Modeling and estimation of focused ultrasound radiation force for modal excitation

Abstract

To date, conventional excitation techniques such as impact hammer or mechanical shaker excitations are commonly used in experimental modal testing. However, these excitations require that the excitation device be in direct contact with test articles, resulting in measurement distortions, particularly for small structures like MEMS cantilever. In addition, it is physically difficult or even impossible to apply these contact type excitations to certain structures, for example, biological tissues and thumb nail sized turbine blade. Moreover, these conventional excitations have limited bandwidth, usually below than 10 kHz, and thus not applicable for structures with interest in higher frequency modes. Focused ultrasound radiation force, having a much broader frequency bandwidth, has recently been used to excite structures with sizes ranging from micro to macro-scale. Therefore, it can potentially be used as an alternative non-contact excitation method for experimental modal analysis. Yet, this force remains to be quantified in order to obtain the force-response relationship, i.e., the frequency response functions (FRFs) of test articles. The dynamic focused ultrasound radiation force is modeled and estimated using the calibrated sound pressure fields generated by a spherically focused ultrasonic transducer (UT) driven by amplitude modulated signals. Its application for modal excitation is to be discussed.