Post‐Doctoral position In
Low profile 3D acoustic imaging devices using few transducers At Institute Langevin, Paris (FR) The conventional acoustic imaging relies on the use of a linear or 2D array of transducers. This technique is well mastered but it is cumbersome to implement, in particular when the number of channels is high in which case the amount of information to be processed may also be very high. Since the end of last century, it has been demonstrated through experiments on time reversal, that an image can be formed using a single transducer [1]. With multiple echoes in a 2D cavity, the acoustic signature of a source is generally unique and contains exhaustive information on its position [2]. A single sensor is then able to locate it. In continuity, current research is directed towards the design of antennas capable of imaging devices that will replace the classical 2D transducer arrays. The principle of this antenna is described in the right figure. A single transducer on a Dural plate is used to excite the modes of this cavity. Waves propagating in the plate are mixed and radiate into the air. The plate is turned into an antenna able to radiate acoustic volume wave at a point outside the plate. Using the time reversal process radiated acoustic waves are focused in echographic mode at a desired point in space for imaging purpose [3]. These preliminary results although encouraging, are limited both in resolution and contrast. Focusing at a point located in front of the antenna requires a fine discretization of the vibration of the surface of the antenna. This is equivalent to having a large number of acoustic actuators on a transducer, which means higher spatial resolution. This discretization requires a high number of modes and is not achievable with a simple homogeneous plate. Our research is directed toward the ideal plate that would offer large density of states (DOS). We propose to design a plate with a periodic or random array of resonant scatterers that have a large DOS in some frequency bands and that is able to radiate efficiently into the air. Blind holes turn out to be an interesting solution to this problem. Such an assumption was numerically verified using the Comsol software. Result is shown in the left figure where a high DOS value is observed at 40 kHz frequency. The aim of this work is to develop the approach outlined, to determine the limits and to extrapolate to new structures and solutions. The candidate must demonstrate initative, he will be comfortable in both theoretical and experimental acoustics, and have knowledge in Matlab and Comsol. The project is part of an ANR and collaboration will be required. The position is open for a period of 18 months starting in January 2013. The salary is about 2000 euros net per month. The applicant should provide a CV, a motivation letter and the names of two referees. Send it all to the following address: Dr. Ros Kiri Ing (
[email protected] ).
[1] C. Draeger and M. Fink, “One-Channel Time Reversal of Elastic Waves in a Chaotic 2D-Silicon Cavity”, Phys. Rev. Lett. 79, 407 (1997). [2] R. K. Ing, N. Quieffin, S. Catheline and M. Fink, “In solid localization of finger impacts using acoustic time-reversal process”, Appl. Phys. Lett. 87, 204104, 1 (2005). [3] N. Etaix, M. Fink and R. K. Ing, “Acoustic imaging device with one transducer”, J. Acoust. Soc. Am. 131, EL395 (2012).
www.institut‐langevin.espci.fr/
Required qualifications – Eligibility No restrictions of citizenship apply to the postdoctoral contract. To apply for a postdoctoral contract, candidates must hold an internationally-recognized PhDequivalent degree in a field related to Acoustics. Experience in experimental and theoretical research on acoustics, plate vibration and plate radiation will be highly appreciated. Terms of employment – Postdoc The position is intended as full-time (38 hrs / week, 12 months / year) appointment under CNRS contract. The contracts are offered for periods of 18 months. The selected Postdoc researcher will work under close supervision of a senior associate professor. Application procedure Suitable candidates are requested to submit: • a presentation letter with declaration of interests and a description of your past achievements (max. 1 page) • a Curriculum Vitae, including a fully referenced list of publications • contact email of two potential referees Applications should be submitted by email to:
[email protected], please label your email submission with your name followed by the tag “Postdoctoral contract”. Selection is based on merit and potential, measured in terms of the academic record and personal achievements. Proactivity, participation in community activities, and capacity for teamwork are also taken into account. The call will remain open until position is filled.
www.institut‐langevin.espci.fr/
