Abstract: The invention concerns a method for focusing acoustic waves useful for obtaining an image of a field to be observed in a dissipative heterogeneous medium (2, 3) around which acoustic transducers (T1–Tn, T?1–T?m) forming an imaging network and a target network. The method consists in following a training step during which pulse responses from the medium are measured between each transducer (Ti) of the imaging network (5) and several transducers (Tj) of the target network (6); deducing therefrom reference signals to be emitted by the transducers of the imaging network to produce a focused acoustic pulse in each transducer of the target network, then cumulatively, in determining reference signals to be emitted to focus an acoustic pulse on predetermined points in the medium. Said reference signals are stored and used subsequently to generate an acoustic image of the medium.

Abstract: The invention relates to an ultrasonic medical imaging apparatus intended for analyzing an organic medium potentially including defects within a noisy structure. Ultrasound signals focused at a given depth according to M distinct successive excitations arc emitted and an image formation module makes it possible to obtain an image of said depth after reception of responses from the medium. The invention is such that the apparatus includes a module for using said responses for constructing a rectangular response matrix of dimension N*M, a coefficient Knm of which represents the response from the medium received by the transducer n following an excitation m, decomposing said response matrix into singular values, using the singular vectors corresponding to said singular values for locating singular zones corresponding to defects in the medium. Application: Ultrasonic apparatus particularly in the medical field.

Abstract: A method of generating photons by sonoluminescence, from a gas bubble trapped in a liquid reservoir (2) by a standing ultrasound wave. An ultrasound impulse emitted by high-frequency transducers (T1–T8) is superposed on the standing wave, the high-frequency transducers being pre-focused onto the gas bubble and pre-synchronized with the light emissions from the gas bubble during an initial training stage in which said focusing and said synchronization are optimized.

Abstract: After emission of an acoustic pulse, having a first duration, from a given location, acoustic signals coming from the location are gathered through a multi-scattering medium on an array of transducers and recorded, for a second duration greater by at least one order of magnitude than the first duration. Return signals obtained by temporal inversion and amplification of the signals gathered during the second duration are emitted back from said transducers toward the multiscattering medium in order to focus acoustic energy to the location while providing temporal compression of the focussed acoustic energy.

Abstract: A non-invasive method of obtaining a target soundwave field in the brain by means of an array of transducers positioned outside the skull, the method comprising a training stage during which, on the basis of a three-dimensional image giving the porosity of the skull at all points, digital simulation is used to determine individual sound signals to be emitted by the transducers in order to obtain the target soundwave field in the brain. After the training stage, the array of transducers is used to locate the position of the array of transducers relative to the skull by echography and to ensure that the array of transducers is accurately positioned.

Abstract: The invention relates to a method of generating a predetermined objective wave field in a medium using a first network of transducers T1-Tn). The inventive method consists in first using each transducer i of the first network to emit an approximation of the signal ei(t). Subsequently, each transducer of a second network of transducers (T?1-T?m) is used to emit an error signal corresponding to the time reversal of the difference between the signals captured from said first emission and objective signals. Finally, approximation ei(t) is corrected by subtracting the time reversal of the signal captured by each transducer i using the error signal.

Abstract: An imaging method for observing the propagation of a shear wave simultaneously at a multitude of points in a diffusing viscoelastic medium. The shear wave is caused to be generated by firing at least one focused ultrasound compression wave into the viscoelastic medium by means of an array of transducers, and then emitting at a fast rate and using the same array of transducers, unfocused ultrasound compression waves serving to obtain a succession of images of the medium, and processing the images obtained in this way in deferred time in order to determine the movements of the medium during the propagation of the shear wave.

Abstract: Apparatus and methods for locating an impact point on a surface of an object. The object is provided with an acoustic sensor that senses the impact from the acoustic waves that are generated when the object is subjected to the impact. The location of the impact on the surface of the object is determined by a recognition step that includes a comparison of the sensed signal to one or more predetermined signals. Each predetermined signal represents an active zone on the surface of the object. A predetermined signal corresponds to the sensed signal when the impact causing the sensed signal is generated in the active zone represented by the predetermined signal. The impact is associated with the active zone represented by a predetermined signal when the sensed signal and the predetermined signal sufficiently correspond to each other.

Abstract: Apparatus and methods for locating an impact point on a surface of an object. The object is provided with an acoustic sensor that senses the impact from the acoustic waves that are generated when the object is subjected to the impact. The location of the impact on the surface of the object is determined by a recognition step that includes a comparison of the sensed signal to one or more predetermined signals. Each predetermined signal represents an active zone on the surface of the object. A predetermined signal corresponds to the sensed signal when the impact causing the sensed signal is generated in the active zone represented by the predetermined signal. The impact is associated with the active zone represented by a predetermined signal when the sensed signal and the predetermined signal sufficiently correspond to each other.

Abstract: The present invention relates to analysis apparatus for analyzing the skin, the apparatus comprising:

Abstract: The invention concerns an image method for observing the propagation of low-frequency shearing pulse wave simultaneously in multiple points of a diffusing viscoelastic medium. The method consists in transmitting at a very high rate ultrasonic compression waves enabling to obtain a succession of images of the medium; then in delayed processing of the resulting images by intercorrelation to determine in each point of each image the movements of the medium while the shearing wave is being propagated.

Abstract: A method of generating photons by sonoluminescence, from a gas bubble trapped in a liquid reservoir (2) by a standing ultrasound wave. An ultrasound impulse emitted by high-frequency transducers (T1-T8) is superposed on the standing wave, the high-frequency transducers being pre-focused onto the gas bubble and pre-synchronized with the light emissions from the gas bubble during an initial training stage in which said focusing and said synchronization are optimized.

Abstract: The invention concerns a method for focusing acoustic waves useful for obtaining an image of a field to be observed in a dissipative heterogeneous medium (2, 3) around which acoustic transducers (T1-Tn, T′1-T′m) forming an imaging network and a target network. The method consists in following a training step during which pulse responses from the medium are measured between each transducer (Ti) of the imaging network (5) and several transducers (Tj) of the target network (6); deducing therefrom reference signals to be emitted by the transducers of the imaging network to produce a focused acoustic pulse in each transducer of the target network, then cumulatively, in determining reference signals to be emitted to focus an acoustic pulse on predetermined points in the medium. Said reference signals are stored and used subsequently to generate an acoustic image of the medium.

Abstract: After emission of an acoustic pulse, having a first duration, from a given location, acoustic signals coming from the location are gathered through a multi-scattering medium on an array of transducers and recorded, for a second duration greater by at least one order of magnitude than the first duration. Return signals obtained by temporal inversion and amplification of the signals gathered during the second duration are emitted back from said transducers toward the multiscattering medium in order to focus acoustic energy to the location while providing temporal compression of the focussed acoustic energy.

Abstract: Public announcements are made in a space using n speakers after having determined the impulse response hij(t) between a plurality of calibration points j belonging to the space and each speaker i. To transmit an information-bearing acoustic signal S(t) through at least one target area in the space in which announcements are to be made, each speaker i is made to transmit a signal (a), where j is an index representing calibration points in the target area.

Abstract: During a passive initial stage, acoustic signals received by a receiving transducer array are recorded, and the corresponding electric signals are stored. To search for the possible presence of a sound source whose contribution to the signal recorded in the passive initial stage may be faint, window of each electric signal stored in the initial stage is time reversed and amplified to produce excitation signals which are applied to emitting transducers of an array corresponding to that of the receiving transducers. The acoustic echo signals received by the receiving transducers are recorded, and the corresponding electric signals are stored, and can be exploited to detect the possible presence of a reflecting sound source.

Abstract: A method of optimizing radio communication between a fixed base station having a plurality of antennas and a mobile station by applying, in the base station, processing to all signals S.sub.i (t) received or transmitted via each of the antennas so as to determine corresponding corrected signals S.sub.i (t)=h.sub.i (-t).times.S.sub.i (t), where h.sub.i (-t) is an approximation to the time reversal of the impulse response h.sub.i (t) between antenna and the mobile station.

Abstract: To protect a volume (2) arranged inside a room (3) in regard to outside noises E, use is made of an array of acoustic sensors (11.sub.j) receiving the noise E and arranged a distance A from the volume and of an array of acoustic sources (15.sub.k) arranged a distance B less than A from the volume and signals S are applied to these sources, these signals being summations of the double convolution products of the function E.sub.j (t) with two functions f.sub.ij (t) and g.sub.ik (-t) which are directly deducible from the impulse responses gathered, on the one hand, at the sensors (11.sub.j) from pulses emitted by the sources (10.sub.i) carried by a fictitious barrier (6) delimiting the volume and, on the other hand, at sensors (12.sub.i) stationed at the same places as these latter sources (10.sub.i), from pulses emitted by the above sources (15.sub.k).

Abstract: A method for internal inspection of pieces having an interface with a propagation medium, is described. The steps include: illuminating a reference piece with an ultrasound beam from a first array of transducers excited by stored excitation signals; sensing reflected echo signals received by transducers, which may be the transducers of the first array, and storing the waveforms and time distribution thereof; simultaneously sensing refracted signals, received by transducers belonging to a second array placed opposite to the the first relative to the piece and storing the waveforms and time distribution of the signals received by the transducers of the second array; replacing the reference piece with a piece to be inspected having the same shape and occupying the same location, and applying, to each of the transducers, energization signals obtained by time reversal of the stored waveforms and time distribution; and sensing the signals received by the transducers of the second network.

Abstract: A method for acoustic examination of a medium and detection of reflective targets includes a preliminary step of injecting a divergent sound beam into the medium from at least one transducer. Then the echo signals reflected by the medium and received by several transducers in an array are picked up. A time gate is used to select echoes coming from a particular zone of the medium. The echoes are stored, time-reversed and re-emitted. The signals newly reflected by the medium are stored and the time-reversal operation is repeated. After a final time reversal of rank 2n+1 (where n is a positive non-zero integer) over the full depth of the measurement time gate, the characteristics of the wavefront passing closest to the maxima of the signals are determined, advantageously in the form of a time distribution of the maxima. The characteristics can often be approximated with a polynomial law. An apparatus is disclosed for implementing the method.