High Sound Pressure Research Articles

High-Power Ultrasonic Transducer for Effective Hemolysis.

To realize compact and portable hemolysis devices, an ultrasonic transducer with a blood channel is proposed in this study. Ultrasound waves are focused by a parabolic reflector to generate high sound pressure inside the channel for hemolysis. The hemolysis performance of the transducer is evaluated using simulations and experiments. Experiments are performed with various voltages and flow rates to verify the feasibility of hemolysis. The hemolysis rate is more than 93% at an applied voltage of 80 Vp-p, a flow rate of 0.25 mL/min, and a driving frequency of 1.28 MHz.

Influence of the type of acoustic transducer in pure-tone audiometry.

To compare the air-conduction hearing thresholds obtained with different acoustic transducers and verify the users' preferences regarding them. This is a cross-sectional, analytical, observational study with 26 participants aged 18 to 30 years, with normal hearing and no history of exposure to high sound pressure levels or complaints of tinnitus at the time of the assessment. We surveyed their medical history and performed meatoscopy, pure-tone threshold audiometry, speech audiometry, and acoustic immittance. The auditory thresholds were surveyed twice, each time with a different type of acoustic transducer: insert (E-A-RTONE) and circumaural earphones (HDA200). The assessments were performed in a random order, with 5-minute intervals. In the end, we asked the participants which earphones they found more comfortable in the tests. The data were submitted to nonparametric statistical analysis. Assessing the medians in the auditory threshold survey, the circumaural earphones obtained better results at 250, 500, 2000, and 6000 Hz, while the insert earphones were better at 3000 and 4000 Hz; there were no statistical differences at 1000 and 8000 Hz. The circumaural was elected the most comfortable earphone. The circumaural earphones had better auditory thresholds at 250, 500, 2000, and 6000 Hz than the insert earphones and were reported by the patients as the most comfortable type of transducer.

Fabrication of microchannel and diaphragm for a MEMS acoustic sensor using wet etching technique

This paper reports a new technique for fabrication of diaphragm and microchannel in a single step for the development of a piezoelectric MEMS acoustic sensor. It describes the design of the sensor based on ZnO to be utilized for aero-acoustic measurements. A primary requirement for such devices is a high maximum sound pressure level [(SPL) ~180 dB] and flat frequency response in the audio band (20 Hz - 20 kHz). The Si-diaphragm thickness was optimized for the desired SPL range using Coventorware. The complete frequency response of the structure was determined using analytical formulations based on lumped element modeling (LEM). The fabricated device was tested using Laser Doppler Vibrometer (LDV). The lower cut-off frequency, bandwidth, resonance frequency and flat band sensitivity of the optimized device have been found to be 26.3 Hz, 40.0 kHz, 78.688 kHz and 148 μV/Pa respectively.

Improving primary Nbss morphology and fracture toughness in hypoeutectic Nb-Si-Ti ternary alloy by ultrasonic treatment

Nb-Si ultra-high temperature alloys have been a hot topic in aviation materials, but low fracture toughness limits the application. Ultrasound treatment has a significant advantage on the grain refinement and properties improvement, successfully induced into hypoeutectic Nb-Si-Ti ternary alloys to improve primary morphology and fracture toughness. In this work, Nb-16Si-22Ti alloy was treated by ultrasound of 0 s, 80 s, 120 s, 160 s and 200 s. Meanwhile, the coupled physical fields were simulated in Comsol Multiphysics to reveal the mechanism of ultrasonic action. Results show that γ-Nb5Si3 appears with ultrasound induced, and the solidification path is close to the equilibrium transition. Primary Nbss phases were coarsened and spheroidized after ultrasound treatment, and fracture toughness improved by 69.16%. Simulation results show that the strong acoustic active zone is at the height of 15 mm in the ingot, with maximum sound pressure of 36.3 MPa. The high sound pressure can break dendrites. Maximum fluid velocity reaches 0.03 m/s in the longitudinal section and 0.02 m/s in the transversal section with several circulations. Acoustic streaming and cavitation effects break dendrites and spheroidize Nbss phase, benefit to elements distribution uniformly, equilibrium transition and fracture toughness improvement.

Numerical and Experimental Analysis of the Noise Generated in a Ducted Cavity Working in Various Conditions

Flow over a cavity or a gap may induce pressure fluctuations that are emitted as sound waves and perceived by a human as noise. This phenomenon may occur in different kinds of industrial machines or in everyday life devices, e.g., cars. For this reason, it is important to predict the flow conditions that intensify or attenuate the noise. This research paper presents the numerical and experimental analysis of the pressure fluctuations in a deep, ducted cavity. The experimental test stand made it possible to investigate the flow over a cavity with air velocity in the range of 30–80 m/s. The pressure fluctuations were measured using miniature microphones located in the duct and the cavity wall and processed with LabView software. The phenomena were also analysed using the computational fluid dynamics (CFD) technique. The several modelling approaches were tested and validated against the experimental data. The highest sound pressure levels were obtained for 40 and 70 m/s. The sound frequency increased with the flow velocity.

Geometrically Nonlinear Random Response of Stiffened Laminated Plates by Proper-Orthogonal-Decomposition-Based Reduced-Order Modeling

The geometrically nonlinear random vibration response of stiffened laminated plates under acoustic excitation is carried out by using the equivalent linearization (EL) technique combined with the reduced-order model and the finite element method. The nonlinear equations of motion of stiffened laminated plates are obtained based on large deflection finite element formulation. The proper orthogonal decomposition technique is used to select the modal basis, and a reduced-order model of the structures is established. Based on the force error minimization approach, the EL formulation for solving nonlinear random vibration response is derived. Then the EL technique is incorporated into finite element software NASTRAN by the direct matrix abstraction program, and the direct matrix abstraction program also realizes the iterative process of determining the modal equivalent linear stiffness matrix. Then, the statistical dynamic response results obtained by EL and linear method are compared and analyzed. It is verified that the proposed method has high accuracy and efficiency, and it can be applied to the geometric nonlinear random vibration response analysis of stiffened laminated plates. The results show that geometric nonlinearity plays an important role in the vibration response of stiffened laminated plates, especially under high sound pressure loads.

Automotive traffic noise and urban public spaces

In contemporary cities, and usually without realizing it, the population has been exposed to high sound pressure levels, which besides causing discomfort, can lead to health problems. Considering that a large part of this noise comes from emission from motor vehicles, this research aims to evaluate the sound behavior in sound environments configured by voids in the urban fabric, in order to identify whether open spaces can act as attenuators of sound levels. To obtain the expected results, the methodology used was structured from a review of the state-of-the-art and computer simulations relating the variables that influence the formation of urban space and sound emission and propagation, taking as a case study an urban portion of the municipality of Vitória/ES. In parallel, questionnaires were applied to evaluate the user's perception of their exposure. The measurement results indicated that the sound pressure levels caused by traffic noise are above the limit tolerated limit by the NBR norm 10151:2000 for the daytime period. In turn, the results obtained from the population indicated that there is little perception of noise by the users of the spaces surveyed.

Fabrication and Characterization of a Thermophone Based on Laser-Scribed Graphene Intercalated with Multiwalled Carbon Nanotubes.

The low sound pressure level and high operating voltages of thermophones have limited their applications in the past. However, in recent years, utilizing nanomaterials in thermophones has improved their efficiency and applicability. Nanomaterials, especially carbon nanotubes and graphene, have the advantage of low heat capacity per unit area (HCPUA) and high electrical and thermal conductivity. Therefore, they require a low electrical input power and generate a high sound pressure level (SPL) by efficiently transferring heat to the surrounding fluid. Laser-scribed graphene (LSG) can generate smooth spectra acoustic emissions over a wide range of frequencies by means of thermoacoustic (TA) emission. In this work, a thermophone based on LSG intercalated with multiwalled carbon nanotubes (MWCNTs) is proposed. The effects of varying input power, duty cycle percentage and measuring distance on the sound pressure level (SPL) of thermophones are studied to extract maximum efficiency. The achieved SPL of LSG, normalized to the input power, has increased by approximately 11 dB by intercalating it with MWCNTs, which shows that our proposed material can be a potential candidate for an efficient thermophone.

Demodulated sound quality improvement for harmonic sounds in over-boosted parametric array loudspeaker

The parametric array loudspeaker (PAL) can realize sharp directivity utilizing the straightness of ultrasound, but it suffers from low sound quality due to the frequency-dependent response and harmonic distortions. The reproduces sound by PAL has a low sound pressure because it is generated among nonlinear actions in the air. Therefore, we need to over-boost PAL, which means to drive higher voltage than the standard voltage on PAL, to obtain a higher sound pressure in practical use. However, when PAL is over-boosted, the sound quality degrades due to the increasing distortions. Our goal is to reduce the distortion under the over-boosting. As a result, we can improve the sound quality while keeping high sound pressure. In this paper, we propose a sound quality improvement for over-boosted PAL. We involve voltage adaption in the proposed method so that the sound source is processed with optimized parameters for emitting under a determined driving voltage. In the proposed method, the spectral slope of the sound source is modified to reproduce the original slope in the demodulated sound. And then the spectrum of the sound source is further modified to reduce the harmonic distortions in the demodulated sound. The experimental results demonstrated the effectiveness in both sound quality improvement and over-boost adaptation.

Effect of acoustically-induced elastic softening on sound absorption coefficient of hollow glass beads with inner closed cavities.

This study investigated the effects of sound wave magnitude on the sound absorption characteristics of granular materials. The normal incidence sound absorption coefficients of the hollow glass bead packings were measured with different incident sound pressure levels. The measurement results exhibited spectral peaks of sound absorption coefficients at several frequencies, implying that the first peak was caused by the resonance of the hollow glass beads as a layer. Although the first peak in the sound absorption coefficients did not vary when an incident sound pressure was low, the first peak shifted to a lower frequency when the sound pressure exceeded a certain magnitude. These results indicate that the hollow glass beads are softened at high incident sound pressures. Furthermore, by modelling the velocity-dependent elasticity of the hollow glass beads, the velocity and elasticity in the hollow glass beads were simulated in the direction of the sound propagation. The simulation results indicate that the velocity and elasticity profiles depend on the sound wave magnitude. Finally, the velocities of the hollow glass beads under acoustic excitation were measured by inserting an accelerometer into the beads. The measurement results demonstrated that the velocity profile depends on the sound wave magnitude, which parallels the simulation results.

Acoustic study in a main avenue and its effects in classrooms and offices of a university in Mexico City

This study presents the results of a detailed acoustic investigation, systematized and with adequate equipment to the current regulations, carried out in an avenue of intense vehicular traffic located in front of a recently built architectural complex, based on concrete, aluminum, glass, and other materials, called the Postgraduate Unit, belonging to the National Autonomous University of Mexico. These measurements show that, in the initial design of the buildings, the most current knowledge about exterior-interior sound insulation through their facades was not considered. The data collected and the interviews conducted reveal that the Sound Pressure Levels rise, altering the Interior Acoustic Comfort, necessary for the performance of daily academic, administrative and research activities, resulting in permanent inconveniences for users, in addition to the saturation of areas, lack of adequate spaces and excessive unscheduled expenses. Paradoxically, empty spaces are observed in areas with high Sound Pressure Levels, which means that there is a certain level of architectural failure.

Simulation study on characteristics of acoustic metamaterials based on Mie and Helmholtz resonance for low-frequency acoustic wave control

An increasing number of applications require a low-frequency acoustic source to achieve a high sound pressure level (SPL) in the far field; however, controlling low-frequency waves remains a challenge. Recently, phononic crystals have provided a new way to control acoustic waves. For example, the Mie resonant structure, which can reflect low-frequency acoustic waves effectively with its subwavelength size, has been used to realize an acoustic collimated beam. In this work, on the basis of the Mie resonant structure, we designed a Mie-Helmholtz structure (M-H structure) that can use the high sound pressure inside the central cavity to further enhance the far-field SPL and unidirectional directivity. The developed design consists of adding two shells on both sides of the maze-like structure and creating a hole in the middle of the upper shell. We used modal analysis, equivalent medium method to study the structure and obtained lumped parameter model, finding that the M-H structure has physical properties in the XY plane similar to those of the Mie structure while showing a Helmholtz amplification effect in the Z direction. To explore the effect of the new structure on realizing the directivity of low-frequency waves, we also compared the sound field between M-H structure and M-structure. The simulation results showed 8.4% enhancement of the far-field sound intensity and 61.9% enhancement of the directivity index (DI) in main lobe direction. We also provided an example of how this design can be applied to improve low-frequency loudspeaker directivity by adding 4M-H structures and found that the radiation power was restrained in the XY plane and showed better unidirectional directivity (DI ⩾4 dB) in the Z direction. The location of M-H structure for better unidirectional directivity (DI = 9.1 dB) have also been investigated. Finally, we studied the influence of different sizes on the resonance frequency and the SPL gain at the middle hole to explore a guidance for design.

Cam-follower mechanism for airborne ultrasound generation

In this paper, a novel air-coupled concept for high Sound Pressure Level (SPL) and broadband ultrasound generation is presented. The approach is to convert a rotational motion of an electric motor into a multi-period translation motion using a miniature cam-follower mechanism and a sinusoidal cam profile. The design allows the fundamental frequency and generated SPL to be independent of any mechanical resonance phenomenon. A simplified electro-mechanical analysis of the concept is derived in order to obtain the influence of design parameters on the electrical and acoustic performance of the mechanism. Finally, experimental tests are performed on a prototype that has been able to generate up to 120 dB at 1 m and a maximal fundamental frequency of 23 kHz.

Slanted septum and multiple folded cavity liners for broadband sound absorption

The design of acoustic liners with complex cavities for a wide frequency range of attenuation using numerical method is investigated in this paper. Three novel liner concepts are presented, demonstrating predicted improvements in broadband sound absorption when compared with that for conventional designs. The liners include a slanted septum core, a slanted septum core with varying percentage open area, and a MultiFOCAL concept. A finite element model of a normal incidence impedance tube is developed using COMSOL Multiphysics modeling software to predict the acoustic properties (resistance and reactance) of liners at medium and high sound pressure levels, and to study the impact of variations in the liner design parameters. The impedance tube finite element model incorporates non-linear semi-empirical impedance equations, validated by comparing numerical results with measurements performed on a single-degree-of-freedom liner, with a perforated face sheet, at high sound pressure level. The design variables of the novel liner concepts are optimized using a hybrid automated optimisation procedure. The low-frequency optimum slanted septum core concept with an open area of 4.5% for the face sheet and 18% for the short slanted septum is predicted to have an absorption level of at least 14 dB in the frequency range of 400–1000 Hz for normally incident pure tone excitations at 150 dB. The slanted septum core concept with varying percentage open area, with broadband optimum design variables, is predicted to have good broadband sound absorption levels of at least 10 dB in the frequency range of 570–3800 Hz. Finally, the MultiFOCAL liner concept with optimised percentage open areas is predicted to have an excellent broadband sound absorption levels of at least 14 dB, for pure tone excitations at 150 dB, in the frequency range of 900–5300 Hz. This work will be followed by optimisation of the face sheet geometries of these novel liner designs in order to maximise lined duct attenuation for aircraft engine applications.

Design and experimental validation of a high level electropneumatic source

The study and characterization of non-linear phenomena in silencers and microperforated panels under high sound pressure level and mean flow require a dedicated experimental bench with adequate acoustic sources. For this purpose, electropneumatic sources are excellent candidates to reach the expected operating conditions in the laboratory. The challenge is to design a source that can generate a high tonal sound level (> 160 dB SPL) under a significant mean flow (M > 0.1) with a low harmonic distortion. The objective is to focus on mastering the design process of such a tonal source based on an analytical modeling of the physical phenomenon of tonal sound generation and flow as a function of geometrical and pneumatic supply parameters. Based on this validated analytical modeling, a new original source has been developed with the objective of generating a pure harmonic sound in the frequency range [100; 800] Hz, that can reach 180 dB in an infinite duct, combined with a flow up to Mach 0.3. For this purpose, a flow chopper system with a digitally optimized pattern has been specifically developed to minimize harmonic distortion. Considering the need to experimentally evaluate the rate of harmonic distortion with a high degree of accuracy, a complex envelope analysis by Vold-Kalman was implemented in post-processing. Finally, an experimental test campaign was set up on a dedicated bench to test with an open ended duct, for different supply pressures going from 2.07 105 to 3.45 105 Pa, the performances of the new acoustic source. The results of this test campaign show that the device can generate a tonal sound level with a distortion of less than 40 % for the second order and less than 20 % for the higher orders, with a sound pressure level that can reach 186 dB at the resonances in presence of an average flow reaching M = 0.24. These observations are consistent with the predictions of both analytical and numerical models.

High-intensity aerial ultrasonic source with sharp directivity containing a compact circular vibrating plate

An intense aerial ultrasonic source containing a compact circular vibrating plate with a uniform rod-type partially grooved source that can produce large displacement in part of the piston vibration and emit intense sound waves in a direction perpendicular to the vibration surface is investigated. Two different compact circular vibrating plates of intense aerial ultrasonic sources (square grooves and round grooves) are designed by considering the stress generated in ultrasonic sources and the sound pressure of the radiated sound waves. The vibration displacement distribution, the directivity of the emitted sound waves, and the input/output characteristics in designed ultrasonic sources are discussed. It was found that the sound waves can be emitted farther away perpendicular to the vibration surface at a very high sound pressure compared with traditional sources.

How Loud Can you go? Physical and Physiological Constraints to Producing High Sound Pressures in Animal Vocalizations

Sound is vital for communication and navigation across the animal kingdom and sound communication is unrivaled in accuracy and information richness over long distances both in air and water. The source level (SL) of the sound is a key factor in determining the range at which animals can communicate and the range at which echolocators can operate their biosonar. Here we compile, standardize and compare measurements of the loudest animals both in air and water. In air we find a remarkable similarity in the highest SLs produced across the different taxa. Within all taxa we find species that produce sound above 100 dBpeak re 20 μPa at 1 m, and a few bird and mammal species have SLs as high as 125 dBpeak re 20 μPa at 1 m. We next used pulsating sphere and piston models to estimate the maximum sound pressures generated in the radiated sound field. These data suggest that the loudest species within all taxa converge upon maximum pressures of 140–150 dBpeak re 20 μPa in air. In water, the toothed whales produce by far the loudest SLs up to 240 dBpeak re 1 μPa at 1 m. We discuss possible physical limitations to the production, radiation and propagation of high sound pressures. Furthermore, we discuss physiological limitations to the wide variety of sound generating mechanisms that have evolved in air and water of which many are still not well-understood or even unknown. We propose that in air, non-linear sound propagation forms a limit to producing louder sounds. While non-linear sound propagation may play a role in water as well, both sperm whale and pistol shrimp reach another physical limit of sound production, the cavitation limit in water. Taken together, our data suggests that both in air and water, animals evolved that produce sound so loud that they are pushing against physical rather than physiological limits of sound production, radiation and propagation.

Effects of a secondary high amplitude stimulus on the impedance of perforated plates.

High sound pressure levels cause impedance changes in orifices and perforated plates due to vortex shedding and jet formation at the orifices. The effects of an additional high amplitude stimulus, unrelated in terms of frequency and phase, on the impedance of perforated plates received little attention. This work experimentally studies the impedance changes of perforated plates at various primary frequencies when an additional unrelated high-level single tone actuation is applied. It is shown that the impedance, the primary sound field faces, is altered dependent on the particle velocity induced in the orifices by the secondary actuation. Dimensionless quantities correlating the change of impedance with the secondary excitation are identified from the measurements and an empirical model for the change of resistance at quasi-steady flow conditions is derived. The results show that for low amplitude primary sound fields, the change of impedance is completely dependent on the secondary sound field. In case of a high amplitude primary sound field, the impedance is dependent on the particle velocities induced by both sound fields, whereas the larger induced particle velocity is the main contributor to the impedance changes. For unsteady flow conditions, a dependency on the frequency of the secondary actuation is found.

Vertical green walls for noise and temperature reduction – An experimental investigation

The abundance of heat-trapping asphalt and concrete, smog, and heat emitted from buildings and vehicles is one of the major reasons for the prevailing high temperature, air and noise pollution in cities. Incorporation of green wall in buildings is considered to be an effective method to reduce temperature and mitigate environmental pollution. This study investigated and compared the performance of two types of climbing green wall (CGW) and paving green wall (PGW) vegetation for temperature and noise reduction. Besides, the biological characteristics of Parthenocissus tricuspidata and Sedum lineare Thunb were also analyzed to substantiate the temperature and noise reduction performance of these plants. The results revealed that, the average temperature reduction by CGW and PGW were 4.9% ± 1.3% and 16.6% ± 7.4%, respectively, under no irrigation condition, and 18.4% ± 9.4% and 23.8% ± 8.7%, respectively, under irrigation condition. The noise reduction by CGW in high (75–80 dB), medium (50–55 dB) and low (30–35 dB) sound pressure level was 12.4, 7.5 and 5.7 dB, respectively, and 15.6, 9.3 and 7.0 dB, respectively, by PGW. The results demonstrated that green wall has an excellent effect on buildings toward temperature and noise pollution reduction.

Inverse identification of the acoustic pressure inside a U-shaped pipe line based on acceleration measurements

In Oil & Gas industry, the high internal sound pressure levels in pipe lines often cause significant structural vibrations. Quantification of the internal acoustic pressures is therefore an important step in understanding the global fluid–structure behaviour of such systems. However, direct acoustic measurements are often not possible since they generally require intrusive access to the pipe interior. In this paper an inverse procedure is proposed to identify the internal sound pressure field within the bend of a U-shaped pipe, from non-intrusive acceleration measurements on the mechanical structure. First, the accelerance transfer functions are measured in the bends and synthesized using a modal expansion. Under operational excitation conditions, the internal sound pressure is then obtained from a Tikhonov regularization of the inverse problem. The limits of the methodology are investigated numerically and experimentally to serve as a fast diagnostic tool for in situ vibration treatment of piping systems.