Modal analysis of a beam structure excited by the ultrasound radiation force

Abstract

The use of conventional modal excitation techniques (e.g., impact hammers, piezoelectric actuators, and mechanical shakers) may be challenging if high-frequency dynamic measurements on lightweight structures need to be performed. The use of the high-frequency radiation force generated by focused ultrasonic transducers (FUTs) can help to resolve this problem. In this research, the acoustic pressure generated by a FUT is measured using an acoustic microphone and used for determining the force distribution in the focal plane of the FUT by employing a boundary element model (BEM). The results indicate that the radiation pressure field has a spot size of ∼3 mm in diameter and the radiation force has a maximum intensity equal to 2.5 10−5 N. To validate the capability of the FUT as an excitation technique for modal analysis, a back-to-back comparison with a modal test performed using a traditional excitation system (i.e., shaker) was completed. Analysis of the results when the two excitation techniques are used, shows a good agreement between the data sets. Excellent correlation is also observed when the mode shapes are compared using the Modal Assurance Criterion (MAC). Overall, the good match of both resonant frequencies and mode shapes indicates that the focused ultrasound radiation force excitation technique is helpful in performing modal tests.