Ultra slow acoustic energy transport in dense fish aggregates.

A dramatic slowing down of acoustic wave transport in dense fish shoals is observed in open-sea fish cages. By employing a multi-beam ultrasonic antenna, we observe the coherent backscattering phenomenon. We extract key parameters of wave transport such as the transport mean free path and the energy transport velocity of diffusive waves from diffusion theory fits to the experimental data.

Acoustic density estimation of dense fish shoals.

Multiple scattering of acoustic waves offers a noninvasive method for density estimation of a dense shoal of fish where traditional techniques such as echo-counting or echo-integration fail. Through acoustic experiments with a multi-beam sonar system in open sea cages, multiple scattering of sound in a fish shoal, and, in particular, the coherent backscattering effect, can be observed and interpreted quantitatively. Furthermore, a volumetric scan of the fish shoal allows isolation of a few individual fish from which target strength estimations are possible.

Low-frequency source for very long-range underwater communication.

Very long-range underwater acoustic communication (UAC) is crucial for long cruising (>1000 km) autonomous underwater vehicles (AUVs). Very long-range UAC source for AUV must exhibit high electro-acoustic efficiency (>60%) and compactness. This paper describes the Janus-Hammer Bell (JHB) transducer that has been designed for this purpose and meets those requirements.

Dual-pulse frequency compounded superharmonic imaging.

Tissue second-harmonic imaging is currently the default mode in commercial diagnostic ultrasound systems. A new modality, superharmonic imaging (SHI), combines the third through fifth harmonics originating from nonlinear wave propagation through tissue. SHI could further improve the resolution and quality of echographic images.

Optimization of a phased-array transducer for multiple harmonic imaging in medical applications: frequency and topology.

Second-harmonic imaging is currently one of the standards in commercial echographic systems for diagnosis, because of its high spatial resolution and low sensitivity to clutter and near-field artifacts. The use of nonlinear phenomena mirrors is a great set of solutions to improve echographic image resolution. To further enhance the resolution and image quality, the combination of the 3rd to 5th harmonics--dubbed the superharmonics--could be used.

Broadband reduction of the second harmonic distortion during nonlinear ultrasound wave propagation.

Ultrasound contrast harmonic imaging and detection techniques are hampered by the harmonic distortion of the ultrasound wave caused by the nonlinearities of the medium. To increase the discrimination between the tissue and ultrasound contrast agents at higher harmonics, we investigate a tissue harmonic suppression technique. The main attention of the research is the signal that is introduced at the source and is constructed out of several discrete frequency components from the second harmonic band.

Super-harmonic imaging: development of an interleaved phased-array transducer.

For several years, the standard in ultrasound imaging has been second-harmonic imaging. A new imaging technique dubbed "super-harmonic imaging" (SHI) was recently proposed. It takes advantage of the higher - third to fifth - harmonics arising from nonlinear propagation or ultrasound-contrast-agent (UCA) response.

A new transesophageal probe for newborns.

Current transesophageal probes are designed for adults and are used both in the operating theatre for monitoring as well as in the outpatient clinic for patients with specific indications, like obesity, artificial valves, etc. For newborns (<5 kg), transesophageal echocardiography (TEE) is not possible because the current probes are too big for introducing them into the esophagus. There is a clear need for a small probe in newborns that are scheduled for complicated cardiac surgery and catheterization.

Estimating acoustic peak pressure generated by ultrasound transducers from harmonic distortion level measurement.

Pressure amplitude measurement is important for general research on ultrasound. Because it requires high accuracy, it is usually done using a hydrophone calibrated by an accredited laboratory. In this paper, a method is proposed for estimating the pressure amplitude in the ultrasound field using an uncalibrated single-element transducer and Khokhlov-Zabolotskaya-Kuznetsov simulations of the ultrasound field.

Preliminary investigation of nonlinear dual frequency mixing technique for the estimation of the nonlinear parameter B/A.

The nonlinear parameter B/A, better know as the Beyer parameter, is a measure of the nonlinearity between variations of the pressure and density. Because of these variation propagating wave is distorted. Media with the different Beyer parameter, will distort wave differently.

Transfer functions of US transducers for harmonic imaging and bubble responses.

Current medical diagnostic echo systems are mostly using harmonic imaging. This means that a fundamental frequency (e.g.