Acoustic Reflection Research Articles

A theoretical analysis of the logging-while-drilling dipole acoustic reflection measurement

Post-drilling wireline acoustic single-well imaging technology can now detect geological structures tens of meters away from boreholes. Further development of this single-well imaging technology in the logging-while-drilling (LWD) environment will have significant values in real-time applications such as geosteering and reservoir navigation. Based on the wireline imaging application, we propose a new method for the LWD application. In wireline imaging, the four-component (4C) dipole acoustic data are azimuthally rotated to scan the reflectors around the borehole. In LWD, azimuthal scanning is achieved by drilling rotation such that the 4C dipole system in the wireline is replaced by a one-dipole-source and two-receiver LWD system, where the two receivers are mounted on opposite sides of the drill collar. For the LWD application, we first developed the theory for LWD dipole shear-wave reflection imaging and validated the theory using 3D finite-difference waveform modeling. Using the analytical solution, we analyzed the far-field radiation directivity of an acoustic LWD dipole source and the effect of drilling rotation on the shear-wave reflection imaging using the LWD acoustic system. The LWD analysis results show that, for fast formations, the SH-wave is the dominant component for imaging, whereas for slow formations, the P-wave becomes important and can be used for imaging. Our results also indicate that the reflection data acquired by the system are affected by the speed of drilling rotation. The take-off azimuth at the wave radiation may be different from the incident azimuth at the wave reception. Knowing the rotation speed, this azimuth difference can be corrected. A further advantage of using the oppositely mounted receivers is that the reflected wave arrives earlier (later) at the front (back)-side receiver; thus, the arrival time difference between the receivers can be used to eliminate the 180°-azimuth ambiguity of dipole acoustic imaging. For reflection imaging, using the proposed LWD system configuration, we tested its azimuth sensitivity and validated its 180°-ambiguity solution using synthetic LWD and field wireline dipole data. The results of this work, therefore, provide a theoretical foundation for the development of the LWD acoustic reflection imaging system.

Ultra-thin low-frequency broadband absorber based on layered coiled channel structure

To improve and broaden the performance in absorbing sound waves of metamaterials at the lower and mid-frequency ranges, a layered coiled channel composite structure (LCCS) with deep subwavelengths is proposed in this paper, which extends the acoustic wave propagation paths longitudinally by connecting the Helmholtz resonator channels in each layer and achieves the multistep resonance of the coupling cavities, which results in the cancellation of acoustic energies, reduces the acoustic reflections and scattering, and enhances the absorption performance. A model to simulate theoretical sound absorption and finite elements simulation of the metamaterial were evolved to reveal its potential mechanismfor absorbing sound. Using the single-variable method to study the impact of altering structural parameters on the effectiveness of sound absorption, it shows good tunability in the target frequency range and obtains four fundamental unit LCCSs having distinct frequency absorption peaks, and designs a multi-unit coupling construction having low frequencies wideband sound absorption performance by connecting them in parallel to realize a large-broadband continuous and high-efficiency sound absorption within the scope of 370–1400 Hz, using a mean peak sound absorption value higher than 0.7. The structure was put together by 3D printing, and the impedance tube method test verified the precision of the simulation’s findings. This study offers a practical means to create lightweight, low-frequency broadband acoustic absorbing metamaterials.

Reduction of TCF effect in FBAR devices using DC bias

This study investigates the effect of applied DC bias on the resonant and antiresonant frequency of FBAR devices. In our model, we introduce linear electrostrictive coefficients and compare the theoretical results with experimental data. The FBAR structure utilizes an air cavity as the acoustic reflector layer, with Mo and AlN as the materials for the top/bottom electrodes and the piezoelectric layer, respectively. The resonant and antiresonant frequencies of the FBAR are designed at 2313.1 and 2374.7 MHz, respectively. Under an applied DC bias ranging from −10 to +10 V, the frequency shifts for the resonant and antiresonant frequencies are 37.7 and 27.7 ppm/V, respectively. The theoretical results, incorporating linear electrostrictive coefficients N=−7×1010 and G=−5×109, show excellent agreement with the measured results of the FBAR device. Finally, we compensated for the frequency drift by applying a 20 V DC bias at high temperatures to the FBAR device. These findings have significant implications for improving the performance of RF communication systems in varying temperature environments.

Honeycomb-Shaped Phononic Crystals on 42°Y-X LiTaO3/SiO2/Poly-Si/Si Substrate for Improved Performance and Miniaturization

A SAW device with a multi-layered piezoelectric substrate has excellent performance due to its high Q value. A multi-layer piezoelectric substrate combined with phononic crystal structures capable of acoustic wave reflection with a very small array can achieve miniaturization and high performance. In this paper, a honeycomb-shaped phononic crystal structure based on 42°Y-X LT/SiO2/poly-Si/Si-layered substrate is proposed. The analysis of the bandgap distribution under various filling fractions was carried out using dispersion and transmission characteristics. In order to study the application of PnCs in SAW devices, one-port resonators with different reflectors were compared and analyzed. Based on the frequency response curves and Bode-Q value curves, it was found that when the HC-PnC structure is used as a reflector, it can not only improve the transmission loss of the resonator but also reduce the size of the device.

Bulk acoustic wave—Solidly mounted resonator with a-SiOCN:H as low-Z material

Bulk acoustic wave (BAW) filters have been proven to be of high demand in today's low power RF front-ends for mobile communication devices. Within the launch of 5G applications worldwide, especially in the region of new radio (nr-1) up to 6 GHz, defined frequency bands require filters of wide bandwidths, while simultaneously featuring steep edges and high out-of-band rejection. Due to the coexistence with 4G LTE (long term evolution) wireless standards as well as advanced data transfer concepts such as carrier aggregation, the increasing complexity of antenna systems forces the implementation of highly selective acoustic filters. In contrast to the widely used surface acoustic wave (SAW) technology, BAW filters appear with superior performance for frequencies above 1 GHz. This work describes the fabrication of a BAW-solidly mounted resonator (BAW-SMR) with a tailored material system of a-SiOCN:H as a low impedance (low-Z) material integrated within its acoustic Bragg mirror. A direct comparison to the widely used low-Z material of SiO2 with an acoustic impedance of around 13 MRayl is demonstrated by two equal resonator stacks by replacing only the uppermost low-Z thin film of the acoustic reflector. A single-mask design was chosen with platinum as a bottom electrode to ensure the most equal growth conditions for the piezoelectric aluminum nitride (AlN) layers on both reflectors’ surfaces featuring either the tailored a-SiOCN:H or standard SiO2. The a-SiOCN:H thin films were deposited by plasma-enhanced chemical vapor deposition and the according acoustic impedance was priorly depicted to 7.1 MRayl, which could be exploited to achieve an increase in the effective coupling coefficient beyond 7% as well as a resonator bandwidth of more than 60 MHz.

Temperature effect on acoustic waves reflection condition in anisotropic crystals

The reflection of acoustic waves in anisotropic media has found important applications in acousto-optics (AO). It may be realized both with changing the type of acoustic mode and without it. The latter case is applied for the realization of the quasi-collinear AO diffraction geometry for which the incident light and ultrasound wave group velocity vectors are collinear. The acoustic wave involved into the AO interaction exists due to the reflection from the AO cell input optical face. Quasi-collinear configuration of AO interaction enables achieving exceptionally high spectral resolution and diffraction efficiency, therefore, it is applied for the laser pulse shaping. However, the application of AO tunable filters for such purposes requires high acoustic power values, which induce the temperature gradients in the AO crystal. Temperature variations influence the stiffness constants of the AO crystal, impacting the characteristics of incident and reflected acoustic waves, affecting the acoustic wave reflection condition and consequently, the AO diffraction characteristics. This study presents the theoretical and experimental examination of the temperature influence on the acoustic beam reflection in anisotropic crystals on the example of tellurium dioxide crystal. This paper is supported by the Russian Science Foundation, grant 23-12-00057.

Reflectivity characterization of in-flow acoustic floor treatment for the NASA Langley 14- by 22-Foot Subsonic Tunnel

An experimental campaign was performed to assess acoustic modifications to the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel. Recent acoustic testing campaigns in this facility have emphasized the reduction of aerodynamic noise due to flow scrubbing across acoustically treated floor baskets. However, the measures implemented to address this noise contaminant have resulted in the installation of floor basket coverings of high acoustic reflectivity. Therefore, a controlled testing campaign was performed to identify a suitable acoustic basket configuration in terms of both acoustic absorptivity and reduced flow scrubbing noise. This testing campaign was conducted in two phases: the first in an anechoic chamber facility on a single acoustic basket panel to identify a notional configuration of acceptable absorptivity, and the second in a complete floor basket installation checkout test in the NASA Langley 14- by 22-Foot Subsonic Tunnel. Results show that the newly implemented floor treatment exhibits suitable performance in both desired categories of acoustic absorptivity and reduced flow scrubbing noise. This campaign has also validated the effectiveness and usefulness of the anechoic chamber test configuration as a means of assessing acoustic reflections at oblique angles of incidence.

Numerical modeling of acoustic scattering characteristic with wavenumber domain admittance

A conversion from the wavenumber domain acoustic reflection coefficient to the wavenumber domain acoustic admittance is formulated to deal with the acoustic reflection properties of arbitrary materials in numerical simulation. This method, which can represent arbitrary reflection directional properties, is an extended reactive boundary condition modelling method based on a spatial Fourier transform over the boundary surface. The advantages are that it is computationally inexpensive because it does not need to consider the interior of the material in the analysis, and that it can handle reflection characteristics obtained from actual measurements, etc. From the results of applying the wavenumber domain acoustic admittance to the numerical analysis, it has been confirmed that the proposed method can handle not only the specular reflection component, but also when arbitrary scattering components are included, or when the main reflection direction is changed from the specular reflection direction.

Acoustic reflector remotely tunable by the acoustic radiation force

Specifically structured surface can be used to control acoustic waves reflection enabling wavefront shaping tailored for desired applications such as imaging or cloaking. With the development of metasurfaces, which enable changing the reflection of an incident acoustic wave at an interface using a sub-wavelength structure, it is possible to explore new frontiers of Snell-Descartes laws. However, the control over wave propagation is pre-established when using fixed structures, directing research towards metasurfaces reconfigurable in both time and space. This work proposes a metamaterial architecture using deformations of a fluid interface between two media through the acoustic radiation pressure (ARP). An analytical and numerical study is conducted to assess the phase shift on airborne acoustic wave induced by a unit cell featuring a Helmholtz resonator tuned by the water surface elevation induced by ARP. The possibility to program in real-time the phase shift is successfully tested experimentally for an incident wave of frequency 3400 Hz. The extension to a metasurface is introduced through the juxtaposition of 15 unit cell. A retroreflection effect is then numerically demonstrated, highlighting the effectiveness of the proposed approach. This concept of real-time and non-contact reconfigurable metasurface opens new possibilities for beam deflection, acoustic holography or information encoding.

Design and optimization of acoustic reflector for uniform diffusion

Sound diffusion performance is considered as an important issue in building acoustics. A well-diffused sound field can effectively enhance the human listening experience. To this end, we have investigated several optimization strategies to design a sub-wavelength acoustic metasurface that can achieve broadband uniform diffuse reflections. These designs are based on Fresnel lens surface, groove-like structure, level-set method, topology optimization approach, respectively. Meanwhile, a strategy combining Monte-Carlo searches and other derivative-free algorithms has been analyzed and used to ensure, as far as possible, a global optimum for the objective function when dealing with the multi-peak problem encountered in complex sound fields. Numerical simulations show that the resulting metasurfaces with the best diffusion performance have similar configurations between different design methods. The simulated sound pressure field was also verified by experimental measurements. From a general perspective, the proposed optimization strategy and simulation framework can provide a greater degree of freedom for geometric configuration and benefit the design of interior components in building acoustics.

Comparison of standard Bayesian methods and PINNs for the reconstruction of acoustic fields in 'in situ' combustion chambers

Acoustic measurements, utilizing sensors such as microphones strategically placed, are commonly employed to monitor acoustic systems and extract quantities of interest, such as acoustic reflection coefficients. Typically, a specialized test rig must be constructed to allow for external harmonic acoustic forcing via loudspeakers. In this study, we propose two different methods: physics-informed neural networks (PINNs) and the extended Kalman filter, to reconstruct the acoustic field of a system and assess the acoustic reflection coefficient at a defined boundary. We demonstrate numerically that a single external broadband forcing signal suffices for these methods. This implies that these methods can be applied to 'in situ' configurations, such as industrial combustion chambers, where the broadband nature of combustion noise serves as the acoustic forcing element. Furthermore, we investigate the performance of the two aforementioned methods in reconstructing the acoustic systems and corresponding acoustic boundaries.

Application Study of Acoustic Reflectivity Based on Phased Array Ultrasonics in Evaluating Lubricating Oil Film Thickness

Bearings play a key role in rolling mills, and the uniformity of their lubricant film directly affects the degree of wear of bearings and the safety of equipment. Due to long-term stress, the lubricant film inside the bearing is not uniformly distributed, resulting in uneven wear between the journal and the shaft tile, which increases the potential safety hazards in production. Traditional disassembly inspection methods are complex and time-consuming. Ultrasonic nondestructive testing technology, which has the advantages of nondestructive and adaptable, has become an effective means of assessing the thickness of the oil film in bearings. In this study, an experimental platform for calibrating the lubricant film thickness in bearings was constructed for the first time, and the acoustic characteristics of different thicknesses of the oil film were measured using ultrasonic detection equipment to verify the accuracy of the simulation process. The experimental results show that after discrete Fourier transform processing, the main features of the frequency channels of the reflected acoustic signals of different thicknesses of the oil film are consistent with the finite element simulation results, and the errors of the oil film thicknesses calculated from the reflection coefficients are within 10% of the set thicknesses, and the measurement ranges cover from 5 μm to 250 μm. Therefore, the above method can realize the accurate measurement of the thicknesses of the oil film in bearings.

Beam–plasma dynamics in finite-length, collisionless inhomogeneous systems

This study investigates the streaming instability triggered by ion motion in a plasma system that is finite in length, collisionless, and inhomogeneous. Employing numerical simulations using particle-in-cell techniques and kinetic equations, the study examines how inhomogeneity emerges from integrating a cold ion beam with a background plasma within a confined system. The findings suggest that steady ion flow can modify ion sound waves through acoustic reflections from system boundaries, leading to instability. Such phenomena are known to be a hydrodynamic effect. However, there are also signatures of the beam-driven ion sound instability where kinetic resonances play a pivotal role. The main objective is to understand the impact of a finite-length system on beam–plasma instability and to identify the wave modes supported in such configurations.

Reflection function, reflectance, and area function measurements in ears of children and adults.

The main experiment concerned time-domain measurements of the acoustical reflection function (RF) of the human ear in adults and children (aged 5 to 8 years) using a probe inserted into the ear canal. This RF was used to calculate the area function of the ear canal versus distance along its centerline. Acoustical reflectance was calculated in the frequency domain from the RF, as was the difference in sound pressure level near the tympanic membrane relative to the probe tip. Group responses in area function, total ear-canal length, absorbance and group delay, and admittance magnitude and phase were analyzed based on sex, ear, and age. Responses were compared between children/adults and younger/older adults relative to age 50 years. Ear and sex were never significant. Significant differences were observed in children compared to adults in the area function, absorbance and group delay, and admittance magnitude and phase (0.25-4 kHz). Group delay differed between younger and older adults. A second experiment assessed level dependence of responses to better understand limitations in probe performance observed in the main experiment. These results show the utility of time-domain measurements of the area function and derived reflectance to understand sound-transmission differences across age at frequencies important to middle-ear function.

Acoustic flow resonances in installed rectangular jets

Zonal Large Eddy Simulations (LES) of complex installed rectangular jet flows are performed for subsonic jet conditions of the Central Institute for Aviation Motors (CIAM) experiment, where a strong tone was reported. For far-field noise modelling, the zonal LES solutions are coupled with the permeable formulation of the Ffowcs Williams and Hawkings (FW-H) method. The obtained noise spectra predictions are compared with the acoustic measurements in the CIAM facility. To reduce statistical noise of the relatively short LES time series, contributions due to several dominant low frequency tones and the remaining broadband signal are computed separately, using a tailored Fourier transform technique for each signal type. For cross-validation, noise spectra measurements of an equivalent isolated round jet in the CIAM facility are compared with the empirical sJet model calibrated on the NASA Small Hot Jet Acoustic Rig (SHJAR) jet noise database. While the two datasets agree reasonably well for mid to high frequencies, larger discrepancies are observed for low frequencies, which are attributed to acoustic reflections in the non-anechoic CIAM facility. The differences in noise levels between the CIAM dataset and the sJet model representing the NASA jet noise data are used to determine the experimental uncertainty of the CIAM noise measurements for each frequency and observer angle. For the installed rectangular jet, it is shown that far-field noise spectra predictions of the zonal LES-FW-H method for both the fundamental tone, its sixth harmonic corresponding to the jet Strouhal number of around 1, and the broadband component are broadly within the experimental error bar for most observer angles. Some discrepancies between predictions of the zonal LES method and the CIAM measurements for the main low frequency tone for the 30o and 90o, where the experimental uncertainty at low frequencies is largest are also noted. After validating the acoustic solutions, spectral and conditional averaging analysis methods are applied to elucidate mechanisms of the acoustic-flow resonance in the installed rectangular jet flow. The numerical dispersion relation is obtained to analyse phase velocities of the upstream and downstream travelling pressure waves in the stream-wise direction. The conditional analysis of pressure fluctuations inside the jet reveals the emergence of internal reflection points corresponding to a rapid change of the acoustic wave phase as well as the saddle points interpreted as localised zones of vorticity shed from the side-wall edges. To independently investigate the effect of trailing edges and corner points of the jet embodiment geometry on closing the acoustic-flow resonance cycle, several modifications of the baseline rectangular nozzle are considered, such as introducing chevron-like lobes and cuts on the trailing edges of the side walls as well as smoothing the sharp corner points of the wall edges. Following the series of additional zonal LES runs with the modified installed nozzle geometries, an optimized tone-less modification of the original installed nozzle was obtained, in broad agreement with the conditional analysis results. The obtained tone-less modification of the installed rectangular jet is further analyzed to provide insights into its similarity and differences from the aeroacoustics of the reference isolated round jet in the same CIAM facility.

Estimating direction of arrival in reverberant environments for wake-word detection using a single structural vibration sensora).

The vibrational response of an elastic panel to incident acoustic waves is determined by the direction-of-arrival (DOA) of the waves relative to the spatial structure of the panel's bending modes. By monitoring the relative modal excitations of a panel immersed in a sound field, the DOA of the source may be inferred. In reverberant environments, early acoustic reflections and the late diffuse acoustic field may obscure the DOA of incoming sound waves. Panel microphones may be especially susceptible to the effects of reverberation due to their large surface areas and long-decaying impulse responses. An investigation into the effect of reverberation on the accuracy of DOA estimation with panel microphones was made by recording wake-word utterances in eight spaces with reverberation times (RT60s) ranging from 0.27 to 3.00 s. The responses were used to train neural networks to estimate the DOA. Within ±5°, DOA estimation reliability was measured at 95.00% in the least reverberant space, decreasing to 78.33% in the most reverberant space, suggesting an inverse relationship between RT60 and DOA accuracy. Experimental results suggest that a system for estimating DOA with panel microphones can generalize to new acoustic environments by cross-training the system with data from multiple spaces with different RT60s.

CONCEPTUAL ANALYSIS ON THE IMPACT OF ACOUSTIC LINERS IN FAN FLUTTER

Abstract This work investigates the impact of acoustically treated intakes on fan flutter. The propagation of the fan acoustic perturbations is studied using a simplified model, where the frequency of the waves in the intake is the natural frequency of the fan blade in the stationary frame of reference. The model consists of a constant cross-section annular duct, where the acoustic modes are computed for hard wall and lined wall regions, assuming a uniform axial flow. The interfaces between the lined and hard wall sections are solved by doing mode matching. The acoustic reflections in the zero-thickness intake are computed using the Wiener-Hopf technique following Rienstra's model. Analytical results show that the waves propagating from the fan are reflected and scattered radially at the interfaces between the hard wall and the liner. Furthermore, the liner damps and changes the phase velocity of acoustic modes. Due to the low frequency of the flutter waves, the radial scattering can activate different cut-off modes, which need to be retained in order to make accurate predictions. The likelihood of fan flutter is estimated using the phase of the reflected cut-on waves reaching the fan. This strategy is used to assess the impact of the acoustic liners on the stability of a realistic fan. It is concluded that the impact of the phasing and reflections induced by the acoustic liners is comparable to that of the intake and can alter the flutter characteristics of the fan significantly.

Risk of Narrow Upper Airway in Class II Children with Large Horizontal Maxillary Overjet Assessed By Acoustic Reflection: a Case-Control Study

Risk of Narrow Upper Airway in Class II Children with Large Horizontal Maxillary Overjet Assessed By Acoustic Reflection: a Case-Control Study

Experimental Study on Submerged Nozzle Damping Characteristics of Solid Rocket Motor

Acoustic instabilities in solid rocket motors (SRMs) can lead to severe performance deterioration and structural damage. Nozzle damping accounts for the main acoustic dissipation source, and it is highly dependent on geometric parameters and operating conditions. This study experimentally investigated the acoustic damping characteristics of submerged nozzles in SRMs, focusing on the effects of submerged cavity dimensions, nozzle convergent angle, throat-to-port area ratio, and mean pressure variations on the longitudinal instability. The steady-state wave decay method was used to quantify the acoustic damping, and a designed rotary valve system was employed to introduce periodic pressure oscillations in the high-pressure combustion chamber. The results revealed that a larger submerged cavity would reduce the nozzle damping efficiency, with the elimination of the submerged cavity enhancing the nozzle decay coefficient magnitude by 41.9%. Furthermore, increasing the nozzle convergent angle was found to amplify acoustic wave reflection, thereby diminishing damping performance. A linear inverse relationship was observed between the throat-to-port area ratio and the decay coefficient, with a 125% increase in the ratio resulting in a 24.3% reduction in the decay coefficient. Interestingly, despite the formation of complex vortices in the submerged cavity, the mean pressure variation presented negligible effects on acoustic damping characteristics, and its damping performance is similar to a simple nozzle without a cavity. These findings provide valuable experimental data for predicting the stability of a solid rocket motor with a submerged nozzle and offer insights into the optimization of submerged nozzle designs for higher acoustic damping in SRMs.

REWARE: a seismic processing algorithm to retrieve geological information from the water column

SUMMARY When interpreting marine very high-resolution (VHR) single-channel seismic reflection data, the signal in the water column is generally considered as noise and is often eliminated by a water-mute application to focus on geological information under the seafloor. Alternatively, the signal in the water column can be used to study ocean currents or gas/fluid emissions. To provide images of the sedimentary formations and tectonic structures beneath the seafloor in shallow water regions, such as continental shelves and lakes, marine seismic reflection profiles are often acquired using a single-channel streamer and sparker-type source, providing VHR data, with limited penetration depth. To exploit the full potential of these single-channel data, we propose a simple algorithm, called REWARE (Recovery of Water-column Acoustic Reflectors). This algorithm allows to extract further geological information from the water-column data using open-source codes (Seismic Un*x), adding the coherent signal from the previous shots, recorded in the water column, to the previous traces. The record length becomes longer while maintaining a very high trace-to-trace consistency. To demonstrate its efficiency, we present two examples of the REWARE processing in two different geological contexts: the East Sardinia shelf (Italy) and the North Evia Gulf (Greece). This method provides deeper images than with original data for seismic data acquired across steep slopes, such as canyons or continental shelf breaks. Thus, depending on the seafloor geometry and subseafloor structures, it is possible to image or map sediment layers and tectonic structures at depth, keeping a very high structural resolution.