Investigation of acoustic field calculation and measurement method for air-coupled ultrasonic transducer

The field characteristic of an air-coupled planar ultrasonic transducer was investigated using the spatial impulse response of transducer transmitting aperture, which is based on the assumption of linear sound theory. The impulse response of arbitrary point in field space is calculation by the summation of spherical wave from all of the small area on the transmitting aperture. Attenuation is one of important factor impacting acoustical field distribution for the air-coupled ultrasonic transducer, and which increases with the frequency, a frequency-dependent attenuation function is considered in the field calculation of frequency domain, and then the pressure distribution is obtained by convolution integral of the impulse response with excitation impulse. Compared field measurement experiments are implemented using a multiple-axis scanning system and a miniature aperture detector. The results of theoretic analysis and that of experiment are in a good agreement. Finally, the effects of the receiving aperture size are also considered in sound field measurements, the results indicate that because of the low efficiency and interface loss in air couple, a compromise between resolution and signal to noise ratio (SNR) should be taken into account to choose the receiving aperture size. And a smaller aperture could improve the measuring resolution on condition that the receiving amplification coefficient and the SNR are valid.