Impedance Modulation by Pulsed Ultrasound

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Abstract

ABSTRACT:

The propagation of an acoustic wave in an electrolyte solution produces local and periodic conductivity changes. This acousto-electrical interaction is due to the variations of the parameters controlling ionic conductivity against pressure and temperature. The overall effect is about 10−7 % Pa−1 for solutions of physiological ions and is practically independent of the ionic species involved. The bulk compressibility of the medium is responsible for about 47% of the effect, the change in viscosity due to pressure changes is responsible for about 18%, and the changes of ionic mobility against temperature are responsible for about 35%. Detectable impedance changes were produced in the focal zone of a 500-kHz focused transducer using moderate intensity ultrasound (peak pressure < 1 MPa). This technique potentially enables the association of the spatial resolution of pulsed ultrasound and impedance measurement, although technical improvements and feasibility studies are still needed prior to practical applications.

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