Technomed Internatl. S.A., Bron, France
INSERM unite 281, 151 Cours Albert Thomas, 69003 Lyon, France
INSERM unite 281, Lyon, France
The purpose of this communication is to investigate the pressure fields, for a large range of cw excitation levels, of two different focusing transducers such as those used for the medical applications. The first one (45-mm diameter, 200-mm focal distance, and 6.15 linear gain) works at 1.16 MHz, and the second one (70-mm diameter, 90-mm focal distance, and 63.85 linear gain) works at 2.24 MHz. The pressure signal measured along and across the acoustic axis is transmitted to a computer where its maximum and minimum are recorded, analyzed, and displayed. For the low gain and small aperture source and at low excitation levels, the highest pressure of the field does not occur at the geometrical focus but before it. For the high gain and large aperture source, the highest pressure is measured around the geometrical focus, whatever the excitation level used. Special attention is devoted to the saturation phenomenon.