Source Radiation Pattern Research Articles

Acoustic Radiation Patterns of Different Polygon Piston Surfaces

Transducers are used in acoustic remote sensing and several other modern applications. The radiating surface geometry of a single acoustic transducer affects its beam pattern and has a cumulative effect on the overall performance of an array configuration. In addition, the transducers with polygon radiating surfaces provide more compact structure in an array than the circular pistons due to their flat surface edges. However, until now, the radiation patterns of acoustic polygonal pistons have not been exclusively studied and documented. In this study, the directional factors of acoustic pistons with polygonal surfaces of three to ten sides were derived analytically from the first principle using the Rayleigh integral. These directional factors were used to synthesise and characterise the radiation patterns of the piston sources in comparison with the baffled circular piston of an equivalent surface area. The rectangular, the triangular, and the rest of the polygons have the same performance with the circular piston when the surface diameter is not higher than 0.5λ, 0.28λ and 0.43λ, respectively. The main lobe of the acoustic emissions from the square is very close to that of the circular piston whose diameter is greater than a wavelength while that of the rectangle is wider. The results show that the radiating surface perimeter and symmetry are the two most critical factors affecting the beam characteristics of a piston source rather than the surface area or the number of sides. The theoretical results were validated using the finite element method with an excellent compliance.

Factors Influencing Radiation Sound Fields in Logging While Drilling Using an Acoustic Dipole Source

With the increasing number of complex well types in the development stage of oil and gas fields, it is becoming increasingly urgent to use remote detection logging while drilling (LWD) to explore the geological structures in a formation. In this paper, the feasibility and reliability of the dipole remote detection of logging while drilling are demonstrated theoretically. For this purpose, we use an asymptotic solution of elastic wave far-field displacement to derive the calculation formula for the radiation pattern and energy flux of an LWD dipole source. The effects of influencing factors, including the source frequency, formation property, drill collar size, and mud parameter, on the radiation pattern and energy flux are analyzed. The results show that the horizontally polarized shear wave (SH-wave) has a greater advantage in imaging the reflector compared with the cases of the compressive wave (P-wave) and vertically polarized shear wave (SV-wave), which indicates the dominance of the SH-wave in dipole remote detection while drilling. The optimal source excitation frequency of 2.5 kHz and inner and outer radii of the drill collar of 0.02 and 0.1 m, respectively, should be considered in the design of an LWD dipole shear wave reflection tool. However, the heavy drilling mud is not conducive to remote detection during logging while drilling. In addition, the reflection of the SH-wave for the LWD condition is simulated. Under the conditions of optimal source frequency, drill collar size, and mud parameters, the reflection of the SH-wave signal is still detected under the fast formation.

Multipole transfer matrix model-based sparse Bayesian learning approach for sound source identification

Accurate source identification is key to solving complex flow-induced noise problems, and sources often have non-uniform radiation patterns. At the same time, traditional methods have many application limitations, including the need for prior knowledge of the sound field, as well as inability to apply to coherent sources or coexisting multipoles. A multipole transfer matrix model-based sparse Bayesian learning approach for sound source identification (MT-SBL) is proposed. In this algorithm, the transfer relationship for the multipole radiation patterns of sound sources is established. Then, the signal sparse reconstruction is transformed into an iterative updating problem of the feature parameters under a sparse Bayesian learning (SBL) framework, which leads to the accurate identification of multipole sources. Numerical simulations and experiments on electric speakers in an anechoic environment validate the proposed algorithm. Compared with the existing methods, the algorithm is more advantageous in terms of accuracy, resolution, and computational efficiency. Further experiments were conducted on the identification of supersonic jet noise sources, verifying the effectiveness of the method for identifying strongly directional sound sources.

Shear-Wave Velocity Model for the Dead Sea Transform from Multimode Inversion of Surface Waves Excited by the February 2023 Southeast Türkiye Earthquake Sequence

Abstract The dispersive nature of surface waves can be used for shear-wave velocity inversion at different scales. We show that four large earthquakes from the 2023 Türkiye earthquake sequence generate visible surface waves recorded by a dense strong-motion network deployed along the Dead Sea Transform (DST) in Israel. Thanks to favorable geometrical conditions and source radiation patterns, we observe both Rayleigh and Love waves that travel predominantly parallel to the network. We can reliably compute the dispersion of three Love-wave modes and two Rayleigh-wave modes. Using these dispersion curves, we invert for a 1D S-wave velocity model of the entire DST, outperforming an existing model. Statistical and kernel sensitivity analysis show high certainty down to a depth of 30 km thanks to the multimode joint inversion in the frequency band of 0.03–0.3 Hz. Using a multiwindow approach, we invert for an along-strike laterally varying velocity model of the DST. Although it is limited to the fundamental Love-wave mode, using the 1D model as a constraint allows us to recover a shallow (10 km) velocity structure in agreement with previous studies of the area. Despite the simplicity of our used approach, it can be used as a basis for more advanced studies.

Experimental demonstration of indoor 3D optical wireless positioning and azimuth estimation using steerable line lasers

We present an indoor three-dimensional (3D) optical wireless positioning and azimuth estimation (OWPAE) scheme that utilizes steerable line lasers. This approach enables the simultaneous acquisition of precise 3D coordinate and azimuth of a mobile receiver without requiring a priori knowledge of the radiation pattern of the light source and photo-detector (PD) characteristics. Our work begins with an analysis of the feasibility of using line lasers for OWPAE. Subsequently, by leveraging the geometric relationship between two line lasers and a pair of PDs, we establish the OWPAE model, considering receiver tilt, and design the frame structure for conveying essential information. To evaluate the effectiveness of our proposed OWPAE scheme, we set up an experimental platform. Experimental results confirm that when the receiver is oriented upwards, the system accurately determines the receiver's location with a mean 3D positioning error of 6.3 cm and its azimuth with a mean azimuthal error of 2.8°. When the receiver tilts at a polar angle of 30°, the system remains effective, yielding a mean 3D positioning error of 8.3 cm and a mean azimuthal error of 5.6°.

Discrimination of Seismic Events in the North Korean Test Site and Surrounding Area Using MDAC Spectral Ratio

ABSTRACT An event of ML 3.7 occurred near the Punggye-ri nuclear test site on 11 February 2022. It was stronger than the known historical earthquakes around the North Korean test site (NKTS). How to accurately identify whether this event and future events near NKTS are explosions or natural earthquakes is worth paying attention to. For moderate and small earthquakes, the regional P/S spectral ratio has the advantage of identifying explosions and earthquakes. However, the P/S spectral ratio depends on magnitude and ray path. Magnitude and distance amplitude correction (MDAC) was proposed and demonstrated to be an effective method to correct magnitude and path effect. Different from the traditional MDAC method, we use explosions to build the MDAC model to reduce the influence of the source radiation pattern. After building the MDAC model, we analyze the Pg/Lg and Pn/Lg spectral ratios of 6 nuclear tests and 60 earthquakes at the NKTS from 2013 to 2021. The results show that the spectral ratio residuals of the 6 nuclear tests are mainly distributed around 0 after correction, whereas the spectral ratio residuals of earthquakes are obviously <0 above 3 Hz and are clearly distinguished from explosions as expected. The Pg/Lg and Pn/Lg spectral ratios of the ML 3.7 earthquake near the NKTS on 11 February 2022 exhibit similar characteristics to historical natural earthquakes. We further discuss the influence of magnitude on P/S spectral ratios. In the NKTS, the differences in the P/S ratio between earthquakes and explosions are similar before and after magnitude correction at 4–8 Hz. Nevertheless, the magnitude correction increases by ∼27% of the difference between explosions and natural earthquakes at 6–9 Hz to better separate explosions from natural earthquakes.

Simultaneous waveform inversion of seismic-while-drilling data for P-wave velocity, density, and source parameters

Full-waveform inversion (FWI), as an optimization-based approach to estimating subsurface models, is limited by incomplete acquisition and illumination of the subsurface. The incorporation of additional data from new and independent raypaths should be expected to result in significant increase in the accuracy of FWI models. In principle, seismic-while-drilling (SWD) technology can supply these additional raypaths; however, it introduces a new suite of unknowns, namely precise source locations (i.e., drilling path), source signature, and radiation characteristics. A new FWI algorithm is formulated in which the source radiation patterns and positions join the velocity and density values of the grid cells as unknowns to be determined. Several numerical inversion experiments are then conducted with different source settings using a synthetic model. The SWD sources are supplemented by explosive sources and multicomponent receivers at the surface, simulating a conventional surface acquisition geometry. The subsurface model and SWD source properties are recovered and analyzed. The analysis is suggestive that SWD involvement can enhance the accuracy of FWI models, with varying degrees of enhancement depending on factors such as trajectory inclination, source density, and drill path extension. The impact of SWD-FWI over standard FWI is reduced when low-frequency data are missing, but improvements over the models constructed with no subsurface sources remain. This formulation permits general source information, such as position and moment tensor components, to be independently obtained. This inversion scheme may lead to a range of potential applications for which medium properties and source information are required.

Quantifying Site Effects and Their Influence on Earthquake Source Parameter Estimations Using a Dense Array in Oklahoma

AbstractWe investigate the effects of site response on source parameter estimates using earthquakes recorded by the LArge‐n Seismic Survey in Oklahoma (LASSO). While it is well known that near‐surface unconsolidated sediments can cause an apparent breakdown of earthquake self‐similarity, the influence of laterally varying site conditions remains unclear. We analyze site conditions across the 1825‐station array on a river plain within an area of 40 km by 23 km using vertical ground motions from 14 regional earthquakes. While the source radiation pattern controls P‐wave ground motions below 8 Hz, the surface geology correlates with P‐wave ground motions above 8 Hz and S‐wave ground motions at 2–21 Hz. Stations installed in alluvial sediments have vertical ground motions that can exceed three times the array median. We use the variation of ground motion of regional earthquakes across the array as a proxy for site effects. The corner frequencies and stress drops of local earthquakes (ML = 0.01–3) estimated using a standard single‐spectra approach show negative correlations with the site‐effect proxy, while the seismic moments show positive correlations. In contrast, the spectral‐ratio approach effectively shows no correlation. The overall bias is small as expected for this relatively homogeneous structure; accurate estimation of site‐related biases requires at least 30 stations. Correcting for site‐related biases reduces the standard deviations of the source parameters by less than 13% of the total variations. Remaining variations are partially associated with source directivity and model misfits— as small earthquakes can have complex ruptures.

Suboptimal controller design of global active noise control system for various acoustic environments

Conventional active noise control (ANC) systems in enclosed spaces are not easy to implement experimentally because they require a large number of microphones to measure sound pressure in global areas. Even if such systems are possible, if there are any changes in the locations of noise sources or surrounding objects, or if ANC system moves to another enclosed space, an expensive and time-consuming experimental calibration is again required. Implementation of global ANC in enclosed spaces is thus difficult. Therefore, we designed a global ANC system that can be used in various acoustic environments. The main idea involves suboptimal open-loop controller design in the free field. By using an open-loop controller, a controller calibrated once can be used in various acoustic environments. A controller designed in the free field derive a suboptimal solution without bias toward a specific acoustic environment. For controller design in the free field, we propose an experimental calibration approach in which the arrangement and the number of control speakers and microphones are determined by the frequency range and radiation pattern of the noise source. We conducted simulations and experiments to show that the designed controller in the free field is sufficiently effective in other enclosed spaces.

Elastic wave radiation and reception of a borehole dipole source in a vertically transverse isotropic formation

Single-well acoustic imaging using a dipole tool has been applied in anisotropic formations. For this application, the effect of anisotropy on the radiation and reception of acoustic waves in the borehole needs to be analyzed and a proper analysis method needs to be developed. We use the far-field asymptotic solution of the wavefield to calculate the radiation pattern of the dipole source in a borehole penetrating vertically transverse isotropic (VTI) formation. We model the spherical wave propagation characteristics of the radiated and reflected waves in the VTI formation and the receiving of the waves in the borehole for the on- and off-axis positions. Based on the developed analytical modeling methods, we study systematically the effects of the formation anisotropy on the radiation pattern and borehole response characteristics. Our modeling result demonstrates that due to the coupling between the longitudinal and the transverse particle motions, quasi-P-(qP-) and quasi-SV-(qSV-) wave radiation patterns contain two components. The result also indicates that the anisotropy causes the arrival time of the SH-reflection wave to differ from that of the qSV wave, and the misposition of the imaged targets would occur if the velocity measured along the borehole is used for migration. The azimuth sensitivity of the off-axis data can be used to help eliminate the 180° ambiguity for the dipole acoustic imaging in the VTI formation. Understanding the effects of anisotropy on borehole acoustic imaging can help improve the accuracy of the imaging result in anisotropic formations.

Creating acoustic spiral waves with quadrature and tertiary phase-biased dipoles

Acoustic spiral waves have been demonstrated by exciting orthogonal modes of vibration in cylinders with just one electroacoustic transducer [J. Acoust. Soc. Am. 132(6) (2012)]. Applications including navigation, active sonar, and imaging are emerging. We demonstrate several practical engineering approaches to create constituent signaling with either quadrature or tertiary phase bias to excite spiral waves and compare their effectiveness. Approaches using CODECs, DSP, and flip flops are designed and characterized then tested on underwater transducers in realistic operating conditions. Tradeoffs of source level, effective coupling, bandwidth, and radiation patterns are summarized. [Work supported in part by BTech Acoustics LLC and ONR 321MS.]

Field Evaluation of Two Impulsive Downhole Seismic Sources in Crosswell and Reverse VSP Geometries and High-Resolution Characterization of Near-Surface Texas Gulf Coast Sediments

Borehole seismic methods have been widely used for characterizing the shallow subsurface. Accurate analysis of their data is aided by a solid understanding of the borehole sources' characteristics. This study presents a field evaluation of two impulsive borehole seismic sources (Trident's Scorpion sparker and RT Clark's Ballard weight drop) in crosswell and reverse vertical seismic profile (RVSP) geometries at a Gulf of Mexico coastal site with two shallow vertical wells. The acquired data is then utilized to characterize the near-surface coastal sediments. The Scorpion source generated P-wave dominant frequencies that were recorded as 650 Hz and 250 Hz in the crosswell and RVSP geometries, respectively. For the Ballard source in the two geometries, the P-wave dominant frequencies were 1100 Hz and 250 Hz. We were also able to pick direct S-wave arrivals with the Ballard source, and their dominant frequencies were 100 Hz and 40 Hz for in situ and surface recordings, respectively. The average signal-to-noise ratio (SNR) recorded with the Scorpion data for the crosswell geometry and RVSP, respectively, is 13 and 6, and for the Ballard source, 62 and 30. We also investigated the source radiation patterns and signature wavelets. Seismic tomography was performed for the area between the two wells. Low P-wave and S-wave velocities correspond to three fresh water-saturated sand zones identified from drilling cuttings and previous well log data. Also, the plot of velocity of P-wave (Vp) versus S-wave (Vs) fits reasonably to the Mudrock Line. Both sources can excite repeatable energetic seismic signals up to 150 m away and could be useful in many geotechnical settings and even single-well imaging.

A Novel 3D Non-Stationary Channel Model for 6G Indoor Visible Light Communication Systems

The visible light communication (VLC) technology has attracted much attention in the research of the sixth generation (6G) communication systems. In this paper, a novel three dimensional (3D) space-time-frequency non-stationary geometry-based stochastic model (GBSM) is proposed for indoor VLC channels. The proposed VLC GBSM can capture unique indoor VLC channel characteristics such as the space-time-frequency non-stationarity caused by large light-emitting diode (LED) arrays in indoor scenarios, long travelling paths, and large bandwidths of visible light waves, respectively. In addition, the proposed model can support special radiation patterns of LEDs, 3D translational and rotational motions of the optical receiver (Rx), and can be applied to angle diversity receivers (ADRs). Key channel properties are simulated and analyzed, including the space-time-frequency correlation function (STFCF), received power, root mean square (RMS) delay spread, and path loss (PL). Simulation results verify the space-time-frequency non-stationarity in indoor VLC channels. In addition, the influence of light source radiation patterns, receiver rotations, and ADRs on channel characteristics have been investigated. Finally, the accuracy and practicality of the proposed model are validated by comparing the simulation result of channel 3dB bandwidth with the existing measurement data. The proposed channel model will play a supporting role in the design of future 6G VLC systems.

The opening workspace control strategy of a novel manipulator-driven emission source microscopy system

Emission source microscopy (ESM) technique can be utilized for localization of electromagnetic interference sources in the electronic systems, but its accuracy is limited by the typical planar scanning mode. In order to increase the accuracy, this paper presents a novel cylinder-aperture ESM measurement system driven by 6-DOF manipulator, and investigated the control strategy to generate the maximum-area aperture and optimized scanning trajectory. Based on the multiple constraints of the cylinder-aperture ESM measurement, we proposes analyzing the impact of the constraints by steps. This can obtain the analytical solution of the manipulator workspace and support solving the maximum aperture area. Besides, a modified RRT*(Rapidly-exploring Random Trees) algorithm is addressed to optimize the manipulator trajectory. The simulation and tests have proven that this algorithm could obviously reduce the joint mutation and cumulative tracking error. In the experimental section, the near-field scanning (NFS) tests, planar-aperture ESM measurement and proposed cylinder-aperture ESM measurement were conducted to measure one benchmark emission source. The results have demonstrated that the cylinder-aperture ESM measurement has the best convergences on the radiation pattern of the emission source.

Modeling of 2D Acoustic Radiation Patterns as a Control Problem

A problem of modeling radiation patterns of wave sources in two-dimensional acoustic tomography is considered. Each source has its own radiation patterns, and their modeling will be used to improve the solvability of inverse problems of recovering the acoustic parameters of human soft tissues and come closer to building a digital twin of acoustic tomography. The problem is considered as a control problem of the right side for the velocities by spatial variables. Two statements are investigated—control by time or space functions. A numerical solution method is implemented. The results of numerical calculations are presented.

PS interferometric imaging condition for microseismic source elastic time-reversal imaging

SUMMARYThe time-reversal imaging method utilizes the wave equation to back-propagate recorded seismic data and a proper imaging condition to locate a passive seismic source. For an explosive source, the reconstructed wavefield is focused at the seismic source location and origin time. Although the elastic time-reversal wavefield for a moment tensor source may not exhibit a maximum at the true location at the origin time, it does exhibit a quasi-symmetrical spatial distribution around the source location that represents the radiation pattern of the moment tensor source. We propose the use of an interferometric imaging condition to solve the radiation pattern problem, which is combined with elastic PS cross-correlation imaging condition (referred to as the PS interferometric cross-correlation imaging condition) to locate a moment tensor source using elastic time-reversal imaging method. 2-D and 3-D numerical tests demonstrate that our proposed method can identify the moment tensor source location in complex velocity models with a high noise level. In tests of the sensitivity of the method to the accuracy of the velocity model, we find that the method can still get focused images under about 10–25 per cent random perturbations in P- and S-wave velocities, but only under about 5 per cent correlated perturbation of global P- and S-wave velocities with a potential bias in the location.

Pulsed-laser source characterization in laboratory seismic experiments

The present study aimed to characterize the properties of a laser-generated seismic source for laboratory-scale geophysical experiments. This consisted of generating seismic waves in aluminum blocks and a carbonate core via pulsed-laser impacts and measuring the wave-field displacement via laser vibrometry. The experimental data were quantitatively compared to both theoretical predictions and 2D/3D numerical simulations using a finite element method. Two well-known and distinct physical mechanisms of seismic wave generation via pulsed-laser were identified and characterized accordingly: a thermoelastic regime for which the incident laser power was relatively weak, and an ablation regime at higher incident powers. The radiation patterns of the pulsed-laser seismic source in both regimes were experimentally measured and compared with that of a typical ultrasonic transducer. This study showed that this point-like, contact-free, reproducible, simple-to-use laser-generated seismic source was an attractive alternative to piezoelectric sources for laboratory seismic experiments, especially those concerning small scale, sub-meter measurements.

Creating a spatial optical tube of prescribed characteristics

Based on the radiation pattern of a spatial uniform magnetic current line source (UMLS) antenna, we propose a method for creating a spatial optical tube with a variable length and arbitrary orientation for a 4π focusing system. A virtual spatial UMLS antenna situated at the foci of two high numerical aperture objectives is used to obtain the required illumination at the entrance pupil plane. Numerical results demonstrate that the length of the created optical tube is approximately equal to that of the UMLS antenna. Its orientation is consistent with that of the line source. Its polarization is pure azimuthal, and the transverse size of the optical tube shell and the dark tunnel is uniform over the entire depth of focus. This optical tube can be customized according to application requirements. The generated optical tube can be used for such applications as arbitrary orientation particle trapping and guiding, micromanipulation, and optical microscopy.

Elastogravity Waves and Dynamic Ground Motions in the Korean Peninsula Generated by the March 11, 2011MW9.0 Tohoku‐Oki Megathrust Earthquake

AbstractThe mass dislocations caused by large coseismic slips in megathrust earthquakes are large enough to produce elastogravity waves. Despite, successful identification of elastogravity‐wave development during megathrust earthquakes, the nature of ground motions and hazard potentials in regional and teleseismic distances remains unknown. The dynamic ground motions from the March 11, 2011MW9.0 Tohoku‐Oki megathrust earthquake are retrieved from broadband seismic records throughout the Korean Peninsula. The dynamic ground motions of the megathrust earthquake are dominated by low‐frequency (<0.1 Hz) energy that is a mixture of elastogravity waves and seismic waves. The peak dynamic ground displacements in the Korean Peninsula reached ∼20 cm with horizontal permanent displacements of ∼2 cm or more. Radially‐polarized elastogravity waves developed instantly at the event origin time. Very‐long‐period (<0.004 Hz) energy is a mixture of seismic waves and coseismic permanent displacements, presenting radially polarized retrograde particle motions for ∼600 s. The peak ground displacements (PGDs) and velocities for the Tohoku‐Oki earthquake are larger than those for a localMW5.4 earthquake. The peak ground motions vary azimuthally following the source radiation pattern. The tangential PGD increases with distance along continental ray paths due to the development of crustally guided waves. Large and slow dynamic ground motions cause dynamic stress changes of ∼1.8 MPa in the lithosphere of the Korean Peninsula, while the properties of the mantle are scarcely affected by slow dynamic motions. The large long‐period displacements induced by megathrust earthquakes may cause considerable long‐duration distortion on large buildings at regional and teleseismic distances. The characteristic elastogravity‐wave features may be used for detection of mass‐dislocation events.

On the problem of modeling the acoustic radiation pattern of source for the 2D first-order system of hyperbolic equations

In this paper the problem of modeling the acoustic radiation pattern of source is considered. The problem is formulated in the form of control problem for the 2D first-order system of hyperbolic equations. This problem is related to ultrasound tomography for early breast cancer detection. The modelling of the acoustic radiation patterns of sources allows us to improve the resolution of acoustic tomography.