A laboratory at the interface of many fields
The LOA (Laboratoire Ondes et Acoustique - Waves and Acoustics Laboratory) of the ESPCI is linked
to the University Denis Diderot (Paris VII) and the CNRS. Its research activities take place at the interface of many fields The common
denominator is the comprehensive study of wave propagation in complex media. Applications of ultrasound, and more specifically
«ultrasound time-reversal», made our reputation. But since then our interest has been extended to sound waves, seismic
waves and electromagnetism.
A continuous balance between fundamental and applied physics.
One of our aims is to exploit the analogies between acoustics, optics and quantum mechanics to perform orignal
experiments that, from a practical point of view, take advantage of the flexibility of ultrasound transducer arrays. In this way, research topics such
as time-reversal, multiple scattering, wave chaos and wave-flow interaction (sound-vorticity) are studied. Concurrently, a lot of applications are
developed in a large variety of fields: medical imaging and therapy, non-destructive testing, telecommunications, seismology, underwater acoustics,
domotics. On all these subjects, the LOA is collaborating with a lot of companies from various industrial areas (medical, aeronautical, nuclear,
steel production, cars, agronomics, domotics…). With 4 start-ups originating from it and 24 patents taken out since 2000, the LOA is also greatly
involved in the innovation process.
The LOA is formally divided in four teams but most of our researchers are actually involved in more than
Waves in complex media
The study of ultrasound propagation in complex media (random media, chaotic cavities, or non-stationary media, phononic crystals) concerns
all fields of physics described by a wave formalism. Among our favorite research topics: wave time-reversal, multiple scattering, coherent
backscaterring effect and its breakdown, wave chaos, correlations of diffuse fields, super-resolution, phononic crystals, ultrasound /dislocation
interaction, sonoluminescence …
Waves physics for Medicine
This team develops new medical intruments for imaging and therapy. These intruments rely on techniques using ultrasound and their mixing
with other kinds of waves (optical and electromagnetic waves). Especially, various imaging methods of the viscoelastic properties of the human
body have been developed, using either an ultra-fast imaging echograph (supersonic shear imaging) or modified MRI systems. Systems of
ultrasound therapy, including the control of the treatment, are also developed for the brain, the breast and the abdomen.
Non Destructive Testing, Underwater acoustics
and Sensitive materials
Based on the concept of Time- Reversal Mirrors, our lab is studying new methods for target detection in the most complex environments.
In underwater acoustics, we are working on target detection in reverberating bottoms. In non-destructive testing, we study the detection
of defects in objects with complex microstructures, such as titanium alloys. In this research field, very original methods based on laser-ultrasound
interaction are also implemented with the advantage of avoiding any contact with the material under inspection. Finally, we have developed
a great expertise in guided elastic waves. Based on this expertise, we have also created a new concept of intelligent tactile objects.
Electromagnetism and Telecommunications
This team is transposing to electromagnetic waves the technique of time-reversal (TR) focusing, widely studied in acoustics. One of
the potential applications is high-data rate wireless communications in complex environments. Indeed, TR compensates for reverberation
and scattering undergone in the medium (this problem is crucial for the new UWB (Ultra Wide-Band) techniques. It also exploits spatial diversity,
as in MIMO (Multiple Input-Multiple Output) techniques, to increase the data-rate and security of transmissions. We have built a first
electromagnetic Time Reversal Mirror prototype, working in the WiFi frequency band. Other applications of electromagnetic waves are also
currently being studied (medical therapy, photonic crystals…).