Design of Acoustical Bessel-Like Beam Formation by a Pupil Masked Soret Zone Plate Lens.

Daniel Tarrazó-Serrano,Oleg Minin,Constanza Rubio,Igor Minin,Pilar Candelas,Sergio Castiñeira-Ibáñez

doi:10.3390/s19020378

Abstract

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

Highlights

The necessity of manipulating waves has been one of the main objectives of the scientific community
Soret Zone Plates (SZPs) are based on ring sections known as Fresnel regions
The purpose of this work is to prove that an SZP with a Pupil mask (PSZP) is able to increase the

Summary

Introduction

The necessity of manipulating waves has been one of the main objectives of the scientific community. Lenses are devices that achieve, through different physical phenomena such as refraction or diffraction, beam focusing and modulating effects. Lenses have been developed for different areas such as biomedicine, engineering, and industry. One type of acoustic lens changes the refractive index between media, known as gradient-index lenses, using labyrinthine structures [12,13,14]. Phononic crystals [15], acoustic metamaterials [16], and acoustic resonators [17] have been used in the implementation of acoustic lenses. Another type of acoustic lens, which is proposed to be used in High Intensity Focused

Objectives

Methods

Results

Conclusion