Search

Several studies have been conducted to reduce the idling noise of circular saws because the sound level is extremely high and harms the environment. However, conventional noise suppression technology only controls the vibrations of the circular saw itself, whereas idling noise can be generated when the air inside the enclosure is resonant. In this study, the relationship between the rotational speeds of the circular saw blade and the frequencies of the resonance sound when the circular saw blade is running idle in an enclosure was examined. Additionally, the sound pressure modes and frequencies of the air in the enclosure were analyzed using the finite element method of acoustic analysis. The results showed that resonance sound was generated only when the circular saw blade was enclosed. The frequencies of the resonance sound generated by a circular saw blade made of acrylic plastic were the same as those generated by a steel saw blade. The resonance sound was generated regardless of the outer diameter of the circular saw blade. The peak resonant frequencies formed a step-like line during the analysis in which the rotational speed of the saw blade was steadily increased.

The present paper focuses on the synchronization behavior of vortex shedding in in-line tube banks with and without acoustic resonance. We have studied the characteristics of acoustic resonance generated by in-line tube banks with a tube pitch ratio of 2.8 in the flow direction. The single high peak in the sound pressure level spectrum was formed at the gap velocity from 5.0 m/s to 48.0 m/s. As the gap velocity increased, the peak frequency increased. The Strouhal number became approximately 0.145. At the gap velocity of 23.0 m/s, the acoustic resonance of the first mode occurred in the transverse direction. The flow patterns and vortex shedding of in-line tube banks at acoustic resonance have been experimentally investigated. The vortex flow field in the tube banks was measured by PIV with and without the acoustic resonance phenomenon. The alternative vortices were shed from each tube in tube banks with and without the acoustic resonance. A pair of vortices has been created at the top and bottom of the jet stream flowing between the gaps of two tubes. On the other hand, the phase-aligned alternative vortices were occasionally shed from each tube in tube banks. No acoustic resonance occurred, the phase-aligned alternative vortices were shed for 11.7 % of the 0.4 s period. When acoustic resonance occurred, the proportion of phase-aligned alternate vortices increased from 11.7 % to 31.0 %. The rate of increase in wall sound pressure is approximately equal to the rate of increase in vortex synchronization. The increase in wall sound pressure due to acoustic resonance is primarily due to the synchronization of vortices in the tube banks during the occurrence of weak resonance phenomena.

Abstract—It has been observed that strong earthquakes and volcanic eruptions are sometimes followed by geomagnetic oscillations with frequencies of 3.5–4.0 mHz. This paper describes the theoretical study of the probable cause of these phenomena, which is related to the vertical acoustic resonance between the Earth's surface and the thermosphere, produced by the propagation of the atmospheric wave corresponding to the acoustic branch generated by surface displacements. The propagation of two-dimensional (2D) harmonic acoustic wave is analyzed in a plane layered model of the atmosphere and ionosphere with oblique geomagnetic field. The altitude of the reflecting atmospheric layer corresponds to the region of a sharp temperature change in the vicinity of the thermosphere boundary ~80–90 km. The calculated fundamental resonant frequency is close to the observed oscillations. The obtained solution is used to calculate currents and electromagnetic perturbations in the atmosphere and ionosphere. Assuming thin-layer approximation for the ionospheric E-layer, we derive formulas describing the geomagnetic disturbances (GMD) in the ionosphere and on the Earth's surface. The GMD spectrum has a sharp peak at the frequency corresponding to the acoustic resonance. According to the calculations, close to the resonance frequency, the power spectral density of GMD on the ground can reach 5–30 nT2/Hz, which is consistent with the results of ground-based measurements. [ABSTRACT FROM AUTHOR]

Lime is used extensively in steel industry as fluxing material. Lime is produced by calcination of limestone in a lime kiln. The calcination process takes place at elevated temperatures near 900 °C to convert limestone into quick lime. Lances are distributed along the periphery of the kiln to provide uniform heating with by-product gases LD, COG, and BF as fuel. During the operation, lance tip is immersed in limestone and gets choked eventually which results in premature cracking. This reduces the length of the lance tubes which can be found only during their highly labor-intensive manual inspection performed every fortnight. Hence, a non-destructive method was developed, wherein an ultrasonic waveguide made of the same material of the lance was inserted to estimate chokage and real-time length of the lance. Additionally, the acoustic resonance of the air column-based method was also attempted to measure the length of the lance. These methods were able to guide operations by predicting remnant length with an accuracy > 95% and aiding in pre-planning shutdowns for replacement of damaged lances. [ABSTRACT FROM AUTHOR]

The reassigned spectrogram (RS) has emerged as the most accurate way to infer vocal tract resonances from the acoustic signal [Shadle, Nam, and Whalen (2016). "Comparing measurement errors for formants in synthetic and natural vowels," J. Acoust. Soc. Am. 139(2), 713–727]. To date, validating its accuracy has depended on formant synthesis for ground truth values of these resonances. Synthesis is easily controlled, but it has many intrinsic assumptions that do not necessarily accurately realize the acoustics in the way that physical resonances would. Here, we show that physical models of the vocal tract with derivable resonance values allow a separate approach to the ground truth, with a different range of limitations. Our three-dimensional printed vocal tract models were excited by white noise, allowing an accurate determination of the resonance frequencies. Then, sources with a range of fundamental frequencies were implemented, allowing a direct assessment of whether RS avoided the systematic bias towards the nearest strong harmonic to which other analysis techniques are prone. RS was indeed accurate at fundamental frequencies up to 300 Hz; above that, accuracy was somewhat reduced. Future directions include testing mechanical models with the dimensions of children's vocal tracts and making RS more broadly useful by automating the detection of resonances. [ABSTRACT FROM AUTHOR]

The low-frequency (74 kHz) shear elasticity of the homologous series of normal hydrocarbons (alkanes) is studied using acoustic resonance. The shear modulus and mechanical loss tangent are measured, and the relaxation frequency and effective viscosity are calculated. The dependences of these parameters on homologue viscosity are established. It is shown that the mechanical loss tangent of all studied liquids is less than 1, demonstrating that the relaxation frequency is below the experimental frequency. [ABSTRACT FROM AUTHOR]

Previous experimental studies suggested that restraining the vocal fold vertical motion may reduce the coupling strength between the voice source and vocal tract. In this study, the effects of vocal fold vertical motion on source-filter interaction were systematically examined in a two-dimensional two-mass model coupled to a compressible flow simulation. The results showed that when allowed to move vertically, the vocal folds exhibited subharmonic vibration due to entrainment to the first vocal tract acoustic resonance. Restraining the vertical motion suppressed this entrainment. This indicates that the vertical mobility of the vocal folds may play a role in regulating source-filter interaction. [ABSTRACT FROM AUTHOR]

Acoustically actuated magnetoelectric (ME) antennas utilize acoustic wave resonance to complete the process of receiving and transmitting signals, which promotes the development of antenna miniaturization technology. This paper presents a bilayer magnetostrictive/AlN ME laminated antenna. The proposed laminated antenna uses the FeGa/FeGaB bilayer materials as magnetostrictive materials, which combine the advantages of soft magnetic properties of FeGa and the low loss of FeGaB. First, multiphysics modeling and analysis are performed for the proposed ME laminated antenna by finite element method (FEM). The positive/inverse ME effects and the influences of the volume ratio of the FeGa/FeGaB bilayer on the antenna performance are studied. The results show that the output voltage and ME coefficient of the FeGa/FeGaB bilayer magnetostrictive material with a volume ratio of 1:1 are 3.97 times and 195.8% higher than that of the single FeGaB layer, respectively. The eddy current loss is 52.08% lower than that of single-layer FeGa. According to the surface equivalence principle, the far-field radiation process is simulated. The results show that the gain of the ME antenna is 15 dB larger than that of the same-size micro-loop antenna, and the gain of the ME antenna is about −44.9 dB. The improved performance and magnetic tunability of the proposed bilayer magnetostrictive materials make ME antennas excellent candidates for portable devices and implantable medical devices. [ABSTRACT FROM AUTHOR]

The degree of material anisotropy in additive manufacturing (AM) components is greatly influenced by the AM process parameters and machine setup. It is crucial to develop an effective technique for evaluating the material anisotropy in AM components to optimize AM process parameters and component design. This paper proposed a non-contact ultrasonic characterization method using the electromagnetic acoustic resonance technique to characterize the anisotropy of AM components. Various electromagnetic acoustic transducers (EMATs) were designed and utilized to characterize the material anisotropy and to determine the principal direction of the AM components. The degree of anisotropy in AM components was characterized using radial radiation EMATs. The relationship between the degree of anisotropy and the laser scanning angle was explored and further determined through the acoustic birefringence factor. Experimental results demonstrated that the anisotropy of AM components is intricately associated with the laser scanning angle, and specific angles can render the AM components isotropic. Moreover, understanding the principal directions is of significance for structural design and analyzing stress distribution in anisotropic components. Therefore, the principal directions of AM components were obtained by rotating the linear polarization EMAT. Changes in the resonance spectrum captured by the linear polarization EMAT while evaluating of principal directions were clearly illustrated, despite negligible alterations in linear ultrasonic features. Metallographic diagrams further validated the experimental findings. This investigation presented a highly accurate and reliable alternative for characterizing the anisotropy of AM components. [ABSTRACT FROM AUTHOR]

One method for reducing flue gas emissions is oxygen enrichment combustion. In this study, propane has been used as a fuel. The oxygen-enriched combustion study was carried out by increasing the oxygen ratio in the air used for combustion. Experiments have been performed at a constant equivalence ratio (1.2) and the number of swirl (s = 1) at 7 kW thermal power. Combustion has been performed under different oxygen ratios of 21%, 24%, 27%, and 28%, respectively. During combustion, acoustic enforcement has been carried out on the propane flame by utilizing loudspeakers, and so flame instability has been observed by changing enforcement levels and investigating dynamic pressure, luminous intensity, and flame images. The acoustic resonance of the combustion chamber was determined by basing abrupt changing dynamic pressure on 110, 175, and 330 Hz. The flue gas emission value and temperature effect of oxygen-enriched combustion were investigated under different acoustic excitations. Dynamic pressure and luminous intensity went up with oxygen enrichment. CO emission decreased about 97%, and adiabatic flame temperature increased, and NOx emissions increased about 2.5 times as the oxygen ratio increased. The flame length reduced under acoustic enforcement. The flue gas emissions decreased at all acoustic enforcement levels, especially at 110 Hz. As a result of acoustic enforcement, flame instability was reduced and the flame burned strongly. [ABSTRACT FROM AUTHOR]

Noise reduction, located in a narrow frequency band, is easily achieved by using resonant acoustic systems, such as Helmholtz resonators, dampers or acoustic tubes. However, a major disadvantage arises if there are significant variations in the noise emitted by certain equipment, but in a relatively narrow frequency band. This paper presents an acoustic system whose acoustic characteristics can be easily modified, which can lead, through appropriate automation, to the transformation of a passive acoustic vibration damping system into an active one. [ABSTRACT FROM AUTHOR]

In this study, the combustion instability characteristics of gaseous methane–gaseous oxygen atmospheric flame were investigated. A swirl coaxial injector was used under external modulation with a central methane flow and a loudspeaker. The flame transfer function with a photomultiplier tube was examined for possible errors, and an injector transfer function was defined to study the influence of the input perturbation on the cold gas flow without combustion. Both the results of flame transfer function and injector transfer function were affected by acoustic resonance. However, a higher mode of resonance did not appear in the flame transfer function. To analyze this difference, the flame movement was visualized using a high-speed camera by capturing the OH* chemiluminescence signal. Furthermore, a local flame transfer function was defined to examine the flame response zone-by-zone through a light signal. A higher-mode reaction appeared again in the local flame transfer function. It was found that flame separation due to modulation was the cause of the difference among the flame transfer function, injector transfer function, and local flame transfer function. By capturing the entire flame, its periodicity could be lost; hence, the local flame transfer function could prevent misinterpretation of the flame fluctuation. • A difference between dynamic response of cold gas flow and hot firing test is found. • In the flame transfer function results, the higher mode of resonance disappeared. • Using divided flame signal image, the response at high frequency is found again. • Separated flame clusters emit flame transfer function signals individually. • With interaction of each cluster signals, periodicity of flame could be missed. [ABSTRACT FROM AUTHOR]

This study covers the critical concerns related to the sizing, selection, installation, maintenance, and testing of pressure safety valves (PSVs). The aim is to ensure the safety of pressurized systems, hydrostatic transmission systems, and hydraulic plants, including process plants, thermal power plants, and nuclear reactor systems. PSVs are devices that ensure the safety and reliability of pressurized vessels, lines, and systems during overpressure events. The task of selecting which PSV features are of greatest value for a specific purpose is complex—especially in the design of a high-pressure experimental thermal–hydraulic facility for hydrostatic and transient testing of the reactor system—when the systems are in the design and development phases and require qualification and demonstration to prove that they have reached a given level of technological readiness. The present study highlights the required steps for users to follow the associated rules, guidelines, and recommendations. As a part of this research, case studies are presented to help readers better understand the applicable strategy and standards. A discussion and a review of PSV performance degradation and failure are summarized to provide a better understanding of varied process applications and conditions, including fluid flow dynamics, boundary-layer formation and pressure drops, gas bubble formation and collapse, geometric configurations, inlet/outlet piping, abrupt pressure fluctuations, and acoustic resonance. Moreover, this study discusses the servicing and testing of PSVs in a multiphase pressurized system. Overall, it provides a basic overview of how PSVs ensure the safety of pressurized systems, supported by case studies and industrial practices. [ABSTRACT FROM AUTHOR]

Applying a focused ultrasonic field on a free liquid surface results in its growth eventually leading to the so-called acoustic fountain. In this work, a numerical approach is presented to further increase the understanding of the acoustic fountain phenomenon. The developed simulation method enables the prediction of the free surface motion and the dynamic acoustic field in the moving liquid. The dynamic system is a balance between inertia, surface tension and the acoustic radiation force, and its nonlinearity is demonstrated by studying the relation between the ultrasonic excitation amplitude and corresponding liquid deformation. We show that dynamic resonance is the main mechanism causing the specific acoustic fountain shapes, and the analysis of the dynamic acoustic pressure allows us to predict Faraday-instability atomisation. We show that strong resonance peaks cause atomisation bursts and strong transient deformations corresponding to previously reported experimental observations. The quantitative prediction of the dynamic acoustic pressure enables us to assess the potential of cavitation generation in acoustic fountains. The observed local high acoustic pressures above both the cavitation and the atomisation threshold hint at the coexistence of these two phenomena in acoustic fountains. [ABSTRACT FROM AUTHOR]

A resonant voltage frequency doubler using the nonlinear magnetoelectric effect in planar heterostructure containing a piezoelectric langatate single crystal placed between two layers of amorphous ferromagnetic Metglas alloy was fabricated and studied. The frequency doubling occurred due to the nonlinear dependence of the Metglas magnetostriction on the magnetic field. A nonlinear magnetoelectric coefficient of 7.1 V/(cm Oe2) was obtained at acoustic resonance frequency of the structure due to high acoustic quality factor of ~2820. The power conversion coefficient of the doubler reached ~1% at optimal bias magnetic field of 2 Oe and matched load resistance of 0.8 kΩ. [ABSTRACT FROM AUTHOR]

Electromagnetic acoustic resonance (EMAR) technology has potential to improve signal-to-noise ratio (SNR) and reduce noise effects in metal plate thickness measurement. However, using traditional EMAR to detect inhomogeneous-thickness specimens can result in difficulties accurately determining thickness and identifying interfaces due to multiple resonant frequencies. This paper proposes a signal processing method called frequency-frequency energy density separation (FFEDS) to obtain the energy density ratio (EDR) for different thicknesses using EMAR. A new coil structure, the Acentric Archimedes Spiral Coil (A-AS-Coil), and two scanning schemes (transverse and rotational) are designed. Experimentally, transverse scanning with the A-AS-Coil shows a nonlinear change in EDR, improving sensitivity in identifying interfaces. Rotational scanning with the A-AS-Coil increases the change in EDR by 106.2%, different from the conventional spiral coil. [ABSTRACT FROM AUTHOR]

Nonlinear acoustic methods demonstrate high sensitivity for concrete damage evaluation. Among these methods, nonlinear resonance acoustic methods have been widely used in laboratory tests on small scale test samples. In this study, a nonlinear impact-echo (IE) method for concrete damage evaluation was introduced, in which the IE frequency shift was measured at different impact force levels. The nonlinear IE test and the nonlinear impact resonance acoustic spectroscopy (NIRAS) test share similarities in the experimental setup and analysis method. However, the nonlinear IE test excites a local thickness resonance mode of a member instead of the global resonance vibration. Therefore, the analyzed mode is unaffected by member boundary conditions and is applicable to large concrete structural members. To identify the fundamental IE frequencies, multiple impacts were applied along the members. Once the fundamental IE frequencies were determined, the effectiveness of the nonlinear IE method was evaluated by testing seven concrete beam specimens with varying levels of alkali-silica reaction (ASR) damage. The nonlinear IE test demonstrates high sensitivity to concrete damage and allows for quantitative assessment of the damage state of concrete without a baseline measurement. [ABSTRACT FROM AUTHOR]

The effect of acoustic low-intensity oscillations in a homogeneous tube and in a tube with a conical extension is experimentally investigated for the same resonator volumes. The resonator shape is shown to have an effect on the oscillation spectrum and intensity and the pressure wave shape at constant values of the resonance frequency and the piston displacement amplitude. An increase in the resonator Q-factor is observable, when the resonator has a conical extension. An accelerated aerosol sedimentation in tubes is revealed in the case of acoustic oscillation with the resonance frequency. In the presence of a conical extension the aerosol drop concentration is reduced by a factor of 1.2 more rapidly than in the case of a uniform tube and three times more rapidly as compared with natural sedimentation. The results obtained can be used for increasing the efficiency of acoustic methods of gas purification from the disperse phase. [ABSTRACT FROM AUTHOR]

Sound generation in human phonation and the underlying fluid–structure–acoustic interaction that describes the sound production mechanism are not fully understood. A previous experimental study, with a silicone made vocal fold model connected to a straight vocal tract pipe of fixed length, showed that vibroacoustic coupling can cause a deviation in the vocal fold vibration frequency. This occurred when the fundamental frequency of the vocal fold motion was close to the lowest acoustic resonance frequency of the pipe. What is not fully understood is how the vibroacoustic coupling is influenced by a varying vocal tract length. Presuming that this effect is a pure coupling of the acoustical effects, a numerical simulation model is established based on the computation of the mechanical-acoustic eigenvalue. With varying pipe lengths, the lowest acoustic resonance frequency was adjusted in the experiments and so in the simulation setup. In doing so, the evolution of the vocal folds' coupled eigenvalues and eigenmodes is investigated, which confirms the experimental findings. Finally, it was shown that for normal phonation conditions, the mechanical mode is the most efficient vibration pattern whenever the acoustic resonance of the pipe (lowest formant) is far away from the vocal folds' vibration frequency. Whenever the lowest formant is slightly lower than the mechanical vocal fold eigenfrequency, the coupled vocal fold motion pattern at the formant frequency dominates. [ABSTRACT FROM AUTHOR]

To overcome the agglomeration and insufficient combustion of nano-boron (n-B) powders, this study successfully prepared two novel types of boron-based nanocomposites using the acoustic resonance technology, namely highsubstitute nitrochitosan/nano-boron (NCh-B) with ratios of 1:3, 1:5, 1:7 and 1:9, and nitrochitosan/nano-boron powder/nano-titanium (NCh-B-Ti) with Ti contents of 5 wt%, 10 wt%, 15 wt% and 20 wt%. The structural morphologies, laser ignition and combustion properties of the composites were systematically investigated. The results suggest that the addition of NCh can significantly improve the dispersion of n-B. NCh-B exhibited a higher combustion performance than n-B, as evidenced by their ignition delay and flame areas. When the laser power density was 81 W, NCh-B5-Ti15% exhibited a combustion time and an ignition delay of 240 ms and 5.5 ms respectively, which were higher and lower than those of NCh-B5 (199 ms and 17 ms, respectively). Furthermore, NCh-B5-Ti15% displayed a lower ignition delay than both n-B powders (12 ms) and NCh-B (11 ms), as well as brighter flames and a larger combustion area. Therefore, the addition of n-Ti can promote the combustion of n-B powders, with the combustion products of NCh-B-Ti including H3BO3, B2O3, TiB2, and TiO. This study provides a new method for improving the ignition performance and combustion efficiency of n-B powders. [ABSTRACT FROM AUTHOR]

Here we describe the development of a sustainable and cost‐effective approach for catalytic cross‐coupling reactions in mechanochemistry. It is found that the substrate's impact with the vessel wall alone is sufficient to initiate the reaction, thus indicating that milling balls function primarily as a mixing agent for direct mechanocatalytic Suzuki coupling. The absence of milling balls can be offset by adjusting the rheology using liquid‐assisted grinding (LAG). The LAG sweet spot of 0.25 μL mg−1 is confirmed for both resonance acoustic mixers (RAMs) and ball‐free mixer mills, and is higher than in the presence of milling balls. RAMs exhibit excellent performance in the Suzuki reaction, achieving yields of 90 % after 60 min and complete conversion after 90 min. The longevity of the milling vessel is significantly improved in a RAM, allowing for at least 20 reactions without deterioration. [ABSTRACT FROM AUTHOR]

This work reports on the fabrication and characterization of an Au/ZnO/Pt-based high-overtone bulk acoustic resonator (HBAR) on SiC substrates. We evaluate its microwave characteristics comparing with Si substrates for micro-electromechanical applications. Dielectric magnetron sputtering and an electron beam evaporator are employed to develop highly c-axis-oriented ZnO films and metal electrodes. The crystal structure and surface morphology of post-growth layers are characterized using X-ray diffraction, atomic force microscopy, and scanning electron microscopy techniques. HBAR on SiC substrate results in multiple longitudinal bulk acoustic wave resonances up to 7 GHz, with the strongest excited resonances emerging at 5.25 GHz. The value of f.Q (Resonance frequency.Quality factor) parameter obtained using a novel Q approach method for HBAR on SiC substrate is 4.1 × 10 13 Hz, which to the best of our knowledge, is the highest among all reported values for specified ZnO-based devices. [ABSTRACT FROM AUTHOR]

The Hunga Tonga–Hunga Ha'apai (HTHH) undersea volcanic eruption that occurred at 04:15 UT on 15 January 2022 is one of the most explosive events in the modern era, and a vertical plume reached approximately 55 km, corresponding to a height of the lower mesosphere. The intense explosion and subsequent plume generated acoustic and atmospheric gravity waves detected by ground-based instruments worldwide. Because a global-scale atmospheric and ionospheric response to the large volcanic eruption has not yet been observed, it provides a unique opportunity to promote interdisciplinary studies of coupling processes in lithosphere–atmosphere–ionosphere with ground-based and satellite observations and modeling. Further, this event allows us to elucidate the propagation and occurrence features of traveling ionospheric disturbances, the generation of equatorial plasma bubbles, the cause of electron density holes around the volcano, and the magnetic conjugacy of magnetic field perturbations. The most notable point among these studies is that the medium-scale travelling traveling ionospheric disturbances (MSTIDs) have magnetic conjugacy even in the daytime ionosphere and are generated by an external electric field, such as an E-region dynamo field, due to the motions of neutrals in the thermosphere. This advocates a new generation mechanism of MSTIDs other than the neutral oscillation associated with atmospheric gravity waves and electrified MSTIDs, which are frequently observed during daytime and nighttime, respectively. This paper reviews the recent studies of atmospheric and ionospheric disturbances after the HTHH volcanic eruption and summarizes what we know from this extreme event analysis. Further, we analyzed new datasets not shown in previous studies to give some new insights to understanding of some related phenomena. As a result, we also found that 4-min plasma flow oscillations caused by the acoustic resonance appeared with the amplitude of approximately 30 m/s in the northern hemisphere a few hours before the initial arrival of the air pressure waves. The propagation direction was westward, which is the same as that of the daytime MSTIDs with a magnetic conjugate feature. This result suggests that the 4-min oscillations are generated by an external electric field transmitted to the northern hemisphere along magnetic field lines. [ABSTRACT FROM AUTHOR]

Acoustic metamaterials are increasingly being considered as a viable technology for sound insulation. Fractal patterns constitute a potentially groundbreaking architecture for acoustic metamaterials. We describe in this work the behaviour of the transmission loss of Hilbert fractal metamaterials used for sound control purposes. The transmission loss of 3D printed metamaterials with Hilbert fractal patterns related to configurations from the zeroth to the fourth order is investigated here using impedance tube tests and Finite Element models. We evaluate, in particular, the impact of the equivalent porosity and the relative size of the cavity of the fractal pattern versus the overall dimensions of the metamaterial unit. We also provide an analytical formulation that relates the acoustic cavity resonances in the fractal patterns and the frequencies associated with the maxima of the transmission losses, providing opportunities to tune the sound insulation properties through control of the fractal architecture. [ABSTRACT FROM AUTHOR]

The influence of high-frequency vibrations on the shape of a compressible drop placed on an oscillating solid substrate is studied in this paper. Due to the significant difference in characteristic temporal scales, the average and pulsating motions of the drop can be considered separately. For nearly hemispherical drop, the solution to the problem of pulsating motion is found in the form of series in Legendre polynomials. Frequencies of natural sound oscillations of hemispherical axisymmetric drop are obtained. Resonances of the acoustic mode of drop oscillations are found. The problem of forced oscillations of hemispherical drop in the limit of weakly compressible liquid is considered. It is found that drop oscillation amplitude grows with vibration intensity according to quadratic law, which is consistent with the solution of the pulsation problem for finite compressibility assumption. A variational principle for calculation of average drop shape is formulated based on minimization of energy functional for the case, so the compressibility of the liquid should be taken into account. It is shown that the functional (the sum of the kinetic and potential energies of the pulsating flow, the kinetic energy of the averaged flow, and the surface tension energy of the drop) decreases and reaches a minimum value at quasi-equilibrium state, in which the average shape of the drop becomes static. The influence of vibrations on the drop shape is studied for small values of the vibrational parameter. The surface of the drop in the absence of vibrations is assumed to be hemispherical. Calculations showed that under vibrations, drop height decreases, while the area of the base increases. [ABSTRACT FROM AUTHOR]

In order to improve the logging interpretation accuracy for complex oil and water layers developed in tight sandstone reservoirs, this study takes the Chang 8 member of the Yanchang Formation in the Huanxian area as the research object, and two new fluid identification methods were constructed based on nuclear magnetic resonance (NMR) logging and array acoustic logging. Firstly, the reservoir characteristics of physical properties and conductivity were studied in the research area, and the limitations of conventional logging methods in identifying complex oil and water layers were clarified. Then, the sensitive parameters for identifying different pore fluids were established by analyzing the relationship between NMR logging and array acoustic logging with different pore fluids. On this basis, the fluid identification plate, composed of movable fluid apparent diffusion coefficient and effective porosity difference (Da-Δφe) by NMR logging data of D9TWE3 observation mode, and the other fluid identification plate, composed of apparent bulk modulus of pore fluid and elastic parameter sensitive factor (Kf-Fac), were constructed, respectively. Finally, these two fluid identification methods were used for reservoir interpretation of actual logging data. This study shows that the two new fluid identification methods constructed by NMR logging and array acoustic logging can effectively eliminate the interference of rock skeleton on logging interpretation, which make them more effective in identifying complex oil and water layers than the conventional logging method. Additionally, the two methods have their own advantages and disadvantages when used separately for interpreting complex oil and water layers, and the comprehensive interpretation of the two methods provides a technical development direction for further improving the accuracy of logging the interpretation of complex oil and water layers. [ABSTRACT FROM AUTHOR]

Resonance acoustic mixing (RAM) technology is an attractive and safe mixing method for material mass and energy exchange. However, the mixing mechanism of this technology and the evolution law of the material in the container are complicated, and improper mixing conditions will make the material unable to reach uniformity quickly and efficiently. In this paper, a 90% solid polymer-bonded explosive (PBX) was prepared by RAM, and the evolution of materials in different mixing containers, mixing acceleration, and mixing time was studied. The binder system consisted of hydroxyl-terminated polybutadiene (HTPB)/dioctyl adipate (DOA) and was cured by isophorone diisocyanate (IPDI). Scanning electron microscopy (SEM) and Energy dispersive spectroscopy (EDS) were used to observe the microcosmic change of the sample during the mixing process, and a rheometer was used to measure the viscosity change of the slurry at different stages. The results showed that the hemispherical bottom vessel could achieve uniform mixing of materials within 45 minutes, and the mixing efficiency was highest when the acceleration was 40 g. According to the evolution state of typical materials, the mixing process was divided into 3 stages: rough cladding stage, the stage of converging into a smooth ball, and the flat fluidization stage. In the range of shear rates from 0.1 to 100s−1, the apparent viscosity of the material tended to be flat with the extension of mixing time, and the rheological behavior index of the material had little change after the material aggregates into a smooth ball. The density test of the cured sample further proved that the PBX was very uniform. [ABSTRACT FROM AUTHOR]

• Modified the experimental procedure or the sound-speed measurements of mixtures. • Reported the first set of gaseous speed of sound data for R1234yf(1) + R134a(2). • Established the method of determining the accurate component molar fraction. • Derived the molecular potential parameters and the interaction virial coefficient. • Reported a modified virial-coefficient correlation for the mixtures. The binary mixture 2,3,3,3-tetrafluoropropene (R1234yf) + 1,1,1,2-tetrafluoroethane (R134a) is commercially interesting and is widely studied in thermodynamics properties, but except for gaseous speed of sound. In this work, we modified the experimental procedure of the cylindrical fixed-path acoustic resonance method for the sound speed measurement of mixtures. Then we obtained the first two sets of gaseous sound speed data at the molar fraction of about (0.207/0.793) and (0.580/0.420) with a combined relative expanded uncertainty (k = 2) of 0.03%. The accurate molar fractions along each isotherm line were determined by extrapolating the experimental data with the absolute expanded uncertainty (k = 2) of 0.003. The interaction virial coefficients were derived from the experimental sound speed data and were used to establish a hard-core square-well molecular potential model. A previous virial coefficient correlation was modified to predict the virial coefficients for mixtures. The experimental results and model calculations agree well with each other, confirming the correctness of the experimental method. The data could provide references to test and develop the mixing model. [ABSTRACT FROM AUTHOR]

An experimental investigation is carried out to study the effects of Mach number on the acoustic resonance characteristics of a rectangular cavity with and without multiple stores. Measurements are conducted for a cavity with a length-to-depth ratio of 4.5 at Mach numbers of 2, 3, 4, and 5. Dynamic pressures are measured within the cavity and on the store surfaces. An increase in Mach number results in a decrease in overall sound pressure levels at all measurement locations within the cavity. Pressure spectra indicate that increasing the Mach number decreases both the peak and broadband amplitudes of the cavity pressure fluctuations. At Mach 5, the amplitude of the cavity modes is significantly reduced in the upstream half of the cavity, and the modes are either indistinguishable from broadband levels or absent in the downstream half. The addition of stores reduces cavity acoustics, with two stores offering greater reduction than a single store. The effect of Mach number and the presence of stores on the aeroacoustic feedback loop in a cavity align with literature. Additionally, the pressure fluctuations on the windward store surface scale with Mach number in a similar trend as the cavity acoustics. [ABSTRACT FROM AUTHOR]

The Tonga volcano is among the five most powerful volcanoes in the world. The explosion of the Tonga volcano on January 15, 2022, was unique. It has led to disturbances in the lithosphere, World Ocean, atmosphere, ionosphere, magnetosphere, and all geophysical fields. A number of studies have been devoted to the disturbance of the Earth's magnetic field. The transport of magnetic field disturbances by atmospheric gravity waves and tsunamis, disturbances in magnetically conjugated regions due to acoustic resonance, the effect on the equatorial electrojet, etc., have been studied. This is far from the end of the variety of magnetic effects of the Tonga volcano. This study is aimed at describing the results of the analysis of global bay disturbances in the geomagnetic field observed after the Tonga volcano explosion on January 15, 2022. The results of measuring the temporal variations in the level of the X, Y, and Z components by the INTERMAGNET world network of stations are used as initial data. The analysis of the magnetic data is preceded by an analysis of space weather conditions. A preliminary analysis of temporal variations in the level of the X-, Y-, and Z-components indicates that these variations on the reference days are smoother than on January 15, 2022. An analysis of the temporal variations in the level of the X-, Y-, and Z-components of the geomagnetic field and a statistical analysis of the disturbance parameters have shown the following. Bay disturbances of all components of the geomagnetic field are observed with a time delay that varies depending on the distance to the volcano from several tens of minutes to 100–200 min. The magnitude of the effect varies from approximately 10 to approximately 60 nT. The largest disturbances occur in the Y component. The delay time and duration of disturbances increase with an increase in the distance from the volcano, while their amplitude, on the contrary, decreases. The speed of propagation of bay disturbances is close to the speed of the blast wave. Bay disturbances are weakly expressed or completely absent on the night side of the planet. It is substantiated that bay disturbances are closely related to the occurrence of an ionospheric hole under the action of a blast wave from the volcano. The results of estimates of bay disturbances are in good agreement with the observation results. [ABSTRACT FROM AUTHOR]

Copyright of Polish Otorhinolaryngological Review / Polski Przegląd Otorynolaryngologiczny (Index Copernicus) is the property of Index Copernicus International and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Objective: We introduce a non-invasive MR-Acoustic Radiation Force Imaging (ARFI)-based elastography method that provides both the local shear modulus and temperature maps for the monitoring of High Intensity Focused Ultrasound (HIFU) therapy. Materials and methods: To take tissue anisotropy into account, the local shear modulus μ is determined in selected radial directions around the focal spot by fitting the phase profiles to a linear viscoelastic model, including tissue-specific mechanical relaxation time τ. MR-ARFI was evaluated on a calibrated phantom, then applied to the monitoring of HIFU in a gel phantom, ex vivo and in vivo porcine muscle tissue, in parallel with MR-thermometry. Results: As expected, the shear modulus polar maps reflected the isotropy of phantoms and the anisotropy of muscle. In the HIFU monitoring experiments, both the shear modulus polar map and the thermometry map were updated with every pair of MR-ARFI phase images acquired with opposite MR-ARFI-encoding. The shear modulus was found to decrease (phantom and ex vivo) or increase (in vivo) during heating, before remaining steady during the cooling phase. The mechanical relaxation time, estimated pre- and post-HIFU, was found to vary in muscle tissue. Discussion: MR-ARFI allowed for monitoring of viscoelasticity changes around the HIFU focal spot even in anisotropic muscle tissue. [ABSTRACT FROM AUTHOR]

One of the uses of Helmholtz resonators is as sound absorbers for room acoustic applications, especially for the low frequency range. Their efficiency is centered around their resonance frequency which mainly depends on elements of their geometry such as the resonator volume and neck dimensions. Incorporating additional necks on the body of a Helmholtz resonator (depending on whether they are open or closed) has been found to alter the resulting resonance frequency. For this study, tunable Helmholtz resonators to multiple resonance frequencies, are proposed and investigated utilizing additional necks. The resonance frequencies of various multi-neck Helmholtz resonators are first modeled with the use of the finite element method (FEM), then calculated with the use of an analytical approach and the results of the two approaches are finally compared. The results of this study show that Helmholtz resonators with multiple resonances at desired frequencies are achievable with the use of additional necks, while FEM and analytical methods can be used for the estimation of the resonance frequencies. Analytical and FEM approach results show a good agreement in cases of small number of additional necks, while the increasing differences in cases of higher neck additions, were attributed to the change in effective length of the necks as demonstrated by FEM. The proposed approach can be useful for tunable sound absorbers for room acoustics applications according to the needs of a space. Also, this approach can be applied in cases of additional tunable air resonances of acoustic instruments (e.g., string instruments). [ABSTRACT FROM AUTHOR]

An analytical model of the vertical acoustic resonance between the thermosphere and the earth's surface and its geomagnetic effect has been constructed. Resonance with a frequency of several mHz occurs when an atmospheric acoustic wave (AW) is excited by vibrations of the earth or ocean surface. The derived analytical relationships give a possibility to examine the dependence of the fundamental resonant frequency on the height of the reflecting atmospheric layer and horizontal AW number. Geomagnetic disturbances caused by the impact of AW on the ionosphere are calculated within the framework of a multi‐layered model of the ground‐atmosphere‐ionosphere system. The E‐layer of the ionosphere is treated in the approximation of a thin layer with an inclined geomagnetic field, while the topside ionosphere is assumed to consist of a cold collisionless plasma. The dependence of the spectral power of magnetic perturbations on the direction of the horizontal AW propagation is examined. The magnetic perturbation spectra are shown to have maxima at frequencies close to the acoustic resonance frequency. The spectral powers of magnetic perturbations and barometric variations measured during the Iwate‐Miyagi Nairik earthquake are in accordance with the model predictions for realistic media and AW parameters. Field‐aligned currents that arise when AWs enter the ionospheric E‐layer is shown to carry measurable electromagnetic disturbances into the geomagnetically conjugated region. Plain Language Summary: Geophysical phenomena with large energy yield, such as earthquakes and volcano eruptions, can excite specific oscillations of the geomagnetic field and ionospheric plasma with frequencies around a few mHz. These oscillations are spatially localized in the vicinity of earthquake/volcano epicenter and last up to 1–2 hr. This phenomenon was interpreted as the vertical resonance of the acoustic wave (AW) trapped between the ground/ocean surface and thermosphere (∼80 km). It is important to know geomagnetic response to the acoustic resonance because it will give possibility to use data from magnetometer array for in‐depth study of this phenomenon. Presented theoretical model of the acoustic resonance provides analytical relationships to examine the dependence of geomagnetic signature of the acoustic resonance on atmosphere/ionosphere parameters. These simple relationships anybody can use to estimate without sophisticated computer modeling an expected geomagnetic effect of the acoustic resonance for any atmosphere/ionosphere parameters. Recorded spectral powers of magnetic perturbations and variations of atmospheric pressure are found to be in accordance with the model predictions. Currents along the geomagnetic field line that arise when AW interacts with ionospheric plasma can carry electromagnetic disturbances into the opposite hemisphere. This theoretical prediction has been confirmed by observations by Pacific magnetometers. Key Points: Theory describes analytically magnetic pulsations observed after seismic/volcano events driven by vertical acoustic resonance in atmosphereA dominant magnetic component of pulsations excited on the ground is directed along the horizontal wave vector of the acoustic waveTheory predicts that ionospheric field‐aligned currents can cause detectable magnetic response to acoustic resonance in conjugate ionosphere [ABSTRACT FROM AUTHOR]

Finding new energy-efficient methods for exciting magnetization dynamics is one of the key challenges in magnonics. In this work, we present an approach to excite the gyrotropic dynamics of magnetic vortices through the phenomenon of inverse magnetostriction, also known as the Villari effect. We develop an analytical model based on the Thiele formalism that describes the gyrotropic motion of the vortex core including the energy contributions due to inverse magnetostriction. Based on this model, we predict excitations of the vortex core resonances by surface acoustic waves whose frequency is resonant with the frequency of the vortex core. We verify the model's prediction using micromagnetic simulations and show the dependence of the vortex core's oscillation radius on the surface acoustic wave amplitude and the static bias field. Our study contributes to the advancement of energy-efficient magnetic excitations by relying on voltage-induced driven dynamics, which is an alternative to conventional current-induced excitations. [ABSTRACT FROM AUTHOR]

Tire acoustic cavity resonance noise (TACRN) contributes significantly to the interior noise of electric cars and passenger cars with lower powertrain noise, which affects the comfort of the ride. To suppress TACRN effectively, it is crucial to clarify the characteristics of TACRN. In previous studies, the acoustic wave in the tire acoustic cavity is straightforwardly assumed to be the plane wave for convenience. In fact, there exist strict conditions for the acoustic wave propagating in the pipeline to act as a plane wave. The aim of this paper is to make the characteristics and evolution of acoustic waves in tire acoustic cavities clear. To do so, a simplified model of the tire cavity is established, and the sound field distribution and the acoustic wave propagation characteristics in the tire cavity are analyzed based on the theory of acoustic waveguide. Then, the existence ranges of higher-order waves (non-plane waves), the conditions of an acoustic wave evolving into a plane wave, and the frequency range of a plane wave are investigated. Finally, the characteristics and evolution law of an acoustic wave in a tire acoustic cavity are obtained. The work in this paper may deepen the understanding of the characteristics and mechanism of acoustic waves in the tire cavity and be helpful and meaningful for analyzing and suppressing TACRN. Therefore, it is of practical significance to reduce TACRN transmitted to the vehicle and improve the sound quality inside the vehicle. [ABSTRACT FROM AUTHOR]

Hot fire tests were performed using a single-injector research combustor featuring a large optical access window (255 × 38 mm) for flame visualisation. Three test campaigns were conducted with the propellant combination of liquid oxygen and hydrogen, liquid oxygen and compressed-natural-gas, as well as liquid oxygen and liquefied-natural-gas at conditions relevant for main- and upper-stage rocket engines. The large optical access enabled synchronised flame imaging using ultraviolet and blue radiation wavelengths covering a large portion of the combustion chamber for various sets of sub- and supercritical operating conditions. Combined with temperature, pressure and unsteady pressure measurements, this data provides a high-quality basis for the validation of numerical modelling. Flame width, length and opening angle as features describing the flame topology were extracted from the imaging. The suitability of flame imaging using ultraviolet and blue radiation wavelengths as qualitative markers of heat release was evaluated. Two-dimensional distributions of the Rayleigh Index were calculated for intervals with and without high-amplitude, self-excited oscillations of the longitudinal acoustic resonance modes. The calculated Rayleigh Index values properly reflect the thermoacoustic state of the chamber, indicating that both types of imaging may be used for qualitative study of thermoacoustic coupling of high-pressure cryogenic flames. [ABSTRACT FROM AUTHOR]

We review recent determinations of the Boltzmann constant kB and the differences T − T90 that used cylindrical acoustic gas thermometry (c-AGT). These determinations measured the acoustic resonance frequencies of argon gas enclosed by metal-walled, cylindrical cavities. (Here, T is the thermodynamic temperature and T90 is the temperature measured on the International Temperature Scale of 1990, ITS-90.) In the range 234–303 K, the standard uncertainty of c-AGT ranges from 1.9 × 10−6T to 2.6 × 10−6T. This uncertainty is much smaller than the errors in ITS-90; therefore, c-AGT can help improve ITS-90. Moreover, we are extending c-AGT up to 1358 K. With increasing temperatures, c-AGT becomes advantageous relative to AGT based on quasi-spherical cavities because long cylindrical cavities (1) naturally fit into cylindrical heat pipes or multi-shelled thermostats; (2) provide the immersion required by transfer temperature standards, such as long-stemmed platinum resistance thermometers; and (3) have more useful, low-frequency acoustic resonances. In preparation for high-temperature c-AGT, we identified suitable materials for fabricating cylindrical cavities and we developed techniques for measuring acoustic resonance frequencies using sources and detectors outside the high-temperature thermostat. We also considered alternative test gases and optimal dimensions of cavities. [ABSTRACT FROM AUTHOR]

Tunable interaction strength between a side-coupled ring resonator and an acoustic waveguide structure is demonstrated. Fano resonances in the weak coupling regime are observed from the interference between a discrete state of the ring resonator and a continuum state of the waveguide. As the distance between the two structures is decreased, a transition from weak to strong coupling regime is obtained, where we observe splitting in the transmission spectrum and Rabi oscillations in the temporal behavior for smaller values. The findings of the finite-element method simulations are supported with the results obtained from a simple theoretical model in which one can explain the dynamics of the hybrid modes. The results can contribute to device applications in acoustic sensors, switches, and surface acoustic wave integrated circuits. [ABSTRACT FROM AUTHOR]

Periodic pressure fluctuations were studied experimentally in the model of a jet-driven Helmholtz oscillator with a cylindrical chamber with a round air jet impinging on the sharp edge of the outlet. The evolution of the amplitude–frequency spectrum of the hole tone from its appearance at a jet velocity of about 2 m/s to excitation of the first acoustic resonance mode at the Helmholtz frequency was studied. The hole tone was a family of harmonics that progressively became more complex as the length and velocity of the jet increased. The successive occurrence of a family of acoustic modes on the harmonics of the jet tone with a further increase in jet velocity is studied. Modes at the Helmholtz frequency arose alternately on the harmonics of the hole tone in the gain band of the oscillator, starting from the highest harmonic. The first mode occurred at the highest harmonic; the second mode, at the previous harmonic; and so on. The final mode arose at the fundamental harmonic of the hole tone and had the maximum amplitude. With a further increase in the Reynolds number, periodic pressure fluctuations became disordered turbulent fluctuations. With a sufficient chamber size and jet velocity, azimuthal and half-wave resonances appeared at the highest harmonic of the hole tone. The largest Reynolds number at which resonance at the Helmholtz frequency was observed was 105. [ABSTRACT FROM AUTHOR]

Summary: Background: The prevalence of liver fibrosis detected by non‐invasive imaging in alpha‐1‐antitrypsin (AAT) deficiency has not been systematically assessed. Aims: We conducted a systematic review and meta‐analysis to determine the prevalence of significant fibrosis and advanced fibrosis in AAT deficiency based on non‐invasive imaging. Methods: Medline and Embase electronic databases were searched for studies from inception to 13 November 2022 that provided data for the prevalence of fibrosis in adults with AAT deficiency. A generalised linear mixed model with Clopper–Pearson intervals was used to pool single‐arm outcomes. Results: Of the 214 records identified, 8 studies were included. Five studies assessed fibrosis using vibration‐controlled transient elastography. The prevalence of significant fibrosis (defined as ≥7.1 kPA) in Z homozygosity, Z heterozygosity and non‐carrier status was 22.10% (five studies, 95% CI: 17.07–28.12), 9.24% (three studies, 95% CI: 4.68–17.45) and 5.38% (one study, 95% CI: 3.27–8.73), respectively, p < 0.0001, and the prevalence of advanced fibrosis (defined as ≥9.5 kPa) was 8.13% (five studies, 95% CI: 4.60–13.96), 2.96% (three studies, 95% CI: 1.49–5.81) and 1.08% (one study, 95% CI: 0.35–3.28), respectively, p = 0.003. There were limited data regarding the use of magnetic resonance elastography or acoustic radiation force impulse to assess for fibrosis. Conclusion: More than one in five adult individuals with AAT deficiency and Z homozygosity harbour significant fibrosis, and nearly 1 in 10 harbours advanced fibrosis. The risk of fibrosis increases incrementally with the frequency of Pi*Z mutations. [ABSTRACT FROM AUTHOR]

The time-resolved magneto-optical Kerr effect in epitaxial thin films of the FePt compound and the FePt0.84Rh0.16 solid solution with the perpendicular magnetic anisotropy on MgO (001) substrates has been studied. The evolution of hysteresis loops at short (100 fs–1 ns) and long (1–20 ms) time scales after the excitation by a femtosecond light pulse has been studied. Long-lived nonthermal reduction of the coercive field has been detected. The coercive field is recovered in several milliseconds. It has been proposed to explain the observed phenomenon by the excitation of high-Q-factor acoustic resonances in the substrate/film system and to the strong magnetoelastic interaction in FePt and FePt0.84Rh0.16 films. [ABSTRACT FROM AUTHOR]

We study the resonances for scattering of acoustic waves by cell membrane. Due to the fact that we deal with this phenomenon only, we use the simplest model of the membrane as a potential supported by a surface. The asymptotics of the Green's function with the singularity at the surface is obtained. The influence of the surface curvature on the resonances is investigated. An application of the result to explanation of selective cancer cell membrane destruction in ultrasonic field is discussed. [ABSTRACT FROM AUTHOR]

This experimental work was aimed at the characterization of new hybrid fiber wet-laid felts (HFWFs), which consisted of wood pulp fibers, glass fibers as well as hot-meltable fibers. The effect of different fiber ratios in the hybrid of felts was investigated. Mechanical-physical properties of HFWFs had been evaluated for tensile strength, burst strength, flexural strength, air permeability, sound transmission loss (STL) and sound absorption coefficient (SAC). The results showed that hybrid ratios affected the mechanical-physical properties. HFWFs with fiber weight ratios 1:0:1(WPF:GF:HMF) exhibited the best mechanical properties (tensile strength, burst strength and flexural strength) due to the increasing interfacial adhesion. Furthermore, weight ratios affected air permeability and resulted in different acoustic properties. HFMFs with fiber weight ratios of 1:1:2 and 2:3:1 had good SAC and excellent STL, respectively. It also found that the greater the tensile strength of HFWFs, the higher the acoustic resonance frequency. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In recent years, micromachined microphones have evolved into versatile transducers for gas-sensing applications in the fields of both direct and indirect photoacoustics. However, their noise properties have not yet caught much attention. In this contribution, we present an analysis of the noise spectrum of a MEMS microphone and show how it may be employed as a gas-sensing tool and to characterize photoacoustic detectors. The results highlight the potential to determine the speed of sound, ambient temperature, and gas composition via Fourier analysis of the microphone noise.