A Sadr - Iran University of Science & Technology

A new laser-ultrasound technique is used for tissue characterisation non-invasively. A fibre optic probe with a concentric PVDF transducer receiver is used to interrogate the tissue. In laser-ultrasound medical probe with thickness-driven PVDF transducer, it is necessary to have backing, electrode, and possibly, bonding layers in the ultrasound transmission path. If these layers have characteristic impedances that are substantially different from those of the piezo-polymer transducer and the front load medium, they act as mismatched transmission line sections between the transducer and its load, and transform the normally real load impedance into a complex one. The resulting shifted and deformed response curves are computed for a large number of layer parameters by means of MatLab™ implementation of the modified KLM model. From these plots, information as to permissible layer thickness, etc., may be obtained and used in the design procedure of the medical probe. Applying the proper parameters in the model, it was found that for transducers made from thicker films working at lower frequency, the effects of bonding and electrode layers are smaller so that they do not change the resonance peak significantly. It was also realised that the greater are the bonding layers’ thicknesses, the lower is the minimum insertion loss frequency.

PVDF, Piezoelectric Transducers,KLM Modelling, Bonding layers, Electrode layers, ultrasound, tissue characterisation