Singular beams

Nondifracting acoustic beams can be generated under specific conditions. Now I'm working in the generation of zero-th and higher order Bessel beams generated by diffraction gratings and metamaterials. Focusing of the beams is also considered and acoustic vortices can be easily generated by passive devices. Furthermore, nondifracting nonlinear beams have been also obtained by using periodic materials under self-collimation regime.


Vortex beams

I'm studying the generation of acoustic vortex using the diffraction of plane waves over spiral shaped structures. We find-out that the diffraction of acoustic waves on multiple-arm Arquimedean spirals generate arbitrary order Bessel beams based in spirals. Moreover vortex focusing can eb achieved by combining Fresnel zone-plates with spiral gratings. Using Fresnel-spirals geometrically-optimal focused vortex beams are observed. This technique can be used to generate cheap lenses for acoustic particle manipulation and acoustic radiation force applications.

pdf link doi Formation of high-order acoustic Bessel beams by spiral diffraction gratings
N. Jiménez, R. Picó, V. Sánchez-Morcillo, V. Romero-García, L. García-Raffi, K. Staliunas,
Phys. Rev. E, 94 (5), pp 053004, (2016)

pdf link doi Sharp acoustic vortex focusing by Fresnel-spiral zone plates
N Jiménez, V Romero-García, LM García-Raffi, F Camarena, K Staliunas,
Applied Physics Letters, 112, pp 204101, (2018)

Nonlinear acoustic beams

I'm studiying the phenomenon of the displacement of the position of the pressure, intensity and acoustic radiation force maxima along the axis of high intensity focused acoustic beams. Here, we study the case of a moderately focused beams excited with continuous and amplitude modulated signals, both in water and tissue. We prove that in amplitude modulated beams the linear and nonlinear propagation effects coexist in a semi-period of modulation, giving place to a complex dynamic behaviour, where the singular points of the beam (peak pressure, rarefaction, intensity and acoustic radiation force) locate at different points on axis as a function of time. These entire phenomena are explained in terms of harmonic generation and absorption during the propagation in a lossy nonlinear medium both for a continuous and an amplitude modulated beam.

pdflinkdoi Dynamic Nonlinear Focal Shift in Amplitude Modulated Moderately Focused Acoustic Beams
N. Jiménez, F. Camarena, N. González-Salido,
Ultrasonics, 75, pp 106–114, (2016)

pdf link doi Nonlinear focal shift beyond the geometrical focus in moderately focused acoustic beams
F. Camarena, S. Adrián-Martinez, N. Jiménez, V. Sánchez-Morcillo,
The Journal of the Acoustical Society of America, 134 (2), pp 1463-1472, (2013)

pdf link doi Time-Domain Simulation of Ultrasound Propagation in a Tissue-Like Medium Based on the Resolution of the Nonlinear Acoustic Constitutive Relations
N. Jiménez, F. Camarena, J. Redondo, V. Sánchez-Morcillo, Y. Hou, E. E. Konofagou,
Acta Acustica united with Acustica, 102 (5), pp 876–892, (2016)

Nonlinear acoustic radiation forces

I'm studing the finite-amplitude dependence of the acoustic radiation force (ARF) in soft tissue-like media. The amplitude dependent ARF and its spatial distribution is used to correct elasticity imaging techniques as Harmonic Motion Imaging to precisely estimate the elasticity of the tissue. The results obtained show that the nonlinear dependence of the acoustic radiation force highly depends on the tissue attenuation frequency dependence for both, weakly and strong nonlinear regime. We also show the underestimation of the momentum transfer in the nonlinear regime by calculating the ARF by using the wave intensity. Considerations due to nonlinear absorption are included and the relation between the momentum transfer and energy deposition is underlined.

pdflinkdoi Dynamic Nonlinear Focal Shift in Amplitude Modulated Moderately Focused Acoustic Beams
N. Jiménez, F. Camarena, N. González-Salido,
Ultrasonics, 75, pp 106–114, (2016)

Thermal patterns

The knowledge of the shape of thermal patterns is essential to acurately predict the result of ultrasound therapy techniques for HIFU or hyperthermia applications. Here, I'm working in numerical simulations of the thermal patterns produced by nonlinear acoustic focused beams in practical applications.

Bessel beams

We report Bessel-like beam formation of acoustic waves by means of an axisymmetric grating of rigid tori. The results show that the generated beam pattern is similar to that of Bessel beams, characterized by elongated non-diffracting focal spots. A multiple foci structure is observed, due to the finite size of the lens. The dependence of the focal distance on the frequency is also discussed, on the basis of an extended grating theory. Experimental validation of acoustic Bessel-like beam formation is also reported for sound waves. The results can be generalized to wave beams of different nature, as optical or matter waves.

pdf link doi Acoustic Bessel-like beam formation by an axisymmetric grating
N. Jiménez, V. Romero-García, R. Picó, A. Cebrecos, V. Sánchez-Morcillo, L. García-Raffi, J. V. Sánchez-Pérez, K. Staliunas,
Europhysics Letters, 106, pp 24005, (2014)

Self-collimated beams

We investigate the propagation of high-intensity sound beams in a sonic crystal, under self-collimation or reduced-divergence conditions. The medium is a fluid with elastic quadratic nonlinearity, where the dominating nonlinear effect is harmonic generation. We explored the conditions for the efficient generation of narrow, nondiverging beam of second harmonic. Numerical simulations are in agreement with the analytical predictions made, based on the linear dispersion characteristics in modulated media and the nonlinear interaction in a quadratic medium under phase matching conditions.

pdf link doi Nonlinear self-collimated sound beams in sonic crystals
E. M. Hamham, N. Jiménez, R. Picó, V. Sánchez-Morcillo, L. G. Raffi, K. Staliunas,
Phys. Rev. B, 92, pp 054302, (2015)

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