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Research

Acoustic levitation

We are interested in levitating large droplets and solid particles in air.

Ultrasound images with super-resolution

Using a ball-shaped lens, we beat the diffraction limit of an ultrasound system and doubled its resolution. See below a super-resolution image of a coin.

moeda

 

2D acoustic patterning of cells and microparticles

We study possible arrangements of 2D patterning of cells using ultrasound waves in lab-on-a-chip technology [G. T. Silva, J. H. Lopes, J. P. Leão-Neto, M. K. Nichols, and B. W. Drinkwater, Phys. Rev. Applied 11 054044, 2019].

Mechanophenotyping of cells with ultrasound

We developed a method to squeeze soft cells and microvesicles with ultrasonic standing waves. Partial results have been reported in [L. Tian, G. T. Silva, B. W. Drinkwater, J. Acoust. Soc. Am. 142, 2609 (2017)].

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Acoustic radiation force on spheroids

How do acoustic waves drive spheroidal particles? We have answered that question in [G. T. Silva and B. W. Drinkwater, J. Acoust. Soc. Am. 144 EL453 (2018)]

Spheroid

 

Ultrasound propagation and scattering in solids

Understanding ultrasound wave propagation in solids has a direct application in biomedical imaging and non-destructive testing. We have studied some fundamental aspects of ultrasound propagation and scattering in isotropic solids [J. P. Leao-Neto, J. H. Lopes, G. T. Silva, J. Appl. Phys. 121 144902 (2017)]. Also, we are investigating how a Bessel vortex beam propagates in solids (see figure below).

Iz_besselbeam_1

Figure: The axial intensity of a Bessel vortex beam of first-order propagating in a stainless steel matrix.

Ultrasound super-resolution

We have employed ball-shaped lenses to superfocus of ultrasound waves. Compared to conventional diffraction-limited systems, 100% better spatial resolution of ultrasound images can be achieved using polymer lenses [J. H. Lopes et al., Phys. Rev. Applied 8, 024013 (2017)].

 Ball-shaped lens super focusing an ultrasound beam.

 

Ultrasound scattering in fluids

Ultrasound scattering refers to a process where an ultrasound beam deviates from a straight trajectory due to a change in the medium impedance. In Fig. 1, we depict the scattering of a zero-order Bessel beam by a rigid sphere in water [G. T. Silva, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 58 298, 2011]. Also, we have done some pretty fundamental work in this field proposing a generalized optical theorem in acoustic scattering in [G. T. Silva, Phys. Rev. E 90, 053204, 2014].

 

bessel0_scatt

Our goal is to develop theoretical methods to model ultrasound scattering. Especially for nondiffracting and focused beams.  Multiple scattering is also an exciting topic we are interested in.

Ultrasound intermodulation components

When two ultrasound waves of distinct frequencies overlap, difference- and sum-frequency components (intermodulation components) are generated due to nonlinear interaction of the waves. This has found an application on an imaging method called vibro-acoustography as described in [G. T. Silva,  Phys. Med. Biol. 56 5985, 2011]. 

Acoustic radiation force and torque

When an acoustic wave hits an obstacle, part of its momentum flux is transferred to the obstacle. This gives rise to a time-averaged force referred to as the acoustic radiation force. Our group has given a significant contribution to this field. For instance, in Ref. [G. T. Silva, J. Acoust. Soc. Am. 130, 3541, 2011] [J. H. Lopes, M. Azarpeyvand, and G. T. Silva, IEEE Trans. Ferroelectr. Freq. Control 63 186, 2015]. 

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Acoustophoresis

This is an exciting field full of research activity in the last 20 years - moving objects with radiation force. The application range of acoustophoresis is increasing. Trapping and controlled manipulation of biological cells is a hot topic.  We have proposed an acoustical tweezer which may trap several particles in a region near to the device [G. T. Silva and A. L. Baggio, Ultrasonics 56, 449-455, 2014].

tweezer