Fabrication of a 50 MHz annular array transducer for opthtalmology and development of its driving electronics

Bruno François (1) , Emilie Courjon (1) , Jean-Luc Guey (2) , Roland Salut (1) , Sylvain Ballandras (1)

1 FEMTO-ST - Franche-Comté Électronique Mécanique, Thermique et Optique - Sciences et Technologies (UMR 6174)
2 Imasonic SAS [Voray sur l’Ognon]

Modern ophthalmologic transducers consist in one channel pre-focused transducers operating at frequencies ranging from 25 to 50 MHz. This notably reduces the degree of freedom of physicians to accurately observed various regions of the ocular cavity. We develop then an annular array operating at 50 MHz for high resolution dynamic and its driving electronics. At first, we present the technological fabrication of a 6 channel annular array built on a piezopelectric ceramic to address that demand. The devices are batch-processed on a 2” wafer in order to obtain several probes on a single substrate. The rings are connected by means of electroformed pads and each channel is separated using a femto-laser ablation process. This innovative approach allows for an efficient addressing of each channel considering requirements concerning the final packaging of the probe. Several probes have been fabricated and tested. Although this approach is not completely new, we show that very thin kerfs can be achieved, compatible with the fabrication of the whole probe. A dedicated electronics has been developed to control the probes. The basic principle of the electronics consists in using a micro-controler ADuC7026 which mainly sequences the whole system operation. It drives first a Direct Digital Synthesis (DDS AD9954) circuit to create a high frequency clock. An Erasable Programmable Logic Device (EPLD) is then cadenced using this clock to build the transducer driving signal, consisting in a simple period voltage alternation. Once this signal generated, it enters the amplifier stage consisting in generating high voltage signal (80 Vp-p) in order to control each annular ring (6 channels). A switch is used to isolate the emitting and the receiving parts of the system. The devices and the driving electronics have been successfully fabricated and tested. As expected, their operating frequency of the probe is 50 MHz. We have also used a axi-symmetric finite element analysis to simulate the implemented devices and a comparison between the theoretical and experimental admittance measurements are used to optimize the probe shape.

Mots clés: Annular; Transducer

Domaines: Acoustique [physics.class-ph]; Acoustique [physics.class-ph]

Bruno François, Emilie Courjon, Jean-Luc Guey, Roland Salut, Sylvain Ballandras. Fabrication of a 50 MHz annular array transducer for opthtalmology and development of its driving electronics. 10ème Congrès Français d'Acoustique, Apr 2010, Lyon, France. ⟨hal-00542601⟩