HIGH-FREQUENCY ULTRASONIC PROBE WITH ACTIVE DAMPING

The characterization and visualization of smaller and smaller structures become nowadays feasible in the biomedical ultrasonics area, owing to the design and construction of very high frequency ultrasonic probes (above 100MHz). These probes consist in a very thin piezoelectric transducer cemented on to an a delay line. The classical problems of ultrasonic attenuation and electrical and mechanical impedance matching are encountered. Moreover, in the used frequency range, multiple reflections on the various boundaries induce an acoustic noise which reduces the probe sensitivity. To overcome this, an ultrasonic probe radiating directly into biological medium, without buffer delay line has been built. An active damping using a second piezoelectric transducer has been designed in order to increase the available frequency bandwidth and then the axial resolution of the probe. In this paper, the experimental and theoretical results for this new kind probe are computed.