Design and fabrication of a miniaturized annular array

Advances in microtechnology reinforce the interest in the development of miniaturized transducers for endoscopic imaging applications. The present work is devoted to the design and fabrication of miniaturized annular array transducer. A first design of the transducer has been performed using an analysis of the radiated pressure in a semi-infinite liquid based on a time-domain computation (DREAM program). The selected structure has been then simulated using an harmonic FEA taking piezoelectricity and material losses into account. A simplified boundary condition based on a plane wave radiation condition was used to simulate the immersed regime of the transducer. However, this approach allows one to estimate the pressure at the radiation surface of the transducer which can be used to improve the calculation of the acoustic pressure distribution in the liquid. The results of this design approach can be used to fabricate a test structure using ultrasound micromachining techniques adapted to sub-millimeter structure applications (resolution in the range 50 microns, machining depth close to 1 mm). A 2 mm diameter annular PZT structure has been built and tested. Theoretical and experimental results concerning the admittance of the annular array are compared. Design consideration for the fabrication of the 1.2 mm diameter transducer are exposed and discussed.