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transducteurs MINIatures à cristal PHONonique – MINIPHON

Submission summary

The project aims at investigating the fundamentals that are needed to design miniature phononic crystal transducers, in view of immersed applications in the ultrasonic frequency range (from 500 kHz to 100 MHz). The objective is to pave the way for novel small, versatile and flat transducers and receivers. The application of these phononic transducers is to non-destructive testing of small areas, medical investigations using a catheter, and micro-scale laboratories, to cite some examples. The technology of transducers is mature and is based on the coupling of elastic waves inside solid materials (for instance piezoelectric crystals) either with acoustic waves in a fluid (for example water) or elastic waves in solids (for example steel, a fibre reinforced composite or parts of the human body). Transducers are typically used for non-destructive testing or for medical investigations. Beam shaping and steering in space is usually achieved through the acoustic antenna principle (a phased array of individual transducer elements). The goal of the MINIPHON project is to investigate potential benefits of phononic crystals for transduction, especially as regards their passive diffraction and beam-shaping properties. Phononic crystals are periodic media that produce stop band effects in the frequency response depending on the physical properties of their structure. They are applied as acoustic filters for electronic applications. So far, they have never been studied for the transformation (transduction) of sound within a solid into a surrounding liquid. Whereas a lot of knowledge has been gathered and published about filtering and refraction effects within phononic crystals, we want to investigate a totally new application for such heterogeneous materials by studying transduction properties. The idea is to apply diffraction effects to transform plate waves and surface waves into bulk waves, and vice-versa. Diffraction (comparable to an optical diffraction grating that splits white light into every color of the rainbow) caused by the periodic structure results in an amplitude and direction of sound generation depending on the frequency and the properties of the diffraction grating. From our experience with phononic crystals and corrugated surfaces, we know that the physical characteristics of the diffraction grating strongly determine the diffraction effect, leading the way to versatile transduction. The general general aim of the project is to develop theoretical and experimental knowledge on phononic crystals, especially for the frequency range that falls in the diffraction regime. From the theoretical point of view, and especially for computation methods, what is needed is to fill the gap between propagation inside phononic crystals and outside of them. The work program of the MINIPHON project includes the design and the experimental demonstration of three basic different possibilities for miniature phononic crystal transducers: 1. The possibility of steering and dispersing an acoustic beam with high efficiency; 2. The possibility of converting bulk to surface acoustic waves, for non destructive evaluation applications, for instance; 3. The possibility of converting efficiently and focusing the surface waves generated in a piezoelectric solid to bulk acoustic waves. The obtained knowledge will also be applicable to the development of micro-scale ultrasonics laboratories (micromachined devices to separate different blood cells in one drop, for example). We are not aware of any national or international projects with a similar goal (phononic crystals considered as diffraction gratings for ultrasonic transducers). In France and internationally, there are presently a number of projects in the world making use of phononic crystals as metamaterials (for negative refraction, for tailored refraction, for acoustic cloaking, for collimated acoustic sources, etc.). All these ideas have been published during the previous years and generally exploit the homogenization regime, not the diffraction regime. For this reason, we emphasize the basic ideas put forward in MINIPHON are (I) strongly original and (ii) have a strong potential for excellent publications in renewed international journals.

Project coordination

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

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Beginning and duration of the scientific project: - 0 Months

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