder and 4-stroke engine is evaluated, analyzed, and improved under acceleration. Firstly, a sporty feeling evaluation method with engine speed divided is proposed, and the influence of exhaust sound order components on sporty exhaust sound is analyzed. The results show that while the A-weighted sound pressure level (ASPL) of Order 2 is lower and the ASPLs of Orders 4 and 6 are higher, the exhaust sound is sportier. Then, a hybrid predicted model of vehicle sporty exhaust sound under acceleration is established based on convolutional neural network (CNN) and support vector regression (SVR) algorithm. The relative errors between the predicted results of CNN-SVR hybrid model and the subjective evaluation results are limited within 2%, which indicates that the CNN-SVR hybrid prediction model achieves a high accuracy in assessing the sporty feeling of exhaust sound. Finally, considering the frequency ranges corresponding with the above order components under the practical accelerating condition, a strategy is proposed to enhance the sporty feeling of exhaust sound by reducing the sound energy within 100 Hz and increasing the sound energy within 100–450 Hz. Based on this strategy, a muffler with different structure is selected and installed on the economical vehicle, and the sporty feeling of exhaust sound is 0.63 points higher than before.

Sound-mediated nucleation and growth of amyloid fibrils

Mechanical energy, specifically in the form of ultrasound, can induce pressure variations and temperature fluctuations when applied to an aqueous media. These conditions can both positively and negatively affect protein complexes, consequently altering their stability, folding patterns, and self-assembling behavior. Despite much scientific progress, our current understanding of the effects of ultrasound on the self-assembly of amyloidogenic proteins remains limited. In the present study, we demonstrate that when the amplitude of the delivered ultrasonic energy is sufficiently low, it can induce refolding of specific motifs in protein monomers, which is sufficient for primary nucleation; this has been revealed by MD. These ultrasound-induced structural changes are initiated by pressure perturbations and are accelerated by a temperature factor. Furthermore, the prolonged action of low-amplitude ultrasound enables the elongation of amyloid protein nanofibrils directly from natively folded monomeric lysozyme protein, in a controlled manner, until it reaches a critical length. Using solution X-ray scattering, we determined that nanofibrillar assemblies, formed either under the action of sound or from natively fibrillated lysozyme, share identical structural characteristics. Thus, these results provide insights into the effects of ultrasound on fibrillar protein self-assembly and lay the foundation for the potential use of sound energy in protein chemistry.

Auditory perception based milling posture detection and depth control enhancement for orthopedic robots

The use of robots for bone milling is thought to improve surgical efficiency and reduce surgeon fatigue. Surgeons can use their hearing to perceive the milling state and adjust the position of surgical tools. Inspired by this, this paper proposes an automatic tool position control method based on acoustic signal feedback. Firstly, the mapping model between milling depth and sound energy was calibrated through experiments, and the influence of different angles on depth estimation accuracy was tested. Then, a network of CNN-GRU with an attention mechanism is designed to realize milling angle recognition using acoustic features as inputs. Finally, a milling depth automatic control framework with angle optimization was designed and validated through relevant experiments. The results of the experiment showed that the depth estimation error was larger when the milling angle of ball end milling tools (BMT) was within 70-90°. After adding the angle adjustment function, the milling depth accuracy in angle interval 1 (80-90°) and angle interval 2 (70°-80°) increased by about 30% and 10%, respectively.

Fibro-porous materials: 3D-printed hybrid porous materials for multifunctional applications

This work demonstrates the additive manufacturing of fibro-porous materials—hybrid materials with a fiber mesh integrated within the open cells of a base porous scaffold. The presented method allows seamless incorporation of fibers, with precise control of the fiber diameter and mesh density, into the scaffold without requiring any additional postprocessing steps. Here, using a gyroid pore architecture as the base scaffold, this study fabricates the fibro-porous materials using an extrusion-based additive technique and investigates their resultant sound absorption, pressure drop, mechanical stiffness, and energy absorption properties. Two-microphone normal incidence impedance tube measurements reveal significant improvements in the sound absorption performance compared to that of denser, fiberless porous material counterparts while maintaining a 33 % lighter weight. Additional tests, including pressure drop and static airflow resistivity measurements, indicate that fiber integration reduces the effective pore size and increases flow resistance, boosting sound absorption at lower frequencies. The mechanical properties are also markedly improved, with stiffness and yield stress increasing by 27 % and 37.85 %, respectively. The fibro-porous samples provide 30 % more energy absorption per unit volume due to their increased resistance to deformation. This research demonstrates that additively manufactured fibro-porous materials provide substantial multifunctional performance gains without significant weight increase. The adaptable manufacturing process is compatible with various extrudable materials and opens a new route to designing complex, customized engineering structures with application-specific functionalities.

Complications after liposuction: current state of the problem (literature review)

The variety of body shape correction techniques based on liposuction and currently used in plastic surgery is largely due to the desire to achieve the greatest possible cosmetic effect and, at the same time, minimize the possible negative consequences of invasive intervention. The choice of a specific method depends on a number of factors, among which are the treatment plan agreed with the patient, the individual characteristics of the patient being operated on, the presence or absence of medical contraindications to the use of certain techniques, the qualifications of the personnel, the level of material equipment of the operating unit. Liposuction is the aspiration of fat from subcutaneous tissue. It can be used for aesthetic lipoplasty or combined with body contouring surgery. The article is of a review nature and contains modern data on the medical effects of liposuction, VASER (Vibration Amplification of Sound Energy at Resonance) and PAL (Power Assisted Liposuction) techniques, and possible complications after liposuction.

Comparative study of aeroacoustic performance of 1/8 and 1/1 pantographs coupled with cavity

The technology of pantograph sinking in the cavity is generally adopted in the new generation of high-speed trains in China for aerodynamic noise reduction in this region. This study takes a high-speed train with a 4-car formation and a pantograph as the research object and compares the aerodynamic acoustic performance of two scale models, 1/8 and 1/1, using large eddy simulation and Ffowcs Williams–Hawkings integral equation. It is found that there is no direct scale similarity between their aeroacoustic performance. The 1/1 model airflow is separated at the leading edge of the panhead and reattached to the panhead, and its vortex shedding Strouhal number (St) is 0.17. However, the 1/8 model airflow is separated directly at the leading edge of the panhead, and its St is 0.13. The cavity’s vortex shedding frequency is in agreement with that calculated by the Rooster empirical formula. The two scale models exhibit some similar characteristics in distribution of sound source energy, but the energy distribution of the 1/8 model is more concentrated in the middle and lower regions. The contribution rates of their middle and lower regions to the radiated noise in the two models are 27.3% and 87.2%, respectively. The peak frequencies of the radiated noise from the 1/1 model are 307 and 571 Hz. The 307 Hz is consistent with the frequency of panhead vortex shedding, and the 571 Hz is more likely to be the result of the superposition of various components. In contrast, the peak frequencies of the radiated noise from the 1/8 scale model are 280 and 1970 Hz. The 280 Hz comes from the shear layer oscillation between the cavity and the bottom frame, and the 1970 Hz is close to the frequency at which the panhead vortex sheds. This shows that the scaled model results need to be corrected before applying to the full-scale model.

The effect of information integration on team communication in a simulated submarine control room task

Submarine control rooms are characterised by dedicated individual roles for information types (e.g. Sonar operator processes sound energy), with individuals verbally reporting the information that they receive to other team members to help resolve uncertainty in the operational environment (low information integration). We compared this work design with one that ensured critical information was more readily available to all team members (high information integration). We used the Event Analysis of Systemic Teamwork (EAST) method to analyse task, information, and social networks for novice teams operating within a simulated submarine control room under low versus high information integration. Integration impacted team member centrality (importance relative to other operators) and the nature of information shared. Team members with greater centrality reported higher workload. Higher integration across consoles altered how team members interacted and their relative status, the information shared, and how workload was distributed. However, overall network structures remained intact.

Sound transmission loss and energy absorbing performance of stiffened doubly-curved shells with corrugated-honeycomb hybrid cores

Compared to traditional lightweight corrugation and cellular cores, the novel cellular cores auxetic metamaterials with negative and zero Poisson's ratios possess distinctive mechanical deformation traits, making them suitable for modeling lightweight sandwich structures. Therefore, the concept of combining auxetic metamaterial cellular with folded corrugation is proposed to construct a new type of corrugated honeycomb hybrid cores for studying the sound insulation and energy absorption characteristics of the stiffened sandwich doubly-curved shells, wherein the honeycomb core possesses a full range of Poisson's ratio characteristic and is composed of cellular cores exhibiting positive, negative, and zero Poisson's ratios (PPR, NPR, and ZPR). The Hamilton's principle is hired to derive the governing equations and considers fluid-structure coupling by applying normal velocities continuity conditions at the fluid-structure interface, which is further analytically solved using Navier's techniques, and the sound transmission loss (STL) is described analytically. The accuracy of these results is validated through comparisons with both experimental measurements conducted in an impedance tube and simulated outcomes generated by the COMSOL commercial software. The properties of stiffened sandwich doubly-curved shells with corrugated honeycomb hybrid cores are meticulously evaluated and compared, and the results show that the hybrid cellular core type significantly impacts the STL, wherein the average STL of the corrugation ZPR cellular hybrid cores stands at 42.06 dB within the broad low-frequency range of 380–2422 Hz, which has increased by 9.11% and 8.31% compared to the values of the corrugation NPR and traditional PPR cellular hybrid cores, the specific energy absorption (SEA) of the corrugation ZPR cellular hybrid cores is 13.06 kJ/m3, which has increased by 16.19% and 18.08% compared with the corrugation NPR and PPR cellular hybrid cores, respectively, indicating that the corrugation ZPR cellular hybrid cores have better sound insulation and energy absorption characteristics than the corrugation NPR and PPR cellular hybrid cores.

Far-focus compound ultrasound imaging with lag-one coherence-based zero-cross factor

BACKGROUND: Ultrasound imaging has been widely used in clinical examination because of portability, safety, and low cost. However, there are still some main challenges of imaging quality that remain in conventional ultrasound systems. OBJECTIVE: Improving image quality of SA-based methods using an improved imaging mode named far-focus compound (FSC) imaging. METHODS: A far-focus compound (FSC) imaging based on full-aperture transmission and full-aperture reception is proposed in this paper. In transmission, it uses the full aperture to transmit the focused beam to ensure image resolution and emission of sound field energy. In reception, the full aperture is used to receive the reflected beam to ensure the image quality. A lag-one coherence-based zero-cross factor (LOCZF) is then implemented in FSC for improvement of contrast ratio (CR). The LOCZF uses lag-one coherence as zero-cross factor’s adaptive coefficient. Comparisons were made with several other weighting techniques by performing simulations and experiments for performance evaluation. RESULTS: Results confirm that LOCZF applied to FSC offers a good image contrast and simultaneously the speckle pattern. For simulated cysts, CR improvement of LOCZF reaches 194.1%. For experimental cysts, CR improvement of LOCZF reaches 220%. From the in-vivo result, compared with FSC, CR improvement of LOCZF reaches 112.7%. CONCLUSION: Proved gCNR performance. In addition, the LOCZF method shows good performance in experiments. The proposed method can be used as an effective weighting technique for improvement of image quality in ultrasound imaging.

Topology optimization of chiral metamaterials with application to underwater sound insulation

Chiral metamaterials have been proven to possess many appealing mechanical phenomena, such as negative Poisson’s ratio, high-impact resistance, and energy absorption. This work extends the applications of chiral metamaterials to underwater sound insulation. Various chiral metamaterials with low acoustic impedance and proper stiffness are inversely designed using the topology optimization scheme. Low acoustic impedance enables the metamaterials to have a high and broadband sound transmission loss (STL), while proper stiffness guarantees its robust acoustic performance under a hydrostatic pressure. As proof-of-concept demonstrations, two specimens are fabricated and tested in a water-filled impedance tube. Experimental results show that, on average, over 95% incident sound energy can be isolated by the specimens in a broad frequency range from 1 kHz to 5 kHz, while the sound insulation performance keeps stable under a certain hydrostatic pressure. This work may provide new insights for chiral metamaterials into the underwater applications with sound insulation.

Modification of the transfer matrix method for the sonic black hole and broadening effective absorption band

Sonic black hole (SBH) is capable of the concentration for the sound energy by the shrinking duct and appropriate wall admittance. However, the concentrated energy cannot be dissipated due to the weak air damping. Meanwhile, when the inserted rings are insufficient, the accuracy of the conventional transfer matrix method (TMM) is less than satisfactory for the simulation of the original SBH. In this study we commit to modify this simulation method and broaden the effective absorption band by using porous materials. First, we derived the acoustic transfer relationship of the conical cavity and the acoustic admittance of the toroidal cavity, via formulating the basic equation. After combining with the two method, the modified TMM (MTMM) results show excellent agreement with the finite element results. The applicability of the derived wall admittance is analyzed in detail. The MTMM has also been applied to obtain the sound absorption of a SBH configuration with embedded porous materials (PMSBH). The proposed PMSBH can effectively dissipate the concentrated sound energy, leading to the ultra-low cut-on frequency of near-perfect absorption. Specifically, the cut-on frequency of the PMSBH is 387 Hz, with the corresponding wavelength being 8.8 times than the structural length. In addition, the parametric analysis shows the near independence of the absorption performance of the PMSBH on the damping loss, so that the PMSBH can achieve excellent absorption without adding other acoustic materials. These appealing characteristic could promote the application of the PMSBH in noise control.

RESEARCH OF THE NOISE LOAD OF VEHICLES

Noise can be viewed as an undesirable component of a signal that can affect the quality of perception or transmission of information in a system. In different contexts, the term «noise» may have different meanings, but a common feature is the random impulsive nature of this phenomenon. Automotive noise is sound energy generated by the movement of a vehicle and its components. The study of road traffic noise is an important area, especially in environments where noise can have a significant impact. This includes analyzing noise levels, identifying noise sources, assessing its impact on the environment, and developing strategies to reduce noise. This study analyzes the causes of automobile noise and their noise sources, and provides classification features. The research methodology included measuring the noise level at different points of the bus interior using a specialized acoustic sound level meter Testo 816. The Sound Meter program was additionally used to obtain current time values of noise level changes with graphical data interpretation. When the bus is idling, a monotonous noise load level in the range of 58-63 dB is observed in the cabin, which is typical for a running diesel engine, which is the main source of noise. The movement of the bus in urban conditions is accompanied by a change in traffic conditions, which in turn increases the maximum noise load to 73 dB. The movement of the bus in the city is accompanied by an increase in the noise load up to 74 dB and the equivalent up to 67 dB. This is due to an increase in speed, contact of tires with the asphalt road, interaction of the air environment with bus elements, the appearance of vibrations and other noises.Although the noise load in the bus interior is within the upper permissible limits, it requires the introduction of noise reduction measures, especially for long-distance buses for a comfortable ride for passengers. Therefore, it is important to take noise levels into account when designing and operating vehicles, as well as when planning urban infrastructure projects.