Light Focusing and Two-Dimensional Imaging Through Scattering Media using the Photoacoustic Transmission-Matrix with an Ultrasound Array

We implement the photoacoustic transmission-matrix approach on a two-dimensional photoacoustic imaging system, using a 15 MHz linear ultrasound array. Using a black leaf skeleton as a complex absorbing structure, we demonstrate that the photoacoustic transmission-matrix approach allows to reveal structural features that are invisible in conventional photoacoustic images, as well as to selectively control light focusing on absorbing targets, leading to a local enhancement of the photoacoustic signal

End conditions of piano strings

International audienceThe research of a trade-off between loudness and sustain (duration) is a major issue for piano designers and manufacturers. The way the energy of vibration is transferred from the piano string to the soundboard depends on the end conditions of the strings at the bridge: these conditions can be approximated by the input admittance at the connecting point between the string and the resonator. Therefore, proper measurements of this value are needed. Given this, we propose here a method of validation of admittance measurements on simple structures. Parameters such as frequencies and damping factors of the string partials depend directly on the end conditions. The analysis of the vibratory signal of the string, based on high resolution estimation methods (ESPRIT algorithm), allows us to evaluate efficiently those parameters and leads to the calculation of the input admittance. This method is implemented on a simplified device composed of a piano string coupled to a thin steel beam. The comparative study of two experimental cases (isolated string and string coupled) leads us to the input admittance. This value, deducted from vibratory measurements of the string is eventually compared to direct admittance measurements effected on the beam, in order to validate the method

Improving Photoacoustic-guided Focusing in Scattering Media by Spectrally Filtered Detection

We experimentally and numerically study the potential of photoacoustic-guiding for light focusing through scattering samples via wavefront-shaping and iterative optimization. We experimentally demonstrate that the focusing efficiency on an extended absorber can be improved by iterative optimization of the high frequency components of the broadband photoacoustic signal detected with a spherically focused transducer. We demonstrate more than 8-fold increase in the photoacoustic signal generated by a 30 microns wire using a narrow frequency band around 60MHz. We numerically confirm that such optimization leads to a smaller optical focus than using the low frequency content of the photoacoustic feedback

Super-resolution photoacoustic imaging via flow induced absorption fluctuations

In deep tissue photoacoustic imaging the spatial resolution is inherently limited by the acoustic wavelength. We present an approach for surpassing the acoustic diffraction limit by exploiting temporal fluctuations in the sample absorption distribution, such as those induced by flowing particles. In addition to enhanced resolution, our approach inherently provides background reduction, and can be implemented with any conventional photoacoustic imaging system. The considerable resolution increase is made possible by adapting notions from super-resolution optical fluctuations imaging (SOFI) developed for blinking fluorescent molecules, to flowing acoustic emitters. By generalizing SOFI mathematical analysis to complex valued signals, we demonstrate super-resolved photoacoustic images that are free from oscillations caused by band-limited detection. The presented technique holds potential for contrast-agent free micro-vessels imaging, as red blood cells provide a strong endogenous source of naturally fluctuating absorption

Tour de Londres

Londres a décidément la cote ! Après le groupe Midi-Pyrénées en 2006 1, et quelques semaines avant celui de Lorraine, huit membres de l’ABF-PACA et une collègue de la BnF ont choisi cette destination pour un séjour marathon : pas moins de sept visites en moins de trois jours ! Leur investigation concernait les « services innovants » des bibliothèques anglo-saxonnes, et en particulier ces nouveaux concepts – Idea Stores et Learning Centres – qui suscitent à la fois enthousiasme et interrogations

Super-resolution photoacoustic fluctuation imaging with multiple speckle illumination

In deep tissue photoacoustic imaging, the spatial resolution is inherently limited by acoustic diffraction. Moreover, as the ultrasound attenuation increases with frequency, resolution is often traded-off for penetration depth. Here we report on super-resolution photoacoustic imaging by use of multiple speckle illumination. Specifically, we show that the analysis of second-order fluctuations of the photoacoustic images combined with image deconvolution enables resolving optically absorbing structures beyond the acoustic diffraction limit. A resolution increase of almost a factor 2 is demonstrated experimentally. Our method introduces a new framework that could potentially lead to deep tissue photoacoustic imaging with sub-acoustic resolution

Wind turbine noise modeling: prediction of amplitude modulation and influence of atmospheric conditions

International audienceAeroacoustic noise from a wind turbine is mainly caused by the interaction between the wind turbine blade and the air flow. For a modern wind turbine, trailing edge noise is often the dominant noise source. In this paper, a detailed study of trailing edge noise is carried out using Amiet's frequency domain analytical source model. Model results are compared with experimental data. Features of wind turbine noise, such as amplitude modulation, ground directivity, influence of blade twist and pitch are studied. In the last part, the influence of realistic wind profiles is investigated. Wind shear is seen to increase the sound power level and the amplitude modulation

Effets météorologiques sur le bruit rayonné par les éoliennes

National audienceCette étude vise à expliquer les différences observées entre le bruit rayonné par une éolienne en champ proche et en champ lointain, en montrant l'influence des conditions météorologiques à la fois sur les sources de bruit d'une éolienne et sur la propagation de ce bruit dans l'atmosphère. Des données expérimentales ont été analysées afin d'obtenir des profils de vent et de température réalistes dans l'atmosphère. Dans certains cas, les profils de vent prédits par la théorie de la similitude différent fortement des profils mesurés, ce qui conduit à des prédictions erronées du bruit rayonné en champ proche (100m) comme en champ lointain (jusqu'à 1km). Le modèle de source montre que les plus fortes amplitudes de modulation sont obtenues dans la direction perpendiculaire au vent, alors que le modèle de propagation met en évidence des niveaux sonores plus importants dans la direction du vent pour des distances supérieures à 800mètres environ