Resonance-enhanced compact nonlinear acoustic source of low frequency collimated beam for imaging applications in highly attenuating media

Abstract

Acoustic imaging in highly attenuating materials requires special acoustic sources that can generate a collimated beam of low frequency. Lower frequencies, in the range of 10-120 kHz, have the advantage of deeper penetration in the medium due to lower acoustic attenuation. However, typical acoustic sources at these low frequencies have a large beam spread, resulting in poor lateral resolution. We report on the latest advancements in the development of a very compact source, with approximate dimensions of a cylinder with a diameter of 25-50 millimeters and approximately 10 mm tall. Low frequency, collimated and steerable acoustic beam source are some of the main characteristics of this source. The newly developed source takes advantage of (1) frequency mixing in an acoustical nonlinear fluid in a cavity to generate the difference frequency of two high frequencies, around 1 MHz, and (2) resonance enhancement of the difference frequency in the cavity. An order of magnitude enhancement in amplitude was observ...