Theoretical and experimental study of the field radiated by ultrasonic focussed transducers

Abstract In this paper, the impulse response method is used to study, theoretically, the transient pressure field radiated by focussed transducers under different types of excitation. The pressure field is explained using the useful concept of the geometrical wave and edge waves. This method has been extended to take account of the finite size of the receiver used to detect the pressure field and it has been demonstrated that the effect of receiver size on the results is not negligible. An experimental study of the field radiated by a planar transducer coupled to a lens has also been carried out. Although the hydrophone used was rather small (radius 0.25 mm), it was seen that it is important to take its size into account to interpret some of the signals observed. Transverse profiles have also been studied and it has been shown that the shape of the ultrasonic beam strongly depends on the electrical excitation of the transmitter (sinusoidal or transient mode). In the transient mode, it is shown that the perceived shape of the ultrasonic beam depends on whether the positive or negative cycle of the pulse was detected.