Since it has already been demonstrated that point‐to‐point seismic propagation Green Functions can be extracted from noise, should possible to image Earth structure using the ambient noise field. Seismic data 148 broadband stations in Southern California were used extract surface wave arrival‐times between all station pairs network. The then a simple, but densely sampled tomographic procedure estimate velocity within frequency range of 0.1–0.2 Hz for region California. result compares...

It has been demonstrated experimentally and theoretically that an estimate of the Green's function between two seismic stations can be obtained from time‐derivative long‐time average cross correlation ambient noise these stations. This TDGF just field includes all tensor components estimates used to infer Earth structure. We have computed correlations using 1 30 continuous days recorded by over 150 broadband located in Southern California. The data processing yielded thousands...

It has been experimentally demonstrated that the Green’s function between two points could be recovered using cross-correlation of ambient noise measured at these points. This paper investigates theory behind this result in simple case a homogeneous medium with attenuation.

We present results from the cross‐correlations of seismic noise recordings among pairs stations in Parkfield network, California. When performed on many station at short ranges, correlation function (NCF) is passive analog to a shot gather made with active sources. demonstrate presence both P‐wave and Rayleigh wave NCF. A time‐frequency analysis allows us separate two packets that are further identified through their polarization. Arrival times were estimated NCF they compared favorably...

A stand-alone ultrasound shear wave imaging technology has been developed to quantify and visualize Young's modulus distribution by remotely applying radiation force tracking the resulting microvibrations in soft tissues with ultrafast imaging. We report first preliminary data that detected of local muscle stiffness within between resting contracting muscles at different lengths this technology. This technique may assist clinicians characterizing injuries or neuromuscular disorders.

It has been demonstrated experimentally and theoretically that an estimate of the Green’s function between two receivers can be obtained from time derivative long-time average ambient noise cross-correlation these receivers. The emergence rate deterministic coherent arrival times function, which yield recordings isotropic distribution random sources is studied by evaluating amplitude variance function. leading term in expression depends on recorded energy both time-bandwidth product...

Purpose To validate a real‐time phase contrast magnetic resonance imaging (RT‐PCMRI) sequence in controlled phantom model, and to quantify the relative contributions of respiration cardiac pulsations on cerebrospinal fluid (CSF) velocity at level foramen magnum (FM). Materials Methods 3T MRI techniques, vitro studies used realistic model spinal subarachnoid space driven by pulsatile flow waveforms mimicking respiratory components CSF flow. Subsequently, was measured continuously during...

Developing persistent and smart underwater markers is critical for improving navigation accuracy communication capabilities of autonomous vehicles (AUVs). A wireless acoustic identification tag, which uses a piezoelectric transducer tuned in the broadband ultrasonic range (200–500 kHz), was experimentally demonstrated to achieve highly efficient power transfer (source-to-tag electrical efficiency >2% at 6 m) concurrent high data rate backscatter level (>83.3 kbit s−1,...

Coherent deterministic arrival times can be extracted from the derivative of time-averaged ambient noise cross-correlation function between two receivers. These coherent are related to those time-domain Green’s these receivers and have been observed experimentally in various environments frequency range interest (e.g., ultrasonics, seismology, or underwater acoustics). This nonintuitive result demonstrated based on a simple image formulation function, for uniform distribution sources Pekeris...

We use crosscorrelations of seismic noise data from 151 stations in southern California to extract the group velocities surface waves between station pairs for purpose determining surface-wave velocity structure. developed an automated procedure estimating Green’s functions and subsequent tomographic inversion 11,325 based on characteristics field. eliminate specific events by a that does not introduce any spurious spectral distortion band interest, 0.05–[Formula: see text]. Further, we only...

Beamforming of seismic noise recorded on 150 Southern California stations was used to identify body and surface waves generated by Katrina. Surface wave microseisms are commonly associated with oceanic storms; there no previous comprehensive observations. The temporal evolution the different, indicating a different source mechanism for two types. body‐waves originated in shallow water east New Orleans propagated deep inside Earth. have location that varies frequency lowest originating west...

Estimates of the travel times between elements a bottom hydrophone array can be extracted from time-averaged ambient noise cross-correlation function (NCF). This is confirmed using 11-min-long data blocks recordings that were collected in May 1995 near southern California coast at an average depth 21 m 150-700 Hz frequency range. Coherent horizontal wavefronts emerging time derivative NCF are obtained across array's aperture and related to direct arrival time-domain Green's (TDGF). These...

A 3D-printed gradient-index phononic crystal structure based on air inclusions in a polymer is introduced to manipulate underwater acoustic waves. The proposed approach enables simple configuration without heavy or geometrically complex unit cells create the required refractive-index profile and focus incident plane waves propagating known direction. Based band-structure analysis, lens designed, fabricated, tested, yielding an excellent agreement between experimental results finite-element...

Measuring the in vivo elastic properties of muscles (e.g., stiffness) provides a means for diagnosing and monitoring muscular activity. The authors demonstrated passive elastography technique without an active external radiation source. This instead uses cross correlations contracting skeletal muscle noise recorded with skin-mounted sensors. Each sensor becomes virtual shear wave results point to low-cost, noninvasive biomechanical properties. efficacy originates from high density paths...

This letter demonstrates the potential for using diffuse ultrasound measurements to detect damage in concrete. Two different solutions diffusion equation, an infinite three-dimensional (3D) volume model that neglects geometric boundaries and a finite 3D cuboid model, are used required curve fitting procedure determine influence of on solution. The consider two types microcrack concrete, alkali-silica reaction thermal damage, show measured diffusivity parameter is related amount each specimen.

Source localization by matched-field processing (MFP) generally involves solving a number of computationally intensive partial differential equations. This paper introduces technique that mitigates this computational workload “compressing” these computations. Drawing on key concepts from the recently developed field compressed sensing, it shows how low-dimensional proxy for Green’s function can be constructed backpropagating small set random receiver vectors. Then source located performing...

Abstract Measuring temperature changes of the deep oceans, important for determining oceanic heat content and its impact on Earth's climate evolution, is typically done using free‐drifting profiling oceanographic floats with limited global coverage. Acoustic thermometry provides an alternative complementary remote sensing methodology monitoring fine variations ocean over long distances between a few underwater sources receivers. We demonstrate simpler, totally passive (i.e., without...

It has been demonstrated theoretically and experimentally that an estimate of the impulse response (or Green’s function) between two receivers can be obtained from cross correlation diffuse wave fields at these in various environments frequency ranges: ultrasonics, civil engineering, underwater acoustics, seismology. This result provides a means for structural monitoring using ambient structure-borne noise only, without use active sources. paper presents experimental results flow-induced...

Recent theoretical and experimental studies in a wide range of applications have demonstrated that Green’s functions (impulse responses) can be extracted from cross-correlation diffuse fields using only passive sensors. This letter demonstrates the passive-only reconstruction coherent Lamb waves (dc–500kHz) an aluminum plate thickness comparable to aircraft fuselage wing panels. It is further shown passively reconstructed are sensitive presence damage as it would expected typical “active”...

This letter describes a ray-based blind deconvolution technique for ocean sound channels that produces broadband estimates of the source-to-array impulse response and original source waveform from array-measured signals corrupted by (unknown) multipath propagation. The merely requires elementary knowledge array geometry speed at location. It is based on identifying ray arrival direction to separate acoustic-propagation phase contributions received signals. successfully decoded underwater...

This paper investigates the applicability of a ray-based blind deconvolution (RBD) method for underwater acoustic sources opportunity such as ships recorded on receiver array. The RBD relies first estimating unknown phase random source by beamforming along well-resolved ray path, and then matched-filtering each received signal using knowledge this to estimate full channel impulse responses (CIRs) between array elements (up an arbitrary time-shift) well recovering radiated source. performance...

We investigate the harvesting of sound waves by exploiting a 3D-printed gradient-index phononic crystal lens. The concept is demonstrated numerically and experimentally for focusing audio frequency range acoustic in air to enhance energy harvesting. A finite-element model developed design unit cell dispersion properties construct 3D lens wave field simulations. Numerical simulations are presented confirm incident plane study sensitivity refractive index profile direction propagation....

Acoustic waves carry information about their source and collect environment as they propagate. This article reviews how these information-carrying -collecting features of acoustic that travel through fluids can be exploited for remote sensing. In nearly all cases, modern sensing involves array-recorded sounds array signal processing to recover multidimensional results. The application realm spans an impressive range frequencies (10 −2 10 7 Hz) distances m) biomedical ultrasound imaging,...

Ocean acoustic tomography (OAT) methods aim at estimating variations of sound speed profiles (SSP) based on measurements between multiple source-receiver pairs (e.g., eigenray travel times). This study investigates the estimation range-dependent SSPs in upper ocean over short ranges (<5 km) using classical ray-based OAT formulation as well iterative or adaptive formulations (i.e., when sources and receivers configuration can evolve across successive iterations this inverse problem). A...