Multi-spectral acoustical imaging

Visualization of object through acoustic waves is generally called as acoustical imaging. This concept contain noise source localization, ultrasonic non-destructive testing, medical ultrasound, underwater sonars, etc. In these conventional imaging techniques, frequency information has not yet utilized effectively, though shape, material and even structure behind the surface reflect on the frequency characteristics of their acoustic responses. In this report, we introduce a concept of multi-spectral acoustical imaging, where wide range of frequency responses are investigated with a fine frequency pitch. As typical examples, we demonstrate the responses from a surface with several different holes for the frequency band from 1 to 20 kHz with 30-Hz pitch. The position and depth of the holes are clearly identified by their resonance frequencies. The volume of a small droplet in a well can be precisely measured using the present method. A method for displaying the multi-spectral acoustical data is also discussed.