Ultrasonic Far-Field Holography of Point Scatterers and Interfaces

Sergey A. Tsysar (1) , Oleg A. Sapozhnikov (1)

1 Department of Acoustics, MSU

Modern ultrasound imaging is usually performed using pulse-echo principle, i.e. it utilizes backscattering of short acoustic pulses. In contrary, conventional optical imaging is based on continuous light waves. Similar approach is possible in acoustics as well. Holography is a method of recording wave scattering from an object such that the object's shape and position can be reconstructed later. The holographic approach used here relies on the principle of a time-reversal mirror and the Rayleigh integral. An ultrasonic beam consisting of long tone bursts is directed at a target object and the resulting acoustic field is measured at a large number of points surrounding the object. A computer-controlled positioning system is used to scan a small broadband hydrophone across a grid of measurement points in a single surface near the target. Object reconstruction is then accomplished numerically by back-propagating of the acoustic field from measurement locations to a 3D region representing the object. Theoretically, the accuracy and the optimal parameters of the method were studied by modeling forward and backward propagation from a point scatterer. Experimentally set of 3-mm diameter plastic beads and a piece of styrofoam with a rough surface and a diameter of several cm were investigated. Ultrasound frequencies from 1 to 4 MHz were considered, while hologram measurements were collected with grid spacings between 0.2 and 0.4 mm. Using this 3D ultrasonic holography method, it is possible to reconstruct the position and shape of objects or collections of objects that do not involve a significant amount of multiple scattering. Because the spatial resolution of the method has a typical diffraction limit on the order of a wavelength, improved spatial resolution can be achieved with higher frequencies and increased angular size of scanning region. Work supported by RFBR 08-02-00368, ISTC 3691 and NIH R01EB007643

Mots clés: Acoustic holography; Time-reversal principle; Rayleigh integral

Domaines: Acoustique [physics.class-ph]; Acoustique [physics.class-ph]

Sergey A. Tsysar, Oleg A. Sapozhnikov. Ultrasonic Far-Field Holography of Point Scatterers and Interfaces. 10ème Congrès Français d'Acoustique, Apr 2010, Lyon, France. ⟨hal-00541727⟩