Acoustic Horn Research Articles

Methodology for 3D sound synthesis of directional acoustic sources by higher-order ambisonics

This paper presents the 3D sound field synthesis using both the multimodal method and higher-order ambisonics (HOA) of the pressure field radiated by directional acoustic sources. Ambisonics is a technique for encoding and reproducing measured or modeled (virtual) sound pressure field, based on a decomposition of the acoustic field over spherical harmonics. The directional source considered in this work is an acoustic horn excited by a flat piston. The free-field radiation from this horn is first modeled accurately over a wide frequency range using the multimodal method, which requires relatively low computational resources. This radiated pressure field, collected on a dual-layer sphere of virtual sensors distributed over a Lebedev geometry, allows its projection into the ambisonic domain. The pressure field is then synthetized in the laboratory's 3D 5th order HOA spatialization sphere, which consists of fifty-six loudspeakers. This offers the ability of listening to the radiated sound using a higher-order ambisonic synthesis of a 'virtual' source before it is manufactured. To qualitatively evaluate the performance of the proposed procedure, the transfer function of the synthesized horn is measured around the listening point within the spatialization sphere. Key words : 3D sound synthesis, high-order ambisonics, directive sources, waveguides, horn, multimodal method

Analytical modeling of acoustic exponential materials and physical mechanism of broadband anti-reflection

Spatially exponential distributions of material properties are ubiquitous in many natural and engineered systems, from the vertical distribution of the atmosphere to acoustic horns and anti-reflective coatings. These media seamlessly interface different impedances, enhancing wave transmission and reducing internal reflections. This work advances traditional transfer matrix theory by integrating analytical solutions for acoustic exponential materials, which possess exponential density and/or bulk modulus, offering a more accurate predictive tool and revealing the physical mechanism of broadband anti-reflection for sound propagation in such non-uniform materials. Leveraging this method, we designed an acoustic dipole array that effectively mimics exponential mass distribution. Through experiments with precisely engineered micro-perforated plates, we demonstrate an ultra-low reflection rate of about 0.86% across a wide frequency range from 420 Hz to 10,000 Hz. Our modified transfer matrix approach underpins the design of exponential materials, and our layering strategy for stacking acoustic dipoles suggests a pathway to more functional gradient acoustic metamaterials.

Procedure in developing a longitudinal-torsional vibration-assisted micro-milling system

Micromachining is an advanced microfabrication technique for micro-sized or micro-accuracy products through subtractive manufacturing such as micro-milling. Vibration-assisted machining (VAM) is a method in which small amplitude vibrations are applied to the tool or workpiece to enhance the fabrication process. Milling results could be improved by adding longitudinal and torsional vibration to the tool using piezoelectric components vibrating at the ultrasonic frequency with an amplitude of less than 1 μm is used. A slip ring is required to transmit electric power from a static structure to a rotating frame. After the power has been transmitted to the system, an ultrasonic horn, called an acoustic horn or sonotrode, amplifies the vibrations at the tool’s tip. Since the excitation vibration is only longitudinal, the magnification of the vibration at the tooltip is also only longitudinal. Grooves are added to the side of the ultrasonic horn to produce torsional vibrations. This vibration is then simulated through finite element analysis software, explicitly using explicit dynamics. A 3D simulation is run for a quarter cycle of micro-milling through a Ti-6Al-4V material. It could be concluded that the LTVAM application may improve machining quality, such as temperature reduction of up to 9%, cutting force reduction of up to 35%, and surface roughness improvement of up to 27%.

Acoustic lens that diffuses plane waves composing of multiple spherical obstacles

Recently, a non-electrical smartphone loudspeaker based on acoustic horn has been created and marketed. An acoustic horn is directional and has the advantage of propagating strong sound pressure in the direction the horn is facing. However, it has the disadvantage that sound pressure cannot be expected in any direction other than the direction in which the form facing. This study proposed an acoustic lens in the form of a cylinder composed of multiple spherical obstacles. The density of the sphere was calculated using the phase difference equation and the equation proposed by Kock et al. The density of the sphere at the center of the lens is lower than at the circumferential direction. This change in density slows down the apparent sound speed passing through the further from the center. In this work, FDTD simulations were performed to evaluate the sound directivity for the acoustic lens. This work also test manufactured the acoustic lens and performed an experiment in an anechoic chamber to evaluate the characteristics of the lens.

Design and Analysis of Acoustic Horn for Assistance in Die-Sinking EDM

Many industrial applications and production technologies are based on the application of ultrasound. In many cases, the phenomenon of ultrasound is also applied in the technological processing of the machining of materials. The main element of equipment that uses the effect of ultrasound for machining is the ultrasonic horn. It is also called a sonotrode. The performance of ultrasonic machining technologies depends on the properly designed sonotrode shape. The dependence of fundamental modal properties (natural frequencies, mode shapes) of various sonotrode shapes for various geometrical parameters is analyzed. Modal analysis of the models is determined by the numerical simulation using the finite element method (FEM) design procedure. In ultrasonic machining, the ultrasonic horn plays a vital part in the high-energy machining process. Electric discharge machining (EDM) is used to achieve high processing quality but the machining efficiency is low. The new (EDM+USM) is used for high machining efficiency. The acoustic analysis of the ultrasonically vibrating tool is done with the assistance of the finite element method (FEM) so that it can be used for EDM applications. Key Words: Modal analysis, Ultrasonic horn, Numerical analysis, efficiency of machining, acoustic analysis.

Efficient multimodal-based shape optimization of acoustic horns with application to subwavelength perfect transmission

This paper presents an efficient multimodal-based shape optimization method for maximizing sound radiation from open-ended acoustic horns. The proposed method tightly integrates the improved multimodal admittance method with interpolation-based geometry parameterization to allow flexible design degrees of freedom, with computational cost for gradient evaluation nearly independent of the number of design variables. We demonstrate that our method outperforms an existing discrete-model-based approach in solving typical narrowband and wideband horn design problems, offering increased efficiency and flexibility. For the first time, we achieve novel resonator-like waveguide designs with subwavelength perfect transmission well below the cut-off frequency of classical horns by performing shape optimization. The optimal waveguides exhibit single to multiple transmission peaks or bandpass characteristics. We validate the designs numerically and experimentally and demonstrate that the perfect transmission is related to the excitation of the acoustic resonant mode. Our method has potential applications in the design of compact high-output subwoofers, anechoic duct terminations, and acoustic filters.

In-situ formation of amorphous Al2O3 interphase during ultrasonic-assisted soldering process of ZrO2 ceramic and 1060Al using Sn filler at low temperature

The dissimilar ZrO2/Sn/Al butt joints were successfully achieved by ultrasonic-assisted soldering using a needle-shape acoustic horn at 350 °C. It was found that the bonding mechanism of the dissimilar butt joints was based on the interfacial sono-oxidation reactions leading to the formation of the amorphous Al2O3 layers of 6 nm and 12 nm thickness at the ZrO2/Sn and Al/Sn interfaces, respectively. The average tensile strength of the ZrO2/Sn/Al butt joints was tested to be 29.2 MPa.

Physical acoustics homework problems written by students: Undisciplined, irreverent, and original

“Study hard what interests you the most in the most undisciplined, irreverent and original manner possible” [Perfectly Reasonable Deviations from the Beaten Track, Richard P. Feynman, Basic Books, 2005]. Writing original homework problems is a powerful way students of physical acoustics can practice Feynman’s advice. Three problems that involve a broad range of concepts covered in introductory graduate-level physical acoustics courses illustrate how the student-author unleashed his creativity in an undisciplined manner, injected his problems with an irreverent sense of humor, and derived a great sense of originality and ownership over physical acoustics. The problems synthesize David T. Blackstock’s problems 1D-2, 1E-3, 1G-1, 1G-3, 7-6, 10-10, and 10-11 [Fundamentals of Physical Acoustics, David T. Blackstock, Wiley, 2000], addressing concepts including acoustic intensity, impedance, horns, enclosures, and radiation. [CAG was supported by the ARL:UT Chester M. McKinney Graduate Fellowship in Acoustics.]

Frequency range of acoustic horn enclosing gas with various sound speeds

Frequency range of acoustic horn enclosing gas with various sound speeds

Control of Acoustic Energy Input for Cleaning of Industrial Boilers

A non-intrusive cleaning method for boiler tubes at Sasol Synfuels power station at Secunda, in the Mpumalanga province of South Africa, is preferred over conventional methods that require boiler shutdown. The elected non-intrusive cleaning method utilizes sound energy waves, produced by an acoustic horn. Due to the nature of sound propagation and the effectiveness required, there is a requisite to control and operate the sonic horn. If the acoustic horn’s sound frequency is too low, it will produce higher sound energy waves that will resonate with the plant’s harmonious frequency and cause structural damage. Conversely, if the sonic horn’s sound frequency is too high, excessive noise levels may be reached and annoy plant personnel. To prevent these undesirable outcomes posed by adopting acoustic cleaning, there needs to be a regulatory system incorporated into the configuration to mitigate vibrations and limit noise. The regulatory system comprises a control system that drives the acoustic horn’s sound frequency as intended through a set point. The designed control system meets the anticipated requirements, such that it has an ideal transient response of 0.562 s, a steady-state error achieved in 1.05 s, with 0.201% overshoot, and most importantly the closed-loop system is stable.

Analysis and design of 2-dimensional acoustic particle velocity horns

A two-dimensional acoustic horn packaged with a 2-D acoustic particle velocity sensor (APVS) is presented. The particle velocity amplification factor of the 2-D acoustic horn is analyzed theoretically and experimentally. The experimental results show a good agreement with the theoretical expectations. Compared with the previous horn model, this model considers the gain attenuation at low frequency and the influence of chip assembly deviation. As the particle velocity distribution changes greatly in the boundary layer, the assembly deviation of the chip has a great influence on the package gain. Furthermore, a microphone and the 2-D particle velocity sensor was packaged in the acoustic horn to detect the acoustic pressure and 2-D particle velocity at one point. The acoustic horn has an omnidirectional response for acoustic pressure. By using the mode domain beamforming, the direction of the incident wave was estimated with this two-dimensional sound intensity probe.

Acoustic horn tool assembly design for ultrasonic assisted turning and its effects on performance potential

ABSTRACT Principally, hard material such as SS304 deployed a huge stress to process through conventional machining. Since, ultrasonic-assisted turning involves a synchronized ultrasonic vibration to the tool to establish intermittent cutting and could be a feasible choice. Thus, a comprehensive study was exercised to design horn-tool assembly for ultrasonic assisted turning and fabricated a potential experimental setup to address its machining potential to machine stainless steel. ANSYS® was incorporated to perform Harmonic and Modal analysis to obtained the horn-tool natural frequency, optimum shape and length respectively. The analysis showed 19925.5 Hz natural frequency and amplitude propagation approximately 4 times for 126 mm length along with 5 mm tool insert thickness. Further Taguchi method employed for the design of experiment and performed gray Taguchi for multi objective optimization. Investigation shows the induced cutting force and the surface roughness reduced significantly as low as to 53.89% and 54.5%, respectively, by ultrasonic turning. The machining parameters found optimum at a parametric setting: depth of cut 0.2 mm, feed 0.06 mm/rev and cutting velocity 38.48 m/min respectively favorable for getting low cutting force and high surface finish. Finally, results of the experiment invoked that ultrasonic assisted turning is a promising technique for hard material.

Multi-fidelity regression using artificial neural networks: Efficient approximation of parameter-dependent output quantities

Highly accurate numerical or physical experiments are often very time-consuming or expensive to obtain. When time or budget restrictions prohibit the generation of additional data, the amount of available samples may be too limited to provide satisfactory model results. Multi-fidelity methods deal with such problems by incorporating information from other sources, which are ideally well-correlated with the high-fidelity data, but can be obtained at a lower cost. By leveraging correlations between different data sets, multi-fidelity methods often yield superior generalization when compared to models based solely on a small amount of high-fidelity data. In the current work, we present the use of artificial neural networks applied to multi-fidelity regression problems. By elaborating a few existing approaches, we propose new neural network architectures for multi-fidelity regression. The introduced models are compared against a traditional multi-fidelity regression scheme — co-kriging. A collection of artificial benchmarks are presented to measure the performance of the analyzed models. The results show that cross-validation in combination with Bayesian optimization leads to neural network models that outperform the co-kriging scheme. Additionally, we show an application of multi-fidelity regression to an engineering problem. The propagation of a pressure wave into an acoustic horn with parametrized shape and frequency is considered, and the index of reflection intensity is approximated using the proposed multi-fidelity models. A finite element, full-order model and a reduced-order model built through the reduced basis method are adopted as the high- and low-fidelity, respectively. It is shown that the multi-fidelity neural networks return outputs that achieve a comparable accuracy to those from the expensive, full-order model, using only very few full-order evaluations combined with a larger amount of inaccurate but cheap evaluations of the reduced order model.

Geographic variation in the skulls of the horseshoe bats, Rhinolophus simulator and R. cf. simulator: Determining the relative contributions of adaptation and drift using geometric morphometrics.

The relative contributions of adaptation and genetic drift to morphological diversification of the skulls of echolocating mammals were investigated using two horseshoe bat species, Rhinolophus simulator and R. cf. simulator, as test cases. We used 3D geometric morphometrics to compare the shapes of skulls of the two lineages collected at various localities in southern Africa. Size and shape variation was predominantly attributed to selective forces; the between‐population variance (B) was not proportional to the within‐population variance (W). Modularity was evident in the crania of R. simulator but absent in the crania of R. cf. simulator and the mandibles of both species. The skulls of the two lineages thus appeared to be under different selection pressures, despite the overlap in their distributions. Difference in the crania of R. cf. simulator was centered largely on the nasal dome region of R. cf. simulator but on the cranium and mandibles of R. simulator. It is likely that the size and shape of the nasal dome, which acts as a frequency‐dependent acoustic horn, is more crucial in R. cf. simulator than in R. simulator because of the higher echolocation frequencies used by R. cf. simulator. A larger nasal dome in R. cf. simulator would allow the emission of higher intensity pulses, resulting in comparable detection distances to that of R. simulator. In contrast, selection pressure is probably more pronounced on the mandibles and cranium of R. simulator to compensate for the loss in bite force because of its elongated rostrum. The predominance of selection probably reflects the stringent association between environment and the optimal functioning of phenotypic characters associated with echolocation and feeding in bats.

Early works of David Blackstock in nonlinear acoustics: A view from the former Soviet Union

This presentation outlines some moments in the development of modern nonlinear acoustics in the 1960s–1980s, in which Professor David Blackstock played a significant role. In those times of limited contacts between the American and Soviet scientific communities, David was the first to notice our works in the area. He initiated and supported our contacts, first by regular mail (no Internet at that time!) and then, when it became possible, by inviting us to the USA. Our areas of common interest included, among others, radiation and diffraction of nonlinear acoustic beams, horn antennas, and parametric arrays. A few examples of parallel developments in these areas will be described.

Spray characteristics of an ultrasonic microdroplet generator with a continuously variable operating frequency.

Droplet spraying is utilized in diverse industrial processes and biomedical applications, including nanomaterial synthesis, biomaterial handling, and inhalation drug delivery. Ultrasonic droplet generators transfer energy into bulk liquids using acoustic waves to disrupt the free liquid surface into fine microdroplets. We previously established a method combining ultrasonic actuation, resonant operation, and acoustic wave focusing for efficient spraying of various liquids (e.g., low surface tension fuels, high viscosity inks, and suspensions of biological cells). The microfabricated device comprises a piezoelectric transducer, sample reservoir, and an array of acoustic horn structures terminated by microscale orifices. Orifice size roughly dictates droplet diameter, and a fixed reservoir height prescribes specific device resonant frequencies of operation. Here, we incorporate a continuously variable liquid reservoir height for dynamic adjustment of operating parameters to improve spray efficiency in real-time and potentially tune the droplet size. Computational modeling predicts the system harmonic response for a range of reservoir heights from 0.5 to 3 mm (corresponding to operating frequencies from ∼500 kHz to 2.5 MHz). Nozzle arrays with 10, 20, and 40 μm orifices are evaluated for spray uniformity and stability of the active nozzles, using model predictions to explain the experimental observations.

Design and Optimization of Sensitivity Enhancement Package for MEMS-Based Thermal Acoustic Particle Velocity Sensor.

In this paper, small-sized acoustic horns, the sensitivity enhancement package for the MEMS-based thermal acoustic particle velocity sensor, have been designed and optimized. Four kinds of acoustic horns, including tube horn, double cone horn, double paradox horn, and exponential horn, were analyzed through numerical calculation. Considering both the amplification factor and effective length of amplification zone, a small-sized double cone horn with middle tube is designed and further optimized. A three-wire thermal acoustic particle velocity sensor was fabricated and packaged in the 3D printed double cone tube (DCT) horn. Experiment results show that an amplification factor of 6.63 at 600 Hz and 6.93 at 1 kHz was achieved. A good 8-shape directivity pattern was also obtained for the optimized DCT horn with the lateral inhibition ratio of 50.3 dB. No additional noise was introduced, demonstrating the DCT horn’s potential in improving the sensitivity of acoustic particle velocity sensors.

Finite Element Simulation and Shape Optimization of Acoustic Horn

Horn refers to the tube with continuous change of cross-sectional area, which can improve the matching of diaphragm and air load, so as to improve the electro acoustic conversion efficiency. For long-distance strong sound equipment, the purpose of using horn is to pursue higher sound pressure level, and control directivity and smoothness of sound pressure level response. In order to obtain higher sound pressure level and sharper directivity, parametric curve expressions of conical, exponential, hyperbolic and parabolic horn were derived. By using COMSOL multiphysics software, two-dimensional axisymmetric finite element simulation models of conical, exponential, hyperbolic and parabolic horn were established. Combined with if + end if programming function of the software, the effects of different cross-section shapes of horn on far-field sound pressure level and directivity were analyzed. The simulation results show that the parabolic horn can achieve a higher sound pressure level, and the sound pressure level is more than 3dB higher than the other three in the frequency band above 2000Hz. In the aspect of directivity, the beam width of parabolic horn is the smallest and more stable, and the overall directivity is the strongest. By using the shape optimization function of the software and constructing 8-order Bernstein polynomials, based on the parabolic horn, the shape of the horn was optimized for the most sensitive frequency range of 2000-4000hz, and the sound pressure level of the optimized horn was significantly improved in a large frequency range. This paper can provide technical reference for the design and development of horn loudspeaker.

MfEGRA: Multifidelity efficient global reliability analysis through active learning for failure boundary location

This paper develops mfEGRA, a multifidelity active learning method using data-driven adaptively refined surrogates for failure boundary location in reliability analysis. This work addresses the issue of prohibitive cost of reliability analysis using Monte Carlo sampling for expensive-to-evaluate high-fidelity models by using cheaper-to-evaluate approximations of the high-fidelity model. The method builds on the Efficient Global Reliability Analysis (EGRA) method, which is a surrogate-based method that uses adaptive sampling for refining Gaussian process surrogates for failure boundary location using a single-fidelity model. Our method introduces a two-stage adaptive sampling criterion that uses a multifidelity Gaussian process surrogate to leverage multiple information sources with different fidelities. The method combines expected feasibility criterion from EGRA with one-step lookahead information gain to refine the surrogate around the failure boundary. The computational savings from mfEGRA depends on the discrepancy between the different models, and the relative cost of evaluating the different models as compared to the high-fidelity model. We show that accurate estimation of reliability using mfEGRA leads to computational savings of $\sim$46% for an analytic multimodal test problem and 24% for a three-dimensional acoustic horn problem, when compared to single-fidelity EGRA. We also show the effect of using a priori drawn Monte Carlo samples in the implementation for the acoustic horn problem, where mfEGRA leads to computational savings of 45% for the three-dimensional case and 48% for a rarer event four-dimensional case as compared to single-fidelity EGRA.

Shape optimization of acoustic horns for improved directivity control and radiation efficiency based on the multimodal method.

The multimodal method is used to develop an approach for optimizing the shape of axisymmetric acoustic horns for both well-controlled directivity and high radiation efficiency over a wide frequency range. A horn with an arbitrary profile can be efficiently modeled with the multimodal method by projecting the wave field over transverse modes in connected short cylinders; the radii of the cylinders are used directly as design variables. Many design variables are employed in the optimization process to ensure design flexibility and computational accuracy. The relative weights for the design objectives of constant directivity, high radiation efficiency, and acceptable shape smoothness are adjusted by two coefficients in the objective function. The optimization problem is solved with a gradient-based algorithm, which takes advantage of algebraic gradient expressions. Numerical experiments demonstrate that the optimization procedure generates smooth horn contours that exhibit considerably improved performance over the target frequency band. Interestingly, a high-quality horn produced with moderate weight coefficients is similar in shape to constant-directivity horns invented earlier while having good low-frequency loading properties. The proposed method provides an attractive alternative to conventional horn design approaches.