An examination of the scaling rules for sound emissions from targets excited by point-like forces

Abstract

In earlier work [T. Daniel et al., JASA 140, 3123 (2016)] we had showed experimentally that the modes of small elastic targets in water could be excited using modulated radiation pressure (MRP) generated by focused ultrasound to create detectable sound emissions. A potential advantage of the MRP approach is that the narrow beam of the ultrasound beam permits the generation of point-like forces on the target’s surface with surgical precision. But an important question is how this technique scales with target size, e.g., the amount of force required to achieve a desired sound emission level. Here we examine how the sound emission levels and surface velocities of target modes driven by a point force scale with target size a. We will show that for a constant driving force, the far-field sound emission pressure levels scale as 1/a and the surface velocity as 1/a2. Specific examples are presented for circular plates, spheres, and cylindrical-like targets. Finally, results will be shown from a recent tank experiment at Washington State University where we attempted to experimentally determine the scaling rules using small targets excited by MRP.