Summary:

In imaging systems based on the use of ultrasonic waves, resolution is highly dependent on the resonance frequency of the piezoelectric sensors. So, to achieve high resolution, it is necessary to use transducers operating at ultra-high frequency. In addition, the development of multi-element imaging systems with operating frequencies above 100 MHz raises a number of difficulties, such as the technological limitations for the manufacture of small multi-element sensors, the problems of electrical and mechanical adaptation, and the high-frequency phase delay system. In this work, we proposed the study of a microsystem for generating and focusing ultra-high-frequency (1 GHz) acoustic waves by integrating ZnO-based piezoelectric transducers in front of a chaotic silicon cavity. The operating principle of this device is based mainly on the focusing of acoustic waves using the time-reversal (TR) technique. The study is validated by analysing the signals received on sub-millimetre diameter receiving transducers positioned at different points in a pre-defined analysis zone. This thesis therefore focuses on three specific aspects: -Optimising the acoustic sensitivity of sub-millimetre transducers by electrical adaptation. -Creating a chaotic cavity in silicon by chemical etching. Validation of the concept of ultra-high-frequency RT by focusing acoustic energy onto a receiving transducer.

Abstract:

In imaging systems based on the use of ultrasonic waves, the resolution depends strongly on the resonance frequency of the piezoelectric sensors. Thus, to achieve a high resolution, it is necessary to use transducers operating at ultra high frequency. In addition, the development of multi-element imaging systems with operating frequencies above 100 MHz raises many difficulties such as the technological limitation for the fabrication of small size multi-element sensors, the electrical and mechanical adaptation problems, as well as the high frequency phase delay system. In this work, we have proposed the study of a microsystem allowing the generation and focusing of ultra high frequency (1 GHz) acoustic waves by integrating ZnO-based piezoelectric transducers in front of a chaotic silicon cavity. The operating principle of this device is mainly based on the focusing of acoustic waves by the time-reversal technique (RT). The validation of the study is carried out by the exploitation of the signals received on transducers receivers of submillimeter diameter positioned in various points of a pre-defined zone of analysis. This thesis focuses on three specific aspects: -The optimization of the acoustic sensitivity of sub-millimeter transducers by electrical adaptation. -The realization of a chaotic cavity in silicon by chemical etching. -The validation of the concept of RT in ultra high frequency by focusing the acoustic energy on a receiving transducer.