4aPA7. Generation of localized low-frequency vibrations by remote ultrasound sources.

Session: Thursday Morning, May 16

Time: 9:45

Author: Mostafa Fatemi
Author: James F. Greenleaf
Location: Biodynamics Res. Unit, Dept. of Physiol. and Biophys., Mayo Clinic/Foundation, Rochester, MN 55905


This paper presents a new method of inducing localized low-frequency acoustic energy in an object by remote sources. In this method two interacting high-power, high-frequency, ultrasound beams at two different frequencies are used. These beams are positioned to interact at the object's surface (or any other impedance discontinuity inside the object). The result is a radiation force at the difference frequency, df, exerted in a small area defined by the beamwidths. Experiments are performed on a small steel needle and blocks of gelatin. To monitor the vibration, a high-frequency probing transducer is used in pulse echo mode with the beam aimed at the vibrating part of the object. This transducer shoots tone bursts at a rate much higher than df. Echoes are quadrature detected and the resulting in-phase and quadrature signals are recorded. These signals are used to calculate the phase of the returned echo which is shown to be proportional to the target displacement. In the experiments, the power beams were driven at 20 W each and df=10 Hz. Amplitude of the resulting vibrations were 5 (mu)m for the gelatin block and 1.2 (mu)m for the needle.

from ASA 131st Meeting, Indianapolis, May 1996