Finite-element modeling of acoustic chaos to sonic infrared imaging

The technique of sonic infrared imaging (SIR) consists of the excitation of an object with a short pulse of high-power 15-40-kHz sound, in combination with imaging of the object's surface temperature as a function of time with an infrared video camera. SIR is effective for detecting both surface and subsurface cracks. The recent discovery of acoustic chaos has provided a means for greatly enhancing the effectiveness of SIR. Some of the authors have recently shown analytically that a simple mechanical model of a transducer, in forced contact with a structureless sample, and driven by a pure 20-kHz source will produce chaotic sound. The chaos results from the combination of the 20-kHz vibration and the bouncing of the transducer from the sample surface. Here we describe a more realistic, finite-element model, including bouncing, that also spontaneously produces chaotic sound.