Daniel Tarrazó-Serrano

An Ultrasonic Lens Design Based on Prefractal Structures

The improvement in focusing capabilities of a set of annular scatterers arranged in a fractal geometry is theoretically quantified in this work by means of the finite element method (FEM). Two different arrangements of rigid rings in water are used in the analysis. Thus, both a Fresnel ultrasonic lens and an arrangement of rigid rings based on Cantor prefractals are analyzed. Results show that the focusing capacity of the modified fractal lens is better than the Fresnel lens. This new lens is believed to have potential applications for ultrasonic imaging and medical ultrasound fields.

Manipulation of focal patterns in acoustic Soret type zone plate lens by using reference radius/phase effect.

HighlightsA free parameter (reference radius r0) allows obtaining a much finer focus.When r0 is bigger than r1, an expansion of the focus along the longitudinal axis is achieved.When r0 smaller than r1, a control of the Sidelobe Level can be achieve.The prospect of these results are important in some medical applications.Possibility to control a spatial frequency to obtain a finer focus. ABSTRACT The manipulation of focal patterns of acoustic underwater Soret Zone Plate lens in far fields, such as manipulation (optimization) of Sidelobe Level and the design of long depth of focus by selecting the simple free parameter called reference radius (phase) has been demonstrated.Two effects have been studied by means of numerical simulations. Regarding the first effect, simulations demonstrate diffraction limited focal spot (0.47 wavelength) and 3 dB reduction of the first Side Lobe Level using Soret ZP with an optimal reference radius and without causing neither main lobe broadening or gain reduction. In the second effect, by using numerical simulations an increasing of depth of focus, more than 2 times, in comparison with classical Soret ZP with high numerical aperture (F/D = 2.5), was observed.

Design of Acoustical Bessel-Like Beam Formation by Tunable Angular Spectrum in Soret Zone Plate Lens

The image performance of acoustic and ultrasound sensors depends on several fundamental 1 parameters such as depth of focus or spatial resolution. There are currently two different type 2 of acoustic diffractive lenses: those which form a diffraction-limited spot with a shallow depth 3 of focus (zone plates) and lenses which form an extended focus (quasi-Bessel beams). In this 4 paper, we investigate a pupil-masked Soret zone plate which allows the tunability of a normalized 5 angular spectrum. It is shown that the depth of focus and the spatial resolution can be modified, 6 without changing the lens structure, by choosing the size of the amplitude pupil mask. This effect 7 is based on the transformation of spherically converging waves into quasi-conical waves, due to 8 the apodization of the central part of the zone plate. The theoretical analysis is verified with both 9 numerical simulations and experimental measurements. A Soret zone plate immersed in water 10 with D/2F=2.5 and F=4.5λ, changes its depth of focus from 2.84λ to 5.9λ and the spatial resolution 11 increases from 0.81λ to 0.64λ at a frequency of 250 kHz, by modifying the pupil mask dimensions of 12 the Soret zone plate. 13

Sound focusing of a wavelength-scale gas-filled flat lens

This work has been supported by TEC2015-70939-R (MINECO/FEDER). The research was partially supported by Tomsk Polytechnic University Competitiveness Enhancement Program. IVM and OVM would like to thank Dr RUBEN PICO VILA for useful discussions.

Frequency dependence of Fresnel zone plates focus

Fresnel zone plates (FZPs) focus waves through constructive interference of diffracted fields. They are used in multiple fields, such as optics, microwave propagation or acoustics, where refractive focusing by conventional lenses is difficult to achieve. FZPs are designed to work and focus at a design frequency. At this frequency, the behavior of the FZP is optimum and focusing at a certain focal length is achieved. In most medical applications using lenses, it is critical to have a fine and dynamic control on the lens focal length. In this work, the variation of the FZP focus parameters when working at operating frequencies different from the design frequency is analyzed, and a focal length control mechanism is proposed. It is shown that the FZP focal length shifts linearly with the operating frequency, becoming a dynamic control parameter that can be useful in many different applications. However, other focusing parameters, such as focal depth and distortion, are also affected by the operating frequency...

Analysis and design of Fresnel zone plates with multiple foci

Fresnel Zone Plates (FZPs) become an interesting alternative to traditional lenses when planar fabrication is advantageous, and are used in a wide range of physical disciplines such as optics, microwave propagation, or ultrasounds. Conventional FZPs produce a single focus, which is optimal in most applications. However, certain medical applications, such as MRI (magnetic resonance imaging) guided ultrasound surgery, require multiple foci ultrasound exposures. In this work, new multi-focus Fresnel lenses (MFFLs) based on conventional FZPs are presented. The advantages and drawbacks of these new MFFL structures are thoroughly analyzed. There is a tradeoff on the number of foci achieved in a single MFFL and its focusing efficiency. Therefore, the most efficient MFFL is that with two foci. A procedure for designing 2-foci MFFLs, in which the focal length of both foci may be selected independently, is established. For each 2-foci MFFL, there are several physical implementations. The focusing properties of all ...